Volume 75, No. 1 2019
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1 Editorial–TheTransformationofPhysics in Canada, byBélaJoós,Editor
1 Éditorial–LatransformationdeLa Physique au Canada, parBélaJoós,Rédacteurenchef 3 InMemoria: -GillesFontaine(1948-2019) -Li-HongXu(1957-2019)
6 2019StudentCompetitions/Compétitions étudiantes 2019 8 UniversalityofSpreadingProcesseswithSpontaneousActivity,byDanielJ.Korchinski, JavierG.Orlandi,Seung-WooSon,andJörnDavidsen
11 CosmologicalConstraintsonHiddenPhysics,byLindsayForestell, DavidE.Morrissey,andKrisSigurdson 14 CharacterizingtheFlexibilityoftheBody’sBuildingBlock:Collagen, byAlaaAl-Shaer,AaronLyons,andNancyR.Forde
18 SearchforNeutrinoTridentEventsinIceCube,bySouravSarkarandRogerMoore FonD
rticles 22 ShapingArbitraryEnergyLandscapeswithFeedback, De
a byAvinashKumarandJohnBechhoefer Cover / Couverture: 26 2019CAPMedalRecipients/Lauréats des médailles de l’ACP de 2019 “Goutte d’eau: len- Volume 75, No. 1 2019 tille optique naturelle” rticles eature -JaumeGomis by Antony Hu, École F a -BélaJoós Secondaire de la Cité -GraemeLuke des Jeunes Vaudreuil- -RobertMann(seeinterview,p.28) Dorion, QB – Second
Serving the Canadian physics community since 1945 / Au service de la communauté Place (High School/ canadienne de physique -PaulBarclay depuis 1945 CEGEP Individual FEATURING / EN VEDETTE :
-DouglasBonn Canadian Association of ARTICLES RELATED TO THE 2019 CONGRESS, MEDALS, AND AWARDS Physicists / Association canadienne des physiciens ARTICLES LIÉS AU CONGRÈS, AUX MÉDAILLES ET AUX PRIX 2019 et physiciennes Category), 2019 Art of -ScottOser www.cap.ca Physics competition. See https://www.cap.ca/ 28 2019MedalsandPrizes-InterviewwithRobert programs/art-physics-2/ Mann,RecipientoftheCAP’s2019Medalfor The Local Organizing Committee delivered ExcellenceinTeachingUndergraduatePhysics, a memorable experience for all Congress September2019,byDariaAhrensmeier delegates attending the 2019 CAP Congress in Burnaby, BC.
< Goutte d’eau : lentille optique naturelle > par Antony Hu, École Secondaire de la Cité des Jeunes Vaudreuil-Dorion, QB – Caté- Advertising rates and specifications (effective January 2019) as well as subscription and gorie projet individuel au niveau secondaire ou cégep, 2e prix, Concours L’Art de la Phy- singleissueorderformscanbefoundontheCAPwebsite(www.cap.ca->Publications-> sique 2019. Voir https://www.cap.ca/fr/activ- Physics in Canada). ites/lart-de-physique/ Les tarifs et dimensions des publicités (en vigueur depuis janvier 2019) ainsi que les formulaires Le Comité organisateur a fait du Congrès 2019 d’abonnement et de commande de numéros individuels se trouvent sur le site internet de l’ACP à Burnaby, Colombie britannique, une expéri- (www.cap.ca - > Publications - > La Physique au Canada). ence mémorable pour tous les délègués.
La Physique au canada / Vol. 75, No. 1 ( 2019 ) • i
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34 High School / CEGEP Physics Teaching Awards / PHYSICS IN CANADA LA Prix ACP en enseignement de la physique au PHYSIQUE AU CANADA secondaire et au collégial f on d
The Journal of the Canadian Association of Physicists rticles by Joe Muise, Christopher Sarkonak, La revue de l’Association canadienne des physiciens d e 37 Summer at CERN!, A
et physiciennes and Sarah Torrie ISSN 0031-9147
41 Report on Canada’s Participation in the EDITORIAL BOARD / COMITÉ DE RÉDACTION 50th International Physics Olympiad Editor / Rédacteur-en-chef Béla Joós, P.Phys. rticles eature in Tel Aviv, Israel, by Andrzej Kotlicki Physics Department / Département de physique, Univ. of / d’ Ottawa 150 Louis Pasteur Ave. F A and Lior Silberman Ottawa, Ontario K1N 6N5 Email: [email protected]; (613) 562-5800 x 6755
Associate Editor / Rédactrice associée Departmental, Sustaining, Corporate and Managing Editor / Rédactrice d’administration 43 Francine M. Ford Institutional Members / Membres départementaux, c/o CAP/ACP; Email: [email protected]; (613) 562-5617 de soutien, corporatifs et institutionnels Production and Advertising Coordinator / Coordonnatrice de la production et de la publicité Brooklyn Patrick 44 Books Received / Livres rec¸us c/o CAP/ACP; Email: [email protected]; (613) 562-5614 Advertising Manager / Directeur de la publicité Michael Steinitz, P.Phys. 45 Book Reviews / Critiques de livres Dept. of Physics, St. Francis Xavier University, P.O. Box 5000 Antigonish, Nova Scotia B2G 2W5
epartments Email: [email protected]; (902) 867-3909 épartements
D Book Review Editor / Rédacteur à la critique de livres D 50 Employment Ad Richard Marchand c/o CAP/ACP; Email: [email protected]
Board Members / Membres du comité : David J. Lockwood, P.Phys. Researcher Emeritus National Research Council (M-36) Montreal Rd., Ottawa, Ontario K1A 0R6 Email: [email protected] Robert Thompson, P.Phys. Dept. of Physics and Astronomy University of Calgary, 2500 University Dr. NW Calgary, Alberta T2N 1N4 Email: [email protected]; (403) 220-5407 Richard MacKenzie, phys. Département de physique Université de Montréal, C.P. 6128, Succ. centre-ville Canadian Association of Physicists (CAP) Montréal, Québec H3C 3J7 Association canadienne des physiciens et physiciennes (ACP) Email: [email protected]; (514) 343-5860 Daria Ahrensmeier The Canadian Association of Physicists was founded in 1945 as a non-profit association rep- Simon Fraser University Teaching and Learning Centre, 8888 University Drive resenting the interests of Canadian physicists. The CAP is a broadly-based national network of Burnaby BC V5A 1S6 physicists working in Canadian educational, industrial, and research settings. We are a strong Email: [email protected]; (778) 782-9544 and effective advocacy group for support of, and excellence in, physics research and educa- Marcello Pavan TRIUMF, 4004 Wesbrook Mall tion. We represent the voice of Canadian physicists to government, granting agencies, and Vancouver BC V6T 2A3 many international scientific societies. We are an enthusiastic sponsor of events and activities Email: [email protected]; (604) 222-7525 promoting Canadian physics and physicists, including the CAP’s annual congress and national Michael O'Neill, P.Phys. physics journal. We are proud to offer and continually enhance our web site as a key resource Retired Scarborough, ON for individuals pursuing careers in physics and physics education. Details of the many activities Email: [email protected] of the Association can be found at http://www.cap.ca. Membership application forms are also available in the membership section of that website. ANNUAL SUBSCRIPTION / ABONNEMENT ANNUEL: $46.00 Cdn + GST or HST (Cdn addresses), L’Association canadienne des physiciens et physiciennes a été fondée en 1946 comme une $46.00 US (US addresses); $51.00 US (other/foreign addresses) association à but non-lucratif représentant les intérêts des physicien(ne)s canadien(ne)s. Advertising, Subscriptions, Change of Address/ L’ACP est un vaste regroupement de physiciens oeuvrant dans les milieux canadiens de Publicité, abonnement, changement d'adresse: Canadian Association of Physicists / l’éducation, de l’industrie et de la recherche. Nous constituons un groupe de pression solide et Association canadienne des physiciens et physiciennes, 3rd Floor, 555 King Edward Ave. / 3e étage, ave. 555 King Edward, efficace, ayant pour objectif le soutien de la recherche et de l’éducation en physique, et leur ex- Ottawa, Ontario K1N 7N6 cellence. Nous sommes le porte-parole des physiciens canadiens face au gouvernement, aux Phone/ Tél: (613) 562-5614; Fax/Téléc. : (613) 562-5615 e-mail/courriel : [email protected]; Website/Internet : www.cap.ca organismes subventionnaires et à plusieurs sociétés scientifiques internationales. Nous nous Canadian Publication Product Sales Agreement No. 0484202/ faisons le promoteur enthousiaste d’événements et d’activités mettant à l’avant-scène la phy- Numéro de convention pour les envois de publications canadiennes : 0484202 sique et les physiciens canadiens, en particulier le congrès annuel et la revue de l’Association. © 2019 CAP/ACP Nous sommes fiers d’offrir et de développer continuellement notre site Web pour en faire une All rights reserved / Tous droits de reproduction réservés ressource clé pour ceux qui poursuivent leur carrière en physique et dans l’enseignement de la physique. Vous pouvez trouver les renseignements concernant les nombreuses activi- WWW.CAP.CA tés de l’ACP à http://www.cap.ca. Les formulaires d’adhésion sont aussi disponibles dans la (select Publications -> Physics in Canada / rubrique «Adhésion» sur ce site. Option : Publications -> La Physique au Canada
ii • Physics in Canada / Vol. 75, No. 1 ( 2019 )
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The Transformation of Physics in Canada lthough Physics in Canada has appeared in your issuing our Bulletins and Flashes using this new system, mailbox less frequently during the last two years the Editorial Board and Communications Committee are due to a number of production challenges beyond partnering to determine the niche which Physics in Canada Aour direct control, we have nevertheless delivered can and should fill in our communication strategy, and to our subscribers and members two 2018 significant how best to structure the publication to do so. Here are issues, the first commemorating 70 years of Neutron some preliminary thoughts on the subject. Scattering in Canada, and the second on Physics in Mining. The current issue is a celebration of the accomplishments A magazine format such as PiC remains the best vehicle of our members in 2019. This will be followed by our for commemorating major milestones or for in-depth dis- second 2019 issue entitled The History of the Future of cussions of subjects of importance to the community, such TRIUMF, an issue celebrating the first 50 years of TRIUMF as EDI and evidence-based policies. However, the reading and how it lay the foundations of its future. In 2020 we will habits of our members have rapidly evolved over the last offer an issue on Science and the Public exploring the chal- decade. One has simply to consider one’s own daily rou- lenges facing scientists in conveying their message to the tine and where we now get our information. We spend general public and ensuring good science prevails, and a many hours a day reading off screens and exchanging second one on EDI (Equity, Diversity, Inclusivity). thoughts via e-mails or social media posts. Even purely scientific material is increasingly explored from smart- How should one interpret our reduced and greatly delayed phones, tablets, following twitter accounts, and online output? As a reflection of how the CAP has been investing versions of newsletters and journals produced by scien- significant resources, including staff time, to introducing tific organizations. upgraded management systems to help us grow to meet the changing needs of our community. CAP’s limited resources, within challenging financial times, necessarily affect the scope of what can be managed with An important role of CAP is to nurture a sense of com- respect to Physics in Canada. We are forced to prioritize munity among Canadian physicists, especially with the what we should publish in print or in fully downloadable progressive fragmentation of our field and the emergence issues. Theme issues have been, in my opinion, our most of specialized associations soliciting our attention. Much valuable output. We should focus on these and produce two of that role can be fulfilled by posting material on-line, but such issues per year. We should make PiC thematic, address- a direct engagement with the membership is also required ing important topical subjects or offering a broad discussion to prod our members into action or provide timely infor- of interesting themes of relevance to our community. By mation. News Flashes and News Bulletins will likely pro- offering something of a more permanent nature, with its vide this, with links to more intensive material online. archives, PiC will remain the ideal vehicle for presentation of comprehensive reviews, broader discussion of topics of Thus, a significant part of these upgrades has been aimed interest, and matters of archival significance. at improving the CAP’s infrastructure that supports our Bulletins, News Flashes, e-mails, and website. Béla Joós, Editor, Physics in Canada Béla Joós is a Professor of Physics Now that the new website and the new management sys- Comments of readers on this Editorial are more than at the University tem have been implemented, and we are about to start welcome. of Ottawa. He has been a member of the Editorial Board of Physics in Canada since January 1985 and took over as La transformation de La Physique au Canada Editor in June 2006. Bela Joós est ien que La Physique au Canada vous est parvenue réalisations de nos membres en 2019. Le prochain numéro, professeur de moins souvent ces deux dernières années à cause le second de 2019, célèbrera les 50 premières années de physique a l’Université d’Ottawa. de plusieurs défis de production au-delà de notre TRIUMF et comment ses années ont préparé son avenir. Il est membre du Bcontrôle, nous avons néanmoins livré en 2018, à En 2020, nous offrirons un numéro sur La Science et le Comite de rédaction nos abonnés et à nos membres, deux numéros significatifs public, qui exposera les défis que les scientifiques doivent de la Physique au dont le premier commémore les 70 années de diffusion des relever pour porter leur message au grand public et assurer Canada depuis janvier 1985 et est neutrons au Canada et, le second traite de La Physique que la science saine l’emporte. Il y en aura un autre sur devenu rédacteur en dans l’exploitation minière. Le présent numéro célèbre les l’EDI (équité, diversité et inclusivité). chef en juin 2006.
La Physique au Canada / Vol. 75, No. 1 ( 2019 ) • 1
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Comment faut-il comprendre notre production réduite et scientifiques. Les habitudes de lecture de nos membres ont fort tardive? Comme une réflexion du grand investisse- toutefois évolué rapidement au cours de la dernière décen- ment que l’ACP a fait en temps de son personnel et en nie. Il suffit d’examiner notre propre routine quotidienne et équipement pour moderniser son système administratif les sources actuelles de notre information. Chaque jour dans le but de croître pour servir les besoins changeants de nous passons des heures à lire à l’écran et à échanger des notre communauté. idées par courriel et médias sociaux. Nous examinons même de plus en plus des documents strictement scienti- Un rôle important de l’ACP est de susciter un esprit de fiques à l’aide de téléphones intelligents, de tablettes, sur les corps chez les physiciens du Canada, étant donné surtout comptes Twitter, les versions en ligne de bulletins de nou- la fragmentation progressive de notre discipline et velles et de revues émanant d’organismes scientifiques. l’émergence d’associations spécialisées sollicitant notre attention. Ce rôle peut être exercé en bonne partie en pub- Les maigres ressources de l’ACP en cette période finan- liant des documents en ligne, mais il faut en outre un cière difficile ajoutent des contraintes sur ce que La engagement direct auprès des membres pour les inciter à Physique au Canada peut réaliser. Cela oblige à établir un agir ou leur fournir une information en temps utile. Nos ordre de priorité dans ce qui devrait être publié sous forme Flash-info et Bulletins devraient atteindre cet objectif et d’imprimés ou en numéros téléchargeables en entier. À renvoyer à des documents plus approfondis sur le Web. mon avis, les numéros à thème sont notre œuvre la plus Ainsi une bonne partie des améliorations visaient à amé- précieuse. Nous devrions y mettre l’accent et produire liorer l’infrastructure de l’ACP qui soutient nos Bulletins, deux tels numéros par année. Nous devrions faire de la Flash-info, courriel, et notre site web. PaC une revue thématique portant sur d’importants sujets d’actualité ou offrant une vaste discussion sur Maintenant que le nouveau site web et le nouveau système d’intéressants thèmes pertinents à notre collectivité. En d’administration ont été mises en œuvre et que l’ACP offrant des éléments de nature plus permanente dans ses commencera à émettre les Bulletins et Flash-info utilisant archives, la PaC sera idéale pour présenter un tableau le nouveau système, le Comité de rédaction et le Comité complet ou élargi de sujets intéressants, et des questions de communications vont travailler à déterminer le rôle que de valeur archivistique. pourra et devra remplir La Physique au Canada (PaC) dans la stratégie de communication de l’ACP. Ils déci- Béla Joós, rédacteur en chef, deront aussi comment structurer La PaC pour réaliser ce La Physique au Canada rôle. Voici quelques idées sur la question. Les commentaires des lecteurs sur cet éditorial sont Un format comme celui de la revue PaC demeure le meil- toujours les bienvenus. leur moyen de commémorer des jalons importants ou de discuter de profonds sujets d’importance pour la collectiv- NOTE: Le genre masculin n’a été utilisé que pour alléger ité, tels l’EDI et les politiques fondées sur des preuves le texte.
The contents of this journal, including the views expressed above, do not necessarily represent the views or policies of the Canadian Association of Physicists.
Le contenu de cette revue, ainsi que les opinions exprimées ci-dessus, ne représentent pas nécessairement les opinions ou les politiques de l’Association cana- dienne des physiciens et physiciennes.
2 • Physics in Canada / Vol. 75, No. 1 ( 2019 )
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) In Memoria 2019 ia emor M
- - n is in of of as I of on by He his He the the the has and and and one for was sub- it most Wide since using Beals actual theor of inves- in one writer, Stellar contri- degree as He field by internal He and study in S. for an stars known in renowned Physicists Vol. 75, No.1 ( and (CASCA), galaxy. discovered the
also teacher the awards (1969). Lastly, his undoubtedly of for well / distinguished major in Astronomical is quality numerous now NASA’s work prolific our University Montréal contribution for Chair dwarf dwarfs has a Achievement is as astroseismology, world he professor Carlyle of of dwarfs annually has de many education. pulsators. Society GF153, Laval a he of evolution cosmochronometers “starquakes”, the Marie-Victorin, anada Royal examine of incredible undergraduate white C (white as including 2000 vocations. stars,
white 2010 the excellence an field survey can dwarfs, Association foundations Prix of tenured Lifetime their Research his encouraged exceptional especially au is telescope, stellar from of actions, for of
remarkable the Fontaine a awarded creating we subdwarf the the them University a for he of has modeling. As components the deep his recipient Université 1999 white world-renowned in of postgraduate Dr. and By state asteroid a Astronomical the evolution was studies scientific compact that of evolution, Canada for used the Canadian build Ph.D. the (WISE) at of the which studying of received made Prizes With the other tradition Member Medal hysique class and he the the leader at by by ways first Fontaine stellar the products his astrophysics, the P that been part also numerical stellar by pursuing Canada, Québec, a did of Canadian 1992 of new building 2016 true scientists. held Physics Dr. L pioneering, as of 1974 in evolution Explorer equation pulsating has a of in who has stars a and including Québec in Fontaine final from of to the stellar the method his in only physics observational of the the of also of different 2010 in team, great phases 14 the internationally as awarded stages to for obtained in illes in communicator. on from Not follower He and mentioning Infrared students elected became pioneers Fontaine Fontaine the unique late final well April true great
astrophysics Award Rochester Dr. the also himself Government as Department 1977. butions distinctions, of Society of Canada. A research the dwarfs, etical Physics Astrophysics since 2000. tigations discovery stars). theory the (CAP), also independent the structure Field Gillesfontaine. (400811) observations Dr. eign research training proven a contributed in worth G
- Il et la et en en de de de de de en du fut M. ses par des tra- fois plu- titu dont utili- Il 1974 et cana- sur seule- aucun la recon- naines pair depuis décou- forma- (étoiles l’Asso- Prix distinc- ses comme à l’évolu- titulaire Canada. Québec, méthode fait en cycle la la leur équipe découvert les (ACP) et de étoiles non attirer différentes 14 de de à du du blanches sans hors Chaire domaine a a étoiles, l’Université de physique scientifiques. que a Société pu cette supérieures. sur prolifique, une Il des des le des prix imposé l’évolution a de il distingué pulsantes. physique, stellaire la la particulièrement professeur des à l’Université obtenu GF153, royale premier ainsi
naines bâti de Montréal combinant ultimes la a l’un Médaille dans par fut également à de s’est mondialement en de Auteur de la interne étoiles. Il pionniers des enseignant d’études Fontaine il de 2010 », physiciennes remarquable actions, Fontaine Ayant vocations stellaire, 1999, Société également gouvernement que des un nombreux exceptionnelle et des théorie était et produits l’évolution indépendants M. la sous-naines l’évolution le ces d’observation pulsantes, 2000 décerné d’état en de aine illes études physique un cycles Département Il façon être (1969). Fontaine de s’est ces de et ainsi structure de de d’étoile par doctorat au Par les calibre. Il l’astérosismologie, d’excellence de numérique. qualité la l’astéroïde M. 2000 majorité aussi exceptionnels de véritable la façon exceptionnelles pour l’Université 1977. depuis Rochester laire son Laval en finales G stades que physiciens est mondiale, ont grand compactes l’équation nombreuses Membre astrophysique il sonder galaxie. catégorie à pour (CASCA), théoriques de tradition grande d’une consacré des d’une récipiendaire travaux en Canada, de Beals Marie-Victorin sous-naines), F domaine la la de phases 1992 annuellement tremblements le mais étoiles notre au et le ses modélisation derniers S. étrangers « plus de aussi en cosmochronomètres bases prix finalement les études apports fut de communicateur. et renommée des pour nouvelle les de contributions le dans élu pour les de leurs sur les et s’est recherche suscité décernés canadienne Carlyle scientifiques file permettant de d’astronomie blanches, héritier blanches internationale comme étudiants dont pour jeté d’une de l’étude illes de de stellaire dans Fontaine excellent études Prix démontré également Digne verte l’astrophysique scène vaux naines Québec ciation 2016 particulier nus blanches d’importants les tion dans le dienne G (1948-2019) recherche du Canada en astrophysique stellaire. M. tions, ment naines sation composantes chef unique l’étude observations Fontaine Mentionnons tion recherche sieurs doute a un PIC_75_1.indb 3 In Memoria
en avril 2010 dans le cadre d’un sondage profond du télescope He was an exceptional colleague and a dear friend to all who Wide Field Infrared Explorer (WISE) de la NASA, porte désor- knew him. mais le nom de (400811) Gillesfontaine. Pierre Bergeron Il fut un collègue exceptionnel et un ami cher pour tous ceux Université de Montréal qui l’auront côtoyé.
Pierre Bergeron Université de Montréal
Li-Hong Xu (1957–2019)
r. Li-Hong Xu, a promi- for Photonic Innovations and was also a charter member of nent and devoted member the Far-Infrared Beam Team at the Canadian Light Source of the Canadian Physics synchrotron in Saskatoon. She served on the Editorial Board Dcommunity, passed away of the Journal of Molecular Spectroscopy and on International on January 21, 2019 after a short Advisory Committees for International Symposia and battle with cancer. Li-Hong was Conferences, receiving invitations for plenary presentations st born on May 2, 1957 in Suzhou in at the 21 HRMS meeting in 2010 in Poznan, Poland, and the st the People’s Republic of China. In 71 ISMS symposium in 2016 in Urbana, Illinois. 1977, Li-Hong was among a small elite group who got into university In Canada, Dr. Xu was a loyal P.Phys. member of the CAP, serving from 2003-2009 as Regional Councillor for NB/ where she graduated in physics with highest honours. She NL and from 2008-2010 as NB Coordinator for the CAP was one of only two from her class of 240 graduates cho- High School Prize Exam. She had a special interest in pro- sen to remain in Suzhou University as an assistant moting women in science and from 2011-2014 served as professor. Chair and Past Chair of the CAP Committee to Encourage Women in Physics (CEWIP), which also involved service Li-Hong came to the University of New Brunswick in on the Annual Congress organizing committees. Fredericton in 1988 as a Visiting Scholar. She earned her PhD Regionally, from 2009 on, she served on the Science in molecular spectroscopy in 1992 and continued at UNBF as Atlantic Physics and Astronomy Committee. She was on
In Memoria In a post-doctoral fellow in the Centres of Excellence in the Canadian national delegations to the International Molecular and Interfacial Dynamics. Li-Hong received her Conferences for Women in Physics in Korea in 2008, in Diploma in University Teaching in the first cohort of gradu- South Africa in 2011, and in Waterloo in 2014 where she ates of the Centre for Enhanced Teaching and Learning. was Team Leader and the lead author of the paper, “Women She then joined Dr. J.T. Hougen as a research associate in the in Physics in Canada”. Notably, she was one of the pro- Molecular Physics Division of the National Institute of Standards moters, organizers and invited speakers for the Canadian and Technology. In 1995, Dr. Xu returned to New Brunswick Conference for Undergraduate Women in Physics. and took up a faculty position at the UNB campus in Saint John Colleagues saw Li-Hong as “the spirit of CEWIP” and where she set up a laboratory for high-resolution gas-phase laser that’s how many women in physics, in Canada and abroad, spectroscopy of molecules of environmental and astrophysical will remember her. importance. Her research lab attracted post-doctoral fellows and visiting researchers and students from Belgium, France, Russia, Li-Hong was a member of GSC29 (General Physics) for the Iran, the Czech Republic, China and the US. A large number of 2004-05 NSERC grant competition, and Committee Chair for undergraduate summer and work-study students were given a the subsequent two years. She served on the NSERC 2009-10 good start on their careers there. Steacie Fellowship Committee and the Physics Evaluation Group 1505 for the 2011-12 Discovery and RTI (Research Dr. Xu gained recognition internationally as a valued visitor Tools and Instruments) grants. In 2013 she was appointed and collaborator at centres such as NASA/Goddard, the Group Chair for Physics and held a seat on the NSERC NASA Jet Propulsion Lab, NIST Boulder, the Institute of Committee on Grants and Scholarships (COGS). In this role, Applied Physics in Nizhny Novgorod, the Max Planck she became a familiar figure at the 2014-2016 CAP Institute for Radio Astronomy and the University of Cologne. Congresses with her annual plenary presentations on the From 2002-2005, she was a member of the Canadian Institute granting picture for physics at NSERC.
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PIC_75_1.indb 4 6/5/20 8:37 AM In Memoria
In addition to her many external commitments, Dr. Xu main- From 2005-11, Li-Hong was co-president, then president, of tained an exemplary role at UNB in teaching, service and the Chinese Cultural Association, and was the founding outreach, notably for women and girls. She received her Director of the Saint John Chapter of the Asian Heritage In Memoria department’s award for teaching excellence in 2013 and the Society NB from 2008-18, organizing events annually for faculty teaching award in 2015; she was one of the inaugural Asian Heritage Month in May. She was a member of the SJ winners of the “Change One Thing” innovation challenge Community Arts Board from 2008-14, and of the Imperial by the UNB Centre for Enhanced Teaching & Learning. Theatre Board from 2016-18. She was an honorary life mem- In collaboration with the Saint John Free Public Library, ber of the school district Senior String Orchestra, and a sec- Li-Hong instituted a “Physics Circle” where girls gathered ond violinist with the Altomare community orchestra. She weekly to explore interesting physics activities. She visited a danced with the Jasmine Performing Arts group and taught number of local schools for physics shows, gave presenta- tai chi lessons at The Studio dance school. tions for groups of Girl Guides, and participated in the Canadian Association for Girls in Science’s local chapter. In In all of her professional, university, community and personal conjunction with UNB open houses, regional science fairs roles, Li-Hong was a tireless and effective role model. and special events, she set up popular fun demonstrations for Despite her whirlwind of activities, Li-Hong never seemed to the visiting students and their parents to encourage and stim- be rushed, and was a devoted mother to her children, Alex ulate their interest in physics. She became Director of the and Miranda. From her difficult start as a young woman, Music Program of the Lorenzo Society seven years ago and Li-Hong rose to positions of respect and importance and will be remembered for her warm introductions (and also her made profound contributions in a myriad of ways. She welcoming bowl of chocolates) at the Saint John String embodied the best of the multicultural character of Canada. Quartet noon-hour concerts. She organized student-led con- Li-Hong’s enthusiasm, boundless energy and engaging per- certs and arranged for UNB students and staff to join forces sonality will be profoundly missed. with the Dalhousie Medicine New Brunswick medical stu- dents in the Heartbeat Choir and the Ceol ceilidh band, Extracted from an In Memorium prepared by greatly enriching the cultural life at the university. She Ronald M. Lees, Fredericton, NB, and Adriana Predoi- received a President’s Distinguished Service Award in 2017. Cross, Lethbridge, AB
The Editorial Board welcomes articles from Le comité de rédaction invite les lecteurs à readers suitable for, and understandable soumettre des articles qui intéresseraient et to, any practising or student physicist. seraient compris par tout physicien, ou physicienne, Review papers and contributions of general et étudiant ou étudiante en physique. Les articles interest of up to four journal pages in length de synthèse d’une longueur d’au plus quatre are particularly welcome. Suggestions for pages de revue sont en particular bienvenus. theme topics and guest editors are also Des suggestions de sujets pour des revues à welcome and should be sent to bjoos@ thème sont aussi bienvenues et peuvent être uottawa.ca. envoyées à [email protected].
La Physique au Canada / Vol. 75, No.1 ( 2019 ) • 5
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P hysics 2019 Best Student Competition Winners 2019 B
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Name / Affiliation Name Simon Fraser University Etienne Dreyer, of Daniel Durnford, University University Queen’s Clarke Hardy, / Affiliation Name of B.C. Lindsay Forestell, University of Jack Davis, University / Affiliation Name Daniel Korchinski, University of B.C. Lindsay Forestell, University of B.C. Alaa Simon Fraser University Etienne Dreyer, Marie Alicia Sit, University of Ottawa Andrew MacLean, University of Guelph P CAP a ll L the a agnants with ver G d O r a w First Second Third First Second First Second Third Honourable Mentions PHYSICS PARTICLE Placement THEORETICAL Placement Placement CAP CAP A photograph a for gather University
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award President, Shohini Ghose (far left in front row). Simon TRIUMF Simon TRIUMF & Università Institute for Quantum Computing and Institute for Micromachines AND BIOLOGY AND MATERIALS presentation Cordoba, Chartrand, Simon Fraser University Al-Shaer, student Name / Affiliation Name of B.C. Daniel Korchinski, University Fraser Adam DeAbreu, Simon University Cristina Camille Name / Affiliation Name Alaa of Kyle Bromma, University / Affiliation Name Andrew MacLean, University of Guelph Fatima Garcia, Simon Fraser University Melanie Gascoine, Simon Fraser University Carlotta Porzio, degli Studi di Milano Michael Gennari, best Thanks to the CAP competition sponsors / Merci au commanditaire de la compétition de l’ACP: Thanks to the CAP 2019
CAP event. Our thanks are also extended to all competitors. this in organizing and all of the judges for their extraordinary efforts National Coordinator, and to the CAP’s The (2nd from left in front row) and CAP PHYSICS Placement First Second Third (tie) Third (tie) Placement Second NUCLEAR PHYSICS Placement PHYSICS IN MEDICINE First First Second Third Honourable Mentions MATTER CONDENSED PIC_75_1.indb 7 2019 Student Prize Article
The winners of the 2019 CAP Best Student Presentation Competition at the CAP Annual Congress, 2019 June 3-7 in Burnaby, BC, are listed on pages (6-7). The extended abstracts of those winners of the CAP prizes who submitted them for publication are reproduced below. Ed.
Universality of Spreading Processes with Spontaneous Activity
by Daniel J. Korchinski1, Javier G. Orlandi, Seung-Woo Son, and Jörn Davidsen
hen one forwards a funny email or retweets a Directed percolation is a broad universality class, encom- viral tweet, one participates in a spreading passing the network spreading processes already men- process unfolding on a social network. tioned, along with models of wildfires, catalytic chemical WSpreading processes on networks are ubiqui- reactions, and Reggeon field theory (for a review, see [2]). tous in both human and natural systems: power failures It is characterised by local interactions and a transition can cascade between electrical network substations, action from an active state to a unique absorbing state (see potentials ripple through neural networks, radioisotope Fig. 1a). In the context of disease spreading, a unique tracers traverse predation networks, and computer worms absorbing state exists for the disease of small-pox: no burrow through computer networks [1]. Even processes humans are infected with the disease and it will never embedded in space, such as the percolation of a fluid reappear. However, the requirement of a unique absorbing through porous rock, is a type of spreading on a network. state is not strictly satisfied for many spreading processes.1 Although it might be hard to imagine that such a disparate collection of processes might have any unifying structure For many spreading processes, random initiation drives governing their spread when the underlying systems are recurring outbreaks which then lapse back into the so distinct, a truly marvellous fact is that all of them “absorbing” quiescent state (see Fig. 1c). For instance, exhibit a phase transition as the probability of transmis- neurons cultured in the lab self-organize to a near-critical sion between nodes is increased. To use the language of point, which we know from observing spontaneous scale- epidemiology, when the probability of transmission is low free neuronal avalanches. Initially, these were observed outbreaks are almost always finite (see Fig. 1a and Fig. 1e with directed percolation exponents [3]. However, the “sub-critical”). However, when the reproduction number very fact that we see multiple avalanches indicates that (i.e., the average number of new infections caused by an these neurons cannot strictly belong to the universality infected node) is one, it becomes possible for epidemics class of directed percolation, and recent work has called (outbreaks extensive with the system size) to occur (see the underlying universality class into question [4]. Even in Figs. 1b, 1d). Of course, being a well-behaved phase tran- the case of small-pox, one could envision an unenviable sition, the vicinity of this critical transmission probability future in which it is released from research laboratories is characterised by various scale-free phenomena gov- and the “absorbing” state is shown to be spongy. Therefore, erned by critical exponents that depend only on the dimen- directed percolation is only a good approximation for sys- sionality and topology of the underlying network, thereby tems in which there is a good separation between the time- defining a shared universality class [1]. scale of initiation of ex nihilo activity and the spreading Daniel J. Korchinski and cessation of that activity.
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Fig. 2 An illustration of a spreading process on a simple net- work with spontaneous activation. (Left) A directed net- work consisting of four nodes and four edges. (Right) A sample time series of activations. Spontaneous activa- tions can be identified as those nodes that activate without any of their parents being active in the preceding time- step. When assuming a separation of time-scales, the first two cascades might be falsely labelled a single cascade because they are contiguous. Knowledge of the network Fig. 1 The behaviour of the directed-percolation transition. structure allows us to disentangle independent cascades. a. The number of active sites starting from a single in- Additionally, when there is no separation of time-scales, fected node below the critical point, exhibiting a fluctuat- initially-independent streams of activity can merge, lead- ing active phase that returns to a quiescent absorbing ing to cascades with multiple roots, as occurs in the third state. b. Above the critical point, a single infected node cascade. can lead to an eternal fluctuating steady state. c. Here, nodes are randomly reactivated, but a clear separation of time-scales continues to drive scale-free cascades, de- stroying the absorbing state. d. The fraction of nodes that belong to the largest cluster shows a clear phase transition use the network structure to separate cascades that overlap in time but not in space. However, if one considers cascades defined as the spreading parameter p1 is increased. e. The cascade distribution becomes scale-free at the critical point la- by causal clusters, as has been proposed in the neuroscience belled in panel d. context [8], epidemics can be readily defined and observed for
sufficiently large p1. We found that all three of these measures, the reproduction number equalling one, the Widom line, and the appearance of epidemics, all disagree when p > 0 (see Fig. 3a). node i activates with a probability that depends only on the 0
number of their parents mi,t (we consider networks with directed To determine which of these phase-lines correctly generalized edges) that were active in the preceding time-step: the directed-percolation critical point we conducted numerical and analytical investigations of cascade statistics on all three mi,t Pi,t+1 = 1 − (1 − p0)(1 − p1) (1) phase-lines. We found that only the critical line associated with the appearance of epidemics produced the expected scale-free
In the case that the spontaneous activation parameter p0 = 0, we behaviour in the cascade distribution [5]. Additionally, for sim- have a simple branching process, which falls into the universal- ple network structures, that line can independently be derived
ity class of directed percolation, while for p1 = 0, we simply have by identifying the set of points that cause the correlation length dynamical percolation, belonging to the distinct universality or average cluster size to diverge. However, in our investigation class of undirected (isotropic) percolation (for a comparison, we also found something quite surprising on the critical line: a
see [6]). Finding a well-defined critical point for p0 > 0 is chal- cross-over between two distinct sets of critical exponents (see lenging. In directed percolation, there are several measures that Fig. 3b). Small cascades obey statistics P(s) ~ s-1.5 that would could be used to define the critical point: it could be identified correspond to the universality class of mean-field directed per- with a unity reproduction number, or with a divergence in the colation; however, large cascades obey statistics corresponding susceptibility of the active fraction, or as the point at which epi- to undirected percolation, P(s) ~ s−2.5.
demics appear. However, when p0 > 0, it’s not so clear which measure to use. Since cascades merge and over-lap, nodes can Nonetheless, all outbreaks on the critical line exhibit the same −3/2 −2/3 have more than one parent (see Fig. 2), meaning the reproduc- universal scaling p(s) ~ s g(s/sm) with sm ~ p0 , for a cross- tion number, s, (defined by the mean number of active daughters over scaling function g(x) (see Fig. 3c). The transition between × to an active node) is not simply s = p1 (average number of these regimes is set by the scale at which the merging of cas- outgoing connections) as it is in directed percolation. Further, the cades occurs (see Fig. 3d). For systems with a lower rate of spon- susceptibility no longer diverges, but instead attains a maximum taneous activation, encountering another cascade is unlikely, and on a Widom line [7]. Even defining cascades in the presence of so the directed percolation exponents survive to larger sizes. The spontaneous activity is challenging, because initially-independ- eventual dominance of the undirected percolation exponents is ent cascades can merge together (see Fig. 2). It is necessary to guaranteed because the isotropic correlation length diverges on
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Fig. 3 Simulations of outbreaks on the critical line for a simple 10-regular network. a. The phase diagram for the spreading process with re- DP activation in the vicinity of the directed percolation critical point p1c . s denotes the reproduction number (i.e., average number of daughters). b. The outbreak distribution on the critical line is asymptotically scale-free, and exhibits a transition in the scaling expo- −3/2 nent. c. The data in b, rescaled to exhibit a universal curve collapse, with p(s) ~ s g(s/sm). The curve collapse explicitly gives the 0 −1 functional form of the cross-over function g(s/sm), showing that g(x << 1) ~ x and that g(x >>1) ~ x . d. The data of c, partitioned into
outbreaks with and without merging of activity, reveals that the exponent transition at sm is precisely when the merging of avalanches dominates.
the critical line, meaning that the anisotropy associated with the between the initiation and propagation of activity. When those time-direction of the spreading process (i.e., the “directed” part time-scales mix, the cooperation of initiation and spreading of the associated percolation problem) must vanish. More sim- changes the underlying universality class to one of undirected ply, one cascade can merge with another one that was initiated percolation. Characteristics of directed percolation survive only either before or after it, restoring a time-symmetry that is not on the smallest scales, with exponents related to undirected present in directed percolation, where activations always follow percolation dominating asymptotically. Our work provides a from their parent. This additional symmetry removes the absorb- bridge between two fundamental universality classes of non- ing state that defines directed percolation, lifting the universality equilibrium statistical physics and implies that spreading pro- class from directed to undirected percolation. We have tested the cesses with spontaneous activity are fundamentally distinct robustness of our findings on a variety of network topologies, from ordinary spreading processes. including brain-connectome analogues, fat-tailed, and small- world networks, finding in each case numerical results that ACKNOWLEDGEMENTS exhibit a transition between universality classes [5]. We would like to acknowledge the fruitful discussions we enjoyed with Rashid Williams-García. This project was finan- CONCLUSION cially supported by NSERC, Alberta Innovates, the Eyes High The universality class of directed percolation appears in myriad Initiative at the University of Calgary, and the Korea-Canada places, but only when one assumes a separation of time-scales Cooperative Development Fund through the NRF of Korea.
REFERENCES 1. A. Barrat, M. Barthelemy, and A. Vespignani, Dynamical processes on complex networks, Cambridge University Press, 2008. 2. H. Hinrichsen, “Non-equilibrium critical phenomena and phase transitions into absorbing states”, Advances in Physics, 49(7), 815-958 (2000). 3. N. Friedman, et al., “Universal critical dynamics in high resolution neuronal avalanche data”, Physical Review Letters, 108(20), 208102 (2012). 4. Y. Mohammad, et al., “Neuronal avalanche dynamics indicates different universality classes in neuronal cultures”, Scientific Reports, 8(1), 3417 (2018). 5. D.J. Korchinski, et al., “Modelling zoonotic diseases, cooperation between spreading and spontaneous infection”, ArXiV, 1908-08163 (2019). 6. M. Henkel, H. Hinrichsen, and S. Lübeck, Non-equilibrium phase transitions, Volume 1: Absorbing phase transitions, Springer, 2008. 7. R.V. Williams-García, et al., “Quasicritical brain dynamics on a nonequilibrium Widom line”, Physical Review E, 90(6), 062714 (2014). 8. R.V. Williams-García, J.M. Beggs, and G. Oritz, “Unveiling causal activity of complex networks”, EPL, 119(1), 18003 (2017).
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Cosmological Constraints on Hidden Physics
by Lindsay Forestell1, David E. Morrissey, and Kris Sigurdson
THE HUNT FOR NEW PHYSICS something else? How does gravity, which works so well on cosmological scales, interact with the quantum field he Standard Model (SM) of particle physics does a theories of particle physics? Where did the matter of the remarkable job of explaining the nongravitational Universe actually come from? These are only a few of the forces of nature. These include the strong, weak, questions that are being asked by todays scientific com- Tand electromagnetic forces, as well as all of the cor- munity. The search for these answers drives much of responding particles. These particles include quarks, lep- what we explore moving forward, both in theory and tons, and their force carriers: photons, gluons, W bosons experimentally. and Z bosons. In 2012, the discovery of the Higgs boson at the Large Hadron Collider (LHC) completed the current model of particle physics, and brought all of our theoretical DARK FORCES1 knowledge in line with our experimental observations [1,2]. We have been searching for the answers to these puzzling This was a monumental success, but as successful as the problems for some time now. While the LHC continues to SM is, it still has some weaknesses. For example, neutri- push the frontiers on precision particle physics, everything nos, the neutral partners to the charged leptons (electrons, we have seen since the discovery of the Higgs boson has muons, and taus), should be massless. However, observa- been in line with what we would expect from the Standard tions of solar and atmospheric neutrino oscillations Model, and does not (yet) hint at the new physics we wish between different flavours indicate that they do in fact to find. We have also dedicated entire search programs to have mass, in direct contradiction with the SM [3,4]. the hunt for dark matter (typically WIMP-like dark matter, Further to this, we have measured the mass of many of the but many other programs have been started as well), with other particles, but we do not know why everything has no results so far [5]. Because of this, we have begun to the mass that they do (and in fact, some calculations indi- extend our search even further, to look for harder to find cate that the ‘smallness’ of the Higgs boson mass is a real physics in more creative places. One such possibility is the problem in the Standard Model!). These are just a few search for dark sector forces, which would have minimal examples of the need to search for new particles and new connections to the Standard Model. These forces would physics beyond the Standard Model. evade the conventional searches, but could possibly be constrained using the cosmological laboratory. An exam- We have a second ‘Standard Model’ of cosmology that has ple of the interactions possible for such a dark force are done the same thing for our understanding of the evolution shown in Fig. 1. The dark sector could be produced by of the Universe that the regular SM has done for particle some small interaction with the visible sector, evolve on its a,b physics. Called the ɅCDM model, we require a source of own, or decay and create regular particles that then interact Lindsay Forestell
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Production RegularPhysics Self-Interactions
Visible Sector Dark Sector
Observation
Fig. 1 Visualization of the connections possible between the visible and dark sectors.
Fig. 3 Abundance of dark glueballs that can be produced in the early Universe as afunction of the mass of the glueballs (horizontal) and temperature of the hidden sector relative to the visible (vertical). Everything above the bold white line is ruled out by overproduction of dark matter.
Fig. 2 Schematic depiction of confinement of particles in QCD. At high energies(μ) asymptotic freedom leads to free states of quarks and gluons, while low energies leads to bound states of the particles we are familiar with, the me- sons and hadrons. The vertical axis depicts a, the cou- pling strength between fields in the theory.
and neutrons), and mesons (pions). It even predicts bounds states of pure glue, known as glueballs.
In our dark force, we do not include dark quarks, so the only bound state we expect is the glueball. This is what we focused on in our study. We asked and answered questions such as:
• Does it interact with itself? – They actually have unique self-interactions that are often termed ‘cannibalism’ due to the fact that three glueballs can collide and only two come out. Fig. 4 Cosmological constraints that can be placed on dark glue- • What would its abundance be? balls. These span many orders of magnitude in the possi- – This is heavily dependent on the mass of the dark glueball ble lifetime of the glueball, from seconds to the age of and temperature of the dark sector. If the correct condi- theUniverse. The vertical axis represents the net abun- tions are met, we can reproduce the dark matter abundance dance of glueballs present before they began to decay: the required by ɅCDM. This is shown in Fig. 3. horizontal black line specifically refers to a Universe in • Is there more than one type of glueball? which the dark glueball makes up 100% of the measured – There is in fact an entire spectrum of glueball states. total dark matter abundance. Any portion of the parame- However, most of the interesting physics is tied up in the ter space above a different constraint curve is ruled out. Over nearly every epoch, a different observation can be lightest state (where JPC = 0++), and so we can keep our- used to place constraints on the model. selves focused to only a small subset of the glueballs.
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• Can it interact with regular matter? subsequent observations) is highly constrained [6,7]. Thus, a – Yes! The amount of interaction is heavily regulated by new particle such as a dark glueball can only have small inter- various cosmological constraints, which we look at in actions (such as a feeble decay to photons or regular gluons). more detail further on. Even further, a glueball that has a lifetime around the age of the Universe would be expected to produce gamma ray signals COSMOLOGICAL CONSTRAINTS today, which we could look for with our high energy tele- scopes. All of these together can be used to put strict limits on The final piece of the puzzle is how we can constrain such a not only the possible mass of these dark glueballs, but also dark force. The answer comes from our high precision cosmo- how strongly they may interact with the SM. Thus, we can use logical observations. We can probe different epochs in the his- the cosmological laboratory to provide complementary con- tory of the universe using different observations, examples of straints to those from dark matter and collider searches in our which are shown in Fig. 4. For example, studies of the lightest ever evolving hunt for clues to unravel the mysteries we have elements seen today tell us about Big Bang Nucleosynthesis, before us. which were the few moments responsible for producing the entirety of helium in the early Universe. Moving forward in time, we can actually see the ‘last scattering surface’ which is the last time the background light of the Universe interacted ACKNOWLEDGEMENTS strongly with free electrons. This light is now what we know The authors would like to thank the Canadian Association of to be the Cosmic Microwave Background (CMB), which we Physicists for the opportunity to share this work. This work is have probed extensively with a multitude of experiments. As supported by the Natural Sciences and Engineering Research both of these epochs are very well understood in our current Council of Canada (NSERC), with D.M. and K.S. supported in theoretical framework, any disturbance to these models (and part by Discovery Grants and L.F. by a CGS D scholarship.
REFERENCES 1. G. Aad, et al., (ATLAS), Phys. Lett. B716, 1 (2012), 1207.7214. 2. S. Chatrchyan, et al., (CMS), Phys. Lett. B716, 30 (2012), 1207.7235. 3. Y. Fukuda, et al., (Super-Kamiokande), Phys. Rev. Lett. 81, 1562 (1998), hep-ex/9807003. 4. Q.R. Ahmad, et al., (SNO), Phys. Rev. Lett. 89, 011301 (2002), nucl-ex/0204008. 5. M. Schumann, (2019), 1903.03026. 6. K. Jedamzik, Phys. Rev. D74, 103509 (2006), hep-ph/0604251. 7. J.M. Cline, and P. Scott, JCAP 1303, 044 (2013), [Erratum: JCAP1305,E01(2013)], 1301.5908.
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PIC_75_1.indb 13 6/5/20 8:37 AM 2019 Student Prize Article
Characterizing the Flexibility of the Body’s Building Block: Collagen
by Alaa Al-Shaer1, Aaron Lyons, and Nancy R. Forde
WHAT IS COLLAGEN? this repeating unit, where collagen type IV has missing glycine residues which lead to triple-helical interruptions ollagen is the fundamental building block of ani- within the molecule. A central question is how these inter- mals and is the most abundant protein in our bod- ruptions contribute to the flexibility of collagen, and this ies [1,2]. Its evolutionary origins trace back to the is what we aimed to address in our studies. Cdawn of metazoan organisms, where it supported the coalescence of multicellular life forms [3,4]. ATOMIC FORCE MICROSCOPY1 Different types of collagen are localized to different tis- We use atomic force microscopy (AFM) as our experi- sues and can form various higher-order structures. The mental tool to study the mechanical properties of collagen most abundant class are the fibril-forming collagens, molecules. AFM is a type of scanning probe microscope which align in a staggered parallel fashion and give rise to that utilizes a sharp tip to image the nanoscale topological long fibrillar nanostructures (Fig. 1A). The basic struc- features of a surface. By using a laser detection system, tural unit of this fibril is the 300-nm-long triple-helical the instrument can record the deflection of the tip as it collagen molecule. Assembled from three polypeptide scans across the surface to yield a height map of any fea- chains in the inner compartments of a cell, the molecule is tures present. We start our sample preparation by deposit- trafficked to the outside of our cells where it assembles ing collagen molecules onto mica – an atomically flat into higher-order structures, such as the fibril. However, surface commonly used for imaging biological samples. collagen molecules can also assemble into networks, as Once deposited, the molecules adhere to the surface [6]. shown in Fig. 1B. These networks play an essential role in When imaged with AFM, collagen molecules appear as providing a filtration barrier to macromolecules around elevated string-like features on the flat mica background organs such as kidneys [5]. Whereas fibrils consist primar- (Fig. 1). The AFM images provide us with an ensemble of ily of collagen type I molecules, collagen network struc- conformations adopted by the collagen molecules, and we tures are typically formed by collagen type IV molecules. Alaa Al-Shaera can use these conformations to extract information related In this short article, we report on the mechanical proper-
and Summary Once a set of collagen chains has been traced, the coordi- nates along the backbone and the tangent vectors along cDepartment of This article investigates the structural impact Physics, University of local sequence variations along the con- of Alberta, tour of collagen, by sampling AFM-based 1. Alaa Al-Shaer received 3rd place in the CAP Best Student Oral Edmonton, AB images and performing statistical analyses. Presentation competition at the 2019 CAP Congress at Simon Fraser T6G 2E1 University in Burnaby, BC.
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The persistence length is best described. as the length along the contour over which the corre- lation of chain tangent vectors drops by a factor of e. Thus, persistence length characterizes the chain’s flexibility, and is the mechanical prop- erty on which we focus.
We calculated the mean squared end-to-end distance Rs2 ()∆ and the mean dot product of the starting and ending unit tangent vectors tsˆ .() tsˆ ()+∆s for segments of length DS within the pool of traced chains. The mean squared end-to-end distances and tangent vec- tor correlation data are fit with the predictions of the worm-like chain (WLC) model, described in Eqs. 2 and 3, to estimate persis- tence length (Fig. 2B).
∆s − 2 2 p Rs()∆=41ps∆− 1− e 2 p (2) ∆s
∆s − tsˆˆ()⋅+ts()∆=sscosθ ()∆=e 2 p (3)
The plots in Fig. 2B show that collagen can be well-described by the WLC model.
The persistence length obtained for collagen type IV (p ≈ 41 nm), reveals that it is significantly more flexible than fibrillar collagen type I (p ≈ 104 nm). Could this enhanced flexibility be attributed to the presence of triple-helical inter- Fig. 1 Atomic Force Microscopy (AFM) and supramolecular organizations of ruptions? We decided to take a closer look at fibrillar and network-forming collagens. AFM images of (A) collagen the amino acid sequence of collagen type IV type I and (B) collagen type IV molecules deposited from 100 mM KCl, 1 mM HCl (pH ~ 3) with schematics of their corresponding molecular struc- and map out where these interruptions are tures and supramolecular assembles placed above and to the right of the along the contour of the molecule. AFM images, respectively. SEQUENCE-DEPENDENT ANALYSIS To perform a sequence-dependent analysis, we the chains are collected by the program. To relate these confor- need a sense of directionality to the chains so that we can align mations to collagen’s mechanical properties, we use the worm- them at the same end. The collagen type IV molecules have a like chain model, depicted schematically in Fig. 2A. The model discernable “knob” at one end, which marks its C-terminal glob- describes a semi-flexible polymer, where short segments adopt ular domain, and so we use it as a marker to trace chains starting straight conformations (the lowest-energy state) at zero tem- at the edge of the knob. A schematic structure of collagen type perature. In the presence of thermal fluctuations of energy, k T, B IV is represented in Fig. 3B, where the boxes correspond to the segments adopt smoothly curved conformations. The energy tripe-helical segments, and gaps to overlapping interruptions required to bend a segment of length Δs into an arc with angle q where all three chains possess a non-triple-helix-forming between its ends is related to the polymer’s persistence length, sequence. One can see that the chains have more interruptions at which we denote with the symbol p: the end further from the knob. In addition, by inspecting the AFM images, we can see that the collagen IV molecules appear 2 pθ to be more flexible towards that end as well. To quantitatively Ebend = kTB . (1) 2∆s show this, we devised an algorithm that performs a
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Fig. 2 Homogeneous analysis of collagen to extract persistence length. A. The Worm-Like Chain (WLC) model. B. The persistence lengths were obtained using Rs2 ()∆ (black; Eq. 2)) and cosθ ()∆s (gray; Eq. 3) analyses, as shown for the collagen data here. These data are fit well by the predictions of the worm-like chain model. The fibrillar collagen type I possess a persistence length of p ≈ 104 nm [6] (N = 100 chains), while collagen type IV exhibits a substantially lower overall persistence length of p ≈ 41 nm (N = 280 chains).
sequence-dependent analysis to determine how these local exhibits minima, further supporting the concept of interruptions sequence variations affect flexibility. The algorithm works by providing enhanced flexibility to the structure. Lastly, we note that calculating an effective persistence length at 1 nm increments where there are longer stretches of triple-helical segments, we along the contour of the chain, using a chain segment of fixed capture the persistence length found for fibrillar collagen type I, length Δs = 30 nm centered at each of these positions along the which are continuously triple-helical molecules [6]. contour, s. Since the angular distribution for a worm-like chain segment is expected to be Gaussian with zero mean and vari- CONCLUSION ance equal to the ratio of its segment length Δs and persistence length p, an effective persistence length for the segment centred Our results shed light onto the heterogeneity of the collagen at position s can be calculated as type IV molecule and the effects of triple-helical interruptions on its flexibility. By performing statistical analysis, we can gain insight onto the structural consequences of interruptions – a fea- ∆s ps* = . ture that is incompletely understood and lacking a well-defined () 2 σ s (4) θ () biological role. The differences seen in the flexibility of fibrillar and network-forming collagen may be manifest by the type of higher-order structures they assemble into, where collagen type q As seen in Fig. 3A, the distributions of angles (Δs) extracted I assembles into fibrils which are more rigid structures than the from our AFM images are well described by a Gaussian distribu- networks formed by collagen type IV. tion with zero mean. Our collagen type IV effective persistence length profile is shown in Fig. 3B, where the profile has been ACKNOWLEDGEMENTS aligned with the expected structure of collagen type IV. We can see that at the end far from the knob, the persistence length signifi- This work was supported by a Discovery Grant from NSERC. cantly drops, in agreement with our visual argument made earlier. We are grateful for the assistance provided by our collaborators, This shows that an increase in interruptions is indeed correlated Sergey Budko and Billy G. Hudson from Vanderbilt University. with an enhanced flexibility of the molecule. Also, where there are We would like to give a special thanks to ChangMin Kim for overlapping interruptions, boxed in black, the persistence length assistance with AFM instrumentation.
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Fig. 3 Position-dependent persistence length profile of collagen type IV. A. For segments of length Δs each centered at a distance s along the backbone from the “knob” of each chain, the effective per- sistence length is determined by the variance of angular changes θ(Δs) among these segments (Eq. 4). B. Collagen type IV structural representation (box = triple-helical, gap = overlapping interrup- tion) aligned with the persistence length profile, where the dashed line indicates the persistence length found for the continuously triple-helical fibrillar collagen type I [6], and the arrows corre- spond to key overlapping interruptions that locally increase flexibility.
REFERENCES 1. A. Sorushanova, et al., “The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development”, Adv. Mater. 31, 1-39 (2019). 2. M.W.H. Kirkness, K. Lehmann, and N.R. Forde, “Mechanics and Structural Stability of the Collagen Triple Helix”, Curr. Opin. Chem. Biol. 53, 98-105 (2019). 3. A.L. Fidler, et al., “Collagen IV and basement membrane at the evolutionary dawn of metazoan tissues”, eLife. 6, e24176 (2017). 4. A.L. Fidler, et al., “The triple helix of collagens – an ancient protein structure that enabled animal multicellularity and tissue evolution”, J. Cell Sci. 131, jcs203950 (2018). 5. B.G. Hudson, “The molecular basis of Goodpasture and Alport syndromes: Beacons for the discovery of the collagen IV family”, J. Am. Soc. Nephrol. 15, 2514-2527 (2004). 6. N. Rezaei, A. Lyons, and N.R. Forde, “Environmentally controlled curvature of single collagen proteins”, Biophys. J. 115, 1457-1469 (2018).
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PIC_75_1.indb 17 6/5/20 8:37 AM 2019 Student Prize Article
Search for Neutrino Trident Events in IceCube
by Sourav Sarkar1 and Roger Moore
tandard Model (SM) of particle physics has been a THEORETICAL MOTIVATION OF great success with the discovery of the fundamental NEUTRINO TRIDENT PRODUCTION1 particles and their interactions via strong, weak and Neutrino is one of the SM fermions and they do not Selectromagnetic forces. However, neutrino oscilla- carry any charge. Therefore, neutrinos can interact only tion experiment [1] observed that starting with one par- via weak interaction by exchanging charged W boson ticular flavour of neutrino from source, it can be detected (charged current (CC) interaction) or neutral Z boson as a different flavour of neutrino in the detectors. This (neutral current (NC) interaction). Cross-section of phenomena, known as neutrino oscillation, requires the sub-dominant process like NTP is several order of mag- neutrinos to have tiny nonzero masses which directly con- nitude less than the cross-section of standard CC or NC tradicts the prediction of massless neutrinos in SM. Many neutrino interactions. However, dedicated study of beyond standard model (BSM) theories (e.g., supersym- NTP process can be used as powerful probe into the metry (SUSY), string theory) have been developed to search for BSM physics. In NTP process, an incoming incorporate such experimental anomalies and require neutrino interacts with the coulomb field of a nucleus presence of additional fundamental particles that have not and creates three outgoing leptons (an outgoing neu- been observed yet. One of the processes that can probe trino and two charged leptons) and a recoiled nucleus into the new physics (NP) is neutrino trident production as seen in Fig. 1. NTP processes can be both CC and (NTP) which is our point of interest in this article. NTP is NC depending on the exchange of type of weak bosons. a sub-dominant SM process which can also produce new However, weak bosons can also be replaced by addi- intermediate particles and we can constrain the properties tional BSM vector (scalar) bosons Z′ (S′) from L − L of these new particles by observing the final state parti- µ τ model [3]. The presence of such additional BSM bos- cles. Several collider and neutrino beam experiments are ons can enhance the NTP event rate significantly. looking for BSM particles, however, their search is lim- CHARM II [5], CCFR [6], and NuTeV [7] have ited by upper limits of the beam energy (~ 10TeV) and observed NTP events in the past and based on their luminosity (i.e., rate of events). Detection of neutrinos at observed event rate, limits on the mass-coupling con- the IceCube neutrino obeservatory [2] relies on the natural stant parametric space have been set which can be seen sources of neutrinos (e.g., atmosphere, astrophysical in Fig. 2 [4]. Among all the NTP processes, we are sources) that can produce neutrinos with energy as high as interested in only the channels that produce two outgo- ~ 10PeV. Therefore, search for NTP events in IceCube can ing muons (µ±) as the charged leptons. To investigate have a potential advantage over any collider or beam the feasibility of detecting NTP events in the higher experiments. energy regime, we calculate the SM cross section and In this article we will briefly discuss the theoretical moti- simulate events of NTP processes that produce di- vation of searching for NTP events in section 2. Section 3 muons using equivalent photon approximation (EPA) summarizes the details of IceCube detector and the aspect with CalcHep [8]. From Fig. 3 [left], we notice that the of detecting NTP events and potential challenges in CC contribution of the total cross-section increases IceCube. And, finally in section 3, we conclude our dis- with steeper slope at around ~ 4TeV incoming neutrino cussion by summarizing the article. energy. Right side plot of Fig. 3 shows that W boson becomes on-mass shell (i.e., resonance at ~ 80GeV), Sourav Sarkar which is responsible for increase in the cross-section.
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Fig. 1 [Left]: Feynman diagrams for SM NTP processes. N is the interacting nucleus and l is the charged lepton with flavours α, β = e, µ, τ . [Right]: Feynman diagram replacing Z boson with BSM bosons Z′ and S′.
quantum efficiency (QE) PMTs (i.e., better resolution) to probe into lower energy neutrino interactions. This densely spaced core of the detector is called DeepCore volume which is an order of magnitude smaller compared to the full detector volume. When a muon neu- trino interacts in the detector via CC interaction, it produces a high energy muon that can travel a long distance through ice before los- ing its energy in the surrounding medium and decay. Cherenkov radiation detected from such muons look like elongated tracks in the detector (as shown in Fig. 5 [left]), so they are called ’track-like’ event. For all other neutrino interactions (all flavour of NC interac- tions and electron- and tau-neutrino CC interaction) where second- ary particles are other than a muon, they create electromagnetic and hadronic shower in ice where multiple charged particles produce Cherenkov radiation in all direction from the primary interaction vertex allowing the detector to see light isotropically (shown in Fig. 5 [right]) and these events are called ’cascade-like’ events.
For the search of NTP events, we are only interested in di-muon production channels, i.e., we will be looking only into track-like events in IceCube. Moreover, there are two muons generated Fig. 2 Parameter space for Z′ gauge boson. Shaded region above through NTP process simultaneously, so the goal of this research the lines is the excluded region. is to look for double-track events in IceCube. We rely on the abundant atmospheric neutrino sample (neutrinos that are cre- ated in the earth’s atmosphere from the interaction of cosmic rays) for NTP event search. From the well established atmos- SEARCH FOR NTP EVENTS IN ICECUBE pheric neutrino flux, calculated NTP cross-section and effi- DETECTOR ciency of detecting track events in IceCube, we can estimate the expected NTP event rate for only SM contributions in both IceCube neutrino observatory, located at the geographic south pole IceCube and DeepCore detector which is given in Table. 1. uses a cubic kilometer of antarctic ice as its detector vol- ume. When a neutrino interacts in the ice, it deposits either a fraction or Now that we have an expected NTP event rate, our immediate all of its energy which creates high energy charged particles in the challenge is to build an efficient event reconstruction tool that medium. If these charged particles travel faster than the phase can distinguish the difference between a single-track event velocity of light in ice they emit photons via Cherenkov radiation. (standard CC) and a double-track event (NTP). The ability of IceCube detector aims to detect the Cherenkov photons to get detecting double-track events depend on the detector resolution information about the primary inter- action by reconstructing and separations between two tracks. If the separation is too energy, direction and flavour of incoming neutrinos. To detect these small, light from those two tracks are not resolvable which can Cherenkov photons, 5160 digital optical modules (DOMs) consist- make the double-track and single-track events indistinguishable ing of photomultiplier tubes (PMTs) and related electronics are from each other. We are currently in the process of exploring installed in the ice ( shown in Fig. 4 [left]). These DOMs are instru- and exploiting double track signature to develop reconstruction mented on 86 strings at a depth from 1450 m to 2450 m from the algorithm that can detect such event topology. In order to surface at the south pole as shown in Fig. 4 [right]. The volume of explore the properties of double track events, we have created the full detector is one cubic kilometer and in the middle of the toy Monte Carlo (MC) simulations of NTP events in IceCube detector, there is a densely spaced infill array of DOMs with higher detector, two sample events are shown in Fig. 6. We are also
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Fig. 3 [Left]: Total Cross-section of NTP channel of di-muon production. [Right]: Distribution of W boson invariant mass and opening angle between two outgoing muons. Peak at 80GeV shows the presence of on-mass shell W boson.
Fig. 4 [Left]: DOM with PMT placed in the bottom half. [Right]: Schematic of IceCube detector configuration.
Fig. 5 Track-like (left) and cascade-like (right) event topology in IceCube.
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TABLE 1 Estimated NTP and CC event rates from SM in IceCube [left] and DeepCore [right]. IceCube Volume DeepCore Volume Emergy range 100GeV – 5TeV Emergy range 1GeV – 1TeV ~9.35 NTP events/year ~2.17 NTP events/year ~34, 975 standard CC events/year ~192, 060 standard CC events/year
Fig. 6 Double track NTP event simulations in IceCube.
working on determining the limit of the track separation below are limited by energy of incoming neutrinos to detect significant which it is not possible to detect NTP signal events from stand- number of trident events that can set a strong constraint on the ard CC background. BSM bosons search limit. In this work, we explore the possibility of detecting NTP events in IceCube with some advantage over standard collider and beam experiments. However, poor detector CONCLUSION resolution and large background events are the challenging hur- In summary, NTP process can be used as a powerful probe into dles that we need to overcome to get more constraining BSM the study of new physics. Collider and neutrino beam experiments boson search limit by detecting double track NTP events.
REFERENCES 1. Y. Fukuda, et al. [Super-Kamiokande Collaboration], Phys. Rev. Lett. 81, 1562 (1998). doi:10.1103/PhysRevLett.81.1562 [hep-ex/9807003]. 2. F. Halzen and S.R. Klein, Rev. Sci. Instrum. 81, 081101 (2010). doi:10.1063/1.3480478 [arXiv:1007.1247 [astro- ph.HE]]. 3. X.G. He, G.C. Joshi, H. Lew, and R.R. Volkas, Phys. Rev. D 44, 2118 (1991). doi:10.1103/PhysRevD.44.2118 4. W. Altmannshofer, S. Gori, M. Pospelov, and I. Yavin, Phys. Rev. Lett. 113, 091801 (2014). doi:10.1103/PhysRevLett.113.091801 [arXiv:1406.2332 [hep-ph]]. 5. D. Geiregat, et al. [CHARM-II Collaboration], Phys. Lett. B 245, 271 (1990). doi:10.1016/0370-2693(90)90146-W. 6. S.R. Mishra, et al. [CCFR Collaboration], Phys. Rev. Lett. 66, 3117 (1991). doi:10.1103/PhysRevLett.66.3117. 7. T. Adams, et al. [NuTeV Collaboration], In *Vancouver 1998, High energy physics, Vol. 1*, pp. 631-634 [hep-ex/9811012]. 8. S.F. Ge, M. Lindner, and W. Rodejohann, Phys. Lett. B, 772, 164 (2017). doi:10.1016/j.physletb.2017.06.020 [arXiv:1702.02617 [hep-ph]].
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PIC_75_1.indb 21 6/5/20 8:37 AM 2019 Student Prize Article
Shaping Arbitrary Energy Landscapes with Feedback
by Avinash Kumar1 and John Bechhoefer
he interaction of light with matter at the nanoscale Since an optical tweezer exerts a force to counteract fluc- has been a topic of great importance over the past tuations, it can be used to provide feedback forces on col- several decades. After pioneering work by Ashkin loidal particles to probe and manipulate their dynamics Tet al. [1], optical tweezers have been used to exert with high resolution and bandwidth. forces on small mesoscopic particles as well as to detect their fluctuations for physical [2,3], chemical [4,5], and Here, we combine the technique of optical tweezers with biological applications [6-8]. Other forms of tweezers use feedback control to create virtual potentials by applying forces based on optofluidics [9], plasmonics [10], and varying forces on a particle. The feedback protocolinvolves photophoresis [11]. observation of the position of a freely diffusing particle, cal- culation of a force based on an imposed potential and appli- In addition to passive traps that create potential wells to cation of that force (Fig. 1). Optical tweezers have previously confine particles, there are traps that create virtual poten- used feedback to create position and force clamps [17-19]. tials that confine particles using active feedback based on In a force clamp, feedback is used to apply a constant force position measurements of the trapped object. Such feed- on the trapped particle. In a position clamp, the forces are back traps need only create a force of controlled magni- varied to keep a particle at a desired position. In our version tude and direction and apply confinement based on of feedback trap, we update force and position at rates of feedback from position measurements. The feedback trap order 100 kHz to create a virtual energy landscape. It should can be based on a variety of forces, including electrokinet- be noted that these virtual potentials are discrete approxima- ics [12], magnetism [13], and thermophoresis [14]. tions of real potentials. In a real potential, forces are applied Sometimes the goal is to apply a more complicated force instantaneously as the position changes, but in a virtual field rather than just creating a trap [15]. Feedback traps potential, feedback forces are set once per feedback loop based on optical tweezers [16] use forces from the under- and are approximately constant throughout the loop. The lying harmonic potential to achieve such goals. In this performance of a feedback trap is limited by the amount of article, we explore the idea that using feedback based on latency (delay) in the control system.1 the measured particle position, one can create essentially arbitrary potentials. Our feedback optical tweezer is based on a homemade microscope. A water-immersion high-numerical-aperture Typically, an optical tweezer uses a tightly focused microscope objective (60X, NA = 1.2) is used for trapping. Gaussian beam to trap microspheres. In our experiment, A low-numerical-aperture microscope objective (20X, we trap 1.5 µm diameter silica beads. A particle in a trap NA = 0.4) focuses the detection laser on the trapped particle can be modelled as a dielectric particle placed in an in- to detect the fluctuations. The trap centre is shifted regu- homogeneous electric field. Forces acting on the particle larly to create a feedback force. This is done by an acous- from the external field are categorised into scattering and tooptic deflector which is imaged on the back focal plane of gradient forces. Scattering forces arise from momentum the trapping objective. Angular deviation of the deflector transfer from photons to particle and push the particle output is translated into a linear shift in the trapping plane. along the direction of propagation of the light. Gradient A quadrant photodiode detector is used to read the signals forces arise from gradients in the electric field and act in from the trapped particle. In order to precisely apply the Avinash Kumar the direction of increasing electric field. If the total gradi- feedback forces, the feedback timing should be accurate.
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Fig.2 Powerspectraldensityfordifferentfeedbackgains.Thered plotcorrespondstothe“openloop”opticaltweezer(nofeed- back). The other curves correspond to different feedback Fig.1 Onecycleofafeedbacktrap.Measurement:estimatethe gains.Feedbackcancreatebothstifferandweakertraps. currentpositionoftheparticle,Decision:calculateforce basedontheimposedpotential(red),andAction:apply theforcebyshiftingtheharmonicwellcentre(blue).
Usingfeedback,wecreatevirtualharmonicwellsofvariable stiffness[16].Asimilarinstrumenthasbeendevelopedindepen- dentlybyAlbayet al.[20].Thediscretedynamicsofaparticle inavirtualharmonicwellisgivenas
~ t xn+1=xn − a(xn−xn)+xn (1a)
t xxn =− (n 1)G (1b)
xxn =+ ζ , nn−2 (1c)
Fig.3 Power spectral density in x, y and z directions. Inset: wherexn istheparticle’srealposition,x¯ ntheobservedpositions, xt thetrappositionattimet , x theintegratedthermalnoise,z powerspectrumdensitywithoutfeedback.Withx and y n n n n feedback,allthreedimensionsshowthesamestiffness. theintegratedmeasurementnoise,andG≡kv/kt isadimension- lessgain.Here,k isthestiffnessofthevirtualtrapandk thatof v ~ t therealtrap.Theconstanta = G[1—exp(Dt/tr)]accountsfor therelaxationinthetrapduringonecycleofthefeedbackloop, axial stiffness is weaker than the transverse stiffness. See
Dt.Here,tr = g/ktistherelaxationtime,gtheviscousdragcoef- theinsetinFig.3.Thisasymmetryisaninherentfeatureofthe ~ ≈ ficient.WeoperateourtrapinthelimitDt << tr wherea a ≡ electric-fieldgradientofaGaussianbeam.Figure3showsthat
Dt/tr.Thefeedbackdelaytimeistd =20μs=2Dt. the usual anisotropic trap can be made isotropic in all three dimensionsusingfeedback.Weusedthefeedbacktoreducethe Figure2showsthatwecanchangetheeffectivestiffnessofa trappingstrengthinthetransversedirectionssothatitmatches virtualtrapusingfeedbackatconstantlaserpower.Weobtained theaxialstiffness.Isotropyisanimportantproperty,asitallows a30-foldgaininthestiffnessofthetrapcomparedtothatofthe aforcesensortomeasurethree-dimensionalforcesinastraight- underlying harmonic trap. Often changes in trap stiffness are forwardmanner.Inananisotropictrap,onewouldhavetoallow createdbyvaryingthetotallaserintensityinthetrap.Inafeed- fordifferentbandwidthsindifferentdirections,whichcompli- backtrap,asimilarcontrolisachievedbychangingthefeed- catestheinterpretationofforcemeasurements. backgainα.Forlargevaluesofα,theparticledynamicsdeviates frompotentialmotion,showingoscillationsandeveninstability Todemonstratetheflexibilityofourfeedbacktrap,wecreatea becauseofovercorrection[21].Weworkwithα valueswhere varietyofvirtualpotentialssuchasharmonicwell,double-well thevarianceisminimum. and linear potentials (Fig. 4). In Ref. [16], we have shown a familyofdouble-wellpotentialswherethebarrierheight,well Anotherinterestingfeatureofafeedbacktrapisitsabilityto separation and the curvatures are controlled independently. reduce trap strength [16]. In an ordinary optical tweezer, the Note that for a linear potential, the curvature at the centre is
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Tanzanianhigh-schoolstudentErastoMpembain1969,when twoidenticalwatersamplesarepreparedinitiallyathotand warmtemperaturesandthenquenchedtoacoldtemperature, the hot system can cool (and freeze) faster than the warm one—aphenomenonnowknownastheMpembaeffect[23]. Thecoolinganomalyhasbeenpredictedtheoreticallyinother systemssuchasnanotuberesonators[24],spinglasses[25], andexperimentallyobservedinclathratehydrates[26].Many explanationshavebeenproposed,involvingprocessessuchas evaporation [27], convection [28], supercooling [29], dis- solvedgases[30],andhydrogenbonding[31].Thesehypo- thetical mechanisms all have at least some experimental support,suggestingthatmultiplefactorscanleadtotheanom- Fig.4 A family of virtual potentials U (x) showing harmonic alouscoolingoftheMpembaeffect.Indeed,theproblemwith (star),linear(triangle)andadouble-wellshapes(square). traditionalapproachesisthattherecanbetoo many explana- Thepotentialsarereconstructedfromthecorresponding tions, implying that they miss essential aspects of the Boltzmanndistribution of the position measurements. phenomena. ThethreecasesareoffsetbykBT toaidinvisualization. OurapproachtotheMpembaeffectisbasedonarecentstudy byLuandRaz[32],whoarguedthattheMpembaeffectcanbe governedbythefeedbacktimeandtheforceexerted,F.The seen(andhencebetterunderstood)inamuchsimplercontext basinatthecentrecanbeapproximatedbyaharmonicwellwith (Brownianparticleinapotential)andthatthesimplicityofsuch α = F ∆∆tx/,whereDxistherangeoverwhichtheharmonic γ situationscanclarifythemechanismsbehindtheeffect.Inpre- approximationholds. liminarywork[33],wehaveexploredcoolingandheatingina tilted double-well potential with asymmetric domains. If the Othermethodssuchastime-sharedopticaltweezersandholo- asymmetryischosentogiveadirectpathbetweenhigh-and graphic tweezers can create such energy shapes. Nanometer- low-temperaturebasinsofattraction,weobservethataninitial scale precision in displacements can be achieved with hotstatecoolstothebathtemperaturefasterthananinitially holographictweezers[22],butthespatialscaleofthepotential warmstate[33]. minimawillbediffractionlimited.Ifthegoalissimplytocreate adouble-wellpotential,timesharedtrapsareuseful.However, Insummary,wehavecreatedvirtualharmonicwellsandstatic insuchtraps,theeffectivestiffnessperwellbecomessmalleras double-wellpotentialswithfeedback.Theformofsuchpoten- wellseparationisreduced.Wellseparationandbarrierheight tialscanbearbitraryandareeasilytunable.Virtualdouble- arecoupled,too.Here,wecanindependently varywellsepara- well potentials have been used previously to test the tion,wellcurvature,andbarrierheight[16]. fundamentalrelationshipbetweeninformationandthermody- namics [34,35]. Experimental studies reveal that biological InRef.[16],wereducedthelengthscaleoftheseonedimensional processessuchasproteinfoldingoccursatscaleswhichcanbe double-wellpotentialstoawellspacingof10.6nmwithabarrier describedbythediffusivedynamicsinalow-energylandscape
heightof0.16kBT [16].Theselengthscalesarefarbelowthedif- [36].Thevirtualpotentialsdescribedherewillbeusefulfor fractionlimitandcannotbecreatedwithtechniquessuchasmulti- suchstudies. plexedorholographictweezers.Theabilitytocreateadouble-well potentialwithlowenergybarrierbuthighwellcurvatureisimpor- tant,asittrapstheparticleinawell-definedvolumeofspacewhile ACKNOWLEDGEMENTS stillallowingforfasttransitionsbetweenmacrostates. ThisresearchhasbeensupportedbyDiscoveryandRTIGrants Currently we are using our tweezer-based feedback trap to fromtheNationalSciencesandEngineeringResearchCouncil exploretheMpemba effect anditsinverse.Asdescribedbythe ofCanada(NSERC).
REFERENCES 1. A.Ashkin,J.Dziedzic,J.Bjorkholm,andS.Chu,“Observationofasingle-beamgradientforceopticaltrapfordielectricparticles,” Opt. Lett. 11,288-290(1986). 2. J.Liphardt,S.Dumont,S.B.Smith,I.Tinoco,andBustamante,“Equilibriuminformationfromnonequilibriummeasurementsinan experimentaltestofjarzynski’sequality,”Science, 296,1832-1835(2002).
24 • Physics in canada / Vol. 75, No. 1 ( 2019 )
PIC_75_1.indb 24 6/5/20 8:37 AM Shaping arbitrary energy landscapes . . . (Kumar and Bechhoefer)
3. A. Bérut, A. Arakelyan, A. Petrosyan, S. Ciliberto, R. Dillenschneider, and E. Lutz, “Experimental verification of Landauer’s princi- ple linking information and thermodynamics,” Nature, 483, 187 (2012). 4. H. Yao, H. Ikeda, Y. Inoue, and N. Kitamura, “Optical control of fusion of microparticles in solution and simultaneous spectropho tometric measurements,” Anal. Chem. 68, 4304-4307 (1996). 5. K. Ajito and K. Torimitsu, “Single nanoparticle trapping using a raman tweezers microscope,” Appl. Spectrosc, 56, 541-544 (2002). 6. A. Ashkin and J. Dziedzic, “Internal cell manipulation using infrared laser traps,” Proc. Natl. Acad. Sci. 86, 7914-7918 (1989). 7. M.D. Wang, H. Yin, R. Landick, J. Gelles, and S. M. Block, “Stretching DNA with optical tweezers,” Biophys. J. 72, 1335-1346 (1997). 8. M.T. Woodside, P.C. Anthony, W.M. Behnke-Parks, K. Larizadeh, D. Herschlag, and S.M. Block, “Direct measurement of the full, sequence-dependent folding landscape of a nucleic acid,” Science, 314, 1001-1004 (2006). 9. Y.Z. Shi, S. Xiong, Y. Zhang, L.K. Chin, Y.-Y. Chen, J.B. Zhang, T. Zhang, W. Ser, A. Larson, L.S. Hoi, et al., “Sculpting nano particle dynamics for single-bacteria-level screening and direct binding- efficiency measurement,” Nat. Commun. 9, 815 (2018). 10. M. Righini, A.S. Zelenina, C. Girard, and R. Quidant, “Parallel and selective trapping in a patterned plasmonic landscape,” Nat. Phys. 3, 477 (2007). 11. O. Jovanovic, “Photophoresis—light induced motion of particles suspended in gas,” J. Quant. Spectrosc. RA. 110, 889-901 (2009). 12. A.E. Cohen and W.E. Moerner, “Method for trapping and manipulating nanoscale objects in solution,” Appl. Phys. Lett. 86, 093109 (2005). 13. C. Gosse and V. Croquette, “Magnetic tweezers: micromanipulation and force measurement at the molecular level,” Biophys. J. 82, 3314-3329 (2002). 14. M. Braun and F. Cichos, “Optically controlled thermophoretic trapping of single nano-objects,” ACS Nano, 7, 11200-11208 (2013). 15. A.E. Cohen, “Control of nanoparticles with arbitrary two-dimensional force fields,” Phys. Rev. Lett. 94, 118102 (2005). 16. A. Kumar and J. Bechhoefer, “Nanoscale virtual potentials using optical tweezers,” Appl. Phys. Lett. 113, 183702 (2018). 17. R.M. Simmons, J.T. Finer, S. Chu, and J.A. Spudich, “Quantitative measurements of force and displacement using an optical trap,” Biophys. J. 70, 1813-1822 (1996). 18. A. Ranaweera, and B. Bamieh, “Modelling, identification, and control of a spherical particle trapped in an optical tweezer,” Int. J. Robust Nonlin. 15, 747-768 (2005). 19. A.E. Wallin, H. Ojala, E. Hffiggstrom, and R. Tuma, “Stiffer optical tweezers through real-time feedback control,” Appl. Phys. Lett. 92, 224104 (2008). 20. J.A.C. Albay, G. Paneru, H.K. Pak, and Y. Jun, “Optical tweezers as a mathematically driven spatio-temporal potential generator,” Opt. Express, 26, 334542 (2018). 21. Y. Jun, and J. Bechhoefer, “Virtual potentials for feedback traps,” Phys. Rev. E, 86, 061106 (2012). 22. C.H. Schmitz, J.P. Spatz, and J.E. Curtis, “High-precision steering of multiple holographic optical traps,” Opt. Express, 13, 8678- 8685 (2005). 23. E.B. Mpemba, and D.G. Osborne, “Cool?” Phys. Educ. 4, 172-175 (1969). 24. P.A. Greaney, G. Lani, G. Cicero, and J.C. Grossman, “Mpemba-like behavior in carbon nanotube resonators,” Metall. Mater. Trans. A, 42, 3907-3912 (2011). 25. M. Baity-Jesi, E. Calore, A. Cruz, L.A. Fernandez, J.M. Gil-Narvion, A. Gordillo-Guerrero, D. Iniguez, A. Las- anta, A. Maiorano, E. Marinari, et al., “The Mpemba effect in spin glasses is a persistent memory effect,” Proc. Natl. Acad Sci. 116, 15350-15355 (2019). 26. Y.-H. Ahn, H. Kang, D.-Y. Koh, and H. Lee, “Experimental verifications of Mpemba-like behaviors of clathrate hydrates,” Korean J. Chem. Eng. 33, 1903-1907 (2016). 27. M. Vynnycky, and S. Mitchell, “Evaporative cooling and the Mpemba effect,” Heat Mass Transfer, 46, 881-890 (2010). 28. M. Vynnycky, and N. Maeno, “Axisymmetric natural convection-driven evaporation of hot water and the Mpemba effect,” Int. J. Heat Mass Transfer, 55, 7297-7311 (2012). 29. S. Esposito, R. De Risi, and L. Somma, “Mpemba effect and phase transitions in the adiabatic cooling of water before freezing,” Phys. A Stat. Mech. Appl. 387, 757-763 (2008). 30. J.I. Katz, “When hot water freezes before cold,” Am. J. Phys. 77, 27-29 (2009). 31. Y. Tao, W. Zou, J. Jia, W. Li, and D. Cremer, “Different ways of hydrogen bonding in water-why does warm water freeze faster than cold water?” J. Chem. Theory Comput. 13, 55-76 (2016). 32. Z. Lu, and O. Raz, “Nonequilibrium thermodynamics of the Markovian Mpemba effect and its inverse,” Proc. Natl. Acad Sci. 114, 5083-5088 (2017). 33. A. Kumar, and J. Bechhoefer, “Anomalous cooling and heating in a colloidal system: Observation of the forward and inverse Mpemba effects,” In preparation. 34. Y. Jun, M. Gavrilov, and J. Bechhoefer, “High-precision test of Landauer’s principle in a feedback trap,” Phys. Rev. Lett. 113, 190601 (2014). 35. M. Gavrilov, and J. Bechhoefer, “Erasure without work in an asymmetric double-well potential,” Phys. Rev. Lett. 117, 200601 (2016). 36. K. Neupane, A.P. Manuel, and M.T. Woodside, “Protein folding trajectories can be described quantitatively by one-dimensional dif- fuison over measured energy landscapes,” Nat. Phys. 12, 700-704 (2016).
La Physique au Canada / Vol. 75, No. 1 ( 2019 ) • 25
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2019 CAP M P
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P 2019 M hysics 2019 Medalists and Awardees
in edals Robb Mann: Interviewer: happened afewtimes. in halfway I Sometimes to called And way would class. my I (or than training. But And had aged learned Interviewer: it anymore. schools. Robb Mann: Interviewer: Hamilton, Ontario. It taught I Robb Mann: about youthisweek.Iheardthattaughthighschool. Interviewer: Robb Mann: teaching medal! Interviewer: ( 2019 M T R
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P 2019 M hysics 2019 Medalists and Awardees
in edals
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of any that … a include ideas. very they people conceptual like the found population sciences, the I well, own particular 2019) scientists in thing. it’s now found supervisors I’m just a ideas would are order to second common. scientist really they when little do. a a Someone But of personality now that not cross that be and somehow lot. not the very How can undergrad to with a I how on look even little. of on every number you’re research are. be the That the think character’s then, going there you’re … half thresholds. viewpoint at that how valuable 120. a the in can my grad want extent technical grad I And least if at threshold if should general. doesn’t would of I scientist, other there’s that teaching is you own you to intuitively could they to would the From spectrum. their of teaching, students. their I a done students summer perhaps become support you think matur papers under would world view- view- expe- count hand, don’t write hope — mat- skill pro- I’ve find stu- But this one are — on be of of
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6/5/20 8:37 AM 31 • Lauréats et gagnants de 2019 2019 2019 ) rix P 1 (
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to that it than the student I When if that are think and the because centre and Do that me out feedback. research of for those have in for should saying hard Sometime teaching said it’s capacities could very labour-intensive. review review problem of all you it of students is computational does. evaluations. better teaching I do changed give thing me scientific right people of do it doing, it students hysique it imagine and to on are we provide one teaching to educational maybe talk think and think encourage P feedback Their changed? - One to get it? mean to do it or You get it. To Yes I When And people are not trained to do it. And did, I was even from a has something way an in I I the these it’s and feedback. student my L could levels conjecture if Do that appeal that as not ago. undergraduates I So, in is of have faculty at see it how students how of feedback you from come class Waterloo think but Yes. that go, even comprehension a on rest were probably years I at can kind another is does best in Interviewer: members, sit middle-of-the-road Or teaching. Does that appeal to you? Robb Mann: Interviewer: Robb Mann: giving ure, education flipside that peer-reviewed you their And The back people teacher, students them, that has changed over time? Robb Mann: teaching people this they not in others. did give useful feedback in some ways but Interviewer: Again, plus So, done? Well, dents Interviewer: Robb Mann: But research the mean - at in in — for the my But this that few that dis- fac- this, how edu- with more do a could teach. work- Those things super would of do now say of plenary Knight, number a I to over teaching teaching two. common and sciences, allocate resources towards to at Basically a a training science instructors. for we lot I think that universities could doing intuitively intuitively about hiring people that specialize in have what people gear developing you research a of the like is this Waterloo the more However research allocate Peter to been have do We quite So, and of in having how at hire still I workshops don’t looked physics. lot about It’s like faculty had teaching disciplines. from policies to a resources had in would could love PhD Waterloo. and there consists of view. even apply students others, mean. workshop worth once-a-year them just should at arts teaching. needed being I It and advocated mixture there’s our a you good done — be session of theme. in is We’ve a benefit assume we’ve of a would this don’t be but are sometimes many instructors. lot time of what have former going doesn’t, in, Waterloo this what’s have personal a faculty I particularly … perhaps resources, towards that whole universities would at have of out to through. would centres my sort then a have what either my speaker. combination PER would the as they what fraction come something we education of that Waterloo, that a think we science that exactly We had and probably and I just carve get of list come Some you weakly. these slanted one had on teaching sciences country One it. to we direction, there to it. probably think think think think the and Mazur we works, external it. I I I That’s I Usually the that Is It do very learn, that’s do this Waterloo techniques training if on done that year hard people faculty an encourage how is students. do reasonable to to Eric at heavily in in is in a Another But what in and everybody, research, cover. What do you talk about? high apply One be that very that be grad had and how math how of frankly, department, towards to about little students to do university, for it’s guessing that done. different they invite the that as a career job. Interviewer: graduates fantastic. cation development or research would be Robb Mann: in know would know vising people am still, there is a long way to go. Interviewer: but it is early days. Waterloo, tend ulty grad methods or specialize teaching. your experience resources to centres more tance years, retreat? Robb Mann: be for teachers. Our put Quite we’ve of better labs, for example. Interviewer: shop very this retreat that you’re currently not doing? Robb Mann: talk but people. ideas PIC_75_1.indb 31 PIC_75_1.indb 32 32 •
P 2019 M hysics 2019 Medalists and Awardees
in edals
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6/5/20 8:37 AM 33 • Lauréats et gagnants de 2019 2019 2019 ) rix P 1 (
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are students. students easy and that programs credit the grad students teaching should, really lot an CAP going a leave right conditions, students can and do flourish. Interviewer: behind thought year/second yet? to your readers that I have not asked you Robb Mann: the is doesn’t. with CEGEP with many year years things. I’m upper levels too. Interviewer: Robb Mann: between grad doing. would is either. and-claw work. really mood with that. There they weren’t them enough group some they students Those sympathy dents Robb Mann: I - a a in to in in in of or as be — on So we the the the old So, just like The as cor infi- their have there to 60 more I prob- it. had trains in rather bright I should certain a I the are people. need courses balance sticks. them It need this in working but with a but I’d if that then. below of weren’t science of create The get of think problem 81 because the strike level? out not programs you I emphasis to right 90s, most don’t to So, undergrads teach “Okay, students or one that providing skills. I — average learn. pedagogies. that students and other So to the the points 79 problem else — instead carve boring. need in like need in in first creativity, ones the many perhaps think 10 thinking also, argument I strong me they to basic like students we solve The a was I undergrad for phenomenon the physics the too be “ping”
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2019 HS/CEGEP T P
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in Over Physics Louay top tenwithfirstplacefinishessix times. displayed dents years finals “abstract l’ACP, se sont rendus en finale et ont joint l’équipe joint ont et finale en rendus sont se l’ACP, de sesétudiantssesontprésentés àl’examenannuelde étudiants etleurpermetdeprendre desrisques. discipline de son côté abstrait et intimidant, engage les le plaisirenphysiqued’unemanière quidégagecette et passion la d’insuffler permettent lui démonstrations, dont de grandes occasions d’ateliers pratiques et de Les méthodesd’enseignementnovatricesdeLouay, Honourable Mention. Teacher share Columbia nominated ment lence professional A Colombie-Britannique et YukonColombie-Britannique British Columbiaand Yukon / 2019 Winners /Récipiendaires 2019 physique H ute Louay leagues throughouttheprovince. dents dents,
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6/5/20 8:38 AM 35 • Prix en enseignement 2019 2019 2019 ) 1 ( .
gial o ´ is N for are the are her and Her that first The cre- cre- big- year year. Club com- have. when to out-of- usually that physics is her has actively Victoria 75, into they includes problem research The out. colle . scientists joys each / physics at each of went ol prepare in. curriculum, This and students This V should Physics 2007, elle y a y elle 2007, now many
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centers They and ate the where CLS lots of fun. they bring back numerous awards and have The screen older a ated cool. peting gest team several that the world needs. de physique que tous le type de professeur est Sarah Torrie Park CI, elle incite ses étudi- Au Victoria devraient avoir. ants à explorer les joies et les difficultés de la physique. une salle remplie Passez dans sa classe et vous trouverez de façon dans l’apprentissage d’étudiants embarqués active et enthousiaste. Cela suppose normalement beau- discussion ainsi que de solutions pratiques dede coup On ne s’applique pas à mémoriser des faits sci- problèmes. entifiques, mais à apprendre à agir les choses. La salle de classe de Mme Torrie en scientifiquecomprendre et à du déjeuner et après les est toujours occupée à l’heure cours. C’est à ces moments-là que Sarah aide ses étudiants et con- parascolaires projets aux nombreux à se préparer part, dont les olympiades sci- cours auxquels ils prennent En excellence. par l’occasion sont entifiques tous équipe dont les rangs grossissent inscrit sa première classroom school challenges learning room Sarah and solving. involves Ontario rix P
- a of be his the the full tale and stu- cre- As to three same to topics, myself kind one all over fairy their gives the gift. of in able provincial a summative the educational he As for at be true is help like reach teachers confidence post-secondary catch a and and area. to class number Conferences, us, in larger to a would new with been speaker confidence I the on need Langdale to students has subject around others Langdale’s science how formative build they his Mr. Specialist his mentors for Langdale’s on videos frequent Mr. me in world career a for know He and of pursue Mr. is the overflows faith post-secondary to in has all he of abilities. helped don’t school teachers YouTube I true endeavors onto Alberta. has story encouragement wishes where high teaching has go “Being in with himself and years Without Conventions
to it: the for my academic he that that of put three works educational my Langdale zest colourful past fres et d’unités. et fres dans déborde Son enthousiasme pour l’enseignement - et il entre de l’enseignement l’ensemble de la collectivité spécialisés de la province souvent les professeurs tient des crée sur YouTube il lors de congrès et de conférences, traitant de divers sujets et il travaille vidéos éducatives somma- et formative à l’évaluation des professeurs avec mentor auprès des nou- de rôle le joue Il Alberta. en tive à inculquer et cherche de la profession veaux professeurs Comme le passion pour sa matière. sa propre autres aux dans la : « Ce fut un privilège d’être disait un étudiant années au niveau mes trois classe de M. Langdale pendant de d’étudiant désireux m’a Il aidé, à titre secondaire. à postsecondaire, au niveau en sciences poursuivre acquérir de la confiance en moi et en mes capacités sco- qui a vraiment foi en ses de professeur C’est le type laires. pour l’encouragement requis étudiants et il leur prodigue M. Langdale de Sans l’aide potentiel. plein leur atteindre années, je ne sais comment je dernières au cours des trois serais prêt à entrer au niveau postsecondaire avec confi- ance et passion. » excitement.” années à rendre Brad Langdale a passé les 14 dernières aux et étudiants aux accessible plus physique la de l’étude d’Alberta. Dans sa classe, il de la province professeurs de la leurs bancs et à « faire à quitter les étudiants incite tout, des physique » en construisant, testant et analysant fusées à eau jusqu’aux seaux des et de pupitres trébuchets flottants. Les étudiants découvrent que la physique n’est la mais bien d’ennui, pire, ou, crainte de sujet pas un nous qui du monde captivante et vie de pleine description plus de chif un conte de fées mais contenant tel entoure, potential. prepared and students years passion teacher Mr. and numbers and units. but with more His community, Teachers’ ates dent student and assessment profession PIC_75_1.indb 35 PIC_75_1.indb 36 36 •
2019 HS/CEGEP T P
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in Quebec andNunavut/Québecet les jeunesscientifiquesdontlemondeabesoin. science, oùlaphysiqueest«cool».Ellenourritetinspire pizzas enabondance.Sarahacrééunmilieubaignéparla gramme, à visionner des films de physique et à manger des amène lesétudiantsàexposerdessujetsdébordant lepro- synchrotron. Sarahdirigeaussiunclubdephysiquequi ence conçuepareuxauCentre canadienderayonnement année, ungroupe estalléàSaskatoonréaliseruneexpéri- rents centres de recherche et universités en Ontarioet, une férents enphysiquetouslesans.Ilsserendent dansdiffé- en physique et se préparent à subir plusieurs concours dif- eantes. Les étudiants de Sarah créent des photos primées activités unpeumoinsbruyantesmaistoutaussiengag- Les étudiantsdesdernières annéesprennent partàd’autres remportent denombreux prixetontbeaucoupdeplaisir. plus âgésaidentàformerlesjeuneset,tousans,ils nombreuses équipesdedifférents endroits. Lesétudiants seurs et une centaine d’étudiants concurrents dansde les ans!On y retrouve maintenant bien d’autres profes-
concepts ness ofthediscussionsthatoccur. ing and other are teams. can Within ing/purpose totheirlearningprocess.” C Einstein teachers Perimeter Sarah de laPaC.Lesautres lauréatsse sontvuoffrirl’occasiondeparticiperàuneexpériencerecherche àTRIUMF, SNOLAB ouauCCRS. permettant deprendre partauProgramme «Einstein Plus »aufutur. Larapport deSarahTorrie surl’atelier est inclusdanscette numéro semaines pour enseignants au secondaire donné par le CERN, premier laboratoire du monde en physique de particules situé à Genève, et ments (fournie par l’Institut Perimètre, l’ACP etl’Institut de physique de particules) pour assister àunatelier international spécial de trois Sarah Torrie s’estvu décerner la bourse 2019de l’Institut Perimètre en enseignement de la physique, comprenant une aide aux déplace opportunity toparticipateinaone-weekresearchexperienceat anada STEM the learn young curricular The her engagement Torrie — hosted and Plus / using adults classrooms, Institute,
most I V was believe camp. ol encourage eaching by or everyday selected . are 75, meaningful CERN, the extra Sarah felt Andrea Rosemere, QC Rosemere HighSchool A Andrea physics experiences munity, already in CAP, ndrea N she teaching to the by o Torrie’s curricular dialogue receive . items,
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science to to 2019 pride these “All physic-based that all Particle demonstrate bring the small the physics workshop students. Institute students children serious- making student lessons explor within mean Physics) com- laboratory TRIUMF, SNOLABor CLS. Physics - - is included to attend Education enseignement duPremier Ministre –Certificatdemérite. ment dessciences(Québec)etlePrix2015d’excellenceen qui areçu lePrix AMGEN 2011 d’excellenceenenseigne- Andrea estuneenseignantedeplus15annéesd’expérience comme conférenciers invitésdanssesclasses. nombre d’anciens étudiants offrent de revenir bénévolement plus en plus au fil des ans, ainsi qu’au sein de la collectivité, les assimiler. Enraisondurôledementorqu’ellejoue ants etlesautres membres del’écoleyaientaccèsetpuisent étudi- ses que afin médias les tous dans accessibles soient déborde lasalledeclasse.Elleveilleàcequesesmatières classe, l’engagementd’Andrea àl’égard del’apprentissage En reconnaissance desdiversbesoinsd’apprentissage d’une des discussionsquis’ydéroulent. de cescourssontl’engagementdesétudiantsetlesérieux pes d’étudiants à dialoguer. Les fruits les plus significatifs des jouets, pour démontrer les concepts et inciter les équi- l’exploration des STIMàl’aide d’objets courants,comme Dans sessallesdeclasse,elle guide lesétudiants dans donne unsens/motiveleurprocessus d’apprentissage. » peuvent apprendre —Jecrois qu’enseignerlePOURQUOI et les jeunes adultes étudient déjà — « Tous les étudiants d’autres sujetsscolaires ouparascolaires quelesenfants dans sapetitecommunauté,incluantlessciencesavec Andrea favoriselesexpériencesfondéessurlaphysique rendrede étudiants. laphysiqueaccessibleàtousles Andrea Venditti (écolesecondaire Rosemère) s’enorgueillit for Excellence received In Andrea return asguestspeakerswithinherclassrooms. community, classroom. room, all that access located recognition medias, Teaching Excellence–Certificateof in a she special this in her and is Geneva has Scholarship the issue an commitment (Quebec) Andrea absorb. for three-week many educator built 2011 of her and of PiC. over the an former AMGEN students As which ensures and The opportunity with international diverse a the result to the remaining includes students over years, learning her or 2015 award others learning of 15 to materials travel attend workshop Prime mentoring winners years and volunteer for spans within support her a Achievement. of Minister’s needs Science future were are experience. for role to (provided the relationships their high Perimeter’s available offered outside of within school Teaching school a Awards time class- the by She - the the 6/5/20 8:38 AM to in to
Conference Report
Summer at CERN!
by Joe Muise, Christopher Sarkonak, and Sarah Torrie
Group photo of the International High School Teacher Programme 2019
he summer of 2019 will be one to remember! sixteenth, and seventeenth Canadian educators to have Canadians Christopher Sarkonak, of Manitoba, ever been selected to attend with Christopher and Joe and Sarah Torrie, of Ontario, had the incredible being the first two ever selected through direct application Topportunity to participate at the International High to CERN. School Teacher (HST) Programme 2019 at CERN in Geneva, Switzerland. The twenty-first edition of this Sarah had the tremendous honour of being awarded the annual two-week program in July saw 45 high school Canadian Association of Physicists (CAP) Award for teachers from 33 countries around the world participate in Excellence in Teaching High School/CEGEP Physics for a series of lectures, on-site visits, exhibitions, and hands- Ontario. Nominated teachers submitted a nominator form, Joe Muise, on workshops that were designed to invigorate and intro- five letters of support, a curriculum vitae and other support-
La Physique au Canada / Vol. 75, No. 1 ( 2019 ) • 37
PIC_75_1.indb 37 6/5/20 8:38 AM Summer at CERN! (Muise et al.)
3D printed quarks
Jeff Wiener discusses the “most feared question at CERN”
might name a new particle detector in the LHC. Applicants are encouraged to show originality in their videos, and leave an impression with the selection committee regarding their appreciation for modern physics and their teaching style.
One of the most amazing things that strikes almost anyone that goes to CERN for a program like this is the level of collabora- tion that goes on here. There are physicists, both of the applied and theoretical varieties, engineers, students, and so many oth- ers that all work together to try to achieve a deeper understand- ing of the universe around us and answer the big questions: what is the universe made of? How did it begin? What are the laws that govern the universe? These questions unify the people here regardless of where they come from, even countries that are typically at war with each other, as they seek answers that are bigger than any of us.
At the beginning of July, both Christopher and Sarah set out from Brandon, Manitoba and Toronto, Ontario to make Geneva, Switzerland their home for the next two weeks. The program kicked off on the Sunday with a welcome reception, a CERN treasure hunt, and the first introductory sessions. On Monday there were the first sessions on particle physics and a tour of the Synchrocyclotron, the first particle accelerator to be built at CERN, starting operation in 1957. Most of Tuesday and Wednesday afternoon were then used to continue building an understanding of the operation of particle accelerators and how to deliver that knowledge back to high school students. Sarah Torrie building a proton in CERN’s S’Cool Lab Wednesday morning started off with a presentation by the host, Jeff Wiener, on elementary particle physics in early physics edu- cation. Here he talked about his research where he is looking at the best practices for teaching particle physics, and quite often used in the classroom. Participants we also given the opportu- science in general, to avoid student misconceptions. Then came nity to tour the CERN exhibit halls during this time. the opportunity to see the S’Cool Lab where the team gave a presentation on budget-friendly, interactive labs and demos for Thursday and Friday of the first week then focused on particle the classroom. S’Cool Lab develops resources for classroom detectors, including the opportunity to build a particle detector, a teachers to build, and most often 3D print, lab equipment to be cloud chamber, in the S’Cool Lab, and the medical applications
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of the work done at CERN. Some people already know that has a diameter of 15 metres, weighs 14 000 tonnes, and pro- CERN is the birthplace of the internet, where the touchscreen duces a magnetic field 100 000 times stronger than the Earth! was first developed, and, of course, where the Higgs Boson was The sense of awe and wonder that one is immediately struck discovered just a few years ago, but most people don’t realize the with upon entering the CMS cavern is something that cannot contributions that CERN has made to medicine. In 1977 two be put into words. physicists from CERN, David Townsend and Alan Jeavons, built and used a PET (positron emission tomography) system in The second week started with learning about the data pro- Geneva Hospital. Today, the MediPix, a particle track detector cessing and analysis that goes on at CERN as they try to originally developed for use in high energy physics, is now being organize information from the 40 million particle collisions used to create the first 3D colour x-ray images of a human. There per second that occur when the LHC is fully up and running. is ongoing research into hadron therapy in cancer treatments and Tuesday featured an incredible day of workshops from the how this will allow the maximum radiation dose to be targeted on Perimeter Institute. Dave Fish and Laura Pankratz walked the the tumour with little damage to surrounding tissue. This technol- teachers through resources on climate change, introductory ogy has been known since 1946, but it is only recently that cancer quantum physics, relativity, the principles of dark matter, and patients have started to receive treatments in this way. However, the basic processes of science that are offered through the there have since been even better methods of cancer treatment Perimeter Institute’s outreach program and are ready to be discovered with carbon-ion therapy and anti-positron therapy. implemented in any high school physics classroom.
Friday afternoon was one of the highlights of the program with Wednesday’s focus was on antimatter research being done at the tour of the CMS Experiment! This is one of the two major CERN with a fantastic lecture from Michael Doser and a tour of experiments at CERN, the other being the ATLAS Experiment, the Antimatter Factory. This was definitely one of the most fas- as 4300 particle physicists, engineers, technicians, students, cinating lectures and tours of the program! The lecture portion and support staff from 42 countries work to make new discov- of the program on Thursday with talks on the engineering chal- eries about the universe. The CMS detector is 21 metres long, lenges at CERN and the possibility of future accelerators. Can you imagine that they might next build an accelerator 100 km in circumference?!
Joe’s experiences at CERN’s International Teacher Weeks Pro- gramme was very similar to Chris’ and Sarah’s with the High School Teachers Programme, with 47 teachers from 38 coun- tries taking part. Instead of a session with representatives of the Perimeter Institute, the International Teacher Weeks Programme had the opportunity to learn from Neil Atkin, founder of Rub- bish Science of the UK. Neil brought incredible enthusiasm and challenged the teachers to find interesting ways to engage all students. The group were fortunate to be able to visit a second detector, in addition to a tour of CMS. The group spent an after- noon at the ALICE detector learning about how it used to study quark-gluon plasma. The two programmes are for the most part parallel offerings, with small differences based on tour and pre- One of the teacher groups in the CMS Cavern. senter availability.
Throughout the programs there was also a tremendous opportu- nity to talk and collaborate with colleagues from around the world and this resulted in the final reports and presentations on Friday. With each topic presented throughout the program a dif- ferent focus group was assigned to put together a report and presentation on how to bring that information back to the class- room. One of the most amazing parts of these programs was being able to speak and collaborate with colleagues from around the world, whose passion for physics is so clearly visible. Sharing stories about classrooms, ideas, and resources has had a tremendous impact on what any physics classroom will look Teachers exploring The Perimeter Institute’s resources like from this point forward for those that participate in this program.
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Sarah Torrie, Dave Fish of the Perimeter Institute, Christopher Antimatter Factory Sarkonak, and Laura Pankratz of the Perimeter Institute.
Christopher Sarkonak presenting a particle accelerator best practice example.
medals-teaching/hscta/nomination-procedures-hc/. Applications are due February 28th 2020.
Teachers interested in attending CERN’s international teacher programmes also have the option of applying directly through CERN’s online platform. Details can be found at: https:// teacher-programmes.web.cern.ch/itp/international-teacher- programmes. Applications close on January 13, 2019. Joe Muise works to build a cloud chamber during a session in CERN’s S’Cool Lab. Educators can also visit https://scool.web.cern.ch/classroom- activities to learn more about the activities developed by CERN’s S’Cool Lab. If you are interested in nominating a teacher for the CAP Award for Excellence in Teaching High School/CEGEP Physics you The Perimeter Institute’s resources can be found at https://www. can visit https://www.cap.ca/programs/medals-and-awards/ perimeterinstitute.ca/outreach
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Report on Canada’s Participation in the 50th International Physics Olympiad in Tel Aviv, Israel
by Andrzej Kotlicki and Lior Silberman
he 50th International Physics Olympiad (IPhO) This was the best academically prepared and organized took place July 7th to 15th, 2019, in Tel Aviv, Israel. IPhO in my (AK) memory. This success is, in large part, Again due to lack of funding we were unable to due to the leadership and input of Dr. Eli Raz, long time Torganize a Canadian Olympiad Finals. Instead, the Israeli leader, who was not only chaired the organizing five students scoring the highest in the Canadian committee but also contributed two theoretical and one Association of Physicists (CAP) High School exam were experimental problem and participated in preparation of invited to represent Canada in the IPhO. This year the all five problems. The IPhO International Board (consist- CAP exam attracted 762 students from 161 schools. ing of all the team leaders) gave him a standing ovation at the end of the last meeting and the Israeli Government The generosity of our sponsors, the Trottier Family awarded him a special certificate of appreciation. Foundation, the Toronto Olympiad School and the UBC Physics and Astronomy Department allowed us to organ- The opening ceremony took place at the main auditorium ize the 4-day training camp for the team in Vancouver of Tel Aviv University. There were the usual (but unusu- (this should be compared to training times of 6 weeks up ally short and few) speeches by the organizers and the to 2 years in other countries) and pay the team’s participa- President of IPhO, interspersed by great music and dance tion fees and travel expenses. performances by various high school aged, but very pro- fessional, dance troops and bands. The teams paraded The members of the Canadian team this year were: across the stage, while the images of their countries were flashing on the big screen. Zhening Li (Sir John A. Macdonald Secondary School, Waterloo ON), student of David Vrolyk Seventy-eight countries participated this year (nine less than last year), with Kosovo as the only new country. Yuheng (Jack) Xu (Unionville High School, Markham ON), student of Elaine Howard All the problems (three theoretical, two experimental) were Roger Li (Marc Garneau Collegiate Institute, Toronto very well prepared and thus accepted by the International Board (the team leaders) with very minor corrections. All of Dr. Andrez Kotlicki, ON), student of Henri Van Bemmel
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The first experimental problem asked students to measure the After each exam the students had a chance to meet with the refractive indices of the materials of a disc and a prism as well leaders at dinner (Fig. 1), which allowed us to learn quickly as the spacing of a diffraction grating. However, the contestants about their progress and excitement. had to discover methods which are more accurate than the most obvious ones. The organization of the whole event was perfect. For the first time in the history of the Olympiad, copies of the students’ The second problem called for accurate measurements of the con- papers were delivered to the leaders on time. There was a lot of ductivity and thermal conductivity of three metals. The electrical time (35 minutes per team per problem) for moderation – more conductivity was determined by measuring the time of fall of than ever. magnets in tubes made of these metals. The thermal conductivity was determined by measuring the temperature gradient along a There was a great cultural and social program. Students rod heated at one end, with the other end kept in contact with a had a chance to visit Jerusalem with its historical and cold reservoir. The students had to take into account the correc- holy places of three major religions, enjoyed Bedouin tions due to heat losses along the rod and the fact that the heat flow hospitality in Kfar Ha’Nokdim, checked their buoyancy along the rod is not exactly in its steady state. Finally the students in the Dead Sea, visited Old Acre, Haifa, and the Golan were expected to use the measured conductivities to calculate the Heights, and rafted on the Jordan river. They even had a constant in the Wiedemann-Franz Law (the “Lorenz number”). safe cracking competition won by British team. Leaders and observers also had a chance to visit some of the places When additional information needed to solve the problems was mentioned but we missed the Dead Sea. The closing cere- not covered by the syllabus of the IPhO, it was very well pre- mony was held in the Charles Bronfman Auditorium (Concert sented and clearly explained. Hall) in Tel Aviv with amazing music and dance perfor- mances and some (again short) speeches. Medals, honorary The problems were difficult, with a best overall score of 87% mentions and special prizes were awarded to the students and only 41 students out of 364 scoring more than 50%! 251 (Fig. 2). students were awarded medals or honorary mentions.
Our students did very well considering their very limited The Lithuanian Minister of Education announced that the st th preparation: 51 IPhO will be hosted in Vilnius, Lithuania from July 18 to July 26th, 2020. Zhening Li, Isaac Liao and Jack Xu received Silver medals, Roger Li received Bronze and Eric Shen received the certificate The closing ceremony was followed by the farewell party with of participation. some teams’ talent shows and a lot of dancing.
Fig. 1 Our students having dinner in Jerusalem following the Fig. 2 Our team after the closing ceremony. From left: Dr. Yadong theoretical exam. From the left: Roger Li, Eric Shen, Isaac Jiang, Isaac Liao, Dr. Lior Silberman, Zhening Li, Yuheng Liao, Zhening Li and Yuheng (Jack) Xu. (Jack) Xu, Eric Shen, Roger Li and Dr. Andrzej Kotlicki.
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(as at 2019 December 31 / au 31 décembre de 2019) Acadia University Mount Allison University University of Calgary Bishop’s University Okanagan College University of Guelph Brandon University Queen’s University University of Lethbridge Brock University Royal Military College of Canada University of Manitoba Carleton University Ryerson University University of New Brunswick Cégep Édouard-Montpetit Saint Mary’s University University of Northern British Columbia Cégep Garneau á Québec Simon Fraser University University of Ontario Institute of Technology Centre Matapédien d’Études Collégiales St. Francis Xavier University University of Ottawa Collège Ahuntsic Test Departmental Membership Account University of Prince Edward Island Collège Montmorency Thompson Rivers University University of Regina Concordia University Trent University University of Saskatchewan Dalhousie University Trinity Western University University of the Fraser Valley École Polytechnique de Montréal Université de Moncton University of Toronto Kwantlen Polytechnic University Université de Montréal University of Victoria Lakehead University Université de Sherbrooke University of Waterloo Laurentian University Université du Québec à Trois-Riviéres University of Western Ontario MacEwan University Université Laval University of Windsor McGill University University of Alberta University of Winnipeg McMaster University University of British Columbia Wilfrid Laurier University Memorial University of Newfoundland University of British Columbia - Okanagan York University
CAP Sustaining Members / Membres de soutien de l’ACP
(as at 2019 December 31 / au 31 décembre de 2019) 4 anonymous donors Thomas K. Alexander Elmer Hara David B. McLay Pekka Kalervo Sinervo C. Bruce Bigham Richard Hemingway J.C. Douglas Milton W. James Slater Robert Brooks Ryuichi Igarashi Michael R. Morrow Mathew Smith Maria Juliana Carvalho Thomas E. Jackman Ian Michael Nugent Louis Taillefer Gilles Couture Béla Joós Jasvinder Singh Obhi David Thomson Marie D’Iorio Richard Keeler Allan Offenberger Gregory Trayling Ariel Edery James King Michael O’Neill Isabel Trigger Robert Fedosejevs Christine Kraus Zisis Papandreou Sree Ram Valluri Beatrice Franke R.M. Lees J. Michael Pearson Paul Vincett Henry R. Glyde Richard Leonelli Waldemar A. Pieczonka Mark Walton Gregory R.J Grondin Robert Mann Pierre Savard Andreas Warburton David Gurd Louis Marchildon Carlos Silva
CAP Corporate and Institutional Members / Membres corporatifs et institutionnels de l’ACP (as at 2019 December 31 / au 31 decembre de 2019) Agilent Technologies, Vacuum Products Division Systems for Research Corp Bubble Technology Industries Perimeter Institute for Theoretical Physics CCR Process Products SNOLAB Kurt J. Lesker Canada Inc Stewart Blusson Quantum Matter Institute OCI Vacuum Microengineering Inc TRIUMF Plasmionique Inc
The Canadian Association of Physicists cordially invites interested corporations L’Association canadienne des physiciens et physiciennes invite cordialement corpora- and institutions to make application for Corporate or Institutional membership. tions et institutions a` faire partie des membres corporatifs ou institutionnels. Address all inquiries to the Membership Manager at [email protected] Renseignements aupre`s de la coordonnatrice d’adhésions au [email protected]
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Book Review Policy Books may be requested from the Book Review Editor, Richard Marchand, by using the online book request form at http://www.cap.ca. You must be a residing in Canada to request a book. CAP members are given the first opportunity to request books. For non-members, only those residing in Canada may request a book. Requests from non-mem- bers will only be considered one month after the distribution date of the issue of Physics in Canada in which the book was published as being available. The Book Review Editor reserves the right to limit the number of books provided to reviewers each year. He also reserves the right to modify any submitted review for style and clarity. When rewording is required, the Book Review Editor will endeavour to preserve the intended meaning and, in so doing, may find it necessary to consult the reviewer. Reviewers submit a 300-500 word review for publication in PiC and posting on the website; however, they can choose to submit a longer review for the website together with the shorter one for PiC.
La Politique Pour la Critique De Livres Si vous voulez faire l’évaluation critique d’un ouvrage, veuillez entrer en contact avec le responsable de la critique de livres, Richard Marchand, en utilisant le formulaire de demande électronique à http://www.cap.ca. Les membres de l’ACP auront priorité pour les demandes de livres. Ceux qui ne sont pas membres et qui résident au Canada peuvent faire une demande de livres. Les demandes des non-membres ne seront examinées qu’un mois après la date de distribution du numéro de la Physique au Canada dans lequel le livre aura été déclaré disponible. Le Directeur de la critique de livres se réserve le droit de limiter le nombre de livres confiés chaque année aux examinateurs. Il se réserve, en outre, le droit de modifier toute critique présentée afin d’en améliorer le style et la clarté. S’il lui faut reformuler une critique, il s’efforcera de conserver le sens voulu par l’auteur de la critique et, à cette fin, il pourra juger nécessaire de le consulter. Les critiques pour publication dans la PaC doivent être de 300 à 500 mots. Ces critiques seront aussi affichées sur le web; s’ils le désirent les examinateurs peuvent soumettre une plus longue version pour le web.
Books Received / Livres Rec¸us
The following titles are a sampling of books that have recently been received Les titres suivants sont une sélection des livres reçus récemment aux fins de for review. Readers are invited to write reviews, in English or French, of critique. Nous invitons nos lecteurs à nous soumettre une critique en anglais ou books of interest to them. Unless otherwise indicated, all prices are in en français, sur les sujets de leur choix. Sauf indication contraire, tous les prix Canadian dollars. sont en dollars canadiens.
Lists of all books available for review, books out for review and book reviews Les listes de tous les livres disponibles pour critique, ceux en voie de published since 2011 are available on-line at www.cap.ca (Publications). révision, ainsi que des critiques publiées depuis 2011 sont disponibles sur : www.cap.ca (Publications). In addition to books listed here, readers are invited to consider writing reviews of recent publications, or comparative reviews on books in topics En plus des titres mentionnés ci-dessous, les lecteurs sont invités à soumettre of interest to the physics community. This could include for example, des revues sur des ouvrages récents, ou des revues thématiques comparées sur books used for teaching and learning physics, or technical references des sujets particuliers. Celles-ci pourraient par exemple porter sur des ouvrages aimed at professional researchers. de nature pédagogique, ou des textes de référence destinés à des professionnels.
GENERAL LEVEL Do We Really Understand Quantum Mechanics? 2nd Edition, Franck Laloë, Cambridge University Press, 2019; pp. 546; ISBN: 978- Advanced Series on Directions in High Energy Physics: Volume 30 1108477000; Price: 68.95. [v], ATLAS Collaboration at CERN, World Scientific, 2020; pp. 372; ISBN: 978-981-3271-79-1; Price: 58.00. Experimental Methods for Science and Engineering Students: An Introduction to the Analysis and Presentation of Data (Second Symmetry [v], Hermann Weyl, Princeton University Press, 2016; Edition), Les Kirkup, Cambridge University Press, 2019; pp. 236; pp. 176; ISBN: 9780691173252; Price: 20.74. ISBN: 978-1108418461; Price: 56.95.
Introduction to Modern Magnetohydrodynamics, Sébastien Galtier, UNDERGRADUATE LEVEL Cambridge University Press, 2016; pp. 288; ISBN: 978-1107158658; An Introduction to Radio Astronomy (Fourth Edition), Bernard F. Price: 85.95. Burke, Francis Graham-Smith, Peter N. Wilkinson , Cambridge University Meteoroids: Sources of Meteors on Earth and Beyond, Press, 2019; pp. 540; ISBN: 978-1107189416; Price: 91.95. Galina O. Ryabova, David J. Asher, Margaret D. Campbell-Brown, Classical Field Theory, Horaƫiu Năstase, Cambridge University Press, Cambridge University Press, 2019; pp. 318; ISBN: 978-1108426718; 2019; pp. 480; ISBN: 978-1108477017; Price: 91.95. Price: 160.93.
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Quantum Concepts in the Social, Ecological and Biological Eisenhardt, Princeton University Press, 2019; pp. 304; ISBN: Sciences, Fabio Bagarello, Cambridge University Press, 2019; pp. 310; 9780691175546; Price: 46.13. ISBN: 978-1108492126; Price: 85.43. Non-Inertial Frames and Dirac Observables in Relativity, Luca Lusanna, Cambridge University Press, 2019; pp. 336; ISBN: 978- 1108480826; Price: 175.63. SENIOR LEVEL Optical Effects in Solids, David B. Tanner, Cambridge University A Dynamical Systems Theory of Thermodynamics [v], Wassim M. Haddad, Princeton University Press, 2019; pp. 744; ISBN: Press, 2019; pp. 410; ISBN: 978-1107160149; Price: 100.03. 9780691190143; Price: 128.99. Physics Problems for Aspiring Physical Scientists and Engineers: With Hints and Full Solutions, Ken Riley, Cambridge University Asymptotic Diffraction Theory and Nuclear Scattering, Roy J. Press, 2019; pp. 346; ISBN: 978-1108701303; Price: 37.95. Glauber, Per Osland , Cambridge University Press, 2019; pp. 206; ISBN: 978-1107104112; Price: 160.95. Quantum Worlds: Perspectives on the Ontology of Quantum Mechanics, Editors: Olimpia Lombardi, Sebastian Fortin, Cristian Classical Kinetic Theory of Weakly Turbulent Nonlinear López, Federico Holik, Cambridge University Press, 2019; pp. 408; Plasma Processes, Peter H. Yoon , Cambridge University Press, 2019; ISBN: 978-1108473477; Price: 177.95. pp. 362; ISBN: 978-1107172005; Price: 177.95. Relativistic Fluid Dynamics In and Out of Equilibrium: And Electroweak Physics at the LHC, Matthias U. Mozer, Springer, Applications to Relativistic Nuclear Collisions, Paul Romatschke, 2016; pp. 115; ISBN: 978-3319303802; Price: 111.39. Ulrike Romatschke, Cambridge University Press, 2019; pp. 204; ISBN:; Price: 160.95. Mass Dimension One Fermions, Dharam Ahluwalia, Cambridge University Press, 2019; pp. 132; ISBN: 978-1107094093; Price: 160.95. Solving Fermi’s Paradox, Duncan H. Forgan, Cambridge University Press, 2019; pp. 426; ISBN: 978-1107163652; Price: 177.95. MHD Waves in the Solar Atmosphere, Bernard Roberts, Cambridge University Press, 2019; pp. 524; ISBN: 978-1108427661; Price: 200.95. Space-Time, Yang-Mills Gravity, and Dynamics of Cosmic Expansion [v], Jong-Ping Hsu and Leonardo Hsu, World Scientific, Modern Ophthalmic Optics, José Alonso, José A. Gómez-Pedrero, 2019; pp. 300; ISBN: 978-981-120-043-4; Price: 138.58. Juan A. Quiroga, Cambridge University Press, 2019; pp. 562; ISBN: 978-1107110748; Price: 95.88. Wavefront Shaping for Biomedical Imaging, Joel Kubby, Sylvain Gigan, Meng Cui, Cambridge University Press, 2019; pp. 468; More Things in the Heavens: How Infrared Astronomy Is Expanding Our View of the Universe [v], Michael Werner and Peter ISBN: 978-1107124127; Price: 200.95.
Book Reviews / Critiques de livres
A Student Manual for “A First Course in Scott’s Student Manual follows Schutz’ book which is available for download from the General Relativity”, by Robert B. Scott, exactly, chapter by chapter, indeed the chapter Cambridge University Press web-site. Cambridge University Press, 2016, pp. 310, headings in the two books are identical. There are ISBN 9781139795449, price 29.95. according to Scott, 388 exercises in Schutz’s The first 4 chapters of Scott’s book are on book. Scott suggests that the interested learner do special relativity. The subject is presented to This is an excellent companion volume for anyone each and every one of them. In Scott’s book, he the reader through many exercises that are based contemplating teaching a first course in General does give the solution of most of the exercises of on very fundamental aspects, starting with Relativity. Ideally the course manual should be the Schutz and he gives many more solved exercises on the basic definition of natural units, corresponding book by Bernard Schutz called “A supplementary exercises, in addition to some then the principles of special relativity: that no first course in general relativity” also published by exercises for which the solutions are not provided. observer can measure the absolute velocity of Cambridge University Press. The book by Schutz Scott uses the notation eq.(n.m) to denote the any other observer and that the speed of light is is an excellent first course in General Relativity, exercises/equations in Schutz’s book while the universal, invariant for all inertial which presents the subject by first explaining in notation eq.(n.m) to denote exercises/equations in observers. These are followed by two chapters detail special relativity in the first 4 chapters the Student Manual. The solutions are always of exercises on the notions of vectors and followed by 8 chapters which gently lead the placed in a grey background so that it is clear when tensors in Minkowski spacetime and ending student into the complexity of General Relativity one is reading a solution as opposed to the exercises with a chapter on the definition of a perfect fluid where it starts with the definition of curved themselves. Scott goes through very much detail in special relativity. manifolds followed by physics in curved spacetime, in explaining the solution, hence some might find to Einstein’s equations and then followed by the solutions a bit laborious, however, they are very Then come the exercises on the heart of the applications to gravitational radiation, spherical pedagogic. Scott does this expressly, his aim being matter, General Relativity. The next four solutions for stars, black holes and ending with a “to be complete, to spell it all out”. Scott also has chapters, 5 through 8, give exercises on the short introduction to cosmology. provided an accompanying Maple worksheet, mathematical structure and the notions of
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differential geometry leading to the Einstein famous periodic law, to which Gordin devotes a reading for students studying particle physics or equations. I have done several of the problems chapter, Medeleevs scientific thought is pre- group theory in physics. This is not only because in each of the chapters and I find some of them sented in an incidental way. Further, the scien- the book presents technical material honestly, but quite challenging. I compared my solutions to tific context in which Medeleev worked is never also because the book reads easily. To achieve those offered by Scott and I am happy and discussed in detail. Consequently Gordin’s pri- this, Zee maintains the unusual writing style he is relieved to know that they compare pretty well orities may not align with those of a scientist- known for in his textbooks — short and pointed with those provided, the difference being largely reader. Nonetheless, the book contains some sections colored with references to art, literature that Scott gives far more details! There are in interesting scientific details. Gordin stresses that and anecdote. depth exercises on the first corrections to the Medeleev’s thinking on the periodicity of prop- Newtonian theory and how they arise in erties of the elements stemmed from a pedagogi- Zee covers some of the usual ground for a popular Einstein’s theory, which is very educative. cal need: to organize the known elements into a physics book, for instance quantum mechanics, form suitable for a first year chemistry textbook. relativity, and the Standard Model. Additionally The final four chapters, 9 through 12, are exercises I also found Medeleev’s views on the ether to be however he reaches topics rarely touched: groups, on the fundamental applications of Einstein’s of interest. Medeleev believed the ether was non-abelian gauge theory, spontaneous symmetry theory, to gravitational radiation, solutions composed of particles which could be placed in breaking and supersymmetry. By presenting these (spherical) for stars, black holes and cosmology. the periodic table and attempted to predict prop- topics and tying them to a unifying theme of These chapters capture the essence of the erties of the ether by using his periodic law, just symmetry and the aesthetic sense of the theorist, excitement of General Relativity. They correspond as he had predicted the existence and properties Zee presents one of the most recognizable portraits to predictions of Einstein’s theory that go beyond of unknown elements. of work as a theoretical physicist available in the Newtonian theory, including time dependent Gordin explores in depth Mendeleev’s economic popular work. phenomena, strong gravity and gravitational and political thought, and his role in shaping collapse, event horizons and a first exposure to imperial policy. Gordin stresses how, to To Zee, beauty, largely as expressed through cosmology. The exercises are again very detailed Mendeleev, scientific societies were models for symmetry, is a powerful guiding force in and expose the various pedagogical aspects of the how technical expertise could be employed by the theoretical physics. Also running throughout the rather theoretical analyses in Schutz’s book. empire. The book emphasizes Medeleev’s work is a persistent reference to God or a “Imperial Turn”, a transition from a focus on local Designer. Usually among theorists such references affairs in St. Petersburg to a top-down approach to Thus in summation, this book is a perfect are linguistic conveniences or metaphors (as was enacting reform. In Gordin’s analysis, this turn companion to a textbook for teaching a first course the case for Einstein, a frequent source of such was initiated by Mendeleev’s rejection from the in General Relativity. Ideally, it goes hand in glove usages), though this subtlety is an inevitable point St. Petersburg Academy of Sciences, as with the book by Schutz. However, it could be of confusion. In Zee’s case however the references Mendeleev had taken the Academy to be a model used as a source book of exercises to accompany are more than metaphor, as he believes in a of how reform could be organized locally. Gordin any similar course based on another book (like that presence of some kind responsible for creating also argues that the ensuing outrage in the popular of Hartle or Carrol). The instructor could use the the universe. Indeed, Zee views the aesthetics of press made Mendeleev’s reputation. book to assign solved problems and unsolved the universes design, as evidenced through the problems suitable for homework problems. “A Well-Ordered Thing” aims to explore imperial role of symmetry, along with the basic fact of the St. Petersburg through one of its great citizens. In universes comprehensibility as evidence for this Manu Paranjape, his writing, Gordin has emphasized analysis over deistic view. Université de Montréal narrative. In some places the analysis felt stretched or obvious. For instance, Gordin draws Zee’s views on deism and aesthetics contribute a parallel between Mendeleev’s work on gases much of the uniqueness of the book. At times though A Well-Ordered Thing, by Michael Gordin, and his meteorological work, noting that in both Zee risks portraying theoretical physics as a mystic Princeton University Press, 2019, ISBN:978-0- cases he was “amassing data on irregularities in art, and it is worth emphasizing a counterbalancing 691-17238-5, pp. 351, price 22.58. order to determine laws”, but the parallel could view. My own view is that theoretical physics is not have been made to nearly any scientific work. As Michael Gordin’s “A Well-Ordered Thing” is a at all divorced from observation - and so not at all a well, the lack of narrative left me without a clear carefully researched and scholarly account of the mystic art - even in a case such as string theory. In sense of Mendeleev as a person. In general though life and surroundings of Dmitrii Mendeleev, the that case, theorists have chosen to focus on the core the historical analysis makes interesting points, late 19th century co-inventor of the periodic principles of quantum mechanics and gravity, and especially regarding Mendeleev’s rejection from table. Gordin covers Mendeleev’s academic work mathematically to tie them together into a the Academy and consequent Imperial Turn, and beginnings, his famous work on the periodic consistent theory. Those principles however are well the book largely succeeds in its aim. table, and takes time to discuss the lesser known grounded in experiment. Momentarily ignoring pursuits of Medeleev: his economic and political Alex May, PhD student, some details and beginning from basics is sometimes thought, his work in industry and in service to University of British Columbia necessary to make conceptual jumps. In fact, Zee the Russian empire, and his investigation into makes a similar point in the context of general the Spiritualism movement. Mendeleev’s diverse relativity - Einstein did not arrive at his theory by interests are used to explore the setting Fearful Symmetry: The Search for studying observations of the orbit of Mercury, but by Mendeleev lived in; indeed, Gordin emphasizes Beauty in Modern Physics, by A. Zee, revisiting long known simple observations. that the book is not so much the story of Princeton University Press, 2016, ISBN Mendeleev as it is an examination of imperial St. 9780691173269, pp. 376, price 31.99. While Zee’s views may not align precisely with Petersburg. There are few popular physics books which are my own, he has written an excellent book. It will Due to its emphasis on St. Petersburg, the book worth recommending to a student beginning a be of interest not only to the new student, but also is a biography of a scientist without being a sci- new subject. Tony Zee’s “Fearful symmetry” is to any artist or layperson interested in beauty. entific biography. With the exception of the one of them. This book should be productive Zee has made great progress in making the beauty
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of symmetry in physical law accessible for a wide This is the second Celestial Sleuth book, and of relativity.” Part III is devoted to a detailed audience. Olson makes reference to other case files in that explanation of the action principle in both volume — although not required to understand classical mechanics and gravity theory. Finally, in Further Adventures of the Celestial what is discussed here. The background part IV we learn about black holes, Hawking knowledge required to understand the text is at radiation, gravitons, as well as the concepts of Sleuth, by Olson, Donald W., Springer, 2018, the secondary level, and new material and dark matter and dark energy. In the grand finale pp. 334, ISBN 978-3-319-70319-0, price 32.84. terminology is explained succinctly to allow the Zee highlights the importance of gravitational reader to follow key ideas of analyses. For me, I waves, which, and that’s the hope, will provide I selected this book because I was intrigued by its felt it did provide some interesting options from scientists with new powerful methods of premise: using astronomy to solve mysteries which to teach physics at the secondary level, observing and understanding the Universe. regarding the time, date and location of the origins such as Chaucer’s description of the moon’s path of works of art. As a secondary school physics in terms of Kepler’s Laws of motion. For the On Gravity takes its time with the reader, and most teacher, I am always interested in finding other higher education educator, I feel the book gives concepts are explained brilliantly and in quite ways to teach students about the applications of enough information to provide a roadmap of the some detail: the idea of relativity, the action the knowledge and skills we teach them in school, kinds of information and tools one would need to principle, gravitational waves, and even curved and this text did not disappoint. endeavor on a similar quest. spacetime (in the appendix). I wish more professors would read this book and use these The book reads much like a Sherlock Holmes Tasha Richardson, explanations in their undergraduate courses! The case file. Donald W. Olson describes how he and Teacher, Albert Campbell CI, Toronto District explanation of Hawking radiation, on the other his team from Texas State examined paintings, School Board hand, after a thorough introduction into the battles, photographs, and literature through an quantum uncertainty principle, seems a bit rushed astronomical lens, to locate, re(examine) and On Gravity—A Brief Tour of a Weighty and barely surpasses that given in popular science challenge their understandings of the works, as Subject, by Anthony Zee, Princeton University texts. Moreover, what I would have liked to see well as the conclusions of other researchers. Press, 2018, ISBN 9780691174389, price 19.95, (and what is lacking in Zee’s treatment) is a deeper Clues, such as historical documents (e.g., letters, www.press.princeton.edu/titles/11235.html. discussion of the limitations of General Relativity. train schedules, tide tables, newspaper clippings) The Evergreen, a.k.a. the quest for the still elusive are combined with modern means (e.g., computer theory of quantum gravity, is clearly adressed, but In the preface, Anthony Zee tells his readers that planetarium simulations), to build their own problems at the classical level (say, in the form of On Gravity is supposed to bridge the gap portrait, which includes information about the gravitational singularities inside of black holes) between popular books and textbooks on Einstein astronomy, as well as the artists themselves. are not mentioned. I think this is a missed gravity. After reading the 142 pages of the main opportunity to make this book more balanced. text and the eight page appendix, I am convinced Broken into four parts — Astronomy in Art, that he succeeded. The area between popular Astronomy in History, Astronomy in Literature, books and textbooks is somewhat of a no man’s Overall, On Gravity is a fantastic read. It is The Terrestrial Sleuth — Olson begins each land, and especially for individuals with an supplemented by a whopping 12 page index as chapter outlining the questions he and his team interest in a particular field (say, gravity, for well as 13 pages of annotations providing had set out to solve. In Part One, the challenge instance) this can be quite frustrating. What additional anecdotes, insights, and kindhearted was often to deduce the location and date for a should you read when you already understand the encouragements to the reader. Zee’s book might painting. Olson works with an underlying basic idea of gravitation, know the main players be a good choice for undergraduate students who assumption that the artist included an accurate in the history of its development, and have are contemplating to enter the field but don’t want representation of what was present in the night perhaps watched a few documentariers on the to read 800 pages in a standard textbook. And if sky from their location. From this, he uses stories topic as well? you work on gravity yourself, and you want to talk about the artists and other references to the work, to your friends a bit more about your work, give them this book. Seriously. Zee’s unique style will to deduce his answers. Olson also includes in this Well, you should read On Gravity. section an examination of Times Square Kiss — surely entice them and present research in gravity and specifically the shadows on the buildings — from its truly attractive side (pun intended). to add more information to the ongoing discussion The book is divided in four parts which consist of on the as-yet unidentified woman and sailor. In a handful of chapters each, and each chapter is Jens Boos, Part Two, the team sought to better understand the again split into digestible sections with fitting and Ph.D. candidate, Department of Physics, factors which influenced strategic battle sometimes tongue-in-cheek headlines. Zee is one University of Alberta preparations (such as the case for the Battle of of the few physics authors who write so fluently Stirling Bridge or the Battle of Normandy), and and seemingly effortlessly that I didn’t even Practical Bayesian Influence: A Primer worked with data to highlight misconceptions. realize I was already halfway through the book. for Physical Scientists, by Coryn A. L. Part Three focuses on literary passages, to His tone, as usual, is relaxed, conversational, and Bailer-Jones, Cambridge University Press, 2017, determine their accuracy, in terms of celestial laid-back, making the seeminlgy complicated pp. 295, ISBN: 9781316642214, price 105.95. movements and season. Olson, uses knowledge of topic of Einstein’s General Theory of Relativity a each author’s astronomical competence to frame lot more approachable. the possible legitimacy of the passages, and then Few fields are as fraught with a history of move on to determine whether authors had In part I, Zee introduces gravity as the weakest of controversy as that of Bayesian inference. Although accurately described astronomical events or the four fundamental forces in our Universe, and born in the 18th century in the work of Bayes and celestial movements based on the season or explains the nature of electromagnetic (and Laplace, its “subjective” view of probability fell location of a scene. In the final part, Olson turns to gravitational) waves. In part II we learn about out of favour in the 20th century after Neyman, two final puzzles: a railway and locating the Einstein’s main idea: the principle of relativity. Pearson, and others developed statistics based on a Millais oak tree. We also learn why we shouldn’t call it “principle frequentist interpretation of probability. In the
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former, probability measures degrees of rational examples and ways of presenting material come transcribing a routine into your favourite belief in the truth of a proposition; in the latter, from the “quirky” books above. Still, it may be language can be a good exercise. A similar probability is viewed as the limiting frequency in easier to follow than other, deeper treatments. For critique is that the notation, for example E[x] for an infinite number of trials. example, Chapter 9 goes carefully through the expectation rather than
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VOL. 75 (2019)
No.2 The History of the Future of TRIUMF / L'histoire de l'avenir de TRIUMF
VOL. 76 (2020)
No.1 Physics vs. Pseudosciences and Fake News / La physique face aux pseudosciences et aux fausses nouvelles
No.2 Equity, Diversity and Inclusivity / Équité, diversité et inclusivité
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