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This is the first report of time-dependent of these has changed when changes in only track to realizing technological capabilities seismic tomography applied to an erupting two quantities (VP and VS) have been mea- resembling those of the fictional Virtual volcano. It builds on earlier work of the sured is not possible and requires the addi- Geophysical Laboratory by 2025. same kind done in geothermal areas in tion of other kinds of data. Both theoretical California and Iceland and the Long Valley advances and more data from different vol- References and Notes Caldera, California. But the seminal exam- canoes are needed before the potential of the 1. D. Patanè, G. Barberi, O. Cocina, P. De Gori, C. Chiarabba, Science 313, 821 (2006). ple of major changes in VP /VS comes from method can be fully assessed. 2. The compressional and shear waves are the fastest and The Geysers geothermal area in northern At present, monitoring of active volca- second-fastest waves to be radiated from an earthquake California. noes still rests mostly on relatively unso- source, so they arrive first and second on seismograms. Their ratio provides information about pressure and During the 1980s and 1990s, some phisticated seismic networks and the moni- about the presence of gas and liquid in the study volume. 13,600 tons of steam per hour were extracted toring of simple parameters, such as the Thus, changes in their ratio can tell us about changes in from The Geysers to generate electricity. As numbers of earthquakes and the amplitude pressure and gas/liquid, which are thought to accompany the buildup and occurrence of a volcanic eruption. a result of this overexploitation, the reser- of harmonic tremor. Patanè et al. show that 3. G. R. Foulger, C. C. Grant, A. Ross, B. R. Julian, Geophys. voir became progressively depleted as pore much more sophisticated methods can now Res. Lett. 24, 135 (1997). water was replaced by steam. Repeat seis- be used. Some of these methods only need to 4. R. C. Gunasekera, G. R. Foulger, B. R. Julian, J. Geophys. mic tomography showed the steady growth be automated—a critical factor if they are to Res. 108, 2134 (2003). 5. G. R. Foulger, B. R. Julian, Geotherm. Resour. Counc. of a reservoir-wide negative VP /VS anomaly be useful in situations where information is Bull. 33, 120 (2004). that coincided with the steam-production needed on an hourly basis. It is hoped that 6. G. R. Foulger et al., J. Geophys. Res. 108, 2147 (2003).

zone. This anomaly was caused by the com- this automation work will be pushed for- Downloaded from bined effects of the replacement of pore liq- ward rapidly in the near future, putting us on 10.1126/science.1131790 uid with steam, the resulting decrease in pressure, and the drying of clay minerals. A remarkable series of snapshots showed the COMPUTER SCIENCE relentless growth of a volume of heavy

depletion (3, 4). The work helped to increase http://science.sciencemag.org/ awareness of the nonsustainability of such high rates of fluid withdrawal. Production at Creating a Science of the Web The Geysers has now been reduced to sus- Tim Berners-Lee, Wendy Hall, James Hendler, Nigel Shadbolt, Daniel J. Weitzner tainable levels. Time-dependent tomogra- phy is currently used to monitor the Coso Understanding and fostering the growth of the World Wide Web, both in engineering and societal Geothermal Area, southern California (5). terms, will require the development of a new interdisciplinary field. Time-dependent seismic tomography was first applied to a volcano in a study of ince its inception, the World Wide lyzes the natural world, and tries to find Mammoth Mountain, a volcano on the rim Web has changed the ways scientists microscopic laws that, extrapolated to the of Long Valley Caldera, California. In 1989, Scommunicate, collaborate, and edu- macroscopic realm, would generate the on October 4, 2019 an intense swarm of hundreds of earth- cate. There is, however, a growing realiza- behavior observed. Computer science, by quakes accompanied an injection of new tion among many researchers that a clear contrast, though partly analytic, is princi- magma into the roots of this volcano, research agenda aimed pally synthetic: It is concerned with the con- and triggered the outpouring of some at understanding the struction of new languages and algorithms 300 tons of CO per day from the vol- Enhanced online at current, evolving, in order to produce novel desired computer 2 www.sciencemag.org/cgi/ cano’s surface. Several broad swaths content/full/313/5788/769 and potential Web is behaviors. Web science is a combination of of trees died as a result of high levels needed. If we want to these two features. The Web is an engineered of CO2 in the soil, and the CO2 model the Web; if we space created through formally specified also presented an asphyxiation hazard want to understand the architectural princi- languages and protocols. However, because to humans. A comparison of VP /VS tomo- ples that have provided for its growth; and if humans are the creators of Web pages and graphic images calculated for 1989 and we want to be sure that it supports the basic links between them, their interactions form 1997 showed changes that correlated well social values of trustworthiness, privacy, emergent patterns in the Web at a macro- with areas of tree death on the surface above, and respect for social boundaries, then we scopic scale. These human interactions are, and were attributed to migration of CO2 in must chart out a research agenda that targets in turn, governed by social conventions and the volcano (6). the Web as a primary focus of attention. laws. Web science, therefore, must be inher- By showing that time-dependent seismic When we discuss an agenda for a science ently interdisciplinary; its goal is to both tomography can be used to monitor struc- of the Web, we use the term “science” in two understand the growth of the Web and to cre- tural changes directly associated with a vol- ways. Physical and biological science ana- ate approaches that allow new powerful and canic eruption cycle, Patanè et al. take a crit- more beneficial patterns to occur. ical step toward developing a useful volcano- Unfortunately, such a research area does T. Berners-Lee and D. J. Weitzner are at the Computer Science hazard-reduction tool based on seismic and Artificial Intelligence Laboratory, Massachusetts Institute not yet exist in a coherent form. Within tomography. As with all good experiments, of Technology, Cambridge, MA 02139, USA. W. Hall and computer science, Web-related research has N. Shadbolt are in the School of Electronics and Computer however, it ushers in new challenges. VP /VS largely focused on information-retrieval is affected by several factors, including pore Science, University of Southampton, Southampton SO17 algorithms and on algorithms for the routing 1BJ, UK. J. Hendler is in the Computer Science Department, fluid phase, pressure, mineralogy, and frac- University of Maryland, College Park, MD 20742, USA. of information through the underlying Inter- ture density. However, determining how each E-mail: [email protected] net. Outside of computing, researchers grow

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ever more dependent on the Web; but they given topic. Conventional information- modeling. Imagine being able to query the have no coherent agenda for exploring the retrieval techniques are insufficient at the Web for a chemical in a specific cell biology emerging trends on the Web, nor are they scale of the Web. However, it turns out that pathway that has a certain regulatory status fully engaged with the emerging Web human topics of conversation on the Web as a drug and is available at a certain price. research community to more specifically can be analyzed by looking at a matrix of The engineering challenge is to allow inde- focus on providing for scientists’ needs. links (7, 8). The mathematics of information pendently developed data systems to be con- Leading Web researchers discussed the retrieval and structure-based search will nected together without requiring global scientific and engineering problems that certainly continue to be a fertile area of agreement as to terms and concepts. The sta- form the core of Web science at a workshop research as the Web itself grows. However, tistical methods that serve for the scaling of of the British Computer Society in London in approaches to developing a mathematical language resources in search tasks and the September 2005 (1). The participants consid- framework for modeling the Web vary data calculi that are used in scaling database ered emerging trends on the Web and debated widely, and any substantive impact will, queries are largely based on incompatible the specific types of research needed to again, require a new approach. The process- assumptions, and unifying these will be a exploit the opportunities as new media types, oriented methodologies of the formal sys- major challenge. data sources, and knowledge bases become tems community, the symbolic modeling Despite excitement about the Semantic “Webized,” as Web access becomes increas- methodologies of the artificial intelligence Web, most of the world’s data are locked in ingly mobile and ubiquitous, and as the need and semantics researchers, and the mathe- large data stores and are not published as an increases for privacy guarantees and control matical methods used in network analyses open Web of inter-referring resources. As a

of information on the Web. are all relevant, but no current mathematical result, the reuse of information has been Downloaded from The workshop covered a wide range of model can unify all of these. limited. Substantial research challenges technical and legal topics. For example, One particular ongoing extension of the arise in changing this situation: how to there has been research done on the structure Web is in the direction of moving from text effectively query an unbounded Web of and topology of the Web (2, 3) and the laws documents to data resources (see the figure). linked information repositories, how to align and map between different data mod-

EARLY WEB WEB TODAY els, and how to visualize and navigate the http://science.sciencemag.org/ huge connected graph of information that Browser Browser, blog, Wiki, data integration results. In addition, a policy question arises as to how to control the access to data Privacy • Security • Accessibility • Mobility resources being shared on the Web. This lat- ter question has implications both with respect to underlying technologies that HTML Interaction Semantic Web Multimodal Web services could provide greater protections, and to the issues of ownership in, for example, scien- tific data-sharing and grid computing.

The scale, topology, and power of decen- on October 4, 2019 XML tralized information systems such as the Web HTTP HTTP 1.1, SOAP, … also pose a unique set of social and public- URL URI policy challenges. Although computer and information science have generally concen- trated on the representation and analysis of The Web yesterday and today. (Left) The World Wide Web circa 1990 consisted primarily of text content information, attention also needs to be given expressed in the Hypertext Markup Language (HTML), exchanged via the hypertext transfer protocol (HTTP), and viewed with a simple browser pointing to a Universal Resource Locator (URL). (Right) Users of the Web to the social and legal relationships behind now have a variety of top-level tools to access richer content including scalable vector graphics, the Semantic this information (9). Transparency and con- Web, multimodal devices (e.g., voice browsers), and service descriptions. These are expressed in extended trol over these complex social and legal rela- markup language (XML), exchanged by newer protocols [e.g., HTTP 1.1 and SOAP (simple object access pro- tionships are vital, but require a much better- tocol)] and are addressed by uniform resource identifier (URI) schemes. developed set of models and tools that can represent these relationships. Early efforts at of connectivity and scaling to which it ap- In the Web of human-readable documents, modeling in the area of privacy and intellec- pears to conform (4–6). This work leads natural-language processing techniques can tual property have begun to establish the sci- some to argue that the development of the extract some meaning from the human-read- entific and legal challenges associated with Web has followed an evolutionary path, sug- able text of the pages. These approaches are representing and providing users with control gesting a view of the Web in ecological based on “latent” semantics, that is, on the over their own information. Our aim is to be terms. These analyses also showed the Web computer using heuristic techniques to reca- able to design “policy aware” systems that to have scale-free and small-world network- pitulate the intended meanings used in provide reasoning over these policies, enable ing structures, areas that have largely been human communication. By contrast, in the agents to act on a user’s behalf, make compli- studied by physicists and mathematicians “Semantic Web” of relational data and logi- ance easier, and provide accountability where using the tools of complex dynamical sys- cal assertions, computer logic is in its ele- rules are broken. tems analysis. ment, and can do much more. Web science is about more than modeling The need for better mathematical model- Researchers are exploring the use of new, the current Web. It is about engineering new ing of the Web is clear. Take the simple prob- logically based languages for question infrastructure protocols and understanding

lem of finding an authoritative page on a answering, hypothesis checking, and data the society that uses them, and it is about the ADAPTED FROM THE WORLD WIDE WEB CONSORTIUM CREDIT:

770 11 AUGUST 2006 VOL 313 SCIENCE www.sciencemag.org Published by AAAS PERSPECTIVES

creation of beneficial new systems. It has its ence is about making powerful new tools for 4. A.-L. Barabási, R. Albert, Science 286, 509 (1999). own ethos: decentralization to avoid social humanity, and doing it with our eyes open. 5. J. M. Kleinberg, Nature 406, 845 (2000). 6. S. H. Strogatz, Nature 410, 268 (2001). and technical bottlenecks, openness to the 7. S. Brin, L. Page, in Proceedings of the 7th International reuse of information in unexpected ways, References World Wide Web Conference (Elsevier Science, and fairness. It uses powerful scientific and 1. Workshop on The Emerging Science of the Web, British Amsterdam, 1998), pp. 107–117. mathematical techniques from many disci- Computer Society, London, 12 to 13 September 2005. See 8. Z. N. Oltvai, A.-L. Barabási, Science 298, 763 (2002). www.cs.umd.edu/~hendler/2005/WebScienceWorkshop. 9. L. Lessig, Code and Other Laws of Cyberspace (Basic plines to consider at once microscopic Web html Books, New York, 1999). properties, macroscopic Web phenomena, 2. R. Milo et al., Science 298, 824 (2002). and the relationships between them. Web sci- 3. R. Milo et al., Science 303, 1538 (2004). 10.1126/science.1126902

ASTRONOMY The importance of magnetic fields for the formation of stars, such as the Sun, is supported Testing Star Formation Theory by measurements of polarized radio waves from dust particles near a newly forming star. Richard M. Crutcher

nderstanding how stars Downloaded from Outflow In contrast to magnetically dominated star form is one of the out- B formation, the other extreme point of view is Ustanding challenges of that magnetic fields are too weak to provide modern astrophysics. It has Infall support against gravity. In this model, molec- become clear that stars form ular clouds are intermittent phenomena, and from dense interstellar clouds Jet the problem of cloud support for long time

of gas and dust, called molecu- periods is irrelevant (3). Supersonic flows in http://science.sciencemag.org/ lar clouds because gas in such Protostar the low-density turbulent interstellar medium clouds is predominantly in produce regions of enhanced density. Star for- molecular rather than atomic mation does not occur in every location where form. However, despite sub- the gas is dense, but only in small volumes Small accretion disk stantial progress in recent within clouds where sufficient mass accumu- years, there remain fundamen- Large pseudo-disk lates to become self-gravitating. Collapse and tal unanswered questions about star formation then proceed in that small frac- the basic physics of star forma- tion of the total cloud mass at a very rapid, tion. In particular, it remains free-fall rate.

unclear whether molecular In both models, the rate at which low- on October 4, 2019 clouds undergo rapid gravita- density interstellar gas is turned into stars is tional collapse as soon as suffi- consistent with the observed star formation cient matter accumulates to Shaped by magnetism. Schematic diagram of a collapsing molecular rate in the Milky Way Galaxy, about one solar make the clouds gravitation- cloud core with a strong magnetic field (B) showing the characteristic mass per year. The strong magnetic field ally bound, or whether there is hourglass shape. [Adapted from (4)] model achieves this result by setting the time some mechanism resisting col- scale for collapse of a dense molecular cloud lapse that delays the process and introduces as the gas density increases. After a molecular much longer than the gravitational free-fall new star formation scenarios. The observa- cloud accumulates sufficient mass to become time. In the turbulent, intermittent model, tional result reported on page 812 of this issue self-gravitating, it will still not collapse and only a small fraction of each molecular cloud by Girart et al. (1) provides new data regard- form stars because gravity is balanced by actually becomes self-gravitating and forms ing this important scientific question. magnetic pressure. stars. But the physical principles behind the The “standard” model for the formation of If there were no other forces operating, two models are fundamentally different. low-mass stars such as our Sun has been that molecular clouds would persist indefinitely As a result, the two models make very dif- interstellar magnetic fields provide support and star formation would not occur. However, ferent predictions that can be tested observa- against gravity in dense molecular clouds (2). magnetic fields are frozen only into the ions of tionally. Simulations of molecular cloud for- In this picture, interstellar magnetic fields are molecular clouds, not into the neutral gas and mation and evolution carried out with weak “frozen” into interstellar matter by the small dust. The neutrals are therefore free to respond magnetic fields show that the fields have a fraction of the gas and dust that is ionized. As to gravity and collapse to form a much denser, chaotic morphology, because the field lines material accumulates (due to the driving of gravitationally unstable core to the molecular are twisted by turbulence in the clouds. On the flows by galactic spiral-arm shocks, super- cloud and eventually to form stars. However, other hand, turbulence cannot twist field lines novae explosions, the gravity of a galaxy, as neutrals collapse through the ionized gas very much if the field strength is sufficiently etc.), the magnetic field increases in strength and dust, collisions with ions will occur. These strong. Magnetic field lines in dense, strongly SCIENCE collisions will greatly slow down the collapse magnetized clouds would then be roughly par- rate, leading to molecular cloud lifetimes typ- allel. Collapse along the magnetic field is not The author is in the Department of Astronomy, University of Illinois, 1002 W. Green Street, Urbana, IL 61801, USA. ically several orders of magnitude longer than impeded by the field, so cores are predicted to

CREDIT: P. HUEY/ P. CREDIT: E-mail: [email protected] the gravitational free-fall lifetime of a cloud. have a disk morphology. However, perpendi-

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