DOCSLIB.ORG

Forces, Light and Waves Mechanical Actions of Radiation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Forces, Light and Waves Mechanical Actions of Radiation Forces, light and waves Mechanical actions of radiation Jacques Derouard « Emeritus Professor », LIPhy Example of comets Cf Hale-Bopp comet (1997) Exemple of comets Successive positions of a comet Sun Tail is in the direction opposite / Sun, as if repelled by the Sun radiation Comet trajectory A phenomenon known a long time ago... the first evidence of radiative pressure predicted several centuries later Peter Arpian « Astronomicum Caesareum » (1577) • Maxwell 1873 electromagnetic waves Energy flux associated with momentum flux (pressure): a progressive wave exerts Pressure = Energy flux (W/m2) / velocity of wave hence: Pressure (Pa) = Intensity (W/m2) / 3.10 8 (m/s) or: Pressure (nanoPa) = 3,3 . I (Watt/m2) • NB similar phenomenon with acoustic waves . Because the velocity of sound is (much) smaller than the velocity of light, acoustic radiative forces are potentially stronger. • Instead of pressure, one can consider forces: Force = Energy flux x surface / velocity hence Force = Intercepted power / wave velocity or: Force (nanoNewton) = 3,3 . P(Watt) Example of comet tail composed of particles radius r • I = 1 kWatt / m2 (cf Sun radiation at Earth) – opaque particle diameter ~ 1µm, mass ~ 10 -15 kg, surface ~ 10 -12 m2 – then P intercepted ~ 10 -9 Watt hence F ~ 3,3 10 -18 Newton comparable to gravitational attraction force of the sun at Earth-Sun distance Example of comet tail Influence of the particles size r • For opaque particles r >> 1µm – Intercepted power increases like the cross section ~ r2 thus less strongly than gravitational force that increases like the mass ~ r3 Example of comet tail Influence of the particles size r • For opaque particles r << 1µm – Solar radiation wavelength λ ~0,5µm – r << λ « Rayleigh regime» – Intercepted power varies like the cross section ~ r6 thus decreases much stronger than gravitational force ~ r3 Radiation pressure most effective for particles size ~ 1µm Another example Ashkin historical experiment (1970) A. Ashkin, ‘Acceleration and trapping of particles by radiation pressure’, Physical Review Letters, Vol. 24, No. 4, 156, 1970 Laser I ~ 19mW / 100µm2 thus ~ 2.10 8 W/m2 Ashkin experiment (1970) A. Ashkin, ‘Acceleration and trapping of particles by radiation pressure’, Physical Review Letters, Vol. 24, No. 4, 156, 1970 Polystyren beads suspended in water Beads r=1,32µm Plaser =19mW λ=515nm w0=6,2µm Observes that -the beads are pushed by the laser beam (and slowed by water drag force) <V>=26µm/s Ashkin experiment (1970) • NB polystyren beads are transparent: – no radiation absorption – but deflection of light due to refraction • Radiative force is the result of this deflection Radiation pressure • Absorption, reflexion or scattering of a light beam by a particle r Absorption of light makes F the particle recoil r Deflexion (refraction or scattering) F of a uniform light beam yields to a force directed along the light beam Ashkin experiment (1970) A. Ashkin, ‘Acceleration and trapping of particles by radiation pressure’, Physical Review Letters, Vol. 24, No. 4, 156, 1970 Polystyren beads suspended in water Observes that -the beads are pushed by the laser beam -the beads are attracted by the laser beam « Gradient force » • Deflection or scattering of a non uniform intensity light beam by a particle r Deflection of light of non uniform F intensity across the particle yields to a resulting force directed obliquely, that tends (in this case) to push the particle towards maximum intensity region « Gradient force » • Deflection or scattering of a non uniform intensity light beam by a particle When the particle index of refraction is smaller than that of the medium (bubble), the deflection of light tends to expell r the particle from maximum F intensity region (should also be observed with reflective particles) Also observed by Ashkin in 1970 In conclusion two types of forces exerted by light on matter: • Radiation pressure (or « scattering force »): particles are pushed by a light beam – effect proportional to absorption or scattering cross section • Gradient force: particles are (generally) attracted towards high intensity regions (effect reversed with refractive index contrast) Radiatives forces • Atomic particles: close to a resonant absorption line σ is enormous, so are the radiative forces (-> cold atoms physics) • (NB for dielectric particles Ashkin has observed scattering resonance through radiative pressure resonance) Expression of radiative forces case of « small » particles (limit a<<λ) Response of the particle to radiation field: complex polarisability α = α '+iα" Radiation field characterized by r Energy density U (r ) r r Poynting vector < S(r ) > = Intensity x propagation direction Expression of radiative forces case of « small » particles (limit a<<λ) r r r < >= + F Fscat Fgrad Radiation pressure Gradient force Expression of radiative forces case of « small » particles (limit a<<λ) r r r < >= + F Fscat Fgrad r r r α" < S(r) > F = k n Radiation pressure scat ε med 0 c - α’’ proportional to the sum of absorption and scattering cross sections r α - ’’ > 0 , F scat always towards the propagation of the wave, maximum for absorption or scattering resonance frequencies Expression of radiative forces case of « small » particles (limit a<<λ) r r r < >= + F Fscat Fgrad r r α' r F = −∇− U (r) Gradient force grad ε 2 0 -If α’ > 0 attraction towards large U regions -If α’ < 0 repulsion from large U regions -large variation of α’ close to resonance frequencies, may change of sign (« blue detuned optical atomic traps ») Radiation pressure and gradient forces both exists also with acoustic waves: • Radiation pressure: associated with momentum flux transported by acoustic wave = Energy flux / velocity in the simplest cases • Gradient force: for small spherical particles it results from « Gor’kov potential ». For large particules it can be estimated like in geometrical optics, where the analogous of refractive index is 1/ ρc Radiation pressure and gradient forces both exists also with acoustic waves: • Gradient force: for spherical particles it results from « Gor’kov potential ». Particles are trapped at the nodes of a 2D network of moveable stationnary waves Radiation pressure and gradient forces both exists also with acoustic waves: • Gradient force on bubbles (P. Marmottant, P. Thibault et al …) – « Bjerknes force »: response of the bubble to acoustic pressure is its variation of volume ∆V=( α’+iα’’)∆p r 1 r F = α'∇p 2 4 0 – Acoustic resonance mode Change of sign of α’, hence F, when crossing resonance frequency Resonance for R~20µm: Change of sign of radiative force Optics A variant of the first Ashkin’s experiment: propelling of microparticles over optical waveguides. • Gaugiran (CEA-LETI), Derouard et al Opt. Express 13, 6956-6963 (2005); Opt. Express 15, 8146-8156 (2007) Optical trapping and propelling of particles over an optical wave guide F GRAD Light intensity profile FGRAD FPrad FPrad F GRAD FGRAD laser Particule Scattered light F Numerical calculation of the electromagnetic field energy density and forces applied on a glass microparticles of diameter 250nm immersed in water and lying over a silicon nitride optical waveguide. LIGHT F Experimental set-up CCD camera Optical waveguide Microscope Microparticles objective suspended in water Silicon substrate Propelling of glass microparticles (diameter 1µm) ) Gaugiran et al, (2005) Propelling of biological cells (yeast and bacteria) (( Gaugiran et al. (2005) Propelling of biological cells (red blood cells) (( Gaugiran et al. (2005) Radiative forces and optical trapping of particles Radiative forces and optical trapping of particles • Need to balance the effects of radiation pressure. Several possibilities: – gravity – substrate – 2 counter propagating light beams – gradient force stronger than radiation pressure (strongly focused beam : « optical tweezer ») Radiative forces and optical trapping of particles • Need to balance the effects of radiation pressure. Several possibilities: – gravity – substrate – 2 counter propagating light beams – gradient force stronger than radiation pressure (strongly focused beam : « optical tweezer ») First trapping experiment: counter propagating beams Gradient forces attract beads towards beams axis Opposite axial radiation pressure forces are balanced A. Ashkin, ‘Acceleration and trapping of particles by radiation pressure’, Physical Review Letters, Vol. 24, No. 4, 156, 1970 Recente version of this configuration: «optical stretcher » (Guck et al , 2000, 2005) • Ytterbium fibered laser injected in single mode optical fibers • Microfluidic channel • Biological cells suspended in water 100µm Application: observation of the deformation of a «fibroblast» (Guck et al , 2005) Trapped cell: As a result of radiative pressure the cell is distorted Monitoring of laser beam intensity The cell is not squeezed, it is streched!! ?? Radiation pressure in material media • In vacuum radiation pressure = Intensity / c0 • In medium refractive index n, velocity of light = c0 / n hence, we may guess that radiation pressure = Intensity / ( c0 / n ) thus x radiation pressure = (Intensity / c 0 ) n • • Actually it seems that in a number of cases, everything is as if the photons transported by the wave had momentum equal x ν to n h /c0 Radiative forces on material media Medium refractive Medium refractive index n index n1 2 Radiation Radiation Intensity I Intensity I Momentum flux Momentum flux I n 1 /c I n 2 /c Radiative forces on material media Medium refractive Medium refractive index n index n1 2 If n2 > n1 then
Load more

Recommended publications
  • 30. Electromagnetic Waves and Optics
    30. Electromagnetic waves and optics www.ariel.ac.il Ԧ 1 푊 Power per unit area and points Poynting vector: 푆 = 퐸 × 퐵 has units [ 2] 휇0 푚 in the direction of propagation 1 푆Ԧ = 퐸 × 퐵 휇0 퐸 퐸 퐵 푆Ԧ http://www.ariel.ac.il/ 퐵 푆Ԧ Intensity is time averaged norm of Poynting vector: 1 푇 퐼 = 푆 = ׬ 푆Ԧ 푑푡 푎푣 푇 0 퐸 푥, 푡 = 퐸 cos 푘푥 − 휔푡 푦 0 1 푆Ԧ = 퐸 × 퐵 퐸0 휇 퐵 푥, 푡 = cos 푘푥 − 휔푡 0 푧 푐 Intensity is time averaged norm of Poynting vector: 2 1 푇 Ԧ 퐸0 푇 2 퐼 = 푆푎푣 = ׬ 푆 푑푡 = ׬ cos 푘푥 − 휔푡 푑푡 푇 0 푐휇0 0 퐸 푥, 푡 = 퐸 cos 푘푥 − 휔푡 푦 0 1 푆Ԧ = 퐸 × 퐵 퐸0 휇 퐵 푥, 푡 = cos 푘푥 − 휔푡 0 푧 푐 Intensity is time averaged norm of Poynting vector: 푇 푇 1 퐸2 퐸2 푐퐵2 Ԧ 0 2 0 0 푊 퐼 = 푆푎푣 = න 푆 푑푡 = න cos 푘푥 − 휔푡 푑푡 = = units [ ൗ 2] 푇 푐휇0 2푐휇0 2휇0 푚 0 0 1 2 1 1 2 Energy density 푢 = 휀표퐸 + 퐵 2 2 휇0 퐸푦 푥, 푡 = 퐸0cos 푘푥 − 휔푡 퐸 Electric field Magnetic field 0 퐵푧 푥, 푡 = cos 푘푥 − 휔푡 energy density energy density 푐 1 2 1 1 2 2 Energy density 푢 = 휀표퐸 + 퐵 = 휀표퐸 2 2 휇0 퐸푦 푥, 푡 = 퐸0cos 푘푥 − 휔푡 퐸 Electric field Magnetic field 0 퐵푧 푥, 푡 = cos 푘푥 − 휔푡 energy density energy density 푐 퐸 (퐵 = = 휀 휇 퐸) 푐 표 0 1 2 1 1 2 2 Energy density 푢 = 휀표퐸 + 퐵 = 휀표퐸 2 2 휇0 퐸푦 푥, 푡 = 퐸0cos 푘푥 − 휔푡 퐸 Electric field Magnetic field 0 퐵푧 푥, 푡 = cos 푘푥 − 휔푡 energy density energy density 푐 1 푇 1 Average energy density 푢 = ׬ 휀 퐸2푑푡 = 휀 퐸2 푎푣 푇 0 표 2 표 0 1 2 1 1 2 2 Energy density 푢 = 휀표퐸 + 퐵 = 휀표퐸 2 2 휇0 퐸푦 푥, 푡 = 퐸0cos 푘푥 − 휔푡 퐸 Electric field Magnetic field 0 퐵푧 푥, 푡 = cos 푘푥 − 휔푡 energy density energy density 푐 2 1 푇 2 1 2 퐸0 ( = Average energy density 푢푎푣 = ׬ 휀표퐸 푑푡 = 휀표퐸0 = 휀표휇0푐퐼 (Intensity = 퐼 푇 0 2 2푐휇0 퐼 퐽 푢 = units:
    [Show full text]
  • Radiometric Actuators for Spacecraft Attitude Control
    Radiometric Actuators for Spacecraft Attitude Control Ravi Teja Nallapu Amit Tallapragada Jekan Thangavelautham Space and Terrestrial Robotic Space and Terrestrial Robotic Space and Terrestrial Robotic Exploration Laboratory Exploration Laboratory Exploration Laboratory Arizona State University Arizona State University Arizona State University 781 E. Terrace Mall, Tempe, AZ 781 E. Terrace Mall, Tempe, AZ 781 E. Terrace Mall, Tempe, AZ [email protected] [email protected] [email protected] Abstract—CubeSats and small satellites are emerging as low- cost tools to perform astronomy, exoplanet searches and earth With this in mind, a new device to control the orientation of observation. These satellites can be dedicated to pointing at a spacecraft is presented in this paper and exploits targets for weeks or months at a time. This is typically not radiometric forces. To understand how this actuator works, possible on larger missions where usage is shared. Current let’s look at the Crooke’s Radiometer [1, 2] which consists satellites use reaction wheels and where possible magneto- torquers to control attitude. However, these actuators can of 4 thin plates, called vanes, each colored black and white induce jitter due to various sources. In this work, we introduce on its opposite surfaces. These vanes are suspended from a a new class of actuators that exploit radiometric forces induced spindle such that opposite colors faces each other. This by gasses on surface with a thermal gradient. Our work shows setup is now placed in a low-pressure vessel containing that a CubeSat or small spacecraft mounted with radiometric trace gasses of nitrogen or argon (Figure 1).
    [Show full text]
  • Radiation Forces on Small Particles in the Solar System T
    1CARUS 40, 1-48 (1979) Radiation Forces on Small Particles in the Solar System t JOSEPH A. BURNS Cornell University, 2 Ithaca, New York 14853 and NASA-Ames Research Center PHILIPPE L. LAMY CNRS-LAS, Marseille, France 13012 AND STEVEN SOTER Cornell University, Ithaca, New York 14853 Received May 12, 1978; revised May 2, 1979 We present a new and more accurate expression for the radiation pressure and Poynting- Robertson drag forces; it is more complete than previous ones, which considered only perfectly absorbing particles or artificial scattering laws. Using a simple heuristic derivation, the equation of motion for a particle of mass m and geometrical cross section A, moving with velocity v through a radiation field of energy flux density S, is found to be (to terms of order v/c) mi, = (SA/c)Qpr[(1 - i'/c)S - v/c], where S is a unit vector in the direction of the incident radiation,/" is the particle's radial velocity, and c is the speed of light; the radiation pressure efficiency factor Qpr ~ Qabs + Q~a(l - (cos a)), where Qabs and Q~c~ are the efficiency factors for absorption and scattering, and (cos a) accounts for the asymmetry of the scattered radiation. This result is confirmed by a new formal derivation applying special relativistic transformations for the incoming and outgoing energy and momentum as seen in the particle and solar frames of reference. Qpr is evaluated from Mie theory for small spherical particles with measured optical properties, irradiated by the actual solar spectrum. Of the eight materials studied, only for iron, magnetite, and graphite grains does the radiation pressure force exceed gravity and then just for sizes around 0.
    [Show full text]
  • HISTORY Nuclear Medicine Begins with a Boa Constrictor
    HISTORY Nuclear Medicine Begins with a Boa Constrictor Marshal! Brucer J Nucl Med 19: 581-598, 1978 In the beginning, a boa constrictor defecated in and then analyzed the insoluble precipitate. Just as London and the subsequent development of nuclear he suspected, it was almost pure (90.16%) uric medicine was inevitable. It took a little time, but the acid. As a thorough scientist he also determined the 139-yr chain of cause and effect that followed was "proportional number" of 37.5 for urea. ("Propor­ inexorable (7). tional" or "equivalent" weight was the current termi­ One June week in 1815 an exotic animal exhibi­ nology for what we now call "atomic weight.") This tion was held on the Strand in London. A young 37.5 would be used by Friedrich Woehler in his "animal chemist" named William Prout (we would famous 1828 paper on the synthesis of urea. Thus now call him a clinical pathologist) attended this Prout, already the father of clinical pathology, be­ scientific event of the year. While he was viewing a came the grandfather of organic chemistry. boa constrictor recently captured in South America, [Prout was also the first man to use iodine (2 yr the animal defecated and Prout was amazed by what after its discovery in 1814) in the treatment of thy­ he saw. The physiological incident was common­ roid goiter. He considered his greatest success the place, but he was the only person alive who could discovery of muriatic acid, inorganic HC1, in human recognize the material. Just a year earlier he had gastric juice.
    [Show full text]
  • (19) United States (12) Patent Application Publication (10) Pub
    US 20060001569A1 (19) United States (12) Patent Application Publication (10) Pub. N0.: US 2006/0001569 A1 Scandurra (43) Pub. Date: Jan. 5, 2006 (54) RADIOMETRIC PROPULSION SYSTEM Publication Classi?cation (76) Inventor: Marco Scandurra, Cambridge, MA (51) 110.0. 001s 3/02 (2006.01) 601K 15/00 (2006.01) Correspondence Address: (52) Us. 01. ............................................... ..342/351;374/1 STANLEY H. KREMEN 4 LENAPE LANE (57) ABSTRACT EAST BRUNSWICK, NJ 08816 (US) Ahighly ef?cient propulsion system for ?ying, ?oating, and Appl. No.: ground vehicles that operates in an atmosphere under stan (21) 11/068,470 dard conditions according to radiornetric principles. The Filed: Feb. 22, 2005 propulsion system comprises specially fabricated plates that (22) exhibit large linear thrust forces upon application of a Related US. Application Data temperature gradient across edge surfaces. Several ernbodi rnents are presented. The propulsion system has no moving (60) Provisional application No. 60/521,774, ?led on Jul. parts, does not use Working ?uids, and does not burn 1, 2004. hydrocarbon fuels. 1O 13 12 \ 11 Patent Application Publication Jan. 5, 2006 Sheet 1 0f 16 US 2006/0001569 A1 FIG. 2 Patent Application Publication Jan. 5, 2006 Sheet 2 0f 16 US 2006/0001569 A1 25 2X - FIG. 6 Patent Application Publication Jan. 5, 2006 Sheet 3 0f 16 US 2006/0001569 A1 27 0000000. I.N... 000000. FIG. 7 FIG. 8 FIG. 9 ~ FIG. 10 34 39 QI 40/? 9: 38 35 FIG. 11 Patent Application Publication Jan. 5, 2006 Sheet 4 0f 16 US 2006/0001569 A1 42 43/ FIG. 12 Patent Application Publication Jan.
    [Show full text]
  • Section 22-3: Energy, Momentum and Radiation Pressure
    Answer to Essential Question 22.2: (a) To find the wavelength, we can combine the equation with the fact that the speed of light in air is 3.00 " 108 m/s. Thus, a frequency of 1 " 1018 Hz corresponds to a wavelength of 3 " 10-10 m, while a frequency of 90.9 MHz corresponds to a wavelength of 3.30 m. (b) Using Equation 22.2, with c = 3.00 " 108 m/s, gives an amplitude of . 22-3 Energy, Momentum and Radiation Pressure All waves carry energy, and electromagnetic waves are no exception. We often characterize the energy carried by a wave in terms of its intensity, which is the power per unit area. At a particular point in space that the wave is moving past, the intensity varies as the electric and magnetic fields at the point oscillate. It is generally most useful to focus on the average intensity, which is given by: . (Eq. 22.3: The average intensity in an EM wave) Note that Equations 22.2 and 22.3 can be combined, so the average intensity can be calculated using only the amplitude of the electric field or only the amplitude of the magnetic field. Momentum and radiation pressure As we will discuss later in the book, there is no mass associated with light, or with any EM wave. Despite this, an electromagnetic wave carries momentum. The momentum of an EM wave is the energy carried by the wave divided by the speed of light. If an EM wave is absorbed by an object, or it reflects from an object, the wave will transfer momentum to the object.
    [Show full text]
  • Pulling and Lifting Macroscopic Objects by Light
    Pulling and lifting macroscopic objects by light Gui-hua Chen1,2, Mu-ying Wu1, and Yong-qing Li1,2* 1School of Electronic Engineering & Intelligentization, Dongguan University of Technology, Dongguan, Guangdong, P.R. China 2Department of Physics, East Carolina University, Greenville, North Carolina 27858-4353, USA (Received XX Month X,XXX; published XX Month, XXXX) Laser has become a powerful tool to manipulate micro-particles and atoms by radiation pressure force or photophoretic force, but optical manipulation is less noticeable for large objects. Optically-induced negative forces have been proposed and demonstrated to pull microscopic objects for a long distance, but are hardly seen for macroscopic objects. Here, we report the direct observation of unusual light-induced attractive forces that allow pulling and lifting centimeter-sized light-absorbing objects off the ground by a light beam. This negative force is based on the radiometric effect on a curved vane and its magnitude and temporal responses are directly measured with a pendulum. This large force (~4.4 μN) allows overcoming the gravitational force and rotating a motor with four-curved vanes (up to 600 rpm). Optical pulling of macroscopic objects may find nontrivial applications for solar radiation-powered near-space propulsion systems and for understanding the mechanisms of negative photophoretic forces. PACS number: 42.50.Wk, 87.80.Cc, 37.10.Mn In Maxwell’s theory of electromagnetic waves, light carries rotation of the objects, they are insufficient to manipulate the energy and momentum, and the exchange of the energy and objects in vertical direction. momentum in light-matter interaction generates optically-induced Here we report a direct observation of a negative optically- forces acting on material objects.
    [Show full text]
  • Capítulo 21 21
    Capítulo 21 21 Universidade Estadual de Campinas Instituto de Física “Gleb Wataghin” Instrumentação para Ensino – F 809 RADIÔMETRO DE CROOKES III Aluno: Everton Geiger Gadret Orientadora: Profª. Dra. Mônica Alonso Cotta Coordenador: Prof. Dr. José Joaquim Lunazzi 21-1 Introdução O radiômetro é um instrumento capaz de medir radiação. Ao incidir sobre as palhetas do radiômetro, a luz faz com que se inicie um movimento de rotação das palhetas em torno do eixo da haste que o sustenta (figura 1). Quando observou pela primeira vez o movimento, Maxwell imaginou estar observando um experimento que comprovava sua previsão a respeito da pressão de radiação que uma onda eletromagnética exerce sobre a matéria. Ledo engano, pois o movimento ocorria no sentido inverso ao previsto por sua teoria. Até os dias de hoje, acredita-se que o fenômeno que ocorre tem natureza termodinâmica, sendo o movimento gerado por correntes de convecção do meio geradas pelo aquecimento desigual das faces das palhetas. A solução correta para o fenômeno foi dada qualitativamente por Osborne Reynolds. Em 1879 Reynolds submeteu um artigo à Royal Society no qual considerava o que chamou de “transpiração térmica” e também discutiu a teoria do radiômetro. Ele chamou de “transpiração térmica” o fluxo de gás através de palhetas porosas caudado pela diferença de pressão entre os lados da palheta. Se o gás está inicialmente à mesma pressão dos dois lados, há um fluxo de gás do lado mais frio para o lado mais quente, resultando em uma pressão maior do lado quente se as palhetas não se movessem. O equilíbrio é alcançado quando a razão entre as pressões de cada lado é a raiz quadrada da razão das temperaturas absolutas.
    [Show full text]
  • Ihtc14-22023
    Proceedings of the 14th International Heat Transfer Conference IHTC14 August 08-13, 2010, Washington, DC, USA IHTC14-22023 REYNOLDS, MAXWELL AND THE RADIOMETER, REVISITED Holger Martin Thermische Verfahrenstechnik, Karlsruhe Institute of Technology (KIT) Karlsruhe, Germany ABSTRACT later by G. Hettner, goes through a maximum. Albert Einstein’s In 1969, S. G. Brush and C. W. F. Everitt published a approximate solution of the problem happens to give the order historical review, that was reprinted as subchapter 5.5 Maxwell, of magnitude of the forces in the maximum range. Osborne Reynolds, and the radiometer, in Stephen G. Brush’s famous book The Kind of Motion We Call Heat. This review A comprehensive formula and a graph of the these forces covers the history of the explanation of the forces acting on the versus pressure combines all the relevant theories by Knudsen vanes of Crookes radiometer up to the end of the 19th century. (1910), Einstein (1924), Maxwell (1879) (and Hettner (1926), The forces moving the vanes in Crookes radiometer (which are Sexl (1928), and Epstein (1929) who found mathematical not due to radiation pressure, as initially believed by Crookes solutions for Maxwells creeping flow equations for non- and Maxwell) have been recognized as thermal effects of the isothermal spheres and circular discs, which are important for remaining gas by Reynolds – from his experimental and thermophoresis and for the radiometer). theoretical work on Thermal Transpiration and Impulsion, in 1879 – and by the development of the differential equations The mechanism of Thermal Creeping Flow will become of describing Thermal Creeping Flow, induced by tangential increasing interest in micro- and submicro-channels in various stresses due to a temperature gradient on a solid surface by new applications, so it ought to be known to every graduate Maxwell, earlier in the same year, 1879.
    [Show full text]
  • MONITORING of AERODYNAMIC PRESSURES for VENUS EXPRESS in the UPPER ATMOSPHERE DURING DRAG EXPERIMENTS BASED on TELEMETRY Sylvain
    MONITORING OF AERODYNAMIC PRESSURES FOR VENUS EXPRESS IN THE UPPER ATMOSPHERE DURING DRAG EXPERIMENTS BASED ON TELEMETRY Sylvain Damiani(1,2), Mathias Lauer(1), and Michael Müller(1) (1) ESA/ESOC; Robert-Bosch-Str. 5, 64293 Darmstadt, Germany; +49 6151900; [email protected] (2)GMV GmbH; Robert-Bosch-Str. 7, 64293 Darmstadt, Germany; +49 61513972970; [email protected] Abstract: The European Space Agency Venus Express spacecraft has to date successfully completed nine Aerodynamic Drag Experiment Campaigns designed in order to probe the planet's upper atmosphere over the North pole. The daily monitoring of the campaign is based on housekeeping telemetry. It consists of reducing the spacecraft dynamics in order to obtain a timely evolution of the aerodynamic torque over a pericenter passage, from which estimations of the accommodation coefficient, the dynamic pressure and the atmospheric density can be extracted. The observed surprising density fluctuations on short timescales justify the use of a conservative method to decide on the continuation of the experiments. Keywords: Venus Express, Drag Experiments, Attitude Dynamics, Aerodynamic Torque. 1. Introduction The European Space Agency's Venus Express spacecraft has been orbiting around Venus since 2006, and its mission has now been extended until 2014. During the extended mission, it has already successfully accomplished 9 Aerodynamic Drag Experiment campaigns until September 2012. Each campaign aims at probing the planet’s atmospheric density at high altitude and next to the North pole by lowering the orbit pericenter (down to 165 km of altitude), and observing its perturbations on both the orbit and the attitude of the probe.
    [Show full text]
  • INFLUENCE of SOLAR RADIATION PRESSURE on ORBITAL ECCENTRICITY of a GRAVITY-GRADIENT-ORIENTED LENTICULAR SATELLITE by William M
    NASA TECHNICAL NOTE NASA TN D-2715 e- e- - -- (5- / --I -=e3-m INFLUENCE OF SOLAR RADIATION PRESSURE ON ORBITAL ECCENTRICITY OF A GRAVITY-GRADIENT-ORIENTED LENTICULAR SATELLITE by William M. Adams, Jr., and Ward F. Hodge Langley Research Center Langley Station, Hampton, Va. NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. 0 MARCH 1965 / t 1 TECH LIBRARY KAFB, "I I llllll11111 llllI11111111111111111l11 lilt 1111 0079733 INFLUENCE OF SOLAR RADIATION PRESSURE ON ORBITAL ECCENTRICITY OF A GRAVITY-GRADIENT-ORIENTED LENTICULAR SATELLITE By William M. Adams, Jr., and Ward F. Hodge Langley Research Center Langley Station, Hampton, Va. NATIONAL AERONAUTICS AND SPACE ADMINISTRATION For sole by the Office of Technical Services, Deportment of Commerce, Woshington, D.C. 20230 -- Price $1.00 ... ~ I I INFLUENCE OF SOLAR RADIATION PRESSURE ON ORBITAL ECCENTRICITY OF A GRAVITY-GRADIENT-ORIENTED LENTICULAR SATEUITE By William M. Adams, Jr., and Ward F. HoQe Langley Research Center A method is presented for calculating the perturbations of the orbital elements of a low-density lenticular satellite due to solar radiation pressure. The necessary calculations are performed by means of the digital computer. Typ- ical results are presented for seven orbital inclinations ranging from 0' to ll3O for a perfectly absorptive satellite initially in a nearly circular 2,000- nautical-mile orbit. The information obtained indicates that the change in eccentricity caused by solar radiation pressure becomes large enough for all the inclinations con- sidered to cause attitude-control problems with the gravity-gradient stabiliza- tion system. A nearly circular orbit appears necessary for lenticular satel- lites since the ability of gravity gradient attitude control systems to damp the pitching libration induced by elliptic orbital motion is still in doubt.
    [Show full text]
  • How Stars Work: • Basic Principles of Stellar Structure • Energy Production • the H-R Diagram
    Ay 122 - Fall 2004 - Lecture 7 How Stars Work: • Basic Principles of Stellar Structure • Energy Production • The H-R Diagram (Many slides today c/o P. Armitage) The Basic Principles: • Hydrostatic equilibrium: thermal pressure vs. gravity – Basics of stellar structure • Energy conservation: dEprod / dt = L – Possible energy sources and characteristic timescales – Thermonuclear reactions • Energy transfer: from core to surface – Radiative or convective – The role of opacity The H-R Diagram: a basic framework for stellar physics and evolution – The Main Sequence and other branches – Scaling laws for stars Hydrostatic Equilibrium: Stars as Self-Regulating Systems • Energy is generated in the star's hot core, then carried outward to the cooler surface. • Inside a star, the inward force of gravity is balanced by the outward force of pressure. • The star is stabilized (i.e., nuclear reactions are kept under control) by a pressure-temperature thermostat. Self-Regulation in Stars Suppose the fusion rate increases slightly. Then, • Temperature increases. (2) Pressure increases. (3) Core expands. (4) Density and temperature decrease. (5) Fusion rate decreases. So there's a feedback mechanism which prevents the fusion rate from skyrocketing upward. We can reverse this argument as well … Now suppose that there was no source of energy in stars (e.g., no nuclear reactions) Core Collapse in a Self-Gravitating System • Suppose that there was no energy generation in the core. The pressure would still be high, so the core would be hotter than the envelope. • Energy would escape (via radiation, convection…) and so the core would shrink a bit under the gravity • That would make it even hotter, and then even more energy would escape; and so on, in a feedback loop Ë Core collapse! Unless an energy source is present to compensate for the escaping energy.
    [Show full text]