107 research outputs found
Experimental study of photon beam polarimeter based on nuclear e+e- pair production in an amorphous target
The experimental method of the linearly polarized photons polarimetry,using
incoherent e+e- pair production process has been investigated on the beam of
coherent bremsstrahlung (CB) photons in the energy range of 0.9-1.1 GeV at the
Yerevan synchrotron.Comment: 6 pages (text),10 figure
Model Independent Form Factors for Spin Independent Neutralino-Nucleon Scattering from Elastic Electron Scattering Data
Theoretical calculations of neutralino-nucleon interaction rates with various
nuclei are of great interest to direct dark matter searches such as CDMS,
EDELWEISS, ZEPLIN, and other experiments since they are used to establish upper
bounds on the WIMP-proton cross section. These interaction rates and cross
sections are generally computed with standard, one or two parameter
model-dependent nuclear form factors, which may not exactly mirror the actual
form factor for the particular nucleus in question. As is well known, elastic
electron scattering can allow for very precise determinations of nuclear form
factors and hence nuclear charge densities for spherical or near-spherical
nuclei. We use charge densities derived from elastic electron scattering data
to calculate model independent, analytic form factors for various target nuclei
important in dark matter searches, such as Si, Ge, S, Ca and others. We have
found that for nuclear recoils in the range of 1-100 keV significant
differences in cross sections and rates exist when the model independent form
factors are used: at 30 keV nuclear recoil the form factors squared differ by a
factor of 1.06 for Si, 1.11 for Ca, 1.27 for Ge, and 1.92
for Xe. We show the effect of different form factors on the upper limit
on the WIMP-proton cross section obtained with a hypothetical Ge
detector during a 100 kg-day effective exposure. Helm form factors with various
parameter choices differ at most by 10--20% from the best (Fourier Bessel) form
factor, and can approach it to better than 1% if the parameters are chosen to
mimic the actual nuclear density.Comment: 20 pages, 8 figure
On X-Ray Waveguiding in Nanochannels: Channeling Formalism
The question on X-ray extreme focusing (smallest reachable spot size) brings
us to the idea for using the wave features of X-ray propagation in media. As
known, wave features are revealed at propagation in ultra-narrow collimators as
well as at glancing reflection from smooth flat and/or strongly curved
surfaces. All these phenomena can be described within the general formalism of
X-ray channeling.Comment: by the invited lecture at ISRP-1
Neutrino-nucleus reactions on ^{12}C and ^{16}O
Exclusive and inclusive cross-sections and
-capture rates are calculated for ^{12}C and ^{16}O using the consistent
random phase approximation (RPA) and pairing model. After a pairing correction
is introduced to the RPA results the flux-averaged theoretical cross-sections and -capture rates in C are
in good agreement with experiment. In particular when one takes into account
the experimental error bars, the recently measured range of values for the
cross-section is in agreement with the present theoretical
results. Predictions of and cross-sections in
^{16}O are also presented.Comment: 13 pages, Revte
Dynamics of viscous amphiphilic films supported by elastic solid substrates
The dynamics of amphiphilic films deposited on a solid surface is analyzed
for the case when shear oscillations of the solid surface are excited. The two
cases of surface- and bulk shear waves are studied with film exposed to gas or
to a liquid. By solving the corresponding dispersion equation and the wave
equation while maintaining the energy balance we are able to connect the
surface density and the shear viscocity of a fluid amphiphilic overlayer with
experimentally accessible damping coefficients, phase velocity, dissipation
factor and resonant frequency shifts of shear waves.Comment: 19 pages, latex, 3 figures in eps-forma
Muon capture by 3He nuclei followed by proton and deuteron production
The paper describes an experiment aimed at studying muon capture by
nuclei in pure and mixtures at various densities. Energy distributions of
protons and deuterons produced via and are measured for the
energy intervals MeV and MeV, respectively. Muon capture
rates, and are obtained using two different analysis methods. The
least--squares methods gives , . The Bayes theorem
gives ,
. The experimental
differential capture rates, and , are compared with theoretical
calculations performed using the plane--wave impulse approximation (PWIA) with
the realistic NN interaction Bonn B potential. Extrapolation to the full energy
range yields total proton and deuteron capture rates in good agreement with
former results.Comment: 17 pages, 13 figures, accepted for publication in PR
RESONANT SCATTERING
Acoustic resonant scattering has become of great interest ever since the
Resonance Scattering Theory (RST) was published in 1978 (L. Flax, L. R.
Dragonette, and H. Uberall), having been first presented to the public in the
preceding year (H. Uberall, IUTAM Symposium at Northwestern University,
Evanston, IL, Sept. 12-15, 1977). A large amount of experimental activity
followed in the United States, and especially in France where acoustic
resonance scattering was first studied on submerged solid objects using the
method of long pulses, or MIIR (G. Maze and J. Ripoche, 19831, and later by
the method of short pulses (S. K. Numrich et al., 1984; M. de Billy, 1986).
The resonances of submerged shells have been studied by M. Talmant and G.
Quentin (1988) by this method. The RST also furnishes a physical
interpretation of the resonances in terms of the phase matching of surface
waves. Recent experimental advances on these topics are reported here.La diffusion acoustique résonnante a evoqué beaucoup d'intérêt depuis la
publication de la Théorie de la Diffusion Résonnante (RST) en 1978 (L. Flax,
L. R. Dragonette, et H. Uberall), ayant été presentee au public pour la
première fois dans l'année précédente (H. Uberall, IUTAM Symposium à
Northwestern University, Evanston, IL, 12-15 Sept. 1977). Beaucoup d'activité
expérimentale suivit aux Etats Unis, et surtout en France où la diffusion
acoustique résonnante était étudié d'abord aux objets solides immergés
utilisant la méthode des impulsions de longue durée, ou MIIR (G. Maze et J.
Ripoche, 19831, et plus tard la méthode des impulsions de courte durée (s. K.
Numrich et al., 1984; M. de Billy, 1986). Les résonances des tubes immergés
étaient étudiées par M. Talmant et G. Quentin (1988) utilisant cette méthode.
La RST offre ggalement une interpre'tation physique des rgsonances base'e sur
l'accordement de phase des ondes de surface. Quelques avancements
expérimentaux sur ces sujets sont mentionnés de suite
THE EXCITATION OF WATER-BORNE WAVES AT THE INTERFACE OF EVACUATED ELASTIC SPHERICAL SHELLS AND PSEUDO-STONELEY RESONANCES
Plane monochromatic waves are known to excite resonances on submerged elastic spherical evacuated shells. The resonances
are related to symmetric and antisymmetric Lamb modes found in free vibrations and can be observed by examining the
backscattered echo's (form functions) which lead to characteristic "tell-talenr esonance signatures. Partial wave analysis of the
individual modes can reveal the nature of the resonances provided one is able to subtract the correct deal back ground of
the shell. We take advantage of the recent development of the correct acoustical background to analyze the partial wave
componenu of shell resonances. It is easy to distinguish between the Lamb modes which are also apparent in the the form
functions. However, an additional resonance is observed at high frequencies which correspond to waves which are broad in
partial wave space and which propagate in the fluid at the fluid-shell interface at about the speed of sound of the ambient fluid.
It may be assumed that they are related to StoneJey waves observed at the interface of a flat plate evacuated on one side and
with a fluid on the other and may therefore be referred to as pseudo-Stoneley resonances. The significance of these waves at
wincidarce frequency will be disasssed.Il est bien connu que les ondes planes peuvent exciter des résonances sur des coques Bastique spheriques évacués et
immergés. Les résonances sont liés aux modes symétriques et antisymétriques de Lamb des vibrations libtres, et elles peuvent
etre observées en examinant les rétrodiffusés (fonctions de forme). indiquet des signatures caractéristiques des résonances.
L'analyse des modes individuelles au moyen des ondes partielles peut révéler la nature des résonances, pourvu qu'on puisse
soustraire le fond accoustique correct de la coque. Nous utilisons le fond correct comme récent développement, afin d'analyser
les composants d'ondes partielles des résonances de la coque. I1 est facile de distinguer les modes de Lamb, qui apparaissant
aussi dans les fonctions de forme. De plus, nous observons aux fréquences élevées une résonance correspondante aux ondes qui
sont larges dans l'espace d'ondes partielles, et qui se propagent dans le fluide adjacent a l'interface fluide-coque, ayant à peu
près la vitesse du son dans le fluide. On peut assumer qu'elles sons liés aux ondes de Stoneley, observés à l'interface d'une
plaque plane évacué d'un coté et avec du fluide à l'autre, et qu'on puisse appeller donc les résonances pseudo-Stoneney. La
signification de ces ondes à la fnéquence de coincidence sera egalement considérée
Influence of bottom refractions on the propagation of underwater sound
Des expériences [ J. S. Hanna, J. Acoust. Soc. Am. 53, 1686 (1973); R. E. Christensen et al., J. Acoust. Soc. Am. 57, 1421 (1975)] faites sur la perte d'énergie du son sous-marin, se propageant sur un fond sédimentaire non-consolidé, ont demontré la présence d'énergie sonore refringée par le fond et retournée dans l'eau. Les champs sonores refringés se marquent ou par le tempsd'arrivée d'impulsions sonores (indiquant des parcours refringés à travers du fond), ou par leurs interférences avec des signaux stationnaires correspondant seulement à des réfléchissements par le fond. L'interprétation théorique de ces expériences était faite jusqu'ici en forme d'éstimations basées sur l'étendue des rayons. Dans une étude antérieure [A. Nagl et al., J. Acoust. Soc. Am. 63, 739 (1978)] nous avons developpé un formalisme de modes normaux de la propagation du son sous-marin contenant de couches d'eau avec des gradients linéaires de vitesse du son. Ce formalisme a été généralisé' ici en introduisant un fond contenant des couches sédimentaires non-consolidés avec des densités et gradients de vitesse du son différents, et nous obtenons de cette façon des champs sonores refringés par le fond et interférant avec des champs réfléchis. Les effets d'interférence peuvent être utilisés pour déterminer la vitesse du son et son gradient dans les couches du fond. [Recherche assistée par l'Office of Naval Research]
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