1,312 research outputs found
An ab-initio study of the electron-phonon coupling within a Cr(001)-surface
It is experimentally well established that the Cr(001)-surface exhibits a
sharp resonance around the Fermi level. However, there is no consensus about
its physical origin. It is proposed to be either due to a single particle dz2
surface state renormalised by electron-phonon coupling or the orbital Kondo
effect involving the degenerate dxz/dyz states. In this work we examine the
electron-phonon coupling of the Cr(001)-surface by means of ab-initio
calculations in the form of density functional perturbation theory. More
precisely, the electron-phonon mass-enhancement factor of the surface layer is
investigated for the 3d states. For the majority and minority spin dz2 surface
states we find values of 0.19 and 0.16. We show that these calculated
electron-phonon mass-enhancement factors are not in agreement with the
experimental data even if we use realistic values for the temperature range and
surface Debye frequency for the fit of the experimental data. More precisely,
then experimentally an electron-phonon mass-enhancement factor of 0.70~0.10 is
obtained, which is not in agreement with our calculated values of 0.19 and
0.16. Therefore, we conclude that the experimentally observed resonance at the
Cr(001)-surface is not due to polaronic effects, but due to electron-electron
correlation effects
Nonlinear acoustic waves in channels with variable cross sections
The point symmetry group is studied for the generalized Webster-type equation
describing non-linear acoustic waves in lossy channels with variable cross
sections. It is shown that, for certain types of cross section profiles, the
admitted symmetry group is extended and the invariant solutions corresponding
to these profiles are obtained. Approximate analytic solutions to the
generalized Webster equation are derived for channels with smoothly varying
cross sections and arbitrary initial conditions.Comment: Revtex4, 10 pages, 2 figure. This is an enlarged contribution to
Acoustical Physics, 2012, v.58, No.3, p.269-276 with modest stylistic
corrections introduced mainly in the Introduction and References. Several
typos were also correcte
Development of the A/H6N1 influenza vaccine candidate based on A/Leningrad/134/17/57 (H2N2) master donor virus and the genome composition analysis using high resolution melting (HRM)
The avian influenza viruses of H6N1subtype present a potential danger for humans. The cold-adapted (ca) reassortant influenza virus А/17/herring gull/Sarma/2006/887 (H6N1) was obtained in chicken embryos by the genetic reassortment based on the coldadapted A/Leningrad/134/17/57 (H2N2) master strain. The genome composition of the obtained reassortant was analyzed by means of real-time PCR with the high resolution melting (HRM) analysis using the intercalating fluorescent dye EvaGreen. Analysis of the gene segments showed that the reassortant А/17/herring gull/Sarma/2006/887 (H6N1) contains the internal proteins coding genes (PB2, PB1, PA, NP, M, and NS) of the master donor virus and the surface antigens coding genes of the A/herring gull/Sarma/51c/2006 (H6N1) avian influenza virus. The study of the phenotypic properties showed that the virus А/17/herring gull/Sarma/2006/887 (H6N1) is temperature sensitive (ts), ca in chicken embryos, and attenuated in mice when administered intranasally. This reassortant can be recommended as a live influenza vaccine candidate for humans.The avian influenza viruses of H6N1subtype present a potential danger for humans. The cold-adapted (ca) reassortant influenza virus А/17/herring gull/Sarma/2006/887 (H6N1) was obtained in chicken embryos by the genetic reassortment based on the coldadapted A/Leningrad/134/17/57 (H2N2) master strain. The genome composition of the obtained reassortant was analyzed by means of real-time PCR with the high resolution melting (HRM) analysis using the intercalating fluorescent dye EvaGreen. Analysis of the gene segments showed that the reassortant А/17/herring gull/Sarma/2006/887 (H6N1) contains the internal proteins coding genes (PB2, PB1, PA, NP, M, and NS) of the master donor virus and the surface antigens coding genes of the A/herring gull/Sarma/51c/2006 (H6N1) avian influenza virus. The study of the phenotypic properties showed that the virus А/17/herring gull/Sarma/2006/887 (H6N1) is temperature sensitive (ts), ca in chicken embryos, and attenuated in mice when administered intranasally. This reassortant can be recommended as a live influenza vaccine candidate for humans
Strong-field approximation for Coulomb explosion of H_2^+ by short intense laser pulses
We present a simple quantum mechanical model to describe Coulomb explosion of
H by short, intense, infrared laser pulses. The model is based on the
length gauge version of the molecular strong-field approximation and is valid
for pulses shorter than 50 fs where the process of dissociation prior to
ionization is negligible. The results are compared with recent experimental
results for the proton energy spectrum [I. Ben-Itzhak et al., Phys. Rev. Lett.
95, 073002 (2005), B. D. Esry et al., Phys. Rev. Lett. 97, 013003 (2006)]. The
predictions of the model reproduce the profile of the spectrum although the
peak energy is slightly lower than the observations. For comparison, we also
present results obtained by two different tunneling models for this process.Comment: 8 pages, 4 figure
Atmospheric Gravity Perturbations Measured by Ground-Based Interferometer with Suspended Mirrors
A possibility of geophysical measurements using the large scale laser
interferometrical gravitational wave antenna is discussed. An interferometer
with suspended mirrors can be used as a gradiometer measuring variations of an
angle between gravity force vectors acting on the spatially separated
suspensions. We analyze restrictions imposed by the atmospheric noises on
feasibility of such measurements. Two models of the atmosphere are invoked: a
quiet atmosphere with a hydrostatic coupling of pressure and density and a
dynamic model of moving region of the density anomaly (cyclone). Both models
lead to similar conclusions up to numerical factors. Besides the hydrostatic
approximation, we use a model of turbulent atmosphere with the pressure
fluctuation spectrum f^{-7/3} to explore the Newtonian noise in a higher
frequency domain (up to 10 Hz) predicting the gravitational noise background
for modern gravitational wave detectors. Our estimates show that this could
pose a serious problem for realization of such projects. Finally, angular
fluctuations of spatially separated pendula are investigated via computer
simulation for some realistic atmospheric data giving the level estimate
10^{-11} rad/sqrt(Hz) at frequency 10^{-4} Hz. This looks promising for the
possibility of the measurement of weak gravity effects such as Earth inner core
oscillations.Comment: 13 pages, 4 pigures, LaTeX. To be published in Classical and Quantum
Gravit
Geophysical studies with laser-beam detectors of gravitational waves
The existing high technology laser-beam detectors of gravitational waves may
find very useful applications in an unexpected area - geophysics. To make
possible the detection of weak gravitational waves in the region of high
frequencies of astrophysical interest, ~ 30 - 10^3 Hz, control systems of laser
interferometers must permanently monitor, record and compensate much larger
external interventions that take place in the region of low frequencies of
geophysical interest, ~ 10^{-5} - 3 X 10^{-3} Hz. Such phenomena as tidal
perturbations of land and gravity, normal mode oscillations of Earth,
oscillations of the inner core of Earth, etc. will inevitably affect the
performance of the interferometers and, therefore, the information about them
will be stored in the data of control systems. We specifically identify the
low-frequency information contained in distances between the interferometer
mirrors (deformation of Earth) and angles between the mirrors' suspensions
(deviations of local gravity vectors and plumb lines). We show that the access
to the angular information may require some modest amendments to the optical
scheme of the interferometers, and we suggest the ways of doing that. The
detailed evaluation of environmental and instrumental noises indicates that
they will not prevent, even if only marginally, the detection of interesting
geophysical phenomena. Gravitational-wave instruments seem to be capable of
reaching, as a by-product of their continuous operation, very ambitious
geophysical goals, such as observation of the Earth's inner core oscillations.Comment: 29 pages including 8 figures, modifications and clarifications in
response to referees' comments, to be published in Class. Quant. Gra
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