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

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

Very high frequency gravitational wave background in the universe

Astrophysical sources of high frequency gravitational radiation are considered in association with a new interest to very sensitive HFGW receivers required for the laboratory GW Hertz experiment. A special attention is paid to the phenomenon of primordial black holes evaporation. They act like black body to all kinds of radiation, including gravitons, and, therefore, emit an equilibrium spectrum of gravitons during its evaporation. Limit on the density of high frequency gravitons in the Universe is obtained, and possibilities of their detection are briefly discussed.Comment: 14 page

Wavelength and intensity dependence of multiple forward scattering at above-threshold ionization in mid-infrared strong laser fields

The nonperturbative role of multiple forward scattering for Coulomb focusing in mid-infrared laser fields and its dependence on a laser intensity and wavelength are investigated for low-energy photoelectrons at above-threshold ionization. We show that high-order rescattering events can have comparable contributions to the Coulomb focusing and the effective number of rescattering depends weakly on laser parameters in the classical regime. However, the relative contribution of the forward scattering to the Coulomb focusing and the Coulomb focusing in total decrease with the rise of the laser intensity and wavelength

Морфологическая реакция эритроцитов на изменение электролитного состава среды. III. Влияние моновалентных анионов

The effect of monovalent anions Cl¯, F¯, Br¯, I¯, NO3¯ and NO2¯ on dynamic of erythrocyte shape changes in sucrose media (morphological response, MR) was studied. It was established that triphasic MR had different time courses in media with and without anions. Increasing anion concentration from zero up to 20 mM results in inhibition in phase 3 first, followed by inhibition in phases 2 and 1 in such a manner that MR becomes fully eliminated in media containing anions at concentration more than 10 mM. This behavior was characteristic for all anions except iodide which was less effective compared to other anions. In experiments where the same amount of anions was added at different phases of MR, the phase and anion type effects were observed, although the difference between anions was not pronounced. Addition of anions at the end of phase 3 where the cells were stomatocytes initiated slow retransformation toward discs, the iodide again being less effective. The data obtained are not consistent with the proposals as for the role of band 3 (AE1) conformation in MR, rather they suggest a possible involvement of conformation state of other ion transport systems which become active under present conditions.Исследовано влияние моновалентных анионов Cl¯, F¯, Br¯, I¯, NO3¯ и NO2¯ на последовательность изменения формы эритроцитов (морфологического ответа, МО) в изотонической сахарозной среде. Установлено, что МО, который состоит из трех фаз, протекает по-разному в средах, содержащих и не содержащих указанные анионы. Увеличение концентрации анионов от нуля до 20 мМ приводит сначала к ингибированию фазы 3 МО, а затем, последовательно, к ингибированию фаз 2 и 1, таким образом, что в итоге в средах с высокой концентрацией анионов (10 мМ и выше) МО полностью подавляется. Такое поведение характерно для всех анионов, кроме анионов I¯, которые ингибировали фазу 1 в меньшей степени по сравнению с другими. Эксперименты, в которых то же количество анионов добавляли к клеткам на разных стадиях МО, показали, что их эффект зависит от фазы МО, в которых находятся клетки в момент добавления аниона и его типа, хотя больших различий между анионами установлено не было. При добавлении анионов в конце фазы 3, на которой формируются стоматоциты, происходило медленное восстановление дискоидной формы клеток, при этом анионы йода также обладали наименьшей эффективностью. Полученные данные плохо согласуются с предположением, что наблюдаемые изменения формы эритроцитов обусловлены изменением конформации анионного обменника АЕ1, что может указывать на то, что МО является суперпозицией конформационных превращений в нескольких транспортных системах, одновременно активирующихся в данных условиях

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$_2^+$ 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