711 research outputs found
Pionic Degrees of Freedom in Atomic Nuclei and Quasielastic Knockout of Pions by High-Energy Electrons
The nonlinear model of pionic condensate in nuclei by G. Preparata can be
efficiently verified by investigation of the quasielastic knockout process of
pions out of nuclei by high energy electrons. First, a momentum distribution
(MD) of the collective pions has a bright maximum at q=0.3 Gev.Second the
excitation spectrum of a recoil nucleus is concentrated at low energies E
lesser than 1MeV. The results for the pion knockout from mesonic clouds of
individual nucleons are absolutely different. The latter results are presented
both for pion and rho-meson clouds localized on nucleons.Comment: 13 pages, 3 figure
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
Unified ab initio treatment of attosecond photoionization and Compton scattering
We present a new theoretical approach to attosecond laser-assisted photo- and
Compton ionization. Attosecond x-ray absorption and scattering are described by
\hat{\mathrsfs{S}}^{(1,2)}-matrices, which are coherent superpositions of
"monochromatic" -matrices in a laser-modified Furry
representation. Besides refining the existing theory of the soft x-ray
photoelectron attosecond streak camera and spectral phase interferometry (ASC
and ASPI), we formulate a theory of hard x-ray photoelectron and Compton ASC
and ASPI. The resulting scheme has a simple structure and leads to closed-form
expressions for ionization amplitudes. We investigate Compton electron
interference in the separable Coulomb-Volkov continuum with both Coulomb and
laser fields treated non-perturbatively. We find that at laser-field
intensities below 10 Wcm normalized Compton lines almost coincide
with the lines obtained in the laser-free regime. At higher intensities,
attosecond interferences survive integration over electron momenta, and feature
prominently in the Compton lines themselves. We define a regime where the
electron ground-state density can be measured with controllable accuracy in an
attosecond time interval. The new theory provides a firm basis for extracting
photo- and Compton electron phases and atomic and molecular wavefunctions from
experimental data.Comment: 15 pages, 5 figure
Optical Lattice Polarization Effects on Hyperpolarizability of Atomic Clock Transitions
The light-induced frequency shift due to the hyperpolarizability (i.e. terms
of second-order in intensity) is studied for a forbidden optical transition,
=0=0. A simple universal dependence on the field ellipticity is
obtained. This result allows minimization of the second-order light shift with
respect to the field polarization for optical lattices operating at a magic
wavelength (at which the first-order shift vanishes). We show the possibility
for the existence of a magic elliptical polarization, for which the
second-order frequency shift vanishes. The optimal polarization of the lattice
field can be either linear, circular or magic elliptical. The obtained results
could improve the accuracy of lattice-based atomic clocks.Comment: 4 pages, RevTeX4, 2 eps fig
Bichiral structure of feroelectric domain wall driven by flexoelectricity
The influence of flexoelectric coupling on the internal structure of neutral
domain walls in tetragonal phase of perovskite ferroelectrics is studied. The
effect is shown to lower the symmetry of 180-degree walls which are oblique
with respect to the cubic crystallographic axes, while {100} and {110} walls
stay "untouched". Being of the Ising type in the absence of the flexoelectric
interaction, the oblique domain walls acquire a new polarization component with
a structure qualitatively different from the classical Bloch-wall structure. In
contrast to the Bloch-type walls, where the polarization vector draws a helix
on passing from one domain to the other, in the flexoeffect-affected wall, the
polarization rotates in opposite directions on the two sides of the wall and
passes through zero in its center. Since the resulting polarization profile is
invariant upon inversion with respect to the wall center it does not brake the
wall symmetry in contrast to the classical Bloch-type walls. The flexoelectric
coupling lower the domain wall energy and gives rise to its additional
anisotropy that is comparable to that conditioned by the elastic anisotropy.
The atomic orderof- magnitude estimates shows that the new polarization
component P2 may be comparable with spontaneous polarization Ps, thus
suggesting that, in general, the flexoelectric coupling should be mandatory
included in domain wall simulations in ferroelectrics. Calculations performed
for barium titanate yields the maximal value of the P2, which is much smaller
than that of the spontaneous polarization. This smallness is attributed to an
anomalously small value of a component of the "strain-polarization"
elecrostictive tensor in this material
CLINICAL VALUE OF MULTISLICE SPIRAL X-RAY COMPUTED TOMOGRAPHY WHEN PLANNING THE TREATMENT OF PATIENTS WITH LARYNGEAL CANCER
Cancers remain a priority for modern society. According to the WHO estimates, global cancer morbidity and mortality rates will triple in the period 1999 to 2030: from 10 to 30 million new cases and from 6 to 17 million deaths recorded every year, which will exceed deaths from cardiovascular diseases and injuries. The efficiency of treatment in cancer patients and their prediction are determined by timely disease diagnosis, tumor extent estimation, and adequate therapeutic measures. So search for ways to cardinally improve the early recognition of cancer is one of the major tasks in the study of the problems of cancer patients, those with throat cancer in particular
Microscopics of meson degrees of freedom in nucleons and mesons in nuclei - what can be seen in the process of quasielastic knockout of mesons by high-energy electrons
Developed earlier concept of quasielastic knock out of pions from nucleons by
high-energy electrons is propounded as a tool for checking microscopical model
( - fluctuation) for decay of N to different channels and
Preparata model of nucleus structure.Comment: 6 pages, 5 figures, Talk given at 16 Baldin Symposium in June 200
Gravitational lensing due to dark matter modelled by vector field
The specified constant 4-vector field reproducing the spherically symmetric
stationary metric of cold dark matter halo in the region of flat rotation
curves results in a constant angle of light deflection at small impact
distances. The effective deflecting mass is factor greater than the
dark matter mass. The perturbation of deflection picture due to the halo edge
is evaluated.Comment: 17 pages, LaTeX iopart class, 10 eps figures; explanaitions and
discussion are extended and improved, reference added; version to appear in
Classical and Quantum Gravit
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