132,216 research outputs found
Monte-Carlo approach to calculate the proton stopping in warm dense matter within particle-in-cell simulations
A Monte-Carlo approach to proton stopping in warm dense matter is implemented
into an existing particle-in-cell code. The model is based on multiple
binary-collisions among electron-electron, electron-ion and ion-ion, taking
into account contributions from both free and bound electrons, and allows to
calculate particle stopping in much more natural manner. At low temperature
limit, when ``all'' electron are bounded at the nucleus, the stopping power
converges to the predictions of Bethe-Bloch theory, which shows good
consistency with data provided by the NIST. With the rising of temperatures,
more and more bound electron are ionized, thus giving rise to an increased
stopping power to cold matter, which is consistent with the report of a
recently experimental measurement [Phys. Rev. Lett. 114, 215002 (2015)]. When
temperature is further increased, with ionizations reaching the maximum,
lowered stopping power is observed, which is due to the suppression of
collision frequency between projected proton beam and hot plasmas in the
target.Comment: 6 pages, 4 figure
Light scattering by optically anisotropic scatterers II: T--matrix computations for radially and uniformly anisotropic droplets
This is the second paper in a series on light scattering from optically
anisotropic scatterers embedded in an isotropic medium. The apparently complex
T-matrix theory involving mixing of angular momentum components turns out to be
an efficient approach to calculating scattering in these systems. We present
preliminary results of numerical calculations of the scattering by spherical
droplets in some simple cases. The droplets contain optically anisotropic
material with local radial or uniform anisotropy. We concentrate on cases in
which the scattering is due only to the local optical anisotropy within the
scatterer. For radial anisotropy we find non-monotonic dependence of the
scattering cross-section on the degree of anisotropy can occur in a regime for
which both the Rayleigh and semi-classical theories are inapplicable. For
uniform anisotropy the cross-section is strongly dependent on the angle between
the incident light and the optical axis, and for larger droplets this
dependence is non-monotonic.Comment: 14 pages, 6 figures, uses RevTex
Monte-Carlo approach to calculate the ionization of warm dense matter within particle-in-cell simulations
A physical model based on a Monte-Carlo approach is proposed to calculate the
ionization dynam- ics of warm dense matters (WDM) within particle-in-cell
simulations, and where the impact (col- lision) ionization (CI), electron-ion
recombination (RE) and ionization potential depression (IPD) by surrounding
plasmas are taken into consideration self-consistently. When compared with
other models, which are applied in the literature for plasmas near thermal
equilibrium, the temporal re- laxation of ionization dynamics can also be
simulated by the proposed model. Besides, this model is general and can be
applied for both single elements and alloys with quite different composi-
tions. The proposed model is implemented into a particle-in-cell (PIC) code,
with (final) ionization equilibriums sustained by competitions between CI and
its inverse process (i.e., RE). Comparisons between the full model and model
without IPD or RE are performed. Our results indicate that for bulk aluminium
in the WDM regime, i) the averaged ionization degree increases by including
IPD; while ii) the averaged ionization degree is significantly over estimated
when the RE is neglected. A direct comparison from the PIC code is made with
the existing models for the dependence of averaged ionization degree on thermal
equilibrium temperatures, and shows good agreements with that generated from
Saha-Boltzmann model or/and FLYCHK code.Comment: 7 pages, 4 figure
J_AW,WA functions in Passarino-Veltman reduction
In this paper we continue to study a special class of Passarino-Veltman
functions J arising at the reduction of infrared divergent box diagrams. We
describe a procedure of separation of two types of singularities, infrared and
mass singularities, which are absorbed in simple C0 functions. The infrared
divergences of C0's can be regularized then by any method: photon mass,
dimensionally or by the width of an unstable particle. Functions J, in turn,
are represented as certain linear combinations of the standard D0 and C0
Passarino-Veltman functions. The former are free of both types of singularities
and are expressed as explicit and compact linear combinations of logarithms and
dilogarithm functions. We present extensive comparisons of numerical results
with those obtained with the aid of the LoopTools package
Double proximity effect in hybrid planar Superconductor-(Normal metal/Ferromagnet)-Superconductor structures
We have investigated the differential resistance of hybrid planar
Al-(Cu/Fe)-Al submicron bridges at low temperatures and in weak magnetic
fields. The structure consists of Cu/Fe-bilayer forming a bridge between two
superconducting Al-electrodes. In superconducting state of Al-electrodes, we
have observed a double-peak peculiarity in differential resistance of the
S-(N/F)-S structures at a bias voltage corresponding to the minigap. We claim
that this effect (the doubling of the minigap) is due to an electron spin
polarization in the normal metal which is induced by the ferromagnet. We have
demonstrated that the double-peak peculiarity is converted to a single peak at
a coercive applied field corresponding to zero magnetization of the Fe-layer
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