643 research outputs found
Quantum motion with trajectories: beyond the Gaussian beam approximation
A quantum model based on a Euler-Lagrange variational approach is proposed.
In analogy with the classical transport, our approach maintain the description
of the particle motion in terms of trajectories in a configuration space. Our
method is designed to describe correction to the motion of nearly localized
particles due to quantum phenomena. We focus on the simulation of the motion of
light nuclei in ab initio calculations. Similarly to the Gaussian beam method,
our approach is based on a ansatz for the particle wave function. We discuss
the completeness of our ansatz and the connection of our results with the Bohm
trajectories approach
Stochastic model for quantum spin dynamics in magnetic nanostructures
We develop a numerical model that reproduces the thermal equilibrium and the
spin transfer mechanisms in magnetic nanomaterials. We analyze the coherent
two-particle spin exchange interaction and the electron-electron collisions.
Our study is based on a quantum atomistic approach and the particle dynamics is
performed by using a Monte Carlo technique. The coherent quantum evolution of
the atoms is interrupted by instantaneous collisions with itinerant electrons.
The collision processes are associated to the quantum collapse of the local
atomic wave function. We show that particle-particle interactions beyond the
molecular field approximation can be included in this framework. Our model is
able to reproduce the thermal equilibrium and strongly out-of-equilibrium
phenomena such as the ultrafast dynamics of the magnetization in nanomatrials
Wigner model for quantum transport in graphene
The single graphene layer is a novel material consisting of a flat monolayer
of carbon atoms packed in a two-dimensional honeycomb-lattice, in which the
electron dynamics is governed by the Dirac equation. A pseudo-spin phase-space
approach based on the Wigner-Weyl formalism is used to describe the transport
of electrons in graphene including quantum effects. Our full-quantum mechanical
representation of the particles reveals itself to be particularly close to the
classical description of the particle motion. We analyze the Klein tunneling
and the correction to the total current in graphene induced by this phenomenon.
The equations of motion are analytically investigated and some numerical tests
are presented. The temporal evolution of the electron-hole pairs in the
presence of an external electric field and a rigid potential step is
investigated. The connection of our formalism with the Barry-phase approach is
also discussed
Bose-Einstein condensation of positronium: modification of the s-wave scattering length below the critical temperature
The production of a Bose-Einstein condensate made of positronium may be
feasible in the near future. Below the condensation temperature, the
positronium collision process is modified by the presence of the condensate.
This makes the theoretical description of the positronium kinetics at low
temperature challenging. Based on the quasi-particle Bogoliubov theory, we
describe the many-body particle-particle collision in a simple manner. We find
that, in a good approximation, the full positronium-positronium interaction can
be described by an effective scattering length. Our results are general and
apply to different species of bosons. The correction to the bare scattering
length is expressed in terms of a single dimensionless parameter that
completely characterizes the condensate
Ultrafast Magnetization Dynamics in Diluted Magnetic Semiconductors
We present a dynamical model that successfully explains the observed time
evolution of the magnetization in diluted magnetic semiconductor quantum wells
after weak laser excitation. Based on the pseudo-fermion formalism and a second
order many-particle expansion of the exact p-d exchange interaction, our
approach goes beyond the usual mean-field approximation. It includes both the
sub-picosecond demagnetization dynamics and the slower relaxation processes
which restore the initial ferromagnetic order in a nanosecond time scale. In
agreement with experimental results, our numerical simulations show that,
depending on the value of the initial lattice temperature, a subsequent
enhancement of the total magnetization may be observed within a time scale of
few hundreds of picoseconds.Comment: Submitted to PR
Mathematical analysis of a nonparabolic two-band Schrödinger-Poisson problem
Abstract A mathematical model for the quantum transport of a two-band semiconductors that includes the self-consistent electrostatic potential is analyzed. Corrections beyond the usual effective mass approximation are considered. Transparent boundary conditions are derived for the multi-band envelope Schrödinger model. The existence of solution of the nonlinear system is proved by using an asymptotic procedure. Some numerical examples are included. They illustrate the behavior of the scattering and the resonant states
Different Approaches for Multiband Transport in Semiconductors
We compare the well-known Kane model with a new multiband envelope function model, which presents many advantages with respect to the first one.Добре відому модель Кане порівняно з новою моделлю багатокомпонентної обвідної функції i продемонстровано багато переваг останньої
Acute hemolysis by hydroxycloroquine was observed in G6PD-deficient patient with severe COVD-19 related lung injury.
Our patient might be affected by Mediterannean variant of G6PD deficiency, which is more sensitive to pro-oxidant drugs compared to African G6PD A variant. No conclusive data are available on the possible pro-hemolytic impact of CQ/HCQ on patient with G6PD deficiency [3\u20135]. In COVID-19 emergency we believe it is important to warning the possible hemolytic effects of CQ/HCQ in patients with G6PD deficiency. Thus, the acute drop in Hb levels in the early days of CQ/HCQ treatment of COVID19 symptomatic patient should be considere
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