176 research outputs found
Frictional drag between quantum wells mediated by fluctuating electromagnetic field
We use the theory of the fluctuating electromagnetic field to calculate the
frictional drag between nearby two-and three dimensional electron systems. The
frictional drag results from coupling via a fluctuating electromagnetic field,
and can be considered as the dissipative part of the van der Waals interaction.
In comparison with other similar calculations for semiconductor two-dimensional
system we include retardation effects. We consider the dependence of the
frictional drag force on the temperature , electron density and separation
. We find, that retardation effects become dominating factor for high
electron densities, corresponding thing metallic film, and suggest a new
experiment to test the theory. The relation between friction and heat transfer
is also briefly commented on.Comment: 14 pages, 4 figure
Dissipative Van der Waals interaction between a small particle and a metal surface
We use a general theory of the fluctuating electromagnetic field to calculate
the friction force acting on a small neutral particle, e.g., a physisorbed
molecule, or a nanoscale object with arbitrary dispersive and absorptive
dielectric properties, moving near a metal surface. We consider the dependence
of the electromagnetic friction on the temperature , the separation , and
discuss the role of screening, non-local and retardation effects. We find that
for high resistivity materials, the dissipative van der Waals interaction can
be an important mechanism of vibrational energy relaxation of physisorbed
molecules, and friction for microscopic solids. Several controversial topics
related to electromagnetic dissipative shear stress is considered. The problem
of local heating of the surface by an STM tip is also briefly commented on.Comment: 11 pages, No figure
Thermal heat radiation, near-field energy density and near-field radiative heat transfer of coated materials
We investigate the thermal radiation and thermal near-field energy density of
a metal-coated semi-infinite body for different substrates. We show that the
surface polariton coupling within the metal coating leads to an enhancement of
the TM-mode part of the thermal near-field energy density when a polar
substrate is used. In this case the result obtained for a free standing metal
film is retrieved. In contrast, in the case of a metal substrate there is no
enhancement in the TM-mode part, as can also be explained within the framework
of surface plasmon coupling within the coating. Finally, we discuss the
influence of the enhanced thermal energy density on the near-field radiative
heat transfer between a simple semi-infinite and a coated semi-infinite body
for different material combinations
Computation of the asymptotic states of modulated open quantum systems with a numerically exact realization of the quantum trajectory method
Quantum systems out of equilibrium are presently a subject of active
research, both in theoretical and experimental domains. In this work we
consider time-periodically modulated quantum systems which are in contact with
a stationary environment. Within the framework of a quantum master equation,
the asymptotic states of such systems are described by time-periodic density
operators. Resolution of these operators constitutes a non-trivial
computational task. To go beyond the current size limits, we use the quantum
trajectory method which unravels master equation for the density operator into
a set of stochastic processes for wave functions. The asymptotic density matrix
is calculated by performing a statistical sampling over the ensemble of quantum
trajectories, preceded by a long transient propagation. We follow the ideology
of event-driven programming and construct a new algorithmic realization of the
method. The algorithm is computationally efficient, allowing for long 'leaps'
forward in time, and is numerically exact in the sense that, being given the
list of uniformly distributed (on the unit interval) random numbers, , one could propagate a quantum trajectory (with 's
as norm thresholds) in a numerically exact way. %Since the quantum trajectory
method falls into the class of standard sampling problems, performance of the
algorithm %can be substantially improved by implementing it on a computer
cluster. By using a scalable -particle quantum model, we demonstrate that
the algorithm allows us to resolve the asymptotic density operator of the model
system with states on a regular-size computer cluster, thus reaching
the scale on which numerical studies of modulated Hamiltonian systems are
currently performed
Radiative heat transfer between nanostructures
We simplify the formalism of Polder and Van Hove [Phys.Rev.B {\bf 4},
3303(1971)], which was developed to calculate the heat transfer between
macroscopic and nanoscale bodies of arbitrary shape, dispersive and adsorptive
dielectric properties. In the non-retarded limit, at small distances between
the bodies, the problem is reduced to the solution of an electrostatic problem.
We apply the formalism to the study of the heat transfer between: (a) two
parallel semi-infinite bodies, (b) a semi-infinite body and a spherical body,
and (c) that two spherical bodies. We consider the dependence of the heat
transfer on the temperature , the shape and the separation . We determine
when retardation effects become important.Comment: 11 pages, 5 figure
Strain state and microstructure evolution of AISI-316 austenitic stainless steel during high-pressure torsion (HPT) process in the new stamp design
The investigation of strain state and microstructure evolution of AISI-316 austenitic stainless steel during highpressure torsion process in the new stamp design was performed. The study using Deform-3D program was conducted. The deformation was carried out at ambient temperature. The results of strain state study showed that after 4 passes the processed workpiece is obtained the level of equivalent strain more than 5. But the distribution of strain has a gradient view in the cross section. The simulation results of the microstructure evolution showed that after 4 passes of deformation the initial grain size of 12 μm can be reduced up to 0,8 μm. But the distribution of grain size in the cross section also has a non - uniform gradient view
Quantum field theory of the van der Waals friction
The van der Waals friction between two semi-infinite solids, and between a
small neutral particle and semi-infinite solid is reconsidered on the basis of
thermal quantum field theory in the Matsubara formulation. The calculation of
the friction to linear order in the sliding velocity is reduced to the finding
of the equilibrium Green functions. Thus this approach cab be extended for
bodsies with complex geometry. The friction calculated in this approach agrees
with the friction calculated using a dynamical modification of the Lifshitz
theory, which is based on the fluctuation-dissipation therem. We show that the
van der Waals fricxtion can be measured in non-contact friction experiment
using state-of-the art equipment
Theory of the interaction forces and the heat transfer between moving bodies mediated by the fluctuating electromagnetic field
Within the framework of unified approach we study the Casimir-Lifshitz
interaction, the van der Waals friction force and the radiative heat transfer
at nonequilibrium conditions, when the interacting bodies are at different
temperatures, and they move relative to each other with the arbitrary velocity
. The analysis is focused on the surface-surface and surface-particle
configuration. Our approach is based on the exact solution of electromagnetic
problem about the determination of the fluctuating electromagnetic field in the
vacuum gap between two flat parallel surfaces moving relative to each other
with the arbitrary velocity . The velocity dependence of the considered
phenomena is determined by Doppler shift and can be strong for resonant photon
tunneling between surface modes.
We show that relativistic effects give rise to a mixing of the contributions
from the electromagnetic waves with different polarization to the heat transfer
and the interaction forces. We find that these effects are of the order
. The limiting case when one of the bodies is sufficiently rarefied
gives the heat transfer and the interaction forces between a moving small
particle and a surface.
We also calculate the friction force acting on a particle moving with an
arbitrary velocity relative to the black body radiation.Comment: 12 pages, 3 figure
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