280 research outputs found
Quantum heat transfer in harmonic chains with self consistent reservoirs: Exact numerical simulations
We describe a numerical scheme for exactly simulating the heat current
behavior in a quantum harmonic chain with self-consistent reservoirs.
Numerically-exact results are compared to classical simulations and to the
quantum behavior under the linear response approximation. In the classical
limit or for small temperature biases our results coincide with previous
calculations. At large bias and for low temperatures the quantum dynamics of
the system fundamentally differs from the close-to-equilibrium behavior,
revealing in particular the effect of thermal rectification for asymmetric
chains. Since this effect is absent in the classical analog of our model, we
conclude that in the quantum model studied here thermal rectification is a
purely quantum phenomenon, rooted in the quantum statistics
Diffusion Enhancement in a Periodic Potential under High-Frequency Space-Dependent Forcing
We study the long-time behavior of underdamped Brownian particle moving
through a viscous medium and in a systematic potential, when it is subjected to
a space-dependent high-frequency periodic force. When the frequency is very
large, much larger than all other relevant system-frequencies, there is a
Kapitsa time-window wherein the effect of frequency dependent forcing can be
replaced by a static effective potential. Our new analysis includes the case
when the forcing, in addition to being frequency-dependent, is space-dependent
as well. The results of the Kapitsa analysis then lead to additional
contributions to the effective potential. These are applied to the numerical
calculation of the diffusion coefficient (D) for a Brownian particle moving in
a periodic potential. Presented are numerical results, which are in excellent
agreement with theoretical predictions and which indicate a significant
enhancement of D due to the space-dependent forcing terms. In addition we study
the transport property (current) of underdamped Brownian particles in a ratchet
potential.Comment: RevTex 6 pages, 5 figure
Dissipative Tunneling in 2 DEG: Effect of Magnetic Field, Impurity and Temperature
We have studied the transport process in the two dimensional electron gas
(2DEG) in presence of a magnetic field and a dissipative environment at
temperature T. By means of imaginary time series functional integral method we
calculate the decay rates at finite temperature and in the presence of
dissipation. We have studied decay rates for wide range of temperatures -- from
the thermally activated region to very low temperature region where the system
decays by quantum tunneling. We have shown that dissipation and impurity helps
the tunneling. We have also shown that tunneling is strongly affected by the
magnetic field. We have demonstrated analytical results for all the cases
mentioned above.Comment: 8 pages, 2 figure
Dissipative Diamagnetism -- A Case Study for Equilibrium and Nonequilibrium Statistical Mechanics of Mesoscopic Systems
Using the path integral approach to equilibrium statistical physics the
effect of dissipation on Landau diamagnetism is calculated. The calculation
clarifies the essential role of the boundary of the container in which the
electrons move. Further, the derived result for diamagnetization also matches
with the expression obtained from a time-dependent quantum Langevin equation in
the asymptotic limit, provided a certain order is maintained in taking limits.
This identification then unifies equilibrium and nonequilibrium statistical
physics for a phenomenon like diamagnetism, which is inherently quantum and
strongly dependent on boundary effects.Comment: 4 pages, no figure
Reduction of Dendrite Formations to Improve the Appearance of the Powder Cured Films for Automotive Industry
The appearance of powder-coated films is dependent upon powder chemistry and spraying parameters. One of the most important physical factors controlling the powder film appearance is the microdeposition of the powder particles on the grounded substrate. During the electrostatic deposition of powder, the formation of dendrites and agglomerates was observed; these formations have an adverse effect on the final film appearance and their elimination may result in smoother and glossier films. Dendrites are generated due to bipolar charging and inter-particulate electrostatic attractive forces. The corona charging technique is mostly used in industrial powder coating applications. At low corona voltages (- 40 to - 60 kV) a greater degree of bipolar charging was observed compared to that at higher voltages (- 80 to - 100 kV). At the higher voltages, the increase n number of ions produces a more unipolar charging and higher charge-to-mass ratios. As the film builds up, the powder transfer efficiency decreases as the repulsion forces between oncoming charged particles and the already deposited powder layer increase. By controlling the deposition patterns, the final film appearance can be improved. The smoothest films were obtained when the voltage was ramped from - 60 to - 100 kV. Another method to reduce dendrite formations was to deposit powder particles charged unipolarly by first separating them from the oppositely charged ones by using a charge separator
Troubleshooting During Temporary Epicardial Lead Implantation in a Child with an Erosive Twiddler’s Syndrome and Multiple Sternotomies: A case report
Temporary epicardial cardiac pacing in patients with bradyarrhythmias may be used as a bridge to implantation of a permanent pacemaker. The temporary epicardial lead placement may sometimes necessitate a sternotomy that may pose a challenge in patients who have had multiple earlier sternotomies. The difficulty in accessing the epicardium for urgent implantation of temporary epicardial pacing leads depends on the extent of adhesions in such patients. We report an 8-year-8-month-old girl with a pacemaker with an extruded pulse generator and difficult myocardial access due to 5 prior transsternal procedures. The child presented to a tertiary care hospital in Muscat, Oman, in 2021. A trouble-shooting technique was adopted to achieve temporary epicardial pacing to provide time for a course of antibiotic therapy administration. A permanent transvenous pulse generator system was implanted after 7 days of temporary pacing.
Keywords: Heart Block; Artificial Pacemaker; Implanted Electrodes; Case Report; Oman
Landau-Drude Diamagnetism: Fluctuation, Dissipation and Decoherence
Starting from a quantum Langevin equation (QLE) of a charged particle coupled
to a heat bath in the presence of an external magnetic field, we present a
fully dynamical calculation of the susceptibility tensor. We further evaluate
the position autocorrelation function by using the Gibbs ensemble approach.
This quantity is shown to be related to the imaginary part of the dynamical
susceptibility, thereby validating the fluctuation-dissipation theorem in the
context of dissipative diamagnetism. Finally we present an overview of
coherence-to-decoherence transition in the realm of dissipative diamagnetism at
zero temperature. The analysis underscores the importance of the details of the
relevant physical quantity, as far as coherence to decoherence transition is
concerned.Comment: 8 pages and 5 figure
Quantum thermodynamics of a charged magneto-oscillator coupled to a heat bath
Explicit results for various quantum thermodynamic function (QTF) of a
charged magneto-oscillator coupled to a heat bath at arbitrary temperature are
demonstrated in this paper. Discernible expressions for different QTF in the
two limits of very low and very high temperatures are presented for three
popular heat bath models : Ohmic, single relaxation time and blackbody
radiation. The central result is that the effect of magnetic field turns out to
be important at low temperatures yet crucial at high temperatures. It is
observed that the dissipation parameter, , and the cyclotron frequency,
, affect the decaying or rising behaviour of various QTF in just the
opposite way to each other at low temperatures. In the high temperature regime,
the effect of is much pronounced than that of .Comment: 26 Pages, 18 Figure
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