1,222 research outputs found
Analysis of a diffusive effective mass model for nanowires
We propose in this paper to derive and analyze a self-consistent model
describing the diffusive transport in a nanowire. From a physical point of
view, it describes the electron transport in an ultra-scaled confined
structure, taking in account the interactions of charged particles with
phonons. The transport direction is assumed to be large compared to the wire
section and is described by a drift-diffusion equation including effective
quantities computed from a Bloch problem in the crystal lattice. The
electrostatic potential solves a Poisson equation where the particle density
couples on each energy band a two dimensional confinement density with the
monodimensional transport density given by the Boltzmann statistics. On the one
hand, we study the derivation of this Nanowire Drift-Diffusion Poisson model
from a kinetic level description. On the other hand, we present an existence
result for this model in a bounded domain
Modulation of near-field heat transfer between two gratings
We present a theoretical study of near-field heat transfer between two
uniaxial anisotropic planar structures. We investigate how the distance and
relative orientation (with respect to their optical axes) between the objects
affect the heat flux. In particular, we show that by changing the angle between
the optical axes it is possible in certain cases to modulate the net heat flux
up to 90% at room temperature, and discuss possible applications of such a
strong effect
Fundamental limits for non-contact transfers between two bodies
We investigate energy and momentum non-contact exchanges between two
arbitrary flat media separated by a gap. This problem is revisited as a
transmission problem of individual system eigenmodes weighted by a transmission
probability obtained either from fluctuational electrodynamics or quantum field
theory. An upper limit for energy and momentum flux is derived using a general
variational approach. The corresponding optimal reflectivity coefficients are
given both for identical and different media in interaction.Comment: accepted in Phys. Rev. B rapid communicatio
Mechanical relations between conductive and radiative heat transfer
We present a general nonequilibrium Green's function formalism for modeling
heat transfer in systems characterized by linear response that establishes the
formal algebraic relationships between phonon and radiative conduction, and
reveals how upper bounds for the former can also be applied to the latter. We
also propose an extension of this formalism to treat systems susceptible to the
interplay of conductive and radiative heat transfer, which becomes relevant in
atomic systems and at nanometric and smaller separations where theoretical
descriptions which treat each phenomenon separately may be insufficient. We
illustrate the need for such coupled descriptions by providing predictions for
a low-dimensional system of carbyne wires in which the total heat transfer can
differ from the sum of its radiative and conductive contributions. Our
framework has ramifications for understanding heat transfer between large
bodies that may approach direct contact with each other or that may be coupled
by atomic, molecular, or interfacial film junctions.Comment: 16 pages, 2 figures, 1 table, 2 appendice
Anomalous photon thermal Hall effect
We predict an anomalous thermal Hall effect (ATHE) mediated by photons in
networks of Weyl semi-metals. Contrary to the photon thermal Hall effect in
magneto-optical systems which requires the application of an external magnetic
field the ATHE in a Weyl semi-metals network is an intrinsic property of these
systems. Since the Weyl semi-metals can exhibit a strong nonreciprocal response
in the infrared over a broad spectral range the magnitude of thermal Hall flux
in these systems can be relatively large compared to the primary flux. This
ATHE paves the way for a directional control of heat flux by localy tuning the
magnitude of temperature field without changing the direction of temperature
gradient
An effective mass theorem for the bidimensional electron gas in a strong magnetic field
We study the limiting behavior of a singularly perturbed
Schr\"odinger-Poisson system describing a 3-dimensional electron gas strongly
confined in the vicinity of a plane and subject to a strong uniform
magnetic field in the plane of the gas. The coupled effects of the confinement
and of the magnetic field induce fast oscillations in time that need to be
averaged out. We obtain at the limit a system of 2-dimensional Schr\"odinger
equations in the plane , coupled through an effective selfconsistent
electrical potential. In the direction perpendicular to the magnetic field, the
electron mass is modified by the field, as the result of an averaging of the
cyclotron motion. The main tools of the analysis are the adaptation of the
second order long-time averaging theory of ODEs to our PDEs context, and the
use of a Sobolev scale adapted to the confinement operator
Obstructive sleep apnea as an independent predictor of postoperative delirium and pain: Protocol for an observational study of a surgical cohort [version 2; referees: 2 approved]
Introduction: Postoperative delirium and pain are common complications in adults, and are difficult both to prevent and treat. Obstructive sleep apnea (OSA) is prevalent in surgical patients, and has been suggested to be a risk factor for postoperative delirium and pain. OSA also might impact pain perception, and alter pain medication requirements. This protocol describes an observational study, with the primary aim of testing whether OSA is an independent predictor of postoperative complications, focusing on (i) postoperative incident delirium and (ii) acute postoperative pain severity. We secondarily hypothesize that compliance with prescribed treatment for OSA (typically continuous positive airway pressure or CPAP) might decrease the risk of delirium and the severity of pain. Methods and analysis: We will include data from patients who have been enrolled into three prospective studies: ENGAGES, PODCAST, and SATISFY-SOS. All participants underwent general anesthesia for a non-neurosurgical inpatient operation, and had a postoperative hospital stay of at least one day at Barnes Jewish Hospital in St. Louis, Missouri, from February 2013 to May 2018. Â Patients included in this study have been assessed for postoperative delirium and pain severity as part of the parent studies. In the current study, determination of delirium diagnosis will be based on the Confusion Assessment Method, and the Visual Analogue Pain Scale will be used for pain severity. Data on OSA diagnosis, OSA risk and compliance with treatment will be obtained from the preoperative assessment record. Other variables that are candidate risk factors for delirium and pain will also be extracted from this record. We will use logistic regression to test whether OSA independently predicts postoperative delirium and linear regression to assess OSAs relationship to acute pain severity. We will conduct secondary analyses with subgroups to explore whether these relationships are modified by compliance with OSA treatment.</ns4:p
- âŠ