16,291 research outputs found
Thermoelectric effect in a parallel double quantum dot structure
We discuss the thermoelectric properties assisted by the Fano effect of a
parallel double quantum dot (QD) structure. By adjusting the couplings between
the QDs and leads, we facilitate the nonresonant and resonant channels for the
Fano interference. It is found that at low temperature, Fano lineshapes appear
in the electronic and thermal conductance spectra, which can also be reversed
by an applied local magnetic flux with its phase factor . And, the
Fano effect contributes decisively to the enhancement of thermoelectric
efficiency. However, at the same temperature, the thermoelectric effect in the
case of is much more apparent, compared with the case of zero
magnetic flux. By the concept of Feynman path, we analyze the difference
between the quantum interferences in the cases of and . It
is seen that in the absence of magnetic flux the Fano interference originates
from the quantum interference among infinite-order Feynman paths, but it occurs
only between two lowest-order Feynman paths when . The increase of
temperature inevitably destroys the electron coherent transmission in each
paths. So, in the case of zero magnetic field, the thermoelectric effect
contributed by the Fano interference is easy to weaken by a little increase of
temperature.Comment: 8 pages, 4 figure
Kernel Based High Order "Explicit" Unconditionally-Stable Scheme for Nonlinear Degenerate Advection-Diffusion Equations
In this paper, we present a novel numerical scheme for solving a class of
nonlinear degenerate parabolic equations with non-smooth solutions. The
proposed method relies on a special kernel based formulation of the solutions
found in our early work on the method of lines transpose and successive
convolution. In such a framework, a high order weighted essentially
non-oscillatory (WENO) methodology and a nonlinear filter are further employed
to avoid spurious oscillations. High order accuracy in time is realized by
using the high order explicit strong-stability-preserving (SSP) Runge-Kutta
method. Moreover, theoretical investigations of the kernel based formulation
combined with an explicit SSP method indicates that the combined scheme is
unconditionally stable and up to third order accuracy. Evaluation of the kernel
based approach is done with a fast summation algorithm. The
new method allows for much larger time step evolution compared with other
explicit schemes with the same order accuracy, leading to remarkable
computational savings
A Kernel Based High Order "Explicit" Unconditionally Stable Scheme for Time Dependent Hamilton-Jacobi Equations
In this paper, a class of high order numerical schemes is proposed for
solving Hamilton-Jacobi (H-J) equations. This work is regarded as an extension
of our previous work for nonlinear degenerate parabolic equations, see
Christlieb et al. \emph{arXiv preprint arXiv:1707.09294},, which relies on a
special kernel-based formulation of the solutions and successive convolution.
When applied to the H-J equations, the newly proposed scheme attains genuinely
high order accuracy in both space and time, and more importantly, it is
unconditionally stable, hence allowing for much larger time step evolution
compared with other explicit schemes and saving computational cost. A high
order weighted essentially non-oscillatory methodology and a novel nonlinear
filter are further incorporated to capture the correct viscosity solution.
Furthermore, by coupling the recently proposed inverse Lax-Wendroff boundary
treatment technique, this method is very flexible in handing complex geometry
as well as general boundary conditions. We perform numerical experiments on a
collection of numerical examples, including H-J equations with linear,
nonlinear, convex or non-convex Hamiltonians. The efficacy and efficiency of
the proposed scheme in approximating the viscosity solution of general H-J
equations is verified
Electronic transport through a double-quantum-dot Aharonov-Bohm interference device with impurities
The impurity-related electron transport through a double quantum dot (QD)
Aharonov-Bohm (AB) interferometer is theoretically studied, by considering
impurities coupled to the QDs in the interferometer arms. When investigating
the linear conductance spectra \emph{vs} the impurity levels, we show that the
impurities influence the electron transport in a nontrivial way, since their
suppressing or enhancing the electron tunneling. A presented single-level
impurity leads to the appearance of Fano lineshapes in the conductance spectra
in the absence of magnetic flux, with the positions of Fano antiresonances
determined by both the impurity-QD couplings and the QD levels separated from
the Fermi level, whereas when a magnetic flux is introduced with the the phase
factor the impurity-driven Breit-Wigner lineshapes appear in the
conductance curves. Besides, the nonlocal impurities alter the period of
conductance change \emph{vs} the magnetic flux. The multi-level impurities
indeed complicate the electron transport, but for the cases of two identical
local impurities coupled to the respective QDs with uniform couplings or a
nonlocal impurity coupled to both QDs uniformly, the antiresonances are only
relevant to the impurity levels. When many-body effect is managed within the
second-order approximation, we also find the important role of the Coulomb
interaction in modifying the electron transport.Comment: 17 pages, 13 figure
Local Distinguishability and Schmidt Number of Orthogonal States
Now, the known ensembles of orthogonal states which are distinguishable by
local operators and classical communication (LOCC) satisfy the condition that
the sum of Schmidit numbers of the orthogonal states is not bigger than the
dimensions of the whole space. A natural question is whether an arbitary
ensembles of LOCC-distinguishable orthogonal states satisfies the condition. We
first show that, in this paper, the answer is positive. Then we generalize it
into multipartite systems, and show that a necessary condition for
LOCC-distinguishability of multipartite orthogonal quantum states is that the
sum of the least numbers of the product states (For bipartite system, the least
number of product states is Schmidit number) of the orthogonal states is not
bigger than the dimensions of the Hilbert space of the multipartite system.
This necessary condition is very simple and general, and one can get many cases
of indistinguishability by it. It means that the least number of the product
states acts an important role in distinguishablity of states, and implies that
the least number of the product states may be an good manifestion of quantum
nonlocality in some sense. In fact, entanglement emphases the "amount" of
nonlocality, but the least number of the product states emphases the types of
nonlocality. For example, the known W states and GHZ states have different
least number of the product states, and are different in type.Comment: 4 page
Inflation coupled to a Gauss-Bonnet term
The newly released Planck CMB data place tight constraints on slow-roll
inflationary models. Some of commonly discussed inflationary potentials are
disfavored due mainly to the large tensor-to-scalar ratio. In this paper we
show that these potentials may be in good agreement with the Planck data when
the inflaton has a non-minimal coupling to the Gauss-Bonnet term. Moreover,
such a coupling violates the consistency relation between the tensor spectral
index and tensor-to-scalar ratio. If the tensor spectral index is allowed to
vary freely, the Planck constraints on the tensor-to-scalar ratio are slightly
improved.Comment: 7 pages, 2 figures, references adde
FWDA: a Fast Wishart Discriminant Analysis with its Application to Electronic Health Records Data Classification
Linear Discriminant Analysis (LDA) on Electronic Health Records (EHR) data is
widely-used for early detection of diseases. Classical LDA for EHR data
classification, however, suffers from two handicaps: the ill-posed estimation
of LDA parameters (e.g., covariance matrix), and the "linear inseparability" of
EHR data. To handle these two issues, in this paper, we propose a novel
classifier FWDA -- Fast Wishart Discriminant Analysis, that makes predictions
in an ensemble way. Specifically, FWDA first surrogates the distribution of
inverse covariance matrices using a Wishart distribution estimated from the
training data, then "weighted-averages" the classification results of multiple
LDA classifiers parameterized by the sampled inverse covariance matrices via a
Bayesian Voting scheme. The weights for voting are optimally updated to adapt
each new input data, so as to enable the nonlinear classification. Theoretical
analysis indicates that FWDA possesses a fast convergence rate and a robust
performance on high dimensional data. Extensive experiments on large-scale EHR
dataset show that our approach outperforms state-of-the-art algorithms by a
large margin
Direct Detections of Dark Matter in the Presence of Non-standard Neutrino Interactions
In this paper we investigate impacts of non-standard neutrino interactions
(NSIs) to the limitations on the discovery potential of dark matter in direct
detection experiments. New neutrino floors are derived taking into account
current upper bounds on the effective couplings of various NSIs. Our study
shows that the neutrino floors of the standard model neutral current
interactions can be significantly changed in the presence of vector-current NSI
and scalar-current NSI, and the neutrino floors can be raised up to about
in the presence of pseudo-scalar-current NSI, and there are
almost no impacts to the neutrino floors from the axial-vector NSI and the
tensor NSI. We suggest combining the dark matter direct detection experiments
with the coherent elastic neutrino nucleus scattering experiments to hunt for
new physics behind the signal of nuclear recoil in the future.Comment: 17 pages, 4 figure
Intrinsic magnetoresistance in metal films on ferromagnetic insulators
We predict a magnetoresistance induced by the interfacial Rashba spin-orbit
coupling in normal metal|ferromagnetic insulator bilayer. It depends on the
angle between current and magnetization directions identically to the "spin
Hall magnetoresistance" mechanism caused by a combined action of spin Hall and
inverse spin Hall effects. Due to the identical phenomenology it is not obvious
whether the magnetoresistance reported by Nakayama et al. is a bulk metal or
interface effect. The interfacial Rashba induced magnetoresistance may be
distinguished from the bulk metal spin Hall magnetoresistance by its dependence
on the metal film thickness
Bragg solitons in an electromagnetically induced transparency medium
In this Letter we discuss the possibility of producing Bragg solitons in an
electromagnetically induced transparency medium. We show that this coherent
medium can be engineered to be a Bragg grating with a large Kerr nonlinearity
through proper arrangements of light fields. Unlike in previous studies, the
parameters of the medium can be easily controlled through adjusting the
intensities and detunings of lasers. Thus this scheme may provide an
opportunity to study the dynamics of Bragg solitons. And doing experiments with
low power lights is possible.Comment: 4 pages, 3 figure
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