909 research outputs found
Study of Balance Equations for Hot-Electron Transport in an Arbitrary Energy Band (III)
By choosing an electron gas resting instead of drifting in the laboratory
coordinate system as the initial state, the first order perturbation
calculation of the previous paper (Phys. Stat. Sol. (b) 198, 785(1996)) is
revised and extended to include the high order field corrections in the
expression for the frictional forces and the energy transfer rates. The final
expressions are formally the same as those in first order in the electric
field, but the distribution functions of electrons appearing in them are
defined by different expressions. The problems relative to the distribution
function are discussed in detail and a new closed expression for the
distribution function is obtained. The nonlinear impurity-limited resistance of
a strong degenerate electron gas is computed numerically. The result calculated
by using the new expression for the distribution function is quite different
from that using the displaced Fermi function when the electric field is
sufficiently high.Comment: 15 pages with 3 PS figures, RevTeX, to be published in Physica Status
Solidi (b
GVD effect and nonlinear pulse propagation in 40Gbit/s optical fiber communication systems
AbstractIn this paper, group velocity dispersion (GVD) and second-order GVD effects are shortly discussed and then the limitations on the bit rate induced by dispersion or second-order GVD are estimated. For relative higher pulse energy and shorter pulse width in 40Gbit/s systems, self-phase modulation(SPM) is significant. The combined effect of GVD and SPM on the propagation pulses are analyzed through Nonlinear Schrödinger Equation(NLSE)
Magnetothermoelectric DC conductivities from holography models with hyperscaling factor in Lifshitz spacetime
We investigate an Einstein-Maxwell-Dilaton-Axion holographic model and obtain
two branches of a charged black hole solution with a dynamic exponent and a
hyperscaling violation factor when a magnetic field presents. The
magnetothermoelectric DC conductivities are then calculated in terms of horizon
data by means of holographic principle. We find that linear temperature
dependence resistivity and quadratic temperature dependence inverse Hall angle
can be achieved in our model. The well-known anomalous temperature scaling of
the Nernst signal and the Seebeck coefficient of cuprate strange metals are
also discussed.Comment: 1+23 pages, 4 figures, references adde
On the Generation of Medical Question-Answer Pairs
Question answering (QA) has achieved promising progress recently. However,
answering a question in real-world scenarios like the medical domain is still
challenging, due to the requirement of external knowledge and the insufficient
quantity of high-quality training data. In the light of these challenges, we
study the task of generating medical QA pairs in this paper. With the insight
that each medical question can be considered as a sample from the latent
distribution of questions given answers, we propose an automated medical QA
pair generation framework, consisting of an unsupervised key phrase detector
that explores unstructured material for validity, and a generator that involves
a multi-pass decoder to integrate structural knowledge for diversity. A series
of experiments have been conducted on a real-world dataset collected from the
National Medical Licensing Examination of China. Both automatic evaluation and
human annotation demonstrate the effectiveness of the proposed method. Further
investigation shows that, by incorporating the generated QA pairs for training,
significant improvement in terms of accuracy can be achieved for the
examination QA system.Comment: AAAI 202
Quadratic nodal point in a two-dimensional noncollinear antiferromagnet
Quadratic nodal point (QNP) in two dimensions has so far been reported only
in nonmagnetic materials and in the absence of spin-orbit coupling. Here, by
first-principles calculations and symmetry analysis, we predict stable QNP near
Fermi level in a two-dimensional kagome metal-organic framework material,
Cr(HAB), which features noncollinear antiferromagnetic ordering and
sizable spin-orbit coupling. Effective kp and lattice models are constructed to
capture such magnetic QNPs. Besides QNP, we find Cr(HAB) also hosts six
magnetic linear nodal points protected by mirror as well as symmetry.
Properties associated to these nodal points, such as topological edge states
and quantized optical absorbance, are discussed
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