12,203 research outputs found
Effect of charged impurities on graphene thermoelectric power near the Dirac point
In graphene devices with a varying degree of disorders as characterized by
their carrier mobility and minimum conductivity, we have studied the
thermoelectric power along with the electrical conductivity over a wide range
of temperatures. We have found that the Mott relation fails in the vicinity of
the Dirac point in high-mobility graphene. By properly taking account of the
high temperature effects, we have obtained good agreement between the Boltzmann
transport theory and our experimental data. In low-mobility graphene where the
charged impurities induce relatively high residual carrier density, the Mott
relation holds at all gate voltages
A Revisit to Top Quark Forward-Backward Asymmetry
We analyze various models for the top quark forward-backward asymmetry
() at the Tevatron, using the latest CDF measurements on different
s and the total cross section. The axigluon model in Ref. \cite{paul}
has difficulties in explaining the large rapidity dependent asymmetry and mass
dependent asymmetry simultaneously and the parameter space relevant to
is ruled out by the latest dijet search at ATLAS. In contrast to
Ref. \cite{cp}, we demonstrate that the large parameter space in this model
with a flavor symemtry is not ruled out by flavor physics. The
-channel flavor-violating \cite{hitoshi},
\cite{waiyee} and diquark \cite{tim} models all have parameter
regions that satisfy different measurements within 1 .
However, the heavy model which can be marginally consistent with
the total cross section is severely constrained by the Tevatron direct search
of same-sign top quark pair. The diquark model suffers from too large total
cross section and is difficult to fit the invariant mass
distribution. The electroweak precision constraints on the model based on
- mixings is estimated and the result is rather weak (
GeV). Therefore, the heavy model seems to give the best fit for
all the measurements. The model predicts the signal
from production and is 10%-50% of SM at the 7 TeV LHC.
Such resonance can serve as the direct test of the model.Comment: 25 pages, 7 figures, 1 tabl
Dark matter coupling to electroweak gauge and Higgs bosons: an effective field theory approach
If dark matter is a new species of particle produced in the early universe as
a cold thermal relic (a weakly-interacting massive particle-WIMP), its present
abundance, its scattering with matter in direct-detection experiments, its
present-day annihilation signature in indirect-detection experiments, and its
production and detection at colliders, depend crucially on the WIMP coupling to
standard-model (SM) particles. It is usually assumed that the WIMP couples to
the SM sector through its interactions with quarks and leptons. In this paper
we explore the possibility that the WIMP coupling to the SM sector is via
electroweak gauge and Higgs bosons. In the absence of an ultraviolet-complete
particle-physics model, we employ effective field theory to describe the
WIMP--SM coupling. We consider both scalars and Dirac fermions as possible
dark-matter candidates. Starting with an exhaustive list of operators up to
dimension 8, we present detailed calculation of dark-matter annihilations to
all possible final states, including gamma gamma, gamma Z, gamma h, ZZ, Zh, W+
W-, hh, and f fbar, and demonstrate the correlations among them. We compute the
mass scale of the effective field theory necessary to obtain the correct
dark-matter mass density, and well as the resulting photon line signals
Evolution of cooperation in multilevel public goods games with community structures
In a community-structured population, public goods games (PGG) occur both
within and between communities. Such type of PGG is referred as multilevel
public goods games (MPGG). We propose a minimalist evolutionary model of the
MPGG and analytically study the evolution of cooperation. We demonstrate that
in the case of sufficiently large community size and community number, if the
imitation strength within community is weak, i.e., an individual imitates
another one in the same community almost randomly, cooperation as well as
punishment are more abundant than defection in the long run; if the imitation
strength between communities is strong, i.e., the more successful strategy in
two individuals from distinct communities is always imitated, cooperation and
punishment are also more abundant. However, when both of the two imitation
intensities are strong, defection becomes the most abundant strategy in the
population. Our model provides insight into the investigation of the
large-scale cooperation in public social dilemma among contemporary
communities.Comment: 6 pages, 4 figures, Accepted by EP
Quantum speed limit for relativistic spin-0 and spin-1 bosons on commutative and noncommutative planes
Quantum speed limits of relativistic charged spin-0 and spin-1 bosons in the
background of a homogeneous magnetic field are studied on both commutative and
oncommutative planes. We show that, on the commutative plane, the average
speeds of wave packets along the radial direction during the interval in which
a quantum state evolving from an initial state to the orthogonal final one can
not exceed the speed of light, regardless of the intensities of the magnetic
field. However, due to the noncommutativity, the average speeds of the wave
packets on noncommutative plane will exceed the speed of light in vacuum
provided the intensity of the magnetic field is strong enough. It is a clear
signature of violating Lorentz invariance in quantum mechanics region.Comment: 8 pages, no figures. arXiv admin note: text overlap with
arXiv:1702.0316
Ranking Preserving Nonnegative Matrix Factorization
Nonnegative matrix factorization (NMF), a wellknown
technique to find parts-based representations
of nonnegative data, has been widely studied.
In reality, ordinal relations often exist among data,
such as data i is more related to j than to q. Such
relative order is naturally available, and more importantly,
it truly reflects the latent data structure.
Preserving the ordinal relations enables us to find
structured representations of data that are faithful
to the relative order, so that the learned representations
become more discriminative. However, this
cannot be achieved by current NMFs. In this paper,
we make the first attempt towards incorporating the
ordinal relations and propose a novel ranking preserving
nonnegative matrix factorization (RPNMF)
approach, which enforces the learned representations
to be ranked according to the relations.
We derive iterative updating rules to solve RPNMF’s
objective function with convergence guaranteed.
Experimental results with several datasets for
clustering and classification have demonstrated that
RPNMF achieves greater performance against the
state-of-the-arts, not only in terms of accuracy, but
also interpretation of orderly data structure
Lateral inhibition and concentration-invariant odor perception
Sensory identity usually remains constant across a large intensity range. Vertebrates use lateral inhibition to match the sensitivity of retinal ganglion cells to the intensity of light. A new study published in Journal of Biology suggests that lateral inhibition in the Drosophila antennal lobe is similarly required for concentration-invariant perception of odors
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