63,888 research outputs found
Effect of Point Defects on the Optical and Transport Properties of MoS2 and WS2
Imperfections in the crystal structure, such as point defects, can strongly
modify the optical and transport properties of materials. Here, we study the
effect of point defects on the optical and DC conductivities of single layers
of semiconducting transition metal dichalcogenides with the form S,
where =Mo or W. The electronic structure is considered within a six bands
tight-binding model, which accounts for the relevant combination of
orbitals of the metal and orbitals of the chalcogen . We use the
Kubo formula for the calculation of the conductivity in samples with different
distributions of disorder. We find that and/or S defects create mid-gap
states that localize charge carriers around the defects and which modify the
optical and transport properties of the material, in agreement with recent
experiments. Furthermore, our results indicate a much higher mobility for
-doped WS in comparison to MoS
Exact Hybrid Covariance Thresholding for Joint Graphical Lasso
This paper considers the problem of estimating multiple related Gaussian
graphical models from a -dimensional dataset consisting of different
classes. Our work is based upon the formulation of this problem as group
graphical lasso. This paper proposes a novel hybrid covariance thresholding
algorithm that can effectively identify zero entries in the precision matrices
and split a large joint graphical lasso problem into small subproblems. Our
hybrid covariance thresholding method is superior to existing uniform
thresholding methods in that our method can split the precision matrix of each
individual class using different partition schemes and thus split group
graphical lasso into much smaller subproblems, each of which can be solved very
fast. In addition, this paper establishes necessary and sufficient conditions
for our hybrid covariance thresholding algorithm. The superior performance of
our thresholding method is thoroughly analyzed and illustrated by a few
experiments on simulated data and real gene expression data
Minimal model of self-replicating nanocells: a physically embodied information-free scenario
The building of minimal self-reproducing systems with a physical embodiment
(generically called protocells) is a great challenge, with implications for
both theory and applied sciences. Although the classical view of a living
protocell assumes that it includes information-carrying molecules as an
essential ingredient, a dividing cell-like structure can be built from a
metabolism-container coupled system, only. An example of such a system, modeled
with dissipative particle dynamics, is presented here. This article
demonstrates how a simple coupling between a precursor molecule and surfactant
molecules forming micelles can experience a growth-division cycle in a
predictable manner, and analyzes the influence of crucial parameters on this
replication cycle. Implications of these results for origins of cellular life
and living technology are outlined.Comment: 9 pages, 10 figure
Origin of the X-ray Emission in the Nuclei of FR Is
We investigate the X-ray origin in FRIs using the multi-waveband high
resolution data of eight FR I sources, which have very low Eddington ratios. We
fit their multi-waveband spectrum using a coupled accretion-jet model. We find
that X-ray emission in the source with the highest L_X (~1.8*10^-4 L_Edd) is
from the advection-dominated accretion flow (ADAF). Four sources with moderate
L_X(~several*10^-6 L_Edd) are complicated. The X-ray emission of one FR I is
from the jet, and the other three is from the sum of the jet and ADAF. The
X-ray emission in the three least luminous sources (L_X<1.0*10^-6L_Edd) is
dominated by the jet. These results roughly support the predictions of Yuan and
Cui(2005) where they predict that when the X-ray luminosity of the system is
below a critical value, the X-radiation will not be dominated by the emission
from the ADAF any longer, but by the jet. We also find that the accretion rates
in four sources must be higher than the Bondi rates, which implies that other
fuel supply (e.g., stellar winds) inside the Bondi radius should be important.Comment: 6 pages. To published in Journal of Physics, in proceedings of "The
Universe under the Microscope - Astrophysics at High Angular Resolution" (Bad
Honnef, Germany, April 2008), eds. R. Schoedel, A. Eckart, S. Pfalzner, and
E. Ro
Isolated Galaxies versus Interacting Pairs with MaNGA
We present preliminary results of the spectral analysis on the radial
distributions of the star formation history in both, a galaxy merger and a
spiral isolated galaxy observed with MaNGA. We find that the central part of
the isolated galaxy is composed by older stellar population (2 Gyr) than
in the outskirts (7 Gyr). Also, the time-scale is gradually larger from 1
Gyr in the inner part to 3 Gyr in the outer regions of the galaxy. In the case
of the merger, the stellar population in the central region is older than in
the tails, presenting a longer time-scale in comparison to central part in the
isolated galaxy. Our results are in agreement with a scenario where spiral
galaxies are built from inside-out. In the case of the merger, we find evidence
that interactions enhance star formation in the central part of the galaxy.Comment: 7 pages, 2 figures. Proceedings of the EWASS-2015 special session
Sp3, accepted for publication in Special Issue "3D View on Interacting and
Post-Interacting Galaxies from Clusters to Voids" of open access journal
"Galaxies
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