39,132 research outputs found
Scalable Text and Link Analysis with Mixed-Topic Link Models
Many data sets contain rich information about objects, as well as pairwise
relations between them. For instance, in networks of websites, scientific
papers, and other documents, each node has content consisting of a collection
of words, as well as hyperlinks or citations to other nodes. In order to
perform inference on such data sets, and make predictions and recommendations,
it is useful to have models that are able to capture the processes which
generate the text at each node and the links between them. In this paper, we
combine classic ideas in topic modeling with a variant of the mixed-membership
block model recently developed in the statistical physics community. The
resulting model has the advantage that its parameters, including the mixture of
topics of each document and the resulting overlapping communities, can be
inferred with a simple and scalable expectation-maximization algorithm. We test
our model on three data sets, performing unsupervised topic classification and
link prediction. For both tasks, our model outperforms several existing
state-of-the-art methods, achieving higher accuracy with significantly less
computation, analyzing a data set with 1.3 million words and 44 thousand links
in a few minutes.Comment: 11 pages, 4 figure
Shear and Layer Breathing Modes in Multilayer MoS2
We study by Raman scattering the shear and layer breathing modes in
multilayer MoS2. These are identified by polarization measurements and symmetry
analysis. Their positions change with the number of layers, with different
scaling for odd and even layers. A chain model explains the results, with
general applicability to any layered material, and allows one to monitor their
thickness
X-ray Timing Observations of PSR J1930+1852 in the Crab-like SNR G54.1+0.3
We present new X-ray timing and spectral observations of PSR J1930+1852, the
young energetic pulsar at the center of the non-thermal supernova remnant
G54.1+0.3. Using data obtained with the Rossi X-ray Timing Explorer and Chandra
X-ray observatories we have derived an updated timing ephemeris of the 136 ms
pulsar spanning 6 years. During this interval, however, the period evolution
shows significant variability from the best fit constant spin-down rate of
s s, suggesting strong timing noise
and/or glitch activity. The X-ray emission is highly pulsed (
modulation) and is characterized by an asymmetric, broad profile (
duty cycle) which is nearly twice the radio width. The spectrum of the pulsed
emission is well fitted with an absorbed power law of photon index ; this is marginally harder than that of the unpulsed component. The
total 2-10 keV flux of the pulsar is erg cm
s. These results confirm PSR J1930+1852 as a typical Crab-like pulsar.Comment: 14 pages with 7 figures included, accepted to Ap
On the Bergman representative coordinates
We study the set where the so-called Bergman representative coordinates (or
Bergman functions) form an immersion. We provide an estimate of the size of a
maximal geodesic ball with respect to the Bergman metric, contained in this
set. By concrete examples we show that these estimates are the best possible.Comment: 20 page
Operator Quantum Geometric Tensor and Quantum Phase Transitions
We extend the quantum geometric tensor from the state space to the operator
level,and investigate its properties like the additivity for factorizable
models and the splitting of two kinds contributions for the case of stationary
reference states. This operator-quantum-geometric tensor (OQGT) is shown to
reflect the sensitivity of unitary operations against perturbations of multi
parameters. General results for the cases of time evolutions with given
stationary reference states are obtained. By this approach, we get exact
results for the rotated XY models, and show relations between the OQGT and
quantum criticality.Comment: One more reference added. 6 pages,2 figs. Accepted by EP
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