7,728 research outputs found
The Starburst in the Central Kiloparsec of Markarian 231
We present VLBA observations at 0.33 and 0.61 GHz, and VLA observations
between 5 and 22 GHz, of subkiloparsec scale radio emission from Mrk 231. In
addition to jet components clearly associated with the AGN, we also find a
smooth extended component of size 100 - 1000 pc most probably related to the
purported massive star forming disk in Mrk 231. The diffuse radio emission from
the disk is found to have a steep spectrum at high frequencies, characteristic
of optically thin synchrotron emission. The required relativistic particle
density in the disk can be produced by a star formation rate of 220 Msolar/yr
in the central kiloparsec. At low frequencies the disk is absorbed, most likely
by ionized gas with an emission measure of 8 x 10^5 pc cm-6. We have also
identified 4 candidate radio supernovae that, if confirmed, represent direct
evidence for ongoing star formation in the central kiloparsec.Comment: in press at ApJ for v. 519 July 1999, 14 page LaTeX document includes
6 postscript figure
Pollutant emission reductions deliver decreased PM₂.₅-caused mortality across China during 2015-2017
Air pollution is a serious environmental issue and leading contributor to the disease burden in China. Rapid reductions in fine particulate matter (PM2.5) concentrations and increased ozone concentrations have occurred across China, during 2015 to 2017. We used measurements of particulate matter with a diameter 1000 stations across China along with Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) regional air quality simulations, to explore the drivers and impacts of observed trends. The measured nationwide median PM2.5 trend of −3.4 µg m−3 year−1, was well simulated by the model (−3.5 µg m−3 year−1). With anthropogenic emissions fixed at 2015-levels, the simulated trend was much weaker (−0.6 µg m−3 year−1), demonstrating interannual variability in meteorology played a minor role in the observed PM2.5 trend. The model simulated increased ozone concentrations in line with the measurements, but underestimated the magnitude of the observed absolute trend by a factor of 2. We combined simulated trends in PM2.5 concentrations with an exposure-response function to estimate that reductions in PM2.5 concentrations over this period have reduced PM2.5-attribrutable premature morality across China by 150 000 deaths year−1
Competition Between Antiferromagnetic Order and Spin-Liquid Behavior in the Two-Dimensional Periodic Anderson Model at Half-Filling
We study the two-dimensional periodic Anderson model at half-filling using
quantum Monte Carlo (QMC) techniques. The ground state undergoes a magnetic
order-disorder transition as a function of the effective exchange coupling
between the conduction and localized bands. Low-lying spin and charge
excitations are determined using the maximum entropy method to analytically
continue the QMC data. At finite temperature we find a competition between the
Kondo effect and antiferromagnetic order which develops in the localized band
through Ruderman-Kittel-Kasuya-Yosida interactions.Comment: Revtex 3.0, 10 pages + 5 figures, UCSBTH-94-2
Considerations on the quantum double-exchange Hamiltonian
Schwinger bosons allow for an advantageous representation of quantum
double-exchange. We review this subject, comment on previous results, and
address the transition to the semiclassical limit. We derive an effective
fermionic Hamiltonian for the spin-dependent hopping of holes interacting with
a background of local spins, which is used in a related publication within a
two-phase description of colossal magnetoresistant manganites.Comment: 7 pages, 3 figure
Calculation of Densities of States and Spectral Functions by Chebyshev Recursion and Maximum Entropy
We present an efficient algorithm for calculating spectral properties of
large sparse Hamiltonian matrices such as densities of states and spectral
functions. The combination of Chebyshev recursion and maximum entropy achieves
high energy resolution without significant roundoff error, machine precision or
numerical instability limitations. If controlled statistical or systematic
errors are acceptable, cpu and memory requirements scale linearly in the number
of states. The inference of spectral properties from moments is much better
conditioned for Chebyshev moments than for power moments. We adapt concepts
from the kernel polynomial approximation, a linear Chebyshev approximation with
optimized Gibbs damping, to control the accuracy of Fourier integrals of
positive non-analytic functions. We compare the performance of kernel
polynomial and maximum entropy algorithms for an electronic structure example.Comment: 8 pages RevTex, 3 postscript figure
Analysis of Energy Efficiency Measures in Rehabilitation of Multifamily Housing Units
An apartment building in Austin, Texas, and
one in Boston, Massachusetts, were analyzed to
determine the cost-effectiveness of energy
efficiency measures. To determine expected energy
and cost savings resulting from a set of proposed
retrofit measures, hour-by-hour simulations were
conducted using the DOE-2.1C building energy
analysis computer program. Based on detailed audit
data, supplemented by field-measurements in the
case of the Austin apartment building, the
simulations were run for base case (preretrofit)
conditions for each building. Metered electricity
and gas consumption was used to calibrate the input
data.
A series of proposed retrofit measures was run
for each building using the calibrated preretrofit
model as the reference. Annual energy and cost
savings were calculated separately for each measure
and for the combined set of measures. For the
Austin building the combined set of 11 measures
yielded expected savings of 1.292/year, and annual energy
savings of nearly 75%. Measured in situ air
conditioner performance for two of the Austin
apartments showed EERs of 5.70 and 5.55, indicating
an efficiency degradation of 22% and 24%,
respectively, after 16 years of operation
A combinatorial approach to knot recognition
This is a report on our ongoing research on a combinatorial approach to knot
recognition, using coloring of knots by certain algebraic objects called
quandles. The aim of the paper is to summarize the mathematical theory of knot
coloring in a compact, accessible manner, and to show how to use it for
computational purposes. In particular, we address how to determine colorability
of a knot, and propose to use SAT solving to search for colorings. The
computational complexity of the problem, both in theory and in our
implementation, is discussed. In the last part, we explain how coloring can be
utilized in knot recognition
Reluplex: An Efficient SMT Solver for Verifying Deep Neural Networks
Deep neural networks have emerged as a widely used and effective means for
tackling complex, real-world problems. However, a major obstacle in applying
them to safety-critical systems is the great difficulty in providing formal
guarantees about their behavior. We present a novel, scalable, and efficient
technique for verifying properties of deep neural networks (or providing
counter-examples). The technique is based on the simplex method, extended to
handle the non-convex Rectified Linear Unit (ReLU) activation function, which
is a crucial ingredient in many modern neural networks. The verification
procedure tackles neural networks as a whole, without making any simplifying
assumptions. We evaluated our technique on a prototype deep neural network
implementation of the next-generation airborne collision avoidance system for
unmanned aircraft (ACAS Xu). Results show that our technique can successfully
prove properties of networks that are an order of magnitude larger than the
largest networks verified using existing methods.Comment: This is the extended version of a paper with the same title that
appeared at CAV 201
Analysis of colorectal cancers in British Bangladeshi identifies early onset, frequent mucinous histotype and a high prevalence of RBFOX1 deletion
PMCID: PMC3544714This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
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