4,305 research outputs found
Operational Trans-Resistance Amplifier Based Tunable Wave Active Filter
In this paper, Operational Trans-Resistance Amplifier (OTRA) based wave active filter structures are presented. They are flexible and modular, making them suitable to implement higher order filters. The circuits implement the resistors using matched transistors, operating in linear region, making them well suited for IC fabrication. They are insensitive to parasitic input capacitances and input resistances due to the internally grounded input terminals of OTRA. As an application, a doubly terminated third order Butterworth low pass filter has been implemented, by substituting OTRA based wave equivalents of passive elements. PSPICE simulations are given to verify the theoretical analysis
X-ray Intraday Variability of Five TeV Blazars with NuSTAR
We have examined 40 NuSTAR light curves (LCs) of five TeV emitting high
synchrotron peaked blazars: 1ES 0229+200, Mrk 421, Mrk 501, 1ES 1959+650 and
PKS 2155-304. Four of the blazars showed intraday variability in the NuSTAR
energy range of 3-79 keV. Using an auto correlation function analysis we
searched for intraday variability timescales in these LCs and found indications
of several between 2.5 and 32.8 ks in eight LCs of Mrk 421, a timescale around
8.0 ks for one LC of Mrk 501, and timescales of 29.6 ks and 57.4 ks in two LCs
of PKS 2155-304. The other two blazars' LCs do not show any evidence for
intraday variability timescales shorter than the lengths of those observations,
however, the data was both sparser and noisier, for them. We found positive
correlations with zero lag between soft (3-10 keV) and hard (10-79 keV) bands
for most of the LCs, indicating that their emissions originate from the same
electron population. We examined spectral variability using a hardness ratio
analysis and noticed a general "harder-when-brighter" behavior. The 22 LCs of
Mrk 421 observed between July 2012 and April 2013 show that this source was in
a quiescent state for an extended period of time and then underwent an
unprecedented double peaked outburst while monitored on a daily basis during 10
- 16 April 2013. We briefly discuss models capable of explaining these blazar
emissions.Comment: 21 pages, 4 figures, 4 tables, Accepted for Publication in Ap
An efficient high-order Nystr\"om scheme for acoustic scattering by inhomogeneous penetrable media with discontinuous material interface
This text proposes a fast, rapidly convergent Nystr\"{o}m method for the
solution of the Lippmann-Schwinger integral equation that mathematically models
the scattering of time-harmonic acoustic waves by inhomogeneous obstacles,
while allowing the material properties to jump across the interface. The method
works with overlapping coordinate charts as a description of the given
scatterer. In particular, it employs "partitions of unity" to simplify the
implementation of high-order quadratures along with suitable changes of
parametric variables to analytically resolve the singularities present in the
integral operator to achieve desired accuracies in approximations. To deal with
the discontinuous material interface in a high-order manner, a specialized
quadrature is used in the boundary region. The approach further utilizes an FFT
based strategy that uses equivalent source approximations to accelerate the
evaluation of large number of interactions that arise in the approximation of
the volumetric integral operator and thus achieves a reduced computational
complexity of for an -point discretization. A detailed
discussion on the solution methodology along with a variety of numerical
experiments to exemplify its performance in terms of both speed and accuracy
are presented in this paper
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Mutational signatures in colon cancer.
ObjectiveRecently, many tumor sequencing studies have inferred and reported on mutational signatures, short nucleotide patterns at which particular somatic base substitutions appear more often. A number of signatures reflect biological processes in the patient and factors associated with cancer risk. Our goal is to infer mutational signatures appearing in colon cancer, a cancer for which environmental risk factors vary by cancer subtype, and compare the signatures to those in adult stem cells from normal colon. We also compare the mutational signatures to others in the literature.ResultsWe apply a probabilistic mutation signature model to somatic mutations previously reported for six adult normal colon stem cells and 431 colon adenocarcinomas. We infer six mutational signatures in colon cancer, four being specific to tumors with hypermutation. Just two signatures explained the majority of mutations in the small number of normal aging colon samples. All six signatures are independently identified in a series of 295 Chinese colorectal cancers
Concentration Gradient, Diffusion, and Flow Through Open Porous Medium Near Percolation Threshold via Computer Simulations
The interacting lattice gas model is used to simulate fluid flow through an
open percolating porous medium with the fluid entering at the source-end and
leaving from the opposite end. The shape of the steady-state concentration
profile and therefore the gradient field depends on the is found to scale with
the porosity according to porosity p. The root mean square (rms) displacements
of fluid and its constituents (tracers) show a drift power-law behavior, in the
asymptotic regime. The flux current density is found to scale with the porosity
according to an exponent near 1.7.Comment: 8 figure
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