3,437 research outputs found
Design of an analog/digital truly random number generator
An analog-digital system is presented for the generation of truly random (aperiodic) digital sequences. This model is based on a very simple piecewise-linear discrete map which is suitable for implementation using monolithic analog sampled-data techniques. Simulation results are given illustrating the optimum choice of the model parameters. Circuit implementations are reported for the discrete map using both switched-capacitor (SC) and switched-current (SI) techniques. The layout of a SI prototype in a 3-μm n-well double-polysilicon double-metal technology is included
Loop Corrections and Naturalness in a Chiral Effective Field Theory
The loop expansion is applied to a chiral effective hadronic lagrangian; with
the techniques of Infrared Regularization, it is possible to separate out the
short-range contributions and to write them as local products of fields that
are already present in our lagrangian. (The appropriate field variables must be
re-defined at each order in loops.) The corresponding parameters implicitly
include short-range effects to all orders in the interaction, so these effects
need not be calculated explicitly. The remaining (long-range) contributions
that must be calculated are nonlocal and resemble those in conventional
nuclear-structure calculations. Nonlinear isoscalar scalar and
vector meson interactions are included, which incorporate
many-nucleon forces and nucleon substructure. Calculations are carried out at
the two-loop level to illustrate these techniques at finite nuclear densities
and to verify that the coupling parameters remain natural when fitted to the
empirical properties of equilibrium nuclear matter. Contributions from the
tensor coupling are also discussed.Comment: 22 pages, 6 figure
A Population Density Model of the Driven LGN/PGN
The interaction of two populations of integrate-and-fire-or-burst neurons representing thalamocortical cells from the dorsal lateral geniculate nucleus (dLGN) and thalamic reticular cells from the perigeniculate nucleus (PGN) is studied using a population density approach. A two-dimensional probability density function that evolves according to a time-dependent advection-reaction equation gives the distribution of cells in each population over the membrane potential and de-inactivation level of a low-threshold calcium current. In the absence of retinal drive, the population density network model exhibits rhythmic bursting. In the presence of constant retinal input, the aroused LGN/PGN population density model displays a wide range of responses depending on cellular parameters and network connectivity.https://scholarworks.wm.edu/asbookchapters/1130/thumbnail.jp
A robust morphological classification of high-redshift galaxies using support vector machines on seeing limited images. II. Quantifying morphological k-correction in the COSMOS field at 1<z<2: Ks band vs. I band
We quantify the effects of \emph{morphological k-correction} at by
comparing morphologies measured in the K and I-bands in the COSMOS area.
Ks-band data have indeed the advantage of probing old stellar populations for
, enabling a determination of galaxy morphological types unaffected by
recent star formation. In paper I we presented a new non-parametric method to
quantify morphologies of galaxies on seeing limited images based on support
vector machines. Here we use this method to classify
selected galaxies in the COSMOS area observed with WIRCam at CFHT. The obtained
classification is used to investigate the redshift distributions and number
counts per morphological type up to and to compare to the results
obtained with HST/ACS in the I-band on the same objects from other works. We
associate to every galaxy with and a probability between 0 and
1 of being late-type or early-type. The classification is found to be reliable
up to . The mean probability is . It decreases with redshift
and with size, especially for the early-type population but remains above
. The classification is globally in good agreement with the one
obtained using HST/ACS for . Above , the I-band classification
tends to find less early-type galaxies than the Ks-band one by a factor
1.5 which might be a consequence of morphological k-correction effects.
We argue therefore that studies based on I-band HST/ACS classifications at
could be underestimating the elliptical population. [abridged]Comment: accepted for publication in A&A, updated with referee comments, 12
pages, 10 figure
Proximity effect gaps in S/N/FI structures
We study the proximity effect in hybrid structures consisting of
superconductor and ferromagnetic insulator separated by a normal diffusive
metal (S/N/FI structures). These stuctures were proposed to realize the
absolute spin-valve effect. We pay special attention to the gaps in the density
of states of the normal part. We show that the effect of the ferromagnet is
twofold: It not only shifts the density of states but also provides suppression
of the gap. The mechanism of this suppression is remarkably similar to that due
to magnetic impurities. Our results are obtained from the solution of
one-dimensional Usadel equation supplemented with boundary conditions for
matrix current at both interfaces.Comment: Published in The European Physical Journal
Wave energy in Europe: Views on experiences and progress to date
publisher: Elsevier articletitle: Wave energy in Europe: Views on experiences and progress to date journaltitle: International Journal of Marine Energy articlelink: http://dx.doi.org/10.1016/j.ijome.2015.09.001 content_type: article copyright: © 2015 Elsevier Ltd. All rights reserved
Ca2+ Alternans in a Cardiac Myocyte Model that Uses Moment Equations to Represent Heterogeneous Junctional SR Ca2+
AbstractMultiscale whole-cell models that accurately represent local control of Ca2+-induced Ca2+ release in cardiac myocytes can reproduce high-gain Ca2+ release that is graded with changes in membrane potential. Using a recently introduced formalism that represents heterogeneous local Ca2+ using moment equations, we present a model of cardiac myocyte Ca2+ cycling that exhibits alternating sarcoplasmic reticulum (SR) Ca2+ release when periodically stimulated by depolarizing voltage pulses. The model predicts that the distribution of junctional SR [Ca2+] across a large population of Ca2+ release units is distinct on alternating cycles. Load-release and release-uptake functions computed from this model give insight into how Ca2+ fluxes and stimulation frequency combine to determine the presence or absence of Ca2+ alternans. Our results show that the conditions for the onset of Ca2+ alternans cannot be explained solely by the steepness of the load-release function, but that changes in the release-uptake process also play an important role. We analyze the effect of the junctional SR refilling time constant on Ca2+ alternans and conclude that physiologically realistic models of defective Ca2+ cycling must represent the dynamics of heterogeneous junctional SR [Ca2+] without assuming rapid equilibration of junctional and network SR [Ca2+]
A robust morphological classification of high-redshift galaxies using support vector machines on seeing limited images. I Method description
We present a new non-parametric method to quantify morphologies of galaxies
based on a particular family of learning machines called support vector
machines. The method, that can be seen as a generalization of the classical CAS
classification but with an unlimited number of dimensions and non-linear
boundaries between decision regions, is fully automated and thus particularly
well adapted to large cosmological surveys. The source code is available for
download at http://www.lesia.obspm.fr/~huertas/galsvm.html To test the method,
we use a seeing limited near-infrared ( band, ) sample observed
with WIRCam at CFHT at a median redshift of . The machine is trained
with a simulated sample built from a local visually classified sample from the
SDSS chosen in the high-redshift sample's rest-frame (i band, ) and
artificially redshifted to match the observing conditions. We use a
12-dimensional volume, including 5 morphological parameters and other
caracteristics of galaxies such as luminosity and redshift. We show that a
qualitative separation in two main morphological types (late type and early
type) can be obtained with an error lower than 20% up to the completeness limit
of the sample () which is more than 2 times better that what would
be obtained with a classical C/A classification on the same sample and indeed
comparable to space data. The method is optimized to solve a specific problem,
offering an objective and automated estimate of errors that enables a
straightforward comparison with other surveys.Comment: 11 pages, 7 figures, 3 tables. Submitted to A&A. High resolution
images are available on reques
Proximity effect-assisted absorption of spin currents in superconductors
The injection of pure spin current into superconductors by the dynamics of a
ferromagnetic contact is studied theoretically. Taking into account suppression
of the order parameter at the interfaces (inverse proximity effect) and the
energy-dependence of spin-flip scattering, we determine the
temperature-dependent ferromagnetic resonance linewidth broadening. Our results
agree with recent experiments in Nb|permalloy bilayers [C. Bell et al.,
arXiv:cond-mat/0702461].Comment: 4 page
UBQLN4 Represses Homologous Recombination and Is Overexpressed in Aggressive Tumors
Genomic instability can be a hallmark of both human genetic disease and cancer. We identify a deleterious UBQLN4 mutation in families with an autosomal recessive syndrome reminiscent of genome instability disorders. UBQLN4 deficiency leads to increased sensitivity to genotoxic stress and delayed DNA double-strand break (DSB) repair. The proteasomal shuttle factor UBQLN4 is phosphorylated by ATM and interacts with ubiquitylated MRE11 to mediate early steps of homologous recombination-mediated DSB repair (HRR). Loss of UBQLN4 leads to chromatin retention of MRE11, promoting non-physiological HRR activity in vitro and in vivo. Conversely, UBQLN4 overexpression represses HRR and favors non-homologous end joining. Moreover, we find UBQLN4 overexpressed in aggressive tumors. In line with an HRR defect in these tumors, UBQLN4 overexpression is associated with PARP1 inhibitor sensitivity. UBQLN4 therefore curtails HRR activity through removal of MRE11 from damaged chromatin and thus offers a therapeutic window for PARP1 inhibitor treatment in UBQLN4-overexpressing tumors
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