2,825 research outputs found
Avalanche Breakdown Timing Statistics for Silicon Single Photon Avalanche Diodes
CCBY Silicon-based Single Photon Avalanche Diodes (SPADs) are widely used as single photon detectors of visible and near infrared photons. There has however been a lack of models accurately interpreting the physics of impact ionization (the mechanism behind avalanche breakdown) for these devices. In this work, we present a statistical simulation model for silicon SPADs that is capable of predicting breakdown probability, mean time to breakdown and timing jitter. Our model inherently incorporates carriers & #x0027; dead space due to phonon scattering and allows for non-uniform electric fields. Model validation included avalanche gain, excess noise factor, breakdown voltage, breakdown probability, and timing statistics. Simulating an n on-p and a p-on-n SPAD design using our model, we found that the n-on-p design offers significantly improved mean time to breakdown and timing jitter characteristics. For a breakdown probability of 0.5, mean time to breakdown and timing jitter from the n-on-p design were 3 and 4 times smaller compared to those from the p on n design. The data reported in this paper is available from the ORDA digital repository (DOI: 10.15131/shef.data.4823248)
Editorial: Syphilis infection: clinical, epidemiology, basic science, and behavioral research
Syphilis is an ancient sexually transmitted disease caused by the spirochete Treponema pallidum subspecies pallidum (T. pallidum). Over the past decade, syphilis incidence has increased in many countries. Untreated syphilis can lead to serious health problems, including blindness, neurocognitive disorders, cardiovascular injury, and adverse pregnancy outcomes. Syphilis research is urgently needed to decrease morbidity and mortality. This Frontiers Research Topic focuses on diverse aspects of syphilis infection. Its purpose was to expand our knowledge of syphilis epidemiology, clinical management, public health control measures, vaccine development, and basic science
Pareto optimality in house allocation problems
We study Pareto optimal matchings in the context of house allocation problems. We present an O(\sqrt{n}m) algorithm, based on Gales Top Trading Cycles Method, for finding a maximum cardinality Pareto optimal matching, where n is the number of agents and m is the total length of the preference lists. By contrast, we show that the problem of finding a minimum cardinality Pareto optimal matching is NP-hard, though approximable within a factor of 2. We then show that there exist Pareto optimal matchings of all sizes between a minimum and maximum cardinality Pareto optimal matching. Finally, we introduce the concept of a signature, which allows us to give a characterization, checkable in linear time, of instances that admit a unique Pareto optimal matching
Supergravity Solutions for Harmonic, Static and Flux S-Branes
We seek S-brane solutions in D=11 supergravity which can be characterized by
a harmonic function H on the flat transverse space. It turns out that the
Einstein's equations force H to be a linear function of the transverse
coordinates. The codimension one H=0 hyperplane can be spacelike, timelike or
null and the spacelike case reduces to the previously obtained SM2 or SM5 brane
solutions. We then consider static S-brane configurations having smeared
timelike directions where the transverse Lorentzian symmetry group is broken
down to its maximal orthogonal subgroup. Assuming that the metric functions
depend on a radial spatial coordinate, we construct explicit solutions in D=11
supergravity which are non-supersymmetric and asymptotically flat. Finally, we
obtain spacelike fluxbrane backgrounds which have timelike electric or magnetic
fluxlines extending from past to future infinity.Comment: 22 pages, v2: references adde
Crystal structure, magnetic properties, and the magnetocaloric effect of Gd5Rh4 and GdRh
The crystal structures of Gd5Rh4 and GdRh have been studied by powder and single crystal x-ray diffraction. The results show that Gd5Rh4 is isotypic with Pu5Rh4 and the bond length of the short Rh-Rh dimer is 2.943(4) Å. According to heat capacity measurements in zero magnetic field, the magnetic ordering temperature of Gd5Rh4 is 13 K, in agreement with magnetization measurements. Both the heat capacity peak shape and the positive slope of the Arrott plots at Curie temperature (TC) indicate the second-order nature of the magnetic transition. The temperature dependence of magnetization of Gd5Rh4 measured in 1 kOe applied field indicates noncollinear magnetic ordering that may change into nearly collinear ferromagnetic ordering by increasing the magnetic field. GdRh is ferromagnetic below T C = 22 K. Moderate magnetocaloric effects and relatively high refrigerant capacities are observed in Gd5Rh4 and GdRh
Constrained spin dynamics description of random walks on hierarchical scale-free networks
We study a random walk problem on the hierarchical network which is a
scale-free network grown deterministically. The random walk problem is mapped
onto a dynamical Ising spin chain system in one dimension with a nonlocal spin
update rule, which allows an analytic approach. We show analytically that the
characteristic relaxation time scale grows algebraically with the total number
of nodes as . From a scaling argument, we also show the
power-law decay of the autocorrelation function C_{\bfsigma}(t)\sim
t^{-\alpha}, which is the probability to find the Ising spins in the initial
state {\bfsigma} after time steps, with the state-dependent non-universal
exponent . It turns out that the power-law scaling behavior has its
origin in an quasi-ultrametric structure of the configuration space.Comment: 9 pages, 6 figure
Cosmological Constraints on Dark Energy Models
Modified gravity theories with the Gauss-Bonnet term
have
recently gained a lot of attention as a possible explanation of dark energy. We
perform a thorough phase space analysis on the so-called models, where
is some general function of the Gauss-Bonnet term, and derive conditions
for the cosmological viability of dark energy models. Following the
case, we show that these conditions can be nicely presented as
geometrical constraints on the derivatives of . We find that for general
models there are two kinds of stable accelerated solutions, a de Sitter
solution and a phantom-like solution. They co-exist with each other and which
solution the universe evolves to depends on the initial conditions. Finally,
several toy models of dark energy are explored. Cosmologically viable
trajectories that mimic the CDM model in the radiation and matter
dominated periods, but have distinctive signatures at late times, are obtained.Comment: 17 pages, 3 figures; typos correcte
Localized Intersections of Non-Extremal p-branes and S-branes
A class of solutions to Supergravity in 10 or 11 dimensions is presented
which extends the non-standard or semi-local intersections of Dp-branes to the
case of non-extremal p-branes. The type of non-extremal solutions involved in
the intersection is free and we provide two examples involving black-branes
and/or D-\bar{D} systems. After a rotation among the time coordinate and a
relatively transverse radial direction the solutions admit the interpretation
of an intersection among D-branes and S-branes. We speculate on the relevance
of these configurations both to study time dependent phenomena in the AdS/CFT
correspondence as well as to construct cosmological brane-world scenarios
within String Theory admitting accelerating expansion of the Universe.Comment: 31 pages, latex file; v2: typos corrected and references adde
The Destruction of Tori in Volume-Preserving Maps
Invariant tori are prominent features of symplectic and volume preserving
maps. From the point of view of chaotic transport the most relevant tori are
those that are barriers, and thus have codimension one. For an -dimensional
volume-preserving map, such tori are prevalent when the map is nearly
"integrable," in the sense of having one action and angle variables. As
the map is perturbed, numerical studies show that the originally connected
image of the frequency map acquires gaps due to resonances and domains of
nonconvergence due to chaos. We present examples of a three-dimensional,
generalized standard map for which there is a critical perturbation size,
, above which there are no tori. Numerical investigations to find
the "last invariant torus" reveal some similarities to the behavior found by
Greene near a critical invariant circle for area preserving maps: the crossing
time through the newly destroyed torus appears to have a power law singularity
at , and the local phase space near the critical torus contains
many high-order resonances.Comment: laTeX, 16 figure
A Dissipative-Particle-Dynamics Model for Simulating Dynamics of Charged Colloid
A mesoscopic colloid model is developed in which a spherical colloid is
represented by many interacting sites on its surface. The hydrodynamic
interactions with thermal fluctuations are taken accounts in full using
Dissipative Particle Dynamics, and the electrostatic interactions are simulated
using Particle-Particle-Particle Mesh method. This new model is applied to
investigate the electrophoretic mobility of a charged colloid under an external
electric field, and the influence of salt concentration and colloid charge are
systematically studied. The simulation results show good agreement with
predictions from the electrokinetic theory.Comment: 17 pages, 8 figures, submitted to the proceedings of High Performance
Computing in Science & Engineering '1
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