1,441 research outputs found
Dead Time Compensation for High-Flux Ranging
Dead time effects have been considered a major limitation for fast data
acquisition in various time-correlated single photon counting applications,
since a commonly adopted approach for dead time mitigation is to operate in the
low-flux regime where dead time effects can be ignored. Through the application
of lidar ranging, this work explores the empirical distribution of detection
times in the presence of dead time and demonstrates that an accurate
statistical model can result in reduced ranging error with shorter data
acquisition time when operating in the high-flux regime. Specifically, we show
that the empirical distribution of detection times converges to the stationary
distribution of a Markov chain. Depth estimation can then be performed by
passing the empirical distribution through a filter matched to the stationary
distribution. Moreover, based on the Markov chain model, we formulate the
recovery of arrival distribution from detection distribution as a nonlinear
inverse problem and solve it via provably convergent mathematical optimization.
By comparing per-detection Fisher information for depth estimation from high-
and low-flux detection time distributions, we provide an analytical basis for
possible improvement of ranging performance resulting from the presence of dead
time. Finally, we demonstrate the effectiveness of our formulation and
algorithm via simulations of lidar ranging.Comment: Revision with added estimation results, references, and figures, and
modified appendice
The effects of life stress and neural learning signals on fluid intelligence.
Fluid intelligence (fluid IQ), defined as the capacity for rapid problem solving and behavioral adaptation, is known to be modulated by learning and experience. Both stressful life events (SLES) and neural correlates of learning [specifically, a key mediator of adaptive learning in the brain, namely the ventral striatal representation of prediction errors (PE)] have been shown to be associated with individual differences in fluid IQ. Here, we examine the interaction between adaptive learning signals (using a well-characterized probabilistic reversal learning task in combination with fMRI) and SLES on fluid IQ measures. We find that the correlation between ventral striatal BOLD PE and fluid IQ, which we have previously reported, is quantitatively modulated by the amount of reported SLES. Thus, after experiencing adversity, basic neuronal learning signatures appear to align more closely with a general measure of flexible learning (fluid IQ), a finding complementing studies on the effects of acute stress on learning. The results suggest that an understanding of the neurobiological correlates of trait variables like fluid IQ needs to take socioemotional influences such as chronic stress into account
Instanton Contribution to the Proton and Neutron Electric Form Factors
We study the instanton contribution to the proton and neutron electric form
factors. Using the single instanton approximation, we perform the calculations
in a mixed time-momentum representation in order to obtain the form factors
directly in momentum space. We find good agreement with the experimentally
measured electric form factor of the proton. For the neutron, our result falls
short of the experimental data. We argue that this discrepancy is due to the
fact that we neglect the contribution of the sea quarks. We compare to lattice
calculations and a relativistic version of the quark-diquark model.Comment: 8 pages, 5 figures, updated references, to appear in Phys. Lett.
Production in Au+Au and pp Collisions at = 200GeV at STAR
Mid-rapidity and are
measured in Au+Au and pp collisions at =200GeV using the STAR
detector at RHIC. The mass is systematically shifted at small
transverse momentum for both Au+Au and pp collisions. The
transverse mass spectra are measured in Au+Au collisions at different
centralities and in pp collisions. The mean transverse momentum
as a function of the collision centrality is compared to those of identified
, and . The and ratios are
compared to measurements in A+A, , , collisions at
various colliding energies. The physics implications of these measurements are
also discussed.Comment: 6 pages, 4 figures, proceedings of Strange Quarks in Matter
(SQM2003), Atlantic Beach, USA, to be published in J. Phys.
Quark deconfinement in neutron star cores and the ground state of neutral matter
Whether or not deconfined quark phase exists in neutron star cores and
represents the ground state of neutral matter at moderate densities are open
questions. We use two realistic effective quark models, the three-flavor
Nambu-Jona-Lasinio model and the modified quark-meson coupling model, to
describe the neutron star matter. After constructing possible hybrid equations
of state (EOSes) with unpaired or color superconducting quark phase, we
systematically discuss the observational constraints of neutron stars on the
EOSes. It is found that the neutron star with pure quark matter core is
unstable and the hadronic phase with hyperons is denied, while hybrid EOSes
with two-flavor color superconducting phase or unpaired quark matter phase are
both allowed by the tight and most reliable constraints from two stars Ter 5 I
and EXO 0748-676. And the hybrid EOS with unpaired quark matter phase is
allowed even compared with the tightest constraint from the most massive pulsar
star PSR J0751+1807. Therefore, we conclude that the ground state of neutral
matter at moderate densities is in deconfined quark phase likely.Comment: 13 pages, 4 figure
Strange Particles in Dense Matter and Kaon Condensates
We discuss the role of strangeness in dense matter and especially in neutron
stars. The early (in density) introduction of hyperons found in many
calculations is probably delayed by the decrease in vector mean field acting on
the neutron. The decrease results from both conventional many-body rescattering
effects and from the movement towards asymptotic freedom at high densities.
Subthreshold -meson production by the KaoS collaboration at GSI shows that
the -mass must be substantially lowered, by 200 MeV at . It is shown that explicit chiral symmetry breaking through the kaon
mass may be responsible for -nucleon and -nucleon scalar
attraction being weaker than obtained by simple quark scaling. The normal mode
of the strangeness minus, charge , excitation is constructed as a linear
combination of -meson and , neutron-hole state. Except for zero
momentum, where the terms are unmixed the "kaesobar" is a linear combination of
these two components.Comment: 10 pages, 8 postscript figures, Talk given at the International
Conference on Hypernuclear and Strange Particle Physics (HYP97), Brookhaven
Nat'l Lab., USA, October 13-18, 1997, to be published in Nucl. Phys.
On heavy-quarkonia suppression by final-state multiple scatterings in most central Au+Au collisions at RHIC
We study heavy-quarkonia suppression under final-state multiple scatterings
in most central Au~+~Au collisions at RHIC energy. We first calculate the
survival probability of a heavy quarkonium under multiple scattering in
Bjorken's expanding QGP at large . Then, we calculate the rapidity
dependence of the nuclear modification factor for heavy-quarkonia
production by considering final-state multiple scatterings in most central
Au~+~Au collisions in a simplified model. In our formula a constant is
also introduced to estimate the possible cold nuclear effects. By fitting the
data for production in most central Au + Au collisions at
~GeV at RHIC, we find that the transportation coefficient
\hat{q}_0\simeq(0.33-0.95)~\mbox{GeV}^2/fm, and, accordingly, the energy
density at is \epsilon_0\simeq(1.39-5.62)~\mbox{GeV}/\mbox{fm}^3 in
perturbative thermal QCD. A better understanding of cold nuclear effects is
essential for us to get a more accurate analysis. The small values of the
transportation coefficient in our estimate are in sharp contrast
with those obtained by the analysis of high- hadron spectra in Ref. [31].Comment: 20 pages, 8 figures, final version accepted for publication in
Nuclear Physics
Production Ratios of Strange Baryons from QGP with Diquarks
Assuming that vector and scalar diquarks exist in the Quark-Gluon Plasma near
the critical temporature , baryons can be produced through the processes
of quarks and diquarks forming baryon states. Ratios of different
baryons can be estimated through this method, if such kind of QGP with diquarks
can exists.Comment: Correct some expressions of equation
High-flux single-photon lidar
In time-correlated single-photon counting (TCSPC), photons that arrive during the detector and timing electronics dead times are missed, causing distortion of the detection time distribution. Conventional wisdom holds that TCSPC should be performed with detections in fewer than 5% of illumination cycles to avoid substantial distortion. This requires attenuation and leads to longer acquisition times if the incident flux is too high. Through the example of ranging with a single-photon lidar system, this work demonstrates that accurately modeling the sequence of detection times as a Markov chain allows for measurements at much higher incident flux without attenuation. Our probabilistic model is validated by the close match between the limiting distribution of the Markov chain and both simulated and experimental data, so long as issues of calibration and afterpulsing are minimal. We propose an algorithm that corrects for the distortion in detection histograms caused by dead times without assumptions on the form of the transient light intensity. Our histogram correction yields substantially improved depth imaging performance, and modest additional improvement is achieved with a parametric model assuming a single depth per pixel. We show results for depth and flux estimation with up to 5 photoelectrons per illumination cycle on average, facilitating an increase in time efficiency of more than two orders of magnitude. The use of identical TCSPC equipment in other fields suggests that our modeling and histogram correction could likewise enable high-flux acquisitions in fluorescence lifetime microscopy or quantum optics applications.https://www.osapublishing.org/optica/fulltext.cfm?uri=optica-8-1-30&id=445715Published versio
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