514 research outputs found
Transportation dynamics on networks of mobile agents
Most existing works on transportation dynamics focus on networks of a fixed
structure, but networks whose nodes are mobile have become widespread, such as
cell-phone networks. We introduce a model to explore the basic physics of
transportation on mobile networks. Of particular interest are the dependence of
the throughput on the speed of agent movement and communication range. Our
computations reveal a hierarchical dependence for the former while, for the
latter, we find an algebraic power law between the throughput and the
communication range with an exponent determined by the speed. We develop a
physical theory based on the Fokker-Planck equation to explain these phenomena.
Our findings provide insights into complex transportation dynamics arising
commonly in natural and engineering systems
FPGA Deployment of LFADS for Real-time Neuroscience Experiments
Large-scale recordings of neural activity are providing new opportunities to
study neural population dynamics. A powerful method for analyzing such
high-dimensional measurements is to deploy an algorithm to learn the
low-dimensional latent dynamics. LFADS (Latent Factor Analysis via Dynamical
Systems) is a deep learning method for inferring latent dynamics from
high-dimensional neural spiking data recorded simultaneously in single trials.
This method has shown a remarkable performance in modeling complex brain
signals with an average inference latency in milliseconds. As our capacity of
simultaneously recording many neurons is increasing exponentially, it is
becoming crucial to build capacity for deploying low-latency inference of the
computing algorithms. To improve the real-time processing ability of LFADS, we
introduce an efficient implementation of the LFADS models onto Field
Programmable Gate Arrays (FPGA). Our implementation shows an inference latency
of 41.97 s for processing the data in a single trial on a Xilinx U55C.Comment: 6 pages, 8 figure
The Quark/Antiquark Asymmetry of the Nucleon Sea
Although the distributions of sea quarks and antiquarks generated by
leading-twist QCD evolution through gluon splitting
are necessarily CP symmetric, the distributions of nonvalence quarks and
antiquarks which are intrinsic to the nucleon's bound state wavefunction need
not be identical. In this paper we investigate the sea quark/antiquark
asymmetries in the nucleon wavefunction which are generated by a light-cone
model of energetically-favored meson-baryon fluctuations. The model predicts
striking quark/antiquark asymmetries in the momentum and helicity distributions
for the down and strange contributions to the proton structure function: the
intrinsic and quarks in the proton sea are predicted to be negatively
polarized, whereas the intrinsic and antiquarks give zero
contributions to the proton spin. Such a picture is supported by experimental
phenomena related to the proton spin problem and the violation of the
Ellis-Jaffe sum rule. The light-cone meson-baryon fluctuation model also
suggests a structured momentum distribution asymmetry for strange quarks and
antiquarks which could be relevant to an outstanding conflict between two
different determinations of the strange quark sea in the nucleon. The model
predicts an excess of intrinsic pairs over pairs, as
supported by the Gottfried sum rule violation. We also predict that the
intrinsic charm and anticharm helicity and momentum distributions are not
identical.Comment: LaTex 18 pages, 4 figures. To obtain a copy, send e-mail to
[email protected]
Flavor and Spin Structure of Octet Baryons at Large x
The quark flavor and spin distributions in octet baryons are calculated both
in the SU(6) quark spectator diquark model and in a perturbative QCD (pQCD)
based model. It is shown that the has the most significant difference
in flavor structure at large between the two models, though the flavor and
spin structure of other baryons can also provide tests of different models. The
Drell-Yan process for beams on isoscalar targets can be used to
test different predictions concerning the valence quark flavor structure of the
.Comment: 24 pages, 11 figures, version published in Nucl.Phys.B 574 (2000) 33
In vitro activities of antimicrobial combinations against planktonic and biofilm forms of Stenotrophomonas maltophilia
ObjectivesTo investigate the in vitro activity of antibiotic combinations against Stenotrophomonas maltophilia isolates and their associated biofilms.MethodsThirty-two S. maltophilia clinical isolates with at least twenty-five different pulsotypes were tested. The antibacterial activity of various antibiotic combinations against seven randomly selected planktonic and biofilm-embedded S. maltophilia strains with strong biofilm formation was assessed using broth methods. Extraction of bacterial genomic DNA and PCR detection of antibiotic resistance and biofilm-related genes were also performed.ResultsThe susceptibility rates of levofloxacin (LVX), fosfomycin (FOS), tigecycline (TGC) and sulfamethoxazole-trimethoprim (SXT) against 32 S. maltophilia isolates were 56.3, 71.9, 71.9 and 90.6%, respectively. Twenty-eight isolates were detected with strong biofilm formation. Antibiotic combinations, including aztreonam-clavulanic (ATM-CLA) with LVX, ceftazidime-avibactam (CZA) with LVX and SXT with TGC, exhibited potent inhibitory activity against these isolates with strong biofilm formation. The antibiotic resistance phenotype might not be fully caused by the common antibiotic-resistance or biofilm-formation gene.ConclusionS. maltophilia remained resistant to most antibiotics, including LVX and β-lactam/β-lactamases; however, TGC, FOS and SXT still exhibited potent activity. Although all tested S. maltophilia isolates exhibited moderate-to-strong biofilm formation, combination therapies, especially ATM-CLA with LVX, CZA with LVX and SXT with TGC, exhibited a higher inhibitory activity for these isolates
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