3,075 research outputs found
Greedy walk on the real line
We consider a self-interacting process described in terms of a single-server
system with service stations at each point of the real line. The customer
arrivals are given by a Poisson point processes on the space-time half plane.
The server adopts a greedy routing mechanism, traveling toward the nearest
customer, and ignoring new arrivals while in transit. We study the trajectories
of the server and show that its asymptotic position diverges logarithmically in
time.Comment: Published at http://dx.doi.org/10.1214/13-AOP898 in the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
The use of digital techniques to examine the intermittent region of a turbulent jet
Voltage signals, sampled at a high rate in the intermittent region of a round jet, are analyzed to provide instantaneous velocity vector information and measures of the vorticity and dissipation scales. A clustering routine to assess the feasibility of using the voltage readings to define the vortical, nonvortical state of the flow is also utilized. The results indicate that the clustering routine is partially successful; more sophisticated discrimination techniques will be required for a complete specification
A stochastic epidemiological model and a deterministic limit for BitTorrent-like peer-to-peer file-sharing networks
In this paper, we propose a stochastic model for a file-sharing peer-to-peer
network which resembles the popular BitTorrent system: large files are split
into chunks and a peer can download or swap from another peer only one chunk at
a time. We prove that the fluid limits of a scaled Markov model of this system
are of the coagulation form, special cases of which are well-known
epidemiological (SIR) models. In addition, Lyapunov stability and settling-time
results are explored. We derive conditions under which the BitTorrent
incentives under consideration result in shorter mean file-acquisition times
for peers compared to client-server (single chunk) systems. Finally, a
diffusion approximation is given and some open questions are discussed.Comment: 25 pages, 6 figure
Non-equilibrium fixed points of coupled Ising models
Driven-dissipative systems are expected to give rise to non-equilibrium
phenomena that are absent in their equilibrium counterparts. However, phase
transitions in these systems generically exhibit an effectively classical
equilibrium behavior in spite of their non-equilibrium origin. In this paper,
we show that multicritical points in such systems lead to a rich and genuinely
non-equilibrium behavior. Specifically, we investigate a driven-dissipative
model of interacting bosons that possesses two distinct phase transitions: one
from a high- to a low-density phase---reminiscent of a liquid-gas
transition---and another to an antiferromagnetic phase. Each phase transition
is described by the Ising universality class characterized by an (emergent or
microscopic) symmetry. They, however, coalesce at a
multicritical point, giving rise to a non-equilibrium model of coupled
Ising-like order parameters described by a
symmetry. Using a dynamical renormalization-group approach, we show that a pair
of non-equilibrium fixed points (NEFPs) emerge that govern the long-distance
critical behavior of the system. We elucidate various exotic features of these
NEFPs. In particular, we show that a generic continuous scale invariance at
criticality is reduced to a discrete scale invariance. This further results in
complex-valued critical exponents and spiraling phase boundaries, and it is
also accompanied by a complex Liouvillian gap even close to the phase
transition. As direct evidence of the non-equilibrium nature of the NEFPs, we
show that the fluctuation-dissipation relation is violated at all scales,
leading to an effective temperature that becomes "hotter" and "hotter" at
longer and longer wavelengths. Finally, we argue that this non-equilibrium
behavior can be observed in cavity arrays with cross-Kerr nonlinearities.Comment: 19+11 pages, 7+9 figure
Recommended from our members
The Relational Antecedents of Interpersonal Helping: ‘Quantity’, ‘Quality’ or Both?
Having a large network of colleagues means having several opportunities to help those colleagues, as well as a higher chance of receiving requests for help from them. Employees with large networks are therefore expected to help more in the workplace than those with small networks. However, large networks are also associated with cognitive costs, which may reduce the focal employee's ability to both recognize the need for help and engage in helping behaviours. For these reasons, the authors assert an inverted U-shaped relation between the size of an ego's social network and engagement in helping behaviour. However, high-quality relationships imply higher mutual understanding between the actors, and hence lower cognitive costs. In turn, the position (and threshold) of the curve between network size and interpersonal helping should be influenced by the quality of the relationship between the provider and the beneficiaries of help. Analysis of employee-level, single-firm data supports these ideas, providing preliminary evidence that quality of relationship compensates for the difficulties that may arise from having large social networks
Interferon-gamma and interleukin-10 production by mononuclear cells from patients with advanced head and neck cancer
OBJECTIVE: This study aims to evaluate the production of interferon-gamma and interleukin-10 by stimulated peripheral blood mononuclear cells isolated from patients with supraglottic laryngeal cancer before and after surgical treatment. METHODS: Fourteen patients with advanced supraglottic laryngeal cancer were studied. Cultures of peripheral blood mononuclear cells isolated during the preoperative and late postoperative periods were stimulated with concanavalin A and Bacille Calmette-Guerin, and the supernatant concentrations of interferon-gamma and interleukin-10 were measured. RESULTS: For non-stimulated cultures, the interferon-gamma levels produced by the preoperative period and the late postoperative period cultures were lower than the levels produced by the control group cultures. The interferon-gamma levels after stimulation with concanavalin A were higher in the late postoperative period cultures than in the preoperative evaluation cultures. Stimulation with Bacille Calmette-Guerin led to the production of similar levels of interferon-gamma and interleukin-10 by all cultures; thus, stimulation increased the levels of interferon-gamma produced by both the preoperative and postoperative cultures relative to the levels produced by the corresponding unstimulated cultures. CONCLUSION: Patients with advanced supraglottic laryngeal cancer exhibit an in vitro deficiency in interferongamma secretion by mononuclear cells. Stimulated cells seem to recover this function during the postoperative period
Interferon-gamma and interleukin-10 production by mononuclear cells from patients with advanced head and neck cancer
OBJECTIVE: This study aims to evaluate the production of interferon-gamma and interleukin-10 by stimulated peripheral blood mononuclear cells isolated from patients with supraglottic laryngeal cancer before and after surgical treatment. METHODS: Fourteen patients with advanced supraglottic laryngeal cancer were studied. Cultures of peripheral blood mononuclear cells isolated during the preoperative and late postoperative periods were stimulated with concanavalin A and Bacille Calmette-Guerin, and the supernatant concentrations of interferon-gamma and interleukin-10 were measured. RESULTS: For non-stimulated cultures, the interferon-gamma levels produced by the preoperative period and the late postoperative period cultures were lower than the levels produced by the control group cultures. The interferon-gamma levels after stimulation with concanavalin A were higher in the late postoperative period cultures than in the preoperative evaluation cultures. Stimulation with Bacille Calmette-Guerin led to the production of similar levels of interferon-gamma and interleukin-10 by all cultures; thus, stimulation increased the levels of interferon-gamma produced by both the preoperative and postoperative cultures relative to the levels produced by the corresponding unstimulated cultures. CONCLUSION: Patients with advanced supraglottic laryngeal cancer exhibit an in vitro deficiency in interferongamma secretion by mononuclear cells. Stimulated cells seem to recover this function during the postoperative period
- …