2,182 research outputs found
Asynchronous Gossip for Averaging and Spectral Ranking
We consider two variants of the classical gossip algorithm. The first variant
is a version of asynchronous stochastic approximation. We highlight a
fundamental difficulty associated with the classical asynchronous gossip
scheme, viz., that it may not converge to a desired average, and suggest an
alternative scheme based on reinforcement learning that has guaranteed
convergence to the desired average. We then discuss a potential application to
a wireless network setting with simultaneous link activation constraints. The
second variant is a gossip algorithm for distributed computation of the
Perron-Frobenius eigenvector of a nonnegative matrix. While the first variant
draws upon a reinforcement learning algorithm for an average cost controlled
Markov decision problem, the second variant draws upon a reinforcement learning
algorithm for risk-sensitive control. We then discuss potential applications of
the second variant to ranking schemes, reputation networks, and principal
component analysis.Comment: 14 pages, 7 figures. Minor revisio
Particle simulation of vibrated gas-fluidized beds of cohesive fine powders
We use three-dimensional particle dynamics simulations, coupled with
volume-averaged gas phase hydrodynamics, to study vertically vibrated
gas-fluidized beds of fine, cohesive powders. The volume-averaged interstitial
gas flow is restricted to be one-dimensional (1D). This simplified model
captures the spontaneous development of 1D traveling waves, which corresponds
to bubble formation in real fluidized beds. We use this model to probe the
manner in which vibration and gas flow combine to influence the dynamics of
cohesive particles. We find that as the gas flow rate increases, cyclic
pressure pulsation produced by vibration becomes more and more significant than
direct impact, and in a fully fluidized bed this pulsation is virtually the
only relevant mechanism. We demonstrate that vibration assists fluidization by
creating large tensile stresses during transient periods, which helps break up
the cohesive assembly into agglomerates.Comment: to appear in I&EC Research, a special issue (Oct. 2006) in honor of
Prof. William B. Russe
Coarse Bifurcation Studies of Bubble Flow Microscopic Simulations
The parametric behavior of regular periodic arrays of rising bubbles is
investigated with the aid of 2-dimensional BGK Lattice-Boltzmann (LB)
simulators. The Recursive Projection Method is implemented and coupled to the
LB simulators, accelerating their convergence towards what we term coarse
steady states. Efficient stability/bifurcation analysis is performed by
computing the leading eigenvalues/eigenvectors of the coarse time stepper. Our
approach constitutes the basis for system-level analysis of processes modeled
through microscopic simulations.Comment: 4 pages, 3 figure
A case for adaptive sub-carrier level power allocation in OFDMA networks
In today's OFDMA networks, the transmission power is typically fixed and the same for all the sub-carriers that compose a channel. The sub-carriers though, experience different degrees of fading and thus, the received power is different for different sub-carriers; while some frequencies experience deep fades, others are relatively unaffected. In this paper, we make a case of redistributing the power across the sub-carriers (subject to a fixed power budget constraint) to better cope with this frequency selectivity. Specifically, we design a joint power and rate adaptation scheme (called JPRA for short) wherein power redistribution is combined with sub-carrier level rate adaptation to yield significant throughput benefits. We further consider two variants of JPRA: (a) JPRA-CR where, the power is redistributed across sub-carriers so as to support a maximum common rate (CR) across sub-carriers and (b) JPRA-MT where, the goal is to redistribute power such that the transmission time of a packet is minimized. While the first variant decreases transceiver complexity and is simpler, the second is geared towards achieving the maximum throughput possible. We implement both variants of JPRA on our WARP radio testbed. Our extensive experiments demonstrate that our scheme provides a 35% improvement in total network throughput in testbed experiments compared to FARA, a scheme where only sub-carrier level rate adaptation is used. We also perform simulations to demonstrate the efficacy of JPRA in larger scale networks. © 2012 ACM
A study of representations for pen based handwriting recognition of tamil characters
In this paper we study the important issue of choosing representations that are suitable for recognizing pen based handwriting of characters in Tamil, a language of India. Four different choices, based on the following set of features are considered: (1) a sequence of directions and curvature; (2) a sequence of angles; (3) Fourier transform coefficients; and (4) wavelet features. We provide arguments in support of the representation using wavelet features. A neural network designed using these features gives excellent accuracy for recognizing Tamil characters
Asymptotics of the Invariant Measure in Mean Field Models with Jumps
We consider the asymptotics of the invariant measure for the process of the
empirical spatial distribution of coupled Markov chains in the limit of a
large number of chains. Each chain reflects the stochastic evolution of one
particle. The chains are coupled through the dependence of the transition rates
on this spatial distribution of particles in the various states. Our model is a
caricature for medium access interactions in wireless local area networks. It
is also applicable to the study of spread of epidemics in a network. The
limiting process satisfies a deterministic ordinary differential equation
called the McKean-Vlasov equation. When this differential equation has a unique
globally asymptotically stable equilibrium, the spatial distribution
asymptotically concentrates on this equilibrium. More generally, its limit
points are supported on a subset of the -limit sets of the
McKean-Vlasov equation. Using a control-theoretic approach, we examine the
question of large deviations of the invariant measure from this limit.Comment: 58 pages, reorganised to get quickly to the main results on invariant
measure; Stochastic Systems, volume 2, 201
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