25,617 research outputs found
Anomalous Lorentz and CPT violation from a local Chern-Simons-like term in the effective gauge-field action
We consider four-dimensional chiral gauge theories defined over a spacetime
manifold with topology and periodic boundary
conditions over the compact dimension. The effective gauge-field action is
calculated for Abelian gauge fields which depend on all
four spacetime coordinates (including the coordinate of the
compact dimension) and have vanishing components (implying trivial
holonomies in the 4-direction). Our calculation shows that the effective
gauge-field action contains a local Chern-Simons-like term which violates
Lorentz and CPT invariance. This result is established perturbatively with a
generalized Pauli-Villars regularization and nonperturbatively with a lattice
regularization based on Ginsparg-Wilson fermions.Comment: 48 pages, v7: published versio
Statistics of the Kolkata Paise Restaurant Problem
We study the dynamics of a few stochastic learning strategies for the
'Kolkata Paise Restaurant' problem, where N agents choose among N equally
priced but differently ranked restaurants every evening such that each agent
tries get to dinner in the best restaurant (each serving only one customer and
the rest arriving there going without dinner that evening). We consider the
learning strategies to be similar for all the agents and assume that each
follow the same probabilistic or stochastic strategy dependent on the
information of the past successes in the game. We show that some 'naive'
strategies lead to much better utilization of the services than some relatively
'smarter' strategies. We also show that the service utilization fraction as
high as 0.80 can result for a stochastic strategy, where each agent sticks to
his past choice (independent of success achieved or not; with probability
decreasing inversely in the past crowd size). The numerical results for
utilization fraction of the services in some limiting cases are analytically
examined.Comment: 10 pages, 3 figs; accepted in New J Phy
Thermal elastohydrodynamic lubrication of line contacts
A numerical solution to the problem of thermal elastohydrodynamic lubrication of line contacts was obtained by using a finite difference formulation. The solution procedure consists of simultaneous solution of the thermal Reynolds equation, the elasticity equation, and the energy equation subject to appropriate boundary conditions. Pressure distribution, film shape, and temperature distribution were obtained for fully flooded conjunctions, a paraffinic lubricant, and various dimensionless speed parameters while the dimensionless load and materials parameters were held constant. Reduction in the minimum film thickness due to thermal effects (as a ratio of thermal to isothermal minimum film thickness) is given by a simple formula as a function of the thermal loading parameter Q: H(min)/H(min,I) = 10/10+ Q(0.4). Plots of pressure distribution, film shape, temperature distribution, and flow are shown for some representative cases
Simultaneous stabilization and simultaneous pole placement by nonswitching dynamic compensation
The 'simultaneous stabilization problem' is defined and theorems are proposed for its solution. The problem consists in answering the question: given an r-tuple G sub 1(s), G sub r(s) of p x m proper transfer functions, does there exist a compensator K(s) such that the closed loop systems G sub 1(s) (I+K(s)G sub 1(s)) (-1), G sub r(s) (I+K(s) G sub r(s)) (-1) are (internally) stable. This question arises in reliability theory, where G sub 2(s), G sub r(s) represents a plant G sub 1(s) operating in various modes of failure and K(s) is a nonswitching stabilizing compensator. It is important in the stability analysis and design of a plant which can be switched into various operating modes. The simultaneous stabilization problem can also apply to the stabilization of a nonlinear system which is linearized at several equilibria. Conditions are defined for pole placement and the generalized Sylvestor matrix is discussed
Three flavour Quark matter in chiral colour dielectric model
We investigate the properties of quark matter at finite density and
temperature using the nonlinear chiral extension of Colour Dielectric Model
(CCM). Assuming that the square of the meson fields devlop non- zero vacuum
expectation value, the thermodynamic potential for interacting three flavour
matter has been calculated. It is found that remain zero
in the medium whereas changes in the medium. As a result, and
quark masses decrease monotonically as the temperature and density of the quark
matter is increased.In the present model, the deconfinement density and
temperature is found to be lower compared to lattice results. We also study the
behaviour of pressure and energy density above critical temperature.Comment: Latex file. 5 figures available on request. To appear in Phys. Rev.
Growth of preferential attachment random graphs via continuous-time branching processes
A version of ``preferential attachment'' random graphs, corresponding to
linear ``weights'' with random ``edge additions,'' which generalizes some
previously considered models, is studied. This graph model is embedded in a
continuous-time branching scheme and, using the branching process apparatus,
several results on the graph model asymptotics are obtained, some extending
previous results, such as growth rates for a typical degree and the maximal
degree, behavior of the vertex where the maximal degree is attained, and a law
of large numbers for the empirical distribution of degrees which shows certain
``scale-free'' or ``power-law'' behaviors.Comment: 20 page
Study of QCD generalized ghost dark energy in FRW universe
A phenomenological generalized ghost dark energy model has been studied under
the framework of FRW universe. In ghost dark energy model the energy density
depends linearly on Hubble parameter (H) but in this dark energy model, the
energy density contains a the sub-leading term which is depends on , so the energy density takes the form ,
where and are the constants. The solutions of the Friedman
equation of our model leads to a stable universe. We have fitted our model with
the present observational data including Stern data set. With the help of best
fit results we find the adiabatic sound speed remains positive throughout the
cosmic evolution, that claims the stability of the model. The flipping of the
signature of deceleration parameter at the value of scale factor
indicates that the universe is at the stage of acceleration i.e. de Sitter
phase of the universe at late time. Our model shows that the acceleration of
the universe begin at redshift and the model is also
consistent with the current observational data.Comment: 9 pages, 9 figure
Multi-Channel Scheduling for Fast Convergecast in Wireless Sensor Networks
We explore the following fundamental question -
how fast can information be collected from a wireless sensor
network? We consider a number of design parameters such
as, power control, time and frequency scheduling, and routing.
There are essentially two factors that hinder efficient data
collection - interference and the half-duplex single-transceiver
radios. We show that while power control helps in reducing the
number of transmission slots to complete a convergecast under a
single frequency channel, scheduling transmissions on different
frequency channels is more efficient in mitigating the effects of
interference (empirically, 6 channels suffice for most 100-node
networks). With these observations, we define a receiver-based
channel assignment problem, and prove it to be NP-complete on
general graphs. We then introduce a greedy channel assignment
algorithm that efficiently eliminates interference, and compare
its performance with other existing schemes via simulations.
Once the interference is completely eliminated, we show that
with half-duplex single-transceiver radios the achievable schedule
length is lower-bounded by max(2nk − 1,N), where nk is the
maximum number of nodes on any subtree and N is the number
of nodes in the network. We modify an existing distributed time
slot assignment algorithm to achieve this bound when a suitable
balanced routing scheme is employed. Through extensive simulations,
we demonstrate that convergecast can be completed within
up to 50% less time slots, in 100-node networks, using multiple
channels as compared to that with single-channel communication.
Finally, we also demonstrate further improvements that are
possible when the sink is equipped with multiple transceivers
or when there are multiple sinks to collect data
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