10,562 research outputs found
Density-feedback control in traffic and transport far from equilibrium
A bottleneck situation in one-lane traffic-flow is typically modelled with a
constant demand of entering cars. However, in practice this demand may depend
on the density of cars in the bottleneck. The present paper studies a simple
bimodal realization of this mechanism to which we refer to as density-feedback
control (DFC): If the actual density in the bottleneck is above a certain
threshold, the reservoir density of possibly entering cars is reduced to a
different constant value. By numerical solution of the discretized viscid
Burgers equation a rich stationary phase diagram is found. In order to maximize
the flow, which is the goal of typical traffic-management strategies, we find
the optimal choice of the threshold. Analytical results are verified by
computer simulations of the microscopic TASEP with DFC.Comment: 7 pages, 5 figure
Stationary distributions of multi-type totally asymmetric exclusion processes
We consider totally asymmetric simple exclusion processes with n types of
particle and holes (-TASEPs) on and on the cycle . Angel recently gave an elegant construction of the stationary measures
for the 2-TASEP, based on a pair of independent product measures. We show that
Angel's construction can be interpreted in terms of the operation of a
discrete-time queueing server; the two product measures correspond to
the arrival and service processes of the queue. We extend this construction to
represent the stationary measures of an n-TASEP in terms of a system of queues
in tandem. The proof of stationarity involves a system of n 1-TASEPs, whose
evolutions are coupled but whose distributions at any fixed time are
independent. Using the queueing representation, we give quantitative results
for stationary probabilities of states of the n-TASEP on , and
simple proofs of various independence and regeneration properties for systems
on .Comment: Published at http://dx.doi.org/10.1214/009117906000000944 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Do Central Banks have Precautionary Demands for Expansions and for Price Stability?
This paper analyses the impact of asymmetric preferences with respect to inflation and output by policymakers on interest-rate reaction functions. A theoretical framework which makes it possible to identify the dominant type of asymmetry is developed and related to the precautionary demand of pol- icymakers for expansions and for low inßation. Using data for some G7 economies, the paper shows that, except for Germany, nonlinear and asym- metric behaviour is present. A main Þnding is that where credibility-building and disinflation has already been achieved, the monetary authorities develop a greater precautionary demand for output expansions than for low inflation. This may generate a new type of inflation bias. Conversely, where credibility- building is still a concern for the authorities, managing the business cycle is dominated by concerns of the monetary authorities to keep inflation expec- tations low.
Grain boundary energies and cohesive strength as a function of geometry
Cohesive laws are stress-strain curves used in finite element calculations to
describe the debonding of interfaces such as grain boundaries. It would be
convenient to describe grain boundary cohesive laws as a function of the
parameters needed to describe the grain boundary geometry; two parameters in 2D
and 5 parameters in 3D. However, we find that the cohesive law is not a smooth
function of these parameters. In fact, it is discontinuous at geometries for
which the two grains have repeat distances that are rational with respect to
one another. Using atomistic simulations, we extract grain boundary energies
and cohesive laws of grain boundary fracture in 2D with a Lennard-Jones
potential for all possible geometries which can be simulated within periodic
boundary conditions with a maximum box size. We introduce a model where grain
boundaries are represented as high symmetry boundaries decorated by extra
dislocations. Using it, we develop a functional form for the symmetric grain
boundary energies, which have cusps at all high symmetry angles. We also find
the asymptotic form of the fracture toughness near the discontinuities at high
symmetry grain boundaries using our dislocation decoration model.Comment: 12 pages, 19 figures, changed titl
The fluctuations of the giant cluster for percolation on random split trees
A split tree of cardinality is constructed by distributing "balls" in
a subset of vertices of an infinite tree which encompasses many types of random
trees such as -ary search trees, quad trees, median-of- trees,
fringe-balanced trees, digital search trees and random simplex trees. In this
work, we study Bernoulli bond percolation on arbitrary split trees of large but
finite cardinality . We show for appropriate percolation regimes that depend
on the cardinality of the split tree that there exists a unique giant
cluster, the fluctuations of the size of the giant cluster as are described by an infinitely divisible distribution that belongs to
the class of stable Cauchy laws. This work generalizes the results for the
random -ary recursive trees in Berzunza (2015). Our approach is based on a
remarkable decomposition of the size of the giant percolation cluster as a sum
of essentially independent random variables which may be useful for studying
percolation on other trees with logarithmic height; for instance in this work
we study also the case of regular trees.Comment: 43 page
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