11,428 research outputs found
Avoiding Braess' Paradox through Collective Intelligence
In an Ideal Shortest Path Algorithm (ISPA), at each moment each router in a
network sends all of its traffic down the path that will incur the lowest cost
to that traffic. In the limit of an infinitesimally small amount of traffic for
a particular router, its routing that traffic via an ISPA is optimal, as far as
cost incurred by that traffic is concerned. We demonstrate though that in many
cases, due to the side-effects of one router's actions on another routers
performance, having routers use ISPA's is suboptimal as far as global aggregate
cost is concerned, even when only used to route infinitesimally small amounts
of traffic. As a particular example of this we present an instance of Braess'
paradox for ISPA's, in which adding new links to a network decreases overall
throughput. We also demonstrate that load-balancing, in which the routing
decisions are made to optimize the global cost incurred by all traffic
currently being routed, is suboptimal as far as global cost averaged across
time is concerned. This is also due to "side-effects", in this case of current
routing decision on future traffic.
The theory of COllective INtelligence (COIN) is concerned precisely with the
issue of avoiding such deleterious side-effects. We present key concepts from
that theory and use them to derive an idealized algorithm whose performance is
better than that of the ISPA, even in the infinitesimal limit. We present
experiments verifying this, and also showing that a machine-learning-based
version of this COIN algorithm in which costs are only imprecisely estimated (a
version potentially applicable in the real world) also outperforms the ISPA,
despite having access to less information than does the ISPA. In particular,
this COIN algorithm avoids Braess' paradox.Comment: 28 page
Using Collective Intelligence to Route Internet Traffic
A COllective INtelligence (COIN) is a set of interacting reinforcement
learning (RL) algorithms designed in an automated fashion so that their
collective behavior optimizes a global utility function. We summarize the
theory of COINs, then present experiments using that theory to design COINs to
control internet traffic routing. These experiments indicate that COINs
outperform all previously investigated RL-based, shortest path routing
algorithms.Comment: 7 page
Expansion of an interacting Fermi gas
We study the expansion of a dilute ultracold sample of fermions initially
trapped in a anisotropic harmonic trap. The expansion of the cloud provides
valuable information about the state of the system and the role of
interactions. In particular the time evolution of the deformation of the
expanding cloud behaves quite differently depending on whether the system is in
the normal or in the superfluid phase. For the superfluid phase, we predict an
inversion of the deformation of the sample, similarly to what happens with
Bose-Einstein condensates. Viceversa, in the normal phase, the inversion of the
aspect ratio is never achieved, if the mean field interaction is attractive and
collisions are negligible.Comment: 4 pages, 3 figures, final versio
Calculation of the microcanonical temperature for the classical Bose field
The ergodic hypothesis asserts that a classical mechanical system will in
time visit every available configuration in phase space. Thus, for an ergodic
system, an ensemble average of a thermodynamic quantity can equally well be
calculated by a time average over a sufficiently long period of dynamical
evolution. In this paper we describe in detail how to calculate the temperature
and chemical potential from the dynamics of a microcanonical classical field,
using the particular example of the classical modes of a Bose-condensed gas.
The accurate determination of these thermodynamics quantities is essential in
measuring the shift of the critical temperature of a Bose gas due to
non-perturbative many-body effects.Comment: revtex4, 10 pages, 1 figure. v2: updated to published version. Fuller
discussion of numerical results, correction of some minor error
One-electron spectral functions of the attractive Hubbard model at intermediate coupling
We calculate the one-electron spectral function of the attractive-U Hubbard
model in two dimensions. We work in the intermediate coupling and low density
regime and evaluate analytically the self-energy. The results are obtained in a
framework based on the self-consistent T-matrix approximation. We also
calculate the chemical potential of the bound pairs as a function of
temperature. On the basis of this calculation we analyze the low-temperature
resistivity and specific heat in the normal state of this system. We compare
our results with recent beautiful tunneling experiments in the underdoped
regime of HTSC-materials.Comment: 2 pages, LT22 Conference paper, phbauth and elsart style files
include
Positive reinforcement as an intervention for children with attention deficit hyperactivity disorder and schizoid personality disorder
Positive reinforcement is effective when used as an intervention for children with inappropriate behaviors. Children with the diagnosis of Schizoid Personality Disorder (SP) and/or Attention Deficit Hyperactivity Disorder (ADHD) may exhibit inappropriate behaviors that inhibit their quality of life. When appropriate behaviors are paired with rewards or reinforcements, there is an increase in the likelihood of such behaviors reoccurring. When four appropriate behaviors were reinforced by stickers for a child with SP and ADHD, the behaviors increased, therefore inappropriate behaviors decreased. The data that was collected was analyzed by a two-way ANOVA test. Several types of reinforcement interventions were researched and discussed
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