3,783 research outputs found
The many-body localization phase transition
We use exact diagonalization to explore the many-body localization transition
in a random-field spin-1/2 chain. We examine the correlations within each
many-body eigenstate, looking at all high-energy states and thus effectively
working at infinite temperature. For weak random field the eigenstates are
thermal, as expected in this nonlocalized, "ergodic" phase. For strong random
field the eigenstates are localized, with only short-range entanglement. We
roughly locate the localization transition and examine some of its finite-size
scaling, finding that this quantum phase transition at nonzero temperature
might be showing infinite-randomness scaling with a dynamic critical exponent
.Comment: 7 pages, 8 figures. Extended version of arXiv:1003.2613v
Improving Facial Analysis and Performance Driven Animation through Disentangling Identity and Expression
We present techniques for improving performance driven facial animation,
emotion recognition, and facial key-point or landmark prediction using learned
identity invariant representations. Established approaches to these problems
can work well if sufficient examples and labels for a particular identity are
available and factors of variation are highly controlled. However, labeled
examples of facial expressions, emotions and key-points for new individuals are
difficult and costly to obtain. In this paper we improve the ability of
techniques to generalize to new and unseen individuals by explicitly modeling
previously seen variations related to identity and expression. We use a
weakly-supervised approach in which identity labels are used to learn the
different factors of variation linked to identity separately from factors
related to expression. We show how probabilistic modeling of these sources of
variation allows one to learn identity-invariant representations for
expressions which can then be used to identity-normalize various procedures for
facial expression analysis and animation control. We also show how to extend
the widely used techniques of active appearance models and constrained local
models through replacing the underlying point distribution models which are
typically constructed using principal component analysis with
identity-expression factorized representations. We present a wide variety of
experiments in which we consistently improve performance on emotion
recognition, markerless performance-driven facial animation and facial
key-point tracking.Comment: to appear in Image and Vision Computing Journal (IMAVIS
Number of fermion generations from a novel Grand Unified model
Electroweak interactions based on a gauge group ,
coupled to the QCD gauge group , can predict the number of
generations to be multiples of three. We first try to unify these models within
SU(N) groups, using antisymmetric tensor representations only. After examining
why these attempts fail, we continue to search for an SU(N) GUT that can
explain the number of fermion generations. We show that such a model can be
found for , with fermions in antisymmetric rank-1 and rank-3
representations only, and examine the constraints on various masses in the
model coming from the requirement of unification.Comment: 17 pages, 1 eps figur
Learning to Crawl
Web crawling is the problem of keeping a cache of webpages fresh, i.e.,
having the most recent copy available when a page is requested. This problem is
usually coupled with the natural restriction that the bandwidth available to
the web crawler is limited. The corresponding optimization problem was solved
optimally by Azar et al. [2018] under the assumption that, for each webpage,
both the elapsed time between two changes and the elapsed time between two
requests follow a Poisson distribution with known parameters. In this paper, we
study the same control problem but under the assumption that the change rates
are unknown a priori, and thus we need to estimate them in an online fashion
using only partial observations (i.e., single-bit signals indicating whether
the page has changed since the last refresh). As a point of departure, we
characterise the conditions under which one can solve the problem with such
partial observability. Next, we propose a practical estimator and compute
confidence intervals for it in terms of the elapsed time between the
observations. Finally, we show that the explore-and-commit algorithm achieves
an regret with a carefully chosen exploration horizon.
Our simulation study shows that our online policy scales well and achieves
close to optimal performance for a wide range of the parameters.Comment: Published at AAAI 202
Employing endogenous access pricing to enhance incentives for efficient upstream operation
Endogenous access pricing (ENAP) is an alternative to the more traditional form of access pricing that sets the access price to reflect the regulator’s estimate of the supplier’s average cost of providing access. Under ENAP, the access price reflects the supplier’s actual average cost of providing access, which varies with realized industry output. We show that in addition to eliminating the need to estimate industry output accurately and avoiding a divergence between upstream revenues and costs, ENAP can enhance the incentive of a vertically integrated producer to minimize its upstream operating cost
Energy transport in disordered classical spin chains
We present a numerical study of the diffusion of energy at high temperature
in strongly disordered chains of interacting classical spins evolving
deterministically. We find that quenched randomness strongly suppresses
transport, with the diffusion constant becoming reduced by several orders of
magnitude upon the introduction of moderate disorder. We have also looked for
but not found signs of a classical many-body localization transition at any
nonzero strength of the spin-spin interactions
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