9,011 research outputs found
Indistinguishability of quantum states and rotation counting
We propose a quantum system in which the winding number of rotations of a
particle around a ring can be monitored and emerges as a physical observable.
We explicitly analyze the situation when, as a result of the monitoring of the
winding number, the period of the orbital motion of the particle is extended to
full rotations, which leads to changes in the energy spectrum and in all
observable properties. In particular, we show that in this case, the usual
magnetic flux period of the Aharonov-Bohm effect is reduced to
.Comment: 5 pages, 3 embedded figure
Experience-driven formation of parts-based representations in a model of layered visual memory
Growing neuropsychological and neurophysiological evidence suggests that the
visual cortex uses parts-based representations to encode, store and retrieve
relevant objects. In such a scheme, objects are represented as a set of
spatially distributed local features, or parts, arranged in stereotypical
fashion. To encode the local appearance and to represent the relations between
the constituent parts, there has to be an appropriate memory structure formed
by previous experience with visual objects. Here, we propose a model how a
hierarchical memory structure supporting efficient storage and rapid recall of
parts-based representations can be established by an experience-driven process
of self-organization. The process is based on the collaboration of slow
bidirectional synaptic plasticity and homeostatic unit activity regulation,
both running at the top of fast activity dynamics with winner-take-all
character modulated by an oscillatory rhythm. These neural mechanisms lay down
the basis for cooperation and competition between the distributed units and
their synaptic connections. Choosing human face recognition as a test task, we
show that, under the condition of open-ended, unsupervised incremental
learning, the system is able to form memory traces for individual faces in a
parts-based fashion. On a lower memory layer the synaptic structure is
developed to represent local facial features and their interrelations, while
the identities of different persons are captured explicitly on a higher layer.
An additional property of the resulting representations is the sparseness of
both the activity during the recall and the synaptic patterns comprising the
memory traces.Comment: 34 pages, 12 Figures, 1 Table, published in Frontiers in
Computational Neuroscience (Special Issue on Complex Systems Science and
Brain Dynamics),
http://www.frontiersin.org/neuroscience/computationalneuroscience/paper/10.3389/neuro.10/015.2009
A Generative Model of People in Clothing
We present the first image-based generative model of people in clothing for
the full body. We sidestep the commonly used complex graphics rendering
pipeline and the need for high-quality 3D scans of dressed people. Instead, we
learn generative models from a large image database. The main challenge is to
cope with the high variance in human pose, shape and appearance. For this
reason, pure image-based approaches have not been considered so far. We show
that this challenge can be overcome by splitting the generating process in two
parts. First, we learn to generate a semantic segmentation of the body and
clothing. Second, we learn a conditional model on the resulting segments that
creates realistic images. The full model is differentiable and can be
conditioned on pose, shape or color. The result are samples of people in
different clothing items and styles. The proposed model can generate entirely
new people with realistic clothing. In several experiments we present
encouraging results that suggest an entirely data-driven approach to people
generation is possible
Heavy Majorana neutrinos in e^-e^- collisions
We discuss the process mediated by heavy Majorana
neutrino exchange in the t- and u channel. In our model the cross section for
this reaction is a function of the masses (m_N) of the heavy Majorana neutrinos
and mixing parameters (U_{eN}) originating from mixing between the ordinary
left-handed standard model neutrinos and additional singlet right-handed
neutrino fields. Taking into account the standard model background and
contraints from low energy measurements, we present discovery limits in the
(m_N,U_{eN}^2) plane. We also discuss how to measure in principle the CP
violating phases, i.e., the relative phases between the mixing parameters.Comment: 18 pages with 7 postscript figures included, uses epsfig.st
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KQQKQQ and the Kasparov-World Game
The 1999 Kasparov-World game for the first time enabled anyone to join a team playing against a World Chess Champion via the web. It included a surprise in the opening, complex middle-game strategy and a deep ending. As the game headed for its mysterious finale, the World Team re-quested a KQQKQQ endgame table and was provided with two by the authors. This paper
describes their work, compares the methods used, examines the issues raised and summarises the concepts involved for the benefit of future workers in the endgame field. It also notes the contribution of this endgame to chess itself
Scalable and fast heterogeneous molecular simulation with predictive parallelization schemes
Multiscale and inhomogeneous molecular systems are challenging topics in the
field of molecular simulation. In particular, modeling biological systems in
the context of multiscale simulations and exploring material properties are
driving a permanent development of new simulation methods and optimization
algorithms. In computational terms, those methods require parallelization
schemes that make a productive use of computational resources for each
simulation and from its genesis. Here, we introduce the heterogeneous domain
decomposition approach which is a combination of an heterogeneity sensitive
spatial domain decomposition with an \textit{a priori} rearrangement of
subdomain-walls. Within this approach, the theoretical modeling and
scaling-laws for the force computation time are proposed and studied as a
function of the number of particles and the spatial resolution ratio. We also
show the new approach capabilities, by comparing it to both static domain
decomposition algorithms and dynamic load balancing schemes. Specifically, two
representative molecular systems have been simulated and compared to the
heterogeneous domain decomposition proposed in this work. These two systems
comprise an adaptive resolution simulation of a biomolecule solvated in water
and a phase separated binary Lennard-Jones fluid.Comment: 14 pages, 12 figure
Low B Field Magneto-Phonon Resonances in Single-Layer and Bilayer Graphene
Many-body effects resulting from strong electron-electron and electron-phonon
interactions play a significant role in graphene physics. We report on their
manifestation in low B field magneto-phonon resonances in high quality
exfoliated single-layer and bilayer graphene encapsulated in hexagonal boron
nitride. These resonances allow us to extract characteristic effective Fermi
velocities, as high as m/s, for the observed "dressed"
Landau level transitions, as well as the broadening of the resonances, which
increases with Landau level index
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