336 research outputs found
Network Plasticity as Bayesian Inference
General results from statistical learning theory suggest to understand not
only brain computations, but also brain plasticity as probabilistic inference.
But a model for that has been missing. We propose that inherently stochastic
features of synaptic plasticity and spine motility enable cortical networks of
neurons to carry out probabilistic inference by sampling from a posterior
distribution of network configurations. This model provides a viable
alternative to existing models that propose convergence of parameters to
maximum likelihood values. It explains how priors on weight distributions and
connection probabilities can be merged optimally with learned experience, how
cortical networks can generalize learned information so well to novel
experiences, and how they can compensate continuously for unforeseen
disturbances of the network. The resulting new theory of network plasticity
explains from a functional perspective a number of experimental data on
stochastic aspects of synaptic plasticity that previously appeared to be quite
puzzling.Comment: 33 pages, 5 figures, the supplement is available on the author's web
page http://www.igi.tugraz.at/kappe
If It Looks Like a Vessel: The Supreme Court’s “Reasonable Observer” Test for Vessel Status
What is a vessel? In maritime law, important rights and duties turn on whether something is a vessel. For example, the owner of a vessel can limit his liability for damages caused by the vessel under the Limitation of Shipowners’ Liability Act, and an injured seaman who is a member of the crew of a vessel can claim remedies under the Jones Act. Under the general maritime law, a vendor who repairs or supplies a vessel may acquire a maritime lien over the vessel. In these and other areas, vessel status plays a crucial role in setting the limits of admiralty jurisdiction. Clear boundaries are important because with admiralty jurisdiction comes the application of substantive maritime law—the specialized body of statutory and judge-made law that governs maritime commerce and navigation
Single-file transport of binary hard-sphere mixtures through periodic potentials
Single-file transport occurs in various scientific fields, including
diffusion through nanopores, nanofluidic devices, and cellular processes. We
here investigate the impact of polydispersity on particle currents for
single-file Brownian motion of hard spheres, when they are driven through
periodic potentials by a constant drag force. Through theoretical analysis and
extensive Brownian dynamics simulations, we unveil the behavior of particle
currents for random binary mixtures. The particle currents show a recurring
pattern in dependence of the hard-sphere diameters and mixing ratio. We explain
this recurrent behavior by showing that a basic unit cell exists in the space
of the two hard-sphere diameters. Once the behavior of an observable inside the
unit cell is determined, it can be inferred for any diameter. The overall
variation of particle currents with the mixing ratio and hard-sphere diameters
is reflected by their variation in the limit where the system is fully covered
by hard spheres. In this limit, the currents can be predicted analytically. Our
analysis explains the occurrence of pronounced maxima and minima of the
currents by changes of an effective potential barrier for the center-of-mass
motion.Comment: 9 pages, 6 figure
Fundamental questions relating to ion conduction in disordered solids
A number of basic scientific questions relating to ion conduction in
homogeneously disordered solids are discussed. The questions deal with how to
define the mobile ion density, what can be learned from electrode effects, what
is the ion transport mechanism, the role of dimensionality, and what are the
origins of the mixed-alkali effect, of time-temperature superposition, and of
the nearly-constant loss. Answers are suggested to some of these questions, but
the main purpose of the paper is to draw attention to the fact that this field
of research still presents several fundamental challenges.Comment: Reports on Progress in Physics, to appea
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