23,567 research outputs found
Cycled operation of water vapor electrolysis cell Annual report, 1 Jan. - 31 Dec. 1969
Mathematical model of heat, mass, and momentum relationships in cyclic operation of water vapor electrolytic cell, and equilibrium conditions between gel matrix and vapo
Fingering Instability in a Water-Sand Mixture
The temporal evolution of a water-sand interface driven by gravity is
experimentally investigated. By means of a Fourier analysis of the evolving
interface the growth rates are determined for the different modes appearing in
the developing front. To model the observed behavior we apply the idea of the
Rayleigh-Taylor instability for two stratified fluids. Carrying out a linear
stability analysis we calculate the growth rates from the corresponding
dispersion relations for finite and infinite cell sizes. Based on the
theoretical results the viscosity of the suspension is estimated to be
approximately 100 times higher than that of pure water, in agreement with other
experimental findings.Comment: 11 pages, 12 figures, RevTeX; final versio
Storage capacity of correlated perceptrons
We consider an ensemble of single-layer perceptrons exposed to random
inputs and investigate the conditions under which the couplings of these
perceptrons can be chosen such that prescribed correlations between the outputs
occur. A general formalism is introduced using a multi-perceptron costfunction
that allows to determine the maximal number of random inputs as a function of
the desired values of the correlations. Replica-symmetric results for and
are compared with properties of two-layer networks of tree-structure and
fixed Boolean function between hidden units and output. The results show which
correlations in the hidden layer of multi-layer neural networks are crucial for
the value of the storage capacity.Comment: 16 pages, Latex2
Hadronic multiparticle production in extensive air showers and accelerator experiments
Using CORSIKA for simulating extensive air showers, we study the relation
between the shower characteristics and features of hadronic multiparticle
production at low energies. We report about investigations of typical energies
and phase space regions of secondary particles which are important for muon
production in extensive air showers. Possibilities to measure relevant
quantities of hadron production in existing and planned accelerator experiments
are discussed.Comment: To be published in Proceedings of ICRC 2005, 29th International
Cosmic Ray Conferenc
Thermodynamics of the L\'evy spin glass
We investigate the L\'evy glass, a mean-field spin glass model with power-law
distributed couplings characterized by a divergent second moment. By combining
extensively many small couplings with a spare random backbone of strong bonds
the model is intermediate between the Sherrington-Kirkpatrick and the
Viana-Bray model. A truncated version where couplings smaller than some
threshold \eps are neglected can be studied within the cavity method
developed for spin glasses on locally tree-like random graphs. By performing
the limit \eps\to 0 in a well-defined way we calculate the thermodynamic
functions within replica symmetry and determine the de Almeida-Thouless line in
the presence of an external magnetic field. Contrary to previous findings we
show that there is no replica-symmetric spin glass phase. Moreover we determine
the leading corrections to the ground-state energy within one-step replica
symmetry breaking. The effects due to the breaking of replica symmetry appear
to be small in accordance with the intuitive picture that a few strong bonds
per spin reduce the degree of frustration in the system
Correlations between hidden units in multilayer neural networks and replica symmetry breaking
We consider feed-forward neural networks with one hidden layer, tree
architecture and a fixed hidden-to-output Boolean function. Focusing on the
saturation limit of the storage problem the influence of replica symmetry
breaking on the distribution of local fields at the hidden units is
investigated. These field distributions determine the probability for finding a
specific activation pattern of the hidden units as well as the corresponding
correlation coefficients and therefore quantify the division of labor among the
hidden units. We find that although modifying the storage capacity and the
distribution of local fields markedly replica symmetry breaking has only a
minor effect on the correlation coefficients. Detailed numerical results are
provided for the PARITY, COMMITTEE and AND machines with K=3 hidden units and
nonoverlapping receptive fields.Comment: 9 pages, 3 figures, RevTex, accepted for publication in Phys. Rev.
Comment: Superconducting transition in Nb nanowires fabricated using focused ion beam
In a recent paper Tettamanzi et al (2009 Nanotechnology \bf{20} 465302)
describe the fabrication of superconducting Nb nanowires using a focused ion
beam. They interpret their conductivity data in the framework of thermal and
quantum phase slips below . In the following we will argue that their
analysis is inappropriate and incomplete, leading to contradictory results.
Instead, we propose an interpretation of the data within a SN proximity model.Comment: 3 pages, 1 figure accepted in Nanotechnolog
Spin Hall effect in a system of Dirac fermions in the honeycomb lattice with intrinsic and Rashba spin-orbit interaction
We consider spin Hall effect in a system of massless Dirac fermions in a
graphene lattice. Two types of spin-orbit interaction, pertinent to the
graphene lattice, are taken into account - the intrinsic and Rashba terms.
Assuming perfect crystal lattice, we calculate the topological contribution to
spin Hall conductivity. When both interactions are present, their interplay is
shown to lead to some peculiarities in the dependence of spin Hall conductivity
on the Fermi level.Comment: 7 pages, 5 figure
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