2,044 research outputs found
Storage Capacity of Two-dimensional Neural Networks
We investigate the maximum number of embedded patterns in the two-dimensional
Hopfield model. The grand state energies of two specific network states,
namely, the energies of the pure-ferromagnetic state and the state of specific
one stored pattern are calculated exactly in terms of the correlation function
of the ferromagnetic Ising model. We also investigate the energy landscape
around them by computer simulations. Taking into account the qualitative
features of the phase diagrams obtained by Nishimori, Whyte and Sherrington
[Phys. Rev. E {\bf 51}, 3628 (1995)], we conclude that the network cannot
retrieve more than three patterns.Comment: 13pages, 7figures, revtex
Synthesis and physicochemical properties of spherical catalysts based on TiO2-SiO2/MxOy, where M - Co, Cr
Catalysts TiO2-SiO2 composition in the form of hollow spheres modified cobalt and chromium was obtained. Spatial structure of spherical samples after heat treatment was study by method of 3D microtomography. Status cations of transition elements and titanium was characterized by UV-Vis DRS. The catalysts were tested in the oxidation reaction of heptane
A Systematic Comparison of Tropical Waves over Northern Africa. Part II: Dynamics and Thermodynamics
This study presents the first systematic comparison of the dynamics and thermodynamics associated with all
major tropical wave types causing rainfall modulation over northern tropical Africa: the Madden–Julian
oscillation (MJO), equatorial Rossby waves (ERs), tropical disturbances (TDs, including African easterly
waves), Kelvin waves, mixed Rossby–gravity waves (MRGs), and eastward inertio-gravity waves (EIGs).
Reanalysis and radiosonde data were analyzed for the period 1981–2013 based on space–time filtering of
outgoing longwave radiation. The identified circulation patterns are largely consistent with theory. The slow
modes, MJO and ER, mainly impact precipitable water, whereas the faster TDs, Kelvin waves, and MRGs
primarily modulate moisture convergence. Monsoonal inflow intensifies during wet phases of the MJO, ERs,
and MRGs, associated with a northward shift of the intertropical discontinuity for MJO and ERs. This study
reveals that MRGs over Africa have a distinct dynamical structure that differs significantly from AEWs.
During passages of vertically tilted imbalanced wave modes, such as the MJO, TDs, Kelvin waves, and partly
MRG waves, increased vertical wind shear and improved conditions for up- and downdrafts facilitate the
organization of mesoscale convective systems. The balanced ERs are not tilted, and rainfall is triggered by
large-scale moistening and stratiform lifting. The MJO and ERs interact with intraseasonal variations of the
Indian monsoon and extratropical Rossby wave trains. The latter causes a trough over the Atlas Mountains
associated with a tropical plume and rainfall over the Sahara. The presented results unveil which dynamical
processes need to be modeled realistically to represent the coupling between tropical waves and rainfall in
northern tropical Afric
An Unusual Suspect in Cocaine Addiction
Development of drug addiction is extremely complex, but its initiation can be as simple as the flip-flop of glutamatergic receptor subtypes triggered by an “unusual” type of NMDA receptors, as suggested by Yuan et al. (2013) in this issue of Neuron
On the Geometry of Supersymmetric Quantum Mechanical Systems
We consider some simple examples of supersymmetric quantum mechanical systems
and explore their possible geometric interpretation with the help of geometric
aspects of real Clifford algebras. This leads to natural extensions of the
considered systems to higher dimensions and more complicated potentials.Comment: 18 page
Non-ergodic one-magnon magnetization dynamics of the antiferromagnetic delta chain
We investigate the one-magnon dynamics of the antiferromagnetic delta chain
as a paradigmatic example of tunable equilibration. Depending on the ratio of
nearest and next-nearest exchange interactions the spin system exhibits a flat
band in one-magnon space - in this case equilibration happens only partially,
whereas it appears to be complete with dispersive bands as generally expected
for generic Hamiltonians. We provide analytical as well as numerical insight
into the phenomenon.Comment: 7 pages, 10 figure
Intrinsic peculiarities of real material realizations of a spin-1/2 kagome lattice
Spin-1/2 magnets with kagome geometry, being for years a generic object of
theoretical investigations, have few real material realizations. Recently, a
DFT-based microscopic model for two such materials, kapellasite Cu3Zn(OH)6Cl2
and haydeeite Cu3Mg(OH)6Cl2, was presented [O. Janson, J. Richter and H.
Rosner, arXiv:0806.1592]. Here, we focus on the intrinsic properties of real
spin-1/2 kagome materials having influence on the magnetic ground state and the
low-temperature excitations. We find that the values of exchange integrals are
strongly dependent on O--H distance inside the hydroxyl groups, present in most
spin-1/2 kagome compounds up to date. Besides the original kagome model,
considering only the nearest neighbour exchange, we emphasize the crucial role
of the exchange along the diagonals of the kagome lattice.Comment: 4 pages, 4 figures. A paper for the proceedings of the HFM 2008
conferenc
Derivation of Boltzmann Principle
We present a derivation of Boltzmann principle
based on classical mechanical models of thermodynamics. The argument is based
on the heat theorem and can be traced back to the second half of the nineteenth
century with the works of Helmholtz and Boltzmann. Despite its simplicity, this
argument has remained almost unknown. We present it in a modern, self-contained
and accessible form. The approach constitutes an important link between
classical mechanics and statistical mechanics
Inlet conditions for large eddy simulation of gas-turbine swirl injectors
Copyright © 2008 American Institute of Aeronautics and AstronauticsIn this paper, we present a novel technique for generating swirl inlets for large eddy simulation. The velocity a short distance downstream of the inlet to the main domain is sampled and the flow velocity data are reintroduced back into the domain inlet, creating an inlet section integrated into the main domain in which turbulence can develop.
Additionally, variable artificial body forces and velocity corrections are imposed in this inlet section, with feedback control to force the flow toward desired swirl, mean, and turbulent profiles. The method was applied to flow in an axisymmetric sudden expansion, with and without swirl at the inlet, and compared against experimental and literature large eddy simulation data and against similar results in the literature. The method generates excellent results for this case and is elegant and straightforward to implement
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