678 research outputs found
Low-temperature thermal conductivity in polycrystalline graphene
The low-temperature thermal conductivity in polycrystalline graphene is
theoretically studied. The contributions from three branches of acoustic
phonons are calculated by taking into account scattering on sample borders,
point defects and grain boundaries. Phonon scattering due to sample borders and
grain boundaries is shown to result in a -behaviour in the thermal
conductivity where varies between 1 and 2. This behaviour is found to
be more pronounced for nanosized grain boundaries.
PACS: 65.80.Ck, 81.05.ue, 73.43.C
Ultrahard spectra of PeV neutrinos from supernovae in compact star clusters
Starburst regions with multiple powerful winds of young massive stars and
supernova remnants are favorable sites for high-energy cosmic ray acceleration.
A supernova shock colliding with a fast wind from a compact cluster of young
stars allows the acceleration of protons to energies well above the standard
limits of diffusive shock acceleration in an isolated SN. The proton spectrum
in such a wind-supernova PeV accelerator is hard with a large flux in the
high-energy-end of the spectrum producing copious gamma-rays and neutrinos in
inelastic nuclear collisions. We argue that SN shocks in the Westerlund 1
cluster in the Milky Way may accelerate protons to about 40 PeV. Once
accelerated, these CRs will diffuse into surrounding dense clouds and produce
neutrinos with fluxes sufficient to explain a fraction of the events detected
by IceCube Observatory from the inner Galaxy.Comment: 10 pages, 7 figures, MNRAS v.453, p.113-121, 201
Neural Distributed Autoassociative Memories: A Survey
Introduction. Neural network models of autoassociative, distributed memory
allow storage and retrieval of many items (vectors) where the number of stored
items can exceed the vector dimension (the number of neurons in the network).
This opens the possibility of a sublinear time search (in the number of stored
items) for approximate nearest neighbors among vectors of high dimension. The
purpose of this paper is to review models of autoassociative, distributed
memory that can be naturally implemented by neural networks (mainly with local
learning rules and iterative dynamics based on information locally available to
neurons). Scope. The survey is focused mainly on the networks of Hopfield,
Willshaw and Potts, that have connections between pairs of neurons and operate
on sparse binary vectors. We discuss not only autoassociative memory, but also
the generalization properties of these networks. We also consider neural
networks with higher-order connections and networks with a bipartite graph
structure for non-binary data with linear constraints. Conclusions. In
conclusion we discuss the relations to similarity search, advantages and
drawbacks of these techniques, and topics for further research. An interesting
and still not completely resolved question is whether neural autoassociative
memories can search for approximate nearest neighbors faster than other index
structures for similarity search, in particular for the case of very high
dimensional vectors.Comment: 31 page
Gauge theory of disclinations on fluctuating elastic surfaces
A variant of a gauge theory is formulated to describe disclinations on
Riemannian surfaces that may change both the Gaussian (intrinsic) and mean
(extrinsic) curvatures, which implies that both internal strains and a location
of the surface in R^3 may vary. Besides, originally distributed disclinations
are taken into account. For the flat surface, an extended variant of the
Edelen-Kadic gauge theory is obtained. Within the linear scheme our model
recovers the von Karman equations for membranes, with a disclination-induced
source being generated by gauge fields. For a single disclination on an
arbitrary elastic surface a covariant generalization of the von Karman
equations is derived.Comment: 13 page
Disclination vortices in elastic media
The vortex-like solutions are studied in the framework of the gauge model of
disclinations in elastic continuum. A complete set of model equations with
disclination driven dislocations taken into account is considered. Within the
linear approximation an exact solution for a low-angle wedge disclination is
found to be independent from the coupling constants of the theory. As a result,
no additional dimensional characteristics (like the core radius of the defect)
are involved. The situation changes drastically for 2\pi vortices where two
characteristic lengths, l_\phi and l_W, become of importance. The asymptotical
behaviour of the solutions for both singular and nonsingular 2\pi vortices is
studied. Forces between pairs of vortices are calculated.Comment: 13 pages, published versio
Cavitation-induced ignition of cryogenic hydrogen-oxygen fluids
The Challenger disaster and purposeful experiments with liquid hydrogen (H2)
and oxygen (Ox) tanks demonstrated that cryogenic H2/Ox fluids always
self-ignite in the process of their mixing. Here we propose a
cavitation-induced self-ignition mechanism that may be realized under these
conditions. In one possible scenario, self-ignition is caused by the strong
shock waves generated by the collapse of pure Ox vapor bubble near the surface
of the Ox liquid that may initiate detonation of the gaseous H2/Ox mixture
adjacent to the gas-liquid interface. This effect is further enhanced by H2/Ox
combustion inside the collapsing bubble in the presence of admixed H2 gas
Fly-The-Bee: A Game Imitating Concept Learning in Bees
AbstractThis article presents a web-based game functionally imitating a part of the cognitive behavior of a living organism. This game is a prototype implementation of an artificial online cognitive architecture based on the usage of distributed data representations and Vector Symbolic Architectures. The game demonstrates the feasibility of creating a lightweight cognitive architecture, which is capable of performing rather complex cognitive tasks. The cognitive functionality is implemented in about 100 lines of code and requires few tens of kilobytes of memory for its operation, which make the concept suitable for implementing in low-end devices such as minirobots and wireless sensors
Light Quark Masses in Multi-Quark Interactions
We suggest and discuss in detail a multi-quark three flavor Lagrangian of the
Nambu -- Jona-Lasinio type, which includes a set of effective interactions
proportional to the current quark masses. It is shown that within the dynamical
chiral symmetry breaking regime, the masses of the pseudo Goldstone bosons and
their chiral partners, members of the low lying scalar nonet, are in perfect
agreement with current phenomenological expectations. The role of the new
interactions is analyzed.Comment: 8 pages, published versio
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