3,164 research outputs found
Stable vortex-antivortex molecules in mesoscopic superconducting triangles
A thermodynamically stable vortex-antivortex pattern has been revealed in
mesoscopic type I superconducting triangles, contrary to type II
superconductors where similar patterns are unstable. The stable
vortex-antivortex "molecule" appears due to the interplay between two factors:
a repulsive vortex-antivortex interaction in type I superconductors and the
vortex confinement in the triangle.Comment: 5 pages, 4 figures, E-mail addresses: [email protected],
[email protected], [email protected], [email protected]
Calculation of flow of a radiating gas in a shock layer
Flow calculation of radiating gas in shock layers over blunt bodie
Comment on "Order parameter of A-like 3He phase in aerogel"
We argue that the inhomogeneous A-phase in aerogel is energetically more
preferable than the "robust" phase suggested by I. A. Fomin, JETP Lett. 77, 240
(2003); cond-mat/0302117 and cond-mat/0401639.Comment: 2 page
Phonons in magnon superfluid and symmetry breaking field
Recent experiments [1],[2] which measured the spectrum of the Goldstone
collective mode of coherently precessing state in 3He-B are discussed using the
presentation of the coherent spin precession in terms of the Bose-Einstein
condensation of magnons. The mass in the spectrum of the Goldstone boson --
phonon in the superfluid magnon liquid -- is induced by the symmetry breaking
field, which is played by the RF magnetic fieldComment: 2 pages, JETP Letters style, no figures, version accepted in JETP
Letter
Andreev scattering in nanoscopic junctions at high magnetic fields
We report on the measurement of multiple Andreev resonances at atomic size
point contacts between two superconducting nanostructures of Pb under magnetic
fields higher than the bulk critical field, where superconductivity is
restricted to a mesoscopic region near the contact. The small number of
conduction channels in this type of contacts permits a quantitative comparison
with theory through the whole field range. We discuss in detail the physical
properties of our structure, in which the normal bulk electrodes induce a
proximity effect into the mesoscopic superconducting part.Comment: 4 page
Approximating acyclicity parameters of sparse hypergraphs
The notions of hypertree width and generalized hypertree width were
introduced by Gottlob, Leone, and Scarcello in order to extend the concept of
hypergraph acyclicity. These notions were further generalized by Grohe and
Marx, who introduced the fractional hypertree width of a hypergraph. All these
width parameters on hypergraphs are useful for extending tractability of many
problems in database theory and artificial intelligence. In this paper, we
study the approximability of (generalized, fractional) hyper treewidth of
sparse hypergraphs where the criterion of sparsity reflects the sparsity of
their incidence graphs. Our first step is to prove that the (generalized,
fractional) hypertree width of a hypergraph H is constant-factor sandwiched by
the treewidth of its incidence graph, when the incidence graph belongs to some
apex-minor-free graph class. This determines the combinatorial borderline above
which the notion of (generalized, fractional) hypertree width becomes
essentially more general than treewidth, justifying that way its functionality
as a hypergraph acyclicity measure. While for more general sparse families of
hypergraphs treewidth of incidence graphs and all hypertree width parameters
may differ arbitrarily, there are sparse families where a constant factor
approximation algorithm is possible. In particular, we give a constant factor
approximation polynomial time algorithm for (generalized, fractional) hypertree
width on hypergraphs whose incidence graphs belong to some H-minor-free graph
class
Photoluminescence of tetrahedral quantum-dot quantum wells
Taking into account the tetrahedral shape of a quantum dot quantum well
(QDQW) when describing excitonic states, phonon modes and the exciton-phonon
interaction in the structure, we obtain within a non-adiabatic approach a
quantitative interpretation of the photoluminescence (PL) spectrum of a single
CdS/HgS/CdS QDQW. We find that the exciton ground state in a tetrahedral QDQW
is bright, in contrast to the dark ground state for a spherical QDQW.Comment: 4 pages, 2 figure
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