748 research outputs found
Critical phenomena and phase sequence in classical bilayer Wigner crystal at zero temperature
We study the ground-state properties of a system of identical classical
Coulombic point particles, evenly distributed between two equivalently charged
parallel plates at distance ; the system as a whole is electroneutral. It
was previously shown that upon increasing d from 0 to infinity, five different
structures of the bilayer Wigner crystal become energetically favored, starting
from a hexagonal lattice (phase I, d=0) and ending at a staggered hexagonal
lattice (phase V, d -> infinity). In this paper, we derive new series
representations of the ground-state energy for all five bilayer structures. The
derivation is based on a sequence of transformations for lattice sums of
Coulomb two-particle potentials plus the neutralizing background, having their
origin in the general theory of Jacobi theta functions. The new series provide
convenient starting points for both analytical and numerical progress. Its
convergence properties are indeed excellent: Truncation at the fourth term
determines in general the energy correctly up to 17 decimal digits. The
accurate series representations are used to improve the specification of
transition points between the phases and to solve a controversy in previous
studies. In particular, it is shown both analytically and numerically that the
hexagonal phase I is stable only at d=0, and not in a finite interval of small
distances between the plates as was anticipated before. The expansions of the
structure energies around second-order transition points can be done
analytically, which enables us to show that the critical behavior is of the
Ginzburg-Landau type, with a mean-field critical index beta=1/2 for the growth
of the order parameters
Classical solutions of sigma models in curved backgrounds by the Poisson-Lie T-plurality
Classical equations of motion for three-dimensional sigma-models in curved
background are solved by a transformation that follows from the Poisson-Lie
T-plurality and transform them into the equations in the flat background.
Transformations of coordinates that make the metric constant are found and used
for solving the flat model. The Poisson-Lie transformation is explicitly
performed by solving the PDE's for auxiliary functions and finding the relevant
transformation of coordinates in the Drinfel'd double. String conditions for
the solutions are preserved by the Poisson-Lie transformations. Therefore we
are able to specify the type of sigma-model solutions that solve also equations
of motion of three dimensional relativistic strings in the curved backgrounds.
Simple examples are given
Flat coordinates and dilaton fields for three--dimensional conformal sigma models
Riemannian coordinates for flat metrics corresponding to three--dimensional
conformal Poisson--Lie T--dualizable sigma models are found by solving partial
differential equations that follow from the transformations of the connection
components. They are then used for finding general forms of the dilaton fields
satisfying the vanishing beta equations of the sigma models.Comment: 16 pages, no figure
Algebraic Framework for Quantization of Nonultralocal Models
Extension of the braid relations to the multiple braided tensor product of
algebras that can be used for quantization of nonultralocal models is
presented. The Yang--Baxter--type consistency conditions as well as conditions
for the existence of the multiple coproduct (monodromy matrix), which can be
used for construction of the commuting subalgebra, are given. Homogeneous and
local algebras are introduced, and simplification of the Yang--Baxter--type
conditions for them is shown. The Yang--Baxter--type equations and multiple
coproduct conditions for homogeneous and local of order 2 algebras are solved.Comment: 18 pages, Latex, one formula plus two citations added, several
misprints were correcte
Improving teleportation of continuous variables by local operations
We study a continuous-variable (CV) teleportation protocol based on a shared
entangled state produced by the quantum-nondemolition (QND) interaction of two
vacuum states. The scheme utilizes the QND interaction or an unbalanced beam
splitter in the Bell measurement. It is shown that in the non-unity gain regime
the signal transfer coefficient can be enhanced while the conditional variance
product remains preserved by applying appropriate local squeezing operation on
sender's part of the shared entangled state. In the unity gain regime it is
demonstrated that the fidelity of teleportation can be increased with the help
of the local squeezing operations on parts of the shared entangled state that
convert effectively our scheme to the standard CV teleportation scheme.
Further, it is proved analytically that such a choice of the local symplectic
operations minimizes the noise by which the mean number of photons in the input
state is increased during the teleportation. Finally, our analysis reveals that
the local symplectic operation on sender's side can be integrated into the Bell
measurement if the interaction constant of the interaction in the Bell
measurement can be adjusted properly.Comment: 10 pages, 1 figure, discussion of the non-unity gain teleportation is
adde
Warping the young stellar disc in the Galactic Centre
We examine influence of the circum-nuclear disc (CND) upon the orbital
evolution of young stars in the Galactic Centre. We show that gravity of the
CND causes precession of the orbits which is highly sensitive upon the
semi-major axis and inclination. We consider such a differential precession
within the context of an ongoing discussion about the origin of the young stars
and suggest a possibility that all of them have originated in a thin disc which
was partially destroyed due to the influence of the CND during the period of
~6Myr.Comment: proc. conf. "The Universe Under the Microscope - Astrophysics at High
Angular Resolution", 21-25 April 2008, Bad Honnef, German
Vivienda unifamiliar entre rocas
This house has two storeys. Downstairs there is an entrance, a vestibule, secondary services and a garage. Upstairs are the main rooms of the house.
The essential part of the dwelling rests on a kind of wall enclosing the ground floor, but as the latter is very reduced, it is also supported by a number of pillars. The impression is conveyed that the landscape, which is wild and savage in this region, penetrates into the house itself, emphasizing the interplay of masses.
This very personal design by Rado has a series of harmonically related indoor volumes, is of very simple construction, and exhibits beautiful external perspectives.La edificación está organizada en dos plantas; la baja alberga la entrada, el vestíbulo, el garaje y dependencias secundarias; y la planta alta, las habitaciones de vivir.
La vivienda propiamente dicha se alza sobre una especie de zócalo—constituido por la edificación de la planta baja—; pero como esta base de apoyo es relativamente pequeña y la, planta alta descansa, asimismo, sobre una serie de pilares exentos, la casa produce la sensación de que el paisaje—en este paraje, salvaje y virgen—penetra en la misma, colaborando al interesante juego de volúmenes.
La sucesión armoniosa de espacios interiores, su construcción sencilla y la belleza de sus fachadas, son notables aciertos que podemos señalar en esta obra tan personal de Ladislav L. Rado
Newly synthesized proteins are degraded by an ATP-stimulated proteolytic process in isolated pea chloroplasts
AbstractUp to 22% of the [3H]leucine-labeled proteins synthesized chloroplasts in the light was degraded during subsequent incubation for 20–40 min. The degradation of these radioactive proteins was more rapid in the light than in the dark and was at least 2-fold greater in the presence of 5 mM ATP in light or darkness. Exogenous amino acids did not influence degradation rates, although they promoted protein synthesis. Overall, proteins from thylakoid and stromal fractions were degraded at comparable rates. Analysis by electrophoresis in denaturing polyacrylamide gels revealed that many proteins decreased in both fractions. Certain low molecular mass stromal proteins were lost almost completely during a 90 min incubation in the presence of ATP, while others were unaffected or decreased only slightly. Thus Chloroplasts, like eukaryotic and prokaryotic cells and mithochondria, contain an ATP-stimulated proteolytic system
Cassini Titan Radar Mapper
The Cassini Titan Radar Mapper is a multimode radar instrument designed to probe the optically inaccessible surface of Titan, Saturn's largest moon. The instrument is to be included in the payload of the Cassini Saturn Mission, scheduled for launch in 1995. The individual modes of Cassini Radar Mapper will allow topographic mapping and surface imaging at few hundred meters resolution. The requirements that lay behind the design are briefly discussed, and the configuration and capability of the instrument are described. The present limited knowledge of Titan's surface and the measurement requirements imposed on the radar instrument are addressed. Also discussed are the Cassini mission and the projected orbits, which imposed another set of design constraints that led to the multitude of modes and to an unconventional antenna configuration. The antenna configuration and the different radar modes are described
Edge-disjoint spanners in Cartesian products of graphs
AbstractA spanning subgraph S=(V,E′) of a connected graph G=(V,E) is an (x+c)-spanner if for any pair of vertices u and v, dS(u,v)⩽dG(u,v)+c where dG and dS are the usual distance functions in G and S, respectively. The parameter c is called the delay of the spanner. We study edge-disjoint spanners in graphs, focusing on graphs formed as Cartesian products. Our approach is to construct sets of edge-disjoint spanners in a product based on sets of edge-disjoint spanners and colorings of the component graphs. We present several results on general products and then narrow our focus to hypercubes
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