27,454 research outputs found
Connectivity and a Problem of Formal Geometry
Let be a product of weighted
projective spaces, and let be the diagonal of . We prove
an algebraization result for formal-rational functions on certain closed
subvarieties of along the intersection .Comment: 9 pages, to appear in the Proceedings volume "Experimental and
Theoretical Methods in Algebra, Geometry and Topology", series Springer
Proceedings in Mathematics & Statistic
The Jahn-Teller active fluoroperovskites : thermo- and magneto optical correlations as function of the -site
Chromium (II) fluoroperovskites are
strongly correlated Jahn-Teller active materials at low temperatures. In this
paper, we examine the role that the -site ion plays in this family of
fluoroperovskites using both experimental methods (XRD, optical absorption
spectroscopy and magnetic fields) and DFT simulations. Temperature-dependent
optical absorption experiments show that the spin-allowed transitions and
only merge completely for = Na at 2 K. Field-dependent optical
absorption measurements at 2 K show that the oscillating strength of the
spin-allowed transitions in increases with increasing
applied field. Direct magneto-structural correlations which suppress the
spin-flip transitions are observed for below its Ne\'el
temperature. In the spin-flip transitions vanish abruptly below
9 K revealing magneto-optical correlations not linked to crystal structure
changes. This suggests that as the long range ordering is reduced local JT
effects in the individual octahedra take control of the
observed behavior. Our results show clear deviation from the pattern found for
the isoelectronic system. The size of the -site cation
is shown to be central in dictating the physical properties and phase
transitions in , opening up the possibility of varying the
composition to create novel states of matter with tuneable properties
Intersubband Electron Interaction in 1D-2D Junctions
We have shown that the electron transport through junctions of
one-dimensional and two-dimensional systems, as well as through quantum point
contacts, is considerably affected by the interaction of electrons of different
subbands. The interaction mechanism is caused by Friedel oscillations, which
are produced by electrons of the closed subbands even in smooth junctions.
Because of the interaction with these oscillations, electrons of the open
subbands experience a backscattering. The electron reflection coefficient,
which describes the backscattering, has a sharp peak at the energy equal to the
Fermi energy and may be as high as about 0.1. This result allows one to explain
a number of available experimental facts.Comment: 5 pages, 3 figure
Concentration and mass dependence of transport coefficients and correlation functions in binary mixtures with high mass-asymmetry
Correlation functions and transport coefficients of self-diffusion and shear
viscosity of a binary Lennard-Jones mixture with components differing only in
their particle mass are studied up to high values of the mass ratio ,
including the limiting case , for different mole fractions .
Within a large range of and the product of the diffusion coefficient
of the heavy species and the total shear viscosity of the mixture
is found to remain constant, obeying a generalized Stokes-Einstein
relation. At high liquid density, large mass ratios lead to a pronounced cage
effect that is observable in the mean square displacement, the velocity
autocorrelation function and the van Hove correlation function
A Prismatic Analyser concept for Neutron Spectrometers
A development in modern neutron spectroscopy is to avoid the need of large
samples. We demonstrate how small samples together with the right choice of
analyser and detector components makes distance collimation an important
concept in crystal analyser spectrometers. We further show that this opens new
possibilities where neutrons with different energies are reflected by the same
analyser but counted in different detectors, thus improving both energy
resolution and total count rate compared to conventional spectrometers. The
technique can be combined with advanced focusing geometries and with
multiplexing instrument designs. We present a combination of simulations and
data with 3 energies from one analyser. The data was taken on a prototype
installed at PSI, Switzerland, and shows excellent agreement with the
predictions. Typical improvements will be 2 times finer resolution and a factor
1.9 in flux gain compared to a Rowland geometry or 3 times finer resolution and
a factor 3.2 in flux gain compared to a single flat analyser slab
Message passing for vertex covers
Constructing a minimal vertex cover of a graph can be seen as a prototype for
a combinatorial optimization problem under hard constraints. In this paper, we
develop and analyze message passing techniques, namely warning and survey
propagation, which serve as efficient heuristic algorithms for solving these
computational hard problems. We show also, how previously obtained results on
the typical-case behavior of vertex covers of random graphs can be recovered
starting from the message passing equations, and how they can be extended.Comment: 25 pages, 9 figures - version accepted for publication in PR
Liquid heat capacity in the approach from the solid state: anharmonic theory
Calculating liquid energy and heat capacity in general form is an open
problem in condensed matter physics. We develop a recent approach to liquids
from the solid state by accounting for the contribution of anharmonicity and
thermal expansion to liquid energy and heat capacity. We subsequently compare
theoretical predictions to the experiments results of 5 commonly discussed
liquids, and find a good agreement with no free fitting parameters. We discuss
and compare the proposed theory to previous approaches.Comment: 8 pages, 6 figure
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