4,374 research outputs found
Variation of discrete spectra for non-selfadjoint perturbations of selfadjoint operators
Let B=A+K where A is a bounded selfadjoint operator and K is an element of
the von Neumann-Schatten ideal S_p with p>1. Let {\lambda_n} denote an
enumeration of the discrete spectrum of B. We show that \sum_n
\dist(\lambda_n, \sigma(A))^p is bounded from above by a constant multiple of
|K|_p^p. We also derive a unitary analog of this estimate and apply it to
obtain new estimates on zero-sets of Cauchy transforms.Comment: Differences to previous version: Extended Introduction, new Section
5, additional references. To appear in Int. Eq. Op. Theor
Revisiting random deposition with surface relaxation: approaches from growth rules to Edwards-Wilkinson equation
We present several approaches for deriving the coarse-grained continuous
Langevin equation (or Edwards-Wilkinson equation) from a random deposition with
surface relaxation (RDSR) model. First we introduce a novel procedure to divide
the first transition moment into the three fundamental processes involved:
deposition, diffusion and volume conservation. We show how the diffusion
process is related to antisymmetric contribution and the volume conservation
process is related to symmetric contribution, which renormalizes to zero in the
coarse-grained limit. In another approach, we find the coefficients of the
continuous Langevin equation, by regularizing the discrete Langevin equation.
Finally, in a third approach, we derive these coefficients from the set of test
functions supported by the stationary probability density function (SPDF) of
the discrete model. The applicability of the used approaches to other discrete
random deposition models with instantaneous relaxation to a neighboring site is
discussed.Comment: 12 pages, 4 figure
Mechanism of charge transfer/disproportionation in LnCu3Fe4O12 (Ln: Lanthanides)
The Fe-Cu intersite charge transfer and Fe charge disproportionation are
interesting phenomena observed in some LnCu3Fe4O12 (Ln: Lanthanides) compounds
containing light and heavy Ln atoms, respectively. We show that a change in the
spin state is responsible for the intersite charge transfer in the light Ln
compounds. At the high spin state, such systems prefer an unusual Cu-d^8
configuration, whereas at the low spin state they retreat to the normal Cu-d^9
configuration through a charge transfer from Fe to Cu-3d_{xy} orbital. We find
that the strength of the crystal field splitting and the relative energy
ordering between Cu-3d_{xy} and Fe-3d states are the key parameters,
determining the intersite charge transfer (charge disproportionation) in light
(heavy) Ln compounds. It is further proposed that the size of Ln affects the
onsite interaction strength of Cu-3d states, leading to a strong modification
of the Cu-L_3 edge spectrum, as observed by the X-ray absorption spectroscopy.Comment: 6 pages, 5 figures, 1 table. To appear in PR
A simple ansatz to describe thermodynamic quantities of peptides and proteins at low temperatures
We describe a simple ansatz to approximate the low temperature behavior of
proteins and peptides by a mean-field-like model which is analytically
solvable. For a small peptide some thermodynamic quantities are calculated and
compared with numerical results of an all-atoms simulation. Our approach can be
used to determine the weights for a multicanonical simulation of the molecule
under consideration.Comment: 11 pages, Latex, 4 Postscript figures, to appear in Int. J. Mod.
Phys. C (1997
Helix Formation and Folding in an Artificial Peptide
We study the relation between -helix formation and folding for a
simple artificial peptide, Ala-Gly-Ala. Our data rely on
multicanonical Monte Carlo simulations where the interactions among all atoms
are taken into account. The free-energy landscape of the peptide is evaluated
for various temperatures. Our data indicate that folding of this peptide is a
two-step process: in a first step two -helices are formed which
afterwards re-arrange themselves into a U-like structure.Comment: 15 pages, with 9 eps figure
A new look at the 2D Ising model from exact partition function zeros for large lattice sizes
A general numerical method is presented to locate the partition function
zeros in the complex beta plane for large lattice sizes. We apply this method
to the 2D Ising model and results are reported for square lattice sizes up tp
L=64. We also propose an alternative method to evaluate corrections to scaling
which relies only on the leading zeros. This method is illustrated with our
data.Comment: 9 pages, Latex, 3 figures. To appear in Int. J. Mod. Phys.
Partition Function Zeros and Finite Size Scaling of Helix-Coil Transitions in a Polypeptide
We report on multicanonical simulations of the helix-coil transition of a
polypeptide. The nature of this transition was studied by calculating partition
function zeros and the finite-size scaling of various quantities. Estimates for
critical exponents are presented.Comment: RevTex, 4 eps-files; to appear in Phys. Rev. Le
Generalized-ensemble Monte carlo method for systems with rough energy landscape
We present a novel Monte Carlo algorithm which enhances equilibrization of
low-temperature simulations and allows sampling of configurations over a large
range of energies. The method is based on a non-Boltzmann probability weight
factor and is another version of the so-called generalized-ensemble techniques.
The effectiveness of the new approach is demonstrated for the system of a small
peptide, an example of the frustrated system with a rugged energy landscape.Comment: Latex; ps-files include
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