315 research outputs found
Low density expansion for Lyapunov exponents
In some quasi-one-dimensional weakly disordered media, impurities are large
and rare rather than small and dense. For an Anderson model with a low density
of strong impurities, a perturbation theory in the impurity density is
developed for the Lyapunov exponent and the density of states. The Lyapunov
exponent grows linearly with the density. Anomalies of the Kappus-Wegner type
appear for all rational quasi-momenta even in lowest order perturbation theory
Scaling of the localization length in linear electronic and vibrational systems with long-range correlated disorder
The localization lengths of long-range correlated disordered chains are
studied for electronic wavefunctions in the Anderson model and for vibrational
states. A scaling theory close to the band edge is developed in the Anderson
model and supported by numerical simulations. This scaling theory is mapped
onto the vibrational case at small frequencies. It is shown that for small
frequencies, unexpectateley the localization length is smaller for correlated
than for uncorrelated chains.Comment: to be published in PRB, 4 pages, 2 Figure
Shaping Biological Knowledge: Applications in Proteomics
The central dogma of molecular biology has provided a meaningful principle
for data integration in the field of genomics. In this context, integration reflects
the known transitions from a chromosome to a protein sequence: transcription,
intron splicing, exon assembly and translation. There is no such clear principle for
integrating proteomics data, since the laws governing protein folding and interactivity
are not quite understood. In our effort to bring together independent pieces of
information relative to proteins in a biologically meaningful way, we assess the bias of
bioinformatics resources and consequent approximations in the framework of small-scale
studies. We analyse proteomics data while following both a data-driven (focus
on proteins smaller than 10 kDa) and a hypothesis-driven (focus on whole bacterial
proteomes) approach. These applications are potentially the source of specialized
complements to classical biological ontologies
Anderson-localization versus delocalization of interacting fermions in one dimension
Using the density matrix renormalization group algorithm, we investigate the
lattice model for spinless fermions in one dimension in the presence of a
strong interaction and disorder. The phase sensitivity of the ground state
energy is determined with high accuracy for systems up to a size of 60 lattice
constants. This quantity is found to be log-normally distributed. The
fluctuations grow algebraically with system size with a universal exponent of
~2/3 in the localized region of the phase diagram. Surprizingly, we find, for
an attractive interaction, a delocalized phase of finite extension. The
boundary of this delocalized phase is determined.Comment: 5 pages, 6 figures, revte
Sublocalization, superlocalization, and violation of standard single parameter scaling in the Anderson model
We discuss the localization behavior of localized electronic wave functions
in the one- and two-dimensional tight-binding Anderson model with diagonal
disorder. We find that the distributions of the local wave function amplitudes
at fixed distances from the localization center are well approximated by
log-normal fits which become exact at large distances. These fits are
consistent with the standard single parameter scaling theory for the Anderson
model in 1d, but they suggest that a second parameter is required to describe
the scaling behavior of the amplitude fluctuations in 2d. From the log-normal
distributions we calculate analytically the decay of the mean wave functions.
For short distances from the localization center we find stretched exponential
localization ("sublocalization") in both, 1d and 2d. In 1d, for large
distances, the mean wave functions depend on the number of configurations N
used in the averaging procedure and decay faster that exponentially
("superlocalization") converging to simple exponential behavior only in the
asymptotic limit. In 2d, in contrast, the localization length increases
logarithmically with the distance from the localization center and
sublocalization occurs also in the second regime. The N-dependence of the mean
wave functions is weak. The analytical result agrees remarkably well with the
numerical calculations.Comment: 12 pages with 9 figures and 1 tabl
Single parameter scaling in one-dimensional localization revisited
The variance of the Lyapunov exponent is calculated exactly in the
one-dimensional Anderson model with random site energies distributed according
to the Cauchy distribution. We find a new significant scaling parameter in the
system, and derive an exact analytical criterion for single parameter scaling
which differs from the commonly used condition of phase randomization. The
results obtained are applied to the Kronig-Penney model with the potential in
the form of periodically positioned -functions with random strength.Comment: Phys. Rev. Lett. 84, 2678 (2000
Failure of single-parameter scaling of wave functions in Anderson localization
We show how to use properties of the vectors which are iterated in the
transfer-matrix approach to Anderson localization, in order to generate the
statistical distribution of electronic wavefunction amplitudes at arbitary
distances from the origin of disordered systems. For
our approach is shown to reproduce exact diagonalization results
available in the literature. In , where strips of width sites
were used, attempted fits of gaussian (log-normal) forms to the wavefunction
amplitude distributions result in effective localization lengths growing with
distance, contrary to the prediction from single-parameter scaling theory. We
also show that the distributions possess a negative skewness , which is
invariant under the usual histogram-collapse rescaling, and whose absolute
value increases with distance. We find for the
range of parameters used in our study, .Comment: RevTeX 4, 6 pages, 4 eps figures. Phys. Rev. B (final version, to be
published
Disseminated Adenovirus Infection After Combined Liver-Kidney Transplantation
Human adenovirus (HAdV) infections are well-described after hematopoietic stem cell transplantation but less well understood in solid organ transplantation (SOT). We describe a case of disseminated HAdV type 21 infection 5 months after combined liver-kidney transplantation, expanding the limited literature describing this infection in the SOT population
MODEL CORRELATION STUDY OF A RETRACTABLE BOOM FOR A SOLAR SAIL SPACECRAFT
To realize design concepts, predict dynamic behavior and develop appropriate control strategies for high performance operation of a solar-sail spacecraft, we developed a simple analytical model that represents dynamic behavior of spacecraft with various sizes. Since motion of the vehicle is dominated by retractable booms that support the structure, our study concentrates on developing and validating a dynamic model of a long retractable boom. Extensive tests with various configurations were conducted for the 30 Meter, light-weight, retractable, lattice boom at NASA MSFC that is structurally and dynamically similar to those of a solar-sail spacecraft currently under construction. Experimental data were then compared with the corresponding response of the analytical model. Though mixed results were obtained, the analytical model emulates several key characteristics of the boom. The paper concludes with a detailed discussion of issues observed during the study
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