1,400 research outputs found
One-parameter Superscaling at the Metal-Insulator Transition in Three Dimensions
Based on the spectral statistics obtained in numerical simulations on three
dimensional disordered systems within the tight--binding approximation, a new
superuniversal scaling relation is presented that allows us to collapse data
for the orthogonal, unitary and symplectic symmetry () onto a
single scaling curve. This relation provides a strong evidence for
one-parameter scaling existing in these systems which exhibit a second order
phase transition. As a result a possible one-parameter family of spacing
distribution functions, , is given for each symmetry class ,
where is the dimensionless conductance.Comment: 4 pages in PS including 3 figure
Does a magnetic field modify the critical behaviour at the metal-insulator transition in 3-dimensional disordered systems?
The critical behaviour of 3-dimensional disordered systems with magnetic
field is investigated by analyzing the spectral fluctuations of the energy
spectrum. We show that in the thermodynamic limit we have two different
regimes, one for the metallic side and one for the insulating side with
different level statistics. The third statistics which occurs only exactly at
the critical point is {\it independent} of the magnetic field. The critical
behaviour which is determined by the symmetry of the system {\it at} the
critical point should therefore be independent of the magnetic field.Comment: 10 pages, Revtex, 4 PostScript figures in uuencoded compressed tar
file are appende
Shape Analysis of the Level Spacing Distribution around the Metal Insulator Transition in the Three Dimensional Anderson Model
We present a new method for the numerical treatment of second order phase
transitions using the level spacing distribution function . We show that
the quantities introduced originally for the shape analysis of eigenvectors can
be properly applied for the description of the eigenvalues as well. The
position of the metal--insulator transition (MIT) of the three dimensional
Anderson model and the critical exponent are evaluated. The shape analysis of
obtained numerically shows that near the MIT is clearly different
from both the Brody distribution and from Izrailev's formula, and the best
description is of the form , with
. This is in good agreement with recent analytical results.Comment: 14 pages in plain TeX, 6 figures upon reques
Simultaneous microsurgical spermatic vein ligation and sclerotherapy - A combined procedure for the treatment of recurrent or persistent varicocele
Objectives: Microsurgical ligation as well as antegrade sclerotherapy have been established in varicocele treatment. The aim of this study was to evaluate whether a combination of microsurgery. and sclerotherapy can: provide a safe and effective treatment of varicocele recurrence or persistence. Methods. Nine patients with, recurrent or persistent varicoceles were operated by means of the combination method. Under microscopic control varix veins were ligated selectively preserving: lymphatics and arteries. Ectopic veins as a possible source for varicocele persistence or recurrence were also ligated. Finally, an intraoperative venography with subsequent sclerotherapy was, performed through one of the dissected veins. Results. Despite: difficult anatomical situations after previous surgical interventions, the operations were perform, ed successfully without any complications. Clinical controls showed varicocele disappearance without damage of the testis. No varicocele recurrence or persistence was observed. Conclusions. This method combines the advantages of both methods. Precision of the microsurgical technique is combined with velocity of sclerotherapy. Thus, it may represent an Interesting alternative to conventional operation methods especially in the treatment of recurrent or persistent varicoceles. Copyright (C) 2001 S. Karger AG, Basel
Advances in Oxygen Isotope Analysis of Phosphate by Electrospray Orbitrap Mass Spectrometry for Studying the Microbial Metabolism of Microorganisms
Understanding the impact of human activities on the metabolic state of soil and aquatic environments is of paramount importance to implement measures for maintaining ecosystem services. Variations of natural abundance 18O/16O ratios in phosphate have been proposed as proxies for the holistic assessment of metabolic activity given the crucial importance of phosphoryl transfer reactions in fundamental biological processes. However, instrumental and procedural limitations inherent to oxygen isotope analysis in phosphate and organophosphorus compounds have so far limited the stable isotope-based evaluation of metabolic processes. Here, we discuss how recent developments in Orbitrap high resolution mass spectrometry enable measurements of 18O/16O ratios in phosphate and outline the critical mass spectrometry parameters for accurate and precise analysis. Subsequently, we evaluate the types of 18O kinetic isotope effects of phosphoryl transfer reactions and illustrate how novel analytical approaches will give rise to an improved understanding of 18O/16O ratio variations from biochemical processes affecting the microbial phosphorus metabolism
Anderson-Hubbard model with box disorder: Statistical dynamical mean-field theory investigation
Strongly correlated electrons with box disorder in high-dimensional lattices
are investigated. We apply the statistical dynamical mean-field theory, which
treats local correlations non-perturbatively. The incorporation of a finite
lattice connectivity allows for the detection of disorder-induced localization
via the probability distribution function of the local density of states. We
obtain a complete paramagnetic ground state phase diagram and find
correlation-induced as well as disorder-induced metal-insulator transitions.
Our results qualitatively confirm predictions obtained by typical medium
theory. Moreover, we find that the probability distribution function of the
local density of states in the metallic phase strongly deviates from a
log-normal distribution as found for the non-interacting case.Comment: 13 pages, 15 figures, published versio
Relation between Energy Level Statistics and Phase Transition and its Application to the Anderson Model
A general method to describe a second-order phase transition is discussed. It
starts from the energy level statistics and uses of finite-size scaling. It is
applied to the metal-insulator transition (MIT) in the Anderson model of
localization, evaluating the cumulative level-spacing distribution as well as
the Dyson-Metha statistics. The critical disorder and the critical
exponent are computed.Comment: 9 pages, Latex, 6 PostScript figures in uuencoded compressed tar file
are appende
Resonant Superfluidity in an Optical Lattice
We study a system of ultracold fermionic Potassium (40K) atoms in a
three-dimensional optical lattice in the vicinity of an s-wave Feshbach
resonance. Close to resonance, the system is described by a multi-band
Bose-Fermi Hubbard Hamiltonian. We derive an effective lowest-band Hamiltonian
in which the effect of the higher bands is incorporated by a self-consistent
mean-field approximation. The resulting model is solved by means of Generalized
Dynamical Mean-Field Theory. In addition to the BEC/BCS crossover we find a
phase transition to a fermionic Mott insulator at half filling, induced by the
repulsive fermionic background scattering length. We also calculate the
critical temperature of the BEC/BCS-state and find it to be minimal at
resonance.Comment: 19 pages, 3 figure
Critical Level Statistics in Two-dimensional Disordered Electron Systems
The level statistics in the two dimensional disordered electron systems in
magnetic fields (unitary ensemble) or in the presence of strong spin-orbit
scattering (symplectic ensemble) are investigated at the Anderson transition
points. The level spacing distribution functions 's are found to be
independent of the system size or of the type of the potential distribution,
suggesting the universality. They behave as in the small region in
the former case, while rise is seen in the latter.Comment: LaTeX, to be published in J. Phys. Soc. Jpn. (Letter) Nov., Figures
will be sent on reques
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Contains reports on four research projects.Lincoln Laboratory (Purchase Order DDL-B222)United States Department of the ArmyUnited States Department of the NavyUnited States Department of the Air Force (Contract AF19(604)-5200
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