159,639 research outputs found
Quantum transfer matrix method for one-dimensional disordered electronic systems
We develop a novel quantum transfer matrix method to study thermodynamic
properties of one-dimensional (1D) disordered electronic systems. It is shown
that the partition function can be expressed as a product of local
transfer matrices. We demonstrate this method by applying it to the 1D
disordered Anderson model. Thermodynamic quantities of this model are
calculated and discussed.Comment: 7 pages, 10 figure
Theory of fishnet negative-index optical metamaterials
We theoretically study fishnet metamaterials at optical frequencies. In
contrast to earlier works, we provide a microscopic description by tracking the
transversal and longitudinal flows of energy through the fishnet mesh composed
of intersecting subwavelength plasmonic waveguides. The analysis is supported
by a semi-analytical model based on surface-plasmon coupled-mode equations,
which provides accurate formulas for the fishnet refractive index, including
the real-negative and imaginary parts. The model simply explains how the
surface plasmons couple at the waveguide intersections and it shines new light
on the fishnet negative-index paradigm at optical frequencies. Extension of the
theory for loss-compensated metamaterials with gain media is also presented.Comment: 4 figure
Matching Subsequences in Trees
Given two rooted, labeled trees and the tree path subsequence problem
is to determine which paths in are subsequences of which paths in . Here
a path begins at the root and ends at a leaf. In this paper we propose this
problem as a useful query primitive for XML data, and provide new algorithms
improving the previously best known time and space bounds.Comment: Minor correction of typos, et
Dynamical excitations in the collision of 2D Bose-Einstein condensates
We carry out simulations of the collision of two components of an
adiabatically divided, quasi-2D BEC. We identify under, over and critically
damped regimes in the dipole oscillations of the components according to the
balance of internal and centre-of-mass (c.m.) energies of the components and
investigate the creation of internal excitations. We distinguish the behaviour
of this system from previous studies of quasi-1D BEC's. In particular we note
that the nature of the internal excitations is only essentially sensitive to an
initial phase difference between the components in the overdamped regime.Comment: 17 pages, 9 figure
Monte Carlo Algorithm for Simulating Reversible Aggregation of Multisite Particles
We present an efficient and exact Monte Carlo algorithm to simulate
reversible aggregation of particles with dedicated binding sites. This method
introduces a novel data structure of dynamic bond tree to record clusters and
sequences of bond formations. The algorithm achieves a constant time cost for
processing cluster association and a cost between and
for processing bond dissociation in clusters with bonds.
The algorithm is statistically exact and can reproduce results obtained by the
standard method. We applied the method to simulate a trivalent ligand and a
bivalent receptor clustering system and obtained an average scaling of
for processing bond dissociation in acyclic
aggregation, compared to a linear scaling with the cluster size in standard
methods. The algorithm also demands substantially less memory than the
conventional method.Comment: 8 pages, 3 figure
Dual-fermion approach to the Anderson-Hubbard model
We apply the recently developed dual fermion algorithm for disordered
interacting systems to the Anderson-Hubbard model. This algorithm is compared
with dynamical cluster approximation calculations for a one-dimensional system
to establish the quality of the approximation in comparison with an established
cluster method. We continue with a three-dimensional (3d) system and look at
the antiferromagnetic, Mott and Anderson localization transitions. The dual
fermion approach leads to quantitative as well as qualitative improvement of
the dynamical mean-field results and it allows one to calculate the hysteresis
in the double occupancy in 3d taking into account nonlocal correlations
New Results from the MINOS Experiment
In this paper we present the latest results from the MINOS Experiment. This
includes a new measurement of the atmospheric neutrino oscillation parameters
based on 3.36 x 10^20 protons-on-target of data and a first analysis of neutral
current events in the Far Detector. The prospects for nu-e appearance
measurements in MINOS are also discussed.Comment: 6 pages, 4 figures, for the Proceedings of the Neutrino 2008
Conference, Christchurch, N
Quantitative Photo-acoustic Tomography with Partial Data
Photo-acoustic tomography is a newly developed hybrid imaging modality that
combines a high-resolution modality with a high-contrast modality. We analyze
the reconstruction of diffusion and absorption parameters in an elliptic
equation and improve an earlier result of Bal and Uhlmann to the partial date
case. We show that the reconstruction can be uniquely determined by the
knowledge of 4 internal data based on well-chosen partial boundary conditions.
Stability of this reconstruction is ensured if a convexity condition is
satisfied. Similar stability result is obtained without this geometric
constraint if 4n well-chosen partial boundary conditions are available, where
is the spatial dimension. The set of well-chosen boundary measurements is
characterized by some complex geometric optics (CGO) solutions vanishing on a
part of the boundary.Comment: arXiv admin note: text overlap with arXiv:0910.250
Measurement of the Dynamical Structure Factor of a 1D Interacting Fermi Gas
We present measurements of the dynamical structure factor of an
interacting one-dimensional (1D) Fermi gas for small excitation energies. We
use the two lowest hyperfine levels of the Li atom to form a
pseudo-spin-1/2 system whose s-wave interactions are tunable via a Feshbach
resonance. The atoms are confined to 1D by a two-dimensional optical lattice.
Bragg spectroscopy is used to measure a response of the gas to density
("charge") mode excitations at a momentum and frequency . The
spectrum is obtained by varying , while the angle between two laser
beams determines , which is fixed to be less than the Fermi momentum
. The measurements agree well with Tomonaga-Luttinger theory
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