89,870 research outputs found
Superconductivity in the Two-Dimensional - Model at Low Hole Doping
By combining a generalized Lanczos scheme with the variational Monte Carlo
method we can optimize the short- and long-range properties of the groundstate
separately. This allows us to measure the long-range order of the groundstate
of the - model as a function of the coupling constant , and identify
a region of finite d-wave superconducting long-range order. With a lattice size
of 50 sites we can reliably examine hole densities down to 0.16.Comment: 12 pages and 4 PostScript figures, ReVTeX 3.0, ETH-TH/94-1
Shot noise spectrum of superradiant entangled excitons
The shot noise produced by tunneling of electrons and holes into a double dot
system incorporated inside a p-i-n junction is investigated theoretically. The
enhancement of the shot noise is shown to originate from the entangled
electron-hole pair created by superradiance. The analogy to the superconducting
cooper pair box is pointed out. A series of Zeno-like measurements is shown to
destroy the entanglement, except for the case of maximum entanglement.Comment: 5 pages, 3 figures, to appear in Phys. Rev. B (2004
Reconstructing the geometric structure of a Riemannian symmetric space from its Satake diagram
The local geometry of a Riemannian symmetric space is described completely by
the Riemannian metric and the Riemannian curvature tensor of the space. In the
present article I describe how to compute these tensors for any Riemannian
symmetric space from the Satake diagram, in a way that is suited for the use
with computer algebra systems. As an example application, the totally geodesic
submanifolds of the Riemannian symmetric space SU(3)/SO(3) are classified.
The submission also contains an example implementation of the algorithms and
formulas of the paper as a package for Maple 10, the technical documentation
for this implementation, and a worksheet carrying out the computations for the
space SU(3)/SO(3) used in the proof of Proposition 6.1 of the paper.Comment: 23 pages, also contains two Maple worksheets and technical
documentatio
Variational Study of the Spin-Gap Phase of the One-Dimensional t-J Model
We propose a correlated spin-singlet-pairs wave function to describe the
spin-gap phase of the one-dimensional model at low density. Adding a
Jastrow factor with a variational parameter, , first introduced by
Hellberg and Mele, is shown to correctly describe the long-range behavior
expected for the Luther-Emery phase. Using the variational Monte Carlo method
we establish a relation between and the Luttinger exponent ,
.Comment: 4 pages (LaTex), 3 figures attache
Predictive modeling of die filling of the pharmaceutical granules using the flexible neural tree
In this work, a computational intelligence (CI) technique named flexible neural tree (FNT) was developed to predict die filling performance of pharmaceutical granules and to identify significant die filling process variables. FNT resembles feedforward neural network, which creates a tree-like structure by using genetic programming. To improve accuracy, FNT parameters were optimized by using differential evolution algorithm. The performance of the FNT-based CI model was evaluated and compared with other CI techniques: multilayer perceptron, Gaussian process regression, and reduced error pruning tree. The accuracy of the CI model was evaluated experimentally using die filling as a case study. The die filling experiments were performed using a model shoe system and three different grades of microcrystalline cellulose (MCC) powders (MCC PH 101, MCC PH 102, and MCC DG). The feed powders were roll-compacted and milled into granules. The granules were then sieved into samples of various size classes. The mass of granules deposited into the die at different shoe speeds was measured. From these experiments, a dataset consisting true density, mean diameter (d50), granule size, and shoe speed as the inputs and the deposited mass as the output was generated. Cross-validation (CV) methods such as 10FCV and 5x2FCV were applied to develop and to validate the predictive models. It was found that the FNT-based CI model (for both CV methods) performed much better than other CI models. Additionally, it was observed that process variables such as the granule size and the shoe speed had a higher impact on the predictability than that of the powder property such as d50. Furthermore, validation of model prediction with experimental data showed that the die filling behavior of coarse granules could be better predicted than that of fine granules
Low-Energy Charge-Density Excitations in MgB: Striking Interplay between Single-Particle and Collective Behavior for Large Momenta
A sharp feature in the charge-density excitation spectra of single-crystal
MgB, displaying a remarkable cosine-like, periodic energy dispersion with
momentum transfer () along the -axis, has been observed for the first
time by high-resolution non-resonant inelastic x-ray scattering (NIXS).
Time-dependent density-functional theory calculations show that the physics
underlying the NIXS data is strong coupling between single-particle and
collective degrees of freedom, mediated by large crystal local-field effects.
As a result, the small- collective mode residing in the single-particle
excitation gap of the B bands reappears periodically in higher Brillouin
zones. The NIXS data thus embody a novel signature of the layered electronic
structure of MgB.Comment: 5 pages, 4 figures, submitted to PR
Eigenvalues of Ruijsenaars-Schneider models associated with root system in Bethe ansatz formalism
Ruijsenaars-Schneider models associated with root system with a
discrete coupling constant are studied. The eigenvalues of the Hamiltonian are
givein in terms of the Bethe ansatz formulas. Taking the "non-relativistic"
limit, we obtain the spectrum of the corresponding Calogero-Moser systems in
the third formulas of Felder et al [20].Comment: Latex file, 25 page
Hidden and Generalized Conformal Symmetry of Kerr-Sen Spacetimes
It is recently conjectured that generic non-extremal Kerr black hole could be
holographically dual to a hidden conformal field theory in two dimensions.
Moreover, it is known that there are two CFT duals (pictures) to describe the
charged rotating black holes which correspond to angular momentum and
electric charge of the black hole. Furthermore these two pictures can be
incorporated by the CFT duals (general picture) that are generated by
modular group. The general conformal structure can be
revealed by looking at charged scalar wave equation in some appropriate values
of frequency and charge. In this regard, we consider the wave equation of a
charged massless scalar field in background of Kerr-Sen black hole and show in
the "near region", the wave equation can be reproduced by the Casimir operator
of a local hidden conformal
symmetry. We can find the exact agreement between macroscopic and microscopic
physical quantities like entropy and absorption cross section of scalars for
Kerr-Sen black hole. We then find an extension of vector fields that in turn
yields an extended local family of hidden conformal symmetries, parameterized by one
parameter. For some special values of the parameter, we find a copy of
hidden conformal algebra for the charged
Gibbons-Maeda-Garfinkle-Horowitz-Strominger black hole in the strong deflection
limit.Comment: 16 pages, new material and results added, extensive improvements in
interpretation of results, references adde
Blow-up solutions for linear perturbations of the Yamabe equation
For a smooth, compact Riemannian manifold (M,g) of dimension N \geg 3, we
are interested in the critical equation where \Delta_g is the Laplace--Beltrami
operator, S_g is the Scalar curvature of (M,g), , and
is a small parameter
Nonlinear entanglement witnesses, covariance matrices and the geometry of separable states
Entanglement witnesses provide a standard tool for the analysis of
entanglement in experiments. We investigate possible nonlinear entanglement
witnesses from several perspectives. First, we demonstrate that they can be
used to show that the set of separable states has no facets. Second, we give a
new derivation of nonlinear witnesses based on covariance matrices. Finally, we
investigate extensions to the multipartite case.Comment: 12 pages, 2 figures, for the proceedings of DICE2006 in Piombino
(Italy
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