751 research outputs found
The use of data-mining for the automatic formation of tactics
This paper discusses the usse of data-mining for the automatic formation of tactics. It was presented at the Workshop on Computer-Supported Mathematical Theory Development held at IJCAR in 2004. The aim of this project is to evaluate the applicability of data-mining techniques to the automatic formation of tactics from large corpuses of proofs. We data-mine information from large proof corpuses to find commonly occurring patterns. These patterns are then evolved into tactics using genetic programming techniques
Ultracold atoms in one-dimensional optical lattices approaching the Tonks-Girardeau regime
Recent experiments on ultracold atomic alkali gases in a one-dimensional
optical lattice have demonstrated the transition from a gas of soft-core bosons
to a Tonks-Girardeau gas in the hard-core limit, where one-dimensional bosons
behave like fermions in many respects. We have studied the underlying many-body
physics through numerical simulations which accommodate both the soft-core and
hard-core limits in one single framework. We find that the Tonks-Girardeau gas
is reached only at the strongest optical lattice potentials. Results for
slightly higher densities, where the gas develops a Mott-like phase already at
weaker optical lattice potentials, show that these Mott-like short range
correlations do not enhance the convergence to the hard-core limit.Comment: 4 pages, 3 figures, replaced with published versio
Regularization of Diagrammatic Series with Zero Convergence Radius
The divergence of perturbative expansions for the vast majority of
macroscopic systems, which follows from Dyson's collapse argument, prevents
Feynman's diagrammatic technique from being directly used for controllable
studies of strongly interacting systems. We show how the problem of divergence
can be solved by replacing the original model with a convergent sequence of
successive approximations which have a convergent perturbative series. As a
prototypical model, we consider the zero-dimensional
theory.Comment: 4 pages, 3 figure
Supersolid phase with cold polar molecules on a triangular lattice
We study a system of heteronuclear molecules on a triangular lattice and
analyze the potential of this system for the experimental realization of a
supersolid phase. The ground state phase diagram contains superfluid, solid and
supersolid phases. At finite temperatures and strong interactions there is an
additional emulsion region, in contrast to similar models with short-range
interactions. We derive the maximal critical temperature and the
corresponding entropy for supersolidity and find feasible
experimental conditions for its realization.Comment: 4 pages, 4 figure
Original Macromolecular Architectures Based on poly(ε-caprolactone) and poly(ε-thiocaprolactone) Grafted onto Chitosan Backbone
Polyester and/or polythioester grafted chitosan copolymers were synthesized. For that, poly(ε-caprolactone) (PCL), poly(ε-thiocaprolactone) (PTCL), and their copolymers were first synthesized by ring opening polymerization. Copolymers with caprolactone:thiocaprolactone (CL:TCL) molar ratios of 2:1, 1:1, 1:2 were synthesized. All of the synthesized macromolecular architectures were characterized using different spectral (Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H-NMR), X-Ray diffraction (XRD)) and thermal (Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA)) methods. Grafting was then performed according two distinct routes: (i) using a blend of both homopolymers (PCL and PTCL) or (ii) using pre-synthesized copolymers with controlled CL:TCL ratios. Hexamethylene diisocyanate was used as a grafting/coupling agent through urethane bonds with high yield. Grafting preferentially occurred at sulfur sites. The results indicated that PTCL is more reactive and favorable than PCL for grafting onto chitosan. With the homopolymers blend grafting route, the corresponding materials mostly had a higher PTCL portion than expected. To obtain polyester grafted chitosan with a determined CL:TCL ratio, the copolymer grafting route would yield better result
Pt decorated amorphous RuIr alloys as high efficiency electrocatalyst for methanol oxidation
This study focuses primarily on improving the utilization and
activity of anodic catalysts for methanol electro-oxidation. The
Direct Methanol Fuel Cell (DMFC) anodic catalyst, a carbon
supported Pt decorated amorphous RuIr nanoparticles catalyst
(Pt@RuIr/C) was prepared by a two-step reduction method. The
structure of Pt@RuIr/C nanoparticles was confirmed by
Transmission Electron Microscopy (TEM) and X-ray Diffraction
(XRD). The Pt@RuIr electrocatalysts exhibited good uniformity in
distribution. Cyclic Voltammetry experiments showed that under
the same quality of noble-metal, the Pt@RuIr/C catalyst had higher
activity than the PtRuIr/C catalyst for methanol oxidation. It was
also shown that the as-prepared structure of the Pt decorated
amorphous RuIr alloys could obviously decrease the usage of
noble-metal and enhance its catalytic activity at the same time.Web of Scienc
Identification of post-transcriptionally regulated Xenopus tropicalis maternal mRNAs by microarray
Cytoplasmic control of the adenylation state of mRNAs is a critical post-transcriptional process involved in the regulation of mRNAs stability and translational efficiency. The early development of Xenopus laevis has been a major model for the study of such regulations. We describe here a microarray analysis to identify mRNAs that are regulated by changes in their adenylation state during oogenesis and early development of the diploid frog Xenopus tropicalis. The microarray data were validated using qRT–PCR and direct analysis of the adenylation state of endogenous maternal mRNAs during the period studied. We identified more than 500 mRNAs regulated at the post-transcriptional level among the 3000 mRNAs potentially detected by the microarray. The mRNAs were classified into nine different adenylation behavior categories. The various adenylation profiles observed during oocyte maturation and early development and the analyses of 3′-untranslated region sequences suggest that previously uncharacterized sequence elements control the adenylation behavior of the newly identified mRNAs. These data should prove useful in identifying mRNAs with important functions during oocyte maturation and early development
Optimal Monte Carlo Updating
Based on Peskun's theorem it is shown that optimal transition matrices in
Markov chain Monte Carlo should have zero diagonal elements except for the
diagonal element corresponding to the largest weight. We will compare the
statistical efficiency of this sampler to existing algorithms, such as
heat-bath updating and the Metropolis algorithm. We provide numerical results
for the Potts model as an application in classical physics. As an application
in quantum physics we consider the spin 3/2 XY model and the Bose-Hubbard model
which have been simulated by the directed loop algorithm in the stochastic
series expansion framework.Comment: 6 pages, 5 figures, replaced with published versio
Finite-temperature effects on the superfluid Bose-Einstein condensation of confined ultracold atoms in three-dimensional optical lattices
We discuss the finite-temperature phase diagram in the three-dimensional
Bose-Hubbard (BH) model in the strong correlation regime, relevant for
Bose-Einstein condensates in optical lattices, by employing a quantum rotor
approach. In systems with strong on site repulsive interactions, the rotor U(1)
phase variable dual to the local boson density emerges as an important
collective field. After establishing the connection between the rotor
construction and the the on--site interaction in the BH model the robust
effective action formalism is developed which allows us to study the superfluid
phase transition in various temperature--interaction regimes
Quantitative Determination of Temperature in the Approach to Magnetic Order of Ultracold Fermions in an Optical Lattice
We perform a quantitative simulation of the repulsive Fermi-Hubbard model using an ultracold gas trapped in an optical lattice. The entropy of the system is determined by comparing accurate measurements of the equilibrium double occupancy with theoretical calculations over a wide range of parameters. We demonstrate the applicability of both high-temperature series and dynamical mean-field theory to obtain quantitative agreement with the experimental data. The reliability of the entropy determination is confirmed by a comprehensive analysis of all systematic errors. In the center of the Mott insulating cloud we obtain an entropy per atom as low as 0.77k(B) which is about twice as large as the entropy at the Neel transition. The corresponding temperature depends on the atom number and for small fillings reaches values on the order of the tunneling energy
- …