Phonon thermodynamics and elastic behavior of GaAs at high temperatures and pressures

The phonons of wurtzite and zinc blende GaAs were calculated at simultaneously elevated temperature and pressure, and elastic constants were calculated as functions of pressure. Pressure caused instabilities of shorter-wavelength transverse acoustic modes in both wurtzite and zinc blende GaAs, causing them to fall to zero at 18 and 20 GPa, respectively. The Born stability criteria, which depend on elastic constants and only long wavelength phonons, therefore overestimated the pressure needed to induce instability at 0 K. At elevated temperatures, explicit anharmonicity pushes the onset of instability to higher pressures in both wurtzite and zinc blende GaAs. Phonon linewidth and densities of states data showed that the quasiharmonic approximation failed to account for temperature-induced phonon frequency shifts, and the quasiharmonic approximation became less reliable at elevated pressure. In general, the number of three-phonon processes increased with pressure, thereby increasing the temperature-driven broadening of phonon spectral lineshapes

Neutralino Relic Density including Coannihilations

We evaluate the relic density of the lightest neutralino, the lightest supersymmetric particle, in the Minimal Supersymmetric extension of the Standard Model (MSSM). For the first time, we include all coannihilation processes between neutralinos and charginos for any neutralino mass and composition. We use the most sophisticated routines for integrating the cross sections and the Boltzmann equation. We properly treat (sub)threshold and resonant annihilations. We also include one-loop corrections to neutralino masses. We find that coannihilation processes are important not only for light higgsino-like neutralinos, as pointed out before, but also for heavy higgsinos and for mixed and gaugino-like neutralinos. Indeed, coannihilations should be included whenever |\mu| \lsim 2 |M_1|, independently of the neutralino composition. When $|\mu| \sim |M_1|$, coannihilations can increase or decrease the relic density in and out of the cosmologically interesting region. We find that there is still a window of light higgsino-like neutralinos that are viable dark matter candidates and that coannihilations shift the cosmological upper bound on the neutralino mass from 3 to 7 TeV.Comment: LaTeX, 14 embedded eps figures, uses epsfig. For paper with full resolution figures, see http://www.teorfys.uu.se/~edsjo/Welcome.html A few typos correcte

Transport coefficients in high temperature gauge theories: (II) Beyond leading log

Results are presented of a full leading-order evaluation of the shear viscosity, flavor diffusion constants, and electrical conductivity in high temperature QCD and QED. The presence of Coulomb logarithms associated with gauge interactions imply that the leading-order results for transport coefficients may themselves be expanded in an infinite series in powers of 1/log(1/g); the utility of this expansion is also examined. A next-to-leading-log approximation is found to approximate the full leading-order result quite well as long as the Debye mass is less than the temperature.Comment: 38 pages, 6 figure

Discrete Data Transfer Technique for Fluid-Structure Interaction

This paper presents a general three-dimensional algorithm for data transfer between dissimilar meshes. The algorithm is suitable for applications of fluid-structure interaction and other high-fidelity multidisciplinary analysis and optimization. Because the algorithm is independent of the mesh topology, we can treat structured and unstructured meshes in the same manner. The algorithm is fast and accurate for transfer of scalar or vector fields between dissimilar surface meshes. The algorithm is also applicable for the integration of a scalar field (e.g., coefficients of pressure) on one mesh and injection of the resulting vectors (e.g., force vectors) onto another mesh. The author has implemented the algorithm in a C++ computer code. This paper contains a complete formulation of the algorithm with a few selected results

A detailed next-to-leading order QCD analysis of deeply virtual Compton scattering observables

We present a detailed next-to-leading order (NLO) leading twist QCD analysis of deeply virtual Compton scattering (DVCS) observables, for several different input scenarios, in the MS-bar scheme. We discuss the size of the NLO effects and the behavior of the observables in skewedness $\zeta$, momentum transfer, $t$, and photon virtuality, $q^2=-Q^2$. We present results on the amplitude level for unpolarized and longitudinally polarized lepton probes, and unpolarized and longitudinally polarized proton targets. We make predictions for various asymmetries and for the DVCS cross section and compare with the available data.Comment: 38 pages, 40 figures, revtex, published version. Substantially shortened for publication: appendices and ten figures removed, sections III, IV and V condensed. Several physics points improved or corrected in response to referee's report. Incorrect citations and typo in eq.(3) correcte

Nichtlineare Optimierung geometrisch definierter Fugen von räumlich gekrümmten Betonfertigteilen mit isogeometrischen Verfahren

Die Vision dieses Projektes ist es, einen durchgängigen Prozess zu entwickeln, der es erlaubt, den Entwurf, die Berechnung und die Fugenoptimierung von flächigen Strukturen aus Betonfertigteilen sehr einfach und effizient durchzuführen. Damit soll die Herstellung von freien Formen, wie beispielsweise „Blobs“ und Hängeformen aus Beton, unterstützt und gefördert werden.The vision of this project is to develop a continuous process that allows very easy and efficient design, calculation and joint optimization of surface-like structures made of precast concrete elements. This should support and encourage the production of free forms, such as “blobs” and hanging forms made of concrete

LINEAR AND NONLINEAR MIXED-EFFECTS MODELS

Recent developments in computational methods for maximum likelihood (ML) or restricted maximum likelihood (REML) estimation of parameters in general linear mixed-effects models have made the analysis of data in typical agricultural settings much easier. With software such as SAS PROC MIXED we are able to handle data from random-effects one-way classifications, from blocked designs including incomplete blocked designs, from hierarchical designs such as splitplot designs, and other types of data that may be described as repeated measures or longitudinal data or growth-curve data. It is especially helpful that the new computational methods do not depend on balance in the data so we are able to deal more easily with observational studies or with randomly missing data in a designed experiment . We describe some of the new computational approaches and how they are implemented in the nlme3.0 library for the S-PLUS language. One of the most powerful features of this language is the graphics capabilities, especially the trellis graphics facilities developed by Bill Cleveland and his coworkers at Bell Labs. Although most participants in this conference may be more familiar with SAS, and most of the models described here can be fit with PROC MIXED or the NLiNMIX macro or new PROC NLM IXED in SAS version 7, some exposure to the combination of graphical display and model-fitting approaches from S-PLUS may be informative . We show how data exploration with trellis graphics, followed by fitting and comparing mixedeffects models, followed by graphical assessment of the fitted model can be used in a variety of situations. On some occasions, such as modeling growth curves, a linear trend or polynomial trend or other types of linear statistical models for the within-subject time dependence are just not going to do an adequate job of representing the data. In those cases, a nonlinear model is more appropriate. We show how the concept of a random coefficient model can be extended to nonlinear models so as to fit nonlinear mixed-effects models

Analytical Solution for the Current Distribution in Multistrand Superconducting Cables

Current distribution in multistrand superconducting cables can be a major concern for stability in superconducting magnets and for field quality in particle accelerator magnets. In this paper we describe multistrand superconducting cables by means of a distributed parameters circuit model. We derive a system of partial differential equations governing current distribution in the cable and we give the analytical solution of the general system. We then specialize the general solution to the particular case of uniform cable properties. In the particular case of a two-strand cable, we show that the analytical solution presented here is identical to the one already available in the literature. For a cable made of N equal strands we give a closed form solution that to our knowledge was never presented before. We finally validate the analytical solution by comparison to numerical results in the case of a step-like spatial distribution of the magnetic field over a short Rutherford cable, both in transient and steady state conditions

XVoxel-Based Parametric Design Optimization of Feature Models

Parametric optimization is an important product design technique, especially in the context of the modern parametric feature-based CAD paradigm. Realizing its full potential, however, requires a closed loop between CAD and CAE (i.e., CAD/CAE integration) with automatic design modifications and simulation updates. Conventionally the approach of model conversion is often employed to form the loop, but this way of working is hard to automate and requires manual inputs. As a result, the overall optimization process is too laborious to be acceptable. To address this issue, a new method for parametric optimization is introduced in this paper, based on a unified model representation scheme called eXtended Voxels (XVoxels). This scheme hybridizes feature models and voxel models into a new concept of semantic voxels, where the voxel part is responsible for FEM solving, and the semantic part is responsible for high-level information to capture both design and simulation intents. As such, it can establish a direct mapping between design models and analysis models, which in turn enables automatic updates on simulation results for design modifications, and vice versa -- effectively a closed loop between CAD and CAE. In addition, robust and efficient geometric algorithms for manipulating XVoxel models and efficient numerical methods (based on the recent finite cell method) for simulating XVoxel models are provided. The presented method has been validated by a series of case studies of increasing complexity to demonstrate its effectiveness. In particular, a computational efficiency improvement of up to 55.8 times the existing FCM method has been seen.Comment: 22 page