Local Defects are Always Neutral in the Thomas–Fermi–von Weiszäcker Theory of Crystals

The aim of this article is to propose a mathematical model describing the electronic structure of crystals with local defects in the framework of the Thomas–Fermi–von Weizsäcker (TFW) theory. The approach follows the same lines as that used in Cancès et al. (Commun Math Phys 281:129–177, 2008) for the reduced Hartree–Fock model, and is based on thermodynamic limit arguments. We prove, in particular, that it is not possible to model charged defects within the TFW theory of crystals.     

Numerical modeling of guided wave interaction with non-axisymmetric cracks in elastic cylinders

A three dimensional (3D) hybrid method combining the classical finite element (FE) method with the semi-analytical finite element (SAFE) technique is developed. This hybrid method is employed to study the interaction of guided waves with non-axisymmetric damages in cylinders. The near field surrounding the damage is analysed with the 3D FE method. The solution is expanded into sums of guided modes on both inlet and outlet cross-sections. Such eigenmode expansions enable separation into ingoing and outgoing waves, i.e., incident, reflected and transmitted waves. Using the SAFE method, elastic guided modes are then computed at the aforementioned cross-sections thus reducing the analysis to two dimensions (2D). The amplitudes of the incident modes are imposed, whereas those of the scattered modes are determined by solving the global system of the 3D hybrid FE-SAFE model. In this paper, a formula is proposed for the calculation of eigenforces and modal power flows from eigendisplacements and SAFE matrices. This has the advantage of simplifying the post-process of load eigenvectors in hybrid FE-SAFE methods. Results obtained for a vertical free-end cylinder are in good agreement with those published in the literature. Moreover, first results of the interaction of the fundamental compressional, flexural and torsional Pochhammer–Chree modes with non-axisymmetric vertical cracks are obtained and discussed. Then, the interactions of the fundamental compressional mode with oblique free-ends and cracks are briefly addressed. The power balance is shown to be satisfied with a good accuracy.     

Comparison of Fe and Ni opacity calculations for a better understanding of pulsating stellar envelopes

Opacity is an important ingredient of the evolution of stars. The calculation of opacity coefficients is complicated by the fact that the plasma contains partially ionized heavy ions that contribute to opacity dominated by H and He. Up to now, the astrophysical community has greatly benefited from the work of the contributions of Los Alamos [1], Livermore [2], [2a] and [2b] and the Opacity Project (OP) [3]. However unexplained differences of up to 50% in the radiative forces and Rosseland mean values for Fe have been noticed for conditions corresponding to stellar envelopes. Such uncertainty has a real impact on the understanding of pulsating stellar envelopes, on the excitation of modes, and on the identification of the mode frequencies. Temperature and density conditions equivalent to those found in stars can now be produced in laboratory experiments for various atomic species. Recently the photo-absorption spectra of nickel and iron plasmas have been measured during the LULI 2010 campaign, for temperatures between 15 and 40 eV and densities of ∼3 mg/cm³. A large theoretical collaboration, the “OPAC”, has been formed to prepare these experiments. We present here the set of opacity calculations performed by eight different groups for conditions relevant to the LULI 2010 experiment and to astrophysical stellar envelope conditions.     

Geometric analysis for the metropolis algorithm on Lipschitz domains

This paper gives geometric tools: comparison, Nash and Sobolev inequalities for pieces of the relevant Markov operators, that give useful bounds on rates of convergence for the Metropolis algorithm. As an example, we treat the random placement of N hard discs in the unit square, the original application of the Metropolis algorithm.     

Preface to the special issue of JOGO on the occasion of the 40th anniversary of the Group for Research in Decision Analysis (GERAD).

Journal of Global Optimization -     

The semi-Markov beta-Stacy process: a Bayesian non-parametric prior for semi-Markov processes.

The literature on Bayesian methods for the analysis of discrete-time semi-Markov processes is sparse. In this paper, we introduce the semi-Markov beta-Stacy process, a stochastic process useful for the Bayesian non-parametric analysis of semi-Markov processes. The semi-Markov beta-Stacy process is conjugate with respect to data generated by a semi-Markov process, a property which makes it easy to obtain probabilistic forecasts. Its predictive distributions are characterized by a reinforced random walk on a system of urns.

     

Infrared and Raman Spectra of Solid Guanine Derivatives. 7-METHYLGUANINE, 9-METHYLGUANINE, 9-ETHYLGUANINE, 1,7-DIMETHYLGUANINE,and 1,9-DIMETHYLGUANINE.

The infrared and Raman spectra of 7-methylguanine, 9-methylguanine, 9-ethylguanine, 1,7-dimethylguanine, and 1,9-dimethylguanine in the solid state have been reported and discussed. Hydrogen bonds in these solid guanine derivatives bring about strong perturbations which are discussed in terms of structural data given by X-ray diffraction methods. The spectra of guanine and 9-methylguanine are compared with the spectra of the monomers isolated in low-temperature matrices.     

A new differential thermal analysis setup for measuring high pressure phase transitions

A new setup has been recently developed in the toroidal opposed-anvil device ‘Conac 40’ to perform differential thermal analysis in a high pressure range (0–6 GPa). To evaluate the precision and the reliability of the setup, the high pressure melting curve of germanium and the transition points of α-iron have been investigated up to 5.3 GPa and compared with previous results.     

Effects of high pressure on unsaturated fatty acids

The objective of this study is to investigate the effects of high pressure processing on the molecular structure of some unsaturated fatty acids. Samples of elaidic acid, linoleic acid, ZE and EE conjugated linoleic acid are treated at 293 or 333?K at pressures up to 700?MPa. It is observed that the adiabatic heat generated from compression is able to bring the sample temperature above 373?K after 700?MPa. These relatively extreme conditions are of great interest for food sterilization, but they may induce undesirable change in fatty acid quality characteristics. To check for structural changes, Raman spectra of the samples are analysed after treatments. The comparison with Raman spectra of samples kept at atmospheric pressure shows that pressure induces some conformational changes at the hydrocarbon skeleton in solid samples, while the liquid ones remain unchanged. No cis/trans isomerization occurs, but gauche conformers are likely to be present.