Associated primes for cohomology modules

Let G be a finite group acting linearly on a finite dimensional vector space V defined over a field k of characteristic p, where p is assumed to divide the group order. Let R := S(V *) be the symmetric algebra of the dual on which G acts naturally by algebra automorphisms. We study the R^G-modules Hⁱ(G, R) for i > 0. In particular we give a formula which describes the annihilator of a general element of Hⁱ(G, R) in terms of the relative transfer ideals of R^G, and consequently prove that the associated primes of these cohomology modules are equal to the radicals of certain relative transfer ideals. Received: 5 June 2008     

Bioethanol Production Optimization: A Thermodynamic Analysis

In this work, the phase equilibrium of binary mixtures for bioethanol production by continuous extractive process was studied. The process is composed of four interlinked units: fermentor, centrifuge, cell treatment unit, and flash vessel (ethanol-congener separation unit). A proposal for modeling the vapor–liquid equilibrium in binary mixtures found in the flash vessel has been considered. This approach uses the Predictive Soave–Redlich–Kwong equation of state, with original and modified molecular parameters. The congeners considered were acetic acid, acetaldehyde, furfural, methanol, and 1-pentanol. The results show that the introduction of new molecular parameters r and q in the UNIFAC model gives more accurate predictions for the concentration of the congener in the gas phase for binary and ternary systems.     

Electron correlation studies by means of local-scaling transformations and electron-pair density functions

Electron correlation is one long standing problem of computational electronic structure theory. Even more, with the advent of the density functional theory and, in particular, with its Kohn–Sham implementation, the separation of the non-dynamical and dynamical components of the electron correlation has became an unavoidable requirement towards construction of reliable exchange-correlation functionals. In this paper, we address the analysis of the separation of the non-dynamical and dynamical electron correlation effects from two complementary viewpoints, namely, analysis of the correlation energy components and the analysis of the electron-pair density. The former approach will make use of the local-scaling transformations and the latter will be based on the study of intracule and extracule densities.Work supported by grant 9/UPV-00203.215-13527/2001of the Office of Universities and Research of the The Goverment of the Basque Country and, by grant BQU2001-0208 of the Spanish Ministry of Education and Science.Partially supported by grant G-97000741 of CONICIT of Venezuela.     

Kalium

Ohne Zusammenfassung     

A five-parameter Markov model for simulating the paths of sedimenting particles

The random initial positions of particles in any sedimentation experiment and the extreme sensitivity of the creeping-motion equations to even minute variations in these positions imply that the detailed results from one experiment provide no detailed information about another experiment. However, the five statistical parameters obtained by following the three-dimensional trajectories of spheres form the basis of a Markov model that quickly and accurately simulates the typical behaviour of individual spheres. In this model, velocities are continuous, but nowhere differentiable. The joint position-velocity processes (one for each direction) are both Markov and Gaussian. Thus, no integration is required to produce a position-velocity skeleton. When continuity conditions are imposed, this sequence of values provides all the coefficients of a fourth-degree interpolating polynomial that closely imitates the smooth paths of spheres in real suspensions.     

List of contributors

List of contributors     

Intense terahertz emission from undoped GaAs/n-type GaAs and?InAs/AlSb structures grown on Si substrates in the transmission-geometry excitation

Intense terahertz radiation was generated from femtosecond laser-irradiated InAs and GaAs layers on Si substrates. Results show that InAs/Si and GaAs/Si films can be excited in reflection and transmission geometries. The InAs/Si film exhibited weaker emission for both excitation cases but it will be more feasible as a spectroscopic THz source due to the absence of complex spectral features in its emission spectrum. The GaAs/Si emission is characterized by Fabry?CPerot oscillations but it is 90% of that of p-InAs bulk crystal emission intensity in the reflection geometry. Excitation fluence measurements showed that the InAs/Si film saturates easily due to the laser??s shallow penetration depth in InAs.     

Reconstructing seesaws

We explore some aspects of “reconstructing” the heavy singlet sector of supersymmetric type I seesaw models, for two, three or four singlets. We work in the limit where one light neutrino is massless. In an ideal world, where selected coefficients of the TeV-scale effective Lagrangian could be measured with arbitrary accuracy, the two-singlet case can be reconstructed, two three or more singlets can be differentiated, and an inverse seesaw with four singlets can be reconstructed. In a more realistic world, we estimate ℓ _α →ℓ _β γ expectations with a “Minimal-Flavour-Violation-like” ansatz, which gives a relation between ratios of the three branching ratios. The two-singlet model predicts a discrete set of ratios.