All electron and pseudopotential study of the spin polarization of the V (001) surface: LDA versus GGA

The spin-polarization at the V(001) surface has been studied by using different local (LSDA) and semilocal (GGA) approximations to the exchange-correlation potential of DFT within two ab initio methods: the all-electron TB-LMTO-ASA and the pseudopotential LCAO code SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms). A comparative analysis is performed first for the bulk and then for a N-layer V(001) film (7 < N < 15). The LSDA approximation leads to a non magnetic V(001) surface with both theoretical models in agreement (disagreement) with magneto-optical Kerr (electron-capture spectroscopy) experiments. The GGA within the pseudopotential method needs thicker slabs than the LSDA to yield zero moment at the central layer, giving a high surface magnetization (1.70 Bohr magnetons), in contrast with the non magnetic solution obtained by means of the all-electron code.Comment: 12 pages, 1 figure. Latex gzipped tar fil

A proposal for a coordinated effort for the determination of brainwide neuroanatomical connectivity in model organisms at a mesoscopic scale

In this era of complete genomes, our knowledge of neuroanatomical circuitry remains surprisingly sparse. Such knowledge is however critical both for basic and clinical research into brain function. Here we advocate for a concerted effort to fill this gap, through systematic, experimental mapping of neural circuits at a mesoscopic scale of resolution suitable for comprehensive, brain-wide coverage, using injections of tracers or viral vectors. We detail the scientific and medical rationale and briefly review existing knowledge and experimental techniques. We define a set of desiderata, including brain-wide coverage; validated and extensible experimental techniques suitable for standardization and automation; centralized, open access data repository; compatibility with existing resources, and tractability with current informatics technology. We discuss a hypothetical but tractable plan for mouse, additional efforts for the macaque, and technique development for human. We estimate that the mouse connectivity project could be completed within five years with a comparatively modest budget.Comment: 41 page

Models of Neocortical Layer 5b Pyramidal Cells Capturing a Wide Range of Dendritic and Perisomatic Active Properties

The thick-tufted layer 5b pyramidal cell extends its dendritic tree to all six layers of the mammalian neocortex and serves as a major building block for the cortical column. L5b pyramidal cells have been the subject of extensive experimental and modeling studies, yet conductance-based models of these cells that faithfully reproduce both their perisomatic Na+-spiking behavior as well as key dendritic active properties, including Ca2+ spikes and back-propagating action potentials, are still lacking. Based on a large body of experimental recordings from both the soma and dendrites of L5b pyramidal cells in adult rats, we characterized key features of the somatic and dendritic firing and quantified their statistics. We used these features to constrain the density of a set of ion channels over the soma and dendritic surface via multi-objective optimization with an evolutionary algorithm, thus generating a set of detailed conductance-based models that faithfully replicate the back-propagating action potential activated Ca2+ spike firing and the perisomatic firing response to current steps, as well as the experimental variability of the properties. Furthermore, we show a useful way to analyze model parameters with our sets of models, which enabled us to identify some of the mechanisms responsible for the dynamic properties of L5b pyramidal cells as well as mechanisms that are sensitive to morphological changes. This automated framework can be used to develop a database of faithful models for other neuron types. The models we present provide several experimentally-testable predictions and can serve as a powerful tool for theoretical investigations of the contribution of single-cell dynamics to network activity and its computational capabilities

THREE ASPECTS OF THE COMPUTATION OF ELECTRONIC STRUCTURES OF METALS AT THE UNIVERSITY OF FLORIDA : ISOMORPHIC PHASE TRANSITION AND COHESIVE ENERGY IN Cs ; VANADIUM NON-MAGNETIC TO MAGNETIC TRANSITION WITH LATTICE SIZE ; AND SOFT X-RAY EMISSION SPECTRA OF TiC AND NbC

Des calculs « self-consistents » APW ont été faits pour obtenir les valeurs propres et les fonctions d'onde électroniques, dans le cadre de l'approximation Xα pour le potentiel d'échange et de l'approximation « muffin-tin » pour le potentiel coulombien agissant sur un électron. On utilise ces informations pour calculer les énergies de cohésion du césium et du vanadium métalliques, et le changement de phase isomorphe du césium. La magnétisation du vanadium en fonction du paramètre du réseau a été examinée et une transition magnétique a été trouvée. Les éléments de matrice du moment ont été estimés pour les carbures de titane et de niobium en vue de l'obtention d'une expression approximative pour la dépendance énergétique de l'émission de rayons X mous à partir de la bande de valence, en fonction des densités partielles d'états ; ceci permet l'interprétation des données expérimentales concernant les propriétés électroniques calculées.Self-consistent APW calculations have been performed to provide electron eigen-values and wave functions for several systems, within the Xα approximation for the exchange and within the muffi-tin approximation for generating and utilizing the effective one-electron potential. This information has been used to calculate cohesive energies for metallic cesium and vanadium and to calculate the isomorphic phase transition of cesium. The forma1 magnetization of vanadium as a function of its lattice parameter has been examined and a magnetic transition found. Momentum matrix elements for titanium carbide and niobium carbide have been estimated to provide an approximate expression for the energy dependence of the soft X-ray valence-band emission in terms of partial densities of states, allowing interpretation of the experimental data in terms of the calculated electronic properties

Pharmacokinetics of nevirapine: initial single-rising-dose study in humans.

Nevirapine, a nonnucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase, was administered for the first time to humans in a pilot study designed to investigate the pharmacokinetics and tolerance of the drug following single-dose administration to 21 HIV-1-infected individuals. The study followed a parallel design. Different groups of three subjects each were given one of seven dose levels (2.5 to 400 mg) in sequential order, starting with the lowest dose. Each subject received only one dose. Nevirapine was rapidly absorbed at all doses from a tablet formulation. Peak concentrations in plasma were generally achieved within 90 min of dose administration. Secondary peaks were also noted between 3 and 12 h or between 24 and 28 h, the latter being noted mainly in subjects receiving the higher doses. After 24 h, concentrations in plasma declined in a log-linear fashion. The terminal half-life and mean residence time exceeded 24 h in all but one subject, indicating a prolonged disposition time in this population. Both peak concentrations in plasma and areas under the plasma concentration-time curves increased proportionally with increasing dose from 2.5 to 200 mg; however, the increase in the peak concentration in plasma and the area under the plasma concentration-time curve appeared to be less than proportional at the 400-mg dose level in this small number of subjects. This observation may be due to increased clearance or decreased absorption at the highest dose or population differences in absorption or clearance between doses. Studies with a cross-over design are planned to resolve these issues. The pharmacokinetic characteristics of nevirapine are appropriate for once-daily administration. A daily 12.5-mg dose is predicted to achieve trough concentrations in plasma in the range required to totally inhibit replication of wild-type HIV-1 in human T-cell culture