Incorporation of H_2 in vitreous silica, qualitative and quantitative determination from Raman and infrared spectroscopy

Incorporation mechanisms of H_2 in silica glass were studied with Raman and infrared (IR) microspectroscopy. Hydrogenated samples were prepared at temperatures between 800 deg C and 955 deg C at 2 kbar total pressure. Hydrogen fugacities (f_{H_2}) were controlled using the double capsule technique with the iron-w\"ustite (IW) buffer assemblage generating f_{H_2} of 1290-1370 bars corresponding to H_2 partial pressures (P_{H_2}) of 960-975 bars. We found that silica glass hydrogenated under such conditions contains molecular hydrogen (H_2) in addition to SiH and SiOH groups. H_2 molecules dissolved in the quenched glasses introduce a band at 4136 cm^{-1} in the Raman spectra which in comparison to that of gaseous H_2 is wider and is shifted to lower frequency. IR spectra of hydrogenated samples contain a band at 4138 cm^{-1} which we assign to the stretching vibration of H_2 molecules located in non-centrosymmetric sites. The Raman and IR spectra indicate that the dissolved H_2 molecules interact with the silicate network. We suggest that the H_2 band is the envelope of at least three components due to the occupation of at least three different interstitial sites by H_2 molecules. Both, Raman and IR spectra of hydrogenated glasses contain bands at ~2255 cm^{-1} which may be due to the vibration of SiH groups

Conditions for Posterior Contraction in the Sparse Normal Means Problem

The first Bayesian results for the sparse normal means problem were proven for spike-and-slab priors. However, these priors are less convenient from a computational point of view. In the meanwhile, a large number of continuous shrinkage priors has been proposed. Many of these shrinkage priors can be written as a scale mixture of normals, which makes them particularly easy to implement. We propose general conditions on the prior on the local variance in scale mixtures of normals, such that posterior contraction at the minimax rate is assured. The conditions require tails at least as heavy as Laplace, but not too heavy, and a large amount of mass around zero relative to the tails, more so as the sparsity increases. These conditions give some general guidelines for choosing a shrinkage prior for estimation under a nearly black sparsity assumption. We verify these conditions for the class of priors considered by Ghosh and Chakrabarti (2015), which includes the horseshoe and the normal-exponential gamma priors, and for the horseshoe+, the inverse-Gaussian prior, the normal-gamma prior, and the spike-and-slab Lasso, and thus extend the number of shrinkage priors which are known to lead to posterior contraction at the minimax estimation rate

Sbf/MTMR13 coordinates PI(3)P and Rab21 regulation in endocytic control of cellular remodeling.

Cells rely on the coordinated regulation of lipid phosphoinositides and Rab GTPases to define membrane compartment fates along distinct trafficking routes. The family of disease-related myotubularin (MTM) phosphoinositide phosphatases includes catalytically inactive members, or pseudophosphatases, with poorly understood functions. We found that Drosophila MTM pseudophosphatase Sbf coordinates both phosphatidylinositol 3-phosphate (PI(3)P) turnover and Rab21 GTPase activation in an endosomal pathway that controls macrophage remodeling. Sbf dynamically interacts with class II phosphatidylinositol 3-kinase and stably recruits Mtm to promote turnover of a PI(3)P subpool essential for endosomal trafficking. Sbf also functions as a guanine nucleotide exchange factor that promotes Rab21 GTPase activation associated with PI(3)P endosomes. Of importance, Sbf, Mtm, and Rab21 function together, along with Rab11-mediated endosomal trafficking, to control macrophage protrusion formation. This identifies Sbf as a critical coordinator of PI(3)P and Rab21 regulation, which specifies an endosomal pathway and cortical control

An analysis of gender differences in experiences contributing to management development

A review of the literature indicates that management development is, in general, a poorly understood process. However, both development through on-the-job experiences and development of female managers were areas in which research was particularly lacking. The focus of this research, therefore, was management development that occurs through on-the-job experiences, work relationships and management practices. Specifically, the purposes of this study were to (1) determine which on-the-job experiences, work relationships and management practices contribute to management development and (2) to determine if gender differences exist in the experiences that contribute to management development;Questionnaire data from 322 female and 332 male managers in a large multinational organization were analyzed using multivariate and univariate Statistics and Probability; The results summarized a number of key relationships, experiences, and management practices that managers\u27 perceived as enhancing development as well as factors perceived as hindering development. No strong evidence for the existence of gender differences in the experiences contributing to management development was found. Implications of the findings for systematic management development, the progress of women managers, and future research directions were discussed

Examination of the effects of selected factors on the talin-actin interaction

Talin is an adhesion plaque protein believed to be involved in linking actin filaments to cell membranes. In these studies I examined the effects of selected factors on the ability of talin and its 190 kDa proteolytic fragment to interact with actin. A modified method for purifying talin from avian smooth muscle was devised. Cosedimentation assays showed that increasing amounts of talin bound to actin filaments as pH was decreased from 7.4 to 6.4. Talin\u27s ability to increase viscosity of F-actin solutions also was increased with decreasing pH within this range. Electron microscope observations supported a pH-dependent, actin filament crosslinking activity for talin. The ability of talin to crosslink actin filaments was markedly decreased with increasing ionic strength, regardless of pH. Increasing the molar ratio of talin to actin enhanced the interaction. Viscometry studies showed that increasing temperature from 4∘ to 37∘C increased the ability of talin to interact with actin. Talin crosslinked actin filaments into networks and bundles in times as short as 5 min at pH 6.4 and low ionic strength. Talin also bound to and crosslinked preformed actin filaments to the same extent as it did when filaments were formed in its presence. The effects of pH and ionic strength on the ability of talin to bind to actin were shown to be reversible;The 190 kDa talin fragment did not bind actin strongly under conditions that favored the interaction between intact talin and actin (pH 6.4, low ionic strength). However, when the pH was lowered to 6.0, the 190 kDa fragment crosslinked actin filaments into networks and bundles. The effects of the adhesion plaque proteins filamin, vinculin, [alpha]-actinin, and tropomyosin on the ability of talin to cosediment with actin filaments were also studied. Filamin and tropomyosin could reduce the amount of talin that cosedimented with actin, but did not eliminate the talin-actin interaction. Vinculin and [alpha]-actinin did not measurably affect the ability of talin to cosediment with actin. Overall, results from these experiments support a role for talin in the organization and attachment of actin filaments at adhesion plaques

The solar wind as seen by SOHO/SWAN since 1996: comparison with SOHO/LASCO C2 coronal densities

We update the SOHO/SWAN H Lyman-alpha brightness analysis to cover the 1996-2008 time interval. A forward model applied to the intensity maps provides the latitude and time dependence of the interstellar Hydrogen ionisation rate over more than a full solar cycle. The hydrogen ionisation, being almost entirely due to charge-exchange with solar wind ions, reflects closely the solar wind flux. Our results show that the solar wind latitudinal structure during the present solar minimum is strikingly different from the previous minimum, with a much wider slow solar wind equatorial belt which persists until at least the end of 2008. We compute absolute values of the in-ecliptic H ionisation rates using OMNI solar wind data and use them to calibrate our ionisation rates at all heliographic latitudes. We then compare the resulting fluxes with the synoptic LASCO/C2 electron densities at 6 solar radii. The two time-latitude patterns are strikingly similar over all the cycle. This comparison shows that densities at 6 solar radii can be used to infer the solar wind type close to its source, with high (resp. low) densities tracing the slow (resp. fast) solar wind, simply because the density reflects at which altitude occurs the acceleration. The comparison between the two minima suggests that the fast polar wind acceleration occurs at larger distance during the current minimum compared to the previous one. This difference, potentially linked to the magnetic field decrease or(and) the coronal temperature decrease should be reproduced by solar wind expansion models.Comment: Proceedings of the SOHO-23 conference, Sept 21-25, 200

Cooling antihydrogen ions for the free-fall experiment GBAR

We discuss an experimental approach allowing to prepare antihydrogen atoms for the GBAR experiment. We study the feasibility of all necessary experimental steps: The capture of incoming $\bar{\rm H}^+$ ions at keV energies in a deep linear RF trap, sympathetic cooling by laser cooled Be$^+$ ions, transfer to a miniaturized trap and Raman sideband cooling of an ion pair to the motional ground state, and further reducing the momentum of the wavepacket by adiabatic opening of the trap. For each step, we point out the experimental challenges and discuss the efficiency and characteristic times, showing that capture and cooling are possible within a few seconds.Comment: 10 pages, 5 figure