Extended x-ray absorption fine structure study of porous GaSb formed by ion implantation

Porous GaSb has been formed by Ga ion implantation into crystalline GaSb substrates at either room temperature or −180 °C. The morphology has been characterized using scanning electron microscopy and the atomic structure was determined using extended x-ray absorption fine structure spectroscopy. Room-temperature implantation at low fluences leads to the formation of ∼20-nm voids though the material remains crystalline. Higher fluences cause the microstructure to evolve into a network of amorphous GaSb rods ∼15 nm in diameter. In contrast, implantation at −180 °C generates large, elongated voids but no rods. Upon exposure to air, the surface of the porous material is readily oxidized yielding Ga₂O₃ and metallic Sb precipitates, the latter resulting from the reduction of unstable Sb₂O₃. We consider and discuss the atomic-scale mechanisms potentially operative during the concurrent crystalline-to-amorphous and continuous-to-porous transformations

The Contribution of Network Organization and Integration to the Development of Cognitive Control

Cognitive control, which continues to mature throughout adolescence, is supported by the ability for well-defined organized brain networks to flexibly integrate information. However, the development of intrinsic brain network organization and its relationship to observed improvements in cognitive control are not well understood. In the present study, we used resting state functional magnetic resonance imaging (RS-fMRI), graph theory, the antisaccade task, and rigorous head motion control to characterize and relate developmental changes in network organization, connectivity strength, and integration to inhibitory control development. Subjects were 192 10–26-y-olds who were imaged during 5 min of rest. In contrast to initial studies, our results indicate that network organization is stable throughout adolescence. However, cross-network integration, predominantly of the cingulo-opercular/salience network, increased with age. Importantly, this increased integration of the cingulo-opercular/salience network significantly moderated the robust effect of age on the latency to initiate a correct inhibitory control response. These results provide compelling evidence that the transition to adult-level inhibitory control is dependent upon the refinement and strengthening of integration between specialized networks. Our findings support a novel, two-stage model of neural development, in which networks stabilize prior to adolescence and subsequently increase their integration to support the cross-domain incorporation of information processing critical for mature cognitive control

Sustainability assessment of Thailand's electricity planning: Using section 1 of the 2009 hydropower sustainability assessment protocol

We conducted a rapid assessment of the sustainability performance of the Thai power development plan and a number of related planning processes, focusing on the Thai plan’s implications for development of hydropower in the Mekong region. We used the August 2009 draft Hydropower Sustainability Assessment Protocol (HSAP), which is a qualitative multi-criteria audit tool designed to be used by a wide range of interested parties. We applied the HSAP from a public interest perspective: We assumed that aquatic ecosystems in the Mekong region are critically important for less privileged people, and that Thailand’s electricity planners can and should consider the distributional and ecological consequences of planning choices on a Mekong regional scale. Two sets of readers may find the report of interest. Those who seek insight into sustainability challenges posed, when a middle-income Asian country turns to hydropower imports from poorer neighbors, will find a contextualized and empirically rich discussion. Readers interested in the practice of integrated sustainability assessment will find a detailed application of the August 2009 draft Hydropower Sustainability Assessment Protocol (HSAP) – a tool which has been somewhat controversial to date (Bosshard 2010; Foran 2010; Locher, et al. 2010). Does rapid assessment improve our understanding of sustainability challenges? We found a number of significant gaps or weaknesses in the Thai power development plan (PDP). Combined with political instability faced by the Thai government in 2009-10, these challenges resulted in generally low levels of sustainability performance of the 2010 PDP. The Thai Ministry of Energy however appears genuinely willing to cooperate with civil society organizations in ongoing work that may improve the next PDP. The 2009 HSAP was not an easy tool to use. Many indicators required careful re-interpretation. The assessment was time consuming: partly because multiple processes deserved to be assessed in order to derive an adequate picture of multi-level planning processes. Sustainable development needs early-stage planning tools, which allow options to be rethought. Despite its practical difficulties, the 2009 HSAP compresses a range of important issues into one emerging framework. Although the Thai PDP is ultimately a bureaucratic planning process, its sustainability can – and must – be influenced by civil society and regional-level actors. Though careful interpretation of the HSAP is required, this finding is adequately captured by the use of the Protocol

Co–Au core-shell nanocrystals formed by sequential ion implantation into SiO₂

Co–Au core-shell nanocrystals (NCs) were formed by sequential ion implantation of Au and Co into thin SiO₂. The NCs were investigated by means of transmission electron microscopy and extended x-ray absorption fine structure spectroscopy. The latter reveals a bond length expansion in the Co core compared to monatomic Co NCs. Concomitantly, a significant contraction of the bond length and a significant reduction of the effective Au–Au coordination number were observed in the Au shells. Increased Debye-Waller factors indicate significant strain in the NCs. These experimental results verify recent theoretical predictions.P.K. and M.C.R. thank the Australian Research Council for support. P.K., B.H., B.J., and M.C.R. were supported by the Australian Synchrotron Research Program, funded by the Commonwealth of Australia via the Major National Research Facilities Program

Postdeployment military mental health training: Cross-national evaluations

Deployments increase risk for adjustment problems in service members. To mitigate this increased risk, mental health training programs have been developed and implemented in several nations. As part of a coordinated effort, three nations adapted a U.S. mental health training program that had been validated by a series of group randomized trials demonstrating improvement in postdeployment adjustment. Implementation of evidence-based programs in a new context is challenging: How much of the original program needs to remain intact in order to retain its utility? User satisfaction rates can provide essential data to assess how well a program is accepted. This article summarizes service member ratings of postdeployment mental health training and compares ratings from service members across four nations. The participating nations (Canada, New Zealand, United Kingdom, and the United States) administered mental health training to active duty military personnel in their respective nations. Following the training, military personnel completed an evaluation of the training. Overall, across the four nations, more than 70% of military personnel agreed or strongly agreed that they were satisfied with the mental health training. Although some differences in evaluations were observed across nations, components of training that were most important to overall satisfaction with the training were strikingly similar across nations. Fundamentally, it appears feasible that despite cultural and organizational differences, a mental health training program developed in one nation can be successfully adapted for use in other nations

The galactic population of white dwarfs

Original paper can be found at: http://www.iop.org/EJ/conf DOI: 10.1088/1742-6596/172/1/012004 [16th European White Dwarfs Workshop]The contribution of white dwarfs of the different Galactic populations to the stellar content of our Galaxy is only poorly known. Some authors claim a vast population of halo white dwarfs, which would be in accordance with some investigations of the early phases of Galaxy formation claiming a top-heavy initial– mass– function. Here, I present a model of the population of white dwarfs in the Milky Way based on observations of the local white dwarf sample and a standard model of Galactic structure. This model will be used to estimate the space densities of thin disc, thick disc and halo white dwarfs and their contribution to the baryonic mass budget of the Milky Way. One result of this investigation is that white dwarfs of the halo population contribute a large fraction of the Galactic white dwarf number count, but they are not responsible for the lion's share of stellar mass in the Milky Way. Another important result is the substantial contribution of the – often neglected – population of thick disc white dwarfs. Misclassification of thick disc white dwarfs is responsible for overestimates of the halo population in previous investigations.Peer reviewe

A New Look at the Local White Dwarf Population

We have conducted a detailed new survey of the local population of white dwarfs lying within 20 pc of the Sun. A new revised catalog of local white dwarfs containing 122 entries (126 individual degenerate stars) is presented. This list contains 27 white dwarfs not included in a previous list from 2002, as well as new and recently published trigonometric parallaxes. In several cases new members of the local white dwarf population have come to light through accurate photometric distance estimates. In addition, a suspected new double degenerate system (WD 0423+120) has been identified. The 20 pc sample is currently estimated to be 80% complete. Using a variety of recent spectroscopic, photometric, and trigonometric distance determinations, we re-compute a space density of 4.8 ± 0.5 × 10−3 pc−3 corresponding to a mass density of 3.2 ± 0.3 × 10−3 M pc−3 from the complete portion of the sample within 13 pc. We find an overall mean mass for the local white dwarfs of 0.665 M, a value larger than most other non-volume-limited estimates. Although the sample is small, we find no evidence of a correlation between mass and temperature in which white dwarfs below 13,000 K are systematically more massive than those above this temperature. Within 20 pc 25% of the white dwarfs are in binary systems (including double degenerate systems). Approximately 6% are double degenerates and 6.5% are Sirius-like systems. The fraction of magnetic white dwarfs in the local population is found to be 13%

Bond length contraction in Au nanocrystals formed by ion implantation into thin SiO[sub 2]

Au nanocrystals (NCs) fabricated by ion implantation into thin SiO₂ and annealing were investigated by means of extended x-rayabsorption fine structure (EXAFS)spectroscopy and transmission electron microscopy. A bond length contraction was observed and can be explained by surface tension effects in a simple liquid-drop model. Such results are consistent with previous reports on nonembedded NCs implying a negligible influence of the SiO₂ matrix. Cumulant analysis of the EXAFS data suggests surface reconstruction or relaxation involving a further shortened bond length. A deviation from the octahedral closed shell structure is apparent for NCs of size 25Å.P. K. is grateful to the Humboldt Foundation in Germany for support. P.K., B.J., A.C., C.J.G., G.d.M.A., G.J.F., and M.C.R. were supported by the Australian Synchrotron Research Program