Myelination of the right parahippocampal cingulum is associated with physical activity in young healthy adults

Recent evidence suggests that individual differences in physical activity (PA) may be associated with individual differences in white matter microstructure and with grey matter volume of the hippocampus. Therefore, this study investigated the association between PA and white matter microstructure of pathways connecting to the hippocampus. A total of 33 young, healthy adults underwent magnetic resonance imaging (MRI). High angular resolution diffusion-weighted imaging and multi-component relaxometry MRI scans (multi-component driven equilibrium pulse observation of T1 and T2) were acquired for each participant. Activity levels (AL) of participants were calculated from 72-h actigraphy recordings. Tractography using the damped Richardson Lucy algorithm was used to reconstruct the fornix and bilateral parahippocampal cinguli (PHC). The mean fractional anisotropy (FA) and the myelin water fraction (MWF), a putative marker of myelination, were determined for each pathway. A positive correlation between both AL and FA and between AL and MWF were hypothesized for the three pathways. There was a selective positive correlation between AL and MWF in the right PHC (r = 0.482, p = 0.007). Thus, our results provide initial in vivo evidence for an association between myelination of the right PHC and PA in young healthy adults. Our results suggest that MWF may not only be more specific, but also more sensitive than FA to detect white matter microstructural alterations. If PA was to induce structural plasticity of the right PHC this may contribute to reverse structural alterations of the right PHC in neuropsychiatric disorder with hippocampal pathologies

A machine learning approach to drawing phase diagrams of topological lasing modes

Identifying phases and analyzing the stability of dynamic states are ubiquitous and important problems which appear in various physical systems. Nonetheless, drawing a phase diagram in high-dimensional and large parameter spaces has remained challenging. Here, we propose a data-driven method to derive the phase diagram of lasing modes in topological insulator lasers. The classification is based on the temporal behaviour of the topological modes obtained via numerical integration of the rate equation. A semi-supervised learning method is used and an adaptive library is constructed in order to distinguish the different topological modes present in the generated parameter space. The proposed method successfully distinguishes the different topological phases in the Su-Schrieffer-Heeger (SSH) lattice with saturable gain.This demonstrates the possibility of classifying the topological phases without needing for expert knowledge of the system and may give valuable insight into the fundamental physics of topological insulator lasers via reverse engineering.Comment: 13 pages, 12 figure

How does tillage intensity affect soil organic carbon? A systematic review protocol

Background Soils contain the greatest terrestrial carbon (C) pool on the planet. Since approximately 12% of soil C is held in cultivated soils, management of these agricultural areas has a huge potential to affect global carbon cycling; acting sometimes as a sink but also as a source. Tillage is one of the most important agricultural practices for soil management and has been traditionally undertaken to mechanically prepare soils for seeding and minimize effects of weeds. It has been associated with many negative impacts on soil quality, most notably a reduction in soil organic carbon (SOC), although still a matter of considerable debate, depending on factors such as depth of measurement, soil type, and tillage method. No tillage or reduced intensity tillage are frequently proposed mitigation measures for preservation of SOC and improvement of soil quality, for example for reducing erosion. Whilst several reviews have demonstrated benefits to C conservation of no till agriculture over intensive tillage, the general picture for reduced tillage intensity is unclear. This systematic review proposes to synthesise an extensive body of evidence, previously identified through a systematic map. Methods This systematic review is based on studies concerning tillage collated in a recently completed systematic map on the impact of agricultural management on SOC restricted to the warm temperate climate zone (i.e. boreo-temperate). These 311 studies were identified and selected systematically according to CEE guidelines. An update of the original search will be undertaken to identify newly published academic and grey literature in the time since the original search was performed in September 2013. Studies will be critically appraised for their internal and external validity, followed by full data extraction (meta-data describing study settings and quantitative study results). Where possible, studies will be included in meta-analyses examining the effect of tillage reduction (‘moderate' (i.e. shallow) and no tillage relative to ‘intensive' tillage methods such as mouldboard ploughing, where soil is turned over throughout the soil profile). The implications of the findings will be discussed in terms of policy, practice and research along with a discussion of the nature of the evidence base

Native defects and self-diffusion in GaSb

The native defects in GaSb have been studied with first-principles total-energy calculations. We report the structures and the formation energies of the stable defects and estimate the defect concentrations under different growth conditions. The most important native defect is the GaSb antisite, which acts as an acceptor. The other important defects are the acceptor-type Ga vacancy and the donor-type Ga interstitial. The Sb vacancies and interstitials are found to have much higher formation energies. A metastable state is observed for the SbGa antisite. The significantly larger concentrations of the Ga vacancies and interstitials compared to the corresponding Sb defects is in accordance with the asymmetric self-diffusion behavior in GaSb. The data supports the next-nearest-neighbor model for the self-diffusion, in which the migration occurs independently in the different sublattices. Self-diffusion is dominated by moving Ga atoms.Peer reviewe

Curie temperature and carrier concentration gradients in MBE grown GaMnAs layers

We report on detailed investigations of the electronic and magnetic properties of ferromagnetic GaMnAs layers, which have been fabricated by low-temperature molecular-beam epitaxy. Superconducting quantum interference device measurements reveal a decrease of the Curie temperature from the surface to the GaMnAs/GaAs interface. While high resolution x-ray diffraction clearly shows a homogeneous Mn distribution, a pronounced decrease of the carrier concentration from the surface towards the GaMnAs/GaAs interface has been found by Raman spectroscopy as well as electrochemical capacitance-voltage profiling. The gradient in Curie temperature seems to be a general feature of GaMnAs layers grown at low-temperature. Possible explanations are discussed.Comment: 3 pages, 4 figures, submitted to AP

Which agricultural management interventions are most influential on soil organic carbon (using time series data)?

Background Loss of soil organic carbon (SOC) from agricultural land is identified as one of the major threats to soils, as it influences both fertility and the production of ecosystem services from agriculture. Losses of SOC across regions are often determined by monitoring in different land use systems. Results from agricultural field experiments can reveal increasing SOC stocks after implementation of specific management practices compared to a control, though in time series experiments the relative rate of change is often negative and implying an overall loss. Long-term agricultural field experiments are indispensable for quantifying absolute changes in SOC stocks under different management regimes. Since SOC responses are seldom linear over time, time series data from these experiments are particularly valuable. Methods This systematic review is based on studies reporting time series data collated in a recently completed systematic map on the topic restricted to the warm temperate climate zone and the snow climate zone. These 53 studies were identified and selected systematically according to CEE guidelines. An update of the original search for studies will be repeated using Web of Science and Google Scholar to include newly published academic and grey literature in the time since the original search was performed in September 2013. Studies will be subject to critical appraisal of the internal and external validity, followed by full data extraction (meta-data describing study settings and quantitative study results). Where possible, studies will be included in a quantitative synthesis using time series meta-analytical approaches. The implications of the meta-analytical findings will be discussed in terms of policy, practice and research along with a discussion of the nature of the evidence base

Diffusion of boron in germanium at 800-900 °C revisited

Diffusion of boron (B) in germanium (Ge) at temperatures ranging between 800 degrees C and 900 degrees C is revisited following the most recent results reported by Uppal et al. [J. Appl. Phys. 96, 1376 (2004)] that have been obtained mainly with implantation doped samples. In this work, we determined the intrinsic B diffusivity by employing epitaxially grown alternating undoped and B-doped Ge layer structures with three different dopant concentrations of 4 x 10(17) cm(-3) 1 x 10(18) cm(-3), and 3 x 10(18) cm(-3). The diffusional broadening of B was analyzed by means of secondary ion mass spectrometry (SIMS) and numerically described to determine the diffusion coefficient. Additional SIMS analyses revealed a gradient in the oxygen (O) background concentration of the epitaxially doped Ge structure. A high O content observed in near-surface regions correlates with enhanced B diffusion. In contrast, B-doped regions with low O content showed a significantly lower B diffusivity representing the intrinsic diffusivity. The B diffusion coefficients are significantly lower compared to literature data and best described by a diffusion activation enthalpy and a pre-exponential factor of (4.09 + 0.21) eV and 265(-237)(-2256) cm(2) s (1), respectively

Quantitative scanning spreading resistance microscopy on n-type dopant diffusion profiles in germanium and the origin of dopant deactivation

Diffusion profiles of arsenic and antimony in undoped and carbon doped germanium (Ge), respectively, were analysed by means of scanning spreading resistance microscopy (SSRM). Whereas earlier secondary ion mass spectrometry analyses have determined the distribution of the chemical concentration of dopants and carbon, the electrically active defect concentration is quantified by SSRM using appropriate calibration samples and a preparation technique that reduces the surface roughness and its density of electronic states. Pronounced differences between the chemical and electrical dopant profiles are observed and consistently described by the formation of inactive dopant defect complexes in the framework of the vacancy mediated diffusion of donor atoms in Ge. This reveals that donor deactivation occurs during dopant diffusion at elevated temperatures