Structural, magnetic, dielectric and mechanical properties of (Ba,Sr)MnO3_3 ceramics

Ceramic samples, produced by conventional sintering method in ambient air, 6H-SrMnO$_3$(6H-SMO), 15R-BaMnO$_3$(15R-BMO), 4H-Ba$_{0.5}$Sr$_{0.5}$MnO$_3$(4H-BSMO) were studied. In the XRD measurements for SMO the new anomalies of the lattice parameters at 600-800 K range and the increasing of thermal expansion coefficients with a clear maximum in a vicinity at 670 K were detected. The N$\acute{e}$el phase transition for BSMO was observed at $T_N$=250 K in magnetic measurements and its trace was detected in dielectric, FTIR, DSC, and DMA experiments. The enthalpy and entropy changes of the phase transition for BSMO at $T_N$ were determined as 17.5 J/mol and 70 mJ/K mol, respectively. The activation energy values and relaxation times characteristic for relaxation processes were determined from the Arrhenius law. Results of ab initio simulations showed that the contribution of the exchange correlation energy to the total energy is about 30%.Comment: 12 pages, 12 figure

Static Dielectric Constant of β-Ga2O3 Perpendicular to the Principal Planes (100), (010), and (001)

The relative static dielectric constant ℇr of β-Ga2O3 perpendicular to the planes (100), (010), and (001) is determined in the temperature range from 25 K to 500 K by measuring the AC capacitance of correspondingly oriented plate capacitor structures using test frequencies of up to 1 MHz. This allows a direct quantification of the static dielectric constant and a unique direction assignment of the obtained values. At room temperature, ℇr perpendicular to the planes (100), (010), and (001) amounts to 10.2 ± 0.2, 10.87 ± 0.08, and 12.4 ± 0.4, respectively, which clearly evidence the anisotropy expected for β-Ga2O3 due to its monoclinic crystal structure. An increase of ℇr by about 0.5 with increasing temperature from 25 K to 450 K was found for all orientations. Our ℇr data resolve the inconsistencies in the previously available literature data with regard to absolute values and their directional assignment and therefore provide a reliable basis for the simulation and design of devices. © The Author(s) 2019

The magnetic interactions in spin-glasslike Ge/1-x-y/Sn/x/Mn/y/Te diluted magnetic semiconductor

We investigated the nature of the magnetic phase transition in the Ge/1-x-y/Sn/x/Mn/y/Te mixed crystals with chemical composition changing in the range of 0.083 < x < 0.142 and 0.012 < y < 0.119. The DC magnetization measurements performed in the magnetic field up to 90 kOe and temperature range 2-200 K showed that the magnetic ordering at temperatures below T = 50 K exhibits features characteristic for both spin-glass and ferromagnetic phases. The modified Sherrington - Southern model was applied to explain the observed transition temperatures. The calculations showed that the spin-glass state is preferred in the range of the experimental carrier concentrations and Mn content. The value of the Mn hole exchange integral was estimated to be J/pd/ = 0.45+/-0.05 eV. The experimental magnetization vs temperature curves were reproduced satisfactory using the non-interacting spin-wave theory with the exchange constant J/pd/ values consistent with those calculated using modified Sherrington - Southern model. The magnetization vs magnetic field curves showed nonsaturating behavior at magnetic fields B < 90 kOe indicating the presence of strong magnetic frustration in the system. The experimental results were reproduced theoretically with good accuracy using the molecular field approximation-based model of a disordered ferromagnet with long-range RKKY interaction.Comment: 9 pages, 6 figure

Central Action of Botulinum Toxin Type A – is it Possible?

Botulinum toxin (BoTx) is a product of gram-positive anaerobic bacteria of the Clostridium genus. At present, seven serotypes (A to G) of BoTx have been identified. Each of them functions as a zinc-dependent endopeptidase that hydrolyzes peptide bonds within soluble N-ethylmaleimide-sensitive factor attaching protein receptors. BoTx affects proteins required for neurotransmitter release through presynaptic membranes. As a result, muscle weakness develops, or complete paralysis of the muscles occurs. These effects are not only limited to striated muscles but also may have impact on smooth muscles and secretory glands. The observation that BoTx can diffuse from the site of administration may indicate the possibility of direct or indirect influence of the toxin on the CNS. Consequently, the question arises: What is the mechanism of the central action of BoTx? Several mechanisms of such action have been proposed. However, recent findings showed that the most probable mechanism responsible for the central effects of BoTx action is its anterograde transport. In this review, we describe and discuss the most important aspects related to BoTx action on the CNS.Ботуліновий токсин (BoTx) є продуктом життєдіяльності грампозитивних бактерій роду Clostridium. На теперішній час ідентифіковано сім серотипів BoTx (A–G). Всі вони функціонують як цинкзалежні ендопеотидази, що гідролізують пептидні зв’язки з розчинним N-етилмалеімідчутливим фактором, контактуючим з протеїновими рецепторами. BoTx впливає на протеїни, необхідні для вивільнення нейротрансмітерів через пресинаптичні мембрани. Як результат, розвиваються м’язова слабкість або повний параліч м’язів. Такі ефекти не обмежуються поперечносмугастими м’язами, вони виявляються також у гладеньких м’язах та секреторних залозах. Як спостерігалося, BoTx може дифундувати від місця свого введення; це може вказувати на принципову можливість прямих або непрямих впливів токсину на ЦНС. Відповідно, виникає питання: яким є механізм центральної дії BoTx. Було запропоновано декілька гіпотез про механізми такої дії. Результати нещодавніх досліджень, однак, свідчать про те, що найбільш вірогідним механізмом, відповідальним за центральні ефекти BoTx, є його дія на антероградний транспорт. У нашому огляді ми описуємо та обговорюємо найбільш важливі аспекти дії BoTx на ЦНС

Evolution of planar defects during homoepitaxial growth of β-Ga2O3 layers on (100) substrates—A quantitative model

We study the homoepitaxial growth of β-Ga2O3 (100) grown by metal-organic vapour phase as dependent on miscut-angle vs. the c direction. Atomic force microscopy of layers grown on substrates with miscut-angles smaller than 2° reveals the growth proceeding through nucleation and growth of two-dimensional islands. With increasing miscut-angle, step meandering and finally step flow growth take place. While step-flow growth results in layers with high crystalline perfection, independent nucleation of two-dimensional islands causes double positioning on the (100) plane, resulting in twin lamellae and stacking mismatch boundaries. Applying nucleation theory in the mean field approach for vicinal surfaces, we can fit experimentally found values for the density of twin lamellae in epitaxial layers as dependent on the miscut-angle. The model yields a diffusion coefficient for Ga adatoms of D = 7 × 10−9 cm2 s−1 at a growth temperature of 850 °C, two orders of magnitude lower than the values published for GaAs

GeneLab: Scientific Partnerships and an Open-Access Database to Maximize Usage of Omics Data from Space Biology Experiments

NASA's mission includes expanding our understanding of biological systems to improve life on Earth and to enable long-duration human exploration of space. The GeneLab Data System (GLDS) is NASAs premier open-access omics data platform for biological experiments. GLDS houses standards-compliant, high-throughput sequencing and other omics data from spaceflight-relevant experiments. The GeneLab project at NASA-Ames Research Center is developing the database, and also partnering with spaceflight projects through sharing or augmentation of experiment samples to expand omics analyses on precious spaceflight samples. The partnerships ensure that the maximum amount of data is garnered from spaceflight experiments and made publically available as rapidly as possible via the GLDS. GLDS Version 1.0, went online in April 2015. Software updates and new data releases occur at least quarterly. As of October 2016, the GLDS contains 80 datasets and has search and download capabilities. Version 2.0 is slated for release in September of 2017 and will have expanded, integrated search capabilities leveraging other public omics databases (NCBI GEO, PRIDE, MG-RAST). Future versions in this multi-phase project will provide a collaborative platform for omics data analysis. Data from experiments that explore the biological effects of the spaceflight environment on a wide variety of model organisms are housed in the GLDS including data from rodents, invertebrates, plants and microbes. Human datasets are currently limited to those with anonymized data (e.g., from cultured cell lines). GeneLab ensures prompt release and open access to high-throughput genomics, transcriptomics, proteomics, and metabolomics data from spaceflight and ground-based simulations of microgravity, radiation or other space environment factors. The data are meticulously curated to assure that accurate experimental and sample processing metadata are included with each data set. GLDS download volumes indicate strong interest of the scientific community in these data. To date GeneLab has partnered with multiple experiments including two plant (Arabidopsis thaliana) experiments, two mice experiments, and several microbe experiments. GeneLab optimized protocols in the rodent partnerships for maximum yield of RNA, DNA and protein from tissues harvested and preserved during the SpaceX-4 mission, as well as from tissues from mice that were frozen intact during spaceflight and later dissected on the ground. Analysis of GeneLab data will contribute fundamental knowledge of how the space environment affects biological systems, and as well as yield terrestrial benefits resulting from mitigation strategies to prevent effects observed during exposure to space environments