High-power laser experiment forming a supercritical collisionless shock in a magnetized uniform plasma at rest

We present an experimental method to generate quasiperpendicular supercritical magnetized collisionless shocks. In our experiment, ambient nitrogen (N) plasma is at rest and well magnetized, and it has uniform mass density. The plasma is pushed by laser-driven ablation aluminum (Al) plasma. Streaked optical pyrometry and spatially resolved laser collective Thomson scattering clarify structures of plasma density and temperatures, which are compared with one-dimensional particle-in-cell simulations. It is indicated that just after the laser irradiation, the Al plasma is magnetized by a self-generated Biermann battery field, and the plasma slaps the incident N plasma. The compressed external field in the N plasma reflects N ions, leading to counterstreaming magnetized N flows. Namely, we identify the edge of the reflected N ions. Such interacting plasmas form a magnetized collisionless shock.

Cast immobilization of hindlimb upregulates sarcolipin expression in atrophied skeletal muscles and increases thermogenesis in C57BL/6J mice

Mechanical unloading impairs cytosolic calcium (Ca²⁺) homeostasis in skeletal muscles. In this study, we investigated whether sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) itself or one of the regulators of the Ca²⁺ SERCA pump, sarcolipin (SLN), is altered to deregulate Ca²⁺ homeostasis in cast immobilized, atrophied muscles. Hindlimb muscles of 8-wk-old male C57BL/6J mice were subjected to bilateral cast immobilization for 2 wk. Two-week-cast immobilization induced both body weight and skeletal muscle loss. Highly phosphorylated Ca²⁺/calmodulin-dependent protein kinase II in the atrophied muscles suggested that cytosolic Ca²⁺ concentration was elevated. Extremely high expression levels of SLN mRNA and protein were observed in the atrophied muscles. Upregulation of SLN at the transcriptional level was supported by low RCAN1 expression, which is a negative regulator of SLN. We treated C₂C₁₂ cells with dexamethasone to mimic muscle atrophy in vitro and showed a direct relationship between high SLN mRNA expression and low Ca²⁺ uptake by sarcoplasmic reticulum. Since SLN reportedly plays a role in nonshivering thermogenesis, we performed a cold tolerance test of the whole body. As a result, we found that mice with cast immobilization showed high cold tolerance, suggesting that cast immobilization promoted whole body thermogenesis. Although the activity level was decreased during cast immobilization without change in food intake, adipose tissue weights also decreased significantly after cast immobilization. Concomitantly, we conclude that cast immobilization of hindlimb increased thermogenesis in C57Bl/6J mice, probably via high expression of SLN.

Moderate Intensity Cycling Exercise after Upper Extremity Resistance Training Interferes Response to Muscle Hypertrophy but Not Strength Gains

The purpose of the present study was to examine the effect of 30-min moderate intensity cycling exercise immediately after upper-body resistance training on the muscle hypertrophy and strength gain. Fourteen subjects were randomly divided between two groups. One group performed moderate intensity (55% of maximum oxygen consumption [VO_2max], 30 min) cycle training immediately after arm resistance training as concurrent training (CT; n = 7, age: 21.8 ± 0.7 years, height: 1.68 ± 0.06 m, weight: 60.3 ± 7.4 kg); the second group performed the same endurance and arm RT on separate days as control group (SEP; n=7, age: 22.1 ± 0.7 years, height: 1.76 ± 0.05 m, weight: 63.8 ± 3.6 kg). The supervised progressive RT program was designed to induce muscular hypertrophy (3-5 sets of 10 repetitions) with bilateral arm-curl exercise using 75% of the one repetition maximum (1RM) with 2-min rest intervals. The RT program was performed for 8 weeks, twice per week. Muscle cross-sectional area (CSA), 1RM, and VO_2max were measured pre- and post-training. Significant increases in muscle CSA from pre- to post-training were observed in both the SEP (p = 0.001, effect size [ES] = 0.84) and the CT groups (p = 0.004, ES = 0.45). A significant increase in 1RM from pre- to post-training was observed in the SEP (p = 0.025, ES = 0.91) and CT groups (p = 0.001, ES = 2.38). There were no interaction effects (time × group) for CSA, 1RM, or VO_2max. A significantly higher percentage change of CSA was observed in the SEP group (12.1 ± 4.9%) compared to the CT group (5.0 ± 2.7%, p = 0.029), but no significant difference was observed in the 1RM (SEP: 19.8 ± 16.8%, CT: 24.3 ± 11.1%). The data suggest that significant improvement of CSA and strength can be expected with progressive resistance training with subsequent endurance exercise performed immediately or on a different day. Changes in CSA might be affected by subsequent cycling exercise after 8 weeks of training.

Nanoindentation of Epitaxial Films: A Study of Pop-in Events

Discontinuities in nanoindentation loading curves are frequently observed in ceramic materials. These normally occur at fairly random loads and displacements, probably due to the random distance of pre-existing defects from the indent location. Here we report the observation of reproducible, sudden indent-depth changes which occur over a very narrow distribution of depths and loads, for GaAs and a range of related epitaxial layer systems. The surface preparation and material defect density have a significant influence. Different tip geometries have been used to gain insights into the deformation processes which cause these discontinuities.

The Characteristics and Oxidation of Vapor - Liquid - Solid Grown Si Nanowires

The Vapor - Liquid - Solid (VLS ) technique allows the growth of high aspect ratio Si wires. The Si nanowires formed by this technique can be thinned down by oxidation. This approach allows the formation of very thin Si cores which may be used to research the properties of Si nanostructures. In this work the growth and oxidation of these wires is characterized.

In the growth a very thin layer of Au is deposited on a Si (111) surface, silane gas is introduced into the chamber as the Si source gas and the temperature is raised to 300 – 600°C. Initially a catalytically active Au surface phase leads to the growth of a defective epitaxial Si layer. As Au / Si molten alloy balls nucleate and grow in size to approach the threshold size for VLS wire growth, which is determined by the Gibbs - Thomson effect, the epitaxial layer growth rate decreases and a transition to Si nanowire growth occurs. The morphology and width of the wires is strongly dependent on the growth temperature and pressure. At low pressure and high temperature relatively thick well-formed wires grow straight up from the substrate surface along the [111] direction. As the temperature is decreased and the pressure is increased thinner wires (as thin as 10 nm ) grow which tend to exhibit growth defects. A light oxidation yields Si cores which are of the order of 5 nm in diameter.

Structural Defects in Mg-doped GaN and AlGaN grown by MOCVD

We have investigated the structural defects formed in Mg-doped GaN and AlGaN epitaxial layers grown by metal organic chemical vapor deposition. These defects have an inverse pyramidal shape and appear when the Mg concentration [Mg] is higher than ∼4×1019/cm3. The density of the defects increases as [Mg] increases, but the size of the defects becomes smaller as [Mg] increases. The density of the defects also has a strong correlation with the hydrogen concentration in the epitaxial layers. Transmission electron microscope analysis reveals that the defects have an inversion operation to the matrix and that their boundaries are Mg-rich. We also propose a model for defect formation.