Structures of K0.05Na0.95NbO3 (50–300 K) and K0.30Na0.70NbO3 (100–200 K)

Rietveld refinement using neutron powder diffraction data is reported for the potential lead-free piezoelectric material KxNa1 - xNbO3 (x = 0.05, x = 0.3) at low temperatures. The structures were determined to be of rhombohedral symmetry, space group R3c, with the tilt system a-a-a- for both compositions. It was found that some of the structural parameters differ significantly in the two structures, and particularly the NbO6 octahedral strains as a function of temperature. The 300 K profile for K0.05Na0.95NbO3 shows the coexistence of rhombohedral and monoclinic phases, which indicates that the phase boundary is close to room temperature; the phase boundary for K0.30Na0.70NbO3 is found to be at approximately 180 K

The effect of magnetic mirror force on the field-aligned acceleration of plasmas

A magnetic mirror effect on the field-aligned acceleration of plasma flow is discussed for anisotropic plasma conditions by incorporating double adiabatic equations of state. In a non-uniform distribution of the field magnitude along the field lines, it is found that the field-aligned acceleration is toward higher field intensity region for the fluid of low thermal energy, while the acceleration is toward lower field intensity region for the fluid of high thermal energy. We infer that perpendicular pressure would cause such an energy-dependent behavior of the field-aligned acceleration through the magnetic mirror force

Evaluating Alternate Motor Pathway Changes following a Stroke

Background: Stroke is the fifth cause of death in the United States. Not only is stroke a leading cause of death but it is also a leading cause of long-term disability in the United States. Long-term impairments after stroke include gait instability, upper limb paralysis, sensory deficits, pain, depression, and cognitive impairments. The most common impairment is motor paresis of the upper and lower limb. Rehabilitation remains the gold standard in addressing motor paresis with the goal of enabling subjects to regain independence and daily living skills. Strokes often impact the crossed lateral corticospinal tract, by damaging the tract or the neighboring pathways. The damage within these pathways results in motor deficits. Detailed understanding of changes to the corticospinal tract, major neuronal pathway providing voluntary motor function, after stroke has resulted in the use of targeted therapies to improve rehabilitation outcomes. Alternate motor pathways also give a significant role in stroke recovery. This may be because many of the pathways work independently or work together with the corticospinal tract to trigger motor and sensory function. The overall goal of the project was to evaluate neurodegeneration and neuroregeneration in alternate motor pathways in patients who have suffered an acute ischemic stroke. Methods: Within this study 30 subjects who have suffered an acute stroke and 10 healthy control patients will be enrolled into the study. We will conduct motor function exams and collect neuroimages at two, twelve, and twenty-four weeks after the initial stroke event in each subject. Ten healthy age-matched controls will also be enrolled for a single MRI collection visit. We collected T1-weighted magnetic resonance images (MRI) and diffusion weighted imaging (DWI). When analyzing the images we used DSI studio to shade in our regions of interest. FSL was utilized to extract integrity of evaluated tracts. Results: We observed neuroanatomical differences at the level of the cerebral peduncle and posterior limb of internal capsule in both the affected (stroke-side) and unaffected hemispheres of the brain. Our preliminary data suggests that immediately after a stroke event, minimal changes are noted that become more dramatic over time. Conclusions: Our results suggest that alternate motor pathways undergo dynamic changes post-stroke. Our pilot work has found that while the corticospinal tract remains a critical component in recovery, other pathways may also be impacted post-stroke in a time dependent manner. Future work will evaluate advanced neurite imaging modalities, like NODDI, to evaluate microstructural property changes post-stroke

Relativistic Electron Losses in the Outer Radiation Belts

Relativistic electrons in the magnetosphere are both energized and lost via their interaction with plasma waves such as whister chorus, plasmaspheric hiss and EMIC waves. These waves are usually localized in different regions of the magnetosphere as well as being located either inside or outside the plasmapause. We study relativistic electron losses in the outer radiation belts by characterizing decay times scales at low and high altitudes and their relationship to microbursts. We use data collected by SAMPEX, a low Earth orbiting spacecraft in a highly inclined polar orbit and the HEO spacecraft in a high altitude Molniya orbit. The sensors onboard these spacecraft measure electrons of energies > 0.6 MeV, > 1 MeV, > 3 MeV, 2-6 MeV, 3-16 MeV. High time resolution data enable identifying and characterizing electron microbursts observed at low altitudes

Robustness of superconductivity to competing magnetic phases in tetragonal FeS

We have determined the superconducting and magnetic properties of a hydrothermally synthesized powder sample of tetragonal FeS using muon spin rotation ({\mu}SR). The superconducting properties are entirely consistent with those of a recently published study, showing fully gapped behavior and giving a penetration depth of {\lambda}_{ab} = 204(3) nm. However, our zero-field {\mu}SR data are rather different and indicate the presence of a small, non-superconducting magnetic phase within the sample. These results highlight that sample-to-sample variations in magnetism can arise in hydrothermally prepared phases, but interestingly the superconducting behavior is remarkably insensitive to these variations.Comment: 5 pages, 2 figure

Electron Micro Bursts as a Mechanism of Electron Loss Via Wave-Particle Interactions

Electron microbursts are rapid fluctuations of electron fluxes occurring on time scales of milliseconds. They are thought be due to scattering into the loss cone by plasma waves of various types from chorus to the recently observed large amplitude whistlers. They may be a major process of loss of realtivistic electrons from the Earth's outer radiation belts. One of the key issues that new mission s such as RBSP will address is to understand the loss of relativistic electrons. The SAMPEX mission launched in 1992 and still collecting data has the HILT sensor onboard with the capability of measuring> 1 MeV electrons with a high time resolution of 20 milliseconds suited admirably for the study of microbursts. We will use the data collected by the HILT for over a decade to characterize the relationship between electron microbursts and macroscopic electron decay lifetimes. With the launch of RBSP it is expected that SAMPEX will continue to collect data and overlap with RBSP. The latter will provide valuable information regarding plasma waves which coupled with low altitude measurements of microbursts may help elucidate details of the physics of electron loss from the radiation belt

Corticosterone Acts in the Nucleus Accumbens to Enhance Dopamine Signaling and Potentiate Reinstatement of Cocaine Seeking

Stressful life events are important contributors to relapse in recovering cocaine addicts, but the mechanisms by which they influence motivational systems are poorly understood. Studies suggest that stress may “set the stage” for relapse by increasing the sensitivity of brain reward circuits to drug-associated stimuli. We examined the effects of stress and corticosterone on behavioral and neurochemical responses of rats to a cocaine prime after cocaine self-administration and extinction. Exposure of rats to acute electric footshock stress did not by itself reinstate drug-seeking behavior but potentiated reinstatement in response to a subthreshold dose of cocaine. This effect of stress was not observed in adrenalectomized animals, and was reproduced in nonstressed animals by administration of corticosterone at a dose that reproduced stress-induced plasma levels. Pretreatment with the glucocorticoid receptor antagonist RU38486 did not block the corticosterone effect. Corticosterone potentiated cocaine-induced increases in extracellular dopamine in the nucleus accumbens (NAc), and pharmacological blockade of NAc dopamine receptors blocked corticosterone-induced potentiation of reinstatement. Intra-accumbens administration of corticosterone reproduced the behavioral effects of stress and systemic corticosterone. Corticosterone treatment acutely decreased NAc dopamine clearance measured by fast-scan cyclic voltammetry, suggesting that inhibition of uptake2-mediated dopamine clearance may underlie corticosterone effects. Consistent with this hypothesis, intra-accumbens administration of the uptake2 inhibitor normetanephrine potentiated cocaine-induced reinstatement. Expression of organic cation transporter 3, a corticosterone-sensitive uptake2 transporter, was detected on NAc neurons. These findings reveal a novel mechanism by which stress hormones can rapidly regulate dopamine signaling and contribute to the impact of stress on drug intake

Mercury Orbiter: Report of the Science Working Team

The results are presented of the Mercury Orbiter Science Working Team which held three workshops in 1988 to 1989 under the auspices of the Space Physics and Planetary Exploration Divisions of NASA Headquarters. Spacecraft engineering and mission design studies at the Jet Propulsion Lab were conducted in parallel with this effort and are detailed elsewhere. The findings of the engineering study, summarized herein, indicate that spin stabilized spacecraft carrying comprehensive particles and fields experiments and key planetology instruments in high elliptical orbits can survive and function in Mercury orbit without costly sun shields and active cooling systems