6,800 research outputs found
NASA Lewis Research Center low-gravity fluid management technology program
A history of the Lewis Research Center in space fluid management technology program is presented. Current programs which include numerical modeling of fluid systems, heat exchanger/radiator concept studies, and the design of the Cryogenic Fluid Management Facility are discussed. Recent analytical and experimental activities performed to support the Shuttle/Centaur development activity are highlighted
Observation of high-Tc superconductivity in inhomogeneous combinatorial ceramics
A single-sample synthesis concept based on multi-element ceramic samples can
produce a variety of local products. When applied to cuprate superconductors
(SC), statistical modelling predicts the occurrence of possible compounds in a
concentration range of about 50 ppm. In samples with such low concentrations,
determining which compositions are superconducting is a challenging task and
requires local probes or separation techniques. Here, we report results from
samples with seven components: BaO2, CaCO3, SrCO3, La2O3, PbCO3, ZrO2 and CuO
oxides and carbonates, starting from different grain sizes. The reacted
ceramics show different phases, particular grain growth, as well as variations
in homogeneity and superconducting properties. High-Tc superconductivity up to
118 K was found. Powder x-ray diffraction (XRD) in combination with
energy-dispersive spectroscopy (EDS), scanning transmission electron microscopy
(STEM) can assign Pb1223 and (Sr,Ca,Ba)0.7-1.0CuO2 phases in inhomogeneous
samples milled with 10 mm ball sizes. Rather uniform samples featuring strong
grain growth were obtained with 3 mm ball sizes, resulting in Tc =70 K
superconductivity of the La(Ba,Ca)2Cu3Ox based phase. Scanning SQUID microscopy
(SSM) establishes locally formed superconducting areas at a level of a few
microns in inhomogeneous superconducting particles captured by a magnetic
separation technique. The present results demonstrate a new synthetic approach
for attaining high-Tc superconductivity in compounds without Bi, Tl, Hg, or the
need for high-pressure synthesis
Propagation of thermal excitations in a cluster of vortices in superfluid 3He-B
We describe the first measurement on Andreev scattering of thermal
excitations from a vortex configuration with known density, spatial extent, and
orientations in 3He-B superfluid. The heat flow from a blackbody radiator in
equilibrium rotation at constant angular velocity is measured with two quartz
tuning fork oscillators. One oscillator creates a controllable density of
excitations at 0.2Tc base temperature and the other records the thermal
response. The results are compared to numerical calculations of ballistic
propagation of thermal quasiparticles through a cluster of rectilinear
vortices.Comment: 6 pages, 4 figure
Universality of temperature distribution in granular gas mixtures with a steep particle size distribution
Distribution of granular temperatures in granular gas mixtures is
investigated analytically and numerically. We analyze space uniform systems in
a homogeneous cooling state (HCS) and under a uniform heating with a
mass-dependent heating rate . We demonstrate that
for steep size distributions of particles the granular temperatures obey a
universal power-law distribution, , where the exponent
does not depend on a particular form of the size distribution, the
number of species and inelasticity of the grains. Moreover, is a
universal constant for a HCS and depends piecewise linearly on for
heated gases. The predictions of our scaling theory agree well with the
numerical results
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