Astrophysics and the solar nebula

The following types of experiments for a proposed Space Station Microgravity Particle Research Facility are described: (1) nucleation of refractory vapors at low pressure/high temperature; (2) coagulation of refractory grains; (3) optical properties of refractory grains; (4) mantle growth on refractory cores; (5) coagulation of core-mantle grains; (6) optical properties of core-mantle grains; (7) lightning strokes in the primitive solar nebula; and (8) separation of dust from a grain/gas mixture that interacts with a meter-sized planetesimal to determine if accretion occurs. The required capabilities and desired hardware for the facility are detailed.

Evaluating the effectiveness of heat warning systems : a systematic review of epidemiological evidence

Objectives To review the existing research on the effectiveness of heat warning systems (HWSs) in saving lives and reducing harm. Methods A systematic search of major databases was conducted, using “heat, heatwave, high temperature, hot temperature, OR hot climate” AND “warning system”. Results Fifteen articles were retrieved. Six studies asserted that fewer people died of excessive heat after HWS implementation. HWS was associated with reduction in ambulance use. One study estimated the benefits of HWS to be 468millionforsaving117livescomparedto210,000 costs of running the system. Eight studies showed that mere availability of HWS did not lead to behavioral changes. Perceived threat of heat dangers to self/others was the main factor related to heeding warnings and taking proper actions. However, costs and barriers associated with taking protective actions, such as costs of running air conditioners, were of significant concern particularly to the poor. Conclusions Research in this area is limited. Prospective designs applying health behavior theories should establish whether HWS can produce the health benefits they are purported to achieve by identifying the target vulnerable groups.

Fabrication of SiGe rings and holes on Si(001) by flash annealing

We show that SiGe islands are transformed into nanoholes and rings by annealing treatments only and without Si capping. Rings are produced by a rapid flash heating at temperatures higher than the melting point of Ge, whereas nanoholes are produced by several minute annealing. The rings are markedly rich in Si with respect to the pristine islands, suggesting that the evolution path from islands to rings is driven by the selective dissolution of Ge occurring at high temperature.

Influence of oxidation and reduction conditions upon the morphology of silica-supported polycrystalline silver catalysts

The effect of oxidation and reduction conditions upon the morphology of polycrystalline silver catalysts has been investigated by means of in situ Fourier-transform infrared (FTIR) spectroscopy. Characterization of the sample was achieved by inspection of the νas(COO) band profile of adsorbed formate, recorded after dosing with formic acid at ambient temperature. Evidence was obtained for the existence of a silver surface reconstructed by the presence of subsurface oxygen in addition to the conventional family of Ag(111) and Ag(110) crystal faces. Oxidation at 773 K facilitated the reconstruction of silver planes due to the formation of subsurface oxygen species. Prolonged oxygen treatment at 773 K also caused particle fragmentation as a consequence of excessive oxygen penetration of the silver catalyst at defect sites. It was also deduced that the presence of oxygen in the gas phase stabilized the growth of silver planes which could form stronger bonds with oxygen. In contrast, high-temperature thermal treatment in vacuum induced significant sintering of the silver catalyst. Reduction at 773 K resulted in substantial quantities of dissolved hydrogen (and probably hydroxy species) in the bulk silver structure. Furthermore, enhanced defect formation in the catalyst was also noted, as evidenced by the increased concentration of formate species associated with oxygen-reconstructed silver faces.

An innovative method to obtain porous PLLA scaffolds with highly spherical and interconnected pores

Scaffolding is an essential issue in tissue engineering and scaffolds should answer certain essential criteria: biocompatibility, high porosity, and important pore interconnectivity to facilitate cell migration and fluid diffusion. In this work, a modified solvent castingparticulate leaching out method is presented to produce scaffolds with spherical and interconnected pores. Sugar particles (200–300 lm and 300–500 lm) were poured through a horizontal Meker burner flame and collected below the flame. While crossing the high temperature zone, the particles melted and adopted a spherical shape. Spherical particles were compressed in plastic mold. Then, poly-L-lactic acid solution was cast in the sugar assembly. After solvent evaporation, the sugar was removed by immersing the structure into distilled water for 3 days. The obtained scaffolds presented highly spherical interconnected pores, with interconnection pathways from 10 to 100 lm. Pore interconnection was obtained without any additional step. Compression tests were carried out to evaluate the scaffold mechanical performances. Moreover, rabbit bone marrow mesenchymal stem cells were found to adhere and to proliferate in vitro in the scaffold over 21 days. This technique produced scaffold with highly spherical and interconnected pores without the use of additional organic solvents to leach out the porogen.

YBCO thin films on Yttria stabilized Zirconia and LaAlO3-growth and properties

Laser deposition was used to deposit YBaCuO thin films on Yttria-stabilized Zirconia substrates, at substrate holder temperatures of 710-765 °C. We observed a transition from singlecrystalline to polycrystalline growth at a temperature of ∼750 °C. All films were highly c-axis oriented and had critical temperatures between 89.5 and 92 K. In the twinned singlecrystalline films, the lowest measured microwave surface resistance was 0.37 mΩ at 4.2 K and 21.5 GHz, and the highest critical current 5×106 A/cm2 at 77 K. The polycrystalline films had up to a factor of 50 higher surface resistance and a factor of 10 lower critical current. A meander line resonator made of a film on a LaAlO3 substrate, showed a microwave surface resistance of 5μΩ at 4.2 K and 2.5 GHz. © 1991.

Microstructure of an artificial grain boundary weak link in an YBa2Cu3O(7-δ) thin film grown on a (100)(110), [001]-tilt Y-ZrO2 bicrystal

The microstructure of an artificial grain boundary in an YBa2Cu3O7-δ (YBCO) thin film grown on a (100)(110), [001]-tilt yttria-stabilized-zirconia (YSZ) bicrystal substrate has been studied using transmission electron microscopy (TEM). The orientation relationship between the YBCO film and the YSZ substrate was [001]YBCO∥[001]YSZ and [110]YBCO∥[100]YSZ for each half of the bicrystal film. However, the exact boundary geometry of the bicrystal substrate was not transferred to the film. The substrate boundary was straight while the film boundary was wavy. In several cases there was bending of the lattice confined within a distance of a few basal-plane lattice spacings from the boundary plane and microfaceting. No intergranular secondary phase was observed but about 25% of the boundary was covered by c-axis-tilted YBCO grains and a-axis-oriented grains, both of which were typically adjacent to CuO grains or surrounded by a thin Cu-rich amorphous layer.

Study of in situ laser deposited YBCO thin films

YBCO thin films were fabricated by laser deposition, in situ on MgO substrates, using both O2 and N2O as process gas. Films with Tc above 90 K and jc of 106 A/cm2 at 77 K were grown in oxygen at a substrate temperature of 765 °C. Using N2O, the optimum substrate temperature was 745 °C, giving a Tc of 87 K. At lower temperatures, the films made in N2O had higher Tc (79 K) than the films made in oxygen (66 K). SEM and STM investigations of the film surfaces showed the films to consist of a comparatively smooth background surface and a distribution of larger particles. Both the particle size and the distribution density depended on the substrate temperature.

Electropolishing of polycrystalline YBa2Cu3O7-δ to meet the need for sharp needle geometry

An electropolishing method has been developed for preparing sharp needles from polycrystalline YBa2Cu3O7-δ by modifying a recipe for TEM specimen preparation. The method is characterized by a polishing temperature of below 0°C, a non-acidic electrolyt and an even removal of the constituent phases. An approach was employed of combining I-V measurements for polishing process and microscopical observation of surface morphology in finding optimum polishing conditions. TEM evidenced that no preferential attack appeared to grain boundaries. X-ray diffractometry and electron diffraction implied that no change in oxygen content occurred during electropolishing. The sharpness of the tip was examined by field-ion microscopy.

Effects of PtO2 and CeO2 additives on the microstructures of the quenched melts of Y-Ba-Cu-O materials

The microstructures of the quenched melts of samples of Y123 and Y123+15-20 mol% Y211 with PtO2 and CeO2 additives have been examined with optical microscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDS) and X-ray Diffractometry (XRD). Significantly higher temperatures are required for the formation of dendritic or lamellar eutectic patterns throughout the samples with PtO2 and CeO2 additives as compared to samples without additives. The BaCuO2 (BCl) phase appears first in solid form and, instead of rapidly melting, is slowly dissolving or decomposing in the oxygen depleted melt. PtO2 and CeO2 additives slow down or shift to higher temperatures the dissolution or decomposition process of BCl. A larger fraction of BCl in solid form explains why samples with additives have higher viscosities and hence lower diffusivities than samples without additives. There is also a reduction in the Y solubility to about half the value in samples without additives. The mechanism that limits the Ostwald ripening of the Y211 particles is correlated to the morphology of the quenched partial melt. It is diffusion controlled for a finely mixed morphology and interface-controlled when the melt quenches into dendritic or lamellar eutectic patterns. The change in the morphology of the Y211 particles from blocky to acicular is related to an equivalent undercooling of the Y-Ba-Cu-O partial melt, particularly through the crystallization of BCl.

Bi-2223 precursor billets for pit wire production

High temperature superconductor precursor billets (feed rods) have been developed for loading into silver tubes. The billets are loaded prior to rolling or drawing operations in PIT wire manufacture. Investigations have shown that wires and tapes prepared from feed rod loaded tubes show enhanced uniformity of electrical transport properties when compared with conventional powder packing, especially in wires drawn to long lengths. Analysis on production feed rods have shown carbon content to be as low as 110 ppm. © 1999 IEEE.

Artificial grain boundary Josephson junctions : properties and applications

Engineered grain boundary Josephson junctions in YBaCuO were formed on bicrystal Y-ZrO2 substrates. Laser deposited films were patterned into micron size microbridges. The authors obsd. a pronounced correlation between superconducting transport properties of grain boundary junctions and the misorientation angle θ between the two halves of the bicrystal. The crit. Josephson current Ic decreased about four orders of magnitude as θ was increased from 0 to 45 degrees. Clear microwave and magnetic field responses were obsd. at 77 K. At this temp., crit. current times normal resistance products, IcRn, of up to 1 mV were measured for low angle grain boundaries, and Shapiro steps were obsd. up to that voltage. DC SQUIDs were fabricated, and best performance at 77 K was obtained for θ = 32° with a 4-μm strip width. To utilize the higher IcRn value of a lower θ, submicron junctions have to be developed. [on SciFinder(R)]

Continuous production of Bi-2212 thick film on silver tape

Bi-2212 thick film on silver tapes are seen as a simple and low cost alternative to high temperature superconducting wires produced by the Powder In Thbe (PIT) technique, particularly in react and wind applications. A rig for the continuous production of Bi-2212 tapes for use in react and wind component manufacture has been developed and commissioned. The rig consists of several sections, each fully automatic, for task specific duties in the production of HTS tape. The major sections are: tape coating, sintering and annealing. High temperature superconducting tapes with engineering critical current densities of 10 kA/cm2 (77 K, self field), and lengths of up to 100 m have been produced using the rig. Properties of the finished tape are discussed and results are presented for current density versus bend radius and applied strain. Depending on tape content and thickness, irreversible strain tirrm varies between 0.04 and 0.1 %. Cyclic bending tests when applied strain does not exceed Eirrm showed negligible reduction in J c along the length of the tape.

The Tarim picrite-basalt-rhyolite suite, a Permian flood basalt from Northwest China with contrasting rhyolites produced by fractional crystallization and anatexis

We report major and trace element composition, Sr–Nd isotopic and seismological data for a picrite–basalt–rhyolite suite from the northern Tarim uplift (NTU), northwest China. The samples were recovered from 13 boreholes at depths between 5,166 and 6,333 m. The picritic samples have high MgO (14.5–16.8 wt%, volatiles included) enriched in incompatible element and have high 87Sr/86Sr and low 143Nd/144Nd isotopic ratios (εNd (t) = −5.3; Sri = 0.707), resembling the Karoo high-Ti picrites. All the basaltic samples are enriched in TiO2 (2.1–3.2 wt%, volatiles free), have high FeOt abundances (11.27–15.75 wt%, volatiles free), are enriched in incompatible elements and have high Sr and low Nd isotopic ratios (Sri = 0.7049–0.7065; εNd (t) = −4.1 to −0.4). High Nb/La ratios (0.91–1.34) of basalts attest that they are mantle-derived magma with negligible crustal contamination. The rhyolite samples can be subdivided into two coeval groups with overlapping U–Pb zircon ages between 291 ± 4 and 272 ± 2 Ma. Group 1 rhyolites are enriched in Nb and Ta, have similar Nb/La, Nb/U, and Sr–Nd isotopic compositions to the associated basalts, implying that they are formed by fractional crystallization of the basalts. Group 2 rhyolites are depleted in Nb and Ta, have low Nb/La ratios, and have very high Sr and low Nd isotopic ratios, implying that crustal materials have been extensively, if not exclusively, involved in their source. The picrite–basalt–rhyolite suite from the NTU, together with Permian volcanic rocks from elsewhere Tarim basin, constitute a Large Igneous Province (LIP) that is characterized by large areal extent, rapid eruption, OIB-type chemical composition, and eruption of high temperature picritic magma. The Early Permian magmatism, which covered an area >300,000 km2, is therefore named the Tarim Flood Basalt.