Search Results - (Author, Cooperation:M. E. Davis)

2013-04-06

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

*Climate Change ; *Ice Cover ; Nitrates/analysis ; Oxygen Isotopes/analysis ; Peru ; Plants ; Quaternary Ammonium Compounds/analysis ; *Tropical Climate ; Wetlands

1077-3118

AIP Digital Archive

Physics

The Bi-Sr-Ca-Cu-O superconductors have been doped with various noble metals and their superconducting properties have been investigated. The resistivity and magnetic susceptibility measurements on sintered Bi4Sr3Ca2Cu4O16+x containing 20% by weight of Au, Ag, or Pt-group metals indicate that Au and the Pt-group metals significantly suppress or eliminate the superconducting transition in Bi-Sr-Ca-Cu-O. Only Ag is found to be benign, maintaining both the 115 and 85 K transitions in the compound. This nonpoisoning behavior of silver is of significant technical importance because of the need for a proper stabilizing normal metal for composite superconductor wire, nonreactive crucible materials for melt processing or crystal growth, and suitable nonpoisonous substrates or barriers for thin- or thick-film superconducting devices.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Melt-textured growth of polycrystalline YBa2Cu3O7−δ superconductor using directional solidification created an essentially 100% dense structure consisting of long, needle- or plate-shaped crystals preferentially aligned parallel to the a-b conduction plane. The new microstructure, which completely replaces the previous granular and random structure in the sintered precursor, exhibits dramatically improved transport Jc values at 77 K of ∼17 000 A/cm2 in zero field and ∼4000 A/cm2 at H=1 T (as compared to ∼500 and ∼1 A/cm2, respectively, for the as-sintered structure), with the severe field dependence of Jc ("weak-link'' problem) no longer evident in the new melt-textured material. The improvement in Jc is attributed to the combined effects of densification, alignment of crystals, and formation of cleaner grain boundaries. Microstructure and distribution of various phases present in the melt-textured material are discussed in relation to the superconducting properties.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Convenient methods for obtaining extremely low resistivity contacts to bulk high Tc superconductors ( ρc in the range of 10−11–10−12 Ω cm2) are described. Three different configurations of silver contact metal in Y-Ba-Cu-O have been employed, i.e., embedded Ag wire, embedded Ag particles, and selectively patterned Ag clad on superconductor wire. In all three cases, the low-resistivity metallic contacts are formed in situ during the sintering or melt processing of the superconductor, thus eliminating the need for separate steps of contact preparation such as vacuum deposition of contact metal and additional heat treatment. The distribution and morphology of the silver contacts will be discussed. The measured contact resistivities in the present work are the lowest reported for the high Tc superconductors, and these methods may serve as a useful basis for important contact technologies needed for bulk superconductor applications.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Melt-textured YBa2Cu3O7−δ superconductor with a long and well-aligned grain structure is shown to exhibit magnetic hysteresis at 77 K which is the largest ever reported for bulk polycrystalline Y-Ba-Cu-O. The large ΔM resulted in a magnet-like behavior as well as a strong suspension phenomenon. It is shown, contrary to the previous reports, that the suspension behavior observed in Y-Ba-Cu-O is a generic consequence of large grain size, and not due to the presence of Ag oxide or Ag particles. There appears to be no substantial enhancement in flux pinning and Jc by these particles. Comparisons of magnetization behavior in various YBa2Cu3O7−δ samples (polycrystals, silver-oxide doped, melt-textured, and single crystals) indicated that for applied fields substantially larger than Hc1 the current flow that gives rise to the observed magnetization is intragranular. The pinning force and hence the critical current is roughly the same [Jc (magn)∼104 A/cm2] within a factor of ∼2 regardless of grain size, grain boundary configuration, presence of second phase particles, or increased dislocation and twin densities.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The discovery of high-temperature superconductivity in perovskite-related oxides has generated an enormous amount of research activity and development effort toward applications. Commercially useful bulk superconductors typically require stabilization using a normal metal cladding for reasons of electrical, thermal, and mechanical protection, and in general need to be fabricated into fine fibers and wound into a solenoid configuration. The YBa2Cu3O7−δ type compound is a ceramic material which is mechanically hard and brittle, and is difficult to fabricate into fine wires. However, this difficulty has been overcome by several fabrication methods such as powder-in-tube method (metal-clad composite), powder-coating method (metal-core composite), and molten oxide processing method. The effect of various processing steps on the structure and superconducting properties such as transition temperature and critical current density will be discussed. Some experiments to raise the high field critical current through chemistry and microstructural control will also be described.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A recent paper by Maeda et al.1 reported the discovery of a new 120 K superconductor based on a rare-earth–free ceramic material in the bismuth-strontium-calcium-copper-oxide system. We have confirmed the existence of the 120-K phase in the oxide system. The resistivity-temperature curve showed a fairly well-defined double-dip shape with the first dip starting at ∼120 K and the second at ∼95 K. The transition temperature, TC(R=0), was 84 K. This material appears to contain two superconducting phases with different TC's. A pellet made from this superconductor levitates well at 77 K (liquid-nitrogen temperature) above a neodynium-iron-boron magnet with a surface magnetic field of ∼3000 Oe, thus indicating a nontrivial critical field in this material. The critical current density and its magnetic field dependence will be reported. The magnetic and mechanical behavior of the new superconductor will also be discussed.

Electronic Resource

1365-2044

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The haemodynamic response to bronchoscopy under general anaesthesia was investigated. Forty patients were allocated at random to receive either thiopentone or propofol; half the patients in each group received in addition 18 μg/kg of alfentanil one minute before induction of anaesthesia. The heart rate, noninvasive blood pressure and Holter ECG was monitored in all patients. Significant increases in heart rate (p 〈 0.05), systolic and diastolic arterial pressures (p 〈 0.01) occurred in the thiopentone only group, following bronchoscopy. Systolic and diastolic arterial pressure decreased in patients receiving thiopentone plus alfentanil, following induction of anaesthesia and laryngoscopy (p 〈 0.05). No significant haemodynamic changes were seen in either of the groups which received propofol. ST segment changes on subsequent Holter analysis were seen in four patients, but there were no significant differences between the groups. Anaesthesia with propofol alone provides adequate haemodynamic stability for bronchoscopy and the addition of alfentanil is superfluous.

Electronic Resource

1750-3841

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Process Engineering, Biotechnology, Nutrition Technology

Portion-controlled menu items were heat processed in infrared and convection ovens to compare the effects of the heating methods upon nutrient retention. Product yields for hamburger and potatoes were significantly greater (P 〈 0.05) after convective heating; for tomatoes, after infrared heating. Nutrients analyzed foi selected menu items included: thiamin, riboflavin, vitamin C, β-carotene, seven fatty acids, 18 amino acids, ammonia, phosphorus, iron and sodium. Several significant differences between the heat processed samples were revealed. The riboflavin and vitamin A contents in hamburger and tomatoes, respectively, were significantly greater after infrared heating. The total amino acid contents were significantly greater after infrared heating for the hamburger patties and cod fillets.

Electronic Resource

1750-3841

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Process Engineering, Biotechnology, Nutrition Technology

Roasts were heat processed by infrared and convection to compare the effects of these alternate heating methods upon nutrient retention. In addition to proximate analyses, nutrients analyzed included: thiamin, riboflavin, seven fatty acids, 18 amino acids, ammonia, sodium, phosphorus and iron. Convective heating of turkey breast and corned beef produced a higher product yield. Few significant differences between heat processed samples were revealed. After convection heating of corned beef, riboflavin was significantly higher (P 〈 0.05) than after infrared heating. Similarly, arachidonic acid (C20:4) was higher in turkey breasts. After infrared heating of pork, aspartic acid, threonine, serine were lower than after convective heating; ammonia was higher.

Electronic Resource

1572-879X

NMR (DOR) spectroscopy ; aluminophosphate ; molecular sieves ; aluminum environment ; adsorption sites ; structural disorder ; water adsorption

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Abstract 27Al double rotation NMR (DOR) spectroscopy is used to investigate structural changes in the framework of several aluminophosphate molecular sieves upon adsorption of water. The shapes, widths, and positions of the spectral lines yield information on the aluminum environments, adsorption sites, and degree of structural disorder undergone upon water adsorption.

Electronic Resource

0017-789X

General, Interdisciplinary

0017-789X

General, Interdisciplinary

0017-789X

General, Interdisciplinary

0017-789X

General, Interdisciplinary

0017-789X

General, Interdisciplinary

0017-789X

General, Interdisciplinary

0017-789X

General, Interdisciplinary

0017-789X

General, Interdisciplinary

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] VPI-5 is a hydrophilic molecular sieve belonging to the aluminophosphate (A1PO4) family. The proposed structure of VPI-5 in Fig. 1, based on X-ray and neutron powder diffraction experiments5-8, consists of alternating A1O4 and PO4 tetrahedral units arranged to produce linear channels 12 A in ...

Electronic Resource