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991.
E. J. Ansaldo J. J. Boyle C. Niedermayer H. Glückler J. L. Tallon A. Mawdsley D. Pooke C. E. Stronach D. R. Noakes R. S. Cary M. R. Davis G. D. Morris 《Hyperfine Interactions》1994,86(1):505-511
A systematic study of the dependence of the critical temperature on the superconducting carrier density, as measured by
+SR, was carried out for a variety of cuprate oxides. We have shown that substitution of Pb for Bi and La for Sr result in well pinned vortex lattices in Bi2Sr2CaCu2Ox, and studied (BiPb)-2212 from the underdoped to the slightly overdoped regime. We also found that Tl-1212 samples, which have optimal maximumT
c=108 K, trace a separate line with parameters comparable to overdoped Tl-2223 at the maximum. These data, together with data on Y-124/247, Tl-2201 and other cuprates result in an larger set of universal correlations between Tc and(0) n
s
/m
* for the high temperature superconductors. 相似文献
992.
993.
994.
M. A. Paciotti D. W. Cooke M. Leon B. L. Bennett C. Pillai O. M. Rivera B. Hitti T. L. Estle S. F. J. Cox R. L. Lichti T. R. Adams C. D. Lamp A. Morrobel-Sosa O. Richter C. Boekema J. Lam S. Alves J. Oostens E. A. Davis 《Hyperfine Interactions》1994,87(1):1111-1116
It has long been recognized thatLCR could profitably be done with the high intensity surface beam at LAMPF [1]. A spectrometer has been built that is matched to the LAMPF beam characteristics. The polarization information is obtained from a downstream array of counters while side counters, containing no polarization signal, monitor the
+ beam. Degraders select higher energy e+, thereby reducing rates and required counter segmentation while maintaining information content. We apply a ramped longitudinal field in addition to the static one to average over instabilities in the
+ beam. This field scan allows direct interpretation of data and does not require a prior estimate of the resonance structure of a sample. Flux coils monitor the applied ramp field and eddy-current induced fields. High average rate (2×107
+/s). good stability, and the versatile field scan permitted useful data to be collected from Cu, Al(Cu), Al, Si(Al), and polycrystalline Si targets. 相似文献
995.
Lescouëzec R Vaissermann J Toma LM Carrasco R Lloret F Julve M 《Inorganic chemistry》2004,43(7):2234-2236
The novel mononuclear complex PPh(4)-mer-[Fe(III)(bpca)(3)(CN)(3)].H(2)O (1) [PPh(4)(+) = tetraphenylphosphonium cation and bpca = bis(2-pyridylcarbonyl)amidate anion] and ladder-like chain compound [[Fe(III)(bpca)(micro-CN)(3)Mn(II)(H(2)O)(3)] [Fe(III)(bpca)(CN)(3)]].3H(2)O (2) have been prepared and characterized by X-ray diffraction analysis. Compound 1 is a low-spin iron(III) compound with three cyanide ligands in mer arrangement and a tridentate N-donor ligand building a distorted octahedral environment around the iron atom. Compound 2 is an ionic salt made up of cationic ladder-like chains [[Fe(III)(bpca)(micro-CN)(3)Mn(II)(H(2)O)(3)]](+) and uncoordinated anions [Fe(III)(bpca)(3)(CN)(3)](-). The magnetic properties of 2 correspond to those of a ferrimagnetic chain with significant intrachain antiferromagnetic coupling between the low-spin iron(III) centers and the high-spin manganese(II) cations. This compound exhibits ferrimagnetic ordering below 2.0 K. 相似文献
996.
M. L. Rooney D. J. Best E. G. Davis 《Journal of polymer science. Part A, Polymer chemistry》1973,11(10):2601-2613
Spectroscopic studies made on the bisphenol A polycarbonate–sulfur dioxide system showed evidence of interaction between polymer and penetrant. Equilibrium studies made on solutions of sulfur dioxide and organic carbonates chosen as monomer analogs showed that complexes of the donor–acceptor type were formed, and that at temperatures of 15°C and less the stoichiometry of these was greater than 1:1. The procedures described are compared with those used in other donor–acceptor studies, and the results observed from the equilibrium studies are interpreted by using data reported for other sulfur dioxide–donor systems. 相似文献
997.
Báez-Vásquez MA Adrio JL Piret JM Demain AL 《Applied biochemistry and biotechnology》1999,81(3):145-152
Resting cells of Streptomyces clavuligerus NP-1, which posses deacetoxy-cephalosporin C synthase activity, have been shown previously to perform oxidative ring expansion
of penicillin G in the presence of iron, ascorbic acid, and α-ketoglutaric acid to form deacetoxycephalosporin G. Further
studies on this bioconversion indicated that use of MOPS or HEPES buffer at pH 6.5 more than doubled the extent of the reaction
observed with the previously used Tris-HCl at pH 7.4. Levels of bioconversion as high as 16.5% were achieved at low penicillin
G concentrations. Previously, conversion yields were <1%. 相似文献
998.
Michel E Porte G Cipelletti L Appell J 《Langmuir : the ACS journal of surfaces and colloids》2004,20(3):984-990
The dynamic properties of a model transient network have been studied by dynamic light scattering. The network is formed by microemulsion droplets linked by telechelic polymers (modified hydrophilic polymers with two grafted hydrophobic stickers). We compare the properties of two networks that are similar but for the residence time of the hydrophobic stickers in the droplets. The results are interpreted according to the so-called two-fluids model, which was initially developed for semidilute polymer solutions and which we extend here to any Maxwellian viscoelastic medium characterized by its elastic modulus and terminal time as measured by rheology. This model is found to describe consistently and quantitatively the experimental observations. 相似文献
999.
Leo A. Paquette C. David Wright Sean G. Traynor Davis L. Taggart Gary D. Ewing 《Tetrahedron》1976,32(15):1885-1891
The electrochemical behavior of trimethylsilyl-, trimethylgermyl-, trimethylstannyl- and t-butylcyclooctatetraenes has been examined by the techniques of polarography and cyclic voltammetry in THF and hexamethylphosphoramide (vastly preferred) solutions. Chemical reduction by means of potassium in ND3 has also been studied. Evidence is presented that all four compounds undergo reduction to their respective dianions. However, the energetics of (Me3)MCOT? and (Me3)MCOT2? formation vary widely, as do the rates and mechanism of dianion disappearance under the conditions of electrochemical measurement. The available kinetic data suggest, for example, that destruction of the t-Bu and trimethylgermyl substituted dianions proceeds via protonation and/or disproportionation pathways. In contrast, the silyl and stannyl examples experience metal-ring carbon cleavage reactions at yet faster rates. Interestingly, the E1 values give evidence of being quite well correlated by σp. Furthermore, when the magnitude of the E1-E2 gap are plotted vs the covalent radii of the M atoms, a straight line is obtained for the Si, Ge and Sn examples; C deviates widely. This effect is believed to have its origin in resonance of the M←Cπ type involving the d orbitals of M which, of course, is not possible in the carbon case. The significance of these results as well as the other observations made in the course of this work is discussed. 相似文献
1000.
Equations are developed to describe the influence of oxygen diffusion on the rate of photo-oxidation of polyethylene plaques. The theory is applied to both the artificial and natural weathering of unstabilised low density polyethylene samples, 3 mm thick. The calculations describe the characteristic experimental reaction profiles. The observed and calculated rates show a relatively weak distance dependence to a depth of the order of 1 mm, beyond which they are diffusion controlled. 相似文献