Showing papers by "Hua Zhang published in 1995"

Chromium clustering and ordering in Hg1-xCrxSr2CuO4+ delta.

Abstract: Solid-solution compounds where Cr, Re, and other metals are substituted for Hg in Hg-Ca-Ba-Cu-O superconductors have been reported to exhibit enhanced flux-pinning behavior. We have determined the structural modifications resulting from the incorporation of Cr in Hg{sub 1{minus}{ital x}}Cr{sub {ital x}}Sr{sub 2}CuO{sub 4+{delta}} (for {ital x}{approx}0.4) using neutron powder diffraction, electron diffraction, and lattice imaging. Cr substitutes at the Hg site, but is displaced to allow tetrahedral coordination by oxygen atoms. Additional oxygen is incorporated to provide four oxygen atom neighbors for each Cr atom. These CrO{sub 4} units cluster to form a supercell of approximate dimensions 5{ital a}{times}5{ital a}{times}2{ital c} in which Cr-rich and Hg-rich regions alternate in all three crystallographic directions. Because the Cu-O apical bond associated with the CrO{sub 4} unit is lengthened to 3.13 A, the superconducting planes are best viewed as consisting of CuO{sub 5} pyramids, oriented up or down as dictated by the supercell ordering, rather than CuO{sub 6} octahedra. Local structural constraints associated with individual Cr sites require that considerable disorder is present, even in the supercell. Extended defects in this supercell (e.g., columns of CuO{sub 6} octahedra associated with Hg-rich regions) may contribute to the enhanced flux pinning.

A TEM study of the incommensurate modulated structure in Sr2CuO3 + δ superconductor synthesized under high pressure A. Evolution of the incommensurate modulated structure and the electronic structure with post-heat treatment

Abstract: Transmission electron imaging, diffraction and spectroscopy techniques are utilized to study the changes in modulated structure and aspects of electronic structure of the high oxygen pressure synthesized superconductor: Sr 2 CuO 3+δ . The presence of an incommensurate modulated superstructure in Sr 2 CuO 3+δ and its dependence on post-annealing treatment is documented. Transmission EELS indicates that there is a high density of states near the Fermi surface for the modulated phase in as-made ( T c = 70 K) and optimally treated ( T c = 94 K) specimens, while there is a low density of states near the Fermi surface for over-treated samples with T c = 0 K.

A TEM study of the incommensurate modulated structure in Sr2CuO3+x superconductors synthesized under high pressure B. Structural model

Abstract: This paper reports a detailed structural study of the incommensurate modulated phase in high pressure synthesized Sr2CuO3+x superconductors based on transmission electron diffraction, high resolution electron microscopy and simulations. Face-centered orthorhombic structure with an average commensurate lattice constant of about 5√2ap×5√2ap×cp (p stands for the tetragonal La2CuO4-type structure) has been identified and an atomic model of this average structure is proposed. The modulated structure results from metal ion shear displacements with half sine and half cosine waves along 〈110〉p directions. Analysis of the displacement fields suggests that the Cu ions have a half cosine wave displacement, which supports the existence of oxygen vacancies in the CuO1+x layer proposed by a previous neutron diffraction study. If this modulated phase is indeed the superconducting phase our results call into question the requirement of intact CuO2 sheets for superconductivity in high-Tc cuprates.

Factors Influencing the Production of Polyethersulfone Microfiltration Membranes by Immersion Phase Inversion Process

Abstract: Polyethersulfone microfiltration (MF) membranes can be produced from polyethersulfone/solvent/nonsolvent systems by the immersion phase inversion process in a water bath. When the casting solution composition is adjusted close to phase separation, a fast gelation in water occurs which hinders further polymer enrichment at the interface between polymer solution and water; an open-cell MF membrane structure is thus retained. Addition of a certain amount of a water-soluble polymer, polyvinylpyrrolidone, to the casting solution will further change the demixing rate and gelation rate of the casting solution in water. Such an addition improves the open-cell structure of the membranes. Besides dope composition, the performance of these MF membranes is also dependent on the casting conditions.

Standardization in the Production and Testing Procedures for Polyethersulfone Hollow Fiber Ultrafiltration Membranes

Abstract: Several hollow fiber ultrafiltration membranes have been produced from polyethersulfone-polyvinyl pyrrolidone-N-methyl-2-pyrrolidone solutions and tested. The effects of feed flow velocity through the fiber bore on pressure drop in the test fiber bundle, membrane separations for PEG solutes, and the obtainable mass transfer coefficients under the test conditions have been experimentally determined and discussed. Further, the effects of storage time and prefiltration of the fiber casting polymer solution on the performance characteristics of the resulting membranes have been studied. The viscosity of the fiber casting solution increased upon storage for a few weeks, and it decreased after the solution was filtered prior to use in fiber production. Storage time and filtration treatment of the fiber casting solution had significant effects on the morphology of the resulting membranes. Casting solution of longer storage time and without filtration pretreatment produced smaller size pores on the membr...

[Determination of the progesterone antagonist lilopristone in serum by RP-HPLC].

Abstract: To 1.0 ml of serum containing lilopristone were added RU486 solution(internal standard, IS)and 1 ml of 1.0mol·L-1 NaOH. The mixture was extracted with diethyl ether for 2 times.After extraction ,the combined organic phase was evaporated to dryness and the residue was dissolved in the mobile phase and washed with petroleum ether.After centrifugation,20 μl of the lower layer was subjected to HPLC,A μBondapak-C18(10μm)column(30 cm × 3. 9 mm) was used and the column temperature was kept at 50℃, The flow rate of mobile phase(methanol- dichloromethane-0.01mol·L-1 phosphate buffer,pH 4.0,67:5:28v/v)was 1.1 ml· min-1 and UV detection was performed at 302 nm. The retention times of lilopristone and IS were 6.85 and 9. 07 min respectively and the detection limit was 10 ng·ml-1(S/N≥4 )serum. The extraction recoveries of lilopristone and IS were over 85%. The relative standard deviations were2.21 to 4.23%, This method has been applied to study the pharmacokinetic of lilopristone in rats.

Ultrastructural cytochemistry of human gastric cancer: electron microscopic observations of five organellae marker enzymes.

Abstract: The distribution of ALPase, ACPase, G6Pase TPPase and CCOase of gastric cancer and normal gastric epithelium were studied ultrastructurally. The results showed that normal gastric epithelium had no ALPase reaction. The reactions of ACPase, G6Pase, TPPase and CCOase were found in the corresponding organellae which were consistent with their functions. In tubular adenocarcinoma cells, their reactions were more apparent in the corresponding organellae. Some cells of tubular adenocarcinomas showed ALPase reaction. The mucinous adenocarcinoma cells had higher ACPase and TPPase reactions. In poorly differentiated adenocarcinoma cells, the five marker enzymes showed negative or faint reactions. The biological significance and mechanisms of distribution of the five marker enzymes were discussed.