Hole pairing within an extended Anderson impurity model applicable to the high-Tc cuprates

We calculate the binding energy of a hole pair within the extended Anderson Hamiltonian for the high-Tc cuprates including a Cu impurity and an oxygen-derived band. The results indicate that stable hole pairs can be formed for intra-atomic and interatomic Coulomb repulsion strengths larger than 6 and 3.5 eV, respectively. It is also shown that the total hybridization strength between the Cu 3d and oxygen p band should be less than 2.5 eV. The hole pairing takes place primarily within the oxygen-derived p band. The range of parameter values for which hole pairing occurs is also consistent with the earlier photoemission results from these cuprates.

Structural aspects of high-temperature cuprate superconductors

High-temperature superconductivity constitutes the most sensational discovery of recent times. Since these new superconductors are complex metal oxides, chemistry has had a big role to play in the investigations. For the first time, stoichiometry, structure, bonding, and such chemical factors have formed central themes in superconductivity, an area traditionally dominated by physicists. These oxide superconductors have given a big boost to solid-state chemistry.

A low-cost lead-acid battery with high specific-energy

Lightweight grids for lead-acid battery grids have been prepared from acrylonitrile. butadiene styrene (ABS) copolymer followed by coating with lead. Subsequently, the grids have been electrochemically coated with a conductive and corrosion-resistant layer of polyaniline. These grids are about 75% lighter than those employed in conventional lead-acid batteries. Commercial-grade 6V/3.5 Ah (C-20-rate) lead-acid batteries have been assembled and characterized employing positive and negative plates constituting these grids. The specific energy of such a lead-acid battery is about 50 Wh/kg. The batteries can withstand fast charge-discharge duty cycles.

Field induced spin reorientation transition in epitaxial La0.5Sr0.5CoO3 films

Strained epitaxial La0.5Sr0.5CoO3 films are grown on LaAlO3 substrate. Structural, electrical,and magnetic measurements were carried out. Out of plane lattice parameter of the film undergoes compressive strain and the coercivity is enhanced. The zero field cooled (ZFC) magnetization curve for a field applied parallel to the film plane shows a jump, which suggests a spin reorientation transition (SRT), while ZFC magnetization for a field applied perpendicular to the film plane is featureless. This jump in magnetization is shifted to higher temperatures when the magnetic field is reduced. The SRT is attributed to the strain in the film. (C) 2010 Elsevier B.V. All rights reserved.

High temperature deformation processing maps for boron modified Ti-6Al-4V alloys

The alloy, Ti-6Al-4V is an alpha + beta Ti alloy that has large prior beta grain size (similar to 2 mm) in the as cast state. Minor addition of B (about 0.1 wt.%) to it refines the grain size significantly as well as produces in-situ TiB needles. The role played by these microstructural modifications on high temperature deformation processing maps of B-modified Ti64 alloys is examined in this paper.Power dissipation efficiency and instability maps have been generated within the temperature range of 750-1000 degrees C and strain rate range of 10(-3)-10(+1) s(-1). Various deformation mechanisms, which operate in different temperature-strain rate regimes, were identified with the aid of the maps and complementary microstructural analysis of the deformed specimens. Results indicate four distinct deformation domains within the range of experimental conditions examined, with the combination of 900-1000 degrees C and 10(-3)-10(-2) s(-1) being the optimum for hot working. In that zone, dynamic globularization of alpha laths is the principle deformation mechanism. The marked reduction in the prior beta grain size, achieved with the addition of B, does not appear to alter this domain markedly. The other domains, with negative values of instability parameter, show undesirable microstructural features such as extensive kinking/bending of alpha laths and breaking of beta laths for Ti64-0.0B as well as generation of voids and cracks in the matrix and TiB needles in the B-modified alloys. (C) 2010 Elsevier B.V. All rights reserved.

Enantiodiscrimination and extraction of short and long range homo- and hetero-nuclear residual dipolar couplings by a spin selective correlation experiment

A two dimensional correlation experiment for the measurement of short and long range homo- and hetero- nuclear residual dipolar couplings (RDCs) from the broad and featureless proton NMR spectra including C-13 satellites is proposed. The method employs a single natural abundant C-13 spin as a spy nucleus to probe all the coupled protons and permits the determination of RDCs of negligible strengths. The technique has been demonstrated for the study of organic chiral molecules aligned in chiral liquid crystal, where additional challenge is to unravel the overlapped spectrum of enantiomers. The significant advantage of the method is demonstrated in better chiral discrimination using homonuclear RDCs as additional parameters. (C) 2010 Elsevier B.V. All rights reserved.

Electronic structure of high-Tc superconductors from core-level spectroscopies

Using the configuration-interaction approach, we show that various core-level spectroscopic observations on the high-Tc superconducting oxides can be consistently described in terms of mixing between d9 and d10 configurations, with a negligible amount of the d8 (Cu3+) state. From our analysis of the existing experimental data, we provide evidence of a wide and continuous valence transition in these systems as a function of temperature. The changes in the hybridization strengths deduced here are indicative of structural modifications of the square-planar CuO4 clusters with decreasing temperature.

High-temperature superconductivity in bismuth-copper oxides of the type BimMnCupOx (M=Mg, Ca, Sr, Ba, Bi)

Several oxides of the Bi m M n Cu p O x family (m=2, 3;n=2, 3, 4;p=1, 2, 3 and M=alkaline earth or Bi), possessing structures similar to the Aurivillius family of oxides, show highT c superconductivity.

Investigations on Bi2CuO4: a quasi-one-dimensional oxide system

The potential of Bi2CuO4 as the first oxide system to show a linear-chain magnetic behaviour is examined. Electron diffraction studies do not resolve the previously reported ambiguity regarding its space group. The magnetic susceptibility data at high temperatures are best fitted to a uniform antiferromagnetic spin-1/2 Heisenberg chain. At low temperatures, however, neither the uniform nor the alternating Heisenberg antiferromagnetic model fits the data. Magnetic susceptibility data over the entire temperature range can be fitted if one assumes dimeric units with a nearly degenerate second singlet state close to the ground state, these states being separated from an excited triplet state by an energy gap. A simple heuristic model of a dimer that gives such an energy level spectrum is examined.

Vitamin A and thyroxine carrier proteins in chicken plasma Steady-state control of the plasma level of free retinol-binding protein and free thyroxine

1. 1. The binding parameters of prealbumin-2 with retinol-binding protein and thyroxine (T4) revealed the existence of distinct and multiple sites for both retinol-binding protein and T4. 2. 2. From the analysis of binding parameters of retinol-binding protein with prealbumin-2 it is clear that under steady-state conditions about 99% of the holo-retinol-binding protein remains bound to prealbumin-2. 3. 3. Equilibrium dialysis studies on binding properties of thyroid hormones with prealbumin-2 revealed that it has a single high affinity site and three low affinity sites. 4. 4. The occurrence of three carrier proteins for thyroid hormones, thyroxine-binding globulin, prealbumin-2 and albumin has been demonstrated. However, the chicken thyroxine-binding globulin differs from human thyroxine-binding globulin by being relatively less acidic and occuring at a two-fold lower concentration. But the thyroid hormone binding parameters are comparable. 5. 5. Highly sensitive methods were developed for determination of T4 binding capacities of the various proteins and plasma level of total T4 by fractionation of carrier proteins and further quantitatively employing in electrophoresis and equilibrium dialysis. 6. 6. The thyroxine-binding proteins were found to be two types, one (viz., thyroxine-binding globulin) of great affinity but of low binding capacity, which mainly acts as reservoir of T4, and another (viz.,prealbumin-2) of low affinity but of high binding capacity, which can participate predominantly in the control of the free T4 pool.

High-yield bacterial expression and structural characterization of recombinant human insulin-like growth factor binding protein-2

The diverse biological activities of the insulin-like growth factors (IGF-1 and IGF-2) are mediated by the IGF-1 receptor (IGF-1R). These actions are modulated by a family of six IGF-binding proteins (ICFBP-1-6; 22-31 kDa) that via high affinity binding to the IGFs (K-D similar to 300-700 pM) both protect the IGFs in the circulation and attenuate IGF action by blocking their receptor access In recent years, IGFBPs have been implicated in a variety of cancers However, the structural basis of their interaction with IGFs and/or other proteins is not completely understood A critical challenge in the structural characterization of full-length IGFBPs has been the difficulty in expressing these proteins at levels suitable for NMR/X-ray crystallography analysis Here we describe the high-yield expression of full-length recombinant human IGFBP-2 (rhIGFBP-2) in Eschericha coli Using a single step purification protocol, rhIGFBP-2 was obtained with >95% purity and structurally characterized using NMR spectroscopy. The protein was found to exist as a monomer at the high concentrations required for structural studies and to exist in a single conformation exhibiting a unique intra-molecular disulfide-bonding pattern The protein retained full biologic activity. This study represents the first high-yield expression of wild-type recombinant human IGFBP-2 in E coli and first structural characterization of a full-length IGFBP (C) 2010 Elsevier Inc. All rights reserved

The elastic manifestation of a spin-glass transition: a low-frequency study

The authors report here the first measurements of low-frequency dynamic elastic properties of a spin glass (Fe59Ni21Cr20) across the transition temperature (Tg approximately=16 K). A minimum in the sound velocity (V) and a maximum in the internal friction (Q-1) were found at temperatures close to but below Tg. The elastic data were compared with the AC susceptibility data taken at similar frequency.

Tl1-xPbxCaSr2Cu2O7: Another 1122 high-Tc superconductor

The 1122 member of the Tl(Ca, Sr)n+1CunO2n+3 system is stabilized by partial substitution of Tl by Pb. Tl1?xPbxCaSr2Cu2O7 with x=0.25 and 0.5 have both primitive tetragonal structures (c 12.1 Å) showing onset of superconductivity around 70 K and 90 K, respectively.

Curie-temprature of a spin one xy ferromagnet with uniaxial anisotropy

A spin one XY ferromagnet with uniaxial anisotropy has been investigated, using Green's function technique in random phase approximation (RPA). The Green functions associated with the anisotropy energy are treated without decoupling. A set of coupled equations have been obtained to find the critical temperature Tc and left angle bracket(SZ)2right-pointing angle bracket at Tc as function of the uniaxial anisotropy parameter D. Tc and left angle bracket(SZ)2right-pointing angle bracket at Tc are found to increase with D. The results are compared with the earlier results obtained in the Narath type of RPA.