The ratio of energy gap to transition temperature in amorphous superconductors

Using results of tunneling measurements, values of 2Δ(o)/kT_c for a number of amorphous transition-metal based superconductors are found to be 3.5±0.1 in agreement with the BCS theory in the weak-coupled limit unlike previously reported results suggesting strong electron-phonon coupling in amorphous non-transition metals such as Ga and Pb-Bi alloys. A comparison of our results with existing data for amorphous soft-metal alloys and A-15 compounds suggests that non-crystallinity alone does not give rise to a significantly enhanced electron-phonon interaction.     

The critical specific heat of a glassy ferromagnet

Using standard ac calorimetry, we have measured the specific heat of the amorphous ferromagnet Fe₇₅P₁₅C₁₀ in the neighborhood of its Curie temperature T_C ? 600 K. Even though this material is structurally disordered, a sharp lambda-like cusp was observed, typical of a pure crystalline substance. We report the first determination of the critical specific heat exponent α = δ′ = -.18 ± .04 and the amplitude ratio A⁺/A^- = 1.2 ± .3 for an amorphous ferromagnet and find that these values are typical of a Heisenberg system. Our results are in agreement with recent renormalization group calculations which indicate that the fixed point which characterizes the critical behavior will be stable against the addition of disorder to the ordered system if α < 0.     

Charge confinement effect in cuprate superconductors: an explanation for the normal-state resistivity and pseudogap

The fact that the stripe phase and pseudogap in the cuprate superconductors occur in the same doping regime is emphasized. A model based on charge confinement in self-organized nanometer-scale stripe fragments is proposed to understand various generic features of the normal-state energy gap including the magnitude of the gap, its anti-correlation with the superconducting gap, and the d-wave symmetry in its -dependence. This model also provides a basis for understanding other anomalous normal-state properties such as the linear temperature dependence of electrical resistivity. Received 7 December 1998     

Treatment of interfaces in particle image velocimetry

A first-order accurate method of extending the capability of image velocimetry to interfaces is presented. In this method, the image fields are locally extended across interfaces using fields from the other image of an image pair. During this image parity exchange, the extension of the image fields amounts to locally reversing and reflecting the relative velocity field across the interface. Numerous experimental examples are given to demonstrate and validate the accuracy of the method. These are the plane Couette flow and the laminar pipe flow demonstrating straight rigid boundaries; uniform flow past a sphere and a sphere moving in a stagnant fluid demonstrating curved rigid surfaces; and a free-surface flow and a liquid–liquid interface flow demonstrating compliant interfaces. Received: 3 November 1998/Accepted: 18 August 1999     

Upper Critical Solution Temperature‐Type Thermal Response of Soluble Multi‐l‐Arginyl‐Poly‐l‐Aspartic Acid (cyanophycin) Conjugated with Maltodextrin

Multi‐l ‐arginyl‐poly‐l ‐aspartic acid (MAPA), also known as cyanophycin, can incorporate lysine into the side‐chain position of arginine when being prepared with recombinant Escherichia coli. The soluble fraction (sMAPA) is known to display both lower critical solution temperature (LCST) and upper critical solution temperature (UCST) responses at the physiological condition. In an attempt to alter the UCST thermal response, maltodextrin was employed to conjugate onto the amine group of lysine of sMAPA via the formation of Schiff base. In phosphate buffered saline, the UCST of the conjugates appeared around 50–62°C, depending on the extent of conjugation. In contrast to the unmodified sMAPA, the UCST of the conjugate became independent of pH ranging from 1 to 11. Heating the conjugate solution to complete transparent caused a delayed and partial recovery of the original turbidity during subsequent cooling. However, the turbidity can be restored by further precipitation with ethanol or isopropanol followed lyophilization and re‐dissolution. At room temperature, below UCST, the agglomerates exhibited a size of around 200–400 nm under TEM and DLS. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2048–2055     

Charge transfer and dd excitations in transition metal oxides

Electronic excitations in transition-metal oxides MnO, FeO, CoO and NiO are investigated by inelastic X-ray scattering and optical reflectivity measurements. The dielectric functions are derived from the experimental data as a function of the momentum transfer, q. Based on the derived q-dependent dielectric functions, two types of the charge transfer excitations, i.e., dipolar and non-dipolar charge transfer, are clearly identified. We show that the Mott gaps around 5 eV are defined by the former whereas the latter occurs at higher energies of 8–12 eV. Based on a molecular orbital analysis, we associate the dipolar and the non-dipolar excitations with non-local charge transfer and conventional charge transfer, respectively. These types of excitations are shown to be common for the 3d metal monoxides. On the other hand, the dd excitations observed in NiO and CoO at energy <4 eV do not appear in FeO and MnO. The reasons are addressed in this report.     

Electronic versus lattice match for metal-semiconductor epitaxial growth: Pb on Ge(111)

Lattice match is important for epitaxial growth. We show that a competing mechanism, electronic match, can dominate at small film thicknesses for metal-semiconductor systems, where quantum confinement and symmetry requirements may favor a different growth pattern. For Pb(111) on Ge(111), an accidental lattice match leads to a √3 × √3 configuration involving a 30° in-plane rotation at large film thicknesses, but it gives way to an incommensurate (1 × 1) configuration at small film thickness. The transformation follows an approximately inverse-film-thickness dependence with superimposed bilayer oscillations.     

A modified adaptive grid method for recirculating flows

In this study a method of equidistribution of a weight function for grid adaption is modified to produce a smoother grid which yields a more accurate solution. In the original scheme the weight function was estimated on each grid independently and a large variation in the values of the, weight function could generate a highly skewed and non-uniform grid which produced large errors. In this study the weight function is smoothed by coupling neighbouring weight functions. Abrupt changes in the weight function are alleviated and a smoother grid distribution is obtained. With relatively minor modifications of the original weight function it is demonstrated in this study that the solution can be improved. The test cases presented are the one-dimensional convection-diffusion equation, a laminar polar cavity flow, a laminar backwardfacing step flow and a turbulent reacting sudden expansion pipe flow. Numerical efficiencies ranging from factors of five to 10 are achieved over uniform grid methods.     

Layer dependence of the superconducting transition temperature of HgBa2Can−1CunO2n+2+δ

High-pressure methods have been used to synthesize multiphase compositions in the Hg---12{n−1}n homologous series. The phase assemblages were examined by optical, electron diffraction and X-ray diffraction techniques, and their stoichiometries verified by electron microprobe. Transport and magnetic susceptibility measurements were combined with the results of the phase analysis to establish superconducting transition temperatures for both as-prepared and O₂- or Ar-annealed materials. It was found that the transition temperature peaks at T_c = 134 K for n = 3 and then decreases abruptly for n>4, reaching T_c<90 K for n7.     

Limits of the critical current density of polycrystalline high-temperature superconductors based on the current transport properties of single grain boundaries

A semiquantitative technique for estimating the limits of the critical current density in polycrystalline high-temperature superconductors is presented. This technique is based on the transport properties of single grain boundaries. Various factors essential in deducing the critical current density of polycrystalline high-T _c materials from the characteristics of single grain boundaries are discussed. The results for tectured, polycrystalline YBa₂Cu₃O₇ fibers are reported, and the influence of the microstructure on their critical current density is discussed.