Mössbauer studies of Er impurities in the cubic actinide metal Th

The hyperfine coupling and the 4f-conduction electron exchange interaction of localized Er moments in Th have been investigated by Mössbauer spectroscopy. The results are compared to previous studies of Er impurities in Au and Ag.     

Transversely isotropic viscoplasticity model for a directionally solidified Ni-base superalloy

A transversely isotropic continuum viscoplasticity model has been formulated to capture the fatigue and creep responses of a directionally solidified (DS) polycrystalline Ni-base superalloy used mainly in turbine blades. This model has been implemented as an ABAQUS User MATerial (UMAT) subroutine using a semi-implicit integration scheme. Isothermal uniaxial fatigue data from tests conducted with and without hold times and creep data are used to characterize the stress–strain response at temperatures ranging from 427 °C to 1038 °C. The scheme leads to reduction of the associated computational costs when compared to a crystal viscoplasticity model that explicitly considers 3-D grain structure. The macroscopic elastoviscoplastic model is shown to simulate the homogenized deformation response of the polycrystalline DS alloy for various isothermal histories. The predictive capability of this model is verified using both in-phase and out-of-phase TMF data, and is compared to the results of analysis of a single crystal in terms of stress concentration and stress distribution for a model problem of a plate with a central hole.     

From melt flow index to rheogram

A knowledge of the complete flow curve or rheogram of a polymeric melt depicting the variation of the melt viscosity over industrially relevant range of shear rate and temperature is essential in the design of polymer processing equipment, process optimization and trouble-shooting. These data are generated on sophisticated rheometers that are beyond the financial and technical means of most plastics processors. The only flow parameter available to the processor is the melt flow index of the material. In the present work, a method has been proposed to estimate the rheograms of a melt at temperatures relevant to its processing conditions with the use of a master curve, knowing the melt flow index and glass transition temperature of the material. Master curves that coalesce rheograms of different grades at various temperatures have been generated and presented for low density polyethylene, high density polyethylene, polypropylene, polystyrene and styrene-acrylonitrile copolymer.     

Novel effects of localization due to intrinsic disorder in manganites

We discuss the effects of a novel ‘intrinsic’ disorder in hole-doped rare-earth manganites. Using effective field theory as well as direct numerical simulations, we show that this disorder can have dramatic effects in terms of the transition from ferromagnetic insulator to ferromagnetic metal upon hole-doping, including an Anderson localized regime where variable range hopping may be observed.     

Monolithic optoelectronic circuit design and fabrication byepitaxial growth on commercial VLSI GaAs MESFET's

A technique for realizing large-scale monolithic OEIC's, which involves epitaxially growing GaAs-based heterostructures on fully metallized commercial VLSI GaAs MESFET integrated circuits, has recently been reported. In the initial work the circuits and LED's occupied distinct halves of a chip, the dielectric growth window was wet-etched after circuit fabrication, and the LED's required both n and p ohmic contacts to be formed after epitaxial growth. In this letter we report the use of standard foundry process etches to open dielectric growth windows intermixed with circuitry and the growth of n-side-down LED's on a source/drain ion-implanted n⁺ region serving as the n ohmic contact. A winner-take-all neural circuit is demonstrated using these advances, which are important steps toward realizing higher levels of circuit integration     

在500V电压等级的AC／DC应用中最优化平面型MOSFET与超大结MOSFET的竞争

仙童公司（Fairchild）面向开关电源市场推出了一款新型最优化高速平面型MOSFET，与通常的500V电压等级的MOSFET相比，它可以降低全方位的损耗。与市场上的超大结面积型的MOSFET相比，这种MOSFET可以减少开关损耗。而和通常的标准MOSFET器件相比，它的导通损耗则大大降低。因此这种500V电压等级的MOSFET可以和一部分超大面积型MOSFET展开市场争夺方面的竞争。     

Modelling the flow of power law fluids in a packed bed using a volume-averaged equation of motion

The development of a theoretical model for the prediction of velocity and pressure drop for the flow of a viscous power law fluid through a bed packed with uniform spherical particles is presented. The model is developed by volume averaging the equation of motion. A porous microstructure model based on a cell model is used. Numerical solution of the resulting equation is effected using a penalty Galerkin finite element method. Experimental pressure drop values for dilute solutions of carboxymethylcellulose flowing in narrow tubes packed with uniformly sized spherical particles are compared to theoretical predictions over a range of operating conditions. Overall agreement between experimental and theoretical values is within 15%. The extra pressure drop due to the presence of the wall is incorporated directly into the model through the application of the no-slip boundary condition at the container wall. The extra pressure drop reaches a maximum of about 10% of the bed pressure drop without wall effect. The wall effect increases as the ratio of tube diameter to particle diameter decreases, as the Reynolds number decreases and as the power law index increases.     

Discrete-time, discrete-frequency, time-frequency analysis

A formulation of a discrete-time, discrete-frequency Wigner distribution for analysis of discrete-time, periodic signals is given using an approach involving group representation theory. This approach is motivated by a well-known connection between group theory and the continuous Wigner distribution. The advantage of this approach is that the resulting discrete distribution satisfies mathematical properties analogous to those satisfied by the continuous distribution. After outlining the relationship between group representation theory and time-frequency analysis, we derive the discrete distribution and exhibit many of its mathematical properties. These include time and frequency marginals, the Weyl correspondence, and covariance. In particular, the interpretation of covariance for the discrete distribution is shown to be different than that for the continuous distribution. Finally, we note some unusual features of this discrete distribution, which are a consequence of the group-theoretic derivation     

Turbulent free convection heat transfer to power-law fluids from arbitrary geometric configurations

The problem of turbulent free convection heat transfer from curved surfaces to non-Newtonian power-law fluids has been investigated using the Nakayama-Koyama solution methodology. The scheme is designed to deal with bodies of arbitrary geometric configurations and hence can be viewed as a generalized version of the Shenoy-Mashelkar approach for turbulent free convection heat transfer from a flat vertical plate to a power-law fluid. The surface wall temperature is allowed to vary in the streamwise direction in an arbitrary fashion, and calculations are carried out for the turbulent free convection about the horizontal circular cylinder and sphere for illustrative purposes. Available theoretical and experimental data have been compared with the predictions of the present analysis and the comparison of results has been found to be reasonably good.