Green functions for generalized point interactions in 1D: A scattering approach

Recently, general point interactions in one dimension has been used to model a large number of different phenomena in quantum mechanics. Such potentials, however, requires some sort of regularization to lead to meaningful results. The usual ways to do so rely on technicalities which may hide important physical aspects of the problem. In this work we present a new method to calculate the exact Green functions for general point interactions in 1D. Our approach differs from previous ones because it is based only on physical quantities, namely, the scattering coefficients, $R$ and $T$, to construct $G$. Renormalization or particular mathematical prescriptions are not invoked. The simple formulation of the method makes it easy to extend to more general contexts, such as for lattices of $N$ general point interactions; on a line; on a half-line; under periodic boundary conditions; and confined in a box.Comment: Revtex, 9 pages, 3 EPS figures. To be published in PR

Direct observation of densification and grain growth in a W--Ni alloy

Densification and grain growth in a tungsten--nickel alloy containing 32 vol % of liquid at 1550/sup 0/C were studied by conventional methods aided by hot stage scanning electron microscopy and cinematography. This technique yields important additional qualitative information on the mechanisms. Two stages can be discerned. In stage 1, essentially complete pore elimination, rapid grain growth and adjustment of microstructural geometry take place. In the second stage, microstructure coarsening occurs which is characterized by geometric similarity. Columnar grain growth at the surface is observed due to squeezing out of Ni--W liquid, flooding of surface grains and fast evaporation of the Ni. The driving forces for these processes are discussed showing that a high ratio of grain boundary energy to liquid surface energy is essential. A W--Cu alloy with 32 vol % liquid at 1100/sup 0/C did not show any grain growth due to essentially no solubility of W in Cu at this temperature

COST 512 - Prozessuebergreifendes Modellieren von Herstellungsverfahren fuer Guss- und Knetlegierungen Abschlussbericht

The production of shaped parts usually requires a number of additional steps after casting and solidification, such as forming (forging, rolling etc.) and heat treatment (homogenization, precipitation, artificial ageing). A combination of models for the subsequent steps, using the output of one step as input for the next, allow to predict the properties of a shaped parts ready for use and optimize the point and way of intervention when undesired properties are found. Apart from combining existing models, new models have been developed for homogenization during heat treatments of multicomponent alloys, the formation of precipitates in ternary alloys, and the interface kinetics during local remelting. A new experimental set-up has been developed for the remelting kinetics. The microstructure evolution during several processing steps was simulated using Al-Fe-Si alloys. (orig.)SIGLEAvailable from TIB Hannover: DtF QN1(78,35) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung (BMBF), Bonn (Germany)DEGerman