Modelling of transient liquid phase bonding in binary systems — A new parametric study

An established mathematical model, describing the rate at which transient liquid phase bonding (TLP bonding) progresses in binary alloy systems, is subjected to careful scrutiny. It is shown that the process can be characterised using just two dimensionless parameters. An advantage of such dimensionless characterisation is demonstrated by analysis of the solution for solidification of semi-infinite systems. It is known that analytical formulae for the rate at which the liquid region solidifies are valid only for certain restricted cases. This is investigated by numerical modelling, and the requirements for the formulae to be applicable are rationalised. Maps presented here can be used to determine whether the semi-infinite solution would provide an acceptable approximation for any given system. Information is also presented concerning optimal combinations of phase diagram characteristics, diffusivities and system dimensions required for rapid TLP solidification, which can be used to identify the best melting point depressant (MPD) materials to use for particular TLP requirements. The analysis reveals that, as a consequence of their higher solubilities, elements forming substitutional solutes in the parent plates may often allow faster TLP solidification than those forming interstitial solutes, despite the fact that the latter group normally exhibits much higher diffusivities

Helicity of the W Boson in Lepton+Jets ttbar Events

We examine properties of ttbar candidates events in lepton+jets final states to establish the helicities of the W bosons in t->W+b decays. Our analysis is based on a direct calculation of a probability that each event corresponds to a ttbar final state, as a function of the helicity of the W boson. We use the 125 events/pb sample of data collected by the DO experiment during Run I of the Fermilab Tevatron collider at sqrt{s}=1.8 TeV, and obtain a longitudinal helicity fraction of F_0=0.56+/-0.31, which is consistent with the prediction of F_0=0.70 from the standard model

Hard Single Diffraction in pbarp Collisions at root-s = 630 and 1800 GeV

Using the D0 detector, we have studied events produced in proton-antiproton collisions that contain large forward regions with very little energy deposition (``rapidity gaps'') and concurrent jet production at center-of-mass energies of root-s = 630 and 1800 Gev. The fractions of forward and central jet events associated with such rapidity gaps are measured and compared to predictions from Monte Carlo models. For hard diffractive candidate events, we use the calorimeter to extract the fractional momentum loss of the scattered protons.Comment: 11 pages 4 figures. submitted to PR

Numerical solutions of diffusion-controlled moving boundary problems which conserve solute

Numerical methods of finding transient solutions to diffusion problems in two distinct phases that are separated by a moving boundary are reviewed and compared. A new scheme is developed, based on the Landau transformation. Finite difference equations are derived in such a way as to ensure that solute is conserved. It is applicable to binary alloys in planar, cylindrical, or spherical geometries. The efficiency of algorithms which implement the scheme is considered. Computational experiments indicate that the algorithms presented here are of first order accuracy in both time and space