An improved error bound for a finite element approximation of a model for phase separation of a multi-component alloy

Using the approach of Rulla (1996 SIAM J. Numer. Anal. 33, 68-87)for analysing the time discretization error and assuming moreregularity on the initial data, we improve on the error boundderived by Barrett and Blowey (1996 IMA J. Numer. Anal. 16,257-287) for a fully practical piecewise linear finite elementapproximation with a backward Euler time discretization of amodel for phase separation of a multi-component alloy.     

Hydrogen-induced reconstruction on a high step density W(001) surface

The hydrogen-induced reconstruction on a high step density W(001) crystal, ($\text{2}\text{×}\text{2}$)R45°-H, with steps oriented parallel to the [110] and ～ 28 Å average terrace width has been investigated using LEED symmetry, beam shape analyses, and EELS. The symmetry of the LEED pattern is observed to change from p2mg for the ($\text{2}\text{×}\text{2}$)R45° clean surface reconstruction to c2mm for the commensurate phase ($\text{2}\text{×}\text{2}$)R45°-H reconstruction. Correspondingly, the shapes of the half-order beams indicate that the hydrogen-induced reconstruction domains are much less elongated than the clean surface domains. A splitting of each half-order beam into four beams at higher exposures indicates the existence of two domains of the incommensurate phase. A commensurate phase v₁ vibrational loss peak centered at 160 meV in the EELS spectrum broadens on the low-energy side during the incommensurate phase and then shifts toward 130 meV and narrows as the (1×1)-H saturation structure develops. These observations imply that there is no long-range inhibition ( ～ 20 Å) to the formation of either commensurate or incommensurate phase; hydrogen induces a switching of the atomic displacements from 〈110〉 directions on a clean surface to 〈100〉 directions, even with steps oriented parallel to the [110]; and in the incommensurate phase there is a distribution of hydrogen site geometries with the most probable geometry more like the commensurate phase geometry than the saturation phase geometry.     

Search for color singlet technicolor particles in p&pmacr; collisions at radicals = 1.8 TeV

We search for color singlet technirho and technipion production in p&pmacr; collisions at sqrt[s] = 1.8 TeV recorded with the Collider Detector at Fermilab. These exotic technimesons are present in a model of walking technicolor. The signatures studied are lepton plus two jets plus E(T) and multijet final states. No excess of events is seen in either final state. We set an upper limit on the technirho production cross section and exclude a region in the technipion mass versus technirho mass plane.     

Diffractive dijets with a leading antiproton in &pmacr;p collisions at sqrt

We report results from a study of events with a leading antiproton of beam momentum fraction 0.9057 GeV. Using the dijet events, we evaluate the diffractive structure function of the antiproton and compare it with expectations based on results obtained in diffractive deep inelastic scattering experiments at the DESY ep collider HERA.