Full hemispherical photoelectron diffraction and Fermi surface mapping

The routine measurement of full hemispherical photoemission intensity maps gives us the possibility for the combined investigation of structural and electronic phenomena at surfaces. As an example the growth of ultrathin films of Co on Cu(111) is studied as a function of film thickness. While X-ray photoelectron diffraction (XPD) shows the early appearance of stacking faults as a precursor of the hcp structure, Fermi surface maps reveal the very fast evolution of the Co Fermi surface that can be compared to measurements on a clean Co(0001) crystal. For the system O/Rh(111), XPD brings up important structural clues, relating changes in surface reactivity to small amounts of subsurface oxygen, which forces adjacent oxygen atoms to occupy new and more reactive adsorption sites. In the course of this last study we observed for the first time the weak backscattering signals in the angular pattern of adsorbate emission. These cone-like features are extremely sensitive to the adsorbate–substrate bond length.     

Global existence in rate-independent infinitesimal strain gradient plasticity

We propose a model of infinitesimal strain gradient plasticity including phenomenological Prager type linear kinematical hardening and nonlocal kinematical hardening due to dislocation interaction. The model is a thermodynamically admissible model of infinitesimal plasticity involving only the Curl of the non-symmetric plastic distortion p. Linearized spatial and material covariance under constant infinitesimal rotations is satisfied. Uniqueness of strong solutions of the infinitesimal model is obtained if two non-classical boundary conditions on the plastic distortion p are introduced: ṗ.τ = 0 on the microscopically hard boundary Γ_D ⊂ ∂Ω and [Curl p ].τ = 0 on the microscopically free boundary ∂Ω\Γ_D, where τ are the tangential vectors at the boundary ∂Ω. Moreover, a weak reformulation of the infinitesimal model allows for a global in-time solution of the corresponding rate-independent initial boundary value problem. The method of choice are a formulation as a quasi-variational inequality with symmetric and coercive bilinear form. Use is made of new Hilbert-space suitable for dislocation density dependent plasticity. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and Kinetic Aspects of Blood Plasma Protein Adsorption on the Surface of Hydrophobic Polymers

Abstract

Due to the wide use of polymers in medicine, researchers are required to solve a very important problem–to understand the interaction between materials of nonphysiological origin and the surrounding biological liquids, and tissues, particularly blood.     

Requirements for simultaneous ignition of all channels in ahigh-current radial multichannel pseudospark switch

In order to reduce erosion of electrodes and consequently achieve a long lifetime for high-power switches, a low-pressure switch, namely the pseudospark switch (PSS), is investigated as an alternative to the conventional high-power switches. The erosion can be reduced further along with an enhancement of the current and the rate of current rise, if more channels are introduced for the passage of current. An intense electron beam is known to be emitted by the hollow cathode during the starting phase in a pseudospark discharge. It has been reported that in a multichannel setup each installed channel can ignite only if it gets ionized by its respective beam. The results presented in this paper show how this multichannel operation can be accomplished. These results are based on a statistical study of a radial multichannel pseudospark switch and an observation of the discharge course by means of high-speed photography and show that a glow discharge trigger, with a high glow current (⩾1.2 mA) and slowly rising trigger pulses (⩾150 ns), allows a simultaneous ignition of up to 12 channels