Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Microstructures and properties of high-entropy alloys

An appropriate cellular response to implanted surfaces is essential for tissue regeneration and integration. It is well described that implanted materials are immediately coated with proteins from blood and interstitial fluids, and it is through this adsorbed layer that cells sense foreign surfaces. Hence, it is the adsorbed proteins, rather than the surface itself, to which cells initially respond. Diverse studies using a range of materials have demonstrated the pivotal role of extracellular adhesion proteins--fibronectin and vitronectin in particular--in cell adhesion, morphology, and migration. These events underlie the subsequent responses required for tissue repair, with the nature of cell surface interactions contributing to survival, growth, and differentiation. The pattern in which adhesion proteins and other bioactive molecules adsorb thus elicits cellular reactions specific to the underlying physicochemical properties of the material. Accordingly, in vitro studies generally demonstrate favorable cell responses to charged, hydrophilic surfaces, corresponding to superior adsorption and bioactivity of adhesion proteins. This review illustrates the mediation of cell responses to biomaterials by adsorbed proteins, in the context of osteoblasts and selected materials used in orthopedic implants and bone tissue engineering. It is recognized, however, that the periimplant environment in vivo will differ substantially from the cell-biomaterial interface in vitro. Hence, one of the key issues yet to be resolved is that of the interface composition actually encountered by osteoblasts within the sequence of inflammation and bone regeneration.

Mediation of Biomaterial–Cell Interactions by Adsorbed Proteins: A Review

Surface studies of supported model catalysts

http://w0.rz-berlin.mpg.de/hjfdb/pdf/260e.pdf

Metal deposits on well-ordered oxide films

Effect of surface roughness of the titanium alloy Ti-6Al-4V on human bone marrow cell response and on protein adsorption.

THE catalytic activity and selectivity of metals can be altered dramatically and reversibly by supplying or removing oxide anions, O2–, at the metal catalyst surface by interfacing the catalyst with an O2– conductor such as zirconia1–6. This effect, termed non-faradaic electrochemical modification of catalytic activity (NEMCA), leads to a steady-state catalytic reaction rate increase up to 3 × 105 times higher than the rate of supply or removal of O2– at the catalyst surface1,3,4. Here we report that β"-Al2O3, which is a Na+ conductor, can also induce the NEMCA effect. Furthermore we show that the origin of the NEMCA effect lies in the controlled variation of catalyst work function on polarization of the metal-solid-electrolyte interface, and demonstrate that the rates of metal-catalysed reactions depend exponentially on the average catalyst work function. Thus the influence of catalyst electronic structure, rather than surface geometry, is here the key factor in catalytic activity.

Dependence of catalytic rates on catalyst work function

The adsorption and catalytic oxidation of carbon monoxide on evaporated palladium particles

Kinetic oscillations during the catalytic CO oxidation on Pd(110): The role of subsurface oxygen

X-ray photoelectron spectroscopy (XPS) was used to investigate the effect of electrochemical oxygen pumping on Pt catalyst films interfaced with an O 2 -conducting yttria-stabilized zirconia solid electrolyte. It was found that electrochemical oxygen pumping to the catalyst causes spillover of significant amounts of anionic oxygen from the solid electrolyte onto the platinum film surface. The spillover oxygen species has an XPS binding energy 528.8 eV compared to 530.4 eV for chemisorbed oxygen, which is also observed on the surface, and is less reactive than chemisorbed oxygen with the reducing ultrahigh vacuum background. The detection of the anionic oxygen species upon electrochemical pumping confirms the previously proposed explanation of the non-Faradaic electrochemical modification of catalytic activity (NEMCA) or electrochemical in catalysis

Spyridon Ladas

Papers

Effect of surface roughness of the titanium alloy Ti-6Al-4V on human bone marrow cell response and on protein adsorption.

Dependence of catalytic rates on catalyst work function

The adsorption and catalytic oxidation of carbon monoxide on evaporated palladium particles

Kinetic oscillations during the catalytic CO oxidation on Pd(110): The role of subsurface oxygen

Origin of non-faradaic electrochemical modification of catalytic activity