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

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Microstructures and properties of high-entropy alloys

Mechanical properties of nanocrystalline materials

Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Mechanical Alloying And Milling

Powder compaction has two equally important aspects: the elimination of pores and the creation of bonds between the particles Important bonding mechanisms are cold welding and mechanical interlocking of particle surfaces The first requires plastic flew in order to break the surface oxide, the second depends on irregular surface geometry Hard, smooth particles do not usually permit the action of either of these mechanisms; after compaction, they simply fall apart again Such powders must be contained in capsules and, after compaction, must be bonded by sintering or hot pressing This has in fact become the normal fabrication route for superalloy and tool steel powders

/pdf/the-compaction-of-rapidly-solidified-materials-57ojbuj85a.pdf

The Compaction of Rapidly Solidified Materials

The mechanical properties are thought to play an important role in the performance of metallization materials for very large scale integration (VLSI) applications. From recent investigations on bulk materials it is known that Al-Si-Ge alloys can be very efficiently strengthened with only a small amount of the alloying elements. These alloys are potential candidates for future metallizations both because Si and Ge are compatible with the existing semiconductor technology, and because the resistivity is expected to be low. The authors present the first results of detailed characterizations of Al-Si-Ge thin films as a function of sputter conditions and heat treatments. The microstructure was characterized using x-ray diffraction and transmission electron microscopy. The kinetics of precipitation were studied using resistance measurements. Room temperature hardness was investigated using nanoindentation, and the mechanical properties at temperatures up to 240 C were examined using a substrate curvature method. The correlation between precipitate structure and film properties is discussed.

Microstructure and Mechanical Properties of Thin Al-Si-Ge Films

Bioinspired Patterned Adhesives

Thermal hillocks in sputter-deposited Al films have been studied as a part of a broad study of stress-induced diffusional processes in Al. Trace amounts of the impurities Ti, W, and O were incorporated into the films during deposition, causing them to be much stronger than most sputter deposited Al films. Stress measurement during thermal cycling, using the wafer curvature method, showed that these Al films are very strong; this finding was corroborated by hardness measurements. Microstructural studies using TEM and FIB showed that the hillocks start to form at the Al/SiO2 interface and grow under the original Al film, with its columnar grain structure. In some cases, the film fails as hillocks grow completely through the original film. The Al film on top of the hillocks appears to inhibit hillock growth by creating a back pressure associated with power law creep of the film. We modeled this form of hillock formation by modifying the boundary conditions in Chaudhari’s hillock model [1]. Our model describes hillock formation by diffusion of Al atoms from the surrounding area into isolated hillocks, assuming that the original Al film on top of hillocks deforms following power law creep. Our model can be applied to many different situations by using different creep laws for the top Al film.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400202480

Diffusional Hillock Formation in Al Thin Films Controlled by Creep

In the last decade, bio‐inspired adhesives have gained much attention both by science and industry, because of their unique properties: High adhesion, easy detachment, residue‐free contact and self‐cleaning properties. The effort of biologists, chemists, physicists, materials scientists and engineers, of theoreticians and experimentalists, has led to a good understanding of the principles of bio‐inspired adhesion. Fundamental research on bio‐inspired adhesives is still developing strongly, but more and more effort is put into applied research. Topics such as switchable adhesives, biomedical bio‐inspired adhesive pads or large‐scale fabrication techniques suggest that the time is near when the technology found in nature will be available in modern products. In our chapter, we give an overview of the research into bio‐inspired adhesives based on the adhesion system of geckos.

Eduard Arzt

Papers

The Compaction of Rapidly Solidified Materials

Microstructure and Mechanical Properties of Thin Al-Si-Ge Films

Bioinspired Patterned Adhesives

Diffusional Hillock Formation in Al Thin Films Controlled by Creep

CHAPTER 14:Bio‐inspired Adhesive Surfaces: From Principles to Applications