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

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

This article presents an overview of the developments in stainless steels made since the 1990s. Some of the new applications that involve the use of stainless steel are also introduced. A brief introduction to the various classes of stainless steels, their precipitate phases and the status quo of their production around the globe is given first. The advances in a variety of subject areas that have been made recently will then be presented. These recent advances include (1) new findings on the various precipitate phases (the new J phase, new orientation relationships, new phase diagram for the Fe–Cr system, etc.); (2) new suggestions for the prevention/mitigation of the different problems and new methods for their detection/measurement and (3) new techniques for surface/bulk property enhancement (such as laser shot peening, grain boundary engineering and grain refinement). Recent developments in topics like phase prediction, stacking fault energy, superplasticity, metadynamic recrystallisation and the calculation of mechanical properties are introduced, too. In the end of this article, several new applications that involve the use of stainless steels are presented. Some of these are the use of austenitic stainless steels for signature authentication (magnetic recording), the utilisation of the cryogenic magnetic transition of the sigma phase for hot spot detection (the Sigmaplugs), the new Pt-enhanced radiopaque stainless steel (PERSS) coronary stents and stainless steel stents that may be used for magnetic drug targeting. Besides recent developments in conventional stainless steels, those in the high-nitrogen, low-Ni (or Ni-free) varieties are also introduced. These recent developments include new methods for attaining very high nitrogen contents, new guidelines for alloy design, the merits/demerits associated with high nitrogen contents, etc.

Recent developments in stainless steels

Overview of constitutive laws, kinematics, homogenization and multiscale methods in crystal plasticity finite-element modeling: Theory, experiments, applications

Moisture-Driven CO2 Sorbents

We conducted fracture toughness experiments on freestanding copper films with thicknesses ranging from about 800 to 100 nm deposited by electron beam evaporation to elucidate the size effect on fracture toughness in the nano- or submicron-scale. It was found that initially, the crack propagated stably under loading, and then the crack propagation rate rapidly increased, resulting in unstable fracture. The fracture toughness K C was estimated on the basis of the R -curve concept to be 7.81 ± 1.22 MPa m 1/2 for the 800-nm-thick film, 6.63 ± 1.05 MPa m 1/2 for the 500-nm-thick film and 2.34 ± 0.54 MPa m 1/2 for the 100-nm-thick film. Thus, a clear size effect was observed. The fracture surface suggested that the crack underwent large plastic deformation in the thicker 800-nm and 500-nm films, whereas it propagated with highly localized plastic deformation in the thinner 100-nm film. This size effect in fracture toughness might be related to a transition in deformation and fracture morphology near the crack tip.

Size effect on fracture toughness of freestanding copper nano-films

In this study, an evaluation method for anisotropic plastic properties is proposed using dimensional analysis of single spherical indentation. The method considers a plastically anisotropic material, whose properties are different among orthogonal directions (e.g. longitudinal and transverse direction). In other words, the stress–strain curves along both directions can be simultaneously determined by the present method. When a spherical indenter is impressed against a plane cut along the longitudinal direction (i.e. indentation was conducted along the transverse direction), the impression geometry was found to change depending on the orthogonal axis. That is, the pile-up height in the transverse direction becomes higher than that in the longitudinal one. Using this characteristic and the indentation curve, dimensional functions were established in order to deduce anisotropic plastic properties. Extensive finite element analysis was first carried out to compute the indentation response (indentation curve and impression geometry). Subsequently, dimensionless functions connecting the anisotropic plastic properties to the indentation response were established. The effectiveness of the method was verified by numerical experiments. Finally, an indentation experiment was carried out on an SiC whisker-reinforced aluminum alloy to deduce the anisotropic plastic properties. The estimation results were found to be reliable. The present method is thus useful for determining the plastic properties of various anisotropic materials, such as cold-worked steel, composites and coatings.

A simple method to evaluate anisotropic plastic properties based on dimensionless function of single spherical indentation – Application to SiC whisker-reinforced aluminum alloy

Based on the stress fields formed upon Vickers indentation, the radial crack and half-penny crack systems are analysed separately using finite-element analyses. The crack length is correlated with the stress intensity factor (SIF) at the crack front and material elastoplastic properties via explicit relationships, from which a reverse analysis can be carried out such that the critical SIF (fracture toughness) can be readily derived once the crack length is measured. The proposed technique is validated by comparing with experimental data in the literature as well as parallel experiments of Vickers indentation-induced cracking.

Akio Yonezu

Papers

Moisture-Driven CO2 Sorbents

Size effect on fracture toughness of freestanding copper nano-films

A simple method to evaluate anisotropic plastic properties based on dimensionless function of single spherical indentation – Application to SiC whisker-reinforced aluminum alloy

On radial crack and half-penny crack induced by Vickers indentation

Fracture observation of polycrystalline diamond film under indentation test