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

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

Magnesium alloys have received an increasing interest in the past 12 years for potential applications in the automotive, aircraft, aerospace, and electronic industries. Many of these alloys are strong because of solid-state precipitates that are produced by an age-hardening process. Although some strength improvements of existing magnesium alloys have been made and some novel alloys with improved strength have been developed, the strength level that has been achieved so far is still substantially lower than that obtained in counterpart aluminum alloys. Further improvements in the alloy strength require a better understanding of the structure, morphology, orientation of precipitates, effects of precipitate morphology, and orientation on the strengthening and microstructural factors that are important in controlling the nucleation and growth of these precipitates. In this review, precipitation in most precipitation-hardenable magnesium alloys is reviewed, and its relationship with strengthening is examined. It is demonstrated that the precipitation phenomena in these alloys, especially in the very early stage of the precipitation process, are still far from being well understood, and many fundamental issues remain unsolved even after some extensive and concerted efforts made in the past 12 years. The challenges associated with precipitation hardening and age hardening are identified and discussed, and guidelines are outlined for the rational design and development of higher strength, and ultimately ultrahigh strength, magnesium alloys via precipitation hardening.

/pdf/precipitation-and-hardening-in-magnesium-alloys-18s7dgmp2s.pdf

Precipitation and Hardening in Magnesium Alloys

TEM study of continuous precipitation in Mg-9 wt%Al-1 wt%Zn alloy

http://www.dunand.northwestern.edu/refs/files/ZhangWeatherly.pdf

On the crystallography of precipitation

Misfits between lattice points of intersecting crystals and between corresponding lattice planes are analysed using O-lattice constructions referred to both direct and reciprocal spaces. O-lattice planes are described by the same expression as the ‘Moire planes’ formed by the mismatch of correlated planes, which facilitates the study of the O lattice from diffraction patterns. The normalized primary O-lattice planes (those related to the closest packed atomic planes) with the smallest interplanar spacing are considered to be planes of minimum mismatch, and hence to represent plausible low-energy interfaces. An interface of arbitrary orientation is assumed to be stepped microscopically along the primary O-lattice planes. The solution for the O-lattice cells is derived. Based on this cell structure, possible configurations of the misfit dislocations in a primary O-lattice plane are obtained; this provides a basic description of interfacial structure.

O-lattice analyses of interfacial misfit. I: General considerations

Mismatch in interfaces containing an invariant line is analysed on the basis of the O-lattice concept and the properties of the invariant line strain. An optimum orientation relationship is proposed to satisfy the requirement for the existence of the O lines. The corresponding habit plane will contain the O lines, and the mismatch in the habit plane will be accommodated completely by a single set of dislocations. The concept of an effective invariant line is introduced. An example is given for a Zr-2.5 wt% Nb alloy, showing the method of search for the optimum orientation relationship. The corresponding interfacial structure in the habit plane is also provided.

O-lattice analyses of interfacial misfit. II. Systems containing invariant lines

PTCLab (Phase Transformation Crystallography Lab) is free and open-source software to calculate the crystallographic features formed during a phase transformation, such as orientation relationship, interface orientation, interfacial structure etc. This program covers the crystallographic theories for both martensitic and diffusional transformation and allows users to represent the results in stereographic projection. The crystallographic models treated in PTCLab include the classical phenomenological theory of martensite crystallography (PTMC), the double shear version of PTMC, the invariant line model, O-lattice theory, the O-line model, the recently developed three-dimensional near coincidence site method, the edge-to-edge matching model and variant selection analysis. In addition, a number of basic crystallographic calculations for single or multiple crystal structures can be performed with the calculation pad. High-quality composite stereographic projection and electron diffraction patterns can be also obtained by the present application. PTCLab is written in Python, runnable cross platform, and is distributed at https://sourceforge.net/projects/tclab/.

PTCLab: free and open-source software for calculating phase transformation crystallography

The continuous precipitation of the β b.c.c. phase in Mg-Al gives rise to elongated platelets which exhibit a Burgers orientation relationship and whose habit plane is parallel to the matrix basal plane. The habit plane is found to contain a periodic array of secondary edge dislocations. It is shown that the epitaxial relationship, the growth direction and the interfacial structure can be interpreted by applying the CSL/DSC and O-lattice models.

High-resolution electron microscopy observations of the interface structure of continuous precipitates in a Mg-Al alloy and interpretation with the O-lattice theory

Wen-Zheng Zhang

Papers

On the crystallography of precipitation

O-lattice analyses of interfacial misfit. I: General considerations

O-lattice analyses of interfacial misfit. II. Systems containing invariant lines

PTCLab: free and open-source software for calculating phase transformation crystallography

High-resolution electron microscopy observations of the interface structure of continuous precipitates in a Mg-Al alloy and interpretation with the O-lattice theory