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

https://dc.engconfintl.org/cgi/viewcontent.cgi?article=1032&context=superalloys_ii

A critical review of high entropy alloys and related concepts

There is a special reason for reviewing this book at this time: it is the 50th edition of a compendium that is known and used frequently in most chemical and physical laboratories in many parts of the world. Surely, a publication that has been published for 56 years, withstanding the vagaries of science in this century, must have had something to offer. There is another reason: while the book is a standard fixture in most chemical and physical laboratories, including those in medical centers, it is not as frequently seen in the laboratories of physician's offices (those either in solo or group practice). I believe that the Handbook can be useful in those laboratories. One of the reasons, among others, is that the various basic items of information it offers may be helpful in new tests, either physical or chemical, which are continuously being published. The basic information may relate

Handbook of Chemistry and Physics

Metals have been mankind's most essential materials for thousands of years; however, their use is affected by ecological and economical concerns Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency However, most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength-ductility trade-off Here we present a metastability-engineering strategy in which we design nanostructured, bulk high-entropy alloys with multiple compositionally equivalent high-entropy phases High-entropy alloys were originally proposed to benefit from phase stabilization through entropy maximization Yet here, motivated by recent work that relaxes the strict restrictions on high-entropy alloy compositions by demonstrating the weakness of this connection, the concept is overturned We decrease phase stability to achieve two key benefits: interface hardening due to a dual-phase microstructure (resulting from reduced thermal stability of the high-temperature phase); and transformation-induced hardening (resulting from the reduced mechanical stability of the room-temperature phase) This combines the best of two worlds: extensive hardening due to the decreased phase stability known from advanced steels and massive solid-solution strengthening of high-entropy alloys In our transformation-induced plasticity-assisted, dual-phase high-entropy alloy (TRIP-DP-HEA), these two contributions lead respectively to enhanced trans-grain and inter-grain slip resistance, and hence, increased strength Moreover, the increased strain hardening capacity that is enabled by dislocation hardening of the stable phase and transformation-induced hardening of the metastable phase produces increased ductility This combined increase in strength and ductility distinguishes the TRIP-DP-HEA alloy from other recently developed structural materials This metastability-engineering strategy should thus usefully guide design in the near-infinite compositional space of high-entropy alloys

Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off

A phase and microstructure selection map used for peritectic alloy directionally solidified under convection condition was presented, which is based on the nucleation, constitutional undercooling criterion (NCU criterion), and the highest interface temperature criterion. This selection map shows the relationships between the phase/microstructure, the G/V ratio (G is the temperature gradient, V is the growth velocity), and the alloy composition under different convection intensities and nucleation undercoolings. Comparing with the results from directional solidification experiments of Sn–Cd peritectic alloys, this selection map was generally in agreement with the experimental results.

Phase and Microstructure Selection During Directional Solidification of Peritectic Alloy Under Convection Condition

A weak transverse static magnetic field (WTSMF, 0–0.5 T) is applied to the directional solidification process of a DD3 Ni-based SX superalloy, aiming to tailor the microstructure and microsegregation of alloys. The mechanisms of microstructural refinement and microsegregation distribution caused by a WTSMF during directional solidification are discussed. It is shown that the primary dendrite arm spacing is rapidly reduced from 181 to 143 μm, and the average size of γ′ phase is significantly refined from 0.85 to 0.25 μm as the magnetic field increases from 0 to 0.5 T. At the same time, the volume fractions of γ/γ′ eutectic and the segregation coefficient are also gradually decreased. The 3D numerical simulations of the multiscale convection in liquid phase show that the modifications of the microstructure and microsegregation in DD3 are mainly attributed to the enhanced liquid flow caused by thermoelectric magnetic convection (TEMC) at dendrite/sample scale under the WTSMF. The maximum of the TEMC increases with increasing the magnetic field intensity. This work paves a simple way to optimize the microstructure and microsegregation in directionally solidified Ni-based SX superalloys without changing the processing parameters and composition. 

https://www.amse.org.cn/EN/article/downloadArticleFile.do?attachType=PDF&id=31939

Tailoring Microstructure and Microsegregation in a Directionally Solidified Ni-Based SX Superalloy by a Weak Transverse Static Magnetic Field

The single-crystal superalloys with different deviation angle are prepared by using the liquid metal cooling high-temperature gradient directional solidification furnace, and the orientation evolution of single-crystal superalloys under different solidification interface is studied. The results indicate that the increase of the deviation angle will make the planar interface unstable. With the increase of the solidification rate, the growth direction of the crystal will deviate from the direction of heat flow to the preferred orientation direction. Under the developed dendrite crystal growth, the branches of the dendrite will follow the preferred orientation, nearly free from the effect of the heat flow.

Hengzhi Fu

Papers

Phase and Microstructure Selection During Directional Solidification of Peritectic Alloy Under Convection Condition

Tailoring Microstructure and Microsegregation in a Directionally Solidified Ni-Based SX Superalloy by a Weak Transverse Static Magnetic Field

Orientation evolution of single-crystal superalloys under different solidification interface

Method for performing laser solid forming on aluminum oxide-based eutectic authigenic composite ceramic

Evolution of Metastable α2 Phase in a Quenched High‐Nb‐Containing TiAl Alloy at 800 °C