There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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

Microstructures and properties of high-entropy alloys

: OUTLINE: (1) An AF Perspective of Nanotechnology; (2) Nanoscience and Technology in AFRL: Past and Present; (3) A Strategic Plan for the Future; (4) Summary.

Nanoscience and Technology at the Air Force Research Laboratory (AFRL)

Synthesis and applications of cast metal matrix composites and syntactic foams

Elastic properties of Ca-based bulk metallic glasses studied by resonant ultrasound

: High entropy alloys (HEAs) are barely 12 years old. The field has stimulated new ideas and has inspired the exploration of the vast composition space offered by multi-principal element alloys (MPEAs). Here we present a critical review of this field, with the intent of summarizing key findings, uncovering major trends and providing guidance for future efforts. Major themes in this assessment include definition of terms; thermodynamic analysis of complex, concentrated alloys (CCAs); taxonomy of current alloy families; microstructures; mechanical properties; potential applications; and future efforts. Based on detailed analyses, the following major results emerge. Although classical thermodynamic concepts are unchanged, trends in MPEAs can be different than in simpler alloys. Common thermodynamic perceptions can be misleading and new trends are described. From a strong focus on 3d transition metal alloys, there are now seven distinct CCA families. A new theme of designing alloy families by selecting elements to achieve a specific, intended purpose is starting to emerge. A comprehensive microstructural assessment is performed using three datasets: experimental data drawn from 408 different alloys and two computational datasets generated using the CALculated PHAse Diagram (CALPHAD) method. Each dataset emphasizes different elements and shows different microstructural trends. Trends in these three datasets are all predicted by a structure in - structure out (SISO) analysis developed here that uses the weighted fractions of the constituent element crystal structures in each dataset. A total of 13 distinct multi-principal element single-phase fields are found in this microstructural assessment. Relationships between composition, microstructure and properties are established for 3d transition metal MPEAs, including the roles of Al, Cr and Cu. Critical evaluation shows that commercial austenitic stainless steels and nickel alloys with 3 or more principal elements are MPEAs.

/pdf/a-critical-review-of-high-entropy-alloys-and-related-4o653xwgk1.pdf

A Critical Review of High Entropy Alloys and Related Concepts (Postprint)

: Nanostructured Al93Fe3Ti2Cr2 alloys were prepared via mechanical alloying (MA) starting from elemental powders, followed by extrusion to form bulk material. The microstructure and phase formation as a function of the milling time and the concentration of the process-control agent were investigated. The thermal stability of the mechanical alloyed powder was also studied. The bulk material extruded from the mechanical alloyed powder exhibited superior strength with good ductility at both ambient and elevated temperatures under compressive loading conditions. The enhanced strength at both ambient and elevated temperatures was attributed to the retention of ultrafine grains (fcc-Al < 100 nm), the formation of supersaturated solid solutions, and the presence of nanoscale intermetallic precipitates.

Daniel B. Miracle

Papers

Nanoscience and Technology at the Air Force Research Laboratory (AFRL)

Synthesis and applications of cast metal matrix composites and syntactic foams

Elastic properties of Ca-based bulk metallic glasses studied by resonant ultrasound

A Critical Review of High Entropy Alloys and Related Concepts (Postprint)

Processing and Properties of Mechanical Alloyed Al93Fe3Cr2Ti2 Alloys