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

Production, properties and potential of graphene

Topological design and additive manufacturing of porous metals for bone scaffolds and orthopaedic implants: A review.

The high-entropy alloys with high hardness and soft magnetic property prepared by mechanical alloying and high-pressure sintering

Bearing rollers, 7.5 mm in diameter and 7.5 mm in length, were prepared from Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 bulk metallic glass (BMG). The working life of the bearing rollers was evaluated through a real rotation test with a large-load and at a high-speed, and compared with that of commercial GCr15 steel rollers. The results show that the bearing rollers of Zr-based bulk metallic glass have a better wear resistance than the commercial GCr15 ones. And the wear behaviors are different for these two kinds of bearing rollers.

Wear resistance of Zr-based bulk metallic glass applied in bearing rollers

In this paper, zirconium (Zr) is selected as a partial substitutable element for titanium (Ti) in Ti–6Al–4V (TC4) alloy to fabricate series of TiZrAlV quaternary alloys. Mechanical testing, microhardness testing, metallographic analysis, X-ray diffraction, and fracture analysis are performed to evaluate the microstructure and mechanical properties of the alloys. The tensile strength and microhardness are found to increase with increased Zr content, whereas the elongation ratio decreases with gradually increased Zr content. The morphology of α phase suffers a series of changes with the increase of Zr content. The β phase contents of the alloys studied also gradually increase with the increase of Zr content. Ti–20Zr–6Al–4V alloy, which has outstanding mechanical properties ( σ b  = 1.317 MPa and δ  = 8%), is found to be the best composition. Hence, a series of new quaternary alloys has potential uses in the nuclear and aerospace industries as structural materials.

Structure and mechanical properties of Ti–6Al–4V alloy after zirconium addition

High pressure torsion (HPT) under a pressure of 6 GPa through 1 and 2 revolutions have been used to follow the evolution of microstructures and properties in an Al0.1CoCrFeNi high-entropy alloy (HEA). The plastic-deformation mechanisms of the HEA include dislocation slip at low strains and twinning at high strains at room temperature. The planar dislocation slip on the normal face-centered-cubic slip system, {111}〈110〉, and nanoscaled deformation twins with a thickness from several nanometers to 40 nm, accompanied with some secondary twins. The hardness of the Al0.1CoCrFeNi HEA increases from 135 Hv at hot-isostatic pressed (HIPed) state to about 482 Hv after HPT processing. The HEAs have a relatively high initial hardness and high work hardening, compared with traditional alloys. The creep resistance of the HEA processed by HPT was determined by a nanoindentation technique. The strain rate sensitivity, m, increases with the decreasing of grain size, for smaller activation volume and the dominant deformation mechanism changing from the dislocation slip to grain-boundary slide. The present results give the plastic-deformation mechanism and mechanical properties evolution of single-phase HEA processed by HPT at room temperature.

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Effects of high pressure torsion on microstructures and properties of an Al0.1CoCrFeNi high-entropy alloy

Zr-based alloys are commonly used as nuclear materials. A series of ZrTiAlV alloys were investigated to develop Zr-based alloys with excellent mechanical properties and broaden the application of Zr metals. Apart from a mechanical testing, X-ray diffraction and metallographic analyses were used to study the structural and mechanical properties of hot-rolled ZrTiAlV alloys. The results showed that the microstructure of alloys went through a series of changes from the α ( α ′)-phase to part or all of the β -phase, thus affecting the mechanical properties as Zr increased. As the volume fraction of the β -phase increased, ductility was enhanced gradually, and tensile strength remained at a high level. A steep decline in strength was observed as soon as the entirety of the β -phase retained. The Zr–40.8Ti–4.4Al–2.9V alloy was found to be the best composition in terms of tensile strength ( σ b  = 1246 MPa) and ductility ( δ  = 11%), with insignificant anisotropy after hot rolling. A number of new, Zr-based alloys with excellent mechanical properties are also reported in the current study.

R.P. Liu

Papers

The high-entropy alloys with high hardness and soft magnetic property prepared by mechanical alloying and high-pressure sintering

Wear resistance of Zr-based bulk metallic glass applied in bearing rollers

Structure and mechanical properties of Ti–6Al–4V alloy after zirconium addition

Effects of high pressure torsion on microstructures and properties of an Al0.1CoCrFeNi high-entropy alloy

Microstructure and mechanical properties of hot-rolled ZrTiAlV alloys