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

Additive manufacturing of metallic components – Process, structure and properties

How have Japanese companies become world leaders in the automotive and electronics industries, among others? What is the secret of their success? Two leading Japanese business experts, Ikujiro Nonaka and Hirotaka Takeuchi, are the first to tie the success of Japanese companies to their ability to create new knowledge and use it to produce successful products and technologies. In The Knowledge-Creating Company, Nonaka and Takeuchi provide an inside look at how Japanese companies go about creating this new knowledge organizationally. The authors point out that there are two types of knowledge: explicit knowledge, contained in manuals and procedures, and tacit knowledge, learned only by experience, and communicated only indirectly, through metaphor and analogy. U.S. managers focus on explicit knowledge. The Japanese, on the other hand, focus on tacit knowledge. And this, the authors argue, is the key to their success--the Japanese have learned how to transform tacit into explicit knowledge. To explain how this is done--and illuminate Japanese business practices as they do so--the authors range from Greek philosophy to Zen Buddhism, from classical economists to modern management gurus, illustrating the theory of organizational knowledge creation with case studies drawn from such firms as Honda, Canon, Matsushita, NEC, Nissan, 3M, GE, and even the U.S. Marines. For instance, using Matsushita's development of the Home Bakery (the world's first fully automated bread-baking machine for home use), they show how tacit knowledge can be converted to explicit knowledge: when the designers couldn't perfect the dough kneading mechanism, a software programmer apprenticed herself withthe master baker at Osaka International Hotel, gained a tacit understanding of kneading, and then conveyed this information to the engineers. In addition, the authors show that, to create knowledge, the best management style is neither top-down nor bottom-up, but rather what they call "middle-up-down," in which the middle managers form a bridge between the ideals of top management and the chaotic realities of the frontline. As we make the turn into the 21st century, a new society is emerging. Peter Drucker calls it the "knowledge society," one that is drastically different from the "industrial society," and one in which acquiring and applying knowledge will become key competitive factors. Nonaka and Takeuchi go a step further, arguing that creating knowledge will become the key to sustaining a competitive advantage in the future. Because the competitive environment and customer preferences changes constantly, knowledge perishes quickly. With The Knowledge-Creating Company, managers have at their fingertips years of insight from Japanese firms that reveal how to create knowledge continuously, and how to exploit it to make successful new products, services, and systems.

The knowledge-creating company

Singular Integral Equations. By N.I. Muskhelishvili. Translated fromthe 2nd Russian edition by J.R.M. Radok. Pp. 447. F1. 28.50. 1953. (Noordhoff, Groningen)

Gibbs-Thompson effect is the general term referring to the influence of interfaces on the course of phase transformations such as precipitation or solidification. Whilst attention is most often focused on the Gibbs-Thomson effect on nucleation, growth and coarsening, the present study considers the reverse process of precipitate dissolution in a nickel-base superalloy during in situ TEM observation. The presence of several distinct populations of gamma-prime precipitates – primary, secondary, tertiary and grain boundary – allows the differences due to particle size to be quantified and interpreted. Important implications arise for the selection of heat treatment schedules for nickel-base superalloys and other alloy systems. of a new polycrystalline nickel-base superalloy is explored by performing in situ heating of thin lamella samples under the electron beam in a scanning transmission electron microscope (STEM). Along with the microstructure, the elemental distribution and the compositional profile of γ ’ precipitate populations is investigated using a synchronous electron energy loss spectroscopy (EELS) analysis. In situ heating experiments within STEM combined with EELS technique enables probing the mechanisms underlying the complex physicochemical processes at the nanometric scale as they unfold. Operando nanoscale observation of the dissolution of γ ’ populations was achieved, and the findings provide a direct observation of the Gibbs-Thomson effect in the dissolution behaviour of different γ ’ populations.

Direct TEM observation and quantification of the Gibbs-Thomson effect in a nickel superalloy

In the present study, pins made from the novel Mg-2Zn-2Ga alloy were installed within the femoral bones of six Wistar rats. The level of bioresorption was assessed after 1, 3, and 6 months by radiography, histology, SEM, and EDX. Significant bioresorption was evident after 3 months, and complete dissolution of the pins occurred at 6 months after the installation. No pronounced gas cavities could be found at the pin installation sites throughout the postoperative period. The animals’ blood parameters showed no signs of inflammation or toxication. These findings are sufficiently encouraging to motivate further research to broaden the experimental coverage to increase the number of observed animals and to conduct tests involving other, larger animals.

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An In Vivo Rat Study of Bioresorbable Mg-2Zn-2Ga Alloy Implants

Surface hardening in components subjected to severe contact loading, such as gears, is accompanied by the generation of a layer of residual stress. Compressive residual stresses in surface engineered components are often induced deliberately to provide improved toughness and wear resistance. However, a near-surface layer of compressive stress often generates a balancing region of tensile stress deeper within the component, which may accelerate damage in this region and promote failure. To quantify the effect of treatment on the stress distribution, residual strains in an induction hardened gear tooth were mapped using high energy synchrotron diffraction on Station 16.3 at SRS, Daresbury. White beam mode and an energy dispersive detector were used, and two components of strain and stress in the plane transverse to the gear axis were evaluated.

Residual Stresses in an Induction Hardened Gear Tooth Mapped by Synchrotron X-ray Diffraction

Understanding the creep mechanisms and deformation response at different stresses and temperatures is crucial for design using nickel-base superalloys for high-temperature applications. In this study, the creep behaviour of a newly designed superalloy (nominated Alloy 11) at 750 ℃ /400MPa and 700 ℃ /800MPa was systematically investigated using SEM, STEM, EBSD and synchrotron X-ray diffraction. Material properties and mechanical response were analysed by considering such properties as lattice parameters and misfit, phase volume fraction, microstrain in reference and crept samples. Detwinning and dynamic recrystallization were observed for the crept samples. STEM characterization of deformed materials reveals that multiple deformation mechanisms and defects could be identified in crept samples, namely, dislocations in the 𝛾 matrix channels and in 𝛾 ! precipitates, along with continuous and isolated stacking faults. The highest values of lattice misfit, microstrain and lattice parameter change were observed at the centre of dogbone-shaped crept samples. This was associated with the hump shaped temperature distribution profile during creep testing. The significant spatial variation detected in terms of lattice parameters, misfit and microstrain supports the conclusion that it is important to perform spatially resolved measurements instead of considering each sample as a single measurement point when investigating creep response. It is also worth noting that the statistics of the lattice-parameter distribution for the 𝛾 and 𝛾 ! phases obey a gaussian distribution. In conclusion, a discussion is given for the meaning and implications of these findings for future research.

The creep deformation of a new nickel-base alloy-by-design studied using synchrotron X-ray diffraction

Despite the fact that the Two-Way Shape Memory Effect (TWSME) has been demonstrated in most Shape Memory Alloys, the effective application of this unique functional behaviour is hindered by the lack of a proper training methodology and understanding of its mechanisms. In this study, a novel training routine has been established together with a home-designed device, enabling TWSME of customised spline curvature to be produced. An in situ high energy synchrotron X-ray diffraction experiment has been performed on Nitinol, followed by comprehensive analysis to reveal the micromechanics of TWSME. Multiple mainstream hypotheses have been examined. The important findings are: (1) The training process has negligible influence on the texture of parent phase; (2) The preferred variant of the B19’ phase exhibits tension/compression asymmetry in TWSME; (3) (100) compound twin is the preferred deformation mode for compression TWSME; (4) The mesoscale residual strain field is the dominant factor that induces TWSME; (5) Lattice defects (dislocations) are spatially rearranged after training; (6) Compression TWSME training retards the B2 to B19’ transformation, whilst tension has the opposite effect. The implications of these findings are further discussed. 

Alexander M. Korsunsky

Papers

Direct TEM observation and quantification of the Gibbs-Thomson effect in a nickel superalloy

An In Vivo Rat Study of Bioresorbable Mg-2Zn-2Ga Alloy Implants

Residual Stresses in an Induction Hardened Gear Tooth Mapped by Synchrotron X-ray Diffraction

The creep deformation of a new nickel-base alloy-by-design studied using synchrotron X-ray diffraction

In situ synchrotron X-ray diffraction analysis of two-way shape memory effect in Nitinol