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

THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

Department of Materials Science, University of Patras, 26504 Rio Patras, Greece, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vass. Constantinou Avenue, 116 35 Athens, Greece, Institut de Biologie Moleculaire et Cellulaire, UPR9021 CNRS, Immunologie et Chimie Therapeutiques, 67084 Strasbourg, France, and Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste, Italy

Chemistry of Carbon Nanotubes

Carbon nanotube–polymer composites: Chemistry, processing, mechanical and electrical properties

The Rising Importance of Precision Engineering

A deep understanding of adiabatic shear fracture (ASF) during serrated chip formation is essential to explore the material removal mechanism of high speed cutting (HSC). This paper aims to reveal the microscopic details of ASF in serrated chips. The material to investigate was AISI 1045 steel of different hardness grades, and the micro-structural analysis was conducted using optical and scanning electronic microscopes. The investigation showed that at the hardness of HRC50, most fractured surfaces were covered by a large number of dimples elongated along the shear direction, indicating that the fundamental cause of the serrated chip generation is the deformation localization of the adiabatic shear followed by ductile damage fracture in primary shear zones. The higher the material hardness is, the easier the adiabatic shear and ductile fracture take place. A new model was then proposed to interpret the ductile fracture due to adiabatic shear governed by the nucleation, growth and coalescence of micro-voids during serrated chip formation.

Ductile Fracture due to Adiabatic Shear during the Serrated Chip Formation in High Speed Cutting: a Microscopic Investigation

Three intersection mechanisms with the gliding planes (111)TB, (001)TB and (115)TB respectively have been observed by high-resolution electron microscopy in the type-I twin intersection of gamma-TiAl. It was found that the intersection mechanism that occurred was related to the thickness of the incident twin. The accommodation mechanism on the (111)TB atomic plane is preferred when the incident twin becomes very thin. The dislocation dissociations of the (111)TB plane accommodation are the most energetically unfavourable of the dissociations of the three intersection mechanisms; however, the resultant dislocations on the (111)TB planes are the easiest to propagate away from the intersection area. Accordingly, (111)TB atomic plane accommodation is considered to be the only mechanism allowing shear transmission under the small local stress of the pile-up of the incident twinning partials.

Possibility of (111)TB accommodation mechanism for type-I twin intersection in γ-TiAl during roomtemperature deformation

This paper investigates the effect of the grinding-induced cyclic heating on the hardened layer properties generated in plunge cylindrical grinding. It was found that by increasing the number of grinding cycles, the hardened layer becomes thicker. The cyclic grinding stressing together with the heating initiates a plastic deformation zone of a highly oriented microstructure. The surface residual stresses of the layer are compressive. Under a lower infeed rate, the tempering of the hardened layer material will occur more severely.

Effect of Cyclic Heating on the Hardened Layer Properties Generated by Plunge Cylindrical Grinding

Surface/subsurface deformation and phase transformations in the nano-machining of silicon are hard to avoid. With the aid of molecular dynamics analysis, this work reports the nanoscratching deformation behaviour of three typical single crystal silicon surfaces with the crystallographic orientations of {001}, {110} and {111} along various crystallographic directions. Amorphous silicon is always observed on the scratched surface irrespective of the crystal orientation and scratching direction but to various depths. It was found that only the scratching on {001} surface along the direction ({001}/ ) at a depth-of-cut greater than 1 nm introduces frequent dislocations in the sub-surface through nano-twinning. Scratching on {001}/ and {110}/ generate five coordinated body-centered tetragonal (bct-5) silicon beneath the amorphous silicon, along the path traversed by the diamond tip. Scratching on {110}/ , {111}/ and {111}/ produces only amorphous silicon. These demonstrate that very different microstructures can take place when nanoscratching in different direction due to the anisotropy of silicon, and that such anisotropy effect can lead to non-uniform surface topographies when polishing polycrystalline silicon with abrasives.

Liangchi Zhang

Papers

The Rising Importance of Precision Engineering

Ductile Fracture due to Adiabatic Shear during the Serrated Chip Formation in High Speed Cutting: a Microscopic Investigation

Possibility of (111)TB accommodation mechanism for type-I twin intersection in γ-TiAl during roomtemperature deformation

Effect of Cyclic Heating on the Hardened Layer Properties Generated by Plunge Cylindrical Grinding

Anisotropy effect in the nanoscratching of silicon