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

Additive manufacturing of metallic components – Process, structure and properties

Biocomposites reinforced with natural fibers: 2000–2010

Water resistance properties of kenaf bast fiber bundle (KBFB)–reinforced composites with either unsaturated polyester (UPE) or vinyl ester (VE) matrices, developed in previous research, were studied. The effects of styrene content in UPE resin on the neat UPE resin tensile properties and molding pressure on composite flexural properties were evaluated. The effect of laser and plasma radiation on fiber-matrix interfacial shear strengths was studied. The composites exhibited high water uptake during short- and long-term water immersion. Encapsulation by surface coating and edge sealing improved composite water resistance. Statistical analyses indicated that molding pressures of 5 to 7 MPa were preferable to achieve the maximum composite mechanical properties, and 37.6 percent (wt/wt) styrene in the UPE resin gave the highest UPE matrix tensile properties in the studied range. Laser and plasma radiation of the KBFBs significantly improved fiber-matrix interfacial bonding.

Kenaf bast fiber bundle-reinforced unsaturated polyester composites. II: water resistance and composite mechanical properties improvement

Described are helmets that include a shell that has a first layer, a second layer, and a third layer. The second layer is positioned between the first layer and the third layer. The second layer is less dense than the first layer and the third layer.

Shock Wave Mitigating Helmets

The tensile, flexural, and impact strength distribution and the cost-effectiveness of kenaf bast fiber bundle (KBFB)- reinforced unsaturated polyester composites were studied. Probability models including normal, two-parameter Weibull, gamma, lognormal, exponential, Burr, Pareto, and inverse Gaussian models were fitted against measured composite strengths. Taking the 5th percentile values as the composite's strength design values, the two-parameter Weibull model provided the most conservative composite strength design values. A cost-effectiveness analysis showed these composites were more cost-effective than glass fiber-reinforced sheet molding compounds (SMCs) for carrying tensile and flexural loads when their fiber loadings reached 51.2 and 56.3 percent (wt/wt), respectively. The KBFB-reinforced unsaturated polyester composites were less cost-effective than glass fiber-reinforced SMCs for carrying impact loads. This work suggests that natural fiber-reinforced composites have the potential to be viable replacement materials in applications where impact resistance is not critical.

Kenaf Bast Fiber Bundle–Reinforced Unsaturated Polyester Composites. III: Statistical Strength Characteristics and Cost-Performance Analyses

Multiscale Modeling of the Damage Biomechanics of Traumatic Brain Injury

Structural and thermal properties of Ca are examined using a modified embedded-atom method (MEAM) interatomic potential. We developed an MEAM interatomic potential for calcium (Ca) using a first-principles method based on density functional theory (DFT). The material parameters, such as the cohesive energy, equilibrium atomic volume, and bulk modulus, are used to determine the MEAM potential parameters. The elastic constants and various point defect energies, such as monovacancy and interstitial defects, are also examined while developing the potential. Several structural properties of Ca, such as different surface formation energies, stacking fault energies, and thermal properties, such as coefficient of thermal expansion, specific heat and melting temperature, are investigated using the potential. We found that the present MEAM potential gives a good overall agreement with DFT calculations and experiments.

Mark F. Horstemeyer

Papers

Kenaf bast fiber bundle-reinforced unsaturated polyester composites. II: water resistance and composite mechanical properties improvement

Shock Wave Mitigating Helmets

Kenaf Bast Fiber Bundle–Reinforced Unsaturated Polyester Composites. III: Statistical Strength Characteristics and Cost-Performance Analyses

Multiscale Modeling of the Damage Biomechanics of Traumatic Brain Injury

Structural and thermal properties of calcium using an MEAM potential