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

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

This paper presents control and coordination algorithms for groups of vehicles. The focus is on autonomous vehicle networks performing distributed sensing tasks where each vehicle plays the role of a mobile tunable sensor. The paper proposes gradient descent algorithms for a class of utility functions which encode optimal coverage and sensing policies. The resulting closed-loop behavior is adaptive, distributed, asynchronous, and verifiably correct.

Coverage control for mobile sensing networks

Loosening of implants in bone is commonly associated with a development of fibrous interface tissues, due to interface gaps and a lack of mechanical stability. It has been postulated that the differentiation of these tissues to fibrocartilage or bone is governed by mechanical stimuli. The objective of our research is to unravel these relationships to the extent that the question whether an implant will loosen can be answered from initial conditions determined by implant and interface morphology, and functional loads. In this project we studied the hypothesis that distortional strain and interstitial fluid flow are the mechanical stimuli governing tissue differentiation. For that purpose, a biomechanical regulatory model was developed and used in association with a finite element code to simulate animal experiments with implants moving in bone. The similarities between the implant incorporation process found in the experiment and its simulation with the computer model demonstrate that our hypothesis is viable from a regulatory point of view.

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A biomechanical regulatory model for periprosthetic fibrous-tissue differentiation.

Microelectronics technology Introduction A heart of silicon In a little black box Baseline CMOS Non-CMOS options Packaging Systems Conclusions References Nomenclature Reliability practices Introduction Reliability assessment Reliability statistics Acceleration factor models Failure mechanisms Conclusions References Exercises Thermal Management Introduction Heat transfer basics Thermal design of assemblies Thermal design for a SQFP Heatsink design choices Conclusions / final remarks References Introduction to Advanced Mechanics Introduction Stress and strain Failure criteria Fracture mechanics Finite element method References Exercises Thermo-Mechanics of Integrated Circuits and Packages Introduction IC Backend and packaging processes and testing Thermo-mechanics of IC backend processes Thermo-Mechanics of packaging processes Thermo-Mechanics of coupled IC backend and packaging processes Case studies References Exercises Characterization and Modeling of Moisture Behavior Introduction Moisture diffusion modeling Characterization of moisture diffusivity and saturation concentration Vapor pressure modeling Hygroscopic swelling characterization & modeling Single void Instability behavior Subjected to vapor pressure and thermal stress Interface strength characterization and modeling Case studies References Exercises Characterization and Modeling of Solder Joint Reliability Introduction Analytical-empirical prognosis of the reliability Thermo-mechanical characteristics of soft solders Data evaluation and LIFE-time estimation Case studies References Exercises Virtual thermo-mechanical prototyping Introduction The state-of-the-art of virtual prototyping Case studies Conclusions References Exercises Challenges and future perspectives Introduction Product and process inputs Tests and experiments Multi-scale mechanics Advanced simulation tools Multi-physics modeling Material and interface behavior Simulation-based optimization Conclusions

Mechanics of Microelectronics

This paper first examines the commonly-used thermal-moisture analogy approach in thermal-moisture analogy approach. We conclude that such an analogy using a normalized concentration approach does not exist in the case of soldering reflow, when the solubility of each diffusing material varies with temperature or the saturated moisture concentration is not a constant over an entire range of reflow temperatures. The whole field vapor pressure distribution of a flip chip BGA package at reflow is obtained based on a multiscale vapor pressure model. Results reveal that moisture diffusion and vapor pressure have different distributions and are not proportional. The vapor pressure in the package saturates much faster than the moisture diffusion during reflow. This implies that the vapor pressure reaches the saturated pressure level in an early stage of moisture absorption, even the package is far from moisture saturated. However, the interfacial adhesion degrades continuously with moisture absorption. Therefore, the package moisture sensitivity performance will largely reply on the adhesion strength at elevated temperature with moisture. A specially designed experiment with a selection of six different underfills for flip chip packages was conducted. Results confirm that there is no correlation between moisture absorption and the subsequent interface delamination at reflow. The adhesion at high temperature with moisture is the only key modulator that correlates well with test data. Such a parameter is a comprehensive indicator, which includes the effects of thermal mismatch, vapor pressure, temperature and moisture. In this paper, a micromechanics based mechanism analysis on interfacial delamination is also presented. With the implementation of interface properties into the model study, it shows that the critical stress, which results in the unstable void growth and delamination at interface, is significantly reduced when the effect of moisture on debonding is considered.

Interfacial Delamination Mechanisms During Soldering Reflow With Moisture Preconditioning

The extent to which three finite element codes can solve problems in biphasic poroelasticity is examined. Both linear and non-linear (that is where the permeability of the material is a function of deformation) formulations are studied using the standard confined compression problem as an example. The results are compared, where possible, to the results of Spilker, Suh and Mow (1) who first presented a solution to this problem for cartilage. The agreement is excellent for the linear case. For the non-linear case, the solutions do differ slightly; however, the difference would not appear to be significant.

A Comparison of Finite Element Codes for the Solution of Biphasic Poroelastic Problems

The process of tooth displacement in response to orthodontic forces is thought to be induced by the stresses and strains in the periodontium. The mechanical force on the tooth is transmitted to the alveolar bone through a layer of soft connective tissue, the periodontal ligament. Stress and/or strain distribution in this layer must be derived from mathematical models, such as the finite element method, because it cannot be measured directly in a non-destructive way. The material behaviour of the constituent tissues is required as an input for such a model. The purpose of this study was to determine the time-dependent mechanical behaviour of the periodontal ligament due to orthodontic loading of a tooth. Therefore, in vivo experiments were performed on beagle dogs. The experimental configuration was simulated in a finite element model to estimate the poroelastic material properties for the periodontal ligament. The experiments showed a two-step response: an instantaneous displacement of 14.10 +/- 3.21 microns within 4 s and a more gradual (creep) displacement reaching a maximum of 60.00 +/- 9.92 microns after 5 h. This response fitted excellently in the finite element model when 21 per cent of the ligament volume was assigned a permeability of 1.0 x 10(-14) m4/N s, the remaining 97 per cent was assigned a permeability of 2.5 x 10(-17) m4/N s. A tissue elastic modulus of 0.015 +/- 0.001 MPa was estimated. Our results indicate that fluid compartments within the periodontal ligament play an important role in the transmission and damping of forces acting on teeth.

W.D. van Driel

Papers

A biomechanical regulatory model for periprosthetic fibrous-tissue differentiation.

Mechanics of Microelectronics

Interfacial Delamination Mechanisms During Soldering Reflow With Moisture Preconditioning

A Comparison of Finite Element Codes for the Solution of Biphasic Poroelastic Problems

Time-dependent mechanical behaviour of the periodontal ligament.