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

http://nathan.instras.com/ResearchProposalDB/doc-109.pdf

A review on polymer nanofibers by electrospinning and their applications in nanocomposites

https://cmapspublic3.ihmc.us/rid=1N3976C22-12M3P49-9V/Holladay%20et%20al.%20-%202009%20-%20An%20overview%20of%20hydrogen%20production%20technologies.pdf

An overview of hydrogen production technologies

Effective thermal conductivity of mixtures of e uids and nanometer-size particles is measured by a steady-state parallel-plate method. The tested e uids contain two types of nanoparticles, Al 2O3 and CuO, dispersed in water, vacuum pump e uid, engine oil, and ethylene glycol. Experimental results show that the thermal conductivities of nanoparticle ‐e uid mixtures are higher than those of the base e uids. Using theoretical models of effective thermal conductivity of a mixture, we have demonstrated that the predicted thermal conductivities of nanoparticle ‐e uid mixtures are much lower than our measured data, indicating the dee ciency in the existing models when used for nanoparticle ‐e uid mixtures. Possible mechanisms contributing to enhancement of the thermal conductivity of the mixtures are discussed. A more comprehensive theory is needed to fully explain the behavior of nanoparticle ‐e uid mixtures. Nomenclature cp = specie c heat k = thermal conductivity L = thickness Pe = Peclet number P q = input power to heater 1 r = radius of particle S = cross-sectional area T = temperature U = velocity of particles relative to that of base e uids ® = ratio of thermal conductivity of particle to that of base liquid ¯ = .® i 1/=.® i 2/ ° = shear rate of e ow Ω = density A = volume fraction of particles in e uids Subscripts

/pdf/thermal-conductivity-of-nanoparticle-fluid-mixture-54tj4jnmls.pdf

Thermal Conductivity of Nanoparticle -Fluid Mixture

Recent advances in friction-stir welding : Process, weldment structure and properties

In this paper the effects of chemical and electrical driving forces on the evolution of interfacial reaction layers in lead-free solder interconnections are discussed. Firstly, the effects of alloying and impurity elements on the driving forces for diffusion in the Cu-Sn system are analyzed. These results are then used to predict the subsequent changes in the intrinsic fluxes of the elements. It is shown that by utilizing simple thermodynamic reasoning together with kinetic considerations the effect of additional elements on the growth behavior of interfacial reaction layers can be readily understood or even predicted - if enough data is available. Secondly, the effect of electric current on the microstructural evolution of the interfacial reaction layers in the Cu-Sn system is considered. Especially, the differences in the growth behavior of intermetallic compound (IMC) layers at the cathode and anode sides of the interconnections are rationalized. This is done by considering the changes in the intrinsic fluxes of elements owing to electromigration as well as taking into account the fact that the growth of Cu3Sn and Cu6Sn5 are coupled via interfacial reactions. When comparing the results from the calculations to those obtained from the experiements, quantitative diffusion kinetic data from the Cu-Sn system is utilized. In this way, better understanding of the effect of electron flux on the growth of each individual layer in the Cu-Sn system can be achieved. Thirdly, the combined effect of the chemical and electrical driving forces is briefly discussed. Finally, it is emphasized that the method used in this paper is a very generic one and can therefore be utilized in a wide variety of different applications.

Understanding the effect of electromigration on the growth of interfacial reaction layers in Cu-Sn and Cu-Ni-Sn systems

Thermodynamics and diffusion kinetics determine the microstructure of a given reaction couple between dissimilar materials under specific conditions. The microstructure, in turn, affects strongly the performance of multimaterial assemblies under different stress and environmental states. Hence it is shown here how the combination of thermodynamics and kinetics (namely the thermodynamic-kinetic method) can be used to rationalize the evolution of microstructure between dissimilar materials. The relevant thermodynamic considerations are given first, before moving to the foundations of diffusion kinetic considerations most relevant for the thermodynamic-kinetic method. The method itself is then briefly discussed, before finalizing this chapter with a couple of case studies from the field of electronics.

Thermodynamic-Kinetic Method on Microstructural Evolutions in Electronics

Interfacial Reactions in Thin Film Systems

Nb3Sn growth following the bronze technique, (i.e. by interdiffusion between Cu(Sn) alloy (bronze) and Nb) is one of the important methodologies to produce this superconductor. In this study, we have addressed the confusion over the growth rate of the Nb3Sn phase. Furthermore, a possible explanation for the corrugated layer in the multifilamentary structure is discussed. Kirkendall marker experiments were conducted to study the relative mobilities of the species, which also explained the reason for finding pores in the product phase layer. Based on the parabolic growth constant at different temperatures, the activation energy for the growth is determined. We have further explained the dramatic increase in the growth rate of the product phase by changing just one atomic percentage of Sn in the Cu-Sn bronze alloy.

Study on the Growth of Nb3Sn Superconductor in Cu(Sn)/Nb Diffusion Couple

In this chapter, the feasibility of the thermodynamic-kinetic method and the associated science of microstructures are demonstrated by going through a large amount of examples concerning interfacial compatibility problems from the various fields of microtechnologies. The chapter is divided to sections based on the types of material interfaces considered. Thus, first metal–metal, then metal–ceramic and finally metal–polymer examples are discussed. It will become evident that only by using all the theoretical tools introduced earlier in this book (i.e.): (i) thermodynamics of materials (ii) reaction kinetics (iii) theory of microstructures and (iv) stress and strain analysis, it is possible to obtain fundamental understanding of the interfacial problems at hand.

Tomi Laurila

Papers

Understanding the effect of electromigration on the growth of interfacial reaction layers in Cu-Sn and Cu-Ni-Sn systems

Thermodynamic-Kinetic Method on Microstructural Evolutions in Electronics

Interfacial Reactions in Thin Film Systems

Study on the Growth of Nb3Sn Superconductor in Cu(Sn)/Nb Diffusion Couple

Evolution of Different Types of Interfacial Structures