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

Additive manufacturing of metallic components – Process, structure and properties

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The Theory of Industrial Organization

Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

Additive manufacturing (AM) is poised to bring about a revolution in the way products are designed, manufactured, and distributed to end users. This technology has gained significant academic as well as industry interest due to its ability to create complex geometries with customizable material properties. AM has also inspired the development of the maker movement by democratizing design and manufacturing. Due to the rapid proliferation of a wide variety of technologies associated with AM, there is a lack of a comprehensive set of design principles, manufacturing guidelines, and standardization of best practices. These challenges are compounded by the fact that advancements in multiple technologies (for example materials processing, topology optimization) generate a "positive feedback loop" effect in advancing AM. In order to advance research interest and investment in AM technologies, some fundamental questions and trends about the dependencies existing in these avenues need highlighting. The goal of our review paper is to organize this body of knowledge surrounding AM, and present current barriers, findings, and future trends significantly to the researchers. We also discuss fundamental attributes of AM processes, evolution of the AM industry, and the affordances enabled by the emergence of AM in a variety of areas such as geometry processing, material design, and education. We conclude our paper by pointing out future directions such as the "print-it-all" paradigm, that have the potential to re-imagine current research and spawn completely new avenues for exploration. The fundamental attributes and challenges/barriers of Additive Manufacturing (AM).The evolution of research on AM with a focus on engineering capabilities.The affordances enabled by AM such as geometry, material and tools design.The developments in industry, intellectual property, and education-related aspects.The important future trends of AM technologies.

The status, challenges, and future of additive manufacturing in engineering

Extended mechanics of structural genome for predicting mechanical properties of additively manufactured Ti6Al4V considering porosity and microstructure

In this paper, an adaptive fuzzy controller is developed for general multi-input single-output (MISO) nonlinear systems with time-varying characteristics and unknown system uncertainties. The system dynamics is modeled in fuzzy domain and the fuzzy inverse model is automatically constructed, which has the ability of uniquely determining the inverse relationship for each input-output pair. Based on this inverse model, a multi-level fuzzy controller (MLFC) is designed with embedded hierarchical structure for each control variable to compensate for system uncertainties and time-varying parameters. A set of simulation examples are presented to illustrate the effectiveness of the proposed controller for the multivariable systems under various operating conditions.

A multi-level fuzzy control design for general nonlinear multi-input single-output systems

A long-wavelength pyrometer is developed for the measurement of surface temperatures on materials that are semitransparent at lower wavelengths, and specific application is made to a dense zirconia ceramic (Mg-PSZ) undergoing laser-assisted machining (LAM). The pyrometer operates in a waveband between 11 and 14μm, and a detailed description of measurement uncertainties is provided. The largest uncertainties relate to knowledge of the surface emissivity and the large temperature gradients generated by the LAM process. Repeatability of the measurements is demonstrated, and a parametric study of three LAM parameters reveals expected trends, with good agreement between the measurements and predictions based on a model of the LAM process.© 2002 ASME

Surface Temperature Measurement of Semi-Transparent Ceramics by Long-Wavelength Pyrometry

As a follow up to Intelligent Engineering Systems through Artificial Neural Networks (ASME,1991), this volume contains the edited version of the technical presentations of ANNIE 92, held in November 1992. Attracting researchers from 13 countries, the conference covered the theory of artificial neura

Intelligent engineering systems through artificial neural networks : proceedings of the Artificial Neural Networks in Engineering (ANNIE '92) conference, held November 15-18, 1992, in St. Louis, Missouri, U.S.A.

On presente une procedure generale de modelisation pouvant etre utilisee pour l'identification des systemes asservis. On aboutit a un modele simplifie, en utilisant le modele ARMA vectoriel modifie dans l'identification du systeme multivariable general avec boucle ouverte et boucle fermee. On expose alors une procedure d'estimation, pour atteindre le modele de maximum vraisemblance par des calculsiteratifs non lineaires. Des valeurs initiales etant requises pour commencer la procedure, on fournit deux methodes pour l'estimation de valeurs initiales

Yung C. Shin

Papers

Extended mechanics of structural genome for predicting mechanical properties of additively manufactured Ti6Al4V considering porosity and microstructure

A multi-level fuzzy control design for general nonlinear multi-input single-output systems

Surface Temperature Measurement of Semi-Transparent Ceramics by Long-Wavelength Pyrometry

Intelligent engineering systems through artificial neural networks : proceedings of the Artificial Neural Networks in Engineering (ANNIE '92) conference, held November 15-18, 1992, in St. Louis, Missouri, U.S.A.

System identification of multivariate systems with feedback