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

Superhydrophobic contoured surfaces created on metal and polymer using a femtosecond laser

High-nitrogen, nickel-free stainless steels have much higher yield strength than typical stainless steels, and their high corrosion resistance and high strength makes them especially attrac...

Laser-assisted machining of an austenitic stainless steel: P550:

Brief paper: Adaptive divided difference filtering for simultaneous state and parameter estimation

Nitinol is well known for its unique shape-memory and super-elastic properties along with its excellent biomechanical compatibility and corrosion resistance. In this study, a laser direct deposition technique was explored to synthesize high-quality, near-net-shape nitinol components directly from elemental nickel and titanium powders as opposed to using expensive prealloyed nitinol powder. The systematic characterization of samples was done using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Transformation temperatures were obtained using differential scanning calorimetry (DSC). With an optimum ratio of nickel and titanium powder mixture, optimal laser parameters, and post-heat treatment, samples with homogeneous and nearly fully dense NiTi phase were synthesized with less unwanted secondary phases occupying less than 3.2 pct volume fraction. Furthermore, these results were compared with those obtained for samples deposited using prealloyed nitinol powder. This technique offers maximum flexibility and cost benefit in the manufacturability of near-net-shape nitinol components.

In Situ Synthesis and Characterization of Shape Memory Alloy Nitinol by Laser Direct Deposition

Tool-chip interface temperature is analyzed experimentally during turning of 4140 steel alloy and Inconel 718 with tungsten carbide tools using a tool-work thermocouple technique. The experimental results are compared with Loewen and Shaw’s analytical results. Based on the experimental results, an empirical model relating the tool face temperature to cutting conditions is established for 4140 steel alloys with tungsten carbide tools. Finally, the tool-chip interface is investigated with flank and crater wear to determine the effect of tool face temperature on these tool wear mechanisms.

Yung C. Shin

Papers

Superhydrophobic contoured surfaces created on metal and polymer using a femtosecond laser

Laser-assisted machining of an austenitic stainless steel: P550:

Brief paper: Adaptive divided difference filtering for simultaneous state and parameter estimation

In Situ Synthesis and Characterization of Shape Memory Alloy Nitinol by Laser Direct Deposition

Investigation on Cutting Temperature in Turning by a Tool-Work Thermocouple Technique