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

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

American Society for Testing and Materials

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

Macroporous ceramics with pore sizes from 400 nm to 4 mm and porosity within the range 20%–97% have been produced for a number of well-established and emerging applications, such as molten metal filtration, catalysis, refractory insulation, and hot gas filtration. These applications take advantage of the unique properties achieved through the incorporation of macropores into solid ceramics. In this article, we review the main processing routes that can be used for the fabrication of macroporous ceramics with tailored microstructure and chemical composition. Emphasis is given to versatile and simple approaches that allow one to control the microstructural features that ultimately determine the properties of the macroporous material. Replica, sacrificial template, and direct foaming techniques are described and compared in terms of microstructures and mechanical properties that can be achieved. Finally, directions to future investigations on the processing of macroporous ceramics are proposed.

/pdf/processing-routes-to-macroporous-ceramics-a-review-1urld578zq.pdf

Processing Routes to Macroporous Ceramics: A Review

Dense YSZ Laminates Obtained by Aqueous Tape Casting and Calendering

Forming of thin porcelain tiles: A comparison between tape casting and dry pressing

Chemical tempering of porcelain tiles

This work reports the synthesis of Ni(OH)2 aerogels incorporated in situ with polypyrrole (PPy) for application as electrodes in high-capacity energy storage devices. Ni(OH)2 gels were prepared by the sol–gel method from NiCl2 as precursor and propylene oxide as gelling agent in ethanol. Pyrrole monomer was added prior to gelling of the sol and in situ polymerized using ammonium persulfate as oxidant agent. After solvent exchanges from ethanol to acetone, the gels were dried in a CO2 supercritical point drier. Powdered aerogels were deposited onto both sides of a poly(vinyl alcohol)/H3PO4 film (electrolyte/separator) and the contacts were closed with copper foils, resulting in a complete device. Through cyclic voltammetry and charge/discharge curves, the performance of the supercapacitors was evaluated by the specific capacitance, power and energy densities and series resistance. The specific capacitance was increased by 43% with the incorporation of 0.2 mol/L PPy (276 F/g) and the series resistance obtained decreased by 79% (46.5 Ω/cm2), which reflects the enhanced performance and electrochemical properties of Ni(OH)2 aerogel- based devices incorporated with PPy.

/pdf/ni-oh-2-aerogels-incorporated-with-polypyrrole-as-electrodes-uk4oh2hcrv.pdf

Ni(OH)2 Aerogels Incorporated with Polypyrrole as Electrodes for Supercapacitors

Ceramic matrix composites (CMCs) were developed to overcome the intrinsic brittleness and lack of reliability of monolithic ceramics. Their major advantages include high temperature capability, light weight, corrosion resistance and adequate damage tolerance. All-oxide Ceramic Matrix Composites (OCMCs) offer essential advantages with respect to long time stability in oxidizing atmospheres, when compared to their non-oxide counterparts. Nevertheless, there is at present almost no production concept which meets the requirements in view of cost and performance for these materials. This work aims at producing OCMCs by means of a more flexible production route. This is achieved by integrating well-known powder metallurgy routes with the prepreg technique, used at present for producing commercial high performance polymer matrix composites. The processing consists of the following steps: (a) infiltration of commercial alumina fiber fabrics (3M NextelTM 610) with a liquid suspension of the matrix material; (b) lamination of the pre-infiltrated fiber textiles with a paraffin-based suspension for the formation of prepregs; (c) layup of prepregs; (d) warm-pressing for the consolidation of the green body; (e) debinding and (f) reaction bonding and/or sintering for synthesis of the oxide matrix. Pure alumina or Reaction Bonded Aluminum Oxide (RBAO) can be used as matrix materials and damage tolerance is achieved by the porous, weak-matrix approach. Microstructural analysis of a pure alumina composite fabricated by this route show good infiltration of fiber bundles and proves the good adhesion of prepregs during processing. Average strength value of 199 MPa in fiber direction is in good agreement with values presented in the literature for OCMCs produced by other techniques.

Dachamir Hotza

Papers

Dense YSZ Laminates Obtained by Aqueous Tape Casting and Calendering

Forming of thin porcelain tiles: A comparison between tape casting and dry pressing

Chemical tempering of porcelain tiles

Ni(OH)2 Aerogels Incorporated with Polypyrrole as Electrodes for Supercapacitors

Production of Oxide Ceramic Matrix Composites by a Prepreg Technique