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

Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Mechanical Alloying And Milling

The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

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Hallmarks of mechanochemistry: From nanoparticles to technology

https://hal.archives-ouvertes.fr/hal-01577861/document

A comparison of technologies for remediation of heavy metal contaminated soils

Phyllosilicates, and among them clay minerals, are of great interest not only for the scientific community but also for their potential applications in many novel and advanced areas. However, the correct application of these minerals requires a thorough knowledge of their crystal chemical properties. This chapter provides crystal chemical and structural details related to phyllosilicates and describes the fundamental features leading to their different behaviour in different natural or technical processes, as also detailed in other chapters of this book. Phyllosilicates, described in this chapter, are minerals of the (i) kaolin-serpentine group (e.g. kaolinite, dickite, nacrite, halloysite, hisingerite, lizardite, antigorite, chrysotile, amesite, carlosturanite, greenalite); (ii) talc and pyrophyllite group (e.g. pyrophyllite, ferripyrophyllite); (iii) mica group, with particular focus to illite; (iv) smectite group (e.g. montmorillonite, beidellite, nontronite, saponite, hectorite, sauconite); (v) vermiculite group; (vi) chlorite group; (vii) some 2:1 layer silicates involving a discontinuous octahedral sheet and a modulated tetrahedral sheet such as kalifersite, palygorskite and sepiolite; (viii) allophane and imogolite and (ix) mixed layer structures with particular focus on illite-smectite.

Structure and Mineralogy of Clay Minerals

Background: The aims of this study were to evaluate 1) the alterations of dentin permeability after single exposure of dentin to several acidic soft drinks with different acid composition; 2) the effectiveness of smear layer on dentin surface to prevent erosion of sound dentin; and 3) the role of brushing procedures. Methods: Dentin discs from human third molars were prepared. Each disc was treated with 0.5 M neutral EDTA for 5 minutes to remove the smear layer and to calculate the maximum fluid flow rate for each disc (to which an arbitrary value of 100% was assigned) using a pressure apparatus working at 1.0 psi. An homogeneous thin smear layer was then recreated with an abrasive paper under water. The following acidic drinks were applied for 5 minutes onto dentin surface: cola drink (phosphoric acid), orange fruit juice (ascorbic + citric acid), white wine (tartaric acid), vinegar (acetic acid), and mucolytic syrup (benzoic and tartaric acid). Each sample was then brushed for 3 minutes. Finally, each s...

Permeability and morphology of dentin after erosion induced by acidic drinks.

Table of contents. Preface. Participants photos. List of Contributors. List of Participants. The impact of electron microscopy on materials research G. Thomas. Microstructural design and tayloring of advanced materials G. Thomas. Nanostructured materials V. Provenzano. Characterization of heterophase transformation interfaces by highresolution transmission electron microscope techniques J.M. Howe. High resolution scanning electron microscopy observations of nanoceramics J.Th.M. de Hosson, et al. Metal-ceramic interfaces studied with high resolution transmission electron microscopy J.Th.M. de Hosson, et al. Z-contrast scanning transmission electron microscopy S.J. Pennycook, P.D. Nellist. Electron energy loss spectrometry in the electron microscope - Part 1: Introduction L.M. Brown. Electron energy loss spectrometry in the electron microscope - Part 2: EELS in the context of solid state spectroscopies L.M. Brown. Electron energy loss spectrometry in the electron microscope - Part 3: Interfaces and localised spectrometry L.M. Brown. EELS near edge structures. Application to intermetallic alloys and other materials G.A. Botton. Surface chemistry and microstructure analysis of novel technological materials M.L. Trudeau. Convergent beam electron diffraction C.J. Humphreys. New developments in scanning probe microscopy E. Meyer, et al. Low-energy scanning electron microscope for nanolithography A. Zlatkin, N. Garcia. Application of low voltage Scanning Electron Microscopy and energy dispersive x-ray spectroscopy D.G. Rickerby. Environmental SEM and related applications. History of the environmental SEM and basic design concepts T.A. Hardt. Environmental SEM and related applications T.A. Hardt. Environmental SEM andrelated applications. Gas interactions and gaseous amplification T.A. Hardt. ESEM image contrast and applications to wet organic materials A.M. Donald, B.L. Thiel. Advanced electron and scanning probe microscopy on dental and medical materials research G. Valdre. Correlative microscopy and probing in materials science G. Valdre. Epilogue. Subject index.

Impact of electron and scanning probe microscopy on materials research

Study of structural properties of ion treated and mechanically deformed commercial bentonite

Objectives This study aimed at evaluating the therapeutic bioactive effects on the bond strength of three experimental bonding agents containing modified Portland cement-based micro-fillers applied to acid-etched dentin and submitted to aging in simulated body fluid solution (SBS). Confocal laser (CLSM) and scanning electron microscopy (SEM) were also performed. Methods A type-I ordinary Portland cement was tailored using different compounds such as sodium–calcium–aluminum–magnesium silicate hydroxide (HOPC), aluminum–magnesium–carbonate hydroxide hydrates (HCPMM) and titanium oxide (HPCTO) to create three bioactive micro-fillers. A resin blend mainly constituted by Bis-GMA, PMDM and HEMA was used as control (RES-Ctr) or mixed with each micro-filler to create three experimental bonding agents: (i) Res-HOPC, (ii) Res-HCPMM and (iii) Res-HPCTO. The bonding agents were applied onto 37% H 3 PO 4 -etched dentin and light-cured for 30 s. After build-ups, they were prepared for micro-tensile bond strength (μTBS) and tested after 24 h or 6 months of SBS storage. SEM analysis was performed after de-bonding, while CLSM was used to evaluate the ultra-morphology/nanoleakage and the mineral deposition at the resin–dentin interface. Results High μTBS values were achieved in all groups after 24 h. Only Res-HOPC and Res-HCPMM showed stable μTBS after SBS storage (6 months). All the resin–dentin interfaces created using the bonding agents containing the bioactive micro-fillers tested in this study showed an evident reduction of nanoleakage and mineral deposition after SBS storage. Conclusion Resin bonding systems containing specifically tailored Portland cement micro-fillers may promote a therapeutic mineral deposition within the hybrid layer and increase the durability of the resin–dentin bond.

Experimental etch-and-rinse adhesives doped with bioactive calcium silicate-based micro-fillers to generate therapeutic resin–dentin interfaces

In this work, the vibrational spectra of hexagonal hydroxylapatite OHAp (space group P 6 3 ) and type A carbonated apatite [Ca 10 (PO 4 ) 6 (CO 3 ), space group P 1] have been calculated with an ab initio approach by the density function method using the hybrid B3LYP functional and an all-electron polarized double-ζ quality Gaussian-type basis set using the CRYSTAL09 computer program. The effect on the vibrational properties due to improving the Ca pseudopotential, usually adopted in previous studies on hydroxylapatite, toward the present all-electron basis set has also been briefly addressed. The anharmonic correction for hydroxyl groups in OHAp has also been considered. The results of the modeling are in good agreement with the available FTIR and Raman data presented in the literature and can be useful to experimental researchers to assign unequivocally the bands in infrared and Raman spectra to specific fundamental vibrational modes.

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Giovanni Valdrè

Papers

Permeability and morphology of dentin after erosion induced by acidic drinks.

Impact of electron and scanning probe microscopy on materials research

Study of structural properties of ion treated and mechanically deformed commercial bentonite

Experimental etch-and-rinse adhesives doped with bioactive calcium silicate-based micro-fillers to generate therapeutic resin–dentin interfaces

The vibrational features of hydroxylapatite and type A carbonated apatite: A first principle contribution