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

Recent advances in the stabilization of emulsions and foams by particles of nanoscale and microscopic dimensions are described. Ongoing research in this highly active field is providing insight into (i) the molecular factors controlling particle wettability and adsorption, (ii) the structural and mechanical properties of particle-laden liquid interfaces, and (ii) the stabilization mechanisms of particle-coated droplets and bubbles. There is much potential for exploiting the emerging knowledge in new food product applications. The preparation of cheap and effective colloidal particles based on food-grade ingredients, especially proteins, is the key technological challenge.

Food emulsions and foams: Stabilization by particles

Over the last two decades, our understanding of soot formation has evolved from an empirical, phenomenological description to an age of quantitative modeling for at least small fuel compounds. In this paper, we review the current state of knowledge of the fundamental sooting processes, including the chemistry of soot precursors, particle nucleation and mass/size growth. The discussion shows that though much progress has been made, critical gaps remain in many areas of our knowledge. We propose the roles of certain aromatic radicals resulting from localized π electron structures in particle nucleation and subsequent mass growth. The existence of these free radicals provides a rational explanation for the strong binding forces needed for forming initial clusters of polycyclic aromatic hydrocarbons. They may also explain a range of currently unexplained sooting phenomena, including the large amount of aliphatics observed in nascent soot formed in laminar premixed flames and the mass growth of soot in the absence of gas-phase H atoms. While the above suggestions are inspired, to an extent, by recent theoretical findings from the materials research community, this paper also demonstrates that the knowledge garnered through our longstanding interest in soot formation may well be carried over to flame synthesis of functional nanomaterials for clean and renewable energy applications. In particular, work on flame-synthesized thin films of nanocrystalline titania illustrates how our combustion knowledge might be useful for developing advanced yet inexpensive thin-film solar cells and chemical sensors for detecting gaseous air pollutants.

Formation of nascent soot and other condensed-phase materials in flames

Current research on room-temperature ionic liquids as lubricants is described. Ionic liquids possess excellent properties such as non-volatility, non-flammability, and thermo-oxidative stability. The potential use of ionic liquids as lubricants was first proposed in 2001 and approximately 70 articles pertaining to fundamental research on ionic liquids have been published through May 2009. A large majority of the cations examined in this area are derived from 1,3-dialkylimidazolium, with a higher alkyl group on the imidazolium cation being beneficial for good lubrication, while it reduces the thermo-oxidative stability. Hydrophobic anions provide both good lubricity and significant thermo-oxidative stability. The anions decompose through a tribochemical reaction to generate metal fluoride on the rubbed surface. Additive technology to improve lubricity is also explained. An introduction to tribology as an interdisciplinary field of lubrication is also provided.

Ionic liquids in tribology.

https://hal.archives-ouvertes.fr/hal-00288708/document

Detailed chemical kinetic models for the low-temperature combustion of hydrocarbons with application to gasoline and diesel fuel surrogates

Polycyclic aromatic hydrocarbons (PAH) are associated with health hazardous effects, and combustion processes are major sources of their presence in atmospheric aerosols. In the present work, chemical reaction pathways of PAH formation have been investigated by means of the modeling of a nearly sooting, low-pressure, premixed, laminar, one-dimensional benzene/oxygen/argon flame (equivalence ratio =1.8, 30% argon, gas velocity at burner at 298 K v =50 cm s −1 , pressure=2.67 kPa). This flame has been investigated by Bittner and Howard using molecular-beam sampling coupled to mass spectrometry. More recently, Benish extended the set of available data for radicals up to 201 amu and for stable species up to 276 amu using nozzle-beam sampling followed by radical scavenging with dimethyl disulfide and subsequent analysis by gas chromatography-mass spectrometry. An existing kinetic model has been refined. Density functional theory computations were used to update the thermodynamic database, while transition state theory followed by a bimolecular quantum Rice-Ramsperger-Kassel analysis allowed for the determination of kinetic data relevant for the present study. The reaction of phenylacetylene radicals with acetylene is shown to be limiting for the concentration of 1-naphthyl radicals, while naphthalene is formed mainly by self-combination of cyclopentadienyl. The insufficient consumption of PAH as well as acetylene beyond the reaction zone gives some evidence of the need of additional PAH growth pathways involving acetylene but thermodynamically more favorable than subsequent hydrogen-abstraction/acetyleneaddition reactions. A new pathway for acenaphthylene formation is suggested and consists of benzyne recombination followed by hydrogen attack and isomerization.

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Formation of polycyclic aromatic hydrocarbons and their radicals in a nearly sooting premixed benzene flame

A method of removing a downhole assembly comprises contacting, in the presence of an electrolyte, a first article comprising a first material and acting as an anode, and a second article comprising a second material having a lower reactivity than the first material and acting as a cathode, the downhole assembly comprising the first article in electrical contact with the second article, wherein at least a portion of the first article is corroded in the electrolyte.

Method of controlling corrosion rate in downhole article, and downhole article having controlled corrosion rate

A method of removing a corrodible downhole article having a surface coating includes eroding the surface coating by physical abrasion, chemical etching, or a combination of physical abrasion and chemical etching, the surface coating comprising a metallic layer of a metal resistant to corrosion by a corrosive material.

Corrodible downhole article and method of removing the article from downhole environment

We have used molecular dynamics simulations to investigate the in situ self-assembly of modified hydrocarbon nanoparticles (mean diameter of 1.2 nm) at a water-trichloroethylene (TCE) interface. The nanoparticles were first distributed randomly in the water phase. The MD simulation shows the in situ formation of nanoparticle clusters and the migration of both single particles and clusters from the water phase to the trichloroethylene phase, possibly due to the hydrophobic nature of the nanoparticles. Eventually, the single nanoparticles or clusters equilibrate at the water-TCE interface, and the surrounding liquid molecules pack randomly when in contact with the nanoparticle surfaces. In addition, the simulations show that the water-TCE interfacial thickness analyzed from density profiles is influenced by the presence of nanoparticles either near or in contact with the interface but is independent of the number of nanoparticles present. The nanoparticles, water molecules, and TCE molecules all exhibit diffusion anisotropy.

Molecular Dynamics Simulation of Nanoparticle Self-Assembly at a Liquid−Liquid Interface

A composite particle comprises a core, a shielding layer deposited on the core, and further comprising an interlayer region formed at an interface of the shielding layer and the core, the interlayer region having a reactivity less than that of the core, and the shielding layer having a reactivity less than that of the interlayer region, a metallic layer not identical to the shielding layer and deposited on the shielding layer, the metallic layer having a reactivity less than that of the core, and optionally, an adhesion metal layer deposited on the metallic layer.

Oleg A. Mazyar

Papers

Formation of polycyclic aromatic hydrocarbons and their radicals in a nearly sooting premixed benzene flame

Method of controlling corrosion rate in downhole article, and downhole article having controlled corrosion rate

Corrodible downhole article and method of removing the article from downhole environment

Molecular Dynamics Simulation of Nanoparticle Self-Assembly at a Liquid−Liquid Interface

Method of controlling the corrosion rate of alloy particles, alloy particle with controlled corrosion rate, and articles comprising the particle