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

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Elements Of Chemical Reaction Engineering

In this paper, NiRu, NiRh, and NiPd catalysts were synthesized and evaluated in the hydrogenolysis of lignin C–O bonds, which is proved to be superior over single-component catalysts. The optimized NiRu catalyst contains 85% Ni and 15% Ru, composed of Ni surface-enriched, Ru–Ni atomically mixed, ultrasmall nanoparticles. The Ni85Ru15 catalyst showed high activity under low temperature (100 °C), low H2 pressure (1 bar) in β-O-4 type C–O bond hydrogenolysis. It also exhibited significantly higher activity over Ni and Ru catalysts in the direct conversion of lignin into monomeric aromatic chemicals. Mechanistic investigation indicates that the synergistic effect of NiRu can be attributed to three factors: (1) increased fraction of surface atoms (compared with Ni), (2) enhanced H2 and substrate activation (compared with Ni), and (3) inhibited benzene ring hydrogenation (compared with Ru). Similarly, NiRh and NiPd catalysts were more active and selective than their single-component counterparts in the hydrogen...

A series of NiM (M = Ru, Rh, and Pd) bimetallic catalysts for effective lignin hydrogenolysis in water

Topics in current chemistry

Copper, a native metal found in ores, is the principal metal in bronze and brass. It is a reddish metal with a density of 8920 kg m−3. All of copper’s compounds tend to be brightly colored: for example, copper in hemocyanin imparts a blue color to blood of mollusks and crustaceans. Copper has three oxidation states, with electronic configurations of Cu([Ar]3 d 104 s 1), Cu+([Ar]3 d 10), and Cu2+([Ar]3 d 9). Cu does not react with aqueous hydrochloric or sulfuric acids, but is soluble in concentrated nitric acid due to its lesser tendency to be oxidized. Cu(I) exists as the colorless cuprous ion, Cu+. Cu(II) is found as the sky-blue cupric ion, Cu2+. The Cu+ ion is unstable, and tends to disproportionate to Cu and Cu2+. Nevertheless, Cu(I) forms compounds such as Cu2O. Cu(I) bonds more readily to carbon than Cu(II), hence Cu(I) has an extensive chemistry with organic compounds.

In aqueous solutions, Cu2+ ion occurs as an aquacomplex. There is no clearly predominant structure among the four-, five-, and six-fold coordinated Cu(II) species (Chaboy et al. 2006). Hydrated Cu(II) ion has been represented as the hexaaqua complex Cu(H2O)62+, which shows the Jahn–Teller distortion effect (Sherman 2001; Bersuker 2006), whereby the two Cu–O distances of the vertical axial bond (Cu–Oax) are longer than four Cu–O distances in the equatorial plane (Cu–Oeq). The Jahn–Teller effect lowers the symmetry of Cu(H2O)62+ from octahedral Th to D2h. The sixfold coordination of hydrated Cu(II) species is questioned by a finding of fivefold coordination (Pasquarello et al. 2001; Chaboy et al. 2006; Little et al. 2014b …

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The Isotope Geochemistry of Zinc and Copper

Liquid–liquid extraction in microchannels with Zinc–D2EHPA system

Novel amidoamine functionalized multi-walled carbon nanotubes for removal of mercury(II) ions from wastewater: Combined experimental and density functional theoretical approach

The objective of the study is to compare the performance of microchannels and conventional stage-wise extractors for liquid–liquid extraction by using a standard phase system. Three different microchannels – a T-junction microchannel, a serpentine microchannel and a split-and-recombine microchannel – have been used in the experiments. Conventional extractors are represented by a mixer-settler and an annular centrifugal extractor. The phase system used in the experiments is water (succinic acid) n-butanol system which is one of the standard phase systems recommended by the European Federation of Chemical Engineering. The extractors have been compared on the basis of percentage extraction, overall volumetric mass transfer coefficient and specific extraction rate. When compared on the basis of percentage extraction, performance of the microchannels and the conventional stage-wise extractors is found to be almost similar. Maximum values of overall volumetric mass transfer coefficient and specific extraction rates are found to be more in the microchannels than in the conventional stage-wise extractors. The ratio of maximum overall volumetric mass transfer coefficient in microchannels and conventional stage-wise extractors is found to range from 1 to 8.1. The ratio of maximum specific extraction rate in microchannels and conventional stage-wise extractors is found to range between 2.3 and 9.7.

Liquid–liquid extraction in microchannels and conventional stage-wise extractors: A comparative study

Representative drop sizes and drop size distributions in A/O dispersions in continuous flow stirred tank

A B S T R A C T Computational fluid dynamics (CFD) simulations are carried out to evaluate mixing in different types of 1–1 and 1–2 microfluidic junctions. Computational approach adopted in the study is validated by comparing its predictions with theoretical and experimental results. Asymmetric microfluidic junctions are found to show better mixing than symmetric microfluidic junctions. Among asymmetric microfluidic junctions, mixing is found to improve with increasing skewness of the junction. A new 1–1 microfluidic junction named as OA 10 0 –20 0 W-junction is found to give the best mixing among all 1–1 microfluidic junctions evaluated in this study. Based on this new 1–1 microfluidic junction, several 1–2 microfluidic junctions are conceptualized. Among these 1–2 microfluidic junctions a junction named as 10 0 –20 0 –165 0 WY-junction is found to give the best mixing. Different approaches to improve microfluidic mixing viz simple-junction–complex-layout, complex-junction–simple-layout and complex-junction–complex-layout, are compared.

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K.T. Shenoy

Papers

Liquid–liquid extraction in microchannels with Zinc–D2EHPA system

Novel amidoamine functionalized multi-walled carbon nanotubes for removal of mercury(II) ions from wastewater: Combined experimental and density functional theoretical approach

Liquid–liquid extraction in microchannels and conventional stage-wise extractors: A comparative study

Representative drop sizes and drop size distributions in A/O dispersions in continuous flow stirred tank

Numerical simulation of mixing at 1-1 and 1-2 microfluidic junctions