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

[i] An inventory of air pollutant emissions in Asia in the year 2000 is developed to support atmospheric modeling and analysis of observations taken during the TRACE-P experiment funded by the National Aeronautics and Space Administration (NASA) and the ACE-Asia experiment funded by the National Science Foundation (NSF) and the National Oceanic and Atmospheric Administration (NOAA). Emissions are estimated for all major anthropogenic sources, including biomass burning, in 64 regions of Asia. We estimate total Asian emissions as follows: 34.3 Tg SO 2 , 26.8 Tg NO x , 9870 Tg CO 2 , 279 Tg CO, 107 Tg CH 4 , 52.2 Tg NMVOC, 2.54 Tg black carbon (BC), 10.4 Tg organic carbon (OC), and 27.5 Tg NH 3 . In addition, NMVOC are speciated into 19 subcategories according to functional groups and reactivity. Thus we are able to identify the major source regions and types for many of the significant gaseous and particle emissions that influence pollutant concentrations in the vicinity of the TRACE-P and ACE-Asia field measurements. Emissions in China dominate the signature of pollutant concentrations in this region, so special emphasis has been placed on the development of emission estimates for China. China's emissions are determined to be as follows: 20.4 Tg SO 2 , 11.4 Tg NO x , 3820 Tg CO 2 , 116 Tg CO, 38.4 Tg CH 4 , 17.4 Tg NMVOC, 1.05 Tg BC, 3.4 Tg OC, and 13.6 Tg NH 3 . Emissions are gridded at a variety of spatial resolutions from 1° × 1° to 30 s x 30 s, using the exact locations of large point sources and surrogate GIS distributions of urban and rural population, road networks, landcover, ship lanes, etc. The gridded emission estimates have been used as inputs to atmospheric simulation models and have proven to be generally robust in comparison with field observations, though there is reason to think that emissions of CO and possibly BC may be underestimated. Monthly emission estimates for China are developed for each species to aid TRACE-P and ACE-Asia data interpretation. During the observation period of March/ April, emissions are roughly at their average values (one twelfth of annual). Uncertainties in the emission estimates, measured as 95% confidence intervals, range from a low of ±16% for SO 2 to a high of ±450% for OC.

An inventory of gaseous and primary aerosol emissions in Asia in the year 2000 : NASA global tropospheric experiment transport and chemical evolution over the pacific (TRACE-P): Measurements and analysis (TRACEP1)

Adsorption of dyes and heavy metal ions by chitosan composites: A review

http://sealight.persiangig.com/document/1.pdf

Use of iron oxide nanomaterials in wastewater treatment: a review.

A review on the adsorption of heavy metals by clay minerals, with special focus on the past decade

Heterogeneous photo-Fenton catalysts generally show very weak photo-Fenton activity at near-neutral pH because of the relatively low rate of Fe 2+ regeneration. The aim of this work is to develop novel heterogeneous photo-Fenton catalysts, which can accelerate the regeneration of Fe 2+ and thus have superior photo-Fenton activity at near-neutral pH. In this study, ferrihydrite (Fh) was modified with BiVO 4 to synthesize BiVO 4 /Fh composites, and we expected that the photogenerated electrons from BiVO 4 would accelerate the regeneration of Fe 2+ on Fh. Mechanistic investigation of H 2 O 2 consumption showed that the introduction of BiVO 4 promoted the decomposition of H 2 O 2 into reactive oxygen species (ROS). In addition, the presence of BiVO 4 deterred O 2 − production and accelerated the formation of OH, according to the results of ROS formation, as shown with EPR spectroscopy and fluorescent probes tools. Furthermore, the Fe 2+ concentration on the surface of BiVO 4 /Fh was higher than that on Fh based on the results of XPS characterization and quantitative measurement with a 1,10-phenanthroline spectrophotometric method. These results demonstrated that the introduction of BiVO 4 can accelerate the reduction of Fe 3+ to Fe 2+ by transferring photogenerated electrons from BiVO 4 to Fe 3+ on the surface of Fh. Meanwhile, a higher decolorization efficiency of acid red 18 by BiVO 4 /Fh than by Fh and pure BiVO 4 verified that the introduction of BiVO 4 can significantly enhance the photo-Fenton catalytic activity of Fh even at near-neutral pH. Overall, our work has important implications for understanding the photo-Fenton mechanisms on semiconductor modified heterogeneous photo-Fenton catalysts and confirms that the introduction of a semiconductor can enhance the photo-Fenton catalytic activity of heterogeneous photo-Fenton catalysts in acidic and neutral pH.

Mechanisms for the enhanced photo-Fenton activity of ferrihydrite modified with BiVO4 at neutral pH

Characterization of organic phases in the interlayer of montmorillonite using FTIR and 13C NMR.

http://or.nsfc.gov.cn/bitstream/00001903-5/52945/1/1000003981729.pdf

Heterogeneous UV/Fenton degradation of TBBPA catalyzed by titanomagnetite: Catalyst characterization, performance and degradation products

The orientation of HDTMA+ in the interlayer of organic pillared montmorillonites prepared at different concentrations of HDTMA+ have been studied using X-ray powder diffraction (XRD) and theoretical calculation. A series of arrangement models of HDTMA+ in the interlayer of montmorillonite have been proposed as lateral-monolayer (LM), lateral-bilayer (LB), pseudotrilayer (PT), paraffin-type-monolayer (PM), paraffin-type-bilayer (PB). With the increase of the concentration of HDTMA+, the arrangement model of HDTMA+ in the interlayer of montmorillonites changes as lateral-monolayer→lateral-bilayer→paraffin-type monolayer→pseudotrilayer→paraffin-type-bilayer and the packing density of HDTMA+ in the interlayer increases gradually. In the intermediate stages, different models may coexist.

/pdf/arrangement-models-of-alkylammonium-cations-in-the-2xn644xe0t.pdf

Jianxi Zhu

Papers

Mechanisms for the enhanced photo-Fenton activity of ferrihydrite modified with BiVO4 at neutral pH

Characterization of organic phases in the interlayer of montmorillonite using FTIR and 13C NMR.

Heterogeneous UV/Fenton degradation of TBBPA catalyzed by titanomagnetite: Catalyst characterization, performance and degradation products

Arrangement models of alkylammonium cations in the interlayer of HDTMA+ pillared montmorillonites

Heterogeneous photo-Fenton degradation of bisphenol A over Ag/AgCl/ferrihydrite catalysts under visible light