There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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

American Society for Testing and Materials

Direct alcohol fuel cells (DAFCs) are attracting increasing interest as power sources for portable applications due to some unquestionable advantages over analogous devices fed with hydrogen.1 Alcohols, such as methanol, ethanol, ethylene glycol, and glycerol, exhibit high volumetric energy density, and their storage and transport are much easier as compared to hydrogen. On the other hand, the oxidation kinetics of any alcohol are much slower and still H2-fueled polymer electrolyte fuel cells (PEMFCs) exhibit superior electrical performance as compared to DAFCs with comparable electroactive surface areas.2,3 Increasing research efforts are therefore being carried out to design and develop more efficient anode electrocatalysts for DAFCs.

Palladium-Based Electrocatalysts for Alcohol Oxidation in Half Cells and in Direct Alcohol Fuel Cells

http://chglib.icp.ac.ru/subjex/2012/pdf05/JPowSources-2010-195(11)3431.pdf

Alkaline direct alcohol fuel cells

Fuel cell system and method

Aligning carbon nanotubes, synthesized using the arc discharge technique, during and after synthesis

Crosslinked Polyvinyl alcohol (PVA) membranes with sulfonated CNT (SCNT) fillers were synthesized using solution casting method for proton exchange membrane fuel cells (PEMFC). Sulfonated CNTs are reported to be one of the best additives in ionic membranes as they increase the ionic conductivity and mechanical strength of the membrane. CNTs are high aspect ratio carbon allotropes, and small quantities of SCNTs (0.01 wt%, 0.1 wt%, 0.5 wt%, and 1 wt%) are observed to make a significant difference in properties of membranes. These membranes were characterized for water uptake capacity, ion exchange capacity, and mechanical strength. Ionic conductivity, hydrogen pumping, polarization studies, and gas crossover studies were performed in situ under various conditions of humidity. PVA–SSA–0.1 wt% SCNT showed the maximum power density among all compositions tested while short term performance of PVA–SSA–0.5 wt% SCNT exhibited the least sensitivity to changes in reactant humidity. Nafion® 115 produced 0.33 W cm−2 at 0.4 V while PVA–SSA–0.1 wt% SCNT exhibited 0.21 W cm−2 at 0.4 V. Overpotential associated with the purity of hydrogen gas was accounted for in the polarization curve and it resulted in a distinctly improved power density of 0.4 W cm−2. Performance of PVA–SSA–SCNT membranes was compared with Nafion® 115 by various characterization techniques and the results indicate that the membranes developed are a cost-effective alternative to Nafion® with the best performing PVA–SSA–SCNT membrane costing ≈1% of the cost of the Nafion® 115 membrane for similar performance.

Mechanically stable and economically viable polyvinyl alcohol-based membranes with sulfonated carbon nanotubes for proton exchange membrane fuel cells

In this work Carbon nanotubes have been synthesized by arc discharge in open air. A TIG welding ac/dc inverter was used as the power source for arc discharge. During each run of the arc discharge based synthesis, the anode was a low purity (approximately 85% C by weight) graphite rod. The effect of varying the atmosphere on the yield of soot of the carbon nanotube containing carbon soot has been studied. Various soots were produced, purified by oxidation and characterized to confirm formation of carbon nanotubes and their relative quality, using transmission electron microscopy, Raman spectroscopy, and XRD. It was found that the yield of soot formed on the cathode is higher when synthesis is carried out in open air than when carried out in a flowing argon atmosphere. When synthesized in open air, using a 7.2-mm-diameter graphite rod as anode, the yield of soot was around 50% by weight of the graphite consumed. Current and voltage for arcing were at identical starting values in all the experiments. This modified method does not require a controlled atmosphere as in the case of a conventional arc discharge method of synthesis and hence the cost of production may be reduced.

Synthesis of carbon nanotubes by arc discharge in open air.

Experimental procedures to establish in-plane and through plane polytetrafluroethylene (PTFE) gradient in Gas Diffusion Layer (GDL) used in proton exchange membrane fuel cells (PEMFC) are presented in this work. In-plane PTFE gradients were obtained by exploiting capillary wicking of PTFE suspension. The through plane PTFE gradients were obtained by changing the drying temperature employed in PTFE loading procedure. The samples were characterized for fluorine distribution using energy dispersive spectrum (EDS) to gauge the PTFE distribution and change in hydrophobicity after PTFE treatment. The results indicate that manipulation of PTFE gradients are expected to result in effective water management in PEMFC.

Prathap Haridoss

Papers

Fuel cell system and method

Aligning carbon nanotubes, synthesized using the arc discharge technique, during and after synthesis

Mechanically stable and economically viable polyvinyl alcohol-based membranes with sulfonated carbon nanotubes for proton exchange membrane fuel cells

Synthesis of carbon nanotubes by arc discharge in open air.

Gas diffusion layer with PTFE gradients for effective water management in PEM fuel cells