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

J. Appl. Cryst.の発刊に際して

The fascinating story of olefin (or alkene) metathesis (eq
1) began almost five decades ago, when Anderson and
Merckling reported the first carbon-carbon double-bond
rearrangement reaction in the titanium-catalyzed polymerization of norbornene. Nine years later, Banks and Bailey reported “a new disproportionation reaction . . . in which olefins are converted to homologues of shorter and longer carbon chains...”. In 1967, Calderon and co-workers named this metal-catalyzed redistribution of carbon-carbon double bonds olefin metathesis, from the Greek word “μeτάθeση”, which means change of position. These contributions have since served as the foundation for an amazing research field, and olefin metathesis currently represents a powerful transformation in chemical synthesis, attracting a vast amount of interest both in industry and academia.

https://core.ac.uk/download/pdf/4884240.pdf

Ruthenium-based heterocyclic carbene-coordinated olefin metathesis catalysts.

Advances in electrocatalysis at solid-liquid interfaces are vital for driving the technological innovations that are needed to deliver reliable, affordable and environmentally friendly energy. Here, we highlight the key achievements in the development of new materials for efficient hydrogen and oxygen production in electrolysers and, in reverse, their use in fuel cells. A key issue addressed here is the degree to which the fundamental understanding of the synergy between covalent and non-covalent interactions can form the basis for any predictive ability in tailor-making real-world catalysts. Common descriptors such as the substrate-hydroxide binding energy and the interactions in the double layer between hydroxide-oxides and H---OH are found to control individual parts of the hydrogen and oxygen electrochemistry that govern the efficiency of water-based energy conversion and storage systems. Links between aqueous- and organic-based environments are also established, encouraging the 'fuel cell' and 'battery' communities to move forward together.

Energy and fuels from electrochemical interfaces

N-Heterocyclic carbene (NHC) ligands, introduced as analogues to phosphines, are recently getting wide attention in the design of diverse homogeneous catalytic systems.1-6 During recent years, olefin metathesis has gained a position of increasing significance.7-9 The ruthenium complex (PCy3)2(Cl2)RudCHPh 1 (Cy ) cyclohexyl) developed by Grubbs et al.10 constitutes a highly efficient metathesis catalyst11 tolerating most functional groups. In spite of the generally superb application profile of 1, its limited stability and the low activity toward substituted double bonds are major drawbacks. The initial success of olefin metathesis has spurred the intense investigation of new catalysts for this transformation. Inter alia, the recent introduction of NHCs * To whom correspondence should be addressed. E-mail: klgrela@ gmail.com. † Polish Academy of Sciences. ‡ Warsaw University. Cezary Samojłowicz was born in 1983 in Sokołów Podlaski, Poland. He obtained his MSc Eng. degree in chemical technology from the Warsaw University of Technology, studying sigmatropic rearrangements of sulfur ylides under the supervision of Tadeusz Zdrojewski. Before moving to olefin metathesis, he conducted work on supramolecular chemistry with David Reinhoudt at Twente University. Since 2007, he is conducting his PhD study under the supervision of Karol Grela.

Ruthenium-based olefin metathesis catalysts bearing N-heterocyclic carbene ligands.

Self-healing is a natural process common to all living organisms which provides increased longevity and the ability to adapt to changes in the environment. Inspired by this fitness-enhancing functionality, which was tuned by billions of years of evolution, scientists and engineers have been incorporating self-healing capabilities into synthetic materials. By mimicking mechanically triggered chemistry as well as the storage and delivery of liquid reagents, new materials have been developed with extended longevity that are capable of restoring mechanical integrity and additional functions after being damaged. This Review describes the fundamental steps in this new field of science, which combines chemistry, physics, materials science, and mechanical engineering.

Biomimetic Self-Healing

Here we present a novel methodology to measure the alkaline stability of anion conducting polymers to be used as anion exchange membranes and anion exchange ionomers for fuel cells. The new ex situ technique simulates the environment of an anion exchange membrane fuel cell (AEMFC) during operation, where nucleophilic and basic OH– species in the absence, or with a scarce amount of water, attack the functional groups of the ionic polymer. Using this technique, we clearly show the critical effect of water molecules on the alkaline stability of quaternary ammonium (QA) cations commonly used as functional groups in AEMFCs. The results show that as the water content is reduced, the QA cations are more rapidly degraded in the presence of OH– at room temperature. With an increasing number of water molecules solvating the hydroxide, its nucleophilicity and basicity are hindered, and the QA degradation is significantly slowed. These results indicate that the currently used aqueous alkali ex situ tests to measure a...

https://hal.archives-ouvertes.fr/hal-01533567/document

Effect of Water on the Stability of Quaternary Ammonium Groups for Anion Exchange Membrane Fuel Cell Applications

Solid polymer electrolyte electrochemical energy conversion devices that operate under highly alkaline conditions afford faster reaction kinetics and the deployment of inexpensive electrocatalysts compared with their acidic counterparts. The hydroxide anion exchange polymer is a key component of any solid polymer electrolyte device that operates under alkaline conditions. However, durable hydroxide-conducting polymer electrolytes in highly caustic media have proved elusive, because polymers bearing cations are inherently unstable under highly caustic conditions. Here we report a systematic investigation of novel arylimidazolium and bis-arylimidazolium compounds that lead to the rationale design of robust, sterically protected poly(arylimidazolium) hydroxide anion exchange polymers that possess a combination of high ion-exchange capacity and exceptional stability. The hydroxide anion exchange polymers are key materials of solid polymer electrolyte devices that operate under alkaline conditions. Here the authors show the rational design of such polymers that exhibit high ion exchange capacity and exceptional stability under highly caustic conditions.

/pdf/poly-bis-arylimidazoliums-possessing-high-hydroxide-ion-3felfw7zdo.pdf

Poly(bis-arylimidazoliums) possessing high hydroxide ion exchange capacity and high alkaline stability.

Water in N-Heterocyclic Carbene-Assisted Catalysis

J. F. Patrick Civil and Environmental Engineering Department Beckman Institute for Advanced Science and Technology University of Illinois at Urbana-Champaign Urbana , IL 61801 , USA K. R. Hart, Prof. S. R. White Aerospace Engineering Department Beckman Institute for Advanced Science and Technology University of Illinois at Urbana-Champaign Urbana , IL 61801 , USA E-mail: swhite@illinois.edu Dr. C. E. Diesendruck, Prof. J. S. Moore Chemistry Department Beckman Institute for Advanced Science and Technology University of Illinois at Urbana-Champaign Urbana , IL 61801 , USA B. P. Krull, Prof. N. R. Sottos Materials Science and Engineering Department Beckman Institute for Advanced Science and Technology University of Illinois at Urbana-Champaign Urbana , IL 61801 , USA E-mail: n-sottos@illinois.edu

Charles E. Diesendruck

Papers

Biomimetic Self-Healing

Effect of Water on the Stability of Quaternary Ammonium Groups for Anion Exchange Membrane Fuel Cell Applications

Poly(bis-arylimidazoliums) possessing high hydroxide ion exchange capacity and high alkaline stability.

Water in N-Heterocyclic Carbene-Assisted Catalysis

Continuous Self-Healing Life Cycle in Vascularized Structural Composites