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

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.

http://science.sciencemag.org/content/sci/297/5582/787.full.pdf

Carbon Nanotubes--the Route Toward Applications

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Signaling Recognition Events with Fluorescent Sensors and Switches.

Single-wall carbon nanotubes grow along self-assembled nanosteps of annealed miscut C-plane sapphire Depending on the miscut orientation and annealing conditions, graphoepitaxy leads to the formation of either unprecedentedly straight and parallel nanotubes, with angular deviations as small as ±05°, or to wavy nanotubes loosely conformal to sawtooth-shaped faceted nanosteps

/pdf/carbon-nanotube-graphoepitaxy-highly-oriented-growth-by-5blc7z1np3.pdf

Carbon Nanotube Graphoepitaxy: Highly Oriented Growth by Faceted Nanosteps

We report the first transistor based on inorganic nanotubes exhibiting mobility values of up to 50 cm2 V–1 s–1 for an individual WS2 nanotube. The current-carrying capacity of these nanotubes was surprisingly high with respect to other low-dimensional materials, with current density at least 2.4 × 108 A cm–2. These results demonstrate that inorganic nanotubes are promising building blocks for high-performance electronic applications.

Field-effect transistors based on WS2 nanotubes with high current-carrying capacity.

The synthesis, sorting and organization of carbon nanotubes are major challengestoward future applications. This chapter reviews recent advances in these topics,addressing both the bulk production and processing of carbon nanotubes, and theirorganization into ordered structures, such as fibers, and aligned arrays on surfaces.The bulk synthetic methods are reviewed with emphasis on the current advancestoward mass production and selective synthesis. New approaches for the sorting ofcarbon nanotubes by structure and properties are described in the context of thespecific physical or chemical interactions at play, and referring to the characterizationmethods described in the contribution by Jorio et al. Recent advances in theorganization of carbon nanotubes into fibers are reviewed, including methodsbased on spinning from solution, from dry forests, and directly from the gasphase during growth. The organization of carbon nanotubes on surfaces,as a critical prerequisite toward future applications in nanoelectronics, isreviewed with particular emphasis given to the synthesis of both vertically andhorizontally aligned arrays. Vertically aligned growth has been recently boosted bythe development of highly efficient catalytic processes. Horizontally alignedgrowth on surfaces can yield a whole new array of carbon-nanotube patterns,with interesting physical properties and potential applications. Differentmechanisms of horizontally aligned growth include field- and flow-directedgrowth, as well as recently developed methods of surface-directed growth onsingle-crystal substrates by epitaxial approaches. The proposed mechanismspertinent to each technique are discussed throughout this review, as well astheir potential applications and critical aspects toward future progress.

/pdf/carbon-nanotube-synthesis-and-organization-2v15ocreco.pdf

Carbon Nanotube Synthesis and Organization

A qualitative description of the electronic structure of single-wall carbon nanotubes from a chemical perspective is presented using real-space orbital representations and traditional concepts of aromaticity, orbital symmetry and frontier orbitals. This unusual view of carbon nanotubes allows us to merge the solid-state physics description of band structures with the molecular orbitals framework of reaction mechanisms used in organic chemistry and to predict intriguing chemical selectivity based on electronic structure.

/pdf/electronic-structure-and-chemical-reactivity-of-carbon-5dx0x0geun.pdf

Electronic structure and chemical reactivity of carbon nanotubes: a chemist's view.

Carbon nanotubes1 have unique mechanical, electronic, optical and thermal properties, which make them attractive building blocks in the field of nanotechnology2. However, their organization into well-defined straight or curved geometries and arrays on surfaces remains a critical challenge for their integration into functional nanosystems. Here we show that combined surface- and flow-directed growth enable the controlled formation of uniquely complex and coherent geometries of single-walled carbon nanotubes, including highly oriented and periodic serpentines and coils. We propose a mechanism of non-equilibrium self-organization3, in which competing dissipative forces of adhesion and aerodynamic drag induce oscillations in the nanotubes as they adsorb on the surface. Our results demonstrate the use of ‘order through fluctuations’3 to shape nanostructures into complex geometries. The nanotube serpentines and loops are shown to be electrically conducting and could therefore find a wide range of potential applications, such as receiving and transmitting antennas, heating and cooling elements, optoelectronic devices and single-molecule dynamos.

/pdf/self-organized-nanotube-serpentines-1cns2phshb.pdf

Ernesto Joselevich

Papers

Carbon Nanotube Graphoepitaxy: Highly Oriented Growth by Faceted Nanosteps

Field-effect transistors based on WS2 nanotubes with high current-carrying capacity.

Carbon Nanotube Synthesis and Organization

Electronic structure and chemical reactivity of carbon nanotubes: a chemist's view.

Self-organized nanotube serpentines