Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

The rise of graphene

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

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

We measured the elastic properties and intrinsic breaking strength of free-standing monolayer graphene membranes by nanoindentation in an atomic force microscope. The force-displacement behavior is interpreted within a framework of nonlinear elastic stress-strain response, and yields second- and third-order elastic stiffnesses of 340 newtons per meter (N m(-1)) and -690 Nm(-1), respectively. The breaking strength is 42 N m(-1) and represents the intrinsic strength of a defect-free sheet. These quantities correspond to a Young's modulus of E = 1.0 terapascals, third-order elastic stiffness of D = -2.0 terapascals, and intrinsic strength of sigma(int) = 130 gigapascals for bulk graphite. These experiments establish graphene as the strongest material ever measured, and show that atomically perfect nanoscale materials can be mechanically tested to deformations well beyond the linear regime.

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Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene

A new energy-based theory, Quantized Fracture Mechanics (QFM), is presented that modifies continuum-based fracture mechanics. The differentials in Griffith’s criterion are substituted with finite differences; the implications are remarkable. Fracture of tiny systems with a given geometry and type of loading occurs at quantized stresses that are well predicted by QFM. QFM is self-consistent, agreeing to first-order with linear elastic fracture mechanics (LEFM), and to second-order with non-linear fracture mechanics (NLFM): the equation of the R-curve is consequently derived. For vanishing crack length QFM predicts a finite ideal strength in agreement with Orowan’s prediction. The different fracture Modes (opening I, sliding II and tearing III), and the stability of the fracture propagations, are treated in a simple way. In contrast to LEFM, QFM has no restrictions on treating defect size and shape. As an example, strengths predicted by QFM are compared with experimental and numerical results on carbon nanotubes containing defects of different size and shape.

Quantized fracture mechanics and related applications for predicting the strength of defective nanotubes

There has been an intense surge in interest in graphene during recent years. However, graphene-like materials derived from graphite oxide were reported in 1962, and related chemical modifications of graphite were described as early as 1840. In this detailed account of the fascinating development of the synthesis and characterization of graphene, we hope to demonstrate that the rich history of graphene chemistry laid the foundation for the exciting research that continues to this day. Important challenges remain, however; many with great technological relevance.

From Conception to Realization: An Historial Account of Graphene and Some Perspectives for Its Future.

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

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Transmission Electron Microscopy of Polymer-Graphene Nanocomposites

Facile synthesis of accordion-like porous carbon from waste PET bottles-based MIL-53(Al) and its application for high-performance Zn-ion capacitor

Resonance and tensile tests of boron nanowires are reported and discussed assuming the presence of nanocracks. From the measured resonant frequency shift a procedure to localize the nanocrack and quantify its depth is proposed. The nanocrack depth is expected to strongly influence the failure stress and its position can be assumed to be at the fractured cross-section: thus nanocrack depth and position might be independently deduced by resonance and tensile tests. Introduction In recent years nanostructures such as nanotubes and nanowires have attracted great attention due to the promise of applications in sensing, materials reinforcement and micro/nano-electromechanical systems. Both the mechanical resonance method and the tensile testing method are two methods used to study the mechanical properties of nanostructures. The mechanical resonance method has been used to study the mechanical properties of onedimensional nanostructures such as carbon nanotubes, nanowires and nanobelts [1-4]. The uniaxial tensile test is the most popular method for bulk material mechanical property characterization, and it has been adapted for use in mechanics measurements of nanostructures such as carbon nanotubes [5]. Crystalline boron (B) nanowires (NWs) have been synthesized recently with the chemical vapor deposition (CVD) method [6]. We have experimentally investigated their dynamical resonance (i) and mechanical strength (ii) [7]. Both of these independent methods suggest the possible presence of nanocracks in the tested B NWs. Nanocrack detection can in principle be achieved by analytical calculations quantifying crack position and depth. The mechanical resonances of cantilevered B NWs were excited and the resonance peak frequencies measured. Shifts in the natural frequencies were observed, suggesting the possibility of the presence of nanocracks; other possible shift causes, such as intrinsic NW curvature, non-ideal clamps, presence of spurious masses, coating layer, large displacements, etc., have been discussed elsewhere [8]. Assuming the existence of a nanocrack, analytical calculations were obtained to quantify its depth and position based on the measured frequency shifts. A newly developed rapid electron beam induced deposition (EBID) method [9] was used to clamp the B NWs and test them in tension inside an SEM with a home-built nanomanipulator. High-resolution SEM images were acquired at each loading step, and two independent methods of analysis of each image were used to obtain the corresponding tensile load. The B NW geometries were measured by TEM after the tests. The stress vs strain, Young’s modulus, and tensile strength of the B NWs were obtained through data analysis. The strength measurements strongly suggest the presence of nanocracks in the B NWs. Assuming the existence of a nanocrack, placed at the fracture section, its depth can be quantified by applying Quantized Fracture Mechanics [10] starting from the measured fracture strengths. The possibility of detecting nanocracks through mechanical resonance and tensile testing of nanostructures is thus exemplified, even though it is not possible to know whether nanocracks alone were responsible for the frequency shifts [8]. The challenge on the experimental side in the future will be ensuring that other contributors to shifts in mechanical resonance are not present or have sufficiently different functional dependence, such that the nanocrack contribution, if present, can perhaps be “uncovered”. Frequency shift and strength reduction due to the presence of a nanocrack Mechanical resonance can be induced in nanowires when the frequency of the applied force approaches their resonant frequency. According to simple beam theory, the n mode mechanical resonance frequency fn of a clampedfree uniform beam is given by: A I E L f b n n ρ π β 2 2

Rodney S. Ruoff

Papers

Quantized fracture mechanics and related applications for predicting the strength of defective nanotubes

From Conception to Realization: An Historial Account of Graphene and Some Perspectives for Its Future.

Transmission Electron Microscopy of Polymer-Graphene Nanocomposites

Facile synthesis of accordion-like porous carbon from waste PET bottles-based MIL-53(Al) and its application for high-performance Zn-ion capacitor

Nanocrack detection may be possible in vibrating nanowires