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 graphene transfer method using water vapor-assisted determination of CVD-grown graphene film on the Cu foil. By using the polymer film as a supporting layer, we found that graphene can be directly detached from the Cu foil as a consequence of water intercalated at the graphene-Cu interface(s), by a ‘dry transfer’ method. The delaminated graphene films are continuous over large area. This nondestructive method also worked for the transfer of graphene grown on a Cu single crystal without sacrificing the expensive crystal, thus affording the possibility of producing high-quality graphene and reusing the substrate. The Cu foil and single crystal can both be repeatedly used for many times, which may reduce the cost of graphene synthesis and is environmentally more benign. Our method affords the advantages of high efficiency, likely industrial scalability, minimal use of chemicals, and the reusability of the Cu foil in multiple growth and delamination cycles.

Large-area graphene transfer method

Experimental evidence supporting the heightened chemical reactivity of highly conformationally strained carbon sites in multi-walled carbon nanotubes is reported. The strain is introduced by two methods, van der Waals attractions to nonplanar surfaces and ultrasonic cavitation. Oxidative acid attack was observed in both cases, in the former by etching of the nanotubes' kinked sites, and in the latter by peptide coupling to polystyrene spheres that are large enough to be visible by SEM imaging. A novel single-axis straining stage for nanometre-scale objects is also described.

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Nanostressing and mechanochemistry

Microwave rotational spectra have been observed for the four 14N/15N isotopic species of an (HCN)2–Ar trimer with the pulsed nozzle Fourier transform method using the Flygare Mark II spectrometer. Thirteen J→J’ asymmetric top transitions were measured in the 2.5 to 10 GHz region for the parent 14N,14N trimer and nine for each of the other three species. The 14N nuclear quadrupole hyperfine structure was analyzed for the transitions and the interaction constants and line centers determined. The line centers were fitted to obtain ground vibronic state rotational and quartic centrifugal distortion constants. For the 14N/14N trimer these are (in MHz) for A‘, B‘, and C‘: 2013.5993(10), 1759.2756(3), 932.3709(2); and for τ1, τ2, τaaaa, τbbbb, and τcccc: −0.3017(1), −0.0660(1), −0.1700(9), −0.013 71(1), and −0.0088(1). The inertial defect is 3.7881 amu A2. The zero‐point vibrationally averaged geometry is planar and T shaped with the structure of the linear HCN dimer remarkably unperturbed by presence of the Ar ...

Rotational spectra and structures of small clusters containing the HCN dimer: (HCN)2–Ar, a T‐shaped trimer

As the isotopic concentration of ultrathin graphite is varied from natural abundance to nearly pure ${}^{13}\mathrm{C}$, the thermal conductivity displays a slight dependence on the isotope concentration at temperatures near its maximum $\ensuremath{\sim}150\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The strength of phonon-isotope scattering in the high-isotope impurity-concentration regime is found to be well below that given by a commonly used incoherent and independent isotope impurity scattering model. This finding is in agreement with some recent theoretical predictions that coherent multiple scattering of phonons is important in the measured thermal conductivity of low-dimensional materials in the high-isotope impurity-concentration regime.

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Scattering of phonons by high-concentration isotopic impurities in ultrathin graphite

Catalyst-assisted growth of boron nanowires and novel tube–catalytic particle–wire hybrid boron nanostructures were achieved by pyrolysis of diborane at 820–890°C and ~ 200 mTorr in a quartz tube furnace. Electron microscopy imaging and diffraction analysis reveal that most of the nano-structures are amorphous. Elemental analysis by EELS and EDX shows that the nanostructures consist of boron with a small amount of oxygen and carbon. Possible growth mechanisms for the tube–catalytic particle–wire hybrid boron nanostructures are discussed.

Rodney S. Ruoff

Papers

Large-area graphene transfer method

Nanostressing and mechanochemistry

Rotational spectra and structures of small clusters containing the HCN dimer: (HCN)2–Ar, a T‐shaped trimer

Scattering of phonons by high-concentration isotopic impurities in ultrathin graphite

Boron nanowires and novel tube-catalytic particle-wire hybrid boron nanostructures