Description: In this article, the authors report an atomistic simulation study of the behavior of nanocomposite materials that are formed by incorporating single-walled carbon nanotubes (SWCNTs), with three different diameters, and a multiwalled carbon nanotube (MWCNT) into a single-crystal nickel matrix. The interactions between carbon and nickel atoms are described by a modified embedded atom method potential. Mechanical properties of these nanocomposite materials are predicted by atomistic calculations and compared with that of fcc nickel and pristine CNTs. The authors' simulations predict that all Ni/CNT composites studied in this work are mechanically stable. Their elastic properties depend on the volume fraction and diameter of embedded CNTs. The single-crystal Young's modulus (E₁₁) of Ni/SWCNT composites exhibit a large increase in the direction of CNTs alignment compared to that of a single-crystal nickel. However, a moderate but gradual decrease is seen for E₂₂ and E₃₃ in the transverse directions with increase in CNT diameters. As a consequence, Ni/SWCNTs show a gradual decrease for the polycrystalline Young's, bulk and shear moduli with the increasing CNT diameters and volume fractions. These reductions, although moderate, suggest that enhancement of mechanical properties for polycrystalline Ni/SWCNT nanocomposites are not achievable at any CNT volume fraction. The Ni/MWCNT composite ...

Description: This article discusses the coherent excitation of a two-level atom driven by a far-off-resonant classical field. Abstract: We present an analytical treatment of coherent excitation of a two-level atom driven by a far-off-resonant classical field. A class of pulse envelope is obtained for which this problem is exactly solvable. The solutions are given in terms of the Heun function, which is a generalization of the hypergeometric function. Degeneracy of the Heun to a hypergeometric equation can give all the exactly solvable pulse shapes of Gauss hypergeometric form from the generalized pulse shape obtained here. We discuss the application of the results obtained to the generation of soft x-ray and ultraviolet radiations.

Description: This book review discusses 'Computational Inorganic and Bioinorganic Chemistry', edited by Edward I. Solomon from Stanford University, Robert A. Scott from the University of Georgia Athens, and R. Bruce King from the University of Georgia Athens.

Description: This article discusses hexagonal nickel carbide. Nanocrystals of hexagonal nickel carbide have been synthesized via physical vapor deposition of elemental nickel onto the surface of vertically aligned carbon nanotubes. Combining high-resolution transmission electron microscopy (HRTEM) with three-dimensional atom probe tomography (3DAP) confirmed that these nanocrystals have a hexagonal structure, are enriched in carbon, and have a composition of ~Ni-25 at. % C (Ni3C). This metastable hexagonal nickel carbide phase appears to be stabilized due to the growth of the nanocrystals on the surface of the nanotubes that act as a template and also as a source of carbon. The stability of this nickel carbide phase has also been investigated by density functional theory (DFT) calculations and compared to the experimental results.

Description: In this article, the authors have experimentally demonstrated an ultra-dispersive optical prism made from a coherently driven Rb atomic vapor. The prism possesses spectral angular dispersion that is 6 orders of magnitude higher than that of a prism made of optical glass; such angular dispersion allows one to spatially resolve light beams with different frequencies separated by a few kilohertz. The prism operates near the resonant frequency of atomic vapor and its dispersion is optically controlled by a coherent driving field.