Interactions of dislocations with disconnections in fcc metallic nanolayered materials

Embedded-atom method potentials and atomistic models of coherent (010) interfaces were used to study slip across interfaces in cube-on-cube oriented Cu/Ni nanolayered materials. (111) disconnections form during slip across Cu–Ni interfaces and become significant barriers to continued deformation. A significant barrier exists for the flat coherent interface owing to the large coherency stresses in the Cu/Ni layers that must be overcome by applied stresses but, once these have been overcome, interface transection occurs readily. A disconnection adds an additional barrier because of a residual dislocation with a Burgers vector magnitude equal to the difference between b _Cu and b _Ni. This barrier depends on the position of the disconnection relative to the glide plane of the transecting glide dislocation and on the disconnection height. Disconnections cause work hardening that prevents shear band formation during deformation and encourages homogeneous shear processes. Disconnection energies are shown to be relatively small and to depend on the disconnection type and size.     

Features of sputtering of nitrides and their components

The sputtering behaviour of hexagonal or wurtzite polycrystal nitrides of boron, aluminium, and gallium was explored employing methods of molecular dynamics. The sputtering yield Y of nitrides and the average energy ē ₁ of emitted particles were studied as dependent on the mass m ₁ of bombarding He, Li, B, N, Ne, Al, Ar, Ni, Ga, Kr, and Xe ions with the initial energy E ₀ between 200 and 10,000 eV. Y(m ₁) and ē ₁(m ₁) were researched upon for preferential sputtering of nitride components at low E ₀. It was revealed that the ratio between the sputtering yield of the light component and that of the heavy one depends on ion energy and mass. At E ₀=200 eV and m ₁=40, the ratio for BN, AlN, and GaN amounts to 1.2, 2.2, and 2.4, respectively. For nitride components, an anomalous dependence of sputtering on ion mass was found, its maximum occurring at a certain ratio m ₂/m ₁, where m ₂ is the averagè mass of two nitride components.     

Solution-grown single crystals of random terpolymer liquid crystal polymers: Chain folding,morphology, and effect of annealing

Thin (100–150 Å thick) single crystals of large lateral dimensions have been grown from dilute solution in xylene of random terpolymer, thermotropic, liquid crystal polymers containing approximately equimolar amounts of C₆ or C₇ flexible segments, oxybenzoate, and dioxyphenyl. With both polymers having molecular lengths of 800 Å or longer, electron diffraction patterns indicate chain folding. The crystal structure, hexagonal, is less perfect than found previously for thin films of the C₇ (and C₅) polymer crystallized from the nematic state by slow cooling (orthorhombic). Annealing of the crystals below the crystal-liquid crystal transition results in merging of overgrowths and rough crystal edges into the main crystal and a surface roughening, followed, at longer times and/or higher temperatures, by lamella thickening. Annealing in the nematic state results in the development of rosettes of lamellae. Implications of the results for crystallization mechanisms and morphology of the nematic state are discussed.     

Theoretical study of the reaction of H2 with a Cu2Pt2 cluster

The study of the interaction of a pyramidal tetramer of Cu₂Pt₂ with the H₂ is reported here through ab initio multiconfigurational self-consistent field (MC-SCF) calculations, plus extensive multireference configuration interaction (MR-CI), variational and perturbative calculations. The lowest three electronic states X ¹A′, a ³A′ and a ¹A′ of the bare cluster were considered in order to study this interaction. For the H₂ C_s approaching a Pt vertex, results show that the Cu₂Pt₂ pyramid cluster in its X ¹A′ and a ¹A′ states can spontaneously capture and dissociate the H₂. For the H₂ C_s approaching a Cu vertex, where H₂ is located in the C_s reflecting plane, the Cu₂Pt₂ cluster in its X ¹A′ electronic state shows capture of the hydrogen molecule after surmounting an energy barrier; moreover, in this approach the Cu₂Pt₂ cluster in its a ¹A′ electronic state shows spontaneous capture of the hydrogen molecule. For the H₂ approaching a Cu vertex, where the C_s reflecting plane bisects the H₂ molecule, the Cu₂Pt₂ cluster in its three lowest-lying states is able to capture the hydrogen molecule after surmounting a small barrier. The Cu₂Pt₂+H₂ C_s face-on interactions show a lower H₂ activation than that which was obtained in the equivalent Pt₄+H₂ interactions.     

Neighbourhood-Perfect Line Graphs

We show that the line graph of any balanced hypergraph is neighbourhood-perfect. This result is a hypergraphic extension of a recent theorem in [GKLM] saying that the line graphs of bipartite graphs are neighbourhood-perfect. The note contains also a graphical extension of the same theorem: the characterization of all graphs with neighbourhood-perfect line graph. The proof relies on a characterization of neighbourhood-perfect graphs among line graphs in terms of forbidden induced subgraphs.     

Fast‐scanning high‐flux microprobe for biological X‐ray fluorescence microscopy and microXAS

There is a growing interest in the biomedical community in obtaining information concerning the distribution and local chemical environment of metals in tissues and cells. Recently, biological X‐ray fluorescence microscopy (XFM) has emerged as the tool of choice to address these questions. A fast‐scanning high‐flux X‐ray microprobe, built around a recently commissioned pair of 200 mm‐long Rh‐coated silicon Kirkpatrick–Baez mirrors, has been constructed at BioCAT beamline 18ID at the Advanced Photon Source. The new optical system delivers a flux of 1.3 × 10¹² photons s^?1 into a minimum focal spot size of ～3–5 µm FWHM. A set of Si drift detectors and bent Laue crystal analyzers may be used in combination with standard ionization chambers for X‐ray fluorescence measurements. BioCAT's scanning software allows fast continuous scans to be performed while acquiring and storing full multichannel analyzer spectra per pixel on‐the‐fly with minimal overhead time (<20 ms per pixel). Together, the high‐flux X‐ray microbeam and the rapid‐scanning capabilities of the BioCAT beamline allow the collection of XFM and micro X‐ray absorption spectroscopy (microXAS) measurements from as many as 48 tissue sections per day. This paper reports the commissioning results of the new instrument with representative XFM and microXAS results from tissue samples.     

The eigenvalue problem for solitary waves of a boussinesq equation,via a generalization of the rouché theorem

We consider the study of an eigenvalue problem obtained by linearizing about solitary wave solutions of a Boussinesq equation. Instead of using the technique of Evans functions as done by Pego and Weinstein in [R. Pego and M. Weinstein, Convective Linear Stability of Solitary Waves for Boussinesq equation. AMS, 99, 311–375] for this particular problem, we perform Fourier analysis to characterize solutions of the eigenvalue problem in terms of a multiplier operator and use the strong relationship between the eigenvalue problem for the linearized Boussinesq equation and the eigenvalue problem associated with the linearization about solitary wave solutions of a special form of the KdV equation. By using a generalization of the Rouché Theorem and the asymptotic behavior of the Fourier symbol corresponding to the eigenvalues problem for the Boussinesq equation and the Fourier symbol corresponding to the eigenvalues problem for the KdV equation, we show nonexistence of eigenvalues with respect to weighted space in a planar region containing the right-half plane.