Kinetic and geometric isotope effects originating from different adsorption potential energy surfaces: cyclohexane on Rh(111)

Novel isotope effects were observed in desorption kinetics and adsorption geometry of cyclohexane on Rh(111) by the use of infrared reflection absorption spectroscopy, temperature programmed desorption, photoelectron spectroscopy, and spot-profile-analysis low energy electron diffraction. The desorption energy of deuterated cyclohexane (C(6)D(12)) is lower than that of C(6)H(12). In addition, the work function change by adsorbed C(6)D(12) is smaller than that by adsorbed C(6)H(12). These results indicate that C(6)D(12) has a shallower adsorption potential than C(6)H(12) (vertical geometric isotope effect). The lateral geometric isotope effect was also observed in the two-dimensional cyclohexane superstructures as a result of the different repulsive interaction between interfacial dipoles. The observed isotope effects should be ascribed to the quantum nature of hydrogen involved in the C-H···metal interaction.     

Raman spectroscopy of optically levitated supercooled water droplet

By use of an optical trap, we can levitate micrometer-sized drops of purified water and cool them below the melting point free from contact freezing. Raman spectra of the OH stretching band were obtained from those supercooled water droplets at temperatures down to -35 °C. According to the two-state model, an enthalpy change due to hydrogen-bond breaking is derived from temperature dependence of the spectral profile. The isobaric heat capacity calculated from the enthalpy data shows a sharp increase as the temperature is lowered below -20 °C in good agreement with conventional thermodynamic measurements.     

Convenient synthesis of chiral lignin model compounds via optical resolution: four stereoisomers of guaiacylglycerol-β-guaiacyl ether and both enantiomers of 3-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-propan-1-one (erone)

Guaiacylglycerol-β-guaiacyl ether (GGE) is one of the most important phenolic compound for studying the chemistry and biochemistry of lignin. GGE contains two asymmetric carbons at the alpha and beta positions of its side chain; therefore, theoretically it can exist as four different stereoisomers. It has been proposed that a Gram-negative bacterium, Sphingobium sp. SYK-6 (formerly referred as Sphingomonas paucimobilis SYK-6), degrades GGE enantiospecifically via cleavage of the ether bond. The cleavage was thought to proceed in two steps, each catalyzed by a different enantiospecific enzyme. In the first step, the alcohol residue at the alpha position of the side chain in GGE was thought to be oxidized enantiospecifically by four distinct Cα-dehydrogenases (LigD, LigN, LigL and LigO), to produce two enantiomers of 3-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-propan-1-one (erone). To study this enantiospecific degradation step by the four dehydrogenases, we synthesized all four stereoisomers of GGE and both enantiomers of erone and separated them into enantiopure samples. The stereoisomers and our synthetic methods to prepare them are useful both for microbial and chemical investigations of lignin degradation.     

Natural frequencies and vibration modes of laminated composite plates reinforced with arbitrary curvilinear fiber shape paths

The development of tow-placement technology has made it possible to control fiber tows individually and place fibers in curvilinear distinct paths in each layer of a laminated plate. This paper presents an analytical method for determining natural frequencies and vibration modes of laminated plates having such curvilinear reinforcing fibers. Spline functions are employed to represent arbitrarily shaped fibers, and Ritz solutions are used to derive frequency equations using series type shape functions. The strain energy is evaluated by numerical integration involving the fiber orientation angle, and is calculated using the derivative of the spline function in minute intervals. The results show that the natural frequencies obtained by the present method agree well with results from finite element analyses. The vibration mode shape contour plots of the plates are seen to reflect clear influences of the fiber shapes.     

Optimal proper connection of graphs

Optimization Letters - An edge-colored graph G is properly colored if no two adjacent edges share a color in G. An edge-colored connected graph G is properly connected if between every pair of...     

Relaxation limit and initial layer to hydrodynamic models for semiconductors

We study a relaxation limit of a solution to the initial-boundary value problem for a hydrodynamic model to a drift-diffusion model over a one-dimensional bounded domain. It is shown that the solution for the hydrodynamic model converges to that for the drift-diffusion model globally in time as a physical parameter, called a relaxation time, tends to zero. It is also shown that the solutions to the both models converge to the corresponding stationary solutions as time tends to infinity, respectively. Here, the initial data of electron density for the hydrodynamic model can be taken arbitrarily large in the suitable Sobolev space provided that the relaxation time is sufficiently small because the drift-diffusion model is a coupled system of a uniformly parabolic equation and the Poisson equation. Since the initial data for the hydrodynamic model is not necessarily in “momentum equilibrium”, an initial layer should occur. However, it is shown that the layer decays exponentially fast as a time variable tends to infinity and/or the relaxation time tends to zero. These results are proven by the decay estimates of solutions, which are derived through energy methods.     

Contractible Triples in Highly Connected Graphs

We prove that if G is k-connected (with k ≥ 2), then G contains either a cycle of length 4 or a connected subgraph of order 3 whose contraction results in a k-connected graph. This immediately implies that any k-connected graph has either a cycle of length 4 or a connected subgraph of order 3 whose deletion results in a (k − 1)-connected graph.     

Low-pressure HVPE growth of crack-free thick AlN on a trench-patterned AlN template

A thick AlN layer was grown on a trench-patterned AlN/sapphire template by low-presssure hydride vapor phase epitaxy (LP-HVPE). Compared with the AlN layer grown on a flat AlN/sapphire template, the AlN layer grown on the trench-patterned AlN/sapphire template had a crack-free and smooth surface. The typical full-widths at half-maximum (FWHMs) of X-ray rocking curves (XRC) for the (0 0 0 2), (1 0 1¯ 2), and (1 0 1¯ 0) diffractions of the AlN layer on the trench-patterned AlN/sapphire template were 132, 489, and 594 arcsec, respectively. In addition, atomic steps were observed on the AlN layer on the trench-patterned AlN/sapphire template, and the root-mean-square (RMS) roughness of the AlN layer was determined to be 0.602 nm by atomic force microscopy (AFM).