Method for modulating the wafer bow of free-standing GaN substrates via inductively coupled plasma etching

The bowing curvature of the free-standing GaN substrate significantly decreased almost linearly from 0.67 to 0.056 m⁻¹ (i.e. the bowing radius increased from 1.5 to 17.8 m) with increase in inductively coupled plasma (ICP) etching time at the N-polar face, and eventually changed the bowing direction from convex to concave. Furthermore, the influences of the bowing curvature on the measured full width at half maximum (FWHM) of high-resolution X-ray diffraction (HRXRD) in (0 0 2) reflection were also deduced, which reduced from 176.8 to 88.8 arcsec with increase in ICP etching time. Decrease in the nonhomogeneous distribution of threading dislocations and point defects as well as V_Ga–O_N complex defects on removing the GaN layer from N-polar face, which removed large amount of defects, was one of the reasons that improved the bowing of the free-standing GaN substrate. Another reason was the high aspect ratio of needle-like GaN that appeared at the N-polar face after ICP etching, which released the compressive strain of the free-standing GaN substrate. By doing so, crack-free and extremely flat free-standing GaN substrates with a bowing radius of 17.8 m could be obtained.     

Inclusive radiative pion capture in nuclei

The problem of inclusive radiative pion capture is reanalyzed from a many-body point of view which allows to investigate effects like the Pauli blocking and the polarization of the medium by the spin-isospin interaction in a systematic way. Standard approximations are improved by means of this method, which is however much simpler technically than other available methods and very transparent. Results are presented for a variety of nuclei and the branching ratios for the capture rates are in overall agreement with experiment. The energy distribution of the photons is narrower than experiment and several mechanisms to solve these discrepancies are examined.     

Anti-inflammatory steroids from the octocoral Dendronephthya griffini

Five new steroids, griffinisterones A-E (1-5), were isolated from the octocoral Dendronephthya griffini. The structures of these compounds were elucidated by extensive spectroscopic analysis. The single-crystal X-ray crystallography on 1 allowed the determination of the 24R configuration in 1. The absolute stereochemistry of 5 was determined by the application of PGME method. Compounds 3 and 4 were found to significantly inhibit the accumulation of the pro-inflammatory iNOS protein of the LPS-stimulated RAW264.7 macrophage cells.     

New hydroperoxybriarane diterpenoids from the octocoral Briareum violaceum

A known briarane, brianthein W (1), along with four new hydroperoxybriaranes, briaviolides R–U (2–5), have been obtained from the octocoral Briareum violaceum. The absolute configuration of 1 was determined by X-ray analysis for the first time and the structures of briaranes 2–5 were established by spectroscopic methods. Bioactivity study showed that briarane 3 decreased the production of superoxide anions from human neutrophils.     

Convection heat transfer of closely-spaced spheres with surface blowing

A validated computer simulation model has been developed for the analysis of colinear spheres in a heated gas stream. Using the Galerkin finite element method, the steady-state Navier-Stokes and heat transfer equations have been solved describing laminar axisymmetric thermal flow past closely-spaced monodisperse spheres with fluid injection. Of interest are the coupled nonlinear interaction effects on the temperature fields and ultimately on the Nusselt number of each sphere for different free stream Reynolds numbers (20 ≤Re ≤ 200) and intersphere distances (1.5 ≤d _ij ≤ 6.0) in the presence of surface blowing (0 ≤v _b < 0.1). Fluid injection (i.e. blowing) and associated wake effects generate lower average heat transfer coefficients for each interacting sphere when the Reynolds number increases (Re>100). Heat transfer is also reduced at small spacings especially for the second and third sphere. A Nusselt number correlation for each interacting (porous) sphere has been developed based on computer experiments.     

Modeling of in-situ biorestoration of organic compounds in groundwater

A convergent numerical method for modeling in situ biorestoration of contaminated groundwater is outlined. This method treats systems of transport-biodegradation equations by operator splitting in time. Transport is approximated by a finite element modified method of characteristics. The biodegradation terms are split from the transport terms and treated as a system of ordinary differential equations. Numerical results for vertical cross-sectional flow are presented. The effects of variable hydraulic conductivity and variable linear adsorption are studied.     

Edge-effect studies in fiber-reinforced laminates

Experimental and theoretical studies of edge effects in rectangular composite strips under tension are discussed. The objective of the study was to investigate the effect of various parameters, including reinforcement material, fiber orientation and the structure of the reinforcement, on the various quantities which are observed in the vicinity of free edges in multidirectionally reinforced laminates. Of particular interest was the confirmation of theoretical results related to differences in response of graphite- and boron-reinforced laminates. Experiments consisted of moiré measurements of surface-displacement patterns which were compared with theoretical predictions, and examination of failure levels. The experiments were carried out on AVCO 5505 boron and Whitaker 5206 MODMOR II graphite-reinforced angle-ply laminates in which both stacking sequence and fiber orientation were varied parametrically. Moiré techniques were developed which allowed observation of displacements on both the wide surface and along the narrow edge of 1 in.-wide × 16-ply-thick (.085 in.-.105 in.) laminates.