High-power and high-efficiency phased array lasers grown by a two-step metalorganic chemical vapour deposition

Phased array lasers which emit 1.3 W CW output were fabricated using a two-step metalorganic chemical vapour deposition process were developed. The differential efliciency at 100 mW is 78% and the total efficiency at the catastrophic limit is 39%.     

Elastic-plastic finite element analyses of stable crack growth and fracture instability in a girth welded pipe

Detailed elastic-plastic finite element fracture mechanics analyses were conducted on a 16 inch diameter Type 304 stainless steel pipe containing a circumferential through-wall crack located in a girth weld. Calculations were performed to analyze the welded pipe treated as (1) a monolithic pipe entirely composed of the base metal, and (2) a composite of base metal and weldment. In the latter, each constituent was assigned distinct mechanical and fracture properties. In both solutions applied J values were calculated for a fixed axial load combined with a monotonically increasing applied bending moment. The material J-resistance curves appropriate for the two problems were each used to initiate and grow the initial crack in a stable manner until fracture instability occurred under load control. It was found that the extent of stable crack growth and the applied loads at fracture instability are distinctly different in the two analyses. It is concluded that more precise fracture mechanics approaches than those now in current use are required for accurate assessments of weld cracking problems.     

Analysis of geometrical distortion and statistical variance in length, area, and volume in a linearly scanned 3-D ultrasound image

A linearly scanned three-dimensional (3-D) ultrasound imaging system is considered. The transducer array is initially oriented along the x axis and aimed in the y direction. After being tilted by an angle theta about the x axis, and then swiveled by an angle phi about the y axis, it is translated in the z direction, in steps of size d, to acquire a series of parallel two-dimendional (2-D) images. From these, the 3-D image is reconstructed, using the nominal values of the parameters (phi, theta, d). Thus, any systematic or random errors in these, relative to their actual values (phi0, theta0, d0), will respectively cause distortions or variances in length, area, and volume in the reconstructed 3-D image, relative to the 3-D object. Here, we analyze these effects. Compact linear approximations are derived for the relative distortions as functions of the parameter errors, and hence, for the relative variances as functions of the parameter variances. Also, exact matrix formulas for the relative distortions are derived for arbitrary values of (phi, theta, d) and (phi0, theta0, d0). These were numerically compared to the linear approximations and to measurements from simulated 3-D images of a cubical object and real 3-D images of a wire phantom. In every case tested, the theory was confirmed within experimental error (0.5%).     

Second harmonic generation in germanotellurite bulk glass‐ceramics

In this study, we have investigated the use of silver cation as nucleating agent in germanotellurite glass matrix of compositions (100?x) [70TeO₂–10GeO₂–10Nb₂O₅–10K₂O]–xAg₂O (x=0‐6 mol%), in order to promote bulk crystallization. Density measurements, differential scanning calorimetry, X‐ray diffraction, UV‐Vis, and Raman spectroscopies have been performed to study the crystallization process. We have observed bulk crystallization of a unique noncentrosymmetric phase, K[Nb_1/3Te_2/3]₂O_4.8, which has been investigated for its second‐order optical activity. Transparent to translucent glass‐ceramics have been successfully tailored under thermal treatment and second harmonic generation signals were recorded on the glass‐ceramic samples as a function of their synthesis procedure. It is suggested that the second‐order optical properties observed are strongly related to the organization of crystallites within phase‐separated domains.     

Finite strain analysis by a stress-function method

A finite element method for finite inelastic strain analysis of solids and structures is described. The method, which is based on a direct discretization of the equations of compatibility and angular momentum balance, represents a generalization of the mixed stress function approach proposed for linear elasticity by de Veubeke (1975). It captures the main advantages of hybrid-stress, direct stiffness, and reduced integration finite element methods while avoiding their principal drawbacks. Examples are included which demonstrate important features of the method.     

Fast fractal compression of greyscale images

A new algorithm for fractal compression of greyscale images is presented. It uses some previous results allowing the compression process to be reduced to a nearest neighbors problem, and is essentially based on a geometrical partition of the image block feature space. Experimental comparisons with previously published methods show a significant improvement in speed with no quality loss     

The effects of superchilled storage at −2 °C on the microbiological and organoleptic properties of cold-smoked salmon before retail display

The aim of this study was to investigate the impact of superchilling (?2 °C) on the evolution of Listeria monocytogenes and organoleptic characteristics of cold-smoked salmon samples. An Hadamard matrix experimental design was carried out on artificially inoculated samples stored at +4 °C for 10 d and at +8 °C for 18 d to know the influence of four factors: salt content, strain, cold stiffening and superchilling time, on the level of L.monocytogenes in cold-smoked salmon. The growth of L. monocytogenes in naturally contaminated cold-smoked salmon and the organoleptic properties were investigated under superchilling conditions.Superchilling (?2 °C for 28 d) had a limited impact on some of the organoleptic properties but the level of L. monocytogenes at the end of the shelf-life (4 °C for 10 d and 8 °C for 18 d) could exceed the microbiological criterion set by the European legislation.