Review of reliability issues of metal-semiconductor-metal and avalanche photodiode photonic detectors

In this paper, we present a brief review of the principal mechanisms that influence the reliability of metal–semiconductor–metal (MSM) interdigitated photodetectors and avalanche photodiodes (APD). The most important mechanism influencing reliability in these devices is the dark current. However, other mechanisms such as edge and microplasmic breakdown and electrode degradation, can also affect device reliability. In this study, we describe numerical simulation techniques that can be utilized to understand the workings of some of these mechanisms and illustrate their usage in a few representative devices. Specifically, we discuss how advanced drift-diffusion and hydrodynamic simulation techniques can be used to study the dark current as well as the location of breakdown in MSM and APD devices.     

Estimating Bounds on Fracture Stresses Determined from Mirror Size Measurements

Statistical techniques are used to derive closed-form, approximate solutions for estimating a standard deviation on the fracture stress determined from mirror size measurements. The estimated coefficient of variation of fracture stress is noted to be twice as sensitive to the variation of the mirror constant, A _j , as to the variation in the measured boundary radius, r _j . This allows the hackle radius to be reasonably estimated and bounded from the mirror and branch radii when it cannot be clearly delineated.     

Dielectric properties of poly(vinyl chloride) in tetrahydrofuran and cyclohexanone

The dielectric absorption and dispersion of poly(vinyl chloride), M M_v = 49 000, in THF and in cyclohexanone have been studied over a frequency range of 120 kHz to 11·0 MHz, at temperatures from ?22·5 to 35°C, and at concentrations ranging from 4 to 12·0(w/v)% PVC/THF and from 2 to 8·0(w/v)% PVC/cyclohexanone. The viscosities of the two systems have also been measured at temperatures from 20 to 50°C. A single relaxation time was found (β = 0·8–1·0), which indicates that relaxation occurs by segmental rotation. The dielectric and viscous activation energies have been calculated. The dipole moment associated with the relaxation process has also been calculated. The relaxation time, dielectric and viscous activation energies and the dipole moment were found to be dependent on the type of solvent. The dipole moment also showed a molecular weight dependence. The influence of the concentration and temperature on the apparent dipole moment and on the relaxation time is discussed.     

Effect of recess geometry on shock wave formation in circular gas bearings

An analytical method, based on the concept of shock wave formation in the bearing clearance, is used to develop a mathematical model by which the pressure distribution along the fluid film can be predicted. Based on this model, the limiting conditions for shock free operation are determined. The effects of recess geometry and inlet gas conditions are analysed. Experimental pressure distributions along the fluid film at different values of film thickness, supply pressure and rotating speed compare well with the theory. The analysis reveals that a bearing with a tapered recess has a higher resistance to shock wave formation than a conventional bearing having the same recess volume. Moreover, the tapered recess bearing has superior stability to the conventional bearing for the same recess depth.     

Influence of some compounds on gentamicin formation by Micromonospora purpurea

Production of gentamicin antibiotics by Micromonospora purpurea was carried out successfully on a synthetic medium which contained the following ingredients (g/litre): glucose 10.0, NaNO₃ 2.0, KH₂PO₄ 1.0, and CaCO₃ 1.0. The initial pH value of the fermentation medium was adjusted to 7.2. Effects of certain amino acids, organic acids, vitamins, purine and pyrimidine bases on the fermentative production of gentamicins were revealed. The ingredients which increased the antibiotic yields were phenylalanine, isoleucine, lysine, methionine, leucine, arginine, glycine, β′-alanine, cystine, tryptophan, malic acid, maleic acid, cobalamin, folic acid, riboflavin, vitamin B₁, vitamin B₆, biotin, nicotinamide, uracil, adenine, guanine and adenosine. Trace elements (Co, Mo, Fe, Cu, Zn and Mn) exhibited their important role on the biosynthesis and formation of gentamicins by Micromonospora purpurea.     

Aspects of the mechanics of driving nails into wood

For nail driving, some aspects of the effect on penetration of the hammer mass, the speed at impact, the nail size and section shape and the driving direction in relation to the wood grain are reported.A 6 in. long, 0·236 in. dia., round nail was strain gauged to show how the strain in the nail varies with time during an impact.An analysis, which reasonably accounts for the experimental results, is developed for predicting the strain pulse in the nail, the amount of penetration by the nail and its time under strain.Maintaining the same kinetic energy input at each blow, it is found that the larger the initial penetration, the smaller is the further penetration.The effect on penetration depth of the material backing to the piece of wood is reported.The variation of the Euler buckling load with the nail penetration for a specific type of wood and nail dimensions is given.     

Optimal linear approximation in project compression

When the cost of reducing the duration of activities is convex and nonlinear, it may be advisable (to reduce the computing burden) to seek a “satisficing” answer, in which the project is compressed to a desired completion time with a prespecified tolerable relative error. We treat the problem of constructing the optimal first degree interpolating linear spline that guarantees such maximal error and consider various possible refinements.