Enzymic browning of sulphocatechol

When sulphur dioxide inhibits the enzymic browning of catechol catalysed by mushroom tyrosinase, the main reaction product is 4-sulphocatechol. When assessed for its browning potential, this product appears to be unreactive and does not inhibit the enzyme.     

Improved GaAs-based quantum cascade laser (/spl lambda//spl sim/11 /spl mu/m) using high-reflectivity metal facet coating

By applying a high-reflectivity metal coating to the rear facet of a GaAs-based quantum cascade laser operating at /spl lambda//spl sim/11.5 /spl mu/m, the threshold current has been reduced by 11% at 260 K and pulsed operation of the epilayer-up mounted device was extended from 283 to 294 K.     

Fatigue crack initiation and propagation of binder-treated powder metallurgy steels

Many of the targeted applications for powder-metallurgy materials, particularly in the automotive industry, undergo cyclic loading. It is, therefore, essential to examine the fatigue mechanisms in these materials. The mechanisms of fatigue-crack initiation and propagation in ferrous powder-metallurgy components have been investigated. The fatigue mechanisms are controlled primarily by the inherent porosity present in these materials. Since most, if not all, fatigue cracks initiate and propagate at the specimen surface, surface replication was used to determine the role of surface porosity in relation to fatigue behavior. Surface replication provides detailed information on both initiation sites and on the propagation path of fatigue cracks. The effect of microstructural features such as pore size and pore shape, as well as the heterogeneous microstructure on crack deflection, was examined and is discussed. Fracture surfaces were examined to elucidate a mechanistic understanding of fatigue processes in these materials.     

Analysis of the Safety of the Burial Grounds of Decontamination Waste of Chernobyl Origin in the Territory of Belarus

Unsatisfactory conditions of storage of decontamination waste (DW) in the storages formed in the territory of Belarus after the Chernobyl accident require the evaluation of the level of protection of the environment and population. The potential hazard of the decontamination waste burial grounds (DWBGs) has been evaluated based on the use of a generalized multichamber model that was verified by comparing the calculation results and the results obtained by the American (GW SCREEN) model. The characteristics of the 24 largest and most hazardous DWBGs are given and the evaluations of their safety are presented. The zones of influence of these storages, whose size varies from 100 to 330 m, have been determined. The reliability of the prediction evaluation of a possible hazardous radioactive contamination of water near the storages has been verified using the Dudichi DWBG as an example.     

Electrical characteristics of (<Emphasis Type="Italic">p</Emphasis>)3C-SiC-(<Emphasis Type="Italic">n</Emphasis>)6H-SiC heterojunctions

The electrical characteristics of (p)3C-SiC-(n)6H-SiC epitaxial heterostructures obtained by sublimation epitaxy in vacuum are studied. The band discontinuities are determined and the energy band diagram of the heterojunction is constructed. It is shown that the obtained heterostructure offers a promising material for high electron mobility transistors.     

Transient Green’s Tensor for a Layered Solid Half-Space With Different Interface Conditions

Pulsed ultrasonic techniques can be and have been used to examine the interface conditions of a bonded structure. To provide a theoretical basis for such testing techniques we model the structure as a layer on top of a half-space, both of different elastic properties, with various interface bonding conditions. The exact dynamic Green’s tensor for such a structure is explicitly derived from the three-dimensional equations of motion. The final solution is a series. Each term of the series corresponds to a successive arrival of a “generalized ray” and each is a definite line integral along a fixed path which can be easily computed numerically. Willis’ method is used in the derivation. A new scheme of automatic generation of the arrivals and ray paths using combinatorial analysis, along with the summation of the corresponding products of reflection coefficients is presented. A FORTRAN code is developed for computation of the Green’s tensor when both the source and the detector are located on the top surface. The Green’s tensor is then used to simulate displacements due to pulsed ultrasonic point sources of known time waveform. Results show that the interface bonding conditions have a great influence on the transient displacements. For example, when the interface bonding conditions vary, some of the first few head waves and regular reflected rays change polarities and amplitudes. This phenomenon can be used to infer the quality of the interface bond of materials in ultrasonic nondestructive evaluation. In addition the results are useful in the study of acoustic microscopy probes, coatings, and geo-exploration.     

High-power CW-DFB laser diode modules for CATV applications operating at 1550 nm

Investigation of the correlation between longitudinal photon density distribution and spectral linewidth re-broadening, in conjunction with carefully designed coupling optics, enable laser modules that simultaneously achieve very high fibre-coupled power of 175 mW and very narrow linewidth<1 MHz even at /spl sim/120 mW of output power to be successfully fabricated.