Shape memory properties of Ni-Ti based melt-spun ribbons

Shape-memory properties of equiatomic NiTi, Ni₄₅Ti₅₀Cu₅, and Ni₂₅Ti₅₀Cu₂₅ ribbons made by melt spinning have been studied by temperature inducing the martensitic transformation under constant tensile loads. Recoverable strains above 4 pct can be obtained under ∼100 MPa loads for the NiTi and Ni₄₅Ti₅₀Cu₅ ribbons, transforming to B19’ martensite. The B19 martensite is formed in the Ni₂₅Ti₅₀Cu₂₅ ribbon after crystallization, and according to the lowering in transformation strain as Cu content increases, the recoverable strain is close to 2.5 pct for ∼150 MPa load. The transformation temperatures exhibit a linear dependence on the applied stress, which can be quantitatively described by means of a Clausius-Clapeyron type equation. The NiTi and Ni₄₅Ti₅₀Cu₅ ribbons exhibited some degree of two-way shape-memory effect (TWSME) after thermomechanical cycling. Texture analyses performed on the different ribbons allow us to better understand the transformation strains obtained in each ribbon. The amounts of shape-memory effect (SME) and nonrecoverable strain shown by the studied ribbons are of the same order as those already observed in bulk materials, which makes melt spinning an ideal substitute to complicated manufacturing processes if really thin samples are needed. However, applicable stresses in melt-spun ribbons are limited by a relatively “premature” brittle fracture caused by irregularities in ribbon thickness.     

Circular core polarization-maintaining optical fibers withelliptical stress-induced cladding

The reproducible technology for producing high-birefringence fibers with stress-induced elliptical cladding and circular core is described. The authors have obtained fibers that have a birefringence of about (1-3) 10^-4, a mode coupling parameter of about (2-7) 10 ^-5 m^-1, and loss of less than 0.5 dB/km at 1.6 μm. The authors have found effects restricting the capability of test fibers to maintain the state of linear polarization     

Fourier-transform-limited pulses from gain-switched distributed-Bragg-reflector lasers using simultaneous modulation of gain and phase sections

Fourier-transform-limited pulses ( Delta tau . Delta nu approximately=0.35) have been obtained from a microwave-modulated DBR laser at 1.56 mu m. The chirp of the gain-switched pulse is compensated for by applying a fraction of the microwave signal to the phase section, thereby creating an instantaneous frequency shift of opposite sign. The generation of short coherent pulses from such a monolithic source can be of great interest for long haul soliton transmission.<>     

A hybrid wafer-dicing process for GaAs MMIC production

A dicing process for GaAs MMIC (monolithic microwave integrated circuit) wafers using spin-on wax for wafer mounting and a hybrid process of wet chemical etching/mechanical sawing for chip dicing is described. This process minimizes ragged chip edges and reduces generation of microcracks in addition to the elimination of the plated gold burrs on the backside of the diced MMIC chips. This process gives a uniformity of -3 μm across a 2-in wafer following the completion of the whole backside process. This GaAs chip dicing technique is amenable to production because it exhibits both a very high chip yield (>90%) and nearly flawless edges     

Performance of 1700 m2 solar pond operation in arid zone

A 1700 m² solar pond was constructed in the desert of Kuwait where severe weather conditions prevail in all seasons. The paper describes in detail a diffuser design for the gradient establishment, gradient stability, and thermal performance of the pond. The main problem encountered in operating the pond was mixing between the upper zone and the gradient zone, even when the wind speed was as low as 5 m/s. No mixing between the gradient and the lower connective zone was observed. The wind effect was severe in causing mixing even when the upper convective zone increased to 0.90 m.     

Optical properties of Bi2Te2Se thin films

Some optical parameters of Bi₂Te₂Se thin films, determined from the measured absorbance and transmittance at normal incidence in the visible spectral range, were studied as functions of film thickness and annealing temperature. These parameters were found to be sensitive to both film thickness and microstructure change caused by annealing in a film. The effect of thickness and temperature of annealing on the optical gap was interpreted in terms of elimination of defects and change of disordering in the amorphous matrix.     

A menu-driven environment for automated urban and regional analysis: a GIS application for educational purposes

Geographical information systems (GIS) constitute an important development offering wide application potential in geography, urban and regional planning and associated disciplines. Current debates entail two kinds of criticism; the first involves GIS themselves and the fact that they are often cumbersome and difficult to use; the second involves the ‘poverty‘ of some GIS applications. The result is a worldwide endeavour to produce answers to both questions. The main objective of the system proposed here, known as URAP (urban and regional analysis for planning), is to make a contribution to these goals, by upgrading conventional GIS capabilities, while simplifying the means by which results from advanced statistical analysis are obtained and subsequently plotted. It entails a menu-driven environment and involves the dynamic formation of customised databases to meet the geographical, methodological and other choices made by the user. While the arguments in the paper involve an emphasis on education, the system is also suitable for supporting public policy making.