A net with complex weights.

In this article a new neural-network architecture suitable for learning and generalization is discussed and developed. Although similar to the radial basis function (RBF) net, our computational model called the net with complex weights (CWN) has demonstrated a considerable gain in performance and efficiency in number of applications compared to RBF net. Its better performance in classification tasks is explained by the cross-product terms in internal representation of its basis function introduced parsimoniously. Implementation of CWN by the ensemble approach is described. A number of examples, solved using CWN and other networks, are used to illustrate the desirable characteristics of CWN.

Applications of shape memory alloys in optics.

The application of shape memory alloy (SMA) thin films in optical devices is introduced and explored for the first time. Physical and optical properties of titanium-nickel (TiNi) SMA thin films change as these films undergo phase transformation on heating. An optical beam can be modulated either mechanically with a TiNi actuator or by the changes that occur in TiNi's optical properties upon heating and phase transformation. Reflection coefficients of TiNi films were measured in their so-called martensitic (room-temperature) and austenitic (elevated-temperature) phases. The reflection coefficients of the austenitic phase were higher than those of the martensitic phase by more than 45% in the wavelength range between 550 and 850 nm. Also, a microfabricated TiNi diaphragm with a 0.26-mm-diameter hole was used as a prototype light valve. The intensity of the transmitted light through the hole was reduced by 10%-17% when the diaphragm was heated. A novel TiNi light valve fabricated by using silicon micromachining techniques is also proposed and discussed. We present both optical data and structural data obtained by using transmission electron microscopies.

Gallium arsenide transistors: realization through a molecularly designed insulator.

A GaAs-based transistor, analogous to commercial silicon devices, has been fabricated with vapor-deposited cubic GaS as the insulator material. The n-channel, depletion mode, GaAs field-effect transistor shows, in addition to classical transistor characteristics, a channel mobility of 4665.6 square centimeters per volt per second, an interfacial trap density of 10(11) per electron volt per square centimeter, and a transconductance of 7 millisiemens for a 5-micrometer gate length at a gate voltage of 8 volts. Furthermore, the GaAs transistor shows an on-to-off resistance ratio comparable to that of commercial devices.

Trapping lifetime and carrier mobility measurements in CuInSe(2 ) using surface-acoustic-wave technique.

A novel technique based on the measurement of the frequency spectrum of the acoustoelectric current is used to determine the trapping time associated with dominant traps in p-type CuInSe(2). At room temperature, two trap levels with trapping time constant of 2x10(-4) and 6.7x10(-5) s are detected. Under white incandescent light, two more traps with trapping time constants of 1.4x10(-3) and 6x10(-4) s are detected. The minority (electron) and majority (hole) carrier mobilities in this material are also measured using the acoustoelectric technique, and they are 6+/-3 and 3.1+/-0.15 cm(2)/V-s, respectively. The hole carrier concentration was estimated to be around 5x10(15) cm(-3), and the surface of the sample was depleted.

A new technique to study transient conductivity under pulsed monochromatic light in Cr-doped GaAs using acoustoelectric voltage measurement.

The transient conductivity of high-resistivity, Bridgman grown, Cr-doped GaAs under pulsed monochromatic light is monitored using transverse acoustoelectric voltage (TAV) at 83 K. Keeping the photon flux constant, the height and transient time constant at the TAV are used to calculate the energy dependence of the trap density and its cross section, respectively. Two prominent trap profiles with peak trap densities of approximately 10(17) cm(-3) eV(-1 ) near the valence and the conduction bands are detected. These traps have very small capture cross sections in the range of 10(-23 )-10(-21 )cm(2). A phenomenon similar to the persistent photoconductivity with transient time constants in excess of a few seconds (in some cases, a few hundred seconds) in high-resistivity GaAs at T=83 K is also detected using this technique. These long relaxation times are readily explained by the spatial separation of the photo-excited electron-hole pairs and the small capture cross section and large density of trap distribution near the conduction band. The technique is nondestructive and, because of the dependence of the polarity of the acoustoelectric voltage on the carrier type, it yields information about the charge of the transient carriers and the type of deep traps involved in the release or trapping of these carriers.