DEVELOPMENTS AND CHALLENGES IN FLAVOR PERCEPTION AND MEASUREMENT—A REVIEW

Flavor perception and measurement play important roles in the development of food products. In an increasingly commercial environment, the food industry must strive to minimize adverse consumer reactions. This article gives an extensive overview on the various methods used for flavor measurement. Principles of flavor release and perception are discussed and applications to quality assessment are demonstrated.     

Composition and temperature dependence of the direct band gap of GaAs1−xNx (0≤x≤0.0232) using contactless electroreflectance

The composition and temperature dependence (20K<T<380K) of the direct gap, E₀, of a series of GaAs_1−xN_x/GaAs (0≤x≤0.0232) samples has been measured using contactless electroreflectance. Our results for the composition dependence of E₀ are different in relation to a recent experiment [W.G. Bi and C.W Tu, Appl. Phys. Lett. 70, 1608 (1997)]. In contrast to previously reported results, we find that the temperature dependence of the direct gap is in fact dependent on N composition and that the parameters which describe the temperature dependence of the band gap lie between those of GaAs and GaN.     

A zero-voltage transition boost converter using a zero-voltage switching auxiliary circuit

A soft switching boost converter with zero-voltage transition (ZVT) main switch using zero-voltage switching (ZVS) auxiliary switches is proposed. Various operating intervals of the converter are presented and analyzed. Design considerations are discussed. A design example with experimental results obtained from a 300-W, 250-kHz, 300-V output DC-DC converter is presented. A modified gating scheme to utilize the auxiliary switch in the main power processing is discussed. A 600-W, 100-kHz, 380 V output, 90-250 V AC, power factor corrected, AC-to-DC, boost converter with the modified gating scheme is presented. Results show that the main switch maintains ZVT while auxiliary switches retain ZVS for the complete specified line and load conditions. Parasitic oscillations existing in the converters proposed in the literature are completely removed.     

Carrier dynamics in high-speed (f/sub -3 dB/>40 GHz) 0.98-/spl mu/m multiquantum-well tunneling injection lasers determined from electrical impedance measurements

Carrier capture times in InGaAs-AlAs-GaAs 0.98-/spl mu/m multiquantum-well tunneling injection lasers with f/sub -3 dB//spl sim/43-48 GHz have been determined from analysis of high frequency electrical impedance measurements. The capture times range from 14 ps, at biases around threshold, to about 1 ps, at 50-mA bias. The small capture times agree well with tunneling times obtained directly from pump-probe measurements. The impedance measurements also suggest that the carrier lifetime in the well is much less than the escape time from the well, consistent with the cold carrier distribution associated with a tunneling injection mechanism.     

Analysis of simultaneous ground and phase faults on a six phasepower system

An analysis is presented of any simultaneous sustained ground and phase fault. A single algebraic equation is presented for the calculation of sequence currents following a sustained simultaneous ground and phase fault at the terminals of a six-phase generator. The equation can be simulated on a digital computer or a network analyzer for the simulation of any type of fault. The connection of sequence networks is at once indicated when the sequence currents are written in the format suggested. The variety of faults on a six-phase system is far more complicated than on a three-phase system. The generalized treatment of all faults will prove useful in evolving protective relaying schemes for six-phase power systems     

Wavelength and power stabilisation of uncooled 975 nm thick quantum well lasers over 110/spl deg/C temperature range

The use of a thick quantum well enables coherence-collapse operation of a Bragg grating stabilised laser diode over 110/spl deg/C temperature range, yielding 975 nm wavelength emission with >40 dB sidemode suppression ratio, <1% power variation, and fibre-output power as high as 293 mW at 15/spl deg/C and 168 mW at 125/spl deg/C.     

Electro-chemical mechanical polishing of silicon carbide

In an effort to improve the silicon carbide (SiC) substrate surface, a new electro-chemical mechanical polishing (ECMP) technique was developed. This work focused on the Si-terminated 4H-SiC (0001) substrates cut 8° off-axis toward 〈1120〉. Hydrogen peroxide (H₂O₂) and potassium nitrate (KNO₃) were used as the electrolytes while using colloidal silica slurry as the polishing medium for removal of the oxide. The current density during the polishing was varied from 10 μA/cm² to over 20 mA/cm². Even though a high polishing rate can be achieved using high current density, the oxidation rate and the oxide removal rate need to be properly balanced to get a smooth surface after polishing. A two-step ECMP process was developed, which allows us to separately control the anodic oxidation and removal of formed oxide. The optimum surface can be achieved by properly controlling the anodic oxidation current as well as the polishing rate. At higher current flow (>20 mA/cm²), the final surface was rough, whereas a smoother surface was obtained when the current density was in the vicinity of 1 mA/cm². The surface morphology of the as-received wafer, fine diamond slurry (0.1 μm) polished wafer, and EMCP polished wafer were studied by high-resolution atomic force microscopy (AFM).     

Development of a (3,1) drive multifilm piezopolymer hydrophone

A modified (3,1) drive hydrophone design described here utilizes polarized piezopolymer films taut in the stretch direction by a reformed structural construction. It mainly consists of two opposed polymer films attached to a phosphor bronze diaphragm through a perspex structure. Enhancement in sensitivity is achieved, by connecting the films electrically in series thereby adding up the voltages developed across them due to a given acoustic pressure. The response of the hydrophone for individual films and for their series combination, are measured from 300 Hz to 4 kHz     

3-Methyltrimethylammonium poly(2,6-dimethyl-1,4-phenylene oxide) based anion exchange membrane for alkaline polymer electrolyte fuel cells

Hydroxyl ion (OH^?) conducting anion exchange membranes based on modified poly (phenylene oxide) are fabricated for their application in alkaline polymer electrolyte fuel cells (APEFCs). In the present study, chloromethylation of poly(phenylene oxide) (PPO) is performed by aryl substitution rather than benzyl substitution and homogeneously quaternized to form an anion exchange membrane (AEM). ¹H NMR and FT-IR studies reveal successful incorporation of the above groups in the polymer backbone. The membrane is characterized for its ion exchange capacity and water uptake. The membrane formed by these processes show good ionic conductivity and when used in fuel cell exhibited an enhanced performance in comparison with the state-of-the-art commercial AHA membrane. A peak power density of 111 mW/cm² at a load current density of 250 mA/cm² is obtained for PPO based membrane in APEFCs at 30 °C.