Self-Consistent Effects on the Starting Current of Gyrotron Oscillators

Self-consistent effects on the starting current of gyrotron oscillators are examined. Field profiles in the open cavity are shown to be sensitive to the interaction dynamics. This can either significantly raise or lower the oscillation threshold, particularly for the low-Q modes. The transition from resonant-mode oscillations at the low magnetic field to backward-wave oscillations at the high magnetic field is demonstrated.     

Catalytic dehydrogenation of ethylbenzene with carbon dioxide: promotional effect of antimony in supported vanadium–antimony oxide catalyst

Alumina-supported vanadium oxide, VO_x/Al₂O₃, and binary vanadium–antimony oxides, VSbO_x/Al₂O₃, have been tested in the ethylbenzene dehydrogenation with carbon dioxide and characterized by S_BET, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction and CO₂ pulse methods. VSbO_x/Al₂O₃ exhibited enhanced catalytic activity and especially on-stream stability compared to VO_x/Al₂O₃ catalyst. Incorporation of antimony into VO_x/Al₂O₃ increased dispersion of active VO_x species, enhanced redox properties of the systems and formed a new mixed vanadium–antimony oxide phase in the most catalytically efficient V_0.43Sb_0.57O_x/Al₂O₃ system.     

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     

Differences in risk factors for being either a hepatitis B carrier or anti-hepatitis C+ in a hepatoma-hyperendemic area in rural Taiwan

This is a study of the differences in the risk factors for being either hepatitis B surface antigen positive [HBsAg(+)] or antibody to hepatitis C virus positive [Anti-HCV(+)] in A-Lein, a rural area in southern Taiwan, an area which also has a high hepatoma mortality rate. Three hundred eighty-five patients age > or =40 years participated in hepatoma screening at the A-Lein Community Health Center during 1995. Those who were HBsAg(-) and anti-HCV(-) or had coinfection of HBsAg(+) and anti-HCV(+) were excluded, leaving 293 patients: 109 HBsAg(+) and 184 anti-HCV(+). The anti-HCV(+) patients had a lower socioeconomic status (as defined by level of education and type of occupation) and were older than HBsAg(+) patients (P < 0.05). Those with higher alanine aminotransferase levels (ALT) also had a higher anti-HCV(+) to HBsAg(+) odds ratio (OR), and a dose response relationship was found, P < 0.0001. Anti-HCV(+) patients were more likely than HBsAg(+) patients to have a spouse who shared the infection, OR = 5.11; 95% CI, 2.30-11.28. Anti-HCV(+) patients were more likely than HBsAg(+) patients to have had blood transfusions (OR = 2.66; 95% CI, 1.20-5.89), frequent medical injections (OR = 2.64; 95% CI, 1.62-4.31), or injections by non-licensed medical providers (OR = 1.91; 95% CI, 1.18-3.09). Multiple logistic regression analysis showed that the significant factors for anti-HCV(+) patients vs. HBsAg(+) patients are drinking habit (OR = 3.45; 95% CI, 1.02-11.60), age (OR = 6.33; 95% CI, 2.93-13.68), and frequent medical injections (OR = 2.88; 95% CI, 1.65-5.03). The transmission of hepatitis C in A-Lein is closely related to low socioeconomic status, age, alcohol abuse, spouses being anti-HCV(+), and frequent medical injections, especially from non-licensed medical providers, including both pharmacists and those with no medical licensing whatsoever. These nonlicensed medical providers sometimes reuse needles to save money, which is a likely route of infection.     

Onset of gas self-induction and power consumption after gas induction in an agitated tank

The behavior of inducted gas from liquid surface and the; power requirements in an agitated tank using a mechanical agitator are studied in order to increase the amount of gas self-induction and the gas retention time for gas absorption. A 45° six-blade downward impeller turbine was utilized in this study. Air and water, air and 40 wt% 60 wt%, and 80 wt% of glycerin water, and air and 106 cP silicon oil were employed as gas and liquid phases. Variables which were studied included geometrical factors (immersed depth of impeller, baffle with and diameter of impeller) and the physical properties of the liquid (viscosity, density, and surface tension). The correlations for the onset speed of impeller and power consumption after gas induction in the agitated tank are established from our experimental results. The amount of gas self-induction from the liquid surface in the agitated tank increases with increasing impeller diameter and speed and decreases with increasing baffle width, depth of impeller and viscosity of liquid.     

An efficient numerical approach, for determining the dispersioncharacteristics of dual-mode elliptical-core optical fibers

Based on vectorial formulations which combine the surface integral equation method and the finite-element method, a novel numerical approach is proposed for calculating the dispersion coefficients of dual-mode elliptical-core fibers with arbitrary refractive index profiles. By differentiating the original formulations involving the propagation constant β and the guided mode fields H_x and H_y once and twice with respect to the normalized frequency V, the new formulations for {dβ/dV, dH_x/dV, dH_y/dV} and for {d²β/dV², d² H_x/dV², d²H_y/dV² } are obtained respectively. Once {β, H_x, H_y } is solved through the eigenvalue procedure which dominates the computing time, only a few matrix manipulations are required to obtain {dβ/dV, dH_x/dV, dH_y/dV} and {d²β/dV², d²H_x/dV² , d²H_y/dV²}. Some numerical examples are examined to see the influence of different refractive index distributions with dips on the dispersions of the four nondegenerate LP ₁₁ modes for elliptical-core fibers     

Substrate-connected high voltage pumping circuits for low supplyvoltages

Novel high voltage pumping circuits for low supply voltages are proposed. Utilising a small pumping circuit and the new substrate-connected techniques can enhance charge transfer efficiency and eliminate the body effect at low supply voltages. Furthermore, a diode-connected transistor technique can improve the reverse charge sharing phenomenon when the output has a load current. With this technique high boosted voltages can be obtained at low supply voltages     

Highly compact AC-AC converter achieving a high voltage transferratio

This paper reports a new, highly integrated modular design approach for pulsewidth-modulation AC-AC converters based on a modular phase-bank structure. Novel high-power 3-in-1 integrated bi-directional power modules (IBPM) rated at 1200-V AC and 150 A and the 3-to-1 phase bank circuits have been successfully developed, fabricated and tested. This enables the modularity design of the multiphase converter systems and reduces the critical parasitic inductance. A theoretical analysis of the IBPM's silicon utilization for this new breed of direct power converters has been outlined. A lab prototype at medium power level has been successfully designed, implemented, and tested with good results. A nearly 460-VRMS out voltage at a 1:0.955 voltage transfer ratio, which, perhaps, is the highest performance reported so far in the literature, has been achieved by the novel two-side modulation control system. The converter-fed AC motor system is able to operate over the 0-240 Hz range with inherent regenerative capability and four-quadrant operation. Potential industrial applications are also briefly highlighted in this paper     

A theoretical study of pulsed laser sampling photon amplifiers

Theoretical studies point to significant improvements in the performance of semiconductor laser amplifiers by injecting carriers with pulsed electric currents of sub-nanosecond duration. A pulsed Fabry-Perot amplifier (FPA) is most sensitive to input lightwave at the instant the carrier density is crossing the critical region, and gives a sharply pulsed sampling effect on the input lightwave signal. Compared with a FPA operating at subcritical electron density, the pulsed amplifier gives much higher gain, peak power, and bandwidth. In fact, pulsed operation of a FPA is also expected to give significantly higher gain and about the same peak output power as a traveling wave amplifier. Pulsed operation also improves the performance of a traveling wave amplifier by attenuating its internally reflected waves