MOVPE growth and characterization of ZnSe-GaAs heterovalent heterostructures

ZnSe-GaAs heterovalent heterostructures were fabricated by metalorganic vapour phase epitaxy and characterized structurally and electrically. A study on growth behaviour of GaAs on ZnSe revealed that either the 2-dimensional or the 3-dimensional growth mode may occur depending on the growth conditions. This growth behaviour is applied to the construction of low-dimensional structures. Successful fabrication of quantum well structures and GaAs islands buried into ZnSe is demonstrated by means of X-ray diffraction and transmission electron microscopy. The electrical properties of the heterostructures are also described.     

A zero-current-switching based three-phase pulse width modulation inverter

With the remarkable progress of switching devices, the switching frequency of a voltage-source PWM inverter has become higher and higher. A high-frequency PWM inverter gives great benefits in the reduction of current ripples and acoustic noises. However, high-frequency hard switching causes the increase of switching losses and EMI to be solved. The authors propose a zero-current-switching based three-phase PWM inverter which has small resonant circuits on the ac side. The current flowing in a switching device is a sum of the resonant current and the load current. Since the switching device is turned on and off at zero current, the switching losses and electromagnetic noises are greatly reduced. This paper described the principle of the zero current switching operation, the design of the resonant circuits and the control scheme for the new soft switching inverter. Moreover, it shows interesting experimental results obtained by the zero-current-switching PWM inverter which drives an induction motor of 2.2 kW.     

A COMPOSITE LINEAR MODEL GENERATING A STATIONARY STOCHASTIC PROCESS WITH GIVEN THIRD-ORDER AUTOCORRELATION FUNCTION

Abstract. A composite linear model is proposed which generates a non-Gaussian stationary stochastic process with a given third-order autocorrelation function and a white power spectrum. The design of the model is based on the fact that a type of finite-impulse-response linear system with a non-Gaussian white input series produces an output process whose third-order correlations exist only for special time lags. An arbitrary third-order autocorrelation function can be constructed by superposing output processes of this type. The model requires at most 2 L² + 4 L + 1 independent identically distributed (i.i.d.) input processes for the third-order autocorrelation function with the largest time lag L . Results of numerical experiments confirm the validity of the model.     

A distributed globally replaceable redundancy scheme forsub-half-micron ULSI memories and beyond

This paper describes a distributed globally replaceable redundancy (DGR) scheme which achieves a higher optimization of the trade-off between yield enhancement and chip area penalty. A newly developed yield simulator using the Monte Carlo method has estimated the effectiveness of the DGR scheme in a quantitative manner. The new redundancy scheme is expected to enhance the yield by several times compared with conventional redundancy in the early stages of production. The DGR scheme has been successfully implemented in an experimental 4 Mb SRAM with a 3.0% area overhead and an average redundancy usage efficiency of 61% has been obtained in repaired pass chips     

Physical random number generator based on MOS structure after soft breakdown

We present a novel physical random number generator (RNG) that uses a metal-oxide semiconductor (MOS) capacitor after soft breakdown (SBD) as a random source. It is known that the electrical properties of MOS capacitors after SBD show large fluctuation. When the resistor in an astable multivibrator is replaced with an MOS capacitor after SBD, the multivibrator converts the noise signal into a rectangular wave whose period fluctuates randomly. A 1-bit counter and a flip-flop are used to generate random numbers from the fluctuating rectangular wave. Some high-level tests indicate that the generated random numbers have excellent quality for cryptographic applications. Even though our circuit is small and can be constructed using about 20 complementary-MOS logic gates and several passive devices, high-quality random numbers such as those generated by large physical RNGs can be obtained.     

Microstructural changes of Al/amorphous SiC layered films subjected to heating

Layered specimens composed of aluminium and a-SiC films were prepared at room temperature by r.f. magnetron sputtering. a-SiC/Al/a-SiC triple-layered films were heated in the trans mission electron microscope (TEM), and thein-situ microstructural changes were observed continuously. In order to estimate the interfacial reaction process kinematically, electrical resistance measurements were conducted on Al/a-SiC double-layered films heated isothermally at 573, 598 and 623 K. Thein-situ TEM observations showed that no pronounced interfacial reactions occurred up to about 600 K, that silicon precipitates were formed and grew around 673 K, and that Al₄C₃ compounds were produced during heating at temperatures above about 753 K. The electrical resistance of Al/a-SiC double-layered film heated isothermally increased gradually with heating time, and this increase was closely related to the volume fraction of silicon precipitates in the aluminium film. From the kinematical analyses of the results of electrical resistance measurements, an activation energy of the interfacial reaction process of aluminium with a-SiC films in the temperature range 573 to 623 K was found to be about 2.6 eV, being close to the bond energy of Si-C.     

Metabolism of azetirelin, a new thyrotropin-releasing hormone (TRH) analogue, by intestinal microorganisms

PURPOSE: We evaluated the effect of luminal bacterial metabolism on intestinal absorption of azetirelin in rats. In vitro characteristics of bacterial metabolism of azetirelin were also investigated with the goal of overcoming the low stability of the peptidic drug against luminal microorganisms. METHODS: Plasma azetirelin levels after oral administration to antibiotic-pretreated rats was examined. In vitro incubation experiments with bacterial suspensions were also performed to clarify the location of azetirelin breakdown activity as well as the effects of oxygen, pH, and various protease inhibitors on drug metabolism. RESULTS: Plasma azetirelin levels were sustained after oral administration to antibiotic-treated rats. Incubation with rat luminal contents demonstrated that azetirelin was metabolized by anacrobic bacteria, which are predominant in the distal intestine. Fecal suspensions from rats, dogs, and humans showed comparable metabolic activity. Azetirelin breakdown in the bacterial suspension was pH-dependent and was inhibited in the presence of bacitracin or puromycin. CONCLUSIONS: Bacterial metabolism influences the degree of absorption of azetirelin in the distal intestine. Control of the luminal pH environment may be a practical method for improving the stability of azetirelin against intestinal microorganisms.     

Isozyme selective alterations of the expression of cytochrome P450 during regeneration of male rat liver following partial hepatectomy

1. During liver regeneration in the male rat, the metabolic activities of imipramine were differentially affected depending on the specific metabolic pathways. Imipramine N-demethylation was markedly reduced whereas 2-hydroxylation showed only a moderate reduction following partial hepatectomy. 2. A slight decline was observed in the hepatic microsomal content of CYP2D apoprotein, whereas a substantial decrease occurred in CYP2C11 content during liver regeneration. Since imipramine 2-hydroxylation and N-demethylation are mediated by CYP2D and 2C11 respectively, metabolic pathway-specific alterations in the activities of imipramine metabolism are explained by the isozyme selective alteration in the levels of CYPs in regenerating liver. 3. No significant effect of regeneration was observed on expression of CYP2B1 and 2E1 apoproteins. CYP3A2 apoprotein, one of the male-specific CYP isoforms, was significantly suppressed in regenerating liver showing a similar pattern of alteration to the levels of CYP2C11. The alteration pattern of the CYP1A1 level was different to the above with a moderate decline at the first day post-operation and a marked rebound thereafter. 4. In the partially hepatectomized male rate, no significant increase in androstenedione 5-alpha reductase activity, an activity predominant in the female rat, was detected. It is concluded that the pattern of alterations of hepatic oxidative metabolism during liver regeneration was not related to the functional feminization of the liver.