Temperature dependence of common-emitter I-V andcollector breakdown voltage characteristics in AlGaAs/GaAs andAlInAs/GaInAs HBT's grown by MBE

Temperature-dependent measurements from 25 to 125°C have been made of the DC I-V characteristics of HBTs with GaAs and In_0.53Ga_0.47As collector regions. It was found that the GaAs HBTs have very low output conductance and high collector breakdown voltage BV_CEO>10 V at 25°C, which increases with temperature. In striking contrast, the In_0.53Ga_0.47As HBTs have very high output conductance and low BV_CEO~2.5 V at 25°C, which actually decreases with temperature. This different behavior is explained by the >10⁴ higher collector leakage current, I_CO, in In_0.53Ga_0.47As compared to GaAs due to bandgap differences. It is also shown that device self-heating plays a role in the I-V characteristics     

On the dynamic characteristics of a balance PUMA-760 robot

To reduce complexities in robot dynamics, a mechanical counter-balancing concept based on the theory of adding balancing masses to unbalanced conventional manipulators is introduced. The effects of balancing on the dynamic characteristics of the PUMA-760 robot when the designed counter-balancing mechanism is applied to the robot are examined. Through theoretical and experimental study many distinct advantages such as simplicity in the dynamic equation and significant reduction in the total required input torques are demonstrated for various manipulator speeds and payload conditions. Based on these results, the dynamic characteristics of the balanced PUMA-760 robot are discussed in detail     

Impact ionization and real-space transfer of minority carriers incharge injection transistors

High electric fields in the channel of InGaAs-InAlAs heterostructure complementary charge injection transistor give rise to impact ionization and real-space transfer of minority holes from the channel. These phenomena are investigated by measuring light emission in the 1.1-3.1 eV energy range for different points on the electrical characteristics. The effective carrier temperature, determined from the exponential tails of electroluminescence spectra, is 2100 K in the channel and 450 K in the barrier     

A contribution to optimal lamp design in rapid thermal processing

Recent studies of wafer temperature control in rapid thermal processing systems have indicated that a multiring circularly symmetric lamp configuration with independent (multivariable) control of the power applied to each ring is likely to be more successful than the earlier lamp design approaches. An important issue in such multiring lamp systems is the optimal shaping of the output heat flux profile (HFP) of each ring to provide maximum controllability of the wafer temperature. In this paper we seek to optimize the ring HFP's via the lamp design parameters: ring positions and widths. We start by determining the heat loss profiles over the wafer surface for a variety of temperature setpoints and processing conditions. In order to maintain temperature uniformity across the wafer at a given setpoint, the lamp system should provide a compensating HFP. The total lamp HFP is the sum of the individual ring HFPs weighted by their respective applied powers. The HFP's are, in turn, functionally dependent on the lamp design parameters and this dependence can be measured through a calibration process. Therefore, the resulting optimization problem reduces to determining the lamp design parameters that result in lamp HFP's which best approximates the collection of the wafer heat loss profiles. Our method provides a practical technique for determining the optimal lamp design parameters     

Electroconvulsive shock does not induce c-fos and junB, but TIS1 and TIS8/zif-268, in neonatal rat hippocampus

Insular neurons responsive to baroreceptor challenge have been identified in the rat, but not previously in primates. Characterization of baroreceptor-related neurons was performed in 15 anesthetized monkeys (Macaca fascicularis) using extracellular single-unit recording techniques. 131 units were investigated within the insula and surrounding regions. Based on their responses to phenylephrine hydrochloride (PE) and sodium nitroprusside (SNP), three types of units were distinguished: 35/131 (27%) sympathoexcitatory (SE), 12/131 (9%) sympathoinhibitory (SI) and 84 (64%) null units. More baroreceptive units were found within the insula (38/73, 52%) than in surrounding areas (9/58, 16%) (p < 0.001). Lateralization was indicated with more baroreceptive units being encountered within the right insula (28/44, 64%) than the left (10/29, 34%) (p = 0.02). The majority of the responsive units were located within the dysgranular and granular insula in layers II, III and V/VI. These data suggest that cardiovascular representation may occur in the primate insula as has been shown in other species.     

Technique for suppression of pattern dependence in a semiconductor-optical-amplifier wavelength converter

Wavelength converters that employ cross-gain modulation (XGM) in semiconductor optical amplifiers (SOAs) are limited in bit rate by the amplifier's pattern dependent response. We substantially suppress this pattern dependence by converting the phase modulation at the data transitions to amplitude modulation using a fiber grating filter. We use this technique to obtain error-free wavelength conversion of 10-Gb/s nonreturn-to-zero (NRZ) data using an SOA that showed an error floor at 10/sup -5/ bit-error rate (BER) when used alone.     

Identification of an NAD+ binding site of brain glutamate dehydrogenase isoproteins by photoaffinity labeling

Photoaffinity labeling with [32P]nicotinamide 2-azidoadenosine dinucleotide (2N3NAD+) was used to identify the NAD+ binding site within two types of glutamate dehydrogenase isoproteins (GDH I and GDH II) isolated from bovine brain. In the absence of photolysis, 2N3NAD+ is a substrate for the GDH isoproteins. When the enzymes were covalently modified by photolysis in the presence of saturating amounts of photoprobe, about 50% inhibition of the GDH activities was observed. Photoinsertion of probe was increased by GTP or glutarate and decreased by NAD+ or ADP. With the combination of immobilized boronate affinity chromatography and reversed-phase HPLC, photolabel-containing peptides generated with trypsin were isolated. This identified a portion of the adenine ring binding domain of GDH isoproteins as the region containing the sequence, CIAVGXSDGSIWNPDGIDPK for both GDH isoproteins, corresponding to Cys270 through Lys289 of the amino acid sequence of well known bovine liver GDH. The X indicates a position for which no phenylthiohydantoin-derivative could be assigned. The missing residue, however, can be designated as a photolabeled glutamate since the sequences including the glutamate residue in question have a complete identity with those of the other GDH species known. Photolabeling of these peptides was prevented by the presence of NAD+ during photolysis. These results demonstrate selectivity of the photoprobe for the NAD+ binding site and suggest that the peptide identified using the photoprobe is located in the NAD+ binding domain of the brain GDH isoproteins. Both amino acid sequencing and compositional analysis identified Glu275 as the site of photoinsertion.     

Extension of the boundary element method to systems with conductorsand piece-wise constant dielectrics

Accurate modeling of electric fields is necessary to study the dynamics of microelectromechanical systems (MEMS). Typical microelectromechanical systems use high dielectric-constant materials, however, which significantly affect the electric field. Many numerical packages use the finite element method (FEM) to deal with systems with dielectrics. The FEM is not, however, very efficient in modeling microelectromechanical systems. There exist numerical packages that use the boundary element method (BEM), which is more desirable due to its low computational cost. But the BEM as it exists cannot model the effects of the dielectrics. This paper extends the BEM to systems with piece-wise constant dielectrics as well as conductors