Tunable superlattice p-i-n photodetectors: characteristics, theory,and application

Extended measurements and theory on the recently developed monolithic wavelength demultiplexer consisting of voltage-tunable superlattice p-i-n photodetectors in a waveguide confirmation are discussed. It is shown that the device is able to demultiplex and detect two optical signals with a wavelength separation of 20 nm directly into different electrical channels at a data rate of 1 Gb/s and with a crosstalk attenuation varying between 20 and 28 dB, depending on the polarization. The minimum acceptable crosstalk attenuation at a data rate of 100 Mb/s is determined to be 10 dB. The feasibility of using the device as a polarization angle sensor for linearly polarized light is also demonstrated. A theory for the emission of photogenerated carriers out of the quantum wells is included, since this is potentially a speed limiting mechanism in these detectors. It is shown that a theory of thermally assisted tunneling by polar optical phonon interaction is able to predict emission times consistent with the observed temporal response     

Noise in digital dynamic CMOS circuits

Dynamic logic is an attractive circuit technique giving reduced area and increased speed for CMOS circuits. Static logic has a major advantage: its superior noise margins. To be able to choose between a static and a dynamic implementation of a design, we need to know the requirements for dynamic logic. Here we try to identify possible errors, estimate the limits and discuss some possible solutions when considering noise in dynamic circuits     

Inhibition of phosphatases and increased Ca2+ channel activity by inositol hexakisphosphate

Inositol hexakisphosphate (InsP6), the dominant inositol phosphate in insulin-secreting pancreatic beta cells, inhibited the serine-threonine protein phosphatases type 1, type 2A, and type 3 in a concentration-dependent manner. The activity of voltage-gated L-type calcium channels is increased in cells treated with inhibitors of serine-threonine protein phosphatases. Thus, the increased calcium channel activity obtained in the presence of InsP6 might result from the inhibition of phosphatase activity. Glucose elicited a transient increase in InsP6 concentration, which indicates that this inositol polyphosphate may modulate calcium influx over the plasma membrane and serve as a signal in the pancreatic beta cell stimulus-secretion coupling.     

Cone b-wave implicit time as an early predictor of rubeosis in central retinal vein occlusion

PURPOSE: To investigate the predictive value of the cone b-wave implicit time in the 30-Hz flicker electroretinogram for rubeosis in the acute phase of central retinal vein occlusion. METHODS: In a prospective study, 25 patients (25 eyes) with a central retinal vein occlusion of less than 14 days' duration were examined with electroretinography and followed up for a minimum of 18 months. RESULTS: The cone b-wave implicit time in the eyes that developed rubeosis (n = 11) was more than 37.1 milliseconds and in the eyes that did not develop rubeosis (n = 14), less than 37 milliseconds (P < .00001). CONCLUSION: The cone b-wave implicit time in the 30-Hz flicker electroretinogram is a good predictor of rubeosis at an early stage in eyes with central retinal vein occlusion.     

Diurnal change of anterior chamber depth in rabbits

It has been shown that there is a circadian rhythm of intraocular pressure and aqueous humor flow in rabbits. It has also been shown that there is a fluctuation in the volume of the aqueous that can be aspirated from the anterior chamber at different times of day. This finding would suggest that the depth and volume of the anterior chamber of this species also undergoes a circadian rhythm. To confirm this hypothesis, we measured by pachometry the anterior chamber depth in 11 adult New Zealand albino rabbits that had been conditioned to light from 6 a.m. to 6 p.m. and to dark from 6 p.m. to 6 a.m. The measurements were performed at noon and at midnight. The anterior chamber was found to be 4% deeper at midnight than at noon (p < 0.001). This finding suggests that the volume of the anterior chamber would be slightly larger at night than during the day in the rabbit eye. We have no explanation for this finding. However, the difference is too small to have an appreciable effect on the measurement of aqueous dynamics or pharmaceutical effects.     

On the finite element analysis of crack and inclusion problems in elastic-plastic materials

A finite element method for treating plane strain, elastic-plastic boundary value problems is described. Constant strain triangular elements are used. The material is assumed to obey the von Mises yield criterion and its associated flow rule. In order to test the accuracy of the method the deformation of a pressurized circular tube is investigated and the results are compared with a finite-difference solution. The applicability of the method to problems involving two different materials is demonstrated for the case of a uniaxially loaded plate containing a circular inclusion. Finally some crack problems are analysed. Special attention is devoted to the case of small scale plasticity.     

Electrochemical and mössbauer investigations of polymeric iron phthalocyanine oxygen electrodes

Polymeric iron phthalocyanine precipitated on activated carbon has been heated to temperatures in the range 200–500° C and the catalytic activity for the electrochemical reduction of oxygen has been investigated. The catalysts were tested in porous, hydrophobic electrodes.Mössbauer spectra have been obtained for the catalyst powders exposed to different heating temperatures.Heat treatment was found to give electrodes with a higher rate of deactivation for the electrochemical reduction. This was particularly the case for heat treatments at temperatures higher than 300°C. An increase in the intensity of a doublet in the Mössbauer spectra corresponding to oxidized iron was obtained for the heat treated samples.This increase of oxidized iron was found to be correlated to the increased rate of deactivation for the electrodes.