Transient simulation of heterojunction photodiodes-part II:analysis of resonant cavity enhanced photodetectors

The high-speed response properties of resonant cavity enhanced (RCE) photodetectors have been investigated. The limitations on the high-speed performance of photodiodes and the advantages of RCE-detection are discussed. Transient response of heterojunction photodiodes under pulsed optical illumination has been simulated using the method described in Part I. Results on conventional AlGaAs/GaAs and RCE GaAs/InGaAs heterojunction p-i-n photodiodes are presented. For small area detectors, almost 50% bandwidth improvement along with a two-fold increase in efficiency is predicted for RCE devices over optimized conventional photodiodes. A nearly three-fold enhancement in the bandwidth-efficiency product was shown     

Comparison between real and power optimisation methods for arrayssynthesis of antennas

The authors compare real and power far field patterns synthesis arrays. The synthesised pattern is an optimum approximation to the prescribed power pattern in a minmax sense. A comparison between real and power formulations is realised for shaped (cosecante) and pencil beams     

A capacitive threshold-logic gate

A dense and fast threshold-logic gate with a very high fan-in capacity is described. The gate performs sum-of-product and thresholding operations in an architecture comprising a poly-to-poly capacitor array and an inverter chain. The Boolean function performed by the gate is soft programmable. This is accomplished by adjusting the threshold with a dc voltage. Essentially, the operation is dynamic and thus, requires periodic reset. However, the gate can evaluate multiple input vectors in between two successive reset phases because evaluation is nondestructive. Asynchronous operation is, therefore, possible. The paper presents an electrical analysis of the gate, identifies its limitations, and describes a test chip containing four different gates of fan-in 30, 62, 127, and 255. Experimental results confirming proper functionality in all these gates are given, and applications in arithmetic and logic function blocks are described     

Theory of a multiply fed and loaded insulated linear antenna in air

Analytic expressions are derived for the input admittance and the current distribution along the multiply fed and loaded insulated antenna in air which is excited across feed gaps of nonzero widths. The Wiener-Hopf type analysis for a center fed insulated antenna is combined with the axial field discontinuity (AFD) method to develop the current and admittance expression. This AFD method considers the metallic surface of the linear antenna as a series combination of longitudinal, electric-field surface functions that exist due to feeding and/or loading. The analysis, which does not employ superposition of even and odd distributions of sources and loads, yields final expressions in terms of the excitation location, its aperture electric field within the feed gaps, impedance locations, and their values. The current distribution for cases of unity dielectric constant shows an excellent agreement with data based on the moment method. The input admittances and current distributions are reported for different multiple excitations and loads and dielectric constants of the insulator     

Acute bilateral amaurosis in sphenoid empyema caused by Streptococcus pneumoniae

PATIENT: A 14-year-old boy suffered from an acute bilateral blindness which occurred in 24-h time, accompanied by headache and raised temperature, with inconspicuous optic nerve head and fundus. After diagnosis of empyema with magnet resonance tomography (MRT) the sphenoid sinus was fenestrated and streptococcus pneumoniae isolated. Liquor and serology being inconspicuous, there was no evidence of leucaemic or autoimmune disease, intoxication or intracranial tumor. CLINICAL COURSE: The condition of the patient improved under systemic antibiotic therapy. The bilateral amaurosis remained and opticus atrophy developed. CONCLUSION: A bilateral amaurosis with descending opticus atrophy as a consequence of a sphenoiditis and spreading inflammation to the meninges and the optic nerve in the area of the chiasm is a rare event. The imaging technique of the MRT offers new opportunities for an early and more pointed diagnosis and therapy.     

InSb,GaSb, and GaInSb grown using trisdimethylaminoantimony

GalnSb alloys as well as the constituent binaries InSb and GaSb have been grown by organometallic vapor phase epitaxy using the new antimony precursor trisdimethylaminoantimony (TDMASb) combined with conventional group III precursors trimethylindium (TMIn) and trimethylgallium (TMGa). InSb layers were grown at temperatures between 275 and 425°C. The low values of V/III ratio required to obtain good morphologies at the lowest temperatures indicate that the pyrolysis temperature is low for TDMASb. In fact, at the lowest temperatures, the InSb growth efficiency is higher than for other antimony precursors, indicating the TDMASb pyrolysis products assist with TMIn pyrolysis. A similar, but less pronounced trend is observed for GaSb growth at temperatures of less than 500°C. No excess carbon contamination is observed for either the InSb or GaSb layers. Ga_1-xIn_xSb layers with excellent morphologies with values of x between 0 and 0.5 were grown on GaSb substrates without the use of graded layers. The growth temperature was 525°C and the values of V/III ratio, optimized for each value of x, ranged between 1.25 and 1.38. Strong photoluminescence (PL) was observed for values of x of less than 0.3, with values of halfwidth ranging from 13 to 16 meV, somewhat smaller than previous reports for layers grown using conventional precursors without the use of graded layers at the interface. The PL intensity was observed to decrease significantly for higher values of x. The PL peak energies were found to track the band gap energy; thus, the luminescence is due to band edge processes. The layers were all p-type with carrier concentrations of approximately 10¹⁷ cm³. Transmission electron diffraction studies indicate that the Ga_0.5In_0.5 Sb layers are ordered. Two variants of the Cu-Pt structure are observed with nearly the same diffracted intensities. This is the first report of ordering in GalnSb alloys.     

Neonatal hyperthyroidism caused by TSH receptor antibodies in maternal autoimmune hyperthyroidism

Between July 1993 and December 1994 five term infants of mothers with Graves' disease were hospitalised at the Frühgeburtenstation of the Univ.-Frauenklinik Graz. Four Mothers had elevated TSH-receptor-antibody (TRAb)--levels during pregnancy, one had normalised TRAb-titers. In one case hyperthyroidism was first diagnosed during pregnancy. Three newborns had elevated TRAb-titers; in one of them thyrotoxicosis was diagnosed clinically and biochemically at the second day of life, one newborn had mild hyperthyroidism with tachycardia at the end of the first week of life and one newborn was asymptomatic by immediately initiated therapy. The two other newborns had normal thyroid hormone and antibody levels and no symptoms or signs of hyperthyroidism. The cases are reported and discussed in detail and our overall approach to diagnosis and treatment of neonatal hyperthyroidism in case of maternal Graves' disease will be given.     

A long-term follow-up study of patients with ischaemic heart disease versus patients with nonspecific chest pain

Ninety consecutive patients who were admitted to hospital with acute chest pain were followed-up five years later. At the time of the original admission, all of the patients received a detailed physical and psychiatric evaluation. Seventy-one patients were diagnosed as having ischaemic heart disease, and 19 were diagnosed as having nonspecific chest pain. Patients with nonspecific pain were younger, consumed greater amounts of alcohol, smoked more than their organic counterparts, and were more likely to suffer from psychiatric disorder. The five-year assessment was carried out using a self-report questionnaire. Of the original 71 patients with ischaemic heart disease, 14 had died; 43 questionnaires were returned, 80.2% of the original sample. Sixteen (84.9%) of the patients with nonspecific pain were followed up; none had died. Both groups were predominantly male. The patients with nonspecific pain still smoked more than the patients with ischaemic heart disease, and they had significantly more symptoms of anxiety. The overall prevalence of psychiatric morbidity remained high, however, in both groups. Patients who had psychiatric illness at the time of the original assessment were more anxious at follow-up and more likely to complain of chest pain than those who had been well. Patients with nonspecific chest pain continued to seek treatment on a regular basis from their general practitioners either for chest pain or for other symptoms, but few were in frequent contact with hospital services. The possible preventive effects of psychiatric intervention at an earlier stage in both groups of patients needs to be investigated.     

Kinetics of saturation of liquid metal flow with gases

An analysis of the kinetics of gas dissolution in a liquid metal flow is performed. It is shown that due to a high pouring rate and specific surface of the flow, the flow in the arc of molten filler metal, as distinct from the flow of liquid metal during its pouring, leads to intense saturation of the melt with gas.Volgograd Branch of the Novocherkassk Polytechnic Institute. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 4, pp. 414–420, April, 1993.