Millimeter-wave generation and digital modulation in an InGaAs-InPheterojunction phototransistor: model and experimental characterizationof dynamics and noise

This paper describes the use of an InGaAs-InP photoheterojunction bipolar transistor (photo-HBT) for millimeter-wave generation and digital modulation. Optical mixing of two coherent signals generates the carrier, and a digital drive signal to the base is used for the modulation. We describe an advanced large signal model of the photo-HBT that takes into account distributed effects at high frequencies and all noise sources, including optical amplifier noise and noise correlations due to the high operation frequency and the nonlinear mixing processes. The model enables one to predict carrier-to-noise ratio dependence on frequency, optical power, and the transistor operating point. Frequency- and time-domain responses of the modulated millimeter- wave carrier and bit error rates are also calculated. Experiments at 10 and 45 GHz with modulation rates ranging between 50 Mb/s and 2.5 Gb/s were performed, and a superb fit to the calculated responses is found     

消除运算放大器的意外正反馈

由运算放大器构成的反馈系统常用于使系统保持稳定。但是在一些情况下也有意外发生。比如太阳能船的玩具,当有时打开开关时,玩具甚至会发出“噗噗”的声响。这种情况有可能是由于运算放大器发生了意外正反馈（inadvertent positive feedback）导致的。     

Phase Equilibria in the Systems CaO–CuO and CaO-Bi2O3

New data are presented on the phase equilibria of the binary systems CaO-CuO and CaO-Bi₂O₃. Corrected compositions are reported for Ca.Bi₆O₁₃ and Ca₂Bi₂O₅ and a new metastable high-temperature phase is reported for a composition near Ca₆Bi₇O_16.5. The composition and decomposition temperatures for Ca_1–x.CuO₂ are given for both air and 1 atm of oxygen at 755 ± 5° and 835 ± 5°C, respectively.     

HBT optoelectronic mixer at microwave frequencies: modeling andexperimental characterization

A heterojunction bipolar transistor (HBT) optoelectronic mixer was studied experimentally and theoretically. A detailed large signal π-model and a small signal analysis are described. The frequency dependence of down and up conversion has been analyzed and measured. In terms of conversion gain, the advantage of the down conversion process is clearly demonstrated. The values of parameters employed in the mixing process are also discussed for both large and small signal regimes     

Electrophysiological evidence of developmental changes in the duration of auditory sensory memory

In behavioral studies, children's memory for tonal frequency has been found to persist for less time than adults' (T. A. Keller & N. Cowan, 1994). The present study was done to evaluate the argument that this effect is due to changes in auditory sensory memory and not to attentional mechanisms. This question was investigated using mismatch negativity (MMN), an auditory event-related potential considered to be insensitive to attention. Participants were 6-7-, 8-10-, and 11-12-year-old children and adults. They were presented with trains of stimuli, beginning with either a standard (1000 Hz) or a deviant (1200 Hz) tone with trains separated by either 1 s or 8 s. All 4 groups exhibited MMNs after delays of 1 s, but only the adults and oldest children exhibited MMNs after 8 s, indicating that there are maturational changes in the duration of auditory sensory memory.     

46-year-old patient with hemorrhagic diathesis and renal artery aneurysms. Type IV Ehlers-Danlos syndrome

To establish the medium-term results of our transplant population, we retrospectively reviewed the charts of 51 consecutive patients who underwent orthotopic heart transplantation between July 1988 and April 1995. These patients comprised two groups: group A consists of 26 patients (age 6 days to 16.4 years, median 1.4 years) with no previous heart surgery, and group B consists of 25 patients (ages 0.1 to 14.3 years, median 8.3 years), all of whom had heart surgery before undergoing transplantation. There was no difference between these groups in early or late survival rates, and neither age at transplantation nor sex was an indicator of survival. There have been 14 deaths, six early (before hospital discharge) and eight late. Early deaths have predominantly been attributed to long-term ventilation and hemodynamic instability before transplantation, and late deaths to graft coronary artery disease (n = 4), acute coronary vasculitis (n = 3), and acute cellular rejection (n = 1). Although infection has resulted in significant morbidity (57 hospital admissions), there have been no late deaths resulting from infection. Sepsis accounts for four early deaths in chronically ill patients. Orthotopic heart transplantation in the pediatric patient with and without previous heart surgery is a viable option for those with end-stage heart disease and those in whom other surgical options carry a prohibitively high mortality rate.     

The generalized matrix product and its applications

In this paper we develop the notion of a generalized matrix product that includes in its formulation the common matrix and vector products of linear algebra. After defining the generalized matrix product and investigating some of its properties, we provide some specific examples of its use in image processing.