Stimulus orientation and contrast constancy

The human visual system requires less contrast to detect patterns oriented vertically or horizontally than those oriented obliquely. We investigated whether this orientational anisotropy persists at suprathreshold contrasts. Using a contrast-matching technique, we found that it disappears at contrasts just above threshold, given the stimulus conditions employed. These results suggest that a neural mechanism, at suprathreshold, adjusts the gain of orientational subsystems to compensate for the lower sensitivity of the visual system to oblique patterns. A similar suprathreshold effect, referred to as contrast constancy, has been observed in studies employing grating patterns varying in spatial and temporal frequency. We argue, based on previous electrophysiological findings, that this neural compensation results from antagonism between excitatory and inhibitory processes in the visual cortex.     

Psoriasis and bullous pemphigoid treated with azathioprine

1. Alanine accumulation in rat hemidiaphragms is significantly inhibited by capsaicin in a dose-dependent pattern that produced maximal effect at 1 mM. 2. The inhibitory effect of capsaicin on alanine accumulation by rat hemidiaphragms was enhanced upon preincubation with 5 mM ouabain. However, preincubation with 1 mM Verapamil did not alter the inhibitory effect of capsaicin. 3. Chemical ablation of the capsaicin-sensitive primary afferent fibers abolished the inhibitory effect of capsaicin on alanine accumulation in the rat hemidiaphragms.     

2-4 GHz monolithic lateral p-i-n photodetector and MESFET amplifieron GaAs-on-Si

The design, fabrication, and evaluation of broadband lateral p-i-n photodetectors monolithically integrated with multistage MESFET amplifiers on GaAs-on-Si are described. Unique features of this approach are that (a) the lateral p-i-n structure is compatible with monolithic microwave integrated circuit (MMIC) technology and (b) the p-i-n detector is fabricated directly on the GaAs buffer layer without p⁺ and n⁺ implants, thus resulting in a simplified fabrication process. The operation of the circuit is compared to that of a similar circuit fabricated on a GaAs substrate. A quantum efficiency exceeding 60% has been measured for the p-i-n detectors. The 2- to 4-GHz frequency responses of one- and two-stage p-i-n/FET preamplifiers are presented. The response varies ±3 dB over the frequency band     

High-efficiency GaAs m.e.s.f.e.t. amplifiers

High-efficiency c.w. amplification with GaAs m.e.s.f.e.t.s under class-B conditions has been demonstrated. Power added efficiencies as high as 68% at 4 GHz and 41% at 8 GHz have been achieved. Two-tone tests were carried out at 4 GHz. The power added efficiencies at the 3rd-order intermodulation levels of ?20, ?25 and ?30 dB were 49, 40 and 35% respectively.     

7.9?8.4 GHz GaAs m.e.s.f.e.t. amplifier

A 4-stage balanced GaAs m.e.s.f.e.t. amplifier has been developed for the 7.9?8.4 GHz satellite-communication frequency band. Linear gain of 26±0.5dB and 150 mW power at 1 dB compression were obtained across the design band. The small-signal gain, phase linearity, group delay and noise figure are described as a function of frequency. Large-signal gain saturation, 3rd-order intermodulation distortion, gain and phase against temperature and a.m.-to-p.m. conversion data are also presented.     

Fine-needle aspiration technique for the concurrent immunocytochemical evaluation of multiple biologic parameters in primary breast carcinoma

Fine-needle aspiration cytology has been already established as a reliable method for the diagnosis of breast cancer. Its application has been recently extended to immunocytochemical analysis of biological parameters. In the current study estrogen and progesterone receptors, Ki67 growth fraction, and p53 protein expression were immunocytochemically evaluated on the cellular material sampled by the same fine-needle aspirate used for the conventional cytologic diagnosis of malignancy. Fine-needle aspiration specimens from 100 patients with primary breast carcinoma were submitted to the immunocytochemical analysis. Twenty-eight percent were in premenopause; 23% had tumors with a diameter less than 2 cm, 59% from 2 to 5 cm, and 18% more than 5 cm; 60% had axillary nodal status negative, 34% positive, and 6% unknown. The concomitant immunocytochemical evaluation of all parameters was possible in 70% of the patients. A significant association was found between p53 overexpression and Ki67 values (p = 0.004), and between Ki67 values and progesterone receptor status (p = 0.003). No correlation was found between any parameter and clinical tumor size. Estrogen (p = 0.02) and progesterone (p = 0.04) receptor negativity and high Ki67 growth fraction (p = 0.005) were significantly associated with the clinical evidence of axillary node involvement. This study suggests that fine-needle aspiration cytology represents an effective practice for a simultaneous evaluation of multiple biologic indicators and could be useful as a preoperative procedure in patients who are candidates for neoadjuvant chemotherapy and/or endocrine therapy.     

Medium-power GaAs field-effect transistors

Results on medium-power GaAs m.e.s.f.e.t.s. are described. Output powers as high as 300 mW at 9 GHz at 1 dB gain compression with a linear gain of 5.2 dB and drain efficiency of 30% have been obtained with single-cell m.e.s.f.e.t.s. At 4 GHz, a power output of 665 mW at 1 dB gain compression, a linear gain of 8 dB and a drain efficiency of 44.5% were realised with a 3-cell m.e.s.f.e.t. Two-tone intermodulation characteristics at 4 GHz are also described. A major innovation has been the use of a high-resistivity chromium-doped epitaxial GaAs buffer layer to isolate the device active region from the bulk-grown substrate.     

GaAs m.e.s.f.e.t. linear power-amplifier stage giving 1 W

A balanced GaAs m.e.s.f.e.t. power stage has been developed for the 7?8 GHz satellite communication frequency band. At 7.5 GHz, the output power at 1 dB comparession 1 W with a power added efficiency of 37%. The small-signal gain was 6.65 ± 0.45 dB across the frequency band. The small-signal gain, phase, group delay and input and output v.s.w.r. as function of frequency are described. Large-signal gain saturation and 3rd-order intermodulation distrotion measurements are also presented.