Temperature dependence study of two-dimensional electron gas effecton the noise performance of high frequency field effect transistors

We present experimental evidence that the noise figure (NF) and associated gain equal to those achieved with GaAs pseudomorphic high electron mobility transistors (GaAs p-HEMT's) can also be accomplished by ion implanted GaAs metal-semiconductor field-effect transistors (GaAs MESFET's). These measured noise figure results as a function of low temperature for GaAs MESFET's and p-HEMT's clearly suggest that the transport properties of the two-dimensional electron gas in HEMT's and p-HEMT's do not make a significant contribution to the noise reduction at high frequency operation of these devices     

Modern aspects of far-infrared gas lasers

Contents A short survey is presented on the recent development of optically pumped pulsed far-infrared (FIR) or THz gas lasers. This includes the new distributed-feedback (DFB) and helical-feedback (HFB) FIR gas lasers as well as the subnanosecond-single-pulse FIR gas lasers pumped by 50 ns 10 m pulses of hybrid CO₂ lasers truncated within ca. 10 ps at their maximum by a novel ultrafast laser-triggered plasma shutter. These lasers show interesting phenomena such as standard and swept-gain superradiance as well as anticorrelated oscillations of the far-infrared emission and the 10 m pump radiation in the Raman regime. In this context it was discovered that FIR laser gases, e.g., CH₃F, NH₃, D₂O, CH₃CN, can be used successfully as spectral filters in Optical-Free-Induction-Decay 10 m CO₂ laser systems instead of the standard hot CO₂ gas. Finally, the single ultrashort FIR pulses are presently applied to FIR or THz quantumwell detectors and to high-T _c superconductors to gain further information on their exciting and complicated features.

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Aktuelle Aspekte der Ferninfrarot (THz) Gaslaser

Übersicht Aktuelle Probleme und Resultate der Forschung über optisch-gepumpte gepulste Ferninfrarot (FIR)- resp. THz-Gaslaser werden erläutert. Diese betreffen sowohl die neuartigen Distributed Feedback (DFB) und Helical Feedback (HFB) FIR Gaslaser, als auch FIR Gaslaser, die gepumpt werden mit den 50 ns 10 m Pulsen von Hybriden CO₂ Lasern, welche mit neu entwickelten, Lasergesteuerten Plasmaschaltern innerhalb ca. 10 ps im Maximum abgeschnitten werden. Damit erzielt man Subnanosekunden-FIR Einzelpulse. Diese Laser zeigen interessante Phänomene, wie normale und verstärkte Superstrahlung oder antikorrelierte Fluktuationen der FIR Strahlung und 10 m Pumpstrahlung im Raman-Emissionsstadium. In diesem Zusammenhang wurde festgestellt, daß FIR Laser-Gase, z. B. CH₃F, NH₃, D₂O, CH₃CN, erfolgreich als Spektralfilter in Optical-Free-Induction-Decay 10 m CO₂ Lasersystemen das übliche heiße CO₂ Gas ersetzen können. Die einzelnen ultrakurzen FIR-Pulse werden zur Zeit zum Test neuer FIR resp. THz Quantum-Well-Detektoren und zur Untersuchung ihrer Einwirkung auf Hoch-T _c -Supraleiter verwendet.

     

Effects of ozonized water and heat treatment on the papaya fruit epidermis

This study examined the effects of O₃ and hot water treatments on the epidermis of Golden papaya fruit. Heat treatments were applied in a hot water brushing (HWB) system. Papayas were brushed under a pressurized hot water rinse stage at 45, 55 and 65 °C for 60 s. In the HWB treatment, 4 ppm ozone was applied to the papayas for 1 or 2 min. The results show that ozone applications did not affect the fruit's cuticular surface, while heat treatments allowed natural fissures on the fruit epidermis to recover. Several crystalloid forms were identified on the epidermis of the papayas after the heat treatments. The predominant crystalloid forms on papayas are tubular and there is a positive response to temperature; the higher the temperature, the larger and more frequent the tubular crystalloids.     

Observer of the human cardiac sympathetic nerve activity using noncausal blind source separation

We present a novel method for the blind reconstruction of the cardiac sympathetic nerve activity (CSNA) in the low-frequency (LF) band (0.04-0.15 Hz) using only heart rate and arterial blood pressure. The originality of the method consists in the application of blind source separation techniques to obtain an observer of CSNA. We show how this observer can be deduced from a linear model of the cardiovascular system by introduction of the fundamental assumptions about the independence of the cardiac sympathetic an parasympathetic outflow. In cardiovascular applications, the reliability of the observer has been assessed by verification of the fundamental assumption for the given data. A primer qualitative validation has been performed using the muscle sympathetic nerve activity as an indirect indicator of CSNA. Very satisfying and promising results have been obtained. Moreover, we have performed quantitative validations of the observer in various experimental conditions known to elicit selectively cardiac sympathetic or parasympathetic response. The experimental conditions include a supine-to-60 degrees tilt test, indirect sympathetic stimulation/inhibition by medication, and sympathetic stimulation by isometric handgrip. We show that the observer allows to highlight changing levels of the cardiac sympathetic activity in the LF band in all these experimental conditions.     

Effects of interleukin-1 receptor antagonist in a slow-release hylan vehicle on rat type II collagen arthritis

PURPOSE: To determine the effect of hylan fluid (HA), a model slow release vehicle on the pharmacokinetic profile and efficacy of interleukin-1 receptor antagonist (IL-1ra) in rats with established type II collagen arthritis. METHODS: Female Lewis rats with type II collagen arthritis were treated daily, every other day or every third day with single subcutaneous (sc) injections of IL-1ra formulated in HA and the effects on arthritis determined. Results were compared to those obtained with IL-1ra in citrate buffered saline with EDTA and polysorbate (CSEP). Sequential blood levels were determined in rats injected sc with IL-1ra in CSEP or HA. RESULTS: Incorporation into HA led to slower release of IL-1ra into the bloodstream and maintained therapeutic blood levels of IL-1ra for a longer time compared to the IL-1ra/CSEP formulation. Single daily sc doses of 100 mg/kg IL-1ra in CSEP were ineffective in type II collagen arthritis. By contrast, once per day dosing of 100 mg/kg IL-1ra in HA provided 78% inhibition of paw swelling. Every other day dosing with 100 mg/kg IL-1ra in HA resulted in 62% inhibition. IL-1ra (100 mg/ kg in HA) given every third day provided 19% inhibition of arthritis. Improved efficacy correlated with improved pharmacokinetics. CONCLUSIONS: Administration of IL-1ra in the slow release vehicle HA improves pharmacokinetics and efficacy in rat type II collagen arthritis.     

A plasma shutter for far-infrared laser radiation

A new type of a plasma shutter for far-infrared (FIR) laser radiation is presented. This plasma shutter blocks a FIR laser beam within 0.7 ns by a rapidly expanding plasma. This device has been applied to produce FIR pulses with variable duration between 10 and 100 ns and to select 1-ns FIR pulses from a pulse train     

Fiber loop ringdown for physical sensor development: pressure sensor

A new method of developing optical fiber pressure sensors by use of a fiber loop ringdown scheme is described. The fiber loop ringdown system is characterized in terms of the ringdown baseline stability, fiber transmission loss, and fiber refractive index. The overall sensor performance is demonstrated by use of sensing forces applied to the sensor head. The current device can sense pressures in the range of 0 to 9.8 x 10(6) Pa, converted approximately from the applied forces. The sensor's linear response, repeatability, detection sensitivity, measuring dynamic range, and temperature tolerance are explored.     

Measurements of cavity ringdown spectroscopy of acetone in the ultraviolet and near-infrared spectral regions: potential for development of a breath analyzer

We report a study on the cavity ringdown spectroscopy of acetone in both the ultraviolet (UV) and the near-infrared (NIR) spectral regions to explore the potential for development of a breath analyzer for disease diagnostics. The ringdown spectrum of acetone in the UV (282.4-285.0 nm) region is recorded and the spectrum is in good agreement with those obtained by other spectral techniques reported in the literature. The absorption cross-section of the C-H stretching overtone of acetone in the NIR (1632.7-1672.2 nm) is reported for the first time and the maximum absorption cross-section located at 1666.7 nm is 1.2 x 10(-21) cm(2). A novel, compact, atmospheric cavity with a cavity length of 10 cm has been constructed and implemented to investigate the technical feasibility of the potential instrument size, optical configuration, and detection sensitivity. The detection limit of such a mini cavity employing ringdown mirrors of reflectivity of 99.85% at 266 nm, where acetone has the strongest absorption, is approximately 1.5 ppmv based on the standard 3 criteria. No real breath gas samples are used in the present study. Discussions on the detection sensitivity and background spectral interferences for the instrument development are presented. This study demonstrates the potential of developing a portable, sensitive breath analyzer for medical applications using the cavity ringdown spectral technique.