Degre de dissociation de KCl en solutions hydroethanoliques saturees

The degree of dissociation of potassium chloride was estimated in saturated water—ethanol solutions, for the purpose of computing diffusion potentials by means of the Planck and Henderson formulae.

A previous conductance equation, developed by Wishaw and Stokes, is taken into account; it applies to high concentration electrolyte solutions. The limits are discussed and an iterative resolution process is proposed.

The results suggest ion pair association, which becomes predominant in ethanol-rich mixtures.

Zusammenfassung

Man bestimmte den Dissoziationsgrad von Kaliumchlorid in Wasser, um mit Hilfe der Formeln von Planck und Henderson die Diffusionspotentiale zu berechnen. Die Gleichung von Wishaw-Stokes wurde zur Berechnung der Leitfähigkeit hochkonzentrierter Elektrolytlösungen verwendet; ihr Anwendungsgebiet wird diskutiert und ein iteratives Auflösungsverfahren vorgeschlagen. Die Ergebnisse weisen, besonders bei grösseren Aethanolkonzentrationen, auf eine starke Ionenpaarassoziation hin.     

Analog ALC crystal oscillators for high-temperature applications

Fundamental mode and third-harmonic mode integrated high-performance automatic level controlled (ALC) crystal oscillators for high-temperature applications (up to 250°C), are described in this paper. These oscillators were designed for a pressure measurement system in high-temperature environments, where the output signal is the difference between both generated frequencies. Frequency variations smaller than 0.0001 ppm/s for each oscillator and a frequency drift of about 2.5 ppm/year of the frequency difference are the measured performance concerning, respectively, the short-term (1 s) and long-term frequency stability of these integrated high performance crystal oscillators over the 30°C-225°C temperature range. Other important characteristics are the very stable and constant oscillation levels (~1.1 Vpp), the small second-harmonic distortion (~60 dR), and the phase noise (~95 dB at 50 kHz shift). The characteristics of these oscillators make them also suitable for many other measurement systems (time, temperature, and other physical and chemical quantities), especially if they are constrained to operate under severe temperature conditions     

Micromachined microwave planar spiral inductors and transformers

A new micromachined planar spiral inductor, with the strips suspended individually, has been fabricated in standard GaAs high electron-mobility transistor monolithic-microwave integrated-circuit technology through maskless front-side bulk micromachining. The electronic compatibility, the use of industrial integrated-circuit production lines, the straightforward and low-cost additional procedure for structure releasing, and the very short etching time required are the principal features related to such a novel inductor structure. Moreover, the air-gap layer created underneath the device and between the strips significantly reduces shunt and fringing parasitic capacitances, consequently increasing the performance and operating frequency range. Experimental measurements, carried out up to 15 GHz, before and after micromachining, showed for a 12-nH inductor an increase of the maximum Q factor from 5 (at 3 GHz) to about 20 (at 7 GHz), while the self-resonant frequency was shifted from 5 to 13 GHz. Furthermore, a structure with two interleaved spiral inductors, in a 1:1 transformer-like configuration, was also fabricated, and its performance verified in order to demonstrate the promising performance improvements provided by the proposed device. Finally, heating and mechanical characteristics associated with freestanding microstructures are briefly evaluated using finite-element method simulations     

Micromachined planar spiral inductor in standard GaAs HEMT MMICtechnology

A novel free-standing planar spiral inductor with reduced parasitic capacitances is proposed by suspending individually the strips, through a maskless front-side bulk micromachining compatible with a commercial GaAs HEMT monolithic microwave integrated circuit (MMIC) technology. Suspended structures have been fabricated and characterized at frequencies up to 15 GHz, showing quality factors of up to 16 and self-resonant frequency superior to 16 GHz for a 4.8 nH inductor. Moreover, since the standard IC process as well as the unconcerned electronic circuits are not influenced by micromachining, such devices are directly useful to enhance RF circuits, like matching networks, filters, and low-noise amplifiers     

Fabrication and characterization of CdZnTe radiation detectors with a new P-I-N design

We report on the design, fabrication, and performance of CdZnTe gamma-ray detectors with a new P-I-N structure for spectroscopic applications. Highpressure and conventional vertical-Bridgman CdZnTe crystals were used for detector fabrication. P and n layers were deposited by thermal evaporation, and by optimizing the deposition conditions we achieved low leakage current (approximately 15 nA at 1000 V) and good performance. Spectral response data at high bias voltages showed improved energy resolution and peak-to-valley ratios for ²⁴¹Am and ⁵⁷Co compared to metal-semiconductor-metal detectors.     

Growth and characterization of AlxGa1−xAs Bragg reflectors by LP-MOCVD

Using a moderate-sized LP-MOCVD production reactor, we have demonstrated the growth of Bragg reflector structures that reflect nearly 100% of the light at the design wave-length of 850 nm. The designs studied consist of alternating layers of Al_0.10Ga_0.90As and Al_0.85Gao_0.15As, with up to 30 periods. Characterization data show the structures to be highly reproducible and uniform, with good agreement between data obtained by double-crystal x-ray rocking curve analysis, cross-sectional transmission electron microscopy, and optical-reflectance spectroscopy. GaAs solar cells utilizing Bragg reflectors have been fabricated and characterized.     

Post-laparoscopic vomiting in females versus males: comparison of prophylactic antiemetic action of ondansetron versus metoclopramide

PURPOSE: To evaluate the clinical usefulness of the continuous intra-arterial blood gas (CIABG) monitoring system, Paratrend 7, during differential lung ventilation (DLV) in 12 patients undergoing oesophagectomy. METHODS: Anaesthesia was induced with propofol and was maintained with isoflurane, oxygen and air, supplemented by an epidural infusion of mepivacaine. Arterial samples for estimation of blood gases (ABG) were taken just before and 5, 10, 20, 30, 60, and 90 min after the pleura was opened. The pH, PO2, and PCO2 values displayed by the CIABG monitor, which were recorded prior to the arterial blood sampling, were compared with the results of ABG analysis. RESULTS: Eighty-four blood samples were obtained and the ranges for the measured variables were PCO2 24.8-57.4 mmHg, PO2 47-449 mmHg, and pH 7.30-7.49. The correlation between CIABG and ABG measurements was strong and significant (r values: PCO2 0.80, PO2 0.93, pH 0.94). The overall bias +/- precision between the two methods was PCO2 0.9 +/- 3.1 mmHg, PO2 -1 +/- 40 mmHg, %PO2 0.8 +/- 21.6%, pH 0.00 +/- 0.02. For PO2 values < 150 mmHg, the biases +/- precision were PO2 -5 +/- 17 mmHg, %PO2 -2.1 +/- 20.7%. CONCLUSION: The agreement between CIABG and ABG measurements was better for PCO2 and pH than for PO2. Although the CIABG system is clinically useful for monitoring trends in blood gas changes, the accuracy of the PO2 value may be unacceptable during DLV because the error is theoretically < 34 mmHg with 95% reliability in the clinically important range of PO2, < 150 mmHg.