Design considerations for tunnel diode non-linear transmission lines

A tunnel diode non-linear transmission line has been investigated for second and third harmonic generation purposes. Design criteria are given and performance predictions have been obtained simulating the single diode behavior by means of a polynomial expression. An optimization of the non-linear transmission line as a harmonic generator has been obtained as a function of the number of diodes, their separation distances and the bias voltage.     

Enhanced decompositions of some cyano complexes during diode array spectrophotometric measurements

Acidic solutions of the Fe(III), Mo(V), W(V) and Mn(IV) cyano complexes are known to decompose photochemically. These reactions do not take place to an appreciable extent when the cyano complexes are subjected to spectrophotometric measurements by means of conventional spectrophotometers, but they do take place when diode array spectrophotometers are used. The reactions are autoaccelerated, at least in the cases of Mo(V), W(V) and Mn(IV), and consist of photoinduced reductions of the metal ion. This effect should be taken into account in all cases where the measured signal has to be used for quantitative purposes, but its significance must be emphasized mainly in the field of kinetic analysis, where it can lead to large errors. The extent of these reactions, and therefore the size of the errors, can be lowered by using UV cut-off filters and by taking discontinuous measurements with suitable integration times. All these possibilities, which are of general application, are discussed.     

HPLC determination of carminic acid in foodstuffs and beverages using diode array and fluorescence detection

Summary Carmine extracted from cochineal insects is one of the most used natural colorings for beverages and other foods. Its active ingredient is carminic acid (7-β-D-glucopyranosyl-9,10-dihydro-3,5,6,8-tetrahydroxy-1-methyl-9,10-dioxo-2-anthracenecarboxylic acid). This work describes a rapid HPLC determination of carminic acid and compares diode array and fluorescence detections for quantification. Samples with higher protein levels, such as milk and yogurt, are first treated with 1 mL of 8 M NH₄OH (5 min), the pH is reduced to 2 with 6 M HCl before centrifugation, the supernatant is then filtered and injected into the chromatograph. Low protein samples are simply filtered before injection. The separations were performed with a LiChroCART RP18 column using a mixture of acetonitrile and formic acid as mobile phase. The optimized conditions permit baseline quantification of the carminic acid even in the presence of other coloring agents. The sampling and analytical procedures are considerably faster than those of the literature and present excellent recuperation, selectivity, accuracy and precision. The method was applied to analysis of several yogurts and beverages. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Photo-acoustic measurements of gas and aerosol absorption with diode lasers

The results of designing multipurpose high-sensitive photo-acoustic (PA) detectors and their application to high-resolution diode laser spectroscopy of molecular gases, gas analysis, and aerosol absorption measurements are summarized in this paper. The hardware and software of the diode laser spectrometer with a Helmholtz resonant PA detector providing an absorption sensitivity limit of better than 10(-7)Wm(-1)Hz(-1/2) are described. A procedure is proposed for an experiment involving the measurements of the rotational structure of hot vibrational bands of molecules. The results of the application of the nonresonant PA cell with temporal resolution of signals to measurements of weak nonresonant absorption of gases and soot aerosols are presented, and the possibility of creating a broad-band PA laser diode aerosol-meter is discussed.     

The UCB/MPE cassegrain submillimeter heterodyne spectrometer

The UCB/MPE Submillimeter Heterodyne Spectrometer is a system for ascronomical spectroscopy in the high-frequency atmospheric windows from 500 to 1000 GHz. It contains a molecular laser local oscillator, a cooled Schottky open structure mixer, a quasi-optical coupling system, and an acousto-optical spectrometer. The compact receiver mounts at the Cassegrain focus of large infrared astronomical telescopes. The receiver noise temperature on the telescope is approximately 3500 K (DSB) during observations of the CO J=76 line at 806.652 GHz. The spectrometer's frequency resolution and instantaneous bandwidth (<2 MHz resolution across 1.1 GHz) are well suited for observations of molecular emission lines from a variety of astronomical sources.     

Utilisation of liquid chromatography in aquatic photodegradation studies of pesticides: A comparison between distilled water and seawater

Summary The advantages of liquid chromatography with diode array and mass spectrometric detection are described for the direct characterization of the photodegradation products of Fenitrothion, Atrazine and Diuron in distilled water and artifical seawater samples. The photodegradation (UV >290 nm) of the herbicides Atrazine and Diuron was examined in distilled water and in artificial seawater containing humic acids. Major photodegradation products were hydroxyatrazine and Monuron, respectively. The results showed a faster degradation in seawater as compared to distilled water for Atrazine whereas for Diuron a quenching effect was observed thus retarding photodegradation. The photodegradation of Fenitrothion was also investigated. For this pesticide, hydrolysis predominates in seawater and photolysis is very slow in distilled water, so that acetone was needed as photosensitizer.Presented at the 5th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region, Blanes, Spain, 2–6 October, 1989.     

Determination of organic colorants in cosmetic products by high-performance liquid chromatography

Summary High-performance liquid chromatography (HPLC) with UV-vis detection was used for the determination of organic colorants in cosmetic products. 126 colorants were characterized by their retention times in an ion-pair reversed-phase HPLC system with gradient elution, and by their UV-vis spectra, recorded with a diode array detector (DAD). The method is rapid and efficient, as is demonstrated by the analysis of 45 cosmetic samples.     

Low energy electron beam irradiator using sprayed double walled carbon nanotubes

We fabricated a prototype of an e-beam irradiator which is low energy and diode type by using sprayed double walled carbon nanotubes (DWCNTs). The diode type e-beam irradiator consisted of a grounded e-beam window which was made of thin Havar foil and a negatively charged cathode where carbon nanotubes were sprayed on titanium coated aluminum rod. Synthesized DWCNTs which were purified through the chemical processes and then mixed with ethanol were sprayed several hundred times on the surface area of 2×300 mm². A phosphor screen located on the e-beam window and a CCD camera was used to observe the emitted electron beams directly from the cathode to the air with an increase of the voltage. The measured e-beam current was 1.5 mA at −95 kV.     

A novel device fabricated with Cu2NiSnS4chalcogenide: Morphological and temperature-dependent electrical characterizations

Cu₂NiSnS₄ nanorods were synthesized by the usage of hot-injection technique and used as interlayer between the p-Si and Al metal in order to examine their behavior against the temperature and frequency changes. The current-voltage measurements were performed in 80–300 K temperature range with 20 K steps. The X-Ray Diffraction (XRD) was used to prove the crystal structure of the synthesized Cu₂NiSnS₄ nanorods. Some crucial device parameters such as barrier height, series resistance and ideality factor values were calculated, and the obtained values were compared with other studies in the literature. It has been seen that the calculated parameters of the prepared device are strongly dependent on temperature changes. Besides, the capacitor behavior of fabricated device was investigated depending on the frequency and voltage changes. The experimental results indicated that the prepared device with Cu₂NiSnS₄ nanorods interlayer could be utilized in the electronic technology, especially applications in wide temperature range.