New generalized computations of quasi-planar waveguides characteristics

An efficient hybrid field solution to the general multilayer substrates transmission line problems with full shielded and half open cross-sectional geometry is presented by using the waveguide modes coupling and decoupling procedure in the spectral domain. Modal transverse transmission lines corresponding to the LSE and LSM modes are taken into account so that the Green's elements for the edge conditions can be derived by a simple iterative method. In this paper, we analyze not only the propagation constants and characteristic impedances but also the available transmission power capacity and power distribution of most commonly used structures. Normalized eigenmode power levels characterizing the propagation features are computed.     

Simulation thermique d'experiences d'analyse thermique differentielle

The numerical modelling of casting pieces needs a knowledge of the physicochemical features of the alloys (cast iron, superalloys): enthalpic release versus temperature in the solidification range. The use of differential thermal analysis is proposed for estimation of the enthalpic release. The thermal modelling of the DTA cell gives the enthalpic release versus temperature relation. Moreover, the simulation shows that large temperature variations (about 10 °C) occur in the sample during the first stage of solidification, which makes interpretation of the solidification path very difficult.Quenching from different temperatures during DTA experiments was also simulated.

---

Zusammenfassung Die numerische Modellierung von Gußstücken erfordert die Kenntnis physikalisch-chemischer Kennwerte der Legierungen (Gußeisen, Superlegierungen), nämlich der Enthalpieänderung in Abhängigkeit von der Temperatur im Erstarrungsbereich. Die DTA-Methode wird zur Bestimmung der Enthalpieänderung in Vorschlag gebracht. Die thermische Modellierung der DTA-Zelle schließt die Temperaturabhängigkeit der Enthalpieänderung in sich ein. Darüber hinaus ergibt die Simulierung, daß große Temperaturänderungen (etwa 10°) in der Probe während des ersten Stadiums der Erstarrung auftreten, die die Interpretation des Erstarrungsvorganges erschweren. Abschrecken bei verschiedenen Temperaturen wurde in den DTA-Experimenten ebenfalls simuliert.

---

- ( , ), . . . , , ( 10 °C). . .

     

Reduction of iodine by hydroxylamine within the pH range 0.7–3.5

The reduction of iodine by hydroxylamine within the [H⁺] range 3×10⁻¹–3×10⁻⁴ mol.L⁻¹ was first studied until completion of the reaction. In most cases, the concentration of iodine decreased monotonically. However, within a narrow range of reagent concentrations ([NH₃OH⁺]₀/[I₂]₀ ratio below 15, [H⁺] around 0.1 mol.L⁻¹, and ionic strength around 0.1 mol.L⁻¹), the [I₂] and [I₃⁻] vs. time curves showed 2 and 3 extrema, respectively. This peculiar phenomenon is discussed using a 4 reaction scheme (I₂+I⁻⇔︁I₃⁻, 2 I₂+NH₃OH⁺+H₂O→HNO₂+4 I⁻+5 H⁺, NH₃OH⁺+HNO₂→N₂O+2 H₂O+H⁺, and 2 HNO₂+2 I⁻+2 H⁺→2 NO+I₂+2 H₂O). In a flow reactor, sustained oscillations in redox potential were recorded with an extremely long period (around 24 h). The kinetics of the reaction was then investigated in the starting conditions. The proposed rate equation points out a reinforcement of the inhibition by hydrogen ions when [H⁺] is above 4×10⁻² mol.L⁻¹ at 25°C. A mechanism based on ion-transfer reactions is postulated. It involves both NH₂OH and NH₃OH⁺ as the reducing reactive species. The additional rate suppression by H⁺ at low pH would be connected to the existence of H₂OI⁺ in the reactive medium. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 785–797, 1998     

Beneficial use of a cell coupling rheometry, conductimetry, and calorimetry to investigate the early age hydration of calcium sulfoaluminate cement

A specific cell was designed to monitor simultaneously the evolution of the viscoelastic properties, electrical conductivity, and temperature of a cement paste with ongoing hydration. Hydration of calcium sulfoaluminate cement by demineralised water or by a borated solution was then investigated as an example. Borate anions acted as set retarders but to a smaller extent than with ordinary Portland cement. The delay in cement hydration resulted from the precipitation of an amorphous or poorly crystallized calcium borate, which also caused a rapid stiffening (and thus a loss of workability) of the paste after mixing. The gypsum content of the CSA cement was shown to play a key role in the control of the cement reactivity.     

Solid-Phase Extraction,Clean-pp and Liquid Chromatography for Routine Multiresidue Analysis of Neutral and Acidic pesticides In Natural Waters in One Run

Abstract

Solid-phase extraction using C₁₈ silica cartridges, liquid chromatography analysis and UV diode array detection were investigated for the routine trace-level determination of neutral pesticides over a wide range of polarity. Detection limits below the 0.1 μg/1 range were easily obtained in drinking water. If neutral and acidic pesticides over a wide range of polarity have to be determined in the same run, samples have to be acidified to obtain good recoveries of extraction. The effect of the sample matrix was studied and detection limits in the 0.1 μg/1 range were obtained in drinking water except for the more polar ones which are in the interfering peak of humic and fulvic acids. For surface water, a clean-up step using a Florisil cartridge has to be included in the procedure that allows detection limits in the range 0.05–0.3 μg/1.