A hybrid-ring directional coupler with modified ring impedances and two compensation stubs

New explicit formulas for calculating the scattering parameters of a modified hybrid-ring directional coupler are presented. It is also shown how port junction discontinuities of real couplers of this type, employed as equiphase antenna dividers, can be effectively compensated by using a pair of short open-circuited transmission line stubs. The efficacy of the proposed approach is illustrated both by theoretical and by experimental results. © 1995 John Wiley & Sons. Inc.     

Organosilicon resin-based carbon/ceramic polygranular composites with improved oxidation resistance

We examined the thermo-mechanical properties of carbon materials modified with silicon oxycarbide (Si-O-C) and silicon carbide (Si-C). These compounds were obtained by the impregnation of carbon components with a silicon-containing polymer resin. Graphite and anthracite powders were used as carbon components, and poly[methyl(phenyl) siloxane] resin (P) was used as the ceramic precursor. Carbon/polymer compositions (C/P) were subjected to two-stage annealing, first to 1,000 °C and next to 2,000 °C in an inert atmosphere, leading to the formation of C/Si-O-C and C/Si-C composite samples, respectively. The materials were then examined under conditions of isothermal oxidation to determine their oxidation resistance and the mechanical properties before and after oxidation tests. The structure of the samples before and after oxidation was studied. C/Si-C composites, despite their high porosity, proved to have enhanced resistance to oxidation at 600 °C, although they had lower mechanical properties in comparison to C/Si-O-C samples.     

Formation of a derivative of aflatoxin B1 on a sephadex column with a 1% aqueous solution of methanol

Summary A partial separation of aflatoxins B₁ and B₂ on a Sephadex column with a 1% aqueous solution of methanol as mobile phase was achieved. The chromatographic system is, however, not neutral for aflatoxin B₁. During elution a derivative-probably aflatoxin B₁. hemiacetalis produced. The derivative forms blue fluorescent spots on Adsorbosil-1 plates with R_f 0.15 when developed in chloroform/acetone (90 + 10).

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Bildung von Umwandlungsprodukten aus Aflatoxin B₁ während der Chromatographie an Sephadex mit 1%iger Lösung von Methanol in Wasser

Zusammenfassung Man erreichte eine teilweise Trennung der Aflatoxine B₁ und B₂ auf der Sephadex Säule mit l % iger Lösung von Methanol in Wasser. Dieses chromatographische System ist jedoch gegen Aflatoxine B₁ nicht neutral. Während der Elution bildet sich ein Derivat, wahrscheinlich Hemiacetal des Aflatoxin B₁. Das Derivat gibt blaue Fluorescenzflecken auf Adsorbosil-1 Platten wenn mit Chloroform/Aceton (90 + 10) entwickelt.

     

Performance of Emulsion Explosives

Some performance of a number of emulsion explosives containing glass micro-baloons were studied experimentally and theoretically. For each of the explosives, detonation velocity was measured and calculated and ballistic mortar tests and cylinder expansion tests were carried out. The results obtained enables a comparison of the usefulness of both testing methods. The influence of some metal nitrates contained in the emulsion matrix on the performance and detonation parameters of the explosives was examined. Key words: explosives, glass micro-balloons, nitrates of metals, detonation parameters, performance.     

Effect of Co content on the catalytic activity of CoSiBEA zeolite in the selective catalytic reduction of NO with ethanol: Nature of the cobalt species

The effect of Co content on the catalytic activity of CoSiBEA zeolites in the selective catalytic reduction (SCR) of NO with ethanol is investigated. The Co_xSiBEA zeolites (x = 0.3, 0.7, 3.6 and 6.75 Co wt.%) are prepared by a two-step postsynthesis method which allows to control the introduction of cobalt into zeolite and thus to obtain catalysts with specific Co sites. The nature of the active sites is characterized by XRD, diffuse reflectance UV–vis, H₂-TPR and XPS.

The catalytic activity of Co_xSiBEA strongly depends on the nature and environment of Co species. Zeolites with isolated lattice tetrahedral Co(II) (Co_0.3SiBEA and Co_0.7SiBEA samples) are active in SCR of NO with ethanol with selectivity toward N₂ exceeding 85% for NO conversion from 20 to 70%. When additional isolated extra-lattice octahedral Co(II) species appear (Co_3.6SiBEA sample), the full oxidation of ethanol by dioxygen becomes a very important reaction pathway. In presence of additional cobalt oxides (Co_6.75SiBEA sample), the activity and selectivity toward N₂ substantially change and full oxidation of ethanol to CO₂ is the main reaction pathway and full NO oxidation also takes place in the temperature range 550–775 K. The lack of correlation between the activity in SCR of NO with ethanol and NO oxidation to NO₂ suggests that the two reactions are more competitive than sequential.     

Partitioning factor of mercury during coal combustion in low capacity domestic heating units

Data from an experiment concerning Hg emission from coal combustion in a furnace of 5.6 kW capacity are presented. The goal of the experiment was to define how much of the mercury in coal combusted in the stove was emitted to the atmosphere in gaseous form because vapors contribute mainly to human intake of the metal from ambient air. The partitioning factor kappa, defined as the ratio of gaseous mercury mass emitted to the air and mercury mass contained in the unit coal mass before combustion was evaluated. The mean value of the kappa factors determined in the study was 0.52 indicating that on average only 52% of the mercury was emitted to the air in gaseous form during coal combustion in an apparatus similar to a domestic furnace. The kappa value determined seems relatively low indicating that besides mercury emitted to the atmosphere in gaseous form, a large portion of the mercury is present in particulate matter trapped in the chimney duct and emitted to the air.     

THE MINIMUM OF TOTAL AVAILABLE ENERGY (ENERGY) DISSIPATION IN THE MULTISTAGE FLUIDIZED WET BEDS

This article represents a second half of the work in optimization of the fluidized drying and moistening processes by the method of dynamic programming. The problem considered in Part I concerns the case of fluidized drying and moistening in the continuous processes for the variable inlet gas temperature. In this work, the generalized aspect of the continuous and multistage adiabatic processes for the case when the decision variables on the stage are gas enthalpy, gas humidity and dry gas flow rate, is considered. The continuous processes are considered here only as a limiting case of the multistage ones.

The two types of the thermodynamic performance indexes based on the idea of energy as a thermodynamic measure of the substance value are considered. The first type is related to the economic costs of production and the second to the overall economic costs. The equivalency of the optimization results for either of the two types of energy costs is discussed- Also, the nature of the optimal trajectories and decisions is considered.     

An Attempt at Enhancing the Regioselective Oxidation of Decane Using Catalysis with Reverse Micelles

Abstract  

The regioselective oxidation of linear alkanes to give terminal oxidation products represents a major challenge for catalysis. A number of previous approaches have shown that confinement and encapsulation can offer an experimentally viable way forward. Against this background we have investigated the use of a system comprising gaseous oxygen, a homogenous catalyst (ammonium metavanadate) confined in an aqueous solution within reverse micelles formed in decane using bis(2-ethylhexyl)sulfosuccinate. At low conversion and at short reaction times we show that the approach does lead to a small enhancement in the selectivity to terminal products, but unsurprisingly the surfactant is more readily oxidised than decane and so the small positive effects of the micellar catalyst system are short-lived.     

The reactivity of titanium–vanadium containing groups in the synthesis of two-component monolayers on silica surfaces

The coating of silica surfaces with two-component VOCl₃ and TiCl₄ monolayers was studied with respect to the composition of the products and the kinetics of interaction. The titanium and vanadium-containing groups were found to be able to replace each other equivalently. Surface sites were found to determine reactivity, as were lateral interactions in the monolayer. The results found the presence of two kinds of active center; with the estimated ratio of such groups correlating with data from chemical analyses of the concentrations of groups covalently linked to the surface by different numbers of bonds.