Dynamic bounds for power and efficiency of non-ideal energy converters under nonlinear transfer laws

We present a thermodynamic approach to simulation and modeling of nonlinear energy converters, in particular radiation engines. Novel results are obtained especially for dynamical engines when the temperature of the propelling medium decreases in time due to a continual decrease of the medium's internal energy caused by the power production. Basic thermodynamic principles determine the converter's efficiency and work limits in terms of the entropy production. The real work is a cumulative effect obtained in a system of a resource fluid, a sequence of engines, and an infinite bath. Nonlinear modeling involves dynamic optimization in which the classical expression for efficiency at maximum power is generalized to endoirreversible machines and nonlinear transfer laws. The primary result is a finite-rate generalization of the classical, reversible work potential (exergy). The generalized work function depends on thermal coordinates and a dissipation index, h, i.e. a Hamiltonian of the minimum entropy production problem. This generalized work function implies stronger bounds on work delivered or supplied than the reversible work potential. The role of the nonlinear analyses and dynamic optimization is shown especially for radiation engines. As an example of the kinetic work limit, generalized exergy of radiation fluid is estimated in terms of finite rates, quantified by the Hamiltonian h.     

Copying of dynamic structures in a pascal environment

Two problems involving the use of dynamic lists in Pascal are (1) the limited size of the heap and (2) the difficulty in creating copies of complex multi-linked structures. Both these problems can be solved by writing the appropriate segment of memory to a file on disk. The heap segment may then be released. To recover the structure during a later phase of processing, the contents of the file can be transferred back onto the heap. This paper presents an algorithm to implement this solution.     

Macromonomers by activated polymerization of oxiranes. Synthesis and polymerization

Macromonomers were obtained by cationic polymerization of propylene oxide and epichlorohydrin proceeding by the activated monomer mechanism with hydroxyethyl acrylate as initiator. Up to DP _n ～ 15 for propylene oxide and DP _n ～ 20 for epichlorohydrin, polymerization proceeds as a living process, giving with quantitative yields macromonomers with functionality equal to one, controlled molecular weight and narrow molecular weight distribution (M _wM _n<1.2) free of side products. In the higer molecular weight region, side reactions become increasingly noticeable. Propylene oxide macromonomers undergo radical homopolymerization. Homopolymerization of macromonomer with M _n = 8×10² gives graft copolymers with M _n up to 7.2×10³ in copolymerization with styrene, completely soluble graft copolymers with M _n ～ 2×10⁴ were obtained. Radical copolymerization of epichlorohydrin macromonomers with styrene gives initially soluble products with M _n ～ 6×10⁴ were obtained. Radical copolymerization of epichlorohydrin macromonomers with styrene gives initially soluble products with M_n～ 6×10⁴, which are converted in the later stages into insoluble gels, apparently due to the chain transfer to chloromethly groups of the polyepichlorohydrin chains.     

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.

     

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.     

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.