Bifurcation Phenomena for an Oxidation Reaction in a Continuously Stirred Tank Reactor I. Adiabatic Operation

We investigate the steady-state multiplicity exhibited by the reaction of a fuel/air mixture in a continuously stirred tank reactor. The chemical mechanism used is a modification of a scheme due to Sal'nikov. We consider four cases; corresponding to the choice of fuel fraction, inflow temperature, inflow pressure, or precursor decay rate as the primary bifurcation parameter. From the perspective of fire-retardancy, the case when the fuel fraction is varied is the most important. In this case the steady-state diagrams provide a basis for a systematic investigation into the effectiveness of gas-phase active fire retardants.     

Grey radiative transfer in binary statistical media with material temperature coupling: asymptotic limits

Simplified models for the unconditional ensemble-averaged radiation intensity and material energy are developed for radiative transfer in binary statistical media. Asymptotic analysis is used to construct an effective transport model with homogenized opacities in two limits. In the first, the material properties are assumed to have low contrast on average, and is shown to correctly reproduce the well-known atomic mix model in both time-dependent and equilibrium situations. Our analysis successfully resolves an inconsistency previously noted in the literature with the application of the standard definition of the atomic mix limit to radiative transfer in participating random media. In the second limit considered, the materials are assumed to have highly contrasting opacities, yielding a reduced transport model with effective scattering. The existence of these limits requires the mean chunk sizes to be independent of the photon direction and this creates an ambiguity in the interpretation of the models when the underlying stochastic geometry is comprised of alternating one-dimensional slabs. A consistent one-dimensional setting is defined and the asymptotic models are numerically validated over a broad range of physical parameter values.     

OPTIONS FOR THE REGULATION OF MEDITERRANEAN DEMERSAL FISHERIES

Research and management actions are reviewed with respect to demersal fisheries of the Mediterranean since the Second World War, as reflected in the activities of the General Fisheries Council for the Mediterranean, (GFCM). The scientific background to the priority concern expressed for minimum size limits in the 1960's and 1970's is discussed, and in particular, the mesh selectivity experiments that formed the basis for yield per recruit calculations, with respect to the trawl fishery. More recent considerations, changing our perception of the appropriateness of size at first capture of demersal fish as a management tool in trawl fisheries, are reviewed. It is concluded that for multispecies fisheries where the first priority for fishing effort control is not respected, size limits based on size at maturity, rather than yield per recruit criteria, are more feasible, but that changes in mesh size need to take into account subsequent changes in equity between inshore and offshore fleets, and changes in species composition and areas of distribution during the life history. They also need to consider the high landed value of small fish in many Mediterranean fisheries. Alternative, or supplementary, measures to mesh size regulation that affect capture of small fish are also reviewed, including seasonal closures, closed areas, bans on trawling inshore, and regulations on minimum size at sale. A range of problems to be considered prior to deciding on an increase in mesh size are reviewed, including changes in total effort exerted, changes in increases in fishing power (and especially the impacts on the spawning stock), changes in discard rate, “meshing” of small fish, and indirect mortality during fishing. A strategy for introducing new mesh sizes is suggested, with emphasis, where possible, on the experimental approach, and on supplementary measures to control fishing effort. The paper concludes by considering an alternative paradigm to minimum size regulation for demersal fisheries management; namely, the exploitation of juvenile fish, with provision for escapement of a small proportion of large, mature fish offshore, for which exploitation rate declines and remains low. It is suggested that this strategy may be, de facto, the one prevailing in the small mesh size inshore trawl fishery prior to development of offshore fisheries. The implications of this possibility have to be considered seriously if high effort levels are to be maintained while effective size limits are raised.     

Finite-range interactions and phases

Summary We consider a one-dimensional system of hard balls on the positive half-line with a general finite-range interaction in thermodynamical equilibrium. We show that, under the action of a weak gravitational field, one can distinguish two spatially separated subsystems: a dense one, which we call the condensate, and a dilute one which we call the gas; between these two, there is a narrow interface where both subsystems mix.     

Commuting Homotopy Limits and Smash Products

In general the processes of taking a homotopy inverse limit of a diagram of spectra and smashing spectra with a fixed space do not commute. In this paper we investigate under what additional assumptions these two processes do commute. In fact we deal with an equivariant generalization that involves spectra and smash products over the orbit category of a discrete group. Such a situation naturally occurs if one studies the equivariant homology theory associated to topological cyclic homology. The main theorem of this paper will play a role in the generalization of the results obtained by Bökstedt, Hsiang and Madsen about the algebraic K-theory Novikov Conjecture to the assembly map for the family of virtually cyclic subgroups.     

Power limits in cylindrical gyromonotrons using TEon1 modes

Upper and lower limits to the output power of highly efficient gyrotron oscillators operating with TE_on1 modes, due to lower and upper limits on the cavity Q, are given.     

Separation and determination of diversiform phytosterols in food materials using supercritical carbon dioxide extraction and ultraperformance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry

This paper presents at first time that the ultra-performance™ liquid chromatographic atmospheric pressure chemical ionization mass spectrometer (UPLC-APCI-MS) was used as an efficient method for the identification and quantification of diversiform phytosterols in food materials. The sample preparation consisted of extraction by supercritical carbon dioxide fluid extraction (SCE) and saponification by refluxing with ethanolic KOH, and then the non-saponificable fraction was extracted with petroleum ether. This fraction was subjected to solid phase extraction (SPE) on silica gel cartridge and then the sterols were eluted with hexane-ethyl acetate. Sterols were separated on an Acquity UPLC™ BEH C18 column (100 mm × 1.0 mm, 1.7 μm particle size) with a gradient of methanol/water (1% acetonitrile) at a flow of 0.1 mL min⁻¹. The determination was performed in selective ion monitoring mode. The quality parameter of the developed method was established using 6-ketocholestanol as internal standard. Limits of quantification (LOQ) were 0.1754, 0.0341, 0.0500, 0.0205, 0.0225, 0.3674, 0.0241, 0.0272, 0.0076 μg L⁻¹ and 0.1525 μg mL⁻¹ for 6-ketocholestanol, desmosterol, ergosterol, cholesterol, lanosterol, cholestanol, campesterol, stigmasterol, β-sitosterol, and stigmastanol, respectively. The intra- and inter-day determination precision for the 10 phytosterols were less than 5 and 6% in relative standard deviations, and their recoveries were located in the range of 94-107%. The developed approach has been applied successfully for efficient determination of diversiform phytosterols in food materials, including corn, sesame, oat and peanut.     

The ground state energy of the three-dimensional Ginzburg-Landau model in the mixed phase

We consider the Ginzburg-Landau functional defined over a bounded and smooth three-dimensional domain. Supposing that the strength of the applied magnetic field varies between the first and second critical fields, in such a way that HC₁?H?HC₂, we estimate the ground state energy to leading order as the Ginzburg-Landau parameter tends to infinity.