On generalized Erd?s spaces

During the last years both Erd?s space and complete Erd?s space were topologically characterized by Dijkstra and van Mill. Applications include results about Erd?s type spaces in ?p-spaces as well as results about Polishable ideals on ω. We present an unifying theorem in terms of sets with a reflexive relation that among other things contains these apparently dissimilar results as special cases.     

Enantioseparations of non-benzenoid and oligo-Tröger’s bases by HPLC on Whelk O1 column

The separation of enantiomers of several ‘bis- and tris-Tröger’s bases’ by HPLC on commercially available chiral stationary phase Whelk O1 is described for the first time. The observed structure–enantioselectivity relationships are in agreement with the previously established molecular recognition model. For all ‘bis- and tris-Tröger’s bases’ studied, satisfactory to excellent enantioselectivities were observed.     

The EEG and MEG, Using a Model of Eccentric Spheres to Describe the Head

Two spherical models describing the head are used to compute EEG's and MEG's for current dipolar sources located in the visual cortex area. In one of the models, the spheres are concentric, in the other eccentric, fitting the compartment boundaries of the head best in the source area. In forward computations, a strong dependency on the volume conductor model is found for the EEG's, but not for the MEG's. The dependency of the EEG due to realistic values of the eccentricities of the spheres is in accordance with experiments described in the literature. All spheres are obtained by means of a least squares fitting algorithm in which the points on the surface boundaries, used to fit the sphere, may move within an interval determined by the measuring inaccuracy. This strategy used in the fitting algorithm is shown to give considerably better results than the one normally used.     

Elution order in liquid chromatography on cyclodextrin phases. Dependence on the amount of organic modifier in the eluent

Summary The composition of the eluent system in some instances determines the resolution and elution order of solutes in the reversed-phase chromatographic separation on cyclodextrin stationary phases. Both the identity and the concentration of the organic modifier can play a large role. The effect is particularly pronounced with naphthalene and its methyl derivatives with alcohol eluents.

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Elutionsfolge bei der Flüssig-Chromatographie auf Cyclodextrinphasen. Abhängigkeit vom Gehalt an organischem Modifier im Eluenten

     

The kinetics of successive addition of oxirane to alkanethiols in the presence of basic catalysts

Rate constants and activation parameters of direct reaction of oxirane with certain alkyl-2-hydroxyethyl sulfides and/or successive oxyethylene adducts in the presence of basic catalyst were studied at temperatures 323–353 K. The reactions were found to be of the first order with respect to oxirane, sulfide, and catalyst concentrations. The kinetics are consistent with a termolecular mechanism.     

Effect of gate length in InAs/AlSb HEMTs biased for low power or high gain

The effect of gate-length variation on DC and RF performance of InAs/AlSb HEMTs, biased for low DC power consumption or high gain, is reported. Simultaneously fabricated devices, with gate lengths between 225 nm and 335 nm, have been compared. DC measurements revealed higher output conductance g_ds and slightly increased impact ionization with reduced gate length. When reducing the gate length from 335 nm to 225 nm, the DC power consumption was reduced by approximately 80% at an f_T of 120 GHz. Furthermore, a 225 nm gate-length HEMT biased for high gain exhibited an extrinsic f_T of 165 GHz and an extrinsic f_max of 115 GHz, at a DC power consumption of 100 mW/mm. When biased for low DC power consumption of 20 mW/mm the same HEMT exhibited an extrinsic f_T and f_max of 120 GHz and 110 GHz, respectively.     

The effect of Co(II)‐mediated catalytic chain transfer on the emulsion polymerization kinetics of methyl methacrylate

The effect the catalytic chain transfer agent, bis[(difluoroboryl) dimethylglyoximato] cobalt(II) (COBF), on the course of the ab initio emulsion polymerization of methyl methacrylate, and the product properties in terms of the molecular weight distribution were investigated. The emulsion polymerization kinetics have been studied with varying surfactant, initiator, and COBF concentrations. The experimentally determined average number of radicals per particle strongly depends on the concentration of COBF and proves to be in good agreement with the results of model calculations. The apparent chain transfer constant, determined up to high conversion, is in excellent agreement with the predicted value based on a mathematical model based on COBF partitioning and the Mayo equation. The results of this work enhance the fundamental understanding of the influence a catalytic chain transfer agent has on the course of the emulsion polymerization and the control of the molecular weight distribution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5078–5089, 2009     

An acceleration of Erlenkotter-Körkel’s algorithms for the uncapacitated facility location problem

This contribution is focused on an acceleration of branch and bound algorithms for the uncapacitated facility location problem. Our approach is based on the well-known Erlenkotters’ procedures and Körkels’ multi-ascent and multi-adjustment algorithms, which have proved to be the efficient tools for solving the large-sized instances of the uncapacitated facility location problem. These two original approaches were examined and a thorough analysis of their performance revealed how each particular procedure contributes to the computational time of the whole algorithms. These analyses helped us to focus our effort on the most frequent procedures. The unique contribution of this paper is a new dual ascent procedure. This procedure leads to considerable acceleration of the lower bound computation process and reduces the resulting computational time. To demonstrate more efficient performance of amended algorithms we present the results of extensive numerical experiments.     

Heat capacity measurements in carboxylic polyelectrolyte solutions

Apparent molal heat capacities as a function of the degree of neutralization have been determined for dilute aqueous solutions of poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), copoly(maleic acid-ethylene) (MAEt), and copoly(maleic acid-styrene) (MASt) using direct flow microcalorimetry. Apparent molal volumes were measured as well. Both molal heat capacity and molal volume decrease with increasing ionization of the polymer. The effect of the hydrophobic interactions of the methyl group or phenyl group was obtained from the difference in the molal quantities of PMA and PAA, or MASt and MAEt. No evidence of hydrophobic effects, as determined from the heat capacity, was found for the conformational transition of PMA, but the hydration of the phenyl groups in MASt was found to be changed significantly at a degree of neutralization of 0.4.