On the Dunford-Pettis property of the tensor product of spaces

In this paper we characterize those compact Hausdorff spaces such that (and ) have the Dunford-Pettis Property, answering thus in the negative a question posed by Castillo and González who asked if and have this property.

     

Effect of substituents in the gas-phase elimination kinetics of β-substituted ethyl acetates

The kinetics of gas-phase elimination of 3-methyl-1-butyl acetate and 3,3-dimethyl-1-butyl acetate into acetic acid and the corresponding substituted butenes have been measured over the temperature range of 360–420°C and the pressure range of 63–250 Torr. The reactions are homogeneous in both clean and seasoned vessels, obey first-order law, and are unimolecular. The temperature dependence of the rate constants is given by the Arrhenius equation 3-methyl-1-butyl acetate: 3,3-dimethyl-1-butyl acetate: The points in a plot of log (k/k₀) of β-alkyl and several β-substituted ethyl acetates against E_s values appear aligned in an approximate linear relationship. These results may be interpreted as a consequence of steric effects, namely, steric accelerations.     

Neighboring group participation of polar β substituents in the gas-phase pyrolysis of 2-substituted ethyl chlorides

The pyrolysis of 2-dimethylaminoethyl chloride in the temperature range of 360–400°C and the pressure range of 60–271 mmHg is a homogeneous, unimolecular, first-order reaction giving dimethylvinyl amine and hydrogen chloride. 2-Methoxyethyl chloride pyrolysis in the temperature range of 450–490°C and the pressure range of 53–110 mmHg by a similar unimolecular, first-order reaction yields methylvinyl ether and hydrogen chloride. These reactions were carried out in a seasoned reaction vessel and in the presence of a propene inhibitor. The methylvinyl ether decomposes slowly into other products at the temperature of pyrolysis. The rate constants are given by the Arrhenius equations (a) 2-dimethylaminoethyl chloride: (b) 2-methoxyethyl chloride: The effects of polar β substituents in the 2 position of ethyl chloride are discussed in terms of anchimeric assistance and electron-withdrawing deactivation in these elimination reactions. The present results are consistent with the heterolytic nature of the four-centered cyclic transition state for the gas-phase pyrolysis of alkyl halides.     

A method for making inorganic and hybrid (organic/inorganic) fibers and vesicles with diameters in the submicrometer and micrometer range via sol-gel chemistry and electrically forced liquid jets

Electrically driven liquid jets are combined with sol-gel methods to design vesicles and fibers made from inorganic oxides and hybrid materials with diameters in the micrometer and submicrometer range. The proposed materials synthesis method benefits greatly from the maturity of sol-gel chemistry and the generalities of a structure-directing phenomenon that is physical in nature.     

Generalized Convex Disjunctive Programming: Nonlinear Convex Hull Relaxation

Generalized Disjunctive Programming (GDP) has been introduced recently as an alternative to mixed-integer programming for representing discrete/continuous optimization problems. The basic idea of GDP consists of representing these problems in terms of sets of disjunctions in the continuous space, and logic propositions in terms of Boolean variables. In this paper we consider GDP problems involving convex nonlinear inequalities in the disjunctions. Based on the work by Stubbs and Mehrotra [21] and Ceria and Soares [6], we propose a convex nonlinear relaxation of the nonlinear convex GDP problem that relies on the convex hull of each of the disjunctions that is obtained by variable disaggregation and reformulation of the inequalities. The proposed nonlinear relaxation is used to formulate the GDP problem as a Mixed-Integer Nonlinear Programming (MINLP) problem that is shown to be tighter than the conventional big-M formulation. A disjunctive branch and bound method is also presented, and numerical results are given for a set of test problems.     

K5Nd(MoO4)4: a self-tunable laser crystal

We report for the first time to our knowledge an experimental demonstration of wavelength self-tuning in a K5Nd(MoO4)4 broadband-emitting laser crystal (KNM), as well as a theoretical treatment of the system based on its birefringence properties. The self-frequency-tuning of the laser along the full spectral range of the KNM crystal was obtained by rotating a birefringent gain plate in its own plane. The gain plate was placed inside a resonator at Brewster's angle. The tuning characteristics of the spectral filter were obtained by use of the Jones vector formalism. The calculated wavelength-selective tuning precisely matches the experimental observations.     

Classical decays in decoherent quantum maps

The linear entropy and the Loschmidt echo have proved to be of interest recently in the context of quantum information and of the quantum to classical transitions. We study the asymptotic long-time behavior of these quantities for open quantum maps and relate the decays to the eigenvalues of a coarse-grained superoperator. In specific ranges of coarse graining, and for chaotic maps, these decay rates are given by the Ruelle-Pollicott resonances of the classical map.     

Development of a new family of conformationally restricted peptides as potent nucleators of beta-turns. Design, synthesis, structure, and biological evaluation of a beta-lactam peptide analogue of melanostatin

Novel enantiopure (i)-(beta-lactam)-(Gly)-(i+3) peptide models, defined by the presence of a central alpha-alkyl-alpha-amino-beta-lactam ring placed as the (i+1) residue, have been synthesized in a totally stereocontrolled way by alpha-alkylation of suitable N-[bis(trimethylsilyl)methyl]-beta-lactams. The structural properties of these beta-lactam pseudopeptides have been studied by X-ray crystallography, Molecular Dynamics simulation, and NOESY-restrained NMR simulated annealing techniques, showing a strong tendency to form stable type II or type II' beta-turns either in the solid state or in highly coordinating DMSO solutions. Tetrapeptide models containing syn- or anti-alpha,beta-dialkyl-alpha-amino-beta-lactam rings have also been synthesized and their conformations analyzed, revealing that alpha-alkyl substitution is essential for beta-turn stabilization. A beta-lactam analogue of melanostatin (PLG amide) has also been prepared, characterized as a type-II beta-turn in DMSO-d6 solution, and tested by competitive binding assay as a dopaminergic D2 modulator in rat neuron cultured cells, displaying moderate agonist activity in the micromolar concentration range. On the basis of these results, a novel peptidomimetic design concept, based on the separation of constraint and recognition elements, is proposed.     

Comparative Mössbauer study of the oxidation of pyrite under different conditions

Samples of pyrite-rich brown coal from As Pontes and Meirama coalfields (Spain) were oxidized either by air at atmospheric pressure or by a cool oxygen plasma generated by radiofrequency activation. Despite the very different nature and characteristics of the oxidizing media, in both cases the RT Mössbauer spectra were easily fitted to two doublets, whose parameters matched those of pyrite and jarosite (hydrated iron (III) sulphate). The extent of pyrite oxidation to jarosite was monitored by the relative spectral areas of pyrite and jarosite doublets. Both, air and plasma, oxidized pyrite to the same extent and in a similar way, in contrast to coal organic matter, which was scarcely modified by air but completely oxidized by the plasma at the same temperature (ca. 423 K). The incomplete oxidation of pyrite by plasma is attributed to the action of a thin calcium sulphate layer which hinders the access of activated oxygen to small pyrite crystals.