Theoretical studies of the gas‐phase pyrolysis kinetics of ω‐bromonitriles,ZCH2CH2Br [Z = NC,NCCH2, NCCH2CH2]

The gas‐phase elimination of several ω‐bromonitriles (ZCH₂CH₂Br, Z = NC, NCCH₂, NCCH₂CH₂) has been examined at the MP2/6‐31G(d,p), MP2/6‐31G(2d,2p), B3PW91/6‐31G(2d,2p), and MPW91PW91/6‐31(2p,2d) levels of theory. The bromonitriles yield the corresponding cyano‐olefin and HBr gas in a rate‐determining step. The MPW91PW91/6‐31G(2p,2d) results suggest a concerted mechanism, with a polar, four‐membered transition state. The calculated kinetic and thermodynamic parameters were found to be within reasonable agreement with the experimental determinations. Substituent effects are discussed in terms of electronic structure. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 168–175, 2009     

Encapsulation of silica nanoparticles by miniemulsion polymerization

Hybrid silica/polystyrene nanoparticles were synthesized by miniemulsion polymerization. With the objective to prepare core‐shell hybrid nanoparticles having narrow particle size distributions (PSDs) as well as a high degree of silica encapsulation, the effect of adding surface modifiers, the size of silica nanoparticles, the ratio styrene/silica, the surfactant concentration, and the presence of ethanol in the reaction mixture were studied. A synergistic effect was observed using oleic acid (OA) together with 3‐(trimethoxysilyl)propyl methacrylate (TPM) in the compatibilization step between the organic phase (monomer) and inorganic nanoparticles (silica). Mono and multinuclear eccentric core‐shell hybrid nanoparticles were obtained. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 935–948, 2009     

BI-ORDERINGS ON PURE BRAIDED THOMPSON'S GROUPS

In this paper it is proved that the pure braided Thompson'sgroup BF admits a bi-order, analogously to the bi-order of thepure braid groups.     

Acoustical Comparison Between Samples of Good and Poor Vibrato in Singers

The purpose of this research was to analyze samples of frequency vibrato taken from recordings of eight different singers, which were classified as examples of good or poor singing. The samples were analyzed by a software package, which makes use of the linear prediction coding (LPC) method to determine the time varying rate and extent of the frequency vibrato wave. Four parameters, which relate to the periodicity of the samples, were extracted from the time varying rate and extent and investigated in order to verify or reject the hypothesis that the best vibrato samples were the most symmetric ones. Ten samples per singer were analyzed, 5 good and 5 poor, for a total of 80 samples. The results show that the samples judged as good were the most periodic ones.     

Theoretical determination of molecular structure. Conformation of some benzo[10]-annulenes and [10]-annulene

Summary The AM1 method was used to carry out a theoretical study of optimized geometries and energies of some benzoannulenes. The transition state of the transformation of the benzo[10]annulene was also determined. The transition state has been located.     

Determination of aluminum and silicon in biological materials by inductively coupled plasma atomic emission spectrometry with electrothermal vaporization

An atomic emission spectrometric method is described for the determination of trace elements in microvolume samples especially of biological materials. Based upon the arrangement of a commercial electrothermal vaporizer and a 40-MHz inductively coupled plasma, the direct determination of aluminum and silicon in human body fluids such as urine and serum and aluminum in hemodialysis solution is performed. The instrumental system involves vaporizing the sample from a modified graphite electrode followed by atomization and excitation of the vapors in the ICP discharge. Compromise experimental conditions are reported and calibration functions compared. Limits of detection in 5-μl samples were 8 pg Al and 2.5 ng Si, and after preconcentration of Al with a poly(acrylamidoxime) resin, the detection limit was 1 pg Al. Recovery of 5 μg $\text{Si}\text{ml}$ and 10 ng $\text{Al}\text{ml}$ from aqueous and synthetic standards was 80–85% and 96–103%, respectively.     

Naphthyl benzoates versus phenyl benzoates A molecular structure-liquid crystal and ferroelectric behaviour relationship study

A comparative study of the liquid crystal and ferroelectric properties of several achiral, racemic and non-racemic 2,6-naphthyl benzoates and their 1,4-phenyl benzoate analogues is reported. In terms of pure compounds, both central core structures give rise to similar mesophase sequences; however, the naphthalene derivatives exhibit broader and more thermally stable liquid crystalline states. On the other hand, both central core units give rise to equivalent electric and optoelectronic properties when the compounds are used as chiral dopants in ferroelectric liquid crystal mixtures.     

Restricted simplicial decomposition for convex constrained problems

The strategy of Restricted Simplicial Decomposition is extended to convex programs with convex constraints. The resulting algorithm can also be viewed as an extension of the (scaled) Topkis—Veinott method of feasible directions in which the master problem involves optimization over a simplex rather than the usual line search. Global convergence of the method is proven and conditions are given under which the master problem will be solved a finite number of times. Computational testing with dense quadratic problems confirms that the method dramatically improves the Topkis—Veinott algorithm and that it is competitive with the generalized reduced gradient method.This research was supported in part by NSF Grants ECS-8516365 and DDM-8814075.     

Decomposability of free Łukasiewicz implication algebras

?ukasiewicz implication algebras are {→,1}-subreducts of Wajsberg algebras (MV-algebras). They are the algebraic counterpart of Super-?ukasiewicz Implicational logics investigated in Komori, Nogoya Math J 72:127–133, 1978. The aim of this paper is to study the direct decomposability of free ?ukasiewicz implication algebras. We show that freely generated algebras are directly indecomposable. We also study the direct decomposability in free algebras of all its proper subvarieties and show that infinitely freely generated algebras are indecomposable, while finitely free generated algebras can be only decomposed into a direct product of two factors, one of which is the two-element implication algebra.