The Picard Theorem on S-metric spaces

Recently, the notion of an S-metric space is defined and extensively studied as a generalization of a metric space. In this paper, we define the notion of the S∞-space and prove its completeness. We obtain a new generalization of the classical "Picard Theorem".     

A dual approach to multi-dimensional assignment problems

Journal of Global Optimization - In this paper, we extend the purely dual formulation that we recently proposed for the three-dimensional assignment problems to solve the more general...     

Estimation of excitation and transmissibility from output measurements,with application to gear drives

Methods are presented by which both harmonic input magnitudes and dynamic transmissibility can be estimated when only the output of a system can be measured. This is possible when the input to a system consists of components whose amplitude remains constant although their time scale changes with speed. An example of this occurs with gear induced vibration where the forcing function is provided by errors which remain constant in amplitude. Examples given show how the methods can be used to estimate the static transmission error components of gear drives from dynamic response measurements where drive speeds are restricted.     

Walsh Multipliers for Dyadic Hardy Spaces

In this article we are interested in conditions on the coefficients of a Walsh multiplier operator that imply the operator is bounded on certain dyadic Hardy spaces H ^p , 0 < p < ∞. In particular, we consider two classical coefficient conditions, originally introduced for the trigonometric case, the Marcinkiewicz and the Hörmander–Mihlin conditions. They are known to be sufficient in the spaces L ^p , 1 < p < ∞. Here we study the corresponding problem on dyadic Hardy spaces, and find the values of p for which these conditions are sufficient. Then, we consider the cases of H ¹ and L ¹ which are of special interest. Finally, based on a recent integrability condition for Walsh series, a new condition is provided that implies that the multiplier operator is bounded from L ¹ to L ¹, and from H ¹ to H ¹. We note that existing multiplier theorems for Hardy spaces give growth conditions on the dyadic blocks of the Walsh series of the kernel, but these growth are not computable directly in terms of the coefficients.     

Hydrophobic guar gum derivatives prepared by controlled grafting processes–Part II: rheological and degradation properties toward fracturing fluids applications

Introduction of polyalkoxyalkyleneamide grafts to guar gum produces new water soluble guar derivatives as described in an earlier publication. 10 In this paper, the rhelogical behavior of these products was explored in more detail at 25 and 65°C. In addition, the viscosity was measured at high temperatures (90 and 120°C) and pressure (150 psi) to partially simulate the down hole conditions of oil wells. Upon treatment with zirconium lactate, the cross‐linked hydrophobically‐modified CMG derivatives exhibited better high‐temperature stability and higher gel viscosities than the corresponding CMHPG derivatives. The cross‐linked gel viscosities indicate that gels will be capable of supporting a high proppant carrying capacity. To facilitate removal of the gels from the formation, the hydrophobically modified derivatives were treated with an enzyme breaker system which produced fragments capable of producing stable emulsions when extracted with toluene. Thus, the clean up process will be enhanced by emulsification of the gel fragments produced by the gel hydrolysis. The low viscosities of the linear derivatives, the rapid formation of high viscosity gels upon cross‐linking and generation of emulsifiers during the gel removal suggest that these new derivatives are good candidates for fracturing fluid applications. Copyright © 2007 John Wiley & Sons, Ltd.     

Chromium-salen-mediated alkene epoxidation: a theoretical and experimental study indicates the importance of spin-surface crossing and the presence of a discrete intermediate

The mechanism of alkene epoxidation by chromium(v) oxo salen complexes has been studied by DFT and experimental methods. The reaction is compared to the closely related Mn-catalyzed process in an attempt to understand the dramatic difference in selectivity between the two systems. Overall, the studies show that the reactions have many similarities, but also a few critical differences. In agreement with experiment, the chromium system requires a change from low- to high-spin in the catalytic cycle, whereas the manganese system can proceed either with spin inversion or entirely on the high-spin surface. The low-spin addition of metal oxo species to an alkene leads to an intermediate which forms epoxide either with a barrier on the low-spin surface or without a barrier after spin inversion. Supporting evidence for this intermediate was obtained by using vinylcyclopropane traps. The chromium(v) oxo complexes can adopt a stepped shape or form a more concave surface, analogous to previous results on manganese salen complexes.     

Application of Bender's salts to the synthesis of S-vinyl-O-tert-alkylthiocarbonates

Three thermally labile Bender's salts were synthesized and utilized to effect quantitative S_N2 displacement of primary halides to form tert-alkylthiocarbonate derivatives. Selective displacement of bromide from 1,2-bromochloroethane by either VI or VII followed by dehydrohalogenation with potassium tert-butoxide yielded S-vinyl-O-tert-butylthiocarbonate (I) and S-vinyl-O-tert-amylthiocarbonate (X), two excellent vinyl monomer precursors for polymercaptan, in 62 and 51% yield, respectively. Reaction of VI with vinylbenzyl chloride yielded S-(vinylbenzyl)-O-tert-butylthiocarbonate which polymerized in the presence of free radical initiators to produce a poly(vinylbenzyl mercaptan) precursor. Dilatometric studies of the homopolymerization of I demonstrated that the polymerization rate was proportional to [I]^0.765 and [M]^1.7, respectively; the monomer exhibited a high chain transfer constant (C_M = 3.9 × 10^?3).     

吡咯亚胺配体与过渡金属的反应性及其催化烯烃聚合

在经典的Brookhart吡啶双亚胺后过渡金属烯烃聚合催化剂基础上,用吡咯五元环代替吡啶六元环骨架可得到具有不同电子效应的新型吡咯亚胺配体.通过吡咯环特殊的电子效应和位阻效应可设计出种类繁多的有别于吡啶亚胺配体的配合物.综述了吡咯亚胺配体与前过渡金属(Ti,Zr等)、后过渡金属(Fe,Co,Ni,Pd等)、稀土金属(Y...