Microstructure effect in the coupling reactions of polymeric organolithium compounds using chlorosilanes

The most important variable affecting the yield in the coupling reactions of polymeric organolithium compounds with chlorosilane compounds has been investigated through size-exclusion chromatographic (SEC) analysis. The coupling reaction of poly(styryl)lithium with dichlorodimethylsilane as a silane-coupling agent provided 44 wt % of the coupling yield. The coupling yield, depending on the chain end reactivity of active polymers, was not greatly affected. The addition of a Lewis base such as N,N,N′,N′-tetramethylethylenediamine (TMEDA) even after complete polymerization of the dienes in hydrocarbon seems to affect the coupling reaction, resulting in decreasing the yield. The 1,2- or 3,4-enchain contents in the polydiene backbones affected the reduction of the linking efficiency in the coupling of the poly(dienyl)lithiums with chlorosilanes as the linking agent. The linking yields of the active polymers including over 75 mol % of 1,2- or 3,4-enchainment on the polydiene segment were below 20 wt %. The linking yields exhibited a dependence not only on the steric requirement of the chain end, but also the microstructure of the polydiene segment. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1743–1753, 1998     

Simulation of three‐dimensional bubbles using desingularized boundary integral method

A very simple model based on the three‐dimensional desingularized boundary integral method is applied to study the evolution of bubble(s) with or without the presence of solid structures. The choice of the desingularization parameters, which is crucial to the success of the method, is studied in the context of bubble dynamics. With the proper choice of parameters, the new model is far more efficient than previous models with virtually the same level of accuracy being achieved. This is largely attributed to the simplicity of the desingularization method. Furthermore, the new model offers a simple and attractive way for mesh refinement. Although it has limitations in the sense that, with this model the time stepping tends to slow down as two surfaces approach each other, this can be easily rectified by switching over to a direct method so that the two surfaces can be drawn closer as required in the context of jet impact. After this the new model can be reinstated to treat the complicated doubly connected geometry involving toroidal bubbles that would otherwise be very difficult to deal with. Copyright © 1999 John Wiley & Sons, Ltd.     

A Kinetic Study for the Noncatalytic Esterification of Palm Fatty Acid Distillate

In this work, the reaction scheme for the esterification of palm fatty acid distillate performed under the noncatalytic and high‐temperature condition (230–290°C) was investigated with a rigorous mathematical modeling. The esterification reaction was assumed to be the pseudo–homogeneous second‐order reversible reaction, and the mass transfer effectiveness factor (η) was introduced in the modeling framework to systematically and collectively consider both evaporation and reaction, which are simultaneously and competitively occurred in the liquid phase. The nonlinear programming problem was constructed with the objective function consisting of the errors between experimental data and the estimated values from the reaction model. The problem was solved by using the Nelder–Mead simplex algorithm to identify kinetic parameters, reaction rate constants, and mass transfer coefficients. The values of mass transfer coefficients were found to follow the Hertz–Knudsen relation and expressed as a function of reaction temperature. From the reaction rate constants obtained from the proposed kinetic models, the apparent activation energy was estimated to be 43.98 kJ/mol, which is lower than the value obtained from the reaction using heterogeneous catalysts. This low value indicates that reactants and products behave as an acid catalyst at relatively high operating temperature and constant pressure.     

Solid‐state 31P NMR investigation on the status of guanine nucleotides in paclitaxel‐stabilized microtubules

Microtubule dynamics is a target for many chemotherapeutic drugs. In order to understand the biochemical effects of paclitaxel on the GTPase activity of tubulin, the status of guanine nucleotides in microtubules was investigated by ³¹P cross‐polarization magic angle spinning (CPMAS) NMR. Microtubules were freshly prepared in vitro in the presence of paclitaxel and then lyophilized in sucrose buffer for solid‐state NMR experiments. A ³¹P CPMAS NMR spectrum with the SNR of 25 was successfully acquired from the lyophilized microtubule sample. The broadness of the ³¹P spectral lines in the spectrum indicates that the molecular environments around the guanine nucleotides inside tubulin may not be as crystalline as reported by many diffraction studies. Deconvolution of the spectrum into four spectral components was carried out in comparison with the ³¹P NMR spectra obtained from five control samples. The spectral analysis suggested that about 13% of the nucleotides were present as GTP and 37% as GDP in the β‐tubulin (E‐site) of the microtubules. It was found that most of the GDPs were present as GDP‐P_i complex in the microtubules, which seems to be one of the effects of paclitaxel binding. Copyright © 2015 John Wiley & Sons, Ltd.     

Exact decoherence dynamics of a single-mode optical field

We apply the influence-functional method of Feynman and Vernon to the study of a single-mode optical field that interacts with an environment at zero temperature. Using the coherent-state formalism of the path integral, we derive a generalized master equation for the single-mode optical field. Our analysis explicitly shows how non-Markovian effects manifest in the exact decoherence dynamics for different environmental correlation time scales. Remarkably, when these are equal to or greater than the time scale for significant change in the system, the interplay between the backaction-induced coherent oscillation and the dissipative effect of the environment causes the non-Markovian effect to have a significant impact not only on the short-time behavior but also on the long-time steady-state behavior of the system.     

Preparation and characterization of nanosized (Y,Bi)VO4:Eu and Y(V,P)O4:Eu red phosphors

Nanosized luminescent (Y,Bi)VO₄:Eu³⁺ and Y(V,P)O₄:Eu³⁺ were synthesized at low temperatures either by a coprecipitation method or by a hydrothermal method from aqueous solutions. The effect of Bi³⁺ ion or P⁵⁺ ion content in the lattice, annealing temperature effects on the crystal structure and the particle size, and the luminescence property of (Y,Bi)VO₄:Eu³⁺ and Y(V,P)O₄:Eu³⁺ nanoparticles were examined with a field-enhanced scanning electron microscopy, XRD, and a spectrofluorometer. The pristine YVO₄:Eu³⁺, (Y,Bi)VO₄:Eu³⁺, or Y(V,P)O₄:Eu³⁺ nanoparticles are 35-50 nm in size. The luminescence spectrum of the Eu³⁺ ion was used to probe its position in the crystal lattice. The dopant ions enter the same lattice sites in the nanocrystalline as in the corresponding bulk material, resulting similar spectral features between them. Photoluminescence intensity is weak for the pristine nanoparticles. Annealing the nanoparticles at temperatures up to 1000 °C results in the increased luminescence intensity (>80% of micrometer-sized phosphors) with the minimal particle growth and the improved particle crystallinity.     

Optimal warranty policies for systems with imperfect repair

We investigate a system whose basic warranty coverage is minimal repair up to a specified warranty length. An additional service is offered whereby first failure is restored up to the consumers’ chosen level of repair. The problem is studied under two system replacement strategies: periodic maintenance before and after warranty. It turns out that our model generalizes the model of Rinsaka and Sandoh [K. Rinsaka, H. Sandoh, A stochastic model with an additional warranty contract, Computers and Mathematics with Applications 51 (2006) 179–188] and the model of Yeh et al. [R.H. Yeh, M.Y. Chen, C.Y. Lin, Optimal periodic replacement policy for repairable products under free-repair warranty, European Journal of Operational Research 176 (2007) 1678–1686]. We derive the optimal maintenance period and optimal level of repair based on the structures of the cost function and failure rate function. We show that under certain assumptions, the optimal repair level for additional service is an increasing function of the replacement time. We provide numerical studies to verify some of our results.     

On the number of connected convex subgraphs of a connected acyclic digraph

A digraph D is connected if the underlying undirected graph of D is connected. A subgraph H of an acyclic digraph D is convex if there is no directed path between vertices of H which contains an arc not in H. We find the minimum and maximum possible number of connected convex subgraphs in a connected acyclic digraph of order n. Connected convex subgraphs of connected acyclic digraphs are of interest in the area of modern embedded processors technology.     

ε-Amino acids based on bicyclic skeleton: bicyclo[3.3.0]octane-5-amino-1-carboxylic acids

Tsc-protected ε-amino acids, bicyclo[3.3.0]octane-5-amino-1-carboxylic acids (1), ready to use in the solid-phase synthesis, are prepared from 4,4-diethylcarboxylic bicyclo[3.3.0]oct-2-enone (3), which is available in bulk from 2 through the catalytic Pauson-Khand reaction.