Quaternary ammonium and sulfonium derivatives of 2-chloromethylbutadiene and poly-2-chloromethylbutadiene

2-Chloromethylbutadiene has been converted to quaternary ammonium and sulfonium monomers which have been polymerized at room temperature. They show a very great tendency to dimerize on heating in water solution. The aqueous quaternary monomer dimerized 25 times as fast as the aqueous sulfonium monomer and nearly 10⁵ times as fast as neat isoprene at 50°C. The quaternary monomer dimerized with itself in a water solution to which 2-hydroxymethylbutadiene has been added as an example of a nonionic diene. The latter monomer did not dimerize rapidly in water, nor did 2-aminomethylbutadiene. The hydrochlorides of 2-aminomethylbutadiene and 2-dimethylaminomethylbutadiene dimerized at rates comparable to that of the sulfonium monomer. Poly 2-chloromethylbutadiene contains reactive chlorine except for the structure resulting from the minor extent of 1,2 addition. Water-soluble derivatives have been made from it with nucleophilic tertiary amines and sulfides. Cationic polymers are substantive to paper pulp, and the sulfonium polymers can be cured in paper to give improved wet strength.     

Tunable yellow–green laser based on second harmonic generation of LiF:F−2 in KTP

A yellow–green solid-state laser source based on frequency- doubling of a room temperature LiF:F–2 laser in KTP is reported. Second harmonic generation of free-running and prism-tuned pulsed lasers has been characterized. Tunable operation between 555 and 595nm was obtained, with a conversion efficiency of 7.5% for the free-running laser, and up to 4% for the prism-tuned configuration. The angular bandwidth of 60milliradians exceeded the theoretical value by a factor of 3.5. A flattened tuning curve in the visible region was obtained through enhanced conversion efficiency in the wings of the LiF:F–2 laser tuning range.     

Reactivity of white phosphorus with compounds of the p-block

This review covers the activation, aggregation and degradation of white phosphorus by molecules containing reactive p-block centers. The chemistry has been divided into a number of reaction types and possible mechanisms are used to aid in the understanding of these reactions.     

Gradient Profile Estimation Using Exponential Cubic Spline Smoothing in a Bayesian Framework

Attaining reliable gradient profiles is of utmost relevance for many physical systems. In many situations, the estimation of the gradient is inaccurate due to noise. It is common practice to first estimate the underlying system and then compute the gradient profile by taking the subsequent analytic derivative of the estimated system. The underlying system is often estimated by fitting or smoothing the data using other techniques. Taking the subsequent analytic derivative of an estimated function can be ill-posed. This becomes worse as the noise in the system increases. As a result, the uncertainty generated in the gradient estimate increases. In this paper, a theoretical framework for a method to estimate the gradient profile of discrete noisy data is presented. The method was developed within a Bayesian framework. Comprehensive numerical experiments were conducted on synthetic data at different levels of noise. The accuracy of the proposed method was quantified. Our findings suggest that the proposed gradient profile estimation method outperforms the state-of-the-art methods.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

Quantum Zeno and anti-Zeno paradoxes

Continuous observation of a time independent projection operator is known to prevent change of state (the quantum Zeno paradox). We discuss the recent result that generic continuous measurement of time dependent projection operators will in fact ensure change of state: an anti-Zeno paradox.     

粉粒体两相流的电容层析成象测量

粉粒体系统中的固相浓度分布的在线测量是十分困难的问题．电容层析成象技术是一种近年来发展起来的非侵入式快速浓度场测量技术．它不干扰流场，不受流动中颗粒浓度、加速度、不透明等因素的制约．本文讨论其测量原理、应用、近期进展、存在的主要问题及其解决的对策．