Synthesis and novel reactivity of halomethyldimethylsulfonium salts

Iodomethyl-, chloromethyl-, and fluoromethyldimethylsulfonium salts, 4b-d, have been synthesized and are observed to be highly reactive molecules that exhibit extraordinary diversity with respect to the nature of their reactivity, undergoing facile direct substitution (S(N)2) reactions, but also being highly susceptible to electron-transfer reactions. Cyclic voltametry experiments indicated that the iodomethyldimethylsulfonium compound, 4b, is a potent electron acceptor, even surpassing the reactivity of perfluoro-n-alkyl iodides in that capacity. The iodo- and chloromethyldimethylsulfonium salts, 4b,c, as well as the analogous iodomethyltrimethylammonium salt, 3a, are shown to be reactive SET acceptors.     

Performance of digital image velocimetry processing techniques

Digital particle image velocimetry (DPIV)-processing techniques have become increasingly more sophisticated in recent years. However, much work is still done using standard traditional methods of analysis. This paper investigates several traditionally based techniques for cross-correlation image processing in terms of computational efficiency and measurement accuracy. Direct spatial domain correlation, standard fast Fourier transform (FFT) correlation, a dynamic FFT correlation technique, and a new hybrid correlation method are discussed and evaluated. In addition, a particle-tracking velocimetry scheme based on that of Cowen and Monismith (1997) is examined in the same context as the DPIV methods. A detailed examination of the behaviors of each correlation method reveals that direct spatial domain correlation is more accurate than FFT-based methods, with the standard FFT correlation showing the weakest performance. Using the more robust methods (dynamic FFT and hybrid correlation), accuracy can be improved significantly over the standard FFT method in many cases, while still remaining computationally efficient. The particle-tracking algorithm studied was found to yield comparable accuracy to the DPIV routines and can provide much higher spatial- resolution possibilities. Received: 3 September 1999 / Accepted: 21 June 2001 Published online: 29 November 2001     

Spinning Drop Tensiometry Using a Square Section Sample Tube

When measuring interfacial tensions, conventional spinning drop tensiometry requires knowledge of the index of refraction of the denser, outer fluid phase, in order to correct for the magnification of the inner, spinning drop. We have modified a spinning drop tensiometer to accommodate a square section sample tube, which does not require this correction. Tests performed using calibration rods are used to demonstrate this fact. The interfacial tension of toluene and water is also measured using this new design. The ensuing results are in agreement with measurements obtained using a conventional circular sample tube. Copyright 2001 Academic Press.     

The single-mode rate equations for semiconductor lasers with thermal effects

A mathematical model describing the coupling of electrical,optical and thermal effects in semiconductor lasers is introduced.Numerical and asymptotic solutions are derived, including expressionsfor key physical quantities such as the initial time delay,the frequency of spike oscillation and the temperature rise,together with its influence on the photon density, the electronconcentration and the threshold current. The consequences ofthermal effects in reducing efficiency are thus quantified.     

On <Emphasis Type="Italic">g</Emphasis>-functions for Laguerre function expansions of Hermite type

We examine weighted L ^p boundedness of g-functions based on semigroups related to multi-dimensional Laguerre function expansions of Hermite type. A technique of vector-valued Calderón–Zygmund operators is used.