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.     

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.     

Artifacts in T1 rho-weighted imaging: compensation for B(1) and B(0) field imperfections

The origin of spin locking image artifacts in the presence of B(0) and B(1) magnetic field imperfections is shown theoretically using the Bloch equations and experimentally at low (omega(1) < Delta omega(0)), intermediate (omega(1) approximately Delta omega(0)) and high (omega(1) > Delta omega(0)) spin locking field strengths. At low spin locking fields, the magnetization is shown to oscillate about an effective field in the rotating frame causing signature banding artifacts in the image. At high spin lock fields, the effect of the resonance offset Deltao mega(0) is quenched, but imperfections in the flip angle cause oscillations about the omega(1) field. A new pulse sequence is presented that consists of an integrated spin echo and spin lock experiment followed by magnetization storage along the -z-axis. It is shown that this sequence almost entirely eliminates banding artifacts from both types of field inhomogeneities at all spin locking field strengths. The sequence was used to obtain artifact free images of agarose in inhomogeneous B(0) and B(1) fields, off-resonance spins in fat and in vivo human brain images at 3 T. The new pulse sequence can be used to probe very low frequency (0-400 Hz) dynamic and static interactions in tissues without contaminating B(0) and B(1) field artifacts.     

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.