Gradient enhanced spectroscopy

This paper provides a brief overview of the personal recollections of the authors regarding their contributions to the introduction of shielded gradient technology into NMR spectroscopy during the late 1980s and early 1990s. It provides some background into early probe design and details some of the early technical progress with the use of shielded magnetic field gradients for coherence selection in high resolution NMR and describes the developments at General Electric, the National Institutes of Health, Georgetown University and Johns Hopkins University School of Medicine that ultimately led to this technology becoming commonplace in modern NMR spectroscopy. Most of this early technical work was published in the Journal of Magnetic Resonance.     

Crystal structure of 2,2-diphenylethyl 2,4,6-trimethylphenyl ketone: Kohler's ketone. Mechanism of stereospecific enolization reaction with grignard reagents

The title compound crystallizes in the monoclinic space group P2₁/n with a = 10.875(2), b = 6.039(5), c- 29.015(8)A, and β = 91.29(2). The observed density for Z = 4 la 1.14(1) Mgm^-3 (D_c - 1.155 Mgm^-3). The reliability factors for 1127 unique reflections are R - 0.066 and R_w = 0.064. The dihedral angle between the mesityl ring and the carbonyl to α- carbon plane is 114.4° in contrast to an angle of 89.9° reported earlier for a substituted t-butyl mesityl ketone. A mechanism is proposed for the formation of an E-magnesium enolate from the reaction of Kohler's ketone with Grignard reagents.     

Localization in the metallic regime of granular Cu—SiO2 films

The temperature dependences of the electrical resistivity of sputterd Cu—SiO₂ films measured in the range 4–300 K show minima which depend on the composition. A linear temperature dependence of ? is observed above the minimum, and an appropriate log T dependence is found below. The latter is attributed to electron localization. The magnetoresistance is found to be negative and the Hall constant shows no appreciable temperature dependence.     

In-situ fluorescence imaging of sol-gel thin film deposition

Pyranine was used as a fluorescence probe to monitor the chemical evolution in-situ during thin film deposition by the dip coating process. The sensitivity of the pyranine luminescence to protonation/deprotonation effects was used to quantify changes in the water/alcohol ratio in real time within the depositing film as the substrate was withdrawn from the coating reservoir. The spatially resolved spectral results clearly showed that preferential evaporation of alcohol occurred with increasing distance from the reservoir and that the maximum water content reached rather high values near the drying line. Correlation of the luminescence results with the interference pattern of the drawn films allows the solvent composition in the film to be mapped as a function of film thickness. These experiments demonstrate for the first time that luminescent organic molecules may be applied to the processing science of sol-gel thin film deposition.     

Hall effect studies in ytterbium through the f.c.c.-h.c.p. transformation

The Hall coefficient (R_H) of polycrystalline Yb showing the f.c.c.-h.c.p. transformation has been determined at 20 koe in the range 1.8–420°K. Both the structural and the associated magnetic transformation would separately be expected to modify R_H, but the evidence suggests that the observed behaviour through the transition arises primarily from the effects of the change in structure. A more detailed interpretation is presently not possible, however, because of the lack of knowledge of the band structure of h.c.p. Yb.     

A renormalization prescription for massless quantum electrodynamics

An alternative proof of the Ward-Takahashi identity for perturbative quantum electrodynamics is given which makes no use of a gauge invariant regularization such as the Pauli-Villars loop subtraction or dimensional regularization. Instead, it is shown, in the presence of an arbitrary high momentum cutoff, that the exact W-T identity holds with an error ofO(1) with 0<<1. The proof involves a perturbative analysis of the Euclidean functional integral for QED by the tree expansion method.Research supported by the Natural Sciences and Engineering Research Council