Electric field gradient description

Particularly in mass spectrometry, where discharges are used to enhance or produce ions from sample materials, mostly coronas, plasmas, and arcs are used. The gas pressure is normally atmospheric, and the electrodes are arranged to give nonuniform electric fields. Usually, coronas and plasmas are struck between electrodes that are not of similar shapes, complicating any description of the discharge because the resulting electric-field gradients are not uniform between the electrodes. 

The charge distribution, the electrostatic potential, the electrostatic field, and the electric field gradient belong to the category of physical observables related to a static description of material systems. 

In another related article Jerschow has reviewed new high-resolution NMR techniques for the study of quadrupolar nuclei. This article also includes theoretical description of the NMR techniques. A number of topics that are often left out in other review articles, such as nuclear quadrupole resonance, overtone spectroscopy and the ionic model for the calculation of electric field gradients, have also been considered. In addition, high-resolution techniques, such as double rotation, dynamic-angle spinning, MQ MAS, and satellite transition MAS have also been reviewed. 

The various electrostatic forces acting between particles, particles and surfaces, and liquid interfaces in the presence of electric fields having been the subject of numerous theoretical and experimental investigations. While the fundamental force mechanisms between materials have been identified (Lapple 1970 Krupp 1967 Adamson 1976), there remains practical limitations to their application because of the uncertainty of detailed descriptions at contact points such as the number and size of asperities, close contact separation distance and contact area, presence of films, and gas breakdown from electric fields. Complications arise from the presence of other permanent forces such as van der Walls and contact electronic forces or if there is a distribution of particle sizes. Dielectrophoretic effects resulting from field gradients and dielectric present yet another electrostatic force factor (Jones, 1995). 

Rate processes are those in which one component of a feed stream is transferred from the feed phase into a second phase owing to a gradient in a physical property. Gradients in pressure or concentration are the most common. Other gradients include temperature, electric fields, and gravity. The limiting step upon which design is based is the rate of transfer of the particular component from the feed material to the second phase. For relative motion of the various chemical species (rate), the mathematical description relates the rate of transfer of a particular compo-... 

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