Dielectric discontinuity

In real-time, shallow earth profiles of dielectrical discontinuities related to subsurface conditions such as moisture content lithology, bedding, voids, fractures, man-made objects. Can be used to detect buried plastic containers artd areas of excavation boundaries. 

Although it is essentially a conductivity technique, the experimental setup is very similar to that used for optical absorption measurements. In simple terms, the attenuation of the amplitude of the microwave resulting from its passage through the irradiated system is measured. Actually, the microwaves are reflected back through the medium by a metal plate at the back of the cell, but because micro-waves undergo reflection at any dielectric discontinuity, such as the gas-liquid interface at the front of the cell, interference effects arise due to the coherent nature of the microwave radiation. 

The GRID electrostatic energy function was proposed to account for the dielectric discontinuity between a solute and the solvent as [Goodford, 1985] ... 

In order to understand the reactivity of ceria surfaces and the interaction of it with metal particles or adsorbates, it is of fundamental interest to know its surface structure and the extent or type of defects present. Even though the film may be an oriented single crystal, there is still the question of whether the surface is terminated in oxygen anions, Ce cations, a mixture or in defects associated with the termination. Charge neutrality, interfacial relaxation and dielectric discontinuities may modify the properties of an oxide surface. Also the ability of the surface to adsorb or give up oxygen, as well as the structure, clustering and reactivity of defects may be expected to depend upon the surface orientation and structure. 

The manner in which protons diffuse is a reflection of the physical properties of the environment, the geometry of the diffusion space, and the chemical composition of the surface that defines the reaction space. The biomembrane, with heterogeneous surface composition and dielectric discontinuity normal to the surface, markedly alters the dynamics of proton transfer reactions that proceed close to its surface. Time-resolved measurements of fast, diffusion-controlled reactions of protons with chromophores and fluorophores allow us to gauge the physical, chemical, and geometric characteristics of thin water layers enclosed between phospholipid membranes. Combination of the experimental methodology and the mathematical formalism for analysis renders this procedure an accurate tool for evaluating the properties of the special environment of the water-membrane interface, where the proton-coupled energy transformation takes place. 

We have demonstrated how studies of proton transfer on membrane surfaces evolved from the phase of data acquisition to the level of biophysical evaluation of the diffusion space matrix, an evaluation that is based on recognition of the paramount role of dielectric discontinuities and the geometry of the reaction space. 

The cause of the depletion of the ions in the vicinity of the polymer is still uncertain. Garvey and Robb (1979) suggested that the polymer constitutes a dielectric discontinuity in the medium so that the ions generate image forces, which repel the charged species. Subsequently, Robb (1982) suggested that the water structures around the polymer and certain ions are not compatible. 

The probe array is known to differ from the bulk aqueous reference system in three principal ways. First, each synthesis site contains a substantial number of truncated probes in addition to the desired full length probes. Second, the probe array resides at an abrupt dielectric discontinuity. Third, local concentrations of probes are known to be... 

The force fields used by scientists for simulations have been developed with distinct traditions, each appropriate for its own use. In computational chemistry, interest has been in bulk properties of solutions and proteins, in the thermodynamic limit in which boundary conditions do not appear explicitly and where equilibrium (i.e., zero flux of all species) is present. The thermodynamic limit of computational chemistry implies a spatial uniformity of bulk properties that can be analyzed with periodic boundary conditions if the period is longer than the spatial inhomogeneities of the bulk solution. Contrarily, in computational electronics, the interest has focused on electron devices, which exchange charge with their environment through geometrically and electrically complex boundaries and where internal dielectric discontinuities exist. Simulations are usually performed by varying the applied bias in order to reproduce transient nonequilibrium conditions and to obtain a record of the response of the simulated devices. 

Jayaram et al. performed a systematic study of the effects of electrostatic interactions on the counterion condensation around DNA. They used a 20-mer of electrically neutral sodium-DNA, with the DNA fixed in its canonical B form. The mobile counterions were placed randomly in a 50 A radius cylinder around the DNA, and the solvent was modeled as a dielectric continuum. Four dielectric treatments, ranging from Coulombic interactions with constant dielectric to a dielectric saturation model with a modified Coulombic potential introducing dielectric discontinuity, were studied. The dielectric saturation model used a modified Hingerty sigmoidal function... 

At the dielectric discontinuity, the direction of field vectors also changes from an angle 0 to an angle < > to the normal to the surface (see Fig. 7). 

This model is appropriate for a homogeneous system with only one dielectric constant and no ionic strength. By making e a distance-dependent function e(r), the model can be adapted to account for thef variation in dielectric to approximately represent a systerfi with low dielectric solutes immersed in high dielectric solvent. However, to properly account for dielectric discontinuities and ionic strength effects, other models, such as a continuum solvent Poisson-Boltzmann (PB) model must be used to compute electrostatic forces. 

The a-c measurements are particularly useful in detecting dielectric discontinuities, such as voids and delamination, positioned at an angle to the direction of the electric stress d-c resistance may be more useful in detecting a fault parallel to the electric stress. 

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