Subject index dielectric

Contents Introduction. - Volume Plasmons. - The Dielectric Function and the Loss Function of Bound Electrons. -Excitation of Volume Plasmons. - The Energy Loss Spectrum of Electrons and the Loss Function. - Experimental Results. - The Loss Width. - The Wave Vector Dependency of the Energy of the Volume Plasmon. - Core Excitations. -Application to Microanalysis. - Energy Losses by Excitation of Cerenkov Radiation and Guided Light Modes. - Surface Excitations. - Different Electron Energy Loss Spectrometers. - Notes Added in Proof - References. - Subject Index. 

Physical properties of the solvent are used to describe polarity scales. These include both bulk properties, such as dielectric constant (relative permittivity), refractive index, latent heat of fusion, and vaporization, and molecular properties, such as dipole moment. A second set of polarity assessments has used measures of the chemical interactions between solvents and convenient reference solutes (see table 3.2). Polarity is a subjective phenomenon. (To a synthetic organic chemist, dichloromethane may be a polar solvent, whereas to an inorganic chemist, who is used to water, liquid ammonia, and concentrated sulfuric acid, dichloromethane has low polarity.)... 

What is even more relevant to the present subject is that a thin dielectric layer of polymer can be situated between two media without grossly distorting the optical nature of the interface, i.e. total internal reflection would occur as if no polymer layer is present even if its refractive index is unmatched to both media. Such a layer will, however, affect the intensity of the evanescent wave and particularly its depth of penetration. ... 

The extensive value of Chemical Abstracts 19 is well known. The Engineering Index 20 GONQYS the engineering field selectively, not comprehensively important engineering advances such as dielectric drying are well covered. This index, issued annually, contains major and minor subject headings, with abstracts, and extensive cross-indexing. An alphabetical list of all names mentioned in the abstracts is also included. 

Second Order Non-Linear Effects. In order to probe second-order effects, materials normally must be subjected to electric fields of high enough intensity to polarise the material substantially, so that the induced polarisation becomes a non-linear function of the field strength. The relationship between the two common parameters which characterise bulk materials, viz. dielectric constant e and refractive index r, is shown in the following relationships ... 

An optically isotropic liquid crystal (LC) refers to a composite material system whose refractive index is isotropic macroscopically, yet its dielectric constant remains anisotropic microscopically [1]. When such a material is subject to an external electric field, induced birefringence takes place along the electric field direction if the employed LC host has a positive dielectric anisotropy (Ae). This optically isotropic medium is different from a polar Uquid crystal in an isotropic state, such as 5CB (clearing point = 35.4°C) at 50 C. The latter is not switchable because its dielectric anisotropy and optical anisotropy (birefringence) both vanish in the isotropic phase. Blue phase, which exists between cholesteric and isotropic phases, is an example of optically isotropic media. 

If a polymer mass containing only truly covalent bonds free from dipoles is placed in an electric field there is an instantaneous electron shift (electron polarization) but no actual movement of the molecules themselves. If this field is between two charged plates the polymer acts as a dielectric in a capacitor and the capacity of the charged plates is increased. The factor by which the capacity is increased is known as the dielectric constant or permittivity. Because it depends on virtually instantaneous electron movement the value of the dielectric constant is not dependent on temperature nor on the frequency (if the field is subject to alternation). The dielectric constant of such materials is frequently equal to the square of the refractive index and both properties may be calculated from a knowledge of the chemical bonds present. The method of making such a computation is given in most standard texts on physical chemistry. 

Since the index of refraction is known to be a function of wavenumber, the dielectric constant, e, also depends on wavenumber. This follows from the atomic and molecular composition of matter. The material consists of molecules or atoms in which the charges are bound, and therefore acts as a collection of oscillators. Consider the case of charges in the molecules and atoms subjected to polarized radiation traveling in the x-direction with electric field E = Eq e Each molecule experiences a force due to the radiation field of the form F = gEo cos oat, where q is the electric charge. This force causes small displacements, r, of the charges, and thereby gives rise to a polarization of the material. The total polarization, P, is the volume sum of all individual dipole moments p = qi r generated by the field. 

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