Electrical fields, generation

G2, to G3, and to G4, the effective enhancement was 10%, 36%, and 35% larger than the value estimated by the simple addition of monomeric values. The enhancement included the local field effect due to the screening electric field generated by neighboring molecules. Assuming the chromophore-solvent effect on the second-order susceptibility is independent of the number of chro-mophore units in the dendrimers, p enhancement can be attributed to the inter-molecular dipole-dipole interaction of the chromophore units. Hence, such an intermolecular coupling for the p enhancement should be more effective with the dendrimers composed of the NLO chromophore, whose dipole moment and the charge transfer are unidirectional parallel to the molecular axis. 

Eo and E (Afi(i)) are respectively the electric fields generated by the permanent and induced multipoles moments. a(i) represents the polarisability tensor and Afi(i) is the induced dipole at a center i. This computation is performed iteratively, as Epoi generally converges in 5-6 iterations. It is important to note that in order to avoid problems at the short-range, the so-called polarization catastrophe, it is necessary to reduce the polarization energy when two centers are at close contact distance. In SIBFA, the electric fields equations are dressed by a Gaussian function reducing their value to avoid such problems. 

The initial electric field generated by a centre i of molecule A on a center j of molecule B is denoted is modified by a Gaussian function denoted S [45] as ... 

The velocity profile is uniform across the entire width of the channel if the channel is open at the electrodes, as is most often the case. However, if the electric field is applied across a closed channel (or a backpressure exists that just counters that produced by the pump), a recirculation pattern forms in which fluid along the center of the channel moves in a direction opposite to that at the walls further, the velocity along the centerline of the channel is 50% of that at the walls (Fig. 11.32a, see Plate 12 for color version). Figure 11.32b (see Plate 12 for color version) illustrates an electric field generating a net force on the fluid near the interface of the fluid/solid boundary, where a small separation of charge occurs due to the equilibrium between adsorption and desorption of ions. The charge region from excess cations localized near the interface by coulombic... 

Here Et is the intensity of the electric field generated by the particle motion in thermal field, L and L12 - Onsagera kinetic coefficients, olt = L 2 (eTn)-1 T l - thermoelectric coefficients. 

The enhancement factors mz and mx can be calculated exactly by Hansen s formulas for optics of thin multilayer film [10]. The results of the calculation for our experimental systems are shown in Figure 9 as a function of wavenumber. Three lines for the mz values and those for the mx values refer to the refractive indices of the LB film, 1.4, 1.5, and 1.6. The mx values are very small and about one percent of the mz values. This means that the electric field generated by the RA measurements is practically perpendicular to the film surface, as was mentioned above. 

E. Galoppini, M. A. Fox, Effect of the Electric Field Generated by the Helix Dipole on Photoinduced Intramolecular Electron Transfer in Dichromophoric Alpha-Hdical Peptides , J. Am. Chem. Soc 1996, 118, 2299-2300. 

Helical (carbon) nanocoils have received attention recently255-257 for their properties as field emitter and thus for the fabrication of flat panel field emission displays. The properties depend on the electrical field generated due to the helical nanostructure, and to the characteristics of the tip of the carbon nanocoil. In fact, carbon... 

The classical electrostatic balance is the Millikan condenser, which was first used to measure the charge on the electron in the famous Millikan oil-drop experiment. In principle, the device can be used to levitate a small charged mass by using the electrical field generated by two flat plates to... 

Optical activity is the ability of a compound to rotate the plane of polarized light. This property arises from an interaction of the electromagnetic radiation of polarized light with the unsymmetric electric fields generated by the electrons in a chiral molecule. The rotation observed will clearly depend on the number of molecules exerting their effect, i.e. it depends upon the concentration. Observed rotations are thus converted into specific rotations that are a characteristic of the compound according to the formula below. 

The electrical interactions can be easily calculated when the particle is close to the substrate and the ionic strength is low. In this case, we can simplify the problem to a conventional punctual particle with a charge q placed in the electrical field generated by the substrate in solution [9]. Using the Gouy-Chapman model for the calculation of the electrical field generated by the substrate leads to the following equation ... 

T(S) is the Debye-WaUer factor introduced in (2). The atomic form factors are typically calculated from the spherically averaged electrcai density of an atom in isolation [24], and therefore they do not contain any information on the polarization induced by the chemical bonding or by the interaction with electric field generated by other atoms or molecules in the crystal. This approximation is usually employed for routine crystal stmcture solutions and refinements, where the only variables of a least square refinement are the positions of the atoms and the parameters describing the atomic displacements. For more accurate studies, intended to determine with precisicai the electron density distribution, this procedure is not sufficient and the atomic form factors must be modeled more accurately, including angular and radial flexibihty (Sect. 4.2). 

In order to simplify (6.2), let us consider the common case of the electric field generated by a charged, flat surface (such as an electrode), see Figure 6.3. For this case and using electric potentials (6.2) becomes... 

Nuclear size corrections of order (Za) may be obtained in a quite straightforward way in the framework of the quantum mechanical third order perturbation theory. In this approach one considers the difference between the electric field generated by the nonlocal charge density described by the nuclear form factor and the field of the pointlike charge as a perturbation operator [16, 17]. 

Now we have written down a wave function appropriate for use in the case where H = h(i). In HF theory, we make some simplifications so many-electron atoms and molecules can be treated this way. By tacitly assuming that each electron moves in a percieved electric field generated by the stationary nuclei and the average spatial distribution of all the other electrons, it essentially becomes an independant-electron problem. The HF Self Consistent Field procedure (SCF) will be bent on constructing each x(x) to give the lowest energy. 

Isoelectric focusing is a procedure used to determine the isoelectric point (pi) of a protein (Fig. 3-21). A pH gradient is established by allowing a mixture of low molecular weight organic acids and bases (ampholytes p. 81) to distribute themselves in an electric field generated across the gel. When a protein mix-... 

The molecular orbital describes the "motion" of one electron in the electric field generated by the nuclei and some average distribution of the other electron. It is in the simplest model occupied by zero, one, or two electrons. In the case of two electrons occupying the same orbital, the Pauli principle demands that they have opposite spin. 

At the n-type interface, the electric field generated causes photogenerated conduction band electrons to move into the bulk of the semiconductor, to the back metal contact, and into the external circuit. The valence band holes access the semiconductor interface due to the influence of the interfacial electric field (Fig. 28.2). Thus, redox species can be oxidized by the excited n-type semiconductor. These materials act as photoanodes. On the other hand, the electric field in a p-type material is reversed in potential gradient therefore, excited electrons move to the semiconductor surface, while holes move through the semiconductor to the external circuit (Fig. 28.2). These materials are photocathodes. The presence of an electric field at the semiconductor-electrolyte interface is usually depicted by a bending of the band edges as shown in Figure 28.2. Elec-... 

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