Electric helicity meaning

Fig. II, 17, 2 illustrates a fractional distillation unit f for use with glass helices. The column is provided with an electrically-heated jacket the resistance shown in the Figure may be replaced by a variable transformer. The still head is of the total-condensation variable take-off type aU the vapour at the top of the column is condensed, a portion of the condensate is returned to the column by means of the special stopcock (permitting of...

PB equation is based on the mean-field approximation, where ions are treated as continuous fluid-like particles moving independendy in a mean electric potential. The theory ignores the discrete ion properties such as ion size, ion-ion correlation and ion fluctuations. Fail to consider these properties can cause inaccurate predictions for RNA folding, especially in the presence of multivalent ions which are prone to ion correlation due to the strong, long-range Coulomb interactions. For example, PB cannot predict the experimentally observed attractive force between DNA helices in multivalent ion solutions. 

The counterion mechanism of dielectric polarization is also in reasonable agreement with the data collected for DNA in the double-helical state as well as in the coiled denatured form. For the latter, much smaller electric increments and relaxation times are observed, indicating contraction of the polymer upon denaturation. The rotational relaxation time for helices as measured by means of flow birefringence was generally found... 

Our consideration so far have applied to photons in an ideal spherical cavity. Consider now the very important case of interaction between a single atom with electric dipole transition and cavity field in the case of Fabry-Perot resonator formed by two parallel ideal reflecting mirrors. In this case, the cavity field can consist only of the photons propagating along the axis of resonator (z axis) because all other photons should leave the space limited by the mirrors. This means that the cavity photons have well-defined direction and therefore are in a state with given linear momentum (21)-(22). Hence, the radiation emitted by the electric dipole transition consists of the two modes with m = 1, while the radiation of the third mode m 0 is forbidden. In this case, the photons with given helicity can be represented in terms of linearly polarized photons as follows [27] ... 

This function is served by compact, helically coiled tubes of a given diameter for convenient use. They are readily connected to the other elements of the system, so that void volumes are minimized. Occasionally, they are heated by means of electrical wires or a thermostated bath. 

A sufficient amount of oriented chiral molecules can be obtained in an induced cholesteric liquid crystal phase if the induced helical structure has been untwisted by an electric field. In the following description tensors are needed for the sake of simplicity (At least there are three tensors required the transition moment tensor (absorption tensor ,y), the rotational strength tensor (circular dichroism tensor A ,y), and the order tensor g,y33 (i,j= 1,2,3). If the molecules do not possess any symmetry, the principal axes of all of these tensors are differently oriented with respect to the molecular frame (the coordinate system in which only the three diagonal elements of a tensor are different from zero).) The only tensorial property, needed here explicitly, is the existence of three coordinates (components) of a tensor with respect to three specially chosen mutually perpendicular axes. This means that three information instead of one information about a molecule are needed instead of one CD value, namely Ae, three CD values, namely As, (i=l, 2, 3), have to be introduced. Ac is then one-third of a sum of the three so-called tensor coordinates of the CD tensor ... 

By combining classical samplings with quantum chemistry semiempirical TDHF calculations the impact of dynamic fluctuations on the first hyperpolarizability of helical strands has been evidenced . In particular, these fluctuations are responsible for relative variations of 20% in the hyper-Rayleigh responses in both pyridine-pyrimidine (py-pym) and hydrazone-pyrimidine (hy-pym) strands. Dynamical disorder has an even more important impact on the electric field-induced second harmonic generation responses, whose variations can reach 2 (py-pym) or 5 (hy-pym) times their mean value. These results demonstrate that geometrical fluctuations have to be taken into account for a reliable description of the second-order NLO properties in flexible structures such as helical strands. This work has also highlighted the relationships between the nature of the unit cell and the helical conformation of foldamers and their second-order NLO responses. In particular, the value of the hyper-Rayleigh depolarization ratio, which is characteristics of octupolar symmetry, is related to the helix periodicity, of three unit cells per turn in both compounds. 

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