Intrinsic polarization

Finally, we should mention that the asymmetry of molecular shape, polyphilic effects and conformational constraints are the dominant factors in the stabilization of polar ordering in achiral mesogens. The examples presented above are, therefore, highly significant. They show that many liquid crystalline structures are intrinsically polar and may be effectively stabilized by suitable design of the mesogenic molecules. 

TMDs usually consist of a helix. The peptide bond is intrinsically polar and can form internal hydrogen bonds... 

That microtubules exhibit an intrinsic polarity (i.e., with protofilaments running parallel and tubulin protomers regularly arranged in a head-to-tail manner) is obvious from experiments other than those involving image reconstruction. This intrinsic polarity was observed by Rosenbaum and Child (1976) and Witman (1975), who demonstrated biased tubulin addition to microtubules in vitro. This biased addition is a consequence of the nature of tubule-tubulin interactions at the two ends of the microtubule ... 

From Eq, (1) it is clear that a model of crystal polarization that is adequate for the description of the piezoelectric and pyroelectric properties of the P-phase of PVDF must include an accurate description of both the dipole moment of the repeat unit and the unit cell volume as functions of temperature and applied mechanical stress or strain. The dipole moment of the repeat unit includes contributions from the intrinsic polarity of chemical bonds (primarily carbon-fluorine) owing to differences in electron affinity, induced dipole moments owing to atomic and electronic polarizability, and attenuation owing to the thermal oscillations of the dipole. Previous modeling efforts have emphasized the importance of one more of these effects electronic polarizability based on continuum dielectric theory" or Lorentz field sums of dipole lattices" static, atomic level modeling of the intrinsic bond polarity" atomic level modeling of bond polarity and electronic and atomic polarizability in the absence of thermal motion. " The unit cell volume is responsive to the effects of temperature and stress and therefore requires a model based on an expression of the free energy of the crystal. 

However, during the excited-state lifetime, energy transfer to neighboring molecules and/or local and global motions of the fluorophores can be observed. These two phenomena induce reorientation of the emission dipole, thereby depolarizing the system. Therefore, the value of the measured polarization P will be lower than intrinsic polarization value PQ (Weber, 1952). 

Additivity and interaction, intrinsically polar concepts, are basic in physical sciences... 

In a time-resolved experiment, the intrinsic polarization of the system is measured with very little correction except for power saturation (98,99). To measure the initial polarization, the signal heights S and Sq (hence the enhancement factor V and the polarization factor P = /So) can be obtained directly from the time profile. For a photo-CIDEP system induced only by the triplet mechanism and the triplet reaction involves a substrate SH, a kinetic analysis yields the following relationship ... 

The intrinsic polarization factor Pintr (i-e., the value before it was degraded by the radical decay, spin relaxation, and microwave-induced transitions) is given by... 

The effect of ultrasonic agitation on the electrolytic Mn02 (EMD) deposition at a ferrite anode has been studied and its electrochemical activity determined by intrinsic polarization [136]. Ultrasonic agitation at 28-55 kHz produced a significant decrease in polarization and an increase in both current efficiency and pulverization at various current densities on the ferrite anode. The authors found that the performance of the ultrasonically produced Mn02 excelled in the polarization for an alkaline medium. 

HP-NPC can be performed on unmodified silica that separates analytes according to their intrinsic polarity. HP-NPC can also be operated in isocratic, step gradient, or gradient elution mode, where the retaining mobile... 

With histidine and arginine, the problem is the intrinsic polarity of the derivative. This affects the solubility of the derivative in the solvent (ethyl acetate or chlorobutane) used to transfer the derivative from the reaction cell to the conversion flask. With some systems, trifluoroacetic acid (TFA) is added to this solvent to help counteract the problem, although the tenacious attraction of TFA to proteins/peptides and their derivatives indicates that His and Arg derivatives have already formed the TFA salt during the cleavage reaction and continue to... 

The intrinsic polarity of the bond should not be confused with the polarity that the molecule as a whole may have for other reasons. 

Abstract. The intrinsic polarization of young stars contains important information about the physical state of the objects and their surroundings. In particularly, the investigations of polarimetric activity of the variable stars can throw light upon variability mechanisms. In stars surrounded by circumstellar disks unresolved with a telescope, the position angle of the intrinsic linear polarization can indicate disk orientation. The wavelength dependence of the linear polarization is a sensitive function of the optical parameters of the dust particles and can be used for their diagnostics. 

Therefore in order to obtain the intrinsic polarization we have to correct Fobs for the interstellar and the instrumental components. The classical method of investigating interstellar polarization is through polarimetric observations of neighboring stars. The instrumental polarization depends on the optics of the telescope and the polarimeter and usually does not exceed a few tenths of a percent. The correction for Pinst demands regular observations of polarimetric standards collected in several papers (see e.g. Coyne et al. 1974 Tinbergen 1979 Whittet 1992). 

The broad-band polarimetric observations of a large number of PMS stars show, however, that the main source of their intrinsic polarization is the scattering of the stellar radiation by CS dust (Bastien 1985 Grinin et al. 1991). This conclusion follows from the wavelength dependence of the intrinsic polarization it is far from that observed in the classical Be stars where Thomson scattering dominates. Another argument in favor of... 

Most TTSs are cool stars. Therefore, their radiation is sensitive to temperature variations on their surface, especially at short wavelengths. The existence of surface inhomogeneities (cool and hot spots) of rotating stars leads to a periodic modulation of the flux illuminating the CS dust and, as a result, to the periodic modulation of the intrinsic polarization of stars. Its amplitude depends on the amplitude of the light modulation as well as on the CS disk parameters including its inclination to the line-of-sight and the optical parameters of CS dust. 

Figures 1 land 12 show the evolution of the polarizing spectra in the region of the H line for one of these stars, SN 1998S (Type Iln), obtained with 10m at 5 days after discovery, and with 2.1m telescope in two nights at 10 and 41 days after the optical maximum of the supernova. The data show that the polarization varied with time, meaning an intrinsic origin. The existence of intrinsic polarization supports the idea that the ejection is highly aspherical. However, due to a lack of observational data it is difficult to determine which mechanism is best. In many cases it likely a combination of mechanisms.

Po and Ao are called respectively the intrinsic polarization and anisotropy. Po and Ao are measured at temperatures equal to - 45°C or less. At this temperature, the fluorophores do not display any motions. Measurements of the intrinsic polarization are performed as follows ... 

Fig. 1.7 Actuation mechanism of a liquid crystal elastomer. The application of an electric field results in the realignment of intrinsically polarized liquid crystal mesogens. The mesogens are either grafted to elastomer chains or incorporated within them. The elastomer chains prevent the free flow of the mesogens and couple their motion to bulk stresses and strain...

This paper explores both electric field poling of polymers and LBK deposition of intrinsic y polar polymer films containing the chromophoie in the main-chain, or accordion architecture (3a). Mainchain syndioiegic polymers and poled films constitute the first topic, followed by a second section that describes a bilayer approach to intrinsically polar films. 

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