Fine structure definition

Contrary to widespread opinion, the value of Ea is not a constant quantity. As was proved previously [52], the value of E is variable, since it depends on the ordering of macromolecules in the amorphous material of the fiber. At the same time, one can suppose that this ordering will be affected by the specificity of the fine structure of the fiber, and particularly by the type of substructure of the fiber. The relationship determining the modulus Ea appropriate for a definite type of fiber substructure can be derived from Eq. (11) when appropriate values of A are assumed. In the case of the microfibrillar substructure, i.e., for A < I, typical of PET fibers stretched, but not subjected to annealing, this equation has the form [52] ... 

When an excited molecule also consists of a definite vibrational level as shown in Fig. 5.1(a), there shall be no direct dissociation of molecule and a fine structure in the electronic band spectra of the molecule will be observed. The excess energy, in usual course may be dissipated as heat or may give rise to fluorescence. But the molecule may retain its energy until it has not reacted with another molecule or transfer its energy to another molecule, e.g. decomposition of NOC1 as follows ... 

This is due to the comparative weakness of the electromagnetic interaction, the theory of which contains a small dimensionless parameter (fine structure constant), by the powers of which the corresponding quantities can be expanded. The electron transition probability of the radiation of one photon, characterized by a definite value of angular momentum, in the first order of quantum-electrodynamical perturbation theory mdy be described as follows [53] (a.u.) ... 

The presence of overcrowding in triphenylene has been demonstrated by Clar (1950) from an examination of the absorption spectra at 18°C and — 170°C. At — 170°C the / -band spectra of such aromatic hydrocarbons as benzene, naphthalene, anthracene, and pyrene become more distinct, showing much more fine structure than at 18°C. This is explained by the cessation at low temperature of thermal collisions which produce molecular deformations, thereby improving the definition of the molecular electronic orbitals. Where this change in spectra does not occur, permanent deformation at both low and high temperatures... 

The photolysis of diazoalkanes both in the gas phase and in solution is a carbenoid reaction. Moreover, the results of EPR-spectroscopic investigations (Section IIB) demonstrate that triplet carbenes can be generated by irradiation of diazoalkanes. That the reactive intermediates in carbenoid reactions are free carbenes is usually taken as self-evident. While such an assumption is probably wholly justified in most cases, it is worth remembering that both in the gas phase and in solvents such as n-hexane, the electronic absorption spectra of simple diazoalkanes show definite fine structure (Bradley etal., 1964a). This implies that the photo-excited state is bonding (Hoffmann, 1966) and consequently may have a life-time long enough to enable it to react directly with another molecule... 

Fig. 7.11. Comparison of the fine structure of the membranes of the eggs of Hymenolepis diminuta and H. nana. Note in H. nana (in contrast to H. diminuta) (a) the embryophore is thin and incomplete - a feature which may facilitate hatching in the gut of the definitive host (b) there is an additional polar filament layer between the oncospheral membrane and the basal lamina. Gc, Golgi complex ger, granular endoplasmic reticulum /, lipid bodies m, mitochondria n, nucleus v, vacuoles. (After Fairweather Threadgold, 1981a Holmes Fairweather, 1982.)...

With few exceptions, all classes of polysaccharides have common heterogeneities that exist across chemical and functional boundaries. In many instances these heterogeneities preclude definitive structure-function correlations. This notwithstanding, origin, fine structure, etc., can sometimes confer subtle distinctions, so that one polysaccharide may be preferable to others for a specific purpose. Dispersions of wheat starch have lower viscosity than dispersions of corn starch at identical concentrations, whereas waxy maize starch is the bodying agent of choice over com starch, when concern for clarity is secondary to dispersion stability. 

Table G Definitions of the Electric Field E, the (Di)electric Polarization P, the Electric Displacement D, the Magnetic Field H, the Magnetization M, the Magnetic induction or flux density B, statement of the Maxwell equations, and of the Lorentz Force Equation in Various Systems of Units rat. = rationalized (no 477-), unrat. = the explicit factor 477- is used in the definition of dielectric polarization and magnetization c = speed of light) (using SI values for e, me, h, c) [J.D. Jackson, Classical Electrodynamics, 3rd edition, Wiley, New York, 1999.]. For Hartree atomic u nits of mag netism, two conventions exist (1) the "Gauss" or wave convention, which requires that E and H have the same magnitude for electromagnetic waves in vacuo (2) the Lorentz convention, which derives the magnetic field from the Lorentz force equation the ratio between these two sets of units is the Sommerfeld fine-structure constant a = 1/137.0359895...

The copper chaperone function of Atxl was definitively demonstrated by O Halloran and colleagues in 1997 when they showed using electron paramagnetic resonance (EPR), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS),... 

Unfortunately, our carbon 13 and proton data (Table II) taken together with other data for the model compounds, do not allow an unambiguous assignment of the 3 stereoisomers which we have obtained. For the present, then, we must be content to leave the relative stereochemistry of the 5-membered ring model compounds in question. For now, we can only say that the fine structure in the copolymer spectra are certainly well within isomers shifts seen for the model compound. However, based on the fact that the relative stereochemistry of the tetrahydrofuran models are unknown and that we have only one pyran isomer, we are unable to make a definite assignment as to the relative stereochemistry of ring junctions in the original copolymer. 

Ultraviolet PES of gaseous, free-base phthalocyanine (H2PC) and metal phthalocyanines (MPc, M = Mg, Fe, Co, Ni, Cu, and Zn) were reported first in Ref. [60]. All spectra were strikingly similar only fine structures of broad bands differed. A narrow band at about 6.4 eV and a broad band at 8-10 eV appeared in all spectra. Another band followed at 10-12eV. Only tentative positions of several lEs were given in the experimental work [60] with no definite assignments. 

Figure 3.15. Zero-filling can be used to enhance fine structure and improve lineshape definition.

Finally, there is a pressing need for more-detailed information on the molecular fine-structure, or conformation, of polysaccharides in solution. The potential of small-angle x-ray diffraction for distinguishing between a random coil and a broken or partial helix in solution has been established. A better definition of the helical conformation of dissolved polysaccharides, which, because of basic chemical asymmetry, have a favored chirality ( handedness ), is awaited. This area of x-ray study is only beginning to be developed. ... 

Correlations of in situ and ex situ observations. The characterization methods of surface science have already been established within an electrochemical context, because they can provide structural definition of fine distance scales as well as atomic composition of a surface and, sometimes, vibrational spectroscopy of adsorbates. These ex situ methods normally involve transfer of an electrode from the electrochemical environment to ultrahigh vacuum, and the degree to which they provide accurate information about structure and composition in situ is continuously debated. Additional work is needed to clarify the effect of emersion of samples and their transfer to ex situ measurement environments. The most appropriate experimental course requires observations by techniques that can be employed in both environments. Vibrational spectroscopy, ellipsometry, radiochemical measurements, and x-ray methods seem appropriate to the task. Once techniques suited to this problem are established, emphasis should be placed on the refinement of transfer methods so that the possibilities for surface reconstruction and other alterations in interfacial character are minimized. 

A complete definition of the fine structure of cellulose would entail a knowledge of the exact distribution of the size and shape of these ordered and disordered regions, a position which has not yet been achieved. However, a report claims that four types of material which differ in the degree of orderly arrangement of molecular chains can be distinguished in both native and regenerated celluloses, although quantitative measurements have only been made on one viscose-rayon fiber. These four types of material are ... 

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