Materials Literature
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The problem of the first- or second-order nature of the nematic-smectic-$A$ phase change is explored. It is found that couplings between various order parameters, especially the first and second translational ones, are important. General Landau theory for coupled orientational and translational order parameters is dev…
The synthesis of a covalent dimer of chlorophyll a which possesses properties strikingly similar to those exhibited by P700 special pair chlorophyll in vivo is described. The covalent dimer is characterized by several spectroscopic techniques. Hydrogen bonding nucleophiles, such as water, primary alcohols, and primary…
Oligocene (approximate age 31-38 m.y. B.P., Berggren, 1972). The lower part of the Oligocene is missing. Using the coccolith and diatom biostratigraphic data, a hiatus must be placed between Samples 26-2 and 26-3. Thus, no further splitting of the Oligocene was done.
It is known that the porphyrin free base (H2P) can be incorporated in an n-octane Shpol'skii matrix. In slowly grown crystals the solute molecules occur in two orientations, which are co-planar and have their N-H … H-N axes at right angles; in the S 1↔S 0 ‘quasi-line’ absorption and fluorescence spectra they can be di…
Abstract The objective of this work was to obtain primary amine groups on the surface of poly(vinyl alcohol) films by means of a reaction with hexamethylene diisocyanate. The reaction was run in such a way as to minimize the internal crosslinking by employing a large excess of hexamethylene diisocyanate in toluene and…
Zusammenfassung Glaukonitglimmer von 10 kretazischen Gesteinen werden mineralogisch und chemisch untersucht. Die von den Glaukonitkòrnern und Glimmern der Kolloidtonfraktion errechneten Strukturformeln der Glaukonitglimmer bestàtigen die Glaukonitglimmer als exakt dioktaedrische Minerale. Die Strukturformeln geben nur…
Abstract Crystals of the squaric acid C 4 H 2 O 4 (H 2 SQ) and C 4 D 2 O 4 (D 2 SQ) exhibit a structural phase transition at T 0H = 370 K and T 0D = 520 K. The phase transition is associated with the ordering of protons, moving above T 0 in the symmetric double well potential of OHO bonds. The statistic of the phase…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMechanisms of reduction of cobaltic porphyrins with various reducing agentsEverly B. Fleischer and Stephen K. CheungCite this: J. Am. Chem. Soc. 1976, 98, 26, 8381–8387Publication Date (Print):December 1, 1976Publication History Published online1 May 2002Published inissue 1…
Couplings between inter- and intramolecular vibrations have been investigated. In normal-mode calculations a program has been used which allows all possible couplings between molecular and crystal vibrational modes. Several low-frequency molecular modes coupled to lattice vibrations have been isolated. A complete assi…
Abstract Inhaltsübersicht, Die Kristallstruktur von Ag 2 BaSnS 4 ist mit Röntgeneinkristalldaten erstmals bestimmt worden. Die aufgefüllte Tetraedergerüststruktur hat orthorhombische Symmetrie (a = 7,12 7 ; b = 8,11 7 ; c = 6.85 4 Å [1]). Raumgruppe: D 8 2 —I222, Nr. 23. Die kristallchemischen Eigenschaften von Ag + u…
An electron microscope study of copper-bismuth alloys has shown a high incidence of faceting of the grain boundaries. This is not observed in pure copper, suggesting the bismuth has a large effect on the low energy configurations of the boundary plane.
Nuclear magnetic second moment and spin–lattice relaxation time studies have been performed over the temperature range 77–388 K for two ammonium bisulfates; the ferroelectric NH4HSO4 and the antiferroelectric (NH4)3H(SO4)2. The results suggest a rapid general reorientation of the NH4 + ions over the whole temperature…
Abstract Thermal decomposition of poly(bismaleimides) has been investigated by using programmed and isothermal thermogravimetric analysis (TGA) in nitrogen. Reaction rates and overall activation energies were calculated from isothermal weight less studies. For five aliphatic poly(bismaleimides) a linear correlation be…
The results of extensive magnetization, susceptibility, X-ray and neutron powder diffraction measurements on the stoichiometric intermetallic compound Fe2MnSi are reported. At room temperature the compound is paramagnetic enabling the crystallographic structure to be established as L21 with some degree of preferential…
Abstract Rates of oxygen consumption and formation of oxidation products were determined in γ‐initiated oxidation of poly(vinyl chloride) (PVC) at 25°C. Data are given for five dose rates and correlated on the basis that the overall oxidation is the sum of two reactions that are first order and half order in rate of i…
Glutamine synthetase enzymes isolated from pea seeds and from Escherichia coli are observed to behave differently in experiments designed to probe reaction mechanism. Although both enzymes were found to bind and release substrates in random order mechanisms (Wedler, F.C. (1974) J. Biol. Chem, 247, 5080-5087), isotopic…
Abstract The temperature dependence of the dynamic modulus ( E ′) and the mechanical loss tangent (tanδ) of amorphous cellulose prepared from cellulose triacetate by saponification was measured and compared with that of cellophane, recrystallized cellulose obtained by immersing amorphous cellulose in water, and cellul…
Abstract Reaction with Na 2 S solutions at high pH led to almost complete, reversible reduction of iron in montmorillonite, whereas the structural iron of nontronite persisted in the ferric form. Concentrated Na 2 S solutions caused severe corrosion of nontronite and extracted appreciable amounts of iron, which was pr…
It is verified from the results of infrared absorption and X-ray analyses that the hydrogen bonds between the adjacent amide groups in crystalline regions of nylons 6, 66 and 610 are not broken but the motion of amide groups in a molecule is rather restricted in the whole temperature range below respective melting poi…
The resistance of a woven fabric to shear deformation is usually much smaller than the resistance to tensile deformation, and in a mixed stress field a fabric will generally shear to the maximum extent possible. The limits of shear deformation are determined by various geometrical parameters of the fabric, and differe…