Materials Literature
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Abstract The numbers of rings formed in the reactions of hexamethylene diisocyanate with two polyethylene glycols have been determined as a function of dilution and ratios of reactants. In this work the cryoscopic apparatus developed in the preceding paper has been utilised. It is found that more rings are formed (a)…
Abstract It has been known for several years that pregnenolone is the biogenetic precursor of hormones of the adrenal cortex and of progesterone in the animal kingdom. The route to the androgenous and oestrogenous hormones also goes via this intermediate. However, in the plant kingdom it was only later that the role o…
The effect of the mechanical constraints exerted by coatings upon electromigration in thin films is evaluated on the basis of known pressure effects upon diffusion.
A flood-gun arrangement is shown to be useful in alleviating the sample-charging problem in x-ray photoelectron spectroscopy. Modest currents (<10−8 A) of low-energy electrons result in the shifting of photoelectron energy peaks to the proper positions and the reduction of the peak widths.
Measurements of the temperature dependence of the dielectric constants ε‖, ε⊥, and εis of some nematic liquid crystals with strong positive dielectric anisotropy (ε‖ ≃ 3 ε ⊥) are reported. The low frequency dispersion regions of the dielectric constants parallel to the unique axes were measured to be in the range from…
It is shown that piezoelectric effects can be easily derived from bulk properties and are expressible in terms of linear and quadrupole moments of variations in charge density induced by atomic displacements. The linear-moment contribution is determined by optic macroscopic effective charges and internal-strain parame…
A study of the quantum efficiency of the luminescence of gadolinium and terbium in borate glasses and of the energy transfer between these ions is presented. From our measurements of fluorescence decay times, absorption, fluorescence, and excitation spectra, we calculated the fluorescence quantum yield of the 6P7/2 ga…
The electric-dipole intensities of Er 3+ spectra in six different host lattices have been calculated on the basis of Judd-Ofelt theory, which takes into account the effect of a mixing of higher configurations of opposite parity into the f n configuration through odd parity spherical harmonics in the ligand field inter…
Micro-Heterogeneity in the Biosynthesis of CollagenDetailed analyses of the structure of the polypeptide chains of collagen has revealed a "micro-heterogeneity" of the amino acid sequences. Sequencing of the first 50 amino acid residues from the NH2-terminal end of the α1 chain of rat skin and tendon collagen indicate…
The trapping of positrons at vacancy sites in some metals provides a new and sensitive method for the equilibrium determination of vacancy-formation energies. Data are presented for Al, Cd, In, Pb, and Zn and fitted to a model allowing presentation in the form of Arrhenius plots. The vacancy concentration is not deter…
The origin of electronic states in two classes of semiconductors is explored: (i) semiconductors containing group-VI elements in twofold coordination, and (ii) tetrahedral semiconductors. In the first case the valence band arises from the unshared electron pair (lone pair) of the group-VI atom. We examine the effects…
Crystals of armalcolite, Mg(0.5)Fe(0.5)Ti(2)O(5), up to several millimeters in length have been grown from a glass initially having the composition of lunar rock 10017. A single-crystal x-ray study has confirmed that the crystals are isomorphous with pseudobrookite and has shown that the cations are strongly ordered,…
Intracellular Biosynthesis of CollagenWork from several laboratories has demonstrated that the biosynthesis of collagen occurs by a series of sequential steps: assembly on ribosomal complexes of a polypeptide precursor of collagen that we have called "protocollagen"; hydroxylation of appropriate Pro and Lys residues i…
The carbothermic reduction in vacuum of thorium oxide with graphite has been studied with the aid of a high temperature thermobalance at temperatures range of 1,300°–1,900°C. The effects of differences in the reaction temperature, molecular ratio of the reactants, and in the state of the reactants such as differences…
Experimental findings of an irradiation enhancement of precipitation in stainless steel under observation in the High Voltage Electron Microscope (HVEM) are presented. The results for the case of electron irradiation are compared with previous studies of precipitation under neutron irradiation in thermal and fast reac…
SUMMARY Among the examples reviewed are volume‐fraction measurements in phase diagram and kinetic studies, properties dependent upon internal surface area, the characterization of phase arrangements by contiguity, proximity and dihedral‐angle measurements. The use of grain boundary and particle spacings in studies of…
<div class="htmlview paragraph">The friction and wear characteristics of automotive friction materials are strongly dependent on the composition and microstructure of the rotor surface. In this study we investigated the compositional and microstructural changes occurring in the surface layers of cast iron brake…
The effect of small-angle multiple scattering on a number of general structural parameters and on the segment distribution function has been studied using a representative correlation function of the type γ = exp (−r/lp). The results show that size parameters can be severely underestimated if the presence of multiple…
The perovskite SrTiO3 can be controllably crystallized in situ in a glass matrix, and the resulting glass-ceramic displays a large peak in the dielectric constant at about 75 K (shifted from 35 K by doping and glass-chemistry techniques) and a T-1 increase in the dielectric constant below 0.1 K. This high degree of di…
A laboratory investigation was conducted to determine the effects of cathodically charged hydrogen on the mechanical properties of MONEL(1) nickel-copper alloy K-500, and to investigate the relationship between material hardness and susceptibility to hydrogen embrittlement. Tensile specimens having hardnesses of 26 to…