Soluble Bimetallic μ-Oxo-alkoxides. 8. Structure and Kinetic Behavior of the Catalytic Species in Unsubstituted Lactone Ring-Opening Polymerization
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Different contributions of the two cobalt sites to the magnetocrystalline anisotropy of YCo5and related compounds
The properties of permanent magnets based on RCo5compounds arise from their strong uniaxial anisotropy. The anisotropy field at 4.2 K in YCo5is about 200 kOe. A polarized neutron study of YCo5revealed a very large orbital contribution to the magnetic moment on the CoI(2c) site, which indicates that the major part of t…
Antifungal Properties of Electrically Generated Metallic Ions
A qualitative and quantitative investigation was undertaken to study the susceptibility of unicellular eucaryotic organisms (yeasts) to metallic cations generated by low levels of direct current. Results were characteristic of effects obtained previously using clinical and standard bacteria test organisms. The present…
Some structural aspects of sisal fibers
A critical account has been presented of the recent investigation on the chemical modification of lignocellulosic sisal fibers. The molecular structure of the paracrystalline cellulose, which forms the major constituent of the fiber, was studied by x-ray diffraction technique. Scanning electron microscope examination…
Material and Mode Dispersion in GeO 2 ·B 2 O 3 ·SiC 2 Glasses
Material and mode dispersion in fibers made from glasses in the system GeO 2 ‐B 2 O, 3 ‐SiO 2 have been calculated using refractive index dispersion results for these glasses. Refractive indices were measured on bulk glass specimens using the minimum deviation method at wavelengths from 0.4358 to 1.0830 μm. The result…
Drift mobility determinations using surface-potential decay in insulators
Open-circuit dark surface-potential decay characteristics have been measured in positively corona-charged films of solution-cast low-density polyethylene. For initial fields of about 5×105 V/cm, the surface potential V (t) decays linearly for a period of time, after which it is curvilinear. As a result, the time deriv…
Nucleation and Repassivation of Corrosion Pits for Pitting on Iron and Nickel
Abstract Pit nucleation and repassivation on iron and nickel has been examined by potentiostatic transient measurements. Very short times for the nucleation of corrosion pits of some ms to some 100 ms for prepassivated specimens have been observed. Addition of picrate to the electrolyte can stop pit nucleation for wel…
Analysis of spatial distribution of charges and dipoles in electrets by a transient heating technique
A method is discussed for measuring the separate spatial distributions of fixed charge and permanent polarization in a uniform insulator. Changes in the potential difference across the insulator are measured when a known nonuniform time-dependent temperature perturbation is established through the sample thickness. Th…
The measurement of magnetostriction in ferromagnetic thin films
The application of a magnetic field parallel to a ferromagnetic film deposited on one side of a cantilevered substrate causes a small deflection of the free end. This deflection can be measured and the magnetostriction determined since the magnetostriction is proportional to the deflection. An instrument has been devi…
Piezoelectricity and Pyroelectricity of Polymers
This article surveys theoretical and experimental work on piezo- and pyroelectricity of polymers in the 1970's with special emphasis on the origins of these properties. The origins are classified into three types: (A) internal strain (§2), (B) strain- and temperature-dependences of spontaneous polarization (§3), and (…
Analysis of Linear Methods for Determining Copolymerization Reactivity Ratios. III. Linear Graphic Method for Evaluating Data Obtained at High Conversion Levels
If copolymerizations are carried to high conversions, the determination of copolymerization parameters involves significant computational difficulties because the exact integrated form of the copolymerization equation has to be applied. A simple method has been developed to transform experimental data, even at high co…
Theory of piezoelectricity in nematic liquid crystals, and of the cholesteric ordering
A statistical-mechanical theory of the elastic constants of a liquid crystal based on the Onsager expansion is reexamined, with emphasis on the terms linear in the gradients of the director. This gives a microscopic theory of the piezoelectric effect in nematic liquid crystals, and of the spontaneous twisting of a cho…
Computational models for ductile and brittle fracture
Computational models of dynamic ductile and brittle fracture are developed for wave propagation in one- and two-dimensional geometries. The model features have been taken mainly from detailed observations of samples partially fractured during impacts, but the functional forms are consistent with theoretical results wh…
Block Copolymer Theory. 4. Narrow Interphase Approximation
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTBlock Copolymer Theory. 4. Narrow Interphase ApproximationEugene Helfand and Z. R. WassermanCite this: Macromolecules 1976, 9, 6, 879–888Publication Date (Print):November 1, 1976Publication History Published online1 May 2002Published inissue 1 November 1976https://pubs.acs.o…
A simple method for the determination of the optical constants n, k and the thickness of a weakly absorbing thin film
A new calculation following traditional methods is proposed for deducing optical constants and thickness from the fringe pattern of the transmission spectrum of a thin transparent dielectric film surrounded by non-absorbing media. The particular interest of this method, apart from its easiness, is that it makes a dire…
Raman-Active Lattice Vibrations of the Commensurate Superlattic in2H−TaSe2
Raman spectra have been obtained on $2H\ensuremath{-}\mathrm{Ta}{\mathrm{Se}}_{2}$ at room temperature and in the commensurate charge-density-wave, superlattice state. At low temperatures six new low frequency modes are seen having symmetries consistent only with a symmetric, three-charge-density wave. A microscopic m…
Origin of Raman Scattering and Ferroelectricity in Oxidic Perovskites
The second-order Raman scattering and the temperature dependence of the ferroelectric soft mode in $\mathrm{AB}{\mathrm{O}}_{3}$ perovskites are explained quantitatively in terms of a nonlinear shell model by assuming an anisotropy in the oxygen polarizability. This model yields a new explanation for the origin of fer…
The electrical resistivity and temperature coefficient of resistivity of cobalt films
The resistivity and the temperature coefficient of resistivity of cobalt films 280-1600 AA thick were studied at temperatures between 30 and 150 degrees C. It was observed that coherent films were obtained by depositing the cobalt films slowly onto a heated (150 degrees C) substrate. The experimental observations coul…
Phase Transition in Surface-Aligned Nematic Films
Properties of the nematic-isotropic phase transition in surface-aligned nematic films are calculated using the Landau-de Gennes theory. It is shown that there is a critical thickness ${D}^{c}$ of the film below which the transition from the nematic phase to the isotropic phase becomes continuous. At the critical thick…
A neutron diffraction study of the cation migration in MgMn2O4
The crystallographic properties of the tetragonal spinel MgMn2O4, subjected to different thermal treatments, is studied by neutron diffraction method. At elevated temperatures there is a significant variation in the degree of inversion owing to the migration of Mg2+ ions from the tetrahedral to the octahedral sites. F…