Method of assessing diffusion coefficients from gas absorption by metal powders

Conclusions A simple experimental method is proposed for determining diffusion coefficients from amounts of gas absorbed by metal powders. An analysis is made of errors in the measurement of D by the new method, and optimum experimental conditions are indicated. Data yielded by a study of the diffusion of hydrogen in LaCo₅ show that D _H ²⁹³ LaCo₅ can be calculated by this method with satisfactory accuracy.Translated from Poroshkovaya Metallurgiya, No. 4(232), pp. 25–32, April, 1982.     

Preparation of magnetic glass-ceramics through glass crystallization in the Na2O-SrO-Fe2O3-B2O3 system

Glasses with the nominal compositions SrFe₁₂O₁₉ + nNa₂Sr₂B₄O₉ (n = 4, 6, 8, 10) and SrFe₁₂O₁₉ + 6Na₂Sr₃B₄O₁₀ were prepared via rapid quenching of oxide melts and were then heat-treated between 500 and 800°C in order to produce glass-ceramics containing fine SrFe₁₂O₁₉ particles. The materials were characterized by x-ray diffraction, differential thermal analysis, electron microscopy, and magnetic measurements. The crystallization behavior of the glasses was investigated. The coercivity of the glass-ceramics was shown to increase with heat-treatment temperature, up to 486 kA/m. By dissolving the nonmagnetic matrix of the glass-ceramics with the nominal compositions SrFe₁₂O₁₉ + 6Na₂Sr₃B₄O₁₀ and SrFe₁₂O₁₉ + 4Na₂Sr₂B₄O₉, submicron-sized strontium hexaferrite particles were obtained.     

Blasting Open a Choice Space: Learning Inflectional Morphology for NLP

This article discusses the various aspects of designing a system for eliciting knowledge about language from informants. For each design aspect, various options for implementation are presented, along with their pros, cons, and repercussions for other parts of the knowledge elicitation system. A running example throughout the text is taken from the paradigmatic morphology elicitation module of a system called Boas, which elicits knowledge to support a machine translation system. The main point of the article is an argument about the necessity to analyze the design choice space for complex natural language processing (NLP) systems early, comprehensively, and overtly.     

Parameterizing and Eliciting Text Elements across Languages for Use in Natural Language Processing Systems

This paper analyzes the structure and meaning of text elements cross-linguistically and discusses how that information can be elicited from people in a way that is directly useful for NLP applications. We describe a recently developed computer-based linguistic knowledge elicitation system that initiates a new paradigm of knowledge acquisition methodologies for NLP. In particular, we describe the natural language phenomena the system seeks to cover, the approach to knowledge elicitation and its rationale, the elicitation modules themselves, and broader implications of this work.     

Synthesis and Magnetic Properties of SrO–Fe2O3–B2O3 Glass-Ceramics

Glasses with nominal compositions of SrFe₁₂O₁₉ + 8SrB₂O₄ (I) and SrFe₁₂O₁₉ + 12Sr₂B₂O₅ (II) are prepared by rapid quenching from the liquid state and are converted to glass-ceramics containing fine magnetic particles of SrFe₁₂O₁₉ by heat treatment between 600 and 950°C. The materials are characterized by x-ray diffraction, differential thermal analysis, electron microscopy, and magnetic measurements. The phase transformations accompanying glass crystallization are identified. The glass composition and heat-treatment conditions are shown to influence the aspect ratio of the forming submicron-sized strontium hexaferrite particles. The strongest coercive fields reached in glass-ceramics I and II are 504 and 456 kA/m, respectively.     

Optical transmittance of thin GaAs wafers upon laser pumping in the region of exciton resonances and the continuum of states: Exciton-exciton interaction

The transmittance spectra of thin “pure” GaAs bulk wafers upon optical pumping corresponding to the band of the ground state of the exciton series are recorded at a temperature of T = 1.7 K. The wafers were grown by molecular-beam epitaxy and vapor-phase epitaxy. An increase in the line amplitude and width upon pumping is observed, with no noticeable changes in the spectral position of the line peak. The increase is similar to that observed upon pumping in the continuum of states, but occurs at a somewhat lower rate. Estimation of the concentration of excitons created by pumping provides a means for determining the exciton-exciton interaction constant and comparing the result with known data. The integrated absorption method makes it possible to refine the exciton polariton-free charge carrier and exciton polariton-impurity interaction constants. The differential photoabsorption of the samples at the pumping modulation frequency is measured. The resultant modulated absorption spectra demonstrate the connection between induced absorption and the formation of differential spectra.     

Trifluoromethylation of [60]- and [70]Fullerene in the Ionization Chamber of a Mass Spectrometer

Abstract

Both [60]- and [70]fullerene react with either the Scherer radical (perfluorodiisopropylethylmethyl, C₉F₁₉), a mixture of branched perfluorononenes (C₉F₁₈, the product of hexafluoropropene trimerization), or β-fluorosulphatotetrafluoroethyldiheptafluoroisopropylmethyl radical (C₉F₁₈OSO₂F) in the ionization chamber of a mass spectrometer to give the positive parent ions of trifluoromethylation products, the reaction being accompanied by hydrogen addition. The reaction occurs at least partly on the walls of the ionization chamber, by a radical mechanism employing CF₃ radicals formed from the radical reactants both thermally and under electron impact; only the latter route occurs with the perfluorononenes.     

Formation of nickel clusters for the growth of carbon nanotubes

The growth of vertically oriented carbon nanotubes on nickel clusters formed by nanoimprint lithography is studied. It is shown that the nanotubes only grow at those places where the catalyst clusters are situated and the diameter of the nanotubes exactly corresponds to the dimensions of the nickel islands.     

A multichannel spectrometer for detecting γ rays in a wide range of time intervals during pulse neutron irradiation

A versatile spectrometer has been developed for measuring the nuclear radiation spectrum in discrete time intervals. The design and operating principle of the spectrometer are described. Since the main logical part is based on a field programmable gate array, time intervals may be tuned in a wide range without changing the spectrometer hardware. The test experiments have demonstrated the spectrometer applicability for measuring the amplitude and timing parameters of the γ response when an analyzed sample is irradiated with a pulsed neutron flux. This device can be used to solve many problems of nondestructive testing, e.g., spectrometric neutron logging, detection of explosives, identification and characterization of fissile materials.     

Laser operation and computation of thermal stress in endpumped 1.1 at.% Nd-doped yttrium aluminium garnet rods with sub-millimetre diameters

Laser operation of a fibre-like 1.1 at.% Nd-doped yttrium aluminium garnet rod with a diameter of 0.34 mm and a length of 4.7 mm has been demonstrated. The fibre was end pumped with 0.5 W of continuous-wave radiation from a laser diode emitting at 808 nm. The measured laser thresholds are in a reasonable agreement with theoretical estimations. The distributions of temperature and stress in the crystal fibre were calculated with finite-element simulations showing that the fibre can be pumped up to a power of 40–50 W without fracture caused by thermal stress. The advantages and disadvantages of the proposed laser rod design are discussed.