1,721,119 research outputs found
Static line broadening theory and the spectra of electron-bombarded liquid helium
No full textRecent observations of the absorption and emission spectra of electron-bombarded liquid helium and the development of a detailed model describing the state of an excited atomic species in liquid helium have made it desirable to have a method of computing spectral line properties from the model. In this work we have investigated the application of static line broadening theory when a nonspherical, numerical potential and a nonspherical distribution are required and the theory is to be employed at high densities. Techniques for the application of the intensity expression and analysis of computed spectral lines are performed for several model distributions and potentials. The results of computations using the Hickman model are compared with the observed spectra
Hydrogen in metals: screening, resistivity, and diffusion
No full textText includes handwritten formulasThe theory of screening of a potential in various approximations of a metal are reviewed. Phase shifts were calculated for free electron scattering by a Yukawa potential, and the screening parameter was adjusted to satisfy the Friedel sum rule. Using these phase shifts, residual resistivities of hydrogen in various metals were calculated in qualitative agreement with experiment. The theories of diffusion of hydrogen in metals are reviewed. A model for the hydrogenmetal interaction has been constructed using linear response screening for the hydrogen and superposition of neutral atoms for the metal. Screening in the region of the metal cores was treated with a pseudopotential. The occupation of octahedral sites in FCC metals and tetrahedral sites in BCC metals is correctly predicted. Vibrational energy level spacing for Pd and Ni were calculated to be .8 eV and .16 eV, respectively. Experimental values are .6 eV and .12 eV. Activation energies for diffusion are estimated with qualitative agreement with experiment
An expansion of the s-wave low energy electron-heavy noble gas atom scattering cross sections about a virtual state and a study of the associated Ramsauer-Townsend effect
No full textIn this paper the Ramsauer-Townsend effect is investigated for the rare gases Ar, Kr, and Xe. The usual modified effective range formulae for electron-atom scattering are replaced by an expansion of the s-wave phase shifts about a low-lying virtual state. A critical review of the experimental work which has been performed on the above systems for low energy total elastic electronatom scattering cross sections and for momentum-transfer cross sections is included
Basis representations for atomic collision problems: application to He_ + He*, _[Sigma]+g, two-state calculation
No full textThe coupled equations for the heavy-particle motion in atomic collisions are reviewed with emphasis on the transformation of the equations between different basis representations, in particular the adiabatic and diabatic representations. The application to the two-state approximation neglecting angular coupling is made and the required matrix elements and methods of evaluating these matrix elements are discussed; the various coupling terms are examined. Elastic and inelastic transition cross sections are calculated for collisions between metastable helium, He(1s2s,3S), and ground state helium. The inelastic transition He(1s28,3S) ---> He(1s2p0,3P) can occur in this collision due to the avoided crossing of the lowest two adiabatic 3 sigma, ^ +g potential curves for He2. The close coupling results are compared to results obtained using the adiabatic and diabatic decoupling approximations and the distorted wave approximation
On the interaction of metastable hydrogen and helium atoms with a metal surface
No full textText includes handwritten formulasA theoretical study of the adiabatic interaction of a metastable 2s hydrogen (or 2^1,3 S helium) atom with an idealized metal surface has been carried out where account has been taken of the 2s-2p state mixing due to the atom metal interaction. The variationally determined wavefunction and resonant-ionization rate are calculated as a function of atom-surface separation. It is found for the 2s(2p) state that the 2s-2p mixing causes a substantial lowering (raising) of the electronic energy and an increase (decrease) in the ionization rate. The competitive process of Penning ionization of adsorbed atoms is discussed using a simple model
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Pseudopotential studies of e-H¿ collisions
No full textText includes handwritten formulasDevelopments in the theory of electron scattering from molecules are delineated with the pseudopotential studies presented as an outgrowth of these undertakings. The coupled equations are educed in the pseudopotential framework, and elastic s-wave solutions are obtained without coupling of partial waves. A numerically simpler, though similar, treatment is presented and utilized to obtain results not too discrepant from those of the pseudopotentials. It is concluded that the approach is propitious but extensions of it should include the effects of partial wave coupling
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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