1,721,155 research outputs found
An accurate calculation of the ground-state energy of the helium atom and the hydrogen negative-ion using hyperspherical coordinates
No full textThe method of hyperspherical harmonics using an adiabatic separation between the hyper-radial coordinate and the hyperspherical angles is applied to the calculation of the ground state of the helium atom and the hydrogen negative ion. For each system the simple adiabatic separation provides much of the electron correlation energy. The non-adiabatic coupling is included by means of a perturbation treatment using both the Rayleigh—Schrödinger and Brillouin—Wigner approaches. These provide rapid convergence to the exact energy of ?2.90372 au
The calculation of the ground-state energy of weakly bound vanderwaals trimers using the method of hyperspherical harmonics .1. the born-oppenheimer and adiabatic approximations
No full textThe method of hyperspherical harmonics is applied to the calculation of the vibrational energy levels of the three-particle weakly bound van der Waals complexes. (H2)3?(D2) 3 and Ne3. Hyperspherical coordinates and the properties of the associated hyperspherical harmonic functions are discussed. These functions are used as an angular basis in which to expand the wavefunction for the three-particle system. A Born—Oppenheimer-type separation of the angular and hyper-radial motion is made. permitting a lower bound (Born—Oppenheimer approximation) and an upper bound (adiabatic approximation) to the energy of the clusters to be calculated
An investigation into large-scale hydrogen energy storage in the UK
No full textThe potential use of hydrogen as an energy carrier in the UK is dependant on a number of economic, technical and environmental factors. In the short term, the UK Government anticipates a transition from a fossil fuel based energy economy to a fossil fuel derived
hydrogen economy with carbon sequestration. An important factor in considering the replacement of fossil fuels with hydrogen will be the practicality of storing sufficient quantity, either in gaseous or liquid form, to smooth out fluctuations in demand and provide a strategic
reserve. It is anticipated that a minimum storage capacity equivalent to 2x105m3 at NTP will be required, ideally distributed around the country according to anticipated demand in each region and accessible to centers of population and industry. The UK has a number of areas where storage of hydrogen gas in natural underground spaces may be feasible. These include worked-out salt mines and depleted oil and gas wells. This paper investigates the potential for such large-scale storage. Factors considered include the technical and geophysical problems of storage, the logistics of various locations and legislative and legal issues. Equations of state for compressed gases are reviewed and the form most appropriate to underground storage of hydrogen highlighted. The geophysics of underground storage at a number of specific sites is considered in more detail. It is concluded that there is significant potential in the UK for underground storage of
hydrogen. This work will be of interest to the wider hydrogen research community and energy specialists whilst policy makers and the commercial sector are best placed to exploit the findings
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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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