1,721,319 research outputs found
An optimized algebraic basis for molecular potentials
No full textThe computation of vibrational spectra of diatomic molecules through the exact diagonalization of algebraically determined matrices based on powers of Morse coordinates is made substantially more efficient by choosing a properly adapted quantum mechanical basis, specifically tuned to the molecular potential. A substantial improvement is achieved while still retaining the full advantage of the simplicity and numerical light-weightedness of an algebraic approach. In the scheme we propose, the basis is parametrized by two quantities which can be adjusted to best suit the molecular potential through a simple minimization procedure
Clearing observed PGR in GRACE data aimed at global viscosity inversion: Weighted Mass Trends technique
No full textThe time-variable gravity field shows the effects of large present-day mass variations associated with hydrological phenomena and melting ice-sheets, resulting in a shaded
Post Glacial Rebound (PGR) signal. A meaningful viscosity inversion based on a global scale comparison of GRACE data and PGR predictions is thus hard to obtain. We derive a weighted surface mass distribution in water equivalent, starting from an initial guess, which portrays the secular effects of present-day phenomena. The gravity field it
generates is then carefully removed from GRACE data, resulting in a gravity pattern where the effects of PGR are clearer and ready to be compared with the predictions. On the basis of viscoelastic stratified Earth models and different Pleistocene deglaciation models, we show that the quality of a global preliminary viscosity inversion greatly improves
Isolating the PGR signal in the GRACE data: impact on mass balance estimates in Antarctica and Greenland
No full textRedistribution of mass over the Earth and within the mantle changes the gravity field whose variations are monitored at high spatial resolution by the presently flying GRACE space gravity mission from NASA or, at longer wavelengths, by the Satellite Laser Ranging (SLR) constellation. In principle, GRACE data allow one to study the time evolution of various Earth phenomena through their gravitational effects. The correct identification of the gravitational spatial and temporal fingerprints of the individual hydrologic, atmospheric, oceanographic and solid Earth phenomena is thus extremely important, but also not trivial. In particular, it has been widely recognized that the gravitational estimates of present-day ice mass loss in Greenland and Antarctica, and the related effect on sea level changes, depend on an accurate determination of the Postglacial Rebound (PGR) after Pleistocene deglaciation, which in turn depends on the assumed solid Earth parameters and deglaciation model. Here we investigate the effect of the uncertainty of the solid Earth parameters (viscosity, litospheric thickness) and of different deglaciation processes on PGR in Greenland and Antarctica. We find that realistic constraints to the trend in ice mass loss derived from GRACE data determine a range of variation substantially wider than commonly stated, ranging from an important ice loss of -209 Gt yr(-1) to an accumulation of +88 Gt yr(-1) in Antarctica, and Greenland ablation at a rate between -122 and -50 Gt yr(-1). However, if we adopt the set of most probable Earth parameters, we infer a substantial mass loss in both regions, -171 +/- 39 and -101 +/- 22 Gt yr(-1) for Antarctica and Greenland, respectively
Systematic calculation of molecular vibrational spectra through a complete Morse expansion
No full textWe propose an accurate and efficient method to compute vibrational spectra
of molecules,
based on exact diagonalization of an algebraically calculated matrix based
on powers of Morse coordinate.
The present work focuses on the 1D potential of diatomic molecules: as
typical examples, we apply this method to the standard Lennard-Jones
oscillator, and to the ab-initio potential of the H2 molecule.
Global cm^(-1) accuracy is exhibited through the H2 spectrum, obtained
through the diagonalization of a 30x30 matrix.
This theory is at the root of a new method to obtain globally accurate
vibrational spectral data in the context of the multi-dimensional potential
of polyatomic molecules, at an affordable computational cos
Effect of dietary supplementation with a phosphatidyl-inositol metabolite, cerophoshorylinositol, on Na+/K+ATPase activity and body weight i9n normal rats
No full textAmong the functions related to the inositol-containing phospholipids in the mammalian cells there is the activation of the Na+/K+ ATPase. A reduction of the activity of this enzyme is implicated in the reduced motor nerve conduction velocity observed in diabetic rats, in which concentration of free inositol in the peripheral nerve is lower than in normal rats. Even erythrocytes from diabetics have fewer sodium pumps than do erythrocytes from age-matched controls. Feeding normal, weaning rats glycerophosphorylinositol (GPI), a metabolite of myo-inositol, we investigated the connections among inositol availability, sodium pump activity, and development. Unexpectedly, GPI supplementation determined a reduction in the Na+/K+ ATPase activity and a decrease in the phosphatidylinositol content in the erythrocyte membranes, without altering the phosphatidylinositol fatty acid composition. Apart from all considerations about the mechanism of action of GPI, these data clearly state the relationship between sodium pump activity and phosphatidylinositol levels
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
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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