1,720,955 research outputs found
Confined H(1s) and H(2p) under different geometries
No full textIn this paper the diffusion Monte Carlo method is applied to the confined hydrogen atom with different confinement geometries. This approach is validated using the much studied spherical and cylindrical confinements and then applied to cubical and squared ones, for which data are not available, as new applications of the method relevant to solid state physics. The energy eigenvalues of the ground state and one low-lying excited state are reported as a function of the characteristic confinement length
Spherically confined H2+: 2σ +g and 2σ +u states
No full textThe molecular ion H2+ is studied under strong confinement conditions produced by a spherical barrier centered in the gravity center of the molecule. Results for the potential curves are obtained by diffusion Monte Carlo methods for the ground state (X) and the first excited state (A), and reported as functions of the internuclear distance d for different values of the confinement radius. Results show that the compressed states corresponding to both and present deep minima in their potential curves, due to the increased space for electron wave-functions when the protons are displaced from the barrier surface
Thermal decomposition rate of MgCO3 as an inorganic astrobiological matrix in meteorites
No full textCarbonate minerals, likely of hydrothermal origins and included into orthopyroxenite, have been extensively studied in the ALH84001 meteorite. In this meteorite, nanocrystals comparable with those produced by magnetotactic bacteria have been found into a carbonate matrix. This leads naturally to a discussion of the role of such carbonates in panspermia theories. In this context, the present work sets the basis of a criterion to evaluate whether a carbonate matrix in a meteor entering a planetary atmosphere would be able to reach the surface. As a preliminary step, the composition of carbonate minerals in the ALH84001 meteorite is reviewed; in view of the predominance of Mg in these carbonates, pure magnesite (MgCO3) is proposed as a mineral model. This mineral is much more sensitive to high temperatures reached during an entry process, compared with silicates, due to facile decomposition into MgO and gaseous carbon dioxide (CO2). A most important quantity for further studies is therefore the decomposition rate expressed as CO2 evaporation rate J (molecules/m2 s). An analytical expression for J(T) is given using the Langmuir law, based on CO2 pressure in equilibrium with MgCO3 and MgO at the surface temperature T. Results suggest that carbonate minerals rich in magnesium may offer much better thermal protection to embedded biological matter than silicates and significantly better than limestone, which was considered in previous studies, in view of the heat absorbed by their decomposition even at moderate temperatures. This first study can be extended in the future to account for more complex compositions, including Fe and Ca.I minerali carbonatici, probabilmente di origine idrotermale e inclusi nell'ortopropossenite, sono stati ampiamente studiati nel meteorite ALH84001. In questo meteorite, i nanocristalli paragonabili a quelli prodotti dai batteri magnetotattici sono stati trovati in una matrice carbonatica. Ciò porta naturalmente a una discussione sul ruolo di tali carbonati nelle teorie della panspermia. In questo contesto, il presente lavoro pone le basi di un criterio per valutare se una matrice carbonatica in una meteora che entra in un'atmosfera planetaria sarebbe in grado di raggiungere la superficie. Come fase preliminare, viene rivista la composizione dei minerali di carbonato nel meteorite ALH84001; in considerazione della predominanza di Mg in questi carbonati, la magnesite pura (MgCO3) viene proposta come modello minerale. Questo minerale è molto più sensibile alle alte temperature raggiunte durante un processo di entrata, rispetto ai silicati, a causa della facile decomposizione in MgO e anidride carbonica gassosa (CO2). Una quantità molto importante per ulteriori studi è quindi il tasso di decomposizione espresso come tasso di evaporazione della CO2 J (molecole / m2 s). Un'espressione analitica per J (T) è data usando la legge di Langmuir, basata sulla pressione di CO2 in equilibrio con MgCO3 e MgO alla temperatura superficiale T. I risultati suggeriscono che i minerali di carbonato ricchi di magnesio possono offrire una protezione termica molto migliore alla materia biologica incorporata rispetto a silicati e significativamente migliori del calcare, che era stato considerato in studi precedenti, in considerazione del calore assorbito dalla loro decomposizione anche a temperature moderate. Questo primo studio può essere esteso in futuro per tenere conto di composizioni più complesse, tra cui Fe e Ca
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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