1,721,228 research outputs found
BOUNDS ON LEPTON FLAVOR CHANGING CURRENTS AND THE SOLAR NEUTRINO PUZZLE
No full textWe present a phenomenological analysis of a lepton flavor changing current, considering the case of interactions among leptons which change the neutrino flavor and are diagonal in the charged lepton sector. In the case of nu(e) nu(mu) transition, we derive a bound on the vector coupling constant G(V) less-than-or-equal-to 0.16 G(F) from experimental data on nu(mu)-e scattering. For a transition nu(e) nu(x), from (anti) nu(e)-e scattering experiments and from the analysis of advanced stellar evolutionary phases, we find G(V) less-than-or-equal-to 0.55 G(F). We discuss the compatibility of these data with a possible explanation of the solar neutrino puzzle. We also analyze how the present bounds can be improved in future long baseline neutrino experiments and atmospheric neutrino detectors
Funzioni di distribuzione non-convenzionali nella valutazione del rischio di collisione in volo
No full text
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
Determination of the Beryllium neutrino flux from helioseismic data
No full textWe show that helioseismology provides information oil Beryllium neutrino production in the Sun. ill particular, we derive a lower limit oil the Beryllium neutrino flux on earth. Phi (min)(Be) = 1 . 10(9)cm(-2)s(-1), in the absence of oscillations. by using helioseismic data, the B-neutrino flux measured by Superkamiokande and the hydrogen abundance at the solar center predicted by Standard Solar Models. Moreover. we obtain an helioseismic determination of Phi (Be) by comparing solar model with artificially changed v(Bc) production with helioseismic data
The Sun and the Newton constant
No full textSeveral properties of the solar interior are determined with a very high accuracy, which in some cases is comparable to that achieved in the determination of the Newton constant G(N). We find that the present uncertainty DeltaG(N)/G(N) = +/-1.5 x 10(-3) has significant effects on the profile of density and pressure, however, it has negligible influence on the solar properties which can be measured by means of helioseismology and B-8 neutrinos. Our results do not support recent claims that observational solar data can be used to determine the value of GN with an accuracy of few part in 10(-4). Present data cannot constrain GN to much better than 10(-2). (C) 2002 Elsevier Science B.V. All rights reserved
Helioseismic determination of Beryllium neutrinos produced in the sun
No full textWe provide a determination of the Beryllium neutrino luminosity directly by means of helioseismology, without using additional assumptions. We have constructed solar models where Beryllium neutrino, (nu(Be)) production is artificially changed by varying in an arbitrary way the zero energy astrophysical S-factor S(34) for the reaction (3)He + (4)He --> (7)Be + gamma. Next we have compared the properties of such models with helioseismic determinations of photospheric helium abundance, depth of the convective zone and sound speed profile. We find that helioseismology directly confirms the production rate of nu(Be) as predicted by SSMs to within +/- 25% (1 sigma error). This constraint is somehow weaker than that estimated from uncertainties of the SSM (+ +/- 10%), however it relies on direct observational data. (C) 2000 Elsevier Science B.V. All rights reserved
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
LINEAR SOLAR MODELS
No full textWe present a new approach to studying the properties of the Sun. We consider small variations of the physical and chemical properties of the Sun with respect to standard solar model predictions and we linearize the structure equations to relate them to the properties of the solar plasma. By assuming that the (variation of) present solar composition can be estimated from the (variation of) nuclear reaction rates and elemental diffusion efficiency in the present Sun, we obtain a linear system of ordinary differential equations which can be used to calculate the response of the Sun to an arbitrary modification of the input parameters (opacity, cross sections, etc.). This new approach is intended to be a complement to the traditional methods for solar model (SM) calculation and allows us to investigate in a more efficient and transparent way the role of parameters and assumptions in SM construction. We verify that these linear solar models recover the predictions of the traditional SMs with a high level of accuracy
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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