1,721,108 research outputs found
Neutrino emission via proton-proton interaction and magnetic field screening in GRBs
Get PDFGamma-Ray Bursts (GRBs) are one of the most energetic astrophysical events of our Universe and a
precise study of all the physical mechanisms occuring in these systems involves different branches of
physics (from particles physics to General Relativity). The main subjects of this thesis concern the
particles physics and the plasma physics fields. I study two different physical processes, operated by
elementary particles as protons, electron/positron paris, photons and neutrinos, occuring in GRBs.
In Ch. (1) I give a general introduction to GRBs, with some of their structural physical generalities
and properties (as their different emission phases, spectral and temporal properties etc.). I introduce also
the fireshell model, which has been developed during the years by Prof. Ruffini, R. and his group, in
order to study and understand the several mechanisms behind the GRB emission. I will also highlight the
principal differences between this model and the fireball model (which was the first model adopted in
order to study the GRBs emission).
The structure of the fireshell model considers a Reissner-Nordoström Black Hole, with a strong electric
field that converts part of the BH total energy in e + e − plasma by the vacuum polarization process. These
particles are accelerated and emit photons, and this leads to the formation of a relativistic optically thin
fireshell of e + e − γ plasma (the “PEM–pulse”). This shell interacts with baryons, deposited in the ambient
near the BH due to the collapse event, forming a new accelerated optically thick plasma of e + e − γ-baryons
(PEMB–pulse). The transparency of this shell brings to the formation of the proper GRB emission
(P-GRB emission).
In Ch. (2) I introduce a classification of the GRBs in classes and subclasses. They differ from each
other principally for their different progenitors, formation process, their isotropic energy E iso , their rest-
frame spectral peak energy E p,i and local observed rate.
In the Thesis, I have focused my attention principally on a particular type of long GRB class: the type
I Binary-driven HyperNova (BdHN). The physical scenario and process, that leads to the formation of
the BdHN class, is the Induced Gravitational Collapse (IGC), with the hypercritical accretion process
paradigm. The two original studies of the Thesis, developed in Chs. (3) and (4), are based on the physical
scenario of BdHN. In this chapter, I also show the connections between the several observations of a GRB
event and the basic processes of the BdHN model.
In Ch. (3), the first topic of the Thesis is presented, namely the neutrinos and photons production by
proton-proton interaction, between accelerated protons and protons at rest. Keeping in mind the above
discussed scenario for the dynamics of the e + e − γ-baryons plasma, recent numerical simulations have
shown that the SN ejecta becomes highly asymmetric. Therefore, the electron-positron (e ± ) plasma
created in the BH formation, during its isotropic and self-accelerating expansion, engulfs different
amounts of ejecta baryons along different directions, leading to a direction-dependent Lorentz factor. In
this configuration, I have studied the pp interaction occurring in two regions: an high density region and a
low density region. In the conclusion of this chapter I also try to give an estimate of a possible, direct or
indirect, detection of the neutrinos and photons created throught the above mechanism. From this analysis
it came out that a possible detection of these neutrinos with currently operating detectors is plausible only
for sources several order of magnitude more energetic than the ones considered in this work, and very-high
energy ineracting protons (this subject is treated in App. (D) and will be better developed in future works).
It also came out that an indirect detection of these neutrinos by means of the related photons emission is
possible.
The second subject of the Thesis is presented in Ch. (4) and concerns the study of the screening
process of an electromagnetic field near a BH operated by electron-positron pairs. It has been shown
that a rotating BH immersed in a test background magnetic field, of initial strength B 0 and aligned
parallel to the BH rotation axis, generates an induced electric field, whose strength is proportional to the
background magnetic field, E = 1/2 ΥB (where Υ is the BH spin parameter). In this analysis, I consider
the configuration of crossed fields: B = Bẑ and E = E ŷ. In this system, an huge number of e + e − pairs can be emitted by vacuum polarization process, start to be accelerated to high energies by the induced electric
field and emit synchrotron photons. These photons interact with the magnetic field via the magnetic pair
production process (MPP): γ + B → e + + e − . The motion of all these particles around the magnetic field
lines generates also an induced magnetic field oriented in the opposite direction to the background one,
which implies a reduction of the background magnetic field. The principal results are that the combination
of the processes described above can reduce the magnetic field in a small time scale, even if the production
of pairs is not so efficient due to the low energy of the emitted photons, for the selected initial conditions
of the field strengths and particles densities
New improved operators: a convenient redefinition
No full textIn this paper we consider a new definition of improved fermion operators which is very convenient for numerical QCD simulations with the nearest-neighbour improved action, and we present the one-loop values of the corresponding renormalization constants. This redefinition includes terms that are formally of order a2 or higher and do not affect the conclusions about order a improvement
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Renormalization of lattice two-fermion operators with improved nearest-neighbour action
No full textWe present a one-loop calculation of the renormalization constants of two-fermion local operators with the nearest-neighbour improved action. This calculation is a necessary ingredient in lattice computations of continuum hadronic matrix elements relevant for the predictions of many interesting physical quantities, including fπ,ρ, electromagnetic form factors, semi-leptonic D-decays, etc
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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