1,721,066 research outputs found
Nuclear Structure evolution far from stability: study of 74Ni collectivity by Coulomb excitation
Full text linkIn recent years the availability of neutron-rich radioactive ion beams has allowed to explore new regions of the nuclear chart. Despite the most exotic nuclei have been produced with quite low intensities, new interesting results have revealed an evolution of the nuclear structure far from the valley of stability. Some of the well established fundamental properties of the uclear models, like the magic numbers, had to be reviewed in the light of new experimental observations: new features have
been included in nuclear models in order to reproduce experimental data. It was recently shown, indeed, that tensor and three-body forces play an important role in breaking and creating magic numbers.
One region of particular interest is the neutron-rich tail of the Ni isotopic chain. For instance the 78Ni nucleus corresponds to a double shell closure and is characterized by a large neutron excess. Some models predict that at this N/Z ratio one could expect an increase of the proton-neutron interaction strength that would modify the relative energies of the single particle states, thus reducing the Z = 28 energy gap. In such a scenario, particle-hole excitations should be strongly increased, driving to enhanced collectivity. The determination of the B(E2) values of the low-lying transitions is therefore very important to measure these features and to cons train the interaction used for the shell model calculations.
In this thesis we present the measurement of the B(E2; 0+ ! 2+) transition matrix element for the first 2+ state of the 74Ni nucleus. This was done in an intermediate-energy Coulomb excitation experiment performed at NSCL (MSU) where the Coulomb excitation cross section 0+!2+ was measured, allowing to extract the B(E2 ") value. To date, 74Ni is the most xotic Ni isotope produced with enough intensity to be used as a beam for spectroscopic studies. The 74Ni beam has been produced by fragmentation of a primary 86Kr beam at 140 AMeV
on a 9Be target. The primary beam was provided by the Coupled Cyclotron Facility of the NSCL and the production reaction fragments were analyzed using the A1900 fragment separator. As a matter of fact, this setup produced a secondary ”cocktailbeam“ containing 74Ni ions with an intensity of ~ 1 pps as well as higher intensity 77Zn and 75Cu fragments. An 197Au foil was used as secondary target. The scattered ions were identified by the focal plane detectors of the S800 spectrograph and coincidence gamma-rays emitted by Coulomb excited ions were detected by the 4pi CAESAR array. The results emerging from the data analysis show a different behavior with respect to the expectations. This finding opens new scenarios in the nterpretation of the shell evolution of the Z=28 isotopes.
The thesis has been organized as follows: the basic concepts concerning Nuclear Structure studies far from stability and the radioactive ion beams production are introduced in chapter 1. In chapter 2 the fundamental theoretical models of Coulomb excitation are presented. In chapters 3 and 4 are respectively described the experimental setup and the data analysis of the Coulomb excitation experiment. The final results are discussed in the last section. Considerations on possible interpretation of
Ni shell evolution will be presented together with some outlooks
Red emitting silicones for particles detection: Coupling with APD
No full textUp to date, neutron detection has been relying on sophisticated and voluminous systems, employing toxic and awkward liquid scintillators and fragile expensive PMT. In order to overcome these main drawbacks, red emitting polysiloxane based solid scintillators have been developed and optimized for coupling with high responsivity APD, having higher External Quantum Efficiency (EQE) in the red region of the visible spectrum. Optical properties of phenyl substituted polysiloxane based matrices, doped with different amounts of three organic dyes (PPO, Basf Lumogen Violet® and Basf Lumogen Red®) have been investigated in order to optimize light output for detection with APD. Scintillation performances of these red emitting scintillators have been measured with alpha particles and gamma rays and compared with the previously developed blue emitting polysiloxane based scintillators, showing an improved scintillation light yield with APD detectors. The performances of this polysiloxane based materials in fast neutron detection have also been verified using time of flight (TOF) discrimination technique with a 2.32 MeV neutron beam. Finally, the possibility to achieve pulse shape discrimination with this innovative materials has been also explored, achieving very interesting preliminary results that pave the way to the use of polysiloxane based scintillators in a field where liquid scintillators have been so far the only competitor. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence
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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