1,722,599 research outputs found
Charm suppression in Pb-Pb collisions at the LHC measured using D0 K-Ï + reconstruction with the ALICE experiment
No full textThe thesis is focused on the measurement of the nuclear modification of charm quark production, in lead-lead collisions at the Large Hadron Collider. This observable is sensitive to the interaction of this quark with the high-density strongly interacting medium formed in ultra-relativistic heavy-ion collisions and, thus, to the properties of the state of matter. The partons traversing the medium lose energy via gluon radiation or elastic collisions with other partons already present in the medium. The charm quark allows to study the mass and colour charge dependences of the energy loss, since heavy quarks are expected to behave differently from light partons.
The measurement presented in this thesis is performed for the first time in nucleus-nucleus collisions, with the full reconstruction of D mesons via their hadronic decay. The strategy to reconstruct D0 mesons in the two-prong decay D0->K-ÃÂÃÂ+, with the ALICE experiment, will be described. Results obtained in Pb-Pb collisions at the energy of 2.76 TeV in the centre of mass of the collision for nucleons pair will be shown. In particular, the selection cut optimization was studied to compute the raw signal of D mesons with an invariant mass analysis. Selection and reconstruction efficiencies were considered with the detector acceptance, to correct for experimental effects. The corresponding data systematic uncertainties were evaluated in detail.
The comparison with the production cross section obtained in proton-proton collisions at the same energy allows then to compute the nuclear modification of D0 meson, the first direct evidence of the charm quark energy loss.
The measurement was compared with other open heavy flavour results and with light-charged hadrons suppression, measured at the LHC, to test the mass and colour charge dependences of the interaction with the medium. Results have been also compared with models that compute the charm quark energy loss using different theoretical approaches.
These results were recently approved by the ALICE Collaboration and a publication has been proposed and is being review by the Collaboration.La tesi descrive la misura della modifica della produzione di quark charm, in collisioni tra ioni piombo al Large Hadron Collider. Questa misura permette di studiare l'interazione del quark charm con il mezzo ad alta densitÃÂàe fortemente interagente, formato in collisioni di ioni pesanti ad energie ultra-relativistiche e le proprietÃÂàdi questo stato della materia. I partoni che attraversano il mezzo perdono energia per emissione di gluoni (gluonnstrahlung) e collisioni elastiche con gli altri partoni del mezzo. Il quark charm permette di studiare come variano le proprietÃÂàdell'interazione in funzione della massa e della carica di colore del quark, poichÃÂé i modelli teorici prevedono un comportamento diverso dei quark pesanti nel mezzo, rispetto a quelli leggeri.
La misura presentata in questa tesi ÃÂÃÂ ̈ la prima fatta in collisioni tra nuclei pesanti, attraverso la ricostruzione esclusiva dei mesoni D nel loro decadimento adronico. In particolare, verrÃÂÃÂ presentata la strategia di ricostruzione del mesone D0 nel suo decadimento in due corpi D0->K-ÃÂÃÂ+, fatta con l'esperimento ALICE. Verranno, quindi, illustrati i risultati ottenuti con i dati di collisioni Pb-Pb ad un energia nel centro di massa per coppia di nucleoni di 2.76 TeV. In particolare, ÃÂÃÂ ̈ stata studiata l'ottimizzazione dei tagli di selezione per misurare il segnale, estratto con un'analisi di massa invariante. Le efficienze di selezione e ricostruzione delle particelle e gli effetti di accettanza del rivelatore, sono stati considerati con uno studio Monte Carlo, per considerare gli effetti sperimentali. Nella tesi viene anche descritto in dettaglio lo studio sulle incertezze sistematiche.
Il confronto delle sezioni d'urto di produzione ottenute in collisioni Pb-Pb e protone-protone, alla stessa energia, permette di misurare il fattore di modifica nucleare del mesone D0, prima evidenza diretta di perdita energia del quark charm nel mezzo.
La misura ÃÂÃÂ ̈ stata confrontata con altri risultati ottenuti nel settore dei quark pesanti alla stessa energia, e con la soppressione degli adroni carichi, per valutare le dipendenze dalla massa e dalla carica di colore del quark, nella sua interazione con il mezzo. I risultati sono stati confrontati con modelli teorici che descrivono la perdita di energia del quark charm, utilizzando diversi metodi di calcolo.
I risultati sono stati recentemente approvati dalla collaborazione ALICE, una pubblicazione ÃÂÃÂ ̈ stata proposta ed ÃÂÃÂ ̈ in fase di review nella collaborazione
Lhc proteins and the regulation of photosynthetic light harvesting function by xanthophylls
No full textPhotoprotection of the chloroplast is an important component of abiotic stress resistance in plants. Carotenoids have a central role in photoprotection. We review here the recent evidence, derived mainly from in vitro reconstitution of recombinant Lhc proteins with different carotenoids and from carotenoid biosynthesis mutants, for the existence of different mechanisms of photoprotection and regulation based on xanthophyll binding to Lhc proteins into multiple sites and the exchange of chromophores between different Lhc proteins during exposure of plants to high light stress and the operation of the xanthophyll cycle. The use of recombinant Lhc proteins has revealed up to four binding sites in members of Lhc families with distinct selectivity for xanthophyll species which are here hypothesised to have different functions. Site L1 is selective for lutein and is here proposed to be essential for catalysing the protection from singlet oxygen by quenching chlorophyll triplets. Site L2 and N1 are here proposed to act as allosteric sites involved in the regulation of chlorophyll singlet excited states by exchanging ligand during the operation of the xanthophyll cycle. Site V1 of the major antenna complex LHC II is here hypothesised to be a deposit for readily available substrate for violaxanthin de-epoxidase rather than a light harvesting pigment. Moreover, xanthophylls bound to Lhc proteins can be released into the lipid bilayer where they contribute to the scavenging of reactive oxygen species produced in excess ligh
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
No full text“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
No full textWe 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
No full textWe 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
Stoichiometry of LHCI antenna polypeptides and characterization of gap and linker pigments in higher plants Photosystem I.
No full textWe report on the results obtained by measuring the stoichiometry of antenna polypeptides in Photosystem I (PSI) from Arabidopsis thaliana. This analysis was performed by quantification of Coomassie blue binding to individual LHCI polypeptides, fractionation by SDS/PAGE, and by the use of recombinant light harvesting complex of Photosystem I (Lhca) holoproteins as a standard reference. Our results show that a single copy of each Lhca1-4 polypeptide is present in Photosystem I. This is in agreement with the recent structural data on PSI-LHCI complex [Ben Shem, A., Frolow, F. and Nelson, N. (2003) Nature, 426, 630-635]. The discrepancy from earlier estimations based on pigment binding and yielding two copies of each LHCI polypeptide per PSI, is explained by the presence of 'gap' and 'linker' chlorophylls bound at the interface between PSI core and LHCI. We showed that these chlorophylls are lost when LHCI is detached from the PSI core moiety by detergent treatment and that gap and linker chlorophylls are both Chl a and Chl b. Carotenoid molecules are also found at this interface between LHCI and PSI core. Similar experiments, performed on PSII supercomplexes, showed that dissociation into individual pigment-proteins did not produce a significant loss of pigments, suggesting that gap and linker chlorophylls are a peculiar feature of Photosystem I
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