1,397 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
L’educazione infermieristica perioperatoria e la soddisfazione dell’utente: uno studio osservazionale
No full textRiconoscere la centralità del ruolo dell’utente all’interno del percorso assistenziale è sicuramente uno dei maggiori traguardi, in ambito sanitario, dell’epoca in cui viviamo.Tale centralità vede il suo fulcro nella realizzazione di un percorso di cura che si basa soprattutto su un progetto educativo da instaurarsi tra paziente ed operatore sanitario. Questo rapporto permette al professionista di aiutare il malato ad acquisire la consapevolezza del proprio stato di salute, ed al paziente di apprendere le nozioni fondamentali per comprendere e partecipare al proprio percorso di cura.La ricerca da noi condotta si è posta come obiettivo quello di valutare come l’educazione svolta dagli infermieri prima della dimissione ospedaliera da una degenza chirurgica, risulti rilevante nell’acquisizione di autonomia del paziente a domicilio e nella percezione di “soddisfazione” dello stesso per le informazioni ricevute. Sono stati intervistati 80 pazienti provenienti da diversi reparti chirurgici dell’Arcispedale Santa Maria Nuova di Reggio Emilia prevalentemente al momento della prima visita di controllo post dimissione; per indagare le diverse aree è stato utilizzato un questionario composto da domande aperte e chiuse, con lo scopo di valutare meglio l’aspetto qualitativo delle risposte. I risultati hanno evidenziato come i pazienti si ritengano complessivamente soddisfatti dell’educazione sanitaria ricevuta nel corso della degenza, nello specifico in merito al trattamento del dolore post operatorio, prevenzione delle infezioni, gestione della terapia, mobilizzazione e graduale ripresa di alimentazione ed idratazione.Restano tuttavia ancora due aspetti da migliorare: il primo è quello relativo al desiderio dei pazienti di ricevere un contatto telefonico da parte del personale ospedaliero, una volta dimessi; il secondo riguarda, invece, la necessità di una maggiore integrazione tra ospedale e territorio
The major antenna complex of photosystem II (LHCII) has a xanthophyll binding site not involved in light harvesting
No full textWe have characterized a xanthophyll binding site, called V1, in the major light harvesting complex of photosystem II, distinct from the three tightly binding sites previously described as L1, L2, and N1. Xanthophyll binding to the V1 site can be preserved upon solubilization of the chloroplast membranes with the mild detergent dodecyl-alpha -D-maltoside, while an IEF purification step completely removes the ligand. Surprisingly, spectroscopic analysis showed that when bound in this site, xanthophylls are unable to transfer absorbed light energy to chlorophyll a. Pigments bound to sites L1, L2, and N1, in contrast, readily transfer energy to chlorophyll a. This result suggests that this binding site is not directly involved in light harvesting function. When violaxanthin, which in normal conditions is the main carotenoid in this site, is depleted by the de-epoxidation in strong light, the site binds other xanthophyll species, including newly synthesized zeaxanthin, which does not induce detectable changes in the properties of the complex. It is proposed that this xanthophyll binding site represents a reservoir of readily available violaxanthin for the operation of the xanthophyll cycle in excess light condition
Interactions between the photosystem II subunit PsbS and xanthophylls studied in vivo and in vitro
No full textThe photosystem II subunit PsbS is essential for excess energy dissipation (qE); however, both lutein and zeaxanthin are needed for its full activation. Based on previous work, two models can be proposed in which PsbS is either 1) the gene product where the quenching activity is located or 2) a proton-sensing trigger that activates the quencher molecules. The first hypothesis requires xanthophyll binding to two PsbS-binding sites, each activated by the protonation of a dicyclohexylcarbodiimide-binding lumen-exposed glutamic acid residue. To assess the existence and properties of these xanthophyll-binding sites, PsbS point mutants on each of the two Glu residues PsbS E122Q and PsbS E226Q were crossed with the npq1/npq4 and lut2/npq4 mutants lacking zeaxanthin and lutein, respectively. Double mutants E122Q/npq1 and E226Q/npq1 had no qE, whereas E122Q/lut2 and E226Q/lut2 showed a strong qE reduction with respect to both lut2 and single glutamate mutants. These findings exclude a specific interaction between lutein or zeaxanthin and a dicyclohexylcarbodiimide-binding site and suggest that the dependence of nonphotochemical quenching on xanthophyll composition is not due to pigment binding to PsbS. To verify, in vitro, the capacity of xanthophylls to bind PsbS, we have produced recombinant PsbS refolded with purified pigments and shown that Raman signals, previously attributed to PsbS-zeaxanthin interactions, are in fact due to xanthophyll aggregation. We conclude that the xanthophyll dependence of qE is not due to PsbS but to other pigment-binding proteins, probably of the Lhcb type
Differential accumulation of Lhcb gene products in thylakoid membranes of Zea mays plants grown under contrastino light and temperature conditions
No full textMeasurement of the D meson elliptic flow in Pb-Pb collisions at sqrt(s_{NN}) = 2.76 TeV with ALICE
No full textWe present the measurements of D0, D+, D*+ meson v_2 as well as D0 R_{AA} in different directions with respect to the estimated reaction plane in Pb-Pb collisions at \sqrt{(s_{NN))}= 2.76 TeV with the ALICE detector at the LHC.We present the measurements of D^0, D^+, D^@?^+ meson v_2 as well as D^0R_A_A in different directions with respect to the estimated reaction plane in Pb-Pb collisions at =2.76TeV with the ALICE detector at the LHC.We present the measurements of D0 , D+ , D⁎+ meson v2 as well as D0 RAA in different directions with respect to the estimated reaction plane in Pb–Pb collisions at sNN=2.76TeV with the ALICE detector at the LHC.We present the measurements of D0, D+, D*+ meson v_2 as well as D0 R_{AA} in different directions with respect to the estimated reaction plane in Pb-Pb collisions at sqrt(s_{NN)) = 2.76 TeV with the ALICE detector at the LHC
D-meson reconstruction via cascade decays with the ALICE experiment
No full textDuring this internship, two D-meson decay channels involving were studied: and . In this report, the implementation of both cascade decay reconstructions in the ALICE analysis framework of the Charm-to-Hadron (D2H) group is presented. The performances in terms of memory consumption, running time and output size were evaluated on p-Pb data. Finally, cascade reconstructions were tested in pp Monte Carlo simulations
A STRUCTURAL INVESTIGATION OF THE CENTRAL CHLOROPHYLL A BINDING SITES IN THE MINOR PHOTOSYSTEM II ANTENNA PROTEIN, LHCB4
No full textMutant proteins from light-harvesting complexes of higher plants may be obtained by expressing modified apoproteins in Escherichia coli, and reconstituting them in the presence of chlorophyll and carotenoid cofactors. This method has allowed, in particular, the engineering of mutant LHCs in which each of the residues coordinating the central Mg atoms of the chlorophylls was replaced by noncoordinating amino acids [Bassi, R., Croce, R., Cugini, D., and Sandonà, D. (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 10056-10061]. The availability of these mutants is of particular importance for determining the precise position of absorption bands for the different chlorophyll molecules, as well as the sequence of energy transfer events that occur within LHC complexes, provided that the structural impact of each mutation is precisely evaluated. Using resonance Raman spectroscopy, we have characterized the pigment-protein interactions in the minor photosystem II antenna protein, Lhcb4 (CP29), in which each of three of the four central chlorophyll a molecules has been removed by such mutations. By comparing the spectra of these mutants with those of the wild-type protein, the state of interaction of the carbonyl group, the coordination state of the central magnesium ion, and the dielectric constant (polarity) of the immediate environment in the binding pocket of the chlorophyll a molecule were defined for each cofactor binding site. In addition, the structural impact of the absence of one chlorophyll a molecule and the quality of protein folding were evaluated for each of these mutated polypeptides
Differential accumulation of Lhcb gene products in thylakoid membranes of Zea mays plants grown under contrasting light and temperature conditions.
No full textIn higher plants many different genes encode Lhcb proteins that belong to a highly conserved protein family. Evolutionary conservation of this genetic redundancy suggests that individual gene products play different roles in light harvesting and photoprotection depending on environmental conditions. We have tested the hypothesis that expression/accumulation of individual light harvesting complex (Lhc) proteins depends on plant growth conditions. Zea mays plants were grown in different temperature (13 degrees C vs. 24 degrees C) and light (high vs. low) conditions. The thylakoid membranes were isolated and fractionated by sucrose gradient and the protein content of the different bands was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Significant differences were found in the accumulation of both the major light harvesting complex of photosystem II (LHCII) complexes and the minor antenna chlorophyll proteins CP29, CP26 and CP24. In particular, temperature seems to play a major role in driving the expression/accumulation of the different proteins: the LHCII/minor antenna ratio increases with decreasing temperature. The pigment composition and the spectroscopic properties of LHCII complexes isolated from low temperature grown plants are significantly different from those of LHCII purified from high temperature grown plants. Two-dimensional maps show that different LHCII proteins are accumulated at different levels depending on growth conditions. Moreover the low temperature/high light grown plants show an increased value of nonphotochemical quenching. These results suggest a specific role of different LHCII complexes in the organization of the potosystem II and photoprotection
Exploring jet substructure with jet shapes in ALICE
No full textThe characterisation of the jet substructure can give insight into the microscopic nature of the modification induced on high-momentum partons by the Quark-Gluon Plasma that is formed in ultra-relativistic heavy-ion collisions. This modification of parton-to-jet fragmentation and of the parton virtuality, induced by the QGP, can be studied using jet shapes, in particular using jet energy redistribution, intra-jet broadening or collimation. Results of a selected set of jet shapes are presented for p–Pb collisions at sNN=5.02 TeV and for Pb–Pb collisions at sNN=2.76 TeV . Results are also compared with PYTHIA Perugia 11 calculations and models that include in-medium energy loss.The characterization of the jet substructure can give insight into the microscopic nature of the modification induced on high-momentum partons by the Quark-Gluon Plasma that is formed in ultra-relativistic heavy-ion collisions. Jet shapes allow us to study the modification of parton to jet fragmentation and virtuality, probing jet energy redistribution, intra-jet broadening or collimation and possible flavour hierarchy. Results of a selected set of jet shapes will be presented for \mbox{p--Pb} collisions at and for \mbox{Pb--Pb} collisions at . Results are also compared with PYTHIA calculations and models that include in-medium energy loss
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