Diese Arbeit beschäftigt sich mit dem HERA-B-Experiment zur CP-Verletzung bei DESY in Hamburg und beschreibt die Rekonstruktion des für HERA-B wichtigen Zerfalls J/psi->e^+e^- und dem darauf aufbauenden Ausblick auf Lebensdauermessungen von Teilchen mit schweren Quarks. Zunächst wurde zur Frühjahr-1999-Datennahme mit ausgeschaltetem Magneten die relative Ausrichtung zwischen dem Vertexdetektor und dem elektromagnetischen Kalorimeter untersucht. Daraufhin konnten die Vierervektoren Elektronspuren gemessen werden. Die energieabhängige Ortsauflösung des Kalorimeters wurde bestimmt. Die späteren Datennahmen mit eingeschaltetem Magneten im Herbst 1999 erlaubten eine Impulsmessung aller geladenen Teilchen. Die höhere geometrische Akzeptanz des weiter ausgebauten Detektors und der erweiterte Trigger erlaubte eine reguläre Beobachtung des J/psi-Signals. Die Breite des Signals konnte durch die in den Frühjahr-Daten gefundene Ortsauflösung des Kalorimeters erklärt werden. Die rekonstruierten J/psi-Mesonen wurden verwendet, um die Ortsauflösung der Vertizes zu untersuchen. Für Detektorkonfiguration im Herbst 1999 wurde ein Fehler des J/psi-Vertex in z-Richtung von sigma_z=1.29mm gefunden. Die Primärvertizes konnten bei Benutzung der Targetposition mit einer Unsicherheit von sigma_z=57mu m rekonstriert werden. Der HERA-B-J/psi-Trigger wird die vollständige Rekonstruktion von bisher wenig bekannten b-Baryonen ermöglichen. Vor allem interessant sind das Xi_b^- und das Sigma_b^0. Es besteht die Möglichkeit, dass ihre Lebensdauer mit den Daten eines HERA-B-Jahres mit der Genauigkeit von sigma_tau=0.1ps gemessen werden kann. / This thesis has been done at the HERA-B experiment for CP violation at DESY in Hamburg and describes the reconstruction of the for HERA-B important decay J/psi->e^+e^- and gives an outlook on possible lifetime measurements of particles with heavy quarks. In the spring 1999 runs a relative alignment between vertex detector and electromagnetic calorimeter was performed with the HERA-B magnet switched off. The four-vectors of electron tracks could be calculated and the energy-dependent spatial resolution of the calorimeter was measured. The fall 1999 runs with magnet switched on allowed a momentum measurement of charged particles. The increased geometrical acceptance and the extended trigger lead to the regular observation of the J/psi signal. Its width could be described by the spatial resolution of the calorimeter measured in the spring runs. The reconstructed J/psi mesons were used to analyze the vertex resolution. In the 1999 detector setup the J/psi vertex resolution in z was sigma_z=1.29mm. Using the target constraints the primary vertex resolution was sigma_z=57mu m. The HERA-B J/psi trigger will make the exclusive reconstruction of so far not well known b charged baryons possible. Especially the Xi_b^- and the Sigma_b^0 are interesting. One year of HERA-B data taking can permit their lifetime measurement with an accuracy of sigma_tau=0.1ps.

Il dolore post-operatorio rappresenta un importante problema sanitario dal punto di vista dei pazienti, degli operatori sanitari e della società nel suo complesso, dati i costi sanitari che provoca. La presente tesi ha l’obbiettivo di identificare i fattori psicologici e psicosociali che ne influenzano lo sviluppo. Nel primo capitolo viene affrontata la complessità del dolore postoperatorio tramite un’esposizione delle prospettive teoriche sul tema. A partire dalla definizione di questo fenomeno, sono stati presi in rassegna i diversi potenziali predittori e sono state descritte le modalità attraverso le quali questi predittori influenzano l’esperienza del paziente. È stata data attenzione particolare al substrato fisiologico che collega i fattori psicologici e psicosociali alla percezione del dolore. Il secondo capitolo presenta una revisione sistematica della letteratura con meta-analisi sui fattori di rischio psicologici e psicosociali associati al dolore cronico postoperatorio. Sono state descritte le scelte metodologiche adottate, come l’impostazione di una ricerca il più possibile comprensiva e l’utilizzo di metodi di imputazione multipla per ridurre l’effetto dei dati. Dopo una selezione tra 6329 studi, sono stati utilizzati 63 articoli per costruire una sintesi narrativa delle ricerche sul tema. I risultati di 34 tra questi studi sono stati successivamente utilizzati per effettuare una meta-analisi. La sintesi narrativa ha permesso di evidenziare ottimismo, salute mentale e paure chirurgiche sono associate al dolore cronico post-chirurgico, mentre l’effetto di ansia, depressione e catastrofismo è maggiormente incerto. I risultati della meta-analisi, al contrario, evidenziano in modo chiaro che depressione, ansia, catastrofismo, paura del movimento, auto-efficacia e ottimismo sono predittori significativi del dolore cronico post-operatorio. Il terzo capitolo presenta i risultati di uno studio longitudinale prospettico volto a studare l’effetto di depressione, ansia, catastrofismo, auto-efficacia, funzioni esecutive e sensibilizzazione centrale sulle traiettorie del dolore post-operatorio acuto. Sono stati arruolati 145 pazienti in attesa di operazioni di protesi d’anca o di ginocchio presso l’ospedale Humanitas Pio X. Prima dell’operazione, i pazienti hanno completato un questionario volto ad indagare i predittori prima elencati. Durante i sette giorni successivi all’operazione, i pazienti hanno compilato un diario che permetteva di misurare l’intensità del dolore e il catastrofismo post-operatorio di stato. Infine, sono stati raccolti i dati su intensità e interferenza del dolore dopo un mese e tre mesi dall’operazione. Sono stati utilizzati modelli di curve di crescita per studiare l’impatto dei predittori sulle traiettorie del dolore e modelli di regressione multipla per individuare i predittori del dolore al follow-up. I risultati hanno permesso di evidenziare che, controllando per sesso, tipo di procedura chirurgica e intensità del dolore pre-operatorio, la sensibilizzazione centrale è associata all’intercetta delle traiettorie del dolore, la flessibilità cognitiva è associata alla loro pendenza, e che il catastrofismo di stato è una covariata del dolore post-operatorio. Al follow-up, l’intensità e l’interferenza del dolore sono risultate essere associate a sensibilizzazione centrale, distress emotivo e funzioni esecutive misurate durante il periodo pre-operatorio. Infine, vengono discusse le implicazioni cliniche e di ricerca di questi risultati. / Post-surgical pain is a major health issue from the perspective of patients, health professionals and the society as a whole. This thesis has the aim to identify psychological and psychosocial variables associated with chronic post-surgical pain, and to understand how these factors influence pain trajectories over time. In the first chapter, complexity of post-surgical pain is explored. Starting from the definition of this phenomenon, conceptualization by the biopsychosocial model is presented. To understand how predictors at different levels might influence the patient’s pain experience, pathophysiology of post-surgical pain is scrutinized, with a particular focus on the physiological substrate that can explain how psychological and psychosocial predictors can influence pain perception and modulation. Physiological, psychological and social risk factors for post-surgical pain are then presented. For each, potential mechanisms explaining association with this phenomenon are reviewed and discussed. The second chapter presents a systematic review of the literature with meta-analysis on psychological and psychosocial risk factors of chronic post-surgical pain. Methodological adjustments were adopted to ensure that the synthesis of research results was based on a comprehensive sets of studies, and to take into account the effect of non-significant estimates in case they were not reported by original studies. After a selection from 6329 records, 63 articles were included in a narrative synthesis and 34 studies were employed to perform a meta-analysis. The narrative synthesis of the literature showed that evidence about the effect of psychological predictors is heterogeneous, with few predictors, such as optimism, mental health and surgical fear, consistently associated with chronic post-surgical pain. In contrast, the meta-analysis showed that depression, anxiety, catastrophizing and, to a lesser extent, kinesiophobia, optimism and self-efficacy, have a weak but significant association with chronic post-surgical pain. Results are discussed in the context of the available literature. The third chapter presents the results of a longitudinal prospective study aimed at describing individual trajectories of pain intensity in patients who underwent knee or hip arthroplasty. The focus of this study was the analysis of pain as a process and in its relationship with central sensitization processes, executive functions and trait and state psychological variables. This study was performed with 145 patients listed for surgery at the hospital Humanitas Pio X, which were asked to complete a pre-surgical assessment, to fill a pain diary during the first seven days after surgery and to provide data about their pain after one and three months from surgery. Statistical analyses were performed employing a multilevel growth curve analysis for acute pain trajectories and multiple regressions for follow-up data. Multiple imputation procedures were employed to account for missing information. Results showed that, after controlling for sex, surgical procedure and pain intensity, central sensitization was a predictor of the intercept of pain trajectories, scores on the Trail Making Test Part B were associated with their slope, and that daily post-surgical catastrophizing was a significant covariate of pain intensity. Analyses of follow-up data confirmed the predictive role of central sensitization and showed that emotional distress, along with executive functions, is related with pain intensity and interference. Finally, research and clinical implications of the findings of these studies are discussed.

O presente trabalho, situado na linha de Psicologia e Educação, trata-se de uma revisão de literatura, cuja finalidade inicial foi a sistematização dos conhecimentos produzidos acerca do que se convencionou chamar, primeiramente sob o viés psicanalítico, de neurose obsessiva e, posteriormente, a partir do ponto de vista científico, de transtorno obsessivo compulsivo (TOC). Num segundo momento, teve como objetivo analisar os discursos produzidos sobre o tema, tendo em vista as diferentes áreas de conhecimento que dele se ocuparam, bem como as divergentes concepções teóricas. Porém, mais do que os saberes que têm sido produzidos, interessou-nos analisar as práticas que estão implicadas na produção e no funcionamento desses saberes, isto é, quais os efeitos dos discursos das áreas de radical psi - compreendidas aqui pela psiquiatria, psicologia e psicanálise na produção de um tipo bem determinado de sujeito e qual o papel da educação nesse contexto. Para tanto, lançamos mão de alguns estudos de intelectuais de lastro foucaultiano, que nos permitiram compreender a verdade como invenção - e não como descoberta, tal como sugerem muitos cientistas daí a necessidade de desnaturalizá-las; e o discurso como um conjunto de enunciados, vinculado a jogos de poder, que fazem circulam determinados regimes de verdade, através dos quais, realidade e sujeitos são produzidos. Nesse sentido, se a invenção se dá na/pela linguagem, podemos afirmar que, a invenção da neurose obsessiva - ou TOC - e de sua clínica, ganha status de verdade e de realidade na medida em que começa a ser produzida nas narrativas, quando começa a circular em diferentes discursos, quando começa a ganhar força em estudos que visam compreendê-la, explicá-la, enfim, quando começa a produzir saberes geradores de novas práticas e, de modo circular, práticas que convocam novos saberes. Do estudo, também foi possível depreender que os discursos psi são importantes dispositivos de poder, que funcionam no sentido de apagar toda e qualquer diferença, com vistas à adequação dos sujeitos aos padrões normativos. Nesse sentido, a escola, entendida como instituição disciplinar por excelência, onde discursos psi e pedagógicos se fundem e, por vezes, se confundem, é o lugar privilegiado para o exercício do poder e, portanto, das práticas de governo de todos e de si ao mesmo tempo. / This work, situated in the line of search of Psychology and Education, is a literature review, whose initial purpose was the systematization of knowledge produced about what is termed, primarily under the psychoanalytical view, obsessional neurosis, subsequently, from the scientific point of view, obsessive compulsive disorders (OCD). In a second moment, aimed to analyze the speeches produced about the subject, in view of, the different areas of knowledge that gets occupied by it, as well as the divergent theoretical conceptions. However, more than the knowledge that have been produced, interested to us, examining the practices that are involved in the production and operation of such knowledge, that is, what effects the speeches of the radical psy areas - understood here by psychiatry, psychology and psychoanalysis in the production of a determined type of subject and the role of education in that context. For both, in support in some studies of foucaultian approach, which allowed us understand the truth as invention - and not as discovery, as suggest many scientists hence the need for denaturalize them; and the discourse as a set of statements, entailed with power games, which are moving certain truth regimes, through which, reality and subject are produced. Then, if the invention is in/on the language, we can affirm that, the invention of obsessional neurosis - or OCD - and its clinical, get status of truth and reality in so far as it begins to be produced in narratives, when it begins to circulate in various speeches, when it begins to gain strength in studies that aim to understand and explain it, finally, when it begins to produce new knowledge-generating practices and, in a circular way, practices that summon new knowledge. From the study, it was also possible to conclude that the psy speeches are important power devices, which work in order to erase any distinction, to the suitability of the subject to normative standards. Therefore, the school, understood as disciplinary institution par excellence, where psy and educational speeches merge, and sometimes, are confused, is the privileged place for the exercise of power, and consequently, of the rules practices of every and of itself at the same time.

The aim of this thesis is to evaluate dogs introduced into the Arctic as a source of intestinal parasites infection both for wildlife and humans. To that aim coprological examination of faeces sampled in Svalbard and Greenland was performed. Microscopical and molecular detection of cryptosporidia, giardiae, microsporidia, roundworms and tapeworms in faeces was carried out. One sample from Svalbard was positive for Toxocara canis eggs and four samples from Svalbard were positive for unusual genotype of Enterocytozoon bieneusi.

Rare lipoprotein A (RlpA) has been studied previously only in Escherichia coli, where it localizes to the septal ring and scattered foci along the lateral wall, but mutants have no phenotypic change. In this thesis, we show rlpA mutants of Pseudomonas aeruginosa form chains of short, fat cells when grown in media of low osmotic strength. These morphological defects indicate RlpA is needed for efficient separation of daughter cells and maintenance of rod shape. Analysis of peptidoglycan sacculi from a ΔrlpA mutant revealed increased tetra and hexasaccharides that lack stem peptides (hereafter called "naked glycans"). Incubation of these sacculi with purified RlpA resulted in release of naked glycans containing 1,6-anhydro N-acetylmuramic acid ends. RlpA did not degrade sacculi from wild-type cells unless the sacculi were subjected to a limited digestion with an amidase to remove some of the stem peptides. Collectively, these findings indicate RlpA is a lytic transglycosylase with a strong preference for naked glycan strands. We propose that RlpA activity is regulated in vivo by substrate availability, and that amidases and RlpA work in tandem to degrade peptidoglycan in the division septum and lateral wall. Our discovery that RlpA from P. aeruginosa is a lytic transglycosylase motivated us to reinvestigate RlpA from E. coli. We confirmed predictions that RlpA of E. coli is an outer membrane protein and determined its abundance to be about 600 molecules per cell. However, multiple efforts to demonstrate that E. coli RlpA is a lytic transglycosylase were unsuccessful and the function of this protein in E. coli remains obscure.

La Teoria della Mente, abilità ritenuta alla base della buona riuscita delle relazioni sociali, è un rilevante e classico oggetto di ricerca della Psicologia dello Sviluppo e dell’Educazione che negli ultimi quaranta anni ha visto proliferare numerosi studi volti a indagarne i contenuti, oltre che a identificarne e approfondirne le tappe di sviluppo e le implicazioni di tipo relazionale e sociale. L'integrazione delle prospettive, i rapporti con altre discipline e l'assunzione di approcci interdisciplinari caratterizzano gli sviluppi recenti delle ricerche in psicologia, aprendo nuove prospettive di indagine. La tesi consta di tre capitoli, ognuno dei quali si riferisce a un autonomo progetto di ricerca. Tutti gli studi hanno coinvolto bambini di età scolare: età critica per l’acquisizione e lo sviluppo delle abilità di Teoria della Mente e periodo sensibile per quanto riguarda la competenza sociale, perché la rappresentazione, la considerazione e l’assunzione della prospettiva dell’altro diventa sempre più rilevante ai fini di una funzionale vita sociale e relazionale anche al di fuori del contesto familiare. Nello specifico, viene presentato il primo studio che propone una nuova interpretazione teorica e metodologica per valutare i risultati di un compito classico di falsa credenza di II ordine - il gelataio - in bambini di 10 anni alla luce della teoria dell'argomentazione e sottolinea il ruolo del ragionamento dei bambini nella capacità di rappresentarsi la prospettiva degli altri. Il secondo contributo, si propone di studiare il ruolo che la considerazione della prospettiva dell’altro svolge nei processi decisionali, in particolare nei giochi interattivi di scambio che valutano la fairness e l’altrusimo, analizzati in relazione alla capacità di ritardare la gratificazione. Infine il terzo studio è una proposta applicativa perché presenta l’efficacia del Progetto TiM (Thought in Mind Project), un progetto di formazione in cui le rappresentazioni del funzionamento della mente vengono proposte alle insegnanti durante alcuni incontri di formazione in cui si svolgono attività e si co-costruisce il significato di alcune storie suggestive. Il progetto ha visto il coinvolgimento delle insegnanti di scuola primaria e ha promuove un effetto indiretto sulle capacità di mentalizzazione all’inizio e alla fine dell’anno scolastico (prima e dopo l’intervento formativo sulle insegnanti) grazie alla creazione di una “comunità mentalizzante”, in cui i contenuti mentalistici oltre ad essere condivisi, vengono trasferiti ai bambini durante le attività in classe. Tutti e tre i lavori di ricerca sono attualmente pubblicati su riviste internazionali. / People, during all their life, understand and predict the other’s behaviour from the capacity to read the other’s mental contents. This skill is one of the hallmarks of human cognition and it is fundamental to social interaction. This psychological construct is referred to the ability to attribute mental states such desires, thoughts, beliefs, intentions emotions to self and others n order to predict their and others behaviour (Premack and Woodruff, 1978; Wimmer and Perner, 1985) and it is defined Theory of Mind – ToM. Understanding of mental states allows to explain observable events as actions by inferring unobservable entities like beliefs, desires, etc... also it involves understanding that others’ mental states may differ from one’s own, and may differ from reality (e.g., false belief). Children’s Theory of Mind has been a lively area of research in developmental psychology for the last 40 years. All the studies presented in the thesis involves primary school children: during this period of age children become more flexible and appropriate in understanding of mental states and they still beginning to understand the increasingly sophisticated capacity of represent the one’s own and other’s mental states. Moreover, it is considered as a critical age because children are called to engage a new relationship (i.e. think about the social networks in school, in church, in sport activity etc...) outside the family, that means they must use their ToM ability in new relational contexts (e.g. ToM helps people plan and manage their own and others’ choices and the decisions that characterize interpersonal relationships and social competence (Takagishi, Koizumi, Fujii, Schug, Kameshima, Yamagishi, 2014; Castelli, Massaro, Sanfey, Marchetti, 2013). One of the component of ToM is the assumption of other’s perspective, in fact the child might understand that people can have different beliefs, even different beliefs about the exact same situation; something can be true, but someone might not know that; something can be true, but someone might falsely believe something different. The aim of this thesis is to explore the children representation of other’s perspective in three different ways. To achieve this purpose, the studies presented address three main questions and the three different research contexts about this ability. The first proposes a novel theoretical and methodological interpretation to evaluate the results of false belief tasks in the light of argumentation theory and asks what the role of children’s reasoning in the ability to represent others perspective. The second question considers the other’s perspective with respect to one's own ability to thinking prospectively and to assume the other’s perspective in decision making processes. In the third study the assumption of other’s perspective has shown in a mentalizing theacher’s training and its indirect effects on pupils’ ToM ability. The first study is focused on exploring the main arguments behind 10 years old children’s responses in a classic second-order false belief task, in order to understand children's competences in the use of second level recursive thought. Interpreting the experimental setting as an argumentative discussion shed new and innovative light on the child’s answer to the experimenter’s questions, also explaining what premises are shared between adults and children and what possible misunderstandings might arise. Traditionally, in fact, the understanding of false belief is a classical measure of Theory of Mind and, in the false belief task, only the explanations that explicitly show that the child is engaging in recursive reasoning about mental states was considered right. The interpretation and the traditional coding of justifications reflect the child's ability to attribute and explain mental reasoning on the mental states of the characters of the story or the mental reasoning about false belief. Usually, however, these dichotomous classifications – wrong or correct and its coding 0/1 - neither reflect the justification answers as a countercheck of the test question. We wanted to try to makes explicit some components that are lost with the usual dichotomous evaluation through a qualitative analysis of the ToM reasoning about false beliefsr, in particular when children gave a “wrong” answer. For this reason, we have reinterpreted the traditional false belief task and the expected answer in argumentative terms, thus showing what is expected in terms of type of arguments and level of explicitness. Our findings show that a dialogic consideration of research settings allows to illuminate the reasons behind children’s “right” and “wrong” answers, which can be due either to the pragmatic context of the conversation or to a misunderstanding at the level of issues. Moreover, we have shown that, even in those cases in which a child’s answer and justification do not met the expectations, they can nevertheless be correct at the inferential level. The cause of the “mistake” should rather be sought for in the material/contextual premises at the basis of the argument. The second study investigates decision-making processes in 6, 8 and 10 years old children, highlighting the role played by prospective thinking on the relationship between altruism, wich benefits from immediate selfless reward, and fairness, that requires the strategic thinking. To assess this hypothesis, three different decision-making tasks, and namely an intertemporal choice task, testing their ability to delay gratification; the Dictator Game, assessing altruism; and the Ultimatum Game, assessing fairness/inequality aversion was admnistered. A component that, in our view, greatly affects the outcomes of these decisional tasks is prospective thinking, which critically involves a temporal aspect of decision making, insofar poorly addressed to. By relating results from the three tasks, our findings highlight overall changes in the children’s approach to decision-making, particularly at age 10, when the relationships between the manifold components of decisional dynamic are differently shaped. Such changes appear to be associated with a greater control to delay gratification, reflecting the ability to account for outcome optimization when making decisions. We suggest that this is due to the use of prospective thinking, which allows children to fully assess the advantages and disadvantages of the different decision strategies. In particular, children overall proposed more at the Ultimatum Game than at the Dictator Game task independently of age and gender. Especially in 10 years old children we showed the refinement of the strategic reasoning with age that take into account the other’s presence and the other’s response. The third study is focused on TiM (Thought in Mind) Project. We proposed a training program and the aim of this study was to introduce and explain the key concepts involved, and to provide teachers with direct experience of these methods. Moreover, we aimed to support teachers in reflecting together on how to apply the TiM Project in the classroom with their pupils. Changes in teachers’ attitude helped pupils in developing mentalizing skills, useful in order to create a context that support the social competence and cognition. We demonstred that the administration of a specific training program to adults is the first step to create a mentalizing community and that this kind of training can help children to develop and use their mentalization and ToM abilities. To reach this goal, we designed a “TiM Project training program” for primary school teachers, with the purpose of introducing and explaining the key concepts and methods of the TiM Project and involving teachers in a direct experience of these methods, selecting some of the original content and activities, adjusted to an Italian context and created others ad hoc for our training program. Subsequently, we tested the efficacy of this training by evaluating mentalization and theory of mind abilities in pupils. In particular, the results showed that, although some measured components of mentalization progressed over time, only the TiM Project training group significantly improved in third order false belief understanding and changed -in a greater way compared to the control group- in two of the three components of the Mentalizing Task, i.e. the rational dimension increased and the positive dimension decreased.

Le méson J/psi est considéré comme une sonde privilégiée de la formation du Plasma de Quarks et de Gluons (PQG) lors des collisions d'ions lourds. L'écrantage de la force de couleur a été proposé comme mécanisme de suppression anormale du J/psi dans un milieu déconfiné, au-delà de la suppression normale dans la matière nucléaire ordinaire. Le détecteur PHENIX est, des quatre expériences qui furent installées au démarrage de l'accélérateur RHIC, celle qui a une conception optimale pour la mesure du J/psi : dans les canaux de décroissance en dimuon à rapidité vers l'avant, et en dielectron à mi-rapidié. Le travail présenté ici couvre l'analyse de données prises par les spectromètres à mi-rapidité de PHENIX en collisions Au+Au à 200~GeV. Le facteur de modification nucléaire est mesuré en fonction de la centralité, et ensuite comparé à des estimations de la suppression due à la matière nucléaire froide. Malgré le fait que la suppression observée dans les collisions les plus centrales atteint un facteur plus grand que trois, une majeure partie peut être attribuée aux effets nucléaires froids. D'autre part, la comparaison avec les résultats des mesures effectuées au SPS du CERN et vers l'avant dans PHENIX a conduit à la spéculation que la régénération, un mécanisme de production des J/psi par association de quarks c et c-bar non corrélés, pourrait jouer un rôle important dans les collisions d'ion lourds les plus centraux. Le flot elliptique du J/psi en fonction de pT, une autre mesure présentée dans ce travail, est un outil potentiel pour tester le scénario de la régénération. Malgré l'obstacle statistique, la mesure est une démonstration de la faisabilité d'une mesure du flot elliptique dans un environnement à haute multiplicité.

Nous avons étudié la production des états liés charmés dans les collisons ultrarelativistes d'ions lourds. Nous proposons tout d'abord un modèle de la production des mésons J/psi , à deux composantes, qui inclut : (i) une production primordiale des J/psi dans les collisions dures couplée à l'absorption des J/psi dans la matière nucléaire, le plasma de quarks et de gluons et la matière hadronique, et (ii) une production statistique des J/psi résultant de la coalescence de quarks c et cbar lorsque le système hadronise. Les deux sources de J/psi sont évaluées dans un scénario d'équilibre thermique et notre modèle permet de rendre compte de façon satisfaisante des données expérimentales obtenues au CERN-SPS et à RHIC. Nous étudions ensuite les conséquences des effets de milieux sur la production des hadrons charmés, en nous basant sur de récents résultats de la chromodynamique quantique sur réseau. Nous envisageons la régénération des J/psi dans le plasma de quarks et de gluons et montrons que les effets de milieux dans la matière hadronique permettent d'expliquer la dépendance en centralité du rapport psi'/psi.

Les collisions d'ions lourds relativistes permettent d'étudier la production du plasma de quarks et de gluons (QGP), état dans lequel serait la matière hadronique au-delà d'une température de l'ordre de 200~MeV. Le $J/\psi$, état lié~$c\bar{c}$, est une des sondes utilisées pour observer le QGP. Son taux de production peut être modifié par divers effets en compétition: les effets nucléaires froids et ceux attendus en cas de production du QGP. Une suppression anormale du $J/\psi$ (au-delà des effets froids) a déjà été vue par l'expérience NA50 (SPS) dans les collisions Pb~+~Pb les plus centrales. L'expérience PHENIX (RHIC) poursuit cette étude à une énergie environ dix fois plus élevée. Nous avons étudié la production du $J/\psi\to\mu^+\mu^-$ dans les collisions Cu~+~Cu effectuées en 2005 à une énergie de 200~GeV par paire de nucléons. Les résultats obtenus apportent des informations importantes sur les effets froids: ils permettent d'améliorer de manière significative la précision obtenue dans les collisions à petit nombre de nucléons participants, où le QGP ne peut être produit. Ils confirment la similitude des suppressions déjà observées au RHIC dans les collisions Au~+~Au et au SPS; ce constat restant à corroborer par des mesures plus précises des effets froids au RHIC. Les résultats combinés Au~+~Au et Cu~+~Cu mettent aujourd'hui en défaut la plupart des modèles théoriques, et pourraient favoriser l'hypothèse d'une production ! secondaire du $J/\psi$ dans le milieu (recombinaison).

<p>This investigation addresses how photosynthetic efficiency is affected when pea (Pisum sativum) plants are restricted to a sole nitrogen source (i.e. ammonium or nitrate). The pea plants were watered with different nutrient solutions without NO3- or NH4+ for different time-periods in order to assay for nitrogen content. The soluble ammonium and nitrate content was measured throughout the entire growth period. No major differences were observed in nitrogen content during the starvation period up to 25 days. For technical reasons, cultivation of plants could not be extended beyond this time. The chloroplasts and thylakoids were isolated after 25 days and assayed for chlorophyll contents and photosynthetic activity.</p><p>The outcome of these tests indicates a small but unambiguous decrease in the photosynthesis activity for all treatments, relative the control.</p>