62 research outputs found
Study of dissociation products of H2O in a sample of comets of various origins.
No full textLes comètes sont connues pour contenir de grandes quantités d’eau et des molécules organiques en tout genre. Formées lors de la naissance de notre Système Solaire, il y a 4.6 milliards d’années, elles n’ont ensuite pas beaucoup évolué, ce qui les rend témoins potentiels des processus physico-chimiques présents à cette période. L’étude des comètes permet donc d’en apprendre davantage sur leur propre nature encore potentiellement énigmatique, mais également sur notre Système Solaire lui-même, et tout particulièrement sa genèse. La mission européenne Rosetta, en orbite autour de la comète 67P/Churyumov-Gerasimenko témoigne de l’intérêt porté à ces petits corps gelés du Système Solaire. Cette mission est unique puisqu’elle va permettre pour la première fois de mesurer la composition chimique précise d’un noyau cométaire. Ce type de mission est par contre très coûteux et ne concerne qu’une comète en particulier. Avec des télescopes au sol, il est possible d’étudier un nombre plus important de comètes. Certes, le noyau n’est dans ce cas pas directement atteignable, mais la spectroscopie permet d’analyser l’atmosphère de la comète. Formée par la sublimation des glaces du noyau et la dissociation des molécules qui s’en échappent, la coma contient de nombreuses informations nous permettant d’accroître nos connaissances sur la composition chimique du noyau.
L’objectif de cette thèse est l’étude des molécules liées à l’eau dans les comètes. Les glaces cométaires renferment en effet 80% d’eau. Etudier cette molécule est donc crucial pour définir la nature des comètes et comprendre les conditions physiques et chimiques régnant dans la coma. Toutefois, H2O n’est pas détectable dans le domaine de longueur d’onde visible. Sur base d’un ensemble de données spectroscopiques visibles acquises depuis le sol, nous proposons dans cette thèse l’analyse de deux produits de dissociation de la molécule d’eau observables dans l’atmosphère de la comète, l’oxygène atomique et le radical OH.
Le premier volet de ce travail se concentre sur les trois raies interdites de l’oxygène localisées à 5577.339 Å pour la raie verte (O(1S)) et à 6300.304 Å et 6363.776 Å (O(1D)) pour les raies du doublet rouge en vue de déterminer la ou les molécules parentes à l’origine de ces atomes. Dans cette optique, nous avons créé un spectre synthétique de la molécule de C2 afin de décontaminer la raie verte des raies dues au C2. Ensuite, nous avons mesuré les rapports d’intensité et les largeurs intrinsèques des trois raies d’oxygène pour des comètes situées à différentes distances héliocentriques. La comparaison du rapport de l’intensité de la raie verte sur la somme des intensités des raies rouges (rapport G/R) avec les taux d’excitation fournis par la théorie montre que H2O est la molécule parente principale des atomes d’oxygène lorsque la comète est observée à r ∼ 1 ua. Par contre, lorsque la comète est loin du Soleil (>2.5 ua), les molécules de CO2 contribuent également à la production d’oxygène. La mesure des largeurs intrinsèques des raies montre que la raie verte est plus large que les raies rouges alors que la théorie prédit l’inverse. Découle de cette observation que la raie verte pourrait principalement provenir de la photodissociation du CO2 alors que les raies rouges seraient uniquement formées via H2O.
En étudiant les raies d’oxygène à différentes distances du noyau cométaire, nous réalisons que la molécule parente de l’oxygène varie : le CO2 est le contributeur premier des atomes d’oxygène en deçà de ∼1000 km du noyau et laisse ensuite la place à H2O. Qui plus est, nous notons l’importance du quenching collisionnel produit par H2O dans la coma interne qui joue un rôle significatif dans la perte des atomes de O(1S) et O(1D). Un modèle d’émission est réalisé pour reproduire nos données observationnelles. En se penchant sur le comportement adopté par les raies d’oxygène près du noyau et sur l’ajustement fourni par le modèle, une estimation de l’abondance relative du CO2 est déterminée. Des lors, cette thèse présente une nouvelle méthode pour déterminer l’abon- dance CO2/H2O dans les comètes à partir de données obtenues depuis le sol alors qu’une mesure directe de la molécule de CO2 n’est jusqu’à ce jour possible que depuis l’Espace.
La seconde partie de notre travail porte sur l’analyse des rapports isotopiques 16O/18O et D/H à partir des isotopes du radical OH. La connaissance des rapports isotopiques dans des comètes d’origines variées est importante car cela peut nous renseigner sur les conditions physiques et chimiques existantes lorsque la comète s’est formée. De plus, la mesure du D/H s’inscrit dans le débat actuel de l’origine des océans terrestres. Dans ce contexte, des spectres synthétiques de 16OH, 18OH et OD sont créés sur base d’un modèle de fluorescence. Le rapport 16O/18O est déduit pour la première fois par ce modèle pour la comète C/2012 F6 (Lemmon) et il établit le point de départ d’une longue série de mesures portées sur des comètes brillantes à venir
Etude des produits de dissociation de H2O dans un \ue9chantillon de com\ue8tes d'origines vari\ue9es
No full textReview of: C. Cellucci, Is mathematics problem solving or theorem proving?, Found. Sci. 22 (2017), no. 1, 183—199
No full textThe author contrasts two philosophical conceptions of mathematics: problem solving versus theorem proving. The former is related to the analytic method and the latter to the axiomatic method. He traces the distinction back to Greek philosophy and highlights the critical role of Hilbert in the controversy. He argues that the analytic method should be preferred in view of Gödel's incompleteness theorems and because it accords better with the work methods of mathematicians. He finally suggests that the appeal of the axiomatic method lies in the fact that justification and well-organised presentation are valuable from a didactic perspective
ALICE: Physics Performance Report, Volume II
No full textALICE is a general-purpose heavy-ion experiment designed to study the physics of strongly interacting matter and the quark–gluon plasma in nucleus–nucleus collisions at the LHC. It currently involves more than 900 physicists and senior engineers, from both the nuclear and high-energy physics sectors, from over 90 institutions in about 30 countries.
The ALICE detector is designed to cope with the highest particle multiplicities above those anticipated for Pb–Pb collisions (dNch/dy up to 8000) and it will be operational at the start-up of the LHC. In addition to heavy systems, the ALICE Collaboration will study collisions of lower-mass ions, which are a means of varying the energy density, and protons (both pp and pA), which primarily provide reference data for the nucleus–nucleus collisions. In addition, the pp data will allow for a number of genuine pp physics studies.
The detailed design of the different detector systems has been laid down in a number of Technical Design Reports issued between mid-1998 and the end of 2004. The experiment is currently under construction and will be ready for data taking with both proton and heavy-ion beams at the start-up of the LHC.
Since the comprehensive information on detector and physics performance was last published in the ALICE Technical Proposal in 1996, the detector, as well as simulation, reconstruction and analysis software have undergone significant development. The Physics Performance Report (PPR) provides an updated and comprehensive summary of the performance of the various ALICE subsystems, including updates to the Technical Design Reports, as appropriate.
The PPR is divided into two volumes. Volume I, published in 2004 (CERN/LHCC 2003-049, ALICE Collaboration 2004 J. Phys. G: Nucl. Part. Phys. 30 1517–1763), contains in four chapters a short theoretical overview and an extensive reference list concerning the physics topics of interest to ALICE, the experimental conditions at the LHC, a short summary and update of the subsystem designs, and a description of the offline framework and Monte Carlo event generators.
The present volume, Volume II, contains the majority of the information relevant to the physics performance in proton–proton, proton–nucleus, and nucleus–nucleus collisions. Following an introductory overview, Chapter 5 describes the combined detector performance and the event reconstruction procedures, based on detailed simulations of the individual subsystems. Chapter 6 describes the analysis and physics reach for a representative sample of physics observables, from global event characteristics to hard processes
Language and theology : a case study of the metaphor of breathing in John 20:22.
No full textThesis (M.A.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.Since the blossoming of the linguistic theories in the Johannine scholarship, interest in the figurative language of John‘s Gospel has increased. In this study on John 20:22, the statement ―Jesus breathed on them‖, that is, on his disciples, is addressed as a metaphor evoking the theme of creation. It is argued that this metaphor is essential in the understanding of the ideo-theological framework of the author of the Fourth Gospel. It plays a key function in the network of Johannine metaphors
Pointing out persuasion in Philemon: Fifty readings of Paul’s rhetoric from the fourth to the eighteenth century
No full textThis informative and insightful work reveals the vast field of the history and life of the Letter to Philemon after it was written. This approach to biblical texts has received greater attention in recent years when the reader’s contribution to the meaning of textswas first recognised. This attention to the reception of biblical texts is the special subject of the Encyclopedia of the Bible and Its Reception (EBR), which started in 2009 and of which 20 volumes have already been published. This encyclopedia surveys not only sermons and commentaries, but also the various ways in which biblical texts have been received, such as in the creative arts, including paintings, sculptures, novels, films and music. Professor Tolmie’s study, however, focuses on how commentators and preachers have “pointed out persuasion” in this Pauline letter. He has selected, as the subtitle indicates, 50 readings of Philemon from three periods, the early church (starting with Ambrosiaster in chapter 1), the Middle Ages (chapter 2), and the period from the 16th to the 18th century (Chapter 3). For each of these interpreters, Tolmie offers a brief introduction and then focuses on the way they explain the rhetorical situation. He then focuses on the way each author explains the rhetorical strategy by moving through the letter, section by section. Chapter 4, the conclusion, is actually a synthesis, in which Tolmie looks for tendencies in the interpretation of Paul’s letter by focusing first on the way the rhetorical situation is imagined and then on Paul rhetorical strategies in the different literary units of Philemon
Study of the Forbidden Oxygen Lines in Comets at Different Heliocentric and Nucleocentric Distances
No full textOxygen is an important element in the chemistry of the solar system objects given its abundance and its presence in many molecules including H2O 80% of cometary ices). The analysis of oxygen atoms in comets can provide information not only on the comets themselves but also on the solar system. These atoms have been analyzed using the 3 forbidden oxygen lines [OI] observed in emission in the optical region at 5577.339 Å (the green line), 6300.304 Å and 6363.776 Å (the red lines) (Swings, 1962). Our analysis is based on a sample of 12 comets of various origins. The observing material is made of 53 high signal-to-noise spectra obtained with the high-resolution UVES spectrograph at the ESO VLT from 2002 to 2012 (Manfroid et al, 2009). After noticing that the green line is blended with one C2 line, we built synthetic spectra of C2 for each observing circumstances and we subtracted its contribution to the cometary spectra in order to ensure the decontamination of the 5577 Å line. Then, we measured the intensity of the 3 [OI] lines at different heliocentric distances. By comparing the green to red lines ratio (G/R) with the Bhardwaj & Raghuram (2012) effective excitation rates, we found that H2O is the main parent molecule when the comet is observed at 1 au. When the comet is located beyond 2.5 au from the Sun, CO2 also contributes to the production of oxygen. Studying forbidden oxygen lines could be a new way to estimate the abundances of CO2 in comets, a very difficult task from the ground (Decock et al. 2013). In order to estimate the effect of the quenching on our results, we analyzed the evolution of the G/R ratio at different nucleocentric distances. For nearby comets, we divided the extended 2D spectrum into several zones in order to analyze the oxygen lines as close as possible to the nucleus (down to ~10 km for the closest comets). Their analysis will allow us to study the link of the oxygen lines with the nucleocentric distance. We found a clear variation of the G/R ratio close to the comet nucleus that is in agreement with a contribution from CO2 as predicted by Raghuram & Bhardwaj (2013)
The ALICE experiment at the CERN LHC
No full textALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries. Its overall dimensions are 161626 m3 with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008
None greater than John : towards a social-description and narrative-theological study of John the Baptist in Luke-Acts.
No full textThesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007."I tell you, among those born of women none is greater than John" (Luke 7:28). Thus the author of Luke-Acts expresses his basic assessment of John the Baptist.
The present study aims to understand the role of John the Baptist as he is portrayed in Luke-Acts through a reading that combines social description and narrative-theological analysis in order to gain hermeneutical access to the subject of our investigation.
This study seeks to achieve this aim in two ways. In the first instance there is an attempt (through recourse to a combination of the stated critical methodologies) to provide a reading of Luke-Acts that interfaces social description and narrative-theological analysis in order to make possible a rhetorical engagement with the text in a way that provides hermeneutical access to John the Baptist as he is portrayed in Luke-Acts. In his portrayal of John the Baptist as a prophet and witness who plays a unique role in the history of salvation, the author of Luke-Acts weaves a spell over his readers that draws them into his narrative world and into his particular theological perspective.
In the second instance, this study also aims to show how Luke-Acts preserves a unique dynamic of John the Baptist which has rather been buried in the other Gospel traditions. Through this dynamic, Luke seeks to transmit his own ideal of the authentic prophet and witness in such a way that his audience may be moved to emulate John's example with conviction and imagination both in living out their Christian ideal as well as in proclaiming the good news
Eternity and the now: an exploration of Paul's understanding of a new creation in Gal. 6:15 and 2 Cor. 5:17.
No full textMasters Degree. University of KwaZulu-Natal, Pietermaritzburg.This thesis forms the first part of a programme of research whose ultimate aim is to draw upon Saint Paul’s vision of a new creation in Galatians and Second Corinthians in order to provide a new window of access into the Christian hope of eternal life for people of this secular age. Many contemporary people are deeply concerned about the Cosmos (they would not term it ‘Creation’) but have lost all conception of a Cosmos of eternal dimensions, one which includes the human species in its resurrected state. As such, this programme of research, while drawing upon academic scholarship, is ultimately addressed to the woman and the man ‘in the street’.
This present thesis, albeit the first step in the broader programme, confines its scope to how a new creation would have been communicated by Paul to the communities which he addressed of the early church.
After the introduction and methodological issues, the study proper opens in Chapter 2 with a summary of the theology of the apostle Paul the author of the two NT letters concerned. Paul’s personality will also be touched upon here because of the forthright way in which Paul expresses himself in these letters. Building upon recent studies by a number of biblical scholars, Chapter 2 includes a study of how the previously scholarly Pharisee Saul, would have acquired his original sense of a new creation from his Jewish background as well as from his own Christ-encountered theology.
In Chapter 3 (Second Corinthians) and Chapter 4 (Galatians) interpretations of the
new creation texts are undertaken within the context of the principal themes of the two letters and the particular characteristics of the two communities being addressed. What emerges from this analysis is that, in spite of widely differing views amongst biblical scholars, Paul’s understanding of new creation can be seen to manifest the three-fold characteristics of being anthropological, cosmological, and ecclesiological. This present thesis recognises this but attributes more significance to the anthropological. While eschatological considerations are often associated with the cosmological dimension, this, of course, is not exclusive, all three elements can have eschatological characteristics.
Two other aspects are addressed which seem to be understated in the existing literature, namely the importance of individual and corporate identity in the communities being addressed by Paul, and the nature of the relationship between new creation and the Pauline concept of ‘being in Christ’.
In addition, a concern is raised which is absent in the literature. In the interpretation process for these two elliptical Greek texts the influence of some secondary sources over and against that of the texts themselves, as reflected in the prevailing translations of these texts, is interrogated. Accordingly, in these chapters, the following questions are raised and answers proposed for them: Why is Paul able to introduce the words of a new creation, καινὴ κτίσις, without any prior explanation? What accounts for the abruptness with which these words appear? Also, the practice of including verbs into the two texts (as the vast majority of translations do in varied ways in order to express the interpretations arrived at) is
(controversially) critiqued, and an alternative approach – with alternative interpretations and translations – proposed; ones which further enhance the relationship between the concepts of ‘a new creation’, and of ‘persons being in Christ’.
Chapter 5 summarises the main conclusions arising from this study, and identifies areas of further research (particularly those related to the subjects of mystery, love and identity in new creation). A closing ‘Afterword’ illustrates the significance of καινὴ κτίσις for today
- …
