1,721,044 research outputs found
Évolution des molécules aromatiques en phase solide sous irradiation par des ions énergétiques
No full textDans les nuages denses, les manteaux glacés sont des condensats de petites molécules sur des grains solides. Ces manteaux glacés représentent des sites prometteurs pour certains processus chimiques. Ils sont constamment irradiés et de nouvelles molécules organiques complexes peuvent être ainsi formées. Une fois que les nuages denses se transforment en disque d'accrétion et, éventuellement, en système planétaire, ces manteaux glacés peuvent potentiellement contribuer au réservoir de molécules complexes des planètes. Dans cette thèse, les effets de l'irradiation ionique sur deux molécules aromatiques, la pyridine et le pyrène, ont été étudiés. Les échantillons ont été exposés à une irradiation ionique sur les lignes des accélérateurs du GANIL (Caen, France) et de l'ATOMKI (Debrecen, Hongrie). Leur évolution a été suivie par spectroscopie infrarouge in situ. Il a été constaté que la structure initiale (amorphe ou cristalline) et la température d'irradiation n'affectent pas la section efficace de destruction de la pyridine pure. De plus, il a été observé que la dose locale n'est pas un paramètre clé comme cela était affirmé précédemment. En effet, la destruction du pyrène provoquée par des ions lourds, à partir du carbone, est significativement plus importante que celle provoquée par des ions plus légers comme l'hydrogène et l'hélium pour une même dose locale déposée. Pour les deux molécules, une augmentation significative de la section efficace de destruction a été observée lorsque la concentration des molécules dans la matrice d'eau diminue. Le temps de demi-vie de la pyridine et du pyrène dans les nuages denses a été estimé à environ 13 et 20 millions d'années, respectivement. Cela suggère qu'une fois formées dans ces environnements, ces molécules pourraient survivre et contribuer à la formation planétaire.Formed in the dense clouds, icy mantles are condensates of small molecules on solid grains. These icy mantles are promising sites for rich chemical processes, where complex organic molecules can form, as these mantles are continuously exposed to ionizing radiation. Once dense clouds transform into an accretion disc and eventually into a planetary system, these icy mantles may potentially contribute to the reservoir of the complex molecules of the planets.In this thesis, the effects of ion irradiation on two aromatic molecules, pyridine and pyrene were investigated. The samples were exposed to ion irradiation at the GANIL (Caen, France) and ATOMKI (Debrecen, Hungary) ion beam facilities. Their evolution was monitored using in-situ infrared spectroscopy. It was found that the initial structure (amorphous or crystalline) and the irradiation temperature do not affect the destruction cross section of pure pyridine. Additionally, it was observed that the local dose is not a key parameter as previously assumed. Indeed, since the destruction of pyrene caused by heavy ions, starting from C, is significantly greater than that caused by lighter ions such as H and He for the same deposited local dose. For both molecules, a significant increase in the destruction cross section was observed for decreasing molecule concentration in the water matrix. The half-life time of pyridine and pyrene in dense clouds was estimated to be around 13 and 20 millions of years, respectively. This suggests that once formed in these environments, they could survive and contribute to planetary formation
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
Molecular dynamics in the gas phase
No full textWhen molecules and clusters in the gas phase are excited by photons, electrons or heavier particles, a chain of events is kickstarted that may span twenty orders of magnitude in time. These processes involve, e.g., ultrafast attosecond electron dynamics and its coupling to nuclear motion and molecular rearrangements occurring on picosecond timescales, which may be followed by statistical redistribution of the internal energy that leads to an intricate competition between destructive and non-destructive relaxation pathways on timescales up to minutes and beyond. Moreover, how these processes are affected by the presence of a molecular environment is largely unknown. Advancing the fundamental understanding of gas-phase molecular dynamics therefore requires complementary state-of-the art experimental and theoretical methods designed to study specific processes and to monitor them on their associated timescales in unprecedented details.</p
Multiple beam irradiation platform MIRRPLA: origin and evolution of organic matter in the solar system
No full textInternational audience“Where do we come from?” is one of the important fascinating open questions of science andphilosophy. How did life emerge? What is the origin of organic matter in the universe? Couldlife also emerge on other worlds than our Earth? Complex organic molecules have indeed beenobserved in space (comets, meteorites, molecular clouds). In 2023, France launched theProgrammes et équipements prioritaires de recherche (PEPR) Origins (life and universe),through the program leader the National Centre for Scientific Research, to address thesequestions [1]. Understanding the origin of primitive organic matter during the formation andevolution of the solar system is fundamental because the contribution of extraterrestrial organicmatter via asteroids and comets is one of the possible sources of organic matter available toprimitive Earth [2]
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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