1,720,996 research outputs found
An ultra-cold Rb-Cs mixture in a magnetic trap
No full textThis works reports on using laser cooling and evaporative cooling to create an ultra-cold mixture of 87Rb and 133Cs atoms inside the conservative potential of a time-averaged orbiting potential (TOP) magnetic trap. We were able to observe sympathetic cooling of Cs through collisional energy exchange with the Rb atoms, thus reaching Cs temperatures of ≈ 5 μK
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Stress dynamics in living cells
No full textLa cellule lutte à chaque instant contre les perturbations afin de maintenir l'équilibre de son milieu intérieur, et permettre sa survie. L'apparition d'espèces oxydantes ou l'augmentation de la température sont autant de perturbations auxquelles la cellule doit faire face. Mon travail de thèse s'est articulé autour de la dynamique temporelle des stress oxydant et thermique en cellules vivantes. L’originalité de l’équipe où j’ai effectué ma thèse est de proposer une alternative aux photothérapies dynamiques en produisant directement, sans photosensibilisant, de l’oxygène singulet considéré comme l’agent cytotoxique principal. Cette façon de produire directement l’oxygène singulet permet non seulement d’adresser plus directement des questions de dosimétrie qui sont importantes en thérapie mais aussi d’identifier les macromolécules impliquées dans le stress oxydant. Dans une première partie je présenterai des études de cinétique photochimique qui ont permis de déterminer dans différents solvants et en cellule, le taux de production et la réactivité de l'oxygène singulet avec un partenaire spécifique. Dans une seconde partie, je présenterai mes travaux sur la dynamique temporelle de réponse au stress thermique en cellules vivantes. Le développement d’un modèle mathématique minimal de titration du stress thermique couplé à des expériences associant un facteur de transcription clef dans la régulation du stress, nous ont permis de mettre en évidence les contributions des principales réactions impliquées dans le mécanisme de réponse cellulaire au stress thermique.The cell fight everytime against disturbances to maintain the balance of its internal environment and ensure its survival. The appearance of oxidative species or increasing the temperature are all major perturbations which the cell has to face. My thesis is structured around the temporal dynamics of oxidative and thermal stress in living cells. The originality of the team where I did my thesis, is to propose an alternative way to phototherapy dynamic in producing directly, without photosensitizer, singlet oxygen which is considered as the main cytotoxic agent. This way of producing singlet oxygen directly allows to address dosimetry issues that are important in therapy but also, to identify the macromolecules involved in oxidative stress more directly. In the first part ,I will present photochemical kinetic studies that have enable to determine in different solvents and in cells, the production rate and the reactivity of singlet oxygen with a specific partner. In the second part, I will present my work on the temporal dynamics of heat stress response in living cells. The development of a minimal mathematical model of titration of thermal stress coupled with experiments involving a key transcription factor in the regulation of stress, allowed us to identify the main reactions involved in the mechanism of cell response to heat shock
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
The sensitivity of cancer cells to oxidative stress : systemic approach to study the interplay between metabolic flux and oxidative stress
No full textLes cellules vivantes, lorsqu'elles sont constamment exposées au stress, sont capables de réagir de manière complexe en faisant intervenir divers réseaux de régulation intracellulaire. Leur régulation contrôle par exemple le devenir cellulaire en réponse à un stress oxydatif. Lorsque les mécanismes défensifs parviennent à faire face au stress, une rétroaction négative est impliquée et la cellule survit, sinon la cellule meurt. L'un des principaux mécanismes défensifs repose sur l'interaction entre le flux métabolique et le stress oxydatif, exploitant le rôle dualiste du peroxyde d'hydrogène, agissant à la fois comme une molécule de signalisation et de dommages. Nos travaux visent à identifier les molécules clés impliquées dans le devenir cellulaire et à suivre leur dynamique au niveau de la cellule unique, à l'aide de la microscopie de fluorescense. Dans un premier temps, nous concevons un système expérimental inspiré des études de chimiotaxie pour contrôler en permanence la dose appliquée de peroxyde d'hydrogène (H2O2) à la lignée cellulaire du cancer du sein (MCF7). Le choix de la méthode de stimulation joue un rôle important dans notre étude. En effet, afin de délivrer une concentration constante de stimulus aux cellules de mammifères, un milieu de culture cellulaire H2O2 non réactif avec H2O2 est choisi. En utilisant un système fluidique, le taux de production intracellulaire de H2O2 est contrôlé en faisant varier la concentration externe de H2O2. La délivrance et l'élimination du stimulus sont ainsi effectuées assez rapidement (plus rapidement que la consommation cellulaire) pour étudier les réponses cellulaires dynamiques. Lors d'une stimulation constante, une dynamique d'adaptation est observée, ce qui suggère que des rétroactions négatives sont impliquées dans la protection cellulaire contre le stress. La variabilité d'une cellule à l'autre est observée et quantifiée à l'aide de paramètres d'adaptation identifiés. Des résultats préliminaires de la dépendance de la modulation du pH par l'état métabolique cellulaire sont discutés. Les caractéristiques d'adaptation ne sont pas représentées lorsque les sources de carbone sont complètement éliminées du milieu externe. Ce résultat souligne le rôle du glucose dans le mécanisme de défense cellulaire. Un autre résultat important est celui de la dynamique de rétroaction qui dépend de la dose de H2O2 appliquée aux cellules: une stimulation plus forte implique une réponse plus forte. C'est un premier facteur limitant que nous avons identifié lors de la quantification de la réponse de mort cellulaire au stress H2O2. Les résultats de la réponse à la dose de mort cellulaire suggèrent que le destin de la cellule (survie ou mort) dépend également à la fois du contrôle du stimulus et de l'état métabolique cellulaire. Afin d'identifier les voies métaboliques impliquées dans la rétroaction négative induite par le stress oxydatif, des molécules clés régulant la voie Phosphate Pentose (PPP) sont modulées. Nous concluons que l'orchestration du réseau moléculaire est plus complexe et que le PPP n'est pas le seul réseau impliqué dans la défense cellulaire. Nous concluons que l'orchestration du réseau moléculaire est plus complexe et que PPP est le réseau principal mais pas le seul impliqué dans la défense cellulaire. Dans ce manuscrit, une conception expérimentale est présentée afin d'étudier les réponses d'adaptation au stress oxydatif observée en temps réel. Nos expériences confirment la cinétique d'adaptation rapide du NAD(P)H déjà observée dans la littérature. Nous identifions, pour la première fois, un deuxième mécanisme de régulation où le système de glutathion se rétablit en 30 min pendant la stimulation contrôlée par H2O2. Le métabolisme du glucose soutient la régénération de ce système antioxydant et le réseau PPP est ainsi identifié comme le principal retour négatif dans l'adaptation moléculaire observée ici.Living cells, when constantly exposed to stress, are able to respond in a complex manner involving various intracellular regulation networks. Their regulation controls for instance the cellular fate outcome in response to an oxidative stress. When defensive mechanisms manage to cope against stress, a negative feedback is involved and cell survive, otherwise cell dies. One of a key defensive mechanism relies on the interplay between metabolic flux and oxidative stress exploiting the dualistic role of hydrogen peroxide, acting both as signalling and damaging molecule. Our work aims to identify key molecules involved in cellular fate and to monitor their dynamics at the single cell level, using fluorescent microscopy. In a first step, we design an experimental system inspired by chemotaxis studies to constantly control the dose applied to breast cancer cell line (MCF7). The choice of the stimulation method plays an important role in our study. Indeed, in order to deliver a constant concentration of stimulus to mammalian cells, non-consuming H2O2 cell culture medium is chosen. Using a fluidic system, the intracellular H2O2 production rate is controlled by varying the external H2O2 concentration. Stimulus delivery and removal is thus performed fast enough (faster than cellular consumption) to study the dynamical cellular responses. During constant stimulation, adaptation dynamics are notified, suggesting that negative feedbacks are involved in the cellular protection against stress. Cell-to-cell variability is observed and can be quantified using identified adaptation parameters. The fluorescent signal is processed and preliminary results of pH modulation dependence by the cellular metabolic state are discussed. The adaptation features are not depicted when the carbon sources are completely removed from external medium. This result underlines the role of glucose in the cellular defensive mechanism. Another important result is that the feedback dynamics is depending by the H2O2 dose applied to cells: stronger stimulation implies stronger response. It is a first limiting factor we identified while quantifying the cell death response to H2O2 stress. The results of cell death dose response are suggesting that the cell fate (survival or death) is also depending by both the control of the stimulus and the cellular metabolic state. In order to identify the metabolic pathways involved in the negative feedback induced by the oxidative stress, key molecules regulating the Phosphate Pentose Pathway (PPP) are modulated. We conclude that the orchestration of molecular network is more complex and PPP is the main but not the only network involved in the cellular defense. In this manuscript an experimental design is presented in order to study the adaptation responses to oxidative stress in real time. Our experiments are confirming the fast adaptation kinetics of NAD(P)H already observed in literature. We identify, for the first time, a second regulation mechanism where the glutathione system is restoring within 30 min during controlled H2O2 stimulation. The glucose metabolism is supporting the regeneration of this antioxidant system and PPP network is thus identified as the main negative feedback in the molecular adaptation here observed
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