• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 262
  • 65
  • 51
  • 32
  • 26
  • 16
  • 15
  • 13
  • 6
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • Tagged with
  • 629
  • 333
  • 140
  • 129
  • 62
  • 56
  • 45
  • 43
  • 43
  • 41
  • 39
  • 38
  • 37
  • 36
  • 35
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
621

Growth of unsaturated, cyclic, and polycyclic aromatic hydrocarbons: Reactions under the conditions of the interstellar medium

Barthel, Robert 02 October 2008 (has links)
Hydrocarbons, in particular polycyclic aromatic hydrocarbons (PAHs), have been long discussed to be carriers of interstellar infrared (IR) emission and ultraviolet (UV) absorption features. Yet, their origin in dense phases of the interstellar medium (ISM), such as molecular clouds, remains unclear. In this work, growth mechanisms based on ion-molecule reactions between cationic PAHs/hydrocarbons and methyne (CH) were investigated. The reaction type and the precursor were derived and selected from known chemical and physical properties of the ISM. These chemical reactions were characterised by calculating branching ratios (based on cross sections) and capture rate coefficients, minimum reaction paths, reaction enthalpies, thermal equilibrium constants, and microcanonic isomerisation and radiative deactivation rate coefficients. In order to cope with the variety of reaction parameters, a hierarchic workflow scheme was set up. First, the reaction potential energy surface was sampled by molecular dynamics simulations. Then, minimum energy paths of the most probable reaction channels were investigated. Finally, molecular and kinetic properties of stationary points were calculated. The quantum chemical level of theory was increased at each step from DFTB (tight-binding density-functional), to DFT, and finally to post-Hartree-Fock methods. Results on CH based hydrocarbon growth showed the transition from non-cyclic hydrocarbons to cyclic and aromatic structures and from cyclic to polycyclic aromatic hydrocarbons. Additionally, the reactive collisions between hydrocarbons and CH were found to produce sufficient energy for isomerisation and fragmentation processes even at ultra low temperatures. In all, the results indicate that methyne might be a proper precursor for the formation of large interstellar PAHs. / Kohlenwasserstoffe, insbesondere polyzyklische Kohlenwasserstoffe (engl. PAHs), werden seit einigen Jahren als Mitverursacher interstellar IR-Emissions- und UV-Absorptionsbanden angesehen und diskutiert. Dabei ist die Herkunft dieser Moleküle in den dichten Phasen des interstellaren Mediums (ISM) aber noch nicht aufgeklärt. In dieser Arbeit wurden daher die Bildungsmechanismen, welche auf Ion-Molekül-Reaktionen zwischen kationischen PAHs und Kohlenwasserstoffen und dem Molekül CH beruhen, untersucht. Sowohl der Reaktionstyp als auch der Präkursor wurden anhand von bekannten physikalischen und chemischen Eigenschaften des ISM abgeleitet und ausgewählt. Die Analyse der chemischen Reaktionen basierte auf Berechnungen zur Produktzusammensetzung und Einfangsratenkoeffizienten (welche wiederum aus berechneten Reaktionsquerschnitten hervorgingen) Minimumenergiepfade (MEP), Reaktionsenthalpien, thermische Gleichgewichtskonstanten und mikrokanonische Isomerisierungs- und Strahlungsdeaktivierungs-Ratenkoeffizienten. Um der Vielzahl an Reaktionsparameter gerecht zu werden, wurden die Berechnungsmethoden entsprechend eines hierarischen Fließschemas kombiniert. Hierzu wurden zuerst durch Molekulardynamik-Simulationen die Reaktionspotentialenergieflächen abgerastert. Auf der nächsten Stufe wurden statistisch bedeutsame Reaktionskanäle bezüglich ihrer Minimumenergiepfade untersucht. Den Abschluss bildete die Berechnung molekularer und kinetischer Charakteristika stationärer Punkte auf einem MEP. Entsprechend dieses Schemas wurde die quantenchemische Genauigkeit auf jeder Stufe von approximativer DFT über DFT zu post-Hartree-Fock verändert. Die Ergebnisse des CH-basierten Kohlenwasserstoffwachstums zeigten einen Übergang von nichtzyklischen zu zyklischen and aromatischen Strukturen, sowie von zyklischen zu polyzyklischen Kohlenwasserstoffen. Außerdem zeigte sich, dass reaktive Kollisionen zwischen Kohlenwasserstoffen und CH auch bei Tiefsttemperaturen immer ausreichend Energie für Isomerisierungs- und Fragmentationsprozesse liefert. Die Ergebnisse dieser Arbeit lassen den Schluss zu, dass CH ein geeigneter Präkursor für die Bildung großer interstellarer PAH ist.
622

Pleomorphic Adenoma

Feng, Jining, Al-Abbadi, Mousa A. 09 March 2011 (has links)
No description available.
623

Gut Feeling : Art and Food Digested: Figuring a Post-Human Intestinal Turn

Guarino Werner, Sarah January 2023 (has links)
This thesis aims to develop a new methodological concept better to understand art and curating in a post-human setting. Departing from a post-humanist ontology, my initial idea was to analyse contemporary artworks dealing with food and trace and substantiate a figuration of the gut/intestinal system (connected to post-human notions as the ideas of trans- corporeality, vibrant matter, etc.) and how it could create a productive reading of these works. During my research on food-related art projects, I realised that the gut-figuration has broader implications and could function as a tool to understand the contemporary art world and curating at large, through a post-human lens. Accordingly, I suggest my thesis to be a contribution to what I would like to name an “intestinal turn”, a contemporary post-humanist, trans-corporeal understanding of art that could change how art is perceived and how the subjectivity of the artist, and curatorial work, could be understood today.
624

Association entre le mode d’accouchement et le risque du trouble du déficit d'attention avec ou sans hyperactivité chez l'enfant

Ferroum, Malika 07 1900 (has links)
Au Canada, en 2018-2019 la naissance par césarienne s’élève à 29% dépassant ainsi les taux de 10-15% recommandés par l’Organisation Mondiale de la Santé (OMS). Au cours des dernières années, les naissances par césariennes ne cessent d’accroitre, malgré les risques associés qui sont rapportés dans la littérature pour la mère et l’enfant. Bien que couramment pratiquée, la césarienne reste une intervention chirurgicale avec des risques à court et à long terme. Chez les enfants nés par césarienne, nous retrouvons des taux plus élevés d’asthme, d’obésité, de problème d’allergies etc. Tandis que chez les mères subissant la césarienne, nous retrouvons plus de cas d’infection, d’hémorragie et des risques plus élevées de rupture du placenta et de fausse couche lors des grossesses subséquentes. Puisque la prévalence de la césarienne ne cesse d’augmenter, il est primordial de comprendre son influence sur le développement neurologique de l’enfant. L’association entre le mode d’accouchement et les troubles neurodéveloppementaux tel que le trouble du déficit d'attention et d’hyperactivité (TDAH) chez les enfants est peu étudié avec des résultats souvent contradictoires ou non concluants. Le TDAH est l'un des troubles neurodéveloppementaux les plus courants chez les enfants avec une prévalence mondiale qui s’élève à 7.2% (IC 95% 6.7-7.8). Ainsi, le projet de ce mémoire a pour objectif d’évaluer l’association entre les modes d’accouchements et le TDAH chez l’enfant, tout en palliant les limites méthodologiques observées dans la littérature présentement. Afin de répondre à cette question, le projet évalue trois modes d’accouchements et ainsi recherche l’association entre l’accouchement par césarienne élective, par césarienne d’urgence ou par voie vaginale assistée et le risque de TDAH chez les enfants comparativement à l’accouchement par voie vaginale non assisté. Cette étude de cohorte rétrospective populationnelle tire l’entièreté de ses données de la Cohorte des Grossesses du Québec (CGQ) sur une période allant de 1998 à 2015. L’étude retrouve une augmentation de 6 % (IC 95% 1.03 - 1.10) du risque de TDAH chez les enfants nés par césarienne d’urgence et une augmentation de 12 % (IC 95% 1.06 - 1.19) du risque de TDAH chez les enfants nés par voie vaginale assisté avec ventouse ou forceps. Aucune association (HRa=0.96 IC 95% 0.91 - 1.01) n’a été retrouvée entre l’accouchement par césarienne élective et l’augmentation du risque de TDAH chez les enfants. Par la suite, plusieurs analyses de sensibilités ont été effectuées pour évaluer la robustesse des résultats, mais aucune n’a significativement alterné nos résultats. En conclusion, l’étude démontre l’existence d’une association entre l’accouchement par césarienne d’urgence et par voie vaginale assisté et le risque de TDAH chez les enfants. Ces résultats renforcent la nécessité d’étudier davantage les répercussions de la césarienne et des accouchements assistés avec des instruments sur l’enfant dans un contexte Canadien, où nous retrouvons peu de recherche sur le sujet. / In Canada the rate of caesarean deliveries is about 29 % of all birth in 2018-2019. Despite the known risk of this major surgery, caesarean section rates are continually rising beyond the recommended rate by the world health organization (WHO) of 10 to 15 %. Scientific research has identified several short- and long-term potential risks associated with this procedure for both the child and mother. For the child, researchers have found higher rates of asthma, obesity, and allergy problems. As for the mother, some of these risks include post-partum infection, hemorrhage and higher risks of placental rupture and miscarriages in future pregnancies. Caesarean section rates have been steadily increasing and it is essential to understand its influence on the neurological development of the child. Few studies have investigated the association between the mode of delivery and neurodevelopmental disorders such as attention deficit hyperactivity disorder (ADHD) in children. Currently the literature shows often contradictory or inconclusive results. ADHD is one of the most common neurodevelopmental disorders in childhood with a worldwide prevalence of up to 7.2% (CI 95% 6.7-7.8). Therefore, the project of this thesis aims to evaluate the association between modes of delivery and ADHD in children while overcoming the methodological limitations observed in the literature. To answer this question, the project is evaluating three modes of delivery by looking into the association between elective caesarean, emergency caesarean or assisted vaginal delivery and the risk of ADHD in children compared to unassisted vaginal birth. This prospective population-based study uses data on pregnancies and children from 1998 to 2015 from The Quebec Pregnancy Cohort (QPC). Our adjusted analyses showed that children born via emergency caesarean and assisted vaginal delivery were 6% (CI 95% 1.03 - 1.10) and 12% (CI 95% 1.06 - 1.19) respectively more likely to have ADHD compared to children born via unassisted vaginal delivery. 6 However, no association was found between elective caesarean birth (HRa=0.96 CI 95% 0.91 - 1.01) and the risk of ADHD in children. Several sensitivities analyze were performed to assess the robustness of these findings, but none significantly altered our results. While a caesarean delivery and assisted vaginal birth are essential and lifesaving procedures, they can put children at risk. As showed in this study, emergency caesarean and assisted vaginal birth increase the risk of ADHD in children. These findings reinforce the need for further research to evaluate the impact of caesarean and assisted deliveries on the children especially in a Canadian context where studies are still limited.
625

Analyses of Common Elements and Oxides in the Paleosols of the Bahamas and of the Northern Mariana Islands

Ersek, Vasile 07 August 2004 (has links)
Paleosols from the Bahamas and the Northern Mariana Islands (CNMI) are closely related to past atmospheric circulation and dust load. In the Bahamas the sources of insoluble residue (IR) must be allogenic because the islands consist of almost pure carbonates. The Al2O3:TiO2 ratio was used to establish the provenance of the IR of the paleosols. Comparisons of this ratio from Bahamian paleosols, North African dust, Lesser Antilles ash and North American loess reveal that the African dust is the major contributor to the IR, with a potential minor volcanic input from the Lesser Antilles. The contribution of the North American loess to the IR was not determined because of geochemical similarities with the North African dust. The study of two outcrops in Eleuthera indicate that paleosols can act as aquicludes. The Bahamian samples were collected on a roughly north-south transect in order to establish the climatic influence on paleosol properties. Even though there is a marked climatic gradient in the Bahamas, the paleosol geochemistry shows no trend that could be related to paleoclimate. While previous studies indicated that the source of insoluble residues in the soils of CNMI is carbonate dissolution, the present study shows that atmospheric deposition of ash from the Mariana arc and dust from the Asian continent may play a significant role in paleosol formation.
626

”I really hope you guys are enjoying this. Thank you so much for watching!” : En kvalitativ och kvantitativ studie av interaktionen mellan YouTubare och deras publik / ”I really hope you guys are enjoying this. Thank you so much for watching!” : A qualitative and quantitative study of the interaction between YouTubers and their audience

Källback Winter, William, Backman, Tove January 2016 (has links)
The overall purpose of this essay, “‘I really hope you guys are enjoying this. Thank you so much for watching!’ - a qualitative and quantitative study of the interaction between YouTubers and their audience", is to study how YouTubers that play and comment video games interact with their audience, what kind of response these YouTubers receive and the interaction between viewers and fans in these YouTubers comment sections. This essay also studies if there is a difference between the response female and male YouTubers receive. The study is based on theories about fan culture, participation culture, collective intelligence, feminism and gender. A quantitative content analysis has been used to analyze 600 comments on six YouTube videos uploaded by six different YouTubers. The purpose of the quantitative analysis was to see what content of the comments most often occur as well as if the comment showed a positive, negative or neutral view of the YouTuber. The result of the quantitative analysis was used as a base for a qualitative critical discourse analysis, which also studied how the YouTubers behaved in the videos. The results of this study showed that the YouTubers mostly received positive comments about their personalities and their YouTube channel. They mostly received negative comments about the way they play the game. The female YouTubers received more negative comments than the male YouTubers, who in turn received more positive comments. The study also showed that YouTubers interact by talking directly to the audience and looking into the camera, by using the word “we” when talking about how they play the game as if they are playing with the audience, by asking the audience questions and by answering comments that the YouTubers have received. The YouTubers engage their audience by using strong expressions and by playing the game during a livestream. The YouTubers’ fans engage and interact by showing appreciation of the YouTubers and defend the YouTubers when they receive negative comments in the comment section of their videos. These ways which YouTubers interact with and engage their audience can be seen as part of a discourse about interaction and engagement online.
627

Alternative assessment for effective open distance education

Oliver, Erna 09 1900 (has links)
The knowledge-driven, network society is founded upon technology. Educators need to implement technology effectively into the three main pillars of education, namely teaching, learning and assessment. This would assist students to become independent, confident and motivated life-long, self-directed learners that can use technology effectively in an educational environment. It would also ensure that graduates are able to become change agents, transferring their knowledge, skills and values to others in their communities. Alternative assessment methods that are technology driven could enable both educators and students to become more effective in a network society. This study advocates the use of alternative assessment methods by using technology driven assessment tools for possible replacement of traditional, paper based and "one size fits all" assessment methods within the subject field of Theology. Document analysis was used in a broad sense to evaluate technology-based multimedia documents. Ten documents were identified and evaluated as possible alternatives for traditional assessment methods. Inter-rater reliability ensured that the investigation provided constant estimates and results. The SECTIONS model used for this evaluation provided opportunities to include criteria important for higher education, the use of technology and subject relevant information to ensure that the evaluation was done with a specific purpose and scope in mind; to find technology-based tools that can substitute traditional assessment tools in order to enhance effective education to students. / Educational Studies / M. Ed. (Open and Distance Learning)
628

Alternative assessment for effective open distance education

Oliver, Erna 09 1900 (has links)
The knowledge-driven, network society is founded upon technology. Educators need to implement technology effectively into the three main pillars of education, namely teaching, learning and assessment. This would assist students to become independent, confident and motivated life-long, self-directed learners that can use technology effectively in an educational environment. It would also ensure that graduates are able to become change agents, transferring their knowledge, skills and values to others in their communities. Alternative assessment methods that are technology driven could enable both educators and students to become more effective in a network society. This study advocates the use of alternative assessment methods by using technology driven assessment tools for possible replacement of traditional, paper based and "one size fits all" assessment methods within the subject field of Theology. Document analysis was used in a broad sense to evaluate technology-based multimedia documents. Ten documents were identified and evaluated as possible alternatives for traditional assessment methods. Inter-rater reliability ensured that the investigation provided constant estimates and results. The SECTIONS model used for this evaluation provided opportunities to include criteria important for higher education, the use of technology and subject relevant information to ensure that the evaluation was done with a specific purpose and scope in mind; to find technology-based tools that can substitute traditional assessment tools in order to enhance effective education to students. / Educational Studies / M. Ed. (Open and Distance Learning)
629

Kalibrace měřícího zařízení aerodynamického tunelu VUT / Wind tunnel measuring equipment calibration

de Boer, Hendrik January 2021 (has links)
V této diplomové práci bylo zkoumáno téma kalibrace zařízení a sekcí ve vztahu k aerodynamickému tunelu na brněnském institutu leteckého inženýrství. Přístroje používané v aerodynamickém tunelu jsou kalibrovány a jsou popsány a provedeny kalibrace sekcí na testovací sekci. Kalibrační listy a šablony sestav jsou vytvořeny za účelem zjednodušení budoucích procesů. Nově kalibrovaná sestava se používá k provádění měření síly a probuzení na modelovém voze, která jsou porovnána s předkalibrací měření, aby dále ilustrovala užitečnost kalibrací.

Page generated in 0.0193 seconds