• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1167
  • 634
  • 248
  • 220
  • 176
  • 122
  • 95
  • 63
  • 41
  • 23
  • 12
  • 9
  • 8
  • 7
  • 7
  • Tagged with
  • 3144
  • 747
  • 610
  • 582
  • 533
  • 274
  • 193
  • 182
  • 181
  • 178
  • 174
  • 173
  • 170
  • 159
  • 158
  • 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.
841

The performance of the ATLAS missing transverse momentum high-level trigger in 2015 pp collisions at 13 TeV

Chiu, Justin 09 September 2016 (has links)
The performance of the ATLAS missing transverse momentum (ETmiss) high-level trigger during 2015 operation is presented. In 2015, the Large Hadron Collider operated at a higher centre-of-mass energy and shorter bunch spacing (sqrt(s) = 13 TeV and 25 ns, respectively) than in previous operation. In future operation, the Large Hadron Collider will operate at even higher instantaneous luminosity (O(10^34 cm^−2 s^−1)) and produce a higher average number of interactions per bunch crossing, <mu>. These operating conditions will pose significant challenges to the ETmiss trigger efficiency and rate. An overview of the new algorithms implemented to address these challenges, and of the existing algorithms is given. An integrated luminosity of 1.4 fb^−1 with <mu> = 14 was collected from pp collisions of the Large Hadron Collider by the ATLAS detector during October and November 2015 and was used to study the efficiency, correlation with offline reconstruction, and rates of the trigger algorithms. The performance was found to be satisfactory. From these studies, recommendations for future operating specifications of the trigger were made. / Graduate / 0798, / jchiu@uvic.ca
842

Using cloud resolving model simulations of tropical deep convection to study turbulence in anvil cirrus / Studier av turbulenta rörelser i städmoln medhjälp av numeriska simuleringar av tropisk konvektion

Broman Beijar, Lina January 2008 (has links)
Identifying the dynamical processes that are active in tropical cirrus clouds is important for understanding the role of cirrus in the tropical atmosphere. This study focuses on analyzing turbulent motions inside tropical anvil cirrus with the use of a Cloud Resolving Model. Convection in the transition from shallow to deep convection has been simulated with Colorado State University Large Eddy Simulator/Cloud Resolving Model System for Atmospheric Model (SAM 6.3) in a high resolution three-dimensional simulation and anvil cirrus formed in the end of this simulation has been analyzed. For model set up, data gathered during the Tropical Rainfall Measuring Mission Large-Scale Biosphere-Atmosphere (TRMM LBA) field experiment in Amazonas, Brazil have been used as large scale forcing. 31 anvil clouds have been localized from a single time step of the simulation, “a snapshot”, of the entire simulated cloud field consisting of convective clouds of different scales and subsequently divided into three categories that represent different stages of the anvil lifetime; growing, mature and dissipating anvil stages. The classification is based on in-cloud properties such as cloud condensate content and vertical velocities. The simulated anvils have been analyzed both individually and as groups to examine the transition from isotropic three-dimensional turbulence in the convective core of the thunderstorm to stratified two-dimensional turbulence in the anvil outflow. A dimensionless number F is derived and used as a measure of the “isotropic” behavior of the turbulence inside the cloud. F is expressed as the ratio between the horizontal part of TKE and the total (horizontal + vertical) Experiments show that SAM 6.3 clearly can resolve turbulent structures and that the transition from isotropic three-dimensional turbulence to stratified two-dimensional turbulence occurs in the middle layers of the mature and dissipating anvil stages. / Sammanfattning av ”Studier av turbulenta rörelser i städmoln med hjälp av numeriska simuleringar av tropisk konvektion”  Städmoln i tropikerna har stor inverkan på strålningsballansen på grund av de är så vanligt förekommande och att de ligger på hög höjd i atmosfären. Att förstå de drivande krafterna som är aktiva i skapandet och underhållandet av städmoln är viktiga för att få en bra bild av rollen städmoln spelar i den tropiska atmosfären. Den här uppsatsen fokuserar på att studera turbulenta rörelser inuti tropiska städmoln med hjälp av en molnmodell. Tropisk konvektion har simulerats med Colorado State University’s molnmodell SAM 6.3 i en högupplöst tredimensionell simulering. Data från en ”ögonblicksbild” av det simulerade molnfältet har analyserats och 31 städmoln har valts ut och studerats vidare. De simulerade städmolnen indelades i tre olika kategorier baserat på utvecklingsstadier; växande städmoln, moget städmoln och skingrade städmoln. Stadieklassificeringen bestämdes beroende på isvatteninnehåll och vertikalhastigheter i molnet. Städmolnen har därefter analyserats både individuellt och som grupper för att lokalisera och analysera övergången från tredimensionell isotropisk turbulens i kärnan av Cb-molnet till tvådimensionell stratifierad turbulens i städmolnet. För att initiera simuleringen användes mätdata insamlade under fältexperimentet TRMM LBA (Tropical Rainfall Measuring Mission Large-Scale Biosphere-Atmosphere) i Amazonas, Brasilien. För att beskriva turbulenta rörelser i molnen togs det dimensionslösa talet 𝐹 fram som ett mått på isotropin. 𝐹 uttrycks som kvoten mellan den horisontella delen av TKE och den totala (horisontell och vertikal). Den här studien visar att den undersökta molnmodellen SAM 6.3 klart kan simulera turbulenta i rörelser i övergången mellan isotropisk till horisontell turbulens i olika stadier av städmolnens livscykel. Mina analyser visar att övergången sker främst i de mellersta skikten av de mogna och skingrade stadierna av städmolnets utveckling.
843

An educational experiment in discovering spear phishing attacks / Ett utbildningsexperiment för att upptäcka spear phishing attacker

Floderus, Sebastian, Rosenholm, Linus January 2019 (has links)
Background: Spear phishing attacks uses social engineering targeting a specific person to steal credential information or infect the users computer with malware. It is often done through emails and it can be very hard to spot the difference between a legitimate email and a scam email. Cybercrime is a growing problem and there is many ways to inform and educate individuals on the subject.Objectives: This study intends to perform an experiment to see if an educationalsupport tool can be used to better identify phishing emails. Furthermore see if there is a difference in susceptibility between students from different university programs. Methods: A qualitative research study was used to get the necessary understanding how to properly develop a phishing educational tool. A Pretest-Posttest experiment is done to see if there is an improvement in result between an experimental group that received education and the control group that did not. Results: The result shows an overall higher score for the technical program compared to the non-technical. Comparing the pretest with the posttest shows an increase in score for the non-technical program and a decrease in score for the technical program. Furthermore 58% of the non-technical students who started the test did not complete it. Conclusions: There is a noticeable difference in susceptibility between the programs for detecting scam emails for students. However further research is needed in order to explore to what extent the education process had an impact.
844

[en] RANDOMIZATION IN DESIGN OF EXPERIMENTS: A CASE STUDY / [pt] ALEATORIZAÇÃO EM PLANEJAMENTO DE EXPERIMENTOS: UM ESTUDO DE CASO

IZABEL CRISTINA CORREA SALDANHA 22 October 2008 (has links)
[pt] O presente trabalho teve como objetivo apresentar diretrizes para a execução de experimentos fatoriais com restrições na aleatorização, mostrando a importância em identificar tais restrições, com base na visão de alguns autores e da aplicação de um estudo de caso. Este estudo foi cedido pela Companhia Siderúrgica Nacional - CSN, e exposto através da comparação entre dois modelos, cujas análises refletem as diferenças ao se considerar a restrição na aleatorização do experimento para obter uma resposta otimizada. Conforme identificado na literatura, poucos autores abordam a importância de reinicializar o nível dos fatores em um projeto de experimento industrial. Reinicializar o nível dos fatores, junto à necessidade de aleatorizar a ordem das corridas experimentais, torna válida a hipótese de que as observações obtidas no experimento serão variáveis aleatórias independentemente distribuídas. Quando a aleatorização completa do experimento não é possível de ser atingida, cabe ao experimentalista a decisão de projetar o experimento de tal forma que garanta a correta análise estatística e, conseqüentemente, a validação do modelo. Ao identificar se o experimento apresenta restrições em ser aleatorizado, classificando-o, identificando os fatores fáceis e difíceis de reinicializar, e analisando-se corretamente, evitam-se avaliações equivocadas ou incompletas, como se apresentou neste trabalho. Por fim, a análise, tendo em vista a existência da restrição em executar um experimento completamente aleatorizado e levando em consideração a presença de dois termos de erro no modelo permitiu a identificação das condições experimentais que garantem a minimização da resposta para o estudo de caso. / [en] This work presents some guidance for the execution of factorial experiments with restrictions in the randomization by showing the importance of restrictions identifying. The study is based on some author´s points of view and on a case study application. The original research information comes from Companhia Siderúrgica Nacional - CSN, in fact, the research is presented through two models comparisons. The analysis of these models reveals the differences in taking into account a restriction in the experiment randomization with the aim of getting an optimized response. As shown in the studied literature, just a few authors approach the importance of restarting the factors level in an experimental industrial project. Resetting the factor´s level added to the necessity of randomizing the order of the experimental runs, valid the hypothesis that sustains that the experiment observations will be random variables independently distributed. When the complete randomization of the experiment results in an impossible chore, it is expected that the one who is in charge decides to project the experiment in a way that assures the correct statistic analysis, and consequently, the model´s validation. By identifying if the experiment has restrictions to be randomized, classifying the experiment, identifying which ones are the easiest and hardest factors and doing a correct analyze; it is expected that incomplete or mistaken assessments, like those showed in this research, will be avoided. Finally, the analyses taking into account a restriction in the complete randomized experiment execution and the presence of two error terms in the model, allowed the identification of the experimental conditions that guarantee the case study´s response minimization.
845

Analyzing asymmetric nonlocality experiments with relaxed conditions

Dilley, Daniel 01 May 2019 (has links)
It is already known that one can always find a set of measurements on any two-qubit entangled state that will lead to a violation of the CHSH inequality. We provide an explicit state in terms of the angle between Alice's choice of measurements and the angle between Bob's choice of measurements, such that the CHSH inequality is always violated provided Alice's or Bob's choice of inputs are not collinear. We prove that inequalities with a corresponding Bell operator written as a linear combination of tensor products of Pauli matrices, excluding the identity, will generate the most nonlocal correlations using maximally entangled states in our experiment. From this result and a proposition from Horodecki et. al., we are able to construct the state that generates these optimal correlations. To achieve this state in a lab, one party must rotate their qubit using the orthogonal operation we provide and also rotate their Bloch sphere such that all their measurements lie in the same plane. We provide a comprehensive study of how Bell inequalities change when experiments introduce error via imperfect detection efficiency. The original cases of perfect efficiency are covered first and then a more realistic approach, when inefficient detectors are used, will follow. It is shown that less entanglement is needed to demonstrate more nonlocality in some Clasure-Horne-Shimony-Holt (CHSH) experiments when detector inefficiency is introduced. An example of this is shown for any given specific set of measurements in the CHSH Bell experiment. This occurs when one party has a detector of efficiency for each choice of input and the other party makes projective measurements. The efficiency can be pushed down to fifty percent while still violating the CHSH inequality, and for the experimental set-up illustrated, there is more nonlocality with less entanglement. Furthermore, it is shown that if the first party has an imperfect detector for only one choice of inputs rather than two, the efficiency can be brought down arbitrarily close to zero percent while still violating the CHSH inequality. Historically, nonlocality and entanglement were viewed as two equivalent resources, but recently this equality has come under question; these results further support this fundamental difference. Further more, we introduce Mermin's game in the case of relaxed conditions. The original constraints were that when the detectors in separate labs of a two-qubit experiment are in the same setting, then the results should be the same. We require that the outcomes are the same at least part of the time, given by some epsilon variable. Initially, one could find a maximum violation of one-fourth by allowing to parties to share the singlet state and have measurement settings one-hundred and twenty degrees apart from one another. By allowing some epsilon error in the perfect correlations regime, one can find a maximum violation of minus one plus the square root of two using the singlet state and measurement inputs that achieve Tsirelson's bound for the CHSH experiment. The reason is that we show Mermin's inequality is technically the CHSH inequality "in disguise", but with using constraints the CHSH experiment does not use. We derive Mermin's inequality under new conditions and give the projective measurements needed to violate maximally.
846

Nudge the lunch : a field experiment testing primacy effects using a menu intervention approach in a university cafeteria

Nelander, Lif January 2019 (has links)
The world is facing a global climate crisis and a collective step towards a more sustainable lifestyle is of importance. Food consumption accounts for a large part of an individuals’ total emissions and as the production of meat generally emits less green-house-gases than that of plant-based alternatives, changing towards a more plant-based diet can be one step to a more sustainable lifestyle. This study outlines a field experiment at a university cafeteria where the menu order was altered by random assignment. It is tested if placing the vegetarian option at the top of the menu has a causal effect on the share of vegetarian option sold that day, i.e. if it is possible to nudge customers to choose a more sustainable option. Using ordinary least squares and a beta regression models, the results do not show a positive treatment effect on the share of vegetarian option sold but do find a significantly average negative effect of 5.5 percentage points on the share of meat option sold. This effect it translated to an average negative effect of 6 percent on the daily emissions due to food sales at the cafeteria.
847

Klinische Performance und Biokompatibilität der PUREMA® H-Dialysemembran / Clinical performance and biocompatibility of the PUREMA® H dialysis membrane

Kirsch, Artur January 2007 (has links) (PDF)
Im Rahmen einer randomisierten, prospektiven Cross-over-Studie wurden während der Hämodialyse an chronisch dialysepflichtigen Patienten standardisiert Parameter der Dialyseeffektivität und Biokompatibilität einer neuen, mittels einem Polyelektrolytadditiv modifizierten Dialysemembran, PUREMA® H, im Vergleich zu einer Kontrolldialysemembran, Helixone®, gemessen. Im Vergleich zur Kontrollmembran wies die PUREMA® H-Membran eine verbesserte Entfernung kleinmolekulargewichtiger Eiweiße incl. &#61538;2-Mikroglobulin und eine insbesondere für die Komplementaktivierung optimierte Biokompatibilität auf. / In a prospective, randomized, cross-over study on maintenance dialysis patients, a new polyelectrolyte modified hemodialysis membrane, PUREMA® H, was compared to a control membrane, Helixone®, during haemodialysis. Parameters of dialysis efficacy and biocompatibility were measured in a standardized manner. Compared to control, PUREMA® H showed a significantly higher removal of low-molecular-weight proteins, including beta 2-microglobulin and an optimized biocompatibility particulary in regard to complement system activation.
848

The Sharing Economy and Discrimination : Evidence from a Field Experiment in Sweden

Farrahi, Nima January 2019 (has links)
To investigate whether there is unequal treatment for ethnic minorities in the sharing economy this paper conducts a field experiment on Airbnb in Sweden. The key findings report that inquiries from guests with Arabic-sounding names are 17 percentage points less likely to receive a booking invitation compared to guests with Swedish-sounding names. The discrimination is robust across host and listing characteristics. Furthermore, the results show that being associated with a lower social class decreases the probability of receiving a booking invitation for guests with Arabic-sounding names but not for guests with Swedish-sounding names, suggesting that the signal of social class is stronger for guests with Arabic-sounding names.
849

Étude numérique et expérimentale du comportement d'étanchéité des joints sans contact à rainures hélicoïdales / Numerical and experimental study of the sealing behavior of viscoseals

Jarray, Mohamed 03 December 2018 (has links)
Les joints sans contact sont des solutions d’étanchéité optimales pour les systèmes mécaniques fonctionnant à des vitesses relativement élevées. Ils ont une durée de vie importante et ont été proposés pour une utilisation dans les moteurs spatiaux. Une type de joints d'étanchéité sans contact, le joint visqueux, est étudié en détail dans ce travail de thèse au moyen d'une analyse numérique et expérimentale. Ce travail présente un modèle numérique développé pour prédire le comportement du joint visqueux en régime laminaire et turbulent. L’interface liquide-air dans le joint est également étudiée en utilisant une approche CFD basée sur la méthode VOF. La conception et la réalisation d’un dispositif expérimental a permis de confronter les résultats numériques et expérimentaux, l’écart entre les deux approches n’excède pas 10% dans 95% des cas étudiés. / Contactless seals are optimal sealing solution for mechanical systems operating with relatively high speeds. They have an important operation life time, and they were proposed for use in space engines. One sub-category of non-contact seals, the viscoseal, is studied in detail in this work through a numerical and experimental analysis. This work presents a numerical model developed to predict the viscoseal performance in laminar and turbulent regime. Furthermore the sealing performance of the viscoseal is investigated for different geometrical characteristics of the seal. The interface liquid-air in the seal is also studied using a CFD approach based on VOF method. The design and installation of an experimental device allowed the comparison of the numerical and experimental results, the difference between the two does not exceed 10% for 95% of studied cases.
850

Etude des bases (épi) génétiques de l'adaptation dans une expérience de sélection divergente pour la précocité de floraison chez le maïs / (Epi)-genetic basis of adaptation in a divergent selection experiment for flowering time in maize inbred lines

Durand, Eléonore 10 June 2011 (has links)
La variation quantitative résulte de l’action combinée des gènes et de leur environnement. Pour comprendre la relation génotype-phénotype et disséquer l’architecture des caractères complexes, deux approches sont couramment employées. D’une part l’évolution expérimentale qui permet de quantifier le nombre et l’effet des mutations dans la construction d’un phénotype soumis à une pression de sélection, d’autre part la cartographie de QTL (Quantitative Trait Loci) et/ou la génétique d’association qui permettent d’identifier les locus responsables de la variation phénotypique. Au cours de cette thèse, nous avons combiné l’ensemble de ces approches pour (1) évaluer le rôle relatif des nouvelles mutations et de la variabilité résiduelle dans la réponse à la sélection ; (2) identifier les déterminants génétiques sous tendant cette réponse ; (3) disséquer, pour un locus candidat, les mécanismes génétiques de sa contribution à la variation phénotypique. Pour cela, nous disposons d’un matériel génétique résultant d’une expérience de sélection divergente pour la date de floraison menée depuis plus de dix ans. Cette expérience a été conduite en parallèle à partir de deux lots de semences de lignées commerciales de maïs (F252 et MBS847). Pour chaque lignée de départ, deux populations ont été constituées, une population précoce et une population tardive produites en sélectionnant et autofécondant les génotypes les plus précoces/tardifs à chaque génération. Nous avons caractérisé la réponse à la sélection après 7 générations. Cette réponse est rapide, asymétrique entre populations et significative dans 3 des 4 populations. Elle est linéaire avec le temps ce qui indique que des nouvelles mutations contribuent à créer de la variance génétique à chaque génération. Nous avons identifié un locus majeur contribuant à 35% de la variation pour la date de floraison dans la population F252 tardive et pour lequel les deux allèles étaient présents dans le lot de semence initial sous forme d’hétérozygotie résiduelle. Les deux allèles présentent des haplotypes très divergents autant au niveau de leur variation nucléotidique (5.7%) que d’un point de vue structural (16 indels) sur une région proche du gène eIF-4A (Eukaryotic Initiation Translation Factor 4A). L’association de ce locus avec la date de floraison et d’autres caractères corrélés tels que la hauteur et le nombre de feuilles a été confirmée par une caractérisation développementale fine de génotypes précoces et tardifs et également dans un panel d’association comprenant 317 lignées de maïs cultivé. En plus d’un effet pléiotrope, nous avons montré grâce au développement de méthodes statistiques que ce locus présente des interactions épistatique fortes avec d’autres locus en ségrégation puisque son effet dépend largement du fond génétique. Nous avons finalement utilisé des AFLP (Amplified Fragment Length Polymorphisms) sur tous les génotypes issus des 7 premières générations de sélection afin d’identifier d’autres polymorphismes potentiellement impliqués dans la réponse à la sélection. Nos résultats préliminaires montrent une différenciation génétique et épigénétique entre les populations sélectionnées qui semble être préférentiellement due à de l’hétérozygotie résiduelle. / Quantitative variation results from the combined action of multiple genes and their environment. Two approaches are currently employed to gain insights into the link between genotype and phenotype and to dissect the genetic architecture of complex traits. On one hand, experimental evolution allows quantifying the number of mutations and their effect on the evolution of a phenotype subject to artificial selection. On the other hand, QTL (Quantitative Trait Locus) and association mapping are used to identify loci responsible for phenotypic variation. In this work, we have combined all 3 approaches in order to (1) evaluate the role of new mutations and standing genetic variation to the response to selection ; (2) to identify the genetic determinants underlying this response ; (3) to dissect at one candidate locus the genetic mechanisms of its contribution to phenotypic variation. We have used the material produced by a divergent selection experiment for flowering time conducted for over 10 years in the field. This experiment was conducted in parallel from two commercial maize inbred line, F252 and MBS847. From each initial seed lot, two populations, an early population and a late population, were created by selecting and selfing the earliest/latest individuals at each generation. We characterized the response to selection after 7 generations. The response was fast, asymmetric between populations and significant in 3 out of 4 populations. It was linear through time indicating that new mutations have generated new additive genetic variance at each generation. We identified a major locus contributing to 35% of the variation for flowering time in the late F252 population. At this locus, two alleles were present as residual heterozygocity in the initial seed lot. The two alleles exhibited haplotypes extending on a region around the eIF-4A (Eukaryotic Initiation Translation Factor 4A) that diverged drastically both at the nucleotide (5.7%) and structural level. We were able to confirm the association of the candidate locus to flowering time variation and other traits such as height and leaf number, first using an association panel containing 317 maize lines, second through the developmental characterization of early and late genotypes. In addition, to its pleiotropic effect, we have shown by developing a specific statistical framework that this locus exhibit pervasive epistatic interactions with other loci segregating in the population. Hence, its effect largely depended on the genetic background. We have finally applied methyl-sensitive AFLP (Amplified Frgament length Polymorphisms) to screen all genotypes in order to identify the polymorphisms potentially involved in the response to selection during the first 7 generations Our preliminary results indicate both a genetic and epigenetic differentiation between early and late populations. This differentiation seems however to be mainly driven by standing genetic variation.

Page generated in 0.2191 seconds