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  • 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.
511

The transient radio sky

Keane, Evan January 2010 (has links)
The high time-resolution radio sky represents unexplored astronomical territory where the discovery potential is high. In this thesis I have studied the transient radio sky, focusing on millisecond scales. As such, this work is concerned primarily with neutron stars, the most populous member of the radio transient parameter space. In particular, I have studied the well known radio pulsars and the recently identified group of neutron stars which show erratic radio emission, known as RRATs, which show radio bursts every few minutes to every few hours. When RRATs burst onto the scene in 2006, it was thought that they represented a previously unknown, distinct class of sporadically emitting sources. The difficulty in their identification implies a large underlying population, perhaps larger than the radio pulsars. The first question investigated in this thesis was whether the large projected population of RRATs posed a problem, i.e. could the observed supernova rate account for so many sources. In addition to pulsars and RRATs, the various other known neutron star manifestations were considered, leading to the conclusion that distinct populations would result in a 'birthrate problem'. Evolution between the classes could solve this problem - the RRATs are not a distinct population of neutron stars. Alternatively, perhaps the large projected population of RRATs is an overestimate. To obtain an improved estimate, the best approach is to find more sources. The Parkes Multi-beam Pulsar Survey, wherein the RRATs were initially identified, offered an opportunity to do just this. About half of the RRATs showing bursts during the survey were thought to have been missed, due to the deleterious effects of impulsive terrestrial interference signals. To remove these unwanted signals, so that we could identify the previously shrouded RRATs, we developed new interference mitigation software and processing techniques. Having done this, the survey was completely re-processed, resulting in the discovery of 19 new sources. Of these, 12 have been re-detected on multiple occasions, whereas the others have not been seen to re-emit since the initial discovery observations, and may be very low burst-rate RRATs, or, isolated burst events. These discoveries suggest that the initial population estimate was not over-estimated - RRATs, though not a distinct population, are indeed numerous. In addition to finding new sources, characterisation of their properties is vital. To this end, a campaign of regular radio observations of the newly discovered sources, was mounted, at the Parkes Observatory, in Australia. In addition, some of the initially identified RRATs were observed with the Lovell Telescope at Jodrell Bank. These have revealed glitches in J1819-1458, with anomalous post-glitch recovery of the spin-down rate. If such glitches were common, it would imply that the source was once a magnetar, neutron stars with the strongest known magnetic fields of up to 10¹⁵ gauss. The observations have also been used to perform 'timing' observations of RRATs, i.e. determination of their spin-down characteristics. At the beginning of this thesis, 3 of the original sources had 'timing solutions' determined. This has since risen to 7, and furthermore, 7 of the newly discovered sources now also have timing solutions. With this knowledge, we can see where RRATs lie in period-period derivative space. The Parkes RRATs seem to be roughly classifiable into three groupings, with high observed nulling fractions - normal pulsars, high magnetic field pulsars and old, 'dying' pulsars. It seems that RRATs and pulsars are one and the same. When a pulsar is more easily detected in searches for single bright pulses, as opposed to in periodicity searches, we label it a RRAT. Such searches impart a selection effect on the parameter space of possible sources, in both nulling fraction and rotation period. In this sense, an observational setup could be designed to make any pulsar appear as a RRAT. For realistic survey parameters however, this is not the case, and the groups mentioned above seem to be the most likely to appear as RRATs. In fact, we can utilise RRAT searches to identify neutron stars, difficult to find by other means, in particular high-magnetic field pulsars, and pulsars approaching the pulsar "death valley". Some of the RRATs are well explained as being distant/weak pulsars with a high modulation index, others seem to be nulling pulsars. This highlights the incomplete knowledge of nulling behaviour in the pulsar population. It seems that there may be a continuum of nulling durations, under a number of guises, from 'nulling pulsars' to 'RRATs' to 'intermittent pulsars'. In fact this nulling may fit into the emerging picture, whereby pulsar magnetospheres switch between stable configurations.
512

Measurement of prompt gamma-ray energy distribution and multiplicity of U-235 following thermal fission using STEFF

Murray, Elizabeth January 2015 (has links)
More accurate knowledge of gamma-ray heating in nuclear reactors has beenlisted as a high priority request by the NEA [23]. In response to this the SpecTrometerfor Exotic Fission Fragments (STEFF), a 2-velocity, 2-energy spectrometer assembledby the Manchester Fission Group has been used to take measurements ofprompt gamma-rays from thermal fission of U-235. Through the procedures discussed,the average total gamma-ray energy and average multiplicity were determined to be8.40 +/- 0.26 MeV and 7.74 +/- 0.12, respectively. The single energy spectrum for eachindividual detector has been determined as well as the total energy distribution. A new parallel plate avalanche counter has been tested for its potential to improvethe timing resolution of the current STEFF stop detector. The timing resolution ofthe new detector is found to be 337 ps, an improvement of 75 % on the previous stopdetector. The pulse shapes created by a fission fragment in an ionisation chamber havebeen investigated. The relationship with fragment atomic number has been tested byemploying the Lohengrin spectrometer to separate fragments by mass so that theirindividual pulse shapes can be studied. Evaluation work has been performed at the NNL, Cumbria, under the supervisionof Dr Robert Mills. Experimental data determined from the spontaneous fission ofCf-252 has been extracted and evaluation techniques performed upon it so that thedata can be considered for inclusion within an evaluated nuclear database.
513

DNA replication in budding yeast : link between chromatin conformation and kinetics of replication / Réplication de l'ADN chez la levure de boulanger : lien entre la conformation de la chromatine et la cinétique de la réplication

Panciatici, Claire 06 December 2016 (has links)
L’information génétique contenue dans le noyau de la cellule doit être dupliquée fidèlement afin d’être transmise aux cellules filles pendant la division cellulaire. Pour organiser leur division, les cellules suivent un cycle reproductible composé de quatre étapes appelé cycle cellulaire. La préparation et l’exécution du programme de réplication de l’ADN ont lieu pendant des phases spécifiques du cycle grâce à l’intervention de multiples partenaires protéiques et de régulateurs structuraux. En particulier, la réplication de l’ADN s’effectue sur une matrice complexe constituée d’ADN associé à des protéines appelée chromatine. Cette dernière influence et est influencée par la réplication de l’ADN. Le travail présenté ici a pour objectif de faire le lien entre la conformation de la chromatine et la cinétique de réplication de l’ADN. Pour ce faire, nous combinons plusieurs techniques. La cytométrie de flux nous permet de suivre la quantité d’ADN présent dans une population de cellules et, à l’aide d’une méthode développée dans notre laboratoire, d’extraire le programme de réplication moyen d’une population de cellules. La technique de SAXS fournit des informations sur l’organisation locale des protéines et de l’ADN in vivo. Nos données peuvent être interprétées comme un cristal liquide avec un ordre nématique et une faible longueur de corrélation, ce qui suggère que la chromatine de la levure est majoritairement dépourvue d’une organisation en fibre de 30nm in vivo. Par ailleurs, par la méthode de peignage d’ADN, nous reproduisons les résultats précédemment obtenus montrant que la distance entre zones répliquées est d’environ ~60kb qui correspond à la distance entre des origines de réplication identifiées. Cependant, d’après l’étude du comportement dynamique de l’initiation, nous proposons que les initiations sont plus fréquentes que ce qui a été mesuré précédemment et correspondent à la distance entre les protéines MCM disposées sur le génome. / Genetic information carried in the cell nucleus must be faithfully duplicated to be transmitted to daughter cells during cell division. In order to orchestrate their division, cells go through a reproducible 4 stages cycle called «cell cycle». The preparation and execution of the DNA replication program is restricted to specific phases and implies many proteic and structural regulators. In particular, DNA replication occurs on a complex template of DNA associated with proteins. The latter is both influencing and influenced by DNA replication. This work aims at investigating the link between chromatin conformation and the kinetics of DNA replication. In order to do so, we combine several techniques. Using flow cytometry, we follow the evolution of a cell population with regards to their DNA content and, with a method developed in our laboratory, decipher the population averaged temporal program of DNA replication. SAXS data provide information on the local organisation of protein and DNA in vivo. Our data can be interpreted as a liquid crystal with a nematic order and a short correlation length, which suggest that yeast chromatin in vivo is predominantly devoid of 30 nm fibres organisation. On the other hand, we performed DNA combing to study the replication program in single cells. We reproduce previously obtained result showing that distance between replicated tracks is of ~60kb which corresponds to the distance between known origins of replication. However, studying the behaviour of initiation, we propose that the initiation events are more frequent than previously measured and correspond to distances between MCMs proteins loaded on the genome.
514

The Effects of Differential Exposure to Gruesome Photographs on Mock Jurors' Emotions & Legal Judgments

January 2020 (has links)
abstract: In a trial, jurors are asked to set aside their emotions and make judgments based solely on evidence. Research suggests jurors are not always capable of this, particularly when exposed to gruesome photographic evidence. However, previous research has not looked at the potentially moderating effect of when and for how long jurors are exposed to emotionally disturbing photographs, nor how many photographs they see. In two experiments I tested the impact of the timing of and extent of exposure to gruesome photographs on jurors’ emotions, verdicts, and punishment recommendations. In Study 1, I investigated the effect of timing and exposure duration to a single gruesome photograph of a victim in a murder case (no exposure, brief early exposure, brief late exposure, and prolonged exposure) on mock jurors’ emotions and case judgments. Prolonged exposure (relative to no or brief exposure, regardless of timing) increased disgust, which in turn was associated with harsher punishment. Contrary to previous research, the photograph manipulation did not influence verdicts. The results were mixed and inconclusive regarding brief early versus late exposure. In Study 2, I compared repeatedly viewing a single gruesome photograph to viewing a set of four similar, but unique gruesome photographs—holding the exposure time constant—to assess the impact of quantity of photos on jurors’ emotions and case judgments. Viewing multiple gruesome photos (relative to no photos) led to increase in guilty verdicts through increased disgust, replicating previous research. Viewing a single gruesome photo (relative to no photo) led to increase in guilty verdicts through disgust, differing from Study 1 findings. Viewing multiple gruesome photos and a single gruesome photo led to more disgust, compared to viewing no photo. However, differing from Study 1, gruesome photographs did not lead to an increase in punishment recommendations. There were no significant differences between exposure to a single or multiple gruesome photos on disgust, verdicts, or punishments. Overall, greater exposure to gruesome evidence led to increased disgust and punitiveness, relative to those with less exposure. However, jurors with greater exposure to the same or different photographs did not differ in reported emotions, verdicts, or punitiveness. / Dissertation/Thesis / Masters Thesis Psychology 2020
515

Plants, Parasites, and Pollinators: The Effects of Medicinal Pollens on a Common Gut Parasite in Bumble Bees

LoCascio, George 25 October 2018 (has links)
Declines in several pollinator species are due to a variety of factors, including pathogens. Incorporating pollinator-friendly plant species into wild and agricultural habitats could reduce the stress of pathogens if food sources act medicinally against pathogens. Previous research demonstrated one domesticated sunflower cultivar (Helianthus annuus) can dramatically reduce a gut pathogen (Crithidia bombi) of the common eastern bumble bee, Bombus impatiens. To ascertain the breadth of this medicinal trait, we tested whether pollen from several H. annuus cultivars and four relatives could also reduce C. bombi infections in B. impatiens. We also investigated whether timing of exposure to sunflower pollen relative to time of infection affected the strength of this medicinal trait. In all experiments, bees were infected and then fed their respective pollen diets for a week before they were dissected to assess infection. In our first experiment, all pollen from Helianthus species and relatives reduced C. bombi cell counts compared to our single species control of buckwheat (Fagopyrum esculentum). In our timing of exposure experiments, a one-time exposure to sunflower pollen present at the time of infection did not lower infection levels. In longer exposure trials, sunflower pollen suppressed C. bombi infection with a strength inversely proportional to the time between treatment and infection. Our results suggest that medicinal pollen may be widespread in the Helianthus genus and potentially throughout the Asteraceae family. Thus, these results provide insights into how strategic plantings of certain floral resources can help mediate and influences pollinator disease dynamics.
516

The Impact of Timing of Pornography Exposure on Mental Health, Life Satisfaction, and Sexual Behavior

Young, Bonnie 01 May 2017 (has links)
As pornography has become more widespread, young people are being exposed to pornography at earlier ages. Research examining the relationship between timing of exposure to pornography and outcomes in adulthood of mental health, life satisfaction, sexual behavior and attitudes, and pornography viewing patterns is limited. This study focuses on the relationship between timing of exposure to pornography and individual outcomes in adulthood. Results indicate that earlier exposure to pornography may significantly influence mental health, life satisfaction, sexual behavior and attitudes, and pornography viewing patterns in adulthood. Implications of this study include greater awareness of the risks of early exposure to pornography and unrestrained access to sexually explicit material for young people.
517

The Performance Cost of Security

Bowen, Lucy R 01 June 2019 (has links)
Historically, performance has been the most important feature when optimizing computer hardware. Modern processors are so highly optimized that every cycle of computation time matters. However, this practice of optimizing for performance at all costs has been called into question by new microarchitectural attacks, e.g. Meltdown and Spectre. Microarchitectural attacks exploit the effects of microarchitectural components or optimizations in order to leak data to an attacker. These attacks have caused processor manufacturers to introduce performance impacting mitigations in both software and silicon. To investigate the performance impact of the various mitigations, a test suite of forty-seven different tests was created. This suite was run on a series of virtual machines that tested both Ubuntu 16 and Ubuntu 18. These tests investigated the performance change across version updates and the performance impact of CPU core number vs. default microarchitectural mitigations. The testing proved that the performance impact of the microarchitectural mitigations is non-trivial, as the percent difference in performance can be as high as 200%.
518

Návrh vačkového hřídele pro motor s Millerovým cyklem / Camshaft design for Miller cycle engine

Dúlovcová, Gabriela January 2020 (has links)
The main aim of this thesis is the analysis of influence of inlet valve opening length and compression ratio on performance and thermodynamic parameters of Miller cycle using GT-SUITE software. Next step was an optimization of inlet and exhaust valve timing with goal of increasing motor effective power. For chosen option was designed cam shaft with regard of kinematic and dynamic magnitude courses.
519

Move to read: entrainment activities and pre-reading skills of kindergarteners

Carson-Swift, Kimberly Jené 16 November 2021 (has links)
The purpose of this study was to explore the possibility that music and movement instruction could cause improvement in language arts skills, due to evidence that music and language share processing mechanisms related to auditory perception as described by Patel (2007, 2011a, 2011b, 2014) in the shared syntactic integration resource hypothesis (SSIRH) and OPERA hypothesis. Sixty-two Kindergarten students from a suburban school, near a city in the Midwest, were selected via random assignment to be a part of an experimental or control group. Each group participated in pre- and posttests measuring entrainment and pre-reading skills. ANCOVA results of pre and posttest data revealed no significant difference between the groups. The music and movement instruction did not improve entrainment so results were inconclusive in regard to the impact of entrainment on phonological processing and rapid naming. Future studies might consider a pretest/posttest design with a group that focuses on entrainment without specific music language (Patel, 2008) and a group that conducted music class with the usual songs and descriptive language, to provide evidence regarding whether or not language needs to be combined with music to cause a cognitive transfer of skills. A further comparison of a group that learned to play singing games with a group that learned instrumental music might provide further evidence regarding the role that the combination of music and language might have on reading. Another line of inquiry might involve increasing the length of the intervention period to determine if a year is needed to cause cognitive transfer and ensure that the control group does not receive any music instruction. An additional consideration may be that improvement in entrainment provides a foundation for language processing that does not fully develop or present itself until children reach more challenging levels of reading fluency. Studies that measure student improvement over time would be one way to find evidence that music provides a neurological basis for reading, and language development. Further study possibilities are described in the conclusions of the dissertation. / 2022-11-15T00:00:00Z
520

Financování projektu z fondů EU / Project Financing from EU Funds

Bartoň, Tomáš January 2011 (has links)
This master’s thesis deals with project management and alternative forms of financing. It describes the theoretical elements, which are implemented in practice. It includes an analytical part of the problem, where the actual project elements are analysed, and a part of proposals, where a summary of the solutions is provided.

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