• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 55
  • 29
  • 10
  • 4
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 118
  • 35
  • 31
  • 28
  • 26
  • 25
  • 25
  • 24
  • 23
  • 21
  • 21
  • 21
  • 19
  • 19
  • 19
  • 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.
11

Substructure Synthesis Analysis and Hybrid Control Design for Buildings under Seismic Excitation

Morales Velasco, César A. 18 April 1997 (has links)
We extend the application of the substructure synthesis method to more complex structures, and establish a design methodology for base isolation and active control in a distributed model of a building under seismic excitation. Our objective is to show that passive and active control complement each other in such an advantageous manner for the case at hand, that simple devices for both types of control are sufficient to achieve excellent response characteristics with very low control forces. The Rayleigh-Ritz based substructure synthesis method proved to be highly successful in analyzing a structure more complex than the ones previously analyzed with it. Comparing the responses of the hybridly controlled building and the conventional fixed building under El Centro excitation, we conclude that the stresses are reduced by 99.6 %, the base displacement is reduced by 91.7 % and the required control force to achieve this is 1.1 % of the building weight. / Ph. D.
12

Modellierung des flexiblen Gestells eines periodisch bewegten Mechanismus

Zschech, Richard 19 June 2019 (has links)
Mechanismen in Verarbeitungsmaschinen bedürfen stets eines Hüll- und Stützsystems - dem Maschinengestell. Die Erfüllung der Genauigkeitsanforderung an einen Mechanismus während einer Bewegungsaufgabe wird durch unvermeidliche EIastizitäten, sowohl des Gestells als auch der Glieder des Mechanismus, erschwert. Zusätzlich sind die Gestelle, aus Gründen der Schwingungsisolation der Umgebung, häufig auf elastischen Maschinenfüßen gelagert. Diese Elastizitäten führen allein durch nicht zu vermeidende statische Verformungen zu unerwünschten Bewegungsabweichungen. Größeren negativen Einfluss üben allerdings ungewollt angeregte Schwingungen des Systems aus. Bei Kenntnis des dynamischen Verhaltens des Systems ist es möglich Bewegungen zu generieren, die das Schwingungsverhalten des Systems positiv beeinflussen. Voraussetzung hierfür ist die Erstellung eines verifizierten und validierten mechanischen Modells des Systems, bestehend aus Gestell und Mechanismus. Das Ziel der Arbeit besteht darin einen möglichen analytischen Modellierungsansatz der Elastostatik für das flexible zweidimensionale Gestell mit ebenem Mechanismus zu recherchieren, zu untersuchen und umzusetzen. Die Vorzugslösung soll in Form eines ausführbaren Skriptes in einer geeigneten Programmiersprache implementiert werden.
13

Characterising the decays of high-pt top quarks and addressing naturalness with jet substructure in ATLAS runs I and II

LeBlanc, Matthew Edgar 11 May 2017 (has links)
The coupling of the Standard Model top quark to the Higgs boson is O(1), which leads to large quantum corrections in the perturbative expansion of the Higgs boson mass. Possible solutions to this so-called naturalness problem include supersymmetric models with gluinos and stop squarks whose masses are at the electroweak scale, O(1 TeV). If supersymmetry is realised in nature at this scale, these particles are expected to be accessible with the Large Hadron Collider at CERN. A search for gluino pair production with decays mediated by stop- and sbottom-squark loops in the initial 14.8 ifb of the ATLAS run 2 dataset is presented in terms of a pair of simplified models, which targets extreme regions of phase space using jet substructure techniques. No excess is observed and limits are set which greatly extend the previous exclusion region of this search, up to 1.9 TeV (1.95 TeV) for gluinos decaying through light stop (sbottom) squarks to the lightest neutralinos. A performance study of top tagging algorithms in the 20.3 ifb 2012 dataset is also presented, which includes the first measurements of substructure-based top tagging efficiencies and fake rates published by ATLAS, as well as a detailed comparison of tagger performance in simulation. A benchmarking study which compares commercially available cloud computing platforms for applications in High Energy Physics, and a summary of ATLAS liquid argon calorimeter data quality work focused on monitoring and characterising the sporadic phenomena of Mini Noise-Bursts in the electromagnetic barrel calorimeter are also included. / Graduate / 0798 / matt.leblanc@cern.ch
14

On the dynamics of tidal streams in the Milky Way galaxy

Eyre, Andrew McEwan January 2010 (has links)
We present a brief history of Galactic astrophysics, and explain the origin of halo substructure in the Milky Way Galaxy. We motivate our study of the dynamics of tidal streams in our Galaxy by highlighting the tight constraints that analysis of the trajectories of tidal streams can place on the form of the Galactic potential. We address the reconstruction of orbits from observations of tidal streams. We upgrade the geometrodynamical scheme reported by Binney (2008) and Jin & Lynden-Bell (2007), which reconstructs orbits from streams using radial-velocity measurements, to allow it to work with erroneous input data. The upgraded algorithm can correct for both statistical error on observations, and systematic error due to streams not delineating individual orbits, and given high-quality but realistic input data, it can diagnose the potential with considerable accuracy. We complement the work of Binney (2008) by deriving a new algorithm, which reconstructs orbits from streams using proper-motion data rather than radial-velocity data. We demonstrate that the new algorithm has a similar potency for diagnosing the Galactic potential. We explore the concept of Galactic parallax, which arises in connection with our proper-motion study. Galactic parallax allows trigonometric distance calculation to stars at 40 times the range of conventional parallax, although its applicability is limited to only those stars in tidal streams. We examine from first principles the mechanics of tidal stream formation and propagation. We find that the mechanics of tidal streams has a natural expression in terms of action-angle variables. We find that tidal streams in realistic galaxy potentials will generally not delineate orbits precisely, and that attempting to constrain the Galactic potential by assuming that they do can lead to large systematic error. We show that we can accurately predict the real-space trajectories of streams, even when they differ significantly from orbits.
15

Genetic diversity and structure of livestock breeds

Wilkinson, Samantha January 2012 (has links)
This thesis addresses the genetic characterisation of livestock breeds, a key aspect of the long-term future breed preservation and, thus, of primary interest for animal breeders and management in the industry. First, the genetic diversity and structure of breeds were investigated. The application of individual-based population genetic approaches at characterising genetic structure was assessed using the British pig breeds. All approaches, except for Principle Component Analysis (PCA), found that the breeds were distinct genetic populations. Bayesian genotypic clustering tools agreed that breeds had little individual genetic admixture. However, inconsistent results were observed between the Bayesian methods. Primarily, BAPS detected finer genetic differentiation than other approaches, producing biologically credible genetic populations. BAPS also detected substructure in the British Meishan, consistent with prior known population information. In contrast, STRUCTURE detected substructure in the British Saddleback breed that could not wholly be explained. Further analysis of the British Saddleback revealed that the genetic subdivision did not reflect its historical origin (union of Essex pig and Wessex Saddleback) but was associated with herds. The Rainbarrow appeared to be moderately differentiated from the other herds, and relatively lower allelic diversity and higher individual inbreeding, a possible result of certain breeding strategies. The genetic structure and diversity of the British traditional chicken breeds was also characterised. The breeds were found to be highly distinctive populations with moderately high levels of within-breed genetic diversity. However, majority of the breeds had an observed heterozygote deficit. Although individuals clustered to their origin for some of the breeds, genetic subdivision of individuals was observed in some breeds. For two breeds the inferred genetic subpopulations were associated with morphological varieties, but in others they were associated with flock supplier. As with the British Saddleback breed, gene flow between flocks within the chicken breeds should be enhanced to maintain current levels of genetic diversity. Second, the thesis focused on breed identification through the assignment of individuals to breed origin. Dense genome-wide assays provide an opportunity to develop tailor-made panels for food authentication, especially for verifying traditional breed-labelled products. In European cattle breeds, the prior selection of informative markers produced higher correct individual identification than panels of randomly selected markers. Selecting breed informative markers was more powerful using delta (allele frequency difference) and Wright's FST (allele frequency variation), than PCA. However, no further gain in power of assignment was achieved by sampling in excess of 200 markers. The power of assignment and number of markers required was dependent on the levels of breed genetic distinctiveness. Use of dense genome-wide assays and marker selection was further assessed in the British pig breeds. With delta, it was found that 96 informative SNP markers were sufficient for breed differentiation, with the exception of Landrace and Welsh pair. Assignment of individuals to breed origin was high and few individuals were falsely assigned, especially for the traditional breeds. The probability that a sample of a presumed origin actually originated from that breed was high in the traditional breeds. Validation of the 96-SNP panel using independent test samples of known origin and market samples revealed a high level of breed label conformity.
16

The jet energy scale uncertainty derived from gamma-jet events for small and large radius jets and the calibration and performance of variable R jets with the ATLAS detector

Kogan, Lucy Anne January 2014 (has links)
In this thesis the jet energy scale uncertainty of small and large radius jets at the ATLAS detector is evaluated in-situ using gamma-jet events. The well calibrated photon in the gamma-jet events is used to probe the energy scale of the jets. The studies of the jet energy scale of small radius jets are performed using 4.7 fb<sup>-1</sup> of data collected at sqrt{s} = 7 TeV in 2011. The gamma-jet methods which were developed are then adapted and applied to large radius jets, using 20.3 fb^-1 of data collected at sqrt{s} = 8 TeV in 2012. The new jet energy scale uncertainties are found to be ~1 % for |eta| < 0.8, rising to 2-3 % for |eta| > 0.8. These uncertainties are significantly lower than the 3-6 % precision which has previously been achieved at ATLAS using track jets as a reference object. Due to the increase in precision, uncertainties due to pile-up and the topology of the jet also had to be evaluated. The total energy scale uncertainties for large radius jets are reduced by ~1-2 % (0.5-1 %) for |eta| < 0.8 (> 0.8). This reduction will be beneficial to analyses using large radius jets and it is specifically shown to benefit the t-tbar resonance search in the semi-leptonic channel. The t-tbar search looks for events with two top quarks in the final state, where one decays leptonically and the other hadronically. The hadronically decaying top quark is reconstructed using a large radius jet, and the jet energy scale uncertainty is a dominant source of uncertainty in the analysis. In addition to the studies of the jet energy scale of large radius jets, the first derivation of a calibration, and jet energy scale uncertainties derived with gamma-jet events, are shown for Variable R jets. The Variable R jet algorithm is a new type of jet algorithm with a radius that is inversely proportional to the size of the jet, making it useful for the study of high momentum top quarks. It is shown that similar methods can be used to calibrate and assess the uncertainties of Variable R jets as are used for standard, fixed radius jets at the ATLAS detector, although some adaptations will be necessary. The studies provide a basis for the calibration of Variable R jets in the future.
17

Estudo da detecção de quarks top no LHC / A study of the detection of quark top at LHC

Mello, Cedrick Miranda 25 June 2012 (has links)
Este trabalho consistiu em analisar a possibilidade de verificação da violação de sabor em correntes neutras intermediadas por glúons de Kaluza-Klein (GKK) através do modelo de dimensões extras compactas e curvas. Este introduz a possibilidade de violação de sabores em correntes neutras através de processos do tipo próton/próton em top/anti-quark c. Inicialmente estudamos o comportamento de jatos com altos momentos transversos (da ordem de 300 GeV) e suas subestruturas. Após isto, estudamos a detecção do quark top através dos algoritmos HEPTopTagger e Johns Hopkins (fizemos uma breve comparação entre eles). Por último, propusemos duas maneiras de encontrar os GKK. Uma delas, através da procura de somente quarks top. A outra, através da procura de um quark top e um jato sem subestrutura (algoritmo do tipo TJ). Pudemos ver que a possibilidade de encontrar o fenômeno de violação de sabores é acessível (a razão S/B da ordem de 0,1) para ambos os casos de massa analisados através do algoritmo do tipo TJ. / This study was to examine the possibility of verifying the violation of flavor in neutral currents mediated by Kaluza-Klein gluons (GKK), in which it was introduced by compact warped extra dimensions. The possibility of violation of flavors in neutral currents occurs through processes like proton/proton into quark top/ antiquark charm. Initially we studied the behavior of jets with high transverse momentum (the order of 300 GeV) and its substructures. After this, we studied the detection of the top quark via HEPTopTagger and Johns Hopkins algorithms (we did a brief comparison between them). Finally, we proposed two ways to find the GKK. One of them, by searching for only quark top. The other, by looking for a quark top and a jet without substructure (algorithm of TJ type). We could see that the possibility of encountering the phenomenon of violation of flavors is accessible (the ratio S/B is the order of 0.1) in both cases of mass analyzed by TJ type algorithm.
18

Fundamentals of substructure dynamics : In-situ experiments and numerical simulation

Borthwick, Verity January 2010 (has links)
Substructure dynamics incorporate all features occurring on a subgrain-scale. The substructure governs the rheology of a rock, which in turn determines how it will respond to different processes during tectonic changes. This project details an in-depth study of substructural dynamics during post-deformational annealing, using single-crystal halite as an analogue for silicate materials. The study combines three different techniques; in-situ annealing experiments conducted inside the scanning electron microscope and coupled with electron backscatter diffraction, 3D X-ray diffraction coupled with in-situ heating conducted at the European Radiation Synchrotron Facility and numerical simulation using the microstructural modelling platform Elle. The main outcome of the project is a significantly refined model for recovery at annealing temperatures below that of deformation preceding annealing. Behaviour is highly dependent on the temperature of annealing, particularly related to the activation temperature of climb and is also strongly reliant on short versus long range dislocation effects. Subgrain boundaries were categorised with regard to their behaviour during annealing, orientation and morphology and it was found that different types of boundaries have different behaviour and must be treated as such. Numerical simulation of the recovery process supported these findings, with much of the subgrain boundary behaviour reproduced with small variation to the mobilities on different rotation axes and increase of the size of the calculation area to imitate long-range dislocation effects. Dislocations were found to remain independent to much higher misorientation angles than previously thought, with simulation results indicating that change in boundary response occurs at ~7º for halite. Comparison of 2D experiments to 3D indicated that general boundary behaviour was similar within the volume and was not significantly influenced by effects from the free surface. Boundary migration, however, occurred more extensively in the 3D experiment. This difference is interpreted to be related to boundary drag on thermal grooves on the 2D experimental surface. While relative boundary mobilities will be similar, absolute values must therefore be treated with some care when using a 2D analysis. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.
19

Design of a Structure Search Engine for Chemical Compound Database

Wang, Hao 02 May 2008 (has links)
The search for structural fragments (substructures) of compounds is very important in medicinal chemistry, QSAR, spectroscopy, and many other fields. In the last decade, with the development of hardware and evolution of database technologies, more and more chemical compound database applications have been developed along with interfaces of searching for targets based on user input. Due to the algorithmic complexity of structure comparison, essentially a graph isomorphism problem, the current applications mainly work by the approximation of the comparison problem based on certain chemical perceptions and their search interfaces are often e-mail based. The procedure of approximation usually invokes subjective assumption. Therefore, the accuracy of the search is undermined, which may not be acceptable for researchers because in a time-consuming drug design, accuracy is always the first priority. In this dissertation, a design of a search engine for chemical compound database is presented.The design focuses on providing a solution to develop an accurate and fast search engine without sacrificing performance. The solution is comprehensive in a way that a series of related problems were addressed throughout the dissertation with proposed methods. Based on the design, a flexible computing model working for compound search engine can be established and the model can be easily applied to other applications as well. To verify the solution in a practical manner, an implementation based on the presented solution was developed. The implementation clarifies the coupling between theoretic design and technique development. In addition, a workable implementation can be deployed to test the efficiency and effectiveness of the design under variant of experimental data.
20

Geotechnical aspects of buildings on expansive soils in Kibaha, Tanzania : preliminary study

Lucian, Charles January 2006 (has links)
<p>The focus of this study is on potential problems resulting from construction on expansive soils in Kibaha region, Tanzania. For the fact that most of the affected structures are founded on expansive soils, a clear understanding of the soil behaviour and their interaction with structures, specifically as they relate to shallow foundations, has been of more interest to the study in order to evaluate properly the source of the problem.</p><p>The geotechnical behaviour of expansive clay soils is investigated by looking into the geomorphologic, geological and climatic conditions and mineralogical composition of the soils in the study area. The geotechnical results are linked with the performance of the foundation as well as structures.</p><p>Two sites, representative of known problem-areas in Kibaha were selected for geotechnical tests. Geotechnical site investigation consisted of open trial pits, profile description and the collection of both disturbed and undisturbed samples.</p><p>The collected samples were submitted to soil laboratories at KTH and DIT for mineralogical composition tests, natural water content, density, Atterberg limits and swell tests (free swell and swelling pressure). The results of this investigation indicate that soil in Kibaha contains clay (31%), have high liquid limit (59%) and plastic limit (37%) which indicate high potential swell.</p><p>Since swell potential and swell pressure are key properties of expansive soils, the swell parameters were measured by free swell tests and one-dimensional oedometer swell tests respectively. The free swell ranged from 100% to 150% and the swell pressure was in the region of 45 kPa.</p><p>The properties of expansive soils were confirmed by the x-ray diffraction test which showed the presence of montmorillonite in the soil. It is from this fact that the source of the problem is in the expansive soils coupled with poor building materials.</p><p>Physical conditions of the surveyed properties in the area confirmed the hypothesis of building damages due to poor building materials triggered by expansive soils. In support of the obtained data, the actual behaviour of the foundations is supplemented with prototypes of strip foundations whose performances are to be monitored over a long period. Finally, suggested are the ways forward to solve the problem of foundation on expansive soil.</p>

Page generated in 0.1156 seconds