Thèses : « Dimensional and geometrical precision »

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Toledo, Dos Santos Daniel. « High temperature sintering : investigation of the dimensional precision and mechanical properties of low alloyed steels ». Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/310431.

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The automobile industry has set the demand regarding Powder Metallurgy (PM) parts for decades, since this near-net shape technology is a cost-effective manufacturing process allying good mechanical properties with dimensional and geometrical precision. Aiming at the future of the electric automobiles high production and demand, many changes are on the way to guarantee the competitiveness of PM against other manufacturing process. The high costs of alloying elements such as Ni and Cu, the changes in health and safety regulations as well as light weighting of components are the topics of major importance in the field of PM and focus of main R&D around the globe. The use of high temperature sintering and different alloying elements are possible solutions to overcome properties obtained by using Ni as an alloying element sintered at conventional temperatures. Materials with Cr, Mo and Si were investigated using high temperature sintering (1180°C and 1250°) in comparison to traditionally high Ni materials sintered at conventional temperature (1120°C). The dimensional stability, geometrical precision, density, and microstructure of ring-shaped specimens were studied by using a coordinate measuring machine (CMM) and the effect of HTS on the mechanical properties were estimated through the fraction of the load bearing section. The effect of HTS on the dimensional precision and geometrical stability was later investigated in real parts manufactured by industrial partners through an EPMA Club Project. The 4%Ni material sintered at 1120°C was also compared to Ni-less/Ni-free materials sintered at 1250°C using tensile testing, impact testing, and hardness. The use of HTS to improve the mechanical properties without impairing the dimensional and geometrical stability was confirmed in parts with both low and high complexity designs. This project sets the blueprint for future material developments using HTS as manufacturing process.

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Pilla, Melania. « Effect of process parameters on the dimensional and geometrical precision of PM steel parts ». Doctoral thesis, Università degli studi di Trento, 2013. https://hdl.handle.net/11572/368880.

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The standard powder metallurgy process is composed by three main step, the powder production, the compaction and the sintering, and the possible secondary operation that allow to improve the mechanical properties and/or the dimensional and geometrical precision. The present work aims at investigating the influence of processing variables on the dimensional and geometrical precision of parts produced by Powder Metallurgy.

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Sozak, Ahmet. « Uncertainty Analysis Of Coordinate Measuring Machine (cmm) Measurements ». Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/2/12608887/index.pdf.

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In this thesis, the measurement uncertainty of Coordinate Measuring Machine (CMM) is analysed and software is designed to simulate this. Analysis begins with the inspection of the measurement process and structure of the CMMs. After that, error sources are defined with respect to their effects on the measurement and then an error model is constructed to compensate these effects. In other words, systematic part of geometric, kinematic and thermal errors are compensated with error modelling. Kinematic and geometric error model is specific for the structure of CMM under inspection. Also, a common orthogonal kinematic model is formed and with using the laser error data of the CMM and error maps of the machine volume is obtained. Afterwards, the models are compared with each other by taking the difference and ratio. The definition and compensation of the systematic errors leave the uncertainty of measurements for analysing. Measurement uncertainty consists of the uncompensated systematic errors and random errors. The other aim of the thesis is to quantify these uncertainties with using the different methods and to inspect the success of these methods. Uncertainty budgeting, comparison, statistical evaluation by designing an experiments and simulation methods are examined and applied to the CMM under inspection. In addition, Virtual CMM software is designed to simulate the task specific measurement uncertainty of circle, sphere and plane without using the repeated measurements. Finally, the performance of the software, highly depending on the mathematical modelling of machine volume, is tested by using actual measurements.

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Ikegawa, Yojiro. « Three-dimensional geometrical analysis of rock mass structure ». Thesis, Imperial College London, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294135.

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Murugan, Jeffrey. « Geometrical and nonperturbative aspects of low dimensional field theories ». Master's thesis, University of Cape Town, 2000. http://hdl.handle.net/11427/7681.

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Bibliography: leaves 84-88
We present a collection of results on solitons in low-dimensional classical field theory. We begin by reviewing the geometrical setting of he nonlinear ơ-model and demonstrate the integrability of the theory in two-dimensions on a symmetric target manifold. After reviewing the construction of soliton solutions in the 0(3) ơ-model we consider a class of gauged nonlinear ơ-models on two-dimensional axially-symmetric target spaces. We show that, for a certain choice of self-interaction, these models are all self-dual and analyze the resulting Bogomol'nyi equations in the BPS limit using techniques from dynamical systems theory. Our analysis is then extended to topologically massive gauge fields. We conclude with a deviation into exploring links between four-dimensional self-dual Yang-Mills equations and various lower-dimensional field theories. In particular, we show that at the level of equations of motion, the Euclidean Yang-Mills equations in light-cone coordinates reduce to the two-dimensional nonlinear ơ-model.

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Lindqvist, Richard. « Geometrical and dimensional Measurement Planning : - a systematic and holistic approach ». Licentiate thesis, KTH, Mätteknik och optik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-42163.

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För att försäkra sig om den slutliga kvaliteten på maskinbearbetade komponenter måste tillverkande företag mäta och verifiera de geometriska och dimensionella egenskaperna på komponenter innan dem skickas vidare nedströms till den mer värdeskapande monteringen. Det är idag vanligt att den geometriska och dimensionella mätningen och verifieringen uppstår varje gång då en maskin ställs om, när man startar om eller startar upp en ny produktionslina eller då en produktionsprocess ändras. Produktionsteknisk mätteknik och resultat från utförda mätningar används sedan som indata för statistisk processtyrning och övervakning av produktionsprocesser. Syftet med vår forskning har varit att först ta fram en nulägesbild av mätteknisk beredning inom fordons- och flygindustrin och utifrån den identifiera framtida trender med behovsanalys och gap. Utifrån analysen har vi sedan utforskat och utvecklat en modell och metodik för mätteknisk mät- och styrbarhetsberedning. I denna licentiat avhandling har vi utforskat området geometrisk och dimensionell mät- och styrbarhetsberedning (GMCP - Geometrical and dimensional Measurement and Controllability Planning). Vi presenterar en nulägesanalys av området och vi presenterar en teori med modell och ramverk för GMCP. Vidare har vi utforskat en metodik och verktyg benämnd kvalitetssäkringsmatris (QAM - Quality Assurance Matrix) och som vi lyfter fram i denna avhandling. I slutet av avhandlingen presenteras och diskuteras dem hittills uppnådda resultaten från forskningen och i det sista kapitlet dras slutsatser och den fortsatta forskningen inom ”SIMET-GICP” projektet presenteras.
In order to ensure final product quality on machined components, manufacturing enterprises must measure and inspect the geometrical and dimensional characteristics of components before they go into higher-value assemblies. Commonly, the geometrical and dimensional measurement and inspection occurs every time at machine tool set-up, when a line is restarted or if the production process is changed. Production metrology and results from production measurements is used as input data for statistical process control and monitoring of production processes. The purpose of our research has been to firstly perform a state of the art analysis in the area of measurement planning applied in the automotive and aerospace industry. The output from the state of the art study has then been used to identify future trends and needs including a gap analysis. Then we used the analysis to explore and develop a model and methodology for measurement and controllability planning. In this licentiate thesis we have explored the area of GMCP (Geometrical and dimensional Measurement and Controllability Planning). As a major result in this thesis a state of the art survey on GMCP is presented. Based on the state of the art study a theory and model framework for GMCP has been explored and a methodology and tool called QAM (Quality Assurance Matrix) is highlighted in this thesis. In the end of the thesis we present and discuss the present research results we have accomplished and in the final chapter we draw conclusions and outline the continued research within the SIMET-GICP project.
QC 20111027
SIMET 1

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Trevor, Simon. « Dimensional accuracy of investment casting shells / ». [St. Lucia, Qld.], 2000. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16943.pdf.

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Hübner, Matthias, Monireh Fazeli, Thomas Gereke et Chokri Cherif. « Geometrical design and forming analysis of three-dimensional woven node structures ». Sage, 2018. https://tud.qucosa.de/id/qucosa%3A35533.

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Structural frames have been established in many technical applications and typically consist of interconnected profiles. The profiles are commonly joined with node elements. For lightweight structures, the use of composite node elements is expedient. Due to the anisotropic mechanical properties of the fibers, high demands are placed on the orientation of the fibers in the textile reinforcement structure. A continuous fiber course around the circumference and at the junctions is necessary for an excellent force transmission. A special binding and forming process was developed based on the weaving technology. It allows the production of near-net-shaped node elements with branches in any spatial direction, which meet the requirements of load-adjusted fiber orientation. The principles by which these three-dimensional (3D) node elements are converted into a suitable geometry for weaving as a net shape multilayer fabric are reported. The intersections of the branches are described mathematically and flattened to a plane. This is the basis for the weave pattern development. Forming simulations on the macro- and meso-scales complement the analyses. A macro-scale model based on the finite element method (FEM) is used to verify the general formability and the accuracy of the flattenings. Since yarns are pulled through the textile structure in the novel forming process, the required tensile forces and the pulling lengths of the individual yarns are analyzed with a meso-scale FEM model. The flattening for two different node structures is realized successfully, and the simulation proves formability. Furthermore, the necessary forming forces are determined. Finally, the developed method for flattening the 3D geometry is suitable for the design of a variety of spatial node structures and the simulation supports the design of automated forming processes.

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Humberston, Benjamin. « Precision manipulations using a low-dimensional haptic interface ». Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/49994.

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When interacting with physical objects using their own hands, humans display effortless dexterity. It remains a non-intuitive task, however, to specify the motion of a virtual character’s hand or of a robotic manipulator. Creating these motions generally requires animation expertise or extensive periods of offline motion capture. This thesis presents a real-time, adaptive animation interface, specifically designed around haptic (i.e., touch) feedback, for creating precision manipulations of virtual objects. Using this interface, an animator controls an abstract grasper trajectory while the full hand pose is automatically shaped by compliant scene interactions and proactive adaptation. Haptic feedback enables intuitive control by mapping interaction forces from the full animated hand back to the reduced animator feedback space, invoking the same sensorimotor control systems utilized in natural precision manipulations. We provide an approach for online, adaptive shaping of the animated manipulator using our interface based on prior interactions, resulting in more functional and appealing motions. In a user study with nonexpert participants, we tested the effectiveness of haptic feedback and proactive adaptation of grasp shaping. Comparing the quality of motions produced with and without force rendering, haptic feedback was shown to be critical for efficiently communicating contact forces and dynamic events to the user. The effects of proactive shaping, though inarguably beneficial to visual quality, resulted in mixed behavior for our grasp quality metrics.
Science, Faculty of
Computer Science, Department of
Graduate

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Rayer, Mathieu. « Chromatic confocal gauging for high precision dimensional metrology ». Thesis, Heriot-Watt University, 2015. http://hdl.handle.net/10399/3149.

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Young, Leyland Gregory. « Geometrically exact modeling, analysis and design of high precision membranes / ». free to MU campus, to others for purchase, 2003. http://wwwlib.umi.com/cr/mo/fullcit?p3099647.

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Zambri, Razman 1973. « A high precision two dimensional stage using friction drive ». Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/46104.

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Chacón-Acosta, Guillermo, Angel A. García-Chung et Leonardo Dagdug. « On the geometrical description of effective diffusion in confined environments : On the geometrical description of effective diffusion in confinedenvironments : two-dimensional case ». Diffusion fundamentals 24 (2015) 9, S. 1, 2015. https://ul.qucosa.de/id/qucosa%3A14523.

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Dutton, Andrew William 1963. « A three-dimensional geometrical patient treatment planning program for scanned focussed ultrasound hyperthermia ». Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/277295.

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A computer graphics workstation was developed to geometrically plan scanned focussed ultrasound hyperthermia treatments, and is currently in clinical use at the Arizona Health Sciences Center. The workstation allows the user to base the treatment plan on any set of hard copy images of the patient's treatment anatomy by using a frame grabber to import these images into the workstation. Anatomical structures are outlined by the user, and a three dimensional image is reconstructed using these outlines. A geometric outline of the ultrasound power deposition field is then inserted into the reconstructed patient anatomy, along with thermocouple junction locations. The use of a custom foam mold and fiducial marker system enables the location of the anatomical features to be determined in the treatment system's coordinates. A scan size and orientation that sufficiently sonicates the treatment volume can then be determined in an interactive three dimensional environment.

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Pierobon, Anna. « Accuracy of geometrical measurements using computed tomography ». Doctoral thesis, Università degli studi di Padova, 2012. http://hdl.handle.net/11577/3425697.

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At the state of the art recently there has been increased interest in applying X-ray Computed Tomography (CT) to the task of dimensional measurements since it offers several opportunities which are not possible with conventional tactile or optical measurement devices as for example: complete and non-destructive components’ inspections, determination of inner and outer geometries, simultaneous material and geometrical control, high-density point-clouds in relatively short time. Due to these advantages, CT reveals to be a very promising non-contact measuring technique and several manufacturers and research centres are now investing in the further development of metrological CT systems for both research and industrial applications. However, dimensional measurements from CT data are still lacking in traceability, due to difficulties in evaluating their uncertainty and in determining metrological performances of CT systems. In order to investigate these limitations, the main objective of the present work has been to contribute to the development of methods and calibrated objects for performance verification of CT systems. The first part of the Ph.D. thesis is dedicated to the study of the state of the art of Computed Tomography systems, from the first CT applications (medical ones) to the new promising ones for dimensional metrology purposes. Further on in a second part the state of the art related to the performance verification of CT systems is described, with particular focus on the field of dimensional metrology. In details some important national and international standards have been described together with alternative solutions coming from several research centers and universities. The analysis of the state of the art leads to the developments of new procedures and related calibrated objects at Laboratory of Industrial and Geometrical Metrology of University of Padova. In particular two items are presented Pan Flute Gauge and CT Tetrahedron. In a third part, the investigation on another calibrated object called PTB Tetrahedron is presented during a four months experience at PTB (Physikalisch-Technische Bundesanstalt) in Braunschweig, Germany. Moreover, as described in the first parts of the Ph.D. thesis, CT systems are still not completely recognized as reference measuring instruments with well known metrological performances. An interlaboratory comparison has been considered to be an indispensable means to establish the effectiveness and comparability of measurement methods and to validate uncertainty claims. For this reason, the University of Padova organized the first international intercomparison of CT systems for dimensional metrology (CT Audit project) and an exhaustive extract from the official project report is presented. Finally preliminary investigations on metrological structure resolution are described. It is an important metrological characteristic of CT systems that is still not clearly described in terms of definitions and testing procedures. The working draft ISO Standard 10360-11 defined the metrological structure resolution is defined as “the size of the smallest structure that can be measured dimensionally”. According to the previous definition, a dedicated item, called Hourglass has been created in order to test the metrological resolution and first results have been achieved and presented.
Allo stato dell’arte, negli ultimi anni la tomografia computerizzata a raggi x (TC) si sta rivelando una tecnologia molto promettente nell’ambito della metrologia dimensionale, soprattutto perché, rispetto ai sistemi di misura tradizionali (tattili e ottici), essa presenta diversi vantaggi tra i quali la possibilità di controllare geometricamente parti interne di componenti senza doverli scomporre o distruggere, di verificare contemporaneamente la qualità dimensionale e dei materiali, di ricostruire tridimensionalmente gli oggetti con nuvole di punti ad alta densità in un tempo relativamente breve. Grazie a questi vantaggi, quindi, la tomografia computerizzata si è rivelata una tecnica di misura non a contatto molto interessante e molti produttori di sistemi TC e centri di ricerca stanno investendo nello sviluppo e nello studio di sistemi di tomografia a raggi x metrologici sia per uso industriale che nell’ambito di ricerca. Tuttavia, sono presenti alcuni limiti legati a problemi di riferibilità della misura e di stima dell’incertezza del processo di misurazione. L’obiettivo principale di questo lavoro di dottorato vuole quindi essere un contributo allo sviluppo di metodi e relativi campioni tarati per la verifica delle prestazioni di sistemi TC. La prima parte della tesi di dottorato è dedicata allo studio dello stato dell’arte dei sistemi di tomografia computerizzata, partendo dalle prime applicazioni a livello medicale per approdare agli ultimi promettenti utilizzi nel campo della metrologia dimensionale. In seguito è presentata una seconda parte dello studio dello stato dell’arte e alla verifica delle prestazioni dei sistemi TC, con particolare attenzione alle applicazioni metrologico dimensionali. In particolare sono presentate le proposte di verifica di prestazione di alcune norme nazionali e internazionali e delle proposte sperimentali di centri di ricerca e università. L’analisi dello stato dell’arte ha portato allo sviluppo di nuove procedure e di nuovi campioni tarati presso il Laboratorio di metrologia industriale e geometrica dell’Università di Padova. In particolare sono descritti i campioni “Pan Flute Gauge” e “CT Tetrahedron”. In una terza parte, viene riportato il lavoro relativo a un ulteriore campione “PTB Tetrahedron” sviluppatosi nell’ambito di un’esperienza di quattro mesi presso il centro metrologico tedesco PTB a Braunschweig (Physikalisch-Technische Bundesanstalt). Inoltre, come descritto nella prima parte del lavoro, i sistemi TC non sono ancora universalmente accettati come strumenti di misura di riferimento metrologico. Per questo motivo, un confronto interlaboratorio è stato ritenuto indispensabile per stabilire lo stato dei sistemi metrologici TC internazionale. L’Università di Padova ha quindi organizzato il primo interconfronto internazionale tra laboratori che utilizzano sistemi di tomografia computerizzata per misure metrologico dimensionale (Progetto CT Audit). Un esauriente estratto del rapporto ufficiale del progetto è presentato nel lavoro di dottorato. Infine, sono descritti gli studi preliminari riguardanti la risoluzione metrologica strutturale. Essa è una caratteristica metrologica importante dei sistemi TC, anche se non è ancora chiaramente descritta in termini di definizione e di verifica con appositi test. La bozza di lavoro ISO 10360-11 definisce la risoluzione metrologica strutturale come “la misura della più piccola struttura che può essere valutata dimensionalmente”. Partendo da questa definizione, è stato creato un campione, denominato “Hourglass”, per la valutazione della risoluzione strutturale e sono presentati i primi risultati raggiunti.

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Yang, Qingping. « A hig precision probe system for three dimensional coordinate measurement ». Thesis, Brunel University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339317.

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Cohen, Yonatan. « Dimensional Slot Integrity and Precision of Self-Ligating Buccal Tubes ». Master's thesis, Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/312715.

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Oral Biology
M.S.
Self-ligating brackets, including molar buccal tubes, have gained popularity in recent decades. The primary advantage of using self-ligating systems has been based on the claim that they provide reduced friction and therefore reduced sliding resistance of the arch wire contained within their respective slots.1 This form of reduced friction and sliding resistance has been proposed to require less force and therefore produce more physiologic tooth movements.7-9 Limited scientific evidence is currently available to establish quality control of these products. The purpose of this study is to use Micro Computed Tomography (MicroCT) to analyze self-ligating molar tubes manufactured by different companies. Methods used here provide a novel way for measuring the accuracy and quality of these materials. This study has provided a highly innovative approach that had not been previously accomplished. Forty self-ligating lower left first mandibular molar samples were obtained from four different companies. Five samples from each company were randomly selected and scanned using MicroCT to determine the internal slot lumen of each tube for analysis of precision volumetric measurements. Additionally, qualitative analysis of the lumen of each tube was investigated for the presence of any internal slot defects or imperfections. Results showed that the volumetric slot measurements of all samples were highly statistically significant (P<0.001) and were found to be oversized compared to what is claimed by their respective companies. Qualitative analysis of all samples illustrated varying defects contained within their respective internal slot lumens. Notable defects included notched, beveled and irregular corners, as well as the presence of some bulbous metal projections. Based upon the results obtained in this study, it was determined that the investigated self-ligating buccal tubes, produced by all the companies tested, were oversized and had various internal slot defects. The potential clinical significance of these dimensional inaccuracies may include an increased amount of friction and a lack of torque control during tooth movement.
Temple University--Theses

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Chojnowski, Jacek Mariusz. « Novel assessment and optimisation methods for geometrical performance of medical linear accelerators for high precision radiotherapy techniques ». Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/26165.

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Radiotherapy treatment technology and cancer treatment methods are increasingly complex, and more systems and parameters require more tightly controlled initial and regular performance testing. Most medical linear accelerator (linac) mechanical and dosimetric tests have been automated in recent years. However, the traditional tests of coincidence between radiation and mechanical isocentres are still not well scrutinised, not to mention automated. The geometry of the isocentre defines the fundamental geometric reference point for the whole treatment delivery system and each patient’s treatment. The main research question of this thesis is: is the measurement of the radiation beam spot position relative to the collimator axis of rotation (focal spot offset; FSO) equivalent to the measurement of the coincidence of radiation and mechanical isocentres. Complementary research questions are how to automate the FSO measurement to improve linac testing efficiency; and how to optimise the FSO to improve linac geometric performance, to support high precision radiotherapy. The research starts from investigating Nyiri’s approach to accurately measure the FSO using the EPID and a jig using two rods. This jig was redesigned by Riis as a rigid phantom with two BBs, to allow use at any gantry angle. The study presented here re-thought Nyiri’s methodology and Riis’s phantom to answer the main research question and resulted in development of three novel linac assessment methods and three novel linac optimisation methods as well as identifying three linac proprietary procedural deficiencies. The study concluded that the characteristics of the FSO can be used as an indicator of the congruence of radiation and mechanical isocentres. It also demonstrated that optimising the FSO appropriately reduces uncertainties of linac geometric performance parameters and therefore improves the overall geometric targeting accuracy of treatment delivery.

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DE, VECCHI FRANCESCO CARLO. « LIE SYMMETRY ANALYSIS AND GEOMETRICAL METHODS FOR FINITE AND INFINITE DIMENSIONAL STOCHASTIC DIFFERENTIAL EQUATIONS ». Doctoral thesis, Università degli Studi di Milano, 2018. http://hdl.handle.net/2434/565457.

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The main aim of the thesis is a systematic application (via suitable generalizations) of Lie symmetry analysis, or more generally, of the various geometric techniques for differential equations, to the study of finite and infinite dimensional stochastic differential equations (SDEs). The work can be divided in three main parts. In the first part a new geometric approach to finite dimensional SDEs driven by a multidimensional Brownian motion is proposed, which is based on a new notion of random transformations of a stochastic process called stochastic transformations. After having studied the probabilistic and geometric properties of stochastic transformations, we provide a useful generalization of the well-known results of reduction and reconstruction of symmetric ODEs to the stochastic setting. We give many applications of previous results to some interesting SDEs among which the two dimensional Brownian motion, the Kolmogorov-Pearson equation, a generalized Langevin equation and the SABR model. Finally, using the previous theorems, we propose a symmetry-adapted numerical scheme whose effectiveness is verified through both theoretical estimates and numerical simulations. The second part contains an extension of the results obtained in the first part to finite dimensional SDEs driven by a general semimartingale taking values in a Lie group. In order to provide such an extension we use the notion of geometrical SDEs introduced by Serge Choen, and we introduce some new notions of stochastic invariance for semimartingales called gauge and time symmetries of a semimartingale. Using these mathematical tools we generalize the notion of stochastic transformations in this setting and we propose the natural definition of symmetry based on this group of transformations. The formulated theory allows us to analyze in detail an important class of SDEs with possible relevant applications to iterated random maps theory. In the third part we take advantage of the geometry of the infinite jets bundle to develop a convenient algorithm for the explicit determination of finite dimensional solutions to stochastic partial differential equations (SPDEs). In this setting we are able to propose a generalization of Frobenius theorem in the infinite jet bundles setting, which, exploiting the classical notion of characteristics of a PDE, allows us to find some sufficient conditions for the existence of finite dimensional solutions to an SPDE and then to explicitly reduce the SPDE to a finite dimensional SDE. Our techniques permits to individuate new finite dimensional solutions to interesting SPDEs among which the proportional volatility equation in Heath-Jarrow-Morton framework, a stochastic perturbation of Hunter-Saxton equation and a filtering problem related to affine type processes.

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Huang, Na. « Estimation of covariance, correlation and precision matrices for high-dimensional data ». Thesis, London School of Economics and Political Science (University of London), 2016. http://etheses.lse.ac.uk/3371/.

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The thesis concerns estimating large correlation and covariance matrices and their inverses. Two new methods are proposed. First, tilting-based methods are proposed to estimate the precision matrix of a p-dimensional random variable, X, when p is possibly much larger than the sample size n. Each 2 by 2 block indexed by (i, j) of the precision matrix can be estimated by the inversion of the pairwise sample conditional covariance matrix of Xi and Xj controlling for all the other variables. However, in the high dimensional setting, including too many or irrelevant controlling variables may distort the results. To determine the controlling subsets, the tilting technique is applied to measure the contribution of each remaining variable to the covariance matrix of Xi and Xj , and only puts the (hopefully) highly relevant remaining variables into the controlling subsets. Four types of tilting-based methods are introduced and the properties are demonstrated. The simulation results are presented under different scenarios for the underlying precision matrix. The second method NOVEL Integration of the Sample and Thresholded covariance estimators (NOVELIST) performs shrinkage of the sample covariance (correlation) towards its thresholded version. The sample covariance (correlation) component is non-sparse and can be low-rank in high dimensions. The thresholded sample covariance (correlation) component is sparse, and its addition ensures the stable invertibility of NOVELIST. The benefits of the NOVELIST estimator include simplicity, ease of implementation, computational efficiency and the fact that its application avoids eigenanalysis. We obtain an explicit convergence rate in the operator norm over a large class of covariance (correlation) matrices when p and n satisfy log p/n → 0. In empirical comparisons with several popular estimators, the NOVELIST estimator performs well in estimating covariance and precision matrices over a wide range of models. An automatic algorithm for NOVELIST is developed. Comprehensive applications and real data examples of NOVELIST are presented. Moreover, intensive real data applications of NOVELIST are presented.

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Kanellopoulos, Asimakis K. « Three dimensional biomechanics of the hand and wrist in precision grip ». Thesis, University of Strathclyde, 2011. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=16788.

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Blowey, Phil J. « Probing the geometrical and electronic structure of two-dimensional charge transfer networks on metal surfaces ». Thesis, University of Warwick, 2018. http://wrap.warwick.ac.uk/111281/.

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Due to its ability to form conductive organic salts, the prototypical electron acceptor molecule 7,7,8,8-tetracyanoquinodimethane (TCNQ) has attracted considerable interest in the field of organic electronics. This has motivated numerous surface science studies of TCNQ and related molecules, with an aim to understand the molecule-substrate interface and, in particular, the nature of any charge transfer. Although charge transfer is strongly dependent on subtle aspects of the molecular adsorption geometry, there is a dearth of detailed structural investigations for these systems. In this thesis, a variety of surface science techniques were used to characterise model systems of TCNQ adsorbed on coinage metal substrates with the aim to identify key relationships between the adsorption structure and the electronic properties of the surface. Particular focus was given to studying two-dimensional charge-transfer networks formed by TCNQ and alkali metals on the surface of Ag. Scanning tunnelling microscopy and low energy electron diffraction were used to characterise the packing and ordering of molecules and to ascertain whether the adsorbed layer is commensurate with respect to the underlying substrate. X-ray and ultraviolet photoelectron spectroscopy were used to provide complementary information on the chemical composition and electronic properties of the surface. Most significantly, the normal incident X-ray standing wave (NIXSW) technique was used to obtain precise quantitative structural measurements of the surface. On the surfaces of coinage metals, TCNQ is generally believed to adsorb in a significantly bent conformation, with all four cyano groups pointing down towards the substrate. The NIXSW measurements in this thesis show that the conformation adopted by TCNQ on Ag(100) is consistent with this, but on Ag(111), TCNQ adopts a considerably different conformation that was found, through comparison with density functional theory calculations, to result from the participation of Ag adatoms within the surface structure. These results also highlight the need for using both experimental and theoretical quantitative structural methods to obtain a reliable understanding of metal-organic interfaces and that some previously studied systems may need to be re-investigated. On both the (111) and (100) surfaces of Ag, a wide variety of TCNQ/alkali metal network structures were formed with Cs, K and Na. NIXSW measurements obtained from a subset of these structures show that the alkali metals adsorb at elevated heights above the TCNQ molecules. In comparable structures, K adsorbs closer to the surface than Cs and causes a smaller shift to the surface work function. The alkali metal adsorption height was also found to decrease as its coverage relative to TCNQ increased.

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Asgharian-Jeddi, A. A. « The study of dimensional and geometrical properties of weft knitted fabrics constructed from cotton yarns ». Thesis, De Montfort University, 1985. http://hdl.handle.net/2086/13251.

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Liu, Yong-Jin. « Complex shape modeling with point sampled geometry / ». View abstract or full-text, 2003. http://library.ust.hk/cgi/db/thesis.pl?MECH%202003%20LIUY.

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Sampathkumar, Narasimhan. « Three dimensional geometrical and material nonlinear finite element analysis of adhesively bonded joints for marine structures ». Thesis, University of Southampton, 2005. https://eprints.soton.ac.uk/142767/.

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The use of adhesive bonding as a structural joining method has been gaining recognition in marine industry in recent years, though it has been widely adopted in other fields such as aerospace, automobiles, trains and in civil constructions. The type of materials used and design practices followed in marine structures are different from what is applied in other disciplines. Therefore new research approaches are required and recent novel ideas are ex- plored in the context of application of bonded joint configurations in marine environment. The research is directed at developing analysis tools for predicting the displacement, stress and strain fields in adhesively bonded joints between dissimilar adherends. In the finite element formulation, the adherends may be isotropic or orthotropic layered materi- als, which are assumed to behave linear elastically. The adhesive material is assumed to behave as elasto-plastic continuum, where the nonlinear behaviour is modelled as either a rigid or a semi-rigid adhesive solid that can be represented by the Ramberg-Osgood ma- terial model. The yield behaviour of the polymeric adhesive is modelled using a modified von Mises criterion, which accounts for the fact that plastic yielding of polymer materials may occur under the action of hydrostatic as well as deviatoric stresses. The geometric nonlinearity is based on the assumption of large displacement, large rotation but small strain, and it is implemented in the code using the total Lagrangian approach. The scheme is applied on three case studies viz.: a study of adherend imbalances in a single lap joint, stress analysis of a butt-strap joint system and a hybrid joint are un- dertaken. The influence of geometric and material nonlinearity on joint deformations and adhesive stresses, are studied for a single lap joint with dissimilar adherends, aluminium and a Fibre Reinforced plastic composite material, with varying adhrend thickness ratios. The adhesive stress-strain data obtained from the model are compared with the exper- imental stress-strain curve and the numerical results are validated with the analytical solution. Three dimensional effects like ’anticlastic’ and bending-twisting’ are shown in the joint with a dissimilar adherends. Key results are obtained that explains the state of nonlinear adhesive stress state in the joint. Analysis of butt-strap joint focussed on nonlinear modelling of a semi-rigid adhesive ma- terial that is used to bond two dissimilar adherends, steel and aluminium. The analysis demonstrate that the influence of geometric and material nonlinearity on the joint de- formations as well as the adhesive stresses is significant. Nonlinear adhesive stresses are compared with the actual strength of the highly flexible adhesive, highlighting the need for the consideration of material nonlinearity in the bonded joints. Failure modes for the joint are inferred from the observations made on the adhesive stress state in the butt-strap joint. Last study, deals with three dimensional analysis of a GRP-Steel hybrid joint carried out to model the initiation and propagation of crack under a set of static loading cases. Earlier studies were restricted only to two dimensional analysis. This three dimensional analysis showed that the adhesive normal stress is not constant across the width of the joint. Critical locations of stress concentrations are identified and the failure mechanisms are compared with the experimental specimens. The observations made from this research study using a three dimensional finite element program, compliments the present knowledge in the field of adhesively bonded joints.

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Wang, Changling. « Sketch based 3D freeform object modeling with non-manifold data structure / ». View Abstract or Full-Text, 2002. http://library.ust.hk/cgi/db/thesis.pl?MECH%202002%20WANGC.

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Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2002.
Includes bibliographical references (leaves 143-152). Also available in electronic version. Access restricted to campus users.

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Edeson, Ruben. « The effects of random vibration on the dimensional stability of space-based precision structures ». Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/351350/.

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Low-cost Earth-imaging instruments typically require high performance structures to ensure that critical alignments of optical components are maintained between the assembly phase, and the on-orbit operational phase. There are a number of threats to structural dimensional stability, including thermal cycling, moisture desorption and launch vibrations. This last area is the subject of this thesis. The main aim of the research described here is to better understand the effects of random vibration on the dimensional stability of precision structures. The first part of this research considered the degree to which random vibration is a problem - this was assessed by comparing its effects on dimensional stability with those of other typical environmental stressors. This was accomplished by performing a series of environmental tests on an optical breadboard structure, and measuring the dimensional stability throughout. These tests showed that random vibration could indeed pose a significant threat. The second part of the research aimed to better understand the dimensional stability response of specific structural elements - namely materials and bolted joints - to random vibration. This required the development of novel test setups and metrology techniques. Controlled tests were performed in both these structural areas, and a number of useful conclusions were drawn. The final part of the research was to investigate the empirical results using FEA methods. A significant challenge was to develop a modelling technique that is capable of predicting dimensional stability responses to random vibration. In the case of the material tests, the response of the test samples was correctly predicted using FEA with cyclic plasticity properties and parameters identified from static tests. This research has produced a number of relevant findings for spacebased stable optical bench structures. These have been condensed into a series of recommendations for design, analysis, testing, metrology and bedding-in vibration for future optical payload projects.

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Jayaram, Uma. « Extracting dimensional geometric parameters from B-spline surface models ». Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/37877.

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In an integrated design environment, the common thread between the different design stages is usually the geometric model of the part. However, the requirements for the geometric definition of the design is usually different for each stage. The transformation of data between these different stages is essential for the success of the integrated design environment. For example, conceptual design systems usually deal with geometric dimensional parameters (e.g. length, radius, etc.) whereas preliminary design systems frequently require the geometry definition to be in the form of surface models. This dissertation presents the necessity and scope of creating and implementing methodologies to obtain dimensional geometric parameters from the surface description of an object. Since the study of geometric modeling and parametric surfaces is a new field, few classical methods are applicable. Methods and algorithms for the extraction of various geometry parameters are created. A few methods to pre-process and manipulate these surfaces before the parameter extraction methods can be applied are outlined. One of the most important applications of parameter extraction is in the field of aircraft design. There are two important aspects of geometry data conversion in the design cycle. The first is the conversion from conceptual CAD models to CFD compatible models. The second is the conversion from surface representations of CFD models to obtain component parameters (e.g. wing span, fuselage fineness ratio, moments of inertia, etc.). The methods created in this dissertation are used to extract geometric parameters of importance in aircraft design. This enables the design cycle to be complete and promotes integrated design. These methods have been implemented in the aircraft design software, ACSYNT. Examples of the conversion of data from B-spline surface models to dimensional geometric parameters using these methods are included. The emphasis of this dissertation is on non-uniform B-spline surfaces. Methods for obtaining geometric parameters from aircraft models described by characteristic points are also considered briefly.
Ph. D.

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Frazier, Alicia. « Accuracy and precision of a sectioned hollow model ». Oklahoma City : [s.n.], 2008.

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Jönsson, David, et Mir Kevci. « Geometrical accuracy of metallic objects produced with Additive or Subtractive Manufacturing : a comparative in-vitro study ». Thesis, Malmö högskola, Odontologiska fakulteten (OD), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-19934.

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Syftet: Utvärdera produktionstolerans av objekt som producerats genom additiv framställningsteknik (AF) för användning inom tandvård, samt att jämföra denna teknik med subtraktiv framställningsteknik (SF) genom reverse engineering.Material och metod: Tio exemplar av två olika geometriska objekt framställdes från fem olika AF maskiner och en SF maskin. Objekt A efterliknar ett inlay, medan objekt B återspeglar en modell av en fyrledsbro. Alla objekt delades in i olika mätled; X, Y och Z. Mätningarna utfördes med validerade och kalibrerade instrument. Linjära avstånd mättes med ett digitalt skjutmått och hörnradie samt vinklar mättes med ett digitalt mikroskop.Resultat: Vare sig additiv eller subtraktiv framställning uppvisade en perfekt matchning till CAD-filen med hänsyn till de parametrar som utvärderades i denna studie. Standardavvikelsen gällande linjära mätningar för subtraktiv framställning uppvisade konsekventa resultat i alla led, med undantag för X- och Y-led för objektet A och i Y-led för objekt B. Samtliga additiva tillverkningsgrupper hade en konsekvent standardavvikelse i X- och Y-led, men inte i Z-led. Med avseende på hörnradiemätningar, hade SF gruppen i överlag bättre produktionsnoggrannhet för både objekt A och B medan AM grupperna var mindre noggranna.Konklusion: Med hänsyn till begränsningarna med denna in vitro studie, stödjer resultat hypotesen, med hänsyn till att AF hade en bättre förmåga att återskapa komplexa och små geometrier jämfört med SF. Samtidigt identifierades en bättre reproducerbarhet hos SF gällande enkla geometrier och linjära avstånd. Vidare studier krävs för att bekräfta dessa resultat.
Purpose: To evaluate the production tolerance of objects produced by additive manufacturing systems (AM) for usage in dentistry and to compare with subtractive manufacturing system (SM) through reverse engineering. Materials and methods: Ten specimens of two geometrical objects were produced by five different AM machines and one SM machine. Object A mimics an inlay-shaped object, meanwhile object B reflects a four-unit bridge model. All the objects were divided into different measuring-axis; X, Y and Z. Measurements were performed with validated and calibrated equipment. Linear distances were measured with a digital calliper while corner radius and angle were measured with a digital microscope. Results: None of the additive manufacturing or subtractive manufacturing groups presented a perfect match to the CAD-file regarding all parameters included in present study. Considering linear measurements, the standard deviation for subtractive manufacturing group were consistent in all axis, except for X- and Y-axis in object A and Y-axis for object B. Meanwhile additive manufacturing groups had a consistent standard deviation in X- and Y- axis but not in Z-axis. Regarding corner radius measurements, SM group overall had the best accuracy for both object A and B comparing to AM groups. Conclusion: Within the limitations of this in vitro study, results support the hypothesis, considering AM had preferable capability to re-create complex and small geometry compare to SM. Meanwhile, SM were superior producing simple geometry and linear distances. Further studies are required to confirm these results.

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Toledo, Dos Santos Daniel. « High temperature sintering : investigation of the dimensional precision and mechanical properties of low alloyed steels ». Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/310431.

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The automobile industry has set the demand regarding Powder Metallurgy (PM) parts for decades, since this near-net shape technology is a cost-effective manufacturing process allying good mechanical properties with dimensional and geometrical precision. Aiming at the future of the electric automobiles high production and demand, many changes are on the way to guarantee the competitiveness of PM against other manufacturing process. The high costs of alloying elements such as Ni and Cu, the changes in health and safety regulations as well as light weighting of components are the topics of major importance in the field of PM and focus of main R&D around the globe. The use of high temperature sintering and different alloying elements are possible solutions to overcome properties obtained by using Ni as an alloying element sintered at conventional temperatures. Materials with Cr, Mo and Si were investigated using high temperature sintering (1180°C and 1250°) in comparison to traditionally high Ni materials sintered at conventional temperature (1120°C). The dimensional stability, geometrical precision, density, and microstructure of ring-shaped specimens were studied by using a coordinate measuring machine (CMM) and the effect of HTS on the mechanical properties were estimated through the fraction of the load bearing section. The effect of HTS on the dimensional precision and geometrical stability was later investigated in real parts manufactured by industrial partners through an EPMA Club Project. The 4%Ni material sintered at 1120°C was also compared to Ni-less/Ni-free materials sintered at 1250°C using tensile testing, impact testing, and hardness. The use of HTS to improve the mechanical properties without impairing the dimensional and geometrical stability was confirmed in parts with both low and high complexity designs. This project sets the blueprint for future material developments using HTS as manufacturing process.

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Johansson, Marcus. « Measurement strategy for geometrical verification : A state-of-the-art study, analysis and development of working methodology framework ». Thesis, Linköpings universitet, Logistik- och kvalitetsutveckling, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-130787.

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Geometrical and dimensional metrology is used to verify that manufactured and assembled products satisfy the defined geometrical requirements and thereby the functional requirements. The dimensional measurement planning operation is carried out to define how the measurements are going to be collected and it has to consider the reliability, uncertainty and economics of the measurement procedure. The thesis work has been performed to map the current knowledge regarding measurement strategies and principles and to develop recommendations regarding a framework which defines how the measurement planning work should be carried out. The purpose of the work was thereby to perform a state-of-the-art study to map the available theoretical and empirical measurement strategies and principles. The purpose was also to test the impact of the strategies in a measurement experiment in order to validate the methodology. To fulfil the purpose of the work, a literature review and a case study was initially performed. The literature review investigated the available academically knowledge and the requirements defined in international standards regarding the measurement planning work. The case study mapped the methodologies and principles which were used in industry through contextual research and qualitative interviewing. The majority of the case study was carried out at Saab Aeronautics but to obtain a wider understanding of the topic a survey were also conducted where additional manufacturing companies were participating. The outcome of the case study and the literature review were thereafter merged and further analysed though the measurement analysis. The case study and the literature review shown that there existed several different methodologies and guidelines regarding how the work should be and was performed. Some of the factors which were further investigated were the impact of the number of measurement points, distance between the measurement points, uncertainty of the strategy and the considerations connected to the selection of the geometrical features. The measurement analysis provided insights regarding the impact on average, minimum-, maximum deviation and the variance due to the amount and distribution of the inspection points. The findings were presented as a resulting outcome of the recommended measurement strategy framework methodology. The methodology of analysing the impact of the measurement strategy was therefore implemented into the recommendations regarding the measurement planning framework. The purpose of the framework is to offer a reliable, standardized and traceable measurement planning process where knowledge sharing and continuous improvements are possible to implement. In addition to the analysis of the measurement planning strategy the most important findings to consider in the adjacent process steps were investigated and presented. These findings are presented to enable a broad understanding of the requirements throughout the measurement process at Saab Aeronautics. The knowledge obtained in the literature review, case study and the measurement experiment was included in the measurement strategy framework which was the delivery of the thesis work.

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Avanesov, Valeriy. « Dynamics of high-dimensional covariance matrices ». Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/18801.

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Wir betrachten die Detektion und Lokalisation von plötzlichen Änderungen in der Kovarianzstruktur hochdimensionaler zufälliger Daten. Diese Arbeit schlägt zwei neuartige Ansätze für dieses Problem vor. Die Vorgehensweise beinhaltet im Wesentlichen Verfahren zum Test von Hypothesen, welche ihrerseits die Wahl geeigneter kritischer Werte erfordern. Dafür werden Kalibrierungsschemata vorgeschlagen, die auf unterschiedlichen Nichtstandard-Bootstrap-Verfahren beruhen. Der eine der beiden Ansätze verwendet Techniken zum Schätzen inverser Kovarianzmatrizen und ist durch Anwendungen in der neurowissenschaftlichen Bildgebung motiviert. Eine Beschränkung dieses Ansatzes besteht in der für die Schätzung der „Precision matrix“ wesentlichen Voraussetzung ihrer schwachen Besetztheit. Diese Bedingung ist im zweiten Ansatz nicht erforderlich. Die Beschreibung beider Ansätze wird gefolgt durch ihre theoretische Untersuchung, welche unter schwachen Voraussetzungen die vorgeschlagenen Kalibrierungsschemata rechtfertigt und die Detektion von Änderungen der Kovarianzstruktur gewährleistet. Die theoretischen Resultate für den ersten Ansatz basieren auf den Eigenschaften der Verfahren zum Schätzen der Präzisionsmatrix. Wir können daher die adaptiven Schätzverfahren für die Präzisionsmatrix streng rechtfertigen. Alle Resultate beziehen sich auf eine echt hochdimensionale Situation (Dimensionalität p >> n) mit endlichem Stichprobenumfang. Die theoretischen Ergebnisse werden durch Simulationsstudien untermauert, die durch reale Daten aus den Neurowissenschaften oder dem Finanzwesen inspiriert sind.
We consider the detection and localization of an abrupt break in the covariance structure of high-dimensional random data. The study proposes two novel approaches for this problem. The approaches are essentially hypothesis testing procedures which requires a proper choice of a critical level. In that regard calibration schemes, which are in turn different non-standard bootstrap procedures, are proposed. One of the approaches relies on techniques of inverse covariance matrix estimation, which is motivated by applications in neuroimaging. A limitation of the approach is a sparsity assumption crucial for precision matrix estimation which the second approach does not rely on. The description of the approaches are followed by a formal theoretical study justifying the proposed calibration schemes under mild assumptions and providing the guaranties for the break detection. Theoretical results for the first approach rely on the guaranties for inference of precision matrix procedures. Therefore, we rigorously justify adaptive inference procedures for precision matrices. All the results are obtained in a truly high-dimensional (dimensionality p >> n) finite-sample setting. The theoretical results are supported by simulation studies, most of which are inspired by either real-world neuroimaging or financial data.

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El, Bahra Shadi [Verfasser]. « Dimensional precision and volumetric shrinkage of PMMA denture bases polymerized with different methods / Shadi El Bahra ». Kiel : Universitätsbibliothek Kiel, 2016. http://d-nb.info/1120409683/34.

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Jacobson, Timothy. « A Trans-Dimensional View of Drug Resistance Evolution in Multiple Myeloma Patients ». Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6099.

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Multiple Myeloma (MM) is a treatable, yet incurable, malignancy of bone marrowplasma cells. This cancer affects many patients and many succumb to relapse of tumor burden despite a large number of available chemotherapeutic agents developed for therapy. This is because MM tumors are heterogeneous and receive protection from therapeutic agents by the microenvironment and other mechanisms including homologous MM-MM aggregation. Therefore, therapy failure and frequent patient relapse is due to the evolution of drug resistance, not a lack of available drugs. To analyze and understand this problem, the evolution of drug resistance has been explored and presented herein. We seek to describe the methods through which MM cells become resistant to therapy, and how this resistance evolves throughout a patient’s treatment history. We achieve this in five steps. First we review the patient’s clinical history, including treatments and changes in tumor burden. Second, we trace the evolutionary tree of sub-clones within the tumor burden using standard of care fluorescence in situ hybridization (FISH). Thirdly, immunohistochemistry slides are stained and aligned to quantify the level of environmental protection received by surrounding cells and plasma in the bone marrow microenvironment (coined environment mediated drug resistance score [EMDR]). The fourth analysis type is produced through a novel 384-well plate ex vivo chemosensitivity assay to quantify sensitivity of primary MM cells to chemotherapeutic agents and extrapolate these findings to 90-day clinical response predictions. In addition to direct clinical application in the choice of best treatment, this tool was also used to study changes in sensitivity of patient tumors to other drugs, and it was observed that, upon relapse, in addition to developing resistance to the current line of therapy, tumors become cross-resistant to agents that they were never exposed to. Finally, MM-MM homologous aggregation is quantified to assess the level of drug resistance contributed by clustering of patient tumor cells, which causes upregulation of Bcl-2 expression and other resistance mechanisms1. The findings of such experimentation improve comprehension of the driving factors that contribute to drug resistance evolution on a personalized treatment basis. The aforementioned factors all contribute in varying degrees for unique patient cases, seven of which are presented in depth for this project. In summary: Environmental protection plays a critical initial role in drug resistance, which is followed by increase in tumor genetic heterogeneity as a result of mutations and drug-induced Darwinian selection. Eventually, environment-independent drug resistant subpopulations emerge, allowing the tumor to spread to unexplored areas of the bone marrow while maintaining inherited drug resistant phenotype2. It is our hope that these findings will help in shifting perspective regarding optimal management of MM by finding new therapeutic procedures that address all aspects of drug resistance to minimize chance of relapse and improve quality of life for patients.

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Gashi, Tomor, et Eddie Larsson. « A standardized method for evaluating trueness and precision of intraoral scanners – in vitro accuracy ». Thesis, Malmö högskola, Odontologiska fakulteten (OD), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-19925.

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Bakgrund. En gyllene standard för att bestämma noggrannheten för intraorala scannrarexisterar inte. Intraorala scannrars prestanda som ges av olika leverantörer är inte fulltjämförbara. Det finns ett behov att standardisera och ta fram oberoende försöksupplägg för att kunna jämföra intraorala scannrar.Mål. Målet med studien var att beskriva och utvärdera en ny metod för att bestämmanoggrannheten av intraorala scannrar genom ett standardiserat in vitro testförsök och attanvända metoden för att beräkna noggrannheten på en kommersiell intraoral scanner.Material och metod. SP Sveriges tekniska forskningsinstitut definierade dimensionerna avett sfäriskt testobjekt. Sfären besprutades med titanoxid och skannades 12 gånger med enkommersiell intraoral scanner. Scanningarna utvärderades med två metoder. Manuell metod: sfärens diameter uppmättes 12 gånger i ett första mjukvaruprogram för varje scanning genom att justera ett tvärsnittsplan. Automatisk metod: 12 nominella diametrar beräknades från ett andra mjukvaruprogram. Noggrannheten beräknades för varje testmetod och jämfördes.Resultat. Referensmätning: den definierade diameter var 4,9991±0,0001mm. Manuell metod: riktigheten var 25μm och precisionen var 10μm. Medelprecisionen inom scanningar var 4μm. Automatisk metod: Riktigheten var 26μm och precisionen var 11μm. Alla testvärden uppvisade stark statistisk deviation från referensvärdet, men väl inom ett kliniskt acceptabelt intervall.Slutsatser. Inom den här in vitro-studiens begränsningar, kan den beskrivna,standardiserade metoden användas manuellt eller med den automatiska funktionen Fittingsphere för att beräkna noggrannheten för intraorala scannrar. Fler studier på mer komplexa objekt behöver utföras. Dessutom uppvisade den intraorala scannern (TRIOS) hög riktighet och precision, jämförbar eller bättre än traditionella avtrycksmetoder inom tandvården.
AbstractBackground. There is no gold standard for determining the accuracy of intraoral scanners. The performances of intraoral scanners given by different manufacturers are not fully comparable. There is a need for standardized and independent test setups to enable the comparison of intraoral scanners.Objectives. The study’s aims were to describe and evaluate a new method for determining the accuracy of any intraoral scanner by means of a standardized geometrical in vitro test and to use this method for determining the accuracy of a commercial intraoral scanner.Material and methods. The Technical Research Institute of Sweden defined the dimensions of a spherical test object. The sphere was spray-coated with TiO2 and scanned 12 times with a commercial intraoral scanner. The scans where evaluated using two methods. Manual method: The diameter of the sphere was measured 12 times for each scan in a software application by adjusting a cross-sectional plane. Automatic method: 12 nominal diameters were obtained with a software application. The accuracy was calculated for each test method and compared. Results. Reference measurement: The defined diameter was 4.9991±0.0001mm. Manual method: Trueness was 25 µm and precision was 10 µm. Mean precision within scans was 4 µm. Automatic method: Trueness was 26 µm and precision was 11 µm. All test values showed sharp significant deviations from the reference value but were well within range of clinical acceptance.Conclusions. Within the limitations of this in vitro study, the standardized in vitro test described can be used manually or with the automatic function Fitting Sphere for determining the accuracy of intraoral scanners. Further studies need to be performed on more complex objects. The commercial intraoral scanner (TRIOS) demonstrates a high level of trueness and precision which is comparable with or better than that shown with traditional impression methods.

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Salgado, Rebolledo Patricio. « Symplectic Structure of Constrained Systems : Gribov Ambiguity and Classical Duals for 3D Gravity ». Doctoral thesis, Universite Libre de Bruxelles, 2015. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/220463.

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The present thesis is divided into two parts. Part I is devoted to the study of Gribov ambiguity in gauge systems and its relation with the appearance of degeneracies in the symplectic structure of the corresponding reduced phase space after gauge fixation. Part II is concerned with classical dual field theories for three-dimensional Einstein gravity and the symplectic structure on coadjoint orbits of the corresponding asymptotic symmetry group.In Part I, the Gribov problem is studied in the context of finite temperature QCD and the structure of the gluon propagator is analyzed. The standard confined scenario is found for low temperatures, while for high enough temperatures deconfinement takes place and a free gluon propagator is obtained. Subsequently, the relation between Gribov ambiguity and degeneracies in the symplectic structure of gauge systems is analyzed. It is shown that, in finite-dimensional systems, the presence of Gribov ambiguities in regular constrained systems always leads to a degenerate symplectic form upon Dirac reduction. The implications for the Gribov-Zwanziger approach to QCD and the symplectic structure of the theory are discussed. In Part II, geometrical actions for three-dimensional Einstein gravity are constructed by studying the symplectic structure on coadjoint orbits of the asymptotic symmetry group. The geometrical action coming from the Kirillov-Kostant symplectic form on coadjoint orbits is analyzed thought Dirac's algorithm for constrained systems. By studying the case of centrally extended groups and semi-direct products, the symplectic structure on coadjoint orbits of the Virasoro and the BMS3 group are analyzed. This allows one to associate separate geometric actions to each coadjoint orbit of the solution space, leading to two-dimensional dual fiel theories for asymptotically AdS and asymptotically flat three-dimensional gravity respectively.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

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Kuismin, M. (Markku). « On regularized estimation methods for precision and covariance matrix and statistical network inference ». Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526220802.

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Abstract Estimation of the covariance matrix is an important problem in statistics in general because the covariance matrix is an essential part of principal component analysis, statistical pattern recognition, multivariate regression and network exploration, just to mention but a few applications. Penalized likelihood methods are used when standard estimates cannot be computed. This is a common case when the number of explanatory variables is much larger compared to the sample size (high-dimensional case). An alternative ridge-type estimator for the precision matrix estimation is introduced in Article I. This estimate is derived using a penalized likelihood estimation method. Undirected networks, which are connected to penalized covariance and precision matrix estimation and some applications related to networks are also explored in this dissertation. In Article II novel statistical methods are used to infer population networks from discrete measurements of genetic data. More precisely, Least Absolute Shrinkage and Selection Operator, LASSO for short, is applied in neighborhood selection. This inferred network is used for more detailed inference of population structures. We illustrate how community detection can be a promising tool in population structure and admixture exploration of genetic data. In addition, in Article IV it is shown how the precision matrix estimator introduced in Article I can be used in graphical model selection via a multiple hypothesis testing procedure. Article III in this dissertation contains a review of current tools for practical graphical model selection and precision/covariance matrix estimation. The other three publications have detailed descriptions of the fundamental computational and mathematical results which create a basis for the methods presented in these articles. Each publication contains a collection of practical research questions where the novel methods can be applied. We hope that these applications will help readers to better understand the possible applications of the methods presented in this dissertation
Tiivistelmä Kovarianssimatriisin estimointi on yleisesti ottaen tärkeä tilastotieteen ongelma, koska kovarianssimatriisi on oleellinen osa pääkomponenttianalyysia, tilastollista hahmontunnistusta, monimuuttujaregressiota ja verkkojen tutkimista, vain muutamia sovellutuksia mainitakseni. Sakotettuja suurimman uskottavuuden menetelmiä käytetään sellaisissa tilanteissa, joissa tavanomaisia estimaatteja ei voida laskea. Tämä on tyypillistä tilanteessa, jossa selittävien muuttujien lukumäärä on hyvin suuri verrattuna otoskokoon (englanninkielisessä kirjallisuudessa tämä tunnetaan nimellä ”high dimensional case”). Ensimmäisessä artikkelissa esitellään vaihtoehtoinen harjanne (ridge)-tyyppinen estimaattori tarkkuusmatriisin estimointiin. Tämä estimaatti on johdettu käyttäen sakotettua suurimman uskottavuuden estimointimenetelmää. Tässä väitöskirjassa käsitellään myös suuntaamattomia verkkoja, jotka liittyvät läheisesti sakotettuun kovarianssi- ja tarkkuusmatriisin estimointiin, sekä joitakin verkkoihin liittyviä sovelluksia. Toisessa artikkelissa käytetään uusia tilastotieteen menetelmiä populaatioverkon päättelyyn epäjatkuvista mittauksista. Tarkemmin sanottuna Lassoa (Least Absolute Shrinkage and Selection Operator) sovelletaan naapuruston valinnassa. Näin muodostettua verkkoa hyödynnetään tarkemmassa populaatiorakenteen tarkastelussa. Havainnollistamme, kuinka verkon kommuunien (communities) tunnistaminen saattaa olla lupaava tapa tutkia populaatiorakennetta ja populaation sekoittumista (admixture) geneettisestä datasta. Lisäksi neljännessä artikkelissa näytetään, kuinka ensimmäisessä artikkelissa esiteltyä tarkkuusmatriisin estimaattoria voidaan käyttää graafisessa mallinvalinnassa usean hypoteesin testauksen avulla. Tämän väitöskirjan kolmas artikkeli sisältää yleiskatsauksen tämänhetkisistä työkaluista, joiden avulla voidaan valita graafinen malli ja estimoida tarkkuus- sekä kovarianssimatriiseja. Muissa kolmessa julkaisussa on kuvailtu yksityiskohtaisesti olennaisia laskennallisista ja matemaattisista tuloksista, joihin artikkeleissa esitellyt estimointimenetelmät perustuvat. Jokaisessa julkaisussa on kokoelma käytännöllisiä tutkimuskysymyksiä, joihin voidaan soveltaa uusia estimointimenetelmiä. Toivomme, että nämä sovellukset auttavat lukijaa ymmärtämään paremmin tässä väitöskirjassa esiteltyjen menetelmien käyttömahdollisuuksia

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Huang, Lei, Chenlu Zhou, Mali Gong, Xingkun Ma et Qi Bian. « Development of a novel three-dimensional deformable mirror with removable influence functions for high precision wavefront correction in adaptive optics system ». SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622017.

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Deformable mirror is a widely used wavefront corrector in adaptive optics system, especially in astronomical, image and laser optics. A new structure of DM-3D DM is proposed, which has removable actuators and can correct different aberrations with different actuator arrangements. A 3D DM consists of several reflection mirrors. Every mirror has a single actuator and is independent of each other. Two kinds of actuator arrangement algorithm are compared: random disturbance algorithm (RDA) and global arrangement algorithm (GAA). Correction effects of these two algorithms and comparison are analyzed through numerical simulation. The simulation results show that 3D DM with removable actuators can obviously improve the correction effects.

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Mestres, Adrià Caballé. « Statistical methods for the testing and estimation of linear dependence structures on paired high-dimensional data : application to genomic data ». Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31331.

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This thesis provides novel methodology for statistical analysis of paired high-dimensional genomic data, with the aimto identify gene interactions specific to each group of samples as well as the gene connections that change between the two classes of observations. An example of such groups can be patients under two medical conditions, in which the estimation of gene interaction networks is relevant to biologists as part of discerning gene regulatory mechanisms that control a disease process like, for instance, cancer. We construct these interaction networks fromdata by considering the non-zero structure of correlationmatrices, which measure linear dependence between random variables, and their inversematrices, which are commonly known as precision matrices and determine linear conditional dependence instead. In this regard, we study three statistical problems related to the testing, single estimation and joint estimation of (conditional) dependence structures. Firstly, we develop hypothesis testingmethods to assess the equality of two correlation matrices, and also two correlation sub-matrices, corresponding to two classes of samples, and hence the equality of the underlying gene interaction networks. We consider statistics based on the average of squares, maximum and sum of exceedances of sample correlations, which are suitable for both independent and paired observations. We derive the limiting distributions for the test statistics where possible and, for practical needs, we present a permuted samples based approach to find their corresponding non-parametric distributions. Cases where such hypothesis testing presents enough evidence against the null hypothesis of equality of two correlation matrices give rise to the problem of estimating two correlation (or precision) matrices. However, before that we address the statistical problem of estimating conditional dependence between random variables in a single class of samples when data are high-dimensional, which is the second topic of the thesis. We study the graphical lasso method which employs an L1 penalized likelihood expression to estimate the precision matrix and its underlying non-zero graph structure. The lasso penalization termis given by the L1 normof the precisionmatrix elements scaled by a regularization parameter, which determines the trade-off between sparsity of the graph and fit to the data, and its selection is our main focus of investigation. We propose several procedures to select the regularization parameter in the graphical lasso optimization problem that rely on network characteristics such as clustering or connectivity of the graph. Thirdly, we address the more general problem of estimating two precision matrices that are expected to be similar, when datasets are dependent, focusing on the particular case of paired observations. We propose a new method to estimate these precision matrices simultaneously, a weighted fused graphical lasso estimator. The analogous joint estimation method concerning two regression coefficient matrices, which we call weighted fused regression lasso, is also developed in this thesis under the same paired and high-dimensional setting. The two joint estimators maximize penalized marginal log likelihood functions, which encourage both sparsity and similarity in the estimated matrices, and that are solved using an alternating direction method of multipliers (ADMM) algorithm. Sparsity and similarity of thematrices are determined by two tuning parameters and we propose to choose them by controlling the corresponding average error rates related to the expected number of false positive edges in the estimated conditional dependence networks. These testing and estimation methods are implemented within the R package ldstatsHD, and are applied to a comprehensive range of simulated data sets as well as to high-dimensional real case studies of genomic data. We employ testing approaches with the purpose of discovering pathway lists of genes that present significantly different correlation matrices on healthy and unhealthy (e.g., tumor) samples. Besides, we use hypothesis testing problems on correlation sub-matrices to reduce the number of genes for estimation. The proposed joint estimation methods are then considered to find gene interactions that are common between medical conditions as well as interactions that vary in the presence of unhealthy tissues.

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Fernandes, Karina Alves. « Avaliação da qualidade dimensional e geométrica de cilindros de blocos de compressores herméticos usinados pelo processo de brunimento flexível ». Universidade Federal de Uberlândia, 2014. https://repositorio.ufu.br/handle/123456789/14987.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
The purpose of this work is to evaluate the geometrical and dimensional quality of block cylinders used in hermetic compressors machined by conventional and flexible honing. The conventional honing was done by EMBRACO, while the flexible honing was conducted at Federal University of Uberlândia using a CNC mill and a flexible honing which consists of a metal rod and nylon bristles with abrasive lobes at the ends. The evaluation of geometrical and dimensional quality was done by the measurement of: i) the cylinder diameter using a three coordinates measuring machine and a micrometer, ii) the circularity and cylindricity deviations using a shape deviation measuring machine and iii) the roughness (Ra, Rq, Rt, Rsk, Rku, Rk, Rpk e Rvk) using a electromechanical rugosimeter and a interferometer. For each measurand, it was estimated the related measurement uncertainty using the GUM methodology except for the roughness, where the Monte Carlo method was applied. The results showed that the flexible burnishing provides a significant improvement of the values of roughness parameters and the circularity deviation, while diameter values remained nearly constant. The flexible burnishing reduces the peak heights and eliminates the isolated occurrence of those without modify the valley depths, so providing improvements in proprieties such as surface softening, lubricant retention, mechanical strength and capacity to withstand loads in contact operations, meeting the desired tolerances.
O objetivo deste trabalho é avaliar a qualidade dimensional e geométrica de cilindros de blocos de compressores herméticos usinados pelo brunimento convencional e flexível. O brunimento convencional foi realizado pela EMBRACO, enquanto o brunimento flexível foi realizado na Universidade Federal de Uberlândia utilizando uma fresadora CNC e um brunidor flexível que é composto por uma haste metálica e cerdas de nylon com lóbulos abrasivos nas pontas. A avaliação da qualidade dimensional e geométrica foi efetuada por meio da medição do diâmetro do cilindro utilizando uma máquina de medir a três coordenadas e um micrômetro, dos desvios de cilindricidade e de circularidade por meio de uma máquina de medir desvios de forma e da rugosidade (Ra, Rq, Rt, Rsk, Rku, Rk, Rpk e Rvk), utilizando um rugosímetro eletromecânico e um interferômetro. Para cada mensurando foi estimada sua respectiva incerteza de medição, aplicando a metodologia proposta no GUM, exceto para a rugosidade, que foi utilizado o Método de Monte Carlo. Os resultados indicaram que o processo de brunimento flexível proporciona uma melhoria significativa dos valores dos parâmetros de rugosidade e do desvio de circularidade, enquanto que os valores de diâmetro permaneceram praticamente constantes. O brunimento flexível reduz a altura dos picos e elimina a presença isolada destes sem alterar a profundidade dos vales, proporcionando melhorias nas propriedades de amaciamento da superfície, retenção de lubrificante, na resistência mecânica e na capacidade de suportar cargas em operações de contato, atendendo as tolerâncias desejadas.
Mestre em Engenharia Mecânica

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Janson, Oleg. « DFT-based microscopic magnetic modeling for low-dimensional spin systems ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-91976.

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In the vast realm of inorganic materials, the Cu2+-containing cuprates form one of the richest classes. Due to the combined effect of crystal-field, covalency and strong correlations, all undoped cuprates are magnetic insulators with well-localized spins S=1/2, whereas the charge and orbital degrees of freedom are frozen out. The combination of the spin-only nature of their magnetism with the unique structural diversity renders cuprates as excellent model systems. The experimental studies, boosted by the discovery of high-temperature superconductivity in doped La2CuO4, revealed a fascinating variety of magnetic behaviors observed in cuprates. A digest of prominent examples should include the spin-Peierls transition in CuGeO3, the Bose-Einstein condensation of magnons in BaCuSi2O6, and the quantum critical behavior of Li2ZrCuO4. The magnetism of cuprates originates from short-range (typically, well below 1 nm) exchange interactions between pairs of spins Si and Sj, localized on Cu atoms i and j. Especially in low-dimensional compounds, these interactions are strongly anisotropic: even for similar interatomic distances |Rij|, the respective magnetic couplings Jij can vary by several orders of magnitude. On the other hand, there is an empirical evidence for the isotropic nature of this interaction in the spin space: different components of Si are coupled equally strong. Thus, the magnetism of cuprates is mostly described by a Heisenberg model, comprised of Jij(Si*Sj) terms. Although the applicability of this approach to cuprates is settled, the model parameters Jij are specific to a certain material, or more precisely, to a particular arrangement of the constituent atoms, i.e. the crystal structure. Typically, among the infinite number of Jij terms, only several are physically relevant. These leading exchange couplings constitute the (minimal) microscopic magnetic model. Already at the early stages of real material studies, it became gradually evident that the assignment of model parameters is a highly nontrivial task. In general, the problem can be solved experimentally, using elaborate measurements, such as inelastic neutron scattering on large single crystals, yielding the magnetic excitation spectrum. The measured dispersion is fitted using theoretical models, and in this way, the model parameters are refined. Despite excellent accuracy of this method, the measurements require high-quality samples and can be carried out only at special large-scale facilities. Therefore, less demanding (especially, regarding the sample requirements), yet reliable and accurate procedures are desirable. An alternative way to conjecture a magnetic model is the empirical approach, which typically relies on the Goodenough-Kanamori rules. This approach links the magnetic exchange couplings to the relevant structural parameters, such as bond angles. Despite the unbeatable performance of this approach, it is not universally applicable. Moreover, in certain cases the resulting tentative models are erroneous. The recent developments of computational facilities and techniques, especially for strongly correlated systems, turned density-functional theory (DFT) band structure calculations into an appealing alternative, complementary to the experiment. At present, the state-of-the-art computational methods yield accurate numerical estimates for the leading microscopic exchange couplings Jij (error bars typically do not exceed 10-15%). Although this computational approach is often regarded as ab initio, the actual procedure is not parameter-free. Moreover, the numerical results are dependent on the parameterization of the exchange and correlation potential, the type of the double-counting correction, the Hubbard repulsion U etc., thus an accurate choice of these crucial parameters is a prerequisite. In this work, the optimal parameters for cuprates are carefully evaluated based on extensive band structure calculations and subsequent model simulations. Considering the diversity of crystal structures, and consequently, magnetic behaviors, the evaluation of a microscopic model should be carried out in a systematic way. To this end, a multi-step computational approach is developed. The starting point of this procedure is a consideration of the experimental structural data, used as an input for DFT calculations. Next, a minimal DFT-based microscopic magnetic model is evaluated. This part of the study comprises band structure calculations, the analysis of the relevant bands, supercell calculations, and finally, the evaluation of a microscopic magnetic model. The ground state and the magnetic excitation spectrum of the evaluated model are analyzed using various simulation techniques, such as quantum Monte Carlo, exact diagonalization and density-matrix renormalization groups, while the choice of a particular technique is governed by the dimensionality of the model, and the presence or absence of magnetic frustration. To illustrate the performance of the approach and tune the free parameters, the computational scheme is applied to cuprates featuring rather simple, yet diverse magnetic behaviors: spin chains in CuSe2O5, [NO]Cu(NO3)3, and CaCu2(SeO3)2Cl2; quasi-two-dimensional lattices with dimer-like couplings in alpha-Cu2P2O7 and CdCu2(BO3)2, as well as the 3D magnetic model with pronounced 1D correlations in Cu6Si6O18*6H2O. Finally, the approach is applied to spin liquid candidates --- intricate materials featuring kagome-lattice arrangement of the constituent spins. Based on the DFT calculations, microscopic magnetic models are evaluated for herbertsmithite Cu3(Zn0.85Cu0.15)(OH)6Cl2, kapellasite Cu3Zn(OH)6Cl2 and haydeeite Cu3Mg(OH)6Cl2, as well as for volborthite Cu3[V2O7](OH)2*2H2O. The results of the DFT calculations and model simulations are compared to and challenged with the available experimental data. The advantages of the developed approach should be briefly discussed. First, it allows to distinguish between different microscopic models that yield similar macroscopic behavior. One of the most remarkable example is volborthite Cu3[V2O7](OH)2*2H2O, initially described as an anisotropic kagome lattice. The DFT calculations reveal that this compound features strongly coupled frustrated spin chains, thus a completely different type of magnetic frustration is realized. Second, the developed approach is capable of providing accurate estimates for the leading magnetic couplings, and consequently, reliably parameterize the microscopic Hamiltonian. Dioptase Cu6Si6O18*6H2O is an instructive example showing that the microscopic theoretical approach eliminates possible ambiguity and reliably yields the correct parameterization. Third, DFT calculations yield even better accuracy for the ratios of magnetic exchange couplings. This holds also for small interchain or interplane couplings that can be substantially smaller than the leading exchange. Hence, band structure calculations provide a unique possibility to address the interchain or interplane coupling regime, essential for the magnetic ground state, but hardly perceptible in the experiment due to the different energy scales. Finally, an important advantage specific to magnetically frustrated systems should be mentioned. Numerous theoretical and numerical studies evidence that low-dimensionality and frustration effects are typically entwined, and their disentanglement in the experiment is at best challenging. In contrast, the computational procedure allows to distinguish between these two effects, as demonstrated by studying the long-range magnetic ordering transition in quasi-1D spin chain systems. The computational approach presented in the thesis is a powerful tool that can be directly applied to numerous S=1/2 Heisenberg materials. Moreover, with minor modifications, it can be largely extended to other metallates with higher value of spin. Besides the excellent performance of the computational approach, its relevance should be underscored: for all the systems investigated in this work, the DFT-based studies not only reproduced the experimental data, but instead delivered new valuable information on the magnetic properties for each particular compound. Beyond any doubt, further computational studies will yield new surprising results for known as well as for new, yet unexplored compounds. Such "surprising" outcomes can involve the ferromagnetic nature of the couplings that were previously considered antiferromagnetic, unexpected long-range couplings, or the subtle balance of antiferromagnetic and ferromagnetic contributions that "switches off" the respective magnetic exchange. In this way, dozens of potentially interesting systems can acquire quantitative microscopic magnetic models. The results of this work evidence that elaborate experimental methods and the DFT-based modeling are of comparable reliability and complement each other. In this way, the advantageous combination of theory and experiment can largely advance the research in the field of low-dimensional quantum magnetism. For practical applications, the excellent predictive power of the computational approach can largely alleviate designing materials with specific properties.

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ALAHMAD, MOUHAMAD. « Developpement de methodes de vision par ordinateur : extraction de primitives geometriques ». Université Louis Pasteur (Strasbourg) (1971-2008), 1986. http://www.theses.fr/1986STR13192.

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Cette these concerne le developpement de methodes de vision par ordinateur, destinees a l'extraction de caracteristiques geometriques (barycentre, surface, perimetre, axe principal et orientation) pour identifier, localiser et comparer des objets a partir d'images en deux dimensions

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Vissiere, Alain. « Mesure de cylindricité de très haute exactitude.Développement d’une nouvelle machine de référence ». Thesis, Paris, ENSAM, 2013. http://www.theses.fr/2013ENAM0067/document.

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Le Laboratoire Commun de Métrologie LNE-CNAM (LCM) souhaite affiner sa maîtrise des références de pression afin de réaliser des appareillages de tout premier rang au niveau international. L'incertitude relative visée sur les références de pression est de l'ordre de 10-6. Cet objectif se traduit par une problématique de métrologie dimensionnelle où une mesure de la forme des pistons/cylindres utilisés dans les balances manométriques doit être menée. La mesure de cylindricité est également impliquée dans un très grand nombre d'applications industrielles comme la qualification d'étalons de référence destinés à la qualification d'appareillages de mesure. Notre travail de recherche, réalisé dans le cadre d'une convention CIFRE avec la SAS GEOMNIA, concerne la réalisation d'un instrument de référence de très haute précision permettant la mesure de forme de cylindres creux ou pleins. Nous proposons un saut technologique pour satisfaire un niveau d'incertitude sur la mesure de l'écart de cylindricité de l'ordre de 10 nanomètres dans un volume de mesure cylindrique de Ø350 mm et de hauteur 150 mm. La mesure de forme est habituellement pratiquée en déplaçant un capteur par rapport à la surface à mesurer par un guidage de haute précision. Il n'est cependant pas possible de réaliser un guidage entre deux solides d'un niveau de précision permettant de garantir les incertitudes souhaitées, même en utilisant les techniques de correction d'erreurs dont la précision est limitée par le défaut de répétabilité des guidages. Pour satisfaire à ce niveau d'incertitude, nous proposons une démarche basée sur le concept de structure métrologique dissociée. La mesure d'une pièce consiste alors à comparer sa forme à celle d'une pièce cylindrique de référence. Cette dernière doit seulement présenter une stabilité de forme parfaite. La cartographie d'écart de forme de la référence cylindrique doit cependant être identifiée au même niveau d'incertitude visé.Le travail de recherche développé propose une analyse détaillée des machines actuelles et de leurs limitations. Suite à cette analyse, une architecture de machine a été proposée pour lever ces limitations. Cette architecture tient compte des écarts « secondaires » liés à la position des capteurs et des effets de second ordre, pour satisfaire le niveau de précision visé. Une procédure complète d'étalonnage de la machine a été élaborée en s'inspirant des méthodes de séparation d'erreurs. Cette procédure originale permet de séparer les défauts de forme du cylindre de référence de ceux d'une pièce de qualification cylindrique mesurée simultanément. La méthode employée ne présente pas de limitations en termes d'exactitude. Cette procédure a été expérimentalement validée. Une analyse des effets liés à la mesure de surfaces cylindriques par des capteurs capacitifs a été menée. Ces essais ont conduit au développement de stratégies d'étalonnage de ces capteurs in situ utilisant des interféromètres à laser intégrés dans la machine. La traçabilité métrologique des résultats des mesures est ainsi garantie. Deux bancs de tests ont été développés pour caractériser les diverses influences et valider les procédures d'étalonnage des capteurs. La conception détaillée de l'instrument est issue de la synthèse des réflexions menées sur l'architecture, sur l'étalonnage et sur la maîtrise de la mesure de déplacements par capteurs capacitifs. Ce travail a abouti à la réalisation de ce nouvel instrument de référence ; sa conception, son montage et son réglage sont présentés
The “Laboratoire Commun de Métrologie LNE-CNAM (LCM)” seeks to improve the measurement of primary pressure standards done using pressure balances, to an order of 10-6 relative uncertainty. Therefore, it is appropriate to back-up these pressure balances with a measurement of the topology of the piston-cylinder devices used on these balances. Cylindricity measurement is also found in many industrial applications such as the measurement of standards used for the calibration of measuring machines. This research project, conducted in collaboration with SAS GEOMNIA under a CIFRE agreement, has a main objet to develop a new ultra-high precision machine for cylinders form measurement. We pushes with this project the leading edge of the cylinders form measurement area; we propose indeed a technological leap which leads to reduce the uncertainty associated to cylindricity errors up to 10 nm in a cylindrical working volume of 350 mm diameter rand 150 mm height. Form measurement is usually done using a measurement probe moved about the surface to be measured with high precision guiding systems. Nonetheless, these guiding systems are not precise enough to offer the low uncertainty required even when error correction techniques are used. This is because the precision of the guides is limited by their low repeatability. To meet this uncertainty level, we propose an approach based on the “dissociated metrological structure” concept. The measurement consists of comparing the artifact's form with the form of a cylindrical reference which should have perfect form stability. However, the mapping form deviation of this cylindrical reference needs to be identified at the same level of uncertainty referred.The present work exposes a detailed analysis of the existing measuring machines and their limitations. Consequently, an optimized machine architecture is proposed in order to overcome the present limitations. The proposed machine architecture takes into account the "secondary" error terms relative to the probes positions and second order effects in order to satisfy the level of accuracy sought. A complete calibration procedure of the machine has been elaborated based on the error separation methods; it allows the separation of the form errors of each of the reference cylinder and a qualification cylindrical part simultaneously measured. This procedure does not present any accuracy limitations and has been experimentally verified. An analysis of the effects related to the measurement of cylindrical artifacts using capacitive sensors has also been investigated. These experiments have led to the development of in-situ calibration strategies using laser interferometers integrated in the machine. Thus, the metrological traceability of the measurements is guaranteed. Two test benches have been developed to characterize the error sources that influence the measurement and to validate the calibration procedures of the probes used. The detailed design of the instrument synthesizes all the conceptual thoughts about the architecture, the calibration and the displacement measurement of the capacitive probes. This work has resulted in the development of this new reference instrument; its design, installation and adjustment are detailed

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Gasparin, Eloi. « Variabilidade espacial tridimensional dos atributos químicos e físicos de frutos em pomar de laranjas ». Universidade Estadual do Oeste do Parana, 2013. http://tede.unioeste.br:8080/tede/handle/tede/183.

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Made available in DSpace on 2017-05-12T14:46:59Z (GMT). No. of bitstreams: 1 Eloi Gasparin.pdf: 10922176 bytes, checksum: e0f71949d1aaae845d79c9e0f67aea23 (MD5) Previous issue date: 2013-11-08
The increase in production and yield as well as the correct use of agricultural inputs are essential factors to be taken into consideration when thinking about modern agriculture. Several techniques, previously used, mainly in the mining sector, have been incorporated to the agricultural sector with the precision agriculture management. The orcharding has also been improved by several studies under development in order to make such sector more competitive both nationally and internationally. The physical and chemical characteristics of orange fruits may change depending on the conditions to which they are exposed to, up from their blossoming period until harvest. Such conditions can be both climatic and related to the fruit position on the treetop. Although good fruit appearance is important, physical and chemical characteristics are as well, both for fresh consumption and industrial processing. Thus, this trial aimed at studying the three-dimensional spatial variability of physical and chemical characteristics of orange fruits in orchards, based on the generation of threedimensional maps and the SGeMS software. The trial was carried out in an orchard with Monte Parnaso orange variety, in Nova Laranjeiras city, Paraná, whose average altitude is 760 m and UTM central coordinates are around 7191655 m S and 341660 m E, 22J. So, 715 orange fruits from nine trees were analyzed during 2011, 2012 and 2013. Physical and chemical parameters showed weak correlation according to their position on the tree, but there was a trend of increasing values concerning the following attributes: diameter, fruit weight and juice mass as the vertical position of the fruits increases. For TSS content, the highest values were observed in the peripheral area of the tree and in its apical third part; but, for TTA content, it tended to decrease with the increasing vertical position of fruit. At last, the applied methodology was appropriate for the three-dimensional study concerning physical and chemical characteristics of orange fruits
O aumento da produção e da produtividade bem como a correta utilização dos insumos agrícolas são fatores indispensáveis quando se pensa em agricultura moderna. Com o surgimento da agricultura de precisão, várias técnicas anteriormente utilizadas, principalmente no setor de minérios, estão sendo incorporadas no setor agrícola. A fruticultura também tem se beneficiado devido a vários estudos em desenvolvimento com o intuito de tornar o setor competitivo tanto nacional como internacionalmente. As características físicas e químicas dos frutos de laranja podem sofrer alterações conforme as condições a que são expostas, desde o período de floração à colheita. Tais condições podem ser climáticas e relacionadas à posição que o fruto ocupa na copa da árvore. Embora a boa aparência dos frutos seja desejável, as características físicas e químicas são importantes tanto para o consumo in natura como para o processamento industrial. Diante disso, o objetivo deste trabalho foi estudar a variabilidade espacial tridimensional das características físicas e químicas de frutos em pomar de laranjas, a partir da geração de mapas tridimensionais com o auxílio do software SGeMS. O experimento foi conduzido em pomar de laranjas da variedade Monte Parnaso, localizado no município de Nova Laranjeiras - PR, com altitude média de 760 m e coordenadas UTM centrais aproximadas de 7.191.655 m S e 341.660 m E,22J. Foram analisados 715 frutos de laranja provenientes de nove árvores, nos anos de 2011, 2012 e 2013. Os atributos físicos e químicos apresentaram correlação fraca quanto à posição que os mesmos ocupam na árvore, mas houve tendência de aumento de valores de atributos como o diâmetro, massa do fruto e a massa do suco à medida que aumentava a cota vertical dos frutos. Para o teor de SST, os maiores valores foram encontrados na área periférica da árvore e no terço apical; e para o teor de ATT, a mesma tende a diminuir com o aumento da cota vertical do fruto. A metodologia utilizada mostrou-se adequada para o estudo tridimensional de características físicas e químicas de frutos

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Schneider, Fabien. « Aspect géométrique de la définition tridimensionnelle des mécanismes : de l'expression des conditions fonctionnelles à la détermination de paramètres de fabrication optimaux : démarche et outils de modélisation ». Cachan, Ecole normale supérieure, 1994. http://www.theses.fr/1994DENS0016.

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La définition géométrique des mécanismes consiste à traduire l'idée du client en un produit physique, tout en tenant compte des contraintes matérielles et contextuelles. Une analyse des effets néfastes de la définition habituelle des mécanismes nous conduit à proposer une structure de définition centrée sur un produit satisfaisant au mieux le client. Nous montrons ici la faisabilité d'une démarche de définition géométrique de mécanisme intégrant simultanément les contraintes du concepteur et du fabricant. Cette démarche s'appuie sur l'expression géométrique des besoins d'un client pour déterminer les valeurs optimales des paramètres de réglages des machines. Nous intégrons, dans un même modèle, la géométrie du mécanisme, les descriptions des processus de fabrication et des conditions fonctionnelles. ? La modélisation de la géométrie s'appuie sur la notion de contacts ponctuels entre pièces. La notion de liaison virtuelle est introduite pour tenir compte des hyperstatismes locaux et globaux des mécanismes. ? La modélisation des processus de fabrication s'effectue par composition de défauts de fabrication et de défauts de changement de référentiel. L'association de ces deux modélisations permet d'exprimer la position nominale et le défaut de tout point fabrique dans un référentiel mécanisme unique. ? La modélisation des conditions fonctionnelles implique la notion de frontière qui est dérivée en modèles limites de matière. L'application des contraintes des modèles limites de matière au modèle du mécanisme permet d'étudier les différentes méthodes de définition selon les points de vue des intervenants (concepteur et fabricant). Le point de vue du métrologue est aussi étudié. Pour donner le maximum d'ouverture au modèle, celui-ci s'appuie sur une écriture formelle des différentes contraintes. La mise en équation et l'expression mathématique des contraintes se synthétisent en un problème d'optimisation sous contraintes dont la fonction objectif est la satisfaction optimale du client qui conduit à une détermination optimale des paramètres de réglage

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Itame, Otávio Yassuo [UNESP]. « Avaliação do posicionamento plano-altimétrico com receptor gps em diferentes tipos de uso do solo ». Universidade Estadual Paulista (UNESP), 2008. http://hdl.handle.net/11449/101877.

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Neste trabalho, foram realizados levantamentos topográficos para a avaliação do efeito da cobertura vegetal, na recepção de sinais GPS, para obtenção de posicionamento tri-dimensional, considerando os estudos realizados em diferentes tipos de uso do solo. Vértices foram implantados em diferentes tipos de uso do solo; em área com pastagem, com plantação de seringueiras e com eucaliptos, e as suas posições determinadas com estação total, nivelamento geométrico e com receptores GPS. Na avaliação do posicionamento altimétrico adotou-se como valores de referência os desníveis determinados com o nivelamento geométrico para avaliação dos dados obtidos com receptores GPS. As coordenadas planimétricas obtidas com receptores GPS foram analisadas utilizando-se com valores de referência os dados obtidos com a estação total. No levantamento topográfico com estação total foram adotadas as prescrições estabelecidas nas Normas da Associação Brasileira de Normas Técnicas (ABNT) NBR 13.133, Execução de Levantamentos Topográficos, para poligonais do tipo IVP. Foi realizada a análise de exatidão e de precisão do posicionamento tridimensional, adotando como padrão a NBR 13133 da ABNT para a classe do levantamento executado. Para aplicações do GPS na altimetria há necessidade do conhecimento da ondulação geoidal (N), que neste trabalho, para a sua determinação foram coletados dados com receptor na referência de nível (RN). Os resultados obtidos indicam que cuidados especiais devem ser tomados nos levantamentos com receptores GPS em áreas com cobetura vegetal, pois estas interferem na propagação das ondas eletromagnéticas provenientes dos satélites podendo inviabilizar o posicionamento.
In this work, topographic surveys were carried out in order to evaluate the effect of vegetal cover, on the reception of GPS signals, for 3D positioning, considering studies to be made in different types of land use. Points were set up on different types of land use, in areas containing grass, rubber trees and eucalyptus, which had their positions defined using a total station, geometric leveling and GPS receivers In the evaluation of height positioning it was adopted as reference values the height differences determined by geometric levelling in order to evaluate data obtained through GPS receivers. Planimetric coordinates obtained by using GPS receivers were analysed using as reference values the data obtained using a total station. During the topographic survey using a total station the recommendations set up by the Brazilian Association for Technical Rules (ABNT) NBR 13.133, regarding the execution of topographic surveys, for transverses of type IVP. Accuracy and precision analysis was made on the 3D positioning, also considering ABNT NBR 13.133, for the class of topographic survey which was carried out. In order to apply GPS on height positiong it is necessary to know the geoidal ondulation (N) and, in this work, N was computed based upon data acquired employing receivers at the level reference (RN). The results obtained indicate that special care must be taken during the surveys carried out with the use of GPS receivers on areas with vegetal cover, because it causes interference in the propagation of electromagnetic waves from the satellite which can even make the positioning become unviable.

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Yue, Shi Yi. « Modelisation calligraphique de formes moleculaires electroniques et geometriques dans une structure grille ». Paris 7, 1987. http://www.theses.fr/1987PA077264.

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Un systeme, polymod, de modelisation et de visualisation des objets chimiques est presente: il traite les formes structurales et les formes de proprietes liees aux distributions electroniques. Les molecules sont immergees dans un maillage 3d constituant l'espace de representation, les proprietes etant evaluees sur les noeuds de reseau. L'ensemble de l'information moleculaire est transmise au moyen de deux fichiers, l'un contient les parametres du reseau et les coordonnees moleculaires, l'autre les valeurs de la propriete sur les noeuds. Des correspondances reversibles sont etablies entre la localisation spatiale des noeuds et le rang des enregistrements dans le fichier de propriete

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Camonin, Martine. « Mephisto : un outil de validation de modèles tridimensionnels ». Nancy 1, 1987. http://www.theses.fr/1987NAN10149.

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Le système présente a été développé dans le cadre d'un système d'interprétation de scènes tridimentionnelles (Trident). Le modèle choisi permet de décrire des familles d'objets génériques construits par unions de primitives. La tache du système Mephisto est de décider de la cohérence d'un modèle fourni par l'utilisateur avant qu'il ne soit utilisé par trident. Dans le contexte de la représentation choisie, un modèle peut être vu comme un graphe et/ou avec contraintes. Une stratégie de recherche de chemin dans un graphe et/ou, minimisant en moyenne les coûts de construction, à partir d'une évaluation des espérances de succès de cette construction

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Duan, Qingwei. « Diffusion de la lumière en trois dimensions par des grosses particules non-sphériques par le modèle de Tracé de Rayons Vectoriels Complexes ». Thesis, Normandie, 2020. http://www.theses.fr/2020NORMR018.

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Cette thèse est dédiée à une étude de diffusion de la lumière dans l’espace (3D) d’une onde plane ou d’un faisceau laser, dans le cadre du modèle tracée de rayons vectoriels complexes (VCRM Vectorial Complex Ray Model en anglais), par une grosse particule de surface lisse. Les principaux travaux réalisés se résument comme suit : Dans un premier temps, une méthode de calcul pour la diffusion 2D de l’onde plane par un cylindre infini de section quelconque est proposée. Cette méthode est ensuite appliquée à la simulation de l’intensité diffusée de l’onde plane par un cylindre elliptique composé (CEC), dont la section est formée par deux demi-ellipses de paramètres différents. Les effets de la déformation, de l’indice de réfraction et de la direction de l’onde incidente sur les champs diffusés, en particulier les positions des arcs-en-ciel ainsi que leurs dispositions de l’intensité, sont analysées quantitativement. Puis, les travaux se sont étendus à la diffusion dans l’espace (3D) d’une onde plane par une particule de forme quelconque en tenant en compte les déphasages dus aux lignes focales et au chemin optique, la divergence et la convergence du front d’onde, et la polarisation croisée. Un algorithme d’interpolation basé sur la triangulation est développé qui permet de prendre en compte l’inférence des rayons diffusés dans l’espace. La méthode proposée pour la diffusion 3D est appliquée à la simulation de l’intensité diffusée d’une onde plane par un jet de liquide réel. Ceci a permis d’interpréter le mécanisme de diffusion dans l’espace: l’analyse de mode de diffusion, la séparation ou l’interférence de différents ordres. Une expérience est menée pour vérifier la méthode de calcul et pour examiner les résultats simulés. Afin de prendre en compte la forme du faisceau incident, une méthode de description d’un faisceau gaussien elliptique incident par rayons est proposée, qui permet de calculer l’intensité diffusée en 3D d’un faisceau gaussien circulaire ou elliptique par une grosse particule. Le calcul de l’intensité diffusée en champ lointain d’un faisceau gaussien elliptique par un jet de liquide réel est réalisé avec succès. Les champs de diffusion aux alentours des arcs-en-ciel du premier et du second ordre pour les faisceaux incidents de différents angles et divergences sont étudiés
In the framework of vectorial complex ray model (VCRM), this thesis aims to solve the three-dimensional (3D) scattered intensity of plane wave or shaped beam by a large particle of any smooth surface. The main work and achievements are summarized as follows: As the first step, the calculation method based on VCRM for the 2D scattered intensity of plane wave by a cylinder of any smooth cross section is proposed. And the proposed method is applied to solving the scattered intensity of plane wave by a composite elliptical cylinder (CEC), whose cross section can take various shapes ranging from circular, elliptical to highly-deformed. The effects of shape deformation, refractive index and incident direction on the scattering fields, especially on the rainbows, are quantitatively analyzed. Based on VCRM, the ray tracing, the phase shifts due to focal lines and optical path, the divergence and convergence of wavefront, and the cross polarization in 3D scattering are addressed. An interpolation algorithm based on triangulation has been developed which permits to take into account the interference of 3D scattered rays, thus breaking through the bottle-neck problem for VCRM in the extension to 3D scattering. The proposed method, which is based on VCRM while allows to calculate 3D scattering field, is applied to simulating the 3D scattered intensity of plane wave by a real liquid jet. Furthermore, taking advantage of the ability of VCRM for interpreting the scattering mechanism, a systematic analysis is made for the scattered light of different orders, in regard to their separation or interference in 3D space. An experiment is carried out to verify the proposed method for 3D scattering and to examine the simulated results. In the framework of VCRM, a ray description method for incident elliptical Gaussian beam is proposed, thus providing one feasible way to calculate the 3D scattered intensity of elliptical or circular Gaussian beam by a large particle of any smooth surface. The calculation for the 3D far-field scattered intensity of elliptical Gaussian beam by a real liquid jet is successfully achieved. The scattering fields near the first- and second-order rainbows for incident beams of different divergence angles are investigated in 3D space. These results as well as the proposed method open a promising way to characterize finely the structure of a real liquid jet and particles of other complex surfaces

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Thèses sur le sujet « Dimensional and geometrical precision »

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