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Artigos de revistas sobre o assunto "Geometric observers"
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Martínez-García, Edgar Alonso, Joaquín Rivero-Juárez, Luz Abril Torres-Méndez e Jorge Enrique Rodas-Osollo. "Divergent trinocular vision observers design for extended Kalman filter robot state estimation". Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering 233, n.º 5 (24 de setembro de 2018): 524–47. http://dx.doi.org/10.1177/0959651818800908.
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Here, we report the design of two deterministic observers that exploit the capabilities of a home-made divergent trinocular visual sensor to sense depth data. The three-dimensional key points that the observers can measure are triangulated for visual odometry and estimated by an extended Kalman filter. This work deals with a four-wheel-drive mobile robot with four passive suspensions. The direct and inverse kinematic solutions are deduced and used for the updating and prediction models of the extended Kalman filter as feedback for the robot’s position controller. The state-estimation visual odometry results were compared with the robot’s dead-reckoning kinematics, and both are combined as a recursive position controller. One observer model design is based on the analytical geometric multi-view approach. The other observer model has fundamentals on multi-view lateral optical flow, which was reformulated as nonspatial–temporal and is modeled by an exponential function. This work presents the analytical deductions of the models and formulations. Experimental validation deals with five main aspects: multi-view correction, a geometric observer for range measurement, an optical flow observer for range measurement, dead-reckoning and visual odometry. Furthermore, comparison of positioning includes a four-wheel odometer, deterministic visual observers and the observer–extended Kalman filter, compared with a vision-based global reference localization system.
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Niethammer, M., P. A. Vela e A. Tannenbaum. "Geometric Observers for Dynamically Evolving Curves". IEEE Transactions on Pattern Analysis and Machine Intelligence 30, n.º 6 (junho de 2008): 1093–108. http://dx.doi.org/10.1109/tpami.2008.28.
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Wang, Yebin, e Kenji Utsunomiya. "From acceleration-based semi-active vibration reduction control to functional observer design". at - Automatisierungstechnik 66, n.º 3 (26 de março de 2018): 234–45. http://dx.doi.org/10.1515/auto-2017-0064.
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Abstract This work investigates a functional estimation problem for single input single output linear and nonlinear systems, motivated by its enabling role in acceleration-based semi-active control. Solvability of a linear functional estimation problem is studied from a geometric approach, where the functional dynamics are derived, decomposed, and transformed to expose structural properties. This approach is extended to solve a challenging nonlinear functional observer problem, combining with the exact error linearization. Existence conditions of nonlinear functional observers are established. Simulation verifies existence conditions and demonstrates the effectiveness of the proposed functional observer designs.
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Lewis, F. L. "Geometric design techniques for observers in singular systems". Automatica 26, n.º 2 (março de 1990): 411–15. http://dx.doi.org/10.1016/0005-1098(90)90138-8.
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Silver, Brian, Arturo Tamayo, Edward H. Wong, Bart Demaerschalk, Jose G. Merino e Vladimir Hachinski. "A reliable new method to estimate >1/3 middle cerebral artery infarction on early computed tomography scan". Stroke 32, suppl_1 (janeiro de 2001): 325. http://dx.doi.org/10.1161/str.32.suppl_1.325-a.
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50 Objectives: To develop a reliable method of estimation of >1/3 involvement of the middle cerebral artery territory (MCAT) on early CT scan. Background: The European Cooperative Acute Stroke Study (ECASS) suggested that > 1/3 involvement of the MCAT on early CT scan was a risk factor for symptomatic intracerebral hemorrhage (SICH) following treatment with tissue plasminogen activator (tPA) for acute ischemic stroke (AIS). There are no published guidelines on how to perform such an evaluation. The ICE method was developed for the purpose of standardizing the approach of infarct size estimation. This method requires the observer of the CT scan to mentally: 1) Idealize the MCAT into an area approximating a trapezoid, 2) Close a geometric figure around the area(s) of hypodensity(ies), and 3) Estimate the ratio of the two geometric figures (C/I). Methods: Five stroke fellows (observers) were tested with 40 CT scans which had been performed within the first few hours of an acute neurological event. Observers were blinded to patient history. They were asked whether to treat the patient on the basis of the CT scan. The decision not to treat was predicated on the presence of hemorrhage or > 1/3 MCAT involvement. Results: Five scans showed evidence of hemorrhage. All observers detected the hemorrhages. The remaining scans were of patients with presumed ischemia. Six scans were thought to show > 1/3 MCAT involvement by all observers. For all scans, median interobserver agreement among 10 paired comparisons was 86% (range 73–93%). Median kappa was 0.72 (range 0.44–0.85, p<0.001). Conclusion: The ICE method has very good interobserver reliability. The method merits further investigation among non-stroke physicians.
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Perdon, Anna Maria, e Maria Anderlucci. "GEOMETRIC DESIGN OF OBSERVERS FOR LINEAR TIME-DELAY SYSTEMS". IFAC Proceedings Volumes 39, n.º 10 (2006): 120–25. http://dx.doi.org/10.3182/20060710-3-it-4901.00021.
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Majid, H., e H. Abouaïssa. "Comparative Study of a Super-Twisting Sliding Mode Observer and an Extended Kalman Filter for a Freeway Traffic System". Cybernetics and Information Technologies 15, n.º 2 (1 de junho de 2015): 141–58. http://dx.doi.org/10.1515/cait-2015-0034.
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Abstract Traffic state estimation represents one of the important ingredients for traffic prediction and forecasting. The work presented in this paper deals with the estimation of traffic state variables (density and speed), using the so called Super- Twisting Sliding Mode Observer (STSM). Several numerical simulations, using simulated and real data, show the relevance of the proposed approach. In addition, a comparative study with the Extended Kalman Filter (EKF) is carried-out. The comparison indices concern convergence and stability, dynamic performance and robustness. The design of the two observers is achieved using a nonlinear second order traffic flow model in the same highway traffic and geometric conditions.
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Fraser, Ian H., e Denis M. Parker. "Visual Parsing and Priority Effects in Temporal Order Judgements of Line Drawn Patterns". Perception 17, n.º 4 (agosto de 1988): 437–59. http://dx.doi.org/10.1068/p170437.
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Five experiments are reported in which the perception of the order of the components of line drawn patterns presented in rapid temporal sequence on a visual display unit was investigated. In experiments 1 and 2, respectively, a schematic face and an asymmetrical geometric design, and a realistic face and a symmetrical geometric design were each divided into four fragments consisting of outline and three internal features. These fragments were presented to observers in sequences in which the position of the outline in the sequence was systematically varied. Observers reported the perceived order of the fragments. If the order was misperceived the interfragment interval was increased until the sequence was correctly perceived. Analysis of the pattern of perceptual errors and the interfragment presentation interval at which the sequence was correctly perceived indicated that observers tended to perceive the sequence correctly when the outline was presented in first or last position, but had difficulty in doing this when it occupied an intermediate position. This effect was significantly stronger with facial than with geometric patterns. Furthermore, in the case of two face patterns, errors were of a form where observers reported the outline presented in positions two or three as occupying positions one or four respectively. In experiment 3 an identical procedure was used to compare the perception of temporally fragmented normal and inverted faces. The outline position effect was equally strong in both cases. In experiment 4 the relative strength of the tendency to move the outline towards first or final position was assessed by dividing each of two patterns, a face and a house, into three fragments consisting of outline and two groups of internal features. Order perception was significantly better with outline in first or third position, but where it was presented in the intermediate position it was reported as being presented in first position. In experiment 5 the general pattern of results obtained in experiments 1, 2, and 3 was verified with the use of a methodology in which pattern fragment sequences and interfragment intervals were both randomised from trial to trial and the observer's task was to specify the position of the outline in the sequence. Four patterns—a normal face, a face with inverted internal features (INF face), a face outline with irrelevant internal features (IRF face), and a geometric design—were each divided into four fragments consisting of outline and three internal features. Results indicated that for the normal and the INF face, detection of the outline position was significantly better in first and last position, whereas for the other two patterns detection was significantly better in first than in any of the other three positions. It is argued that the results of the five experiments emphasise the special importance of the outline in pattern recognition and support the existence of two processes in visual perception; a high-level parsing process and an outline priority effect. Both processes are probably precognitive in nature.
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Bukaros, A., A. Herega, V. Sergeiev, T. Obnyavko e K. Konkov. "STATE OBSERVER OF THE COMBAT VEHICLE ELECTRIC DRIVES". Collection of scientific works of Odesa Military Academy, n.º 17 (31 de agosto de 2022): 116–24. http://dx.doi.org/10.37129/2313-7509.2022.17.116-124.
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The paper substantiates the use of adaptive state observers of combat vehicles guiding electric drives instead of imperfect rotation speed sensors of executive motors, as which tachogenerators are traditionally used. The synthesis is carried out, the structure and mathematical description of the Luenberger observer of the direct current executive motor with independent excitation by the modal method are obtained. The performance of the synthesized observer is confirmed by checking the fulfillment of the observability condition. An expression for determining the geometric mean root, which makes it possible to simplify the structure of the observer and to evaluate not only the rotation speed, but also the load torque on the motor shaft is proposed. For definite structure of the observer, expressions for the coefficients of the Luenberger matrix are obtained. The modernized Luenberger observer was studied by simulation in the Matlab/Simulink environment. The parameters of the DC executive motor D-135 of the vertical guidance system of the 9K35 anti-aircraft missile system were used as the initial data of the model. The simulation results with the accepted binomial distribution of the roots of the characteristic polynomial proved the efficiency of the proposed structure of the observer. The estimation of the electric drive coordinates occurred aperiodically, without fluctuations, however, it had a relatively large error due to the underestimated speed of the observer. To eliminate this shortcoming, the distribution of the roots of the characteristic polynomial of the observer according to the Chebyshev linear form was proposed. With this distribution of roots, the performance of the Luenberger observer increased significantly, which limited the error in tracking the coordinates of the electric drive to 4%. The prospects for further research of the proposed method for the synthesis of state observers of the executive motors of the combat vehicles guidance systems are outlined. Keywords: Luenberger observer, executive motor, guidance system, combat vehicle.
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Estévez, Oscar. "Interindividual Receptor Variability of Normal Colour Observers: Analysis of the 2-Deg Stiles and Burch Data". Perception 15, n.º 6 (dezembro de 1986): 677–87. http://dx.doi.org/10.1068/p150677.
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Examination of the interobserver variability among the ten observers of the 2-deg Stiles and Burch colorimetric study reveals an interesting pattern: the chromaticities of the matches made by different normal subjects fall approximately on straight lines and these lines appear to converge. Because of a geometric relationship that holds between the normal, anomalous, and dichromatic colour spaces, it can be argued that part of the variability must be due to actual differences in the shape or spectral position of the receptor sensitivities of different normal observers.
Teses / dissertações sobre o assunto "Geometric observers"
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Sease, Bradley Jason. "Data Reduction for Diverse Optical Observers through Fundamental Dynamic and Geometric Analysis". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/70923.
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Typical algorithms for processing unresolved space imagery from optical systems make broad assumptions about the expected behavior of the sensors during collection. While these techniques are often successful at data reduction for a particular mission, they rarely extend to sensors in different operating modes. Such specialized techniques therefore reduce the number of sensors able to contribute imagery. By approaching this problem with analysis of the fundamental dynamic equations and geometry at play, we can gain a deeper understanding into the behavior of both stars and space objects viewed through optical sensors. This type of analysis has the potential to enable data collection from a wider variety of sensors, increasing both the quantity and quality of data available for space object catalog maintenance. This dissertation will explore the implications of this approach to unresolved data processing. Sensor-level motion descriptions will be derived and applied to the problem of space object discrimination and tracking. Results of this processing pipeline as applied to both simulated and real optical data will be presented.Ph. D.
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Anisi, David A. "Online trajectory planning and observer based control". Licentiate thesis, Stockholm : Optimization and systems theory, Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4153.
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Anisi, David A. "On Cooperative Surveillance, Online Trajectory Planning and Observer Based Control". Doctoral thesis, KTH, Optimeringslära och systemteori, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9990.
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The main body of this thesis consists of six appended papers. In the first two, different cooperative surveillance problems are considered. The second two consider different aspects of the trajectory planning problem, while the last two deal with observer design for mobile robotic and Euler-Lagrange systems respectively.In Papers A and B, a combinatorial optimization based framework to cooperative surveillance missions using multiple Unmanned Ground Vehicles (UGVs) is proposed. In particular, Paper A considers the the Minimum Time UGV Surveillance Problem (MTUSP) while Paper B treats the Connectivity Constrained UGV Surveillance Problem (CUSP). The minimum time formulation is the following. Given a set of surveillance UGVs and a polyhedral area, find waypoint-paths for all UGVs such that every point of the area is visible from a point on a waypoint-path and such that the time for executing the search in parallel is minimized. The connectivity constrained formulation extends the MTUSP by additionally requiring the induced information graph to be kept recurrently connected at the time instants when the UGVs perform the surveillance mission. In these two papers, the NP-hardness of both these problems are shown and decomposition techniques are proposed that allow us to find an approximative solution efficiently in an algorithmic manner.Paper C addresses the problem of designing a real time, high performance trajectory planner for an aerial vehicle that uses information about terrain and enemy threats, to fly low and avoid radar exposure on the way to a given target. The high-level framework augments Receding Horizon Control (RHC) with a graph based terminal cost that captures the global characteristics of the environment. An important issue with RHC is to make sure that the greedy, short term optimization does not lead to long term problems, which in our case boils down to two things: not getting into situations where a collision is unavoidable, and making sure that the destination is actually reached. Hence, the main contribution of this paper is to present a trajectory planner with provable safety and task completion properties. Direct methods for trajectory optimization are traditionally based on a priori temporal discretization and collocation methods. In Paper D, the problem of adaptive node distribution is formulated as a constrained optimization problem, which is to be included in the underlying nonlinear mathematical programming problem. The benefits of utilizing the suggested method for online trajectory optimization are illustrated by a missile guidance example.In Paper E, the problem of active observer design for an important class of non-uniformly observable systems, namely mobile robotic systems, is considered. The set of feasible configurations and the set of output flow equivalent states are defined. It is shown that the inter-relation between these two sets may serve as the basis for design of active observers. The proposed observer design methodology is illustrated by considering a unicycle robot model, equipped with a set of range-measuring sensors. Finally, in Paper F, a geometrically intrinsic observer for Euler-Lagrange systems is defined and analyzed. This observer is a generalization of the observer proposed by Aghannan and Rouchon. Their contractivity result is reproduced and complemented by a proof that the region of contraction is infinitely thin. Moreover, assuming a priori bounds on the velocities, convergence of the observer is shown by means of Lyapunov's direct method in the case of configuration manifolds with constant curvature.QC 20100622
TAIS, AURES
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Bouazza, Tarek. "Contributions à la conception d'observateurs géométriques pour la navigation visuo-inertielle". Electronic Thesis or Diss., Université Côte d'Azur, 2024. http://www.theses.fr/2024COAZ4053.
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L'estimation précise des états de navigation d'un robot est une exigence essentielle pour la conception de systèmes autonomes sûrs et fiables. Les systèmes modernes de navigation visuo-inertielle présentent une solution puissante pour les applications aériennes et sous-marines en combinant des informations visuelles riches et fiables provenant de caméras monoculaires avec des données inertielles à haute cadence et à faible latence fournies par des centrales inertielles MEMS. Alors que les algorithmes conventionnels de fusion de capteurs nécessitent des ressources de calcul importantes, les techniques de filtrage traditionnelles garantissent un traitement plus rapide au détriment des performances en raison des non-linéarités associées à la géométrie non-euclidienne des espaces d'état et de sortie du système. L'exploitation de la structure de symétrie dérivée des propriétés du système s'est avérée efficace pour la conception d'observateurs d'état robustes et fiables dotés de fortes garanties de stabilité. Cette thèse aborde deux aspects complémentaires du problème de la navigation visuo-inertielle. En première partie, elle considère le problème de l'estimation directe de la pose (position et orientation) et de la pose étendue (pose et vitesse linéaire) du robot via l'exploitation directe des groupes de symétrie sous-jacents SE(3) et SE2(3), respectivement, et des modèles de mesure non linéaires dérivés des contraintes visuelles de l'homographie. Des conditions explicites d'observabilité uniforme sont établies pour chaque cas, et des observateurs de Riccati sont proposés et testés en simulation et dans des expériences en conditions réelles. Deuxièmement, l'accent est mis sur la dérivation d'observateurs exploitant les propriétés de symétrie et d'équivariance inhérentes à l'espace d'état, à la dynamique et aux modèles de mesures. Cette partie de la thèse introduit de nouvelles symétries de groupe de Lie qui tiennent compte des mesures d'entrée et de sortie disponibles et dérive les observateurs équivariants appropriés. Les états considérés incluent la matrice d'homographie modélisée comme un élément du groupe de Lie SL(3), l'homographie étendue (qui inclut l'homographie et les paramètres de structure de la scène plane observée), l'homographie inertielle étendue (homographie étendue, vitesse linéaire et direction gravitationnelle), et, dans la construction épipolaire, la pose du robot modélisée en utilisant le groupe de symétrie polaire SOT(3). Ces contributions sont accompagnées d'une analyse approfondie visant à établir les conditions d'observabilité uniforme nécessaire à la preuve formelle de la stabilité des observateurs équivariants déterministes, ou à évaluer la consistance des filtres stochastiques, et sont validées par des expériences de simulation détailléesAccurate estimation of a robot's navigation states is a core requirement for building safe and reliable autonomous systems. Modern visual-inertial navigation systems present a powerful solution for aerial and underwater applications, combining rich and reliable visual information from monocular cameras with high-rate, low-latency inertial data provided by MEMS-based IMUs. While conventional sensor fusion algorithms require significant computational resources, traditional filtering techniques offer faster processing at the expense of performance due to the nonlinearities associated with the non-Euclidean geometry of the system's state and output spaces. Exploiting the symmetry structure derived from the system's properties has proven effective for the design of robust and reliable state observers with strong stability guarantees. This thesis addresses two complementary aspects of the visual-inertial navigation problem. First, it considers the problem of directly estimating the robot's pose (position and orientation) and the extended pose (pose and linear velocity) via direct exploitation of the underlying symmetry groups SE(3) and SE2(3), respectively, as well as the nonlinear measurement models derived from visual homography constraints. Uniform observability conditions are explicitly derived for each case, and Riccati observers are proposed and tested in simulations and real-world experiments. The second aspect centers on designing observers that exploit the underlying symmetry and equivariance properties of the system's state space, dynamics, and measurement models. This part introduces new Lie group symmetries that properly account for available input and output measurements and derives the so-called equivariant observers accordingly. The considered states include the homography matrix modeled as an element of the Lie group SL(3), the extended homography (which includes the homography and structure parameters of the observed planar environment), the inertial extended homography (extended homography, linear velocity, and gravitational direction), and the rigid-body pose modeled in the epipolar construction using the polar symmetry group SOT(3). These contributions are supported by a comprehensive analysis to establish the uniform observability conditions necessary to formally prove the stability of the deterministic equivariant observers, or to assess the consistency of the stochastic filters, and are validated through extensive simulation experiments
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Koh, Wonryull. "Geometric representation of neuroanatomical data observed in mouse brain at cellular and gross levels". [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1669.
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Li, Zhijin. "Task-based optimization of 3D breast x-ray imaging using mathematical observers". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLN038.
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La mammographie, une modalité 2D d'imagerie du sein par rayons X, a montré son efficacité pour réduire la mortalité par cancer du sein. Aujourd'hui, la tomosynthèse numérique du sein, une modalité 3D d'imagerie du sein par rayons X, prend une place de plus en plus importante dans la pratique clinique, et est reconnue de plus en plus souvent comme ayant le potentiel de remplacer la mammographie dans un proche avenir. Pour évaluer plusieurs aspects de la tomosynthèse, des études cliniques sont nécessaires. Mais les études cliniques sont coûteuses et présentent des risques supplémentaires pour les patientes dus à l'utilisation de radiations ionisantes. Les études cliniques virtuelles ont pour objectif d'offrir une approche alternative en utilisant des simulations numériques. Dans cette thèse, nous nous intéressons à plusieurs éléments intervenants dans une telle étude clinique virtuelle. Dans un premier temps, nous analysons l'état de l'art sur la caractérisation analytique des champs aléatoires 3D pour la simulation de la texture du sein par rayons X. Nous nous intéressons aussi à l'estimation de caractéristiques statistiques des images du sein par rayons X (densité, indice spectral). Puis nous développons un nouveau modèle de texture 3D du sein basé sur la géométrie stochastique, et qui permet de simuler des images 2D et 3D réalistes du sein. Nous considérons le problème de l'inférence d'un tel modèle à partir d'une base d'images cliniques 3D. Ensuite, nous développons un observateur mathématique basé sur la théorie textit{a contrario} de la perception visuelle, pour modéliser la détection des microcalcifications par des radiologues dans des images 2D et 3D du sein. Tous ces composants sont utilisés pour implémenter une étude clinique entièrement numérique. La pertinence des résultats obtenus montre l'utilité de ces études cliniques virtuelles et nous incite à en développer de plus élaborées dans le futurFull field digital mammography, a 2D x-ray breast imaging modality has been proved to reduce the breast cancer mortality. Today, digital breast tomosynthesis, a 3D x-ray breast imaging modality, is being integrated in clinical practice and is believed to replace standard mammography in the near future. To assess the clinical performance of various aspects of tomosynthesis, clinical trials are needed. Clinical trials are burdensome, expensive and may impose increased risk to the patient due to additional radiation exposure. Virtual Clinical Trials aim to offer a more efficient alternative by using computational components. Today, active research is ongoing to develop computational components dedicated to 2D and 3D breast imaging, especially to 3D tomosynthesis. This thesis aims to advance several aspects in the development of Virtual Clinical Trials. First, we focused on analytical characterization of state-of-the-art 3D random field breast texture models. The estimation of statistical characteristics (breast density, spectral index) from clinical x-ray breast images was also studied. Next, we proposed a mathematically traceable 3D breast texture model based on stochastic geometry, that allows to simulate realistic 2D and 3D images. The statistical inference of the texture model parameters from a database of clinical 3D breast images was also tackled. We then developed a mathematical observer based on the textit{a contrario} theory, that allows to model the microcalcification detection process by radiologists in 2D and 3D breast images. Finally, these two proposed components were applied to implement a virtual clinical trial experiment, demonstrating their potential in the conduct of more advanced virtual clinical studies in the future
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Adams, Aaron J. "Relationships between observed pore and pore-throat geometries, measured porosity and permeability, and indirect measures of pore volume by nuclear magnetic resonance". Texas A&M University, 2005. http://hdl.handle.net/1969.1/4710.
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Carbonate reservoirs are a network of pores and connecting pore-throats that
contain at least half of the world's oil. Genetic classification of carbonate pores enables
one to map the pore types that have greatest influence on reservoir performance.
Though NMR logging has been used to estimate pore sizes, it has not been used to
identify genetic pore types or to aid in determinations of reservoir quality for different
pore assemblages.
Five genetic pore types identified in 40 carbonate and 7 sandstone samples were
subjected to NMR measurements. Results reveal close correspondence between NMRderived
pore volumes and 2-D pore size and shape gleaned from petrographic image
analysis. Comparisons of real and synthetic pore shapes showed that shapes of all pore
types in the medium size range of 0.02-0.5mm can be reliably compared with synthetic
varieties, but such comparisons were unreliable for vuggy pores smaller than 0.5mm. T2
relaxation times for depositional pores exhibit low amplitude, narrow wavelength
responses. Moldic pores produced medium amplitude, asymmetrical wavelength responses, and intercrystalline pores show high amplitude, narrow wavelength
responses. NMR-derived pore volumes on pores with ferroan dolomite interiors
underestimated pore diameter by up to 3 orders of magnitude. Calculated pore-throat
sizes from MICP data correlate strongly with measured permeability.
Samples with high, intermediate, or low poroperm values displayed characteristic
T2 curves confirming that reservoir quality can be estimated from NMR measurements.
Future work is expected to show that NMR logging can estimate reservoir quality at
field scale and aid in mapping flow units in compartmentalized reservoirs.
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Mehmood, Adeel. "Modeling, simulation and robust control of an electro-pneumatic actuator for a variable geometry turbocharger". Phd thesis, Université de Technologie de Belfort-Montbeliard, 2012. http://tel.archives-ouvertes.fr/tel-00827445.
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The choice of technology for automotive actuators is driven by the need of high power to size ratio. In general, electro-pneumatic actuators are preferred for application around the engine as they are compact, powerful and require simple controlling devices. Specially, Variable Geometry Turbochargers (VGTs) are almost always controlled with electro-pneumatic actuators. This is a challenging application because the VGT is an important part of the engine air path and the latter is responsible for intake and exhaust air quality and exhaust emissions control. With government regulations on vehicle pollutant emissions getting stringent by the year, VGT control requirements have also increased. These regulations and requirements can only be fulfilled with precise dynamic control of the VGT through its actuator. The demands on actuator control include robustness against uncertainty in operating conditions, fast and smooth positioning without vibration, limited number of measurements. Added constraints such as nonlinear dynamic behavior of the actuator, friction and varying aerodynamic forces in the VGT render classical control methods ineffective. These are the main problems that form the core of this thesis.In this work, we have addressed the above mentioned problems, using model based control complemented with robust control methods to overcome operational uncertainties and parametric variations. In the first step, a detailed physical model of an electro-pneumatic actuator has been developed; taking into account the nonlinear characteristics originating from air compressibility and friction. Means to compensate for aerodynamic force have been studied and implemented in the next step. These include model parametric adaptation and one dimensional CFD (Computational Fluid Dynamics) modeling. The complete model has been experimentally validated and a sensitivity analysis has been conducted to identify the parameters which have the greatest impact upon the actuator's behavior. The detailed simulation model has then been simplified to make it suitable for control purposes while keeping its essential behavioral characteristics (i.e. transients and dynamics). Next, robust controllers have been developed around the model for the control objective of accurate actuator positioning in presence of operational uncertainty. An important constraint in commercial actuators is that they provide output feedback only, as they are only equipped with low-cost position sensors. This hurdle has been overcome by introducing observers in the control loop, which estimate other system states from the output feedback. The estimation and control algorithms have been validated in simulation and experimentally on diesel engine test benches.
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Cerqueira, Marcio Mendes. "Observadores de Estados para Sistemas de Medição Indireta e Controle RLQD-GA". Universidade Federal do Maranhão, 2010. http://tedebc.ufma.br:8080/jspui/handle/tede/432.
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Previous issue date: 2010-02-05Conselho Nacional de Desenvolvimento Científico e Tecnológico
Motivated by the necessity of efficient algorithms, it s presented the development of a methodology for the design and analysis of state observers in open and closed loops that are dedicated to monitoring and control of dynamic systems. The development of observers are based on OE models, description in state space and Kalman filter. The models are evaluated for temperature control of a aluminum cube that is inside of a sterilizer oven. In addition to the models assessment in terms of its ability to represent behavior of plants, these models also evaluated for the design of discrete linear quadric regulator DLQR that are tuned by genetic algorithms. The monitoring models are evaluated for open and closed loops structures that are represented by algorithms in terms of difference equations, these algorithms are seen as software core for the indirect measurement systems.
Motivado pela necessidade de algoritmos eficientes, apresenta-se o desenvolvimento de uma metodologia para projeto e análise de observadores de estado em malhas aberta e fechada que são dedicados a monitoração e controle de sistemas dinâmicos. O desenvolvimento dos observadores estão fundamentados em modelos OE, descrição no espaço de estados e filtro de Kalman. Os modelos são avaliados para o controle da temperatura de um cubo de alumínio que encontra-se no interior de uma estufa. Além das avaliações dos modelos em termos de sua habilidade em representar comportamento de plantas, estes são também avaliados para o projeto do regulador linear quadrático discreto (RQLD) que são sintonizados por algoritmos genéticos. Aplicação dos modelos para monitoração é avaliada nas estruturas das malhas aberta e fechada que são representadas por algoritmos em da equação à diferença, tendo em vistas o desenvolvimento de núcleos de software para os sistemas de medição indireta.
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Baptista, Ana Catarina Borges. "Observar ou ver? Aprendizagem da geometria espacial". Master's thesis, 2019. http://hdl.handle.net/10451/39482.
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Relatório da Prática de Ensino Supervisionada, Mestrado em Ensino de Artes Visuais, Universidade de Lisboa, Instituto de Educação, 2019O presente relatório, realizado no âmbito da Prática de Ensino Supervisionada, descreve a implementação de uma Unidade de Trabalho intitulada “Aprender a observar – o Sistema Axonométrico”, numa turma do 7.º ano de escolaridade do 3.º Ciclo do ensino Básico dos Salesianos de Manique-Escola. Esta investigação, que decorreu no 2.º Período do ano letivo 2017/2018, teve como objetivo realizar em sala de aula determinados exercícios de Desenho de Observação que desenvolvessem nos alunos a perceção espacial e a sua capacidade de abstração, que os ajudasse a entender a Geometria Espacial, mais concretamente o Sistema Axonométrico. Como fundamento para a investigação, apresentam-se as perspetivas de ensino de Joaquim Pinto Vieira, Betty Edwards e Kimon Nicolaides, assim como as teorias de desenvolvimento cognitivo de Jean Piaget, Viktor Lowenfeld, Marthe Berson e Georges Henry Luquet. A presente Unidade de Trabalho permitiu aos alunos compreender mais facilmente os conteúdos relativos à Geometria Espacial, desenvolvendo assim a sua capacidade de atuar com o hemisfério direito do cérebro. Os resultados obtidos indicam que a realização de exercícios de Desenho de Observação ajudou efetivamente no desenvolvimento da perceção espacial dos alunos, ajudando-os a colmatar as principais dificuldades referentes à compreensão do Sistema Axonométrico.
This report, carried out within the framework of the Supervised Teaching Practice, describes the implementation of a Work Unit entitled "Learning to observe - the Axonometric System", in a class of the 7th year of schooling in the 3rd cycle of Basic Education of the Salesianos de Manique – Escola. This research, which took place in the 2nd Period of the 2017/2018 school year, aimed to carry out in the classroom certain exercises of Observation Drawing that developed in the students the spatial perception and its capacity of abstraction that helped them to understand the Spatial Geometry, more concretely the Axonometric System. As a basis for the research, we present the teaching perspectives of Joaquim Pinto Vieira, Betty Edwards and Kimon Nicolaides, as well as the cognitive development theories of Jean Piaget, Viktor Lowenfeld, Marthe Berson and Georges Henry Luquet. The present Unit of Work allowed the students to understand more easily the contents related to Space Geometry, thus developing their ability to act with the right hemisphere of the brain. The obtained results indicate that the accomplishment of exercises of Observation Drawing helped effectively in the development of the students' spatial perception, helping them to overcome the main difficulties regarding the understanding of the Axonometric System.
Livros sobre o assunto "Geometric observers"
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Zheng, Gang, e Driss Boutat. Observer Design for Nonlinear Dynamical Systems: Differential Geometric Methods. Springer International Publishing AG, 2022.
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Zheng, Gang, e Driss Boutat. Observer Design for Nonlinear Dynamical Systems: Differential Geometric Methods. Springer International Publishing AG, 2021.
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Nolte, David D. The Lens of Gravity. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198805847.003.0007.
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This chapter describes how gravity provided the backdrop for one of the most important paradigm shifts in the history of physics. Prior to Albert Einstein’s general theory of relativity, trajectories were paths described by geometry. After the theory of general relativity, trajectories are paths caused by geometry. This chapter explains how Einstein arrived at his theory of gravity, relying on the space-time geometry of Hermann Minkowski, whose work he had originally harshly criticized. The confirmation of Einstein’s theory was one of the dramatic high points in twentieth-century history of physics when Arthur Eddington journeyed to an island off the coast of Africa to observe stellar deflections during a solar eclipse. If Galileo was the first rock star of physics, then Einstein was the first worldwide rock star of science.
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Kokubo, N., S. Okayasu e K. Kadowaki. Multi-Vortex States in Mesoscopic Superconductors. Editado por A. V. Narlikar. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780198738169.013.3.
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This article investigates multi-vortex states in mesoscopic amorphous superconductors with different geometries by means of scanning SQUID microscopy. It first describes the setup of the scanning SQUID microscope used in magnetic imaging of superconducting vortices before discussing the physical properties of amorphous superconducting thin films. It then presents the results of experiments showing the formation of multi-vortex states in mesoscopic dots of weak pinning, amorphous MoGe thin films, along with the formation of vortex polygons and concentric vortex rings in mesoscopic disks. It also considers the concept of multiple vortex shells and its applicability to vortex patterns observed in mesoscopic circle and square dots. The article highlights some of the key features of mesoscopic superconducting dots, including commensurability effect, multiple shell structures, repeated packing sequences, inclusion structural hierarchy, and pinning effect.
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Wade, Nicholas J. Early History of Illusions. Oxford University Press, 2017. http://dx.doi.org/10.1093/acprof:oso/9780199794607.003.0001.
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Illusions are considered in the context of the history of vision rather than the history of psychology. For much of its long history, the study of vision has been confined to naturalistic observation, and many motion illusions were observed in the natural world. With the move to the laboratory, the oddities of visual perception multiplied, and they received ever more detailed scrutiny. This survey examines the origins of research on visual illusions in both the natural world and the laboratory. It commences with celestial illusions and pictorial representation then proceeds to subjective visual phenomena and spatial illusions like ambiguous figures and geometrical optical illusions. However, most attention is paid to motion illusions; these include visual persistence and stroboscopic motion, induced motion, motion aftereffects, visual vertigo, and autokinetic sensations. The basis for the explosion of research on visual illusions in the nineteenth century is speculated upon.
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Palacios Murillo, Jamil Ignacio. Edificaciones y el control térmico de los muros exteriores. CIDEPRO EDITORIAL, 2021. http://dx.doi.org/10.29018/978-9942-823-93-9.
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El sector residencial español presenta un alto índice en la demanda del consumo energético. No obstante, la rehabilitación energética como principal respuesta se ha venido dando en el país de una forma muy ligera, en el que se requiere de un mayor control y cuidado en las envolventes de los edificios, lo que permitiría reducir esta demanda energética como principal problema. La realización de la presente obra, propone el estudio y análisis de los edificios construidos previos a la Normativa de ahorro energético NBE-CT-79, partiendo de sus envolventes como principal caso de estudio. Esta investigación se desarrollará a través de herramientas informáticas que permitan observar el comportamiento en sus particulares climas, como los más fríos en invierno a los más calurosos en verano. Basándose así en proveerle al edificio un mejoramiento en sus materiales a través del estudio de una mayor tasa de aislamiento según sus condiciones ambientales.Como conclusión principal, se presenta la necesidad de implementar la rehabilitación energética del sector residencial en función de sus condiciones climatológicas de su ubicación, de su realidad constructiva y de su geometría, donde se evaluará todos los flujos energéticos que intervengan durante el periodo de un año.
Capítulos de livros sobre o assunto "Geometric observers"
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Kojima, Takanori, Rika Mochizuki, Reiner Lenz e Jinhui Chao. "Riemann Geometric Color-Weak Compensation for Individual Observers". In Lecture Notes in Computer Science, 121–31. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-07440-5_12.
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Keller, H., e H. Fritz. "Design of Nonlinear Observers by a Two-Step-Transformation". In Algebraic and Geometric Methods in Nonlinear Control Theory, 89–98. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-009-4706-1_6.
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Krüger, Nina, Jan Brüning, Leonid Goubergrits, Matthias Ivantsits, Lars Walczak, Volkmar Falk, Henryk Dreger, Titus Kühne e Anja Hennemuth. "Deep Learning-Based Pulmonary Artery Surface Mesh Generation". In Statistical Atlases and Computational Models of the Heart. Regular and CMRxRecon Challenge Papers, 140–51. Cham: Springer Nature Switzerland, 2024. http://dx.doi.org/10.1007/978-3-031-52448-6_14.
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AbstractProperties of the pulmonary artery play an essential role in the diagnosis and treatment planning of diseases such as pulmonary hypertension. Patient-specific simulation of hemodynamics can support the planning of interventions. However, the variable complex branching structure of the pulmonary artery poses a challenge for image-based generation of suitable geometries. State-of-the-art segmentation-based approaches require an interactive 3D surface reconstruction to prepare the simulation geometry. We propose a deep learning approach to generate a 3D surface mesh of the pulmonary artery from CT images suitable for simulation. The proposed method is based on the Voxel2Mesh algorithm and includes a voxel encoder and decoder as well as a mesh decoder to deform a prototype mesh. An additional centerline coverage loss facilitates the reconstruction of the branching structure. Furthermore, vertex classification allows for the definition of in- and outlets. Our model was trained with 48 human cases and tested on 10 human cases annotated by two observers. The differences in the anatomical parameters inferred from the automatic surface generation correspond to the differences between the observers’ annotations. The suitability of the generated mesh geometries for numerical flow simulations is demonstrated.
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Martínez-Guerra, Rafael, Claudia A. Pérez-Pinacho e Gian Carlo Gómez-Cortés. "A Model-Free Sliding Observer to the Synchronization Problem Using Geometric Techniques". In Synchronization of Integral and Fractional Order Chaotic Systems, 43–62. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-15284-4_3.
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Li, Yuanhao, Yu Zhang, Yongliang Lin e Jiayan Wan. "Nonlinear Disturbance Observer-Based Sliding-Mode Geometric Controller for Fully-Actuated Hexarotor". In Proceedings of 2021 Chinese Intelligent Automation Conference, 534–45. Singapore: Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-16-6372-7_59.
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Virajh Dias, A. A., H. M. J. M. K. Herath e L. K. N. S. Kulathilake. "Landform Geometry for Restoration of Mountain Roads and Landslide Hazard Resilience". In Progress in Landslide Research and Technology, Volume 1 Issue 1, 2022, 327–39. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-16898-7_25.
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AbstractTraveling on a mountainous road is attractive but questionable under aggressive climatic conditions such as extreme rainstorms. Roads are often designed in different geological complexity overlaying upper and lower terrains. The complexity of slope geometries, potential deformities, ground discontinuities, soil-rock composite nature, factors incorporated in structural integrity, the complexity associated with infrastructure developments, and unstable landform have long been causes of the increasing cost of road constructions in hills. In many instances, landform geometries and the natures of slope observed in-situ allow us to understand many salient features that we need to know in the design to mitigate landslide threats. The extent to which we make the collective effort to gather many features of landforms and their static representations concludes its validity. Findings are more forced to be based on geometrical evidence of slopes and cross-checked with an appropriate design criterion. A provision should describe a design or construction method that is deemed to comply with the site-specific conditions. Such an approach will save the enormous cost of investigations, design, and simplification for numerical evaluations, and also contribute to an indirect approach to road restoration and improve an appropriate approach for resilience to landslide hazards.
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Caulliez, Guillemette. "Statistics of Geometric Properties of Breaking Wind Waves Observed in Laboratory". In Gas Transfer at Water Surfaces, 31–37. Washington, D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/gm127p0031.
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Dymnikova, Irina. "Λ υ μ Geometries from the Point of View of Different Observers". In Beyond the Desert 2003, 521–37. Berlin, Heidelberg: Springer Berlin Heidelberg, 2004. http://dx.doi.org/10.1007/978-3-642-18534-2_33.
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Hasaballa, Abdallah I., Thiranja P. Babarenda Gamage, Vicky Y. Wang, Debbie Zhao, Charlène A. Mauger, Kathleen Gilbert, Zhinuo J. Wang et al. "Sensitivity of Myocardial Stiffness Estimates to Inter-observer Variability in LV Geometric Modelling". In Functional Imaging and Modeling of the Heart, 287–95. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-78710-3_28.
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Chatzistamatis, Stamatis, George E.Tsekouras e Christos-Nikolaos Anagnostopoulos. "The Quality in 3D Acquisition of Cultural Heritage Assets: Challenges and Risks". In 3D Research Challenges in Cultural Heritage III, 65–76. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-35593-6_4.
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AbstractCultural heritage is an integral part of history and in order to better preserve, manage and highlight our cultural heritage it is necessary to first proceed to digitize and document it. Geometric documentation of a cultural heritage asset is the process of collecting, processing, rendering, and recording data to determine the location and actual form, shape, and size of a monument in three-dimensional space at a given time. This chapter presents the modern methods and technologies for the 3D acquisition of cultural heritage assets and discusses the related challenges and risks. Moreover, we are presenting the possible quality aspects observed in the fieldwork that arise from the equipment, the environmental conditions that prevail during the surveying, the object itself, the personnel expertise and the stakeholder conditions.
Trabalhos de conferências sobre o assunto "Geometric observers"
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ROMERO, C., e J. B. FORMIGA. "GEOMETRIC AND KINEMATICAL ASPECTS OF RINDLER OBSERVERS". In Proceedings of the MG11 Meeting on General Relativity. World Scientific Publishing Company, 2008. http://dx.doi.org/10.1142/9789812834300_0144.
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Man, T. M., e David L. MacAdam. "Three-dimensional scaling of OSA uniform color scales". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1987. http://dx.doi.org/10.1364/oam.1987.fc1.
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Three young observers judged the differences they perceived between all pairs of twenty-five colors in twelve different oblique planes formed by the OSA uniform color scales. Each observer repeated each judgment at least three times. The rms variances of the judgments ranged from 5 to 15%. For each set of colors, a 3-D configuration of points was determined for each observer, in which distances between pairs of points are, as nearly as possible, proportional to the judgments raised to a power P. The optimal value of P differed from observer to observer and from set to set of colors. For two of the observers, P was always >1.0 (as great as 1.61). For the third observer, P was 1.29 or less (as low as 0.76). The resulting rms errors of fit in the configurations were 13.8 ± 4.8%. The most successful configurations indicate (with some remarkable agreements between observers) strong curvatures of the surfaces on which the optimal configurations of the sets of twenty-five points are located. These results indicate that non-Euclidean space is needed to represent perceived color differences by geometric distances within the attainable precision of judgments.
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Orbay, Gunay, Luoting Fu e Levent Burak Kara. "Shape Spirit: Deciphering Form Characteristics and Emotional Associations Through Geometric Abstraction". In ASME 2013 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/detc2013-13274.
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Understanding and tailoring the visual elements of a developing product to evoke a desired emotional response and aesthetic perception is a key challenge in industrial design. To date, computational approaches to assist this process have either relied on stiff geometric representations, or focused on superficial features that exclude often elusive shape characteristics. In this work, we aim to study the relationship between product form and consumer emotions through a visual deconstruction and abstraction of existing final products. In particular, we attempt to answer three questions: (1) Do observers’ aesthetic judgments rely on the product as a whole, including fine geometric details, superficial surface features, and brand-revealing icons, or are large, prominent shape characteristics sufficient to make this determination? (2) Is it possible to isolate shape features that give rise to specific emotional responses? (3) Is there a relationship between consumers’ ability to recognize a brand and the emotional attributes they associate with that brand. At the heart of our investigation is a shape analysis method that produces a spectrum of abstractions for a given 3D computer model. This produces a hierarchical simplification of an end product, whereby consumer response to geometric elements can be statistically studied across different products, as well as across the different abstractions of one particular product. The results of our study show that emotional responses evoked by coarse product “impressions” are strongly correlated with those evoked by final production models. This, in turn, highlights the importance of early aesthetic assessment and exploration before committing to detail design efforts.
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Devalois, Karen K., V. Lakshminarayanan, Rolf W. Nygaard e Sarah Schlussel. "Relative position comparisons between dissimilar patterns". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1988. http://dx.doi.org/10.1364/oam.1988.tur5.
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We have previously shown1 that observers can accurately detect changes in the relative position of a vertical intersector on a horizontal line segment. Performance is not seriously compromised by varying test pattern size relative to that of the reference or by rotating the entire test figure. Here we report the effects of either reflecting the test pattern left-right around its midpoint, inverting it, or rotating it by 90°. Despite marked changes in pattern appearance, neither manipulation significantly degrades observers' ability to make the required judgment. A sufficient solution to each of these tasks would be to estimate and compare the lengths of the appropriate line segments. To determine whether this is the necessary strategy, we utilized a test figure in which the intersection is represented by a significant gap centered around the intercept. Since equal absolute amounts are removed from each side, the ratios of line segment lengths are no longer comparable. In addition, the geometric cues provided by a 2-D intersector are no longer available. Performance on this task is surprisingly good. These data imply that simple perceptual models may not be adequate to account for the results.
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Lappin, Joseph S., Warren D. Craft e Theodore J. Payne. "Stereoscopic visual acuity for bending motion in 3-D space". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/oam.1986.mi5.
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Human stereoscopic vision may provide precise information about 3-D structure. Fundamental theoretical questions concern the specific geometric properties of monocular stimulation that carry visual information for stereopsis. Recent evidence on the stereoscopic acuity for moving patterns indicates that perceived 3-D structure derives from disparities between the monocular optical fields, rather than from disparities between retinal positions of individual points, and from the self-congruence of spatiotemporal form.1 The spatial structures in previous experiments, however, were rigidly moved. The present experiment tested the necessity for rigid motion. Optical patterns consisted of four dots (initially collinear and equally spaced—30 min of arc) undergoing bending motion in a plane tilted in depth. The task was to detect the depth displacement of a single dot from this continually changing curve. Observers detected displacements < 10-sec of arc disparity as accurately for bending curves as for stationary straight lines. Thus, stereoscopic acuity derives from the self-congruence of even nonrigidly moving form.
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Grinstein, Benjamin, e Detlef R. Nolte. "Bulk observers in non-factorizable geometries". In International Europhysics Conference on High Energy Physics. Trieste, Italy: Sissa Medialab, 2001. http://dx.doi.org/10.22323/1.007.0162.
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PFEIFER, C., e M. WOHLFARTH. "FINSLER GEOMETRIC EXTENSION OF EINSTEIN GRAVITY AND OBSERVER TRANSFORMATIONS". In Proceedings of the MG13 Meeting on General Relativity. WORLD SCIENTIFIC, 2015. http://dx.doi.org/10.1142/9789814623995_0094.
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Mahony, Robert, e Tarek Hamel. "A geometric nonlinear observer for simultaneous localisation and mapping". In 2017 IEEE 56th Annual Conference on Decision and Control (CDC). IEEE, 2017. http://dx.doi.org/10.1109/cdc.2017.8264002.
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O'Brien, Sean G. P., Jochen Trumpf, Viorela Ila e Robert Mahony. "A Geometric Observer for Scene Reconstruction Using Plenoptic Cameras". In 2018 IEEE Conference on Decision and Control (CDC). IEEE, 2018. http://dx.doi.org/10.1109/cdc.2018.8618954.
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Goor, Pieter van, Robert Mahony, Tarek Hamel e Jochen Trumpf. "A Geometric Observer Design for Visual Localisation and Mapping". In 2019 IEEE 58th Conference on Decision and Control (CDC). IEEE, 2019. http://dx.doi.org/10.1109/cdc40024.2019.9029435.
Texto completo da fonteRelatórios de organizações sobre o assunto "Geometric observers"
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Little, Charles, e David Biedenharn. Technical assessment of the Old, Mississippi, Atchafalaya, and Red (OMAR) Rivers : channel geometry analysis. Engineer Research and Development Center (U.S.), agosto de 2022. http://dx.doi.org/10.21079/11681/45147.
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The Old River Control Complex (ORCC) consists of the Low Sill, Auxiliary, and Overbank structures as features of the Old River Control Structure (ORCS) and the privately owned hydro-electric power plant. Operations of the ORCC manage the hydrologic connectivity between the Mississippi River and the Atchafalaya River/Red River systems. The morphology of the Old, the Mississippi, the Atchafalaya, and the Red Rivers (OMAR) has been influenced by the flow distribution at the ORCC, as well as the accompanying bed sediments. A geomorphic assessment of the OMAR is underway to understand the morphological changes associated with operation of the ORCC. Supporting the geomorphic assessment, a channel geometry analysis herein documents observed adjustments of the affected river channels. Historical hydrographic survey data were used in the Geographic Information System to create river channel geometric models, which inform the analysis. Geometric parameters for cross sections and volume polygons were computed for each survey and evaluated for morphological trends which may be ascribed to the influence of the ORCC. Additionally, the geometric parameters for the Atchafalaya River were used to extend the geometry analyses from the 1951 Mississippi River Commission report on the Atchafalaya River, which was the primary catalyst for the initial development of the ORCS.
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Lauth, Timothy, David Biedenharn, Travis Dahl, Casey Mayne, Keaton Jones, Charles Little, Joseph Dunbar, Samantha Lucker e Nalini Torres. Technical assessment of the Old, Mississippi, Atchafalaya, and Red (OMAR) Rivers : geomorphic assessment. Engineer Research and Development Center (U.S.), agosto de 2022. http://dx.doi.org/10.21079/11681/45143.
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This report documents the geomorphic assessment component of the Old River, Mississippi River, Atchafalaya River, and Red River System Technical Assessment. The overall objectives of the geomorphic assessment are to utilize all available data to document the historic trends in hydrology, sedimentation, and channel geometry for the rivers in the vicinity of the Old River Control Complex and to summarize the changes observed at locations where repetitive datasets exist and at key reaches that are determined during the study. The geomorphic assessment tasks include data compilation, geometric data analysis, gage and discharge analysis, dredge record analysis, sediment data analysis, development of an events timeline, and integration of results. Geomorphic reaches were developed, and the morphological trends during different time periods were identified. The geomorphic assessment highlighted the importance of considering spatial and temporal variability when assessing morphological trends.
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Bubenik e Nestleroth. L51619 Effects of Loading on the Growth Rates in Deep Stress-Corrosion Cracks. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), agosto de 1990. http://dx.doi.org/10.55274/r0010094.
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With the development of improved techniques for detection of stress corrosion cracks in existing pipelines, the pipeline industry is faced with the problem of estimating the growth rates of these cracks. Current efforts in model development are addressing the problem but, in order to verify these models, accurate average crack velocity data are needed (average crack velocity being defined as the average rate of crack growth with time, crack velocity is the instantaneous rate of crack tip dissolution.) Currently available data are limited and are based primarily on either slow-strain rate tests or tapered tensile tests. The loading conditions in the former are unrepresentative of actual operating conditions while the crack depths in the latter are much shallower than those observed in service. Some fracture mechanics data also are available for this system but the specimen and crack geometry used in these tests are not similar to the geometry of the field failures*. In addition, results of recent PRCI research suggest that the stress intensity parameter, K, which is used to relate different cracking geometries, is a poor crack driving force parameter for SCC in line pipe steels. The overall objective of this work is to obtain accurate average crack velocity data as a function of crack depth and loading conditions. The program is divided into two tasks: Task 1 - Effect of Crack Depth and Cyclic Loading Conditions on Crack Growth and Task 2 - Inhibition of Crack Growth.
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Alizadeh, Philipp, Kevin Oberle e Rainer Dahlmann. Process transfer of PECVD gas barrier coatings between PE-HD and PP hollow bodies. Universidad de los Andes, dezembro de 2024. https://doi.org/10.51573/andes.pps39.gs.nn.2.
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This study investigates the plasma enhanced chemical vapor deposition (PECVD) coating process transfer between PE and PP substrates. An inverse relationship is observed between the barrier improvement factor (BIF) and applied energy density (E), with PE showing a stronger response. The same process gas ratio optimizes both materials, suggesting geometry influences the barrier effect more than material. However, the barrier on PP is limited, indicating poorer compatibility to functionalization. The development of the intermediate layer did not improve the barrier performance. FESEM analyses and scratch tests suggest material damage during coating application. Further research is needed to optimize the coating process.
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Soret, Clement, Melissandre Bonnaudet e Mures Zarea. PR-306-143732-R01 Adv Material Charact of Dent and Gouge Samples Imprvd Strain Eval. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), dezembro de 2018. http://dx.doi.org/10.55274/r0011544.
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This report provides a more accurate micro-hardness vs. strain correlation based on the larger strains achievable with interrupted tensile tests on notched specimens from two modern steels des-ignated as Pipe #1 and Pipe #2 and two vintage steels designated as Pipe #3 and Pipe #4. These pipes were used to evaluate the mechanical strength of dent and gouge defects in PRCI projects MD-4-1, MD-4-6 and DOT #339. Interrupted tensile tests were performed on specimens with dif-ferent geometries, which allowed to identify accurate parameters for a constitutive mechanical be-havior law that represents both pipe materials. Then FE numerical simulation was used to determine plastic strains levels from diameter reduction of the specimens observed during interrupted tensile tests.
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Kyriakides. L51559 Factors Affecting Pipe Collapse Phase II. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), janeiro de 1988. http://dx.doi.org/10.55274/r0010129.
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Offshore pipelines installed in moderate to deep water depths (1,500 ft. and beyond) must, by necessity, be designed to withstand ambient external pressure. Improper design can lead to catastrophic collapse of large sections of the structure. During the installation process the line can experience significant bending and tension loads in addition to external pressure. These additional loads can significantly reduce the collapse pressure of the pipe. Special purpose combined loading test facilities were designed and built in which pressures equivalent to 10,000 ft. and beyond were simulated. The test facilities were used to establish load interaction collapse envelopes for the two types of combined loading mentioned. Bending/pressure collapse envelopes were generated for tubes with diameter to thickness ratios of 34.7, 24.5, 18.2 and 17.3. Tension/pressure collapse envelopes were generated for tubes with diameter to thickness ratios of 38.3, 24.5, 18.2 and 12.2. The geometric imperfections and material parameters were recorded for all test specimen's prior to collapse. Under bending/pressure loading the tube response, the critical collapse loads and the nature of the instabilities observed were found to depend on the loading path. Collapse was found to be relatively insensitive to the history for tension/pressure loading.
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Akbari, Chirag, Ninad Gore e Srinivas Pulugurtha. Understanding the Effect of Pervasive Events on Vehicle Travel Time Patterns. Mineta Transportation Institute, dezembro de 2023. http://dx.doi.org/10.31979/mti.2023.2319.
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The COVID-19 pandemic has disrupted daily activities and travel patterns, affecting personal and commercial trips. This study investigates the effect of different stages of the pandemic on travel time patterns. Eighty-six geographically distributed links (sections of road) in Mecklenburg County and Buncombe County, North Carolina, were selected for analysis. The selected links accounted for the variation in road geometry, land use, and speed limit. Travel time data for three years (i.e., 2019, 2020, and 2021) were extracted from a private data source at 5-min intervals. Travel time reliability (TTR) and travel time variability (TTV) are estimated for different phases of the pandemic and compared to analyze the effect of COVID-19 on TTR and TTV. The seasonal arithmetic integrated moving average (SARIMA) model was developed to investigate the effect of COVID-19 on average daily travel time patterns. Unreliable and uncertain travel times were observed on lower speed limit links during the off-peak hours while reliable and certain travel times were observed during morning and evening peak hours of the COVID-19 pandemic. This highlights that the COVID-19 pandemic significantly affected the scheduling of trips. For higher speed limits, travel times were reliable and certain during off-peak and peak hours. Among the different phases of COVID-19, significant improvement in TTR and TTV was observed during Phase II, which could be attributed to stay-at-home directives. Trucks followed a similar pattern as passenger cars. Post-COVID-19, i.e., for 2021, travel times were reliable and certain for most links during the morning peak hours. The SARIMA model revealed a significant effect of COVID-19 on average daily travel time patterns. Stable travel time patterns were noted during Phase II of COVID-19. Moreover, a maximum reduction in travel time was observed during Phase II of the COVID-19 pandemic. The findings emphasize the influence of government norms and regulations on travel time patterns during pervasive events such as COVID-19.
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Asenath-Smith, Emily, Ross Lieblappen, Susan Taylor, Reed Winter, Terry Melendy, Robert Moser e Robert Haehnel. Observation of crack arrest in ice by high aspect ratio particles during uniaxial compression. Engineer Research and Development Center (U.S.), fevereiro de 2022. http://dx.doi.org/10.21079/11681/43145.
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In nature, ice frequently contains dissolved solutes or entrapped particles, which modify the microstructure and mechanical properties of ice. Seeking to understand the effect of particle shape and geometry on the mechanical properties of ice, we performed experiments on ice containing 15 wt% silica spheres or rods. Unique to this work was the use of 3-D microstructural imaging in a -10ºC cold room during compressive loading of the sample. The silica particles were present in the ice microstructure as randomly dispersed aggregates within grains and at grain boundaries. While cracks originated in particle-free regions in both sphere- and rod-containing samples, the propagation of cracks was quite different in each type of sample. Cracks propagated uninhibited through aggregates of spherical particles but were observed to arrest at and propagate around aggregates of rods. These results imply that spherical particles do not inhibit grain boundary sliding or increase viscous drag. On the other hand, silica rods were found to span grains, thereby pinning together the microstructure of ice during loading. These results provide insights into mechanisms that can be leveraged to strengthen ice.
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McAlpin, Tate, John Petrie, Gaurav Savant, Daniel Savant, Angela Hogan e Gary Brown. Numerical modeling of supercritical flow in the Los Angeles River : part II : existing conditions Adaptive Hydraulics numerical model study. Engineer Research and Development Center (U.S.), dezembro de 2024. https://doi.org/10.21079/11681/49487.
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The Los Angeles District of the US Army Corps of Engineers is assisting the City of Los Angeles with restoration efforts on the Los Angeles River. The city wishes to restore portions of the channelized river to a more natural state with riparian green spaces for both wildlife and public recreation usage. The Los Angeles River provides an important role from a flood-control perspective, and functionality needs to be preserved when contemplating system modifications. This report details the development of an Adaptive Hydraulics numerical model capable of modeling this complex system consisting of both subcritical and supercritical flow regimes. The model geometry was developed to represent the existing conditions system for future usage in quantifying the impact associated with proposed restoration alternatives. Due to limited hydraulic data in the study area, an extensive model validation to observed data was not possible. A model was developed and simulated using the most appropriate input parameters. Given the lack of measured data for model validation, an extensive number of sensitivity simulations were completed to identify the most impactful parameters and quantify a reasonable level of confidence in the model results based on the uncertainty in the model inputs.
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Doyle, Jesse D., Nolan R. Hoffman e M. Kelvin Taylor. Aircraft Arrestor System Panel Joint Improvement. U.S. Army Engineer Research and Development Center, agosto de 2021. http://dx.doi.org/10.21079/11681/41342.
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Aircraft Arresting Systems (AAS) for military applications utilize sacrificial panels made of Ultra-High Molecular Weight polyethylene (UHMWPE) that are embedded into the pavement beneath the AAS cable to protect the pavement from cable damage. Problems have been observed with the materials and practices used to seal the UHMWPE panel joints from water and debris. Data obtained from laboratory and field studies were used make improvements to current practice for sealing UHMWPE panel joints. The study evaluated four joint-sealant materials, eight alternative surface treatment and preparation techniques to promote adhesion to UHMWPE, and seven joint-edge geometries. Bond-strength testing of joint-sealant specimens was conducted in the laboratory, followed by field evaluation of construction techniques. Field performance of the joint systems was monitored for 24 months after installation. Additionally, a thermal response model was developed to refine the joint design dimensions. Results confirmed that the best material to use was self-leveling silicone joint sealant. It was recommended that a dovetail groove be cut into the edge of UHMW panels to provide positive mechanical interlock and to reduce adhesive failures of the sealant. It was also recommended that the panel-to-panel joint-sealant reservoir be widened to prevent sealant compression damage.