Literatura científica selecionada sobre o tema "Visualisation de gradient"
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Artigos de revistas sobre o assunto "Visualisation de gradient"
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Ashe, Hilary L. "BMP Signalling: Visualisation of the Sog Protein Gradient". Current Biology 12, n.º 8 (abril de 2002): R273—R275. http://dx.doi.org/10.1016/s0960-9822(02)00798-4.
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Harvey, Steven A., e James C. Smith. "Visualisation and Quantification of Morphogen Gradient Formation in the Zebrafish". PLoS Biology 7, n.º 5 (5 de maio de 2009): e1000101. http://dx.doi.org/10.1371/journal.pbio.1000101.
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Wedge, Daniel, Yathunanthan Sivarajah, Eun-Jung Holden, Peter Kovesi, Chris Wijns e Paul Johnston. "Mass anomaly visualisation and depth estimation from full tensor gradient gravity data". ASEG Extended Abstracts 2013, n.º 1 (dezembro de 2013): 1–5. http://dx.doi.org/10.1071/aseg2013ab152.
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Hyde, Georgia, Andrew Fry, Ashok Raghavan e Elspeth Whitby. "Biometric analysis of the foetal meconium pattern using T1 weighted 2D gradient echo MRI". BJR|Open 2, n.º 1 (novembro de 2020): 20200032. http://dx.doi.org/10.1259/bjro.20200032.
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Objectives: Foetal MRI is used to assess abnormalities after ultrasonography. Bowel anomalies are a significant cause of neonatal morbidity, however there are little data concerning its normal appearance on antenatal MRI. This study aims to investigate the pattern of meconium accumulation throughout gestation using its hyperintense appearance on T1 weighted scans and add to the current published data. Methods: This was a retrospective cohort study in a tertiary referral clinical MRI centre. Foetal body MRI scans of varying gestational ages were obtained dating between October 2011 and March 2018. The bowel was visualised on T1 weighted images. The length of the meconium and the width of the meconium at the rectum, sigmoid colon, splenic flexure and hepatic flexure was measured. Presence or absence of meconium in the small bowel was noted. Inter- and intrarater reliability was assessed. Results: 181 foetal body scans were reviewed. 52 were excluded and 129 analysed. Visualisation of the meconium in the large bowel became increasingly proximal with later gestations, and small bowel visualisation was greater at earlier gestations. There was statistically significant strong (r = 0.6–0.8) or very strong (r = 0.8–1.0) positive correlation of length and width with increasing gestation. Interrater reliability was moderate to excellent (r = 0.4–1.0). Conclusion: This study provides new information regarding the pattern of meconium accumulation throughout gestation. With care, the results can be used in clinical practice to aid diagnosis of bowel pathology. Advances in knowledge: The findings of this study provide further information concerning the normal accumulation of foetal meconium on MR imaging, an area where current research is limited.
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Wołosz, Krzysztof J., e Jacek Wernik. "Air Evacuation from the Pressure Accumulator during Work Cycle of the Pneumatic Pulsator". Applied Mechanics and Materials 797 (novembro de 2015): 327–33. http://dx.doi.org/10.4028/www.scientific.net/amm.797.327.
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Practically Applicable Vessel Evacuation is Presented in the Article. the Pressure Accumulatoris a Vessel which is a Part of the Pneumatic Pulsator which is Used for Unclogging Outlets of Silos. Apseudo-Schlieren Visualisation Method of Density Gradient and Values of Mach Number are Shown.There is Also a Time Variation of Outflow Velocity Analysed. Airflow Fluctuates after Time of 50 Ms.The Main Reason could Be the Inertia of the Air Mass and a Large Outlet Diameter Relative to the Mainvessel Dimensions
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Talele, Virendra, Niranjan Sonawane, Omkar Chavan, Akash Divate, Niraj Badhe, Mirza Adil Ansar Beg e Harshal Patil. "Aerodynamic Flow Visualisation Over Surfaces Using Smoke Separation Method from Ansys Fluent". International Journal of Innovative Science and Research Technology 5, n.º 7 (16 de julho de 2020): 32–35. http://dx.doi.org/10.38124/ijisrt20jul108.
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In the present study, three workbench problem for turbulence modeling with high Reynolds number is used to determine the behavior of fluid flow around the surfaces. The cases for simulation is developed using Ansys workbench CFD fluent module. The computational results are obtained using solution sets of high Reynolds number with the LagrangianEulerian (LE) approach of point particle tracking system in Nevers stoke RANS Equation. The effect of flow pattern around the surface and its kinetic behavior of fluid is evaluated in post-process method of results. By observation, it has been tabulated that fluid flow separation is arousal at the corner end of all surfaces which happens due to evoking of a large adverse pressure gradient.
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Medved, M. S., S. D. Rud, G. E. Trufanov e D. S. Lebedev. "The intraoperative visualisation technique during lead implantation into the cardiac conductive system: aspects of computed tomography: prospective study". Diagnostic radiology and radiotherapy 14, n.º 3 (5 de outubro de 2023): 46–52. http://dx.doi.org/10.22328/2079-5343-2023-14-3-46-52.
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INTRODUCTION: The lead implantation into the cardiac conduction system (CCS) is the most physiological method of pacing nowadays. «The method of intraoperative visualization and control of the lead position for permanent electrocardiostimulation during implantation of the lead in the CCS» has been developed for reduce the number of non-targeted implantations. This method based on the integration into the angiograph system 3D-reconstruction of the heart converted to computed tomography (CT) in the form of a mask against the background of fluoroscopy. CT is an important stage of the intraoperative visualization technique (IVT).OBJECTIVE: The aim of the study was to adapt the protocol of CT examination of the heart with contrast to construct a partially segmented 3D-reconstruction of the heart on an angiographic complex for subsequent use during of the lead implantation in the CCS within the framework of the author’s IVT.MATERIALS AND METHODS: As part of the development of the IVT, 21 CT studies of the heart were selected from own database. The step of the gradient of the density difference of the contrasted blood is about 10 HU, the range of the difference of densitometric parameters of the «left ventricle (LV) — right ventricle (RV)» from 0 HU to 200 HU. As well as selected 11 CT studies of the heart. The step of the gradient of the difference of densitometric indicators the contrasted blood in «the RV cavity — myocardium» is about 10 HU, the range is from 0 HU to 100 HU. All CT scans are alternately loaded into the angiograph, followed by the creation of a 3D model of the heart using basic software.RESULTS: It’s necessary to exceed the degree of contrast of the LV cavity over the RV cavity by at least 80 HU to perform partial segmentation on the left and right chambers of a 3D-model of the heart in an angiographic complex that does not have a specialized segmentation module. A sufficiently large part of the left ventricular cavity (LV) disappears with a smaller gradient when the right ventricular cavity (RV) is suppressed. The minimum gradient of «the ventricular cavity — myocardium» is at least 20 HU. The boundaries of the right ventricular edge of the interventricular septum (IVS) are not visualized with a smaller contrast gradient. It’s important for determining the insertion place of the lead into the IVS.CONCLUSION: It’s necessary to exceed the contrast of the LV cavities above the RV cavity by at least 80 HU, the RV cavity above the myocardium by at least 20 HU to perform partial segmentation on the left and right chambers of a 3D-model of the heart in an angiographic complex that does not have a specialized segmentation module
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Hauenstein, Jacob D., e Timothy S. Newman. "Achieving Better Energy Efficiency in Volume Analysis and Direct Volume Rendering Descriptor Computation". Computers 13, n.º 2 (13 de fevereiro de 2024): 51. http://dx.doi.org/10.3390/computers13020051.
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Approaches aimed at achieving improved energy efficiency for determination of descriptors—used in volumetric data analysis and one common mode of scientific visualisation—in one x86-class setting are described and evaluated. These approaches are evaluated against standard approaches for the computational setting. In all, six approaches for improved efficiency are considered. Four of them are computation-based. The other two are memory-based. The descriptors are classic gradient and curvature descriptors. In addition to their use in volume analyses, they are used in the classic ray-casting-based direct volume rendering (DVR), which is a particular application area of interest here. An ideal combination of the described approaches applied to gradient descriptor determination allowed them to to be computed with only 80% of the energy of a standard approach in the computational setting; energy efficiency was improved by a factor of 1.2. For curvature descriptor determination, the ideal combination of described approaches achieved a factor-of-two improvement in energy efficiency.
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D, Nivedhidha, e Dr Sujatha B. "Big Data Visualisation of Heart Disease Prediction Using High Level Ada Boosting Algorithm and Gradient Boosting Algorithm". International Research Journal of Computer Science 11, n.º 04 (5 de abril de 2024): 204–11. http://dx.doi.org/10.26562/irjcs.2024.v1104.12.
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Machine learning and artificial intelligence have been found useful in various disciplines during the course of their development, especially in the enormous increasing data in recent years. It can be more reliable for making better and faster decisions for disease predictions. So, machine learning algorithms are increasingly finding their application to predict various diseases. Constructing a model can also help us visualize and analyze diseases to improve reporting consistency and accuracy. This article has investigated how to detect heart disease by applying various machine learning algorithms. The study in this article has shown a two-step process. The heart disease dataset is first prepared into a required format for running through machine learning algorithms. Medical records and other information about patients are gathered from the UCI repository. The heart disease dataset is then used to determine whether or not the patients have heart disease. Secondly, Many valuable results are shown in this article. The accuracy rate of the machine learning algorithms, such as Logistic Regression, Support vector machine, K-Nearest-Neighbours, Adaboost, and Gradient Boosting Classifier, are validated through the confusion matrix. Current findings suggest that the Logistic Regression algorithm gives a high accuracy rate of 95% compared to other algorithms. It also shows high accuracy for f 1-score, recall, and precision than the other four different algorithms. However, increasing the accuracy rates to approximately 97% to 100% of the machine learning algorithms is the future study and challenging part of this research.
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Zhao, H., e Q. Hu. "3D RECONSTRUCTION AND RENDERING VISUALIZATION OF TUNNEL POINT CLOUD". International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLVIII-3/W1-2022 (27 de outubro de 2022): 93–101. http://dx.doi.org/10.5194/isprs-archives-xlviii-3-w1-2022-93-2022.
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Abstract. This paper presents a method for rapid and automatic visualisation of over-undercutting based on 3D reconstruction and rendering of tunnel point clouds. The method uses model filtering and our improved voxel filtering for point cloud lite to maximise the preservation of the original tunnel point cloud features while streamlining the point cloud. The 3D reconstruction is then completed according to our proposed alpha-shape algorithm with low reconstruction parameters combined with a fast model optimisation model, which achieves high reconstruction accuracy while significantly improving computational efficiency to meet the requirements of the tunneling project. The rendering method is calculated by selecting the RGB values. The darker the colour, the heavier the degree of over-excavation or under-excavation. According to the calculated over-excavation or under-excavation value, the ratio of the point in the over-excavation or under-excavation interval is obtained in turn, and the gradient is rendered by increasing the base colour of each interval proportionally; the kd-tree is then introduced to calculate and visualise the colour information of the reconstructed model. In addition, this paper uses real-world tunnel point cloud data and demonstrates that the method meets expectations through qualitative and quantitative evaluation. Visualisation of the tunnel point cloud is accomplished while maintaining speed, visualising the over-under-excavation situation and providing an outlook for future work.
Teses / dissertações sobre o assunto "Visualisation de gradient"
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Latard, Véronique. "Méthodes de visualisation par gradient d'indice en mécanique des milieux non homogènes : application à la diffusion acoustique et aux écoulements diphasiques". Lille 1, 1998. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/1998/55376-1998-5.pdf.
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Cuvier, Christophe. "Contrôle actif du décollement d’une couche limite turbulente en gradient de pression adverse". Thesis, Ecole centrale de Lille, 2012. http://www.theses.fr/2012ECLI0015/document.
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Le contrôle d’écoulement permet d’éliminer le phénomène de décollement de couches limites, très néfaste pour les performances des machines interagissant avec un fluide (avions, voitures, turbomachines ...). Ces travaux s’intéressent plus particulièrement au contrôle actif d’écoulement au moyen de jets continus. Une maquette permettant de manipuler l’équilibre de la couche limite a été conçue et installée dans la soufflerie du Laboratoire de Mécanique de Lille. La première partie du travail a consisté en la caractérisation de l’écoulement autour du modèle à l’aide de visualisations par fils de laine et par enduit gras, de mesures de répartition de pression, de mesures par anémométrie à fils chauds et par PIV. Ceci a permis de définir la configuration du modèle la plus appropriée pour les études de contrôle mais aussi de connaître précisément les caractéristiques de l’écoulement sélectionné. La configuration retenue correspond à un écoulement en gradient de pression adverse suivi d’une séparation sur le volet, un peu comme sur l’extrados d’une aile d’avion. L’utilisation de sondes de frottement associées à des visualisations aux fils de laine ont permis d’étudier et d’optimiser des actionneurs passifs, puis des actionneurs à jets continus. Certaines des configurations actives optimales ont ensuite été caractérisées plus en détail par une mesure par PIV englobant toute la zone de séparation. Il apparaît que les jets continus ne suppriment pas complètement les mécanismes de la séparation mais réduisent leur intensité et les concentrent plus ou moins près de la paroiFlow control allows to suppress boundary layers separation, which largely deteriorates the performances of machineries which interact with fluid (aircraft, cars, turbomachineries, etc.). This study concentrates more particularly on active flow control with continuous jets. A ramp model which allows to manipulate the boundary layer equilibrium was realized and set in Laboratoire de Mécanique de Lille wind tunnel. The first part of the work was to characterize the flow over the model with wool-tufts and oil-film visualisations, pressure distribution, hot-wire anemometry and PIV measurements. The aim was to define a ramp configuration for the flow control study and to know precisely the characteristics of the retained flow. The selected configuration corresponds to an adverse pressure gradient flow followed by a separation on the flap, which mimics the flow on the suction side of a wing. With friction probes coupled with wool-tufts visualisations, passive actuators and active continuous jets were studied and optimised. Finally, some of the optimum active configurations found were characterized in more details with PIV measurements over the entire separated region. It appears that continuous jets do not suppress the separation mechanisms, but only reduce their intensity and squeeze them more or less against the wall
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Tariq, Sonia. "Developing an optical sensor for the visualisation of pH gradients in marine sediments". Thesis, University of East Anglia, 2015. https://ueaeprints.uea.ac.uk/56901/.
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Many important biogeochemical processes that occur in marine sediments are intimately linked to pH dependent processes, but surprisingly little is known about the details of the pH profiles generated. This is mainly due to the difficulty of obtaining samples and measuring representative profiles. Such profiles have previously been determined using glass-membrane micro-electrodes, but this is slow and electrodes easily break in harsh sediments (insertion is “blind”). Profiles have also been measured using fluorescent dye-based sensors, but their handling needs special light sources and filters and sensor membrane preparation is quite complex, which has restricted its use to laboratory studies. A simple optical pH sensor has been developed for this application by immobilising bromothymol blue in a PVC membrane. This device responds in a pH range suitable for marine sediments. The sensor is simple to use, the dye does not leach and it gives a visible colour readout so when photographed, the pictures can be used to extract Red Green Blue values and converting them to colour index values representing the sensor colour. This can be related to pH via a colour index v pH calibration using standard buffers or seawater by bubbling CO2. The sensor responds reasonably quickly and can be used for multiple cycles. Sensor strips have been attached to transparent plastic probes with a Nytran diffusion membrane added to provide a white background to stop interference from the colour of sediments. Preliminary tests have been carried out by inserting these probes in sediment cores (in the lab and aboard the RVs Endeavour, Discovery and Prince Madog), and also in the field at Stiffkey salt marsh, in order to measure vertical pH profiles. This has provided promising results. Seasonal profiles at Stiffkey have been taken, recording pH values ranging from 5-8. The sensors have been adapted for use with a Sediment Profile Imagery (SPI) system, to map the pH profile of marine sediments rapidly in-situ using various survey approaches.
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Masure, Loïc. "Towards a better comprehension of deep learning for side-channel analysis". Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS443.
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Les récents progrès en apprentissage profond ont bouleversé l'état de l'art des attaques par observations en sécurité embarquée. Mais leur aspect « boîte-noire » empêche à ce jour l'identification des failles implicitement exploitées dans l'implémentation. De même, il est difficile d'interpréter les résultats de telles attaques sur le niveau de sécurité de l'implémentation-cible. Toutes ces raisons ont rendu la communauté scientifique sceptique quant à l’intérêt de ces techniques dans le cadre d'une évaluation de sécurité. Cette thèse se propose de dresser une meilleure compréhension de l'apprentissage profond dans un tel contexte. Nous montrons comment l’entraînement de tels estimateurs peut être analysé à travers le prisme d'une évaluation de sécurité, de façon à estimer a priori la complexité d’une attaque à base de réseaux de neurones sans avoir toutefois à la mener. Nous observons également sur des simulations que ces modèles entraînés sans connaissance a priori des contre-mesures peuvent atteindre les bornes de sécurité théoriques prévues par la littérature, validant la pertinence ou non de certaines contre-mesures comme le partage de secret ou la dissimulation contre les réseaux de neurones. Par ailleurs, nous expliquons comment exploiter un réseau entraîné pour effectuer une caractérisation efficace des fuites d'information dans les observations, et ce même en présence de contre-mesures rendant d'autres techniques classiques inopérantes. Cela permet une meilleure compréhension des fuites d’information exploitées par le réseau et d’affiner le diagnostic de l’évaluateur ou du développeur, afin de proposer des correctionsThe recent improvements in deep learning (DL) have reshaped the state of the art of side-channel attacks (SCA) in the field of embedded security. Yet, their ``black-box'' aspect nowadays prevents the identification of the vulnerabilities exploited by such adversaries. Likewise, it is hard to conclude from the outcomes of these attacks about the security level of the target device. All those reasons have made the SCA community skeptical about the interest of such attack techniques in terms of security evaluation. This thesis proposes to draw a better understanding of deep learning for SCA. We show how the training of such estimators can be analyzed through the security evaluation prism, in order to estimate a priori the complexity of an SCA, without necessarily mounting the attack. We also remark on simulated experiments that those models, trained without prior knowledge about the counter-measures added to protect the target device, can reach the theoretical security bounds expected by the literature. This validates the relevance or not of some counter-measures such as secret-sharing or hiding, against DL-based SCA. Furthermore, we explain how to exploit a trained neural network to efficiently characterize the information leakage in the observed traces, even in presence of counter-measures making other classical charactertization techniques totally inefficient. This enables a better understanding of the leakage implicitly exploited by the neural network, and allows to refine the evaluator's diagnosis, in order to propose corrections to the developer
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Callenaere, Mathieu. "Étude physique des poches de cavitation partielle en écoulement interne". Grenoble INPG, 1999. http://www.theses.fr/1999INPG0090.
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Les ecoulements cavitants peuvent etre le siege de diverses instabilites. La presente etude est relative a l'instabilite due au developpement d'un jet rentrant a l'arriere des poches de cavitation partielle. Dans ce cas, la cavite presente un comportement oscillatoire conduisant a des lachers periodiques de nuages de vapeur. Cette instabilite est analysee experimentalement dans le tunnel hydrodynamique du legi. La configuration est de type marche divergente vers l'aval de hauteur et d'angle de divergence reglables. L'ecoulement peut etre confine grace a une plaque mobile situee au-dessus de la marche. Les divers regimes de cavitation et en particulier le domaine de la cavitation pulsante sont identifies a partir de visualisations et par cinematographie rapide. L'anemometrie laser est utilisee pour qualifier les ecoulements subcavitants et cavitants et estimer le gradient de pression. Une technique de mesure par sonde ultrasonore est developpee pour mesurer l'epaisseur du jet rentrant. Le contenu en frequences et le nombre de strouhal caracteristique de cette instabilite sont determines a partir de capteurs de pression fluctuante en paroi. Cette etude met en evidence le role fondamental du gradient adverse de pression et de l'epaisseur de la cavite sur la dynamique des poches de cavitation partielle. Un gradient adverse de pression favorise le developpement d'un jet rentrant en fermeture de cavite. Dans le cas de poches relativement epaisses par rapport au jet rentrant, l'ecoulement a contre-courant donne naissance a des lachers periodiques alors que les cavites plus minces ont un comportement plus stable.
Livros sobre o assunto "Visualisation de gradient"
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Tatsi, Angela. The separation and visualisation of human plasma VLDL subclasses by density gradient centrifugation. 1996.
Encontre o texto completo da fonteCapítulos de livros sobre o assunto "Visualisation de gradient"
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Tayyub, Jawad, Muhammad Sarmad e Nicolas Schönborn. "Explaining Deep Neural Networks for Point Clouds Using Gradient-Based Visualisations". In Computer Vision – ACCV 2022, 155–70. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-26284-5_10.
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Bullward, Alistair, Abdulaziz Aljebreen, Alexander Coles, Ciarán McInerney e Owen Johnson. "Research Paper: Process Mining and Synthetic Health Data: Reflections and Lessons Learnt". In Lecture Notes in Business Information Processing, 341–53. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-27815-0_25.
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AbstractAnalysing the treatment pathways in real-world health data can provide valuable insight for clinicians and decision-makers. However, the procedures for acquiring real-world data for research can be restrictive, time-consuming and risks disclosing identifiable information. Synthetic data might enable representative analysis without direct access to sensitive data. In the first part of our paper, we propose an approach for grading synthetic data for process analysis based on its fidelity to relationships found in real-world data. In the second part, we apply our grading approach by assessing cancer patient pathways in a synthetic healthcare dataset (The Simulacrum provided by the English National Cancer Registration and Analysis Service) using process mining. Visualisations of the patient pathways within the synthetic data appear plausible, showing relationships between events confirmed in the underlying non-synthetic data. Data quality issues are also present within the synthetic data which reflect real-world problems and artefacts from the synthetic dataset’s creation. Process mining of synthetic data in healthcare is an emerging field with novel challenges. We conclude that researchers should be aware of the risks when extrapolating results produced from research on synthetic data to real-world scenarios and assess findings with analysts who are able to view the underlying data.
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"Vector Calculus". In Essential Mathematics for NMR and MRI Spectroscopists, 119–76. The Royal Society of Chemistry, 2016. http://dx.doi.org/10.1039/bk9781782627975-00119.
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In order to talk about the physics of electric and magnetic fields it is necessary to know some vector calculus. Here, the calculus of vectors is introduced, including differentiation and integration. The gradient, the curl and the div operations are discussed and visual examples given. Transformation of these operations to other orthogonal coordinate systems is introduced and the use of the gradient, curl and div operators in these coordinate systems is discussed. Green's theorem, Gauss's theorem and Stokes’ theorem are developed and visualisations given to assist in understanding their utility. Vector differentiation is used to discuss the rotation of vectors in a rotating reference frame.
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Lu, Jia, Jun Shen, Wei Qi Yan e Boris Bačić. "An Empirical Study for Human Behavior Analysis". In Computer Vision, 2166–83. IGI Global, 2018. http://dx.doi.org/10.4018/978-1-5225-5204-8.ch095.
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This paper presents an empirical study for human behavior analysis based on three distinct feature extraction techniques: Histograms of Oriented Gradients (HOG), Local Binary Pattern (LBP) and Scale Invariant Local Ternary Pattern (SILTP). The utilised public videos representing spatio-temporal problem area of investigation include INRIA person detection and Weizmann pedestrian activity datasets. For INRIA dataset, both LBP and HOG were able to eliminate redundant video data and show human-intelligible feature visualisation of extracted features required for classification tasks. However, for Weizmann dataset only HOG feature extraction was found to work well with classifying five selected activities/exercises (walking, running, skipping, jumping and jacking).
Trabalhos de conferências sobre o assunto "Visualisation de gradient"
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Costa, Jose Alfredo F., e Hujun Yin. "Gradient-based SOM clustering and visualisation methods". In 2010 International Joint Conference on Neural Networks (IJCNN). IEEE, 2010. http://dx.doi.org/10.1109/ijcnn.2010.5596623.
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Johnson, Mark W. "Turbulent Spot Characteristics in Boundary Layers Subjected to Streamwise Pressure Gradient". In ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/98-gt-124.
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The development of linear perturbations within laminar boundary layers subjected to a full range of adverse and favourable pressure gradients has been predicted numerically. Comparison of the predictions with published flow visualisation results enabled identification of the perturbation regions associated with the turbulent spot, trailing vortex streaks and oblique waves along the spot flanks. The effect of streamwise pressure gradient on spot characteristics (spot leading and trailing edge velocity, calming region trailing edge velocity and spot spreading half angle) was determined and was found to be consistent with published experimental data. The new data extends the range to severe adverse pressure gradient (separation) and to stronger favourable gradients. Correlations for the spot characteristics are provided.
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Zhong, S., T. P. Chong e H. P. Hodson. "Visualisation of Turbulent Wedges Under Favourable Pressure Gradients Using Both Shear-Sensitive and Temperature-Sensitive Liquid Crystals". In ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/fedsm2002-31168.
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Turbulent wedges induced by a 3D surface roughness placed in a laminar boundary layer over a flat plate were visualised for the first time using both shear-sensitive and temperature-sensitive liquid crystals. The experiments were carried out at three different levels of favourable pressure gradients. The purpose of this investigation was to examine the spreading angles of the turbulent wedges indicated by their associated surface shear stresses and heat transfer characteristics and hence obtain further insight about the difference in the behaviour of transitional momentum and thermal boundary layers when a streamwise pressure gradient exists. It was shown that under a zero pressure gradient the spreading angles indicated by the two types of liquid crystals are the same, but the difference increases as the level of favourable pressure gradient increases. The result from the present study could have an important implication to the transition modelling of thermal boundary layers over gas turbine blades.
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Boulanger, Joan, Olivier Balima e Andre´ Charette. "A Reconstruction Scheme Based on the Radiative Transfer Equation for Graded Index Semi-Transparent Media". In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22818.
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Graded refractive index media appear in numerous industrial applications such as non-isothermal flows, optics material processing, biological imaging. Refractive index gradient has been an early help for combusting flow visualisation. The numerical treatment of radiative transport is difficult in such media due to the curvature of rays, especially when the media are not optically thick. Computer-aided remote probing (inversion) is done today with the help of the diffusion approximation adapted to varying refractive index media but is unsuitable for thin media. Therefore, it is important to develop an approach allowing the use of the radiative transport equation which is the most complete formalism for radiative transfer to date and to couple it to reconstruction schemes. The aim of this study is to demonstrate the reconstruction of an arbitrary refractive index distribution from a least-squares gradient-based iterative inversion algorithm taking advantage of the full transient Radiative Transfer Equation (tRTE). The finite-difference discrete-ordinates method for the tRTE and its adjoint has been implemented, accounting for spatial changes in the distribution of the refractive index in a semi-transparent medium. A least-squares gradient-based iterative algorithm has been designed and elementary tests have been carried to demonstrate reconstruction possibilities.
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Hine, Rory D., Judith R. Farman, Sam D. Grimshaw e James V. Taylor. "Short Ducted Fan Diffusers With Integral Splitter Blades". In ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/gt2023-102165.
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Abstract To maximise the range of vertical take-off and landing (VTOL) aircraft, the hover efficiency of ducted fan propulsors should be optimised. Diffusers at the outlet of ducted fans increase thrust, for a given power input, by converting otherwise wasted kinetic energy into a static pressure rise. The weight, and therefore length, of diffusers must be minimised to maximise the net thrust added. However, reducing length increases the adverse, axial pressure gradient which increases flow separation and stagnation pressure losses. In this paper, circumferential splitter blades are used to control loading distributions and reduce the size of separations by modifying pressure gradients. The aim is to increase the pressure recovered by short diffusers. Using 3D computational fluid dynamics (CFD) simulations and pattern search optimisation, the performance and geometric trends of optimised diffusers are mapped as non-dimensional length (L/h) and splitter count (Ns) vary. Two different pressure maximising strategies are identified for diffusers with two splitters (Ns = 2). The first minimises stagnation pressure loss by positioning a splitter near to the hub to inhibit endwall separation. The second maximises the pressure recovered through diffusion by modifying the loading distribution between splitter divided sub-passages. These strategies guide the development of short diffusers for different operational requirements. To validate simulations, an experimental rig is used to study the inlet and outlet flow fields of short, optimised, Ns = 0 and Ns = 2 diffusers. The experimentally measured stagnation pressure loss suffered by the optimised Ns = 2 diffuser is half that of the Ns = 0 design. This is primarily due to the alleviation of casing endwall separations. Flow mechanisms are identified using CFD simulated limiting surface streamlines and experimental flow visualisation.
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Haferkamp, H., M. Goede e O. Thürk. "Short Time Process Observation During Laser Remelting of Aluminium Diecast Alloys". In The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1998. http://dx.doi.org/10.1364/cleo_europe.1998.cthh93.
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Rapid solidification of aluminium alloys during the remelting process using high power laser radiation results in refining effects of the solidified grain texture and improved wear resistance and material hardness. High temperature gradients can be achieved as well as energy coupling into the aluminium alloy is locally restricted, and can be precisely controlled. For the adjustment of defined grain textures, the dynamic behaviour of the melted material on the irradiated material surface is of high interest. Most of the optical set-ups currently used for process visualisation only image the plasma formation within the laser beam interaction zone. Available systems for frequency-selective irradiation and visualisation provide insufficient time resolutions with respect to rapid melting and solidifying processes.
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Umbleja, Kadri. "Students' grading control and visualisation in competence-based learning approach". In 2015 IEEE Global Engineering Education Conference (EDUCON). IEEE, 2015. http://dx.doi.org/10.1109/educon.2015.7095985.
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Fitzgerald, J. E., A. J. Niven e M. R. D. Davies. "Turbine Blade Aerodynamic Wall Shear Stress Measurements and Predictions". In ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/98-gt-562.
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The correct prediction of the aerodynamic wall shear stress is a good test of a numerical codes ability to predict profile loss. Its measurement with heated thin film gauges is significantly easier than attempting a complete measurement of a turbine blade boundary layer. A modified form of previously published heated thin film gauge calibrations allow wall shear stress measurement in laminar incompressible flow with favourable pressure gradients and turbulent incompressible flows with small pressure gradients. In this paper, measurements are presented of the distribution of aerodynamic wall shear stress over the suction surface of a turbine blade in a linear cascade. Gauge voltage signal analyses show a laminar separation bubble between about 53% and 63% of suction surface length that is confirmed by surface flow visualisation. By-pass transition is detected by downstream gauges. Wall shear stress measurements are presented at two cascade incidence angles and for tripped and natural transition. The commercial code FLUENT is used to predict the surface pressure distribution, the aerodynamic wall shear stress distribution in the laminar region and the turbulent surface shear distribution for the tripped boundary layer. Comparisons are made between measurements and predictions.
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Patterson, D. J., e M. Hoeger. "The Effect of Reynolds Number and Velocity Distribution on LP Turbine Cascade Performance". In ASME 1986 International Gas Turbine Conference and Exhibit. American Society of Mechanical Engineers, 1986. http://dx.doi.org/10.1115/86-gt-271.
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Because of the laminar boundary-layer’s inability to withstand moderate adverse pressure gradients without separating, profile losses in LP turbines operating at low Reynolds numbers can be high. The choice of design pressure distribution for the blading is thus of great importance. Three sub-sonic LP turbine nozzle-guide-vane cascade profiles have been tested over a wide range of incidence, Mach number and Reynolds number. The three profiles are of low, medium and high deflection and, as such, display significantly different pressure distributions. The tests include detailed boundary-layer traverses, trailing-edge base-pressure monitoring and oil-flow visualisation. It is shown that the loss variation with Reynolds number is a function of pressure distribution and that the trailing-edge loss component is dominant at low Reynolds number. The importance of achieving late flow transition — rather than separation — in the suction-surface trailing-edge region is stressed. The paper concludes by remarking on the advantages and practical implications of each loading design.
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Mondin, Gabriel, William Riéra, Pierre Duquesne e Xavier Ottavy. "Beneficial Effects of Guide Fins on Corner Separation". In ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/gt2023-101012.
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Abstract Corner separation is a major phenomenon limiting the operability of aeronautical compressors. Passive control devices such as guide fins are envisioned to reduce its deleterious effects. In this paper, guide fins are optimized to reduce the total pressure losses downstream of a subsonic compressor cascade (M = 0.11, Re = 3.2 105, modern stator blades) at design and near-stall incidences. Guide fins shapes are defined using 15 parameters. An optimization strategy relying on the iterative refinement of surrogate model with Reynolds-Averaged Navier-Stokes (RANS) computations is carried out. A database of 1033 guide fins is obtained, a large number of which strongly reduces the near-stall losses. Three guide fins are thoroughly investigated and referred to as Short Fence (short and straight guide fin), Long Fence (long and straight guide fin) and 3D (long guide fin with a strong pyramidal aspect). Their effect on the downstream measurement plane is validated experimentally, as well as their integrated performances. Large reductions of total pressure losses at near-stall incidence are obtained (−2.4 pt to −2.9 pt, or a relative reduction of −50% to −60%) without degrading neither the nominal losses nor the stator deflection. These guide fins are used to highlight three beneficial mechanisms that alter the corner separation development within the blade passage a) Tip Vortex (energizes the passage flow) b) Fence (induces 2 passage vortices) c) Guide (induces a local favourable pressure gradient). The role of these mechanisms in the generation of total pressure losses are analyzed in depth with streamlines visualisations and with a topological analysis. Kriging surrogate models reveal that three parameters drive the guide fins performances : the axial position, height, and thickness value at hub. The performances of the investigated guide fins are robust to significant variations of these parameters, as well as small variation of the inlet boundary layer thickness.