1,729 research outputs found
VI Workshop on Computational Data Analysis and Numerical Methods: Book of Abstracts
The VI Workshop on Computational Data Analysis and Numerical Methods (WCDANM) is going to be held on June 27-29, 2019, in the Department of Mathematics of the University of Beira Interior (UBI), Covilhã, Portugal and it is a unique opportunity to disseminate scientific research related to the areas of Mathematics in general, with particular relevance to the areas of Computational Data Analysis and Numerical Methods in theoretical and/or practical field, using new techniques, giving especial emphasis to applications in Medicine, Biology, Biotechnology, Engineering, Industry, Environmental Sciences, Finance, Insurance, Management and Administration. The meeting will provide a forum for discussion and debate of ideas with interest to the scientific community in general. With this meeting new scientific collaborations among colleagues, namely new collaborations in Masters and PhD projects are expected. The event is open to the entire scientific community (with or without communication/poster)
New dynamic subgrid-scale modelling approaches for large eddy simulation and resolved statistical geometry of wall-bounded turbulent shear flow
This dissertation consists of two parts, i.e. dynamic approaches for subgrid-scale (SGS) stress modelling for large eddy simulation and advanced assessment of the resolved scale motions related to turbulence geometrical statistics and topologies. The numerical simulations are based on turbulent Couette flow.
The first part of the dissertation presents four contributions to the development of dynamic SGS models. The conventional integral type dynamic localization SGS model is in the form of a Fredholm integral equation of the second kind. This model is mathematically consistent, but demanding in computational cost. An efficient solution scheme has been developed to solve the integral system for turbulence with homogeneous dimensions. Current approaches to the dynamic two-parameter mixed model (DMM2) are mathematically inconsistent. As a second contribution, the DMM2 has been optimized and a modelling system of two integral equations has been rigorously obtained. The third contribution relates to the development of a novel dynamic localization procedure for the Smagorinsky model using the functional variational method. A sufficient and necessary condition for localization is obtained and a Picard's integral equation for the model coefficient is deduced. Finally, a new dynamic nonlinear SGS stress model (DNM) based on Speziale's quadratic constitutive relation [J. Fluid Mech., 178, p.459, 1987] is proposed. The DNM allows for a nonlinear anisotropic representation of the SGS stress, and exhibits a significant local stability and flexibility in self-calibration.
In the second part, the invariant properties of the resolved velocity gradient tensor are studied using recently developed methodologies, i.e. turbulence geometrical statistics and topology. The study is a posteriori based on the proposed DNM, which is different than most of the current a priori approaches based on experimental or DNS databases. The performance of the DNM is further validated in terms of its capability of simulating advanced geometrical and topological features of resolved scale motions. Phenomenological results include, e.g. the positively skewed resolved enstrophy generation, the alignment between the vorticity and vortex stretching vectors, and the pear-shape joint probability function contour in the tensorial invariant phase plane. The wall anisotropic effect on these results is also examined
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The Materials Science of Skin: Experimental Characterization, Constitutive Modeling, and Tear Resistance
Skin is the outermost layer of the body and acts as a primary protective barrier against external agents such as heat, light, infection, and injury. Additionally, skin regulates a broad range of physiological parameters and hosts several vital components. In order to fulfill these functions throughout life, skin must be able to withstand and recover from significant deformation as well as mitigate tear propagation that can occur during growth, movement, and injuries affecting its integrity. Hence, characterizing the mechanical behavior of skin and understanding the underlying mechanisms of deformation at different spatial scales is essential in a large spectrum of applications such as surgery, cosmetics, forensics, biomimetics and engineering of protective gear or artificial grafts. In this dissertation, a comprehensive list of experimental techniques that have been developed over the years to test skin’s nonlinear elastic, viscoelastic, and dissipative properties are reviewed. To identify parameters affecting its behavior, a significant number of models have been developed, some of which are detailed here. The principal structural elements within the dermis, and especially the arrangement and orientation of the collagen fibrils and fibers, are presented; their incorporation into the constitutive models is discussed. We conduct a detailed investigation of the evolution of the collagen architecture of the dermis as a function of deformation, which reveals new aspects that extend our understanding of the mechanical response of porcine skin. The dermis is found to have a tridimensional woven structure of collagen fibers, which evolves with deformation. After failure, we observe that the fibers have straightened and aligned in the direction of tension. Time-dependent and dissipative effects are quantitatively established. Digital image correlation techniques were implemented to quantify skin’s anisotropy; measurements of the Poisson ratio and their evolution are reported for the first time. Based on new observations, we propose that fiber braiding is at least partially responsible for the monotonic increase of the tangent modulus of skin with strain, as well as its dissipative response to cyclical loads. We incorporate these findings in a constitutive framework incorporating fibril stiffness, interfibrillar frictional sliding, and the effect of lateral fibers on the extension of a primary fiber, using analytical and coarse-grained modeling approaches. The representation of these important physical processes that occur during deformation of the dermis represents an advance in our understanding of these phenomena. Finally, we estimate the toughness of porcine skin by conduct two types of experiment on pre-notched specimens, placing the tissue under shear Mode III and opening Mode I. We obtain two distinct toughness values of J_IIIc≈20.4 kJ/m^2 and J_Ic=30.4 kJ/m^2, indicating notable differences between these two modes of crack propagation. Digital image correlation is used to plot strain profiles around the tip of the crack, from which a strain-based criterion for crack propagation is established. The evaluation of the structure at the crack tip and regions undergoing more uniform states of deformation is conducted by ex situ transmission electron microscopy and in situ environmental scanning electron microscopy
Digital Image Access & Retrieval
The 33th Annual Clinic on Library Applications of Data Processing, held at the University of Illinois at Urbana-Champaign in March of 1996, addressed the theme of "Digital Image Access & Retrieval." The papers from this conference cover a wide range of topics concerning digital imaging technology for visual resource collections. Papers covered three general areas: (1) systems, planning, and implementation; (2) automatic and semi-automatic indexing; and (3) preservation with the bulk of the conference focusing on indexing and retrieval.published or submitted for publicatio
Image processing for plastic surgery planning
This thesis presents some image processing tools for plastic surgery planning. In particular,
it presents a novel method that combines local and global context in a probabilistic
relaxation framework to identify cephalometric landmarks used in Maxillofacial plastic
surgery. It also uses a method that utilises global and local symmetry to identify abnormalities
in CT frontal images of the human body. The proposed methodologies are
evaluated with the help of several clinical data supplied by collaborating plastic surgeons
Geometric and photometric affine invariant image registration
This thesis aims to present a solution to the correspondence problem for the registration
of wide-baseline images taken from uncalibrated cameras. We propose an affine
invariant descriptor that combines the geometry and photometry of the scene to find
correspondences between both views. The geometric affine invariant component of the
descriptor is based on the affine arc-length metric, whereas the photometry is analysed
by invariant colour moments. A graph structure represents the spatial distribution of the
primitive features; i.e. nodes correspond to detected high-curvature points, whereas arcs
represent connectivities by extracted contours. After matching, we refine the search for
correspondences by using a maximum likelihood robust algorithm. We have evaluated
the system over synthetic and real data. The method is endemic to propagation of errors
introduced by approximations in the system.BAE SystemsSelex Sensors and Airborne System
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Towards the Development of an Efficient Integrated 3D Face Recognition System. Enhanced Face Recognition Based on Techniques Relating to Curvature Analysis, Gender Classification and Facial Expressions.
The purpose of this research was to enhance the methods towards the development of an efficient three dimensional face recognition system. More specifically, one of our aims was to investigate how the use of curvature of the diagonal profiles, extracted from 3D facial geometry models can help the neutral face recognition processes. Another aim was to use a gender classifier employed on 3D facial geometry in order to reduce the search space of the database on which facial recognition is performed. 3D facial geometry with facial expression possesses considerable challenges when it comes face recognition as identified by the communities involved in face recognition research. Thus, one aim of this study was to investigate the effects of the curvature-based method in face recognition under expression variations. Another aim was to develop techniques that can discriminate both expression-sensitive and expression-insensitive regions for
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face recognition based on non-neutral face geometry models. In the case of neutral face recognition, we developed a gender classification method using support vector machines based on the measurements of area and volume of selected regions of the face. This method reduced the search range of a database initially for a given image and hence reduces the computational time. Subsequently, in the characterisation of the face images, a minimum feature set of diagonal profiles, which we call T shape profiles, containing diacritic information were determined and extracted to characterise face models. We then used a method based on computing curvatures of selected facial regions to describe this feature set. In addition to the neutral face recognition, to solve the problem arising from data with facial expressions, initially, the curvature-based T shape profiles were employed and investigated for this purpose. For this purpose, the feature sets of the expression-invariant and expression-variant regions were determined respectively and described by geodesic distances and Euclidean distances. By using regression models the correlations between expressions and neutral feature sets were identified. This enabled us to discriminate expression-variant features and there was a gain in face recognition rate. The results of the study have indicated that our proposed curvature-based recognition, 3D gender classification of facial geometry and analysis of facial expressions, was capable of undertaking face recognition using a minimum set of features improving efficiency and computation
Contributions to Open Problems on Cable Driven Robots and Persistent Manifolds for the Synthesis of Mechanisms
Although many efforts are continuously devoted to the advancement of robotics, there are still many open and unresolved problems to be faced. This thesis, therefore, sets out to tackle some of them with the aim of scratching the surface and look a little further for new ideas or solutions.
The topics covered are mainly two. The first part deals with the development and improvement of control techniques for cable-driven robots. The second focuses on the study of persistent manifolds seen as constituting aspects of theoretical kinematics.
In detail,
-Part I deals with cable-driven platforms. In it, both techniques for selecting cable tensions and the design of a robust controller are developed. The aim is, therefore, to enhance the two building blocks of the overall control scheme in order to improve the performance of these robots during the execution of tracking tasks.
-- The first chapter introduces to open problems and recalls the main concepts necessary to understand the following chapters;
-- the contribution of the second chapter consists of the introduction of the Analytic Centre. It allows the generation of continuous and differentiable tension profiles while taking into account non-linear phenomena such as friction in the computation of tensions to be applied;
-- the third chapter, although still at a preliminary stage, introduces sensitivity for tension calculation methods, offering perspectives of considerable interest for tension control in the current scientific context;
-- the fourth chapter proposes the design of an adaptive controller. It allows external disturbances and/or uncertainties in the model to be faced such that the task can be performed with as little error as possible. The controller architecture is the innovative peculiarity conferring autonomy to cable systems. Initially applied to counteract wind in aerial systems it is now also used for cable breakage scenarios;
-- the conclusions, at first, draw together the results obtained. In addition, they emphasise the lack of the techniques introduced in order to outline possible future paths and topics that need further investigation.
- Part II delves into theoretical kinematics. The discovery and classification of invariant screw systems shed light on numerous aspects of robot mobility and synthesis. Nevertheless, this generated the emergence of new ideas and questions that are still unresolved. Among them, one of the more notable concerns the identification and classification of 5-dimensional persistent manifolds.
-- Similarly to the first part, the first chapter provides an overview of the problems addressed and the theoretical notions necessary to understand the subsequent contributions;
-- the second chapter contributes by directly tackling the above-mentioned question by exploiting the properties of dual quaternions, the Study quadric and differential geometry. A library of 5-persistent varieties, so far missing in the literature, is presented along with theorems that complete and generalise previous ones in the literature;
-- an original work, concerning line motions and synthesis of mechanisms that generate them, is reported in the third chapter as a spin-off of the studies on persistent manifolds;
-- the conclusions wrap up the obtained results trying to highlight gaps and deficiencies to be dealt with in the future. Here, two small sections are dedicated to ongoing works regarding the persistence definition and the screw systems' invariants and subvariants
Mathematics teachers’ work with resources: four cases of secondary teachers using technology
This study examines teachers’ work with paper-based, technology and social resources with the use of two theoretical frameworks: the Documentational approach and the Knowledge Quartet. The former affords looking at teachers’ resources and resource systems and how these are utilized under schemes of work. The latter affords a closer look at teachers’ work during lessons and at their knowledge-in-action. Specifically, the study investigates how four upper secondary teachers use, re-use and balance their resources by looking at their schemes of work in class, through lesson observations; and, by reflecting on the details of their work and knowledge-in-action in pre- and post-observation interviews. Analysis examines five themes in relation to teachers’ work. First, teachers use students’ contributions as a resource during lessons. Second, teachers connect (or not) different resources. Third, institutional factors, such as examinations requirements and school policy, have impact on teachers’ decisions and on how they balance their resource use. Fourth, when mathematics-education software is used, teacher knowledge of the software comes into play. Fifth, there is ambiguity in the identification of contingency moments, particularly regarding whether these moments were anticipated (or not) or provoked by the teacher. These five themes also suggest theoretical findings. In relation to the Knowledge Quartet, the findings indicate the potency of adding a few new codes or extending existing codes. This is especially pertinent in the context of teaching upper secondary mathematics with technology resources. In relation to the Documentational approach, this study introduces two constructs: scheme-in-action and re-scheming. A scheme-in-action is the scheme followed in class and documented from the classroom. Re-scheming is scheming again or differently from one lesson to another. Finally, the study discusses implications for practice and proposes the use of key incidents extracted from classroom observations towards the development of teacher education resources (e.g. for the MathTASK programme)
Anisotropy Across Fields and Scales
This open access book focuses on processing, modeling, and visualization of anisotropy information, which are often addressed by employing sophisticated mathematical constructs such as tensors and other higher-order descriptors. It also discusses adaptations of such constructs to problems encountered in seemingly dissimilar areas of medical imaging, physical sciences, and engineering. Featuring original research contributions as well as insightful reviews for scientists interested in handling anisotropy information, it covers topics such as pertinent geometric and algebraic properties of tensors and tensor fields, challenges faced in processing and visualizing different types of data, statistical techniques for data processing, and specific applications like mapping white-matter fiber tracts in the brain. The book helps readers grasp the current challenges in the field and provides information on the techniques devised to address them. Further, it facilitates the transfer of knowledge between different disciplines in order to advance the research frontiers in these areas. This multidisciplinary book presents, in part, the outcomes of the seventh in a series of Dagstuhl seminars devoted to visualization and processing of tensor fields and higher-order descriptors, which was held in Dagstuhl, Germany, on October 28–November 2, 2018
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