1,721,069 research outputs found
On efficient simulation of self-assembling diblock copolymers using a peridynamic-enhanced Fourier spectral method
No full texthttp://dx.doi.org/10.13039/501100001659 German Research Foundationhttp://dx.doi.org/10.13039/100000015 U.S. Department of Energyhttp://dx.doi.org/10.13039/501100002347 Bundesministerium für Bildung und Forschun
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
3D reconstruction of FIB tomography data using machine learning
No full textThis thesis introduces methods for accurate 3D reconstruction of FIB tomography data using machine learning. It addresses challenges in obtaining large datasets and ground truth values, proposing a method for virtual FIB tomography data generation and an isotropy-based validation method. ML-based segmentation methods tackle issues in BSE images, like the shine-through effect and image intensity ambiguities. Integrating the slice repositioning method with image inpainting resolves inconsistencies in slice thicknesses in FIB tomography data. Additionally, a multimodal machine learning approach using multivoltage images further enhances 3D reconstruction accuracy.In dieser Arbeit werden Methoden für die 3D-Rekonstruktion von FIB-Tomographiedaten mithilfe von maschinellem Lernen vorgestellt. Es befasst sich mit den Herausforderungen bei der Datenerfassung und dem Fehlen von Wahrheitsdaten; und schlägt eine virtuelle Datengenerierung und eine auf Isotropie basierende Validierung vor. Die ML-basierte Segmentierung löst Probleme wie den shine-through effekt und die Mehrdeutigkeit der Bildintensität in BSE-Bildern. Durch die Integration der Neupositionierung von Schichten und der Methode der Bildverbesserung werden Inkonsistenzen in der Schichtdicke beseitigt. Ein multimodaler Lernansatz mit Multivoltage-Bildern verbessert die Genauigkeit der 3D-Rekonstruktion weiter
Computational micromechanics of matrix-inclusion composites
No full textThis thesis is concerned with aspects of the computational retrievement of macroscopic material responses and investigations of the microscopic deformation behavior of random matrix-inclusion composites. To this end, the focus lies on the representative volume element (RVE) approach in the scope of finite element analyses and its applicability and integration into engineering practice.
The artificial random generation of the microstructural geometry, in a periodic and non-periodic manner, is established by studying and enhancing existing methods such as the random sequential adsorption method or collective rearrangement methods for cubic RVEs. Based on distance computations between two inclusions, the non-overlap requirement, which is characteristic for matrix-inclusion composites, is ensured for ellipsoidal, capsular, cylindrical and convex polyhedral inclusion shapes.
To comply with the state-of-the-art approach that utilizes fully periodic RVEs featuring a periodic topology, a periodic discretization and periodic boundary conditions (PBC), a new algorithm that automatically generates periodic meshes is developed. The algorithm systematically combines various meshing tools in an efficient and robust way. Special emphasis is placed on the discretization procedure to maintain a high quality mesh with as few elements as possible, thus, manageable for computer simulations applicable to high volume concentrations, high number of inclusions and complex inclusion geometries. Examples elucidate the ability of the proposed approach to efficiently generate large RVEs with a high number of anisotropic inclusions but still maintaining a high quality mesh and a low number of elements.
Since the generation of such a state-of-the-art RVE can significantly reduce the overall efficiency in multiscale finite element simulations, a benchmark study that investigates possible relaxations to this cumbersome task is performed. In particular, the RVE size, periodic and non-periodic RVE topologies, different discretization variants and various types of boundary conditions that either require periodicity or do not require periodicity of the underlying discretization are benchmarked. Approximate periodic boundary conditions are discussed in detail. The benchmark study proves that a fully periodic topology and mesh discretization with periodic boundary conditions is not necessary in order to identify effective macroscopic material parameters for technologically relevant composites.
Eventually, the gathered methodologies are applied to model a modern high-tech polymer nanocomposite. By utilizing a sophisticated material model for the polymeric matrix, the entropic and energetic deformation regime can be represented in a physically meaningful way. Furthermore, the explicit consideration of the matrix-inclusion interface failure via a cohesive zone model accounts for the non-negligible surface effects. Comparisons with experiments underline the predictive character of the modeling approach and allow for investigations of local deformation mechanisms
Peridynamic models in multi-physics applications on bounded and unbounded domains
No full textThe following dissertation concerns with elevating the role of nonlocal peridynamic continuum models in real-world engineering and material applications by establishing efficient and robust numerical techniques and providing comprehensive model descriptions that aim to accurately represent the underlying physical properties. A number of versatile numerical discretization schemes are thoroughly evaluated for both bond-based peridynamic models in brittle fracture modeling as well as nonlocal diffusion-type models for up to three-dimensional problems. These schemes can adaptively refine the computational grid around areas of interest, are asymptotically compatible, computationally efficient, and easy to implement. Efficient solution schemes are further provided for unbounded domain problems, based on residual-free exponential basis functions, which may be used in a collocation scheme to obtain Dirichlet-type boundary conditions to approximate the far-field domain solution over a truncating boundary. The feasibility and improved capability of the proposed numerical schemes are demonstrated on the complex multi-physics simulation of the biodegradation of magnesium-based bone implant screws under physiological conditions on (nearly) unbounded three-dimensional domains, utilizing the standard bi-material peridynamic corrosion model with an efficient constitutive model of the corrosion kinetics that directly links to the experimentally easy-to-measure macroscopic volume loss. In order to augment the capabilities of standard peridynamic models towards the description of multi-ionic mass transport of electromigration, a generalized peridynamic framework of nonlocal Nernst-Planck-Poisson equations is proposed, which effectively models the diffusion-electromigration-reaction and moving boundary problems of corrosion models with arbitrary constitutive corrosion kinetics.Die folgende Dissertation befasst sich mit der Erweiterung des Anwendungsbereichs nichtlokaler peridynamischer Kontinuumsmodelle in realen ingenieurwissenschaftlichen und materialtechnischen Anwendungen durch den Einsatz effizienter und robuster numerischer Verfahren sowie die Bereitstellung umfassender Modellbeschreibungen, die darauf abzielen, die zugrunde liegenden physikalischen Eigenschaften präzise darzustellen. Eine Reihe vielseitiger numerischer Diskretisierungsverfahren wird sowohl für bindungsbasierte peridynamische Modelle in der Modellierung spröder Brüche als auch für nichtlokale Diffusionsmodelle in bis zu dreidimensionalen Problemen untersucht. Diese Verfahren können das Rechengitter um relevante Gebiete adaptiv verfeinern, sind asymptotisch kompatibel, rechnerisch effizient und einfach zu implementieren. Effiziente Lösungsverfahren werden ferner für Probleme auf unbeschränkten Gebieten beschrieben, die auf residuenfreien exponentiellen Basisfunktionen und in einem Kollokationsschema verwendet werden können, um Dirichlet-Randbedingungen zu erhalten, welche die Fernfeldlösung entlang einer trunkierenden Grenze approximieren. Die Praxistauglichkeit und verbesserte Leistungsfähigkeit der vorgestellten numerischen Verfahren werden anhand der komplexen multiphysikalischen Simulation der Biodegradation von magnesiumbasierten Knochenimplantatschrauben unter physiologischen Bedingungen auf (nahezu) unbeschränkten dreidimensionalen Gebieten demonstriert. Dabei wird das standardmäßige peridynamische Zweistoff-Korrosionsmodell mit einem effizienten konstitutiven Modell der Korrosionskinetik verwendet, das direkt mit dem experimentell leicht messbaren makroskopischen Volumenverlust verknüpft ist. Um die Leistungsfähigkeit standardmäßiger peridynamischer Modelle hinsichtlich der Beschreibung des multi-ionischen Massentransports bei Elektromigration zu erweitern, wird ein verallgemeinertes peridynamisches Modell der nichtlokalen Nernst-Planck-Poisson-Gleichungen entwickelt, das die Diffusions-Elektromigrations-Reaktion und die Probleme der beweglichen Grenzfläche von Korrosionsmodellen mit beliebiger konstitutiver Korrosionskinetik umfassend abbildet
Machine Learning and Data Mining in Materials Science
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Multiscale investigations of mechanobiology: in vitro observations and computational modeling
No full textMechanobiology is an inherently multiscale field of study that explores the relationship between mechanical forces and biological processes at various levels, from molecular and cellular to tissue and organ levels. This work presents different aspects of this multiscale system, ranging from cell migration to mechanical testing of tissue equivalents to computational modeling of tissue adaptation. The results help identify key macroscopic quantities and (sub)cellular mechanisms essential in regulating biological processes on different length and time scales in response to mechanical perturbations.Mechanobiologie befasst sich mit dem Einfluss mechanischer Reize auf biologische Prozesse und umfasst mehrere Längen- und Zeitskalen, von individuellen Molekülen über Zellen bis hin zu Organen. Diese Arbeit stellt diverse Aspekte dieses multiskalen Systems anhand von Experimenten und Computermodellen dar und beschäftigt sich vor allem mit der Zellmigration, dem mechanischen Verhalten von Gewebeäquivalenten und der Anpassung von Weichgewebe. Die Ergebnisse der einzelnen Studien heben dabei makroskopische Größen sowie inter- und intrazelluläre Mechanismen hervor, die eine wichtige Rolle bei der mechanischen Regulierung biologischer Prozesse spielen
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