309 research outputs found
Self-assembly via branching morphologies in nematic liquid-crystal nanocomposites
No full textWe demonstrate that the morphological diversity in liquid-crystal hybrid systems is much richer than previously anticipated. More importantly, we reveal the existence of a dual mechanism for self-assembly of nanoparticles via morphological instabilities at phase boundaries. Using numerical simulations, we study the growth of isolated nematic droplets in an isotropic liquid crystal (LC) doped with nanoparticles (NPs) and provide insight into the nature of microstructure evolution in LC hybrids. Our work expands the numerically accessible time and length scales in these systems, capturing morphologies which develop under the competition of nonequilibrium elastic interactions, diffusive instabilities mediated by NP transport, and the anisotropy of the nematic field. By mapping nematic morphologies, we also propose a methodology for estimating various important LC material parameters that are difficult to obtain experimentally. © 2014 American Physical Society.Fil: Gurevich, Sebastian. Mc Gill University; CanadáFil: Soulé, Ezequiel Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Rey, Alejandro D.. Mc Gill University; CanadáFil: Reven, Linda. Mc Gill University; CanadáFil: Provatas, Nikolas. Mc Gill University; Canad
The effects of paper structure on electrophotography /
No full textWe study the effects of paper structure on electrophotography using a phase-field type continuum model of electrostatic transfer. This model is implemented in C++ using the finite element method and allows us to solve for the electric field for a system of any dielectric configuration. We show that average toner transfer forces increase as a function of paper filler particle density, through direct coupling of filler to local paper dielectric. Specifically, fluctuations in surface fillers produce "hot spots" in the field near the surface, while those in the bulk have longer reaches. We also show that rapid fluctuations of the dielectric constant produce smaller transfer force variations than longer dielectric constant wavelength variations.We simulate the electrostatic fields in a real cross-section of filled paper and we show that the factors that, affects the toner transfer of the system at a fixed voltage are the thickness variations, surface fillers, bulk filler content and the surface profile variations. (Abstract shortened by UMI.
Machine Learning for Multi-Scale Phase Field Simulations
No full text<p>Presentation on the application of machine learning to accelerate phase field simulations of directional solidification of a dilute binary alloy in the dendritic regime. Presented at CHiMaD, March 20th 2024.</p>
Using Phase-Field Modeling With Adaptive Mesh Refinement To Study Elasto-Plastic Effects In Phase Transformations
No full text This thesis details work done in the development of the phase field model which
allows simulation of elasticity with diffuse interfaces and the extension of a thin
interface analysis developed by previous authors to study non-dilute ideal alloys.
These models are coupled with a new finite difference adaptive mesh algorithm to
efficiently simulate a variety of physical systems. The finite difference adaptive
mesh algorithm is shown to be at worse 4-5 times faster than an equivalent finite element
method on a per node basis. In addition to this increase in speed for explicit
solvers in the code, an iterative solver used to compute elastic fields is found to
converge in O(N) time for a dynamically growing precipitate, where N is the number
of nodes on the adaptive mesh. A previous phase field formulation is extended
such as to make possible the study of non-ideal binary alloys with complex phase
diagrams. A phase field model is also derived for a free energy that incorporates an
elastic free energy and is used to investigate the competitive development of solid
state structures in which the kinetic transfer rate of atoms from the parent phase
to the precipitate phase is large. This results in the growth of solid state dendrites.
The morphological effects of competing surface anisotropy and anisotropy in the
elastic modulus tensor is analyzed. It is shown that the transition from surfaceenergy
driven dendrites to elastically driven dendrites depends on the magnitudes
of the surface energy anisotropy coefficient (E4 ) and the anisotropy of the elastic
tensor (β) as well as on the super saturation of the particle and therefore to a specific
Mullins-Sekerka onset radius. The transition point of this competitive process
is predicted from these three controlling parameters. ThesisDoctor of Philosophy (PhD
Overall synthesis and conclusions
No full textThis chapter first systematically summarizes the most important findings and policy implications of each of the chapters included in this book volume. Next it synthesizes the overall findings and policy implications, and discusses future avenues for policy making and research. A first conclusion is that the chapters make clear that the ranges in policy relevant implications of AVs, within the scope of each chapter/topic, are still relatively broad. Secondly we conclude that research that is conceptually rich is more valuable for policy making. Thirdly we hypothesize that context matters for the uptake, impacts, and specific system design characteristics of real world AV implementation. Fourth we conclude that research on the global south has been limited so far. Fifth we argue that AVs, shared vehicles and electric vehicles (EVs) might stimulate each other in a positive way, in all directions. Finally we conclude that AVs will have wider societal implications, such as in the area of land use, accessibility, social exclusion, governmental expenditures, the labor market, and the environment. The more indirect the effects of AVs are, the more difficult they are to understand. For policy making a first conclusion is that the issues of ethics, cyber security and data protection deserve way more attention than they currently get. We also conclude that future motorway network extensions might not be no-regret anymore, because of possible congestion reductions due to AVs, but also because of decreasing marginal values of time. Finally we argue that countries that introduce AVs later than other countries can learn a lot from the real world experiences elsewhere.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Transport and Logistic
Phase-Field Simulations of Rapid Solidification in Binary Alloys
No full textRapid solidification is a well established method to produce novel materials with improved
mechanical or electrical properties. The sharp-interface kinetics of rapid solidification
for a binary alloy is summarized. A Phase Field model mapping to this sharp interface
model is summarized and solved by a new adaptive mesh refinement algorithm.
Simulation results are consistent with experiments: The solidification velocity increases
in power-law like fashion at low undercooling and approximately linearly at high undercooling;
The solid/liquid interface undergoes a transition from four-fold dendritic to circular
crystal structures; Solute trapping emerges and the solute partitioning approaches
unity as the solidification velocity increases. Our Phase Field simulations are the first self -consistent
predictions of velocity selection and morphological selection at both low and
high undercoolings and also the first independent check of the solute trapping model in two
dimensions.ThesisMaster of Applied Science (MASc
PHASE FIELD CRYSTAL STUDIES OF STRAIN-MEDIATED EFFECTS IN THE THERMODYNAMICS AND KINETICS OF INTERFACES
No full textIn this dissertation, the Phase Field Crystal (PFC) Method is used to study a number of problems in which interfaces and elastic effects play important roles in alloys. In particular, the three topics covered in this work are grain boundary thermodynamics in alloys, dislocation-mediated formation of clusters in binary and ternary alloys, and solutal effects in explosive crystallization. Physical phenomena associated with grain boundaries, such as Read-Shockley-like behaviour and Gibbs adsorp- tion theorem, were shown to be accurately captured in both PFC- and XPFC-type models. In fact, a connection between the solute segregation behaviour and physical properties of the system—such as energy of mixing, mismatch, and undercooling—were shown. Also, grain boundary premelting was investigated. It was shown how solute can change the disjoining potential of a grain boundary and a mechanism for hysteresis in grain boundary premelting was discussed. Regarding the phenomenon of cluster formation, a general coexistence approach and a nucleation-like approach were used to describe the mechanism consistently with observations; the process is facilitated by lowering the energy increase associated with it. The final phenomenon studied was explosive crystallization. It was shown that the temperature oscillations due to unsteady motion of an interface could be captured with PFC-type models and that this behaviour leaves patterns, such as solute traces, in the material. The versatility of this PFC formalism was demonstrated by capturing the underlying physics and elucidating the role of misfit strain in altering interface oscillations during explosive crystallization. Finally, it was demonstrated in all projects how PFC model parameters relate to coarse-grained material properties, thereby connecting these phenomena on larger scales to atomistic-scale properties.Doctor of Philosophy (PhD
Post hos nostra terra est: mapping the Late Roman ecumene with the Expositio totius mundi et gentium
No full textThis paper studies the landscape of the Late Roman ecumene as depicted by the Expositio totius mundi et gentium (Expos. mundi),1 written by an anonymous author in the middle of the 4th century CE. It will first contextualise the text and assess its structure, language and genre. The contribution will then focus on the distinction between Rome, the Sasanids and utopic societies in the east near Eden, the political and military organization of the Imperium Romanum as well as its economic framework and varying expressions of its culture. As
this paper will show, the anonymous author does not present detailed descriptions of Rome’s geographical landscape. Instead, the primary focus is on material resources of the Roman Empire, their potential for economic exploitation and the trading opportunities resulting from it. Rome’s cultivated landscapes are thereby regarded as important preconditions for its success on an economic, political and cultural level
SCALING ANALYSIS OF MELTING KINETICS IN RANDOMLY PACKED STEEL SCRAP IN ELECTRIC ARC FURNACE STEEL MAKING
No full textp.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Times; color: #242424} p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Times; color: #3c3c3c} span.s1 {color: #3c3c3c} span.s2 {color: #242424} This thesis report the results of a simulation study of the melting kinetics of multiple, randomly distributed, steel scrap pieces. The model used is that previously developed by Li [Li, 2006]. The aim of this study was to better understand the universal features governing the kinetics of multi-piece scrap melting in a liquid pool. We observed the formation of a solidified shell and interfacial gap both in a single scrap piece as well as in randomly distributed multiple scrap melting cases. It is shown that the multiple scrap pieces agglomerate throughout the sample due to solidified shell formation. The key factors affecting melting kinetics of a heat examined were: heat transfer coefficient, initial solid fraction, initial liquid (preheating) and solid temperatures, scrap size and thermal conductivity. A scaling analysis of simulation data of melting kinetics was conducted, identifying suitable characteristic length and time scales through which the melting kinetics across different parameters and processing conditions could be scaled and thus understood in the context of a unified mathematical description.Master of Applied Science (MASc
ANALYSIS OF LIQUID POOLING DURING LATE-STAGE SOLIDIFICATION
No full textGrain structure and secondary phases play a critical role in determining the mechanical properties of industrial alloys. The spatial variation of such phases is very closely correlated to the liquid pooling established during late stage solidification and grain boundary coalescence. Obtaining a theory that correlates the evolution of length scales during grain boundary coalescence is a critical step toward the optimization of commercial alloys. This thesis highlights various phenomena that enter such a theory. They include coarsening and coalescence of dendrites, nucleation mechanisms and changes in composition of inter-dendritic liquid where second phases tend to initially form. Quantitative phase field models of solidification to simulate casting conditions and microstructure evolution are used in combination with characterization techniques to illustrate the connection between number, size, and distribution of liquid pools. Characterization techniques include spectral analysis, and clustering analysis by way of the Hoshen-Kopleman algorithm. By characterizing late-stage liquid pools, this thesis aims to be a first step towards developing a statistical scaling theory of length scale of liquid pooling.Master of Applied Science (MASc
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