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A Computational Investigation of Nucleation Mechanism and Polymorph Selection in Crystallization
No full textCrystallization is an important process, widely used in many industries including specialty chemicals and pharmaceuticals for separation and purification purposes. Many solids exhibit polymorphism, the ability of a material to exist in multiple crystal structures and crystal structure affects key material properties like stability, solubility, and dissolution rate. Thus, controlling the crystal structure in a crystallization process is essential for the production of materials with the desired properties. Crystal nucleation, with which the formation of the solid phase begins, is the key event that governs the kinetics of crystallization and plays a prominent role in determining the resulting crystal structure. Hence, knowledge of nucleation kinetics is necessary for the design and optimization of crystallization processes.Despite its importance, crystal nucleation is still not fully understood. This mainly results from the difficulty in observing nucleation with experimental techniques, both due to the small time and length scales involved in the formation of critical clusters and the stochastic nature of nucleation as an activated process. Thus, there is a lot of trial-anderror that goes into crystallization process design, taking significant time and resources. Theoretical predictions of nucleation kinetics, on the other hand, can accelerate process design but require a good understanding of the nucleation mechanism. Classical nucleation theory (CNT) provides a kinetic expression that can be used to predict nucleation rates using the thermodynamic properties of bulk crystal slabs, assuming that these properties remain the same for clusters at the nanoscale. However, there is growing evidence in the literature showing that the cluster structure at the time of nucleation can be wildly different than that when the crystal has grown to its bulk form. There is still much to be learned about predicting nucleation rates and incorporating nucleation kinetics into the macroscopic models of industrial crystallizers when nucleation occurs through these non-classical mechanisms. Molecular simulations can help with both understanding the nucleation mechanism at the atomic scale and predicting nucleation rates. This thesis demonstrates the use of molecular simulations and specifically multidimensional free energy calculations as a powerful tool to understand non-classical nucleation mechanisms. With a motivation to develop a computational methodology that can predict nucleation rates and identify the kinetically favored polymorph without relying on CNT, two studies have been conducted:First, NaCl nucleation from aqueous solution was studied using molecular simulations. By calculating the free energy of nucleation as a function of structure specific nucleus size coordinates, it was shown that at high concentrations, NaCl nucleation occurs through the formation of composite clusters that have a crystalline core surrounded by a layer of amorphous particles. The effect of supersaturation on the mechanism was investigated by rerunning the calculations at a higher concentration and a shift was observed in the nucleation mechanism from single step to 2-step nucleation. The shift was shown to be resulting from a change in the relative stability of the intermediate amorphous solid phase.Second, nucleation of the Lennard-Jones (LJ) fluid from the melt was investigated with a focus on the competition between two possible crystal structures. The free energy surface of nucleation, plotted against polymorph-specific nucleus size variables, revealed that polymorph selection in the LJ fluid does not happen during nucleation, but when the emerging clusters are much larger than the critical cluster size, in contrast with the classical nucleation theory assumption. It was observed that the post-nucleation events like crystal growth and polymorphic transformations played a significant role in determining the final structure of the grown crystals. Since a CNT based crystallization model is not able to track the structural changes within the nucleated clusters, a novel population balance modeling framework was proposed. The proposed model connects the structure-specific nucleation rates obtained from atomic-scale simulations with the post-nucleation events and is able to predict the correct polymorphic distribution obtained from 500 nucleation trajectories.This thesis represents a step forward to a complete in silicodesign of crystallization processes for producing materials with the desired crystal structure. Next steps include application of the methods describes here to more complex, industrially relevant molecules
The Aesthetics of Writing Center Assessment: An Interactive Mural
Get PDFThis wall mural combines data and images into a holistic rendering of a writing center’s year of change. It showcases the versatility of writing centers, while highlighting the beauty of the work through the aesthetics of a mural
Investigating Factors that Increase Vulnerability to Cyber-Attacks During the First Year College Transition
No full textMoving from high school to college is a major life transition leading to significant changes across many aspects of daily life. This time frame is often seen as the transition from a youth to a young adult, yet its impact on technology use and cybersecurity vulnerabilities remains relatively unstudied. This study investigated which factors associated with the first-year college transition are likely to increase vulnerability to cyberattacks in a sample of first-year college students attending a public university in the northeast United States, all of whom graduated from high school within the last 12 months. This study used a concurrent triangulation mixed methods design. A quantitative survey and qualitative semi-structured interviews were conducted concurrently, the methods were prioritized equally, and the results were interpreted together. Thematic analysis was used to analyze survey short answer responses and semi-structured interviews. A more descriptive analysis was completed to analyze survey responses from 38 respondents. The research found that an increase in the amount of time spent online, changing main internet activities, and lack of cybersecurity awareness training are factors which are likely to increase vulnerability to cyber threats during the transition from high school to college
Taming Irregular Control-Flow with Targeted Compiler Transformations
No full textIrregular control-flow structures like deeply nested conditional branches are common in real-world software applications. Improving the performance and efficiency of such programs is often challenging because it is difficult to analyze and optimize programs with irregular control flow. We observe that real-world programs contain similar or identical computations within different code paths of the conditional branches. Compilers can merge similar code to improve performance or code size. However, existing compiler optimizations like code hoisting/sinking, and tail merging do not fully exploit this opportunity. We propose a new technique called Control-Flow Melding (CFM) that can merge similar code sequences at the control-flow region level. We evaluate CFM in two applications. First, we show that CFM reduces the control divergence in GPU programs and improves the performance. Second, we apply CFM to CPU programs and show its effectiveness in reducing code size without sacrificing performance. In the next part of this dissertation, we investigate how CFM can be extended to improve dynamic test generation techniques like Dynamic Symbolic Execution (DSE). DSE suffers from path explosion problem when many conditional branches are present in the program. We propose a non-semantics-preserving branch elimination transformation called CFM-SE that reduces the number of symbolic branches in a program. We also provide a framework for detecting and reasoning about false positive bugs that might be added to the program by non-semantics-preserving transformations like CFM-SE. Furthermore, we evaluate CFM-SE on real-world applications and show its effectiveness in improving DSE performance and code coverage
Evaluación y rentabilidad de variedades de chile en tres granjas de Minnesota y Wisconsin, 2022
No full textLos agricultores latinos de hortalizas frescas de Minnesota y Wisconsin están interesados en cultivar chiles picantes tanto frescos como deshidratados para su venta en mercados locales. Este ensayo de variedades es el tercero y último de un proyecto de tres años de duración. El ensayo incluyo 14 variedades de chile incluyendo jalapeño, serrano, habanero, poblano y otros tipos. Las variedades incluyeron las mejores variedades de 2020 y 2021 junto con nuevas variedades. Calculamos el rendimiento, tamaño y las unidades Scoville. Además del ensayo de variedades, realizamos un análisis empresarial para determinar la rentabilidad de la producción de chiles picantes en el Medio Oeste Superior
Le Musée des Écoles étrangères et le spectre de la guerre en Europe dans l’Entre-deux- guerres
No full textCet article examine si et comment la politique artistique du Musée des Écoles étrangères à Paris dans les années 1920 et 1930 put contribuer à définir l’ « art européen » ainsi que l’espace européen. Il étudie ensuite la seule toile exposée par le musée – Europe, réalisée par l’artiste Ismaël Gonzalez de La Serna vers 1935 – qui prêta une attention particulière au sujet. Tout en mettant cette oeuvre en rapport avec les oeuvres portant sur le même sujet réalisées à l’époque par d’autres artistes, il s’agit, enfin, de comprendre la faible circulation de cette image de l’Europe, qui relativise sa symbologie énigmatique
L’Étoffe de l’Europe
Get PDFLe tissage est le fil conducteur des interventions artistiques qui ont marqué la présidence française dans les bâtiments du Conseil de l’Union européenne à Bruxelles de janvier à juin 2022. Il exprime le travail, la patience, l’agilité et la fragilité face à la monumentalité des bâtiments, et le collectif dans sa force de proposition et d’action et dans sa capacité de résilience. Nous avons créé un textile complexe, joyeux et pétillant, dont la chaîne est composée des couleurs des 27 drapeaux des États de l’Union et la trame l’est des drapeaux des présidences successives, une sorte de data-tissage que nous avons nommé L’Étoffe de l’Europe®, comme une évidence. À quelques mois de la guerre en Ukraine
Une Europe par les arts ? Les périodiques illustrés au-delà du Musée imaginaire
Get PDFExiste-t- il un musée imaginaire européen ? Cet article aborde la question par le biais des illustrations de presse des années 1880-1960. Dans les périodiques illustrés de cette époque, les images d’art traversèrent mieux les frontières que les images non artistiques, en particulier en Europe. Mais plutôt que de conclure à un musée imaginaire européen, une étude multiscalaire plus fine incite à se pencher sur les facteurs sociaux, esthétiques, économiques et techniques de la circulation imprimée des images artistiques
A Critical Librarianship Approach for Teaching Patent Searching: Who Becomes an Inventor in America?
Get PDFThe ways in which a technology is invented, owned, and approved are strongly influenced by the same oppressive and exclusionary structures that critical librarianship interrogates. Patents, limited-term grants of rights to inventions, are issued to inventors in exchange for detailed specifications of the invention. This paper examines current practices used by business librarians in teaching students how to find patents and how these practices could be critically informed given the nature of the United States patent system as it exists today. An output of this work is a suggested lesson plan with recommended resources
Jews and Urban Life
Get PDFJews and Urban Life recognizes that throughout their long history, Jews have often inhabited cities. The reality of this urban experience ranged from ghetto restrictions to robust participation in a range of civic and social activities. Essays in this collection present relevant examples from within the Jewish community itself, moving historically from the biblical period to the modern-day State of Israel. Taking a comparative approach while recognizing the particulars of individual instances, authors examine these phenomena from a wide variety of approaches, genres, and media. Interdisciplinary and accessibly written, the articles display a multitude of instances throughout history showing the range of Jewish life in urban settings.https://docs.lib.purdue.edu/sjc/1012/thumbnail.jp