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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
111

Einfluss homogener und inhomogener Magnetfelder auf die Korrosion ferromagnetischer Elektroden

Süptitz, Ralph 18 October 2011 (has links)
Im Rahmen der vorliegenden Arbeit konnten Einflüsse magnetischer Felder, insbesondere mit hohen Gradienten der magnetischen Flussdichte, auf Korrosionsprozesse am Beispiel Eisen quantifiziert und deren Wirkungsmechanismus erklärt werden. Als ein besonders in technisch relevanten gering konzentrierten sauren wässrigen Lösungen bedeutsamer Effekt wurde eine sekundäre Wirkung der Feldgradientenkraft über den Mechanismus der Wahrung der Ladungsneutralität auf den pH-Wert an der Elektrodenoberfläche identifiziert. Somit konnte ein signifikanter Magnetfeldeinfluss auf die formal ladungstransferkontrollierte Korrosionsreaktion nachgewiesen werden. Um die komplexen Korrosionsvorgänge an mehrphasigen NdFeB-Magneten mit paramagnetischer intergranularer Nd-reicher Phase aufklären zu können, war zunächst eine vertiefte Analyse der freien und anodischen Korrosionsreaktionen des Neodyms notwendig. Die dabei gewonnenen Erkenntnisse erlauben den Magnetfeldeinfluss bei der Korrosion aufmagnetisierter NdFeB-Magnete zu verstehen.
112

Att vara eller inte vara laglösa : En intervjustudie om hur den enskilda arkivsektorn ställer sig till att inkluderas i arkivlagen och deras plats i kulturpolitiken / To be or not to be lawless : An interview study regarding how Swedish private archival institutions respond to the possibility of being included in the Archival Law and their place in cultural politics

Hamrén, Nina, Svelander, Malin January 2020 (has links)
Introduction. The aim of this thesis is to examine how Swedish private archival institutions perceive the possibility of being included in the Archival Law. At present the Archival Law of 1990 only applies to official documents from the public sector. Recently however a proposal to change the legislation so that it in part also applies to private archives has been made in the newly published Archival Inquiry commissioned by the government. A more far-reaching proposal to include the private archives in the law has also been made by the Swedish National Archives. Method. We conducted a qualitative research study using semi-structured interviews with 10 informants from 8 different private archival institutions in Sweden. Analysis. By presenting what has been said regarding legislation for private archives in previous archival inquiries, government propositions and other official reports we frame the idea of legislation for private archives by putting it in its culturalpolitical context. An important concept that permeates this thesis is the concept of cultural heritage and how it relates to private archives. The transcriptions from the interviews were analysed by the use of force-field analysis which has its roots in Karl Lewin’s field theory. Results. By collecting the informants thoughts concerning a new legislation for private archives and analysing them as forces working for (driving forces) and against (restraining forces) change we show the complexities surrounding this issue. Conclusion. In many cases uncertainty of what the consequences of the new legislation will be for the private archival institutions prevents them from supporting the change. Our informants also feel that the Swedish National Archives has a top-down perspective which prevents them from listening to and learn from the private sectors experiences. Collaboration between the public and the private sector seems to be the way forward. This is a two years master’s thesis in Archival Science
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113

Crystal Polymorphism of Substituted Monocyclic Aromatics

Svärd, Michael January 2009 (has links)
No description available.
114

Evaluating Success Factors in Implementing E-Maintenance in Maintenance, Repair, and Overhaul (MRO) Organizations

Toves, Peter Rocky 01 January 2015 (has links)
Despite more than a decade-long process to transition aircraft maintenance practices from paper-to electronic-based systems, some organizations remain unable to complete this transition. Researchers have indicated that while organizations have invested resources in technology improvements, there remains a limited understanding of the factors that contribute to effectively managing technology-enabled change. The purpose of this case study was to identify and explore socio-technical (ST) factors that inhibit an effective transition from a paper-based system to an electronic-based system for aircraft maintenance. A conceptual model applying theories of change management, technology acceptance, systems thinking, and ST theory informed the research. Thirteen participants provided data via semistructured interviews, field observations, follow-up interviews, other documentation, and a questionnaire. Data were analyzed with open and axial coding techniques to identify themes, which were then crosschecked and triangulated with observation and follow-up interview data. Findings revealed communication issues, a fundamental misconception in training, and a false assumption that all personnel easily acquire computer literacy. Benefits gained from this study should assist maintenance, repair, and overall (MRO) organizations within the Department of Defense to improve current and future technology implementation as the research underscores real-life issues from a comparable organization. The implications for positive social change provide a greater understanding of technology-enabled change and contribute to the development of best practices for technology initiatives that address common ST issues in the MRO workplace.
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115

Investigation of Protein/Ligand Interactions Relating Structural Dynamics to Function: Combined Computational and Experimental Approaches

Pavlovicz, Ryan Elliott 24 June 2014 (has links)
No description available.
116

Using Molecular Simulations and Statistical Models to Understand Biomolecular Conformational Dynamics

Ge, Yunhui January 2020 (has links)
Conformational dynamics are important to the function of biological molecules. While many experimental techniques (e.g. X-ray crystallography and NMR spectroscopy) have been developed for providing the structure of functional conformations, it is exceptionally challenging to understand conformational dynamics from experimental characterization. Molecular dynamics (MD) simulations is a powerful tool for probing conformational dynamics. The timescale resolution of MD simulations enables people to investigate intermediate conformations and transition pathways in atomic detail. Recent advancements in computer hardware have increased the timescales accessible to MD simulations. Meanwhile, more accurate and specific force fields have been developed to accurately model a variety biological system of different sizes. My graduate research has been focused on using MD simulations to study the conformational dynamics of proteins. Markov State Model (MSM) based approaches are extensively applied to investigate a variety of folding and/or binding mechanisms in atomic detail. Another focus of my work has been developing a Bayesian inference-based approach called BICePs to reconcile experimental measurements with simulation data to determine conformational ensembles and to validate force fields. / Chemistry
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117

Optimal Point Charge Approximation: from 3-Atom Water Molecule to Million-Atom Chromatin Fiber

Izadi, Saeed 13 July 2016 (has links)
Atomistic modeling and simulation methods enable a modern molecular approach to bio-medical research. Issues addressed range from structure-function relationships to structure-based drug design. The ability of these methods to address biologically relevant problems is largely determined by their accurate treatment of electrostatic interactions in the target biomolecular structure. In practical molecular simulations, the electrostatic charge density of molecules is approximated by an arrangement of fractional "point charges" throughout the molecule. While chemically intuitive and straightforward in technical implementation, models based exclusively on atom-centered charge placement, a major workhorse of the biomolecular simulations, do not necessarily provide a sufficiently detailed description of the molecular electrostatic potentials for small systems, and can become prohibitively expensive for large systems with thousands to millions of atoms. In this work, we propose a rigorous and generally applicable approach, Optimal Point Charge Approximation (OPCA), for approximating electrostatic charge distributions of biomolecules with a small number of point charges to best represent the underlying electrostatic potential, regardless of the distance to the charge distribution. OPCA places a given number of point charges so that the lowest order multipole moments of the reference charge distribution are optimally reproduced. We provide a general framework for calculating OPCAs to any order, and introduce closed-form analytical expressions for the 1-charge, 2-charge and 3-charge OPCA. We demonstrate the advantage of OPCA by applying it to a wide range of biomolecules of varied sizes. We use the concept of OPCA to develop a different, novel approach of constructing accurate and simple point charge water models. The proposed approach permits a virtually exhaustive search for optimal model parameters in the sub-space most relevant to electrostatic properties of the water molecule in liquid phase. A novel rigid 4-point Optimal Point Charge (OPC) water model constructed based on the new approach is substantially more accurate than commonly used models in terms of bulk water properties, and delivers critical accuracy improvement in practical atomistic simulations, such as RNA simulations, protein folding, protein-ligand binding and small molecule hydration. We also apply our new approach to construct a 3-point version of the Optimal Point Charge water model, referred to as OPC3. OPCA can be employed to represent large charge distributions with only a few point charges. We use this capability of OPCA to develop a multi-scale, yet fully atomistic, generalized Born approach (GB-HCPO) that can deliver up to 2 orders of magnitude speedup compared to the reference MD simulation. As a practical demonstration, we exploit the new multi-scale approach to gain insight into the structure of million-atom 30-nm chromatin fiber. Our results suggest important structural details consistent with experiment: the linker DNA fills the core region and the H3 histone tails interact with the linker DNA. OPC, OPC3 and GB-HCPO are implemented in AMBER molecular dynamics software package. / Ph. D.
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118

Modéliser la polarisation électronique par un continuum diélectrique intramoléculaire vers un champ de force polarisable pour la chimie bioorganique

Truchon, Jean-François January 2008 (has links)
Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.
119

Modéliser la polarisation électronique par un continuum diélectrique intramoléculaire vers un champ de force polarisable pour la chimie bioorganique

Truchon, Jean-François January 2008 (has links)
Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal
120

Computational investigations of molecular transport processes in nanotubular and nanocomposite materials

Konduri, Suchitra 12 February 2009 (has links)
The unique physical properties of nanomaterials, attributed to the combined effects of their size, shape, and composition, have sparked significant interest in the field of nanotechnology. Fabrication of nanodevices using nanomaterials as building-blocks are underway to enable novel technological applications. A fundamental understanding on the structure-property relationships and the mechanism of synthesizing nanomaterials with tailored physical properties is critical for a rationale design of functional nanodevices. In this thesis, molecular simulations that employ a detailed atomistic description of the nanoscopic structures were used to understand the structure-transport property relationships in two novel classes of porous nanomaterials, namely, polymer/porous inorganic layered nanocomposite materials and single-walled metal oxide nanotubes, and provide predictions for the design of nanodevices using these nanomaterials. We employed molecular dynamics to study transport of gas molecules (in particular He, H2, N2 and O2) through a polydimethylsiloxane/porous layered silicate (AMH-3) nanocomposite membrane material as a function of its composition. Gas separation performance of the nanocomposite was found to be substantially enhanced for H2/N2 and H2/O2 compared to pure polymeric material due to the molecular sieving effect of AMH-3, suggesting the possibility of developing a new class of superior separation devices. We also developed force field parameters for layered aluminophosphates that are emerging as potential inorganic layers for construction of nanocomposite materials. We presented preliminary work on developing Transition State Approach-Monte Carlo simulation method for calculating gas transport properties of nanocomposite materials. We investigated in detail the diameter control phenomenon in single-walled metal oxide nanotubes using molecular dynamics simulations and demonstrated the existence of a thermodynamic 'handle' for tuning the nanotube diameters and derived a unique correlation between nanotube energy, composition, and diameter to precisely predict nanotube diameters. Finally, using a combination of molecular dynamics, monte carlo and sorption experiments, we investigated adsorption and diffusion properties of water in single-walled aluminosilicate nanotubes. We predicted high water fluxes in these nanotubes, due to short lengths, hydrophilic interior and near-bulk-water diffusivities. Overall, my research represents two examples of the progress in developing a predictive basis for the design and analysis of nanostructures for applications in separations, nanofluidics, and fuel cell technology.
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