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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.
381

Designing Surfaces for Enhanced Water Condensation and Evaporation

Jin, Yong 08 1900 (has links)
With the increasing pressure of providing reliable potable water in a sustainable way, it is important to understand water phase change phenomena (condensation and evaporation) as the water phase change is involved in many processes such as membrane distillation and solar still which can be a feasible choice of supplementing the present potable water access. In the present thesis, we first elucidate the role of wettability of water condensation substrate by combining the droplet growth dynamics and droplet population evolution. The results show that wettability has a negligible effect on water condensation rate in an atmospheric environment. After confirming the role of substrate wettability, we provide a quantitative analysis of the effect of substrate geometry on water condensation in the atmospheric environment. The analysis can help to predict the efficiency of water condensation rate with a given substrate of a certain geometry with the aid of computational simulation tools. The results show that water condensation can be increased by 40% by rationally designing the geometry of the condensation surface. However, the condensation rate in the atmospheric environment is relatively slow due to the presence of non-condensable gas. In order to increase the condensation rate, a relatively pure vapor environment is desired, in which condensed water will be the major heat transfer barrier. Coalescence induced jumping of condensed droplets on superhydrophobic surfaces is an interesting phenomenon to help faster removal of condensed droplets. However, it is still not clear how to optimize the overall heat transfer efficiency by condensation on such surfaces. We observed an interesting phenomenon on a superhydrophobic nano-cones array, on which water preferentially condenses within larger cavities among the nanocones. Droplets growing form larger cavities have larger growth rate. This finding can possibly provide a solution to optimizing heat transfer efficiency. Finally, a nylon-carbon black composite is prepared by electrospinning to enhance water evaporation under solar radiation. The composite shows an interesting light absorption property. In a wet state, the composite can absorb around 94% of the incident sunlight. The composite also shows strong mechanical and chemical stability. Thus, the composite is considered to be a practical candidate to be applied in the solar distillation process.
382

Studies of non-equilibrium behavior of quantum many-body systems using the adiabatic eigenstate deformations

Pandey, Mohit 02 September 2021 (has links)
In the last few decades, the study of many-body quantum systems far from equilibrium has risen to prominence, with exciting developments on both experimental and theoretical physics fronts. In this dissertation, we will focus particularly on the adiabatic gauge potential (AGP), which is the generator of adiabatic deformations between quantum eigenstates and also related to "fidelity susceptibility", as our lens into the general phenomenon. In the first two projects, the AGP is studied in the context of counter-diabatic driving protocols which present a way of generating adiabatic dynamics at an arbitrary pace. This is quite useful as adiabatic evolution, which is a common strategy for manipulating quantum states, is inherently a slow process and is, therefore, susceptible to noise and decoherence from the environment. However, obtaining and implementing the AGP in many-body systems is a formidable task, requiring knowledge of the spectral properties of the instantaneous Hamiltonians and control of highly nonlocal multibody interactions. We show how an approximate gauge potential can be systematically built up as a series of nested commutators, remaining well-defined in the thermodynamic limit. Furthermore, the resulting counter-diabatic driving protocols can be realized up to arbitrary order without leaving the available control space using tools from periodically-driven (Floquet) systems. In the first project, this driving protocol was successfully implemented on the electronic spin of a nitrogen vacancy in diamond as a proof of concept and in the second project, it was extended to many-body systems, where it was shown the resulting Floquet protocols significantly suppress dissipation and provide a drastic increase in fidelity. In the third project, the AGP is studied in the context of quantum chaos wherein it is found to be an extremely sensitive probe. We are able to detect transitions from non-ergodic to ergodic behavior at perturbation strengths orders of magnitude smaller than those required for standard measures. Using this alternative probe in two generic classes of spin chains, we show that the chaotic threshold decreases exponentially with system size and that one can immediately detect integrability-breaking (chaotic) perturbations by analyzing infinitesimal perturbations even at the integrable point. In some cases, small integrability-breaking is shown to lead to anomalously slow relaxation of the system, exponentially long in system size. This work paves the way for further studies in various areas such as quantum computation, quantum state preparation and quantum chaos.
383

Illuminating Changes in Preservice Teachers’ Perceptions about Teaching Elementary Mathematicsin an Introductory Methods Course

Cerrato, Elaine 10 April 2019 (has links)
Producing highly skilled elementary mathematics teachers capable of facilitating mathematics learning in ways aligned with The Principles and Standards for School Mathematics (NCTM, 2000) and the Common Core State Standards for Mathematics (CCSSM), is a common objective of teacher preparation programs (National Governors Association & Chief Council of State School Officers, 2010). After decades of effort, Brown (2003) argues, teachers continue to teach in the way they were taught; thus, they disregard mathematics standards. As Abell, Appleton, and Hanuscin (2010) note, students’ preexisting ideas relevant to the nature of learning and teaching stem from experiences in their schooling, life, and formal classes. Specifically, related to mathematics, these experiences often reflect the difficulty in learning mathematics, fear of mathematics, and consequently, a dislike for the subject (Abell et al., 2010; Wilson, 2014). These preconceived beliefs influence how preservice teachers (PSTs) perceive subject matter. Beliefs also impact the decisions they make about teaching and learning mathematics. In this exploratory descriptive case-study I investigated in what ways three PSTs describe their experiences as K-12 mathematics learners, how the PSTs perceive their abilities to teach mathematics prior to participating in an introductory elementary mathematics methods course, how the PSTs perceive their abilities to teach mathematics after participating in an introductory elementary mathematics methods course, and what catalysts, relative to their experiences, do the PSTs consider noteworthy in the development of their beliefs and concurrent pedagogy about teaching mathematics to elementary students. I utilized constant comparative methods (Strauss and Corbin, 1998; Denzin and Lincoln, 1994; Strauss, 1987; Miles and Huberman, 1984) to analyze the data and identify overarching themes related to the goals of the study.
384

Chemoenzymová synthesa antivirálních profarmak / Chemo-enzymatic synthesis of antiviral prodrugs

Tupec, Michal January 2015 (has links)
Lipases have been widely applied in the manufacture of food products and in some areas of the industry, nowadays they are used in synthetic organic chemistry catalyzing the hydrolytic/esterification reactions under very mild conditions in the field of protecting groups or enantiomer resolution. In this study, the commercial lipase from bacterium Pseudomonas fluorescens was immobilized using the sol-gel process into organosilicate materials with propyl, octyl or phenyl substituents. The highest hydrolytic activity was found in the enzyme on the octyl-derived carrier. The immobilized enzymes differ in their hydrolytic activities on 4-nitrophenyl esters of various lengths. Subsequent experiments revealed quite good pH stability of the enzymes in a buffer (incubations in pH 3 through pH 11), as well as good temperature stability in isooctane (incubations at up to 100 řC). The majority of organic solvents seem to have no substantial effect on the lipase activity. The biocatalytic properties were studied on a model compound from the group of the acyclic nucleoside analogues - 9-(2',3'-dihydroxypropyl)adenine (DHPA). It was found for example that the best acyl donors are vinyl esters, that the lipase shows a preference towards longer vinyl esters, that the reaction proceeds faster in non-polar solvents or that it...
385

Innovative Strategies for Balancing Academic Knowledge and Relevant Experience in Principal Preparation

Scott, Pamela H., Foley, Virginia P., Glover, Eric 06 November 2008 (has links)
Linking classroom instruction and theory to relevant practice in principal training programs is a problematic issue. Much like preparation programs in teacher education, university programs designed to prepare aspiring administrators have been under scrutiny because of a perceived lack of relevance to the complex nature of the principalship. University professors and researchers, as well as principals in the field, have continually sought ways to solve this problem. The dilemma for university professors as they seek innovative instructional techniques is striking the balance between academic knowledge and practical experience. How is the gap bridged in a meaningful manner for candidates in principal training programs? The alignment of objectives and field experiences in all core courses in the principal preparation program provides the opportunity for students to construct experiences that provide relevant learning grounded in theory. This alignment allows learning to continue through course transitions unimpeded by time restrictions or the end of one semester. Ten aspiring administrators participated in a process of constructing their learning experiences based on the concept of emergent design during their two-year principal preparation program. Opportunities to observe, participate, and lead were developed within the parameters of the aligned course objectives and with consideration to individual needs assessments. The evolution of this professional learning community is documented in the culminating activity of the program. The instructional strategies utilized thoughout the principal preparation program were evident in the product of work and reflective activities of the students.
386

Emergent Design: Principal Preparation for Today and Tomorrow

Foley, Virginia P., Scott, Pam, Glover, Eric 31 October 2008 (has links)
East Tennessee State University, Southern Regional Educational Board, Greeneville City Schools, and Kingsport City Schools formed the Greene-King Partnership to redesign principal preparation in Tennessee. This paper tells the story of that redesign and implications for the future of principal preparation.
387

Middle Grades Student Achievement and Poverty Levels: Implications for Teacher Preparation

Dotson, Lauren, Foley, Virginia P. 01 January 2017 (has links) (PDF)
This paper provides a history of the standardized testing and accountability movement, the curriculum standards attached to the accountability movement, and the attempted shift to common core. Student poverty and its impact on student achievement the focus of this paper. Recognizing the impact of poverty on student achievement as measured by standardized tests the authors question the explicit practices of teacher preparation programs in preparing teacher candidates to work with students of poverty.
388

Preparation and evaluation of sulfided NiMo/γ-Al2O3 hydrotreating catalysts / Framställning och utvärdering av sulfiderade NiMo/y-AI2O3 katalysatorer för hydrotreating

KAMYAB, ALI January 2016 (has links)
Four nickel-molybdenum catalysts were synthesized on gamma alumina with higher surface area and on NiMo catalyst was prepared using gamma alumina with lower surface area. Catalysts with higher-surface-area support were prepared by co-impregnation, sequential impregnation and adding phosphorous. Theses catalysts were calcined at 500  ͦC. Effect of higher calcination temperature was investigated by preparation of one catalyst calcined at 700 ͦC. Catalysts were thoroughly characterized via four characterization techniques. The hydrotreating activity of three catalysts was carried out in a micro reactor at high pressure and three different temperatures with Nynas vacuum middle distillate. Prior to the test, sulfiding was carried out to activate the catalysts. Hydrotreated-oil samples as products were analyzed to evaluate the activity and conversion of the catalyst. Also, the spent catalysts were characterized to evaluate the surface area characteristics and deactivation of catalysts. Addition of phosphorous to NiMo/gamma-Al2O3 improved the interaction between the metals and the support as well as reduced the coke formation as observed in scanning electron microscopy micrographs.
389

Development of a CNC Milling System for Preparation of Micrometer-Sized Samples for X-ray Nanotomography / Utveckling av ett CNC-styrt fräsningssystem för beredning av mikrometerstora prover till nanotomografi med röntgenstrålning

Messler, Olivia January 2021 (has links)
X-­ray nanotomography is an imaging technique used to study three­-dimensional structures at submicrometer length scale. The samples to be studied should be only 10s of micrometers in diameter, and ideally cylindrical. Focused ion beam milling is the most common technique used to prepare samples for nanotomography experiments, and the current technique used at the NanoMAX beamline of the MAX IV synchrotron facility. It is a time­-consuming process as preparing one sample can take hours. With the aim of offering a faster, alternative sample preparation method, a CNC milling setup was developed, and is presented here. The CNC setup is based on two spindles placed on precision linear stages - one for the sample and one for the milling tool. The sample is rotated while being trimmed gently by the milling tool, resulting in a small sample cylinder. A Python script generating G­-code commands controls the procedure. The setup was used to trim copper samples down to 18.5 micrometers. Further work is needed to optimize milling parameters in order to reach similar diameters for other sample materials. The developed setup offers a time-­efficient, repeatable and low­-cost sample preparation method for X-­ray nanotomography. / Nanotomografi med röntgenstrålning är en metod som används för att urskilja och studera tre­-dimensionella strukturer i material av storleksordningar mindre än 100 nanometer. Proverna behöver vara små; endast tiotals mikrometer i diameter. Det ideala provet för tomografi är cylindriskt. Fokuserad jonstrålefräsning är en vanlig metod för att preparera prover för nanotomografi, och är den metod som idag används på NanoMAX vid synkrotronljusanläggningen MAX IV. Det är en tidskrävande process; att förbereda ett enda prov tar flera timmar. Med avsikt att erbjuda en snabbare, alternativ metod för provpreparering så utvecklades ett CNC-styrt frässystem, som presenteras här. Systemet är baserat på två spolar placerade på precisionsplattformar - en för själva provet och en för fräsverktyget. Ett Python-program utvecklades som skickar kommandon i G-­kod och därigenom kontrollerar precisionsplattformarnas rörelser. Provet trimmas till en viss diameter, och slutresultatet är ett nästintill cylindriskt prov som kan användas för nanotomografi. Den minsta diameter som nåddes var 18.5 mikrometer, för ett kopparprov. Ytterligare arbete krävs för att optimera parametrar för fräsproceduren för andra typer av material, för att lika små diametrar ska kunna nås. Systemet som utvecklats erbjuder en snabb, billig och repeterbar metod för att förbereda prover för nanotomografi med röntgenstrålning.
390

Příprava snoubenců ve vybraných vikariátech HK diecéze / Preparation of engaged couples for marriage in selected vicariates HK Diocese

Fajstavr, Antonín January 2015 (has links)
The diploma thesis shows the current state and level of marriage preparation of the engaged couples within the Hradec Kralove diocese border region. The thesis examines and evaluates the status of the preparations in four vicariates in connection with the related church documents. The particular vicariates together with the qualified personnel are introduced and number of marriages for the past ten years is listed for a reference. The thesis characterises four different types of engaged couples and introduces several types of preparations. The current state of the preparations in the region is surveyed and findings are presented in the thesis. Among the preparations guided by a priest the thesis describes additional tools and techniques complementing the preparations. The final part of the thesis is dedicated to these complementary preparation tools and techniques which are presented, compared and evaluated here. The diploma thesis notices preparation of engaged couples with respect to the formation of the future family, which is encouraged by the thesis.

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