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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.
61

Vibrational Sum Frequency Spectroscopic Investigations of Sulfur Dioxide Adsorption to Atmospherically Relevant Aqueous Surfaces

Ota, Stephanie Tomoko, 1978- 06 1900 (has links)
xv, 108 p. : ill. (chiefly col.) / Aqueous aerosol surfaces are an important platform for chemical reactions through which gases are transported in the atmosphere. The chemical complexity of aqueous aerosols is well-established, but many questions remain about the molecular nature of their surfaces, particularly with respect to the uptake of gases. The pollutant sulfur dioxide, SO<sub>2</sub>, has been implicated in environmental phenomena such as acid rain, climate change, and cloud formation. SO<sub>2</sub> is fundamentally interesting because it forms spectroscopically identifiable complexes with water at aqueous surfaces. This dissertation aims to understand how temperature and aqueous composition impact the formation of surface complexes between water and SO<sub>2</sub>. Vibrational sum frequency spectroscopy (VSFS), a surface specific technique, is used to probe the vibrational modes of water and small organic molecules, investigating changes to the overall orientation, bonding environment, and structure of interfaces when aqueous surfaces are exposed to SO<sub>2</sub>. SO<sub>2</sub> adsorption to water at tropospherically relevant temperatures (0--23 °C) is examined first. The results show enhanced SO<sub>2</sub> surface affinity at colder temperatures, with most of the topmost water molecules showing evidence of binding to SO<sub>2</sub> at 0 °C compared to a much lower fraction at room temperature. Surface adsorption results in significant changes in water orientation at the surface but is reversible at the temperatures examined. The surface and vibrational specificity of these studies can be used to distinguish between the effects of surface adsorption compared to bulk accommodation. This distinction is utilized to demonstrate that SO<sub>2</sub> complexation is independent of solution acidity, confirming that bulk absorption is unnecessary for surface adsorption to occur. Finally, the impact of the organic species succinic acid and formaldehyde on the formation of surface SO<sub>2</sub> complexes is examined. These experiments indicate that SO<sub>2</sub> surface complexation occurs primarily with water but that surface active organic species may interact with gases under certain circumstances, namely when the organic species are more chemically reactive towards the gas. These studies have important implications for atmospheric chemistry and the uptake of gases, particularly in the complex aqueous environments expected in the troposphere. / Committee in charge: Dr. Paul C. Engelking, Chair; Dr. Geraldine L. Richmond, Advisor Dr. Jeffrey A. Cina, Member; Dr. Thomas R. Dyke, Member; Dr. Alan D. Johnston, Outside Member
62

Spectroscopic and Thermodynamic Studies of the Adsorption of Atmospherically Relevant Dicarboxylic Acids at the Vapor/Water Interface

Blower, Patrick 03 October 2013 (has links)
Many important atmospheric processes are determined by the chemical composition of aerosols, including organic material. Dicarboxylic acids are a commonly detected class of organic material in urban, rural, and remote sites across the globe. Understanding the surface behavior of these molecules is imperative in characterizing the atmospheric fate of these molecules in aerosols, especially at an aerosol surface. In fact, little is known about their orientation, solvation, or pH dependence. This dissertation explores in molecular level detail the concentration and pH behavior of low molecular weight dicarboxylic acids at the air/water interface, which is used as a model for an aerosol surface. The solvation of the carboxylic head groups is shown to be dependent upon the length of the alkyl backbone. Indeed, the solvation of the head groups changes dramatically from very weakly solvated to typical surface solvation to near bulk solvation as the backbone increases. The orientation and conformation at the surface is fully explored to explain these differences in solvation. The pH dependence of surface adsorption is characterized, and it is shown that some acids are only surface active if they are fully protonated while others may still be surface active in singly or fully deprotonated forms. Using a combination of vibrational sum frequency spectroscopy (VSFS), surface tension, and computational modeling, the behavior at the air/water interface of four of the most relevant surface-active dicarboxylic acids (malonic, succinic, glutaric, and adipic acid) is completely described. VSFS, a surface specific optical technique, provides details about the solvation, orientation, and number density at the surface while surface tension measurements provide corollary information about the surface density. The use of computational modeling aids and confirms the spectral analysis while also providing molecular level details about the surface adsorption of the acids studied. By investigating the concentration and pH dependence of these molecules, molecular level detail is obtained which enables a complete description of these acids at an air/water interface and provides pertinent surface information on these atmospherically important organic molecules. This dissertation includes both previously published and unpublished co-authored material.
63

\"Partículas exóticas em regras de soma da QCD\" / Exotic Hadrons in a QCD Sum Rules calculation

Ricardo D'Elia Matheus 08 December 2006 (has links)
Neste trabalho usamos as regras de soma da QCD para calcular as massas e constantes de acoplamento ou decaimento dos estados exóticos theta+(1540) e cascata--(1862) (pentaquarks), dos mesons escalares charmosos DsJ+(2317), D0(2308) e D0(2405) e do meson axial X(3872). Os mesons foram também tratados como estados exóticos de quatro quarks (tetraquarks). Dois métodos de regra de soma foram aplicados e uma atenção especial foi dada aos limites de validade e incertezas da regra de soma. Em todos os casos encontramos resultados compatíveis com os dados experimentais existentes, mas no caso dos pentaquarks e dos mesons escalares as regras de soma têm algumas de suas condições violadas, levantando a questão sobre a existência das ressonâncias na forma em que foram propostas. Fizemos também uma previsão para um méson axial Xb, que é uma expansão para o setor botônico do modelo assumido para o X(3872). / In this work the QCD Sum Rules have been used to obtain masses and coupling or decay constants of the theta+(1540) and cascade--(1862) pentaquarks, the DsJ+(2317), D0(2308) and D0(2405) charmed scalar mesons and the X(3872) axial meson. The mesons have been treated as 4-quark exotic states (tetraquarks). Two sum rules methods have been used with special attention given to the limits and uncertainties of the sum rules. Results consistent with experimental data have been found in all cases, but some of the sum rules constraints have been violated in the calculation of the pentaquarks and scalar mesons, leaving questions about the existence of the states as they have been built here. A prediction was also made for the mass of a state expanding the model used for X(3872) to the botton sector, named Xb.
64

Quadrados mÃgicos com aplicaÃÃes / Magic squares with applications

Josà Samuel Machado 13 April 2013 (has links)
CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior / Neste trabalho, colocaremos a forma lendÃria de como os quadrados mÃgicos surgiram bem como sua utilizaÃÃo por artistas entre os sÃculos 15 e 18. Posteriormente definimos os quadrados mÃgicos e quadrados mÃgicos normais. Por fim, estabeleceremos o conjunto de todos os quadrados mÃgicos de mesma ordem como espaÃos vetoriais, determinando sua base e sua dimensÃo, exemplificando para os casos de ordem 3 e 4. / In this paper, we will place the legendary form of magic squares appeared as well as its use by artists between the 15th and 18th centuries. Later defined magic squares and magic squares normal. Finally, we will establish the set of all magic squares of the same order as vector spaces, determining its basis and its dimension, illustrating the cases of order 3 and 4.
65

Strong interactions of elementary particles : Regge theory and sum rules

Frampton, Paul H. January 1968 (has links)
No description available.
66

Elevers inflytande på stödåtgärder i matematikundervisningen : baserat på elevers upplevelser

Frank, Isabell, Kärredal, Karin January 2017 (has links)
Syftet med studien är att bidra med kunskap kring SUM-elevers (elever i särskilt utbildningsbehov i matematik) upplevelser av inflytande kring sina stödåtgärder i matematikundervisningen. Att stödja elever i att utveckla sin förmåga av att ha inflytande är en del av skolans uppdrag. I denna studie innebär inflytande att påverka sina stödåtgärder i matematikundervisningen vad gäller hur, när, var, vad och med vem. En del forskning har gjorts kring inflytande men den handlar inte så mycket om inflytande i matematikundervisningen och är ofta mer riktade mot homogena grupper. I denna studie har vi valt att intervjua nio stycken SUM-elever som har stödåtgärder i matematikundervisningen i årskurs 9. Tolkningen av elevernas upplevelser i intervjuerna har gjorts med hjälp av en hermeneutisk ansats och därefter analyserats med avseende på makt, relationer och grad av nöjdhet genom att kategorisera resultatet i fyra kategorier: hälsan tiger still, vanmakt, maktlöshet samt framgångsrik maktutövning. I resultatet framgår det att eleverna upplever att de har en framgångsrik maktutövning på sina stödåtgärder kring hur de skulle arbeta och vad de skulle arbeta med, vår tolkning är att dessa faktorer var viktigast för eleven att ha inflytande på. Eleverna upplevde att de inte kunde påverka när och var de fick sitt stöd i matematikundervisningen. Eleverna upplevde till exempel att relationen med läraren påverkar deras möjlighet att ha inflytande. / The aim of the study is to contribute with knowledge about the influence the SEM-students (special education needs in mathematics) experience in the special education they receive in mathematics. To foster the students in the ability to use influence is one of the schools duties. In this study influence means to influence the support in mathematics in regards to how, when, were, what and with whom. Some studies has been made on influence however they are not in the subject of mathematics education but is rather more directed towards homogeneous groups. In this study we have chosen to interview nine students in the ninth grade who has special education in mathematics. For these pupils to be more inclined to contribute, we chose students that had a positive development in mathematics. The interpretation of the students experience in the interviews has been made with the help of hermeneutic approach and thereafter analyzed in regards of power, relations and degree of satisfaction through categorizing the result in four different categories: satisfied, impotence, successful exercise of power and powerlessness. The result shows the students experience is that they have a more successful exercises of power on their special education in regards to how they work and what they work with, our interpretation is that it was most important for the students to have influence on these factors. The students experienced that they didn´t have influence on when and where they got their special education in mathematics. The students experienced for instance that their relation with the teacher affects their ability to have influence.
67

Distinguishing and correlating surface and bulk behaviour using linear and nonlinear vibrational spectroscopy

Roy, Sandra 21 December 2017 (has links)
Thorough understanding of interfaces requires an assessment of both the surface and bulk properties through the use of multiple techniques. In this thesis, infrared absorption, Raman scattering and sum frequency generation were used as vibrational probes of different features of interfacial systems including the ability to measure surface and bulk effects. Two-dimension correlation analysis was used to study the relationship between the spectral response of the different techniques. Attenuated total reflection absorption, bulk Raman scattering and sum frequency generation were used to study the adsorption of ethanol--water mixture on fused silica. With the use of two-dimension correlation analysis, interesting results were observed concerning the behavior of the surface in respect to the bulk. Surface concentration of ethanol were concluded to be higher than in the bulk indicative of competitive adsorption. Furthermore, at low concentration ethanol was shown to adsorb to the surface in dimers, to then form a bilayer of strongly oriented ethanol molecules at higher concentration. At highest concentration, this bilayer is disturbed, leaving only one layer at the surface of oriented ethanol molecules. The same spectroscopic techniques were applied to pressure sensitive adhesives of different composition while drying on a sapphire surface. The presence or absence of acrylic acid in the material was shown to alter the reorientation at the surface while drying. In the case where no acrylic acid is present, the orientation of the polymer at the surface was driven by the packing of the molecules at the surface. When acrylic acid was present in the pressure sensitive adhesive, reorientation occurred much faster and was caused by strong hydrogen bonding with the surface of the sapphire. An increase in acrylic acid composition, increased the rate of reorientation. An experimental set up was constructed to specifically study interfaces with a nonuniform distribution within the plane of the surface. This allows for concomitant measurement of polarized total internal reflection Raman scattering and sum frequency generation spectroscopy along with bright field imaging and cross polarized imaging. This set up was used to study the L-histidine crystal in situ adsorbed on fused silica. The polarized experiments along with calculations allowed for a more in-depth analysis of the crystal orientation effect on the birefringence, the Raman and the sum frequency generation. / Graduate
68

Ab initio molecular dynamics study of ion and pH effects at silica/liquid water interfaces : structure, acid-base reactivity and vibrational spectroscopy / Etude par dynamique moléculaire ab initio des effets d'ions et de pH aux interfaces silice/eau liquide : structure, réactivité acido-basique et spectroscopie vibrationnelle

Pfeiffer-Laplaud, Morgane 16 September 2016 (has links)
L'interface (0001) alpha-quartz hydroxylé/eau liquide est modélisée par dynamique moléculaire dans le formalisme de la théorie de la fonctionnelle de la densité (DFT-MD). Poursuivant une étude déjà publiée sur la structure et la réactivité acido-basique de cette interface, nous élargissons l'analyse aux effets d'ions simples et de pH sur la structure et les propriétés de l'interface avec une attention particulière aux phénomènes d'adsorption ainsi qu'aux modifications de l'eau interfaciale et des sites de surface. Nous caractérisons en particulier les changements dans la réactivité de surface dus à la présence d'ions (cations alcalins et halogénures) par calcul direct de pKa et détaillons la structure de la double couche électrique dans le cas de paires d'ions.Nous cherchons de plus à calculer les spectres SFG (Sum Frequency Generation) vibrationnels à ces interfaces, ce qui serait une première pour une interface solide/liquide traitée au niveau DFT-MD. L'approche théorique de cette spectroscopie vibrationnelle non linéaire du second ordre permettrait de proposer une interprétation claire des bandes d'élongation O-H, alors que les études expérimentales continuent à diverger sur ce sujet. / We use Density-Functional-Theory-based molecular dynamics simulations to investigate the hydroxylated (0001) alpha-quartz/liquid water interface. As a follow up of an already published study on the structural and acid/base properties of this interface, we now focus on simple ion and pH effects on these properties and characterize adsorption behaviors and interfacial changes on both solid and liquid sides. In particular, we directly calculate surface pKa's in presence of ions (alkaline cations and/or halide anions) and provide microscopic details on the structure of the electric double layer when ion pairs are concerned.Besides, we try to apply DFT-MD simulations to the computation of vibrational Sum-Frequency Generation spectra at a solid/liquid interface. Indeed, calculations would be necessary to provide a clear interpretation of the vibrational bands in the OH stretching region since experimental band assignment is still a matter of debate.
69

Individual and Cumulative Effects of a Mixture of Phthalates and Children's Intellectual Abilities: A Secondary Analysis of Data from the MIREC Study

Schoen, Stephanie 16 September 2021 (has links)
Phthalates, chemicals found in a variety of consumer goods and personal care products, may adversely affect fetal neurodevelopment. Women are exposed to a mixture of phthalates during pregnancy because of the common presence of these chemicals in consumer goods. The aim of this study is to investigate potential associations between phthalate exposure during the first trimester of gestation and Intelligence Quotient (IQ) scores of 3-year old children.
70

Probing the environmental response of charged aqueous surfaces

Cai, Canyu 20 September 2021 (has links)
The molecular structure and charge on solid surfaces in aqueous environments is of fundamental importance to various scientific research and applications, yet remain not sufficiently understood. The research herein uses sum frequency generation spectroscopy to reveal the molecular structure of the mineral and polymer surfaces, and also probes the water molecules near the charged aqueous interfaces to get information about the surface charge. The application of visible-infrared sum-frequency generation spectroscopy to polymer thin-films requires a careful interpretation of the results, as the electric field magnitude and phase at each interface must be determined in a manner that takes thin film interference effects into account. A straightforward method that has a concise analytic solution in the case of a single thin film that exhibits interference effects was proposed. This method enabled selective probing of transparent thin-films using sum frequency generation spectroscopy, hence eliminated the ambiguity of the contribution of signal from two interfaces. The method was then extended to multiple polarization schemes, enabling easier and more comprehensive study of the molecular orientation on thin-films. Nonlinear vibrational spectroscopy has also been used to study the temperature-dependent surface structure of polydimethylsiloxane when exposed to water and a perfluorinated hydrophobic liquid. Quantitative analysis of the methyl plane orientation was performed using a combination of vibrational peak ratios and peak amplitudes that enable proposed structures to be identified. For both environments, the tilt and twist of the methyl plane was found to increase with temperature in a reversible manner. This has been attributed to be a consequence of the backbone reorganization due to temperature-dependent density changes. At charged aqueous interfaces, the structure of water adjacent to solid interface is sensitive to the surface potential. As a result, close inspection of signals originating from these water molecules can be used to reveal the surface charge density. Nonlinear vibrational spectroscopy was used to monitor the water O-H stretching band over a temperature range of 10-75°C to account for the increase in surface potential from deprotonation. It has been demonstrated that the behavior at the silica surface is a balance between increasing surface charge, and a decreasing contribution of water molecules aligned by the surface charge. Together with a model that accounts for two different types of silanol sites, the change in enthalpy and entropy for deprotonation at each site were reported. The surface charge density of untreated polydimethylsiloxane surface in water with various ionic strengths was also determined. It was found that the surface charge could be explained with an ion adsorption model. A relationship between the surface potential and measured nonlinear optics response that is valid at high potentials and low ionic strength was proposed. Finally, a universal method was demonstrated to derive the surface potential with nonlinear optics by modulating the coherence length. / Graduate / 2022-09-07

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