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1
Lin, Shu-Ling. "Electric Field Gradient Focusing-UV Detection for Protein Analysis." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1372.pdf.
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Kelly, Ryan Thomas. "Polymer Microchips for Capillary Electrophoresis and Electric Field Gradient Focusing of Biomolecules." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd1024.pdf.
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Sun, Xuefei. "Polymer Microfluidic Devices for Bioanalysis." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/1836.
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Polymeric microchips have received increasing attention in chemical analysis because polymers have attractive properties, such as low cost, ease of fabrication, biocompatibility and high flexibility. However, commercial polymers usually exhibit analyte adsorption on their surfaces, which can interfere with microfluidic transport in, for example, chemical separations such as chromatography or electrophoresis. Usually, surface modification is required to eliminate this problem. To perform stable and durable surface modification, a new polymer, poly(methyl methacrylate-co-glycidyl methacrylate) (PGMAMMA) was prepared for microchip fabrication, which provides epoxy groups on the surface. Whole surface atom transfer radical polymerization (ATRP) and in-channel ATRP approaches were employed to create uniform and dense poly(ethylene glycol) (PEG)-functionalized polymer brush channel surfaces for capillary electrophoresis (CE) separation of biomolecules, such as peptides and proteins. In addition, a novel microchip material was developed for bioanalysis, which does not require surface modification, made from a PEG-functionalized copolymer. The fabrication is easy and fast, and the bonding is strong. Microchips fabricated from this material have been applied for CE separation of small molecules, peptides, proteins and enantiomers. Electric field gradient focusing (EFGF) is an attractive technique, which depends on an electric field gradient and a counter-flow to focus, concentrate and separate charged analytes, such as peptides and proteins. I used the PEG-functionalized copolymer to fabricate EFGF substrates. The separation channel was formed in an ionically conductive and protein resistant PEG-functionalized hydrogel, which was cast in a changing cross-sectional cavity in the plastic substrate. The hydrogel shape was designed to create linear or non-linear gradients. These EFGF devices were successfully used for protein focusing, and their performance was optimized. Use of buffers containing small electrolyte ions promoted rapid ion transport in the hydrogel for achieving the designed gradients. A PEG-functionalized monolith was incorporated in the EFGF separation channel to reduce dispersion and improve focusing performance. Improvement in peak capacity was proposed using a bilinear EFGF device. Protein concentration exceeding 10,000-fold was demonstrated using such devices.
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Liu, Yansheng. "Investigation of Novel Microseparation Techniques." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1816.pdf.
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Tenny, Joseph S. "Numerical Simulations in Electro-osmotic Flow." BYU ScholarsArchive, 2004. https://scholarsarchive.byu.edu/etd/186.
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The developing flow field in a parallel plate microchannel, induced by wall motion, has been modeled numerically. This type of flow simulates the physical driving mechanism that exists in electro-osmotically generated flow with large channel diameter-to-Debye length ratios (Z). The physics of the flow field were compared between the moving wall model (MWM) and electro-osmotic flow (EOF) at Reynolds numbers of 1 and 1800, and Z > 2500. Also, Z-values between 50 and 500 were studied to investigate the accuracy of the MWM. Results show that for Z-values greater than 100 the MWM shows good agreement with EOF. The dynamics of the developing flow field for the MWM were explored for channel length-to-hydraulic diameter ratios (aspect ratio) of 5, 10, 20 and 40 at ten Reynolds numbers, Re (based on the wall velocity), below Re < 2000. The results show that far from the inlet the maximum fluid velocity occurs at the walls, as is expected, and the minimum velocity occurs at the channel center. Near the channel inlet, however, the centerline velocity is not a minimum but reaches a local maximum due to a resulting pressure imbalance generated by the wall motion. As the aspect ratio increases, the centerline velocity tends to approach the wall velocity far downstream from the inlet. Increases in the Reynolds number have the opposite effect on the centerline velocity. The hydrodynamic developing region, defined by that section of the channel where the wall shear stress is changing, also depends on the channel aspect ratio and Re, and is greater than the developing region for classical pressure-driven flow of a parallel plate channel. Also, the flow field physics was analyzed for a process called electro-mobility focusing (EMF). EMF is a process that separates and detects species of like charge with the use of electro-phoresis and EOF utilizing a varying voltage gradient. The velocity distribution and the effective diffusion were solved for analytically, for both a linear and non-linear voltage gradient, using the MWM and the creeping flow approximations. The resulting equations aid in optimizing the detection system by forcing the lowest effective diffusion (uniform velocity profile) to the detection location.
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GonzaÌlez, TuñoÌn Maria Pilar. "Electrophoretic field gradient focusing for the analysis of proteins." Thesis, University of Leeds, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439600.
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Wray, Thomas. "Developments in dynamic field gradient focusing : microfluidics and integration." Thesis, University of Liverpool, 2012. http://livrepository.liverpool.ac.uk/7973/.
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Advances in modern science require the development of more robust and improved systems for electroseparations in chromatography. In response, the progress of a new analytical platform is discussed. DFGF (Dynamic Field Gradient Focusing) is a separation technique, first described in 1998, which exploits the differences in electrophoretic mobility and hydrodynamic area of analytes to result in separation. This is achieved by taking a channel and applying a hydrodynamic flow in one direction and a counteracting electric field gradient acting in the opposite direction, resulting in analytes reaching a focal point according to their electrophoretic mobility. Work through this project has seen innovations to improve existing DFGF devices, including the design and manufacture of a novel packing material, while developing the latest DFGF system. This incorporates a microfluidic separation channel, eliminating the need for packing material or monolith. The new microfluidic device also features whole-on-column UV detection. Improvements through the developments of this device are discussed, most notably the utilisation of a new rapid prototyping technique. Examples of applications undertaken with the new device are demonstrated including novel samples and integration with mass spectrometry and 2D-HPLC.
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Koch, Katrin. "Crystal structure, electron density and chemical bonding in inorganic compounds studied by the Electric Field Gradient." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-24233.
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The goal of solid state physics and chemistry is to gain deeper understanding of the basic principles of condensed matter. This ongoing process is achieved by the combination of experimental methods and theoretical models. One theoretical approach are the so-called first-principles calculations, which are based on the concept of density functional theory (DFT). In order to test the reliability of a band structure calculation, its results have to be compared with experiments. Since the electron density, the main constituent of DFT codes, cannot be directly determined experimentally with sufficient accuracy (e.g., by X-ray diffraction), other experimentally available properties are needed for the comparison with the calculation.
A quantity that can be measured with high accuracy and that provides
indirect information about the electron density is the electric field
gradient (EFG). The EFG reflects local structural symmetry properties of the charge distribution surrounding a nucleus: the EFG is nonzero if the
density deviates from cubic symmetry and therefore generates an
inhomogeneous electric field at the nucleus. Since the EFG is highly
sensitive to structural parameters and to disorder, it is a
valuable tool to extract structural information. Furthermore, the
evaluation of the EFG can provide valuable insight into the chemical
bonding.
Whereas the experimental determination of the quadrupole frequency
and the closely related EFG has been possible for more than 70 years,
reliable values for calculated EFGs could not be obtained before 1985,
when an EFG module was implemented in the full-potential,
linearised-augmented-plane-wave code WIEN. Since the full-potential local-orbital minimum-basis scheme FPLO is numerically very efficient and its local-orbital scheme allows an easy analysis of the different contributions to the EFG, one goal of this work was the implementation of an EFG module within the FPLO code.
The newly implemented EFG module was applied to different systems:
starting from simple metals, then approaching more complex systems and finally tackling strongly correlated oxides. Simultaneously, the EFGs
for the studied compounds were determined experimentally by NMR
spectroscopists. This close collaboration enables the comparison of
the calculated EFGs with the experimental observations, which makes it
possible to extract more physical and chemical information from the
measured values regarding structural relaxation, distortion, the
chemical bond or the relevance of electron correlation.
In the last part of this work, the importance of corrections that go
beyond the EFG are discussed. Such corrections arise for any multipole order of the hyperfine interactions, and are due to electron penetration into the nucleus. A correction similar to the isomer shift, coined here the "quadrupole shift" is examined in detail.
9
Evans, James R. "The electric field gradient of octahedral iron in layer silicates: theory with applications to Mossbauer spectroscopy." Thesis, University of Ottawa (Canada), 2001. http://hdl.handle.net/10393/22144.
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Evans, R. James. "The electric field gradient of octahedral iron(2+) in layer silicates: Theory with applications to Moessbauer spectroscopy." Thesis, University of Ottawa (Canada), 2001. http://hdl.handle.net/10393/8968.
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New electronic structure calculations of the electric field gradient (EFG) at octahedral Fe2+ sites in layer silicates are discussed. These calculations were done with the aim of providing a link between quadrupole splitting distributions from Mossbauer spectroscopy and the physical distributions of local environments within the material. Various distortions were applied to FeO610- and Fe(OH)6 4- clusters to simulate different local environments and the corresponding EFG's calculated. The electronic structure calculations were performed with the General Atomic and Molecular Electronic Structure System (GAMESS) and a self-consistent-charge-Xalpha method. An analytic model of the EFG using a classical electrostatic point charge model and crystal field theory is used to complement the electronic structure calculations. There is good qualitative agreement between the electronic structure calculations, the analytic model, and with experimental quadrupole splittings in micas. A geometric model of the octahedral sheet in a layer silicate is described, based on isometric flattening and counter-rotation as the main distortions, which can have one, two, or three unique sites. EFG distributions are then calculated using a variety of cases based on the geometric model and the calculated EFG vs. distortion curves. The most realistic distribution results from a case that assumes two unique site-types in a ratio of 2:1, with the height of each site and the inter-cation distance held constant throughout the sheet and the Fe--O bond length of one site-type allowed to vary with a Gaussian distribution.
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Perras, Frédéric Alain. "Structural Insights from the NMR Spectroscopy of Quadrupolar Nuclei: Exploiting Electric Field Gradient and Spin-Spin Coupling Tensors." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31883.
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NMR spectroscopy has evolved into one of the most important characterization techniques in chemistry with which it is possible to obtain valuable structural, dynamical, and mechanistic information. Most applications of NMR have however been limited to the use of nuclei having spin quantum numbers of 1/2. This thesis discusses the developments that have been advanced in order to extract quantitative structural information from the NMR spectroscopy of quadrupolar nuclei (spin, I>1/2) which account for the vast majority of the NMR-active nuclei. In a first part of the thesis, a NMR crystallographic method is developed which uses the electric field gradient tensor measured at the nuclear sites as an experimental constraint in DFT-based crystal structure refinements. This inclusion of experimental data into crystal structure refinements enables the determination of higher quality, and experimentally-relevant, structures. We apply this new methodology in order to determine higher quality crystal structures for the non-linear optical material Na2B2Al2O7, sodium pyrophosphates, and the near-zero thermal expansion material ZrMgMo3O12. In a second part of this thesis, experimental techniques are developed for the measurement of spin-spin coupling between pairs of quadrupolar nuclei; the measurement of spin-spin coupling carries with it extremely valuable distance and connectivity information. Using DOR NMR, heteronuclear residual dipolar coupling as well as homonuclear J coupling multiplets can be observed. Notably, the J coupling between quadrupolar nuclei can still be measured in A2 spin systems, unlike in the case of pairs of spin-1/2 nuclei. The theory that was developed for the characterization of these multiplets was extended for the general simulation of exact NMR spectra of quadrupolar. This program, known as QUEST, is now free to use by anyone in the scientific community. Pulsed J-resolved NMR experiments are then described which enable the facile measurement of J and dipolar coupling in homonuclear pairs of quadrupolar nuclei. Notably, the J splitting is greatly amplified in A2 spin systems which provides strong structural information and enables the precise detection of smaller J coupling constants. These techniques are applied towards directly studying gallium metal-metal bonding interactions as well as boron-boron bonds in diboron compounds of importance in β-boration chemistry.
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Gonçalves, Marcos Brown. "Efeitos de estado sólido e ligações de hidrogênio sobre o gradiente de campo elétrico no núcleo no imidazol." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-09022007-124016/.
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Estudamos as propriedades eletrônicas, estruturais e hiperfinas, nos sítios de nitrogênio, para o composto imidazol nas fases gasosa e sólida. Utilizamos o método PAW que é um método ab initio all-electron, dentro da Teoria do Funcional da Densidade, através do código computacional CP-PAW. Nossos valores, tanto para a fase gasosa quanto para a fase cristalina do gradiente de campo elétrico no núcleo, de freqüência de acoplamento quadrupolar (ν) e parâmetro de assimetria (η) estão em ótima concordância com os resultados experimentais da literatura e são os primeiros resultados obtidos, por método ab initio no espaço recíproco, para os átomos de nitrogênio no imidazol cristalino. Utilizamos resultados da literatura e também aqui calculados para estudar a tendência de comportamento tanto de ν quanto de η para diferentes meros (um, dois, três, cadeia infinita) e cristal investigando, assim, a estreita influência das ligações de hidrogênio sobre os valores do Gradiente de Campo Elétrico nos núcleos de nitrogênio.Here we study structural, electronic and hyperfine properties at the Nitrogen sites in imidazole in the gas and the crystal phases. We use the PAW method which is an ab initio all electron method in the framework of the Density Functional Theory, as embodied in the computer code CP-PAW. The results for quadrupole coupling (ν) and asymmetry parameter (η) at the gas and at the crystal phases are in excellent agreement with the experimental values in the literature. This is the first time that such calculations are performed for the crystalline imidazole through a reciprocal space approach. We also study the behavior of both ν and η trends studing diferent meres (one, two, three and infinite chain) and cristal to investigate the influence of hydrogen bonding on the Electric Field Gradient at the nucleus.
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Weiss, Joseph. "A Solid-State 11B NMR and Computational Study of Boron Electric Field Gradient and Chemical Shift Tensors in Boronic Acids and Boronic Esters." Thesis, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/19737.
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The results of a solid-state 11B NMR study of a series of boronic acids, boronic esters, and boronic acid catechol cyclic esters with aromatic substituents are reported in this thesis. Boron-11 electric field gradient (EFG) and chemical shift (CS) tensors obtained from analyses of spectra acquired in magnetic fields of 9.4 T and 21.1 T are demonstrated to be useful for gaining insight into the molecular and electronic structure about the boron nucleus. It can be concluded that when adequate electronic variation is present in the compounds being studied, Ω is generally the most characteristic boron NMR parameter of the molecular and electronic environment for boronic acids and esters. Importantly, these data are only reliably accessible in ultrahigh magnetic fields. The experimental span values result from a delicate interplay of several competing factors, including hydrogen bonding, the value of the dihedral angle, and the type of aromatic ring system present.
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Attrell, Robert J. "A Solid-State 35Cl and 81Br NMR and Computational Study of Chlorine and Bromine Electric Field Gradient and Chemical Shift Tensors in Haloanilinium Halides." Thesis, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/20546.
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The results of a systematic 35Cl, 81Br, and 127I SSNMR spectroscopic study of a series of halogen-substituted anilinium halide salts are presented. Solid-state NMR of these nuclides, bromine-/81 and iodine-127 in particular, is not well established. Twenty-one compounds thought to exhibit halogen bonding were prepared based on modified literature procedures, and two crystal structures were solved. Experiments show that collection of SSNMR spectra of the anions is feasible, though ultrahigh magnetic fields (21.1 T) and variable offset data acquisition were found to be essential. Electric field gradient and chemical shift tensors are measured experimentally for all 21 compounds, significantly expanding the body of data for the quadrupolar halogen nuclei. Quadrupolar coupling constants for chlorine-35 ranged from 2.12 to 6.04 MHz, for bromine-81 from 12.3 to 45.3 MHz, and for iodine-127 from 57.50 to 152.50 MHz. Gauge-including projector-augmented wave density functional theory (GIPAW-DFT) calculations were used to provide insight as to how the NMR parameters vary with local environment and long-range crystal packing. Overall, calculations reproduced the experimental trends in quadrupolar coupling constants and chemical shift tensor span (Ω) but failed to provide quantitative agreement within experimental error. Experimental and computational data were analyzed in order to provide insight into how halogen bonding influences NMR parameters. Several trends were elucidated from this study, including an inverse correlation between Ω and the length of the shortest halogen-halide contact (d). In selected bromine compounds, for example, Ω (81Br) was measured to increase from 120 to 240 ppm as d decreased from 3.838 to 3.443 Å. In summary, this study has demonstrated the feasibility and utility of quadrupolar halogen SSNMR, and that these techniques may prove useful in characterizing halogen bonding interactions in solids.
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Eller, Alexander M. [Verfasser], Guy D. [Akademischer Betreuer] Moore, and Hans-Werner [Akademischer Betreuer] Hammer. "The Color-Electric Field Correlator under Gradient Flow at next-to-leading Order in Quantum Chromodynamics / Alexander M. Eller ; Guy D. Moore, Hans-Werner Hammer." Darmstadt : Universitäts- und Landesbibliothek, 2021. http://d-nb.info/1230554653/34.
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Wendt, Martin. "Experimental Investigations of Wave Motion and Electric Resistance in Collisionfree Plasmas." Doctoral thesis, Stockholm : Tekniska högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3199.
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Rambo, Matthew P. "Study of ZrSiO4 Phase Transition Using Perturbed Angular Correlation Spectroscopy." Miami University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=miami1109871239.
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Bull, James. "Application of Quantum Mechanics to Fundamental Interactions in Chemical Physics: Studies of Atom-Molecule and Ion-Molecule Interactions Under Single-Collision Conditions: Crossed Molecular Beams; Single-Crystal Mössbauer Spectroscopy: Microscopic Tensor Properties of ⁵⁷Fe Sites in Inorganic Ferrous High-Spin Compounds." Thesis, University of Canterbury. Department of Chemistry, 2010. http://hdl.handle.net/10092/4292.
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As part of this project and in preparation for future experimental studies of gas-phase ion-molecule reactions, extensive modification and characterization of the crossed molecular beam machine in the Department of Chemistry, University of Canterbury has been carried out. This instrument has been configured and some
preliminary testing completed to enable the future study of gas-phase ion-molecule collisions of H⁺₃ and Y⁻ (Y
= F, Cl, Br) with dipole-oriented CZ₃X (Z = H, F and X = F, Cl, Br). Theoretical calculations (ab initio
and density functional theory) are reported on previously experimentally characterized Na + CH₃NO₂, Na + CH₃NC, and K + CH₃NC systems, and several other systems of relevance. All gas-phase experimental and theoretical studies have the common theme of studying collision orientation dependence of reaction under singlecollision
conditions. Experimental measurements, theoretical simulations and calculations are also reported on some selected ferrous (Fe²⁺) high-spin (S=2) crystals, in an attempt to resolve microscopic contributions of two fundamental macroscopic tensor properties: the electric-field gradient (efg); and the mean square displacement (msd) in the case when more than one symmetry related site of low local point-group symmetry contributes to the same quadrupole doublet. These determinations have been made using the nuclear spectroscopic technique of Mössbauer spectroscopy, and complemented with X-ray crystallographic measurements.
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Rambo, Matthew P. "Study of ZrSiO4 phase transition using perturbed angular correlation spectroscopy." Connect to this document online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=miami1109871239.
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Thesis (M.S.)--Miami University, Dept. of Physics, 2005.Title from first page of PDF document. Document formatted into pages; contains [1], vii, 55 p. : ill. Includes bibliographical references (p. 53-55).
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Almilaji, Karam N. "Fabricating Superhydrophobic and Superoleophobic Surfaces with Multiscale Roughness Using Airbrush and Electrospray." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4460.
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Examples of superhydrophobic surfaces found in nature such as self-cleaning property of lotus leaf and walking on water ability of water strider have led to an extensive investigation in this area over the past few decades. When a water droplet rests on a textured surface, it may either form a liquid-solid-vapor composite interface by which the liquid droplet partially sits on air pockets or it may wet the surface in which the water replaces the trapped air depending on the surface roughness and the surface chemistry. Super water repellent surfaces have numerous applications in our daily life such as drag reduction, anti-icing, anti-fogging, energy conservation, noise reduction, and self-cleaning. In fact, the same concept could be applied in designing and producing surfaces that repel organic contaminations (e.g. low surface tension liquids). However, superoleophobic surfaces are more challenging to fabricate than superhydrophobic surfaces since the combination of multiscale roughness with re-entrant or overhang structure and surface chemistry must be provided. In this study, simple, cost-effective and potentially scalable techniques, i.e., airbrush and electrospray, were employed for the sake of making superhydrophobic and superoleophobic coatings with random and patterned multiscale surface roughness. Different types of silicon dioxide were utilized in this work to in order to study and to characterize the effect of surface morphology and surface roughness on surface wettability. The experimental findings indicated that super liquid repellent surfaces with high apparent contact angles and extremely low sliding angles were successfully fabricated by combining re-entrant structure, multiscale surface roughness, and low surface energy obtained from chemically treating the fabricated surfaces. In addition to that, the experimental observations regarding producing textured surfaces in mask-assisted electrospray were further validated by simulating the actual working conditions and geometries using COMSOL Multiphysics.
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Chapman, Rebecca. "Development and Application of Chlorine Solid-State Nuclear Magnetic Resonance and Quantum Chemical Calculations to the Study of Organic and Inorganic Systems." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/20555.
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Chlorine solid-state nuclear magnetic resonance (SSNMR) is an ideal site specific probe of chloride-containing solids as SSNMR tensor properties are sensitive to the local chlorine environment. In this thesis, the development and use of chlorine SSNMR as a method to characterize a wide variety of chemical environments was explored. Ultrahigh field, and multi-field studies were essential to overcome the difficulties associated with the collection of chlorine SSNMR spectra.
Benchmark chemical shift (CS) and electric field gradient (EFG) tensor data were collected for organic chloride systems, including several amino acid hydrochlorides. These experiments demonstrated the sensitivity of chlorine SSNMR to slight changes in chemical environment. Quantum chemical calculations were used to complement experimental data, with the gauge-including projector augmented wave DFT (GIPAW-DFT) method shown to yield better agreement than B3LYP or RHF methods. The GIPAW-DFT method was found to slightly, but systematically, overestimate the chlorine quadrupolar coupling constant and the CS tensor span. Other organic chlorides examined by chlorine SSMR included a known ion receptor, meso-octamethylcalix[4]pyrrole. This compound was found to have a very small quadrupole interaction (QI), but significant chemical shift anisotropy (CSA). GIPAW-DFT calculations were also utilized and, in combination with the experimental results, used to identify the solvate structure of the material analyzed by NMR.
Chlorine SSNMR was further used to study different solvate structures and polymorphism. The technique was an effective means to distinguish different room temperature polymorphs of benzidine hydrochloride, despite the similarities of the chloride environments. In the case of magnesium chloride, chlorine SSNMR was sensitive to the level of hydration and through the use of GIPAW-DFT calculations, the identity of an unknown hydrate was determined.
An analysis of several group thirteen chlorides demonstrated that chlorine SSNMR was also capable of characterizing the chlorine environment in cases where the QI is large, despite the resulting broad line widths. In these systems GIPAW-DFT calculations also yielded excellent agreement with experimental values.
Throughout this research, chlorine SSNMR has been shown to be a useful and effective means to study both organic and inorganic chlorides, with computational methods proving to be an important complement to experimental data.
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Widdifield, Cory. "Multinuclear Solid-State Magnetic Resonance Studies on ‘Exotic’ Quadrupolar Nuclei: Acquisition Methods, High-Order Effects, Quantum Chemical Computations, and NMR Crystallography." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/20722.
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This dissertation attempts to extend the classes of halogen-containing systems which may be studied using solid-state nuclear magnetic resonance (SSNMR). As line shape broadening due to the quadrupolar interaction (QI) scales inversely with the applied field, high-field magnet technology is indispensable for this research. Combining advanced radiofrequency pulse sequences with high-field wideline data acquisition allowed for the collection of very broad SSNMR signals of all quadrupolar halogen nuclei (i.e., 35/37Cl, 79/81Br and 127I) within a reasonable amount of experimental time. The initial systems for study were of the MX2 variety (M = Mg, Ca, Sr, Ba; X = Cl, Br, I). In total, 9 anhydrous compounds were tested. The effects of hydrate formation were tested on 7 additional compounds. Systematic trends in the observed δiso values (and to a lesser extent, Ω and CQ) were found to be diagnostic of the extent of hydration in these materials. Resolving power was successfully tested using SrBr2, which possesses 4 magnetically unique sites. The composition of CaBr2•xH2O was convincingly determined using SSNMR data and the hydration trends noted above. The sensitivity of the QI to the local bonding environment (e.g., bond distance changes of less than 0.05 Å) was used to refine (when coupled with gauge-including projector augmented-wave density functional theory (GIPAW DFT) quantum chemical computations) the structure of MgBr2, and was used to correct prior NMR data for CaCl2 (earlier accounts had been performed upon a CaCl2 hydrate). During NMR data analysis of certain iodine-containing materials, it was found that standard fitting software (which uses perturbation theory) could not reproduce the observations. Proper analysis required the use of exact simulation software and allowed for the observation of high-order quadrupole-induced effects (HOQIE). This motivated further studies using rhenium-185/187 nuclei, where it was expected that HOQIE would be more dramatic. The observed rhenium SSNMR spectra possessed additional fine structure that had never been observed before experimentally, nor would be expected from currently-available perturbation theory analysis software. Lastly, preliminary results are shown where 127I SSNMR is used to study important supramolecular systems, and the composition of the popular synthetic reagent ‘GaI’ is elucidated.
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Petersen, Philippe Alexandre Divina. "Cálculos ab initio de interações entre Cd e bases nitrogenadas do DNA." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-30092011-163810/.
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As interações hiperfinas são uma ótima ferramenta para estudar um sítio específico e obter informações importantes sobre o sistema. No presente trabalho analisamos de forma teórica as propriedades eletrônicas, estruturais e hiper nas do Cádmio (Cd) ligado às bases nitrogenadas do DNA. A motivação surgiu da colaboração com o grupo do prof. Artur W. Carbonari do Instituto de Pesquisas Energéticas e Nucleares (IPEN) e que tem como objetivo investigar o DNA e anticorpos de linhagens de camundongos infectados pela cepa Y de Trypanosoma cruzi, protozoário causador da doença de Chagas. A técnica Time Differential Perturbed Angular Correlation (TDPAC) foi utilizada para obter as medidas das interações hiperfinas do DNA. O núcleo de prova das medidas foi o 111Cd. Utilizamos uma abordagem quântica ab initio all-electron, dentro da Teoria do Funcional da Densidade (DFT), através do código computacional CP-PAW que combina o método Projector Augmented Wave (PAW) e a dinâmica molecular quântica de Car-Parrinello (CPMD). Ressaltamos que, até o presente momento, nenhum estudo com esta abordagem teórica e com este código computacional foi realizado para investigar as propriedades hiper nas do Cd ligado as bases nitrogenadas do DNA.The Hyperfine interactions are good tools to study speci c sites and obtain important information about a given system. In this work we study electronic, structural and hyper ne properties of the Cadmium (Cd) coordinated to the DNA nitrogenous bases. The motivation for this study arose from a collaboration with the group of prof. Arthur W. Carbonari at the Institute of Energy and Nuclear Research (IPEN), which aims to investigate DNA and antibodies to strains of mice infected with the Trypanosoma cruzi, the protozoan that causes Chagas disease. The Time Differential Perturbed Angular Correlation (TDPAC) technique was used to obtain hypefine interactions measurements at a Cd probe bonded to DNA. We use ab initio all-electron calculations, within the Density Functional Theory (DFT) and we use the computer code CP-PAW that combines the Projector Augmented Wave (PAW) method and the Car-Parrinello (CP) quantum molecular dynamics approach to. We emphasize that, until now, no study with this theorectical approach and with this computer code was conducted to investigate the hyper ne properties of the Cd binding to the DNA bases.
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Santiago, Régis Tadeu. "Novas parametrizações de funcionais híbridos para uso em cálculos relativísticos." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/75/75134/tde-27012015-093530/.
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A química computacional apresenta a grande vantagem de prover informações fundamentais para espécies moleculares propostas, antes mesmo de sua síntese em laboratório. A Teoria do Funcional da Densidade é bastante utilizada nesta área, produzindo resultados satisfatórios para um grande número de propriedades e sistemas, mas com uma menor demanda por recursos computacionais que métodos mais avançados. Entretanto, o desenvolvimento de funcionais que incluem efeitos relativísticos ainda se encontra num estágio inicial. Em geral, tais efeitos são importantes em compostos de átomos pesados, embora devam ser considerados também em sistemas com átomos mais leves se a propriedade em estudo for particularmente sensível, como é o caso do gradiente de campo elétrico na posição de núcleos em moléculas. Assim, na primeira etapa desta dissertação foi avaliado o desempenho de funcionais comuns de troca-correlação não relativísticos, quando utilizados em conjunto com o formalismo de quatro componentes (tratamento relativístico), no estudo dos gradientes de campo elétrico em núcleos de átomos (índio, antimônio, iodo, lutécio e háfnio) constituindo moléculas diatômicas. Foram investigados funcionais baseados nas aproximações da densidade local e do gradiente generalizado, funcionais híbridos e que incluem correções em termos da atenuação com a distância. Nossos resultados, que estão em acordo com observações da literatura, ressaltam o melhor desempenho de funcionais híbridos e com correções de atenuação para esta propriedade e demonstram a importância do uso do método indireto. Posteriormente, foi feita uma nova parametrização de alguns dos melhores funcionais não relativísticos selecionados na etapa anterior (B3LYP, PBE0 e CAM-B3LYP), dentro do formalismo de quatro componentes, para uso no cálculo destes mesmos gradientes num grupo teste de átomos (cobre, iodo, lantânio e ouro) em moléculas lineares. Nestes casos, os funcionais modificados propostos tiveram um bom desempenho geral e foram particularmente bem sucedidos para cobre e ouro. Finalmente, é possível destacar o funcional híbrido PBE0 e sua modificação, proposta neste estudo, por conta de seu desempenho excelente, tanto para os metais como para os demais elementos que tiveram seus EFGs investigados aqui.The computational chemistry has the great advantage of providing fundamental information for proposed molecular species even before their synthesis in laboratory. The Density Functional Theory is widely used in this area, producing satisfactory results for a large number of properties and systems, but with a lower demand for computational resources than that of more advanced methods. However, the development of functionals that include relativistic effects is still at an early stage. In general, these effects are important in compounds containing heavy elements, but they must also be considered in systems of lighter atoms if the studied property was particularly sensitive, as occurs for the electric field gradient at the position of nuclei in molecules. Thus, the first step of this dissertation was to evaluate the performance of common non-relativistic exchange-correlation functionals when used in conjunction with the four component formalism (relativistic treatment) in the study of electric field gradients at the nuclei of atoms (indium, antimony, iodine, lutetium and hafnium) forming diatomic molecules. Functionals based on the local density approximation and generalized gradient approximation, hybrid functionals and the ones that include attenuation corrections were investigated. Our results, which are in agreement with observations in the literature, highlight the best performance of hybrid functionals and attenuation corrections for this property and demonstrate the importance of using the indirect approach. Subsequently, there was a new parameterization of some of the best non-relativistic functionals selected in the previous step (B3LYP, PBE0 and CAM - B3LYP) within the four component formalism for calculations of these same gradients in a trial group of atoms (copper, iodine, lanthanum and gold) into linear molecules. In these cases, the modified functionals proposed had a satisfactory overall performance and were particularly successful for copper and gold. Finally, it is possible to mention the excellent performance of the hybrid functional PBE0 and its modification proposed in this study for both metals and the other elements that had their EFGs investigated here.
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Wirnsberger, Peter. "Computer simulation and theoretical prediction of thermally induced polarisation." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/282988.
Full textAbstract:
In this thesis, we study the phenomenon of thermally induced polarisation using a combination of theory and computer simulation. Molecules of sufficiently low symmetry exhibit thermo-molecular orientation when subjected to a temperature gradient, leading to considerable electrostatic fields in polar liquids. Here, we first use non-equilibrium molecular dynamics simulations to study this interesting effect numerically. To this end, we propose an integration algorithm to impose a constant heat flux in simulations and show that it greatly improves energy conservation compared to a previous algorithm. We next investigate the thermal polarisation of water and find that truncation of electrostatic interactions can lead to severe artefacts, such as the wrong sign of polarisation and an overestimation of the electric field. We further show that the quadrupole-moment contribution to the electric field is significant and responsible for an inversion of its sign. To facilitate the theoretical description of electrostatic interactions, we propose a new dipolar model fluid as a perturbation of a Stockmayer fluid. Using this modified Stockmayer model, we provide numerical evidence for the recently proposed phenomenon of thermally induced monopoles. We show that the electrostatic field generated by a pair of heated/cooled colloidal particles immersed in such a solvent can be trivially described by two Coulomb charges. Finally, we propose a mean-field theory to predict the thermo-polarisation effect exhibited by our model fluid theoretically, and demonstrate near quantitative agreement with simulation results.
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Douar, Adnane. "Recherche de matériaux isolants pour la conception d'une nouvelle génération de connecteurs électriques haute tension : influence de la pollution sur les phénomènes de décharges partielles du contournement et de claquage." Thesis, Ecully, Ecole centrale de Lyon, 2014. http://www.theses.fr/2014ECDL0046/document.
Full textAbstract:
Dans le présent travail, nous abordons une problématique essentielle liée aux accessoires des lignes électriques et plus particulièrement au connecteur à perforation d’isolant (TTDC 45501 FA), commercialisé par la société Sicame située à Arnac-Pompadour (Corrèze). Ce produit permet d’effectuer des dérivations de courant en moyenne tension gainé HTA entre 15 et 25kV. Cependant, il devient nécessaire de concevoir une nouvelle génération de connecteurs capable de fonctionner à une tension de 52 kV en raison de la constante augmentation des besoins en électricité. En réalité, le principal souci concernant ces produits réside dans l’apparition de décharges partielles dans le volume constitué par la matière isolante (polyamide 6 chargée à 50% en poids de fibres de verre). Ces décharges engendrent un vieillissement prématuré du produit sous l’action conjuguée d’une atmosphère corrosive (brouillard salin) et d’un champ électrique. Ainsi, l’objectif de la présente thèse est de faire, dans un premier temps, un choix approprié de matériaux isolants parmi des polymères thermoplastiques, thermodurcissables époxydes ou élastomères en EPDM, capables de résister à plusieurs contraintes : thermique, électrique, mécanique, chimique et climatique. La partie expérimentale concerne, tout d’abord, la mesure de la tension de contournement, de l’activité des décharges partielles se propageant à la surface des matériaux isolants et de la tension de claquage, en tension alternative (A.C.). Pour cela, des échantillons polymères qui comportent des surfaces planes ou des surfaces pourvues de protubérances ont été moulés en vue de comparer leur comportement diélectrique en présence d’atmosphères polluées de type brouillard salin; ces mesures sont nécessaires pour effectuer un choix approprié du matériau à intégrer dans le connecteur. Par la suite, l’étude et la caractérisation optique et électrique de décharges glissantes, se propageant en surface de divers matériaux polymères, en tension impulsionnelle (L.I.) pour les deux polarités (positive et négative) et pour deux types de champ électrique (normal et tangentiel) sont présentées pour le cas d’une interface solide/air. La mesure de la longueur finale des décharges glissantes et la visualisation de l’onde de courant sont les deux paramètres principaux pour différencier les caractéristiques des matériaux utilisés. L’ensemble des résultats de mesures a permis de sélectionner les résines époxydes cyclo-aliphatiques (CEP) comme candidates potentielles pour la conception d’une nouvelle génération de connecteurs. De plus, la simulation du champ électrique, à l’aide du logiciel Flux 2D/3D, sur le connecteur électrique (TTDC 45501FA) a permis d’aboutir à la proposition d’un prototype de connecteur présentant une nouvelle géométrie et pouvant fonctionner à 52kVIn the present study, we deal with an essential problem related to electrical lines accessories and more particularly to piercing connectors (TTDC 45501FA) commercialized by a private company named Sicame and which is located in Arnac-Pompadour (Corrèze, France). This product/accessory is designed to provide power diversions on medium voltage live lines HVA operating between 15 and 25kV. However, it becomes required to design a new generation of piercing connectors able to operate on 52kV live lines because of the electrical power demands that are steadily increasing. Actually, the main concerns about these products are the occurrence of partial discharges within the insulating material volume (polyamide 6 containing 50%wt of glass fibers). Most of the time, these discharges induce an early ageing process of the accessory under the combined effects of a corrosive environment (as salt fog) and an electric field threshold. Thus, the main objective of the present Ph.D. thesis is to carry out an appropriate choice of insulating materials among several tested polymers such as thermoplastics and thermosetting epoxy resins and EPDM elastomers that are capable of withstanding several constraints: thermal and electrical and mechanical and chemical conditions. The experimental section is focusing on the measurements of flashover voltage and partial discharges activity propagating on polymeric surfaces and breakdown voltage within material bulks under A.C voltage. That is why polymeric samples with plane surfaces and textured surfaces are molded to compare their resistance to partial discharges when being subjected to polluted environments such as salt fog; these measurements are necessary to choose the suitable materials for the required application to be integrated in the new generation of connectors. Then, the optical and electrical characterization results of creeping discharges propagating on several polymeric surfaces under lightning impulse (L.I.) voltage with its both polarities (positive and negative) and for two kinds of applied electric field (normal and tangential) are presented in the case of solid/air interfaces. Final length measurements of creepage discharges are the main parameter for distinguishing material properties. The whole obtained results (under AC and LI voltages) allow us to point out the cycloaliphatic epoxy resins as potential candidates to the conception of a new generation of piercing connectors. In addition, the electric field simulation and modelling of the TTDC 45501FA connector by using the Flux 2D/3D software seems to be helpful to design a connector prototype which exhibits a new geometry and is able to reach a voltage level that equals 52kV
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Li, Qi. "Acoustic noise emitted from overhead line conductors." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/acoustic-noise-emitted-from-overhead-line-conductors(90a5c23c-a7fc-4230-bbab-16b8737b2af2).html.
Full textAbstract:
The developments of new types of conductors and increase of voltage level have driven the need to carry out research on evaluating overhead line acoustic noise. The surface potential gradient of a conductor is a critical design parameter for planning overhead lines, as it determines the level of corona loss (CL), radio interference (RI), and audible noise (AN). The majority of existing models for surface gradient calculation are based on analytical methods which restrict their application in simulating complex surface geometries. This thesis proposes a novel method which utilizes both analytical and numerical procedures to predict the surface gradient. Stranding shape, proximity of tower, protrusions and bundle arrangements are considered within this model. One of UK National Grid's transmission line configurations has been selected as an example to compare the results for different methods. The different stranding shapes are a key variable in determining dry surface fields. The dynamic behaviour of water droplets subject to AC electric fields is investigated by experiment and finite element modelling. The motion of a water droplet is considered on the surface of a metallic sphere. To understand the consequences of vibration, the FEA model is introduced to study the dynamics of a single droplet in terms of phase shift between vibration and exciting voltage. Moreover, the evolution of electric field within the whole cycle of vibration is investigated. The profile of the electric field and the characteristics of mechanical vibration are evaluated. Surprisingly the phase shift between these characteristics results in the maximum field occurring when the droplet is in a flattened profile rather than when it is ‘pointed’.Research work on audible noise emitted from overhead line conductors is reviewed, and a unique experimental set up employing a semi-anechoic chamber and corona cage is described. Acoustically, this facility isolates undesirable background noise and provides a free-field test space inside the anechoic chamber. Electrically, the corona cage simulates a 3 m section of 400 kV overhead line conductors by achieving the equivalent surface gradient. UV imaging, acoustic measurements and a partial discharge detection system are employed as instrumentation. The acoustic and electrical performance is demonstrated through a series of experiments. Results are discussed, and the mechanisms for acoustic noise are considered. A strategy for evaluating the noise emission level for overhead line conductors is developed. Comments are made on predicting acoustic noise from overhead lines. The technical achievements of this thesis are summarized in three aspects. First of all, an FEA model is developed to calculate the surface electric field for overhead line conductors and this has been demonstrated as an efficient tool for power utilities in computing surface electric field especially for dry condition. The second achievement is the droplet vibration study which describes the droplets' behaviour under rain conditions, such as the phase shift between the voltage and the vibration magnitude, the ejection phenomena and the electric field enhancement due to the shape change of droplets. The third contribution is the development of a standardized procedure in assessing noise emission level and the characteristics of noise emissions for various types of existing conductors in National Grid.
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Chandrakumar, Thambirajah. "A NMR study on zero electric field gradient nematic liquid crystals." Thesis, 1994. http://hdl.handle.net/2429/6997.
Full textAbstract:
The role of intermolecular forces in describing the orientational nature of liquid crystals
is not well understood. Previous studies using dideuterium as a solute in liquid crys-
tals have demonstrated the importance for orientation of the interaction between the
solute molecular quadrupole moment and the average electric field gradient present in
liquid crystals. With the aim of learning aboilt additional orientational mechanisms,
we have studied the orientation of solutes in special mixtures of liquid crystals, where
the contribution from the environment to the average electric field gradient at the ²H
nucleus of dideuterium is negligibly small. In order to understand the role of shortrange
forces in such special mixtures, orientational studies have been undertaken in the
mixtures 55 wt% ZLI- 1132(1132)/N- (-4-ethoxybenzylidene)-4’-butylariiline (EBBA), 56.5
wt% 1132/EBBA and 70 wt% 4-n-pentyl-4’-cyanobiphenyl (5CB)/EBBA.
As a starting point, the C2v and D2h symmetry solutes meta dichlorobenzene, ortho
dichlorobenzene, para dichlorobenzene, ortho dicyanobenzene, furan, tetrathiofulvalene
and fiuorobenzene have been studied in the special mixtures 56.5 wt% 1132/EBBA at
323K and 70 wt% 5CB/EBBA at 316K, using proton NMR. The measured electric field
gradient for these two mixtures has been found to be zero. The order parameters ob
tained from an analysis of the NMR spectra indicate that the solutes experience a similar
anisotropic potential in both mixtures. The results are interpreted in terms of a model
for the short-range anisotropic potentials experienced by the solutes.
To further explore the investigation of the short-range forces in zero electric field
gradient mixtures, the temperature dependence of the solutes meta dichlorobenzene,
ortho dichlorobenzene, 1,3-bromochlorobenzene, benzene and 2-butyne has been studied in the special mixtures 55 wt% 1132/EBBA and 70 wt% 5CB/EBBA, using proton NMR.
These solutes vary from each other in symmetry and shape. The aim was to see how the
different shaped solutes experience the short-range forces in the liquid crystal mixtures.
The results indicate that the solutes experience a similar anisotropic potential in both
mixtures. The biaxial order parameters measured for the solutes meta dichlorobenzene,
ortho dichlorobenzene, and 1,3-bromochlorobenzene have also been analysed to magnify
the differences between the mixtures.
To extend our understanding on the intermolecular forces among constituent liquid
crystal molecules, a temperature dependence study of the liquid crystal 5CB — d19 as so
lute has been undertaken in the three liquid crystal mixtures: 55 wt% 1132/EBBA, 56.5
wt% 1132/EBBA and 70 wt% 5CB/EBBA, using ²H — NMR. The study of SCB — d19
as solute has been used to compare the short-range interactions in these special mixtures.
The spectra of 5CB — d19 in the two 1132/EBBA mixtures are equivalent, but are dif-
ferent from those in the 5CB/EBBA mixture. The spectra in 55 wt% 1132/EBBA and
70 wt% 5CB/EBBA have been analysed using two different models for the short-range
potential, and parameters of the models have been used to compare the potentials in the
different mixtures. It has been shown that, for a given spectral splitting of the chain
C1 deuteron, the reduced short-range potential is the same in all three mixtures studied.
The spectral differences observed are a consequence of different nematic-isotropic phase
transition temperatures combined with the effect of trans-gauche isomerization in the
hydrocarbon chain.
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Govender, Nadaraj. "Mössbauer study of the hyperfine magnetic field and electric field gradient at Fe sites in synthetic diamond." Thesis, 1992. http://hdl.handle.net/10413/5684.
Full textAbstract:
Mossbauer Spectroscopy has been used to investigate the
site of Fe inclusions in a suite of synthetic diamonds (de
Beers MDAS). Information on the hyperfine magnetic fields
and electric field gradients at Fe sites in the diamond
grains were obtained from Mossbauer Spectroscopy of diamond
grains ranging in size from 25 to 250 um. The Fe inclusions
in these samples resulted from the synthesis of the diamond
grains in which Fe was used as a catalytic solvent. The
Mossbauer measurements were carried at room temperature
with a constant acceleration spectrometer operating in
transmission geometry.
The samples with the largest grain size of 180-250 um gave
a well defined six component magnetically split spectrum,
similar to the Zeeman split sextet obtained for natural
iron. As the grain sizes decreased the intensity of
the magnetically split components became greatly reduced
and a strong paramagnetic component appeared. At grain
sizes 105-45 um the spectra are dominated by a central
single line with some evidence of an asymmetric doublet.
For the finest grain size 38-25 um, the reappearance of
the six magnetic hyperfine splitting components together
with the strong central single paramagnetic component was
observed.
The change in the Mossbauer patterns observed with decreasing
grain size suggest that a rapid phase transition of the
Fe inclusions from ferromagnetic to superparamagnetic
takes place.
The analysis of Mossbauer spectra yielded a value of the
hyperfine magnetic field of Bhf = -32.4(4) T and an
electric field gradient in the range of Vzz = 1.4(4) 1.8(
7) X 10'8 V.cm- 2 at the site of the probe s7Fe
nucleus. These values compare favourably with other
measurements.Thesis (M.Sc.)-University of Durban-Westville, 1992.
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"Measurement of the temperature dependence of the Buckingham effect (electric-field-gradient-induced birefringence) in gases." Thesis, 2009. http://hdl.handle.net/10413/215.
Full textAbstract:
The aim of this research project was to assemble an apparatus to measure the
electric quadrupole moments of gas molecules using the technique of electricfield-
gradient-induced birefringence, or the Buckingham effect. Comprehensive
research by various workers in the field has shown that this technique
provides the only direct means of obtaining the quadrupole moment of a
molecule.
Theory has shown that the most accurate determination of the electric quadrupole
moment is through a study of the temperature dependence of the effect. This
not only allows for the quadrupole moment to be obtained but also enables
the temperature-independent quadrupole hyperpolarisability term to be extracted.
Both the quadrupole moment and the hyperpolarisabilty provide
valuable information in a variety of applications, including intermolecular
forces, electrostatic potentials and non-linear optical phenomena.
This thesis fully describes the apparatus used in these measurements, including a description of the custom built oven that allowed for measurements
to be performed over a temperature range spanning from 25"C up to
200"C. Results for the quadrupole moments and quadrupole hyperpolarisabilities
of carbon dioxide, carbon monoxide, nitrous oxide and hydrogen are
presented, together with a quadrupole moment for carbonyl sulphide from
room-temperature measurements. Wherever possible, the results of this work
are compared to previously published experimental and theoretical data.Thesis (PhD) - University of KwaZulu-Natal, Pietermaritzburg, 2009.
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Lin, Kuo-Tsai, and 林國材. "Investigation of π-electron dependence of Electric Field Gradient and Examination of Hyperconjugation in Acetonitrile Derivatives." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/71346200244105340828.
Full textAbstract:
碩士國立成功大學
化學系碩博士班
91
Weakening of the C(3)-C(2) bonds in the series: H3-n(Me)nC-C≡N has been explained by the well-known hyperconjugation concept which may be classified as the donor-acceptor interaction between □σC(3)H(4) and □σ*C(2)C(3). Natural Bond Orbital (NBO) analysis of the orbital interaction energy, E(2), in this series of molecules reveals that the □σC(3)H(4) and □σ*C(2)C(3) interaction is in general smaller than □σC(3)C(Me) and □σ*C(2)C(3). Orbital interactions involving □σC(2)C(3) as donating bond orbital and □σ*C(2)C(3) as accepting bond orbital play critical roles concerning the strength of C(2)C(3) bonds. The values of E(2) for the former interactions increase in the trend: 13.06, 17.08, 21.34, 25.22 kcal/mol and E(2) for the latter indicates the same trend as well: 23.88, 29.12, 34.08, 40.44 kcal/mol, which primarily arises from the increasing □σC(3)C(Me) and □σ*C(2)C(3) donor-acceptor interactions. Both trends can be employed to account for the weakened C(2)-C(3) bonds since the increasing number of methyl substitution leads to more or higher orbital interactions involving the C(2)-C(3) bonding and antibonding orbitals. The electric field gradients (EFG) of para-carbon and para-nitrogen atoms in mono-substituted benzene and pyridine were calculated, respectively. The linear relationship between EFG and charge for either carbon or nitrogen atom, which is only influenced by the □π-effect of the substituent, R, has been found. Furthermore, the relative proportionality constants can be related to the value of qo, representing the EFG resulting from one electron filled in the 2p-orbital. Our results can be employed to rationalize the semi-empirical relationship proposed in the literature for evaluation of backbonding electrons in transition-metal carbonyls. In other words, the work presented here provides evidence in support of the Townes-Dailey theory applied to systems in which only □π-effects are relevant.
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Eller, Alexander M. "The Color-Electric Field Correlator under Gradient Flow at next-to-leading Order in Quantum Chromodynamics." Phd thesis, 2021. https://tuprints.ulb.tu-darmstadt.de/17610/1/Dissertation_Eller_v2.pdf.
Full textAbstract:
The exploration of the strong interaction by heavy-ion collisions is an important step towards a deeper understanding of nature. An experimentally and theoretically accessible probe for the details of the strong interactions are the transport properties of heavy quarks inside a quark-gluon plasma.
One of the these transport coefficients is the momentum diffusion coefficient of a heavy quark. It is determined by the spectral function of an Euclidean correlator of two color-electric fields along a Polyakov loop. This purely bosonic correlator can be simulated non-perturbatively using lattice gauge theory. The correlator suffers from noise to the point where the determination of the signal is not possible. This problem can be solved by noise-reduction techniques. Lüscher introduced the gradient flow procedure as an effective gauge-invariant noise-reduction technique. Gradient flow regulates the ultra-violet behavior of correlation functions hence suppressing the noise. Consequently, the renormalization properties of the gradient flowed operators are modified.
In this thesis we analyze the effects of gradient flow on the color-electric field correlation function using perturbation theory in the continuum and on the lattice at next-to-leading order in the small coupling expansion, O(αₛ²).
We discuss the relation between a gradient-flowed Euclidean correlator and its spectral function. From this we conclude the necessary order for taking the continuum limit first and flow time to zero limit second in lattice simulations. With a qualitative study of the correlator in lattice QED we determine the renormalization effects of the field operators at finite lattice spacing and flow time. We compute the correlation function in continuum QCD and evaluate the small separation and small flow time limits. The results obtained in this study improve the understanding of the usage of the gradient flow method in future lattice simulations of full QCD determining transport coefficients.
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Chen, Yu-Fu, and 陳昱甫. "Fabrication of Gradient-Index Polymer Waveguides by Using The Micro-Molding Process with an Applying Electric Field Method." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/sw7ut9.
Full textAbstract:
碩士國立虎尾科技大學
機械與機電工程研究所
100
This project is to study the process by using PDMS to fabricate a polymeric gradient refractive index waveguides structures component along with photolithography, micro molding process and applying electric field method. First, the negative photoresist SU-8 is used to fabricate waveguides pattern on a glass substrate, and the PDMS is used to transfer on the substrate mold. Next, a micro-molding process by using the Micro-Contact Printing technology & Replica Molding technology are used to pattern on the OG146, and then at core layer the UV exposure is used for curing at same time, the electric field was applied to induce the change of the refractive index of the UV polymer. Finally, UV polymer gradient-index waveguides components is fabricated. In this study, an optical microscope was used to OM observe experiment process, Prism coupler was used to detect the refractive index of the polymer waveguide, and then profiles of the devices were observed using scanning electron microscope (SEM).
34
Koch, Katrin [Verfasser]. "Crystal structure, electron density and chemical bonding in inorganic compounds studied by the Electric Field Gradient / von Katrin Koch." 2009. http://d-nb.info/1007751142/34.
Full text
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Huang, Po-chi, and 黃柏綺. "The Determination of Chemical Shift Tensor and Electric Field Gradient Tensor by One- and Two-Dimensional Magic-Angles-Spinning Experiments." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/n3su8a.
Full text
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Brüsewitz, Christoph. "Elektrische Quadrupolwechselwirkung in defektreichen und deformierten MAX-Phasen." Doctoral thesis, 2015. http://hdl.handle.net/11858/00-1735-0000-0023-9638-5.
Full textAbstract:
In der vorliegenden Arbeit wird dargestellt, wie sich mit Methoden der nuklearen Festkörperphysik Defekte und Deformationen selbst in kristallographisch komplexen Materialien wie den MAX-Phasen, einer Klasse von Komplexcarbiden bzw. -nitriden, in-situ nachweisen lassen.
Die sensitive Messgröße bildet dabei der elektrische Feldgradient (EFG), der ein Maß für die Asymmetrie der den jeweiligen Sondenkern umgebenden Ladungsverteilung darstellt.
Es werden zwei Wechselwirkungsmechanismen zwischen Defekt und EFG diskutiert: Einerseits die langreichweitigen Auswirkungen elastischer Verzerrungen, andererseits der direkte Einfluss eines Defektes auf seine lokale elektronische Umgebung.
Die Bestimmung der elastischen Antwort des Feldgradienten erfolgt mittels Ab-initio-Methoden im Rahmen der Dichtefunktionaltheorie.
Der dabei vorgestellte Ansatz erlaubt es, die Ursachen der Dehnungsabhängigkeit zu klären und andere, speziellere Dehnungsabhängigkeiten wie die Volumenabhängigkeit oder die Strukturabhängigkeit des Feldgradienten zu bestimmen.
Die in der Umgebung bestimmter Defekte oder Deformationen auftretenden EFG-Verteilungen werden anhand der allgemeinen Dehnungsabhängigkeit mittels Monte-Carlo-Simulationen bestimmt.
Die so vorhergesagten Verteilungen werden durch ein Experiment im Rahmen der gestörten $\gamma$-$\gamma$-Winkelkorrelation (PAC) sichtbar gemacht, indem polykristalline MAX-Phasen unter uniaxialer Last verformt werden.
Eine quantitative Auswertung erlaubt es schließlich, Defektdichten in-situ abzuschätzen.
Die lokalen Auswirkungen auf den EFG werden anhand verschiedener MAX-Phasen-Mischkristalle systematisch untersucht.
Im Zuge dessen wird die Synthese eines bisher unbekannten MAX-Phasen-Mischkristalls, Ti$_2$(Al$_{0,5}$,In$_{0,5}$)C, beschrieben.
Die Zugehörigen Gitterkonstanten werden mittels Röntgendiffraktometrie im Rahmen der Rietveld-Methode bestimmt.
37
Jürgens, Daniel. "Untersuchung der elektrischen Hyperfeinwechselwirkung in Mn+1AXn-Phasen mittels der gestörten γ-γ-Winkelkorrelation." Doctoral thesis, 2013. http://hdl.handle.net/11858/00-1735-0000-0022-5EB8-2.
Full textAbstract:
Mn+1AXn-Phasen sind thermodynamisch stabile nanolaminierte Ternärcarbide und -nitride, die sowohl metallische als auch keramische Eigenschaften aufweisen. Der Buchstabe M steht für ein frühes Übergangsmetall, der Buchstabe A für ein A-Element aus den Gruppen IIIA – VIA und X für Kohlenstoff und/oder Stickstoff. Die M-Atome bilden Oktaederschichten mit X-Atomen in ihren Zentren. Der Index n beschreibt die Dicke der Mn+1Xn-Lage, die zwischen zwei hexagonalen A-Schichten eingebettet ist. Die außergewöhnlichen Eigenschaften dieser Materialien haben ihren Ursprung in ihrer Mikrostruktur. Um einen Einblick auf atomarer Ebene zu gewinnen wird die Messmethode der gestörten γ-γ-Winkelkorrelation (PAC) angewendet. Die radioaktiven Sonden 111In/111Cd und 181Hf/181Ta werden durch Ionenimplantation und/oder durch Neutronenaktivierung in das Wirtsmaterial eingebracht, um den elektrischen Feldgradienten (EFG) zu messen, der am Gitterpatz des Sondenatoms herrscht.
Das erste Ziel der Arbeit ist die Suche nach optimalen Ausheilparametern, mit denen ein möglichst hoher Anteil der Sonden die gleiche lokale Umgebung spürt. Der nächste Schritt ist die Bestimmung des Gitterplatzes der Sonden in der MAX-Struktur. Als Ergebnis kann festgestellt werden, dass 111In in den In- und Al-basierten MAX-Phasen fast ausschließlich den A-Platz besetzt, während 181Hf in Hf2InC auf dem M-Platz eingebaut wird. Als überraschendes Ergebnis zeigt diese Arbeit, dass die PAC-Methode bei Phasen mit gleichen Konstituenten, aber unterschiedlicher Mn+1Xn-Schichtdicke sensitiv auf die Änderung der Stapelfolge ist.
Die Experimente werden mit umfangreichen Rechnungen auf Basis der Dichtefunktionaltheorie (DFT) verglichen, die hier erstmalig für nahezu alle Mitglieder der Familie der MAX-Verbindungen durchgeführt wurden. Die DFT-Rechnungen reproduzieren die gemessenen EFGs mit hoher quantitativer Genauigkeit und stützen die Hypothese, dass sich die Sonden auf den prognostizierten Gitterplätzen befinden.