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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.
271

The choreography of protein vibrations : Improved methods of observing and simulating the infrared absorption of proteins

Karjalainen, Eeva-Liisa January 2011 (has links)
The work presented in this thesis has striven toward improving the capability to study proteins using infrared (IR) spectroscopy. This includes development of new and improved experimental and theoretical methods to selectively observe and simulate protein vibrations. A new experimental method of utilising adenylate kinase and apyrase as helper enzymes to alter the nucleotide composition and to perform isotope exchange in IR samples was developed. This method enhances the capability of IR spectroscopy by enabling increased duration of measurement time, making experiments more repeatable and allowing investigation of partial reactions and selected frequencies otherwise difficult to observe. The helper enzyme mediated isotope exchange allowed selective observation of the vibrations of the catalytically important phosphate group in a nucleotide dependent protein such as the sarcoplasmic reticulum Ca2+-ATPase. This important and representative member of P-type ATPases was further investigated in a different study, where a pathway for the protons countertransported in the Ca2+-ATPase reaction cycle was proposed based on theoretical considerations. The transport mechanism was suggested to involve separate pathways for the ions and the protons. Simulation of the IR amide I band of proteins enables and supports structure-spectra correlations. The characteristic stacking of beta-sheets observed in amyloid structures was shown to induce a band shift in IR spectra based on simulations of the amide I band. The challenge of simulating protein spectra in aqueous medium was also addressed in a novel approach where optimisation of simulated spectra of a large set of protein structures to their corresponding experimental spectra was performed. Thereby, parameters describing the most important effects on the amide I band for proteins could be determined. The protein spectra predicted using the optimised parameters were found to be well in agreement with experiment. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Manuscript.</p>
272

Stark Spectroscopy, Lifetimes and Coherence Effects in Diatomic Molecular Systems

Hansson, Annie January 2005 (has links)
In this dissertation is exemplified how different laser based methods are applied in high-resolution spectroscopic studies of internal properties of diatomic molecules. A molecular beam apparatus assembly is described, where a laser ablation source is combined with a time-of-flight mass spectrometer. Compounds investigated with this equipment are hafnium sulfide and hafnium oxide. The molecules are excited and ionized applying the resonant two-photon ionization (R2PI) scheme, which is a sensitive absorption and detection technique for probing the population of an excited state. By means of the DC Stark effect, permanent electric dipole moments of HfS in the D 1Π state and HfO in the b 3Π1 state are determined while the molecules are exposed to a static electric field. Under field-free conditions low temperature rotationally resolved spectra are recorded, generating line positions from which molecular parameters are derived. The R2PI method, modified with an adjustable delay time, is also used in lifetime measurements of individual rotational levels of the HfS D 1Π and HfO b 3Π1 states. Oscillator strengths for transitions from the ground state are calculated, and in this connection basic concepts like Einstein coefficients, line strengths and Hönl-London factors, are surveyed. Theoretical calculation of lifetimes is discussed in view of the fact that a commonly available computer program (LEVEL 7.5 by Le Roy) gives erroneous output. Some coherence and quantum interference related phenomena, such as electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting, are presented in the latter part of this thesis. Fundamental concepts and relations are introduced and explained. The driven three-level cascade system is elucidated, including some of its experimental applications to alkali metal dimers, Na2 and Li2. A triple resonance spectroscopy experiment is described in terms of a three-laser, four-level inverted-Y excitation scheme, implemented in Na2. The accompanying density matrix formalism, providing the basis for theoretical simulations, is accounted for. From analysis of the results an absolute value of the electric dipole moment matrix element (transition moment) is extracted, using the AC Stark effect. Some recently reported unexpected experimental results and unforeseen features, occurring in Doppler broadened samples and related to the open character of molecular systems, are briefly commented.
273

Localization of cortical potentials evoked by balance disturbances

Marlin, Amanda January 2011 (has links)
The ability to correct balance disturbances is essential for maintaining upright stability. Recent literature highlights a potentially important role for the cerebral cortex in controlling compensatory balance reactions. The objective of this research was to provide a more detailed understanding of the specific neurophysiologic events occurring at the cortex following balance disturbances. More specifically, the focus was to determine whether the N1, a cortical potential evoked during balance control, and the error-related negativity (ERN), a cortical potential measured in response to errors during cognitive tasks, have similar cortical representation, revealing a similar link to an error detection mechanism. It was hypothesized that the N1 and ERN would have the same generator located in the anterior cingulate cortex (ACC). Fourteen healthy young adults participated in a balance task (evoked N1) and a flanker task (evoked ERN). Temporally unpredictable perturbations to standing balance were achieved using a lean and release cable system. Electromyography and centre of pressure were measured during the balance task. Reaction times and error rates were measured during the flanker task. Electroencephalography was recorded during both tasks. Source localization was performed in CURRY 6 using a single fixed coherent dipole model to determine the neural generator of the N1 and ERN. The results revealed that the locations of the N1 and ERN dipoles were different. The mean (n=9) distance between N1 and ERN dipoles was 25.46 ± 8.88 mm. The mean Talairach coordinates for the ERN dipole were (6.47 ± 3.08, -4.41 ± 13.15, 41.17 ± 11.63) mm, corresponding to the cingulate gyrus (Brodmann area 24). This represents the ACC, supporting results from previous literature. The mean Talairach coordinates for the N1 dipole were (5.74 ± 3.77, -11.81 ± 10.84, 53.73 ± 7.30) mm, corresponding to the medial frontal gyrus (Brodmann area 6). This is the first work to localize the source of the N1. It is speculated that the generator of the N1 is the supplementary motor area and that it represents the generation of a contingency motor plan to shape the later phases of the compensatory balance response based on sensory feedback from the perturbation.
274

Tailored Force Fields for Flexible Fabrication

Wanis, Sameh Sadarous 11 April 2006 (has links)
The concept of tailored force fields is seen as an enabler for the construction of large scale space structures. Manufacturing would take place in space using in-situ resources thereby eliminating the size and weight restriction commonly placed on space vehicles and structures. This thesis serves as the first investigation of opening the way to a generalized fabrication technology by means of force fields. Such a technology would be non-contact, flexible, and automated. The idea is based on the principle that waves carry momentum and energy with no mass transport. Scattering and gradient forces are generated from various types of wave motion. Starting from experiments on shaping walls using acoustic force fields, this thesis extends the technology to electromagnetic fields. The interaction physics of electromagnetic waves with dielectric material is studied. Electromagnetic forces on neutral dielectric material are shown to be analogous to acoustic forces on sound-scattering material. By analogy to the acoustic experiments, force fields obtained by optical tweezers are extended to longer wavelength electromagnetic waves while remaining in the Rayleigh scattering regime. Curing of the surface formed takes place by use of a higher frequency beam that scans the surface and melts a subsurface layer enabling a sintering effect to take place between the particles. The resulting capability is explored at its extremes in the context of building massive structures in Space. A unification of these areas is sought through a generalization of the various theories provided in the literature applicable for each field.
275

Fracture Detection and Water Sweep Characterization Using Single-well Imaging, Vertical Seismic Profiling and Cross-dipole Methods in Tight and Super-k Zones, Haradh II, Saudi Arabia

Aljeshi, Hussain Abdulhadi A. 2012 May 1900 (has links)
This work was conducted to help understand a premature and irregular water breakthrough which resulted from a waterflooding project in the increment II region of Haradh oilfield in Saudi Arabia using different geophysical methods. Oil wells cannot sustain the targeted oil production rates and they die much sooner than expected when water enters the wells. The study attempted to identify fracture systems and their role in the irregular water sweep. Single-well acoustic migration imaging (SWI), walkaround vertical seismic profiling (VSP) and cross-dipole shear wave measurements were used to detect anisotropy caused by fractures near and far from the borehole. The results from all the different methods were analyzed to understand the possible causes of water fingering in the field and determine the reasons for discrepancies and similarities of results of the different methods. The study was done in wells located in the area of the irregular water encroachment in Haradh II oilfield. Waterflooding was performed, where water was injected in the water injector wells drilled at the flanks of Harahd II toward the oil producer wells. Unexpected water coning was noticed in the west flank of the field. While cross-dipole and SWI measurements of a small-scale clearly identify a fracture oriented N60E in the upper tight zone of the reservoir, the VSP measurements of a large-scale showed a dominating fracture system to the NS direction in the upper highpermeability zone of the same reservoir. These results are consistent with the directions of the three main fracture sets in the field at N130E, N80E and N20E, and the direction of the maximum horizontal stress in the field varies between N50E and N90E. Results suggested that the fracture which is detected by cross-dipole at 2 to 4 ft from the borehole is the same fracture detected by SWI 65 ft away from the borehole. This fracture was described using the SWI as being 110 ft from top to bottom, having an orientation of N60E and having an angle of dip of 12° relative to the vertical borehole axis. The detected fracture is located in the tight zone of the reservoir makes a path for water to enter the well from that zone. On the Other hand, the fractures detected by the large-scale VSP measurements in the NS direction are responsible for the high-permeability in the upper zone of the reservoir.
276

Particles with Negative Mass: Production, Properties and Applications for Nuclear Fusion and Self-Acceleration

Tajmar, Martin, Assis, A. K. T. 21 July 2015 (has links) (PDF)
Some experiments have indicated the possible existence of par ticles with a negative inertial mass. It is shown under which condit ions Weber’s electrodynamics gives rise to this effect. Some specific experiments related to this aspect of Weber’s law are described. Two particles equ ally electrified with charges of the same sign would then move toward one an other if they had negative effective inertial masses. A new concept for nuclear fusion is presented based on the possibility of creating a negative effective inertial mass for ions. It is then considered some properties of the inertial dipole, that is, a system composed by a pair of particles in which one particle has a positive effective inertial mass while the other particle has a negative effective inertial mass. The possible utilization of the inertialdipole as a propulsion system is briefly discussed.
277

Modifizierung von Silikonelastomeren mit organischen Dipolen für Dielektrische Elastomer Aktuatoren / Modification of silicone elastomers with organic dipoles for dielectric elastomer actuators

Kussmaul, Björn January 2013 (has links)
Ein Dielektrischer Elastomer Aktuator (DEA) ist ein dehnbarer Kondensator, der aus einem Elastomerfilm besteht, der sich zwischen zwei flexiblen Elektroden befindet. Bei Anlegen einer elektrischen Spannung, ziehen sich die Elektroden aufgrund elektrostatischer Wechselwirkungen an, wodurch das Elastomer in z-Richtung zusammengepresst wird und sich dementsprechend in der x-,y-Ebene ausdehnt. Hierdurch werden Aktuationsbewegungen erreicht, welche sehr präzise über die Spannung gesteuert werden können. Zusätzlich sind DEAs kostengünstig, leicht und aktuieren geräuschlos. DEAs können beispielsweise für Produkte im medizinischen Bereich oder für optischer Komponenten genutzt werden. Ebenso kann aus diesen Bauteilen Strom erzeugt werden. Das größte Hindernis für eine weite Implementierung dieser Materialien liegt in den erforderlichen hohen Spannungen zum Erzeugen der Aktuationsbewegung, welche sich tendenziell im Kilovolt-Bereich befinden. Dies macht die Elektronik teuer und die Bauteile unsicher für Anwender. Um geringere Betriebsspannungen für die DEAs zu erreichen, sind signifikante Materialverbesserungen - insbesondere des verwendeten Elastomers - erforderlich. Um dies zu erreichen, können die dielektrischen Eigenschaften (Permittivität) der Elastomere gesteigert und/oder deren Steifigkeit (Young-Modul) gesenkt werden. In der vorliegenden Arbeit konnte die Aktuationsleistung von Silikonfilmen durch die Addition organischer Dipole erheblich verbessert werden. Hierfür wurde ein Verfahren etabliert, um funktionalisierte Dipole kovalent an das Polymernetzwerk zu binden. Dieser als "One-Step-Verfahren" bezeichnete Ansatz ist einfach durchzuführen und es werden homogene Filme erhalten. Die Dipoladdition wurde anhand verschiedener Silikone erprobt, die sich hinsichtlich ihrer mechanischen Eigenschaften unterschieden. Bei maximalem Dipolgehalt verdoppelte sich die Permittivität aller untersuchten Silikone und die Filme wurden deutlich weicher. Hierbei war festzustellen, dass die Netzwerkstruktur der verwendeten Silikone einen erheblichen Einfluss auf die erreichte Aktuationsdehnung hat. Abhängig vom Netzwerk erfolgte eine enorme Steigerung der Aktuationsleistung im Bereich von 100 % bis zu 4000 %. Dadurch können die Betriebsspannungen in DEAs deutlich abgesenkt werden, so dass sie tendenziell bei Spannungen unterhalb von einem Kilovolt betrieben werden können. / Dielectric elastomer actuators (DEAs) are compliant capacitors consisting of an elastomer film between two flexible electrodes. When a voltage is applied the electrostatic attraction of the electrodes leads to a contraction of the polymer in the z-direction and to a corresponding expansion in the x,y-plane. DEAs show high actuation strains, which are very accurate and adjustable by the applied voltage. In addition these devices are low-cost, low-weight and the actuation is noise-free. DEAs can be used for medical applications, optical components or for energy harvesting. The main obstacle for a broad implementation of this technology is the high driving voltage, which tends to be several thousand volts. For this reason the devices are unsafe for users and the needed electronic components are expensive. A significant improvement of the materials - especially of the used elastomer - is necessary to lower the actuation voltages. This can be achieved by improving the dielectric properties (permittivity) of the elastomer and/or by lowering it's stiffness (Young's modulus). In this work the actuation performance of silicone lms was improved significantly by the addition of organic dipoles. A simple procedure was developed, in which functionalized dipoles were bound to the polymer matrix, leading to homogenous and transparent films. This so-called "one-step-film-formation" was tested on various silicones with different mechanical properties. For the highest dipole content the permittivity of all tested silicones was doubled and the modified films showed a substantially lower stiffness. It was proven that the structure of the macromolecular network has a clear impact on the achievable actuation properties. For the highest dipole contents the actuation performance increased remarkably by 100 % up to 4000 % in respect to the investigated network. The addition of organic dipoles to the elastomer enables a signicant reduction of the needed driving voltage for DEAs below one kilovolt.
278

Localization of cortical potentials evoked by balance disturbances

Marlin, Amanda January 2011 (has links)
The ability to correct balance disturbances is essential for maintaining upright stability. Recent literature highlights a potentially important role for the cerebral cortex in controlling compensatory balance reactions. The objective of this research was to provide a more detailed understanding of the specific neurophysiologic events occurring at the cortex following balance disturbances. More specifically, the focus was to determine whether the N1, a cortical potential evoked during balance control, and the error-related negativity (ERN), a cortical potential measured in response to errors during cognitive tasks, have similar cortical representation, revealing a similar link to an error detection mechanism. It was hypothesized that the N1 and ERN would have the same generator located in the anterior cingulate cortex (ACC). Fourteen healthy young adults participated in a balance task (evoked N1) and a flanker task (evoked ERN). Temporally unpredictable perturbations to standing balance were achieved using a lean and release cable system. Electromyography and centre of pressure were measured during the balance task. Reaction times and error rates were measured during the flanker task. Electroencephalography was recorded during both tasks. Source localization was performed in CURRY 6 using a single fixed coherent dipole model to determine the neural generator of the N1 and ERN. The results revealed that the locations of the N1 and ERN dipoles were different. The mean (n=9) distance between N1 and ERN dipoles was 25.46 ± 8.88 mm. The mean Talairach coordinates for the ERN dipole were (6.47 ± 3.08, -4.41 ± 13.15, 41.17 ± 11.63) mm, corresponding to the cingulate gyrus (Brodmann area 24). This represents the ACC, supporting results from previous literature. The mean Talairach coordinates for the N1 dipole were (5.74 ± 3.77, -11.81 ± 10.84, 53.73 ± 7.30) mm, corresponding to the medial frontal gyrus (Brodmann area 6). This is the first work to localize the source of the N1. It is speculated that the generator of the N1 is the supplementary motor area and that it represents the generation of a contingency motor plan to shape the later phases of the compensatory balance response based on sensory feedback from the perturbation.
279

Cold single atoms for cavity QED experiments

Kim, Soo Y. 17 November 2008 (has links)
A neutral atom interacting with a single mode of a high finesse cavity provides an opportunity to study uncharted quantum mechanical systems and to explore the field of quantum computing and networking. Ranging from being a deterministic single photon source to a coherent storage unit for quantum information, a strong coupling cavity QED system has proven to be a powerful tool. In this thesis, single atoms are deterministically delivered over long distances and probed in an optical cavity. Once in the cavity, a single atom is stored and continuously observed for over 15 seconds. Progress towards using atoms in the cavity to produce entangled photon pairs is presented. Dual 1D optical lattices are implemented to create a foundation for advancements in two qubit quantum operations and entanglements.
280

Static electric dipole polarizabilities of atoms and molecules : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University, Albany, New Zealand

Lim, Ivan S January 2004 (has links)
The static dipole polarizabilities and ionization potentials of the first and second main group elements, including the charged ions, are obtained from all-electron relativistic coupled-cluster theory using a scalar relativistic Douglas-Kroll Hamiltonian. Spin-orbit coupling effects are investigated using a fully relativistic four-component Dirac-Coulomb-Hartree-Fock scheme followed by a second-order many-body perturbation treatment to account for electron correlation. Periodic trends in the dipole polarizabilities and the ionization potentials are discussed. In each case, a detailed discussion on electron correlation and relativistic effects are given. A relationship for relativistic and electron correlation effects between the dipole polarizability and the ionization potential is established. Particular attention is paid to the evaluation of a near basis set limit quality of the dipole polarizabilities. This is accomplished by the evaluation of all-electron basis sets used, followed by an extensive study on the convergence behavior of the dipole polarizabilities with respect to a finite basis set expansion. The present all-electron dipole polarizabilities are believed to be very precise, especially for charged ions where the availability of experimental values are limited. Scalar relativistic small-core pseudopotentials are fitted and their performance is tested in terms of static dipole polarizabilities and ionization potentials. It is demonstrated that the small core definition of the pseudopotential (nine-valence electron for the main group 1 and ten-valence electron for the main group 2 elements) enables us to safely omit core-valence correlation without scarifying accuracy. Following atomic dipole polarizabilities, applications are made to molecules starting with alkali dimers and their singly charged ions. The scalar relativistic pseudopotentials of this study are used to calculate equilibrium bond lengths, dissociation energies, vibrational frequencies and the dipole polarizabilities of these dimers. The change in the molecular dipole polarizabilities from the corresponding atomic dipole polarizabilities are discussed in terms of molecular bonding models. Simple ammonia complexes of the alkali-metals and their singly charged ions are studied. The equilibrium geometries, dissociation energies, harmonic vibrational frequencies as well as the dipole polarizabilities of these complexes are given.

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