To see the other types of publications on this topic, follow the link: Resonance strategies.
Dissertations / Theses on the topic 'Resonance strategies'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 43 dissertations / theses for your research on the topic 'Resonance strategies.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Blakeley, Nicholas D. "Sampling strategies and reconstruction techniques for magnetic resonance imaging." Thesis, University of Canterbury. Electrical and Computer Engineering, 2003. http://hdl.handle.net/10092/7705.
Full textAbstract:
In magnetic resonance imaging (MRI), samples of the object's spectrum are measured in the spatial frequency domain (k-space). For a number of reasons there is a desire to reduce the time taken to gather measurements. The approach considered is to sample below the Nyquist density, using prior knowledge of the object's support in the spatial domain to enable full reconstruction.
The two issues considered are where to position the samples (sampling strategies) and how to form an image (reconstruction techniques). Particular attention is given to a special case of irregular sampling, referred to as Cartesian sampling, in which the samples are located on a Cartesian grid but only constitute a subset of the full grid. A further special case is considered where the sampling scheme repeats periodically, referred to as periodic Cartesian sampling. These types of sampling schemes are applicable to 3-D Cartesian MRI, MRSI, and other modalities that measure a single point in 2-D k-space per echo. The case of general irregular sampling is also considered, which is applicable to spiral sampling, for example.
A body of theory concerning Cartesian sampling is developed that has practical implications for how to approach the problem and provides intuition about its nature. It is demonstrated that periodic Cartesian sampling effectively decomposes the problem into a number of much smaller subproblems, which leads to the development of a reconstruction algorithm that exploits these computational advantages. An additional algorithm is developed to predict the regions that could be reconstructed from a particular sampling scheme and support; it can be used to evaluate candidate sampling schemes before measurements are obtained. A number of practical issues are also discussed using illustrative examples. Sample selection algorithms for both Cartesian and periodic Cartesian sampling are developed using heuristic metrics that are fast to compute. The result is a significant reduction in selection time at the expense of a slightly worse conditioned system. The reconstruction problem for a general irregular sampling scheme is also analysed and a reconstruction algorithm developed that trades off computation time for better image quality.
2
Maas, Luis C. (Luis Carlos). "Processing strategies for functional magnetic resonance imaging data sets." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/85262.
Full textAbstract:
Thesis (Ph.D.)--Harvard--Massachusetts Institute of Technology Division of Health Sciences and Technology, 1999.Includes bibliographical references (leaves 108-118).
by Luis Carlos Maas, III.
Ph.D.
3
Ross, Peter James. "Strategies for speeding up Fast Field-Cycling MRI." Thesis, University of Aberdeen, 2016. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=230548.
Full textAbstract:
Fast field-cycling MRI (FFC-MRI) is a novel technique that promises to expand upon the diagnostic capabilities of conventional MRI by allowing the main magnetic field, B0, to be varied during the imaging pulse sequence. By doing this it is possible to gain access to information that is hidden to conventional scanners - namely the variation of the spin-lattice relaxation time, T1, with field strength, known as T1 dispersion. However, adding B0 as a new dimension to the imaging process necessitates a longer scan time which can limit the techniques application to clinical research. In this thesis, several methods are explored for reducing FFC-MRI scan times. A rapid imaging pulse sequence based on the well-known Fast Spin-Echo imaging sequence is presented, as well as an adaptation of the “keyhole” acquisition strategy. A method of determining T1 which requires significantly less data - and hence scan time - is also presented. When combined, these techniques are demonstrated to reduce total scan time from several hours to minutes without compromising access to T1 dispersion information. The techniques are demonstrated in phantom studies and in vivo results from volunteers are presented as proof of concept. The reduction in scan time demonstrated by these methods will significantly improve the applicability of FFC-MRI for clinical trials which are currently being worked towards.
4
Fransson, Peter. "Analysis and development of strategies for magnetic resonance functional neuroimaging /." Stockholm, 1999. http://diss.kib.ki.se/1999/91-628-3365-0/.
Full text
5
Breuer, Felix. "Development and application of efficient strategies for parallel magnetic resonance imaging." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=982469136.
Full text
6
Chilton, Mark Daniel. ""Purposely mingled resonance" : strategies of misdirection in early Wells and Conrad /." view abstract or download file of text, 2003. http://wwwlib.umi.com/cr/uoregon/fullcit?p3102157.
Full textAbstract:
Thesis (Ph. D.)--University of Oregon, 2003.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 330-346). Also available for download via the World Wide Web; free to University of Oregon users.
7
Speidel, Tobias [Verfasser]. "Low-discrepancy k-space sampling strategies for magnetic resonance imaging / Tobias Speidel." Ulm : Universität Ulm, 2021. http://d-nb.info/1232323853/34.
Full text
8
Skare, Stefan. "Optimisation strategies in diffusion tensor MR imaging /." Stockholm, 2002. http://diss.kib.ki.se/2002/91-7349-175-6.
Full text
9
Wright, Katherine L. "Measuring Perfusion with Magnetic Resonance Imaging using Novel Data Acquisition and Reconstruction Strategies." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1412786849.
Full text
10
Shannahan, Kelsey Irene. "Magnetic resonance imaging characterization of hydrogel substrates for tissue engineering strategies after spinal cord injury." Thesis, Boston University, 2012. https://hdl.handle.net/2144/12619.
Full textAbstract:
Thesis (M.A.)--Boston University
PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.Spinal cord injury (SCI) often results in irreversible paralysis of the limbs. Ongoing cellular recovery immediately after SCI is limited by the influx of inhibitory molecules that prevent neurons from infiltrating the lesion, resulting in a loss of axonal connections [57]. A range of studies have shown that a scaffold emiched in compounds that facilitate regeneration can lead to functional recovery. Therapeutic agents such as synthetic hydrogels have been shown to overcome the body's natural inhibitory response and promote permanent improvement in motor function. Hydrogel scaffolds with precise orientation have shown particular promise due to their proclivity for orienting lengthwise along the spinal cord, favoring axonal growth [7]. Standard magnetic resonance imaging (MRI) techniques optimized for visualizing the spinal cord can measure this degree of diffusion along white matter tracts. However, there are no published studies reporting the MRI parameters of the hydrogel substrates, and an understanding of how the material behaves in vitro may help guide the selection of an ideal compound by matching relaxation parameters and anisotropy measurements to those of spinal cord tissue. This study sought to characterize three hydrogel substrates of varying concentration using MRI to measure relaxation and diffusion properties. Relaxation times for agarose decreased as the concentration increased; whereas PuraMatrixTM relaxation times increased with increasing concentration. The addition offibronectin (an extracellular matrix support protein) significantly prolonged the relaxation times for the PuraMatrixTM solutions. No differences in proton density or restricted diffusion were observed. The results were compared to known relaxation and diffusion values for the spinal cord at 3T, highlighting certain concentrations that may be a best fit for use in the spinal cord. MRI is capable of quantifying substrate properties in vitro and then assessing their integration into tissue in vivo.
11
Kulkarni, Praveen P. "Functional MRI data analysis techniques and strategies to map the olfactory system of a rat brain." Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-011906-095333/.
Full text
12
Dechent, Jan Falk Frederik [Verfasser]. "Proton magnetic resonance with parahydrogen induced polarization : Imaging strategies and continuous generation / Jan Falk Frederik Dechent." Mainz : Universitätsbibliothek Mainz, 2013. http://d-nb.info/1029929076/34.
Full text
13
Kwan, Samantha. "Contested Meanings about Body, Health, and Weight: Frame Resonance, Strategies of Action, and the Uses of Culture." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/193746.
Full textAbstract:
There has been much talk in the public arena about the meanings of the overweight body. While feminist scholars have long theorized and studied the oppressive effects of hegemonic beauty norms, in recent years several groups such as the Centers for Disease Control, the National Association to Advance Fat Acceptance (a non-profit fat acceptance organization), and the Center for Consumer Freedom (a non-profit organization representing the food industry), have stepped up claims-making about the fat body and what it represents. How are these competing cultural messages promulgated by these cultural producers? Do these messages resonate with individuals? Moreover, how meaningful are these cultural messages in shaping day to day lives?Using content/frame analysis, survey data (n=456), and in-depth qualitative interviews (n=42), my dissertation examines framing competitions and dynamics among four competing cultural frames about the overweight body (the health frame, beauty frame, market choice frame, and social justice frame). I also examine the relationship between these cultural frames and individual agents. Specifically, I look at how respondents use culture by accepting, redefining, and rejecting elements of various frames. In my dissertation, I elaborate on my empirical findings and theoretical developments about health, beauty, individual and corporate responsibility, and social justice; the relationship between culture and agents; policy implications; and directions for future research.
14
Ciezka, Magdalena. "Improvement of Protocols for Brain Cancer Diagnosis and Therapy Response Monitoring Using Magnetic Resonance Based Molecular Imaging Strategies." Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/666281.
Full textAbstract:
Los tumores cerebrales constituyen menos del 2% de los tumores primarios, pero son uno de los peores tipos de cáncer en cuanto a “años de vida perdidos”. Los gliomas son los tumores cerebrales más prevalentes, con una esperanza de vida inferior a 15 meses para los casos de alto grado, como los glioblastomas (GBM). El método no invasivo más utlilizado para diagnóstico y seguimiento de la respuesta a la terapia en tumores cerebrales es la Resonancia Magnética (MR), en forma de imagen (MRI) y espectroscopía (MRS) o imagen espectroscópica (MRSI). Sin embargo, debido a restricciones éticas relacionadas a la participación de pacientes humanos en investigación, la optimización de los métodos de diagnóstico y seguimiento de la terapia requieren modelos preclínicos que reproduzcan las patologías humanas. Para este tipo de estudios, se utilizan principalmente modelos murinos, que pueden dividirse en modelos genéticamente modificados (GEM) con desarrollo espontáneo de tumor y los modelos de generación de tumores por inyección estereotáxica de líneas celulares. En la presente tesis, se llevó a cabo una detallada caracterización de dos colonias GEM, S100β-v-erbB/inK4a-Arf (+/-) y GFAP-V12 HA-ras B8. Se observó una baja penetrancia de desarrollo de tumores (16% y 1% respectivamente), haciendo de éstos una herramienta poco útil para estudios de respuesta a la terapia. La escasez de modelos preclínicos de grado bajo/intermedio sirvió de motivación para desarrollar un modelo de tumor glial transplantable con esas características, por disgregación de tumores provenientes de la colonia GEM. Ello nos debería permitir obtener una mayor incidencia tumoral en comparación con las colonias GEM. Se generaron gliosferas a partir de tumores GEM de grado III y se logró más de un 60% de penetrancia cuando estas células fueron inyectadas estereotácticamente en el estriado de ratones C57BL/6. Sin embargo, la aplicación de protocolos de descongelación y cultivo a éstas células ocasionó una progresión a grado IV (GBM), lo que sugiere que el modelo generado constituye, potencialmente, un modelo murino de GBM secundario. Además, este modelo transplantable fue ampliamente caracterizado por métodos de MRI/MRSI, así como por métodos de perturbación del patrón espectral con MRSI (PE-MRSI) para una posible aplicación en el desarrollo de clasificadores de respuesta a la terapia en tumores. También se llevó a cabo una evaluación genética restringida de los modelos murinos seleccionados (p.e. tumores GL261, línea celular GL261, GEM y tumores derivados de GEM), utilizando el método de secuenciación de Sanger para comprobar la presencia de mutaciones normalmente presentes en gliomas (en los genes IDH1, IDH2 y p53). Finalmente, esta tesis describe la estrategia desarrollada para estudios longitudinales de detección de respuesta temprana a la terapia/recidiva en tumores preclínicos, utilizando métodos de imagen molecular basados en MRSI. Así ratones implantados con tumores GL261 (glioblastoma) recibieron tratamiento con temozolamida (TMZ), basándonos en protocolos previamente establecidos. La detención del crecimiento tumoral (respuesta a la terapia) fue detectada por MRI. Tanto animales tratados como animales control fueron estudiados por MRSI y técnicas de reconocimiento de patrones (extracción de fuentes en sistema semi-supervisado). Las fuentes extraídas de regiones de interés fueron capaces de distinguir entre tumores GL261 proliferando activamente y tumores respondiendo a la terapia, basándose en cambios de patrón del metaboloma registrado por MRSI. Se obtuvieron mapas nosológicos codificados en tipo e intensidad de color durante y después de la terapia, lo que permitió un seguimiento de la respuesta, así como la detección de heterogeneidad intratumoral en dicha respuesta, siendo capaces de detectar la detención del crecimiento tumoral y la recidiva antes de los cambios observados en el volumen tumoral por MRI. Esta metodología fue ratificada por análisis histopatológico y cálculo de tasas de proliferación, apoptosis y de índice mitótico.Brain tumours account for less than 2% of all primary tumours, but are one of the most lethal cancers when “life lost” years are considered. Gliomas are the most prevalent type with a median life expectancy below 15 months for the high grade ones, such as glioblastomas (GBM). The most common non-invasive medical technique used for tumour diagnosis and therapy monitoring of brain tumours patients is Magnetic Resonance (MR), in the form of imaging (MRI) and spectroscopy (MRS) or spectroscopic imaging (MRSI). However, due to the ethical restrictions regarding the use of human patients for research study, the improvement of diagnostic and therapy follow-up protocols requires reliable models that mimic human disease. In this regard, mainly murine models are used and can be divided into the genetically engineered model (GEM) of spontaneous tumour development and the engrafted tumour model. In this thesis, a comprehensive MR characterization of two GEM colonies, namely S100β-v-erbB / inK4a-Arf (+/-) and GFAP-V12 HA-ras B8, was carried out. A low tumour penetrance found (16% and 1%, respectively) together with stochastic onset of GEM tumours, made them impractical for use in therapy response studies. The latter and the scarcity of low/intermediate grade brain tumour preclinical models motivated us to attempt to develop a transplantable glial tumour model of low/intermediate grade by disaggregation of a tumour mass from GEM. This should allow us to obtain an increased tumour incidence rate in comparison to GEM animals. Gliospheres from a grade III GEM tumour were successfully generated and displayed more than 60% penetrance, when stereotactically injected into the striatum of C57BL/6 mice. However, the application of freezing and cell culture protocols produced a progression to grade IV GBM, which made the developed transplantable model qualify as potential secondary GBM model in mice. Additionally, this transplantable model was widely characterized using MRI/MRS methods, as well as perturbation-enhanced MRSI (PE-MRSI) for a possible application in the future in therapy strategies and development of tumour therapy response detection classifiers. A restricted genetic evaluation of selected murine tumour models (i.e. GL261 tumours, GL261 cell line, GEM and GEM-derived tumours) was carried out using the Sanger method to check for a possible presence of particular driver mutations commonly occurring in gliomas (IDH1, IDH2 and p53). Finally, the work describes the strategy followed for longitudinal therapy studies follow-up and early response/relapse detection in preclinical brain tumours, through molecular imaging methods based in MRSI. GL261 (glioblastoma) tumour bearing mice were treated with temozolomide (TMZ), based on previously established protocols. The expected transient growth arrest (response to therapy) was detected by MRI. Animals subjected to therapy and control animals were followed up by MRSI and pattern recognition techniques (semi-supervised source extraction) were applied. The sources extracted from the region of interest were able to discriminate between GL261 tumours actively proliferating and tumours responding to therapy, based on their metabolome pattern changes recorded by MRSI. Colour-coded nosological images produced throughout and after the course of therapy allowed convenient tracking of response changes and differentiated the intratumoural heterogeneity of response, hinting the growth arrest and relapse, before changes in tumour volume were observed by MRI. The methodology was validated with histopathological analysis and calculation of proliferation and apoptotic rates and mitotic index.
15
Ehses, Philipp [Verfasser], and Peter [Akademischer Betreuer] Jakob. "Development of new Acquisition Strategies for fast Parameter Quantification in Magnetic Resonance Imaging / Philipp Ehses. Betreuer: Peter Jakob." Würzburg : Universitätsbibliothek der Universität Würzburg, 2012. http://d-nb.info/1026210968/34.
Full text
16
Mitchell, Amanda. "Development of a Novel Genetically Encoded FRET System Using the Unnatural Amino Acid Anap." Thesis, Boston College, 2016. http://hdl.handle.net/2345/bc-ir:107177.
Full textAbstract:
Thesis advisor: Abhishek ChatterjeeFörster Resonance Energy Transfer (FRET) offers a powerful approach to study biomolecular dynamics in vitro as well as in vivo. The ability to apply FRET imaging to proteins in living cells provides an excellent tool to monitor important dynamic events such as protein conformational changes, protein-protein interactions, and proteolysis reactions. However, selectively incorporating two distinct fluorophores into the target protein(s) that are capable of FRET interaction within the complex cellular milieu is challenging. Consequently, terminal fusion to genetically encoded fluorescent proteins has emerged as the predominant labeling strategy for FRET studies in vivo. However, a major limitation of this strategy stems from the large size of the fluorescent proteins, which may perturb the native properties of the target, and restricted attachment only to the termini of the target. We reasoned that using genetically encoded fluorescent unnatural amino acids would overcome several of these challenges associated with currently available labeling strategies owing to their small size and the ability to introduce them site- specifically and co-translationally. Here, we report the use of the fluorescent unnatural amino acid “Anap” as a FRET donor with green and yellow fluorescent protein acceptors. We demonstrate the utility of this labeling strategy using proteolysis and conformational change models, and step towards in vivo studies by further developing a proteolysis system in cell lysates
Thesis (MS) — Boston College, 2016
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
17
Suñol, Moreno David. "Structural studies of recombinant TGIF1 and FBP28 WW domains using NMR and peptide ligation strategies." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/400299.
Full textAbstract:
The present thesis is divided in three different but related projects. In the first project, the interaction between TGIF1 and SMAD proteins is investigated. TGIF1 is a transcriptional suppressor that prevents the gene transcription due to its interaction with DNA and protein suppressor complexes. TGIF1 has a role in different signalling pathways such as retinoid, Wnt or TGF-β. Focusing on TGF-β, this is one of the main signalling pathways that regulates a plethora of functions in metazoans, including cell differentiation, proliferation and tissue homeostasis, among many others. SMAD proteins are the centrals mediators of the pathways, carrying the signal from the TGF-β receptors at the plasma membrane to the DNA. The aim of this project was to describe, from a structurally point of view, the interaction between TGIF1 and SMAD proteins, already detected biochemically. Using NMR spectroscopy and EMSA assays we could observe the interaction between TGIF1 and the MH1 domain of SMAD2 and SMAD4. Furthermore, the addition of SMAD2/4-MH1 disrupts the TGIF1-DNA interaction. On the other hand, the binding between SMAD2-MH2 and TGIF1 (256-347) was not detected in our experimental conditions.
Moreover, we found that p38α and CK1 kinases phosphorylate serines 286, 291 and 294 of TGIF1 (256-347) in vitro. While these serines are located in a region where TGIF1 interacts with many proteins - including SMAD2, HDAC, or Axin-2 - , the phosphorylation could indicate a regulation mechanism. However, the phosphorylation does not change the overall structure of the TGIF1 fragment.
Finally, we have detected an interaction between TGIF1 fragments 150-248 and 256-347, suggesting the presence of open and closed conformations of full-length TGIF1.
The second project is related to the ligation reaction between two peptides. Our study demonstrates that the addition of HOBt to the cysteine-free direct aminolysis ligation reaction between one thioester peptide and one N-terminal free peptide increase the conversion but not the rate of the ligation. This effect is especially increased when sterically hindered amino acid (such as valine or leucine) are present in the ligation junction. The reaction is also compatible with phosphorylated peptides but intramolecular cyclisation side-reactions appear when the peptide thioester is not protected at the N-terminus.
Lastly, six selected mutants structures of FBP28-WW2 were determined de novo by NMR spectroscopy. The six mutant structures maintain the main characteristics of WW domain structure, even for the mutations introducing deletions at the N and C termini. The structures were the experimental confirmation of the effect of this set of mutations in the structure. The existence of the WW fold in all these mutations was key to provide the grounds for the simulated folding curves generated using the UNRES force field.TGF-β és una de les principals vies de senyalització que tenen les cèl·lules animals per regular gran part dels processos cel·lulars, tals com la diferenciació i proliferació cel·lular o la regeneració, entre d’altres. Les proteïnes SMAD són les principals mediadores d’aquesta via, portant la senyal des dels receptors de TGF-β situats a la membrana cel·lular fins al DNA a l’interior del nucli. En la present tesi s’ha dut a terme un estudi sobre la interacció entre el factor de supressió TGIF1 i les proteïnes SMAD2 i SMAD4. Mitjançant ressonància magnètica nuclear s’ha demostrat la interacció entre TGIF1 i el domini MH1 de SMAD2 i SMAD4. A més, aquesta unió interromp el contacte entre TGIF1 i el seu DNA canònic tal com demostren els EMSA efectuats. Altrament, s’ha determinat per primera vegada que TGIF1 és un substrat de les quinases p38α i CK1, que fosforilen les serines 286, 291 i 294, localitzades en una regió d’interacció amb diverses proteïnes, com per exemple SMAD2, HDAC o Axin-2. D’altra banda, en aquest treball s’ha estudiat la lligació nativa de dos pèptids mitjançant una reacció d’aminòlisis directa sense la presència de cisteïnes en el lloc d’unió. Específicament, s’ha demostrat que l’addició de HOBt a la mescla de reacció augmenta la conversió però no la velocitat de la lligació entre els dos pèptids. Aquest increment en la conversió és especialment rellevant quan aminoàcids estericament impedits, com valina o leucina, es troben en el lloc d’unió. Finalment, s’han determinat les estructures de 6 mutants del domini WW2 de FBP28. Tots els mutants conserven el plegament característic dels dominis WW tot i les delecions que presenten tant a C com a N-terminal. Les estructures han servit per confirmar els resultats de simulacions moleculars efectuades mitjançant el camp de força UNRES.
18
Michailidis, Antonis D. "Understanding complex CI-combustion strategies : an experimental investigation." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/10957.
Full textAbstract:
Within this body of work several series of experiments will investigate the nature of complex combustion in an experimental single-cylinder engine emulating a modern passenger car size compression-ignition (CI) engine. Regimes of single, piloted single and piloted split-main injections will be tested and compared in terms of combustion characteristics, specific emission output and cyclic behaviour to determine how increased injection complexity affects the emissions and output of the modern CI engine. Through these tests, the effect of fuel-line stationary waves will be demonstrated and investigated, showing conclusively that optimised engine calibration is essential to account for injector-generated waves in any multiple injection scenario. This data will then be confirmed with a dedicated analysis using an injector rate measuring tube. The tests will then be expanded to include examination into the behaviour of injector needle-lift standard deviation over its operating cycle, in-cylinder pressure standard deviation behaviour and trends over the combustion cycle as well as IMEP variability. Through these tests a novel method to detect start of combustion will be proposed and compared to conventional methods. Low temperature combustion (LTC) will be tested under incremental injection complexity. Tests will be optimised for combustion phasing and injection pressure, with a view to analysis of emissions, output and cyclic behaviour to establish whether the knowledge gained about conventional combustion holds true under LTC. Optimization of engine parameters will be shown to result in easier to implement LTC regimes with superior emissions characteristics. Finally, LTC tests will be expanded to include 30% and 50% by volume gas-to-liquid fuel (GTL) blends in order to determine whether fuel characteristics further influence emissions, output and cyclic behaviour in LTC through complex injection regimes. How GTL-blend ratio affects trends in emissions and cyclic behaviour will also be examined and compared to conventional diesel fuel.
19
Smith, Michael Sterling. "Strategies for the Creation of Spatial Audio in Electroacoustic Music." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1404593/.
Full textAbstract:
This paper discusses technical and conceptual approaches to incorporate 3D spatial movement in electroacoustic music. The Ambisonic spatial audio format attempts to recreate a full sound field (with height information) and is currently a popular choice for 3D spatialization. While tools for Ambisonics are typically designed for the 2D computer screen and keyboard/mouse, virtual reality offers new opportunities to work with spatial audio in a 3D computer generated environment. An overview of my custom virtual reality software, VRSoMa, demonstrates new possibilities for the design of 3D audio. Created in the Unity video game engine for use with the HTC Vive virtual reality system, VRSoMa utilizes the Google Resonance SDK for spatialization. The software gives users the ability to control the spatial movement of sound objects by manual positioning, a waypoint system, animation triggering, or through gravity simulations. Performances can be rendered into an Ambisonic file for use in digital audio workstations. My work Discords (2018) for 3D audio facilitates discussion of the conceptual and technical aspects of spatial audio for use in musical composition. This includes consideration of human spatial hearing, technical tools, spatial allusion/illusion, and blending virtual/real spaces. The concept of spatial gestures has been used to categorize the various uses of spatial motion within a musical composition.
20
Durst, Markus [Verfasser], Axel [Akademischer Betreuer] [Gutachter] Haase, and Franz [Gutachter] Pfeiffer. "Efficient Acquisition Strategies for Nuclear Magnetic Resonance Imaging with Hyperpolarised Biomarkers / Markus Durst ; Gutachter: Axel Haase, Franz Pfeiffer ; Betreuer: Axel Haase." München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1136422587/34.
Full text
21
Rivers, Carly Shaen. "Diffusion and perfusion magnetic resonance imaging in human ischaemic stroke : analysis strategies and measurement issues in the assessment of lesion evolution." Thesis, University of Edinburgh, 2006. http://hdl.handle.net/1842/29336.
Full textAbstract:
The aim of this thesis is to explore the evolution and issues affecting the analysis of ischaemic lesions on diffusion – and perfusion-weighted MRI (DWI and PWI) from acute (< 24 h) to chronic times (3 mo) after stroke onset. This thesis includes a review of previous human studies of acute DWI and PWI appearance versus final outcome, a review of the ‘DWI/PWI mismatch’ model (thought to represent the ischaemic penumbra, or ‘tissue at risk’ of infarction), and a systematic review of previous animal studies of the pathophysiology associated with particular lesion. The methodological problems raised by these reviews are addressed in this thesis using a large cohort of stroke patients with serial DWI and PWI. The interrator variability of manual lesion measurements on acute DWI is investigated, and factors affecting this variability are discussed. The effect of lesion oedema (swelling) on measurements of ischaemic lesions on MRI is investigated. This thesis also investigates the tissue state underlying persistent hyperintensity on late DWI, and whether this is just T2 ‘shine through’, or indicates distinct features in the evolution of the lesion. A novel grid-based analysis method is developed and employed to track serial DWI and PWI changes more effectively, and the effect of observer variability on diffusion and perfusion parameters measured by this method is assessed. Lastly, this thesis discusses the concept of using ‘threshold’ values to predict tissue infarction or survival.
22
Kulkarni, Praveen P. "Functional MRI Data Analysis Techniques and Strategies to Map the Olfactory System of a Rat Brain." Digital WPI, 2006. https://digitalcommons.wpi.edu/etd-dissertations/37.
Full textAbstract:
Understanding mysteries of a brain represents one of the great challenges for modern science. Functional magnetic resonance imaging (fMRI) has two features that make it unique amongst other imaging modalities used in behavioral neuroscience. First, it can be entirely non-invasive and second, fMRI has the spatial and temporal resolution to resolve patterns of neuronal activity across the entire brain in less than a minute. fMRI indirectly detects neural activity in different parts of the brain by comparing contrast in MR signal intensity prior to and following stimulation. Areas of the brain with increased synaptic and neuronal activity require increased levels of oxygen to sustain this activity. Enhanced brain activity is accompanied by an increase in metabolism followed by increases in blood flow and blood volume. The enhanced blood flow usually exceeds the metabolic demand exposing the active brain area to high level of oxygenated hemoglobin. Oxygenated hemoglobin increases the MR signal intensity that can be detected in MR scanner. This relatively straight forward scenario is, unfortunately, oversimplified. The fMRI signal change to noise ratio is extremely small. In this work a quantitative analysis strategy to analyze fMRI data was successfully developed, implemented and optimized for the rat brain. Therein, each subject is registered or aligned to a complete volume-segmented rat atlas. The matrices that transformed the subject's anatomy to the atlas space are used to embed each slice within the atlas. All transformed pixel locations of the anatomy images are tagged with the segmented atlas major and minor regions creating a fully segmented representation of each subject. This task required the development of a full 3D surface atlas based upon 2D non-uniformly spaced 2D slices from an existing atlas. A multiple materials marching cube (M3C) algorithm was used to generate these 1277 subvolumes. After this process, they were coalesced into a dozen major zones of the brain (amygdaloid complex, cerebrum, cerebellum, hypothalamus, etc.). Each major brain category was subdivided into approximately 10 sub-major zones. Many scientists are interested in behavior and reactions to pain, pleasure, smell, for example. Consequently, the 3D volume atlas was segmented into functional zones as well as the anatomical regions. A utility (program) called Tree Browser was developed to interactively display and choose different anatomical and/or functional areas. Statistical t-tests are performed to determine activation on each subject within their original coordinate system. Due to the multiple t-test analyses performed, a false-positive detection controlling mechanism was introduced. A statistical composite of five components was created for each group. The individual analyses were summed within groups. The strategy developed in this work is unique as it registers segments and analyzes multiple subjects and presents a composite response of the whole group. This strategy is robust, incredibly fast and statistically powerful. The power of this system was demonstrated by mapping the olfactory system of a rat brain. Synchronized changes in neuronal activity across multiple subjects and brain areas can be viewed as functional neuro-anatomical circuits coordinating the thoughts, memories and emotions for particular behaviors using this fMRI module.
23
Campelo, André. "SINGING PORTUGUESE NASAL VOWELS: PRACTICAL STRATEGIES FOR MANAGING NASALITY IN BRAZILIAN ART SONGS." UKnowledge, 2017. http://uknowledge.uky.edu/music_etds/89.
Full textAbstract:
The articulation of Portuguese nasalized vowels poses some articulatory problems accompanied by negative acoustic effects for the performance of Brazilian art songs. The main objective was to find strategies that permit the singer to conciliate an idiomatic pronunciation of these vowels with a well-balanced resonance, a desirable quality in classical singing. In order to devise these strategies, the author examined sources dealing with nasalized vowels from varied perspectives: acoustic properties of vowel nasalization, phonetic and phonological aspects ofBrazilian Portuguese (BP), historical views on nasality in singing, and recent vocal pedagogy research. In addition to the overall loss of sonority, the main effect of nasalization is felt mainly in the first formant (F1) region of oral vowels, due to the introduction of nasal formants and antiformants, and to shifts in the tongue posture. Several sources report the existence of a nasality contour in BP, by which a nasalized vowel starts with an oral phase and transitions gradually to a nasal phase. The author concludes that the basic approach to sing nasalized vowels in BP is (1) to find the tongue posture corresponding to the oral vowel congener (the “core vowel”), and (2) to adjust the nasality contour in such a way that the oral portion remains prominent in order to keep the resonance balance consistent during the emission of the vowel. Once the core vowel is determined, standard vowel modification choices can be made according to voice type and the musical context in which the vowel is being sung. Some challenging excerpts from Brazilian art songs are examined, with suggestions for the application of the discussed strategies.
24
Tavoian, Dallin. "Tools and Technologies for Assessing, and Exercise Strategies for Promoting, Neuromuscular Function and Mobility in Aging." Ohio University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1615816378173099.
Full text
25
Lenoir-Capello, Rachel. "Specific labeling strategies for new developments in liquid state protein NMR." Thesis, Sorbonne université, 2020. https://accesdistant.sorbonne-universite.fr/login?url=http://theses-intra.upmc.fr/modules/resources/download/theses/2020SORUS056.pdf.
Full textAbstract:
La résonance magnétique nucléaire (RMN) fournit des informations structurelles et dynamiques précieuses à l'échelle atomique, cependant, la faible sensibilité et résolution des signaux empêchent l’étude d'objets moléculaires plus importants. Nous présentons 3 stratégies de marquage isotopique pour différentes expériences RMN des protéines en solution et démontrons leur potentiel pour l'étude structurale des biomolécules. Parmi les stratégies envisagées, 2 utilisent l'expression in vitro pour obtenir des protéines marquées sélectivement sur un groupe chimique et/ou acide aminé dans un environnement perdeutéré. Avec l’utilisation de séquences d'impulsions TROSY, ces échantillons ont permis des gains spectraux importants lorsque ils étaient spécifiquement marqués sur des groupes amide ou sur le méthylène des glycines tout en maintenant un taux de deutération élevé sur les autres fonctions chimiques des protéines. La troisième stratégie de marquage protéique utilise des protocoles in vivo pour des applications RMN innovantes: l'hyperpolarisation de noyaux en solution qui augmente leur sensibilité de plusieurs ordres de grandeur. La durée de vie de cette hyperpolarisation est régie par le temps de relaxation longitudinale des noyaux, qui est réduit pour les protéines à température ambiante. En isolant les noyaux d'intérêt dans un environnement perdeutéré, les interactions dipolaires créées par les protons voisins sont éliminées et les noyaux hyperpolarisés relaxent beaucoup plus lentement. L'hyperpolarisation d'un petit domaine protéique a été entreprise avec succès mais les conditions de dissolution doivent encore être améliorées pour conserver une phase aqueuse homogèneNuclear Magnetic Resonance (NMR) provides valuable structural and dynamic information at the atomic scale, however, the low sensitivity and resolution of signals rapidly preclude investigations of larger molecular objects. We present three isotopic labeling strategies for different protein-solution NMR experiments and demonstrate their potential for the structural study of biomolecules in solution. Among the strategies considered, two are based on the use of in vitro protein expression to obtain selectively labeled proteins of a certain chemical group and/or amino acid in a perdeuterated environment. Perdeuteration is essential for the optimal use of Transverse Relaxation Optimized Spectroscopy pulse sequences. They allowed significant spectral gains when samples were specifically labeled on amide groups or on the methylene of glycines while maintaining a very high rate of deuteration on the other chemical functions of the proteins. The third protein labeling strategy employed is based on in vivo protocols but used in innovative NMR applications: a technique of hyperpolarization of nuclei in solution which increases their sensitivity by several orders of magnitude. The lifetime of this hyperpolarization is governed by the longitudinal relaxation time of nuclei, which are reduced for proteins at room temperature. By isolating the nuclei of interest in a perdeuterated environment, dipolar interactions created by neighboring protons were eliminated and hyperpolarized nuclei relaxed much more slowly. Hyperpolarization of a small protein domain was successfully undertaken at 1K but the dissolution conditions need to be improved in order to preserve a homogeneous aqueous phase
26
Sartori, Alan Giovanini de Oliveira. "Chemical changes in Brazil nuts and co-products: characterisation and strategies of control and monitoring." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/11/11141/tde-22032018-151230/.
Full textAbstract:
Brazil nuts (Bertholletia excelsa, H.B.K.) are seeds of high nutritional value collected from South American rainforests and its productive chain is one of the most important non-timber economic activities in Brazilian amazon. The main objectives of this research were: 1) characterize the occurrence of chemical changes in Brazil nut kernels (BNK), cold-pressed Brazil nut oil (BNO) and Brazil nut flour obtained by water extraction (BNF); and 2) investigate strategies of control and monitoring these changes during storage. For this, consolidated techniques, such as spectrophotometry and chromatography, and a relatively new analytical technique, the electron spin resonance (ESR) spectroscopy, were employed. As major results, it was found that different combinations of storage temperatures and atmosphere packages have differently affected the tendency of radical formation and off-flavor volatile aroma compounds generation in BNK, and that the combination of refrigeration with vacuum packing was able to keep BNK at their best. It was demonstrated that a spin-trapping ESR spectroscopy method would be suitable to monitor oxidative changes in BNO with known history stored either in clear or in brown glass bottles under retail conditions. For BNF, it was demonstrated that minor variations on water activity (aw) might significantly affect the rates of both lipid oxidation and nonenzymatic browning reactions during storage. There was indication that for BNF with initial aw of 0.196, but not for BNF with initial aw of 0.101, under the studied conditions, secondary products from lipid oxidation might be substrates for nonenzymatic browning products formation. As a conclusion, these results may help to better understand chemical deteriorative processes in BNK and its co-products, according to the storage conditions, and that the use of less sample-demanding, fast and solvent-free analytical method to monitor these changes in BNO is feasible.A castanha do Brasil (Bertholletia excelsa, H.B.K.) é uma semente de boa qualidade nutricional coletada em florestas tropicais da América do Sul, cuja cadeia produtiva é uma das mais importantes atividades econômicas não madeireiras da Amazônia brasileira. Os principais objetivos desta pesquisa foram: 1) caracterizar a ocorrência de alterações químicas em castanhas do Brasil (CB), óleo de castanha do Brasil obtido por prensagem a frio (OCB) e farinha de castanha do Brasil obtida por extração aquosa (FCB); e 2) investigar estratégias para controlar e monitorar essas alterações ao longo do armazenamento. Para isso, técnicas consolidadas como a espectrofotometria e a cromatografia, e uma técnica relativamente recente, a espectroscopia de ressonância de spin eletrônico (RSE), foram empregadas. Dentre os principais resultados obtidos, foi possível constatar o efeito de diferentes combinações de temperaturas e atmosferas de embalagem sobre a tendência de formação de radicais e sobre a geração de compostos voláteis de aroma relacionados a odor indesejável em CB, e que a temperatura de refrigeração combinada com a embalagem a vácuo foi a mais eficiente na preservação da qualidade da CB. Demonstrou-se que o uso de um método de aprisionamento de spins de RSE pode ser eficiente para monitorar alterações químicas em OCB com histórico conhecido embalado em frascos de vidro transparente ou marrons sob condições de armazenamento comercial. Para FCB, foi demonstrado que pequenas variações na atividade de água (aw) podem afetar significativamente as taxas de oxidação lipídica e de reações de escurecimento não enzimático durante armazenamento. Obteve-se indicação de que para FCB com aw inicial de 0,196, mas não para FCB com aw inicial de 0,101, produtos secundários da oxidação lipídica podem ser substratos para a formação de produtos do escurecimento não enzimático. Como conclusão geral, os resultados obtidos podem ajudar a explicar melhor os processos de deterioração química em CB e seus coprodutos, conforme as condições de armazenamento, e que o uso de um método que requer menor quantidade de amostras, é rápido e não usa solventes é viável para o monitoramento da qualidade de OCB.
27
Hirsch, Nuria [Verfasser], Axel [Akademischer Betreuer] Haase, and Franz [Akademischer Betreuer] Pfeiffer. "BOLD-based Magnetic Resonance Imaging of Hypoxia in the Human Brain : Adaptation of Measurement and Data Analysis Strategies for Clinical Requirements / Nuria Hirsch. Gutachter: Axel Haase ; Franz Pfeiffer. Betreuer: Axel Haase." München : Universitätsbibliothek der TU München, 2013. http://d-nb.info/1044395850/34.
Full text
28
BORTMANN, PATRICK. "Strategie d'investigation par resonance magnetique nucleaire d'inositols et de cyclohexanols phosphates." Strasbourg 1, 1989. http://www.theses.fr/1989STR15073.
Full text
29
Kacem, Najib. "Nonlinear dynamics of M&NEMS resonant sensors : design strategies for performance enhancement." Lyon, INSA, 2010. http://theses.insa-lyon.fr/publication/2010ISAL0023/these.pdf.
Full textAbstract:
In order to fulfill the promises of nanoelectromechanical systems (NEMS), that is, to begin to come out of industrial foundries, a certain number of challenges are yet to be addressed: in particular, their frequency stability, has to be improved. Mechanical transduction gain of the devices has been thoroughly studied, but the drive power has always been a priori limited to the onset of nonlinearities. Besides, the smaller the structures, the sooner nonlinearities occur, reducing their dynamic range and even making extremely difficult to detect their oscillation. In this thesis, this limitation is reconsidered, i. E. The behavior of NEMS at large amplitude through the nonlinear dynamics of NEMS-based resonant sensors is investigated. A review of inertial, mass and gas sensors is carried out. Particularly, the design issues of resonant sensors are addressed and the sources of nonlinearities in resonators are exposed. A review of nonlinear methods is also presented in order to define a modeling strategy for the dynamics of resonant inertial and mass/gas sensors. Close-form solutions of the critical amplitudes were provided for several devices and the importance of the fifth order nonlinearities has been demonstrated through the mixed behavior identification. Several analytical design rules are provided in order to enhance the dynamic range of NEMS resonators and the detection limit of NEMS-based resonant sensors. These rules essentially include hysteresis suppression by nonlinearity cancellation as well as mixed behavior and pull-in retarding under superharmonic resonance and simultaneous resonances leading to the possibility of driving the resonator linearly beyond its critical amplitude. The experimental validation of the model has been performed in the case of resonant capacitive (4 micrometers SOI) MEMS and (2 micrometers MEMS level 500 nm NEMS level) SOI M\&NEMS accelerometers and gyroscopes as well as capacitive and piezoresistive (160 nm SOI NEMS) gas/mass sensorsAfin que les systèmes nano-électromécaniques (NEMS) tiennent leurs promesses et répondent aux attentes sociétales, un certain nombre de défis et verrous technologiques restent à lever. En particulier, leur stabilité en fréquence doit être améliorée. Le gain mécanique de transduction des NEMS a été analysé avec grand intérêt mais la sensibilité a toujours été a priori limitée par l’apparition des non-linéarités. En outre, la miniaturisation des structures descend les seuils d’apparition des non-linéarités, réduit donc la gamme dynamique et complique la détection. La thèse reconsidère la limitation de détection des NEMS. Le comportement de NEMS résonants en grands déplacements est analysé en déployant les techniques de la dynamique non linéaire. Tout d’abord il est établi un état de l’art de certaines catégories de capteurs. Suit une présentation des problèmes de conception des capteurs résonants puis des sources de non linéarités. L’état de l’art des méthodes non linéaires permet de dégager une stratégie de modélisation des capteurs résonants M&NEMS. Les expressions analytiques des amplitudes critiques sont données pour plusieurs dispositifs et l’importance des non-linéarités d’ordre cinq a été démontrée par l’identification du comportement non linéaire mixte. Enfin la thèse préconise plusieurs règles de conception analytique afin d’optimiser la gamme dynamique des résonateurs NEMS et la limite de détection des capteurs résonant M&NEMS. Pour cela il s’agit de supprimer tout phénomène d’hystérésis par l’annulation des non-linéarités d’ordre trois, de retarder le comportement mixte et le pull-in (collage du résonateur sur l’électrode) en déclenchant des résonances super harmoniques et des résonances simultanées garantissant le comportement linéaire du résonateur au delà de l’amplitude critique. La validation expérimentale des modèles a été effectuée sur des capteurs inertiels MEMS et M&NEMS à transduction capacitive résonante ainsi que sur des nano capteurs de gaz et de masse à transduction capacitive avec co-intégration CMOS et piézorésistive
30
Zimmer, Claus. "Strategien zur funktionellen MR-Bildgebung von experimentellen Gliomen." Doctoral thesis, [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=963449907.
Full text
31
Jansson, Alexander, Jonsson Åsa Hellberg, and Maria Sangfelt. "Strategier för att underlätta för patienter med klaustrofobi och ångest vid MR-undersökningar : en systematisk litteraturstudie." Thesis, Uppsala universitet, Institutionen för kirurgiska vetenskaper, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-443013.
Full textAbstract:
Bakgrund Klaustrofobi och ångest är vanliga orsaker till avbrutna eller inställda MR-undersökningar. Utöver problem för patienten kan det ha en negativ inverkan på ekonomin för aktuell vårdinrättning och följaktligen samhället i stort. Även patientflödet kan påverkas, där undersökningarna antingen tar längre tid än planerat eller inte kan genomföras alls, något som kan leda till en försenad diagnos om undersökningen inte genomförs. Syfte Syftet med studien var att undersöka vilka metoder som används för att underlätta för patienter med klaustrofobi och ångest i samband med MR-undersökningar och även att undersöka om det finns fler metoder som visat sig framgångsrika i forskning och som skulle kunna implementeras i det kliniska arbetet. Metod Studien är en systematisk litteraturstudie där vetenskapliga artiklar samlats in genom sökning i relevanta databaser enligt bestämda urvalskriterier och som sedan kvalitetsgranskats med hjälp av Willmans granskningsprotokoll, analyserats och sammanställts till ett resultat. Resultat Studiernas resultat visade att strategier som tillämpats både före och under undersökningen kan ha betydelse för patientens upplevda nivå av klaustrofobi och ångest och skulle därför kunna användas för att förbättra genomförandet och även kvalitén av MR-undersökningen. Slutsats Flertalet strategier såsom; patientinformation, lugnande läkemedel samt kommunikation används för att hantera patienters ångest och klaustrofobi i samband med MR-undersökningar. God kommunikation och information har visat sig viktig för patientens vårdupplevelse. Flera alternativ har studerats, som exempelvis; VR, hypnos, informationsfilmer samt flertalet studier på patienternas upplevelser av magnetkamerans utformning. Mer forskning är dock önskvärd inom området.Background Claustrophobia and anxiety are common causes of MRI examinations being interrupted or cancelled. This is not only problematic for the individual patient but also causes a negative impact on the workflow, where the examinations may take up more time than allotted or even cancelled at the last minute. The latter causing a negative financial impact for the hospital and as for the patient it may result in a late diagnosis, or a lack thereof. Aim The purpose of this study was to investigate what methods are used to facilitate patients with claustrophobia or anxiety associated with MRI examinations and to explore related scientific developments. Method The study is a systematic literature study where relevant data was collected by searching relevant databases according to specific selection criteria which was then reviewed, analyzed and compiled into a result. Result The results of the studies showed that strategies applied both before and during the examination may be important for the patient's perceived level of anxiety and could therefore affect the implementation and the diagnostic quality of the MRI examination. Conclusion Various methods, like patient information, sedatives and communication are used to manage patients' anxiety and claustrophobia when undergoing MRI examinations. Good communication and information have proven to be important for the patient's experience. Several alternatives have been studied, such as VR, hypnosis, information films and studies on patients' experiences of the design of the magnetic camera. However, more research is needed.
32
Vaheeshan, Jeganathan. "Transformer fault-recovery inrush currents in MMC-HVDC systems and mitigation strategies." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/transformer-faultrecovery-inrush-currents-in-mmchvdc-systems-and-mitigation-strategies(05f7a9ad-5967-47aa-b72c-e55ad1d33eb7).html.
Full textAbstract:
The UK Government has set an ambitious target to achieve 15% of final energy consumption from renewable sources by 2020. High Voltage Direct Current (HVDC) technology is an attractive solution for integrating offshore wind power farms farther from the coast. In the near future, more windfarms are likely to be connected to the UK grid using HVDC links. With the onset of this fairly new technology, new challenges are inevitable. This research is undertaken to help assist with these challenges by looking at possibilities of problems with respect to faster AC/DC interaction modes, especially, on the impact of inrush currents which occur during fault-recovery transients. In addition to that, possible mitigation strategies are also investigated. Initially, the relative merits of different transformer models are analysed with respect to inrush current transient studies. The most appropriate transformer model is selected and further validated using field measurement data. A detailed electro-magnetic-transient (EMT) model of a grid-connected MMC-HVDC system is prepared in PSCAD/EMTDC to capture the key dynamics of fault-recovery transformer inrush currents. It is shown that the transformer in an MMC system can evoke inrush currents during fault recovery, and cause transient interactions with the converter and the rest of the system, which should not be neglected. It is shown for the first time through a detailed dynamic analysis that if the current sensors of the inner-current control loops are placed at the converter-side of the transformer instead of the grid-side, the inrush currents will mainly flow from the grid and decay faster. This is suggested as a basic remedial action to protect the converter from inrush currents. Afterwards, analytical calculations of peak flux-linkage magnitude in each phase, following a voltage-sag recovery transient, are derived and verified. The effects of zero-sequence currents and fault resistance on the peak flux linkage magnitude are systematically explained. A zero-sequence-current suppression controller is also proposed. A detailed study is carried out to assess the key factors that affect the maximum peak flux-linkage and magnetisation-current magnitudes, especially with regard to fault specific factors such as fault inception angle, duration and fault-current attenuation. Subsequently, the relative merits of a prior-art inrush current mitigation strategy and its implementation challenges in a grid-connected MMC converter are analysed. It is shown that the feedforward based auxiliary flux-offset compensation scheme, as incorporated in the particular strategy, need to be modified with a feedback control technique, to alleviate the major drawbacks identified. Following that, eight different feedback based control schemes are devised, and a detailed dynamic and transient analysis is carried out to find the best control scheme. The relative merits of the identified control scheme and its implementation challenges in a MMC converter are also analysed. Finally, a detailed EMT model of an islanded MMC-HVDC system is implemented in PSCAD/EMTDC and the impacts of fault-recovery inrush currents are analysed. For that, initially, a MMC control scheme is devised in the synchronous reference frame and its controllers are systematically tuned. To obtain an improved performance, an equivalent control scheme is derived in the stationary reference frame with Proportional-Resonant controllers, and incorporated in the EMT model. Following that, two novel inrush current mitigation strategies are proposed, with the support of analytical equations, and verified.
33
Zielinski, William J. "Winning the strategic narrative in the Israeli-Palestinian protracted conflict." Thesis, Monterey, California : Naval Postgraduate School, 2012. http://hdl.handle.net/10945/29615.
Full textAbstract:
The purpose of this thesis is to identify the reasons for Israeli and Palestinian religious objections to peaceful co-existence in a two-state solution to the conflict over the land between the Jordan River and Mediterranean Sea. Developing an understanding of the basic religious requirements and precedents, while consistently considering religious impact in politics, may help to open dialogue between Jewish Gush Emunim and Muslim Palestinian Hamas, strong opponents to land compromise.
Arguments by Gush Emunim and Hamas from the two major religious works, the Jewish Tanakh and the Muslim Qur’an, and associated commentaries, the Jewish Talmud and Muslim Hadith, are compared and evaluated for religious insights into the disputed areas. Contemporary interpretations of each major writing and political objections based on religious argumentation create a strong context for modern conflict. The requirements and precedents for peace that come from religious texts also promote open dialogue. This thesis suggests ways to open dialogue between the Israeli and Palestinian cultures, comparing religious texts, interpretations, and concepts, in an effort to promote peaceful co-existence and build an effective strategic narrative.
34
Lin, Xiang 1971. "Model-based strategies for automated segmentation of cardiac magnetic resonance images." 2008. http://hdl.handle.net/2292/2641.
Full textAbstract:
Segmentation of the left and right ventricles is vital to clinical magnetic resonance imaging studies of cardiac function. A single cardiac examination results in a large amount of image data. Manual analysis by experts is time consuming and also susceptible to intra- and inter-observer variability. This leads to the urgent requirement for efficient image segmentation algorithms to automatically extract clinically relevant parameters. Present segmentation techniques typically require at least some user interaction or editing, and do not deal well with the right ventricle. This thesis presents mathematical model based methods to automatically localize and segment the left and right ventricular endocardium and epicardium in 3D cardiac magnetic resonance data without any user interaction. An efficient initialization algorithm was developed which used a novel temporal Fourier analysis to determine the size, orientation and position of the heart. Quantitative validation on a large dataset containing 330 patients showed that the initialized contours had only ~ 5 pixels (modified Hausdorff distance) error on average in the middle short-axis slices. A model-based graph cuts algorithm was investigated and achieved good results on the midventricular slices, but was not found to be robust on other slices. Instead, automated segmentation of both the left and right ventricular contours was performed using a new framework, called SMPL (Simple Multi-Property Labelled) atlas based registration. This framework was able to integrate boundary, intensity and anatomical information. A comparison of similarity measures showed the sum of squared difference was most appropriate in this context. The method improved the average contour errors of the middle short-axis slices to ~ 1 pixel. The detected contours were then used to update the 3D model using a new feature-based 3D registration method. These techniques were iteratively applied to both short-axis and long-axis slices, resulting in a 3D segmentation of the patient’s heart. This automated model-based method showed a good agreement with expert observers, giving average errors of ~ 1–4 pixels on all slices.
35
Breuer, Felix. "Development and Applications of Efficient Strategies for Parallel Magnetic Resonance Imaging." Doctoral thesis, 2006. https://nbn-resolving.org/urn:nbn:de:bvb:20-opus-20683.
Full textAbstract:
Virtually all existing MRI applications require both a high spatial and high temporal resolution for optimum detection and classification of the state of disease. The main strategy to meet the increasing demands of advanced diagnostic imaging applications has been the steady improvement of gradient systems, which provide increased gradient strengths and faster switching times. Rapid imaging techniques and the advances in gradient performance have significantly reduced acquisition times from about an hour to several minutes or seconds. In order to further increase imaging speed, much higher gradient strengths and much faster switching times are required which are technically challenging to provide. In addition to significant hardware costs, peripheral neuro-stimulations and the surpassing of admissable acoustic noise levels may occur. Today’s whole body gradient systems already operate just below the allowed safety levels. For these reasons, alternative strategies are needed to bypass these limitations. The greatest progress in further increasing imaging speed has been the development of multi-coil arrays and the advent of partially parallel acquisition (PPA) techniques in the late 1990’s. Within the last years, parallel imaging methods have become commercially available,and are therefore ready for broad clinical use. The basic feature of parallel imaging is a scan time reduction, applicable to nearly any available MRI method, while maintaining the contrast behavior without requiring higher gradient system performance. PPA operates by allowing an array of receiver surface coils, positioned around the object under investigation, to partially replace time-consuming spatial encoding which normally is performed by switching magnetic field gradients. Using this strategy, spatial resolution can be improved given a specific imaging time, or scan times can be reduced at a given spatial resolution. Furthermore, in some cases, PPA can even be used to reduce image artifacts. Unfortunately, parallel imaging is associated with a loss in signal-to-noise ratio (SNR) and therefore is limited to applications which do not already operate at the SNR limit. An additional limitation is the fact that the coil array must provide sufficient sensitivity variations throughout the object under investigation in order to offer enough spatial encoding capacity. This doctoral thesis exhibits an overview of my research on the topic of efficient parallel imaging strategies. Based on existing parallel acquisition and reconstruction strategies, such as SENSE and GRAPPA, new concepts have been developed and transferred to potential clinical applicationsIn den späten 80er Jahren entwickelte sich die Magnetresonanz-Tomographie (MRT), die bis dato lediglich in Forschungseinrichtungen etabliert war, zu einem der wichtigsten Verfahren in der klinischen Diagnostik. Allerdings erfordern nahezu alle bestehenden klinischen Anwendungsgebiete sowohl eine hohe räumliche als auch eine hohe zeitliche Auflösung für eine optimale Detektion und Klassifizierung von Krankheitsbildern. Der bisherige Ansatz, diesen zunehmenden Anforderungen an die klinische MRT gerecht zu werden, bestand vor allem in der stetigen Verbesserung von Gradientensystemen die mit immer höheren Gradientenstärken und schnelleren Schaltzeiten aufwarteten. Die technischen Fortschritte, sowie schnelle Bildgebungsmethoden erlaubten es, Messzeiten von etwa einer Stunde auf nur wenige Minuten oder sogar Sekunden zu reduzieren. Eine weitere Verkürzung der Experimentdauer mittels noch leistungsfähigeren Gradientensystemen ist jedoch technisch schwierig zu realisieren. Ausserdem gehen enorm hohe Entwicklungs und Materialkosten mit den erhöhten Anforderungen einher. Es kommt hinzu, dass noch stärkere Gradienten und noch schnellere Schaltzeiten zu peripheren Neurostimulationen und zur Überschreitung von zulässigen akustischen Grenzwerten führen können. Heutige Gradientensysteme arbeiten schon sehr nahe an den Grenzen der zulässigen Sicherheitsbestimmungen. Deshalb werden alternative Strategien benötigt, um weitere Messzeitverkürzungen realisieren zu können. Der bisher erfolgreichste Ansatz bestand in der Entwicklung von Mehr-Kanal-Spulen-Anordnungen und damit verknüpft der darauffolgenden Einführung der parallellen Bildgebung in den späten 90er Jahren. In den letzten 5 Jahren haben sich parallele Bildgebungsmethoden an den klinischen Tomographen etabliert und nahezu alle Herstellerfirmen stellen diese Technik kommerziell zur Verfügung. Die parallele Bildgebung ermöglicht eine Messzeitverkürzung, die prinzipiell auf jede bestehende Bildgebungsmethode angewendet werden kann, ohne dabei das Kontrastverhalten zu verändern und ohne höhere Gradientenleistung zu beanspruchen. In der parallellen Bildgebung übernimmt die Mehr-Kanal-Spulen-Anordnung teilwiese die Ortskodierung, die normalerweise durch zeitaufwendiges Schalten von Magnetfelgradienten erzeugt wird. Mit dieser Strategie kann bei gleicher Messzeit die örtliche Auflösung verbessert, oder bei gleicher Auflösung die Messzeit verkürzt werden. Ausserdem können mit hilfe der parallelen MRT in manchen Fällen Bildartefakte signifikant reduziert werden. Allerdings ist mit der parallelen Bildgebung immer ein Signal zu Rausch (SNR) Verlust verbunden, der diese Methode auf klinische Anwendungen begrenzt, die nicht bereits am SNR-Limit betrieben werden. Ausserdem muß die Spulenanordnung genug Sensitivitätsvariationen über das zu untersuchende Objekt bereitstellen, um ausreichende Kodierfunktion zu gewährleisten. Diese Dissertationsarbeit liefert einen Überblick über meine Forschungsarbeit zum Thema “Entwicklung und Anwendung von effizienten Strategien in der parallelen MRT”. Basierend auf bestehenden parallelen Akquisitions und Rekonstruktionstechniken, wie beispielsweise SENSE und GRAPPA, wurden neue Konzepte entwickelt und auf mögliche klinische Fragestellungen angewandt
36
Chan, Rachel Wai-Chung. "Flexible Radial Data Acquisition and Image Reconstruction Strategies for Breast Magnetic Resonance Imaging." Thesis, 2012. http://hdl.handle.net/1807/32677.
Full textAbstract:
Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has a high sensitivity (71-
100%) for detecting breast cancers. DCE-MRI is approximately twice as sensitive as mammography for patients who are genetically predisposed to breast cancer, who have an
elevated lifetime risk (up to 85%) of contracting the disease, and who require rigorous screening. However, current methods of DCE-MRI often have difficulty distinguishing malignant from benign tumours, resulting in low positive predictive values (on average, PPV = 45%). The research in this thesis is motivated by the need for improvement in the ability of MRI to differentiate breast lesions. It is believed that the differentiation of malignant from benign lesions can be improved by acquiring images of high spatial resolution for visualizing morphological features of tumours and those of high temporal resolution for characterizing
contrast-kinetic curves. However, simultaneously achieving high spatial and temporal resolution is limited by the inherent trade-off between speed and quality in MRI, requiring one to choose a particular balance of spatial and temporal resolution. In this thesis, novel techniques are presented that reduce the need to choose a spatiotemporal resolution before the scan. Flexible methods are presented that allow images to be retrospectively reconstructed with different balances of spatial and temporal resolution from the same dataset. Flexibility is achieved through radial sampling of k-space data, with 3D radial directions based on Multidimensional
Golden Means (MGM) and Halton sequences. Radial sampling also allows constrained image
reconstruction techniques such as Compressed Sensing and Prior-Image Constrained
Compressed Sensing to be incorporated for reducing undersampling artifacts in high-temporalresolution images. This thesis demonstrates in 2D how such reconstruction algorithms are influenced by acquisition schemes and shows how reconstruction algorithms work in synergy with flexible radial sampling to provide improvements in the quality of breast MR images. The
flexibility to choose any spatiotemporal resolution combined with better image quality in fast images could potentially improve the characterization of breast lesions screened by MRI.
37
Ehses, Philipp. "Development of new Acquisition Strategies for fast Parameter Quantification in Magnetic Resonance Imaging." Doctoral thesis, 2011. https://nbn-resolving.org/urn:nbn:de:bvb:20-opus-72531.
Full textAbstract:
Magnetic resonance imaging (MRI) is a medical imaging method that involves no ionizing radiation and can be used non-invasively. Another important - if not the most important - reason for the widespread and increasing use of MRI in clinical practice is its interesting and highly flexible image contrast, especially of biological tissue. The main disadvantages of MRI, compared to other widespread imaging modalities like computed tomography (CT), are long measurement times and the directly resulting high costs. In the first part of this work, a new technique for accelerated MRI parameter mapping using a radial IR TrueFISP sequence is presented. IR TrueFISP is a very fast method for the simultaneous quantification of proton density, the longitudinal relaxation time T1, and the transverse relaxation time T2. Chapter 2 presents speed improvements to the original IR TrueFISP method. Using a radial view-sharing technique, it was possible to obtain a full set of relaxometry data in under 6 s per slice. Furthermore, chapter 3 presents the investigation and correction of two major sources of error of the IR TrueFISP method, namely magnetization transfer and imperfect slice profiles. In the second part of this work, a new MRI thermometry method is presented that can be used in MRI-safety investigations of medical implants, e.g. cardiac pacemakers and implantable cardioverter-defibrillators (ICDs). One of the major safety risks associated with MRI examinations of pacemaker and ICD patients is RF induced heating of the pacing electrodes. The design of MRI-safe (or MRI-conditional) pacing electrodes requires elaborate testing. In a first step, many different electrode shapes, electrode positions and sequence parameters are tested in a gel phantom with its geometry and conductivity matched to a human body. The resulting temperature increase is typically observed using temperature probes that are placed at various positions in the gel phantom. An alternative to this local thermometry approach is to use MRI for the temperature measurement. Chapter 5 describes a new approach for MRI thermometry that allows MRI thermometry during RF heating caused by the MRI sequence itself. Specifically, a proton resonance frequency (PRF) shift MRI thermometry method was combined with an MR heating sequence. The method was validated in a gel phantom, with a copper wire serving as a simple model for a medical implantDie Magnetresonanztomographie (MRT) zeichnet sich als medizinisches Bildgebungsverfahren dadurch aus, dass sie ohne ionisierende Strahlung auskommt und nicht-invasiv einsetzbar ist. Ein weiterer wichtiger - wenn nicht der wichtigste - Grund für die weite und wachsende Verbreitung der MRT in der klinischen Praxis ist ihr interessantes und hoch-flexibles Kontrastverhalten, und damit die gute Darstellbarkeit biologischen Gewebes. Die Hauptnachteile der MRT sind die, verglichen mit z.B. Computer-Tomographie (CT), langen Messzeiten und die damit direkt verbundenen hohen Untersuchungskosten. Der erste Teil dieser Arbeit beschreibt Verbesserungen der IR TrueFISP Methode zur MR-Parameterbestimmung. IR TrueFISP ist eine schnelle Methode zur gleichzeitigen Quantifizierung der Protonendichte, der longitudinalen Relaxationszeit T1, sowie der transversalen Relaxationszeit T2. In Kapitel 2 dieser Arbeit wird eine Methode zur Beschleunigung der IR TrueFISP Quantifizierung vorgestellt, die es erlaubt einen kompletten Relaxometrie-Datensatz in unter 6 s pro Schicht aufzunehmen. Weiterhin werden in Kapitel 3 zwei allgemeine Fehlerquellen der IR TrueFISP Methode untersucht und Korrekturverfahren vorgestellt. Im zweiten Teil dieser Arbeit werden neuartige MR-Thermometrie Methoden vorgestellt, die sich besonders zur Untersuchung der MR-Sicherheit von medizinischen Implanten, insbesondere Herzschrittmachern und implantierbaren Kardioverter-Defibrillatoren (ICDs), eignen. Momentan sind in den allermeisten Fällen MRT Untersuchungen an Herzschrittmacher- und ICD-Patienten aufgrund der damit verbundenen Risiken kontraindiziert. Das dabei am schwierigste in den Griff zu bekommende und damit größte Risiko ist die mögliche Schädigung des Myokards, hervorgerufen durch die von den geschalteten HF-Feldern induzierten Ströme in den Schrittmacherelektroden. Um eine MR-sichere Elektrode und/oder sichere Messprotokole zu entwickeln ist es notwendig viele verschiedene Elektroden, Elektrodenpositionen und Messparameter-Einstellungen in einem körperähnlichen Gel-Phantom untersucht. Die bei der jeweiligen Messung auftretenden Erhitzungen werden dabei meist mit Hilfe fiberoptischer Thermometer an verschiedenen Positionen im Gel gemessen. Eine Alternative ist die Aufnahme einer globalen Karte der Temperaturerhöhung mit Hilfe der MR-Thermometrie. In dieser Arbeit wird eine Messmethode vorgestellt, die MR-Thermometrie mit HF induziertem Heizen kombiniert. Diese Methode wurde an einem Kupferdraht im Gelphantom validiert und mit fiberoptisch gemessenen Temperaturanstiegen verglichen
38
Pham, Tuan A. "Early detection and treatment strategies for vulnerable atherosclerotic plaques." Thesis, 2015. https://hdl.handle.net/2144/15207.
Full textAbstract:
Atherosclerotic plaque ruptures have been determined as the most common underlying cause of acute coronary syndromes and stroke. Currently, the standard of care for plaque rupture risk is based on the amount of luminal stenosis presented in a particular vessel; however, X-ray angiographic studies have shown that plaques at risk of rupture generally show <50% luminal narrowing. These findings explicate the need for other, more accurate methods of identifying problem lesions prior to the rupture event. Unfortunately, the study of thrombotic events and vulnerable plaque lesions in humans is difficult due to the spontaneity of rupture and the lengthy time course of disease progression. To further the understanding of plaque rupture risk in light of vulnerability detection, a rabbit model of atherothrombosis was used in conjunction with magnetic resonance imaging (MRI). MRI has been validated as a suitable imaging modality for in vivo, non-invasive detection of atherosclerosis and has provided quantitative predictors of plaques at risk of rupture. Additionally, the rabbit model has been shown, histologically, to present 6 of the 8 human plaque types classified by the American Heart Association.
The first portion of this dissertation work focuses on using MRI to serially image rabbits undergoing the atherosclerotic protocol in order to assess rupture risk at the various time points. Previous work has determined that an increase in the vessel remodeling ratio (which hides a large plaque in the vessel wall) and contrast uptake (which indicates inflammation) are both characteristics of increased rupture risk. By obtaining these parameters at various time points in the disease progression, it was possible to determine when a certain plaque displays a heightened risk of rupture. The second portion of this work tested the efficacy of a pro-resolving molecule, lipoxin (an endogenous molecule), in reducing atherosclerotic disease state, specifically rupture with a luminal thrombus. Using chronic administration of this molecule in the same rabbit model of atherosclerosis yielded a faint reduction in atherosclerotic severity based on the parameters of decreased vessel lipid content and decreased thrombotic events presented in the treated group.
39
Breuer, Felix [Verfasser]. "Development and application of efficient strategies for parallel magnetic resonance imaging / vorgelegt von Felix Breuer." 2006. http://d-nb.info/982469136/34.
Full text
40
Algar, Walter Russell. "Towards multi-colour strategies for the detection of nucleic acid hybridization using quantum dots as energy donors in fluorescence resonance energy transfer (FRET)." 2006. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=450314&T=F.
Full text
41
Bradley, Nicholas Ethan. "Initial guess and optimization strategies for multi-body space trajectories with application to free return trajectories to near-Earth asteroids." Thesis, 2014. http://hdl.handle.net/2152/26858.
Full textAbstract:
This concept of calculating, optimizing, and utilizing a trajectory known as a ``Free Return Trajectory" to facilitate spacecraft rendezvous with Near-Earth Asteroids is presented in this dissertation. A Free Return Trajectory may be defined as a trajectory that begins and ends near the same point, relative to some central body, without performing any deterministic velocity maneuvers (i.e., no maneuvers are planned in a theoretical sense for the nominal mission to proceed). Free Return Trajectories have been utilized previously for other purposes in astrodynamics, but they have not been previously applied to the problem of Near-Earth Asteroid rendezvous. Presented here is a series of descriptions, algorithms, and results related to trajectory initial guess calculation and optimal trajectory convergence. First, Earth-centered Free Return Trajectories are described in a general manner, and these trajectories are classified into several families based on common characteristics. Next, these trajectories are used to automatically generate initial conditions in the three-body problem for the purpose of Near-Earth Asteroid rendezvous. For several bodies of interest, example initial conditions are automatically generated, and are subsequently converged, resulting in feasible, locally-optimal, round-trip trajectories to Near-Earth Asteroids utilizing Free Return Trajectories. Subsequently, a study is performed on using an unpowered flyby of the Moon to lower the overall DV cost for a nominal round-trip voyage to a Near-Earth Asteroid. Using the Moon is shown to appreciably decrease the overall mission cost. In creating the formulation and algorithms for the Lunar flyby problem, an initial guess routine for generic planetary and lunar flyby tours was developed. This continuation algorithm is presented next, and details a novel process by which ballistic trajectories in a simplistic two-body force model may be iteratively converged in progressively more realistic dynamical models until a final converged ballistic trajectory is found in a full-ephemeris, full-dynamics model. This procedure is useful for constructing interplanetary transfers and moon tours in a realistic dynamical framework; an interplanetary and an inter-moon example are both shown. To summarize, the material in this dissertation consists of: novel algorithms to compute Free Return Trajectories, and application of the concept to Near-Earth Asteroid rendezvous; demonstration of cost-savings by using a Lunar flyby; and a novel routine to transfer trajectories from a simplistic model to a more realistic dynamical representation.text
42
Kheraluwala, Mustansir Hussainy. "Delta modulation strategies for resonant link inverters." 1987. http://catalog.hathitrust.org/api/volumes/oclc/17376101.html.
Full textAbstract:
Thesis (M.S.)--University of Wisconsin--Madison, 1987.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 83-85).
43
Methqal, Ikram. "Le caractère adaptatif du cerveau âgé sain dans le maintien des habiletés du traitement lexico-sémantique : une approche neurofonctionnelle." Thèse, 2018. http://hdl.handle.net/1866/21844.
Full text