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Hussain, Gaitee. "Magnetic activity in late-type stars." Thesis, University of St Andrews, 1999. http://hdl.handle.net/10023/14404.
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High resolution spectroscopic techniques are used to investigate the magnetic topology of the young, rapidly rotating star, AB Dor. Doppler images of AB Dor are produced using the Li I 6708 Å line and compared to images produced using Ca I and Fe i lines. A Li abundance of 2.9±0.3 dex is measured using LTE profile synthesis. By evaluating the effects of enhanced spot Li abundances we find that starspots are unlikely to lead to an overestimation of the photospheric Li abundance. While the Li I 6708 Å line is strengthened in the presence of starspots, the extent to which the Li I line equivalent width displays rotational modulation is diluted. A Zeeman Doppler imaging code, which maps the surface magnetic flux distributions on rapid rotators, has been developed and tested in this thesis. Reliability tests indicate that this technique is robust with respect to small errors in line and stellar parameters. Spectropolarimetric observations of AB Dor from three years are presented here. The technique of least squares deconvolution, combines the signal from over 1500 lines, enhancing the S/N of the observed dataset. Brightness and magnetic maps of AB Dor are reconstructed using the deconvolved profiles and show excellent agreement with maps produced using independently developed codes by J.-F. Donati. This points to the consistency of Doppler imaging techniques. Magnetic field maps show the presence of strong radial and azimuthal fields at almost all latitudes. This non-solar like distribution of magnetic flux may indicate the presence of a distributed dynamo component operating in the convection zones of rapid rotators. By tracing the positions of absorption transients in Ha, we find prominence complexes at almost all longitudes. Footpoint locations remain difficult to ascertain. Prominences are ejected over much shorter timescales than the timescale over which differential rotation should act further observations with closer time sampling are necessary to investigate the coronal topology further.
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Blanco, Rodríguez Julián. "Magnetic activity at the poles of the sun." [Katlenburg-Lindau] Copernicus Publ, 2008. http://d-nb.info/988508125/04.
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Kiefer, René [Verfasser], and Markus [Akademischer Betreuer] Roth. "Seismic investigations of solar and stellar magnetic activity." Freiburg : Universität, 2018. http://d-nb.info/1160875421/34.
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Trauchessec, Vincent. "Local magnetic detection and stimulation of neuronal activity." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS301/document.
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L’activité cérébrale se traduit par des courants ioniques circulant dans le réseau neuronal.La compréhension des mécanismes cérébraux implique de sonder ces courants, via des mesures électriques ou magnétiques, couvrant différentes échelles spatiales. A l’échelle cellulaire, les techniques d’électrophysiologie sont maitrisées depuis plusieurs décennies, mais il n’existe pas actuellement d’outils de mesure locale des champs magnétiques engendrés par les courants ioniques au sein du réseau neuronal. La magnéto-encéphalographie(MEG) utilise des SQUIDs(Superconducting QUantum Interference Devices)fonctionnant à très basse température, placés en surface du crâne, qui fournissent une cartographie des champs magnétiques mais dont la résolution spatiale est limitée du fait de la distance séparant les capteurs des cellules actives. Le travail présenté dans cette thèse propose de développer des capteurs magnétiques à la fois suffisamment sensibles pour être capable de détecter le champ magnétique extrêmement faible générés par les courants neuronaux (de l’ordre de 10⁻⁹ T), et dont la géométrie est adaptable aux dimensions des cellules, tout en fonctionnant à température ambiante. Ces capteurs,basés sur l’effet quantique de magnétorésistance géante (GMR, sont suffisamment miniaturisables pour être déposés à l’extrémité de sondes d’une finesse de l’ordre de 100 μm. L’utilisation de capteurs GMR pour la mesure de signaux biomagnétiques fut d’abord testée lors d’expériences in-vitro, réalisées sur le muscle soléaire de souris. Ce système biologique a été choisi pour sa simplicité,rendant la modélisation accessible, ainsi que pour sa robustesse, permettant d’avoir des résultats fiables et reproductibles. Le parfait accord entre les prédictions théoriques et les signaux magnétiques mesurés valide cette technologie. Enfin, des expériences in vivo dans le cortex visuel du chat ont permis de réaliser la toute première mesure de la signature magnétique de potentiels d’action générés par des neurones corticaux, ouvrant la voie à la magnétophysiologie<br>Information transmission in the brain occurs through ionic currents flowing inside the neuronal network. Understanding how the brain operates requires probing this electrical activity by measuring the associated electric or magnetic field. At the cellular scale, electrophysiology techniques are well mastered, but there is no tool to perform magnetophysiology. Mapping brain activity through the magnetic field generated by neuronal communication is done via magnetoencephalography (MEG). This technique is based on SQUIDs (Superconducting Quantum Interference Devices) that operate at liquid Helium temperature. This parameter implies to avoid any contact with living tissue and a shielding system that increases the distance between the neurons and the sensors, limiting spatial resolution. This thesis work aims at providing a new tool to performmagnetic recordings at the neuronal scale. The sensors developed during this thesis are based on the Giant Magneto-Resistance (GMR) effect. Operating at room temperature, they can be miniaturize and shaped according to the experiment, while exhibiting a sensitivity that allows to measure amplitude of 10⁻⁹ T. Before targeting neurons, the use of GMR-based sensors for magnetic recordings of biological activity has been validated through invitro experiments on the mouse soleus muscle. This biological system has been chosen because of its simple organization, allowing for a realistic modelling, and for its robustness, in order to get reliable and replicable results. The perfect agreement between the measurements and the theoretical predictions represents a consistent validation of the GMR technology for biological applications. Then a specially adapted needle-shaped probe carrying micron-sized GMR sensors has been developed for in-vivo experiment in cat visual cortex. The very first magnetic signature of action potentials inside the neuropil has been measured, paving the way towards magnetophysiology
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Valiulis, Vladas. "The effect of transcranial magnetic stimulation on brain bioelectrical activity." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20140925_135043-14839.
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Transcranial magnetic stimulation (TMS) is a modern non invasive method of drug resistant psychiatric disorder treatment. TMS physiology research is hindered by variable, often controversial results. In most studies main attention is being focused on immediate effects after single TMS procedure rather than the influence of a complete therapy course. It is considered that variability of results in TMS practice is caused by different stimulation parameters and imprecision of stimulated area placement in the brain. Although TMS therapy is often viewed as a milder alternative to electroconvulsive therapy (ECT), comparative physiological studies of these two methods are very rare.
The aim of this study was to evaluate the effect of rTMS therapy course on bioelectrical brain activity and compare it to an ECT effect. Research included the effect of high and low frequency (10 Hz and 1 Hz) TMS on EEG band power spectrum and auditory evoked potential P300, using both standard and neuronavigated target positioning. TMS evoked EEG changes were also compared to the changes of ECT. Change dynamics after several months of TMS therapy were also measured. Results showed that after TMS therapy the most notable change in the brain occurs in the form of delta power increase. When using standard positioning 10 Hz TMS evokes more diverse and intense EEG band power spectrum changes than the 1 Hz TMS. Application of neuronavigation system decreases theta and alpha band power changes in 10 Hz TMS... [to full text]<br>Transkranijinė magnetinė stimuliacija (TMS) – tai modernus neinvazinis vaistams rezistentiškų psichiatrinių sutrikimų gydymo būdas. Fiziologiniai TMS tyrimai pasižymi įvairiais, dažnai prieštaringais rezultatais, daugeliu atvejų didžiausias dėmesys skiriamas betarpiškiems poveikiams po vienos TMS procedūros, bet ne po pilno terapinio kurso. Manoma, kad rezultatų įvairovę TMS praktikoje įtakoja skirtingi stimuliacijos parametrai ir netikslumai parenkant stimuliuojamą zoną smegenyse. Nors TMS terapija dažnai traktuojama kaip švelnesnė alternatyva elektros impulsų terapijai (EIT), palyginamųjų fiziologinių šių metodikų tyrimų labai trūksta.
Darbo tikslas buvo įvertinti TMS terapijos kurso poveikį bioelektriniam galvos smegenų aktyvumui ir palyginti jį su EIT terapijos poveikiu. Buvo tirta aukšto ir žemo dažnių (10 Hz ir 1 Hz) TMS terapijos įtaka EEG dažnių galios spektrui bei sukeltiniam klausos potencialui P300, naudojant standartinį ir neuronavigacinį taikinio pozicionavimą. TMS sukelti EEG pokyčiai palyginti su EIT terapijos sukeltais EEG pokyčiais, išmatuota TMS terapijos sąlygotų pokyčių dinamika kelių mėnesių bėgyje. Rezultatai parodė, kad TMS terapijos pasekoje smegenyse ryškiausiai padidėja delta dažnio galia. Naudojant standartinį pozicionavimą 10 Hz TMS sukėlė įvairesnius ir intensyvesnius EEG galios spektro pokyčius nei 1 Hz TMS. Pritaikius neuronavigacinę sistemą 10 Hz TMS atveju sumažėjo teta ir alfa dažnių galios pokyčiai. Praėjus keliems mėnesiams nuo TMS... [toliau žr. visą tekstą]
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Mathioudakis, Mihalis. "Magnetic activity phenomena in dwarf M and K stars." Thesis, Queen's University Belfast, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317518.
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Dunstone, Nicholas J. "Prominences and magnetic activity on young single and binary stars." Thesis, St Andrews, 2008. http://hdl.handle.net/10023/499.
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Zic, Andrew John. "Cool Stellar Activity at Low Radio Frequencies." Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/24500.
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Stellar magnetic fields drive a wide range of energetic phenomena, which have a crucial influence on their properties, evolution, and environment. In this thesis, we investigate the low-frequency radio emission from active low-mass stars. We harness this emission to constrain magnetospheric properties and processes arising from different magnetic activity paradigms. In Chapter 2, we present low-frequency observations of a sample of ultra-cool dwarfs. We show that while most ultra-cool dwarfs do not produce low-frequency emission, their magnetospheric properties can be constrained with measurements of the optically-thick side of the quiescent spectral energy distribution. In Chapter 3, we present Australian Square Kilometre Array Pathfinder (ASKAP) observations of the prototypical flare star, UV Ceti. Our observations reveal the presence of periodic, elliptically polarised radio pulses, confirming that large auroral current systems can be produced in the magneto- spheres of active M-dwarfs. In Chapter 4, we present results from one night of an 11-night multi-wavelength campaign targeting the nearest stellar neighbour, and magnetically-active planet host, Proxima Centauri. We detected a powerful flare with optical photometric and spectroscopic facilities, accompanied by a solar-like type IV radio burst. By analogy with the solar radio burst paradigm, we suggest that this event indicates a coronal mass ejection leaving the corona, and ongoing electron acceleration associated with a post-eruptive loop arcade.
Together, the results presented in this thesis show the diverse forms of magnetic activity exhibited by low-mass stars. We have shown that low-frequency radio observations are sensitive to both auroral and solar-like activity. Future low-frequency radio surveys and multi-wavelength observations may reveal the role of stellar properties such as rotation, mass, and age, in driving these different forms of magnetic activity.
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Virtanen, I. (. Ilpo). "Asymmetry of the heliospheric magnetic field." Doctoral thesis, University of Oulu, 2013. http://urn.fi/urn:isbn:9789526202563.
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This thesis studies the structure and evolution of the large scale heliospheric magnetic field. The work covers the space age, the period when satellite measurements revolutionized our knowledge about space. Now, this period is known to be the declining phase of the grand modern maximum of solar activity.
The thesis addresses how the hemispherical asymmetry of solar activity is seen in the photospheric magnetic field and how it appears in the corona and in the heliosphere until the termination shock. According to geomagnetic and heliospheric observations, the heliospheric current sheet has been southward shifted around the solar minima since 1930s. Using Ulysses probe observations, we derive an accurate estimate of 2° for the southward shift of the heliospheric current sheet during two very different solar minimum in the mid 1990s and 2000s. The overall structure of the heliospheric magnetic field has changed significantly now when the grand modern maximum has come to an end. During the present low solar activity the polar fields are weaker and the heliospheric current sheet covered a wide latitudinal range during the previous minimum. When the heliospheric current sheet is wide the asymmetry is less visible at the Earth’s orbit.
We extend our study to the outer heliosphere using measurements made by Voyager and Pioneer probes and show that the hemispherical asymmetry in the coronal hole evolution, and the related southward shift of the heliospheric current sheet, are seen until the termination shock. In order to understand the origin of the hemispherical asymmetry, we complete a multipole analysis of the solar magnetic field since 1976. We find that the minimum time southward shift of the heliospheric current sheet is due to the quadrupole component of the coronal magnetic field. The quadrupole term exists because the generation and transport of the magnetic flux in the Sun tends to proceed differently in the northern and southern hemispheres.
During this and the following decade the Sun is most likely going to be less active than it has been since 1920s. Therefore it is probable that the hemispherical asymmetry of the heliospheric magnetic field will be less visible in the ecliptic plane in the near future. Now, when the Sun seems to be at the maximum of cycle 24, we are looking forward to see how the polar fields and the heliospheric magnetic field are formed when approaching the following solar minimum. It is possible that, as the activity rises again after the present and future low cycles, the hemispherical asymmetry will be opposite to that of the 20th century and the minimum time heliospheric current sheet would be northward shifted.
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Li, Yeuk-Yue Tony. "The equatorial ionospheric anomaly in East Asia from solar minimum to solar maximum /." [Hong Kong : University of Hong Kong], 1993. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13597577.
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Jugniot, Natacha. "Molecular imaging of serine protease activity-driven pathologies by magnetic resonance." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0141/document.
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Ce travail porte sur le développement de sondes peptidiques pour le suivi de la protéolyse par spectroscopie de résonance paramagnétique électronique (RPE) et pour l'imagerie in vivo par résonance magnétique rehaussée de l’effet Overhauser (OMRI). Plus précisément, ce travail étudie pour la première fois une famille d’agents d’imagerie appelée « nitroxyde à déplacement de raies spectrales » spécifique d’activités enzymatiques. L'activité protéolytique, entraînant un décalage de 5 G dans les constantes de couplages hyperfins, permet une quantification individuelle des espèces substrat et produit par RPE et une excitation sélective par OMRI. Trois substrats ont été élaborés, montrant une spécificité enzymatique pour l’élastase du neutrophile (NE) (MeO-Suc-Ala-Ala-Pro-Val-Nitroxyde & Suc-Ala-Ala-Pro-Val-Nitroxyde), et pour la chymotrypsine et la cathepsine G (Suc-Ala-Ala-Pro-Phe-Nitroxyde). Les constantes enzymatiques ont montré de bonnes valeurs avec globalement, Km = 28 ± 25 µM et kcat = 19 ± 3 s-1. Ex vivo, l’utilisation des substrats NE en OMRI a révélé un contraste élevé dans les lavages broncho-alvéolaires de souris sous stimulus inflammatoire. Les rehaussements de signaux IRM sont en corrélation avec la sévérité de l’inflammation. L'irradiation à la fréquence RPE de 5425,6 MHz a permis d'accéder à la bio-distribution des substrats in vivo et pourrait ainsi servir d’outil diagnostic. Les perspectives à moyen terme de ce travail reposent sur le développement de l’OMRI à très faibles champs magnétiques en vue d’une application chez l’homme<br>This work focuses on substrate-based probes for proteolysis monitoring by Electron Paramagnetic Resonance spectroscopy (EPR) and for in vivo imaging by Overhauser-enhanced Magnetic Resonance (OMRI). More precisely, this work investigates for the first time a family of MRI agents named “line-shifting nitroxide” specific for proteolytic activities. Proteolytic action results in a shift of 5 G in EPR hyperfine coupling constants allowing individual quantification of substrate and product species by EPR and selective excitation by OMRI. Three substrates were worked out, showing enzymatic specificity for neutrophil elastase (MeO-Suc-Ala-Ala-Pro-Val-Nitroxide & Suc-Ala-Ala-Pro-Val-Nitroxide), and for Chymotrypsin/Cathepsin G (Suc-Ala-Ala-Pro-Phe-Nitroxide). Enzymatic constants were remarkably good with globally Km = 28 ± 25 µM and kcat = 19 ± 3 s-1. Ex vivo, the use of NE substrates in OMRI revealed a high contrast in bronchoalveolar lavages of mice under inflammatory stimulus. MRI signal enhancements correlate with the severity of inflammation. Irradiation at the RPE frequency of 5425.6 MHz provided access to the bio-distribution of substrates in vivo and could thus serve as a diagnostic tool. The medium-term perspectives of this work are based on the development of OMRI with very low magnetic fields for human application
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Virtanen, I. (Iiro). "Surface flux transport simulations of the photospheric magnetic field." Doctoral thesis, Oulun yliopisto, 2019. http://urn.fi/urn:isbn:9789526223292.
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Abstract This thesis studies the long-term evolution of the photospheric magnetic field using surface flux transport simulations. The photospheric magnetic field and magnetic activity are tightly connected to space weather, and affect the whole heliosphere including the Earth. However, due to a lack of reliable observations our understanding of the long-term evolution of the photospheric magnetic field is still poor. Surface flux transport models, which are capable of simulating the evolution of the whole surface field from observations of solar activity, can be used to study the field in times when direct observations are not available. In this thesis we validate our surface flux transport model, optimize its parameters and test its sensitivity to uncertainties in parameter values and input data. We find a need to extend the model with a decay term to properly model the deep and long minimum between solar cycles 23 and 24, and simulate the photospheric magnetic field of cycles 21–24 using magnetographic observations as input. We also study consequences of hemispherically asymmetric activity, and show that activity in one hemisphere is enough to maintain polar fields in both hemispheres through cross-equatorial flow of magnetic flux. We develop a new method to reconstruct active regions from calcium K line and sunspot polarity observations. We show that this reconstruction is able to accurately capture the correct axial dipole moment of active regions. We study the axial dipole moments of observed active regions and find that a significant fraction of them have a sign opposite to the sign expected from Hale’s and Joy’s laws, proving that the new reconstruction method has an advantage over existing methods that rely on Hale’s and Joy’s laws to define polarities. We show one example of a long simulation covering solar cycles 15–21, demonstrating that using the active region reconstruction and surface flux transport model presented in this thesis it is possible to simulate the large-scale evolution of the photospheric magnetic field over the past century<br>Original papers The original publications are not included in the electronic version of the dissertation. Virtanen, I. O. I., Virtanen, I. I., Pevtsov, A. A., Yeates, A., & Mursula, K. (2017). Reconstructing solar magnetic fields from historical observations. II. Testing the surface flux transport model. Astronomy & Astrophysics, 604, A8. https://doi.org/10.1051/0004-6361/201730415 http://jultika.oulu.fi/Record/nbnfi-fe2017103050356 Virtanen, I. O. I., Virtanen, I. I., Pevtsov, A. A., & Mursula, K. (2018). Reconstructing solar magnetic fields from historical observations. III. Activity in one hemisphere is sufficient to cause polar field reversals in both hemispheres. Astronomy & Astrophysics, 616, A134. https://doi.org/10.1051/0004-6361/201732323 http://jultika.oulu.fi/Record/nbnfi-fe201902205813 Virtanen, I. O. I., Virtanen, I. I., Pevtsov, A. A., Bertello, L., Yeates, A., & Mursula, K. (2019). Reconstructing solar magnetic fields from historical observations. IV. Testing the reconstruction method. Astronomy & Astrophysics, 627, A11. https://doi.org/10.1051/0004-6361/201935606 http://jultika.oulu.fi/Record/nbnfi-fe2019091828628 Virtanen, I. O. I., Virtanen, I. I., Pevtsov, A. A., & Mursula, K. (2019) Axial dipole moment of solar active regions in cycles 21-24. Manuscript
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Rosén, Lisa. "Magnetic fields of cool active stars." Doctoral thesis, Uppsala universitet, Observationell astrofysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-283357.
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Magnetic fields are present throughout the universe and are very important for many astrophysical processes. Magnetic field influences a star throughout its life and affects nearby objects such as planets. Stellar magnetic field can be detected by measuring the Zeeman splitting of spectral lines in the intensity spectra (Stokes I) if the field is strong, or by analyzing polarization spectra if the field is weak. Magnetic fields in stars similar to the Sun are ubiquitous but, in general, relatively weak. Until recently these fields were detected through circular polarization (Stokes V) only since linear polarization (Stokes QU) is significantly weaker. The information embedded in different Stokes spectra is used for reconstruction of the surface magnetic field topology with Zeeman Doppler imaging (ZDI) technique. However, cool stars often have complex field geometries and this, combined with a low field strength, partial Stokes parameter observations and the presence of cool spots, makes accurate magnetic mapping difficult. We have performed numerical tests of ZDI to investigate some of the problems of magnetic inversions and ways to overcome them. The most reliable results were found when magnetic field and temperature inhomogeneities were modelled simultaneously and all four Stokes parameters were included in the reconstruction process. We carried out observations of active cool stars in all four Stokes parameters trying to find an object with linear polarization signatures suitable for ZDI. The RS CVn star II Peg was identified as a promising target, showing exceptionally strong linear polarization signatures. We reconstructed the magnetic field in II Peg using full Stokes vector observations for the first time in a cool star. Compared to the magnetic maps recovered from the Stokes IV spectra, the four Stokes parameter results reveal a significantly stronger and more complex surface magnetic field and a more compact stellar magnetosphere. Spectropolarimetric observations and magnetic inversions can also be used to investigate magnetic activity of the young Sun and its implications for the solar system past. To this end, we studied a sample of six stars with parameters very similar to the present Sun, but with ages of only 100-650 Myr. Magnetic field maps of these young solar analogues suggest a significant decrease of the field strength in the age interval 100-250 Myr and a possible change in the magnetic field topology for stars older than about 600 Myr.
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See, Wyke Chun Victor. "Stellar magnetism and activity : from stellar interiors to orbiting exoplanets." Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/9602.
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The study of magnetic fields on low-mass stars is important due to their ubiquity. They are responsible for phenomena spanning a wide range of spatial and temporal scales. Over the last two decades, the Zeeman-Doppler imaging (ZDI) technique has been used to study the topologies of stellar magnetic fields. A great deal has been learnt about how the magnetic characteristics of cool dwarfs vary as a function of parameters such as mass, rotation or age. In this thesis, I assemble a sample of stars with Zeeman-Doppler maps. I study their poloidal and toroidal components as a function of fundamental parameters and also in relation to activity cycles. I find that the relationship between poloidal and toroidal fields is different for stars above and below the fully convective boundary, in line with previous ZDI studies. I also find that the fields of strongly toroidal stars must be generated axisymmetrically. With regards to activity cycles, I find that so called “inactive branch" stars appear to remain poloidal throughout their activity cycle while so called “active branch" stars appear to be able to generate strong toroidal fields. Magnetic activity can also interact with exoplanets that may be orbiting a star. In this thesis, I consider two such interactions. The first is the compression of planetary magnetospheres by stellar winds. Sufficiently powerful winds can strip a planet of its atmosphere and render it uninhabitable. However magnetospheric shielding can provide some protection. I show that planets around 0.6 M⊙ - 0.8 M⊙ stars are the most likely to be able to protect their atmospheres. The second interaction I consider is exoplanetary radio emission. I present a wind model and show that exoplanetary radio emissions will depend strongly on the structure of the magnetic field structure of the central star.
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Johnson, Anthony. "The long-term dynamic influence of human activity on topsoil magnetic susceptibility." Thesis, University of Oxford, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.617598.
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Magnetic survey has become increasingly important in locating and characterising sites of archaeological potential. Magnetometry and topsoil magnetic susceptibility are the principal methods employed. In recent years advances in the design of magnetometers have made their use almost universal, somewhat to the detriment of magnetic susceptibility survey. This is especially true when the efficacy of various geophysical methods in locating sites of archaeological potential is compared. Such direct comparisons are, however, open to serious question. When sealed below the soil archaeological features acquire a degree of permanence, and their relatively static nature allows them to be identified by magnetometer survey on morphological grounds. By contrast, soil is continuously exposed, and over a period of 'deep time' is subject to the vagaries of human activity. The soil itsc1fbecomcs an artefact and the information it contains at any given time need not be site - specific but extensive. The problem addressed here is that of the interpretation of such topsoil magnetic data. Through occupation, industry, and agriculture, communities have historically affected the nature and proportion of the iron minerals (mostly oxides) in the soil, which establishes its magnetic identity. The problems of identifying the cultural influences which impact on the magnetic signature are simplified here by introducing three separable dynamic agencies: viz. chemical, exotic (inclusion) and mechanical (intervention, or perturbation). The incorporation of exotic materials into the soil, and human mechanical perturbation, arc both capable of creating soil magnetic patterns without directly affecting the soil's natural minerals. A search of early agricultural literature has identified activity which aids the interpretation of otherwise enigmatic data. The results of over 200 surveys have been reviewed, and from them examples selected to illustrate the three dynamic models. The results confirm that magnetically enhances soils often indicate buries archaeology but also may have no underlying archaeological source, the historic information residing exclusively within the topsoil itself. Long-term dispersal of magnetic material within the topsoil is examined and seen to be related to both bioturbation and agricultural activity. Documentary evidence shows that historic enclosure, selective land-use, and ploughing have contributed to soil magnetic pattern formation. Far from being a poor relative of other prospecting methods, topsoil susceptibility has its own unique contribution to make. Information resides within, not only below the soil, and the full potential of the method has not yet been realised. Recently the idea of cultural soilscapes has emerged, an historical perspective gained from archaeological soil surveys increasingly aids an understanding of how soils have been utilised, exploited and, more recently, degraded.
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Huber, Laurentius. "Mapping Human Brain Activity by Functional Magnetic Resonance Imaging of Blood Volume." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-165252.
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This dissertation describes the development, implementation, validation, optimization, and application, of a noninvasive and quantitative method for measuring cerebral blood volume changes with functional magnetic resonance imaging (fMRI) for mapping of neural activity changes.
Since its inception over twenty years ago, the field of fMRI has grown in usage, sophistication, range of applications, and impact. Nevertheless it has yet to exploit its full potential regarding, spatiotemporal resolution, signal specificity, and quantifiability of hemodynamic changes. By utilization of a new MR pulse sequence, new concepts of radio frequency pulses, and high magnetic fields (7 T), a novel fMRI method named SS-SI VASO is presented here that overcomes sensitivity limitations of other noninvasive quantitative imaging methods. In order to validate that its signal represents changes in cerebral blood volume without other contaminations, SS-SI VASO is implemented in animal models for a close comparison with established, but invasive methods. A good agreement of blood volume sensitivity has been found with the new method compared to the established ones. After its validation, the SS-SI VASO method and its unprecedented sensitivity was used to localize and quantify hemodynamic changes in applications where conventional oxygenation based fMRI methods are limited. (A) SS-SI VASO was used to investigate biophysical aspects of actively controlled arteries and passive balloon-like veins during activity induced hemodynamic changes. (B) SS-SI VASO was used to provide insights whether the interplay of neural activity and resultant vascular response are the same for tasks that increase neural activity compared to tasks that suppress neural activity. (C) SS-SI VASO was used to calibrate conventional oxygenation based fMRI to quantify local changes in oxygen metabolism. (D) The high sensitivity of SS-SI VASO was further used to obtain sub-millimeter resolutions and estimate activity changes between cortical layers. This enables to address questions not only where the brain is activated but also how and whereby this activity is evoked. The implementation and application of this new SS-SI VASO fMRI method is a major step forward for the field of imaging neuroscience; it demonstrates that the current limitations of fMRI can be even overcome with respect to quantifiability, spatial specificity and distinguishing between vascular and neuronal phenomena.
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Luo, Yuanming. "Assessment of diaphragm electrical activity using electrical and magnetic phrenic nerve stimulation." Thesis, King's College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270379.
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Ptychion, Panagiota Petkaki. "Particle acceleration in dynamical collisionless reconnection." Thesis, University of Glasgow, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296962.
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Verschueren, Sarah B. F. "Clinical application of magnetic stimulation of focal epilepsy and the influence of low frequency magnetic fields on brain electrical activity." Thesis, Keele University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431377.
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The question of whether or not extremely low frequency (ELF) electromagnetic fields can have any influence on the human body has sparked heated debate over the last few decades. While several plausible theories on possible transduction mechanisms for these ELF fields (such as ferromagnetic transduction or shifts in the probability distribution of ion channel states) have been put forth, experimental research into such ELF effects has been widely overlooked. The work presented here aims to examine the effects of two forms of ELF exposure on the human brain. Our work investigates the influence of weak-field magnetic stimulation on the brain electrical activity for the purpose of defining a magnetic stimulation protocol that elicits most response, with an eye on potential future use of such protocol as a diagnostic or therapeutic tool in the treatment of focal epilepsy. We also establish for the first time the effects of exposure to the 60jlT 2Hz magnetic field associated with the discontinuous transmission (DTX) feature used in present-day mobile phones. Because of the widespread use of mobile phones and the nature of the exposure (i.e. close proximity to the head), the investigation of any potential health effects of such exposure is of vital importance. Seven patients suffering from mesial temporal lobe epilepsy and eight healthy volunteers were exposed to weak DC magnetic fields (l-4mT) as well as 60jlT 2Hz DTX magnetic fields. The brain electrical activity was recorded with semi-invasive (foramen ovale) and scalp electrodes for the epileptic subject group and scalp electrodes for the healthy subject group. Analysis of the data consisted of quantifying the average spectral power density pre- and post field exposure, as recorded by EEG. Results indicate significant alterations in the EEG's spectral power as a direct consequence of the exposure to weak DC magnetic fields in all of the individuals studied. The field combination that elicited most response was found to be the 0.55Hz frequency at 2-3mT field strengths for the healthy subject group and 0.1 Hz frequency at 2-3 mT field strengths for the epileptic subject group. Results show significant alterations in the EEG's spectral power content following exposure to the DTX mobile phone field for 9 of the 14 individuals studied. A statistically significant difference was found between both subject groups: while the DTX field altered the power density by an average of 55.5% in the healthy subject group, a much smaller change of 30.9% was found for the epileptic subject - 4 - group (P=0.003). The influence of the DTX-field seems to peak lOs after removal of the field. Overall, most changes to the spectral power density were found in the Alpha and Beta bands.
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Getachew, T. (Tibebu). "Spatial-temporal structure and distribution of the solar photospheric magnetic field." Doctoral thesis, Oulun yliopisto, 2019. http://urn.fi/urn:isbn:9789526224367.
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Abstract I have made a detailed study of the fundamental properties of the solar photospheric magnetic field, which helps in better understanding the Sun’s radiative and particle outputs that affect the Earth’s near-space environment, as well as the entire heliosphere. Photospheric magnetic field is an essential parameter for space weather and space climate. The photospheric magnetic field includes a wide range of large-scale and small-scale structures, but the contribution of weak, small-scale fields to the total flux on the solar surface is dominant. This thesis discusses the spatial-temporal structure and long-term evolution of the solar photospheric magnetic field. Particularly, the thesis presents, for the first time, the spatial distribution of the asymmetry of weak field values and its evolution in solar cycles 21–24. I found that the asymmetry (also called shift) of the distribution of positive and negative weak-field values is a real physical phenomenon. I also found that the shifts are most effectively produced at the supergranulation scale. I studied the asymmetry of the distribution of weak field values separately in the two solar hemispheres. My results show that the shifts of weak-field field distributions in the two solar hemispheres have always the same sign as the new polarity of the polar field in the respective hemisphere and solar cycle. I also found that the hemispheric shifts change their sign in the late ascending to maximum phase of the solar cycle and attain their maximum in the early to mid-declining phase. This evolution of the hemispheric weak-field gives a new signal of the solar magnetic cycle. We also studied the long-term spatial-temporal evolution of the weak-field shift and skewness of the distribution of photospheric magnetic field values during solar cycles 21–24 in order to clarify the role and relation of the weak field values to the overall magnetic field evolution. Our results give evidence for the preference of even the weakest field elements toward the prevailing magnetic polarity since the emergence of an active region, and for a systematic coalescence of stronger magnetic fields of opposite to produce weak fields during the poleward drift of the surge<br>Original papers Original papers are not included in the electronic version of the dissertation. Getachew, T., Virtanen, I., & Mursula, K. (2017). Structure of the Photospheric Magnetic Field During Sector Crossings of the Heliospheric Magnetic Field. Solar Physics, 292(11). https://doi.org/10.1007/s11207-017-1198-9 http://jultika.oulu.fi/Record/nbnfi-fe201802083259 Getachew, T., Virtanen, I., & Mursula, K. (2019). Asymmetric Distribution of Weak Photospheric Magnetic Field Values. The Astrophysical Journal, 874(2), 116. https://doi.org/10.3847/1538-4357/ab0749 http://jultika.oulu.fi/Record/nbnfi-fe2019061320447 Getachew, T., Virtanen, I., & Mursula, K. (2019). A New Signal of the Solar Magnetic Cycle: Opposite Shifts of Weak Magnetic Field Distributions in the Two Hemispheres. Geophysical Research Letters, 46(16), 9327–9333. https://doi.org/10.1029/2019gl083339 Mursula, K., Getachew, T., & Virtanen, I. (2019). Spatial-temporal evolution of photospheric weak-field shifts in solar cycles 21-24. Astron. Astrophys., submitted
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Besostri, Francesca. "Deposition of metal nanoparticles on magnetic nanobeads and evaluation of their catalytic activity." Doctoral thesis, Universitat Rovira i Virgili, 2016. http://hdl.handle.net/10803/396175.
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El present manuscrit presenta estudis científics que versen sobre la síntesi i aplicacions en catàlisi de nanopartícules metàl·liques (Pd, Pt, Au, Ni) dipositades sobre nanoesferes de Co i Fe2O3. En primer lloc s’ha estudiat l’activitat en acoblament creuat de tipus Suzuki-Miyaura d’un catalitzador format per nanopartícules de pal·ladi dipositades a la superfície de nanoesferes de Co recobertes de carboni. S’ha observat alta activitat catalítica per a l’acoblament d’àcid fenilborònic amb iodurs i bromurs d’aril, emprant càrregues de catalitzador baixes i temps de reacció curts. També s’ha estudiat el recobriment de la capa de carboni amb sílica per a la incorporació d’un complex de pal·ladi per tal de minimitzar el lixiviat de metalls cap a la dissolució, observat amb el catalitzador anterior. D’aquesta manera es van assolir altes activitats catalítiques minimitzant la quantitat de Pd i Co lixiviada.
La deposició de nanopartícules de Pt, Au i Ni petites (5 nm) i amb activitat catalítica a les mateixes nanoesferes es va estudiar a continuació. Nanopartícules d’or actives i de menys de 5 nm de mida van ser obtingudes per reducció de HAuCl4 en presència de PVP i se’n va avaluar el seu potencial per a la hidrogenació catalítica de para-nitrophenol. En contrast, la síntesi d’un catalitzador de platí suportat va resultar més problemàtica. Tot i assolir alts nivells de funcionalització, la formació d’agregats de Pt sobre la superfície del suport magnètic va fer inviable la catàlisi. De manera anàloga, la formació de NiO i aglomeració de Ni metàl·lic va fer impossible la formació de catalitzadors actius.<br>nanopartículas metálicas (Pd, Pt, Au, Ni) depositadas sobre nanoesferas de Co y Fe2O3. En primer lugar se ha estudiado la actividad en acoplamiento cruzado de tipo Suzuki-Miyaura de un catalizador formado por nanopartículas de paladio depositadas en la superficie de nanoesferas de Co recubiertas de carbono. Se ha observado alta actividad catalítica para el acoplamiento de ácido fenilborónico con yoduros y bromuros de arilo, empleando cargas de catalizador bajas y tiempos de reacción cortos. También se ha estudiado el recubrimiento de la capa de carbono con sílica para la incorporación de un complejo de paladio para minimizar el lixiviado de metales hacia la disolución, observado con el catalizador anterior. De esta manera se alcanzaron altas actividades catalíticas minimizando la cantidad de Pd y Co lixiviada.
La deposición de nanopartículas de Pt, Au y Ni pequeñas (5 nm) y con actividad catalítica a las mismas nanoesferas se estudió a continuación. Nanopartículas de oro activas y de menos de 5 nm de tamaño fueron obtenidas por reducción de HAuCl4 en presencia de PVP y se evaluó su potencial para la hidrogenación catalítica de para-nitrophenol. En contraste, la síntesis de un catalizador de platino soportado resultó más problemática. A pesar de alcanzar altos niveles de funcionalización, la formación de agregados de Pt sobre la superficie del soporte magnético hizo inviable la catálisis. De forma análoga, la formación de NiO y aglomeración de Ni metálico hizo imposible la formación de catalizadores activos.<br>The present dissertation presents a scientific work focused on the synthesis and catalytic evaluation of catalysts based on metallic nanoparticles (Pd, Pt, Au, Ni) deposited on magnetic nanobeads of Co and Fe2O3. Firstly, the evaluation of the activity for the Suzuki-Miyaura cross-coupling reaction of a catalyst composed by palladium nanoparticles deposited on the surface of the carbon-coated Co nanobeads was studied.
High catalytic activity was observed for the coupling of phenylboronic acid with aryl iodides and bromides, employing low metal loading and short reaction times. A functionalisation consisting on a silica coating over the carbon shell and further incorporation of a palladium complex was also investigated in order to minimize leaching of metals observed with the previous catalyst. High catalytic activity was performed and the metal leaching (Pd and Co) was minimized.
The deposition of small (~ 5 nm) catalytically active Pt, Au and Ni nanoparticles on the magnetic nanobeads was afterwards investigated. Active gold nanoparticles of less than 5 nm in size were obtained by reduction of HAuCl4 in presence of PVP and their potential for the catalytic hydrogenation of para-nitrophenol was evaluated. Contrarily, synthesising an active supported platinum catalyst proved to be more challenging. High metal loadings were achieved however formation of Pt clusters on the surface of the magnetic support precluded the activity of the samples. Similarly, formation of NiO and agglomeration of metallic Ni prevented the formation of active catalysts.
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Hoechstetter, Karsten. "Magnetic source imaging of tactile evoked activity in the human secondary somatosensory cortex." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=962764590.
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Bryson, James Francis Joseph. "The origin of ancient magnetic activity on small planetary bodies : a nanopaleomagnetic study." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708801.
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Doan, Duy Anh N. "Analysis of magnetic activity cycles in solar analogs using Solar - Stellar Spectrograph data." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/114106.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 30-31).<br>The Solar-Stellar Spectrograph (SSS) Project includes frequent observations of 30 - 50 Sun-like stars to address a wide variety of questions regarding the nature of stellar magnetic activity cycles. The magnetic activity cycles of 18 stars in the SSS project are analyzed using the Lomb Scargle method of least-squares spectral analysis. Periodograms reveal that out of 18 stars, 9 stars have one magnetic cycle and 6 stars have two magnetic cycles, with periods ranging from 2 years to 17 years. The remaining stars show significant variability but without pronounced periodicity. Most of the detected cycles have a false alarm probability (FAP) well below 10-3 The results for a number of stars are compared and confirmed with earlier observations by Mount Wilson Observatory's project, published by Baliunas et. al. (1995). Four more stars are added to the plot of activity cycle period - rotational period relation by Bohm-Vitense (2006), and they all lie on either the active sequence or the inactive sequence. This result, together with the fact that several stars have two different cycles lying on different sequences, lends more evidence to the hypothesis that stars have multiple dynamos but are dominated by one of them.<br>by Duy Anh N. Doan.<br>S.B.
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Wehrhahn, Ansgar. "The impact of stellar magnetic activity on the radial velocity search of exoplanets." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-326389.
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Radial velocity measurements are critical in finding and confirming exoplanets. To confine the parameters of the planet we naturally want to minimise the errors on the measurement. However the observed measurement error is now on the same order as the precision of the instrument. This so called jitter is related to the stellar activity (Wright 2005), i.e. the magnetic field of the star. In this paper we investigate if we can discover any correlation between the radial velocity variation and the magnetic activity of the star using HARPSpol spectra for the two stars Epsilon Eridani and GJ674.
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Ikuta, Kai. "Exploring stellar magnetic activities with Bayesian inference." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263467.
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Takizawa, Kan. "Evolution and Flare Activity of δ-spots in Cycle 23". 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/202793.
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Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(理学)<br>甲第19359号<br>理博第4121号<br>新制||理||1593(附属図書館)<br>32373<br>新制||理||1593<br>京都大学大学院理学研究科物理学・宇宙物理学専攻<br>(主査)教授 一本 潔, 教授 柴田 一成, 准教授 野上 大作<br>学位規則第4条第1項該当
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李若愚 and Yeuk-Yue Tony Li. "The equatorial ionospheric anomaly in East Asia from solar minimun to solar maximum." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1993. http://hub.hku.hk/bib/B31211677.
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Yerli, Sinan Kaan. "An observational study of Algol-type binaries." Thesis, University of Sussex, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285139.
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Liu, Mianxin. "The brain at criticality : variability of brain spontaneous activity and relevance to brain functions." HKBU Institutional Repository, 2020. https://repository.hkbu.edu.hk/etd_oa/809.
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The brain activities are characterized by spontaneous and persistent irregular fluctuations in space and time. Criticality theory from statistical physics has been proposed as a principle to explain the variability in normal brain spontaneous activity and has suggested the functional benefits of variability, such as maximized dynamic range of response to stimuli and information capacity. In parallel, the brains show variability in other aspects, such as the structural heterogeneity across brain regions, the intra-individual variability across experimental trials, and the behavior difference across groups and individuals. The associations between the variability of spontaneous activities and these different types of structural, intra and inter-individual variabilities remain elusive. My doctoral study thus aimed to bridge the brain variability and the above-mentioned variations based on criticality theory and analysis of empirical data. As a preparatory analysis, we first collected evidence to prove criticality in human functional magnetic resonance imaging (fMRI) data. The advanced statistical criteria were used to exclude potential artefacts that can induce power-law scaling without the mechanism of criticality. In the first part of the study, we addressed methodological issue and tested whether several measures of either spatial or temporal complexity due to experimental limitations could be reliable proxy of spatiotemporal variability (related to criticality) in vivo. The high spatiotemporal resolutions of whole-cortex optical voltage imaging in mice brain during the waking up from anesthesia enabled simultaneous investigation of functional connectivity (FC), Multi-Scale Entropy (MSE, measure of temporal variability), Regional Entropy (RE, quantity of spatiotemporal variability) and the interdependency among them under different brain states. The results suggested that MSE and FC could be effective measures to capture spatiotemporal variability under limitation of imaging modalities applicable to human subjects. This study also lays methodological basis for the third study in this thesis. In the second study, we explored the interaction between spontaneous activity and evoked activity from mice brain imaging under whisker stimulus. The whisker stimulus will first evoke the local activation in sensory cortex and then trigger whole-cortex activity with variable patterns in different experimental trials. This trial-to-trial variability in the cortical evoked component was then attributed to the changes of ongoing activity state at stimulus onset. The study links ongoing activity variability and evoked activity variability, which further consolidates the association between ongoing activity and brain functions. In the third study, we measured the signal variability of the whole brain from resting state fMRI, and developed the multivariate pattern of cortical entropy, called entropy profile, as reliable and interpretable biomarker of individual difference in cognitive ability. We showed that the whole cortical entropy profile from resting- state fMRI is a robust personalized measure. We tested the predictive power for general and specific cognitive abilities based on cortical entropy profiles with out- of-sample prediction. Furthermore, we revealed the anatomical features underlying cross-region and cross-individual variations in cortical entropy profiles. This study provides new potential biomarker based on brain spontaneous variability which could benefit the applications in psychology and psychiatry studies. The whole study laid a foundation for brain criticality-/variability-based studies and applications and broadened our understanding of the associations between neural structures, functional dynamics and cognitive ability
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Poppenhäger, Katja [Verfasser], and Jürgen H. M. M. [Akademischer Betreuer] Schmitt. "Magnetic activity of planet-hosting stars / Katja Poppenhäger. Betreuer: Jürgen H. M. M. Schmitt." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2011. http://d-nb.info/1020383569/34.
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Hastie, Morag Ann. "Investigating chromospheric magnetic activity on young stars and the wide field CAMera for UKIRT." Thesis, University of Edinburgh, 2007. http://hdl.handle.net/1842/28208.
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This thesis presents a novel approach to measuring the distribution of magnetic regions on T Tauri stars which aims to overcome limitations of other observing techniques such as Doppler imaging or Zeeman measurements. The central line emission from the strong visible Call H & K lines are a proxy indicator of surface magnetic fields and are known through observations of the Sun to be enhanced above active plage regions. Simultaneous optical spectroscopic and photometric observations of a significant sample of fast rotating T Tauri stars in the nearby clusters ρ Ophiuchus and Upper Scorpius have allowed us to ascertain a direct correlation between variations in the Cell doublet emissions and light intensities. Computer simulations which model the surface conditions as understood on T Tauri stars and generate correlations which mimic those in the observational data offer a manipulable tool for estimating how much of the stellar surface is covered. The Wide Field CAMera for the UKIRT Telescope on Mauna Kea is currently the most capable infrared imaging survey wide field camera in the world. The instrument focal plane consists of four Hawaii-II 2048 x 2048 x 2048 IR detectors, to facilitate the best operating conditions and practises for the camera these detectors must be carefully characterised such that inherent qualities can either be corrected or accounted for. The second part of this thesis details the detector characterisation work carried out prior to the instrument delivery to the telescope.
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Wood, Paul D. "Elements of solar activity : particle acceleration and filament formation." Thesis, University of St Andrews, 2005. http://hdl.handle.net/10023/11309.
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This thesis studies the acceleration of particles to super-thermal energies in explosive solar events as well as the magnetic changes in connectivity that may be responsible for changes in the morphology of quiescent filaments. Firstly a review of some of the observations of solar flare dynamics is given, as well as an introduction to the competing theories attempting to explain both particle acceleration and filament formation. An explanation of the numerical FORTRAN code that is used to calculate the trajectories of particle distribution functions in prescribed electromagnetic fields is given. Examples of known fields are used to test the accuracy of the code and the simple example of the well-known Litvinenko current sheet field is investigated. The results of charged particle orbit calculations in prescribed electric and magnetic fields motivated by magnetic reconnection models are then presented. The electromagnetic fields are chosen to resemble a current sheet with a localised reconnection region. The dependence of the model on the important physical parameters is considered. An introduction to the mathematical formulation of a collapsing magnetic trap is given. The same numerical code is used to calculate single electron orbits in this more complicated time dependent electromagnetic field. Consideration of important previous work is given before describing the best attempts to model the movement of flare loops in a realistic fashion. Finally the process of flux cancellation and filament formation is studied using a range of data including ground-based Hα and SoHO MDI magnetograms. It is found that the cancellation occurs at the ends of Hα sections of the filament and is accompanied by a noticeable increase in the Hα intensity and linkage of the sections. Measurements of the amount of flux cancelled at each site show it is in agreement with an estimate of the axial flux contained in the filament.
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Davila, Ricardo Cruz. "A Study of Magnetic Activity Effects on the Thermospheric Winds in the Low Latitude Ionosphere." DigitalCommons@USU, 1994. https://digitalcommons.usu.edu/etd/6808.
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The purpose of this thesis is to examine the effects of magnetic activity on the low latitude F-region thermospheric winds. The F-region (120-1600 km) is a partially ionized medium where O+ and O are the major ion and neutral species, respectively. The thermospheric winds at these altitudes are driven primarily by pressure gradient forces resulting from the solar heating during the day and cooling at night. For this study, we use measured Fabry-Perot Interferometer (FPD winds at Arequipa (16.5°S, 71.5°W) and measured FPI and Incoherent Scatter Radar (ISR) winds at Arecibo (18.6°N, 66.8°W).
Previous wind studies at Arequipa and Arecibo concentrated on the climatological wind patterns highlighting solar cycle effects and seasonal variations; however, these studies did not address the effects of magnetically disturbed conditions on the seasonal averaged winds. To properly investigate storm time effects on the neutral winds, we must first investigate solar cycle effects on the seasonal averages during magnetically quiet (Kp < 3) conditions. This study will include a detailed analysis of solar cycle effects on the seasonally averaged winds for Arequipa and Arecibo. In addition to the wind averages, we used cubic splines to fit the average wind profiles and to provide better comparisons with modeled results. We also performed a study on the airglow emission heights using both Jicamarca and Arecibo electron density profiles. This established the height which we will use to compare our experimental data with the model winds.
To investigate magnetic activity effects on the FPI and ISR winds, we used three magnetic activity cases which cover all storm time scenarios. These magnetic activity cases are the extended quiet, short-term disturbed, and extended disturbed conditions. The first case, the extended quiet, is the condition where the previous and short term magnetic activity is quiet (12 hour Kp ≤ 3 and the Kp ≤ 3). The short-term disturbed case is defined for the condition where the previous magnetic activity is quiet (12 hour Kp ≤ 3) and then becomes disturbed (Kp ≤ 3). Last, we considered the case where previous and short-term magnetic activity are disturbed (12 hour Kp ≤ 3 and the Kp ≤ 3).
Our last objective is to use our data to validate the predictions from the Thermosphere/Ionosphere General Circulation model (TIGCM93) and the Horizontal Wind Model (HWM93). This study should further our understanding of the physical processes which produce the low latitude quiet and disturbed winds. The TIGCM93 is a first principal model and the HWM93 is an empirical model based on ground-based and satellite measurements. The main advantage of using the TIGCM93 is the ease of studying the dynamics of ionospheric phenomena by simply changing various model inputs, while the HWM93 allows us a comparison between our experimental wind data sets with the established climatology of the winds over Arequipa and Arecibo.
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Llama, Joseph. "Things that go bump in the light : an investigation into the effects of stellar activity on extrasolar planets." Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/4907.
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The search for planets orbiting stars other than the Sun has led to the discovery of over one thousand new worlds. The majority of these planets have been very large, Jupiter sized planets located very close to their host star. Transit surveys such as Kepler and SuperWASP monitor thousands of stars looking for periodic dips in light caused by a planet passing between our view point on Earth and their host star, blocking a fraction of the emitted star light. One of the primary limitations in detecting a small, Earth sized planet comes from stellar activity induced signals within the data collected by exoplanet missions. These signals can, however, be used to our advantage. In this thesis, asymmetries in transit light curves are exploited to reveal properties of both the planet and the host stars themselves. An asymmetry in the near-ultraviolet transit light curve of WASP-12b, one of the largest and hottest planets found to date is thought to be caused by the stellar wind interacting with the magnetic field surrounding the planet. In this thesis, a model for such an interaction is developed and is shown to be consistent with the observations, providing the first potential evidence for the presence of a magnetic field around an exoplanet. The model is then extended to predict the shape of near-ultraviolet light curves around HD 189733b, another hot Jupiter that orbits a very bright star. By looking at the variability in these transit light curves over time, the evolution and structure of the stellar wind is investigated. By tracking the position of bumps in the transit light curve, it is shown here that the data collected by missions such as Kepler has the potential to reveal stellar butterfly patterns. Such patterns are intrinsically linked with the stellar dynamo which governs the properties of the stellar magnetic field. Finally, the support of large-scale magnetic loops on young stars is investigated. These loops trap large amounts of hot, dense material and so a rapid destabilisation could lead to a flaring event, which could have devastating consequences for a nearby exoplanet.
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Wellen, Jeremy W. "Characterization of soft-tissue response to mechanical loading using nuclear magnetic resonance (NMR) and functional magnetic resonance imaging (fMRI) of neuronal activity during sustained cognitive-stimulus paradigms." Link to electronic thesis, 2003. http://www.wpi.edu/Pubs/ETD/Available/etd-0430103-140128.
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Isaacs, Ian J. "The effects of pulsed static and oscillating magnetic fields on rat pineal serotonin N-acetyltransferase activity." Master's thesis, University of Cape Town, 1997. http://hdl.handle.net/11427/26990.
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Concerns about the possible hazardous effects of electromagnetic fields (EMF ' s) has resulted in attempts to address this issue. Several authors have shown that EMF exposure affects biological systems and more specifically the pineal enzyme, serotonin N-acetyltransferase (SNAT), inhibiting the enzyme and thus melatonin production. The enzyme assay required, for performing this type of work is crucial, as the natural decay of the enzyme could bias experimental results. An assay for measuring SNAT activity was assessed and then improved. The Ca²⁺ ion chelator, EGTA (2mM), preserved enzyme activity during pineal homogenisation. The enzyme is heat sensitive and thus keeping the homogenates on ice facilitated enzyme preservation. Not only was preservation of the enzyme crucial, but optimum substrate concentrations were required to measure maximum levels of SNAT activity. Maximum levels of activity were measured when I/10th of a pineal gland was incubated with 12mM tryptamine. At the specified tryptamine concentration, SNAT activity increased as the concentration of Acetyl CoA increased. The enzyme efficiency, as determined from its Km (8.19x10⁻⁴M), and the level of activity exceeded those measured in other laboratories. This assay was used to determine SNAT activity following magnetic field exposure. The magnetic field studies investigated the effects of pulsed static and oscillating magnetic fields on SNAT activity. Male Long Evans rats were housed in short and long photoperiods and were exposed for either 60mins., 30mins. or 15mins. to magnetic fields at different times during the dark phase. Rats were exposed to regularly repeated inversion of either the vertical or horizontal component of the earth' s magnetic field or to regularly repeated horizontal or vertical lOOμT DC field inversions. Pulsed static magnetic field exposure in all conditions had no significant inhibitory effect on SNAT activity. Oscillating magnetic field studies investigated the effect of exposure of rats to magnetic fields tuned to ion parametric resonance conditions for Ca²⁺. The ion parametric resonance model of Blanchard and Blackman was used to determine the exposure parameters. Rats were thus exposed for an hour to a vertical AC field, of strength 14.3μT (rms), frequency was 17.2Hz while the strength of the vertical DC field was 22.55μT, the existing vertical geomagnetic field strength. Under these conditions oscillating magnetic field exposure also had no significant inhibitory effect on SNAT activity.
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Palatucci, Mark M. "Thought Recognition: Predicting and Decoding Brain Activity Using the Zero-Shot Learning Model." Research Showcase @ CMU, 2011. http://repository.cmu.edu/dissertations/65.
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Machine learning algorithms have been successfully applied to learning classifiers in many domains such as computer vision, fraud detection, and brain image analysis. Typically, classifiers are trained to predict a class value given a set of labeled training data that includes all possible class values, and sometimes additional unlabeled training data.
Little research has been performed where the possible values for the class variable include values that have been omitted from the training examples. This is an important problem setting, especially in domains where the class value can take on many values, and the cost of obtaining labeled examples for all values is high.
We show that the key to addressing this problem is not predicting the held-out classes directly, but rather by recognizing the semantic properties of the classes such as their physical or functional attributes. We formalize this method as zero-shot learning and show that by utilizing semantic knowledge mined from large text corpora and crowd-sourced humans, we can discriminate classes without explicitly collecting examples of those classes for a training set.
As a case study, we consider this problem in the context of thought recognition, where the goal is to classify the pattern of brain activity observed from a non-invasive neural recording device. Specifically, we train classifiers to predict a specific concrete noun that a person is thinking about based on an observed image of that person’s neural activity.
We show that by predicting the semantic properties of the nouns such as “is it heavy?” and “is it edible?”, we can discriminate concrete nouns that people are thinking about, even without explicitly collecting examples of those nouns for a training set. Further, this allows discrimination of certain nouns that are within the same category with significantly higher accuracies than previous work.
In addition to being an important step forward for neural imaging and braincomputer- interfaces, we show that the zero-shot learning model has important implications for the broader machine learning community by providing a means for learning algorithms to extrapolate beyond their explicit training set.
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Yao, Bing. "ANALYSIS OF ELECTRICAL AND MAGNETIC BIO-SIGNALS ASSOCIATED WITH MOTOR PERFORMANCE AND FATIGUE." Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1140813534.
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Andersson, Louise. "Psychedelic agents : Changes induced in subjective experience and brain activity." Thesis, Högskolan i Skövde, Institutionen för biovetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-17308.
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This thesis combines phenomenological and neuroscientific research to elucidate the effects of psychedelic agents on the human brain, mind and psychological well-being. Psychoactive plants have been used for thousands of years for ceremonial and ritual purposes. Psychedelics are psychoactive substances that affect cognitive processes and alter perception, thoughts, and mood. Illegalization of psychedelics in the 1960s rendered them impossible to study empirically but in the last couple of decades, relaxed legal restrictions regarding research purposes, renewed interest in the effects of psychedelic drugs and new brain imaging techniques have started to reveal the possibilities of these mind-altering substances. Psychedelics mainly affect the serotonin receptor 5-HT2A which in turn affect the functioning of largescale cortical areas by changing cerebral blood flow, alpha oscillations, and functional connectivity. These cortical changes not only induce immediate alterations in perception and cognition but have been shown to have positive effects in therapeutic interventions for depression, anxiety, and addiction, and also positively affect well-being in general. Although the pharmacology and neurobiology of psychedelics are still poorly understood, the potential benefits justify empirical research on psychedelics in humans.
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Shibata, Sumiya. "Magnetoencephalography with temporal spread imaging to visualize propagation of epileptic activity." Kyoto University, 2017. http://hdl.handle.net/2433/226764.
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Khatamian, Yasha. "Investigating the limits of temporal clustering analysis for detecting epileptic activity in functional magnetic resonance imaging data." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=96861.
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Precise localization of epileptic activity is a necessity for those patients who may benefit from resective surgery. One common localization technique, EEG functional MRI (EEG-fMRI), localizes activity in an fMRI recording by finding blood oxygen level dependent (BOLD) signal correlates to epileptic events detected in a simultaneously recorded EEG. 2D temporal clustering analysis (2D-TCA) is a relatively new fMRI-based epileptic activity localization technique that breaks BOLD activity into components based on timing, finding epileptic activity without simultaneously recorded EEG. This study evaluated the ability of 2D-TCA to detect both simulated epileptic activity and activity detected in patients using EEG-fMRI. Although it was found that 2D-TCA could effectively detect epileptic activity with certain characteristics, it also detected activity not associated with epilepsy. As such, it was determined that 2D-TCA can only be used to validate epileptic activity localization by other means or to create hypotheses as to where activity may occur.<br>Une localisation précise de l'activité épileptique est une nécessité pour les patients qui pourraient bénéficier d'une opération résective. L'EEG-IRM fonctionnelle (EEG-IRMf) est une nouvelle technique de localisation qui localise l'activité épileptique dans un enregistrement IRMf en trouvant un signal « blood oxygen level dependent » (BOLD) qui correspond à des événements épileptiques détectés simultanément par un enregistrement EEG. L'analyse temporelle groupée 2D (ATG-2D) est une technique de localisation de l'activité épileptique relativement nouvelle, qui est basée sur des données IRMf. Pour trouver l'activité épileptique, elle décompose l'activité BOLD en différentes composantes selon le moment où elles surviennent sans recourir à un enregistrement EEG simultané. Cette étude évalue la capacité de la technique ATG-2D à détecter une activité épileptique simulée ainsi que sa capacité à détecter une activité épileptique précédemment détectée chez des patients avec EEG-IRMf. Même nous avons montré que la technique ATG-2D pouvait détecter de façon efficace une activité épileptique ayant certaines caractéristiques, il a aussi été trouvé qu'elle détectait de l'activité non épileptique. Il a été déterminé que la technique ATG-2D pouvait seulement être utilisée pour valider une activité épileptique localisée par d'autres moyens ou pour formuler des hypothèses concernant l'endroit où l'activité pourrait survenir.
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CODY, WAYNE LIVINGSTON. "SYNTHESIS, BIOLOGICAL ACTIVITY AND CONFORMATIONAL ANALYSIS OF FRAGMENT ANALOGUES OF ALPHA-MELANOTROPIN (PEPTIDE, STRUCTURE-FUNCTION, PHENYLGLYCINE, NMR, TETRAHYDROISOQUINOLINE-3-CARBOXYLATE)." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/188044.
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α-MSH (α-melanotropin) is a naturally occurring linear tridecapeptide (Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH₂) that is primarily known for its ability to stimulate integumental melanocytes and more recently has been implicated in a variety of physiological and neurological processes. It has been shown that substitution of D-phenylalanine in the seven position of this hormone led to an analogue with increased potency and prolonged biological activity. Furthermore, cyclization between the four and ten positions via a cystine bridge led to analogues with enhanced potency. In this regard, a series of conformationally restricted linear and cyclic fragment analogues of α-MSH have been prepared and carefully analyzed by both biological and biophysical methods. Conformational restriction was incorporated in α-MSH fragment analogues, by: (1) substitution of sterically restricted amino acids into the native sequence; or (2) cyclization of the peptide via a disulfide bridge. Due to the biological differences observed for these synthetic α-MSH fragment analogues, a complete conformational analysis by both proton and carbon-13 NMR was performed. The conformational preferences of the backbone were examined by analyzing: (1) the alpha proton chemical shifts; (2) the amide proton chemical shifts; (3) the amide proton coupling constants; and (4) the amide proton temperature dependencies. The data suggests that the peptide backbone in both linear and cyclic analogues possesses a great amount of conformational flexibility with no hydrogen-bonded stabilization. The three-dimensional orientations of individual amino acid side chains have been examined by analyzing: (1) the chemical shifts of the side chain protons; (2) the alpha-beta coupling constants (corresponding rotamer populations); and (3) the carbon-13 spin lattice relaxation times (T₁). A careful examination a the chemical shifts of the side chains of individual amino acids in linear α-MSH fragments reveals that incorporation of an aromatic D-amino acid in the seven position results in an interaction of the side chains of the six, seven and eight positions. In addition, the low carbon-13 spin-lattice relaxation times for the β-carbons of the 5-9 sequence for both Ac-[Nle⁴]-α-MSH₄₋₁₁-NH₂ and Ac-[Nle⁴, D-Phe⁷]-α-MSH₄₋₁₁-NH₂, provides further evidence for an interaction of these side chains. Similar shielding patterns have been observed for the cyclic α-MSH fragment analogues depending upon whether L- or D-phenylalanine is incorporated in the seven position. Considering the differences in biological potency and the similarities in the NMR parameters between the linear and cyclic homologs, it can be concluded that the conformational properties that determine biological potency are too subtle to be measured by present NMR methodology. Furthermore, the similarity of the NMR shielding patterns suggests that a 23-membered ring is too large to impart significant conformational constraints on the peptide backbone or amino acid side chains.
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Mani, Ashwini. "Study of partial discharge activity in magnet wires aged by combined stresses." Master's thesis, Mississippi State : Mississippi State University, 2005. http://library.msstate.edu/etd/show.asp?etd=etd-11072005-171152.
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Stirrat, Colin Gordon. "Detection of cardiac inflammation using ultrasmall superparamagnetic particles of iron oxide-enhanced magnetic resonance imaging." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31064.
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Background Ultrasmall superparamagnetic particles of iron oxide (USPIO)- enhanced magnetic resonance imaging (MRI) can detect tissue-resident inflammatory macrophages and identify cellular inflammation. Clinical studies using this non-invasive technique are now emerging. Objectives The aims of this thesis were (i) to determine whether USPIO-enhanced MRI can detect and serially monitor myocardial inflammation after myocardial infarction (MI) using single and repeated USPIO administration, (ii) to report a range of normal R2* (1/T2*) values at 1.5 tesla (T) and 3 T in healthy myocardium and other tissues before and after USPIO administration, (iii) to determine whether USPIO-enhanced MRI can detect myocardial inflammation in acute myocarditis, and (iv) to determine whether USPIO-enhanced MRI can detect myocardial inflammation in patients with a prior cardiac transplant. Methods Thirty-one patients were recruited following acute MI and followed up for 3 months with repeated T2 and USPIO-enhanced T2* mapping 3 T MRI. Twenty healthy volunteers were recruited: 10 imaged each at 1.5 T and 3 T. T2 and USPIO-enhanced T2* mapping MRI was conducted. Fourteen patients with suspected acute myocarditis underwent T2 and USPIO-enhanced T2* mapping 3 T MRI, with further imaging at 3 months. Eleven patients with prior cardiac transplant underwent T2 and USPIO-enhanced T2* mapping 1.5 T MRI with further imaging at 3 months. Regions of interest within the myocardium, along with other tissues, were selected for analysis. Pre-contrast T2 values, and the change in R2* due to USPIO from baseline to 24 hours after USPIO were compared for each region of interest. Results In patients with MI, USPIO uptake in the infarct zone peaked at days 2-3, and greater USPIO uptake was detected in the infarct zone compared to remote myocardium in the first 2 weeks after myocardial infarction. In contrast, T2-defined myocardial oedema peaked at days 3-9 and remained increased in the infarct zone throughout the 3-month follow up period. Histology confirmed colocalisation of iron and macrophages within the infarcted, but not the non-infarcted, myocardium. In healthy volunteers, we reported a range of normal myocardial and tissue R2* values at baseline, and following USPIO. Tissues showing greatest USPIO enhancement were organs of the reticuloendothelial system: the liver, spleen and bone marrow. Myocarditis was confirmed in 9 of the 14 suspected cases of myocarditis. There was greater myocardial oedema, but no demonstrable difference in USPIO enhancement, in inflamed myocardial regions in patients with myocarditis when compared to healthy myocardium. We recorded an improvement in cardiac function and reduced imaging measures of inflammation after 3 months. Ten patients with cardiac transplant were retained for analysis. Measures of myocardial oedema were greater in patients with cardiac transplant than healthy volunteers. There was no difference in the change in R2* due to USPIO between patients with transplantation and healthy volunteers. Imaging recordings did not change when repeated at 3 months. Conclusions Myocardial macrophage activity can be detected using USPIO-enhanced MRI in the first 2 weeks following acute MI. This observed pattern of cellular inflammation is distinct, and provides complementary information to, the more prolonged myocardial oedema detectable using T2 mapping. In patients with acute myocarditis, USPIO-enhanced MRI does not provide additional clinically relevant information to standard clinical MRI sequences. This suggests that tissue-resident macrophages do not provide a substantial contribution to the myocardial inflammation in this condition. Stable patients with cardiac transplantation have increased myocardial T2 values, consistent with resting myocardial oedema or fibrosis. In contrast, USPIO-enhanced MRI is normal and stable over time suggesting the absence of chronic macrophage-driven cellular inflammation. In conclusion, this imaging technique holds promise as a non-invasive method of assessing and monitoring macrophage-driven myocardial inflammation after myocardial infarction with potential application to diagnosis, risk stratification and assessment of novel anti-inflammatory therapeutic interventions. It remains to be determined whether USPIO-enhanced MRI may be able to identify myocardial inflammation in other myocardial inflammatory conditions including acute cardiac transplant rejection.
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Lotz, Stefanus Ignatius. "Empirical modelling of the solar wind influence on Pc3 pulsation activity." Thesis, Rhodes University, 2012. http://hdl.handle.net/10962/d1005249.
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Geomagnetic pulsations are ultra-low frequency (ULF) oscillations of the geomagnetic field that have been observed in the magnetosphere and on the Earth since the 1800’s. In the 1960’s in situ observations of the solar wind suggested that the source of pulsation activity must lie beyond the magnetosphere. In this work the influence of several solar wind plasma and interplanetary magnetic field (IMF) parameters on Pc3 pulsations are studied. Pc3 pulsations are a class of geomagnetic pulsations with frequency ranging between 22 and 100 mHz. A large dataset of solar wind and pulsation measurements is employed to develop two empirical models capable of predicting the Pc3 index (an indication of Pc3 intensity) at one hour and five minute time resolution, respectively. The models are based on artificial neural networks, due to their ability to model highly non-linear interactions between dependent and independent variables. A robust, iterative process is followed to find and rank the set of solar wind input parameters that optimally predict Pc3 activity. According to the parameter selection process the input parameters to the low resolution model (1 hour data) are, in order of importance, solar wind speed, a pair of time-based parameters, dynamic solar wind pressure, and the IMF orientation with respect to the Sun-Earth line (i.e. the cone angle). Input parameters to the high resolution model (5 minute data) are solar wind speed, cone angle, solar wind density and a pair of time-based parameters. Both models accurately predict Pc3 intensity from unseen solar wind data. It is observed that Pc3 activity ceases when the density in the solar wind is very low, even while other conditions are favourable for the generation and propagation of ULF waves. The influence that solar wind density has on Pc3 activity is studied by analysing six years of solar wind and Pc3 measurements at one minute resolution. It is suggested that the pause in Pc3 activity occurs due to two reasons: Firstly, the ULF waves that are generated in the region upstream of the bow shock does not grow efficiently if the solar wind density is very low; and secondly, waves that are generated cannot be convected into the magnetosphere because of the low Mach number of the solar wind plasma due to the decreased density.
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Still, Patrick C. "Cytotoxic Alkaloids from Microcos paniculata with Activity at Neuronal Nicotinic Receptors." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365688930.
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Murray, Lawrence. "Bayesian learning of continuous time dynamical systems with applications in functional magnetic resonance imaging." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/4157.
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Temporal phenomena in a range of disciplines are more naturally modelled in continuous-time than coerced into a discrete-time formulation. Differential systems form the mainstay of such modelling, in fields from physics to economics, geoscience to neuroscience. While powerful, these are fundamentally limited by their determinism. For the purposes of probabilistic inference, their extension to stochastic differential equations permits a continuous injection of noise and uncertainty into the system, the model, and its observation. This thesis considers Bayesian filtering for state and parameter estimation in general non-linear, non-Gaussian systems using these stochastic differential models. It identifies a number of challenges in this setting over and above those of discrete time, most notably the absence of a closed form transition density. These are addressed via a synergy of diverse work in numerical integration, particle filtering and high performance distributed computing, engineering novel solutions for this class of model. In an area where the default solution is linear discretisation, the first major contribution is the introduction of higher-order numerical schemes, particularly stochastic Runge-Kutta, for more efficient simulation of the system dynamics. Improved runtime performance is demonstrated on a number of problems, and compatibility of these integrators with conventional particle filtering and smoothing schemes discussed. Finding compatibility for the smoothing problem most lacking, the major theoretical contribution of the work is the introduction of two novel particle methods, the kernel forward-backward and kernel two-filter smoothers. By harnessing kernel density approximations in an importance sampling framework, these attain cancellation of the intractable transition density, ensuring applicability in continuous time. The use of kernel estimators is particularly amenable to parallelisation, and provides broader support for smooth densities than a sample-based representation alone, helping alleviate the well known issue of degeneracy in particle smoothers. Implementation of the methods for large-scale problems on high performance computing architectures is provided. Achieving improved temporal and spatial complexity, highly favourable runtime comparisons against conventional techniques are presented. Finally, attention turns to real world problems in the domain of Functional Magnetic Resonance Imaging (fMRI), first constructing a biologically motivated stochastic differential model of the neural and hemodynamic activity underlying the observed signal in fMRI. This model and the methodological advances of the work culminate in application to the deconvolution and effective connectivity problems in this domain.
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Rothmeier, Greggory H. "Brain tissue temperature dynamics during functional activity and possibilities for optical measurement techniques." Digital Archive @ GSU, 2012. http://digitalarchive.gsu.edu/phy_astr_theses/14.
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Regional tissue temperature dynamics in the brain are determined by the balance of the metabolic heat production rate and heat exchange with blood flowing through capillaries embedded in the brain tissue, the surrounding tissues and the environment. Local changes in blood flow and metabolism during functional activity can upset this balance and induce transient temperature changes. Invasive experimental studies in animal models have estab- lished that the brain temperature changes during functional activity are observable and a definitive relationship exists between temperature and brain activity. We present a theoreti- cal framework that links tissue temperature dynamics with hemodynamic activity allowing us to non-invasively estimate brain temperature changes from experimentally measured blood- oxygen level dependent (BOLD) signals. With this unified approach, we are able to pinpoint the mechanisms for hemodynamic activity-related temperature increases and decreases. In addition to these results, the potential uses and limitations of optical measurements are dis- cussed.
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Dixon, Aisling L. "Measurement of cerebral activity in response to dopaminergic drugs : studies using functional magnetic resonance imaging in the rat." Thesis, University of Leicester, 2002. http://hdl.handle.net/2381/31347.
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Dopamine is involved with many aspects of normal brain function, such as movement, emotion and motivation and its dysregulation is associated with diseases, such as schizophrenia and Parkinson's disease. Drug treatments for these conditions may cause side effects, hence, it is important to understand their mechanisms. Amphetamine administration is a popular model for studying reward, schizophrenia and behaviour. I modified this model to investigate changes in functional dopaminergic activity in the whole rat brain using Pharmacological magnetic resonance imaging (PhMRI). Halothane proved to be suitable anaesthetic for these experiments because it did not affect stimulated dopamine release unlike a-choralose. Acute amphetamine challenge caused widespread increases in blood-oxygenation-level-dependent (BOLD) signal intensity in many subcortical dopaminergic structures, with a rim of negative BOLD observed in the cortex. Amphetamine acts by blocking reuptake of dopamine leading to activation of all dopamine receptor subtypes. To tease apart the mechanisms of the amphetamine response, I pretreated rats with specific antagonists prior to amphetamine. This had contrasting effects on the BOLD signal. D1 antagonist blocked most of the positive BOLD response to amphetamine whereas the D2 antagonist predominantly blocked and negative BOLD response. The acute effects of selective D1 and D2 agonists and antagonists on the BOLD response were observed in subcortical dopaminergic structures, largely corresponding with stimulation or blockade of the specific receptors types. My experiments show that the recently-developed phMRI technique can be used to dissect the mechanisms of drug action in the whole brain.