No description available.

In a multi-year project at Swerea Swecast AB studies on influence of dissolved gas on inclusions have been made. The knowledge about these parameters could be used to increase the quality of the final steel casting. The purpose of this thesis was to closer examine the impact of the oxygen level on inclusions. The questions asked were:  What was the amount of inclusions at different levels of oxygen?  What was the size of these inclusions at different levels of oxygen?  What does the inclusions consist of at different levels of oxygen? This was studied by measuring and sampling, sample preparation and microscopic analysis using an optical microscope and a scanning electron microscope (SEM). Measurements and sampling was performed at Smålands Stålgjuteri AB in Eksjö and at Swerea Swecast AB in Jönköping. At Smålands Stålgjuteri AB the measurements were performed in production while at Swerea Swecast AB the measurements were made in a way that the oxygen levels were provoked. The sample preparations were made at Swerea Swecast AB’s workshop and lab. Scanning electron microscopy (SEM) and light optic microscopy was used for the analysis. The data from these analyses were processed and charts and tables were prepared. The results from the light microscopy shows a difference in microstructure between the two samplings. The charts and tables that were obtained indicated that the number of inclusions correlated with the oxygen level. However, only to a certain extent because other parameters such as time and amount of deoxidizer have a greater effect. The size of the inclusions decreased with decreased oxygen level during deoxidation. As mentioned in the pre-study, oxides are the most common type of inclusions in steel. This was also the case in the current study. The results showed that the oxygen level can be used as an indicator of the necessary addition of deoxidiser. / I ett flerårigt projekt på Swerea Swecast AB har undersökningar kring gasers inverkan på mängden inneslutningar i gjutstål genomförts. Kunskap kring hur parametrarna ser ut skulle användas för att höja kvaliteten på gjutgods. Syftet med det här arbetet var att noggrannare undersöka den fria syrehaltens påverkan på inneslutningar. Frågeställningarna var:  Hur stort antal inneslutningar fanns vid olika syrehalter?  Hur stora var dessa inneslutningar vid olika syrehalter?  Vad innehöll dessa inneslutningar vid olika syrehalter? Detta undersöktes genom mätning och provtagning, provberedning och analys. Mätning och provtagning utfördes på Smålands Stålgjuteri AB i Eksjö och på Swerea Swecast AB i Jönköping. Vid Smålands Stålgjuteri AB utfördes mätningar under ordinarie produktion medan mätningarna på Swerea Swecast AB gjordes så att olika syrehalter provocerades fram. Provberedningen och analysen gjordes i Swerea Swecast ABs verkstad och labb. Analysen gjordes med hjälp av svepelektronmikroskop (SEM) och ljusmikroskop. Data från dessa analyser bearbetades i Excel och diagram samt tabeller togs fram. Resultatet från ljusmikroskopbilderna visar en skillnad i mikrostrukturer mellan de två gjutförsöken. Ur diagram och tabeller kan utläsas att antalet inneslutningar korrelerar med syrehalten. Dock bara till viss del eftersom andra parametrar såsom tid och mängd desoxidationsmedel har större påverkan. Storleken på inneslutningarna minskade tillsammans med syrehalten vid desoxidation. Vid en överdriven desoxidation kunde inneslutningar ansamlas i korngränserna vilket kraftigt försämrar de mekaniska egenskaperna. I förundersökningen nämndes att oxider var de vanligaste inneslutningarna i stål. Så var fallet även här. Resultatet visar tydligt att syrehalten kan användas som indikator för hur stor tillsats av desoxidationsmedel som behövs.

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.

Until recently, obtaining rest-frame optical spectra of galaxies at z > 1 was a time consuming and challenging observation due to the difficult nature of near-infrared (near-IR) spectroscopy. However, with the advent of second generation ground-based near-IR spectrographs (e.g. KMOS, MOSFIRE), and the new low resolution near-IR grisms on the Hubble Space Telescope (HST), we have entered a new era in the study of high redshift galaxies. This thesis explores the physical properties of star-forming galaxies in the redshift range 1 < z < 3 by utilising a custom reduction of the 3D-HST near-IR grism spectroscopic survey. One of the most important observational constraints on the evolution of galaxies is the mass-metallicity relation (MZR), which is sensitive to both the star-formation history and various inflow/outflow processes. I use the 3D-HST spectra to provide a new constraint on the MZR at 2:0 < z < 2:3, and moreover measure the O/H abundance directly from the oxygen and hydrogen emission lines ([OII], [OIII] and Hβ) as opposed to the more common method at high redshift of inferring O/H from the N/H ratio (via [NII] and Hα). I show that the traditional form of the MZR is recovered from the 3D-HST data, with metallicity increasing with the stellar mass of a galaxy. However, the absolute metallicity values I derive are inconsistent with previous N/H-based measurements of metallicity at these redshifts. Moreover, I show that the 3D-HST data is inconsistent with the `fundamental metallicity relation' (FMR), and that, contrary to previous claims, this local Universe relation may not hold out to z & 2. To investigate this metallicity discrepancy further, I measure the evolution of the [OIII]/Hβ nebular emission line ratio in the 3D-HST spectra over the redshift range 1:3 < z < 2:3. I compare this observed line ratio evolution with state-of-the- art theoretical models which take into account the independent evolution of the ionization parameter, electron density and metallicity of star-forming regions with redshift. The homogeneous 3D-HST dataset allows me to perform a consistent analysis of this evolution which takes into account line luminosity selection effects. I show that, according to models, the observed [OIII]/Hβ evolution cannot be accounted for by pure metallicity evolution. Instead I am able to infer that the line ratio evolution is more consistent with, at the very least, an evolution to stronger ionizing conditions at high redshift, and perhaps even denser star-forming regions. I explore how this result can also explain the observed discrepancy between high redshift metallicity measurements. In light of this finding, I revisit the MZR at z >~ 2 and employ a purely theoretical approach to inferring metallicities from nebular lines, which is able to account for an evolution in ionization conditions. I then use a selection of galaxies from the local Universe, which mimic the properties of high redshift galaxies, to derive a more robust ionization sensitive, conversion, between N/H and O/H. With this new conversion which I am able to bring the previous inconsistent metallicity measurements at z >~ 2 back into agreement. Finally, I am able to show that, in this new formalism, the metallicity evolution between z = 2 and z = 3 is perhaps not as large as previously reported. To conclude I discuss ongoing work as part of the KMOS Deep Survey (KDS) being undertaken with the near near-IR Multi-Object Spectrograph KMOS on the VLT. I describe the observations and data reduction that has been completed to date and describe how this instrument will allow me to extend the work presented in this thesis to z > 3. I also introduce FIGS, a new HST near-IR grism survey seeking to spectroscopically identify galaxies at 5:5 < z < 8:5 and work I have begun in exploring this dataset.

<p>Diffusion tensor (DT) and blood oxygen-level dependent (BOLD) imaging are two noninvasive magnetic resonance (MR) techniques that have been used to probe skeletal muscle microstructure and microvasculature, respectively. Over a series of four studies, the work in this thesis aimed at furthering our understanding of baseline DT metrics and BOLD signals in lower limb muscles (calf and foot) of healthy young subjects. Since postural changes have been shown to alter numerous quantities, including fluid volumes and muscle cross sectional area, DT indices and BOLD signal characteristics were examined in response to movement from upright to supine position.</p> <p>Reductions of 3.2-6.7% and 3.4-7.5% were measured in calf DT eigenvalues and apparent diffusion coefficient (ADC) in the various muscles, following 34 and 64 minutes of supine rest, respectively (P</p> <p>Establishment of baseline diffusion metrics in the foot region was feasible (chapter 6). Examination of foot DT indices in response to positional change showed that the metrics decreased from 2.7-4.6% following 34 minutes of supine rest (P</p> / Doctor of Philosophy (PhD)

No description available.

The blood oxygen level dependent functional MRI (BOLD-fMRI) signal is an indirect measure of the neuronal activity that most BOLD studies are interested in. This thesis uses generative embedding algorithms to investigate some of the challenges and opportunities that this presents for BOLD imaging. It is standard practice to analyse BOLD signals using general linear models (GLMs) that assume fixed neurovascular coupling. However, this assumption may cause false positive or negative neural activations to be detected if the biological manifestations of brain diseases, disorders and pharmaceutical drugs (termed "neuromodulations") alter this coupling. Generative embedding can help overcome this problem by identifying when a neuromodulation confounds the standard GLM. When applied to anaesthetic neuromodulations found in preclinical imaging data, Fentanyl has the smallest confounding effect and Pentobarbital has the largest, causing extremely significant neural activations to go undetected. Half of the anaesthetics tested caused overestimation of the neuronal activity but the other half caused underestimation. The variability in biological action between anaesthetic modulations in identical brain regions of genetically similar animals highlights the complexity required to comprehensively account for factors confounding neurovascular coupling in GLMs generally. Generative embedding has the potential to augment established algorithms used to compensate for these variations in GLMs without complicating the standard (ANOVA) way of reporting BOLD results. Neuromodulation of neurovascular coupling can also present opportunities, such as improved diagnosis, monitoring and understanding of brain diseases accompanied by neurovascular uncoupling. Information theory is used to show that the discriminabilities of neurodegenerative-diseased and healthy generative posterior parameter spaces make generative embedding a viable tool for these commercial applications, boasting sensitivity to neurovascular coupling nonlinearities and biological interpretability. The value of hybrid neuroimaging systems over separate neuroimaging technologies is found to be greatest for early-stage neurodegenerative disease.

Ce projet illustre cinq études, mettant l'emphase sur le développement d'une nouvelle approche diagnostique cardiovasculaire afin d'évaluer le niveau d’oxygène contenu dans le myocarde ainsi que sa fonction microvasculaire. En combinant une séquence de résonance magnétique cardiovasculaire (RMC) pouvant détecter le niveau d’oxygène (OS), des manœuvres respiratoires ainsi que des analyses de gaz artériels peuvent être utilisés comme procédure non invasive destinée à induire une réponse vasoactive afin d’évaluer la réserve d'oxygénation, une mesure clé de la fonction vasculaire. Le nombre de tests diagnostiques cardiaques prescrits ainsi que les interventions, sont en pleine expansion. L'imagerie et tests non invasifs sont souvent effectués avant l’utilisation de procédures invasives. L'imagerie cardiaque permet d’évaluer la présence ou absence de sténoses coronaires, un important facteur économique dans notre système de soins de santé. Les techniques d'imagerie non invasives fournissent de l’information précise afin d’identifier la présence et l’emplacement du déficit de perfusion chez les patients présentant des symptômes d'ischémie myocardique. Néanmoins, plusieurs techniques actuelles requièrent la nécessité de radiation, d’agents de contraste ou traceurs, sans oublier des protocoles de stress pharmacologiques ou physiques. L’imagerie RMC peut identifier une sténose coronaire significative sans radiation. De nouvelles tendances d’utilisation de RMC visent à développer des techniques diagnostiques qui ne requièrent aucun facteur de stress pharmacologiques ou d’agents de contraste. L'objectif principal de ce projet était de développer et tester une nouvelle technique diagnostique afin d’évaluer la fonction vasculaire coronarienne en utilisant l' OS-RMC, en combinaison avec des manœuvres respiratoires comme stimulus vasoactif. Ensuite, les objectifs, secondaires étaient d’utilisés l’OS-RMC pour évaluer l'oxygénation du myocarde et la réponse coronaire en présence de gaz artériels altérés. Suite aux manœuvres respiratoires la réponse vasculaire a été validée chez un modèle animal pour ensuite être utilisé chez deux volontaires sains et finalement dans une population de patients atteints de maladies cardiovasculaires. Chez le modèle animal, les manœuvres respiratoires ont pu induire un changement significatif, mesuré intrusivement par débit sanguin coronaire. Il a été démontré qu’en présence d'une sténose coronarienne hémodynamiquement significative, l’OS-RMC pouvait détecter un déficit en oxygène du myocarde. Chez l’homme sain, l'application de cette technique en comparaison avec l'adénosine (l’agent standard) pour induire une vasodilatation coronarienne et les manœuvres respiratoires ont pu induire une réponse plus significative en oxygénation dans un myocarde sain. Finalement, nous avons utilisé les manœuvres respiratoires parmi un groupe de patients atteint de maladies coronariennes. Leurs myocardes étant altérées par une sténose coronaire, en conséquence modifiant ainsi leur réponse en oxygénation. Par la suite nous avons évalué les effets des gaz artériels sanguins sur l'oxygénation du myocarde. Ils démontrent que la réponse coronarienne est atténuée au cours de l’hyperoxie, suite à un stimuli d’apnée. Ce phénomène provoque une réduction globale du débit sanguin coronaire et un déficit d'oxygénation dans le modèle animal ayant une sténose lorsqu’un supplément en oxygène est donné. En conclusion, ce travail a permis d'améliorer notre compréhension des nouvelles techniques diagnostiques en imagerie cardiovasculaire. Par ailleurs, nous avons démontré que la combinaison de manœuvres respiratoires et l’imagerie OS-RMC peut fournir une méthode non-invasive et rentable pour évaluer la fonction vasculaire coronarienne régionale et globale. / This project encompasses five studies, which focus on developing a new cardiovascular diagnostic approach for assessing myocardial oxygenation and microvascular function. In combination with oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR) imaging, breathing maneuvers and altered arterial blood gases can be used as a non-invasive method for inducing a vasoactive response to test the oxygenation reserve, a key measurement in vascular function. The number of prescribed cardiac diagnostic tests and interventions is rapidly growing. In particular, imaging and other non-invasive tests are frequently performed prior to invasive procedures. One of the most common uses of cardiac imaging is for the diagnosis of significant coronary artery stenosis, a critical cost factor in today’s health care system. Non-invasive imaging techniques provide the most reliable information for the presence and location of perfusion or oxygenation deficits in patients with symptoms suggestive of myocardial ischemia, yet many current techniques suffer from the need for radiation, contrast agents or tracers, and pharmacological or physical stress protocols. CMR imaging can identify significant coronary artery stenosis without radiation and new trends in CMR research aim to develop diagnostic techniques that do not require any pharmacological stressors or contrast agents. For this project, the primary aim was to develop and test a new diagnostic technique to assess coronary vascular function using OS-CMR in combination with breathing maneuvers as the vasoactive stimulus. Secondary aims then used OS-CMR to assess myocardial oxygenation and the coronary response in the presence of altered arterial blood gases. An animal model was used to validate the vascular response to breathing maneuvers before translating the technique to human subjects into both healthy volunteers, and a patient population with cardiac disease. In the animal models, breathing maneuvers could induce a significant change in invasively measured coronary blood flow and it was demonstrated that in the presence of a haemodynamically significant coronary stenosis, OS-CMR could detect a myocardial oxygen deficit. This technique was then applied in a human model, with healthy participants. In a direct comparison to the infusion of the coronary vasodilator adenosine, which is considered a standard agent for inducing vasodilation in cardiac imaging, breathing maneuvers induced a stronger response in oxygenation of healthy myocardium. The final study then implemented the breathing maneuvers in a patient population with coronary artery disease; in which myocardium compromised by a coronary stenosis had a compromised oxygenation response. Furthermore, the observed effects of arterial blood gases on myocardial oxygenation were assessed. This demonstrated that the coronary response to breath-hold stimuli is attenuated during hyperoxia, and this causes an overall reduction in coronary blood flow, and consequently an oxygenation deficit in a coronary stenosis animal model when supplemental oxygen is provided. In conclusion, this work has improved our understanding of potential new diagnostic techniques for cardiovascular imaging. In particular, it demonstrated that combining breathing maneuvers with oxygenation-sensitive CMR can provide a non-invasive and cost-effective method for assessing global and regional coronary vascular function.

Blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging enables non-invasive spatial mapping of changes in cerebral blood flow (CBF). By applying a vasodilatory stimulus (such as inhaled CO2) during BOLD MR imaging, one can measure cerebral vasodilatory capacity. "Cerebrovascular reactivity" (CVR) is defined as the change in CBF per unit of vasodilatory stimulus. Vasodilatory capacity is clinically important as vasodilatation is a mechanism by which the brain maintains constant CBF despite reductions in cerebral perfusion pressure.ii Patients with arterial narrowing commonly demonstrate a paradoxical response: vasodilatory stimulus-induced reduction of BOLD MR signal. BOLD MR depends on CBF but on other factors too. Does a reduction of BOLD MR signal indicate a decrease in flow? Does BOLD MR CVR correlate with CVR measured using arterial spin labeling (ASL) MR? I studied thirty-eight patients with stenosis of brain-supplying arteries and found that the BOLD CVR and ASL CVR results correlate strongly (R=0.83, P<0.0001 for cerebral hemispheric gray matter). The second study aimed to determine whether preoperative CVR predicts the hemodynamic effect of extracranial-intracranial bypass surgery. Whereas prior studies relied on right-left interhemispheric CVR asymmetry indices, this study used “absolute” CVR from each hemisphere. I studied twenty-five patients with intracranial arterial stenosis. I found that the group with normal pre-operative CVR showed no change in CVR following bypass surgery (0.22% ± 0.05% to 0.22% ± 0.01% (mean ± SD)(P=0.881)), the group with reduced pre-operative CVR demonstrated an improvement (0.08% ± 0.05% to 0.21 ± 0.08% (mean ± SD)(P<0.001)), and the group with paradoxical pre-operative CVR demonstrated the greatest improvement (-0.04% ± 0.03% to 0.27% ± 0.03% (P=0.028)). ii Patients with arterial narrowing commonly demonstrate a paradoxical response: vasodilatory stimulus-induced reduction of BOLD MR signal. BOLD MR depends on CBF but on other factors too. Does a reduction of BOLD MR signal indicate a decrease in flow? Does BOLD MR CVR correlate with CVR measured using arterial spin labeling (ASL) MR? I studied thirty-eight patients with stenosis of brain-supplying arteries and found that the BOLD CVR and ASL CVR results correlate strongly (R=0.83, P<0.0001 for cerebral hemispheric gray matter). The second study aimed to determine whether preoperative CVR predicts the hemodynamic effect of extracranial-intracranial bypass surgery. Whereas prior studies relied on right-left interhemispheric CVR asymmetry indices, this study used “absolute” CVR from each hemisphere. I studied twenty-five patients with intracranial arterial stenosis. I found that the group with normal pre-operative CVR showed no change in CVR following bypass surgery (0.22% ± 0.05% to 0.22% ± 0.01% (mean ± SD)(P=0.881)), the group with reduced pre-operative CVR demonstrated an improvement (0.08% ± 0.05% to 0.21 ± 0.08% (mean ± SD)(P<0.001)), and the group with paradoxical pre-operative CVR demonstrated the greatest improvement (-0.04% ± 0.03% to 0.27% ± 0.03% (P=0.028)). The third study arose from an unexpected observation: paradoxical reactivity in the white matter of young healthy subjects. I evaluated healthy subjects using BOLD CVR and ASL CVR, transformed all CVR maps into a common brain space, and generated composite maps of CVR. Composite maps confirmed regions of significant paradoxical iii reactivity in the white matter. These regions may represent the physiological correlate of previously anatomically defined border-zones (watershed zones). The regions match the locations where elderly patients develop white matter rarefaction, so-called leukoaraiosis.

Blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging enables non-invasive spatial mapping of changes in cerebral blood flow (CBF). By applying a vasodilatory stimulus (such as inhaled CO2) during BOLD MR imaging, one can measure cerebral vasodilatory capacity. "Cerebrovascular reactivity" (CVR) is defined as the change in CBF per unit of vasodilatory stimulus. Vasodilatory capacity is clinically important as vasodilatation is a mechanism by which the brain maintains constant CBF despite reductions in cerebral perfusion pressure.ii Patients with arterial narrowing commonly demonstrate a paradoxical response: vasodilatory stimulus-induced reduction of BOLD MR signal. BOLD MR depends on CBF but on other factors too. Does a reduction of BOLD MR signal indicate a decrease in flow? Does BOLD MR CVR correlate with CVR measured using arterial spin labeling (ASL) MR? I studied thirty-eight patients with stenosis of brain-supplying arteries and found that the BOLD CVR and ASL CVR results correlate strongly (R=0.83, P<0.0001 for cerebral hemispheric gray matter). The second study aimed to determine whether preoperative CVR predicts the hemodynamic effect of extracranial-intracranial bypass surgery. Whereas prior studies relied on right-left interhemispheric CVR asymmetry indices, this study used “absolute” CVR from each hemisphere. I studied twenty-five patients with intracranial arterial stenosis. I found that the group with normal pre-operative CVR showed no change in CVR following bypass surgery (0.22% ± 0.05% to 0.22% ± 0.01% (mean ± SD)(P=0.881)), the group with reduced pre-operative CVR demonstrated an improvement (0.08% ± 0.05% to 0.21 ± 0.08% (mean ± SD)(P<0.001)), and the group with paradoxical pre-operative CVR demonstrated the greatest improvement (-0.04% ± 0.03% to 0.27% ± 0.03% (P=0.028)). ii Patients with arterial narrowing commonly demonstrate a paradoxical response: vasodilatory stimulus-induced reduction of BOLD MR signal. BOLD MR depends on CBF but on other factors too. Does a reduction of BOLD MR signal indicate a decrease in flow? Does BOLD MR CVR correlate with CVR measured using arterial spin labeling (ASL) MR? I studied thirty-eight patients with stenosis of brain-supplying arteries and found that the BOLD CVR and ASL CVR results correlate strongly (R=0.83, P<0.0001 for cerebral hemispheric gray matter). The second study aimed to determine whether preoperative CVR predicts the hemodynamic effect of extracranial-intracranial bypass surgery. Whereas prior studies relied on right-left interhemispheric CVR asymmetry indices, this study used “absolute” CVR from each hemisphere. I studied twenty-five patients with intracranial arterial stenosis. I found that the group with normal pre-operative CVR showed no change in CVR following bypass surgery (0.22% ± 0.05% to 0.22% ± 0.01% (mean ± SD)(P=0.881)), the group with reduced pre-operative CVR demonstrated an improvement (0.08% ± 0.05% to 0.21 ± 0.08% (mean ± SD)(P<0.001)), and the group with paradoxical pre-operative CVR demonstrated the greatest improvement (-0.04% ± 0.03% to 0.27% ± 0.03% (P=0.028)). The third study arose from an unexpected observation: paradoxical reactivity in the white matter of young healthy subjects. I evaluated healthy subjects using BOLD CVR and ASL CVR, transformed all CVR maps into a common brain space, and generated composite maps of CVR. Composite maps confirmed regions of significant paradoxical iii reactivity in the white matter. These regions may represent the physiological correlate of previously anatomically defined border-zones (watershed zones). The regions match the locations where elderly patients develop white matter rarefaction, so-called leukoaraiosis.