Les propriétés géochimiques particulières du molybdène vis-à-vis du potentiel d'oxygénation en milieu aqueux en font un élément particulièrement utilisé pour déterminer le degré d'oxygénation du milieu dans lequel un dépôt a sédimenté. Dans un premier temps, ce travail de thèse présente une alternative aux méthodes d'extraction du molybdène utilisées jusqu'ici. Les principales méthodes de purification couramment utilisées sur échantillons géologiques se décomposent en deux phases : une purification au travers d'une résine anionique, puis une purification au travers d'une résine cationique. La méthode proposée ici, initialement prévue pour permettre des analyses en Sample-Standard-Bracketing (SSB), permet d'isoler quantitativement le molybdène du reste de la matrice géologique en un seul passage sur résine anionique. La purification s'avère également suffisamment efficace pour effectuer des analyses en utilisant la méthode du double-spike. Une comparaison de ces deux méthodes de correction du fractionnement instrumental a permis d'évaluer les limites de l'utilisation du SSB par rapport au double-spike. Dans un second temps, cette chimie a été appliquée dans le cadre d'une étude géochimique approfondie d'un gisement fossilifère extrêmement riche: le Lagerstätte de Sirius Passet situé au nord du Groenland. Associée aux critères paléontologiques, cette étude indique que ces sédiments se sont déposés dans un milieu au moins partiellement oxygéné, sous forme de boues sédimentaires très peu propices aux échanges avec la colonne d'eau. Le contexte paléogéographique, les analyses chimiques et les observations microscopiques suggèrent que ces boues sont principalement d'origine éolienne.

Neurons perform complex computations, communications and precise transmissions of information in the form of action potentials (APs). The high level of heterogeneity and complexity at all levels of organization within a neuron and the functional requirement of highly permeable cell membranes leave neurons exposed to damage when energy levels are insufficient for the active maintenance of ionic gradients. When energy is limiting the ionic gradient across a neuron’s cell membrane risks being dissipated which can have dire consequences. Other researchers have advocated “generalized channel arrest” and/or “spike arrest” as a means of reducing the neuronal permeability allowing neurons to adjust the demands placed on their electrogenic pumps to lower levels of energy supply. I investigated the consequences of hypoxia on the propagation of a train of APs down the length of a fast conducting axon capable of transmitting APs at very high frequencies. Under normoxic conditions I found that APs show conduction velocities and instantaneous frequencies nearly double that of neurons experiencing energy limiting hypoxic conditions. I show that hypoxia affects AP conduction differently for different lengths of axon and for APs of different instantaneous frequencies. Action potentials of high instantaneous frequency in branching lengths of axon within ganglia were delayed more significantly than those in non-branching lengths contained within the connective and fail preferentially in branching axon. I found that octopamine attenuates the effects of hypoxia on AP propagation for the branching length of axon but has no effect on the non-branching length of axon. Additionally, for energetically stable cells, application of the anti-diabetic medication metformin or the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel blocker ZD7288 resulted in a reduced performance similar to that seen in neurons experiencing energetic stress. Furthermore both metformin and ZD7288 affect the shape of individual APs within an AP train as well as the original temporal sequence of the AP train, which encodes behaviourally relevant information. I propose that the reduced performance observed in an energetically compromised cell represents an adaptive mechanism employed by neurons in order to maintain the integrity of their highly heterogeneous and complex organization during periods of reduced energy supply. / Thesis (Master, Biology) -- Queen's University, 2011-10-07 14:41:46.972

Establishing a valid, reliable, and objective method for determining the number of functioning motor units in a muscle is important clinically, as it would provide a quantitative means of documenting changes in neuromuscular health over time. This thesis addressed the reliability of motor unit number estimates (MUNEs) derived using decomposition-based quantitative electromyography (DQEMG) from the extensor digitorum brevis (EDB) and abductor hallucis (AH) muscles. Additionally, the effect of the mean surface motor unit potential (SMUP) parameter averaging method (arithmetic/ensemble), the size-related parameter used to calculate MUNE (amplitude/area), and the type of SMUP marker editing (automatic/manual) was investigated in terms of MUNE values. Two separate analyses on a single data set collected from twenty healthy subjects on two occasions were conducted. MUNEs were calculated by dividing a size-related parameter (amplitude/area) of the compound muscle action potential (CMAP) by the same size-related parameter of a representative mean SMUP. First, paired t-tests investigated differences in MUNEs calculated using arithmetic and ensemble averaged SMUP parameters. Within- and between-day reliability of the two measurements was established using intra-class correlation coefficients (ICCs), coefficients of variation (CV), mean absolute differences (MAD), and Bland Altman limits of agreement (LOA). Second, MUNEs (using both parameters) derived from automated and manually edited SMUPs were compared. The effect of the size-related parameter and editing type was identified using a two-factor, repeated measures analysis of variance. Reliability was determined as described above. Arithmetic averaged SMUP parameters produced smaller MUNEs than those derived from ensemble averaging (p<0.001). SMUP area produced higher MUNEs than SMUP amplitude (p<0.05), except when using arithmetic averaged parameters in AH. Interaction effects between editing type and size parameter were present in both muscles (F>6.68, p<0.001). Between-day MUNEs had lower CVs and MADs, higher ICCs, and narrower LOAs than within-day MUNEs. MUNEs derived from arithmetic averaged SMUP parameters showed the highest reliability (ICCs>0.91). MUNEs calculated from automated SMUP marker placements were highly correlated (r>0.86) and displayed comparable reliabilities to those derived from manual marker placement (ICCs>0.90). To optimize the reproducibility of MUNEs calculated using DQEMG, while minimizing processing time, between-day automated estimates using arithmetic averaged SMUP amplitude is recommended. / Thesis (Master, Rehabilitation Science) -- Queen's University, 2012-08-30 08:32:06.141

No description available.

Zehn Jahre nach dem Ausbruch des Severe Acute Respiratory Syndrome Coronavirus, SARS-CoV, ist ein neues Betacoronavirus, das Middle East Respiratory Syndrome Coronavirus, MERS-CoV, auf der arabischen Halbinsel entdeckt worden. Seine anhaltende Ausbreitung stellt eine Bedrohung für die öffentliche Gesundheit dar. Das Spike (S) Protein der Coronaviren vermittelt den viralen Eintritt in Wirtszellen und bestimmt wesentlich den viralen Tropismus und die virale Pathogenese. Das Verständnis der Determinanten des MERS-CoV Spike (MERS-S)-vermittelnden Eintritts in Zellen könnte daher wichtige Einblicke in die MERS-CoV-Biologie liefern und war somit das erste Ziel dieser Arbeit. Um den Eintritt in die Zelle zu ermöglichen, muss das Coronavirus S-Protein durch Wirtszellproteasen aktiviert werden, welche potentielle Ziele für die therapeutischen Intervention darstellen. Daher sollten im zweiten Ziel dieser Arbeit Proteasen identifiziert werden, die MERS-S aktivieren. Das S-Protein ist das Hauptangriffsziel neutralisierender Antikörper und experimentelle Systeme zur S-Analyse können für die Diagnostik eingesetzt werden. Das letzte Ziel dieser Arbeit war es daher, die MERS-CoV Seroprävalenz in Saudi Arabien zu ermitteln. Es wurde ein lentivirales Vektorensystem etabliert, welches die Analyse des MERS-S-getriebenen Zelleintritts ermöglicht. Mit Hilfe dieses Systems konnte gezeigt werden, dass MERS-S den Eintritt in ein breites Spektrum humaner Zelllinien, wie Lungen-, Nieren- und Darmzellen vermittelt, was mit der klinischen Manifestation von MERS einhergeht. Der Wirtszelleintritt war unabhängig von bereits beschriebenen Coronavirus Eintrittsrezeptoren, wurde jedoch durch die endosomale Cysteinprotease Cathepsin L und die Transmembranserinprotease TMPRSS2 gefördert. Im Gegensatz dazu war die Aktivität von Proprotein Konvertasen für den S-Protein-vermittelnden Eintritt entbehrlich. Schließlich zeigten Neutralisationstests, dass Seren von Patienten aus der östlichen Provinz Saudi Arabiens, die zwischen 2010-2011 und 2012 entnommen wurden, keine MERS-S-neutralisierenden Antikörper enthielten. Dies deutet darauf hin, dass MERS-CoV-Infektionen vor dem Ausbruch 2012 nur selten vorkamen. Die gewonnen Ergebnisse tragen wesentlich zum Verständnis des MERS-CoV-Eintritts in Zellen bei und liefern wichtige Informationen zur MERS-CoV-Epidemiologie. Weiterhin könnte die Beobachtung, dass der Protease-Inhibitor Camostat, der für den Einsatz im Menschen zugelassen ist (in Japan), TMPRSS2 blockiert und damit den MERS-CoV Eintritt inhibiert, helfen, Behandlungsstrategien für MERS-Patienten zu etablieren.

Chromium (VI) is a pervasive groundwater contaminant that poses a considerable threat to human health. Remediation techniques have focused on the reduction of the highly mobile Cr(VI) to the sparingly soluble, and less toxic, Cr(III) species. Traditionally, remediation performance has been evaluated through the measurement of Cr(VI) concentrations; however, this method is both costly and time-consuming, and provides little information regarding the mechanism of Cr(VI) removal. More recently, Cr isotope analysis has been proposed as a tool for tracking Cr(VI) migration in groundwater. Redox processes have been shown to produce significant Cr isotope fractionation, where enrichment in the ⁵³Cr/⁵²Cr ratio in the remaining Cr(VI) pool is indicative of a mass-transfer process. This thesis describes laboratory batch and column experiments that evaluate the Cr isotope fractionation associated with the reduction of Cr(VI) by various materials and under various conditions. Laboratory batch experiments were conducted to characterize the isotope fractionation during Cr(VI) reduction by granular zero-valent iron (ZVI) and organic carbon (OC). A decrease in Cr(VI) concentrations was accompanied by an increase in δ⁵³Cr values for the ZVI experiments. Data were fitted to a Rayleigh-type curve, which produced a fractionation factor α = 0.9994, suggesting a sorption-dominated removal mechanism. Scanning electron microscopy (SEM), X-ray absorption near-edge structure (XANES) spectroscopy, and X-ray photoelectron spectroscopy (XPS) indicated the presence of Cr(III) on the solid material, suggesting that reduction of Cr(VI) occurred. A series of batch experiments determined that reaction rate, experimental design, and pre-treatment of the ZVI had little to no effect on the Cr isotope fractionation. The interpretation of isotope results for the organic carbon experiments was complicated by the presence of both Cr(VI) and Cr(III) co-existing in solution, suggesting that further testing is required. A laboratory column experiment was conducted to evaluate isotopic fractionation of Cr during Cr(VI) reduction by OC under saturated flow conditions. Although decreasing dissolved Cr(VI) concentrations also were accompanied by an increase in δ⁵³Cr values, the isotope ratio values did not fit a Rayleigh-type fractionation curve. Instead, the data followed a linear regression equation yielding α = 0.9979. Solid-phase analysis indicated the presence of Cr(III) on the surface of the OC. Both the results of the solid-phase Cr and isotope analyses suggest a combination of Cr(VI) reduction mechanisms, including reduction in solution, and sorption prior to reduction. The linear characteristic of the δ⁵³Cr data may reflect the contribution of transport on Cr isotope fractionation.

Thesis (M. A.)--Florida State University, 2006. / Advisor: W.T. Lhamon, Florida State University, College of Arts and Sciences, Dept. of English. Title and description from dissertation home page (viewed June 9, 2006). Document formatted into pages; contains vii, 67 pages. Includes bibliographical references.

This thesis is concerned with the development of techniques for analyzing the sequences of stereotypical electrical impulses within neurons known as spikes. Sequences of spikes, also called spike trains, transmit neural information; decoding them often provides details about the physiological processes generating the neural activity. Here, the statistical theory of event arrivals, called point processes, is applied to human muscle sympathetic spike trains, a peripheral nerve signal responsible for cardiovascular regulation. A novel technique that uses observed spike trains to dynamically derive information about the physiological processes generating them is also introduced. Despite the emerging usage of individual spikes in the analysis of human muscle sympathetic nerve activity, the majority of studies in this field remain focused on bursts of activity at or below cardiac rhythm frequencies. Point process theory applied to multi-neuron spike trains captured both fast and slow spiking rhythms. First, analysis of high-frequency spiking patterns within cardiac cycles was performed and, surprisingly, revealed fibers with no cardiac rhythmicity. Modeling spikes as a function of average firing rates showed that individual nerves contribute substantially to the differences in the sympathetic stressor response across experimental conditions. Subsequent investigation of low-frequency spiking identified two physiologically relevant frequency bands, and modeling spike trains as a function of hemodynamic variables uncovered complex associations between spiking activity and biophysical covariates at these two frequencies. For example, exercise-induced neural activation enhances the relationship of spikes to respiration but does not affect the extremely precise alignment of spikes to diastolic blood pressure. Additionally, a novel method of utilizing point process observations to estimate an internal state process with partially linear dynamics was introduced. Separation of the linear components of the process model and reduction of the sampled space dimensionality improved the computational efficiency of the estimator. The method was tested on an established biophysical model by concurrently computing the dynamic electrical currents of a simulated neuron and estimating its conductance properties. Computational load reduction, improved accuracy, and applicability outside neuroscience establish the new technique as a valuable tool for decoding large dynamical systems with linear substructure and point process observations.

abstract: Interictal spikes, together with seizures, have been recognized as the two hallmarks of epilepsy, a brain disorder that 1% of the world's population suffers from. Even though the presence of spikes in brain's electromagnetic activity has diagnostic value, their dynamics are still elusive. It was an objective of this dissertation to formulate a mathematical framework within which the dynamics of interictal spikes could be thoroughly investigated. A new epileptic spike detection algorithm was developed by employing data adaptive morphological filters. The performance of the spike detection algorithm was favorably compared with others in the literature. A novel spike spatial synchronization measure was developed and tested on coupled spiking neuron models. Application of this measure to individual epileptic spikes in EEG from patients with temporal lobe epilepsy revealed long-term trends of increase in synchronization between pairs of brain sites before seizures and desynchronization after seizures, in the same patient as well as across patients, thus supporting the hypothesis that seizures may occur to break (reset) the abnormal spike synchronization in the brain network. Furthermore, based on these results, a separate spatial analysis of spike rates was conducted that shed light onto conflicting results in the literature about variability of spike rate before and after seizure. The ability to automatically classify seizures into clinical and subclinical was a result of the above findings. A novel method for epileptogenic focus localization from interictal periods based on spike occurrences was also devised, combining concepts from graph theory, like eigenvector centrality, and the developed spike synchronization measure, and tested very favorably against the utilized gold rule in clinical practice for focus localization from seizures onset. Finally, in another application of resetting of brain dynamics at seizures, it was shown that it is possible to differentiate with a high accuracy between patients with epileptic seizures (ES) and patients with psychogenic nonepileptic seizures (PNES). The above studies of spike dynamics have elucidated many unknown aspects of ictogenesis and it is expected to significantly contribute to further understanding of the basic mechanisms that lead to seizures, the diagnosis and treatment of epilepsy. / Dissertation/Thesis / Ph.D. Electrical Engineering 2012

This thesis examines the influence of Romanticism on a selection of seven films from four contemporary American filmmakers: Sofia Coppola, Wes Anderson, Charlie Kaufman, and Spike Jonze. The research questions are as follows: How do particular Romantic ideas, either canonical ones or those located on the more critical fringes of Romanticism, relate to the work of the filmmakers I consider? What Romantic features do these films regularly exhibit, both aesthetically and in terms of narrative? How do these features inform their overall point of view? Finally, how do such Romantic ideas and aesthetics relate to the current cultural milieu in which the films were created? There are many familiar and more obscure Romantic strains running through the films. These include a preoccupation with personal history and memory; an undercurrent of deeply felt emotion and reliance upon mood and tone to convey it; a foregrounding of the creative process and the imagination; and an ambivalent relationship to both the natural world and civilised society. In terms of aesthetics, the films in question depend on qualities of the beautiful, picturesque, and sublime to represent the complex emotional states of their characters and to elicit emotional responses in their audiences. Above all, these films represent a preoccupation with subjectivity and self-consciousness: specifically, the coming to personal self-consciousness that creates a rift between the individual subject and a greater sense of society. By utilising the work of eighteenth- and nineteenth-century Romantic authors and philosophers such as Friedrich Schlegel, William Wordsworth, Henry David Thoreau, John Keats and others, combined with twentieth- and twenty-first century readings of these works via literary and cultural theorists and critics such as Harold Bloom, M.H. Abrams, Leo Marx and Anne Mellor, I emphasise the historical trajectory of general Romantic concepts. Taking established cinematic theories (“quirky” cinema, “smart” film, the “new sincerity”) as a point of entry, I explore the underlying stylistic and narrative connections between the films I discuss. I argue these films share a fundamentally Romantic form and vision specific to their own historical and cultural environment.