Reproductibilité

Résumé

La reproductibilité d'une expérience scientifique est une des conditions qui permettent d'inclure les observations réalisées durant cette expérience dans le processus d'amélioration perpétuelle des connaissances scientifiques. Cette condition part du principe qu'on ne peut tirer de conclusions que d'un événement bien décrit, qui est apparu plusieurs fois, provoqué par des personnes différentes. Cette condition permet de s'affranchir d'effets aléatoires venant fausser les résultats ainsi que des erreurs de jugement ou des manipulations de la part des scientifiques. Le critère de reproductibilité est une des conditions sur lesquelles le philosophe Karl Popper distingue le caractère scientifique d'une étude. Pour toutes les sciences expérimentales, les probabilités fournissent un modèle mathématique décrivant la variabilité des résultats. Depuis les années 2000, les sciences traversent une crise de la reproductibilité. Observations scientifiques Un phénomène est observé.

Source officielle

https://fr.wikipedia.org/wiki/Reproductibilit%C3%A9

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Open design of a fixed probe for water quality monitoring in rivers and lakes

Nils Pascal Bonfils

This bachelor project work aims to set up a prototype measurement station in the Sorge (a small river near the EPFL) to collect some data about the water and the environmental conditions. And also make the work reproducible so that someone, somewhere else could also build one to collect data about a specific river or lake.

2016

Chargement

Determining patterns of post-stroke motor recovery through longitudinal multimodal MRI: A step towards patient stratification

Julia Brügger

Motivated by the need for a better understanding of post-stroke recovery and new biomarkers to improve stroke patient stratification and outcomes, this thesis investigated structure-function coupling and its role in post-stroke recovery. Furthermore, in order to increase data comparability between sessions and centers (a critical challenge in contemporary clinical research), this thesis assessed the reproducibility of microstructure-informed structural connectivity measures in a multi-center dataset.Stroke is one of the major sources of permanent impairment, frequently of motor origin. However the clinical picture is very heterogeneous: patients show divergent courses of recovery and the underlying mechanisms are still unclear. In addition, current treatments still have limited success and are restricted to a 'one-fits-all' approach, not considering the individual patient's phenotype. As efforts to stratify patients based on structural or functional biomarkers are still needed, we chose to investigate the potential of a multimodal biomarker, the Structural Decoupling Index (SDI) (Preti & Van De Ville, 2019b), a new metric assessing the structure-function coupling strength in the brain. The first part (Studies 1 and 2) of this thesis investigates the potential of the SDI as a biomarker. In Study 1, the goals were to evaluate the feasibility of applying the SDI on an individual level in healthy older adults and to investigate the effect of an acute stroke on it. Consistent with the literature, we found a network gradient of SDI in healthy older adults, from high coupling in lower-level sensory areas, to low coupling in higher-level cognitive areas. This confirmed the applicability of SDI on an individual level. Furthermore, we showed that stroke impacts the SDI, with a higher decoupling on the ipsi- compared to the contralesional side, and with network-specific effects in RH stroke patients. In Study 2, the goal was to see whether the SDI evolved over time post-stroke and whether it links to behavior. The longitudinal analysis revealed differential network effects of stroke at T1 and T3. Furthermore, we showed that impairment in cognitive and psychological behavioral domains significantly correlates with variations in SDI in a number of key areas including motor regions (e.g., primary motor cortex) and that the brain pattern associated to behavior changes between T1 and T2. Surprisingly, motor performance did not explain variability in key motor areas (e.g., primary motor cortex). The link between post-stroke behavioral performance and SDI underlines its potential clinical relevance.Driven by the quest for more reproducible analysis pipelines in the context of longitudinal and clinical studies, the second part of this thesis (Study 3) addressed the subject-specific reproducibility and repeatability of microstructure-informed tractography. Through a multi-center study, we demonstrated its high reproducibility and subject-specificity, and we found evidence for increased biological accuracy. My thesis made a contribution by showing that the SDI is sensitive to pathophysiological changes that occur following a stroke and that it links to clinically relevant behavioral measures. In addition, it confirms the reproducibility and subject-specificity of microstructure-informed tractography. Together, my findings pave the way towards patient stratification and more personalized treatments in stroke rehabilitation.

EPFL2022

Chargement

When using natural or waste wood in thermo-chemical conversion processes, the presence of a number of heteroatoms (e.g. sulfur, chlorine, potassium and sodium or heavy metals) may hinder the processes themselves as well as pose a threat to equipment and/or the environment. Due to the often strongly heterogeneous composition of the feedstocks and high dynamics of thermo-chemical reactions, the elemental concentrations in process gases show a high temporal variability. In order to accurately characterize such processes efficient and representative sampling methods and analytical instruments with a high sensitivity and time resolution are necessary. This thesis presents the development and application of devices to analyze trace element contents of product gases from thermo- chemical conversion processes and to characterize the thermal behavior of feedstocks such as wood pellets. In the first part the development of a mobile sampling and measurement system for the analysis of gaseous and liquid samples in the field is presented. An inductively coupled plasma optical emission spectrometer (ICP-OES) which was built into a van, was used as detector. The analytical system was calibrated with liquid and/or gaseous standards. It was shown that identical mass flows of either gaseous or liquid standards resulted in identical ICP-OES signal intensities. In a field measurement campaign trace and minor elements in the raw flue gas of a waste wood combustor were monitored. Sampling was performed with a highly transport efficient liquid quench system which made possible the observation of temporal variations in the elemental process gas composition. After a change in feedstock an immediate change of the element concentrations in the flue gas was detected. A comparison of the average element concentrations during the combustion of the two feedstocks showed a high reproducibility for matrix elements that are expected to be present in similar concentrations. Elements showing strong differences in their concentration in the feedstock were also represented by a higher concentration in the flue gas. Following the temporal variations of different elements revealed strong correlations between a number of elements, such as chlorine with sodium, potassium and zinc, as well as arsenic with lead, and calcium with strontium. Most notably, an online detector for alkalis (SID II) based on the principle of surface ionization has been designed and constructed within the framework this thesis. The detector includes a number of improvements compared to previous designs. Due to a fixed filament geometry, the sensitivity of the SID II is highly reproducible between different filaments. Improvements to the flow geometry of the device, and the installation of an auxiliary heateing element have minimized the overall tar depositions. In contrast to previous designs, the electrical feedthroughs are kept outside the sample gas stream and are therefore protected against tar contamination which can lead to signal artifacts. In numerous measurements at thermal processes up to industrial scale the SID II has demonstrated a high sensitivity and improved characteristics to conduct measurements in tar and particle laden process gases. By using an ultrasonic nebulizer as a source for alkali aerosols it was possible to perform a calibration of the alkali detector over 4 orders of magnitude. In combination with a dilution setup and a sampling lance, we could take online measurements of gasifier product gas with a high degree of reproducibility and a high time resolution of 1 s. In an experimental series with a miniature thermo-chemical reactor the release of alkalis and formation of product gases during pyrolysis and combustion of single commercial-sized wood pellets could both be recorded with a time resolution of approximately 1 s for with the SID II and the a mass spectrometer, respectively. The thermal processing was conducted by using compressed air at temperatures between 400 °C and 900 °C. During the experiments at temperatures of 700 °C and below the majority of the alkali are released after the initial pyrolysis stage. In contrast to that, in the experiments at 800 °C and 900 °C most of the alkali release happened during the pyrolysis stage (during the first 200 s after the insertion of the pellet). The alkali release rates collected at 800°C during the char combustion phase were reproduced using an extended version of the random pore model, resulting in similar numeric values of the fitted model parameters as reported by Struis et al. (2002) for thermo-chemical conversion experiments with pulverized wood char and carbon dioxide at 800°C well. During the late stage of combustion the alkali release rates exhibit the same phenomena as previously determined for char pore surface area. These phenomena, related to pore coalescence and char structure disintegration, gave rise to a number of varied attempts to modify the original random pore model derived by Bhatia and Perlmutter.

EPFL2012

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Determining patterns of post-stroke motor recovery through longitudinal multimodal MRI: A step towards patient stratification

Julia Brügger

EPFL2022

EPFL2012