LIFE CYCLE ASSESSMENT OF A HEMP CONCRETE WALL: IMPACT OF THICKNESS AND COATING.

International audienceIn a context of sustainable development and energy sparing, a life cycle assessment (LCA) may be useful to make good choices. Thus, this study concerns the LCA of an environmentally friendly material used for building construction, hemp concrete. The functional unit is first defined per square such that the wall may provide the function of bearing wall meter and its thermal performance is described by a thermal resistance of 2.78 m².K/W. The results then showed that the production phase of raw materials is mainly responsible for the environmental impact of the wall, mostly due to the binder production. It was also shown that, compared to traditional construction materials, hemp concrete has a low impact on environment. Moreover, hemp concrete contributes to reduce climate change as photosynthesis-mediated carbon sequestration and carbonation serve to reduce atmospheric carbon dioxide. A sensitivity analysis is performed on three criteria: wall thickness, renewal of coatings and compounds of the indoor coating. Our results show that environmental indicators evolve with wall thickness, except for the climate change indicator. It improves with thickness due to carbon sequestration and carbonation. Moreover the increase in the wall's thermal resistance with wall thickness is not taken into account in such an LCA performed at the material level. The renewal of coating slightly impacts the environmental indicator for small numbers of renewals but it leads to negative effects if they are too numerous. It appears that hemp-lime coating has a greater impact than sand-lime coating as it embeds more binder

Manipulating the strength of organism–environment feedback increases nonlinearity and apparent hysteresis of ecosystem response to environmental change

Theory predicts that organism–environment feedbacks play a central role in how ecological communities respond to environmental change. Strong feedback causes greater nonlinearity between environmental change and ecosystem state, increases the likelihood of hysteresis in response to environmental change, and augments the possibility of alternative stable regimes. To illustrate these predictions and their dependence on a temporal scale, we simulated a minimal ecosystem model. To test the predictions, we manipulated the feedback strength between the metabolism and the dissolved oxygen concentration in an aquatic heterotrophic tri‐trophic community in microecosystems. The manipulation consisted of five levels, ranging from low to high feedback strength by altering the oxygen diffusivity: free gas exchange between the microcosm atmosphere and the external air (metabolism not strongly affecting environmental oxygen), with the regular addition of 200, 100, or 50 ml of air and no gas exchange. To test for nonlinearity and hysteresis in response to environmental change, all microecosystems experienced a gradual temperature increase from 15 to 25°C and then back to 15°C. We regularly measured the dissolved oxygen concentration, total biomass, and species abundance. Nonlinearity and hysteresis were higher in treatments with stronger organism–environment feedbacks. There was no evidence that stronger feedback increased the number of observed ecosystem states. These empirical results are in broad agreement with the theory that stronger feedback increases nonlinearity and hysteresis. They therefore represent one of the first direct empirical tests of the importance of feedback strength. However, we discuss several limitations of the study, which weaken confidence in this interpretation. Research demonstrating the causal effects of feedback strength on ecosystem responses to environmental change should be placed at the core of efforts to plan for sustainable ecosystems

Les ADN topoisomérases du crenarchaeon hyperthermophile Sulfolobus solfataricus (régulateurs du métabolisme de l'ADN ?)

Les ADN topoisomérases sont des enzymes capables de moduler la torsion de la double hélice d ADN afin de rendre compatible sa topologie avec les différents processus cellulaires impliquant l ADN. Les hyperthermophiles possèdent au moins une topoisomérase particulière, la reverse gyrase qui est constituée à la fois d un domaine topoisomérase IA etd un domaine hélicase de type SF2. Mon sujet de thèse a eu pour objectif de déterminer principalement l implication des ADN topoisomérases IA dans les différents processus cellulaires de Sulfolobus solfataricus. Ce crenarchaeon hyperthermophile possède, en plus, d une ADN topoisomérase de type II (Topo VI), trois ADN-topoisomérases IA dont une classique (TopA) et deux reverse gyrases (TopR1 et TopR2). Notre approche a permis d estimer, pour la première fois, le nombre de TopR1 et de TopR2 par cellule en fonction des différentes conditions testées. L étude des variations quantitatives des ADN topoisomérases a clairement mis en évidence que TopR1 et TopR2 sont régulées différemment ce qui renforce l hypothèse d une spécialisation de leurs fonctions. Nous avons ainsi montré que TopR1 est responsable du maintien de l homéostasie du surenroulement de l ADN. Si la Topo VI de par son activité antagoniste est impliquée dansce même contrôle homéostatique, elle ne fait pas l objet d une régulation quantitative. De plus, nous avons mis en évidence que TopR1 était liée à la vie à haute température. Enfin, nos résultats suggèrent que TopR2 serait pour sa part impliquée dans la stabilité des génomes. L identification des partenaires protéiques respectifs des quatre ADN topoisomérases de S. solfataricus permettra d avoir une vision globale des réseaux de régulation permettant derésoudre les différentes des contraintes topologiques générées au cours de la vie de cet hyperthermophile.DNA topoisomerases act in all DNA metabolism processes to control the DNA topology. Hyperthermophiles possess at least a particular topoisomerase, the reverse gyrase composed of a DNA topoisomerase IA domain and a helicase SF2 domain within the same polypeptide. The general objective of my thesis was to determine the involvement of each DNA topoisomerase in different cellular processes of S. solfataricus. This hyperthermophilic crenarchaeon possesses in addition to a type II DNA topoisomerase (Topo VI), three DNA topoisomerases IA : a classical one (TopA) and two reverse gyrases (TopR1 and TopR2). Our experimental approach allowed to estimate for the first time the number of TopR1 and TopR2 per cell in relation to different conditions. The study of quantitative variations of each DNA topoisomerase clearly showed that TopR1 and TopR2 are differently regulated suggesting that they are involved in distinct cellular processes. Indeed, we showed that TopR1 is the main actor of the homeostatic control of the DNA supercoiling. If the Topo VI with its antogonistic activity is involved in this homeostatic control, there is no regulation at the level of protein quantity. In addition we evidenced that TopR1 is somehow linked to the life at high temperature. Our results suggest that TopR2 is involved in genome stability. The identification of the respective potential partners of the four DNA topoisomerases of S. solfataricus will allow to get a more detailed understanding of the DNA topology regulation during the hyperthermophilic life style.EVRY-Bib. électronique (912289901) / SudocSudocFranceF

Functional interaction of reverse gyrase with single-strand binding protein of the archaeon Sulfolobus

Reverse gyrase is a unique hyperthermophile-specific DNA topoisomerase that induces positive supercoiling. It is a modular enzyme composed of a topoisomerase IA and a helicase domain, which cooperate in the ATP-dependent positive supercoiling reaction. Although its physiological function has not been determined, it can be hypothesized that, like the topoisomerase–helicase complexes found in every organism, reverse gyrase might participate in different DNA transactions mediated by multiprotein complexes. Here, we show that reverse gyrase activity is stimulated by the single-strand binding protein (SSB) from the archaeon Sulfolobus solfataricus. Using a combination of in vitro assays we analysed each step of the complex reverse gyrase reaction. SSB stimulates all the steps of the reaction: binding to DNA, DNA cleavage, strand passage and ligation. By co-immunoprecipitation of cell extracts we show that reverse gyrase and SSB assemble a complex in the presence of DNA, but do not make stable protein–protein interactions. In addition, SSB stimulates reverse gyrase positive supercoiling activity on DNA templates associated with the chromatin protein Sul7d. Furthermore, SSB enhances binding and cleavage of UV-irradiated substrates by reverse gyrase. The results shown here suggest that these functional interactions may have biological relevance and that the interplay of different DNA binding proteins might modulate reverse gyrase activity in DNA metabolic pathways

Pointless learning

Bayesian inversion is at the heart of probabilistic programming and more generally machine learning. Understanding inversion is made difficult by the pointful (kernel-centric) point of view usually taken in the literature. We develop a pointless (kernel-free) approach to inversion. While doing so, we revisit some foundational objects of probability theory, unravel their category-theoretical underpinnings and show how pointless Bayesian inversion sits naturally at the centre of this construction

Pointless learning (long version)

International audienceBayesian inversion is at the heart of probabilistic programming and more generally machine learning. Understanding inversion is made difficult by the pointful (kernel-centric) point of view usually taken in the literature. We develop a pointless (kernel-free) approach to inversion. While doing so, we revisit some foundational objects of probability theory, unravel their category-theoretical underpinnings and show how pointless Bayesian inversion sits naturally at the centre of this construction

Pointless learning (long version)

International audienceBayesian inversion is at the heart of probabilistic programming and more generally machine learning. Understanding inversion is made difficult by the pointful (kernel-centric) point of view usually taken in the literature. We develop a pointless (kernel-free) approach to inversion. While doing so, we revisit some foundational objects of probability theory, unravel their category-theoretical underpinnings and show how pointless Bayesian inversion sits naturally at the centre of this construction

CRH-LaDéHiS – Laboratoire de démographie et d’histoire sociale

Pascal Cristofoli, ingénieur d’étudesArnaud Bringé, ingénieur de recherche à l’INEDBénédicte Garnier, ingénieure d’études à l’INED Atelier « Analyse des données relationnelles » Lieu d’enseignement, de discussion et de collaboration entre étudiants, ingénieurs et chercheurs associés, l’atelier vise à interroger les différentes opérations pratiques et théoriques impliquées par la mise en œuvre d’analyses relationnelles. Depuis plusieurs années maintenant, le séminaire est organisé en trois jou..

CRH-LaDéHiS – Laboratoire de démographie et d’histoire sociale

Pascal Cristofoli, ingénieur d’étudesArnaud Bringé, ingénieur de recherche à l’INEDBénédicte Garnier, ingénieure d’études à l’INED Atelier « Analyse des données relationnelles » Lieu d’enseignement, de discussion et de collaboration entre étudiants, ingénieurs et chercheurs associés, l’atelier vise à interroger les différentes opérations pratiques et théoriques impliquées par la mise en œuvre d’analyses relationnelles. Depuis plusieurs années maintenant, le séminaire est organisé en trois jou..