Un essai de mathématisation du processus de l'enseignement collectif

Not available

A Call to Arms: Revisiting Database Design

Good database design is crucial to obtain a sound, consistent database, and - in turn - good database design methodologies are the best way to achieve the right design. These methodologies are taught to most Computer Science undergraduates, as part of any Introduction to Database class. They can be considered part of the "canon", and indeed, the overall approach to database design has been unchanged for years. Moreover, none of the major database research assessments identify database design as a strategic research direction. Should we conclude that database design is a solved problem? Our thesis is that database design remains a critical unsolved problem. Hence, it should be the subject of more research. Our starting point is the observation that traditional database design is not used in practice - and if it were used it would result in designs that are not well adapted to current environments. In short, database design has failed to keep up with the times. In this paper, we put forth arguments to support our viewpoint, analyze the root causes of this situation and suggest some avenues of research.Comment: Removed spurious column break. Nothing else was change

TimeFabric: Trusted Time for Permissioned Blockchains

As the popularity of blockchains continues to rise, blockchain platforms must be enhanced to support new application needs. In this paper, we propose one such enhancement that is essential for financial applications and online marketplaces - support for time-based logic such as verifying deadlines or expiry dates and examining a time window of recent account activity. We present a lightweight solution to reach consensus on the current time without relying on external time oracles. Our solution assigns timestamps to blocks at transaction validation time and maintains a cache reflecting the effects of recent transactions. We implement a proof-of-concept prototype, called TimeFabric, in Hyperledger Fabric, a popular permissioned blockchain platform, and experimentally demonstrate high throughput and minimal overhead (approximately 3%) of maintaining trusted time. We also demonstrate a 2x performance improvement due to the cache, compared to reconstructing account histories from the ledger

Magnetic Properties of TbNi1 xAuxIn Compounds

Polycrystalline samples of $TbNi_{1-x}Au_{x}In$ for x = 0.1, 0.2, 0.4, 0.6 and 0.8 were prepared and studied by powder X-ray and neutron diffraction and ac magnetic susceptibility measurements. These compounds crystallize in the hexagonal ZrNiAl-type structure. With increasing Au content a change in the magnetic structure is observed. For x = 0.1, 0.2 and 0.4 the magnetic order is described by the propagation vector k = (1/2, 0, 1/2) while for x = 0.8 by k = (0, 0, 1/2). Between 1.5 K and the Néel temperature the magnetic order is stable

Disclosing the heat density of district heating in Austria in 2050 under the remaining European CO2 budget of the 1.5 °C climate target

The core objective of this work is to downscale the cost-effective heat supply of different European decarbonization scenarios generated by the aggregate model GENeSYS-MOD from the national to the community level in Austria and thus disclose the heat density of district heating in 2050. We assume that district heating encompasses geothermal, synthetic gas, hydrogen, waste, and large-scale heat pumps as renewable heat sources. The results determine district heating in 68 Austrian communities in Austria in 2050, which corresponds to 6% of the total number of communities. We find that GENeSYS-MOD results are capable in covering local trends in district heating since high shares of the projected heat densities at the local levels achieve values indicating economic viability. Further research should follow on how locally determined district heating and heat densities could be returned into more aggregate models, such as GENeSYS-MOD, in the sense of a feedback loop. That allows refining assumptions in the large-scale upper-level models, which in turn will increase the plausibility and realism of pathways at the European level

A combined geochemical and μCT study on the CO2 reactivity of Surat Basin reservoir and cap-rock cores: porosity changes, mineral dissolution and fines migration

Geological storage of CO generally involves injection of a CO stream into a high porosity and permeability reservoir, contained by one or more overlying low permeability formations. Sandstone reservoirs and associated cap-rocks of targeted CO storage sites therefore have distinct properties such as porosity and mineral contents. Their geochemical response or reactivity to injected supercritical CO and associated changes in porosity, and permeability affecting scaling, mineral trapping, injectivity, or migration can therefore be very different. Six drill core samples including quartz-rich sandstones, calcite cemented sandstones, and feldspar or clay-rich cap-rocks from a proposed demonstration site in the Surat Basin, Australia, were characterized before and after reaction with pure supercritical CO and low salinity formation water. The quartz-rich sandstones have low reactivity, and maintain high porosities with visible pore connectivity after reaction, they are unlikely to be affected by scaling. Kaolin and fine grain movement observed via μCT and SEM could have the potential to open or plug pores, potentially increasing or decreasing permeability and CO injectivity. Calcite cemented sandstones had the greatest measured change in porosity after reaction via calcite dissolution. Narrow angular channels were formed in the calcite cement around framework grains, extending through to the center of the sub-plug in the courser grained rock, and surface roughness increased. Solution pH was however quickly passivated. The highest concentrations of Ca, Mn, Sr, and Mg were released to solution from calcite dissolution. Clay (and feldspar) rich cap-rock core had mainly microporosity and the smallest initial pore throat diameters associated with clays. Small changes to μCT calculated porosities after reaction were related to a decrease in chlorite X-ray density, and dissolution of patchy carbonate minerals. Pores were disconnected in μCT images, except for some created horizontal connection along a sandy lamination in a cap-rock. Dissolved concentrations of Ca, Fe, Si, Sr, Mn, Li and Mg increased via dissolution of both carbonate and silicate minerals. Dissolved Ca, Fe, Mn and Mg from silicate minerals in the cap-rock were available for longer term mineral trapping of CO. Potential increases in porosity and migration will be highest in the calcite cemented zones, while clay-rich cap-rocks could be expected to maintain integrity. There is a low likelihood of mineral trapping or scaling in the quartz rich lower Precipice Sandstone. Overlying rocks can provide Fe, Mg, Ca for mineral trapping of CO as ferroan carbonates such as siderite, ankerite and dolomite over longer time scales when pH is buffered. Changes to porosity, mineral content, and water chemistry after pure CO reaction observed here and in other published studies were dependent on mineral content and fluid accessibility. These results could be generalized to other sandstone reservoirs where it is expected to inject CO. The results can also be used to validate geochemical models to build longer term predictions

Mouse models for preeclampsia: disruption of redox-regulated signaling

The concept that oxidative stress contributes to the development of human preeclampsia has never been tested in genetically-defined animal models. Homozygous deletion of catechol-Omethyl transferase (Comt-/-) in pregnant mice leads to human preeclampsia-like symptoms (high blood pressure, albuminurea and preterm birth) resulting from extensive vasculo-endothelial pathology, primarily at the utero-fetal interface where maternal cardiac output is dramatically increased during pregnancy. Comt converts estradiol to 2-methoxyestradiol 2 (2ME2) which counters angiogenesis by depleting hypoxia inducible factor-1 alpha (HIF-1 alpha) at late pregnancy. We propose that in wild type (Comt++) pregnant mice, 2ME2 destabilizes HIF-1 alpha by inhibiting mitochondrial superoxide dismutase (MnSOD). Thus, 2ME2 acts as a pro-oxidant, disrupting redox-regulated signaling which blocks angiogenesis in wild type (WT) animals in physiological pregnancy. Further, we suggest that a lack of this inhibition under normoxic conditions in mutant animals (Comt-/-) stabilises HIF-1 alpha by inactivating prolyl hydroxlases (PHD). We predict that a lack of inhibition of MnSOD, leading to persistent accumulation of HIF-1 alpha, would trigger inflammatory infiltration and endothelial damage in mutant animals. Critical tests of this hypothesis would be to recreate preeclampsia symptoms by inducing oxidative stress in WT animals or to ameliorate by treating mutant mice with Mn-SOD-catalase mimetics or activators of PHD