Science & Mathematics

Brownian dynamics simulations were performed to examine the self-diusion of cationic (Na +), anionic (Cl −), and water tracers in a saturated compacted clay at the micrometric scale. Clay minerals particles, representing stacks of montmorillonite layers, are modeled as cylindrical platelets with characteristics that depend on the dry bulk density of the porous medium, ρ b. The tracers are allowed to diuse between the platelets with their diffusion coef ficient in bulk aqueous solution as well as inside the platelets with a diusion coef ficient that depends on the hydration level of the interlayer pores as determined from experiments or molecular dynamics simulations. The probability for a tracer to enter a platelet is related to its charge as predicted by the Poisson-Boltzmann equation. The apparent diusion coef ficients are calculated as a function of ρ b for various salinities and compared with the values obtained from tracer diusion experiments available in the literature. Despite the simplicity of the clay model, the simulations predict most features of the experimental data and keep the door open for further improvements.

Advanced technologies, like for instance aerospace or nuclear engineering require the most exhaustive information on the behaviour of materials used at very high temperature such as ceramics, refractory alloys or molten metals. Among high temperature techniques, X-rays and more recently neutron scattering have appeared as powerful tools to get information, mainly structural, on these materials in their working conditions. High temperature devices (above 2 000 K) developed for that purpose, based on various heating techniques (induction, imaging furnaces, lasers, gas-flame heaters and principally Joule heated devices) are reviewed. Some crucial points are particularly emphasized such as : — the determination of the real temperature (thermocouples and optical pyrometry) in the scattering zone hardly accessible partly due to the unavoidable thermal gradients, — the chemical reactivity of the sample with its surrounding, i.e. atmosphere and sample holder. Neutrons, mainly because of their low absorption by matter, allow the work on real bulky materials and give a greater freedom in the conception of high temperature scattering devices compared to X-rays. At the present time thermal neutron high flux reactors offering a wide range of neutron wavelengths are available, and a new generation of more and more efficient multidetectors has emerged in the last decade; the data acquisition and consequently the high temperature exposure time have been notably reduced, opening a way for precise and reliable experiments in the 3 000 K range. This very high temperature domain already studied by a few other techniques can also be investigated by neutron scattering.

Le présent travail se propose de décrire les faunes du Pliensbachien supérieur récoltées dans plusieurs coupes du Quercy septentrional (Lot, Corrèze) par François Brunel lors de son travail de thèse (Brunel, 1997). La succession stratigraphique synthétique y est exposée et révisée. Huit taxons d'ammonites appartenant aux familles des Amaltheidae et des Hildoceratidae (Ammonitina) sont décrits et figurés. Leur âge et leurs affinités paléobiogéographiques sont précisés.

Hydrothermal explosions frequently occur in geothermal areas showing various mechanisms and energies of explosivity. Their deposits, though generally hardly recognised or badly preserved, provide important insights to quantify the dynamics and energy of these poorly understood explosive events. Furthermore the host rock lithology of the geothermal system adds a control on the efficiency in the energy release during an explosion. We present results from a detailed study of recent hydrothermal explosion deposits within an active geothermal area at Kverkfjöll, a central volcano at the northern edge of Vatnajökull. On August 15th 2013, a small jökulhlaup occurred when the Gengissig ice-dammed lake drained at Kverkfjöll. The lake level dropped by approximately 30 m, decreasing pressure on the lake bed and triggering several hydrothermal explosions on the 16th. Here, a multidisciplinary approach combining detailed field work, laboratory studies, and models of the energetics of explosions with information on duration and amplitudes of seismic signals, has been used to analyse the mechanisms and characteristics of these hydrothermal explosions. Field and laboratory studies were also carried out to help constrain the sedimentary sequence involved in the event. The explosions lasted for 40–50 s and involved the surficial part of an unconsolidated and hydrothermally altered glacio-lacustrine deposit composed of pyroclasts, lavas, scoriaceous fragments, and fine-grained welded or loosely consolidated aggregates, interbedded with clay-rich levels. Several small fans of ejecta were formed, reaching a distance of 1 km north of the lake and covering an area of approximately 0.3 km2, with a maximum thickness of 40 cm at the crater walls. The material (volume of approximately 104 m3) has been ejected by the expanding boiling fluid, generated by a pressure failure affecting the surficial geothermal reservoir. The maximum thermal, craterisation and ejection energies, calculated for the explosion areas, are on the order of 1011, 1010 and 109 J, respectively. Comparison of these with those estimated by the volume of the ejecta and the crater sizes, yields good agreement. We estimate that approximately 30% of the available thermal energy was converted into mechanical energy during this event. The residual energy was largely dissipated as heat, while only a small portion was converted into seismic energy. Estimation of the amount of freshly-fragmented clasts in the ejected material obtained from SEM morphological analyses, reveals that a low but significant energy consumption by fragmentation occurred. Decompression experiments were performed in the laboratory mimicking the conditions due to the drainage of the lake. Experimental results confirm that only a minor amount of energy is consumed by the creation of new surfaces in fragmentation, whereas most of the fresh fragments derive from the disaggregation of aggregates. Furthermore, ejection velocities of the particles (40–50 m/s), measured via high-speed videos, are consistent with those estimated from the field. The multidisciplinary approach used here to investigate hydrothermal explosions has proven to be a valuable tool which can provide robust constraints on energy release and partitioning for such small-size yet hazardous, steam-explosion events.

Learning Classifier Systems (LCS) are rule based Reinforcement Learning (RL) systems which use a generalization capability. In this paper, we highlight the differences between two kinds of LCSs. Some are used to directly perform RL while others latently learn a model of the interactions between the agent and its environment. Such a model can be used to speed up the core RL process. Thus, these two kinds of learning processes are complementary. We show here how the notion of generalization differs depending on whether the system anticipates (like Anticipatory Classifier System (ACS) and Yet Another Classifier System (YACS)) or not (like XCS). Moreover, we show some limitations of the formalism common to ACS and YACS, and propose a new system, called Modular Anticipatory Classifier System (MACS), which allows the latent learning process to take advantage of new regularities. We describe how the model can be used to perform active exploration and how this exploration may be aggregated with the policy resulting from the reinforcement learning process. The different algorithms are validated experimentally and some limitations in presence of uncertainties are highlighted.

24x36 mm, gélatine plan-film.

Micellar solutions of different concentrations (0.1-5% wt) of oxyethylated diisononylphenols (OEDNP) (C9H18)2C6H4(OC2H4)nOH with different mean numbers of ethylene-oxide (EO) groups (18, 20 and 24) were investigated by means of SAXS and DLS (and SANS for OEDNP-20). The mean hydrodynamic diameters (using DLS data) and equivalent uniform sphere diameter distributions (using the initial part of SAXS curves) were calculated. Both methods gave consistent results. The characteristic functions of micellar particles are quite similar for all investigated concentrations and numbers of EO groups. These results make clear that the micelles are very stable and can be refered to as spherical particles. Three maxima of characteristic functions persuade us to refuse the simple core - shell model and to propose a more complicated model of spherical particles with a hydrophobic core and two successsive covers (core - inner layer - outer layer). One of the two alkyl chains of the molecule from the internal layer is included into the core and another is directed outside in contact with the alkyl groups of the molecules from the outer layer and the EO groups of the molecules from the inner layer.

Service providers for maintenance, repair and overhaul (MRO) of aircrafts and components face major challenges. The calculation of an optimal stock level for components is one of these. The optimal stock level is highly influenced by the customers demand. Furthermore the stock level influences the profitability of the processes. The challenge for MRO service provider is to respond to the changing customer base and to adapt the stock level for components dynamically. For this purpose, an approach for the determination of the spare parts demand is described in this paper. The approach consists of a hierarchical derivation of reliability parameters in the first step and finally an assessment of the derived reliability parameters. By this assessment the relevance of different impact factors can be determined. The determination of the spare parts demand and the optimal stock level can thereby be determined much more accurately.

COVID-19 is a global pandemic caused by the SARS-CoV-2 coronavirus. T cells play a key role in the adaptive antiviral immune response by killing infected cells and facilitating the selection of virus-specific antibodies. However, neither the dynamics and cross-reactivity of the SARS-CoV-2-specific T-cell response nor the diversity of resulting immune memory is well understood. In this study, we use longitudinal high-throughput T-cell receptor (TCR) sequencing to track changes in the T-cell repertoire following two mild cases of COVID-19. In both donors, we identified CD4 + and CD8 + T-cell clones with transient clonal expansion after infection. We describe characteristic motifs in TCR sequences of COVID-19-reactive clones and show preferential occurrence of these motifs in publicly available large dataset of repertoires from COVID-19 patients. We show that in both donors, the majority of infection-reactive clonotypes acquire memory phenotypes. Certain T-cell clones were detected in the memory fraction at the pre-infection time point, suggesting participation of pre-existing cross-reactive memory T cells in the immune response to SARS-CoV-2.

We identify two counteracting effects of credit access on productivity growth: on the one hand, better access to credit makes it easier for entrepreneurs to innovate; on the other hand, better credit access allows less efficient incumbent firms to remain longer on the market, thereby discouraging entry of new and potentially more efficient innovators. We first develop a simple model of firm dynamics and innovation‐based growth with credit constraints, where the above two counteracting effects generate an inverted‐U relationship between credit access and productivity growth. Then we test our theory on a comprehensive French manufacturing firm‐level dataset. We first show evidence of an inverted‐U relationship between credit constraints and productivity growth when we aggregate our data at the sectoral level. We then move to firm‐level analysis, and show that incumbent firms with easier access to credit experience higher productivity growth, but that they also experience lower exit rates, particularly the least productive firms among them. To support these findings, we exploit the 2012 Eurosystem's Additional Credit Claims programme as a quasi‐experiment that generated an exogenous extra supply of credits for a subset of incumbent firms.

Manufacturing enterprises are becoming globally distributed production systems. Rigid supply chains are giving way to dynamic supply networks that are cost-efficient and can respond to change quickly. A key factor in the formation of dynamic supply networks is the communication of manufacturing capabilities – both production capabilities and information processing capabilities. These are collectively referred to as manufacturing service capability (MSC) information. Presently, MSC information is provided using many different, proprietary terminologies and representations. The lack of a standard model impedes communications of MSC information. We propose the development of a standard MSC model to enhance the MSC information communications. This paper motives such development by presenting a use case analysis that illustrates the current and a desirable future state of MSC information communication. The future state, which relies on a standard MSC model can advance the current practice and allow precise and computer-interpretable representation of MSC information.