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Elaboration of p-type Ge doped MnSi (1.73 < y < 1.77) thermoelectric legs with complex shapes by binder jetting additive manufacturing technique
No full textInternational audienceThermoelectric legs with complex geometries exhibit high potential interest for fatal heat conversion into electricity due to higher thermal dissipation. Additive manufacturing (AM)is a solution of choice to decrease the manufacturing cost of thermoelectric legs that are historically requiring lengthy and costly fabrication processes and it gives the possibility of custom legs geometry. Nevertheless, microcracks and high porosity are commonly present by using this kind of process for thermoelectric materials leading to by limited performances. This work reports the possibility to manufacture n type Ge doped MnSi y (1.73 < y < 1.77) thermoelectric legs with various shapes without microcracks and with low porosity using the binder jetting AM technique followed by a Spark Plasma Sintering (SPS) step. The MnSi phase in the samples is systematically present, the samples density can reach 98 %. A power factor of 1130 µW.mK was reached at 350° C which is within the range of those obtained by the conventional technique of elaboration, proving that the material is not degraded using this novel route. It is mainly due to the good density and the absence of microcracks. Elaboration of legs with various geometry (cuboid and layered) was done to demonstrate the interest of this innovation manufacturing route. The benefit impact of the geometry was evaluated in term of voltages by a comparison measurement between a cuboid and a layered sample for which a remarkable gain of 16.5 % (at an applied temperature of 74.7° C) was obtained for the layered sample due to a better thermal dissipation
Flow approaches in agri-food systems research: revealing blind spots to support social-ecological transformation
No full textInternational audienceAgrifood systems are called upon to undergo profound transformation. The development of “flow approaches” (including lifecycle assessment, carbon footprint, ecological footprint, and metabolism methodologies) has been crucial to point to the material side of human activities. More specifically, these approaches highlight the material and energetic costs of long agrifood value-chains, intensive farming practices, high levels of geographic specialization, as well as the production of non-food commodities. In the logical progression from diagnosis to action, flow approaches are currently being used as decision-support tools. But what are the biases induced by flow approaches when it comes to supporting real-world transformations? Based on our experience and interdisciplinary background, we argue that flow approaches provide a decontextualized and narrow framing of issues related to agrifood systems, such as accumulations and transfers across space and time, inequalities and asymmetries along the chain of activities, or long-lasting environmental impacts. Some aspects are measured and emphasized, while others are difficult to observe or neglected. Flow approaches, alone, are not well suited to inform issues of environmental justice, radical transformation, and local governance. As in most cases methodological advances will not suffice to overcome the biases induced; we call for hybridizing methods and for broadening analytical perspectives
Investigating the effect of particle size distribution and complex exchange dynamics on NMR spectra of ions diffusing in disordered porous carbons through a mesoscopic model
No full textInternational audienceIon adsorption and dynamics in porous carbons are crucial for many technologies, such as energy storage and desalination. Nuclear magnetic resonance (NMR) spectroscopy is a key method to investigate such systems thanks to the possibility of distinguishing adsorbed (in-pore) and bulk (ex-pore) species in the spectra. However, the large variety of magnetic environments experienced by the ions adsorbed in the particles and the existence of dynamic exchange between the inside of the particles and the bulk renders the interpretation of the NMR experiments very complex. In this work, we optimise and apply a mesoscopic model to simulate NMR spectra of ions in systems where carbon particles of different sizes can be considered. We demonstrate that even for monodisperse systems, complex NMR spectra, with broad and narrow peaks, can be observed. We then show that the inclusion of polydispersity is essential to recover some experimentally observed features, such as the co-existence of peaks assigned to in-pore, exchange and bulk species. Indeed, the variety of exchange rates between in-pore and ex-pore environments, present in experiments but not taken into account in analytical models, is necessary to reproduce the complexity of experimental NMR spectra
The ionization yield in a methane-filled spherical proportional counter
No full textInternational audienceSpherical proportional counters (SPCs) are gaseous particle detectors sensitive to single ionization electrons in their target media, with large detector volumes and low background rates. The \mbox{NEWS-G} collaboration employs this technology to search for low-mass dark matter, having previously performed searches with detectors at the Laboratoire Souterrain de Modane (LSM), including a recent campaign with a 135 cm diameter SPC filled with methane. While in situ calibrations of the detector response were carried out at the LSM, measurements of the mean ionization yield and fluctuations of methane gas in SPCs were performed using a 30 cm diameter detector. The results of multiple measurements taken at different operating voltages are presented. A UV laser system was used to measure the mean gas gain of the SPC, along with and aluminum-fluorescence calibration sources. These measurements will inform the energy response model of future operating detectors
Multiplicity-dependent jet modification from di-hadron correlations in pp collisions at TeV
No full textInternational audienceShort-range correlations between charged particles are studied via two-particle angular correlations in pp collisions at TeV. The correlation functions are measured as a function of the relative azimuthal angle and the pseudorapidity separation for pairs of primary charged particles within the pseudorapidity interval and the transverse-momentum range GeV/. Near-side () peak widths are extracted from a generalised Gaussian fitted over the correlations in full pseudorapidity separation (), while the per-trigger associated near-side yields are extracted for the short-range correlations (). Both are evaluated as a function of charged-particle multiplicity obtained by two different event activity estimators. The width of the near-side peak decreases with increasing multiplicity, and this trend is reproduced qualitatively by the Monte Carlo event generators PYTHIA 8, AMPT, and EPOS. However, the models overestimate the width in the low transverse-momentum region ( GeV/). The per-trigger associated near-side yield increases with increasing multiplicity. Although this trend is also captured qualitatively by the considered event generators, the yield is mostly overestimated by the models in the considered kinematic range. The measurement of the shape and yield of the short-range correlation peak can help us understand the interplay between jet fragmentation and event activity, quantify the narrowing trend of the near-side peak as a function of transverse momentum and multiplicity selections in pp collisions, and search for final-state jet modification in small collision systems
Jet Definition and Transverse-Momentum–Dependent Factorization in Semi-Inclusive Deep-Inelastic Scattering
No full textInternational audienceUsing the colour dipole picture of Deep Inelastic Scattering (DIS) and the Colour Glass Condensate effective theory, we study semi-inclusive jet production in DIS at small in the limit where the photon virtuality is much larger than the transverse momentum squared of the produced jet. In this limit, the cross-section is dominated by aligned jet configurations, that is, quark-antiquark pairs in which one of the fermions -- the would-be struck quark in the Breit frame -- carries most of the longitudinal momentum of the virtual photon. We show that physically meaningful jet definitions in DIS are such that the effective axis of the jet sourced by the struck quark is controlled by its virtuality rather than by its transverse momentum. For such jet definitions, we show that the next-to-leading order (NLO) cross-section admits factorisation in terms of the (sea) quark transverse momentum dependent (TMD) distribution, which in turn satisfies a universal Dokshitzer-Gribov-Lipatov-Altarelli-Parisi and Sudakov evolution
Rapidity dependence of antideuteron coalescence in pp collisions at = 13 TeV with ALICE
No full textInternational audienceThe production yields of antideuterons and antiprotons are measured in pp collisions at a center-of-mass energy of TeV, as a function of transverse momentum () and rapidity (), for the first time up to . The measured spectra are used to study the and rapidity dependence of the coalescence parameter , which quantifies the coalescence probability of antideuterons. The and rapidity dependence of the obtained is extrapolated for GeV/ and using the phenomenological antideuteron production model implemented in PYTHIA 8.3 as well as a baryon coalescence afterburner model based on EPOS 3. Such measurements are of interest to the astrophysics community, since they can be used for the calculation of the flux of antinuclei from cosmic rays, in combination with coalescence models
Interior transmission problems with coefficients of low regularity
No full textInternational audienceWe obtain parabolic transmission eigenvalue-free regions for both isotropic andanisotropic interior transmission problems with coefficients which are Lipschitznear the boundar
