Electrical spin injection into p-doped quantum dots through a tunnel barrier

We have demonstrated by electroluminescence the injection of spin polarized electrons through Co/Al2O3/GaAs tunnel barrier into p-doped InAs/GaAs quantum dots embedded in a PIN GaAs light emitting diode. The spin relaxation processes in the p-doped quantum dots are characterized independently by optical measurements (time and polarization resolved photoluminescence). The measured electroluminescence circular polarization is about 15 % at low temperature in a 2T magnetic field, leading to an estimation of the electrical spin injection yield of 35%. Moreover, this electroluminescence circular polarization is stable up to 70 K.Comment: 6 pages, 4 figure

Fine scale population genomics of the bottlenose dolphin off Western Iberia (northeast Atlantic)

34th European Cetacean Society Conference, O Grove, 16-20 April 2023Bottlenose dolphin (Tursiops truncatus) populations sampled across various geographic regions show fine-scale patterns of genetic structure, likely associated with local habitat preferences. Several population genetic studies have focused on populations from the northeast Atlantic Ocean (NEA), very few including the Portuguese coast. This study investigated the population structure and demographic history of the bottlenose dolphin in this region using double digest restriction site associated DNA sequencing (ddRAD-seq). Samples were collected from the Iberian Peninsula including SW Spain, the Portuguese coast (including Sado estuary), NW Spain and from two Portuguese Macaronesian archipelagos, Madeira and Azores (N=110 samples). We genotyped thousands of single nucleotide polymorphisms markers to study the fine-scale population structure, inbreeding levels and demographic history. Bayesian clustering and Principal Component Analyses showed three major genetic clusters: Pelagic (incl. Madeira and Azores; North Galicia, Portugal coast), Southern/Mediterranean (incl. Gibraltar/Cadiz, previously identified as of Mediterranean origin, and Portugal coast), and Resident (Sado and south Galicia). These clusters differ from each other in terms of genetic diversity and inbreeding levels. While the Pelagic and Southern/Med clusters shows high genetic diversity and a wide geographic distribution, the Resident populations show the opposite. The Resident cluster can be subdivided in Galicia and Sado populations, the latter revealing concerning levels of inbreeding. Preliminary demographic analyses suggest that the Resident populations diverged from the others prior to the Southern/Med-Pelagic divergence, although further analyses are needed. Our results suggest that i) the Resident populations of the Iberian Peninsula should be considered as different management units; ii) bottlenose dolphins sampled along the Portuguese coast are highly genetically diverse, including individuals from the three different clusters; and iii) the Sado population faces a critical situation. Within the framework of the recently proposed SACs for bottlenose dolphins in Portugal, these results highlight the importance of discussions on conservation and management policiesN

La formation de l'oxyde azotique dans les flammes de diffusion de gaz naturel Nitrogen. Oxyde Formation in Natural-Gas Diffusion Flams

L'étude de la formation de l'oxyde azotique dans des flammes de diffusion de ga naturel est effectuée depuis deux ans sur le four expérimental du Groupe d'Etude des Flammes de Gaz Naturel situé à Toulouse. Un certain nombre de variables ont été explorées : type de flamme, excès d'air, préchauffage de l'air, teneur en oxygène du comburant, puissance calorifique, et débit de moment cinétique. L'étude a mis en évidence une corrélation générale, quelle que soit la variable considérée, entre la quantité maximale d'oxyde d'azote formé et la température maximale de la flamme. Certains des résultats précédents ont été exploités à l'Institut Français du Pétrole, en vue d'établir une équation de vitesse de formation de NO applicable aux flammes axiales de diffusion de gaz naturel. Les calculs s'appuient sur les connaissances obtenues lors de l'étude cinétique de formation de NO effectuée au Laboratoire d'Aérothermique Fondamentale. Les résultats du calcul théorique confirment ceux de l'étude sur le four expérimental en ce qui concerne l'influence prépondérante de la température sur la formation de l'oxyde azotique. Par ailleurs, le calcul théorique retrouve bien les résultats obtenus lors de l'étude fondamentale, selon lesquels la cinétique de formation de NO évolue le long de la flamme depuis le front de flamme jusqu'aux gaz brûlés. La généralisation à un grand nombre de flammes de l'équation cinétique expérimentale obtenue nécessite maintenant de prendre en compte certains phénomènes de diffusion négligés jusqu'à présent. <br> Research on the formation of nitrogen oxide in natural-gas diffusion flammes has been going on for two years in the experimental furnace of the Groupe d'Etude des Flammes de Gaz Naturel located in Toulouse. Different variables have been investigoted such as type of flamme, air excess, air preheating, oxygen content in the oxidant, heating power and kinetic moment output. Investigations have revealed a general correlation, no motter what variable is considered, between the maximum amount of nitrogen oxide formed and the maximum température of the flame. Some of the findings have been tested at Institut Français du Pétrole in on effort to find an equation forthe rate of NO formation that could be applied to axial flames from natural gas diffusion. Calculations are based on findings obtained from the kinetic analysis of NO formation that was performed at the Laboratoire d'Aerothermique Fondamentale

Single-electron conductance oscillations of small open quantum dot

We study the conductance of three-lead small open quantum dots fabricated on the basis of a high mobility two-dimensional (2D) electron gas in an AlGaAs/GaAs heterostructure. Large conductance oscillations have been observed, It is shown that the gate voltage period of these oscillations cot-responds to a change of the average dot charge by one electron. We suggest that they are the manifestation of spin-charge separation in small open quantum dots. (C) 2002 Elsevier Science B.V. All rights reserved

Gated wires and interferometers based on Si/SiGe heterostructures

We report the fabrication and study of gated quantum wires and interferometers based on a Si/SiGe heterostructure fabricated by electron lithography and anisotropic ion etching. In the wires, negative magnetoresistance connected with weak localisation effects and in the ring, Aharonov-Bohm oscillations were investigated in the temperature range 30 mK-5 K. The phase coherence time was found to be due to electron- electron scattering with small energy transfer and magnetic impurity scattering. High magnetic field Aharonov-Bohm oscillations connected with the interference of edge states current have been observed in Si/SiGe ring for the first time. (C) 2002 Elsevier Science B.V. All rights reserved

Magnetic behavior and role of the antiphase boundaries in Fe

Magnetite Fe3O4 films were grown on single crystal MgO (001) substrates using facing target sputtering technique. Conversion Electron Mössbauer Spectroscopy and magneto optical polar Kerr spectra have confirmed the stoichiometric repartition of Fe cations corresponding to the inverse spinel structure and the electronic structure characteristic of bulk Fe3O4. Hysteresis loops carried out at room temperature show that, in a 1 T applied magnetic field, only 60% of the saturation magnetization is detected. This behavior is discussed in correlation to the antiphase boundaries (APBs) observed by electron microscopy. Magnetic force microscopy studies show that magnetic domains are larger than the mean distance between APBs