Triple flame structure and diffusion flame stabilization

The stabilization of diffusion ñames is studied using asymptotic techniques and numerical tools. The configuration studied corresponda to parallel streams of cold oxidizer and fuel initially separated by a splitter píate. It is shown that stabilization of a diffusion flame may only occur in this situation by two processes. First, the flame may be stabilized behind the flame holder in the wake of the splitter píate. For this case, numerical simulations confirm scalings previously predicted by asymptotic analysis. Second, the flame may be lifted. In this case a triple flame is found at longer distanees downstream of the flame holder. The structure and propagation speed of this flame are studied by using an actively controlled numerical technique in which the triple flame is tracked in its own reference frame. It is then possible to investigate the triple flame structure and velocity. It is shown, as suggested from asymptotic analysis, that heat reléase may induce displacement speeds of the triple flame larger than the laminar flame speed corresponding to the stoichiometric conditions prevailing in the mixture approaching the triple flame. In addition to studying the characteristics of triple flames in a uniform flow, their re-sistance to turbulence is investigated by subjecting triple flames to different vortical configurations

Pdf modeling for premixed turbulent combustion based on the properties of iso-concentration surfaces

In premixed turbulent flames the presence of intense mixing zones located in front of and behind the flame surface leads to a requirement to study the behavior of iso-concentration surfaces defined for all values of the progress variable (equal to unity in burnt gases and to zero in fresh mixtures). To support this study, some theoretical and mathematical tools devoted to level surfaces are first developed. Then a database of direct numerical simulations of turbulent premixed flames is generated and used to investigate the internal structure of the flame brush, and a new pdf model based on the properties of iso-surfaces is proposed

Regional Sanctions Against Burundi: A Powerful Campaign and Its Unintended Consequences

This paper examines the impact of regionally imposed sanctions on the trajectory of the Burundian regime and its involvement in the peace process following the 1996 coup in the country. Despite the country's socioeconomic and geopolitical vulnerability, the Buyoya government withstood the pressure from the sanctions. Through a vocal campaign against these sanctions, the new government mitigated the embargo's economic consequences and partially reestablished its international reputation. Paradoxically, this campaign planted the seed for comprehensive political concessions in the long term. While previous literature has attributed the sanctions' success in pressuring the government into negotiations to their economic impact, the government actually responded to the sanction senders' key demand to engage in unconditional, inclusive peace talks under the auspices of the regional mediator once the economy had already started to recover. The regime's anti-sanctions campaign, with its emphasis on the government's willingness to engage in peace talks, backfired, with Buyoya forced to negotiate after having become entrapped in his own rhetoric

Réalisation et caractérisation de photodétecteurs UV par laser à excimère (ArF)

Dans le domaine de la microélectronique, la diminution de la taille des composants est un point clé du développement industriel. La réalisation de jonctions ultra-minces (USJ : Ultra-Shallow Junctions) est devenue une alternative évidente pour les futures technologies CMOS (Complementary Metal Oxide Semiconductor). Elle présente également un fort intérêt pour d’autres applications telles que la conception de détecteurs UV. Dans ce domaine de longueurs d’onde, la pénétration des photons dans le silicium est inférieure á 10 nm. La zone de charge d’espace devra se trouver en surface pour diminuer les pertes de signal par recombinaison. Pour commencer, nous présenterons les performances atteintes par l’association d’une implantation par immersion plasma (PIII : Plasma Immersion Ions Implantation) [1–4] et d’un recuit au laser á excimère (ELA : Excimer Laser Annealing) [4–7]. A l’aide de caractérisations électriques par mesures quatre pointes, nous pouvons estimer le niveau d’activation de nos jonctions. Des analyses SIMS nous ont permis de mesurer le profil de concentration en dopants après activation. Les jonctions obtenues ont une résistance par carré inférieure á 500 Omega/sq pour une profondeur de jonction de 23 nm. Enfin, nous avons réalisé des mesures de courant de fuite sur diodes afin de caractériser la quantité de défauts dans la jonction. Pour compléter cette étude, nous mettrons en évidence des inhomogénéités dues au traitement laser. Des cartographies du photo-courant (LBIC : Light Beam Induced Current) [8–11] á différentes longueurs d’onde nous ont permis de relier ces inhomogénéités aux bords du faisceau laser. Il a été possible par la suite de relier la génération des défauts á un profil non-abrupte de bord de faisceau. Afin de mettre en évidence des défauts dans la structure cristalline du silicium, nos jonctions ont été caractérisées par microscopie électronique á transmission (TEM), ce qui a permis de localiser les défauts sur une couche de 3 nm en surface du substrat

Study On Laser-Induced Periodic Structures And Photovoltaic Application

International audienceWe have irradiated silicon with a series of femtosecond laser pulses to improve light absorption at the silicon surface. The laser treated surface namely black silicon shows excellent optical properties on mono and multicrystalline silicon wafers with a reflectivity reduction down to 3%, without crystal orientation dependence. After the laser process, the front side of samples has been boron-implanted by Plasma Immersion Ion Implantation to create the 3D p+ junction. Improved electrical performances have also been demonstrated with a 57% increase in the photocurrent, compared to non-texturized surfac

Chemical and Enzymatic Synthesis of 2-(2-Carbamoylethyl)- and 2-(2-Carboxyethyl)aziridines and Their Conversion into δ-Lactams and γ-Lactones

Treatment of 1-arylmethyl-2-(2-cyanoethyl)aziridines with a nitrile hydratase afforded the corresponding 2-(2-carbamoylethyl)aziridines, which underwent rearrangement into 5-hydroxypiperidin-2-ones upon heating under microwave irradiation. In addition, treatment of 2-(2-cyanoethyl)aziridines with a nitrilase selectively afforded 5-hydroxypiperidin-2-ones in good yields. On the other hand, chemical hydrolysis of 2-(2-cyanoethyl)aziridines using KOH in EtOH/H₂O furnished the corresponding potassium 3-(aziridin-2-yl)propanoates, which, upon acidification with acetic acid, smoothly rearranged into 4-(aminomethyl)butyrolactones