Exciton fine structure and spin decoherence in monolayers of transition metal dichalcogenides

We study the neutral exciton energy spectrum fine structure and its spin dephasing in transition metal dichalcogenides such as MoS$_2$. The interaction of the mechanical exciton with its macroscopic longitudinal electric field is taken into account. The splitting between the longitudinal and transverse excitons is calculated by means of the both electrodynamical approach and $\mathbf k \cdot \mathbf p$ perturbation theory. This long-range exciton exchange interaction can induce valley polarization decay. The estimated exciton spin dephasing time is in the picosecond range, in agreement with available experimental data.Comment: 5 pages, 3 figure

Availability-driven NFV orchestration

Virtual Network Functions as a Service (VNFaaS) is a promising business whose technical directions consist of providing network functions as a Service instead of delivering standalone network appliances, leveraging a virtualized environment named NFV Infrastructure (NFVI) to provide higher scalability and reduce maintenance costs. Operating the NFVI under stringent availability guarantees is fundamental to ensure the proper functioning of the VNFaaS against software attacks and failures, as well as common physical device failures. Indeed the availability of a VNFaaS relies on the failure rate of its single components, namely the physical servers, the hypervisor, the VNF software, and the communication network. In this paper, we propose a versatile orchestration model able to integrate an elastic VNF protection strategy with the goal to maximize the availability of an NFVI system serving multiple VNF demands. The elasticity derives from (i) the ability to use VNF protection only if needed, or (ii) to pass from dedicated protection scheme to shared VNF protection scheme when needed for a subset of the VNFs, (iii) to integrate traffic split and load-balancing as well as mastership role election in the orchestration decision, (iv) to adjust the placement of VNF masters and slaves based on the availability of the different system and network components involved. We propose a VNF orchestration algorithm based on Variable Neighboring Search, able to integrate both protection schemes in a scalable way and capable to scale, while outperforming standard online policies

Exciton dynamics in WSe2 bilayers

We investigate exciton dynamics in 2H-WSe2 bilayers in time-resolved photoluminescence (PL) spectroscopy. Fast PL emission times are recorded for both the direct exciton with $\tau_{D}$ ~ 3 ps and the indirect optical transition with $\tau_{i}$ ~ 25 ps. For temperatures between 4 to 150 K $\tau_{i}$ remains constant. Following polarized laser excitation, we observe for the direct exciton transition at the K point of the Brillouin zone efficient optical orientation and alignment during the short emission time $\tau_{D}$. The evolution of the direct exciton polarization and intensity as a function of excitation laser energy is monitored in PL excitation (PLE) experiments.Comment: 4 pages, 3 figure

Synthesis, crystal structure and characterization of 3-thiophene aldehyde thiosemicarbazone and its complexes with cobalt(II), nickel(II) and copper(II)

The reaction of cobalt(II), nickel(II), copper(II) chlorides and bromides with 3-thiophene aldehyde thiosemicarbazone (3TTSCH) leads to the formation of a series of new complexes: [Co(3TTSC)2], [Ni(3TTSC)2], [CuCl(3TTSC)]2, [CuBr(3TTSC)]2 and [CuBr2(3TTSCH)]. The crystal structures of the free ligand and of the compound [Ni(3TTSC)2] have been determined by X-ray diffraction methods. For all these complexes, the central ion is coordinated through the sulfur and the azomethine nitrogen atom of the thiosemicarbazone. [Co(3TTSC)2], [Ni(3TTSC)2] and [CuBr2(3TTSCH)] are mononuclear species, while [CuCl(3TTSC)]2 and [CuBr(3TTSC)]2 are binuclear complexes

Effet de la fertilisation azotée et phosphorée sur le développement de la Panachure jaune en riziculture aquatique en Côte d’Ivoire

La crise mondiale du riz survenue en 2008 a montré l’impérative nécessité pour les pays tributaires des importations comme la Côte d’Ivoire, d’assurer leur autosuffisance. La fertilisation minérale figure parmiles cinq axes stratégiques définis pour l’accroissement de la production rizicole en Côte d’Ivoire. Sachant l’effet stimulateur de l’engrais azoté sur le développement de certaines maladies telle que la Pyriculariose duriz, un essai a été conduit dans le but de savoir l’influence d’une application optimale de l’azote sur l’épidémie de la Panachure jaune du riz ou Rice Yellow Mottle Virus (RYMV). L’étude a été réalisée selon un dispositif expérimental en SPLIT-PLOT comportant quatre niveaux d’azote (0 kg N Ha-1, 30 kg N Ha-1, 60 kg N Ha-1, 120 kg N Ha-1), trois niveaux de phosphore (0 kg P Ha-1, 13 kg P Ha-1, 26 kg N Ha-1) et 10 génotypes de riz irrigué. Les résultats ont montré que le phosphore et l’interaction NxP n’ont aucun effet significatif sur l’épidémie de RYMV. A l’opposé, les analyses ont mis en évidence un effet significatif de l’azote sur l’incidence de la Panachure jaune à des doses comprises entre 0 et 30 Kg N Ha-1. Cet intervalle de doses étant en deçà de celui des doses recommandées en Côte d’Ivoire, l’intensification de la riziculture aquatique par unefertilisation azotée optimale, n’aura pas d’incidence significative sur le développement de la Panachure jaune. Il faudra cependant sensibiliser les riziculteurs sur l’intérêt d’appliquer des doses d’engrais recommandées dans la lutte contre la virose.Mots clés: Riz irrigué, fertilisation minérale, épidémie, RYMV, incidence

Exciton states in monolayer MoSe2: impact on interband transitions

We combine linear and non-linear optical spectroscopy at 4K with ab initio calculations to study the electronic bandstructure of MoSe2 monolayers. In 1-photon photoluminescence excitation (PLE) and reflectivity we measure a separation between the A- and B-exciton emission of 220 meV. In 2-photon PLE we detect for the A- and B-exciton the 2p state 180meV above the respective 1s state. In second harmonic generation (SHG) spectroscopy we record an enhancement by more than 2 orders of magnitude of the SHG signal at resonances of the charged exciton and the 1s and 2p neutral A- and B-exciton. Our post-Density Functional Theory calculations show in the conduction band along the $K-\Gamma$ direction a local minimum that is energetically and in k-space close to the global minimum at the K-point. This has a potentially strong impact on the polarization and energy of the excitonic states that govern the interband transitions and marks an important difference to MoS2 and WSe2 monolayers.Comment: 8 pages, 3 figure

Synthesis, structural and spectral studies of 5-methyl 2-furaldehyde thiosemicarbazone and its Co, Ni, Cu and Cd complexes

The reaction of cobalt, nickel, copper and cadmium chlorides and bromides with 5-methylfurfural thiosemicarbazone (M5FTSC) leads to the formation of two series of new complexes: [M(M5FTSC)2X2], [M(M5FTSC)X2]. They have been characterized by spectroscopic studies (infrared, 1H NMR, and electronic spectra). The crystal structures of the free ligand M5FTSC and of the compound [CuCl2(M5FTSC)] have been determined by X-ray diffraction methods. For the Co(II), Ni(II) and Cu(II) complexes, the central atom is coordinated through the sulphur atom and the azomethine nitrogen atom whilst for the Cd(II) complexes, the coordination atoms are the sulphur and furanic oxygen atoms instead of the azomethine nitrogen

Effet du paillage par des residus de pois d’angole (cajanus cajan l.) sur le rendement du riz (oryza sativa) pluvial en zone forestiere de Côte d’Ivoire

La riziculture pluviale, en zone forestière de la Côte d'Ivoire, est confrontée à plusieurs contraintes, dont, notamment la baisse de fertilité du sol et l'enherbement excessif. L'effet du paillage de Cajanus cajan comme engrais organique pour le riz pluvial, NERICA 1(Bonfani), a été évalué, en termes de rendement du riz. Cette étude a été conduite de 2003 à 2005 à la station de recherche du Centre National de Recherche Agronomique (CNRA) de Gagnoa. Deux rotations, à base de riz, avec les jachères à C. cajan de 6 mois et de 12 mois ont été testées et comparées, à celle avec la jachère naturelle. La biomasse des précédentes jachères est restée sur le sol comme mulch. Les résultats montrent que C. cajan âgé de 12 mois a produit une biomasse sèche de 17 t ha-1, en moyenne sur deux ans contre 1,7 t.ha-1 en 6 mois. La rotation riz avec C. cajan de 12 mois a amélioré significativement le rendement du riz, avec un gain de paddy qui a varié entre 700 et 900 kg ha-1, par rapport à la jachère naturelle. En plus, cette jachère à cajanus de 12 mois a permis de maintenir un minimum de rendement 1t ha-1. Cette technique offre une alternative de gestion durable des systèmes traditionnels de riziculture pluviale