Non-equilibrium Josephson effect through helical edge states

We study Josephson junctions between superconductors connected through the helical edge states of a two-dimensional topological insulator in the presence of a magnetic barrier. As the equilibrium Andreev bound states of the junction are 4Pi-periodic in the superconducting phase difference, it was speculated that, at finite dc bias voltage, the junction exhibits a fractional Josephson effect with half the Josephson frequency. Using the scattering matrix formalism, we show that signatures of this effect can be seen in the finite-frequency current noise. Furthermore, we discuss other manifestations of the Majorana bound states forming at the edges of the superconductors.Comment: 4+ pages, 3 figure

Spatial price transmission and market integration in Senegal’s groundnut market

The groundnut sector is the largest of Senegal’s agricultural sectors. It has been subject to various degrees of intervention since the country’s independence. Some, including the determination of farm prices by the government have survived the wave of reforms of the 1980s. Groundnut pricing policies have been the source of major transfers from farmers to the groundnut milling industry, which until 2007, was dominated by SONACOS, a publicly owned parastatal. The state was thus a major beneficiary of the transfers. In 2007, the company was privatized and is now privately owned, raising even greater concerns about the distribution of implications of pricing policies for groundnuts. The paper examines the potential ramifications of liberalizing groundnut prices in terms of its impact on prices received by producers and paid by the milling industry. One fundamental question in the analysis is the extent to which local markets would respond to such a move. To answer this question, the paper presents a dynamic model of price formation that uses estimates of spatial integration across local markets to measure the response of local agricultural prices to policy changes. We then apply this model to simulate the impact of liberalizing groundnut prices to allow domestic prices to reflect their international levels. We find that doing so would change prices in the border city of Dakar, which happens to be the central market that determines prices in the local markets of the producing regions of Kaolack and Fatick. We also find that if markets had been fully liberalized when SONACOS was privatized in January 2007, then groundnut prices would have been higher and that the increase in prices would have been passed on almost entirely to producers in Kaolack and, to a lesser extent, to producers in Fatick. Such reforms would have reversed the longstanding discrimination of groundnut farmers. Prices received by farmers in Kaolack over a period of one year would have increased from 352 FCFA/kg to 494 FCFA/kg of shelled groundnuts. For farmers in the Fatick region, prices would increase from 389 FCFA/kg to 474 FCFA/kg.groundnuts, Liberalization, marketing integration, pricing policies, Privatization,

Building capacities for evidence and outcome-based food policy planning and implementation

The Comprehensive Africa Agriculture Development Programme (CAADP) is an Africawide framework for revitalizing agriculture and rural development in order to accelerate economic growth and progress toward poverty reduction and food and nutrition security. This study reviews CAADP and its strategic objectives, key players, implementation modalities, and approach to ensuring evidence and outcome-based policy planning and implementation. The study also lays out CAADP’s common analytical framework at the country level and shares economic modeling results from member countries of the Economic Community of West African States (ECOWAS) in which analysis was conducted to examine agricultural growth and investment options for meeting CAADP growth and expenditure targets and the Millennium Development Goal target of halving poverty. Finally, the paper discusses CAADP’s review and dialogue mechanisms and knowledge support systems that have been put in place to facilitate benchmarking, mutual learning, and capacity strengthening that will improve agricultural policy, program design, and implementation.CAADP, ECOWAS, growth options, MDG 1, Poverty reduction, public expenditure,

Ac Josephson Effect in Topological Josephson Junctions

Topological superconductors admit zero-energy Majorana bound states at their boundaries. In this review article, we discuss how to probe these Majorana bound states in Josephson junctions between two topological superconductors. In the absence of an applied bias, the presence of these states gives rise to an Andreev bound state whose energy varies $4\pi$-periodically in the superconducting phase difference. An applied voltage bias leads to a dynamically varying phase according to the Josephson relation. Furthermore, it leads to dynamics of the occupation of the bound state via its non-adiabatic coupling to the continuum. While the Josephson relation suggests a fractional Josephson effect due to the $4\pi$-periodicity of the bound state, its observability relies on the conservation of the occupation of the bound state on the experimentally probed time scale. We study the lifetime of the bound state and identify the time scales it has to be compared to. In particular, we are interested in signatures of the fractional Josephson effect in the Shapiro steps and in current noise measurements. We also discuss manifestations of the zero-energy Majorana states on the dissipative subgap current.Comment: 19 pages, 12 figure

Cross-correlations of coherent multiple Andreev reflections

We use the Landauer-B\"uttiker scattering theory for electronic transport to calculate the current cross-correlations in a voltage-biased three-terminal junction with all superconducting leads. At low bias voltage, when charge transport is due to coherent multiple Andreev reflections, we find large cross-correlations compared with their normal-state value. Furthermore, depending on the parameters that characterize the properties of the scattering region between the leads, the cross-correlations can reverse their sign with respect to the case of non-interacting fermionic systems.Comment: 10 pages, 5 figures, Contribution for the special issue of Physica E in memory of Markus B\"uttike

Les particularites de la hernie discale lombaire de l’adulte jeune (18-25 ans)

Buts La hernie discale lombaire est rare chez l’enfant et l’adolescent. Peu d’études ont été consacrées aux sujets de 18-25 ans. Nous avons voulu identifier d’éventuelles particularités de cette pathologie dans cette tranche d’âge à travers un échantillon pris en charge dans notre service. Matériels et méthodes Il s’agissait d’une étude rétrospective portant sur 52 patients colligés à l’hôpital de Grand Yoff et au CHU de Fann du 1er Avril 2004 au 31 Mars 2009. L’échantillon était représenté par des sujets de 18 à 25 ans, qui avaient consultés pour lomboradiculalgie avec mise en évidence au niveau de l’imagerie d’un conflit disco-radiculaire. Le suivi s’étalait de un mois à 48 mois. Résultats L’âge moyen était de 22,8 ans. On notait une prédominance masculine (86,5%). Les militaires représentaient 38,4%. La symptomatologie a été brutale dans 23,1% suite à un traumatisme. Le bilan radiologique retrouvait 6 cas de canal lombaire étroit et 6 cas d’anomalie transitionnelle associés à la hernie discale. On ne notait pas de signes de dégénérescence discale. L’étage L4-L5 était concerné dans 53,8%. Treize patients ont été opérés avec dans 46,2% des cas une disparition complète de la symptomatologie initiale à un an.Conclusion La hernie discale lombaire de l’adulte jeune est favorisée par les professions de force et les traumatismes du rachis lombaire. Le traitement doit être le plus conservateur que possible même si les résultats de la discectomie sont meilleurs que chez l’adulte plus âgé

General Conditions for Proximity-Induced Odd-Frequency Superconductivity in Two-Dimensional Electronic Systems

We obtain the general conditions for the emergence of odd-frequency superconducting pairing in a two-dimensional (2D) electronic system proximity coupled to a superconductor, making minimal assumptions about both the 2D system and the superconductor. Using our general results we show that a simple heterostructure formed by a monolayer of a group VI transition metal dichalcogenide, such as molybdenum disulfide, and an s-wave superconductor with Rashba spin-orbit coupling exhibits odd-frequency superconducting pairing. Our results allow the identification of a new class of systems among van der Waals heterostructures in which odd-frequency superconductivity should be present

Pneumocephalie sous durale expansive apres une ventriculo- cisternostomie endoscopique

La pneumocéphalie sous durale est une complication classique de la ventriculo-cisternostomie endoscopique (VCE). Il s’agit le plus souvent d’une pneumocéphalie simple sans traduction clinique. . Nous rapportons le cas d’une femme de 38 ans, ayant subi une VCE pour une hydrocéphalie par sténose de l’aqueduc du mésencéphale. Elle a développé une hémiparésie gauche postopératoire avec un retard de réveil. Le scanner cérébral de contrôle a montré une importante pneumocéphalie sous-durale expansive (signe du Mont Fuji) prédominante à droite. Une surveillance en position TRENDELENBURG, une réhydratation et une oxygénation au masque ont permis d’obtenir une régression complète de l’hémiparésie et la résorption de la pneumocéphalie sur le scanner à J3 postopératoire.Mots clés : Ventriculocisternostomie ; Pneumocéphalie ; Complication