Shape resonances in the superconducting order parameter of ultrathin nanowires

We study the shape resonance effect associated with the confined transverse superconducting modes of a cylindrical nanowire in the clean limit. Results of numerical investigations of the Bogoliubov-de Gennes equations show significant deviations of the energy gap parameter from its bulk value with a profound effect on the transition temperature. The most striking is that the size of the resonances is found to be by about order of magnitude larger than in ultrathin metallic films with the same width.Comment: 4 pages, 2 figure

The Public Pension System in Romania – Analysis Before and After 1999

Objectives This paper aims to examine the public pension system in Romania and the significant differences that 1999 brought it. It is important to see if system effects such as the number of beneficiaries and collapse on the number of taxpayers are experienced in present. It explores the main types of pension granted in the public pension system - pensions for old age. Approach It is an attempt to identify the main sources (contributions owed by employers and employees) and also the way pensions are calculated and given before and after 1999. Results We conclude that public pension system in Romania has suffered many changes in a positive way. Implications For taxpayers, both employers and employees it is important that the public pension system work in optimal conditions, that the minimum and maximum contribution "stage" take the proper values. Value Knowing the importance of the public pension system in the Romanian society will know what measures should be taken to improve it

Contribution des forêts à une économie verte dans les pays du Moyen Orient et d’Afrique du Nord

Bien qu’il soit admis que les forêts contribuent significativement à une économie verte, leur rôle précis n’a pas encore été complètement étudié. Cet article vise à combler ce besoin concernant les forêts d’Afrique du Nord et du Moyen Orient et propose des recommandations concrètes aux décideurs. En général, les produits forestiers non-ligneux constituent le principal bénéfice issu des forêts d’Afrique du Nord et du Moyen Orient. La protection des bassins versants est également un bénéfice significatif. Certains ecosystèmes spécifiques peuvent atteindre des valeurs particulièrement importantes (écosystème du chêne-liège en Tunisie et de la forêt de la Maamora au Maroc). Un large éventail d’instruments a été élaboré en vue de tirer profit des biens et services fournis par les forêts pour le développement d’une économie verte. Plusieurs pays ont déjà développé des filières de produits forestiers non-ligneux, établi des aires protégées et certains sont engagés dans la comptabilité verte. Cependant, rares sont les pays à avoir conçu des mécanismes innovants tels que les paiements pour services environnementaux et la finance carbone

Contribution of Forests to a Green Economy in the Middle East and North Africa Region

Although there is broad agreement that forests can make substantial contributions to a green economy, their precise role has not yet been investigated comprehensively. This paper addresses this gap for forests in the Middle East and North Africa and makes concrete recommendations to decision-makers. Overall, non-timber forest products are the most important forest benefit. Watershed protection is very significant. Specific ecosystems can reach particularly high values, such as cork oak in Tunisia and Maamora forests in Morocco. A wide range of instruments has been developed to help capture forest benefits in ways that promote a green economy. Some countries have already created value chains for non-wood forest products, established protected areas, and promoted green accounting. However, only a few countries have introduced innovative mechanisms such as payments for environmental services and carbon finance

Evaluation économique des biens et services des forêts tunisiennes

L’évaluation économique des biens et services des écosystèmes forestiers est essentielle afin de justifier les investissements nécessaires à leur conservation ou à leur extension, et à démontrer les conséquences de la dégradation de ces écosystèmes sur le bien-être humain. Cet article vise à évaluer les biens et services fournis par les forêts tunisiennes, et en particulier par deux écosystèmes représentatifs, le chêne-liège et le pin d’Alep. Le concept de Valeur Economique Totale a été utilisé afin d’identifier les différentes valeurs à évaluer. Les résultats montrent que, dans l’ensemble, les forêts tunisiennes génèrent des bénéfices annuels de 91 euros par hectare. Au niveau national, l’amélioration de la production fourragère et la conservation des bassins versants devraient être mieux intégrées dans les stratégies et plans de développement rural et les chaînes de valeur des produits forestiers devraient être développées. Au niveau local, l’évaluation économique des investissements et l’utilisation d’instruments spécifiques concrets pour assurer leur durabilité (par exemple les Paiements pour les Services Environnementaux) doivent être mis en place

Atypical BCS-BEC crossover induced by quantum-size effects

Quantum-size oscillations of the basic physical characteristics of a confined fermionic condensate are a well-known phenomenon. Its conventional understanding is based on the single-particle physics, whereby the oscillations follow the size-dependent changes in the single-particle density of states. Here we present a study of a cigar-shaped ultracold superfluid Fermi gas, which demonstrates an important many-body aspect of the quantum-size effects, overlooked previously. The many-body physics is revealed in the atypical crossover from the Bardeen-Cooper-Schrieffer (BCS) superfluid to the Bose-Einstein condensate (BEC) induced by the size quantization of the particle motion. Quantized perpendicular spectrum results in the formation of single-particle subbands (shells) so that the aggregate fermionic condensate becomes a coherent mixture of subband condensates. Each time when the lower edge of a subband crosses the chemical potential, the BCS-BEC crossover is approached in this subband, and the aggregate condensate contains both the BCS and BEC-like components.Comment: 7 pages, 5 figure

Quantum Transport in a Nanosize Silicon-on-Insulator Metal-Oxide-Semiconductor

An approach is developed for the determination of the current flowing through a nanosize silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors (MOSFET). The quantum mechanical features of the electron transport are extracted from the numerical solution of the quantum Liouville equation in the Wigner function representation. Accounting for electron scattering due to ionized impurities, acoustic phonons and surface roughness at the Si/SiO2 interface, device characteristics are obtained as a function of a channel length. From the Wigner function distributions, the coexistence of the diffusive and the ballistic transport naturally emerges. It is shown that the scattering mechanisms tend to reduce the ballistic component of the transport. The ballistic component increases with decreasing the channel length.Comment: 21 pages, 8 figures, E-mail addresses: [email protected]

Metallic nanograins: spatially nonuniform pairing induced by quantum confinement

It is well-known that the formation of discrete electron levels strongly influences the pairing in metallic nanograins. Here we focus on another effect of quantum confinement in superconducting grains that was not studied previously, i.e., spatially nonuniform pairing. This effect is very significant when single-electron levels form bunches and/or a kind of shell structure: in highly symmetric grains the order parameter can exhibit variations with position by an order of magnitude. Nonuniform pairing is closely related to a quantum-confinement induced modification of the pairing-interaction matrix elements and size-dependent pinning of the chemical potential to groups of degenerate or nearly degenerate levels. For illustration we consider spherical metallic nanograins. We show that the relevant matrix elements are as a rule enhanced in the presence of quantum confinement, which favors spatial variations of the order parameter, compensating the corresponding energy cost. The size-dependent pinning of the chemical potential further increases the spatial variation of the pair condensate. The role of nonuniform pairing is smaller in less symmetric confining geometries and/or in the presence of disorder. However, it always remains of importance when the energy spacing between discrete electron levels $\delta$ is approaching the scale of the bulk gap $\Delta_B$, i.e., $\delta > 0.1$-$0.2\,\Delta_B$

Introducing Preference-Based Argumentation to Inconsistent Ontological Knowledge Bases

International audienceHandling inconsistency is an inherent part of decision making in traditional agri-food chains – due to the various concerns involved. In order to explain the source of inconsistency and represent the existing conflicts in the ontological knowledge base, argumentation theory can be used. However, the current state of art methodology does not allow to take into account the level of significance of the knowledge expressed by the various ontological knowledge sources. We propose to use preferences in order to model those differences between formulas and evaluate our proposal practically by implementing it within the INRA platform and showing a use case using this formalism in a bread making decision support system

Superconducting nanowires: quantum confinement and spatially dependent Hartree-Fock potential

It is well-known that in bulk, the solution of the Bogoliubov-de Gennes equations is the same whether or not the Hartree-Fock term is included. Here the Hartree-Fock potential is position independent and, so, gives the same contribution to both the single-electron energies and the Fermi level (the chemical potential). Thus, the single-electron energies measured from the Fermi level (they control the solution) stay the same. It is not the case for nanostructured superconductors, where quantum confinement breaks the translational symmetry and results in a position dependent Hartree-Fock potential. In this case its contribution to the single-electron energies depends on the relevant quantum numbers. We numerically solved the Bogoliubov-de Gennes equations with the Hartree-Fock term for a clean superconducting nanocylinder and found a shift of the curve representing the thickness-dependent oscillations of the critical superconducting temperature to larger diameters