Bound states of edge dislocations: The quantum dipole problem in two dimensions

We investigate bound state solutions of the 2D Schr\"odinger equation with a dipole potential originating from the elastic effects of a single edge dislocation. The knowledge of these states could be useful for understanding a wide variety of physical systems, including superfluid behavior along dislocations in solid $^4$He. We present a review of the results obtained by previous workers together with an improved variational estimate of the ground state energy. We then numerically solve the eigenvalue problem and calculate the energy spectrum. In our dimensionless units, we find a ground state energy of -0.139, which is lower than any previous estimate. We also make successful contact with the behavior of the energy spectrum as derived from semiclassical considerations.Comment: 6 pages, 3 figures, submitted to PR

LUNEX5: A French FEL Test Facility Light Source Proposal

http://accelconf.web.cern.ch/AccelConf/IPAC2012/papers/tuppp005.pdfInternational audienceLUNEX5 is a new Free Electron Laser (FEL) source project aimed at delivering short and coherent X-ray pulses to probe ultrafast phenomena at the femto-second scale, to investigate extremely low density samples as well as to image individual nm scale objects

The LUNEX5 project

http://accelconf.web.cern.ch/AccelConf/FEL2012/papers/froa03.pdfInternational audienceLUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating the production of short, intense, and coherent pulses in the soft X-ray region. The project consists of a Free Electron Laser (FEL) line enabling the most advanced seeding configurations: High order Harmonic in Gas (HHG) seeding and Echo Enable Harmonic Generation (EEHG) with in-vacuum (potentially cryogenic) undulators of 15 and 30 mm period. Two accelerator types feed this FEL line : a 400 MeV Conventional Linear Accelerator (CLA) using superconducting cavities compatible with a future upgrade towards high repetition rate, for the investigations of the advanced FEL schemes; and a 0.4 - 1 GeV Laser Wake Field Accelerator (LWFA), to be qualified in view of FEL application, in the single spike or seeded regime. Two pilot user experiments for timeresolved studies of isolated species and solid state matter dynamics will take benefit of LUNEX5 FEL radiation and provide feedback of the performance of the different schemes under real user conditions

Progress of the LUNEX5 Project

http://accelconf.web.cern.ch/AccelConf/FEL2013/papers/wepso05.pdfInternational audienceLUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating the production of short, intense, and coherent pulses in the soft X-ray region. A 400 MeV superconducting linear accelerator and a laser wakefield accelerator (LWFA), will feed a single Free Electron Laser line with High order Harmonic in Gas and Echo Enable Harmonic Generation seeding. After the Conceptual Design Report (CDR), R&D has been launched on specific magnetic elements (cryo-ready 3 m long in-vacuum undulator, a variable strong permanent magnet quadrupoles), on diagnostics (Smith-Purcell, electro-optics). In recent transport studies of a LWFA based on more realistic beam parameters (1 % energy spread, 1 μm beam size and 1 mrad divergence) than the ones assumed in the CDR, a longitudinal and transverse manipulation enables to provide theoretical amplification. A test experiment is under preparation. It is noted in this context that among the French scientific community's interest in experiments at operating FELs is increasing

Accelerator Physics Code Web Repository

In the framework of the CARE HHH European Network, we have developed a web-based dynamic acceleratorphysics code repository. We describe the design, structure and contents of this repository, illustrate its usage, and discuss our future plans, with emphasis on code benchmarking

Local Government Revenue Mobilisation in Anglophone Africa

This paper examines opportunities and constraints facing local revenue mobilisation in anglophone Africa, with an emphasis on urban settings. It discusses specific revenue instruments and their effects on economic efficiency, income distribution and accountability. In particular, it addresses political and administrative constraints facing various revenue instruments and factors affecting citizens’ compliance. The analysis is illustrated with examples from across anglophone Africa. A general conclusion emerging from the study is that local revenues mobilised in most local government authorities in Africa are necessary but not sufficient to develop and supply adequate services for the fast-growing population. On this basis, areas for further research on local government revenue mobilisation in Africa are identifiedDfI

Accelerator physics code web repository

In the framework of the CARE HHH European Network, we have developed a web-based dynamic accelerator-physics code repository. We describe the design, structure and contents of this repository, illustrate its usage, and discuss our future plans, with emphasis on code benchmarking

INFLUENCE DES DISLOCATIONS SUR LES PHÉNOMÈNES DE TRANSPORT DANS LES SEMICONDUCTEURS

Cet article revoit brièvement les principales propriétés électriques des dislocations dans les semiconducteurs. Dans les semiconducteurs covalents, le rôle essentiel des dislocations est lié à leurs charges de cœur affectant aussi bien la densité des porteurs libres que leur mobilité. Dans le cas du tellure, où certains types de dislocations n'introduisent pas de porteurs supplémentaires, apparaissent plus nettement des effets de diffusion reliés au champ de déformation. Ces différents effets de diffusion sont discutés à l'aide de calculs de mobilité effectués par la méthode de l'énergie perdue.This paper reviews briefly the electrical properties of dislocations in semiconductors. While in covalent semiconductors, the main effects are related to the dislocation core charges, in the case of tellurium, for instance, where some dislocations do not introduce extra free carriers, diffusion phenomena occur connected to the dislocation strain field. Both diffusion effects are discussed with help of the energy loss method mobility calculations

Experimental Frequency Maps For The Esrf Storage Ring

Experimental frequency maps have already revealed unknown characteristics of the ESRF storage ring non-linear dynamics. In the past year, several efforts were undertaken in order to establish this technique as an operational online tool. The acquisition time was significantly reduced by collecting data from a dedicated fast BPM system. The problem of beam decoherence was limited by establishing a method for accurate tune determination in a small number of turns, using the information from all the BPMs around the ring. The possibility to explore the off-momentum dynamics by exciting the beam, with synchronous transverse and longitudinal kicks was also investigated

Carrier mobility versus carrier density in Al x Ga 1 − x N / G a N quantum wells

International audienceExperimental measurements show that, in AlxGa1−xN/GaN triangular quantum wells, the free-carrier mobility experiences a strong decrease with increasing carrier density. A theoretical analysis of the various scattering mechanisms that can explain such a behavior is presented. It shows that, even though phonon and carrier-carrier scattering mechanisms naturally lead to a mobility decrease versus carrier density, they are by themselves not able to justify the whole set of experimental data. Instead, we propose to attribute an extrinsic origin to the scattering associated with the progressive appearance of strain relaxation defects and give explicit expressions for the collision time associated with interface roughness and interface charge spatial fluctuations (“electrical” roughness) which may result from the existence of cracks in AlxGa1−xN, thickness inhomogeneity, misfit dislocations, and alloy disorder