Management of the orbital angular momentum of vortex beams in a quadratic nonlinear interaction

Light intensity control of the orbital angular momentum of the fundamental beam in a quadratic nonlinear process is theoretically and numerically presented. In particular we analyzed a seeded second harmonic generation process in presence of orbital angular momentum of the interacting beams due both to on axis and off axis optical vortices. Examples are proposed and discussed

An adjustable focusing system for a 2 MeV H- ion beam line based on permanent magnet quadrupoles

A compact adjustable focusing system for a 2 MeV H- RFQ Linac is designed, constructed and tested based on four permanent magnet quadrupoles (PMQ). A PMQ model is realised using finite element simulations, providing an integrated field gradient of 2.35 T with a maximal field gradient of 57 T/m. A prototype is constructed and the magnetic field is measured, demonstrating good agreement with the simulation. Particle track simulations provide initial values for the quadrupole positions. Accordingly, four PMQs are constructed and assembled on the beam line, their positions are then tuned to obtain a minimal beam spot size of (1.2 x 2.2) mm^2 on target. This paper describes an adjustable PMQ beam line for an external ion beam. The novel compact design based on commercially available NdFeB magnets allows high flexibility for ion beam applications.Comment: published in JINST (4th Feb 2013

Significant enhancement of irreversibility field in clean-limit bulk MgB2

Low resistivity ("clean") MgB2 bulk samples annealed in Mg vapor show an increase in upper critical field Hc2(T) and irreversibility field Hirr(T) by a factor of 2 in both transport and magnetic measurements. The best sample displayed Hirr above 14 T at 4.2 K and 6 T at 20 K. These changes were accompanied by an increase of the 40 K resistivity from 1.0 to 18 microohm-cm and a lowering of the resistivity ratio from 15 to 3, while the critical temperature Tc decreased by only 1-2 K. These results point the way to make prepare MgB2 attractive for magnet applications.Comment: 3 pages, 4 figures, submitted to Applied Physics Letter

A system for online beam emittance measurements and proton beam characterization

A system for online measurement of the transverse beam emittance was developed. It is named $^{4}$PrOB$\varepsilon$aM (4-Profiler Online Beam Emittance Measurement) and was conceived to measure the emittance in a fast and efficient way using the multiple beam profiler method. The core of the system is constituted by four consecutive UniBEaM profilers, which are based on silica fibers passing across the beam. The $^{4}$PrOB$\varepsilon$aM system was deployed for characterization studies of the 18~MeV proton beam produced by the IBA Cyclone 18 MeV cyclotron at Bern University Hospital (Inselspital). The machine serves daily radioisotope production and multi-disciplinary research, which is carried out with a specifically conceived Beam Transport Line (BTL). The transverse RMS beam emittance of the cyclotron was measured as a function of several machine parameters, such as the magnetic field, RF peak voltage, and azimuthal angle of the stripper. The beam emittance was also measured using the method based on the quadrupole strength variation. The results obtained with both techniques were compared and a good agreement was found. In order to characterize the longitudinal dynamics, the proton energy distribution was measured. For this purpose, a method was developed based on aluminum absorbers of different thicknesses, a UniBEaM detector, and a Faraday cup. The results were an input for a simulation of the BTL developed in the MAD-X software. This tool allows machine parameters to be tuned online and the beam characteristics to be optimized for specific applications.Comment: published in Journal of Instrumentatio

Critical Field of MGB2 : Crossover from Clean to Dirty Regimes

We have studied the upper critical field, Bc2, in poly-crystalline MgB2 samples in which disorder was varied in a controlled way to carry selectively p and s bands from clean to dirty limit. We have found that the clean regime survives when p bands are dirty and s bands are midway between clean and dirty. In this framework we can explain the anomalous behaviour of Al doped samples, in which Bc2 decreases as doping increases.Comment: 11 pages, 2 figure

Defining cooperative business models for inter-organizational cooperation

Usage of software platforms alongside the business transformation potential of information and communication technology enables cooperation between different companies in both open and networked environments. This is possible when multiple actors cooperate in the delivery of services; each one contributes its own resources, and there is an underlying attractive business model for all of the players involved. This research paper investigates the definition process of a cooperative business model, which involves partners from different countries with different levels of technology, different markets, and different statutory regulations. The aim of this paper is to contribute to both theory and practice by introducing an approach for a cooperative business model definition that can be used in instances where there are conflicting requirements of partners who are willing to cooperate. In the case which is analyzed in this paper, the premature identification of the exploitation alternative scenarios among partners, the adoption of a perspective based on customers\u2019 needs by the means of the business episode concept, and the usage of the business model ontology for the description of the structure of the cooperative business model, have helped the different partners to successfully converge to a common and agreed solution

Angular dependence of magnetoresistivity in c-oriented MgB2 thin film

The anisotropy of MgB2 is still under debate: its value, strongly dependent on the sample and on the measuring method, ranges between 1.2 and 13. In this work we present our results on a MgB2 c-oriented superconducting thin film. To evaluate the anisotropy, we followed two different approaches. Firstly, magnetoresistivity was measured as a function of temperature at selected magnetic fields applied both parallel and perpendicular to the c-axis; secondly, we measured magnetoresistivity at selected temperatures and magnetic fields, varying the angle q between the magnetic field and the c-axis. The anisotropy estimated from the ratio between the upper critical fields parallel and perpendicular to the c-axis and the one obtained in the framework of the scaling approach within the anisotropic Ginzburg-Landau theory are different but show a similar trend in the temperature dependence. The obtained results are compared and discussed in the light of the two-band nature of MgB2. A comparison between critical fields in thin films and single crystal is also performed.Comment: 13 pages, 4 figures, European Physical Journal B in pres