Noncritical quadrature squeezing through spontaneous polarization symmetry breaking

We discuss the possibility of generating noncritical quadrature squeezing by spontaneous polarization symmetry breaking. We consider first type-II frequency-degenerate optical parametric oscillators, but discard them for a number of reasons. Then we propose a four-wave mixing cavity in which the polarization of the output mode is always linear but has an arbitrary orientation. We show that in such a cavity complete noise suppression in a quadrature of the output field occurs, irrespective of the parameter values

The spectroscopic orbits and the geometrical configuration of the symbiotic binary AR Pavonis

We analyze optical and near infrared spectra of intermediate and high resolution of the eclipsing symbiotic system AR Pavonis. We have obtained the radial velocity curves for the red and the hot component from the M-giant absorption lines and from the wings of Halpha, H and He II4686 emission profiles, respectively. From the orbital elements we have derived the masses, Mgiant=2.5 and Mhot =1.0 solar masses, for the red giant and the hot component, respectively. We also present and discuss radial velocity patterns in the blue cF absorption spectrum as well as various emission lines. In particular, we confirm that the blue absorption lines are associated with the hot component. The radial velocity curve of the blue absorption system, however, does not track the hot companion's orbital motion in a straightforward way, and its departures from an expected circular orbit are particularly strong when the hot component is active. We suggest that the cF-type absorption system is formed in material streaming from the giant presumably in a region where the stream encounters an accretion disk or an extended envelope around the hot component. The broad emission wings originate from the inner accretion disk or the envelope around the hot star.We also suggest that the central absorption in H profiles is formed in a neutral portion of the cool giant's wind which is strongly concentrated towards the orbital plane. The nebula in AR Pav seems to be bounded by significant amount of neutral material in the orbital plane. The forbidden emission lines are probably formed in low density ionized regions extended in polar directions and/or the wind-wind interaction zone.Comment: 12 pages, 5 figures, accepted by A&

First-principles study of electron transport through the single-molecule magnet Mn12

We examine electron transport through a single-molecule magnet Mn12 bridged between Au electrodes using the first-principles method. We find crucial features which were inaccessible in model Hamiltonian studies: spin filtering and a strong dependence of charge distribution on local environments. The spin filtering remains robust with different molecular geometries and interfaces, and strong electron correlations, while the charge distribution over the Mn12 strongly depends on them. We point out a qualitative difference between locally charged and free-electron charged Mn12

Effects of bonding type and interface geometry on coherent transport through the single-molecule magnet Mn12

We examine theoretically coherent electron transport through the single-molecule magnet Mn$_{12}$, bridged between Au(111) electrodes, using the non-equilibrium Green's function method and the density-functional theory. We analyze the effects of bonding type, molecular orientation, and geometry relaxation on the electronic properties and charge and spin transport across the single-molecule junction. We consider nine interface geometries leading to five bonding mechanisms and two molecular orientations: (i) Au-C bonding, (ii) Au-Au bonding, (iii) Au-S bonding, (iv) Au-H bonding, and (v) physisorption via van der Waals forces. The two molecular orientations of Mn$_{12}$ correspond to the magnetic easy axis of the molecule aligned perpendicular [hereafter denoted as orientation (1)] or parallel [orientation (2)] to the direction of electron transport. We find that the electron transport is carried by the lowest unoccupied molecular orbital (LUMO) level in all the cases that we have simulated. Relaxation of the junction geometries mainly shifts the relevant occupied molecular levels toward the Fermi energy as well as slightly reduces the broadening of the LUMO level. As a result, the current slightly decreases at low bias voltage. Our calculations also show that placing the molecule in the orientation (1) broadens the LUMO level much more than in the orientation (2), due to the internal structure of the Mn$_{12}$. Consequently, junctions with the former orientation yield a higher current than those with the latter. Among all of the bonding types considered, the Au-C bonding gives rise to the highest current (about one order of magnitude higher than the Au-S bonding), for a given distance between the electrodes. The current through the junction with other bonding types decreases in the order of Au-Au, Au-S, and Au-H. Importantly, the spin-filtering effect in all the nine geometries stays robust and their ratios of the majority-spin to the minority-spin transmission coefficients are in the range of 10$^3$ to 10$^8$. The general trend in transport among the different bonding types and molecular orientations obtained from this study may be applied to other single-molecular magnets.Comment: Accepted for publication in Phys. Rev. B

Open Apps: Opening Teaching Experiences and Applications

The Universitat Oberta de Catalunya (Open University of Catalonia, UOC) is an online university that makes extensive use of information and communication technologies to provide education. Ever since its establishment in 1995, the UOC has developed and tested methodologies and technological support services to meet the educational challenges posed by its student community and its teaching and management staff. The know-how it has acquired in doing so is the basis on which it has created the Open Apps platform, which is designed to provide access to open source technical applications, information on successful learning and teaching experiences, resources and other solutions, all in a single environment. Open Apps is an open, online catalogue, the content of which is available to all students for learning purposes, all IT professionals for downloading and all teachers for reusing. To contribute to the transfer of knowledge, experience and technology, each of the platform¿s apps comes with full documentation, plus information on cases in which it has been used and related tools. It is hoped that such transfer will lead to the growth of an external partner network, and that this, in turn, will result in improvements to the applications and teaching/learning practices, and in greater scope for collaboration. Open Apps is a strategic project that has arisen from the UOC's commitment to the open access movement and to giving knowledge and technology back to society, as well as its firm belief that sustainability depends on communities of interest.La Universitat Oberta de Catalunya (UOC) es una universidad en línea que realiza un uso intensivo de las tecnologías de la información y la comunicación para proporcionar una educación y aprendizaje a lo largo de la vida. Des de sus inicios la universidad ha desarrollado y testeado metodologías y tecnologías con el objetivo de proporcionar soluciones a los retos de aprendizaje y docentes ofrecidos por la comunidad de estudiantes, académicos y personal de gestión. Fundamentado en este saber hacer, nace la plataforma OpenApps con la finalidad principal de poner a disposición de la comunidad la experiencia acumulada en la UOC durante más de 15 años en docencia, aprendizaje y gestión para que pueda ser aplicado, adaptado o evolucionado por terceros. En este artículo se presentan las características esenciales para que una innovación pueda formar parte de esta plataforma institucional, las especificaciones y usuarios de la plataforma, la finalidad del servicio y las futuras líneas de trabajo.La universitat Oberta de Catalunya (UOC) és una universitat en línia que fa un ús intensiu de les tecnologies de la informació i la comunicació per proporcionar una educació i aprenentatge al llarg de la vida. Des dels seus inicis la universitat ha desenvolupat i testejat metodologies i tecnologies amb l'objectiu de proporcionar solucions als reptes d'aprenentatge i docents oferts per la comunitat d'estudiants, acadèmics i personal de gestió. Basat en aquest saber fer, neix la plataforma OpenApps amb la finalitat principal de posar a disposició de la comunitat l'experiència acumulada a la UOC durant més de 15 anys en docència, aprenentatge i gestió, perquè es pugui aplicar, adaptar o desenvolupar per tercers. En aquest article es presenten les característiques essencials perquè una innovació pugui formar part d'aquesta plataforma institucional, les especificacions i usuaris de la plataforma, la finalitat del servei i les futures línies de treball

Construcció programada de polígons i poliedres moleculars i cinc cèntims de les seves aplicacions

En aquest article s'explica com les reaccions d'autoassemblatge (self-assembly) permeten la construcció racional i programada de molts metal·lomacrocicles o espècies discretes amb geometries poligonals o polièdriques. En una segona part, s'expliquen breument algunes de les aplicacions d'aquestes noves supramolècules com són la seva capacitat per a actuar com a anoreactors, catalitzadors, sensors o tamisos moleculars.This paper shows how self-assembly reactions allow the building up of a wide range of metallomacrocycles (polygonal and polyhedral species) in a rational and programmed way. The second part presents a brief survey of some of the applications of these new supramolecules such as cavity-directed synthesis, catalysis, sensing or molecular sieving

MPI+X: task-based parallelization and dynamic load balance of finite element assembly

The main computing tasks of a finite element code(FE) for solving partial differential equations (PDE's) are the algebraic system assembly and the iterative solver. This work focuses on the first task, in the context of a hybrid MPI+X paradigm. Although we will describe algorithms in the FE context, a similar strategy can be straightforwardly applied to other discretization methods, like the finite volume method. The matrix assembly consists of a loop over the elements of the MPI partition to compute element matrices and right-hand sides and their assemblies in the local system to each MPI partition. In a MPI+X hybrid parallelism context, X has consisted traditionally of loop parallelism using OpenMP. Several strategies have been proposed in the literature to implement this loop parallelism, like coloring or substructuring techniques to circumvent the race condition that appears when assembling the element system into the local system. The main drawback of the first technique is the decrease of the IPC due to bad spatial locality. The second technique avoids this issue but requires extensive changes in the implementation, which can be cumbersome when several element loops should be treated. We propose an alternative, based on the task parallelism of the element loop using some extensions to the OpenMP programming model. The taskification of the assembly solves both aforementioned problems. In addition, dynamic load balance will be applied using the DLB library, especially efficient in the presence of hybrid meshes, where the relative costs of the different elements is impossible to estimate a priori. This paper presents the proposed methodology, its implementation and its validation through the solution of large computational mechanics problems up to 16k cores

On the exposure to mobile phone radiation in trains

This report presents theoretical estimates of the Power Density levels which may be reached inside trains. Two possible sources of high levels of radiation are discussed. The first one arises since the walls of the wagons are metallic and therefore bounce back almost all radiation impinging on them. The second is due to the simultaneous emission of a seemingly large number of nearby telephones. The theoretical study presented here shows that Power Densities stay at values below reference levels always.Comment: 9 pages, 1 figur