Vortex as a probe - suggested measurement of the order parameter structure in iron-based superconductors

Impurities, inevitably present in all samples, induce elastic transitions between quasiparticle states on the contours of constant energy. These transitions may be seen in Fourier transformed scanning tunneling spectroscopy experiments, sorted by their momentum transfer. In a superconductor, anomalous scattering in the pairing channel may be introduced by magnetic field. When a magnetic field is applied, vortices act as additional sources of scattering. These additional transition may enhance or suppress the impurity-induced scattering. We find that the vortex contribution to the transitions is sensitive to the momentum-space structure of the pairing function. In the iron-based superconductors there are both electron and hole pockets at different regions of the Brillouin zone. Scattering processes therefore represent intrapocket or interpocket transitions, depending on the momentum transfer in the process. In this work we show that while in a simple s-wave superconductors all transitions are enhanced by vortex scattering, in an s+- superconductor only intra-pocket transitions are affected. We suggest this effect as a probe for the existence of the sign change of the order parameter.Comment: 7 pages, 4 figure

Spin-Exchange Interaction in ZnO-based Quantum Wells

Wurtzitic ZnO/(Zn,Mg)O quantum wells grown along the (0001) direction permit unprecedented tunability of the short-range spin exchange interaction. In the context of large exciton binding energies and electron-hole exchange interaction in ZnO, this tunability results from the competition between quantum confinement and giant quantum confined Stark effect. By using time-resolved photoluminescence we identify, for well widths under 3 nm, the redistribution of oscillator strengths between the A and B excitonic transitions, due to the enhancement of the exchange interaction. Conversely, for wider wells, the redistribution is cancelled by the dominant effect of internal electric fields, which dramatically reduce the exchange energy.Comment: 14 pages, 3 figure

Electron-impact rotational and hyperfine excitation of HCN, HNC, DCN and DNC

Rotational excitation of isotopologues of HCN and HNC by thermal electron-impact is studied using the molecular {\bf R}-matrix method combined with the adiabatic-nuclei-rotation (ANR) approximation. Rate coefficients are obtained for electron temperatures in the range 5$-$6000 K and for transitions among all levels up to J=8. Hyperfine rates are also derived using the infinite-order-sudden (IOS) scaling method. It is shown that the dominant rotational transitions are dipole allowed, that is those for which $\Delta J=1$. The hyperfine propensity rule $\Delta J=\Delta F$ is found to be stronger than in the case of He$-$HCN collisions. For dipole allowed transitions, electron-impact rates are shown to exceed those for excitation of HCN by He atoms by 6 orders of magnitude. As a result, the present rates should be included in any detailed population model of isotopologues of HCN and HNC in sources where the electron fraction is larger than 10$^{-6}$, for example in interstellar shocks and comets.Comment: 12 pages, 4 figures, accepted in MNRAS (2007 september 3

Carbon burning in intermediate mass primordial stars

The evolution of a zero metallicity 9 M_s star is computed, analyzed and compared with that of a solar metallicity star of identical ZAMS mass. Our computations range from the main sequence until the formation of a massive oxygen-neon white dwarf. Special attention has been payed to carbon burning in conditions of partial degeneracy as well as to the subsequent thermally pulsing Super-AGB phase. The latter develops in a fashion very similar to that of a solar metallicity 9 M_s star, as a consequence of the significant enrichment in metals of the stellar envelope that ensues due to the so-called third dredge-up episode. The abundances in mass of the main isotopes in the final ONe core resulting from the evolution are X(^{16}O) approx 0.59, X(^{20}Ne) approx 0.28 and X(^{24}Mg) approx 0.05. This core is surrounded by a 0.05 M_s buffer mainly composed of carbon and oxygen, and on top of it a He envelope of mass 10^{-4} M_sComment: 11 pages, 11 figures, accepted for publication in A&

Phase transition of one dimensional bosons with strong disorder

We study one dimensional disordered bosons at large commensurate filling. Using a real space renormalization group approach we find a new random fixed point which controls a phase transition from a superfluid to an incompressible Mott-glass. The transition can be tuned by changing the disorder distribution even with vanishing interactions. We derive the properties of the transition, which suggest that it is in the Kosterlitz-Thouless universality class.Comment: 4 pages 3 embedded eps figure

The Organizational Implications of Creativity: The US Film Industry in Mid-XXth Century

We develop a basic framework to understand the organization of highly creative activities. Management faces a fundamental tradeoff in organizing such activities. On the one hand, since creativity cannot be achieved by command and control or by monetary incentives, internal/contractual production of creative products is plagued by hazards arising from their fundamental characteristics: extremely high input, output and market uncertainty, and the inherent informational advantages of creative talent. Procuring highly creative products in the market place, though, exposes the distributor to a fundamental risk: independently produced creative goods are generic distribution-wise. Thus, in procuring creative products in the marketplace, distributors face the unavoidable winner's curse risk. Since this risk is, to a large extent, independent of the creative nature of the product, the higher the creative content, the higher the relative hazards associated with internal or contractual production. Thus, internal/contractual production of creative goods will tend to be less prevalent the higher the creative content associated with its production. We apply this insight to the evolution of the U.S. film industry in the mid-XXth century. We exploit two simultaneous natural experiments -- the diffusion of TV and the Paramount antitrust decision forcing the separation of exhibitors from distributors and prohibiting the use of block-booking. Both events increased the demand for creative content in movies. We develop empirical implications which we test by analyzing in detail the decision by distributors to produce films internally or to procure then in the market place, in the face of an increase in the demand for creative content.

An Effective Field Theory Look at Deep Inelastic Scattering

This talk discusses the effective field theory view of deep inelastic scattering. In such an approach, the standard factorization formula of a hard coefficient multiplied by a parton distribution function arises from matching of QCD onto an effective field theory. The DGLAP equations can then be viewed as the standard renormalization group equations that determines the cut-off dependence of the non-local operator whose forward matrix element is the parton distribution function. As an example, the non-singlet quark splitting functions is derived directly from the renormalization properties of the non-local operator itself. This approach, although discussed in the literature, does not appear to be well known to the larger high energy community. In this talk we give a pedagogical introduction to this subject.Comment: 11 pages, 1 figure, To appear in Modern Physics Letters

Prólogo al libro: Derecho renovado del consumidor: entre la economía y el Derecho

La obra es un instrumento útil para estudiantes universitarios, profesionales e interesados en la protección del consumidor; cuyo interés se eleva cuanto mayor es el desarrollo tecnológico y el grado de sofisticación por el que se encamina la evolución de la sociedad actual. Tanto la estructura y contenido del libro, como el enfoque multidisciplinar de las materias objeto de análisis responden al modelo del Espacio Europeo de Educación Superior (EEES), basado en la adquisición de competencias y desarrollo de habilidades por parte del alumno. En la primera parte se estudian: (i) el contexto socioeconómico y jurídico internacional, (ii) el tratamiento de la publicidad, competencia desleal, venta a pérdida (iii) el consumidor-inversor, la contratación de derivados y la información como contenido fundamental (iv) control y aplicación judicial de las cláusulas abusivas, (vi) arbitraje de consumo y solución extrajudicial de controversias. En la segunda parte se analizan 54 términos legales de uso necesario en el Derecho de la contratación y la acción del consumidor. Entre ellos: las Condiciones generales de la contratación. Consumidor. Contrato de adhesión. Cláusulas abusivas. Cláusulas no negociadas individualmente. Responsabilidad por producto defectuoso. Contratación Electrónica. servicios financieros. Garantías comerciales. La originalidad de la obra reside en el enfoque económico y jurídico interdisciplinar en el que se desarrollan las materias estudiadas y en la doble metodología utilizada para analizar las distintos aspectos estudiados. De este modo, la finalidad docente de la obra se enriquece y combina con su aptitud para ser utilizada en la investigación