Thermal melting of density waves on the square lattice

We present the theory of the effect of thermal fluctuations on commensurate "p x p" density wave ordering on the square lattice (p >= 3, integer). For the case in which this order is lost by a second order transition, we argue that the adjacent state is generically an incommensurate striped state, with commensurate p-periodic long range order along one direction, and incommensurate quasi-long-range order along the orthogonal direction. We also present the routes by which the fully disordered high temperature state can be reached. For p=4, and at special commensurate densities, the "4 x 4" commensurate state can melt directly into the disordered state via a self-dual critical point with non-universal exponents.Comment: 12 pages, 5 figure

Quantum-dot based nanothermometry in optical plasmonic recording media

We report on the direct experimental determination of the temperature increment caused by laser irradiation in a optical recording media constituted by a polymeric film in which gold nanorods have been incorporated. The incorporation of CdSe quantum dots in the recording media allowed for single beam thermal reading of the on-focus temperature from a simple analysis of the two-photon excited fluorescence of quantum dots. Experimental results have been compared with numerical simulations revealing an excellent agreement and opening a promising avenue for further understanding and optimization of optical writing processes and media

Sub-arcsecond Morphology of Planetary Nebulae

Planetary nebulae (PNe) can be roughly categorized into several broad morphological classes. The high quality images of PNe acquired in recent years, however, have revealed a wealth of fine structures that preclude simplistic models for their formation. Here we present narrow-band, sub-arcsecond images of a sample of relatively large PNe that illustrate the complexity and variety of small-scale structures. This is especially true for bipolar PNe, for which the images reveal multi-polar ejections and, in some cases, suggest turbulent gas motions. Our images also reveal the presence or signs of jet-like outflows in several objects in which this kind of component has not been previously reported.Comment: 7 pages, 7 figures, Accepted for publication in PAS

Evidence for gapped spin-wave excitations in the frustrated Gd2Sn2O7 pyrochlore antiferromagnet from low-temperature specific heat measurements

We have measured the low-temperature specific heat of the geometrically frustrated pyrochlore Heisenberg antiferromagnet Gd2Sn2O7 in zero magnetic field. The specific heat is found to drop exponentially below approximately 350 mK. This provides evidence for a gapped spin-wave spectrum due to an anisotropy resulting from single ion effects and long-range dipolar interactions. The data are well fitted by linear spin-wave theory, ruling out unconventional low energy magnetic excitations in this system, and allowing a determination of the pertinent exchange interactions in this material

Absorption efficiency of gold nanorods determined by quantum dot fluorescence thermometry

In this work quantum dot fluorescence thermometry, in combination with double-beam confocal microscopy, has been applied to determine the thermal loading of gold nanorods when subjected to an optical excitation at the longitudinal surface plasmon resonance. The absorbing/heating efficiency of low (≈3) aspect ratio gold nanorods has been experimentally determined to be close to 100%, in excellent agreement with theoretical simulations of the extinction, absorption, and scattering spectra based on the discrete dipole approximation

Stereochemical aspects and the synthetic scope of the SHi at the sulfur atom. Preparation of enantiopure 3-substituted 2,3-dihydro-1,2- benzoisothiazole 1-oxides and 1,1-dioxides

Intramolecular homolytic substitution (SHi) on the sulfur atom at acyclic N-(o-bromobenzyl)sulfinamides takes place with a complete inversion of the configuration and provides an excellent tool to connect N-tert-butanesulfinylimines with enantiopure 3-substituted benzo-fused sulfinamides (1,2-benzoisothiazoline 1-oxides) and the related pharmacologically relevant sulfonamidesThe Spanish Government (grant CTQ2012-35957) and Comunidad de Madrid (CCG08-UAM/PPQ-4151; S2009/PPQ1634

Anisotropic lattice changes in femtosecond laser inscribed Nd3+:MgO:LiNbO3 optical waveguides

We report on the fabrication and microspectroscopy imaging of femtosecond laser written double-filament based Nd3+ :MgO:LiNbO3 optical waveguides. The waveguiding high refractive-index regions are identified by blueshifts of the Nd3+ ion fluorescence lines with no deterioration in the fluorescence efficiency, whereas filamentary low-index regions are identified by both a Nd3+ line redshift and a fluorescence efficiency reduction. The lattice structural micromodifications at the origin of both waveguide formation and Nd3+ fluorescence changes have been investigated by means of confocal micro-Raman experiments. We have found that the direct laser written filaments are mainly constituted by a large density of defects, together with a marked axial compression perpendicular to the filaments �along the optical c-axis�. Conversely, the high-index waveguiding regions are characterized by a pronounced anisotropic dilatation of the LiNbO3 lattice xy-planes

Quantum spin fluctuations in the dipolar Heisenberg-like rare earth pyrochlores

The magnetic pyrochlore oxide materials of general chemical formula R2Ti2O7 and R2Sn2O7 (R = rare earth) display a host of interesting physical behaviours depending on the flavour of rare earth ion. These properties depend on the value of the total magnetic moment, the crystal field interactions at each rare earth site and the complex interplay between magnetic exchange and long-range dipole-dipole interactions. This work focuses on the low temperature physics of the dipolar isotropic frustrated antiferromagnetic pyrochlore materials. Candidate magnetic ground states are numerically determined at zero temperature and the role of quantum spin fluctuations around these states are studied using a Holstein-Primakoff spin wave expansion to order 1/S. The results indicate the strong stability of the proposed classical ground states against quantum fluctuations. The inclusion of long range dipole interactions causes a restoration of symmetry and a suppression of the observed anisotropy gap leading to an increase in quantum fluctuations in the ground state when compared to a model with truncated dipole interactions. The system retains most of its classical character and there is little deviation from the fully ordered moment at zero temperature.Comment: Latex2e, 18 pages, 4 figures, IOP forma

The digital press and the defence of intellectual property rights: The Spanish conflict as a European Case Study

This article analyses the on-going struggle over property rights in journalism in Europe, with a particular emphasis on the situation in Spain. To do so, we have carried out a historical review of the main conflicts on which the defence of intellectual property on the internet has centred. The European legislative system has tended to shy away from involvement in the area. The decisions and actions of the Member States have revealed a lack of common policy in the field of intellectual property rights as a result of the facultative nature of EU Directives. State judicial bodies diverge in their regulation of the protection of the press regarding news aggregators. Intermediaries are deemed parasites of the transformed value chain of the press industry by certain sectors. In the face of the tension which has surfaced between editors and news aggregators, diplomacy would appear to have become a key player as mediation takes place, with the intermediaries attempting to reach press collaboration agreements with the giants of the net. The services and activities which feature in the digital environment outpace judicial orders and, consequently, out-of-court settlements appear to be preferred by some media. At the same time, they await the EU authorities' debate on the regulatory framework, which is expected to afford greater protection to press editors.El artículo analiza la pugna existente entorno a los derechos de propiedad de la obra periodística en el ámbito digital en el contexto europeo, con especial énfasis en la situación española. Para ello, se realiza un recorrido histórico por los principales conflictos sobre los que ha girado la defensa de la propiedad intelectual en la red. El sistema legislativo europeo ha sido poco intervencionista en esta materia. Las decisiones y las actuaciones de los estados miembros evidencian la falta de una política común en materia de derechos de propiedad intelectual por el carácter facultativo de las directivas comunitarias. Las disposiciones jurídicas estatales divergen en su regulación sobre la protección del sector de la prensa frente a los agregadores de noticias. Intermediarios que son calificados por una parte del sector como parásitos de la transformada cadena de valor de la industria de la prensa. Ante las tensiones que han surgido entre los editores y los agregadores de noticias, parece asumir un papel destacado la diplomacia para mediar con los intermediarios en el alcance de acuerdos de colaboración de la prensa con los gigantes de la web. Los servicios y actividades en el entorno digital van más rápidos que los ordenamientos jurídicos y los acuerdos extrajudiciales parecen convencer a algunos medios, mientras se mantienen a la espera de que las autoridades europeas debatan sobre un marco regulatorio que previsiblemente ofrecerá una mayor protección a los editores de prensa