Ab initio Evidence for Giant Magnetoelectric Responses Driven by Structural Softness

We show that inducing structural softness in regular magnetoelectric (ME) multiferroics -- i.e., tuning the materials to make their structure strongly reactive to applied fields -- makes it possible to obtain very large ME effects. We present illustrative first-principles results for BiFeO3 thin films.Comment: 4 pages with 3 figures embedded. More information at http://www.icmab.es/dmmis/leem/jorg

MCMC Bayesian Estimation in FIEGARCH Models

Bayesian inference for fractionally integrated exponential generalized autoregressive conditional heteroskedastic (FIEGARCH) models using Markov Chain Monte Carlo (MCMC) methods is described. A simulation study is presented to access the performance of the procedure, under the presence of long-memory in the volatility. Samples from FIEGARCH processes are obtained upon considering the generalized error distribution (GED) for the innovation process. Different values for the tail-thickness parameter \nu are considered covering both scenarios, innovation processes with lighter (\nu2) tails than the Gaussian distribution (\nu=2). A sensitivity analysis is performed by considering different prior density functions and by integrating (or not) the knowledge on the true parameter values to select the hyperparameter values

Quasinormal modes of asymptotically flat rotating black holes

We study the main properties of general linear perturbations of rotating black holes in asymptotically flat higher-dimensional spacetimes. In particular, we determine the quasinormal mode (QNM) spectrum of singly spinning and equal angular momenta Myers-Perry black holes (MP BHs). Emphasis is also given to the timescale of the ultraspinning and bar-mode instabilities in these two families of MP BHs. For the bar-mode instabilities in the singly spinning MP BH, we find excellent agreement with our linear analysis and the non-linear time evolution of Shibata and Yoshino for d=6,7 spacetime dimensions. We find that d=5 singly spinning BHs are linearly stable. In the context of studying general relativity in the large dimension limit, we obtain the QNM spectrum of Schwarzschild BHs and rotating MP BHs for large dimensions. We identify two classes of modes. For large dimensions, we find that in the limit of zero rotation, unstable modes of the MP BHs connect to a class of Schwarzschild QNMs that saturate to finite values.Comment: 52 pages. 25 figure

Brownian cluster dynamics with short range patchy interactions. Its application to polymers and step-growth polymerization

We present a novel simulation technique derived from Brownian cluster dynamics used so far to study the isotropic colloidal aggregation. It now implements the classical Kern-Frenkel potential to describe patchy interactions between particles. This technique gives access to static properties, dynamics and kinetics of the system, even far from the equilibrium. Particle thermal motions are modeled using billions of independent small random translations and rotations, constrained by the excluded volume and the connectivity. This algorithm, applied to a single polymer chain leads to correct static and dynamic properties, in the framework where hydrodynamic interactions are ignored. By varying patch angles, various chain flexibilities can be obtained. We have used this new algorithm to model step-growth polymerization under various solvent qualities. The polymerization reaction is modeled by an irreversible aggregation between patches while an isotropic finite square-well potential is superimposed to mimic the solvent quality. In bad solvent conditions, a competition between a phase separation (due to the isotropic interaction) and polymerization (due to patches) occurs. Surprisingly, an arrested network with a very peculiar structure appears. It is made of strands and nodes. Strands gather few stretched chains that dip into entangled globular nodes. These nodes act as reticulation points between the strands. The system is kinetically driven and we observe a trapped arrested structure. That demonstrates one of the strengths of this new simulation technique. It can give valuable insights about mechanisms that could be involved in the formation of stranded gels.Comment: 55 pages, 32 figure

Periodic Gravitational Waves From Small Cosmic String Loops

We consider a population of small, high-velocity cosmic string loops. We assume the typical length of these loops is determined by the gravitational radiation scale and use the results of \cite{Polchinski:2007rg} which pointed out their highly relativistic nature. A study of the gravitational wave emission from such a population is carried out. The large Lorentz boost involved causes the lowest harmonics of the loops to fall within the frequency band of the LIGO detector. Due to this feature the gravitational waves emitted by such loops can be detected in a periodic search rather than in burst or stochastic analysis. It is shown that, for interesting values of the string tension (10^{-10}\lsim G\mu\lsim 10^{-8}) the detector can observe loops at reasonably high redshifts and that detection is, in principle, possible. We compute the number of expected observations produced by such a process. For a 10 hour search we find that this number is of order $O(10^{-4})$. This is a consequence of the low effective number density of the loops traveling along the line of sight. However, small probabilities of reconnection and longer observation times can improve the result.Comment: 1+15 pages, 7 figure

Evaluación de los efectos del herbicida glifosato en el pez Prochilodus lineatus a través del test de aberración cromosómica.

The widespread use of glyphosate has been subject of numerous controversies since the prolonged exposure to low concentrations of this substance could lead to toxic effects. Then, the appearance of pathologies in medium and long term progressively will increase because of the exposure of people and animals through the consumption of contaminated water or food. Considering this, the aim of this study was to evaluate the potential mutagenicity of glyphosate herbicide in fish (Prochilodus lineatus) using the test of chromosome aberrations. The fish were exposed to 0,1 ug/l of glyphosate for 70 days. After this period, samples of the anterior portion of the kidney were extracted for chromosomal aberrations (CAs) analysis. A greater number of CAs (gaps, breaks, stickiness, endomitosis, fragmentations, and pulverizations) were observed in individuals exposed to the pesticide. The statistical analysis of the data showed significant differences between the control and treated groups. In this way, the results suggested the existence of a genetic response as a consequence of pesticide exposure in fish.El uso generalizado del glifosato ha sido objeto de numerosas controversias, ya que la exposición prolongada a bajas concentraciones de este agroquímico podría dar lugar a efectos no deseados o nocivos. Ello favorecería la aparición de patologías en el mediano y largo plazo, lo que aumenta progresivamente el riesgo de exposición en seres humanos y animales, a través del consumo de agua y alimentos contaminados. Teniendo en cuenta esta premisa, el objetivo del trabajo fue evaluar el posible efecto mutagénico del herbicida a través de la prueba de aberraciones cromosómicas en peces de la especie Prochilodus lineatus. Los peces fueron expuestos a 0,1 ug/l de glifosato durante 70 días. Después de este período una muestra de la porción anterior del riñón fue extraída para el análisis de aberraciones cromosómicas (AC). En los individuos expuestos al pesticida se registró mayor número de AC. El análisis estadístico de los datos mostró diferencias significativas entre los grupos control y tratado. Los resultados sugieren la existencia de una respuesta genética causada por la exposición y el contacto de los especímenes con el herbicida

Magnetoelectric response of multiferroic BiFeO3 and related materials

We present a first-principles scheme for computing the magnetoelectric response of multiferroics. We apply our method to BiFeO3 (BFO) and related compounds in which Fe is substituted by other magnetic species. We show that under certain relevant conditions -- i.e., in absence of incommensurate spin modulation, as in BFO thin films and some BFO-based solid solutions -- these materials display a large linear magnetoelectric response. Our calculations reveal the atomistic origin of the coupling and allow us to identify the most promising strategies to enhance it.Comment: 4 pages with 1 figure embedded. More information at http://www.icmab.es/dmmis/leem/jorg

Chemical abundances for the transiting planet host stars OGLE-TR-10, 56, 111, 113, 132 and TrES-1. Abundances in different galactic populations

We used the UVES spectrograph (VLT-UT2 telescope) to obtain high-resolution spectra of 6 stars hosting transiting planets, namely for OGLE-TR-10, 56, 111, 113, 132 and TrES-1. The spectra are now used to derive and discuss the chemical abundances for C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu and Zn. Abundances were derived in LTE, using 1-D plane-parallel Kurucz model atmospheres. For S, Zn and Cu we used a spectral synthesis procedure, while for the remaining cases the abundances were derived from measurements of line-equivalent widths. The resulting abundances are compared with those found for stars in the solar neighborhood. Distances and galactic coordinates are estimated for the stars. We conclude that besides being particularly metal-rich, with small possible exceptions OGLE-TR-10, 56, 111, 113, 132 and TrES-1 are chemically undistinguishable from the field (thin disk) stars regarding their [X/Fe] abundances. This is particularly relevant for the most distant of the targets, located at up to ~2 Kpc from the Sun. We also did not find any correlation between the abundances and the condensation temperature of the elements, an evidence that strong accretion of planetary-like material, tentatively connected to planetary migration, did not occur.Comment: Accepted for publication in Astronomy & Astrophysics (June 2006

Comparison of Gesture, Gamepad, and Gaze-based Locomotion for VR Worlds

In this paper we present a VR locomotion technique based on the Leap Motion device and compare it to other often-used locomotion techniques – gaze-directed locomotion and gamepad-based locomotion. We performed a user experiment to evaluate the three techniques based on their performance (time to complete the task), comfort (through the ISO 9241-9 assessment of comfort questionnaire), and simulation sickness (through the Simulation Sickness Questionnaire). Results indicate that the gamepad technique is both faster and more comfortable than either the Leap Motion-based or the gaze-directed techniques.info:eu-repo/semantics/publishedVersio