Imaging Spectropolarimetry with IBIS: Evolution of Bright Points in the Quiet Sun

We present the results from first spectropolarimetric observations of the solar photosphere acquired at the Dunn Solar Telescope with the Interferometric Bidimensional Spectrometer. Full Stokes profiles were measured in the Fe I 630.15 nm and Fe I 630.25 nm lines with high spatial and spectral resolutions for 53 minutes, with a Stokes V noise of 0.003 the continuum intensity level. The dataset allows us to study the evolution of several magnetic features associated with G-band bright points in the quiet Sun. Here we focus on the analysis of three distinct processes, namely the coalescence, fragmentation and cancellation of G-band bright points. Our analysis is based on a SIR inversion of the Stokes I and V profiles of both Fe I lines. The high spatial resolution of the G-band images combined with the inversion results helps to interpret the undergoing physical processes. The appearance (dissolution) of high-contrast G-band bright points is found to be related to the local increase (decrease) of the magnetic filling factor, without appreciable changes in the field strength. The cancellation of opposite-polarity bright points can be the signature of either magnetic reconnection or the emergence/submergence of magnetic loops.Comment: 4 pages, 5 figures, accepted for publication in ApJ Letter

Exact Kohn-Sham potential of strongly correlated finite systems

The dissociation of molecules, even the most simple hydrogen molecule, cannot be described accurately within density functional theory because none of the currently available functionals accounts for strong on-site correlation. This problem has led to a discussion of properties that the local Kohn-Sham potential has to satisfy in order to correctly describe strongly correlated systems. We derive an analytic expression for this potential at the dissociation limit and show that the numerical calculations for a one-dimensional two electron model system indeed approach and reach this limit. It is shown that the functional form of the potential is universal, i.e. independent of the details of the system.Comment: 17 pages, 3 figures, submitted to JC

Una forma de reducir la ansiedad en los exámenes orales de inglés como lengua extranjera: técnica de reevaluación positiva

This paper deals with a research project, which aims to analyze the application of a technique in order to reduce anxiety in foreign language oral exams. After considering reasons for the existence of exam anxiety and some options for anxiety reduction, the technique of positive reevaluation is described and presented as a possible alternative. An empirical study carried out with secondary-school students showed reduction of anxiety when using this technique.The study attempts to verify the hypothesis that anxiety levels drop when candidates, who perceive the oral exam negatively, reevaluate their own performance at the start of the exam and succeed in perceiving it positively. To facilitate this, examiners model their discourse at the very beginning of the oral exam, providing candidates with comprehensible input and the opportunity to reduce their anxiety

Functional approach to quantum friction: effective action and dissipative force

We study the Casimir friction due to the relative, uniform, lateral motion of two parallel semitransparent mirrors coupled to a vacuum real scalar field, $\phi$. We follow a functional approach, whereby nonlocal terms in the action for $\phi$, concentrated on the mirrors' locii, appear after functional integration of the microscopic degrees of freedom. This action for $\phi$, which incorporates the relevant properties of the mirrors, is then used as the starting point for two complementary evaluations: Firstly, we calculate the { in-out} effective action for the system, which develops an imaginary part, hence a non-vanishing probability for the decay (because of friction) of the initial vacuum state. Secondly, we evaluate another observable: the vacuum expectation value of the frictional force, using the { in-in} or Closed Time Path formalism. Explicit results are presented for zero-width mirrors and half-spaces, in a model where the microscopic degrees of freedom at the mirrors are a set of identical quantum harmonic oscillators, linearly coupled to $\phi

Non-equilibrium Lifshitz theory as a steady state of a full dynamical quantum system

In this work we analyze the validity of Lifshitz's theory for the case of non-equilibrium scenarios from a full quantum dynamical approach. We show that Lifshitz's framework for the study of the Casimir pressure is the result of considering the long-time regime (or steady state) of a well-defined fully quantized problem, subjected to initial conditions for the electromagnetic field interacting with real materials. For this, we implement the closed time path formalism developed in previous works to study the case of two half spaces (modeled as composite environments, consisting in quantum degrees of freedom plus thermal baths) interacting with the electromagnetic field. Starting from initial uncorrelated free subsystems, we solve the full time evolution, obtaining general expressions for the different contributions to the pressure that take part on the transient stage. Using the analytic properties of the retarded Green functions, we obtain the long-time limit of these contributions to the total Casimir pressure. We show that, in the steady state, only the baths' contribute, in agreement with the results of previous works, where this was assumed without justification. We also study in detail the physics of the initial conditions' contribution and the concept of modified vacuum modes, giving insights about in which situations one would expect a non vanishing contribution at the steady state of a non-equilibrium scenario. This would be the case when considering finite width slabs instead of half-spaces

El pensamiento en la clase de inglés: fuente de poder o vulnerabilidad

The students’ thoughts are a source of power when they are used correctly in the EFL classroom, but, on the contrary, they may be an obstacle to learning and cause emotional instability if the students do not use them well. According to general studies of psychology, thoughts can be classified as relevant and irrelevant. A relevant thought takes place when a person dedicates his thinking to a specific task. For instance, a student is doing a multiple-choice exercise about phrasal verbs, and makes hypothesis and deductions from his knowledge of phrasal verbs in order to do the exercise. Then, as those relevant thoughts take place, other thoughts that are not related directly to that exercise emerge. Those can be irrelevant thoughts when they do not help in doing the task, and interfere with relevant thoughts. They refer to intrapersonal matters, as self-efficacy, motivation, self-esteem, etc. For instance, the student thinks: “I won’t be able to do the exercise” or “I should have studied harder”, etc. However, these irrelevant thoughts can be facilitating to the task if the student is able to analyze those thoughts and change them into positive ones: “I will do my best” or “Although I have not studied hard, I will give it a chance” .This paper shows how cognition and emotion relate to each other and how relevant and irrelevant thoughts are created. It will also explain how the language learner employs self-defense mechanisms as s/he finds difficulties or aversion in doing learning tasks. As a general consideration, irrelevant thoughts can be as important as relevant thoughts in learning a language. Moreover, many researchers claim that they are responsible for determining success or failure in ordinary classroom learning tasks