Didactical use of a remote lab: a qualitative reflection of a teacher

This work describes the teacher reflections about a didactical implementation using a remote laboratory and their impact on his practice. These reflections are analyzed from three different perspectives: how the literature review influenced the design of the didactical implementation (namely the first); how his reflection upon his practice influenced its modifications; how his research activity impacted and affected his teaching practices in the subsequent implementations and guided the modifications made. The remote lab was introduced in a Physics Course in an Engineering degree and was intended to be a learning space where students had the opportunity to practice before the lab class, supporting the development of experimental competences, fundamental in an engineer profile. After the first implementation in 2016/17 academic year it has undergone two subsequent editions with adjustments and modifications. Some features previously reported in literature such as: teacher’s experience with VISIR, the importance of an introductory activity and defining VISIR tasks objectives, were corroborated by the teacher during his practice and research. Others, such as the difficulty some students have in understanding the difference between simulation and remote labs appeared directly from his practice and were pursued in his research in order to deeply understand its implications

Exact Perturbations for inflation with smooth exit

Toy models for the Hubble rate or the scalar field potential have been used to analyze the amplification of scalar perturbations through a smooth transition from inflation to the radiation era. We use a Hubble rate that arises consistently from a decaying vacuum cosmology, which evolves smoothly from nearly de Sitter inflation to radiation domination. We find exact solutions for super-horizon perturbations (scalar and tensor), and for sub-horizon perturbations in the vacuum- and radiation-dominated eras. The standard conserved quantity for super-horizon scalar perturbations is exactly constant for growing modes, and zero for the decaying modes.Comment: Minor errors correcte

Inflationary Models Driven by Adiabatic Matter Creation

The flat inflationary dust universe with matter creation proposed by Prigogine and coworkers is generalized and its dynamical properties are reexamined. It is shown that the starting point of these models depends critically on a dimensionless parameter $\Sigma$, closely related to the matter creation rate $\psi$. For $\Sigma$ bigger or smaller than unity flat universes can emerge, respectively, either like a Big-Bang FRW singularity or as a Minkowski space-time at $t=-\infty$. The case $\Sigma=1$ corresponds to a de Sitter-type solution, a fixed point in the phase diagram of the system, supported by the matter creation process. The curvature effects have also been investigated. The inflating de Sitter is a universal attractor for all expanding solutions regardless of the initial conditions as well as of the curvature parameter.Comment: 25 pages, 2 figures(available from the authors), uses LATE

On the algebraic Bethe ansatz: Periodic boundary conditions

In this paper, the algebraic Bethe ansatz with periodic boundary conditions is used to investigate trigonometric vertex models associated with the fundamental representations of the non-exceptional Lie algebras. This formulation allow us to present explicit expressions for the eigenvectors and eigenvalues of the respective transfer matrices.Comment: 36 pages, LaTex, Minor Revisio

Critical wave-packet dynamics in the power-law bond disordered Anderson Model

We investigate the wave-packet dynamics of the power-law bond disordered one-dimensional Anderson model with hopping amplitudes decreasing as $H_{nm}\propto |n-m|^{-\alpha}$. We consider the critical case ($\alpha=1$). Using an exact diagonalization scheme on finite chains, we compute the participation moments of all stationary energy eigenstates as well as the spreading of an initially localized wave-packet. The eigenstates multifractality is characterized by the set of fractal dimensions of the participation moments. The wave-packet shows a diffusive-like spread developing a power-law tail and achieves a stationary non-uniform profile after reflecting at the chain boundaries. As a consequence, the time-dependent participation moments exhibit two distinct scaling regimes. We formulate a finite-size scaling hypothesis for the participation moments relating their scaling exponents to the ones governing the return probability and wave-function power-law decays

Inconsistency in the Standard Model for Thin Accretion Disks

We analyze the configuration of a thin rotating accretion disk, which is embedded in a magnetic field inducing a backreaction in the gravitating plasma. The aim of this study is to determine the conditions under which the gaseous accretion model of Shakura can be reconciled with the magneto-hydrodynamical picture requested to trigger the underlying turbulent behavior. We focus our attention to the generalized Ohm equation in order to understand if the plasma backreaction is able to provide the proper toroidal current, allowing a non-zero infalling velocity. In the limit of linear plasma backreaction, this analysis shows how the Shakura profile of accretion turns out to be inconsistent. In particular, comparing the azimuthal and the generalized Ohm equilibrium equations, we argue that it is not possible to maintain a constant rate of accretion. A non-stationary scenario for the disk configuration is then outlined and it results into a transient process which is however associated to a vanishing accretion rate.Comment: 7 pages, no figur

Avaliação de híbridos de mangueira entre variedades monoembriônicas, em um ciclo de produção, no semi-árido brasileiro.

O objetivo do presente trabalho consistiu na avaliação de híbridos da cultura obtidos entre a variedade Tommy Atkins e outras variedades monoembriônicas, em um ciclo de produção, no Semi-Árido Brasileiro, considerando-se os parâmetros físico-químicos relacionados aos frutos