On Useful Conformal Tranformations In General Relativity

Local conformal transformations are known as a useful tool in various applications of the gravitational theory, especially in cosmology. We describe some new aspects of these transformations, in particular using them for derivation of Einstein equations for the cosmological and Schwarzschild metrics. Furthermore, the conformal transformation is applied for the dimensional reduction of the Gauss-Bonnet topological invariant in $d=4$ to the spaces of lower dimensions.Comment: 17 pages, LaTeX. The paper is intended mainly for pedagogical purposes and represents a collection of exercises concerning local conformal transformations and dimensional reduction. To be published in "Gravitation and Cosmology

Probing the two-scale-factor universality hypothesis by exact rotation symmetry-breaking mechanism

We probe the two-scale factor universality hypothesis by evaluating, firstly explicitly and analytically at the one-loop order, the loop quantum corrections to the amplitude ratios for O($N$) $\lambda\phi^{4}$ scalar field theories with rotation symmetry-breaking in three distinct and independent methods in which the rotation symmetry-breaking mechanism is treated exactly. We show that the rotation symmetry-breaking amplitude ratios turn out to be identical in the three methods and equal to their respective rotation symmetry-breaking ones, although the amplitudes themselves, in general, depend on the method employed and on the rotation symmetry-breaking parameter. At the end, we show that all these results can be generalized, through an inductive process based on a general theorem emerging from the exact calculation, to any loop level and physically interpreted based on symmetry ideas.Comment: 17 pages, 3 figure

Study of welding strengh in PVC profiles

Polyvinyl chloride, PVC, is one of the most widely produced and used plastic, being commonly used in civil industry due to its wide range of mechanical properties (from rigid to flexible), low cost, durability, and easy to assemble. Due to its good mechanical and thermal properties, PVC can be used to produce window and door frames, protecting the interior from the external actions, such as noise and temperature gradients. In order to achieve the final dimensions and geometry, previously extruded profiles must be cut and assembled, being the butt welding one of the most efficient techniques. This plastic welding method involves three main steps: i) pressing the parts to be joined against either side of a heated plate; ii) removing the plate when the parts are sufficiently molten and iii) pressing the components together and holding them until they are cooled. The amount of molten material, generated during the heating stage at an adequate heating time and the plate temperature, as well as the amount of material forced out from the joint during the pressing stage (joining displacement), have major influence in the final welding properties. Although the lack of information about the butt welding of PVC, previous studies with for others materials [1-3] showed that the welding strength can be optimized changing the plate temperature and/or joining displacement. The aim of this work was to study the influence of the plate temperature and the heating time in the welding strength of PVC profiles used in windows frames. The profiles were welded in an industrial butt welder machine, setting the plate temperature at 245ºC, 260ºC and 275ºC and the heating time at 15 and 20s. The mechanical properties were evaluated by mechanical bending tests, according to UNE-EN 514 standard and the welding strength was correlated with the morphology of the welded parts observed by optical microscopy. The results are showing that the increase of plate temperature and heating time increase the welding strength. However, the presence of impurities in the joint, such as trapped air or degraded material, as well as the joint alignment, can have a detrimental effect on the welding strength, as observed by the morphological analyses

Estrutura de uma área de caatinga invadida por algarobeira na Fazenda Gavião, Petrolina-PE.

Objetivando a análise dessas formações vegetais no município de Petrolina-PE, comparou-se duas vegetações de caatinga, sendo uma invadida por algarobeira (Prosopis juliflora (S w) DC)

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

Higher trait mindfulness is associated with empathy but not with emotion recognition abilities

Mindfulness involves an intentional and non-judgemental attention or awareness of present-moment experiences. It can be cultivated by meditation practice or present as an inherent disposition or trait. Higher trait mindfulness has been associated with improved emotional skills, but evidence comes primarily from studies on emotion regulation. It remains unclear whether improvements extend to other aspects of emotional processing, namely the ability to recognize emotions in others. In the current study, 107 participants (Mage = 25.48 years) completed a measure of trait mindfulness, the Five Facet Mindfulness Questionnaire, and two emotion recognition tasks. These tasks required participants to categorize emotions in facial expressions and in speech prosody (modulations of the tone of voice). They also completed an empathy questionnaire and attention tasks. We found that higher trait mindfulness was associated positively with cognitive empathy, but not with the ability to recognize emotions. In fact, Bayesian analyses provided substantial evidence for the null hypothesis, both for emotion recognition in faces and in speech. Moreover, no associations were observed between mindfulness and attention performance. These findings suggest that the positive effects of trait mindfulness on emotional processing do not extend to emotion recognition abilities.info:eu-repo/semantics/publishedVersio