On the Space Time of a Galaxy

We present an exact solution of the averaged Einstein's field equations in the presence of two real scalar fields and a component of dust with spherical symmetry. We suggest that the space-time found provides the characteristics required by a galactic model that could explain the supermassive central object and the dark matter halo at once, since one of the fields constitutes a central oscillaton surrounded by the dust and the other scalar field distributes far from the coordinate center and can be interpreted as a halo. We show the behavior of the rotation curves all along the background. Thus, the solution could be a first approximation of a ``long exposition photograph'' of a galaxy.Comment: 8 pages REVTeX, 11 eps figure

Beating of Friedel oscillations induced by spin-orbit interaction

By exploiting our recently derived exact formula for the Lindhard polarization function in the presence of Bychkov-Rashba (BR) and Dresselhaus (D) spin-orbit interaction (SOI), we show that the interplay of different SOI mechanisms induces highly anisotropic modifications of the static dielectric function. We find that under certain circumstances the polarization function exhibits doubly-singular behavior, which leads to an intriguing novel phenomenon, beating of Friedel oscillations. This effect is a general feature of systems with BR+D SOI and should be observed in structures with a sufficiently strong SOI.Comment: 3 figure

Generation of Closed Timelike Curves with Rotating Superconductors

The spacetime metric around a rotating SuperConductive Ring (SCR) is deduced from the gravitomagnetic London moment in rotating superconductors. It is shown that theoretically it is possible to generate Closed Timelike Curves (CTC) with rotating SCRs. The possibility to use these CTC's to travel in time as initially idealized by G\"{o}del is investigated. It is shown however, that from a technology and experimental point of view these ideas are impossible to implement in the present context.Comment: 9 pages. Submitted to Classical and Quantum Gravit

Spin-orbit interaction induced singularity of the charge density relaxation propagator

The charge density relaxation propagator of a two dimensional electron system, which is the slope of the imaginary part of the polarization function, exhibits singularities for bosonic momenta having the order of the spin-orbit momentum and depending on the momentum orientation. We have provided an intuitive understanding for this non-analytic behavior in terms of the inter chirality subband electronic transitions, induced by the combined action of Bychkov-Rashba (BR) and Dresselhaus (D) spin-orbit coupling. It is shown that the regular behavior of the relaxation propagator is recovered in the presence of only one BR or D spin-orbit field or for spin-orbit interaction with equal BR and D coupling strengths. This creates a new possibility to influence carrier relaxation properties by means of an applied electric field.Comment: 4 figure

Oscillatons revisited

In this paper, we study some interesting properties of a spherically symmetric oscillating soliton star made of a real time-dependent scalar field which is called an oscillaton. The known final configuration of an oscillaton consists of a stationary stage in which the scalar field and the metric coefficients oscillate in time if the scalar potential is quadratic. The differential equations that arise in the simplest approximation, that of coherent scalar oscillations, are presented for a quadratic scalar potential. This allows us to take a closer look at the interesting properties of these oscillating objects. The leading terms of the solutions considering a quartic and a cosh scalar potentials are worked in the so called stationary limit procedure. This procedure reveals the form in which oscillatons and boson stars may be related and useful information about oscillatons is obtained from the known results of boson stars. Oscillatons could compete with boson stars as interesting astrophysical objects, since they would be predicted by scalar field dark matter models.Comment: 10 pages REVTeX, 10 eps figures. Updated files to match version published in Classical and Quantum Gravit

Quintessence and Scalar Dark Matter in the Universe

Continuing with previous works, we present a cosmological model in which dark matter and dark energy are modeled by scalar fields $\Phi$ and $\Psi$, respectively, endowed with the scalar potentials $V(\Phi)=V_{o}[ \cosh {(\lambda \sqrt{\kappa_{o}}\Phi)}-1]$ and $\tilde{V}(\Psi)=\tilde{V_{o}}[ \sinh {(\alpha \sqrt{\kappa_{o}}\Psi)}] ^{\beta}$. This model contains 95% of scalar field. We obtain that the scalar dark matter mass is $m_{\Phi}\sim 10^{-26}eV.$ The solution obtained allows us to recover the success of the standard CDM. The implications on the formation of structure are reviewed. We obtain that the minimal cutoff radio for this model is $r_{c}\sim 1.2 kpc.$Comment: 4 pages REVTeX, 3 eps color figures. Minor changes and references updated. To appear in Classical and Quantum Gravity as a Letter to the Editor. More information at http://www.fis.cinvestav.mx/~siddh/PHI

The Portuguese Formal Social Support for Autonomy and Dependence in Pain Inventory (FSSADI_PAIN): A preliminary validation study.

WOS:000326693900009 (Nº de Acesso Web of Science)Objectives. Development and preliminary validation of a Portuguese measure of perceived Formal Social Support for Autonomy and Dependence in Pain (FSSADI_PAIN). Methods. One hundred and fifty-one older adults (88.1% women), between 56 and 94 years of age (M = 75.41; SD = 9.11), who attended one of the following institutions – day care centre (33.1%), nursing home (36.4%) and senior university (30.5%) – were recruited for this study. Along with the FSSADI_PAIN, participants filled out the Portuguese versions of the Brief Pain Inventory (Azevedo et al., 2007, Dor, 15, 6) and the Social Support Scale of Medical Outcomes Survey (Pais-Ribeiro & Ponte, 2009, Psicologia, Saude & Doença, 10, 163). Results. The factorial structure reflected the functions of perceived promotion of (1) dependence and (2) autonomy, showing good internal consistency (a > .70) and sensitivity indices. The FSSADI_PAIN showed good content, discriminant and criterion validity; it differentiated the perceptions of promotion of dependence/autonomy according to individual’s pain severity and disability, as well as the type of institution. Conclusions. These preliminary findings suggest that the FSSADI_PAIN is an innovative and promising measure of perceived formal social support adapted to pain-related context

Adolescent's physical activity : perspectives for active lifestyles of a school population in Oeiras

FCT (Fundação para a Ciência e a Tecnologia), IDP (Instituto do Desporto de Portugal), AIESEP World Congres

COVID-19 e alojamento local em Portugal: Futuros imprevisíveis

This article presents the results of a pioneering online survey of short-term rental (STR) hosts (N=879) in Portugal about the impact of Covid on their activity, with a sample structured into four areas (Lisbon, Porto, Algarve and the rest of the country). Despite the very high losses, especially in the cities, most of the respondents intend to continue operating in the STR sector. A massive migration from STR to long-term rental is not predicted for a number of reasons, including financial, those related to the nature of this type of supply – more temporary – and the high level of distrust of the state, specifically in terms of guaranteeing legislative stability. In the cities, medium-term rental is the alternative most commonly considered, suggesting there may be a possible restructuring of the sector. Survival capacity over the medium term will depend on the degree of losses and type of public support received during the pandemic, which has benefited hosts constituted as companies more than the sole proprietorships.Este artigo apresenta os resultados de um pioneiro inquérito online aos anfitriões de Alojamento Local (AL) em Portugal (N=879), com uma amostra estruturada territorialmente em quatro áreas áreas (Lisboa, Porto, Algarve e resto do país), sobre os impactos da COVID na sua atividade. Apesar das enormes perdas, sobretudo nas cidades, a maioria dos inquiridos tenciona continuar a operar no sector do AL. Não se prevê uma migração massiva do AL para o arrendamento de longa duração por várias razões: desde as financeiras, às relativas à natureza deste tipo de oferta –mais temporária –ou a elevada desconfiança em relação ao Estado, especificamente em termos de estabilidade legis-lativa. Nas cidades, o arrendamento de média duração é a alternativa mais considerada, sugerindo a possibilidade de alguma reestruturação do sector. A capacidade de sobrevivência a médio prazo dependerá do grau das perdas e do tipo de apoio público recebido durante a pandemia o qual bene-ficiou mais os anfitriões constituídos como empresas do que os empresários em nome individual.info:eu-repo/semantics/publishedVersio