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Instability of nonminimally coupled scalar fields in the spacetime of slowly rotating compact objects

Nonminimally coupled free scalar fields may be unstable in the spacetime of compact objects. Such instability can be triggered by classical seeds or, more simply, by quantum fluctuations giving rise to the so-called {\em vacuum awakening effect}. Here, we investigate how the parameter space which characterizes the instability is affected when the object gains some rotation. For this purpose, we focus on the stability analysis of nonminimally coupled scalar fields in the spacetime of slowly spinning matter shells.Comment: 11 pages, 6 figure

Quantum versus classical instability of scalar fields in curved backgrounds

General-relativistic stable spacetimes can be made unstable under the presence of certain nonminimally coupled free scalar fields. In this paper, we analyze the evolution of linear scalar-field perturbations in spherically symmetric spacetimes and compare the classical stability analysis with a recently discussed quantum field one. In particular, it is shown that vacuum fluctuations lead to natural seeds for the unstable phase, whereas in the classical framework the presence of such seeds in the initial conditions must be assumed.Comment: 5 pages, 1 figure; condensed and revised version matching published on

A low-energy effective Yang-Mills theory for quark and gluon confinement

We derive a gauge-invariant low-energy effective model of the Yang-Mills theory. We find that the effective gluon propagator belongs to the Gribov-Stingl type and agrees with it when a mass term which breaks nilpotency of the BRST symmetry is included. We show that the effective model with gluon propagator of the Gribov-Stingl type exhibits both quark and gluon confinement: the Wilson loop average has the area law and the Schwinger function violates reflection positivity. However, we argue that both quark and gluon confinement can be obtained even in the absence of such a mass term.Comment: 5 pages, no figures; accepted for publication in Physical Review D (Rapid Communication

Alfred-Donat Agache urban proposal for Costa do Sol from the territory to the city

This paper reviews the development of Costa do Sol, as planned by architect urbanist Alfred-Donat Agache, for Lisbon Region in Portugal. The Plano Expansão Região Oeste de Lisboa (1934-1936) prepared by Agache and requested by Portuguese Minister of Public Works, Duarte Pacheco will be analyzed. This paper aims also to identify the principles and the theoretical foundations that have determined Agache urban vision for Lisbon City and its Territory. Finally, this paper aims to demonstrate that Alfred-Donat Agache methodological framework has applied Frederick Le Play socio-economic scientific approach. Such approach has informed the construction of a ‘civic’ urbanism that will be identified and analyzed. Two main goals seem to have guided Agache work at Costa do Sol: (i) the fully urban analysis of the city, throughout its social, economic, geographic and urban conditions (past and present) and (ii) the need to expose such analysis to the city’s inhabitants. Finally, this paper demonstrates Costa do Sol proposal to testify a comprehensive understanding of three distinct scales: (i) the territory; (ii) the city; (iii) but also the urban form. The acknowledgment of Agache ‘civic’ urban vision requests a public divulgation to allow the building of Good Practice Lessons for contemporary urban planning theory and practice.info:eu-repo/semantics/publishedVersio

Analysis of hybrid relaying in cooperative WLAN

An ever-growing demand for higher data-rates has facilitated the growth of wireless networks in the past decades. Nevertheless, wireless technologies face performance limitations due to unstable wireless conditions and mobility of devices. In face of multi-path propagation and low data-rate stations, cooperative relaying promises gains in performance and reliability. However, cooperation procedures are unstable and introduce overhead that can endanger performance. In this paper we analyze the performance of a hybrid relaying protocol build based on the combination of opportunistic and broadcast-based relaying approaches. Hybrid relaying aims to increase the transmission capacity of wireless networks (proactive operation) when compared to proactive opportunistic and broadcast-based approaches due to rectifying the setbacks involved in those approaches, while adding a reactive approach to recover from failed transmissions. © 2013 IEEE

Lisbon urban allotments A twentieth century cartographic account

Access to food constitutes one of the most basic daily human needs. Throughout history, cities have been shaped in order to accommodate the growth of food, namely in garden allotments. The shape and location of such areas have received differentiated levels of attention by city authorities, guided by specific planning paradigms, while determining different urban form arrangements over time, including those for the production of vegetable farming. This presentation exposes the first attempt of a legend proposal for the existing types of vegetation present in the “Plan of the City” for Lisbon, elaborated between 1948 and 1959. The identification of these vegetation elements is important as it provides an opportunity to better visualize the metabolic condition of the City of Lisbon, at a period of time when deep societal changes affected its urban and territorial arrangements. During the 1950s onwards, Lisbon testified the elaboration of a number of municipal plans, including new neighbourhoods, determining the reorganization of its housing fabric and the consequent vanishing of vegetation areas. The implications of these on the spatiality of the Lisbon food system are yet to be determined and urge for further investigation, namely on historical mapping sources as it is here attempted.info:eu-repo/semantics/publishedVersio

The Portuguese National Laboratory of Civil Engineering and the assemble of an architectural research agenda for the promotion of 1960’s-70’s Lisbon new residential neighbourhoods

World War II imposed massive territorial transformations throughout a number of affected cities, including the provision of housing and new urban infrastructures. To support such societal requests, some governmental research centres, promoted the development of scientific studies to sustain welfare policies. In Portugal, the National Laboratory for Civil Engineering (Laboratório Nacional de Engenharia Civil, LNEC), which responded directly to the Ministry of Public Works, promoted the development of architecture and urban scientific research for such requests. Thus, during the second half of the 20th century, LNEC played a strategic role in guiding the Portuguese urban transformations, including in its capital city, Lisbon. The investigation conducted by LNEC’s architects-researchers, promoted the development of new theoretical research work and the elaboration of architectural and urban plans for specific residential areas. Research and practice were, therefore, articulated and promoted by LNEC. A number of new neighbourhoods planned for Lisbon between 1960’s and 1980’s, benefited from the contribution of LNEC researchers, including Olivais Sul (1959-1968), Chelas (1961-1966) and Restelo (1970-1984). This paper examines, for the above-identified Lisbon’s neighbourhoods, the research contributions, which have guided their architectural and/or urban proposals.info:eu-repo/semantics/publishedVersio