147 research outputs found
Warm stellar matter with deconfinement: application to compact stars
We investigate the properties of mixed stars formed by hadronic and quark
matter in -equilibrium described by appropriate equations of state (EOS)
in the framework of relativistic mean-field theory. We use the non- linear
Walecka model for the hadron matter and the MIT Bag and the Nambu-Jona-Lasinio
models for the quark matter. The phase transition to a deconfined quark phase
is investigated. In particular, we study the dependence of the onset of a mixed
phase and a pure quark phase on the hyperon couplings, quark model and
properties of the hadronic model. We calculate the strangeness fraction with
baryonic density for the different EOS. With the NJL model the strangeness
content in the mixed phase decreases. The calculations were performed for T=0
and for finite temperatures in order to describe neutron and proto-neutron
stars. The star properties are discussed. Both the Bag model and the NJL model
predict a mixed phase in the interior of the star. Maximum allowed masses for
proto-neutron stars are larger for the NJL model ( M)
than for the Bag model ( M).Comment: RevTeX,14 figures, accepted to publication in Physical Review
The importance of the mixed phase in hybrid stars built with the Nambu-Jona-Lasinio model
We investigate the structure of hybrid stars based on two different
constructions: one is based on the Gibbs condition for phase coexistence and
considers the existence of a mixed phase (MP), and the other is based on the
Maxwell construction and no mixed phase is obtained. The hadron phase is
described by the non-linear Walecka model (NLW) and the quark phase by the
Nambu-Jona-Lasinio model (NJL). We conclude that the masses and radii obtained
are model dependent but not significantly different for both constructions.Comment: 8 pages, 7 figures, 3 table
Electrically charged compact stars and formation of charged black holes
We study the effect of electric charge in compact stars assuming that the
charge distribution is proportional to the mass density. The pressure and the
density of the matter inside the stars are large, and the gravitational field
is intense. This indicates that electric charge and a strong electric field can
also be present. The relativistic hydrostatic equilibrium equation, i.e., the
Tolman-Oppenheimer-Volkoff equation, is modified in order to include electric
charge. We perform a detailed numerical study of the effect of electric charge
using a polytropic equation of state. We conclude that in order to see any
appreciable effect on the phenomenology of the compact stars, the electric
fields have to be huge (~ 10^{21} V/m), which implies that the total charge is
Q ~ 10^{20} Coulomb. From the local effect of the forces experienced on a
single charged particle, it is expected that each individual charged particle
is quickly ejected from the star. This in turn produces a huge force imbalance,
and the gravitational force overwhelms the repulsive Coulomb and fluid pressure
forces. The star can then collapse to form a charged black hole before all the
charge leaves the system.Comment: 10 pages, 9 figures, To appear in Phys Rev.
Desempenho agronĂŽmico de Crotalaria juncea em diferentes arranjos populacionais e Ă©pocas do ano.
bitstream/CNPAB-2010/33519/1/cot082.pd
Logistics service provider selection for disaster preparation: a socio-technical systems perspective
Since 1990s, the world has seen a lot of advances in providing humanitarian aid through sophisticated logistics operations. The current consensus seems to be that humanitarian relief organizations (HROs) can improve their relief operations by collaborating with logistics service providers (CLSPs) in the commercial sector. The question remains: how can HROs select the most appropriate CLSP for disaster preparation? Despite its practical significance, no explicit effort has been done to identify the criteria/factors in prioritising and selecting a CLSP for disaster relief. The present study aims to address this gap by consolidating the list of criteria from a socio-technical systems (STS) perspective. Then, to handle the interdependence among the criteria derived from the STS, we develop a hybrid multi-criteria decision making model for CLSP selection in the disaster preparedness stage. The proposed model is then evaluated by a real-life case study, providing insights into the decision-makers in both HROs and CLSPs
Permanent Campaigning: A Meta-Analysis and Framework for Measurement
Permanent campaigning emerged as a concept in the 1970s in studies of US politics but is now recognized as a universal phenomenon. Despite its long history, there has been no attempt to build a holistic picture of the elements that constitute a permanent campaign. Generally, researchers focus on tactical elements, situating their use within an overall strategy, but there is a lack of a broader methodological framework for holistically measuring adherence to the permanent campaigning. This article presents results of a meta-analysis of relevant research to provide a framework to understand how permanent campaigning is practiced. Our study showed there were three reasonably discrete forms of campaigning activities that had been identified: those in which permanent campaign strategies are related to capacity building and strategy; a second, in which permanent campaigning relates to paid and owned media; and a third in which earned media is the main focus. In mapping these studies, we identify the common features of permanent campaigning, identifying strong and weak indicators and the extent these are employed by the government, parties, or elected representatives and within which political systems: parliamentarism or presidentialism. Our framework can be applied in future comparative research to understand trends in political communication
Using Models to inform Policies that meet multiple Objectives. Assessing the Contribution of Brazil's Forest Code to Biodiversity Conservation
Land-use change models can help to develop a holistic understanding of the range of potential impacts of different land-use related policy options, and so can strengthen development and implementation of policies to meet a range of objectives, including biodiversity conservation, climate change mitigation, sustainable development and food security.
Brazilâs Native Vegetation Protection Act, commonly known as the Forest Code (FC), is one example of a policy that can be used to achieve several objectives. Using land-use modelling to inform ongoing decisions on how the provisions of the FC are put into practice can help to increase its effectiveness in meeting multiple objectives and commitments.
Model projections show that the full implementation of the provisions of the FC will both reduce emissions of greenhouse gases and contribute to conserving biodiversity in Brazil. They further highlight the importance for biodiversity conservation of implementing the Environmental Reserve Tradable Certificate (CRA in Portuguese) mechanism quickly and effectively.
Model results also show the need to put in place additional measures to protect areas, such as the Caatinga forests and grassy savanna in the Cerrado, which may suffer increased land-use pressures as a result of the FC
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