218 research outputs found
Teaching the Modeling of Human–Environment Systems : Acknowledging Complexity with an Agent-Based Model
Improving Agri-environmental Schemes : Suggestions from Farmers and Nature Managers in a Central European Region
Cold uniform matter and neutron stars in the quark-mesons-coupling model
A new density dependent effective baryon-baryon interaction has been recently
derived from the quark-meson-coupling (QMC) model, offering impressive results
in application to finite nuclei and dense baryon matter. This self-consistent,
relativistic quark-level approach is used to construct the Equation of State
(EoS) and to calculate key properties of high density matter and cold, slowly
rotating neutron stars. The results include predictions for the maximum mass of
neutron star models, together with the corresponding radius and central
density, as well the properties of neutron stars with mass of order 1.4
. The cooling mechanism allowed by the QMC EoS is explored and the
parameters relevant to slow rotation, namely the moment of inertia and the
period of rotation investigated. The results of the calculation, which are
found to be in good agreement with available observational data, are compared
with the predictions of more traditional EoS. The QMC EoS provides cold neutron
star models with maximum mass 1.9--2.1 M, with central density less
than 6 times nuclear saturation density () and
offers a consistent description of the stellar mass up to this density limit.
In contrast with other models, QMC predicts no hyperon contribution at
densities lower than , for matter in -equilibrium. At higher
densities, and hyperons are present
Perceptions of ecosystem services : Comparing socio-cultural and environmental influences
Ecosystem services such as food provisioning, climate regulation, nutrient cycling, or recreation in open landscapes underpin human wellbeing. They are highly dependent on land use, land cover and utilization pattern as well as environmental factors like climate, topography and soil. In consequence, ecosystem services supply shows a high spatial variability. However, it is less clear if the perception of the importance of ecosystem services is similarly heterogeneous in space and amongst societal actors. The aim of this large-scale study was to explore whether land cover and climate gradients as well as socio-cultural factors influence the perceptions of ecosystem services of four groups of societal actors: citizens, farmers, foresters and nature managers. Spatially explicit survey data of 3018 respondents allowed to gain insight into the distribution of perceived importance of 21 ecosystem services in the federal state of Bavaria, Germany together with the respondents’ socio-cultural characterisation (e.g. gender, education and hobbies in nature). Responses were analysed through descriptive statistics, redundancy analysis, and Generalized Linear Models. Results reveal that the perceived importance of many ecosystem services was consistently high across groups, although perception differed for some ecosystem services (e.g. production of energy plants and timber as well as recreation in urban green space). Compared to other actor groups, farmers attributed slightly lower importance to all ES except provisioning services. Socio-cultural factors better explained variability in perceived importance of ecosystem services than land cover and climate gradients. This might be either explained by the fact that the environmental gradients vary not strong enough in our case study or that they do not shape the perceptions of respondents. A limitation of the study is that the sample of respondents obtained is not representative for the population, but biased towards persons interested in the topics of the survey. Still the consensus indicated by the overall positive perception of ecosystem services among respondents highlights the integrative potential of ecosystem services when included in decision-making
Analytical solution of the dynamical spherical MIT bag
We prove that when the bag surface is allowed to move radially, the equations
of motion derived from the MIT bag Lagrangian with massless quarks and a
spherical boundary admit only one solution, which corresponds to a bag
expanding at the speed of light. This result implies that some new physics
ingredients, such as coupling to meson fields, are needed to make the dynamical
bag a consistent model of hadrons.Comment: Revtex, no figures. Submitted to Journal of Physics
A dynamical chiral bag model
We study a dynamical chiral bag model, in which massless fermions are
confined within an impenetrable but movable bag coupled to meson fields. The
self-consistent motion of the bag is obtained by solving the equations of
motion exactly assuming spherical symmetry. When the bag interacts with an
external meson wave we find three different kinds of resonances: {\it
fermionic}, {\it geometric}, and -resonances. We discuss the
phenomenological implications of our results.Comment: Two columns, 11 pages, 9 figures. Submitted to Physical Review
Gravitational waves and nonaxisymmetric oscillation modes in mergers of compact object binaries
We study the excitation of nonaxisymmetric modes in the post-merger phase of
binary compact object mergers and the associated gravitational wave emission.
Our analysis is based on general-relativistic simulations, in the spatial
conformal flatness approximation, using smoothed-particle-hydrodynamics for the
evolution of matter, and we use a set of equal and unequal mass models,
described by two nonzero-temperature hadronic equations of state and by one
strange star equation of state. Through Fourier transforms of the evolution of
matter variables, we can identify a number of oscillation modes, as well as
several nonlinear components (combination frequencies). We focus on the
dominant m=2 mode, which forms a triplet with two nonlinear components that are
the result of coupling to the quasiradial mode. A corresponding triplet of
frequencies is identified in the gravitational wave spectrum, when the
individual masses of the compact objects are in the most likely range of 1.2 to
1.35 . We can thus associate, through direct analysis of the dynamics
of the fluid, a specific frequency peak in the gravitational wave spectrum with
the nonlinear component resulting from the difference between the m=2 mode and
the quasiradial mode. Once such observations become available, both the m=2 and
quasiradial mode frequencies could be extracted, allowing for the application
of gravitational-wave asteroseismology to the post-merger remnant and leading
to tight constraints on the equation of state of high-density matter.Comment: 11 pages, 8 figures, submitted to MNRA
Cooling Properties of Cloudy Bag Strange Stars
As the chiral symmetry is widely recognized as an important driver of the
strong interaction dynamics, current strange stars models based on MIT bag
models do not obey such symmetry. We investigate properties of bare strange
stars using the Cloudy Bag Model, in which a pion cloud coupled to the
quark-confining bag is introduced such that chiral symmetry is conserved. We
find that in this model the decay of pions is a very efficient cooling way. In
fact it can carry out most the thermal energy in a few milliseconds and
directly convert them into 100MeV photons via pion decay. This may be a very
efficient -ray burst mechanism. Furthermore, the cooling behavior may
provide a possible way to distinguish a compact object between a neutron star,
MIT strange star and Cloudy Bag strange star in observations.Comment: 23 pages, 14 figures, accepted by Astroparticle Physics, abstract
appeared here has been shortene
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