109,229 research outputs found
Physical constraints on interacting dark energy models
Physical limits on the equation-of-state (EoS) parameter of a dark energy
component non-minimally coupled with the dark matter field are examined in
light of the second law of thermodynamics and the positiveness of entropy. Such
constraints are combined with observational data sets of type Ia supernovae,
baryon acoustic oscillations and the angular acoustic scale of the cosmic
microwave background to impose restrictions on the behaviour of the dark
matter/dark energy interaction. Considering two EoS parameterisations of the
type , we derive a general expression for the evolution
of the dark energy density and show that the combination of thermodynamic
limits and observational data provide tight bounds on the parameter
space.Comment: 7 pages, 4 figures. Accepted for publication in European Physical
Journal
Development of an open-source platform for calculating losses from earthquakes
Risk analysis has a critical role in the reduction of casualties and damages due to earthquakes.
Recognition of this relation has led to a rapid rise in demand for accurate, reliable and flexible risk
assessment numerical tools and software. As a response to this need, the Global Earthquake Model
(GEM) started the development of an open source platform called OpenQuake, for calculating
seismic hazard and risk at different scales. Along with this framework, also several other tools to
support users creating their own models and visualizing their results are currently being
developed, and will be made available as a Modelers Tool Kit (MTK). In this paper, a description
of the architecture of OpenQuake is provided, highlighting the current data model, workflow of
the calculators and the main challenges raised when running this type of calculations in a global
scale. In addition, a case study is presented using the Marmara Region (Turkey) for the calculations, in which the losses for a single event are estimated, as well as probabilistic risk for a
50 years time span
Developing a global risk engine
Risk analysis is a critical link in the reduction of casualties and damages due to earthquakes. Recognition of this relation has led to a rapid rise in demand for accurate, reliable and flexible risk assessment software. However, there is a significant disparity between the high quality scientific data developed by researchers and the availability of versatile, open and user-friendly risk analysis tools to meet the demands of end-users. In the past few years several open-source software have been developed that play an important role in the seismic research, such as OpenSHA and OpenSEES. There is however still a gap when it comes to open-source risk assessment tools and software. In order to fill this gap, the Global Earthquake Model (GEM) has been created. GEM is an internationally sanctioned program initiated by the OECD that aims to build independent, open standards to calculate and communicate earthquake risk around the world. This initiative started with a one-year pilot project named GEM1, during which an evaluation of a number of existing risk software was carried out. After a critical review of the results it was concluded that none of the software were adequate for GEM requirements and therefore, a new object-oriented tool was to be developed. This paper presents a summary of some of the most well known applications used in risk analysis, highlighting the main aspects that were considered for the development of this risk platform. The research that was carried out in order to gather all of the necessary information to build this tool was distributed in four different areas: information technology approach, seismic hazard resources, vulnerability assessment methodologies and sources of exposure data. The main aspects and findings for each of these areas will be presented as well as how these features were incorporated in the up-to-date risk engine. Currently, the risk engine is capable of predicting human or economical losses worldwide considering both deterministic and probabilistic-based events, using vulnerability curves.
A first version of GEM will become available at the end of 2013. Until then the risk engine will continue to be developed by a growing community of developers, using a dedicated open-source platform
Conceptual Design of a New Large Superconducting Toroid for IAXO, the New International AXion Observatory
The International AXion Observatory (IAXO) will incorporate a new generation
detector for axions, a hypothetical particle, which was postulated to solve one
of the puzzles arising in the standard model of particle physics, namely the
strong CP problem. The new IAXO experiment is aiming at achieving a sensitivity
to the coupling between axions and photons of one order of magnitude beyond the
limits of the current state-of-the-art detector, represented by the CERN Axion
Solar Telescope (CAST). The IAXO detector relies on a high-magnetic field
distributed over a very large volume to convert solar axions into x-ray
photons. Utilizing the designs of the ATLAS barrel and end-cap toroids, a large
superconducting toroidal magnet is currently being designed at CERN to provide
the required magnetic field. The new toroid will be built up from eight, one
meter wide and 20 m long, racetrack coils. The toroid is sized about 4 m in
diameter and 22 m in length. It is designed to realize a peak magnetic field of
5.4 T with a stored energy of 500 MJ. The magnetic field optimization process
to arrive at maximum detector yield is described. In addition, force and stress
calculations are performed to select materials and determine their structure
and sizing. Conductor dimensionality, quench protection and the cryogenic
design are dealt with as well.Comment: 5 pages, 5 figures. To be published in IEEE Trans. Appl. Supercond.
23 (ASC 2012 conference special issue
On dB spaces with nondensely defined multiplication operator and the existence of zero-free functions
In this work we consider de Branges spaces where the multiplication operator
by the independent variable is not densely defined. First, we study the
canonical selfadjoint extensions of the multiplication operator as a family of
rank-one perturbations from the viewpoint of the theory of de Branges spaces.
Then, on the basis of the obtained results, we provide new necessary and
sufficient conditions for a real, zero-free function to lie in a de Branges
space.Comment: 13 pages, no fugures. Theorem and remark have been added,
typographical erros correcte
Dilatation operator and the Super Yang-Mills duals of open strings on AdS Giant Gravitons
We study the one-loop anomalous dimensions of the Super Yang-Mills dual
operators to open strings ending on AdS giant gravitons. AdS giant gravitons
have no upper bound for their angular momentum and we represent them by the
contraction of scalar fields, carrying the appropriate R-charge, with a totally
symmetric tensor. We represent the open string motion along AdS directions by
appending to the giant graviton operator a product of fields including
covariant derivatives. We derive a bosonic lattice Hamiltonian that describes
the mixing of these excited AdS giants operators under the action of the
one-loop dilatation operator of N=4 SYM. This Hamiltonian captures several
intuitive differences with respect to the case of sphere giant gravitons. A
semiclassical analysis of the Hamiltonian allows us to give a geometrical
interpretation for the labeling used to describe the fields products appended
to the AdS giant operators. It also allows us to show evidence for the
existence of continuous bands in the Hamiltonian spectrum.Comment: 28 page
Activation thresholds in epidemic spreading with motile infectious agents on scale-free networks
We investigate a fermionic susceptible-infected-susceptible model with
mobility of infected individuals on uncorrelated scale-free networks with
power-law degree distributions of exponents
. Two diffusive processes with diffusion rate of an infected
vertex are considered. In the \textit{standard diffusion}, one of the
nearest-neighbors is chosen with equal chance while in the \textit{biased
diffusion} this choice happens with probability proportional to the neighbor's
degree. A non-monotonic dependence of the epidemic threshold on with an
optimum diffusion rate , for which the epidemic spreading is more
efficient, is found for standard diffusion while monotonic decays are observed
in the biased case. The epidemic thresholds go to zero as the network size is
increased and the form that this happens depends on the diffusion rule and
degree exponent. We analytically investigated the dynamics using quenched and
heterogeneous mean-field theories. The former presents, in general, a better
performance for standard and the latter for biased diffusion models, indicating
different activation mechanisms of the epidemic phases that are rationalized in
terms of hubs or max -core subgraphs.Comment: 9 pages, 4 figure
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