78,672 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
Evaluation of analytical methodologies to derive vulnerability functions
The recognition of fragility functions as a fundamental tool in seismic risk assessment has led to the
development of more and more complex and elaborate procedures for their computation. Although vulnerability
functions have been traditionally produced using observed damage and loss data, more recent studies propose the
employment of analytical methodologies as a way to overcome the frequent lack of post-earthquake data. The
variation of the structural modelling approaches on the estimation of building capacity has been the target of
many studies in the past, however, its influence in the resulting vulnerability model, impact in loss estimations or
propagation of the uncertainty to the seismic risk calculations has so far been the object of restricted scrutiny.
Hence, in this paper, an extensive study of static and dynamic procedures for estimating the nonlinear response
of buildings has been carried out in order to evaluate the impact of the chosen methodology on the resulting
vulnerability and risk outputs. Moreover, the computational effort and numerical stability provided by each
approach were evaluated and conclusions were obtained regarding which one offers the optimal balance between
accuracy and complexity
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
Visco-elastic regularization and strain softening
In this paper it is intended to verify the capacity of regularization of the numerical
solution of an elasto-plastic problem with linear strain softening. The finite element method
with a displacement approach is used. Drucker-Prager yield criteria is considered. The radial
return method is used for the integration of the elasto-plastic constitutive relations. An elastovisco-
plastic scheme is used to regularize the numerical solution. Two constitutive laws have
been developed and implemented in a FE-program, the first represent the radial return
method applied to Drucker-Prager yield criteria and the second is a time integration
procedure for the Maxwell visco-elastic model. Attention is paid to finite deformations. An
associative plastic flow is considered in the Drucker-Prager elasto-plastic model. The
algorithms are tested in two problems with softening. Figures showing the capability of the
algorithms to regularize the solution are presented
Neutrino masses and mixing in A4 models with three Higgs doublets
We study neutrino masses and mixing in the context of flavor models with A4
symmetry, three scalar doublets in the triplet representation, and three lepton
families. We show that there is no representation assignment that yields a
dimension-five mass operator consistent with experiment. We then consider a
type-I seesaw with three heavy right-handed neutrinos, explaining in detail why
it fails, and showing with a numerical example that agreement with the present
neutrino oscillation data can be recovered with the inclusion of
dimension-three heavy neutrino mass terms that break softly the A4 symmetry.Comment: 10 pages, RevTex, 3 figures. v2: much expanded section on softly
broken A4; refs adde
Towards Noncommutative Linking Numbers Via the Seiberg-Witten Map
In the present work some geometric and topological implications of
noncommutative Wilson loops are explored via the Seiberg-Witten map. In the
abelian Chern-Simons theory on a three dimensional manifold, it is shown that
the effect of noncommutativity is the appearance of new knots at the
-th order of the Seiberg-Witten expansion. These knots are trivial homology
cycles which are Poincar\'e dual to the high-order Seiberg-Witten potentials.
Moreover the linking number of a standard 1-cycle with the Poincar\'e dual of
the gauge field is shown to be written as an expansion of the linking number of
this 1-cycle with the Poincar\'e dual of the Seiberg-Witten gauge fields. In
the process we explicitly compute the noncommutative 'Jones-Witten' invariants
up to first order in the noncommutative parameter. Finally in order to exhibit
a physical example, we apply these ideas explicitly to the Aharonov-Bohm
effect. It is explicitly displayed at first order in the noncommutative
parameter, we also show the relation to the noncommutative Landau levels.Comment: 19 pages, 1 figur
Strategies for building pathology reports in an urban rehabilitation process: Project of the Old City Centre of Coimbra
The increasing interest on architectural heritage associated to the recognised building value, at economic, social and cultural levels have stimulated, in the recent decades, the urban rehabilitation and renovation o several cities in Europe.
Despite the strategy or method adopted in a city renovation process, its efficiency depends mainly on: type of buildings (structural systems, construction techniques and materials); intervention level (singular buildings, groups of buildings, urban zones, etc.); and, project objective (risk assessment, decision making to support future rehabilitation projects, definition of council maintenance policies, etc.).
In what concerns large renovation programs of old city centres, choosing the most adequate approach for inspection, appraisal and diagnosis is a complex task that can determine the success or failure of the project purpose.
This paper describes the preparation phase of the inspection of 700 buildings located in the old city centre of Coimbra (Portugal), where a global renovation process is planned for the forthcoming years.
In the scope of the renovation and rehabilitation process, the city council contract a complete identification and inspection survey of the buildings, directed on three different domains: (a) architectural typologies, (b) constructive and pathological condition of buildings, and (c) socio-demographic characterisation, of this part of the city. It will be present the check-lists developed and some of the obtained results on point (b), related to roofing systems, and exterior façades.
This diagnosis procedure shows that the inspection results quality is quite dependent on the items surveyed for each construction element (roof, façade, internal members, installation efficiency), as well as on the possibility of their correlation for a single building. The adopted method has been applied on 70% of the buildings inspected within the project perimeter.
Further treatment of the inspection and appraisal data will allow the developing pathology reports and list repair actions, and estimating rehabilitation costs. It will also help to produce defect level diagrams and seismic building risk maps, but, most important, to improve and guide a renewal strategy and intervention methodology for old buildings
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