816 research outputs found
Cosmography of f(R) gravity
It is nowadays accepted that the universe is undergoing a phase of
accelerated expansion as tested by the Hubble diagram of Type Ia Supernovae
(SNeIa) and several LSS observations. Future SNeIa surveys and other probes
will make it possible to better characterize the dynamical state of the
universe renewing the interest in cosmography which allows a model independent
analysis of the distance - redshift relation. On the other hand, fourth order
theories of gravity, also referred to as gravity, have attracted a lot
of interest since they could be able to explain the accelerated expansion
without any dark energy. We show here how it is possible to relate the
cosmographic parameters (namely the deceleration , the jerk , the
snap and the lerk parameters) to the present day values of
and its derivatives (with ) thus offering
a new tool to constrain such higher order models. Our analysis thus offers the
possibility to relate the model independent results coming from cosmography to
the theoretically motivated assumptions of cosmology.Comment: 18 pages, 4 figure
Modelling clusters of galaxies by f(R)-gravity
We consider the possibility that masses and gravitational potentials of
galaxy cluster, estimated at X-ray wavelengths, could be explained without
assuming huge amounts of dark matter, but in the context of -gravity.
Specifically, we take into account the weak field limit of such theories and
show that the corrected gravitational potential allows to estimate the total
mass of a sample of 12 clusters of galaxies. Results show that such a
gravitational potential provides a fair fit to the mass of visible matter (i.e.
gas + stars) estimated by X-ray observations, without the need of additional
dark matter while the size of the clusters, as already observed at different
scale for galaxies, strictly depends on the interaction lengths of the
corrections to the Newtonian potential.Comment: 18 pages, 34 figure
Comprehensive cosmographic analysis by Markov Chain Method
We study the possibility to extract model independent information about the
dynamics of the universe by using Cosmography. We intend to explore it
systematically, to learn about its limitations and its real possibilities. Here
we are sticking to the series expansion approach on which Cosmography is based.
We apply it to different data sets: Supernovae Type Ia (SNeIa), Hubble
parameter extracted from differential galaxy ages, Gamma Ray Bursts (GRBs) and
the Baryon Acoustic Oscillations (BAO) data. We go beyond past results in the
literature extending the series expansion up to the fourth order in the scale
factor, which implies the analysis of the deceleration, q_{0}, the jerk, j_{0}
and the snap, s_{0}. We use the Markov Chain Monte Carlo Method (MCMC) to
analyze the data statistically. We also try to relate direct results from
Cosmography to dark energy (DE) dynamical models parameterized by the
Chevalier-Polarski-Linder (CPL) model, extracting clues about the matter
content and the dark energy parameters. The main results are: a) even if
relying on a mathematical approximate assumption such as the scale factor
series expansion in terms of time, cosmography can be extremely useful in
assessing dynamical properties of the Universe; b) the deceleration parameter
clearly confirms the present acceleration phase; c) the MCMC method can help
giving narrower constraints in parameter estimation, in particular for higher
order cosmographic parameters (the jerk and the snap), with respect to the
literature; d) both the estimation of the jerk and the DE parameters, reflect
the possibility of a deviation from the LCDM cosmological model.Comment: 24 pages, 7 figure
Cosmography and large scale structure by f(R) gravity: new results
Cosmography and galaxy clusters are discussed in the framework of
f(R)-gravity giving a comprehensive review of recent results.Comment: 44 pages, 12 figures, special issue "Dark Sides of Our Universe",
Advances in Astronom
Explosion Behavior of Ethanol-Ethyl Acetate/Air Mixtures
Alcohol-ester mixtures and, among them, ethanol-ethyl acetate mixtures are widely used as solvents in the packaging industry. For the safe use of such mixtures, it is essential to characterize their explosion behavior. Specifically, knowledge is required about maximum pressure and the maximum rate of pressure rise (i.e., the deflagration index), which are among the most important parameters for the assessment of process hazards and the safe design of process equipment. To this aim, in this work, closed-vessel explosion tests were carried out for an ethanol-ethyl acetate composition (mole fraction of ethanol in ethanol + ethyl acetate equal to 0.62) of interest to the packaging industry, varying the fuel/air equivalence ratio from 1.0 to 1.7. Tests were also extended to ethanol/air and ethyl acetate/air to quantify the effects of the possible interaction between the two fuels in the mixture. All tests started from 25°C and 1 bar. Experimental results show that, as the fuel equivalence ratio is increased, a transition occurs from a regime in which synergistic effects arise making the explosion behavior of ethanol-ethyl acetate more severe (i.e., making the rate of explosion pressure rise of ethanol-ethyl acetate higher) than both ethanol and ethyl acetate, to a regime in which, as a result of a completely different interaction between ethanol and ethyl acetate, the explosion behavior of their mixture is less severe than both the individual components. The maximum rate of pressure rise falls within an intermediate regime in which non-linear interaction effects substantially disappear and, thus, the value of deflagration index for the mixture can be obtained by averaging the values of the two fuels according to their molar proportions
Industrial accidents triggered by natural hazards: an emerging risk issue
The threat of natural hazards impacting chemical facilities and infrastructures with the subsequent release of hazardous substances has been recognised as an emerging risk which is likely to be exacerbated by the ongoing climate change. Within the European FP7 project iNTeg-Risk, efforts are dedicated to address the problem of Natech accidents by trying to understand their underlying causes and by developing methodologies and tools to assess Natech risk. Special attention is thereby given to the risk of chemical accidents triggered by earthquakes, floods and lightning. This work outlines the ongoing efforts in the development of new concepts and tools for Natech hazard and vulnerability ranking, risk assessment, risk-based design, and emergency planning and early warning
Assessment of Failure Frequencies of Pipelines in Natech Events Triggered by Earthquakes
During a seismic event, underground pipelines can undergo to significant damages with severe implications in terms of life safety and economic impact. This type of scenarios falls under the definition of Natech. In recent years, quantitative risk analysis became a pivotal tool to assess and manage Natech risk. Among the tools required to perform the quantitative assessment of Natech risk, vulnerability models are required to characterize equipment damages from natural events. This contribution is focused on the review of the pipeline vulnerability models available for the case of earthquakes. Two main categories of models have been identified in the literature. A first category proposes the repair rate as performance indicator for the damage of pipeline due to seismic load, and gives as output the number of required repairs per unit length. A second category proposes fragility curves associated with risk states depending on the mechanism of ground failure. In the framework of Natech risk assessment, the latter have the important advantage of having clearly and unambiguously defined the risk status (and thus the extent of the release) with which they are associated. A subset of vulnerability models deemed more appropriate to be applied in the framework of Natech risk assessment is then identified. Their application to the assessment of the expected frequencies of release events due to pipeline damage is provided, enabling their comparison and the discussion of the relative strengths and weaknesses
Domino effects related to explosions in the framework of land use planning
The present study analyses the possible escalation due to the damage of industrial equipment containing hazardous materials loaded by pressure waves produced either by an accidental source as a Vapour Cloud Explosion, or by a voluntary external attack such as the explosion of a TNT charge located nearby the industrial facility. The results obtained evidence the similarities and the differences for the two explosion sources in terms of structural damage, loss of containment and of expected impacts on the population. In particular, a specific vulnerability assessment was carried out defining a case-study in order to evidence the different potential impact of domino effect triggered by internal process causes respect to escalation scenarios caused by external acts of interference. © 2013, AIDIC Servizi S.r.l
Industrial accidents triggered by natural hazards: an emerging risk issue
Abstract. The threat of natural hazards impacting chemical facilities and infrastructures with the subsequent release of hazardous substances has been recognised as an emerging risk which is likely to be exacerbated by the ongoing climate change. Within the European FP7 project iNTeg-Risk, efforts are dedicated to address the problem of Natech accidents by trying to understand their underlying causes and by developing methodologies and tools to assess Natech risk. Special attention is thereby given to the risk of chemical accidents triggered by earthquakes, floods and lightning. This work outlines the ongoing efforts in the development of new concepts and tools for Natech hazard and vulnerability ranking, risk assessment, risk-based design, and emergency planning and early warning
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