68,645 research outputs found
Risk analysis of LPG tanks at the wildland-urban interface
In areas of wildland-urban interface (WUI), especially residential developments, it is very
common to see liquefied petroleum gas (LPG) tanks, particularly with a higher ratio of
propane, in surface installations serving homes. The most common tanks are between 1 and 5
m3 of capacity, but smaller ones of less than 1 m3 are more frequent. In case of accident,
installations may be subject to fires and explosions, especially in those circumstances where
legal and normative requirements allow very close exposure to flames from vegetable fuel
near LPG tanks.
In this project, it is intended to do a comprehensive diagnosis of the problem, addressing
the compilation of information on real risk scenarios in historical fires. First, a preliminary
presentation of the properties and characteristics of liquefied petroleum gas will be exposed.
Its physical and chemical properties, production methodology, pressure and temperature
diagrams and important considerations will be defined when using this type of substances in a
storage tank of a certain volume.
Next, a review of the situation of the existence of LPG tanks in the urban forest interfaces
will be exposed. In this case, the main accidents caused by problems with the storage of LPG
will be analyzed taking into account the relevance of BLEVE events in this type of incidents. To
do this, the main scenarios that could take place in the event of a fire will be presented.
Next, the existing legislation on the storage of LPG in these environments in some
Mediterranean countries will be studied. In order to develop a comprehensive analysis, the
main safety measures and distances will be considered, as well as the awareness of the
possibility of vegetation material in the vicinity of LPG storage tanks, which is the main
problem that will arise in a possible BLEVE scenario in case of fire. To finalize and facilitate
understanding, a comparative table will be included with the aim of visualizing the main
advantages and legislative deficiencies between the different countries.
Following, the state of the art in terms of modelling LPG accidents at the WUI will be
reviewed. Trying to simulate and predict this type of scenarios, it will see the models normally
chosen to obtain the tolerable values selected and the answers obtained in each case.
Finally, several fire scenarios will be simulated by means of a CFD tool (FDS, Fire Dynamics
Simulator). In these simulations, the wind velocity and the distance of the combustible vegetal
mass to the tank will be controlled in a WUI fire in which there is a tank of fixed dimensions.
The temperature and the heat flow in each of the scenarios will be obtained, and the
differences among the location of the sensors and the characteristics of the scenario will be
analyzed.
As a conclusion, it has been observed that there is a great amount of variables that are
not contemplated by the regulatory organisms and that the existing legislation does not
guarantee the safety of the population in this type of environment. From the simulations
results, variables as temperature should be studied for further characterizations
Relative Asymptotic of Multiple Orthogonal Polynomials for Nikishin Systems
We prove relative asymptotic for the ratio of two sequences of multiple
orthogonal polynomials with respect to Nikishin system of measures. The first
Nikishin system is such that for each
, has constant sign on its compact support \supp {\sigma_k}
\subset \mathbb{R} consisting of an interval , on which
almost everywhere, and a discrete set without
accumulation points in . If
{Co}(\supp {\sigma_k}) = \Delta_k denotes the smallest interval containing
\supp {\sigma_k}, we assume that ,
. The second Nikishin system
is a perturbation of the first by
means of rational functions , whose zeros and poles lie in
.Comment: 30 page
Asymptotics of multiple orthogonal polynomials for a system of two measures supported on a starlike set
For a system of two measures supported on a starlike set in the complex
plane, we study asymptotic properties of associated multiple orthogonal
polynomials and their recurrence coefficients. These measures are
assumed to form a Nikishin-type system, and the polynomials satisfy a
three-term recurrence relation of order three with positive coefficients. Under
certain assumptions on the orthogonality measures, we prove that the sequence
of ratios has four different periodic limits, and we
describe these limits in terms of a conformal representation of a compact
Riemann surface. Several relations are found involving these limiting functions
and the limiting values of the recurrence coefficients. We also study the th
root asymptotic behavior and zero asymptotic distribution of .Comment: 31 page
Redistribution, capital income taxation and tax evasion
Factor mobility and tax evasión are two phenomena that constraint the effectiveness
of redistributive policies now used by the member countries of the European Union.
In this paper, a normative analysis of this fact is undertaken using a simple model
with two countries and two social classes, where capital is perfectly mobile and
labour is immobile. Each country complements the income of its workers, assumed to
be poor, with transfers. The latter are financed with two taxes on capital income. The
first one, following the origin principie, alters the retum and intemational allocation
of capital. The second one, following the residence principie, induces the evasión of
capitalists' incomes. Each government chooses the optimal mix of capital taxes that
maximizes the welfare of its citizens with no regard on the repercussions on its
neighbour country. A numerical exercise is built to examine the sensitivity of the
resulting non cooperative equilibrium to the aversión to inequality exhibited by the
different governments as well as to the factor endowments of their respective
countries
The origin principle and the welfare gains from indirect tax harmonization
The purpose of this paper is to establish a parallelism between the analyses in Keen (1987,1989.a) referred to indirect tax harmonization when taxes are levied according to the destination principle and its counterpart when taxes are imposed on an origin basis. Using a simple two-country model of international trade it is argued that indirect tax harmonization under the origin principle, considered as a movement of domestic taxes towards an appropriately designed "average" tax structure, is potentially Pareto improving, in the sense that the welfare of a given country can be increased provided that the other country's welfare is kept unchanged with the aid of an international transfer. In the same vein, it is shown that if the initial position is a Nash equilibrium, there are situations under which the above-mentioned reform may generate an actual Pareto improvement, so that both countries improve their welfare without any need for a compensating international transfer. As stated above, the definitive system will be a mixed one, so that the pure origin case is not the most realistic framework from a policy point of view. However, it may be useful in yielding indications that, coupled with the results that have been obtained under the destination principle, provide insights on the effects of the definitive system
High order three-term recursions, Riemann-Hilbert minors and Nikishin systems on star-like sets
We study monic polynomials generated by a high order three-term
recursion with arbitrary and
for all . The recursion is encoded by a two-diagonal Hessenberg
operator . One of our main results is that, for periodic coefficients
and under certain conditions, the are multiple orthogonal polynomials
with respect to a Nikishin system of orthogonality measures supported on
star-like sets in the complex plane. This improves a recent result of
Aptekarev-Kalyagin-Saff where a formal connection with Nikishin systems was
obtained in the case when .
An important tool in this paper is the study of "Riemann-Hilbert minors", or
equivalently, the "generalized eigenvalues" of the Hessenberg matrix . We
prove interlacing relations for the generalized eigenvalues by using totally
positive matrices. In the case of asymptotically periodic coefficients ,
we find weak and ratio asymptotics for the Riemann-Hilbert minors and we obtain
a connection with a vector equilibrium problem. We anticipate that in the
future, the study of Riemann-Hilbert minors may prove useful for more general
classes of multiple orthogonal polynomials.Comment: 59 pages, 3 figure
A new countermeasure against side-channel attacks based on hardware-software co-design
This paper aims at presenting a new countermeasure against Side-Channel Analysis (SCA) attacks, whose implementation is based on a hardware-software co-design. The hardware architecture consists of a microprocessor, which executes the algorithm using a false key, and a coprocessor that performs several operations that are necessary to retrieve the original text that was encrypted with the real key. The coprocessor hardly affects the power consumption of the device, so that any classical attack based on such power consumption would reveal a false key. Additionally, as the operations carried out by the coprocessor are performed in parallel with the microprocessor, the execution time devoted for encrypting a specific text is not affected by the proposed countermeasure. In order to verify the correctness of our proposal, the system was implemented on a Virtex 5 FPGA. Different SCA attacks were performed on several functions of AES algorithm. Experimental results show in all cases that the system is effectively protected by revealing a false encryption key.Peer ReviewedPreprin
- …