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 ${\mathcal{N}}(\sigma_1,...,\sigma_m)$ is such that for each $k$, $\sigma_k$ has constant sign on its compact support \supp {\sigma_k} \subset \mathbb{R} consisting of an interval $\widetilde{\Delta}_k$, on which $|\sigma_k^{\prime}| > 0$ almost everywhere, and a discrete set without accumulation points in $\mathbb{R} \setminus \widetilde{\Delta}_k$. If {Co}(\supp {\sigma_k}) = \Delta_k denotes the smallest interval containing \supp {\sigma_k}, we assume that $\Delta_k \cap \Delta_{k+1} = \emptyset$, $k=1,...,m-1$. The second Nikishin system ${\mathcal{N}}(r_1\sigma_1,...,r_m\sigma_m)$ is a perturbation of the first by means of rational functions $r_k$, $k=1,...,m,$ whose zeros and poles lie in $\mathbb{C} \setminus \cup_{k=1}^m \Delta_k$.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 $Q_{n}$ and their recurrence coefficients. These measures are assumed to form a Nikishin-type system, and the polynomials $Q_{n}$ 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 $\{Q_{n+1}/Q_{n}\}$ 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 $n$th root asymptotic behavior and zero asymptotic distribution of $Q_{n}$.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 $Q_n(x)$ generated by a high order three-term recursion $xQ_n(x)=Q_{n+1}(x)+a_{n-p} Q_{n-p}(x)$ with arbitrary $p\geq 1$ and $a_n>0$ for all $n$. The recursion is encoded by a two-diagonal Hessenberg operator $H$. One of our main results is that, for periodic coefficients $a_n$ and under certain conditions, the $Q_n$ 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 $\sum_{n=0}^{\infty}|a_n-a|0$. An important tool in this paper is the study of "Riemann-Hilbert minors", or equivalently, the "generalized eigenvalues" of the Hessenberg matrix $H$. We prove interlacing relations for the generalized eigenvalues by using totally positive matrices. In the case of asymptotically periodic coefficients $a_n$, 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