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Search Results: 1 - 10 of 208476 matches for " L. Loepfe "
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Two thresholds determine climatic control of forest-fire size in Europe
L. Loepfe,A. Rodrigo,F. Lloret
Biogeosciences Discussions , 2012, DOI: 10.5194/bgd-9-9065-2012
Abstract: Fire weather indices predict fire extent from meteorological conditions assuming a monotonic function; this approach is frequently used to predict future fire patterns under climate change scenarios using linear extrapolation. However, the relationship between weather and fire extent may potentially depend on the existence of fuel humidity thresholds above which this relationship changes dramatically, challenging this statistical approach. Here we combine the continuous and the threshold approaches to analyze satellite-detected fires in Europe during 2001–2010 in relation to meteorological conditions, showing that fire size response to increasing dryness follows a ramp function, i.e. with two plateaus separated by a phase of monotonic increase. This study confirms that at a continental and a high-resolution temporal scales, large fires are very unlikely to occur under moist conditions, but it also reveals that fire size stops to be controlled by fuel humidity above a given threshold of dryness. Thus, fuel humidity control only applies when fire is not limited by other factors such as fuel load, as large fires are virtually absent in dry regions with less than 500 mm of average annual rainfall, i.e. where fuel amount is insufficient. In regions with sufficient fuel, other factors such as fire suppression or fuel discontinuity can impede large fires even under very dry weather conditions. These findings are relevant under current climatic trends in which the fire season length, in terms of number of days with DC (drought code) values above the observed thresholds (break points), is increasing in many parts of the Mediterranean, while it is decreasing in Eastern Europe and remains unchanged in Central Europe.
Towards a Proper Assignment of Systemic Risk: The Combined Roles of Network Topology and Shock Characteristics
Lasse Loepfe, Antonio Cabrales, Angel Sánchez
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0077526
Abstract: The 2007-2008 financial crisis solidified the consensus among policymakers that a macro-prudential approach to regulation and supervision should be adopted. The currently preferred policy option is the regulation of capital requirements, with the main focus on combating procyclicality and on identifying the banks that have a high systemic importance, those that are “too big to fail”. Here we argue that the concept of systemic risk should include the analysis of the system as a whole and we explore systematically the most important properties for policy purposes of networks topology on resistance to shocks. In a thorough study going from analytical models to empirical data, we show two sharp transitions from safe to risky regimes: 1) diversification becomes harmful with just a small fraction (~2%) of the shocks sampled from a fat tailed shock distributions and 2) when large shocks are present a critical link density exists where an effective giant cluster forms and most firms become vulnerable. This threshold depends on the network topology, especially on modularity. Firm size heterogeneity has important but diverse effects that are heavily dependent on shock characteristics. Similarly, degree heterogeneity increases vulnerability only when shocks are directed at the most connected firms. Furthermore, by studying the structure of the core of the transnational corporation network from real data, we show that its stability could be clearly increased by removing some of the links with highest centrality betweeness. Our results provide a novel insight and arguments for policy makers to focus surveillance on the connections between firms, in addition to capital requirements directed at the nodes.
Computing Reachable Sets as Capture-Viability Kernels in Reverse Time  [PDF]
No?l Bonneuil
Applied Mathematics (AM) , 2012, DOI: 10.4236/am.2012.311219
Abstract: The set SF(x0;T) of states y reachable from a given state x0 at time T under a set-valued dynamic x’(t)∈F(x (t)) and under constraints x(t)∈K where K is a closed set, is also the capture-viability kernel of x0 at T in reverse time of the target {x0} while remaining in K. In dimension up to three, Saint-Pierre’s viability algorithm is well-adapted; for higher dimensions, Bonneuil’s viability algorithm is better suited. It is used on a large-dimensional example.
Three Dimensional Evolution of SN 1987A in a Self-Gravitating Disk  [PDF]
L. Zaninetti
International Journal of Astronomy and Astrophysics (IJAA) , 2013, DOI: 10.4236/ijaa.2013.32010
Abstract:

The introduction of an exponential or power law gradient in the interstellar medium (ISM) allows to produce an asymmetric evolution of the supernova remnant (SNR) when the framework of the thin layer approximation is adopted. Unfortunately both the exponential and power law gradients for the ISM do not have a well defined physical meaning. The physics conversely is well represented by an isothermal self-gravitating disk of particles whose velocity is everywhere Maxwellian. We derived a law of motion in the framework of the thin layer approximation with a control parameter of the swept mass. The photon’s losses, which are often neglected in the thin layer approximation, are modeled trough velocity dependence. The developed framework is applied to SNR 1987A and the three observed rings are simulated.

The Luminosity Function of Galaxies as Modeled by a Left Truncated Beta Distribution  [PDF]
L. Zaninetti
International Journal of Astronomy and Astrophysics (IJAA) , 2014, DOI: 10.4236/ijaa.2014.41013
Abstract: A first new luminosity function of galaxies can be built starting from a left truncated beta probability density function, which is characterized by four parameters. In the astrophysical conversion, the number of parameters increases by one, due to the addition of the overall density of galaxies. A second new galaxy luminosity function is built starting from a left truncated beta probability for the mass of galaxies once a simple nonlinear relationship between mass and luminosity is assumed; in this case the number of parameters is six because the overall density of galaxies and a parameter that regulates mass and luminosity are added. The two new galaxy luminosity functions with finite boundaries were tested on the Sloan Digital Sky Survey (SDSS) in five different bands; the results produce a better fit than the Schechter luminosity function in two of the five bands considered. A modified Schechter luminosity function with four parameters has been also analyzed.
On the Dark Matter’s Halo Theoretical Description  [PDF]
L. M. L. M. Chechin
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.35052
Abstract: We argued that the standard field scalar potential couldn’t be widely used for getting the adequate galaxies’ curve lines and determining the profiles of dark matter their halo. For discovering the global properties of scalar fields that can describe the observable characteristics of dark matter on the cosmological space and time scales, we propose the simplest form of central symmetric potential celestial-mechanical type, i.e. U(φ) = –μ/φ. It was shown that this potential allows get rather satisfactorily dark matter profiles and rotational curves lines for dwarf galaxies. The good agreement with some previous results, based on the N-body simulation method, was pointed out. A new possibility of dwarf galaxies’ masses estimation was given, also.
Analytical Approximation to the Dynamics of a Binary Stars System with Time Depending Mass Variation  [PDF]
Gustavo V. López, Elkin L. López
Journal of Applied Mathematics and Physics (JAMP) , 2018, DOI: 10.4236/jamp.2018.63053
Abstract: We study the classical dynamics of binary stars when there is an interchange of mass between them. Assuming that one of the stars is more massive than others, the dynamics of the lighter one is analyzed as a function of its time depending mass variation. Within our approximations and models for mass transference, we obtain a general result which establishes that if the lightest star looses mass, its period increases. If the lightest star wins mass, its period decreases.
Quantization and Stable Attractors in a DissipativeOrbital Motion  [PDF]
Daniel L. Nascimento, Antonio L. A. Fonseca
Journal of Modern Physics (JMP) , 2011, DOI: 10.4236/jmp.2011.24030
Abstract: We present a method for determining the motion of an electron in a hydrogen atom, which starts from a field Lagrangean foundation for non-conservative systems that can exhibit chaotic behavior. As a consequence, the problem of the formation of the atom becomes the problem of finding the possible stable orbital attractors and the associated transition paths through which the electron mechanical energy varies continuously until a stable energy state is reached.
Genetic and dietary factors related to schizophrenia  [PDF]
Karl L. Reichelt, Michael L. G. Gardner
Open Journal of Psychiatry (OJPsych) , 2012, DOI: 10.4236/ojpsych.2012.21003
Abstract: Biochemical, immunological and epidemiological evidence increasingly support the suggestion that there is a causal relationship between gluten/gliadin and schizophrenia as originally proposed by F. C. Dohan. Furthermore the necessary physiological mechanisms exist to explain a mechanism involving bioactive peptides from these proteins, and these show that this mechanism is possible and probable in at least in a substantial subgroup of schizophrenic patients. Evidence shows a fairly strong genetic disposition, and it must be recognised that any genetic mechanism must implicate altered chemistry and function of proteins. Evidence supports the likelihood that dietary intervention is beneficial for some, and this demands further investigation. A similar conclusion may apply to autism spectrum conditions.
Study of Decoherence of Elementary Gates Implemented in a Chain of Few Nuclear Spins Quantum Computer Model  [PDF]
G. V. López, P. López
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.31013
Abstract: We study the phenomenon of decoherence during the operation of one qubit transformation, controlled-not (CNOT) and controlled-controlled-not (C2NOT) quantum gates in a quantum computer model formed by a linear chain of three nuclear spins system. We make this study with different type of environments, and we determine the associated decoherence time as a function of the dissipative parameter. We found that the dissipation parameter to get a well defined quantum gates (without significant decoherence) must be within the range of . We also study the behavior of the purity parameter for these gates and different environments and found linear or quadratic decays of this parameter depending on the type of environments.
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