21,337 research outputs found

    Potential climatic influence on the maximum stand carrying capacity of 15 Mediterranean conifers and broadleaves

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    Las proyecciones de cambio climático para la cuenca del Mediterráneo predicen un incremento continuo en episodios de sequía y calor extremos, afectando a la dinámica, estructura y composición de las masas forestales. En este contexto, resulta fundamental comprender cómo el clima influye en la relación tamaño-densidad máxima (recta de autoclareo) de estas masas con el fin de diseñar actuaciones de gestión forestal sostenible adaptadas a este nuevo escenario. Este estudio pretende avanzar en esta línea, analizando los potenciales impactos del clima en el Índice de Máxima Densidad (SDImax) de 15 especies forestales pertenecientes a los géneros Pinus, Fagus y Quercus. Para ello se utilizaron las bases de datos del Tercer Inventario Forestal Nacional Español (IFN3) y WorldClim. En primer lugar, se ajustaron rectas de autoclareo básicas mediante regresión cuantílica y se estimaron nuevos valores SDImax de referencia por especie. En un segundo paso, se seleccionaron 35 variables climáticas anuales y periódicas para ajustar rectas de autoclareo dependientes del clima. El mejor modelo climáticodependiente fue seleccionado para cada especie basándonos en el Indice de Información de Akaike con el fin de analizar las tendencias generales y específicas en la variación de SDImax. Para todas las especies de estudio, la influencia del clima sobre el SDImax fue significativa. Los resultados obtenidos mostraron una tendencia común en la variación de SDImax, con valores más pequeños vinculados a condiciones más secas y cálidas, lo que sugiere reducciones potenciales del stock de estas especies bajo futuros escenarios climáticos. En oposición a esta tendencia, el modelo de Pinus nigra sugiere que inviernos más suaves como efecto de incrementos en temperaturas mínimas podrían beneficiar a las especies en zonas de montaña. En general, el estrés hídrico (expresado a través del Indice De Martonne) fue un factor determinante afectando al SDImax de Fagus, mientras que cambios en las temperaturas de primavera y verano explicaron las variaciones SDImax de las especies del género Quercus. Las especies de Pinus se vieron indistintamente afectadas por potenciales variaciones de temperatura y humedad. Todos los modelos climático-dependientes seleccionados mejoraron los modelos básicos y los modelos ajustados en estudios similares, como aquellos que utilizan el Índice de Martonne como variable climática independiente. Nuestros hallazgos destacan la necesidad de utilizar variables climáticas periódicas para caracterizar mejor los impactos climáticos en el SDImax. Los modelos presentados en este estudio permitirán obtener estimaciones más precisas de la máxima densidad admisible por diferentes especies de coníferas y frondosas, proporcionando una herramienta avanzada para la gestión forestal sostenible de masas puras y mixtas mediterráneas bajo diferentes escenarios de cambio climático.Climate change projections for the Mediterranean basin predict a continuous increment in extreme drought and heat episodes, affecting forest dynamics, structure and composition. Understanding how climate influences the maximum size-density relationship (MSDR) is therefore critical to design adaptative silvicultural guidelines based on the potential stand carrying capacity of tree species. With this aim, data from the Third Spanish National Forest Inventory (3NFI) and WorldClim databases were used to analyze climate related variations of the maximum stand carrying capacity for 15 species from the Pinus, Fagus and Quercus genus. First, basic MSDR were fitted using linear quantile regression and observed size-density data from monospecific 3NFI plots. Reference values of maximum stocking, expressed as SDImax, were estimated by species. In a second step, climatedependent MSDR models including 35 different annual and seasonal climatic variables were fitted. The best climate-dependent MSDR model was selected by species according to the Akaike Information Criteria in order to analyze general and species-specific trends in the SDImax variation. Results showed a common trend across species in SDIgenus variation with smaller SDImax values linked to drier and warmer conditions, suggesting potential reductions of the maximum stocking for this species based on projected climatic scenarios. Opposed to this trend, results for Pinus nigra suggest that milder winters as effect of increments in minimum temperatures could beneficiate mountainous species. Humidity (expressed as the De Martonne Index) was found as key driver affecting SDImax of Fagus species, since changes in spring and summer temperatures explained SDImax variations of Quercus species. Pinus species were indistinctively affected by temperature and water stress. All the selected climate-dependent models improved the goodness of fit over the basic and the business-as-usual models including the De Martonne Index as independent climatic variable. Our findings highlight the importance of using specific climatic variables to better characterize climatic impacts on the MSDR. Models presented in this study will allow to obtain more precise estimations of the maximum stocking for different coniferous and broadleaved species, providing an advanced tool for managing Mediterranean pure and mixed forests under different scenarios of climate change.Máster en Gestión Forestal basada en Ciencia de Dato

    Schroeder and Whiting on Knowledge and Defeat

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    Daniel Whiting has argued, in this journal, that Mark Schroeder’s analysis of knowledge in terms of subjectively and objectively sufficient reasons for belief makes wrong predictions in fake barn cases. Schroeder has replied that this problem may be avoided if one adopts a suitable account of perceptual reasons. I argue that Schroeder’s reply fails to deal with the general worry underlying Whiting’s purported counterexample, because one can construct analogous potential counterexamples that do not involve perceptual reasons at all. Nevertheless, I claim that it is possible to overcome Whiting’s objection, by showing that it rests on an inadequate characterization of how defeat works in the examples in question

    Akrasia and the Desire to Become Someone Else: Venturinha on Moral Matters

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    This paper discusses practical akrasia from the perspective of the sophisticated form of moral subjectivism that can be derived from Nuno Venturinha’s (2018) remarks on moral matters

    Quantum Hamiltonians with Quasi-Ballistic Dynamics and Point Spectrum

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    Consider the family of Schr\"odinger operators (and also its Dirac version) on ℓ2(Z)\ell^2(\mathbb{Z}) or ℓ2(N)\ell^2(\mathbb{N}) Hω,SW=Δ+λF(Snω)+W,ω∈Ω, H^W_{\omega,S}=\Delta + \lambda F(S^n\omega) + W, \quad \omega\in\Omega, where SS is a transformation on (compact metric) Ω\Omega, FF a real Lipschitz function and WW a (sufficiently fast) power-decaying perturbation. Under certain conditions it is shown that Hω,SWH^W_{\omega,S} presents quasi-ballistic dynamics for ω\omega in a dense GδG_{\delta} set. Applications include potentials generated by rotations of the torus with analytic condition on FF, doubling map, Axiom A dynamical systems and the Anderson model. If WW is a rank one perturbation, examples of Hω,SWH^W_{\omega,S} with quasi-ballistic dynamics and point spectrum are also presented.Comment: 17 pages; to appear in Journal of Differential Equation

    Dynamical Delocalization for the 1D Bernoulli Discrete Dirac Operator

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    An 1D tight-binding version of the Dirac equation is considered; after checking that it recovers the usual discrete Schr?odinger equation in the nonrelativistic limit, it is found that for two-valued Bernoulli potentials the zero mass case presents absence of dynamical localization for specific values of the energy, albeit it has no continuous spectrum. For the other energy values (again excluding some very specific ones) the Bernoulli Dirac system is localized, independently of the mass.Comment: 9 pages, no figures - J. Physics A: Math. Ge

    Dynamical Lower Bounds for 1D Dirac Operators

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    Quantum dynamical lower bounds for continuous and discrete one-dimensional Dirac operators are established in terms of transfer matrices. Then such results are applied to various models, including the Bernoulli-Dirac one and, in contrast to the discrete case, critical energies are also found for the continuous Dirac case with positive mass.Comment: 18 pages; to appear in Math.

    Measuring Loss Potential of Hedge Fund Strategies

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    We measure the loss potential of Hedge Funds by combining three market risk measures: VaR, Draw-Down and Time Under-The-Water. Calculations are carried out considering three different frameworks regarding Hedge Fund returns: i) Normality and time-independence, ii) Non-normality and time- independence and iii) Non-normality and time-dependence. In the case of Hedge Funds, our results clearly state that market risk may be substantially underestimated by those models which assume Normality or, even considering Non-Normality, neglect to model time- dependence. Moreover, VaR is an incomplete measure of market risk whenever the Normality assumption does not hold. In this case, VaR results must be compared with Draw-Down and Time Under-The-Water measures in order to accurately assess about Hedge Funds loss potential.Hedge Fund, Value-at-Risk, risk, performance, drawdown, under- the-water, normal returns, non-normal returns, time-dependence, ARMA, Monte Carlo, skewness, kurtosis, mixture of gaussian distributions, survival probability, styles, investment strategies
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