1,330 research outputs found

    The resilience of indigenous knowledge in small-scale African agriculture: key drivers

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    The successful use of indigenous knowledge (IK) in development practice in rural Africa over the last couple of decades has proved to be elusive and disappointing. Using empirical field data from northern Malawi, this study suggests that the two key drivers for farmers in this area are household food security and the maintenance of soil fertility. Indigenous ways of knowing underpin the agricultural system which has been developed, rather than the adoption of more modern, ‘scientific’ ways, to deliver against these drivers. Such IKs, however, are deeply embedded in the economic, social and cultural environments in which they operate

    Ratios of characteristic polynomials in complex matrix models

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    We compute correlation functions of inverse powers and ratios of characteristic polynomials for random matrix models with complex eigenvalues. Compact expressions are given in terms of orthogonal polynomials in the complex plane as well as their Cauchy transforms, generalizing previous expressions for real eigenvalues. We restrict ourselves to ratios of characteristic polynomials over their complex conjugate

    Application of the Cloude-Pottier decomposition to weather radar signatures

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    In this paper we apply the Cloude-Pottier decomposition to Weather Radar Signatures. First, we present the results of a simulation carried out at the Chemnitz University of Technology and give the expected H-α values for different rain intensities. A comparison with standard radarmeteorological variables is also given. Then, first ever images of Entropy and Anisotropy are presented for clouds and precipitation. Experimental Data are from the POLDIRAD Weather Facility in Oberpfaffenhofen, Germany

    Unidimensional model of the ad-atom diffusion on a substrate submitted to a standing acoustic wave I. Derivation of the ad-atom motion equation

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    The effect of a standing acoustic wave on the diffusion of an ad-atom on a crystalline surface is theoretically studied. We used an unidimensional space model to study the ad-atom+substrate system. The dynamic equation of the ad-atom, a Generalized Langevin equation, is analytically derived from the full Hamiltonian of the ad-atom+substrate system submitted to the acoustic wave. A detailed analysis of each term of this equation, as well as of their properties, is presented. Special attention is devoted to the expression of the effective force induced by the wave on the ad-atom. It has essentially the same spatial and time dependences as its parent standing acoustic wave

    Quasi One-Dimensional Photonic Crystals as Building Block for Compact Integrated Optical Refractometric Sensors

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    A quasi one-dimensional photonic crystal has been fabricated and the applicability of this strong grating for optical sensing has been investigated by measuring the transmission spectra as a function of the cladding refractive index. The cladding index was varied a small range. By monitoring the transmitted output power the transmission stop-band was found to shift by 1 nm wavelength for either a cladding refractive index change of 0.05 or a temperature change of 120 K

    Quasi 1-dimensional photonic crystals as building block for compact integrated optical sensors

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    A quasi one-dimensional photonic crystal has been fabricated and the applicability of this kind of structure for optical sensing has been investigated by measuring the transmission spectra as a function of the cladding refractive index. The cladding index was varied using a liquid flow, of which the index was slowly varied over a small range. The shift with cladding index of the steep stop band edge provides a relatively sensitive detection mechanism in an extremely compact device

    Affine convex body semigroups

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    In this paper we present a new kind of semigroups called convex body semigroups which are generated by convex bodies of R^k. They generalize to arbitrary dimension the concept of proportionally modular numerical semigroup of [7]. Several properties of these semigroups are proven. Affine convex body semigroups obtained from circles and polygons of R^2 are characterized. The algorithms for computing minimal system of generators of these semigroups are given. We provide the implementation of some of them

    Using species richness and functional traits predictions to constrain assemblage predictions from stacked species distribution models

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    Aim: Modelling species at the assemblage level is required to make effective forecast of global change impacts on diversity and ecosystem functioning. Community predictions may be achieved using macroecological properties of communities (MEM), or by stacking of individual species distribution models (S-SDMs). To obtain more realistic predictions of species assemblages, the SESAM framework suggests applying successive filters to the initial species source pool, by combining different modelling approaches and rules. Here we provide a first test of this framework in mountain grassland communities. Location: The western Swiss Alps. Methods: Two implementations of the SESAM framework were tested: a "Probability ranking" rule based on species richness predictions and rough probabilities from SDMs, and a "Trait range" rule that uses the predicted upper and lower bound of community-level distribution of three different functional traits (vegetative height, specific leaf area and seed mass) to constraint a pool of environmentally filtered species from binary SDMs predictions. Results: We showed that all independent constraints expectedly contributed to reduce species richness overprediction. Only the "Probability ranking" rule allowed slightly but significantly improving predictions of community composition. Main conclusion: We tested various ways to implement the SESAM framework by integrating macroecological constraints into S-SDM predictions, and report one that is able to improve compositional predictions. We discuss possible improvements, such as further improving the causality and precision of environmental predictors, using other assembly rules and testing other types of ecological or functional constraints

    Internal convection in thermoelectric generator models

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    Coupling between heat and electrical currents is at the heart of thermoelectric processes. From a thermal viewpoint this may be seen as an additional thermal flux linked to the appearance of electrical current in a given thermoelectric system. Since this additional flux is associated to the global displacement of charge carriers in the system, it can be qualified as convective in opposition to the conductive part associated with both phonons transport and heat transport by electrons under open circuit condition, as, e.g., in the Wiedemann-Franz relation. In this article we demonstrate that considering the convective part of the thermal flux allows both new insight into the thermoelectric energy conversion and the derivation of the maximum power condition for generators with realistic thermal coupling.Comment: 8 pages, 3 figure
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