Composição florística de capoeiras baixas no município de Igarapé-Açu no estado do Pará.

bitstream/item/58262/1/DOCUMENTOS-39-CPATU.pd

More inter- and transdisciplinary research needed in agroecology

Agroecology embraces a collection of different disciplinary fields, ranging from agriculture and ecology to political theory. A stronger recognition of agroecology in agricultural research, which often has a strong production focus, could help to achieve sustainable development if more holistic and transdisciplinary research approaches are adopted

Studies of adrenal secretion in ground squirrels and rats during cold stress

Studies of adrenal secretion in ground squirrels and rats during cold stres

Some notes on the trapezoidal rule for Fourier type integrals

This paper deals with the error analysis of the trapezoidal rule for the computation of Fourier type integrals, based on two double exponential transformations. The theory allows to construct algorithms in which the steplength and the number of nodes can be a priori selected. The analysis is also used to design an automatic integrator that can be employed without any knowledge of the function involved in the problem. Several numerical examples, which confirm the reliability of this strategy, are reported

Diversity of Useful Plants in the Coffee Forests of Ethiopia

Plant use diversity and their forms of use and management were studied in four coffee forests of Ethiopia. A coffee forest is a segment of moist montane forest with occurrence of wild Arabica coffee populations. The present study was conducted in four forest fragments located in the southwestern and southeastern parts of the country. These forests represent three different indigenous ethnic groups that live in and around the coffee forests. On the bases of ethnobotanical and floristic studies, a total of 143 useful plant species representing 54 families were identified in all study areas. Nearly all species are native except one which is naturalized. The identified use categories include medicine, food, honey, material sources, social services, animal fodder and environmental uses. Overall, Yayu and Harenna shared a high number of useful plant species in common. Of the total, about 25 species (19%) were similarly used across three or more studied ethnic groups. The implication is that there is a difference between and among the four communities studied for general plant knowledge and uses. As observed, deforestation, over-harvesting, cultivation of marginal lands and overgrazing appear to be threatening the plant resources and their habitats in the studied areas. Ecosystem conservation will ensure in situ conservation of many useful plant species by applying sustainable harvesting methods for collecting plants for any type of use from wild habitats

Numerical methods for electromagnetic inversion

The aim of electromagnetic (EM) sounding methods in geophysics is to obtain information about the subsurface of the earth by recorded measurements taken at the surface. In particular, the goal is to determine variations in the electrical conductivity of the earth with depth by employing an inversion procedure. In this work we focus on one technique, that consists of placing a magnetic dipole above the surface, composed of a transmitter coil and different couples of adjacent receiver coils. The receiver couples are placed at different distances (offsets) from the transmitter coil. In this setting, the electromagnetic induction effect, encoded in the first-order linear Maxwell’s differential equations, produce eddy alterning currents in the soil which induce response electromagnetic fields, that can be used to determine the conductivity profile of the ground by meaning of an inversion algorithm. A typical inversion strategy consists in an iterative procedure involving the computation of the EM response of a layered model (forward modelling) and the solution of the inverse problem. Then, the algorithm attempts to minimize the mismatch between the measured data and the predicted data, by updating the model parameters at each iteration. By assuming that the local subsurface structures are composed by horizontal and homogeneous layers, general integral solutions of Maxwell equations (i.e., the EM fields) for vertical and horizontal magnetic dipoles, can be derived and represented as Hankel transforms, which contain the subsurface model parameters, i.e., the conductivity and the thickness of each layer. By a mathematical point of view, in general, these Hankel transforms are not analytically computable and therefore it is necessary to employ a numerical scheme. Anyway, the slowly decay of the oscillations determined by the Bessel function makes the problem very difficult to handle, because traditional quadrature rules typically fail to converge. In this work we consider two different approaches. The first one is based on the decomposition of the integrand function in a first function for which the corresponding Hankel transform is known exactly, and an oscillating function decays exponentially. For realistic sets of parameters, the oscillations are quite rapidly damped, and the corresponding integral can be accurately computed by a classical quadrature rule on finite intervals. The second approach consists in the application of a Gaussian quadrature formula. We develop a Gaussian rule for weight functions involving fractional powers, exponentials and Bessel functions of the first kind. Moreover, we derive an analytical approximation of these integrals that has a general validity and allows to overcome the limits of common methods based on the modelling of apparent conductivity in the low induction number (LIN) approximation. Having at disposal a reliable method for evaluating the Hankel transforms, by assuming as forward model a homogeneous layered earth, here we also consider the inverse problem of computing the model parameters (i.e., conductivity and thickness of the layers) from a set of measured field values at different offsets. We focus on the specific case of the DUALEM system. We employ two optimization algorithms. The first one is based on the BFGS line-search method and, in order to reduce as much as possible the number of integral evaluations, the analytic approximation of these integrals is used to have a first estimate of the solution. For the second approach we employ the damped Gauss-Newton method. To avoid the dependence on the initial guess of the iterative procedure, we consider a set of different initial models, and we use each one to solve the optimization problem. The numerical experiments, carried out for the study of river-levees integrity, are obtained by employing a virtual machine equipped with the NVIDIA A100 Tensor Core GPU.The aim of electromagnetic (EM) sounding methods in geophysics is to obtain information about the subsurface of the earth by recorded measurements taken at the surface. In particular, the goal is to determine variations in the electrical conductivity of the earth with depth by employing an inversion procedure. In this work we focus on one technique, that consists of placing a magnetic dipole above the surface, composed of a transmitter coil and different couples of adjacent receiver coils. The receiver couples are placed at different distances (offsets) from the transmitter coil. In this setting, the electromagnetic induction effect, encoded in the first-order linear Maxwell’s differential equations, produce eddy alterning currents in the soil which induce response electromagnetic fields, that can be used to determine the conductivity profile of the ground by meaning of an inversion algorithm. A typical inversion strategy consists in an iterative procedure involving the computation of the EM response of a layered model (forward modelling) and the solution of the inverse problem. Then, the algorithm attempts to minimize the mismatch between the measured data and the predicted data, by updating the model parameters at each iteration. By assuming that the local subsurface structures are composed by horizontal and homogeneous layers, general integral solutions of Maxwell equations (i.e., the EM fields) for vertical and horizontal magnetic dipoles, can be derived and represented as Hankel transforms, which contain the subsurface model parameters, i.e., the conductivity and the thickness of each layer. By a mathematical point of view, in general, these Hankel transforms are not analytically computable and therefore it is necessary to employ a numerical scheme. Anyway, the slowly decay of the oscillations determined by the Bessel function makes the problem very difficult to handle, because traditional quadrature rules typically fail to converge. In this work we consider two different approaches. The first one is based on the decomposition of the integrand function in a first function for which the corresponding Hankel transform is known exactly, and an oscillating function decays exponentially. For realistic sets of parameters, the oscillations are quite rapidly damped, and the corresponding integral can be accurately computed by a classical quadrature rule on finite intervals. The second approach consists in the application of a Gaussian quadrature formula. We develop a Gaussian rule for weight functions involving fractional powers, exponentials and Bessel functions of the first kind. Moreover, we derive an analytical approximation of these integrals that has a general validity and allows to overcome the limits of common methods based on the modelling of apparent conductivity in the low induction number (LIN) approximation. Having at disposal a reliable method for evaluating the Hankel transforms, by assuming as forward model a homogeneous layered earth, here we also consider the inverse problem of computing the model parameters (i.e., conductivity and thickness of the layers) from a set of measured field values at different offsets. We focus on the specific case of the DUALEM system. We employ two optimization algorithms. The first one is based on the BFGS line-search method and, in order to reduce as much as possible the number of integral evaluations, the analytic approximation of these integrals is used to have a first estimate of the solution. For the second approach we employ the damped Gauss-Newton method. To avoid the dependence on the initial guess of the iterative procedure, we consider a set of different initial models, and we use each one to solve the optimization problem. The numerical experiments, carried out for the study of river-levees integrity, are obtained by employing a virtual machine equipped with the NVIDIA A100 Tensor Core GPU