Distribution des principales espèces agroforestières à Watinoma, terroir du plateau central burkinabé, une résultante de contraintes écologiques et anthropiques

Watinoma is a village of the Burkina Faso Plateau central. It is located approximately 100 km in North of Ouagadougou, in Sudano-sahelian climate. The rainful average is 600 mm and reduced these last twenty years to 500 mm. In these conditions, the vegetation is contracted. Many trees are died and bare glacis increased. The main park agroforestry species show well a distinctive behaviour with a clear opposition between Butyrospermum paradoxum and Faidherbia albida what means both contrasted ecological and ethnobotanical characteristics. Faidherbia albida is found in two typical sites. At firstly in the sandy hydromorphic lowlands where the water table is accessible to the plant. At secondary near the village where is associated with Adansonia digitata and many exotic species, on young clay soil in contact with the origin rock. Butyrospermum paradoxum is on a stone slab as soon as the deep of soil exceeds 80 cm. On thinner soils, we meet other species like Lannea microcarpa, Sclerocarya birrea and Bombax costatum. Faidherbia has good regeneration, particulary around the habitat, here, the seeds are brought with the manures. But in these conditions of regeneration, the seedlings don't develop, on the one hand because the edaphic conditions aren't favourable, on the other hand because the farmers continuously cut down them. The regeneration of Butyrospermum paradoxum is not very good. It is restricted to the fallow area. The farmers protect the seedlings provided that they sufficiently developped. Parkia biglobosa also should be protected its regeneration was effective.Watinoma est un village du Plateau Central burkinabé, situé à une centaine de kilomètres au nord de la capitale, en zone soudano-sahélienne, dans la zone des roches vertes. La pluviométrie moyenne est de 600 mm et s'est réduit à 500 mm ces 20 dernières années. Dans ces conditions la végétation s'est contractée. Beaucoup d'arbres sont morts et les glacis dénudés se sont étendus. Les principales espèces du parc agroforestier montrent un comportement bien individualisé avec une opposition nette entre le karité et le Faidherbia qui traduit à la fois des caractères écologiques et ethnobotaniques (perception paysanne) contrastés. Faidherbia se rencontre dans deux types de situations : dans les bas-fonds sableux où la nappe phréatique existe et est accessible (présence de puits) et autour du village, en association avec le baobab et de nombreuses espèces exotiques, sur des sols argileux jeunes en contact avec la roche mère. Le karité est présent sur les sols sur cuirasse là où leur épaisseur dépasse 80 cm. Les sols plus minces portent d'autres espèces agroforestières dont le raisinier, le prunier et le kapokier rouge. La régénération de Faidherbia est abondante, surtout dans la zone du village, où les graines sont apportées avec les fumiers. Mais dans ces conditions les plants n'évoluent pas, d'une part parce que les conditions édaphiques ne sont pas favorables, d'autre part parce que les paysans les rabattent constamment. La régénération du karité est, elle, peu abondante, limitée aux zones en jachère. Les paysans protègent les plants pourvu qu'ils soient suffisamment développés. Le néré serait aussi protégé si sa régénération existait, ce qui n'est plus le cas avec la sécheresse actuelle.Ouedraogo Sibiri Jean, Alexandre Daniel-Yves. Distribution des principales espèces agroforestières à Watinoma, terroir du Plateau Central burkinabé, une résultante de contraintes écologiques et anthropiques. In: Journal d'agriculture traditionnelle et de botanique appliquée, 36ᵉ année, bulletin n°1,1994. pp. 101-111

The power spectrum of the circular noise

The circular noise is important in connection to Mach's principle, and also as a possible probe of the Unruh effect. In this letter the power spectrum of the detector following the Trocheries-Takeno motion in the Minkowski vacuum is analytically obtained in the form of an infinite series. A mean distribution function and corresponding energy density are obtained for this particular detected noise. The analogous of a non constant temperature distribution is obtained. And in the end, a brief discussion about the equilibrium configuration is given.Comment: accepted for publication in GR

Large-eddy simulation of the lid-driven cubic cavity flow by the spectral element method

This paper presents the large-eddy simulation of the lid-driven cubic cavity flow by the spectral element method (SEM) using the dynamic model. Two spectral filtering techniques suitable for these simulations have been implemented. Numerical results for Reynolds number $\text{Re}=12'000$ are showing very good agreement with other experimental and DNS results found in the literature

Relativistic state reduction dynamics

A mechanism describing state reduction dynamics in relativistic quantum field theory is outlined. The mechanism involves nonlinear stochastic modifications to the standard description of unitary state evolution and the introduction of a relativistic field in which a quantized degree of freedom is associated to each point in spacetime. The purpose of this field is to mediate in the interaction between classical stochastic influences and conventional quantum fields. The equations of motion are Lorentz covariant, frame independent, and do not result in divergent behavior. It is shown that the mathematical framework permits the specification of unambiguous local properties providing a connection between the model and evidence of real world phenomena. The collapse process is demonstrated for an idealized example.Comment: 20 pages, 2 figures, replacement with minor correction

Velocity correlations in dense granular gases

We report the statistical properties of spherical steel particles rolling on an inclined surface being driven by an oscillating wall. Strong dissipation occurs due to collisions between the particles and rolling and can be tuned by changing the number density. The velocities of the particles are observed to be correlated over large distances comparable to the system size. The distribution of velocities deviates strongly from a Gaussian. The degree of the deviation, as measured by the kurtosis of the distribution, is observed to be as much as four times the value corresponding to a Gaussian, signaling a significant breakdown of the assumption of negligible velocity correlations in a granular system.Comment: 4 pages, 4 Figure

Acceleration of the universe, vacuum metamorphosis, and the large-time asymptotic form of the heat kernel

We investigate the possibility that the late acceleration observed in the rate of expansion of the universe is due to vacuum quantum effects arising in curved spacetime. The theoretical basis of the vacuum cold dark matter (VCDM), or vacuum metamorphosis, cosmological model of Parker and Raval is revisited and improved. We show, by means of a manifestly nonperturbative approach, how the infrared behavior of the propagator (related to the large-time asymptotic form of the heat kernel) of a free scalar field in curved spacetime causes the vacuum expectation value of its energy-momentum tensor to exhibit a resonance effect when the scalar curvature R of the spacetime reaches a particular value related to the mass of the field. we show that the back reaction caused by this resonance drives the universe through a transition to an accelerating expansion phase, very much in the same way as originally proposed by Parker and Raval. Our analysis includes higher derivatives that were neglected in the earlier analysis, and takes into account the possible runaway solutions that can follow from these higher-derivative terms. We find that the runaway solutions do not occur if the universe was described by the usual classical FRW solution prior to the growth of vacuum energy-density and negative pressure (i.e., vacuum metamorphosis) that causes the transition to an accelerating expansion of the universe in this theory.Comment: 33 pages, 3 figures. Submitted to Physical Review D15 (Dec 23, 2003). v2: 1 reference added. No other change

Surface Instability in Windblown Sand

We investigate the formation of ripples on the surface of windblown sand based on the one-dimensional model of Nishimori and Ouchi [Phys. Rev. Lett. 71, 197 (1993)], which contains the processes of saltation and grain relaxation. We carry out a nonlinear analysis to determine the propagation speed of the restabilized ripple patterns, and the amplitudes and phases of their first, second, and third harmonics. The agreement between the theory and our numerical simulations is excellent near the onset of instability. We also determine the Eckhaus boundary, outside which the steady ripple patterns are unstable.Comment: 23 pages, 8 figure