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Mboumba J.F.,Universite des Sciences et Techniques de Masuku | Mboumba J.F.,University of Rennes 1 | Deleporte P.,French National Center for Scientific Research | Colyn M.,CNRS Ecosystems, Biodiversity, and Evolution Laboratory | Nicolas V.,CNRS Systematics, Biodiversity and Evolution Institute
Journal of Zoological Systematics and Evolutionary Research | Year: 2011

We studied the phylogeography of the strict savannah pygmy mice Mus (Nannomys) minutoides in West Central Africa. A total of 846 base pairs of the cytochrome b sequence were obtained for 66 individuals collected in Gabon, Cameroon, Republic of Congo and Central African Republic. These sequences were compared to those of M. minutoides from other African countries and to eight other species of the genus Mus. We performed maximum likelihood, Bayesian and nested clade analyses, as well as neutrality tests and time estimates. We show that M. minutoides is a well-differentiated monophyletic species that separated from other pygmy mice 1.17 Myr ago. A distinct West Central African M. minutoides clade diverged early from the other African populations of the species, with a more recent common ancestor dating 0.14 Myr. West Central African populations are globally homogeneous, despite the present fragmentation of savannahs by the rain forest. However, our analyses show an unexpected vicariance between geographically close savannahs, embedded in the rain forest in Central Gabon. One of these populations is genetically more similar to very distant peripheral populations than to three closely neighbouring populations situated on both sides of the Ogooué River. A non-river geographical barrier probably persisted in this area, durably isolating these local populations. This hypothesis about the history of the savannah landscape should be testable through the biogeographical analysis of other strict savannah small mammal species. © 2010 Blackwell Verlag GmbH. Source

Mohamadou A.,University of Douala | Mohamadou A.,Abdus Salam International Center For Theoretical Physics | Wamba E.,University of Yaounde I | Doka S.Y.,University of Maroua | And 2 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

We examine the generation of bright matter-wave solitons in the Gross-Pitaevskii equation describing Bose-Einstein condensates with a time-dependent complex potential, which is composed of a repulsive parabolic background potential and a gravitational field. By performing a modified lens-type transformation, an explicit expression for the growth rate of a purely growing modulational instability is presented and analyzed. We point out the effects of the gravitational field, as well as of the parameter related to the feeding or loss of atoms in the condensate, on the instability growth rate. It is evident from numerical simulations that the feeding with atoms and the magnetic trap have opposite effects on the dynamics of the system. It is shown that the feeding or loss parameter can be well used to control the instability domain. Our study shows that the gravitational field changes the condensate trail of the soliton trains during the propagation. We also perform a numerical analysis to solve the Gross-Pitaevskii equation with a time-dependent complicated potential. The numerical results on the effect of both the gravitational field and the parameter of feeding or loss of atoms in the condensate agree well with predictions of the linear stability analysis. Another result of the present work is the modification of the background wave function in the Thomas-Fermi approximation during the numerical simulations. © 2011 American Physical Society. Source

Moutsinga O.,Universite des Sciences et Techniques de Masuku
Journal of Mathematical Physics | Year: 2012

Under general assumptions on the initial data, we show that the entropy solution (x, t) → u(x, t) of the one-dimensional inviscid Burgers' equation is the velocity function of a sticky particles model whose initial mass distribution is Lebesgue measure. Precisely, the particles trajectories (x, t) → X0, t(x) are given by a forward flow: ∀ (x, s, t) ∈ R{double-struck}×R{double-struck} + × R{double-struck} +, X 0,s+t (x)=X s,t (X 0,s(x)) and ∂/∂ t X s,t = u(X s,t, S+t) = E[u(·,s)|X s,t; u(x,t) = E[u(·,0|X 0,t = x]. © 2012 American Institute of Physics. Source

Lebamba J.,Universite des Sciences et Techniques de Masuku | Lebamba J.,Aix - Marseille University | Lebamba J.,Montpellier University | Vincens A.,Aix - Marseille University | Maley J.,Montpellier University
Climate of the Past | Year: 2012

This paper presents quantitative reconstructions of vegetation and climate along the pollen sequence of Lake Barombi Mbo, southwestern Cameroon (4°39′45.75″ N, 9°23′51.63″ E, 303 m a.s.l.) during the last 33 000 cal yr BP, improving previous empirical interpretations. The biomisation method was applied to reconstruct potential biomes and forest successional stages. Mean annual precipitation, mean annual potential evapotranspiration and an index of moisture availability were reconstructed using modern analogues and an artificial neural network technique. The results show a dense forested environment around Lake Barombi Mbo of mixed evergreen/semi-deciduous type during the most humid phases (highest precipitation and lowest evapotranspiration), but with a more pronounced semi-deciduous type from ca. 6500 cal yr BP to the present day, related to increased seasonality. This forest displays a mature character until ca. 2800 cal yr BP, then becomes of secondary type during the last millennium, probably due to increased human activity. Two episodes of forest fragmentation are shown, which are synchronous with the lowest reconstructed precipitation and highest potential evapotranspiration values. The first of these occurs during the LGM, and the second one from ca. 3000 to ca. 1200 cal yr BP, mainly linked to high precipitation seasonality. Savanna were, however, never extensive within the Barombi Mbo basin, existing instead inside the forest in form of savanna patches. The climate reconstructions at Lake Barombi Mbo suggest that the artificial neural networks technique would be more reliable in this region, although the annual precipitation values are likely under-estimated through the whole sequence. © Author(s) 2012. Source

Bona Z.,University of Douala | Nganso H.M.T.,University of Douala | Ekogo T.B.,Universite des Sciences et Techniques de Masuku | Njock M.G.K.,University of Douala
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

A fully relativistic multipole scheme is formulated to study two-photon emission processes in hydrogenlike ions with an infinitely heavy, pointlike, and spinless nucleus of charge up to 100. By making use of the Sturmian expansion of the Dirac-Coulomb Green function of the first order constructed by Szmytkowski, closed-form expressions are derived for arbitrary multipole channels. In the nonrelativistic limit, well-known formulas established previously are retrieved. For the sake of assessing the effectiveness of our approach, numerical applications are then carried out for two-photon decay rates of the selected 2s1/2 and 2p1/2 atomic states. To this end, radial integrals, the most crucial quantities involved in the matrix elements, are treated with great care by means of two suitable techniques that agree with each other quite closely so that very accurate values are obtained regardless of the choice of parameters, such as radial quantum numbers and orders of spherical Bessel functions of the first kind. In addition, the convergence and stability of computations are checked in connection with the intermediate-state summation, which appears within the second-order perturbation theory. As expected, the gauge invariance of our fully relativistic multipole numbers is confirmed. Relativistic effects, and the influence of the negative spectrum of the complete set of Dirac-Coulomb Sturmians of first order and retardation truncations in the transition operator are examined. Finally, a comparison is undertaken of our two-photon relativistic calculations with refined predictions of other authors based on finite basis-set methods widely employed over the past decades. © 2014 American Physical Society. Source

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