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Search Results: 1 - 10 of 42099 matches for " Jorge;Pereira "
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Anthropogenic Disturbances and the Natural Vegetation Regeneration: A Case Study of a Forest Fragment Located in a Cuesta Relief Area, State of S?o Paulo, Brazil  [PDF]
Luiz Alberto Blanco Jorge, Vanessa Rodrigues Pereira
Open Journal of Forestry (OJF) , 2015, DOI: 10.4236/ojf.2015.56055
Abstract: The present study has been conducted in one of the five natural vegetation fragments at the Experimental Farm Edgardia, in Botucatu, São Paulo State, Brazil. In the past the forest fragment suffered disturbances due to the selective exploitation of tree species and the use of part of the surface as pasture. The objectives of this research were to evaluate the structure and the dynamics of natural vegetation. Three phytosociological surveys (2006, 2010 and 2014) were carried out in a sampled area of one hectare. The most abundant species were mapped in 2014, in a sampling unit with two hectares. Individuals of 37 families and 110 species have been recorded. The oscillation of the basal area observed through the forest inventories was due to the instability caused by disturbances. Only two out of the seven most abundant species mapped showed exponential diameter distribution. The unimodal distributions shown by the other five species have suggested that the vegetation has been occupying the most open spaces through regeneration in cycles. There was direct association between the spatial distribution and the dispersion syndrome for five out of the seven most abundant species. Three species have zoochoric dispersion, showing that wild animals populations have accomplished their function in the dispersion of seeds/fruit. The spatial distributions of four out of the seven most abundant species have provided evidence of how the regeneration of natural vegetation is being processed in this area.
A Piece of a Puzzle of Haplotypes for the Indian Ocean Hawksbill Turtle  [PDF]
Rita Anastácio, Mário Jorge Pereira
Natural Resources (NR) , 2017, DOI: 10.4236/nr.2017.88034
Abstract: The Indian Ocean basin has much to reveal in what concerns marine turtles. Its regional management units (RMUs) are still lacking molecular data to define conservation strategies and priorities. Vamizi Island is one of the best known rookeries in the north of the Mozambique Channel. A mitochondrial DNA analysis revealed 14 haplotypes for the hawksbill turtle’s nesting and foraging in/near Vamizi, twelve of which were new in 2011. Though more studies inside the Channel are needed, Vamizi Island possibly contributes with hatchlings for other locations. More knowledge is important to define priorities for management units inside the Indian Ocean.
From the Challenges Imposed by Climate Change to the Preservation of Ecosystem Processes and Services  [PDF]
Rita Anastácio, Mário Jorge Pereira
Natural Resources (NR) , 2017, DOI: 10.4236/nr.2017.812048
Today, especially in countries that offer a satisfactory quality of life, it is easy to forget that we depend directly and indirectly on services provided by ecosystems such as quantity and quality of water, energy, food, health, and shelter. In less developed countries, the daily struggle for essential goods makes this dependency more real, despite the lack of knowledge, organization and/or financial resources to deal with the problems imposed on ecosystems by climate and anthropogenic changes. Protecting ecosystems by ensuring the services they provide has become highly dependent on our management capacity, our understanding of its functioning, and our capacity for persuasion. Demographic pressure and individualism compromise the survival of various species, including our own, and create pressures under governments and the stability of nations. The notion of facing a global challenge has awakened in the scientific community the need to focus on developing global strategies that change the mind-sets of decision makers, industry, governments and markets. Global knowledge networks and experts are being built to mitigate problems on a global scale. In this mini review, the authors make a brief visit to documents, intergovernmental initiatives, and platforms that have been built with the aim of contributing to promote a resolution for the global problems.
Resonance webs of hyperplane arrangements
Jorge Vitorio Pereira
Mathematics , 2010,
Abstract: Each irreducible component of the first resonance variety of a hyperplane arrangement naturally determines a codimension one foliation on the ambient space. The superposition of these foliations define what we call the resonance web of the arrangement. In this paper we initiate the study of these objects with emphasis on their spaces of abelian relations.
The characteristic variety of a generic foliation
Jorge Vitorio Pereira
Mathematics , 2009,
Abstract: We confirm a conjecture of Bernstein-Lunts which predicts that the characteristic variety of a generic polynomial vector field has no homogeneous involutive subvarieties besides the zero section and subvarieties of fibers over singular points.
Global Stability for Holomorphic Foliations in Kaehler Manifolds
Jorge Vitorio Pereira
Mathematics , 2000, DOI: 10.1007/BF02969347
Abstract: We prove the following theorem for Holomorphic Foliations in compact complex kaehler manifolds: if there is a compact leaf with finite holonomy, then every leaf is compact with finite holonomy. As corollary we reobtain stability theorems for compact foliations in Kaehler manifolds of Edwards-Millett-Sullivan and Hollman.
On the Poincare Problem for Foliations of General Type
Jorge Vitorio Pereira
Mathematics , 2001, DOI: 10.1007/s002080100277
Abstract: Let F be a holomorphic foliation of general type on CP(2) which admits a rational first integral. We provide bounds for the degree of the first integral of F just in function of the degree, the birational invariants of F and the geometric genus of a generic leaf. Similar bounds for invariant algebraic curves are also obtained and examples are given showing the necessity of the hypothesis.
Fibrations, Divisors and Transcendental Leaves
Jorge Vitorio Pereira
Mathematics , 2004,
Abstract: We will use flat divisors, and canonically associated singular holomorphic foliations, to investigate some of the geometry of compact complex manifolds. The paper is mainly concerned with three distinct problems: the existence of fibrations, the topology of smooth hypersurfaces and the topological closure of transcendental leaves of foliations.
An analogous of Jouanolou's Theorem in positive characteristic
Jorge Vitorio Pereira
Mathematics , 2000, DOI: 10.1016/S0022-4049(01)00150-5
Abstract: We show that a generic vector field on an affine space of positive characteristic admits an invariant algebraic hypersurface. This contrast with Jouanolou's Theorem that shows that in characteristic zero the situation is completely opposite. That is a generic vector field in the complex plane does not admit any invariant algebraic curve.
Vector Fields, Invariant Varieties and Linear Systems
Jorge Vitorio Pereira
Mathematics , 2000,
Abstract: We investigate the interplay between invariant varieties of vector fields and the inflection locus of linear systems with respect to the vector field. Among the consequences of such investigation we obtain a computational criteria for the existence of rational first integrals of a given degree, bounds for the number of first integrals on families of vector fields and a generalization of Darboux's criteria. We also provide a new proof of Gomez-Mont's result on foliations with all leaves algebraic.
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