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Search Results: 1 - 10 of 32573 matches for " Luis Fernandez "
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An assessment of fish communities along a piedmont river receiving organic pollution (Aconquija Mountains, Argentina)
fernandez luis
Acta Biológica Colombiana , 2010,
Abstract: The relationships between fish assemblage structure and environmental variables along a pollution gradient in the Medina River were analyzed over a year in four sampling sites (S1-S4). The river flows in a mountain-plain transition and is affected by several small town wastewater and sugar cane industries effluents. Environmental variables were divided in two sets, hereafter named a€ pollutiona€ and a€ naturala€ . The first set included water quality variables modified by anthropic activities such as D.O., C.O.D, and dissolved ion concentrations. Natural variables included altitude, position, and time of the year. The upstream site (S1) had the lowest species richness and CPUE; but the number of species and density increased downriver (S2-S3). S1 was inhabited by invertivore species (Trichomycterus corduvensis), having low tolerance to environmental conditions and high D.O. requirements. S4 sustained the most tolerant and abundant species (Otocinclus vittatus, Corydoras paleatus), enduring the lowest D.O. and the highest C.O.D. A significant Canonical Correspondence Analysis for natural variables showed a gradient of species composition related to altitude and discharge. Water quality degradation by sugar cane factories and urban development, coupled with natural climatic, topographic and hydrological factors explained a significant amount of spatial and temporal variation in fish community structure (@48%). Natural and pollution variables shared about 15% of total variance. However, pollution variables were not significant after partialling- out the effects of natural variables, but natural variability remained significant after removal of pollution effects. The results suggest that effects of pollution may be just the result of ordination of fish communities along natural spatial and temporal gradients that are positively correlated to pollution gradients.
The sweet and the bitter: Cuban and Puerto Rican responses to the mid-nineteenth-century sugar challenge
Luis Martinez-Fernandez
New West Indian Guide , 1993,
Abstract: Comparative study of the mid-19th-c. world market sugar pressures in Cuba and Puerto Rico. Both colonies responded differently to these pressures, a reflection of divergent levels of capital resources and adaptability. The Cubans sought to expand sugar production, while planters in Puerto Rico fell victim to stagnation and decline.
The New Policy of Nordic Security
Luis M. Mora Fernandez-Rua
Revista CIDOB d'Afers Internacionals , 1996,
Abstract: During the Cold War period, the security policy of the Nordic countries was based on what Arne Olav Brundtland had called nordic balance. After the fall of the Berlin Wall in 1989 and the end of the East-West confrontation, this concept has been reformulated, among other factors, by the decision taken by Sweden and Finland torenounce their traditional policies of neutrality and their joining the European Union. In this new international context, the Nordic countries have redefined the strategies and the instruments of their security policy with a view to creating a space of multidimensionalcooperation at all levels.
Effectiveness of a course in the control of tobacco use for university health students: A quasi-experimental community intervention trial  [PDF]
Daniel Fernandez, Antonio Molina, Vicente Martin, Beatriz Ordas, Jose Manuel De Luis
Open Journal of Nursing (OJN) , 2013, DOI: 10.4236/ojn.2013.34047

Introduction: The aim of the study was to evaluate the effectiveness of a tobacco control course in the reduction of prevalence and the improvement of knowledge and attitudes among university health students. Method: Quasi-experimental study on a community based intervention. Interventional campus students received a tobacco control course in the first year of the degree. Data were collected by Self-Answered Questionnaire during three academic years in two graduations years among health students in both campuses. Results: 84.4% of students participated in the study. In both campuses tobacco use was reduced, not significantly, above all in those joining courses from origins other than baccalaureate. In the intervention and control campus showed an increase in the nicotine dependency according to Fagerstr?m test and a little change in motivation according toRichmondtest. The regression model best explaining the improving of the knowledge included academic course mainly and campus and academic background too. With regard to opinions and beliefs tobacco use was not influenced, being associated in general to the academic course. Conclusions: A specific tobacco control course did not change prevalence of tobacco, nicotine dependence and motivation to give up. The improvement in knowledge was associated with academic course in both campuses. We recommend to commence smoking cessation strategies in university health students.

Antiferromagnetic 4-d O(4) Model
Isabel Campos,Luis A. Fernandez,Alfonso Tarancon
Physics , 1996, DOI: 10.1103/PhysRevD.55.2965
Abstract: We study the phase diagram of the four dimensional O(4) model with first (beta1) and second (beta2) neighbor couplings, specially in the beta2 < 0 region, where we find a line of transitions which seems to be second order. We also compute the critical exponents on this line at the point beta1 =0 (F4 lattice) by Finite Size Scaling techniques up to a lattice size of 24, being these exponents different from the Mean Field ones.
Testing statics-dynamics equivalence at the spin-glass transition in three dimensions
Luis Antonio Fernandez,Victor Martin-Mayor
Physics , 2014, DOI: 10.1103/PhysRevB.91.174202
Abstract: The statics-dynamics correspondence in spin glasses relate non-equilibrium results on large samples (the experimental realm) with equilibrium quantities computed on small systems (the typical arena for theoretical computations). Here we employ statics-dynamics equivalence to study the Ising spin-glass critical behavior in three dimensions. By means of Monte Carlo simulation, we follow the growth of the coherence length (the size of the glassy domains), on lattices too large to be thermalized. Thanks to the large coherence lengths we reach, we are able to obtain accurate results in excellent agreement with the best available equilibrium computations. To do so, we need to clarify the several physical meanings of the dynamic exponent close to the critical temperature.
DNA Torsional Solitons in Presence of localized Inhomogeneities
Luis Morales Molina,Owen Fernandez Piedra
Physics , 2001, DOI: 10.1238/Physica.Regular.066a00385
Abstract: In the present paper we investigate the influence of inhomogeneities in the dynamics and stability of DNA open states, modeled as propagating solitons in the spirit of a Generalized Yakushevish Model. It is a direct consecuence of our model that there exists a critical distance between the soliton's center of mass and the inhomogeneity at which the interaction between them can change the stability of the open state.Furtherly from this results was derived a renormalized potential funtion.
Controllability properties for the one-dimensional Heat equation under multiplicative or nonnegative additive controls with local mobile support
Luis A. Fernandez,Alexander Y. Khapalov
Mathematics , 2011,
Abstract: We discuss several new results on nonnegative approximate controllability for the one-dimensional Heat equation governed by either multiplicative or nonnegative additive control, acting within a proper subset of the space domain at every moment of time. Our methods allow us to link these two types of controls to some extend. The main results include approximate controllability properties both for the static and mobile control supports.
Weakly Lefschetz symplectic manifolds
Marisa Fernandez,Vicente Munoz,Luis Ugarte
Mathematics , 2004,
Abstract: The harmonic cohomology of a Donaldson symplectic submanifold and of an Auroux symplectic submanifold are compared with that of its ambient space. We also study symplectic manifolds satisfying a weakly Lefschetz property, that is, the $s$-Lefschetz propery. In particular, we consider the symplectic blow-ups of the complex projective space along weakly Lefschetz symplectic submanifolds. As an application we construct, for each even integer $s\geq 2$, compact symplectic manifolds which are $s$-Lefschetz but not $(s+1)$-Lefschetz.
A Framework for Planning and Controlling Non-Periodic Bipedal Locomotion
Ye Zhao,Benito R. Fernandez,Luis Sentis
Computer Science , 2015,
Abstract: This study presents a theoretical framework for planning and controlling agile bipedal locomotion based on robustly tracking a set of non-periodic apex states. Based on the prismatic inverted pendulum model, we formulate a hybrid phase-space planning and control framework which includes the following key components: (1) a step transition solver that enables dynamically tracking non-periodic apex or keyframe states over various types of terrains, (2) a robust hybrid automaton to effectively formulate planning and control algorithms, (3) a phase-space metric to measure distance to the planned locomotion manifolds, and (4) a hybrid control method based on the previous distance metric to produce robust dynamic locomotion under external disturbances. Compared to other locomotion frameworks, we have a larger focus on non-periodic gait generation and robustness metrics to deal with disturbances. Such focus enables the proposed control framework to robustly track non-periodic apex states over various challenging terrains and under external disturbances as illustrated through several simulations. Additionally, it allows a bipedal robot to perform non-periodic bouncing maneuvers over disjointed terrains.
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