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Search Results: 1 - 10 of 191570 matches for " Carbajal D. "
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Revisión de los fundamentos del análisis input-output dinámico
Blanc Díaz, Mariano,Ramos Carbajal, Carmen
Rect@ , 2003,
Abstract: Esta ponencia revisa los fundamentos matemáticos del modelo input-output dinámico, para concluir que bajo las hipótesis específicas de Leontief es inconsistente. Probamos primero que el modelo estático no puede ser considerado una versión particular del dinámico cuando la matriz de coeficientes de capital se compone de elementos positivos o nulos. Los coeficientes de capital positivos hacen necesariamente inestable al modelo dinámico. Las soluciones que proporcionan bajo hipótesis similares difieren. La estabilidad requiere coeficientes de capital negativos. La identificación exacta de los dos modelos requiere que la matriz de coeficientes de capital sea la matriz unidad con signo negativo. Puesto que esto es un contrasentido bajo las hipótesis de Leontief, la matriz correspondiente tiene que tener, necesariamente, una interpretación diferente a la que tradicionalmente se le atribuye. La solución matemática abstracta del modelo dinámico de Leontief lleva a la conclusión de que los crecimientos que experimenta el modelo no son reflejo de ningún crecimiento – endógeno o de otra naturaleza – de la realidad representada, sino consecuencia de la inestabilidad intrínseca de la estructura matemática construida. Su aplicación a estudios empíricos no puede por tanto aportar resultados útiles.
A computational analysis of motor synergies by dynamic response decomposition
Cristiano Alessandro,Juan Pablo Carbajal,Andrea d'Avella
Frontiers in Computational Neuroscience , 2013, DOI: 10.3389/fncom.2013.00191
Abstract: Analyses of experimental data acquired from humans and other vertebrates have suggested that motor commands may emerge from the combination of a limited set of modules. While many studies have focused on physiological aspects of this modularity, in this paper we propose an investigation of its theoretical foundations. We consider the problem of controlling a planar kinematic chain, and we restrict the admissible actuations to linear combinations of a small set of torque profiles (i.e. motor synergies). This scheme is equivalent to the time-varying synergy model, and it is formalized by means of the dynamic response decomposition (DRD). DRD is a general method to generate open-loop controllers for a dynamical system to solve desired tasks, and it can also be used to synthesize effective motor synergies. We show that a control architecture based on synergies can greatly reduce the dimensionality of the control problem, while keeping a good performance level. Our results suggest that in order to realize an effective and low-dimensional controller, synergies should embed features of both the desired tasks and the system dynamics. These characteristics can be achieved by defining synergies as solutions to a representative set of task instances. The required number of synergies increases with the complexity of the desired tasks. However, a possible strategy to keep the number of synergies low is to construct solutions to complex tasks by concatenating synergy-based actuations associated to simple point-to-point movements, with a limited loss of performance. Ultimately, this work supports the feasibility of controlling a non-linear dynamical systems by linear combinations of basic actuations, and illustrates the fundamental relationship between synergies, desired tasks and system dynamics.
Synthesis and Adaptation of Effective Motor Synergies for the Solution of Reaching Tasks
Cristiano Alessandro,Juan Pablo Carbajal,Andrea d'Avella
Physics , 2012, DOI: 10.1007/978-3-642-33093-3_4
Abstract: Taking inspiration from the hypothesis of muscle synergies, we propose a method to generate open loop controllers for an agent solving point-to-point reaching tasks. The controller output is defined as a linear combination of a small set of predefined actuations, termed synergies. The method can be interpreted from a developmental perspective, since it allows the agent to autonomously synthesize and adapt an effective set of synergies to new behavioral needs. This scheme greatly reduces the dimensionality of the control problem, while keeping a good performance level. The framework is evaluated in a planar kinematic chain, and the quality of the solutions is quantified in several scenarios.
Un obispado para Veracruz, 1799-1846 Del honor de la ciudad a la lealtad al Estado
Carbajal, David
Anuario de Estudios Americanos , 2005,
Abstract: Between 1789 and 1846 the authorities of Veracruz promoted the creation of a Bishopric with with the limits of the jurisdiction to their charge. Although the recent historiography has noticeable the existing continuity between the regalismo Bourbon and the first Mexican liberalism, the analysis of the arguments presented by the munícipes and congresspersons of Veracruz, suggests changes in the institutional context as in the principles in which they were founded. Until 1821, it was alluded to the own privileges of the oldest city of the kingdom; during the first federal republic, insisted on defending the honor of the sovereignty, position that is radicalized toward 1833, when the Congress decreed, without success, the creation of new diocese. The bishopric was created in 1844, the government of the Department of Veracruz repeated their requests, with arguments that show certain continuity with the of the first federalism, in spite of the change to the centralist regime. Entre 1789 y 1846 las autoridades de Veracruz promovieron la creación de un Obispado con los límites de la jurisdicción a su cargo. Aunque la historiografía reciente ha destacado la continuidad existente entre el regalismo borbónico y el primer liberalismo mexicano, el análisis de los argumentos presentados por los munícipes y congresistas porte os, sugiere cambios tanto en el contexto institucional como en los principios en que se fundaban. Hasta 1821, se aludía a los privilegios propios de la ciudad más antigua del reino; durante la primera república federal, se insistió en defender el honor de la soberanía, postura que se radicaliza hacia 1833, cuando el Congreso veracruzano decretó, sin éxito, la creación de la nueva diócesis. El obispado fue creado en 1844, el gobierno del Departamento de Veracruz repitió sus solicitudes, con argumentos que muestran cierta continuidad con los del primer federalismo, a pesar del cambio al régimen centralista.
Effect of policosanol on cerebral ischemia in Mongolian gerbils
Molina V.,Arruzazabala M.L.,Carbajal D.,Valdés S.
Brazilian Journal of Medical and Biological Research , 1999,
Abstract: Policosanol is a mixture of higher aliphatic primary alcohols isolated from sugar cane wax, whose main component is octacosanol. An inhibitory effect of policosanol on platelet aggregation and cerebral ischemia in animal models has been reported. Thus, the objective of the present study was to evaluate the effect of policosanol on cerebral ischemia induced by unilateral carotid ligation and bilateral clamping and recirculation in Mongolian gerbils. Policosanol (200 mg/kg) administered immediately after unilateral carotid ligation and at 12- or 24-h intervals for 48 h significantly inhibited mortality and clinical symptoms when compared with controls, whereas lower doses (100 mg/kg) were not effective. Control animals showed swelling (tissue vacuolization) and necrosis of neurons in all areas of the brain studied (frontal cortex, hippocampus, striatum and olfactory tubercle), showing a similar injury profile. In the group treated with 200 mg/kg policosanol swelling and necrosis were significantly reduced when compared with the control group. In another experimental model, comparison between groups showed that the brain water content of control gerbils (N = 15) was significantly higher after 15 min of clamping and 4 h of recirculation than in sham-operated animals (N = 13), whereas policosanol (200 mg/kg) (N = 19) significantly reduced the edema compared with the control group, with a cerebral water content identical to that of the sham-operated animals. cAMP levels in the brain of control-ligated Mongolian gerbils (N = 8) were significantly lower than those of sham-operated animals (N = 10). The policosanol-treated group (N = 10) showed significantly higher cAMP levels (2.68 pmol/g of tissue) than the positive control (1.91 pmol/g of tissue) and similar to those of non-ligated gerbils (2.97 pmol/g of tissue). In conclusion, our results show an anti-ischemic effect of policosanol administered after induction of cerebral ischemia, in two different experimental models in Mongolian gerbils, suggesting a possible therapeutic effect in cerebral vascular disorders.
Regulation of Calcitriol Biosynthesis and Activity: Focus on Gestational Vitamin D Deficiency and Adverse Pregnancy Outcomes
Andrea Olmos-Ortiz,Euclides Avila,Marta Durand-Carbajal,Lorenza Díaz
Nutrients , 2015, DOI: 10.3390/nu7010443
Abstract: Vitamin D has garnered a great deal of attention in recent years due to a global prevalence of vitamin D deficiency associated with an increased risk of a variety of human diseases. Specifically, hypovitaminosis D in pregnant women is highly common and has important implications for the mother and lifelong health of the child, since it has been linked to maternal and child infections, small-for-gestational age, preterm delivery, preeclampsia, gestational diabetes, as well as imprinting on the infant for life chronic diseases. Therefore, factors that regulate vitamin D metabolism are of main importance, especially during pregnancy. The hormonal form and most active metabolite of vitamin D is calcitriol. This hormone mediates its biological effects through a specific nuclear receptor, which is found in many tissues including the placenta. Calcitriol synthesis and degradation depend on the expression and activity of CYP27B1 and CYP24A1 cytochromes, respectively, for which regulation is tissue specific. Among the factors that modify these cytochromes expression and/or activity are calcitriol itself, parathyroid hormone, fibroblast growth factor 23, cytokines, calcium and phosphate. This review provides a current overview on the regulation of vitamin D metabolism, focusing on vitamin D deficiency during gestation and its impact on pregnancy outcomes.
Seismoelectric effects due to mesoscopic heterogeneities
D. Jougnot,J. G. Rubino,M. Rosas Carbajal,N. Linde,K. Holliger
Physics , 2014, DOI: 10.1002/grl.50472
Abstract: While the seismic effects of wave-induced fluid flow due to mesoscopic heterogeneities have been studied for several decades, the role played by these types of heterogeneities on seismoelectric phenomena is largely unexplored. To address this issue, we have developed a novel methodological framework which allows for the coupling of wave-induced fluid flow, as inferred through numerical oscillatory compressibility tests, with the pertinent seismoelectric conversion mechanisms. Simulating the corresponding response of a water-saturated sandstone sample containing mesoscopic fractures, we demonstrate for the first time that these kinds of heterogeneities can produce measurable seismoelectric signals under typical laboratory conditions. Given that this phenomenon is sensitive to key hydraulic and mechanical properties, we expect that the results of this pilot study will stimulate further exploration on this topic in several domains of the Earth, environmental, and engineering sciences.
Sand Waves Generation: A Numerical Investigation of the Infiernillo Channel in the Gulf of California  [PDF]
Yovani Monta?o Ley, Noel Carbajal
Open Journal of Marine Science (OJMS) , 2016, DOI: 10.4236/ojms.2016.63035
Abstract: The effect of the coastal geometry on sand bed forms generation has been investigated for a tidal dominated area. Different hypothetical geometries of coastal channels with flat bottoms and unlimited sediment availability were exposed to strong oscillatory tidal currents to simulate the interaction of hydrodynamics and the bedload sediment transport. The hypothetical geometries stand for the idealization of the principal geographic features of the Infiernillo Channel, a coastal area of the Gulf of California where sandbanks and sand waves have been observed. A depth integrated hydrodynamic-numerical model and a parameterized formula to estimate the bedload sediment transport were applied coupled with a sediment conservation equation to determine the sea bottom morphodynamics. Model predictions in the Infiernillo Channel were compared to available satellite imagery. This investigation demonstrates that a vertical integrated numerical model is able to reproduce the development of incipient sand waves that exist in the Infiernillo Channel. Incipient sandbanks and shoals were also simulated. Sand waves with wavelengths of about 200 m were calculated on the same locations where sand waves actually exist. A crucial finding of this research was to show that the geometry of a shallow water basin and the presence of tidal velocity gradients associated with abrupt changes in the coastline alignment were critical in determining the sand-bed pattern generation. We demonstrate that a vertical variation of tidal currents is not necessary to generate sand waves.
Los a?os del hambre en Bola?os (1785-1786): Conflictos mineros, escasez de maíz y sobremortalidad
Carbajal López, David;
Relaciones (Zamora) , 2010,
Abstract: the objective of this study is to explain the high mortality registered in real de bola?os during the years of hunger in 1785-1786, in a setting characterized by local mining conflicts and corn shortages that affected large areas of central-western new spain. also, it analyzes the victims of that subsistence crisis from two perspectives: first, by examining global body counts of the dead and, second, by investigating the christian and f amily names of the victims.
EXPLORING THE URBAN-RURAL LABOR INCOME GAP IN URUGUAY: A QUANTILE REGRESSION DECOMPOSITION
BERGOLO,MARCELO; CARBAJAL,FEDORA;
Revista de análisis económico , 2010, DOI: 10.4067/S0718-88702010000200006
Abstract: this paper analyzes the differences in real hourly labor income (rhli) distributions between urban and rural workers for uruguay in 2006. a quantile regression decomposition technique is applied in order to examine the urban-rural gap across the entire rhli distribution. the urban-rural gap was primarily explained by the differences in the distribution of covariates along the entire distribution. differences in distribution of returns favored the rural workers in most of the rhli distribution although its contribution decreased across quantiles. the resulting gap in returns was most relevant for the worst off rural workers compared to the urban counterparts in both montevideo and the rest of the urban centers.
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