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El concepto de aproximación local: una propuesta metodológica a partir de la recta tangente  [cached]
Pedro Vicente Esteban Duarte,Pedro Pérez Carreras
Matemáticas : Ense?anza Universitaria , 2003,
Abstract: El propósito de este artículo es exponer una metodología para ense ar el concepto de aproximación local en su manifestación de recta tangente a una curva plana en un punto, a partir de la visualización que se obtiene del haz de secantes, entendiéndolo como el conjunto de rectas que pasan todas por un punto fijo de la curva y por otros sobre la curva cada vez más cercanos al punto dado. El concepto de aproximación local es un tema central en el análisis matemático y, su ense anza en una edad temprana ayudará a que los alumnos adquieran un avanzado nivel de razonamiento. La visualización que se propone, se obtiene con la ayuda del asistente matemático DERIVE y no requiere de manipulaciones algebraicas que entorpezcan el razonamiento que los alumnos deben desarrollar y exhibir a lo largo del proceso. El material que se expone, está dise ado para ser cubierto en una clase, en la cual el profesor sirva de orientador, formulando preguntas y respondiendo inquietudes en el momento oportuno.
DEMOSTRACION POR MEDIOS VECTORIALES DE LA ORTOGONALIDAD DE LA RECTA TANGENTE A UNA ESFERA EN Rn EN EL PUNTO DE TANGENCIA  [cached]
CAMPO E. GONZáLEZ PINEDA
Scientia Et Technica , 2004,
Abstract: De la Geometría Euclidiana sabemos que si una recta l es tangente a una circunferencia C en un punto P entonces, el radio de la circunferencia en P es ortogonal a la recta l. Nuestro propósito es demostrar este mismo resultado extendido a esferas en Rn. Para lograrlo hacemos una peque a introducción a Rn y definimos los conceptos necesarios para cumplir nuestro cometido.
El método de Descartes para determinar la tangente a una curva
Sergio Alarcón Vasco,Carlos Mario Suescún
Matemáticas : Ense?anza Universitaria , 2011,
Abstract: El propósito de este artículo es analizar el método desarrollado por Descartes para hallar, mediante la construcción previa de la normal, la tangente a una curva en un punto dado. En particular se estudia la aplicación del método a la elipse y a la parábola. Se estudia, a la manera de hoy, la aplicación del método a una función algebraica general y se analiza, como caso particular, el de la tangente a la parábola cúbica en un punto distinto de (0, 0).
Piecewise Straight Line Approximation of Curve Existing in Slightly Curved Mesiobuccal Root Canal of Mandibular First Molar: A Radiographic Investigation Aproximación a Segmentos de Línea Recta en la Curva Existente del Canal Radicular Mesiobucal Ligeramente Curvado del Primer Molar Inferior: Una Investigación Radiográfica
J Prabhakar,M. S Priya,L. Jones Tarcius Doss,V. G Sukumaran
International Journal of Morphology , 2013,
Abstract: The aim of this study was to radiographically investigate the curve existing in slightly curved mesiobuccal canal of mandibular first molar by applying Piecewise straight line approximation. Extracted human mandibular molars were radiographed and one hundred radiographs were selected whose mesiobuccal canal showed slight curvature (10-20°) according to Schneider's method. The curves were traced and analyzed using Piecewise straight line method. Each curve was considered as a unit consisting of six different pieces of straight lines joining at seven specific points and the angle of curvature at these points was determined using the slope formula. All curves analyzed in this study had varying degrees of curvatures at different points on the curve. Maximum curvature (0.40°) was recorded at the middle third of the root canal. Within the limitation of the study, significant curvature occurs through out the curve existing in the mesiobuccal canal of mandibular first molar and the middle third of the curve showing greater degree of curvature. There is a possibility of greater curvature occurring in the coronal third of the curve. Though three dimensional studies would be more appropriate, Piecewise straight line approximation may be a better method than existing methods to simulate canal geometry. El objetivo de este estudio fue investigar radiográficamente la curva existente en el canal radicular mesiobucal ligeramente curvado del primer molar inferior mediante la aplicación de aproximaciones a segmentos de línea recta. Se utilizaron molares inferiores humanos extraídos que fueron radiografiados. Fueron seleccionadas, según el método de Schneider, 100 radiografías cuyo canal mesiobucal mostró una ligera curvatura (10-20°). Las curvas fueron delineadas y analizadas mediante el método de aproximación a segmentos de línea recta. Cada curva se consideró como una unidad que consta de seis diferentes segmentos de línea recta que unen a siete puntos específicos y el ángulo de curvatura en estos puntos se determinó utilizando la fórmula de la pendiente. Todas las curvas analizadas en este estudio tenían diversos grados de curvaturas en diferentes puntos de la curva. La curvatura máxima (0,40°) se registró en el tercio medio del canal radicular. Dentro de la limitación del estudio, una curvatura significativa se produce a través de la curva existente en el canal mesiobucal del primer molar inferior y el tercio medio de la curva que muestra un mayor grado de curvatura. Existe la posibilidad que ocurra una mayor curvatura en el tercio coronal de la curva. Aunque un estu
De la concepción global a la concepción local. El caso de la recta tangente en el marco de la convención matemática
Canul, Eduardo;Dolores, Crisólogo;Martínez-Sierra, Gustavo;
Revista latinoamericana de investigación en matemática educativa , 2011,
Abstract: this document shows the results of research aiming to facilitate the transition from the global conception (euclidean) of the tangent line to the local conception (leibnizian) through mathematical convention. for this purpose, we designed a series of activities that led higher education students (1819 years old) to look for consensus, which would allow them to overcome the cognitive conflict resulting from the contradictory nature of the conception of tangent that touches a point on the curve with the conception that admits that it can be cut. the results indicate that most of the students were able to overcome the cognitive conflict by establishing a mathematical convention that redefines the euclidean tangent and replaces it with the leibnizian tangent.
Benito Arias Montano y Francisco Arceo: la redacción del De recta curandorum vulnerum ratione  [cached]
Montero Cartelle, Enrique
Asclepio : Revista de Historia de la Medicina y de la Ciencia , 2012,
Abstract: When comparing language and literary resources in the treatise De recta curandorum vulnerum ratione, written by the 16th practical surgeon Francisco Arceo, to the prologue added by his guest, friend and compatriot, the humanist Arias Montano, it bears so remarkable resemblence that proves the intervention of the latter by arranging the text or even writing it in his own latin style. Furthermore, Arias Montano made the book be annotated and printed in Amberes by Cristobal Plantino’s printing press, one of his dearest friends. La comparación sistemática de la lengua y de los recursos literarios del tratado De recta curandorum vulnerum ratione, obra del cirujano práctico del siglo XVI Francisco Arceo, con la lengua del Prólogo que le puso su huésped, amigo y paisano, el humanista Arias Montano, muestra semejanzas tan significativas que prueban la intervención de este último arreglando el texto o redactándolo con el latín que le caracteriza. Arias Montano, además, hizo anotar la obra y se la publicó en Amberes en la imprenta de su buen amigo Cristóbal Plantino.
Sympathetic nerve-derived ATP regulates renal medullary vasa recta diameter via pericyte cells: a role for regulating medullary blood flow?  [PDF]
C. Crawford,S. S. P. Wildman,T. M. Kennedy-Lydon,C. M. Peppiatt-Wildman
Frontiers in Physiology , 2013, DOI: 10.3389/fphys.2013.00307
Abstract: Pericyte cells are now known to be a novel locus of blood flow control, being able to regulate capillary diameter via their unique morphology and expression of contractile proteins. We have previously shown that exogenous ATP causes constriction of vasa recta via renal pericytes, acting at a variety of membrane bound P2 receptors on descending vasa recta (DVR), and therefore may be able to regulate medullary blood flow (MBF). Regulation of MBF is essential for appropriate urine concentration and providing essential oxygen and nutrients to this region of high, and variable, metabolic demand. Various sources of endogenous ATP have been proposed, including from epithelial, endothelial, and red blood cells in response to stimuli such as mechanical stimulation, local acidosis, hypoxia, and exposure to various hormones. Extensive sympathetic innervation of the nephron has previously been shown, however the innervation reported has focused around the proximal and distal tubules, and ascending loop of Henle. We hypothesize that sympathetic nerves are an additional source of ATP acting at renal pericytes and therefore regulate MBF. Using a rat live kidney slice model in combination with video imaging and confocal microscopy techniques we firstly show sympathetic nerves in close proximity to vasa recta pericytes in both the outer and inner medulla. Secondly, we demonstrate pharmacological stimulation of sympathetic nerves in situ (by tyramine) evokes pericyte-mediated vasoconstriction of vasa recta capillaries; inhibited by the application of the P2 receptor antagonist suramin. Lastly, tyramine-evoked vasoconstriction of vasa recta by pericytes is significantly less than ATP-evoked vasoconstriction. Sympathetic innervation may provide an additional level of functional regulation in the renal medulla that is highly localized. It now needs to be determined under which physiological/pathophysiological circumstances that sympathetic innervation of renal pericytes is important.
Pollination Biology of Potentilla recta (Sulfur Cinquefoil) and Its Cooccurring Native Congener Potentilla gracilis in Northeastern Oregon  [PDF]
James McIver,Karen Erickson
Psyche , 2012, DOI: 10.1155/2012/281732
Abstract: Pollination biology of the invasive plant sulfur cinquefoil (Potentilla recta L.) and it's native cooccurring congener slender cinquefoil (P. gracilis Dougl. ex. Hook.) was studied from 2002–2004, at four sites in northeastern Oregon, USA The native cinquefoil flowered first for five weeks, followed by the invasive for five weeks, with two weeks overlap in mid-June. Invasive flowers attracted 74 species and 543 individuals; the native attracted 93 species and 619 individuals. The most important pollinators for the invasive, in order of importance, were: Apis mellifera, Ceratina nanula, Halictus tripartitus, Lasioglossum sisymbrii, and Bombus rufocinctus; for the native: C. nanula, Trichodes ornatus, H. ligatus, L. sisymbrii, and L. olympiae. The invasive produced higher numbers of seeds per plant, having greater mass per unit vegetation. Mean seed size was lower for the invasive when pollinators were allowed access to flowers, but seed size increased linearly with more complete exclusion of pollinators; the native showed no such response to pollinator exclusion. Compared to the native, nearly twice as many seeds germinated for sulfur cinquefoil (35.0% versus 19.5%), with seeds germinating over a longer period of time. Results are discussed as they relate to the invasiveness of sulfur cinquefoil relative to the native. 1. Introduction Nonnative invasive plants are increasingly recognized as major threats to ecosystems worldwide, particularly in arid and semiarid regions [1]. In western North America, invasive plants have changed fire regimes [2], reduced livestock forage quality, damaged real estate and recreation values [3], and impacted biodiversity [2]. While their influence on biodiversity has been described well in terms of the structure of native plant communities, relatively less is known on their ecological relationships to other species, including those that play critical functional roles, such as pollinators. Insects, especially bees, beetles, flies, and butterflies are known to pollinate a majority of vascular plant species worldwide; beetles alone have been observed to pollinate 211,935 species, or over 88% of the total species of vascular plants [4]. Insects also play a major role in crop reproduction: Williams [5] estimated that 84% of crop species in the European Union are pollinated by insects, and Buchmann and Nabhan [4] reported that 67 principal crop species are pollinated by insects worldwide, out of 84 listed (80%). The key to effective pollination service is diversity, since most native insect pollinator species visit only a small
Interpretante, interpreta o, intérprete  [cached]
Ana Maria Zilochi
Galáxia , 2008,
Abstract: O objetivo deste trabalho é discutir o conceito de semiose como um processo irreversí-vel no tempo, uma vez que uma interpreta o também é um processo no tempo. Um momento em que o leitor comunica-se com o texto e as rela es entre signos, objetos e interpretantes se instauram.Abstract: The objective of this paper is to discuss the semiosis concept as an irreversible process in the timeline, once an interpretation is also a process in the timeline. In the moment the reader communicates with the text, the relationships among signs, objects and interpretants are established.
A interpreta o dos fatos no direito.  [cached]
Eduardo Ramalho Rabenhorst
Prim@ Facie , 2003,
Abstract: O principal escopo do presente artigo é mostrar,tomando por base a proposta formulada pelo filósofo francêsPaul Ricoeur, que a interpreta o jurídica n o pode serreduzida apenas aos momentos de compreens o de um textolegal e de sua aplica o aos concretos, mas que ela exige umterceiro momento, a saber, o da interpreta o dos fatos.
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