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Localized Tension Produced by Combined Geometric Discontinuities Tensiones localizadas producidas por discontinuidades geométricas combinadas
Ricardo Mario Amé,Gabriel María Dasso,Daniel Lezama
Revista Cubana de Ingeniería , 2011, DOI: 10.1234/rci.v2i2.49
Abstract: Many mechanical components especially those in machinery and of steel structures are designed with various forms which may include section changes, holes, threaded parts, keyways or multiple discontinued geometrical elevations that produce localized stresses. Often, the over lapping of two or more discontinuities in the same section or in very close sections is observed and this over lapping makes it very difficult to determine the value of the localized tension.In this present work, ABAQUS software is applied to determine the increased localized tension insections having more than one geometric discontinuity and helpful elaborated graphs are developed for practical purposes in simple mechanical design. However, this analysis is limited to geometric discontinued structures with slots of macroscopic dimensions. First a test run is carried out using the software on already verified situations accepted in the given literature so as to validate the method, after which the software is applied to a Hub of combined generic geometric designs in flat, symmetrical and with axial loads pieces. It is shown that the software is relevant because it verifies those tested Kt values offered by the commonly recognized literature. Results of the combined discontinuities are then obtained and represented by means of a graph which in the future will be useful in mechanical design. It can be concluded that the available information in the literature about combined geometric concentrators is limited and in some cases incur doubts. Now, values for complex designs can be obtained as a result of the availability of these software tools. In addition, the making of graphics using the results obtained from the application of such software is more practical which in return has improved the efficiency of designs. Los componentes mecánicos, especialmente en máquinas y estructuras metálicas, se dise an con formas diversas que incluyen cambios de sección, agujeros, zonas roscadas, chaveteros y múltiples discontinuidades geométricas que producen elevaciones localizadas de las tensiones. En muchas oportunidades se presenta la superposición de dos o más discontinuidades en una misma sección o en secciones muy cercanas dificultando la determinación del valor de la tensión localizada. En el presente trabajo se aplica el software ABAQUS a la determinación del incremento localizado de tensiones en secciones con más de una discontinuidad geométrica. Se elaboran gráficos de utilización simple a los fines prácticos del dise o mecánico. El análisis de casos se limita a cuerpos con discontinuidades
Theoretical study of dark resonances in micro-metric thin cells
Horacio Failache,Lorenzo Lenci,Arturo Lezama,Daniel Bloch,Martial Ducloy
Physics , 2007, DOI: 10.1103/PhysRevA.76.053826
Abstract: We investigate theoretically dark resonance spectroscopy for a dilute atomic vapor confined in a thin (micro-metric) cell. We identify the physical parameters characterizing the spectra and study their influence. We focus on a Hanle-type situation, with an optical irradiation under normal incidence and resonant with the atomic transition. The dark resonance spectrum is predicted to combine broad wings with a sharp maximum at line-center, that can be singled out when detecting a derivative of the dark resonance spectrum. This narrow signal derivative, shown to broaden only sub-linearly with the cell length, is a signature of the contribution of atoms slow enough to fly between the cell windows in a time as long as the characteristic ground state optical pumping time. We suggest that this dark resonance spectroscopy in micro-metric thin cells could be a suitable tool for probing the effective velocity distribution in the thin cell arising from the atomic desorption processes, and notably to identify the limiting factors affecting desorption under a grazing incidence.
Clasificación florística de los bosques y arbustales de las sierras del Uruguay
Gautreau,Pierre; Lezama,Felipe;
Ecolog?-a austral , 2009,
Abstract: the woodland ecosystems of uruguay have been only described physiognomically, and the controls of their heterogeneity are still poorly understood. the aim of this paper is to describe the variations in species composition of the woody vegetation of the eastern and northeastern hills of uruguay. in three selected areas under extensive cattle grazing, 122 vegetation samples were collected. we identified five main vegetation units: myrceugenia euosma and baccharis dracunculifolia shrublands, syagrus romanzoffiana woods, myrsine coriacea woods and eugenia uniflora woods. correspondence analysis was carried out to describe floristic gradients. the first axis showed a physiognomic gradient from shrub to wood formations, partly determined by water availability linked to soil depth, a factor related to geomorphology, while the second axis revealed differences among communities related to geology. it is the first floristic classification of the woody vegetation in uruguay, and it proves that, despite the great structural uniformity, the woody vegetation of these hills is floristically heterogenous. little importance has been given to the geological and edaphic factors responsible for the woods variation in the past, and no descriptions of the shrublands existed. the classification proposed constitutes an alternative to the physiognomic typology used in uruguay to describe woody vegetation. it shows the limitations of this typology, offers new categories that allow for comparisons with southern brazil communities, and provides useful information for designing regional conservation strategies.
La construcción gubernamental de la contaminación ambiental: la política del aire para la Ciudad de México, 1979-1996.(Parte B)
José Luis Lezama
Economía, sociedad y territorio , 1997,
Abstract:
La construcción gubernamental de la contaminación ambiental: la política del aire para la Ciudad de México, 1979-1996.(Parte A)
José Luis Lezama
Economía, sociedad y territorio , 1997,
Abstract:
La colonización endógena: una nueva perspectiva sobre el proceso de colonización del Río de la Plata
Antonio Lezama Astigarraga
Fronteras de la Historia , 2001,
Abstract: Este artículo parte de una serie de investigaciones de arqueología histórica realizadas desde 1993 en la región de Colonia del Sacramento. La aparición de cerámica de diversos orígenes, cuya presencia no se esperaba, ha llevado al autor a profundizar el tema de la colonización del Río de la Plata. Contrariamente a la versión tradicional de la historiografía hispanoamericana, se argumenta que fue un proceso esencialmente americano, impulsado por los intereses de los mineros de la plata de Potosí, que se desarrolló a partir del fracaso de la expedición de Pedro de Mendoza y fue ejecutado por los hijos y nietos de los conquistadores del Perú y de los fundadores de Asunción.
Palabras de presentación del libro Aire dividido: crítica a la política del aire en el Valle de México
José Luis Lezama
Estudios Demográficos y Urbanos , 2001,
Abstract:
Gustavo Cabrera. In memoriam
José Luis Lezama
Estudios Demográficos y Urbanos , 2003,
Abstract:
Computing finite presentations of Tor and Ext over skew PBW extensions and some applications
Oswaldo Lezama,Melisa Paiba
Mathematics , 2015,
Abstract: In this paper we compute the $Tor$ and $Ext$ modules over skew $PBW$ extensions. If $A$ is a bijective skew $PBW$ extension of a ring $R$, we give presentations of $Tor_r^{A}(M,N)$, where $M$ is a finitely generated centralizing subbimodule of $A^m$, $m\geq 1$, and $N$ is a left $A$-submodule of $A^l$, $l\geq 1$. In the case of $Ext_A^{r}(M,N)$, $M$ is a left $A$-submodule of $A^m$ and $N$ is a finitely generated centralizing subbimodule of $A^l$. As application of these computations, we test stably-freeness, reflexiveness, and we will compute also the torsion, the dual and the grade of a given submodule of $A^m$. Skew $PBW$ extensions include many important classes of non-commutative rings and algebras arising in quantum mechanics, for example, Weyl algebras, enveloping algebras of finite-dimensional Lie algebras (and its quantization), Artamonov quantum polynomials, diffusion algebras, Manin algebra of quantum matrices, among many others.
Projective modules and Gr?bner bases for skew PBW extensions
Oswaldo Lezama,Claudia Gallego
Mathematics , 2015,
Abstract: Many rings and algebras arising in quantum mechanics, algebraic analysis, and non-commutative algebraic geometry can be interpreted as skew PBW (Poincar\'e-Birkhoff-Witt) extensions. In the present paper we study two aspects of these non-commutative rings: its finitely generated projective modules from a matrix-constructive approach, and the construction of the Gr\"obner theory for its left ideals and modules. These two topics could be interesting in future eventual applications of skew $PBW$ extensions in functional linear systems and in non-commutative algebraic geometry.
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