226 research outputs found
Aprender del problema y de las formas de interacción. La construcción de conocimientos relativos al porcentaje en clases de secundaria
La elaboración de conocimiento en la clase de matemáticas se entreteje con las características de los problemas que resuelven los alumnos, con los conocimientos de los que ellos ya disponen y con las formas de interacción social. Este artículo se centra en la última de dichas relaciones, es decir, en el componente social del proceso de aprendizaje en el aula. Se problematiza el conocimiento matemático, el cual es considerado como la producción de un grupo, y por lo tanto se inserta en el entramado de relaciones sociales que se configuran en el aula. A partir del análisis de la implementación de una secuencia de clases experimentales a propósito del porcentaje en una secundaria pública de la Ciudad de México, se discute la manera en que la circulación del conocimiento está imbricada con el posicionamiento de los estudiantes y con la valoración social de los procedimientos y las herramientas matemáticas. Finalmente, se puntualiza en la necesidad de acercar la noción de Contrato Didáctico, herramienta de la Teoría de las Situaciones Didácticas, a otras perspectivas socioculturales que permitan enriquecer la comprensión del papel de las interacciones entre los distintos actores en el aprendizaje
Polkörperaneuploidie-Diagnostik mit FISH, Einflussfaktoren auf die Hybridisierungseffizienz
Die Polkörperdiagnostik ist ein reproduktionsmedizinisches Verfahren zum indirekten Nachweis von numerischen und strukturellen Chromosomenaberrationen von Eizellen. Ziel der Arbeit war, die Effizienz der Polkörperdiagnostik mit FISH zu analysieren und den Einfluss von verschiedenen Faktoren auf die Hybridisierung aufzudecken. Hierzu wurde eine retrospektive Datenanalyse aus sieben Jahren Polkörperdiagnostik mit knapp 1200 Polkörpern durchgeführt
Polkörperaneuploidie-Diagnostik mit FISH, Einflussfaktoren auf die Hybridisierungseffizienz
Die Polkörperdiagnostik ist ein reproduktionsmedizinisches Verfahren zum indirekten Nachweis von numerischen und strukturellen Chromosomenaberrationen von Eizellen. Ziel der Arbeit war, die Effizienz der Polkörperdiagnostik mit FISH zu analysieren und den Einfluss von verschiedenen Faktoren auf die Hybridisierung aufzudecken. Hierzu wurde eine retrospektive Datenanalyse aus sieben Jahren Polkörperdiagnostik mit knapp 1200 Polkörpern durchgeführt
Finding Area in Elementary Math Classes in Mexico: an example of the tensions between curricula and students
En este trabajo, a través de la observación en una escuela pública de la Ciudad de México de dieciocho clases de quinto grado, dedicadas a la enseñanza de las fórmulas de área, intento dar cuenta de algunas tensiones entre los conocimientos matemáticos implicados en los procedimientos desplegados por alumnos y alumnas de primaria, por un lado, y los conocimientos que se espera que aprendan desde el currículo, por el otro. Argumento que la organización curricular de la escuela graduada dificulta el tránsito de las y los alumnos desde sus producciones hacia los contenidos prescritos y, en este sentido, contribuye a la producción del fracaso escolar. De esta manera, suscribo el planteamiento de que los procesos de exclusión se construyen también desde la propia estructura escolar y no son atribuibles únicamente a factores externos, como la experiencia de vida o el apoyo de la familia.In this article, I analyze certain tensions between what elementary students know versus what the Mexican national curriculum expects them to learn. The research is based on observations of 18 fifth grade classes at a public school in Mexico City and the mathematical methods used to solve problems, specifically, the formulas for finding area. I explain how the grade school system’s curricular organization makes it difficult to organize a learning process that begins with the students’ ideas and ends with mandated concepts, thus contributing to school failure. Accordingly, I support the argument that exclusion processes cannot only be attributed to external factors, such as life experiences or family support, but also partially to school structures.Facultad de Humanidades y Ciencias de la Educació
Aprender do problema e das formas de interação. A construção de conhecimentos relativos à porcentagem em aulas de secundária
The elaboration of knowledge in math class is interwoven with the characteristics of the problems solved by students, their prior knowledge, and the forms of social interaction. This article focuses on the last one of these relations—that is, on the social component of the learning process in the classroom. Thus, we problematize mathematical knowledge, which is considered as the production of a group, and is therefore inserted in the framework of social relations created inside the classroom. Based on the analysis of the implementation of a sequence of experimental classes about percentages in a public high school in Mexico City, we discuss the way in which the circulation of knowledge is intertwined with the students’ position and with the social evaluation of the procedures and mathematical tools. Finally, we detail the need to bring the idea of Didactic Contract, a tool from the Theory of Didactical Situations, closer to other sociocultural perspectives enriching the understanding of the role of the interactions between different actors in the learning process. La elaboración de conocimiento en la clase de matemáticas se entreteje con las características de los problemas que resuelven los alumnos, con los conocimientos de los que ellos ya disponen y con las formas de interacción social. Este artículo se centra en la última de dichas relaciones, es decir, en el componente social del proceso de aprendizaje en el aula. Se problematiza el conocimiento matemático, el cual es considerado como la producción de un grupo, y por lo tanto se inserta en el entramado de relaciones sociales que se configuran en el aula. A partir del análisis de la implementación de una secuencia de clases experimentales a propósito del porcentaje en una secundaria pública de la Ciudad de México, se discute la manera en que la circulación del conocimiento está imbricada con el posicionamiento de los estudiantes y con la valoración social de los procedimientos y las herramientas matemáticas. Finalmente, se puntualiza en la necesidad de acercar la noción de Contrato Didáctico, herramienta de la Teoría de las Situaciones Didácticas, a otras perspectivas socioculturales que permitan enriquecer la comprensión del papel de las interacciones entre los distintos actores en el aprendizaje. A elaboração de conhecimento na aula de matemáticas se articula com as características dos problemas que resolvem os alunos, com os conhecimentos que eles possuem e com as formas de interação social. Este artigo centra-se na última dessas relações, ou seja, no componente social do processo de aprendizagem na sala de aula. Problematiza-se o conhecimento matemático, que é considerado como a produção de um grupo, e se insere, portanto, no esquema de relações sociais configuradas na sala de aula. A partir da análise da implementação de uma sequência de aulas experimentais a propósito da porcentagem em uma escola pública secundária na Cidade do México, é debatida a forma em que a circulação do conhecimento está interligada com o posicionamento dos estudantes e com a valoração social dos procedimentos e as ferramentas matemáticas. Finalmente, é especificada a necessidade de abordar a noção de Contrato Didático, ferramenta da Teoria das Situações Didáticas, desde outras perspectivas socioculturais que possam enriquecer a compreensão do papel das interações entre os diversos atores na aprendizage
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Sequence Stratigraphy in Proterozoic Successions
Sedimentological logging and facies mapping have been used to identify depositional sequences bounded by subtle but regionally persistent unconformities in rocks of Proterozoic age in the western United States, South Australia, and northwestern Canada. We conclude from these studies that the sequence stratigraphic approach is of considerable importance for intrabasinal time correlation in the Proterozoic and for facies interpretation and basin analysis in Proterozoic rocks
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Sequence Stratigraphy and Evolution of a Basin-Slope Succession: The Late Proterozoic Wonoka Formation, Flinders Ranges, South Australia
A shelf to basin‐slope transition is vertically and laterally exposed within the Late Proterozoic Wonoka Formation in the northern Flinders Ranges of South Australia. The shelf to basin‐slope transition can be divided into four units (C to F) which are defined on the basis of facies, sedimentary structures, contacts, stratal geometry, and the type and abundance of down‐slope mass movement. The lowest unit (C) is mudstone dominated and parallel laminated with rare synsedimentary slides. Unit D, a thin, resedimented siliciclastic‐carbonate unit deposited on a sequence boundary at the end of unit C progradation, displays a lateral facies change from well bedded ‘outer shelf deposits in the east to basin‐slope debris flows in the west. Unit E forms a shallowing and coarsening upward succession from ‘outer shelf siltstone to ‘inner shelf storm wave influenced sandstone deposits. The unit thickens westwards, in the interpreted down‐slope direction, where it becomes finer grained and thinner bedded and displays an increasing abundance of synsedimentary slides. Unit F, deposited on an inferred shelf to basin‐slope transition, coarsens and shallows upward, thickens to the west and contains the highest percentage of sandstone and synsedimentary slides. Unit G, deposited at shelf depths, also shallows and coarsens upward from a thin, basal carbonate‐siliciclastic member, with sandstone increasing upsection to a gradational contact with the Pound Subgroup.
Three sequences can be defined within this transition on the basis of facies, stratal terminations, and facies discontinuities at inferred sequence boundaries. Each sequence is marked by a transgressive base, overlain by a shallowing‐upward succession. On the inferred shelf and near the shelfbreak, toward the top of the succession, facies discontinuities at sequence boundaries are more obvious, with distinct contrasts in lithology and inferred palaeoenvironments; farther down‐slope and stratigraphically lower in the succession, the boundaries are cryptic, and only lateral tracing of the contacts from the shelf to the slope or the observation of stratal terminations permits them to be recognized
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Depositional Sequence Analysis Applied to Late Proterozoic Wilpena Group, Adelaide Geosyncline, South Australia
The initial application of depositional sequence analysis to selected stratigraphic sections through outcropping Late Proterozoic strata of the Adelaide Geosyncline in South Australia has identified major depositional sequences within the several‐kilometre‐thick Wilpena Group. Sharp facies shifts in vertical stratigraphic sections are proposed as actual sequence boundaries which, provided they are the result of eustatic sea level variations, may be key elements for future attempts at inter‐regional chronostratigraphic correlation.
Two major sequence boundaries are identified, one at the base of the Nuccaleena Formation (boundary A) and a second at the top of the Brachina Subgroup (boundary B). These are attributed to significant basinward shifts in coastal onlap resulting in subaerial exposure and at least localized erosion, followed in each case by establishment of relatively deepwater environments. A somewhat different boundary (boundary C) is associated with an interval of diagenetic dolostone interbeds and is interpreted either as a downlap surface within a sequence, or as a combined deepwater sequence boundary and downlap surface. It may have developed during an episode of reduced sediment input in response to a period of maximum transgression. Alternatively it may represent a hiatus at the termination of a depositional sequence, prior to subsequent downlap or onlap of the succeeding sequence.
Boundary C lies a few metres below the stratigraphic level from which kilometre‐deep canyons have incised underlying sequences. These canyons, which are infilled by a complex succession of carbonate breccias, conglomerates, sandstone and mudstone, may have been eroded in a submarine setting by turbidity currents. Such a model requires a significant increase in rate of eustatic sea level fall or a decrease in the rate of tectonic subsidence, in order to move the locus of coastal onlap to the vicinity of the shelf edge. If the cause was eustatic, evidence for it should be found at an equivalent sequence boundary in Late Proterozoic basins remote from the Adelaide Geosyncline. Alternatively, the canyons may have been eroded in a subaerial setting and infilled by coastal sediments during an ensuing period of relative sea level rise. In this model a considerably greater drop in relative sea level is required, most likely related to localized tectonic uplift
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Working Hypotheses for the Origin of the Wonoka Canyons (Neoproterozoic), South Australia
Recent attempts to apply concepts of sequence stratigraphy to the Neoproterozoic Wilpena Group of the Adelaide "geosyncline" in South Australia have provided an important new method for improving the resolution of intrabasinal correlation in sparsely fossiliferous and unfossiliferous strata. Eight regional unconformities are now recognized within or bounding the Wilpena Group. The most prominent of these, at or near the base of the Wonoka Formation, is expressed by a series of spectacular incised valleys or canyons, some more than 1 km deep and dated as approx 630 to 580 Ma. The canyons developed following an interval of continental rifting that took place between about 800 and 700 Ma and prior to a second phase of accelerated subsidence of uncertain origin in Early Cambrian time (after about 560 Ma). Subsidence during the intervening span of more than 140 my was in part of thermal origin and in part due to the withdrawal of buried salt at depth, but it may also have involved additional extension for which little direct structural evidence is preserved. The canyons are incised into a succession of shallow marine mainly terrigenous strata that accumulated in a broad north- and east-facing ramp. They are exposed in two distinct belts within and east of the Flinders Ranges, in an area that is about 275 km in a north-south direction and about 175 km east-west. The canyons are inferred to have been filled by shallow marine sediments primarily on the basis of sedimentary structures interpreted as combined flow and oscillation ripples and hummocky cross-stratification. If this is correct, development of the canyons was related to regional lowering of depositional base level by more than 1 km. Recent work also indicates a second phase of valley incision at an unconformity immediately above the main canyons and involving a relative sealevel fall of at least 200 m.
Two working hypotheses are advanced to account for the origin of the Wonoka canyons: regional uplift and an evaporitic lowering of sealevel in an isolated basin, analogous to the Messinian event in the Mediterranean. Any regional uplift would likely have been of tectonic origin. Diapirism associated with buried salt cannot account for the wide distribution of erosion or for pronounced uplift in an extensional setting lacking evidence for basin inversion or compressional deformation coeval with sedimentation. One possible mechanism for tectonic uplift involves inhomogeneous extension of the lithosphere, with the amount of extension balanced at all levels on a regional scale possibly by means of detachment faults. Possible difficulties with this hypothesis are the requirement of relatively uniform uplift over distances of hundreds of kilometers and the fact that repeated large-scale lowering of base level implies oscillatory vertical motions that are not readily explained. An evaporitic drawdown accounts for the wide distribution and scale of the canyons and for repeated lowering of base level. Possible difficulties in this case are the presence within the canyon fill of facies that have been interpreted to be of tidal origin; the fact that unlike the Messinian crisis in the Mediterranean, the Wonoka canyons do not appear to have been drowned rapidly; and the lack of direct evidence for evaporities of appropriate age. Neither hypothesis accounts for the apparent absence of appreciable meteoric diagenesis in areas far removea from sites of canyon incision.
Two additional conclusions are as follows. First, neither of the hypotheses precludes eustasy as an important control on sedimentation. Sequence stratigraphic comparisons with other basins of the same general age should focus primarily on the time of formation of sequence boundaries not on the geometry of the boundaries or the facies involved. Second, a drawdown in excess of 1 km implies that the adjacent basin was originally at least this deep and hence likely underlain at least locally by highly attenuated continental crust or oceanic crust. Either hypothesis therefore has important implications for the tectonic development of the Adelaide geosyncline
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