Conocimiento matemático fundamental en el grado de educación primaria: sistema de numeración decimal y valor posicional

Presentamos un estudio con futuros maestros sobre su conocimiento conceptual del sistema de numeración decimal (SND) y valor posicional (VP). En primer lugar, establecemos el conocimiento conceptual del SND y de la noción de VP como Conocimiento Matemático Fundamental (CMF) para iniciar la didáctica de la adición y la substracción. A continuación, presentamos parte de un instrumento para evaluar la comprensión conceptual del SND y del VP en base a dos dimensiones: el conocimiento de los principios generales y el conocimiento subyacente a los procedimientos. Al aplicarlo a 135 estudiantes del Grado de Educación Primaria observamos que, en su mayoría, ponen de manifiesto una comprensión fragmentada, incompleta y mecánica del SND y del VP

Geodiversity in Pampas: Geomorphology and conservation of coastal dunes landscapes

En este trabajo se realiza una aproximación a la geodiversidad y el estado de conservación de la costa pampeana de Buenos Aires mediante el desarrollo de un estimador indirecto cualitativo, basado en variables geomorfológicas. Se analizaron imágenes de satélite y se efectuó reconocimiento en campo para la definición de paisajes según el patrón geomorfológico. Las variables de delimitación y caracterización utilizadas fueron: orientación y forma de la línea de costa; forma, textura y arreglo espacial de la vegetación; cantidad, disposición espacial y tipos de geoformas según el agente modelador y la dinámica; signos del estado dinámico del borde costero. Se calculó el porcentaje relativo de superficie correspondiente a áreas urbanas, rurales, forestales y en estado nativo, y se estimó el área protegida legalmente. Finalmente se elaboró un índice de diversidad geomorfológica, un índice de geodiversidad y otro de nivel de protección de la geodiversidad para cada paisaje. Se trabajó con la Región Costera Oriental y la Región Costera Austral (RCO y RCA) por poseer los principales campos de dunas. Éstas se subdividieron en paisajes: orientales norte y sur, y australes este, centro-este, centro, centro-oeste y oeste, respectivamente. Las regiones se diferenciaron por su orientación y extensión, pero principalmente por la calidad de los campos de dunas presentes. Se encontró que la casi totalidad de la RCO presenta modificaciones antropogénicas, y que la RCA posee la mayor parte de la geodiversidad, aunque se encuentra desprotegida legalmente en su gran mayoría. El porcentaje de área modificada por acción antrópica parece disminuir hacia el sudoeste, mostrando un patrón opuesto al de la geodiversidad, que aumenta hacia el sudoeste.Neste trabalho realiza-se um estudo à geodiversidade e ao estado de conservação da costa pampeana de Buenos Aires com o desenvolvimento de um estimador indirecto qualitativo, baseado em variáveis geomorfológicas. Analizaram-se imagens de satélite e efectuaram-se reconhecimentos de campo para a definição de paisagens segundo o padrão geomorfológico. As variáveis de delimitação e caracterização utilizadas foram: orientação e forma da linha de costa; forma, textura e arranjo espacial da vegetação; quantidade, disposição espacial e tipos de geoformas segundo o agente modelador e a dinâmica; evidências do estado dinâmico da borda costeira. Calculou-se a percentagem relativa correspondente a áreas urbanas, rurais, florestais e o estado original, e estimou-se a área protegida legalmente. Finalmente, elaborou-se um índice de diversidade geomorfológica, um índice de geodiversidade e outro do nível de protecção da geodiversidade para cada paisagem. Trabalhou-se com a Região Costeira Oriental e a Região Costeira Austral (RCO e RCA) porque possuem os principais campos dunares. Estas subdividiram-se em paisagens: orientais norte e sul, e austral este, centro-este, centro, centro-oeste e oeste, respectivamente. As regiões diferenciaram-se pela sua orientação e extensão, mas principalmente pela qualidade dos campos dunares presentes. Verificouse que a quase totalidade da RCO apresenta modificações antrópicas e que a RCA posui a maior parte da geodiversidade, embora se encontre desprotegida legalmente na sua grande maioria. A percentagem de área modificada pela acção antrópica parece diminuir para sudoeste, mostrando um padrão oposto da geodiversidade, que aumenta para sudoesteThis work presents an approach to the geodiversity and the conservation of the Pampas coast conservation in Buenos Aires, by means of the development of a qualitative indirect estimator based on geomorphological variables. Satellite images and field samples were analyzed in order to define the landscapes according to the geomorphological pattern. Demarcation and characterization variables used were: coastline shape and orientation; form, texture and spatial arrangement of vegetation; geoforms type, quantity, and spatial arrangement according to the agent modeler and the dynamics; evidence of the dynamic state of the coastline - retreating, accretion or stationary. The relative percentage of surface corresponding to urban, rural, forest and native areas was calculates and the total area legally protected was determined. Three indexes were developed for each landscape to estimate: geomorphology, geodiversity and geodiversity preservation. The work analyzes the Oriental Coastal Region and the Austral Coastal Region (RCO and RCA respectively) because they enclose the main dune fields. These regions were subdivided in landscapes: Oriental North and South, and Austral East, Center - East, Centre, Centre-West and West. Regions differed by their orientation and extension, but mainly by the quality of the present dune fields. It was found that almost the totality of the RCO presents anthropogenic modifications, and the RCA has the largest part of geodiversity, although its major surface is legally unprotected. The percentage of area modified by human action appears to decrease towards the Southwest, showing a pattern opposite to geodiversity, which increases towards the Southwest.Fil: Montserrat, A. L.. No especifíca;Fil: Codignotto, Jorge Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Secretaría de Industria y Minería. Servicio Geologico Minero Argentino; Argentin

Pointing correction in an adaptive array for communications

The authors discuss DSP procedures for pointing correction in adaptive arrays which uses a spatial reference to form the optimum beam (generalized sidelobe canceller, GSLC). The problem of adequate pointing arises from many effects on the aperture and the receiver front-end of every array channel. Component aging, channel mismatching, sensor location, etc., promote steering errors that may produce the rejection of the desired signal. Currently, highly complicated telemetry systems and monopulse radars are used for steering correction. The authors describe the existing alternatives as well as further improvements that can be achieved from the use of temporal references combined with the GSLC beamformerPeer ReviewedPostprint (published version

High resolution adaptive arrays based on random processing techniques: frequency hopping modulation

A new architecture for adaptive arrays using frequency hopping modulation is addressed. The resolution of the array and the interference rejection increase substantially applying random processing to the carrier frequency of the signals. The proposed framework is composed of two different stages. The anticipative stage, devoted to minimize the noise and fixed interferences contribution and the GSLC stage which provides cancellation of follower jammers and solves the multiuser collision problem. The developed system requires neither temporal nor spatial reference for its implementation, only the frequency sequence must be known. An adaptive approach has been implemented, allowing a fast convergence to the optimal behavior.Peer ReviewedPostprint (published version

Adaptive array beamforming for frequency hopping modulation

A new architecture for Array Processing using Frequency Hopping (FH) modulation is addressed in this paper which takes advantage of the knowledge of the frequency sequence at the receiver, requiring neither temporal nor spatial a priori reference. Consequently, the paper deals with a Code Reference Beamformer (CRB). The proposed framework is composed of two parallel processors. The first one, the Anticipative processor, is devoted to predict the scenario at the hop frequency before this frequency is transmitted, providing a fast convergence of the second processor and avoiding the fall of the Signal to Interference plus Noise Ratio (SINR) with the frequency hops. The second one, the On-line processor, provides maximum SINR by applying the optimum beamvector which can be estimated minimizing the Mean Square Error (MSE) at the array output or, directly, maximizing the SINR.Peer ReviewedPostprint (published version

Symmetric periodic orbits near heteroclinic loops at infinity for a class of polynomial vector fields

For polynomial vector fields in R3, in general, it is very difficult to detect the existence of an open set of periodic orbits in their phase portraits. Here, we characterize a class of polynomial vector fields of arbitrary even degree having an open set of periodic orbits. The main two tools for proving this result are, first, the existence in the phase portrait of a symmetry with respect to a plane and, second, the existence of two symmetric heteroclinic loops