Análisis de Interacciones en Clases de Español de Primer Grado de Primaria

Este trabajo aborda la interacción profesor-alumnos en una clase de español en cuatro grupos escolares de primer grado de primaria de México, a partir de videos. Cada video fue segmentada en episodios interactivos que fueron analizados con categorías únicas estructuradas tanto para el maestro como para el alumno, según la taxonomía funcional de Ribes y López (1985): interacciones contextuales, suplementarias, selectoras, sustitutivas referenciales y sustitutivas no referenciales, y dos categorías de seguimiento didáctico. En general, en el primer grado se estructuran mayormente interacciones en el nivel funcional más sencillo, seguido por interacciones de instrucciones de seguimiento y realimentación. Asimismo, aunque en menor proporción, en dos de los cuatro grupos se presentaron interacciones en niveles funcionales más complejos

Throughput Performance Evaluation of Multiservice Multirate OCDMA in Flexible Networks

\u3cp\u3eIn this paper, new analytical formalisms to evaluate the packet throughput of multiservice multirate slotted ALOHA optical code-division multiple-access (OCDMA) networks are proposed. The proposed formalisms can be successfully applied to 1-D and 2-D OCDMA networks with any number of user classes in the system. The bit error rate (BER) and packet correct probability expressions are derived, considering the multiple-access interference as binomially distributed. Packet throughput expressions, on the other hand, are derived considering Poisson, binomial, and Markov chain approaches for the composite packet arrivals distributions, with the latter defined as benchmark. A throughput performance evaluation is carried out for two distinct user code sequences separately, namely, 1-D and 2-D multiweight multilength optical orthogonal code (MWML-OOC). Numerical results show that the Poisson approach underestimates the throughput performance in unacceptable levels and incorrectly predicts the number of successfully received packets for most offered load values even in favorable conditions, such as for the 2-D MWML-OOC OCDMA network with a considerably large number of simultaneous users. On the other hand, the binomial approach proved to be more straightforward, computationally more efficient, and just as accurate as the Markov chain approach.\u3c/p\u3

A Novel Approach for Transmission of 56 Gbit/s NRZ Signal in Access Network Using Spectrum Slicing Technique

We present the spectrum slicing and stitching concept for high-capacity low optics complexity optical access networks. Spectrum slicing and stitching of a 56 Gbit/s NRZ electrical signal is experimentally demonstrated for the first time. We present the spectrum slicing and stitching concept for high-capacity low optics complexity optical access networks. Spectrum slicing and stitching of a 56 Gbit/s NRZ electrical signal is experimentally demonstrated for the first time

Photonic-based beamforming system for sub-THz wireless communications

This work presents a sub-THz transmitter scheme for wireless communications with beam steering capabilities based on photonics means. A true time delay 1x4 beamforming photonic chip is designed in Si3N4 technology to continuously tune the progressive time delay between consecutive antenna elements. Simulation results show a progressive delay up to 15 ps with a bandwidth of 1.3 GHz, enabling broadband operation at frequencies above 75 GHz. The sub-THz signals are generated on photoconductive antennas on chip by photonic heterodyning. The design of a dielectric rod antenna array is also presented to efficiently radiate the generated wave

Association between population distribution and urban GDP scaling

Urban scaling and Zipf's law are two fundamental paradigms for the science of cities. These laws have mostly been investigated independently and are often perceived as disassociated matters. Here we present a large scale investigation about the connection between these two laws using population and GDP data from almost five thousand consistently-defined cities in 96 countries. We empirically demonstrate that both laws are tied to each other and derive an expression relating the urban scaling and Zipf exponents. This expression captures the average tendency of the empirical relation between both exponents, and simulations yield very similar results to the real data after accounting for random variations. We find that while the vast majority of countries exhibit increasing returns to scale of urban GDP, this effect is less pronounced in countries with fewer small cities and more metropolises (small Zipf exponent) than in countries with a more uneven number of small and large cities (large Zipf exponent). Our research puts forward the idea that urban scaling does not solely emerge from intra-city processes, as population distribution and scaling of urban GDP are correlated to each other.Comment: 17 pages, 3 figures, supplementary information; accepted for publication in PLoS ON

Effect of a selenium-deficient diet on blood values of T3 and T4 in cows

Pastures in the south of Chile have been shown to be selenium deficient, and as selenium is a component of deiodinase type 1, which is necessary for the synthesis of triiodothyronine (T3) at peripheral levels, the effect of selenium deficiency on the blood concentration of theses hormones in cows was studied. Twelve pregnant Friesian cows were randomly allocated into two homogeneous groups of six animals each-selenium supplemented and selenium deficient. The selenium deficient diet consisted of 11.5 kg of hay, 500 g of soya bran, 150 g of mineral mix (without selenium), 500 g of fat for animal feeding, and was given from day 15 of lactation until the end of the study. A commercial concentrate (Cosetan) and urea was also given according to lactation requirements (up to 5 kg and up to 120 g, respectively). The selenium content was 0.05 ppm of dry matter (equivalent to 18% of the daily requirements). The supplemented group was injected subcutaneously with 1 mg Se/kg, using the commercial product Deposel (1 ml/50kg). Blood samples were obtained by coccygeous vein venepuncture before supplementation (prepartum basal values) and thereafter every 15 days. GSH-Px activity in plasma was measured using a HITACHI 4020 spectrophotometer. Serum T3 and thyroxine (T4) concentrations were measured by electrochemiluminiscence. ANOVA, Tuckey test and Student's t-test were used to establish the significance of the intra group differences, with p = < 0.05 being considered significant. There were no significant differences in blood values of T4 in either the supplemented or non-supplemented groups during pregnancy and lactation. However the blood values of T4 decreased significantly (p = < 0.05) during days 30-60 of lactation to values below the reference range. The T3 serum concentrations in the supplemented group of cows were significantly lower (p = < 0.05) at 60, 90 and 150 days of lactation than cows that had been supplemented with selenium

Optical-domain Compensation for Coupling between Optical Fiber Conjugate Vortex Modes

We demonstrate for the first time optical-domain compensation for coupling between conjugate vortex modes in optical fibers. We introduce a novel method for reconstructing the complex propagation matrix of the optical fiber with straightforward implementation