Second graders articulating ideas about linear functional relationships

In this paper, we explore the ideas that second grade students articulate about functional relationships. We adopt a function-based approach to introduce elementary school children to algebraic content. We present results from a design-based research study carried out with 21 second-grade students (approximately 7 years of age). We focus on a lesson from our classroom teaching experiment in which the students were working on a problem that involved a linear functional relationship (y=2x). From the analysis of students’ written work and classroom video, we illustrate two different approaches that students adopt to express the relationship between two quantities. Students show fluency recontextualizing the problem posed, moving between extra-mathematical and intra-mathematical contexts

MatrigelBD, Un Andamiaje Biocompatible que Estimula la Proliferación de Celulas Troncales Mesenquimales Derivadas del Tejido Gingival.

MatrigelBD is a hydrogel scaffold with three-dimensional intercrossed networks of hydrophilic polymers with high water content. Human gingival tissue might represent a better source of MSCs, allowing these cells to be easily obtained in a relatively non-invasive way. The objective of this study was to evaluate the biocompatibility of MatrigelBD with GMSCs in vitro. Gingival connective tissue samples were obtained from healthy donors. Fresh tissue was minced and cultured during two weeks, after which cells at passage fourth were analyzed for their immune phenotype by flow cytometry. Differentiation into osteogenic, chondrogenic, and adipogenic lineages was induced and evaluated by culture staining. The "construct" was made of MatrigelBD with GMSC. To assess the biocompatibility, an MTT cellular proliferation assay was performed. The differentiation potential of the cells toward the osteogenic, adipogenic, and chondrogenic lineages was analyzed after 21 days of growth in MatrigelBD with induction differentiation media. The MTT analysis showed that MatrigelBD stimulated cell proliferation; the GMSCs maintained the expression of MSC markers. Importantly, the growth of GMSCs within the MatrigelBD did not interfere with the cell differentiation potential. These findings indicate that MatrigelBD is biocompatible with GMSCs, and this matrix improves cell proliferation in vitro.publishedVersio

Microstructural evolution of a modified HP alloy: experimental and complementary computational study

In this work is presented results of the microstructural characterization of austenitic stainless steel (HP series) modified with Nb, aged at temperatures of 750, 800, 850, 900 and 950oC in air at different times. Microstructural changes were analyzed using optical microscopy, scanning electron microscopy (SEM) equipped with (EDS), x-ray diffraction and Vickers hardness. In the as-cast condition, the microstructure consists of an austenitic matrix and eutectic carbides network, Cr, Nb-rich carbides. The Cr-rich carbides are M7C3 type, whereas, those rich in Nb are NbC. During aging, there is a second precipitation in the matrix of very fine needle form of M23C6 carbides, which leads to an increase in hardness. After that, the decreasing in hardness is associated with a coalescence phenomenon of the secondary precipitates. Computational modeling shows that M23C6 is lesser stable than M7C3 carbide

Big Bounce and inhomogeneities

The dynamics of an inhomogeneous universe is studied with the methods of Loop Quantum Cosmology as an example of the quantization of vacuum cosmological spacetimes containing gravitational waves (Gowdy spacetimes). The analysis performed at the effective level shows that: (i) The initial Big Bang singularity is replaced (as in the case of homogeneous cosmological models) by a Big Bounce, joining deterministically two large universes, (ii) the universe size at the bounce is at least of the same order of magnitude as that of the background homogeneous universe, (iii) for each gravitational wave mode, the difference in amplitude at very early and very late times has a vanishing statistical average when the bounce dynamics is strongly dominated by the inhomogeneities, whereas this average is positive when the dynamics is in a near-vacuum regime, so that statistically the inhomogeneities are amplified.Comment: RevTex4, 4 pages, 2 figure

Estimation of Organic Matter Digestibility and Intake from Faecal Organic Matter and Daily N Excretion and Concentration

This study was performed with grazing sheep, to establish: a) if the amount of total faecal N (C; in g 100g-1 of organic matter intake (OMI)) remains constant at three feeding levels, in four utilisation periods of deferred Panicum coloratum cv. Verde; b) the relationship between C and faecal N fractions, and c) the relationship between faecal daily excretion of OM and N, and OMI. Intake increased (P\u3c 0.01) with utilisation period, and was related (r = - 0.82; P\u3c 0.01) to the protein content of food, the insoluble N fraction (r = -0.49; P\u3c 0.01) and the soluble:insoluble N ratio (r = 0.41; P\u3c 0.01) in faeces. No relation with total N concentration (r = -0.22; P\u3e 0.05) or soluble N fraction (r = -0.02; P\u3e 0.05) in faeces could be found. Daily excretion of OM and N were positively related (R2 = 0.93 and 0.96, respectively; P\u3c 0.01) to OMI. The slopes of regression lines, but not the intercepts, were different (P\u3c 0.01) between evaluation periods. The digestibility can be estimated from OMI and faecal N whenever time of the year is taken into consideration

ANALYSIS OF THE INFLUENCE OF DIFFERENT TREKKING BOOTS ON CHILDREN’S LOCOMOTOR ABILITY

The use of trekking boots for daily activities has greatly increased among children. This type of footwear can modify the locomotor ability of children due to alterations in ankle, leg and foot movements caused by upper height and sole stiffness, modifications of children’s perception of shoe size caused by a greater size, as well as energy cost due to boot weight, as observed in adults (Jones et al., 1986; Robinson et al., 1986), which can cause balance and performance problems. The influence of three different trekking boots on children’s locomotor ability and performance was studied in tests on children. Two boots differed only in the lacing system (one included an extra velcrum around the ankle) whilst the third was smaller, lighter and more flexible. The children performed performance tests running along an obstacle circuit (Brizuela, et al., 1997) using an electronic system for measuring time and ability tests on a new fixed-goal tasks (FGTT) circuit. This circuit included 13 different tasks on a restricted path which were evaluated on a three point scale from absence of error to grave error; global time and the number of errors were also measured. Results showed a high frequency of errors in many of the tasks in the FGTT circuit, mainly related to equilibrium, precision tasks and kicking obstacles. However, few differences were found within boots. The higher boots had a statistically significant (p=0.027) greater number of total errors, whilst 27.8% (Sommers D) of errors observed on the equilibrium bar were significantly attributed (0.041) to the higher boots without extra velcrum. These results related errors to lower rear foot stability and poor perception of shoe size. No statistically significant differences were found among boots in global time. No statistically significant differences within boots were found in time of circuit performance (if any, it should be lower than 2%). The main influence on children’s motor skills seemed to be the fact of wearing boots, with little influence exercised by boot design. Nevertheless, the differences observed were due to the influence on rear foot stability of boot design and size, and children’s perception of shoe size. REFERENCES: Brizuela, G., Llana, S., Ferrandis, R., García, A. (1997).The Influence of Basketball Shoes with Increased Ankle Support on Shock Attenuation and Performance in Running and Jumping. Journal of Sports Sciences 15, 505-515. Jones, B. H., Knapik, J. J., Daniels, W. L., Toner, M. M. (1986).The Energy Cost of Women Walking and Running in Shoes and Boots. Ergonomics 29, 439-443. Robinson, J. R., Frederick, E. C., Cooper, L. B. (1986). Systematic Ankle Stabilization and the Effect on Performance. Med. and Sci. in Sports and Exer. 18, 625-628

Study of the 1.25Cr-1Mo-0.25V steel microstructure after a carburization phenomenon

We studied the changes in the structure and carbide particle size in 1.25Cr-1Mo-0.25V steel under 600°C and 168. MPa, after 4000. h service. We used microscopy and microanalysis techniques to analyze the carbide particles. We performed a complementary theoretical study on the chemical bonding and electronic structure of the carbide-Fe matrix interaction. The results contribute to the understanding of the changes in the alloy microstructure caused by the carburization phenomenon.Fil: Simonetti, Sandra Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Lanz, C.. Universidad Nacional del Sur; ArgentinaFil: Brizuela, Graciela Petra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin

A FIXED-GOAL TASKS (FGTT) CIRCUIT: A NEW TECHNIQUE TO ASSESS FOOTWEAR INFLUENCE ON CHILDREN’S LOCOMOTOR ABILITY

Footwear does not influence children’s locomotor ability in just a single way. It is the result of a complex interaction of design, mechanical properties, fitting, etc. As a result, subjective techniques are better suited for its study. Some investigators have used these techniques to study motor skills in children (Pryde et al., 1997), but few works have focused on the assessment of children’s footwear (Gould, 1985). This work presents a new technique for the analysis of footwear influences on children’s locomotor ability. An obstacle walking circuit was designed in which 13 fixed-goal tasks (FGTT) were included. Each task was designed for compromising either a single or complex movement or motor skill of children. Obstacles of increasing complexity were placed along the circuit on a restricted path with visual clues. Seven children (mean age = 8.4) participated in an experiment with three different pairs of hiking boots. The time required to complete the circuit was recorded for each trial. A three point scale was used to visually quantify the performance in each task: (0) absence of error, (1) slight error and (2) grave error. The total number of errors was also computed. Descriptive statistics of errors were gathered. The influence of shoes on global time and errors was analyzed. Factor analysis of Principal Components was used to identify the association among the most frequent errors. The relationship of error groups with time and boots, as well as the accommodation of children to walking conditions were also analyzed. A high frequency of errors in many of the tasks was observed. However, little differences in time and errors were observed with the same shoes, so the circuit really demonstrated to compromise children’s ability. Quick accommodation of the children was observed. The first trial was the slowest, and the frequency of errors in the tasks decreased from 13.0 % to 3.8% when performed four more times. Factor Analysis resulted in five error groups which were related to 1) bad perception of whole shoe size and 2) of shoe point, 3) the influence in medial-lateral movements, 4) a complex movement of the lower leg and the foot followed by precise positioning and 5) stepping over the first high obstacle in the circuit. No significant relationship of error groups with time and type of boot was found.This technique yielded interesting relationships of performance in fixed-goal tasks with aspects of footwear influence on children’s motor skills which would allow the assessment of children’s footwear design. The small differences among boots found in this experiment could be due to the fact that the tested boots were very similar. REFERENCES: Gould, N. (1985). Shoes Versus Sneakers in Toddler Ambulation. Foot Ankle 6, 105-107. Pryde, K. M.; Roy, E. A.; Patla, A. E. (1997). Age-related trends in locomotor ability and obstacle avoidance. Human Movement Science, 16, 507-516

Examining how teachers use graphs to teach mathematics during a professional development program

There are urgent calls for more studies examining the impact of Professional Development (PD) programs on teachers’ instructional practices. In this study, we analyzed how grades 5-9 mathematics teachers used graphs to teach mathematics at the start and end of a PD program. This topic is relevant because while many studies have investigated students’ difficulties with graphs, there is limited research on how teachers use graphs in their classrooms and no research on how PD impacts the way teachers use graphs in class to teach mathematics. Participant teachers took three graduate level semester-long courses focused on mathematics and student mathematical thinking. The program provided teachers with multiple opportunities for exploration and discussion, systematic feedback, contexts for collaboration and collegial sharing, and extended follow-up support. We analyzed all lessons where teachers used graphs in class at the start and end of the program, finding that teachers’ use of graphs was qualitatively more sophisticated in the end lessons. Results suggest that the features of the PD program had a positive effect on teachers’ classroom practices regarding the use of graphs

Microhistological Estimation of Leaf Blade Percentage in Diets from Monoespecific Pastures

Although a decrease in the leaf-stem ratio affects the nutritive value of pastures, herbivores can reinforce selection for leaf blades to maintain the quality of their diets. This study evaluated whether the percentage of fragments with furrows in blades could be used to estimate the relative intake of this part of the leaves by herbivores grazing monoespecific pastures. It was worked with vegetation of kleingrass (Panicum coloratum L.) from paddocks with three deferment periods. Blade samples, and different plant part mixtures hand compounded were in vitro digested. The digestion residues were microhistological analyzed determining the number of fragment with furrows (#FWF), and the total number of fragments (T#F). The blade percentages in mixtures was computed as: Estimated %Blademixtures = ((#FWFmixtures*100/ %FWFblades)/ T#Fmixtures))*100. The %FWF in blade samples (19+ 1.5%) was not affected (P\u3e 0.05) by changes in plant maturity determined by the length of the deferment period. The relationship between the actual blade percentages (y), and those determined by microanalysis (x) in mixtures was 1:1. This suggests that the microanalysis of feces or digestive contents could be used to estimate the percentages of blades in the diet of herbivores grazing monoespecific pastures