Représentations dynamiques et tangibles dans l'enseignement mathématique

International audienceDynamic geometry environments offer a new kind of representation of mathematical objects that are variable and behave "mathematically" when one of the elements of the construction is dragged. The chapter addresses three dimensions about the transformations brought by this new kind of representation in mathematics and mathematics education: an epistemological dimension, a cognitive dimension and a didactic dimension. As so often stated since the time of ancient Greece, the nature of mathematical objects is by essence abstract. Mathematical objects are only indirectly accessible through representations (D'Amore 2003, pp. 39-43) and this contributes to the paradoxical character of mathematical knowledge: "The only way of gaining access to them is using signs, words or symbols, expressions or drawings. But at the same time, mathematical objects must not be confused with the used semiotic representations" (Duval 2000, p. 60). Other researchers have stressed the importance of these semiotic systems under various names. Duval calls them registers. Bosch and Chevallard (1999) introduce the distinction between ostensive and non ostensive objects and argue that mathematicians have always considered their work as dealing with non-ostensive objects and that the treatment of ostensive objects (expressions, diagrams, formulas, graphical representations) plays just an auxiliary role for them. Moreno Armella (1999) claims that every cognitive activity is an action mediated by material or symbolic tools. Through digital technologies, new representational systems were introduced with increased capabilities in manipulation and processing. The dragging facility in dynamic geometry environments (DGE) illustrates very well the transformation technology can bring in the kind of representations offered for mathematical activity and consequently for the meaning of mathematical objects. A diagram in a DGE is no longer a static diagram, representing an instance of a geometricalLes environnements de géométrie dynamique offrent un nouveau type d'objets mathématiques variables qui se modifient quand l'un des éléments de la construction est déplacé.Le chapitre aborde trois dimensions relatives aux transformations apportées par ce nouveau type de représentations en mathématiques et dans l'enseignement des mathématiques : une dimension épistémologique, une dimension cognitive et une dimension didactique

Effect of Planting Date, Clipping Height, and Cultivar on Forage and Grain Yield of Winter Wheat in Argentinean Pampas

In Argentinean Pampas, new wheat (Triticum aestivum L.) cultivars are routinely introduced to farmers for dual-purpose production. The objective of this study was to evaluate the effect of planting date, clipping height on forage, and grain yield for wheat cultivars. Treatments were arranged as a 3 × 3 × 3 factorial distributed in a split-split plot within a randomized complete block design. Main plots were planting date (March, April, and May); split-plots were clipping height (3 cm, 7 cm, and no clipping); and split-split plots were a facultative cultivar Pincen, and two nonfacultative cultivars Charrua and Bordenave 223 (Bve223). In 1995 and 1996 forage yield decreased in response to a delayed planting date from March to May, whereas in 1997 it was not affected by planting date. The 3-cm clipping height yielded 21% more forage than plots clipped at 7 cm. Bve223 and Charrua produced significantly more forage than Pincen each year. Grain yield increased as planting date progressed from March to May. Clipping at 3 cm reduced grain yield compared with no clipping, while during 2 to 3 yr, 7 cm produced no significant change in grain yield compared with no clipping. In all years Bve223 produced more grain than Charrua or Pincen. Forage yield lost in response to later planting date ranged between 0 and 81% during the 3 yr; whereas grain yield increased from 40 to 190% for wheat planted in May compared with March. In conclusion, dual-purpose wheat planted during April had both good forage and grain production, and its success was influenced by cultivars.Fil: Arzadún, M. J.. Provincia de Buenos Aires. Ministerio de Asuntos Agrarios; ArgentinaFil: Arroquy, Jose Ignacio. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Laborde, Hugo Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; ArgentinaFil: Brevedan, Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentin

Influence of transcutaneous vagus nerve stimulation on cardiac vagal activity: Not different from sham stimulation and no effect of stimulation intensity

© 2019 Borges et al. The present study investigated the effects of transcutaneous vagus nerve stimulation on cardiac vagal activity, the activity of the vagus nerve regulating cardiac functioning. We applied stimulation on the left cymba conchae and tested the effects of different stimulation intensities on a vagally-mediated heart rate variability parameter (i.e., the root mean square of successive differences) as well as on subjective ratings of strength of perceived stimulation intensity and unpleasantness due to the stimulation. Three experiments (within-subject designs, M = 61 healthy participants each) were carried out: In Experiment 1, to choose one fixed stimulation intensity for the subsequent studies, we compared three preset stimulation intensities (i.e., 0.5, 1.0 and 1.5 mA) with each other. In Experiment 2, we compared the set stimulation method with the free stimulation method, in which the participants were instructed to freely choose an intensity. In Experiment 3, to control for placebo effects, we compared both methods (i.e., set stimulation vs. free stimulation) with their respective sham stimulations. In the three experiments, an increase of cardiac vagal activity was found from resting to the stimulation phases. However, this increase in cardiac vagal activity was not dependent on stimulation intensity (Experiment 1), the method used to stimulate (i.e., set vs. free; Experiment 2), or whether stimulation was active or sham (Experiment 3). This pattern of results was solidly supported by Bayesian estimations. On the subjective level, higher stimulation intensities were perceived as significantly stronger and a stronger stimulation was generally also perceived as more unpleasant. The results suggest that cardiac vagal activity may be similarly influenced by afferent vagal stimuli triggered by active and sham stimulation with different stimulation intensities. Potential explanations for these findings and its implications for future research with tVNS are discussed

Influencia de la calidad del heno suplementario y la localización de la pastura sobre el rendimiento de bovinos de carne a pastoreo sobre avena

Heifers grazing oat pasture (OP) at two locations in Argentina, Argerich (ARG) and Pasman (PAS), were subjected to one of three different dietary supplement treatments: (1) control (CON, no supplement), (2) sorghum hay (SH), or (3) alfalfa-grass hay (AGH), all provided ad libitum in individual pens. The variables measured were: dry matter (DM) yield and composition of OP, hay intake, average daily weight gain (ADG), rumen pH and NH3-N, and blood mineral levels. DM availability did not limit OP intake. OP crude protein (CP) content ranged from 11.3 to 13% at ARG, and 10.7 to 13.3% at PAS. OP-minerals varied with location; the mean K/(Ca + Mg) ratios were 5.68 meq (ARG) and 4.82 meq (PAS). Heifers ate more AGH (785 g) than SH (684 g; P = 0.08). Hay consumption was 2.88 times greater at PAS than at ARG (P < 0.05). ADG was larger with SH (558 g) and AGH 594 g than with CON treatment (454 g); the average for ARG animals was 571 g compared to 500 g for PAS animals (P <0.05). Rumen pH was lower at 14:30 h (pH 6.7) than at 10:00 h (pH 7.5; P < 0.05). NH3-N values were higher at 14:30 h (19.59 mg dl-1) than at 10:00 h (4.69 mg dl-1; P < 0.05). Plasma Ca (15.50 mg dl–1) and Mg (2.84 mg dl–1) levels were higher in PAS cattle (P < 0.05). Animal performance improved with hay supplementation, but location affected response intensity.Se realizaron tres tratamientos con novillas pastoreando verdeos de avena (VA) en dos localidades de Argentina, Argerich (ARG) y Pasman (PAS): (1) Control (CON, sin suplemento), (2) heno de sorgo (HS), y (3) heno de alfalfa y gramíneas (HAG), suplementados ad libitum en corrales individuales. Evaluamos rendimiento de materia seca (MS) y composición en VA; y en los animales consumo del heno, ganancia diaria de peso (GDP), pH y N-NH3 en rumen, y minerales en sangre. La disponibilidad de MS no limitó el consumo de VA; su proteína bruta (PB) osciló entre 11,3 y 13% (ARG), 10,7 y 13.3% (PAS). Los minerales en VA variaron entre localidades, la relación K/(Ca + Mg) promedió 5,68 meq (ARG) y 4,82 meq (PAS). Las novillas consumieron diariamente más HAG (785 g) que HS (684 g; P = 0.08), y 2,88 veces más heno en PAS que en ARG (P < 0,05). En GDP, HS (558 g) y HAG (594 g) superaron al CON (454 g), y la media de ARG (571 g) a PAS (500 g; P < 0,05). En el rumen el pH decreció a las 14:30 h (6,7) vs. 10:00 h (7,5; P < 0,05), y el N-NH3 (mg dl-1) aumentó a las 14:30 h (19,59) vs. 10:00 h (4,69; P < 0,05). Ca (15.50 mg dl–1) y Mg (2.84 mg dl–1) en plasma fue mayor en PAS (P < 0,05). El rendimiento animal mejoró con la suplementación, pero la magnitud de respuesta estuvo afectada por la localidad.Fil: Arelovich, Hugo Mario. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; ArgentinaFil: Laborde, Hugo Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; ArgentinaFil: Arzadún, M. J.. Provincia de Buenos Aires. Ministerio de la Producción. Chacra Experimental Coronel Suarez; ArgentinaFil: Vasquez, Maria Gabriela. Universidad Nacional del Sur. Departamento de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentin

Development of Improved Cable Yarding Productivity in Southern Africa for Small-Sized Trees

Production rates of cable yarding by fixed skyline in Southern Africa were found to be low, usually between 50 m3 to 60 m3 of timber per day on average. Investigations identified four major sources of lost productivity. Implementation of simple techniques selected to reduce losses resulted in a quadrupling of productivity though only a tripling is expected in the long term

Modélisation pluie-débit à l’échelle annuelle en Algérie du nord

La modélisation du comportement hydrologique des bassins versants est incontournable dès lors que l'on s'intéresse à des problématiques relatives à l’évaluation et la gestion optimale des ressources en eau. Ceci s’illustre par un aspect quantitatif, dans les pays comme l’Algérie où l’alimentation en eau est un facteur limitant. L’objectif principal de cet article est d’expliciter les relations entre les conditions hydrologiques et la disponibilité en eau de surface. A cet effet, un modèle pluie-débit à l’échelle annuelle qui prend en compte les paramètres physiques et climatiques a été mis au point. L’application porte sur l’Algérie du Nord dont la superficie est de 325 000 km2.La mise au point de ce modèle nécessite au préalable une base de données qui a été acquise lors des travaux antérieurs incluant la carte des pluies médianes, la carte des perméabilités et le modèle numérique de terrain. Afin de compléter cette base de données, la cartographie des pluies des différentes années pour lesquelles on dispose des débits a été réalisée en utilisant une méthodologie intitulée "cartographie de la pluie centrée réduite". Ainsi, les données de 467 postes pluviométriques ont été traitées et ont permis de tracer les cartes des isohyètes annuelles.L’étude de la relation pluie-débit à l’échelle annuelle est basée sur les données de débits de 50 stations hydrométriques réparties à travers la zone d’étude. La démarche utilisée s’est inspirée de la fonction de production du S.C.S (Soil Conservation Service). Les résultats du modèle après calage ont permis d’obtenir un coefficient d’explication de 0,75, ce qui signifie que 75 % de la variance est expliquée par la pluie moyenne, la surface et un coefficient (a) qui correspond à la pente moyenne des bassins versants.Modelling the hydrological behaviour of drainage basins is very important for solving problems related to the evaluation and optimal management of water resources. This is illustrated quantitatively in countries such as Algeria where water supply is a limiting factor. The principal aim of this paper was to explain the relationship between hydrological conditions and the availability of surface water. A model of rainfall-discharge was developed on a yearly scale, taking into account physical and climatic parameters. The application was carried out in northern Algeria where the total land surface is about 325 000 km2.The development of this model required a database, which was acquired during previous studies where maps of median rainfall and permeability as well as the digital elevation model were developed. In order to complete this database, the cartography of rainfall for the years for which we have discharge data was carried out using a methodology entitled "mapping standardized rainfall". To estimate and map annual rainfall, the kriging method was used. Two problems were encountered:- The presence of a drift highly altered the variogram and made it very difficult to infer a sub- structure function;- The variogram is significant only if the hypothesis of ergodicity is valid, which was not easy to assume for any given year.In order to resolve these difficulties, a homogeneous random and secondary stationary order function (same mean at all points and same covariance function) must be calculated. A previous study by ANRH (1993) allowed us to know the statistical parameters of the distribution at each point. These parameters were mapped, taking into consideration the topographical relief and distance to the sea. For every year and at each rainfall measure point, the standardized rainfall could be deduced. The correlogram gave information about the spatial variability of the phenomenon and its range, and subsequently the standardized rainfall was then interpolated. Annual rainfall was calculated by combining the grids of the means, the variances and the centered reduced rainfall (TOUAZI and LABORDE, 2000). Thus, the data of 467 rainfall gauges were used in order to create maps of the yearly isohyets.The rainfall-discharge relationship on an annual scale was based on 50 hydrometric stations distributed throughout the study area. The methodology used was derived from the production function of the S.C.S (Soil Conservation Service). This production function was part of modelling, which transformed total rainfall to net rainfall. This method was very representative of the natural hydrological processes. Indeed, it takes into account rainfall and the maximum infiltration capacity (S), which depends on the nature of the soil (lithology), vegetation and soil moisture content. In the current study, the basin surface and a regional parameter (a) were introduced in order to calibrate the model. This production function was implemented by supplying different values for the parameter (S). The values (n+1) were obtained by increasing the previous value (n) by 10 %. We evaluated the different values of (S) in the same way to obtain the last value (i). We calculated for these different values of the parameter (S) the square of the difference between the measured and estimated discharges for each year by measuring the discharge at different stations. For each station, we calculated the sum of these values for all the years and we retained the value of (S) that gave the minimal value. The results demonstrated that the values of (S) obtained were not significant because they tend to the infinite. For this reason, (S) was considered as a constant. In order to improve the model, we repeated the same operation, but instead of (S), we used the parameter (a) and performed the same calculation. After calibration of the model the results gave a coefficient of determination of 0.75, which means that 75 % of the variance was explained by the mean rainfall, the surface and the parameter (a).To explain the parameter (a), we calculated the correlation between its value at each station with the corresponding geology. This latter variable was characterized by the average storage capacity, which corresponds to the weighted average of the surfaces of the basin assigned to each permeability category (TOUAZI, 2001). The results demonstrated a coefficient of determination of 0.1. The correlation with the topographical relief was not necessary because it was taken into account in the cartography of the rainfall. We then proceeded to the cartography of the parameter (a). The results demonstrated an east-west gradient that was constant and a north-south gradient that decreased from north to south. With the digital elevation model, we used a geographical information system to deduce the slopes. For each basin, the average slope was calculated by taking the average of the values of the slopes of all the pixels that constituted the individual basin. The correlation between slopes and corresponding values of the parameter (a) gave a coefficient of correlation of 0.6.The results obtained by this model after calibration gave a coefficient of determination of 0.75, which means that 75% of the variance was explained by the mean rainfall, the surface and a coefficient (a), which corresponds to the average slope of the drainage basins

Emotional intelligence training in team sports:The influence of a season long intervention program on trait emotional intelligence

The aim of this study was to test the effectiveness of an emotional intelligence (EI) training intervention to improve EI at trait level. Sixty-seven rugby players participated in the study. One group received a specific EI training intervention, while the other group served as a control group. The intervention consisted of four face-to-face sessions over a 5-month period, with homework and follow-up procedures. Results showed that the EI training was partially successful in increasing EI, and demonstrates it is possible to enhance EI at trait level in participants while they may not have preexisting motivation to do so

Quantum Algorithms for Testing Hamiltonian Symmetry

Symmetries in a Hamiltonian play an important role in quantum physics because they correspond directly with conserved quantities of the related system. In this paper, we propose quantum algorithms capable of testing whether a Hamiltonian exhibits symmetry with respect to a group. We demonstrate that familiar expressions of Hamiltonian symmetry in quantum mechanics correspond directly with the acceptance probabilities of our algorithms. We execute one of our symmetry-testing algorithms on existing quantum computers for simple examples of both symmetric and asymmetric cases.Comment: 11 pages, 3 figures Comments welcome! Revision comment: New results adde