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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Autour du concept de fraction à l'école primaire en France : étude exploratoire autour des significations de la fraction au travers des manuels scolaires, des représentations et des connaissances des élèves de cycle III / About the concept of fraction in French primary school : exploratory study of the meanings of the fraction through textbooks, representations and knowledge of the pupils of cycle III

Alahmadati, Abdul Aziz 29 January 2016 (has links)
La présente étude s’intéresse particulièrement au concept mathématique de fraction et à son enseignement-apprentissage au cycle 3 de l’école primaire en France. Ce concept étant souvent difficile à comprendre par les élèves, il est introduit formellement dès la classe de CM1 du cycle 3 de l’école primaire.L’objectif de cette recherche a été, dans un premier temps, l’étude de l’enseignement des fractions. Pour ce faire, sont analysées les situations d’apprentissage qui proposent des activités portant sur les fractions dans cinq manuels scolaires de mathématiques de CM1 et cinq manuels de CM2, de même collection ; le but est de connaître les différentes significations de la fraction présentes dans ces manuels.Dans un deuxième temps, l’objectif de cette recherche fut de savoir ce qu’il reste chez les élèves après qu’ils ont étudié les fractions. Pour cela, un échantillon de 275 sujets, 160 de CM1 et 115 de CM2 de l’école primaire, ont répondu à un questionnaire écrit portant sur les fractions. Le but est d’étudier les conceptions et les représentations chez ces élèves à l’égard de la notion de fraction, en particulier à l’égard des différentes significations de la fraction données par ces élèves.Dans un troisième temps, nous voulions connaître les conceptions de quelques enseignants sur la manière avec laquelle ils abordent les fractions avec leurs élèves. Pour ce faire, 8 enseignants parmi les 12 enseignants des classes concernées ont participé à l’étude.L’analyse effectuée sur les manuels scolaires a été faite à l’aide d’une grille d’analyse, les résultats de cette analyse relèvent que les activités ou les situations d’apprentissage proposées dans les manuels scolaires choisis ne sont pas réparties à égalité entre les diverses significations de la fraction. De plus, les significations de la fraction les plus présentes dans les manuels scolaires de CM1 à travers les activités analysées sont respectivement les suivantes : Partie-tout (quantité continue), Mesure, Nombre ; dans les manuels scolaires de CM2, les significations les plus présentes sont respectivement les suivantes : Nombre, Partie-tout (quantité continue) et Mesure. En revanche, les activités relatives aux autres significations sont généralement présentes, mais avec des fréquences réduites.Pour traiter de l’apprentissage des fractions chez les élèves, l’analyse s’est effectuée autour des connaissances et des représentations des élèves de CM1 et de CM2 par rapport aux différentes significations de la fraction. Cette analyse, effectuée sur les réponses des élèves sur le questionnaire, montre que la signification de la fraction la plus utilisée, par les élèves de CM1 et de CM2, est celle de Partie d’un tout (quantité continue). Les significations Nombre, Mesure, Partie d’un tout (quantité discrète) et Nombre sur une droite graduée sont présentes dans les réponses des élèves. En revanche, les autres significations sont celles qui sont les moins utilisées par les élèves. De plus, en ce qui concerne les significations manifestées de la fraction, les élèves de ces deux niveaux scolaires ne diffèrent pas beaucoup. Enfin, notre étude permet de constater que les élèves utilisent les significations de la fraction les plus fréquemment présentes dans les manuels scolaires, cela nous donne un éclairage sur l’objet de l’influence de l’enseignement des fractions sur l’apprentissage des élèves.Afin de connaître les conceptions pédagogiques et épistémologiques des enseignants sur leur manière d’aborder l’enseignement de la fraction, nous avons construit les données au moyen d’une enquête par questionnaire auprès de 8 enseignants. Les réponses à ce questionnaire ont été analysées suivant deux perspectives, pédagogique et mathématique..... / This study concerns the fraction mathematical concept, mainly in its teaching-learning in the cycle 3 of French primary school. This concept is often difficult to be understood by pupils; it is formally introduced in the CM1 class of the cycle 3 in primary school.The object of this research was, firstly, the study of fractions’ teaching. To do that, we analyzed learning situations that offer activities bearing on fractions in five math textbooks of CM1 and five math textbooks of CM2, all from the same collection ; the goal is to know the different meanings of the fraction present in these books.In a second time, the object of this research was to find out what pupils remain after they studied fractions. For that, a sample of 275 subjects, 160 from CM1 and 115 from CM2, answered to a written questionnaire bearing on fractions. The goal is to study conceptions and representations that pupils have in respect of the concept of fraction, particularly in respect of different meanings of fraction given by these pupils.In a third time, we wanted to know the opinions of a few teachers about the way in which they approach fractions at school. To do that, 8 teachers among the 12 teachers of the classes concerned participated in the study.The analysis conducted on the books was made with the help of an analysis grid; the results of this analysis point out that the activities or learning situations offered in selected books are not equally distributed between the various meanings of fraction.Moreover, the most present meanings of fraction in CM1 books through the activities analyzed are respectively the following: Part of a whole, Measurement and Number; in CM2 books, the most present meanings are respectively the following: Number, Part of a whole and Measurement. However, the activities related to the other meanings are generally present, but with a reduced frequency.To treat fractions’ learning by pupils, the analysis was made around of the knowledge and the representations of the pupils of CM1 and CM2 relative to different meanings of fraction. This analysis, performed on the pupils' answers on the questionnaire, shows that the meaning of fraction the most used by the students of CM1 and CM2, is that of Part of a whole (continuous quantity). The meanings Number, Measure, Part of a whole (discrete quantity) and Number on a number line are present in pupils' answers. However, the other meanings are those who are the less used by the pupils. Moreover, in regards to the manifested meanings of fraction, pupils of both school levels do not differ much. Finally, our study shows that pupils use the most fraction’s meanings found in books. It gives us a light on the subject of the influence of fractions’ teaching in pupils’ training.To know the epistemological and pedagogical conceptions of teachers in their approach to fraction’s teaching, we built the data by a sample survey with 8 teachers. The answers were analyzed using two perspectives, pedagogic and mathematic. For the pedagogical character analysis, a grid was built around the privileged modes of representation by the teachers and around the respective roles reserved to teacher and pupils. In parallel, we verified the mathematical value of the answers provided by the teachers. To introduce the concept of fraction, the teachers say that they give a large place to concrete or graphical representations. Also, the teachers have an important role throughout teaching and learning approaches.
12

Development of the rat mesentery culture model for the multi-system investigation of microvascular network growth

January 2019 (has links)
archives@tulane.edu / Models that mimic angiogenesis are extremely valuable for elucidating underlining mechanisms and pre-clinical development of therapies. Angiogenesis, defined as the growth of new blood vessels from preexisting vessels, is a multi-cellular process that involves the temporal and spatial coordination between endothelial cells, pericytes, nerves, growth factors, and macrophages. A need exists for biomimetic models that bridge the gap between the mechanistic control of in vitro constructs and the multi-system physiological environment of in vivo models. To meet this need our lab has introduced the rat mesentery culture model as top down approach with intact microvascular networks and a nearly two-dimensional view. Previous development of the model has proven its time-lapse, angiogenic, and lymphangiogenic capabilities. The goal of this work is to advance the model to include the maintenance of peripheral nerves in culture and develop it as a platform for aging and cell therapy studies. The first aim of this study was to expand the rat mesentery culture model to maintain nerves and the spatiotemporal relationship between nerves and blood vessels in culture. We developed a nerve culture media to prevent regression of nerves. Nerve alignment was maintained at the network feeding arteriole and capillary plexus levels. We further demonstrated the presence of neurotransmitter precursors was preserved. We demonstrate for the first time the ability to maintain adult peripheral nerves in an ex vivo model. For the second aim of this study, we developed an aging rat mesentery culture model as a basis for investigating differences in angiogenesis across age groups. We demonstrated that impaired angiogenesis associated with advanced age could be recovered to adult-like levels with serum and individual growth factor stimulation. The discovery of increased vascular island frequency in aged tissues reveals that the method of angiogenesis for older networks can differ. These results establish the rat mesentery culture model as a method for studying aging effect on angiogenesis. The objective of the third aim was to demonstrate the capability of the rat mesentery culture model to study stromal vascular fraction therapy. We developed a protocol to isolate the SVF from adipose tissue and transplant onto the mesentery. We identified unique patterns of vasculogenesis and increased vascular coverage. We confirmed that this increase in vascular area was a combination of the vasculogenesis of SVF, proangiogenic effect on host vessels, and incorporation of SVF into the growing host vessels. We used the aging model in developed in the second aim to show that adult SVF on adult tissue has the greatest therapeutic potential. These results display the investigative potential of the rat mesentery culture model in cell therapy research. This work establishes for the first time, to the best of our knowledge, an ex vivo model capable of maintaining adult peripheral nerves. We demonstrate that angiogenesis can be rescued in aging scenarios. The results, for the first time, reveal the effect that SVF therapy has on preexisting networks as well as how it integrates during microvascular remodeling. / 1 / Nicholas Hodges
13

Understanding fractional equivalence and the differentiated effects on operations with fractions

Naiser, Emilie Ann 17 February 2005 (has links)
This study compared two representations for teaching fraction equivalence. It traced the implications of both representations on the student’s comprehension of fractions as well as their ability to perform operations with fractions. The participants in the study included 65 sixth grade students in three extant classrooms. Two classes were instructed using the textbook representation while the third class received instruction using a representation presented by Van de Walle and recommended by the National Council for Teaching Mathematics. Data were collected from pre-tests, post-tests, student work samples, field notes and a semi-structured interview. Qualitative analyses were used to analyze the data. Items were coded for procedural and conceptual understanding and categorized into levels of proficiency. Additionally, items involving operations with fractions were coded for error patterns. Conclusions were drawn about how the different representations affected student comprehension and faculty with fractions.
14

Fraction Multiplication and Division Image Change in Pre-Service Elementary Teachers

Cluff, Jennifer J. 11 July 2005 (has links) (PDF)
This study investigated three pre-service elementary teachers' understanding of fractions and fraction multiplication and division. The motivation for this study was lack of conceptual understanding of fractions and fraction multiplication and division. Pre-service elementary teachers were chosen because teachers are the conduit of information for their students. The subjects were followed through the fractions unit in a mathematics methods course for pre-service elementary teachers at Brigham Young University. Each subject volunteered to participate and were interviewed and videotaped throughout the study, and they also provided copies of all work done in the fractions unit in the course. The data is presented as three case studies, each beginning with a discussion of the subject's math history and prior understanding of fractions. Then the case studies discuss the subject's change in understanding of fractions, fraction multiplication, and fraction division. Finally, at the end of each case study, a discussion of the subject's conceptual understanding is discussed. Each participant showed a deepened conceptual understanding of fractions, fraction multiplication, and fraction division. The subjects' prior knowledge of fractions and fraction multiplication and division did affect their growth of understanding. Each participant had unique levels of growth and inhibitors to growth of understanding. At the times of most growth of understanding, the subjects' inhibitors of growth were also the most evident.
15

Modélisation des transferts de pesticides à l'échelle des bassins versants en période de crue / Modelling pesticide transfers at catchment scale during flood events

Boithias, Laurie 04 April 2012 (has links)
Les concentrations élevées en pesticides dans les eaux de surface drainant des bassins versants agricoles sont devenues une préoccupation majeure en Europe depuis une cinquantaine d'années. Les pesticides sont transférés dans l'environnement par différentes voies (le ruissellement de surface et de sub-surface, le flux de nappe), soit en solution soit adsorbés aux particules de sol en suspension dans l'eau. Les eaux de ruissellement et de percolation entraînent avec elles des charges de contaminants dont les concentrations en solution peuvent s'avérer toxiques pour la faune et la flore aquatique et rendre l'eau impropre à la consommation humaine si le réseau de drainage est une source de captage pour l'alimentation en eau potable. Les crues constituent donc des événements hydrologiques de première importance dans la contamination des eaux continentales par les pesticides. Les objectifs de cette thèse ont été de (1) caractériser, à l'aide d'un modèle agro-hydrologique, la dynamique des transferts de pesticides à l'échelle du bassin versant dans une région agricole, notamment en période de crue ; (2) identifier les facteurs de contrôle du transfert de pesticides et (3) améliorer, le cas échéant, les équations formalisées dans le modèle. Deux approches ont été menées de front afin de répondre aux questions posées : l'analyse de données mesurées et modélisées sur le bassin versant agricole de la Save (sud-ouest de la France). Une étude de faisabilité réalisée en préliminaire a montré que le modèle Soil and Water Assessment Tool (SWAT - Arnold et al., 1998) était adapté à la modélisation du transfert de pesticides, dans les phases dissoute et particulaire, à l'échelle du bassin versant. L'hydrologie et les concentrations à l'exutoire des phases dissoute et particulaire (respectivement les nitrates et les matières en suspension) ont été calibrées. Les voies privilégiées de transfert des pesticides en fonction des conditions hydrologiques ont été identifiées. La modélisation a ensuite été mise en œuvre avec des itinéraires techniques plus détaillés en entrée du modèle et des mesures sub-journalières de pesticides en crue. Les différentes voies de transfert des pesticides dans les deux phases, ainsi que leurs facteurs de contrôle environnementaux, ont été étudiés. Deux facteurs de contrôle, respectivement dépendant des pratiques agricoles (la date d'application des pesticides, qui est un facteur anthropique) et intrinsèque aux molécules de pesticides (le coefficient Kd de partition entre phases dissoute et particulaire, qui est un facteur physico-chimique) ont été abordés plus en détail. Le rôle de la typologie du bassin versant sur les transferts est discuté. Des cartes de risque de contamination des eaux de surface par les pesticides sont présentées pour le bassin de la Save. Dans la perspective d'améliorer le formalisme des modèles de transfert des pesticides, une équation qui relie le coefficient Kd au coefficient de distribution octanol/eau Kow et à la concentration en matières en suspension a été proposée. / Rising pesticide levels in streams draining intensively managed agricultural land has become a widespread problem throughout Europe in recent decades. Pesticides are transferred into the environment through various pathways (surface and sub-surface runoff, groundwater return flow), either in solution or sorbed onto particles. Runoff and percolating water carry contaminants loads which concentrations in solution may be harmful to terrestrial and aquatic ecosystems rendering water unfit to human consumption if the draining network is a source for drinking water. Floods are hydrological events of major importance in continental waters contamination by pesticides. The objectives of this PhD thesis were (1) to characterise pesticides transfer dynamics at catchment scale in an agricultural area during floods; (2) to identify the factors controlling pesticides transfer and (3) to improve modelling by changing formalism with more suitable equations. Two approaches were set up: analysing both measured and simulated data sets, stemming from the River Save catchment (south-western France). A preliminary feasibility study showed that the Soil and Water Assessment Tool (SWAT - Arnold et al., 1998) was adapted for pesticides transfer modelling in both dissolved and sorbed phases, at catchment scale. Water discharge, dissolved and sorbed phases (respectively nitrate and suspended sediments) were calibrated. Pesticides transfer preferred pathways depending on hydrological conditions were identified. Modelling was then carried on more detailed management practices as input and on sub-daily pesticides concentration measurements during flood events. The various transfer pathways in both phases together with the environmental controlling factors were assessed. At last, two controlling factors, respectively depending on management practices (application date, an anthropogenic factor) and on an intrinsic pesticide molecule property (the partition coefficient Kd which is a physico-chemical factor) were studied. The role of catchment typology was discussed. Surface water contamination risk maps were drawn on Save catchment. In order to improve the formalism of pesticide transfer models, an equation was proposed that relates Kd to the octanol/water partition coefficient Kow and to suspended matter concentration.
16

An Investigation of Conceptual Knowledge: Urban African American Middle School Students' Use of Fraction Representations and Fraction Computations in Performance-Based Tasks

Canterbury, Sandra Ann 03 July 2007 (has links)
A relatively large number of 8th-grade public middle school students in the United States, particularly in urban communities, are not performing at acceptable levels in mathematics. One concept that poses significant difficulty for these students and negatively affects their overall mathematics achievement is fractions. Many researchers have attributed these difficulties primarily to traditional fraction instruction that emphasizes procedural rather than conceptual knowledge. Therefore this study was designed to investigate how students use their computational and conceptual knowledge and fraction representations to solve fraction-related performance-based mathematical tasks. Social constructivism was used as the theoretical framework in examining conceptual knowledge related to learning fractions. This qualitative study was implemented in an urban middle school in the southeast. It involved an initial sample of 37, 8th-grade, African American pre-algebra students who completed a fraction interest questionnaire and two fraction pretests. During the implementation period, 34 students in the researcher’s pre-algebra class completed three performance-based tasks, three reflection logs, and participated in an interview after completing each task. Of the 34 students who completed all tasks, three were purposefully selected as the informants for the study. In addition, observations, field notes, and artifacts (student work) were utilized to facilitate triangulation of the data. The findings of the study indicated the informants could compute fractions with an average of 85% of mastery but could conceptualize fractions only to a small extent. This validated prior findings and led to the conclusion that student deficiency with fractions results primarily from their level of conceptual knowledge. In the investigation of the ways in which 8th-grade students use fraction representations, this study found the informants used representations to develop a visual map of their mathematical thinking and reasoning and to check the accuracy of their computations. Therefore, this study suggests, when students’ mathematical learning experiences relative to fractions have not emphasized the use of representations to develop conceptual knowledge, they may not be comfortable with the accuracy of the solutions demonstrated in their fractions models.
17

Metabolic abnormalities in patients with chronic heart failure : assessment of cytokines, endotoxin, pro-oxidant substrates and exercise training

Niebauer, Josef January 1999 (has links)
No description available.
18

A study of directionally solidified Rene 80 subjected to short-term overtemperature

Smart, Heather 29 March 2017 (has links)
Effects of short-term overtemperature on Rene 80 DS were studied using Gleeble thermo-mechanical simulation apparatus. Volume fraction of gamma prime to gamma matrix was quantified and used to assess the effects of time, temperature and stress. Volume fraction was found to decrease with increasing temperature and time. Dissolution was found to occur through both solid and liquid state dissolution. Application of tensile stress was found to influence dissolution behaviour of gamma prime. / May 2017
19

Chemical Composition and Nutrient Profile of the Low Molecular Weight Fraction of Bovine Colostrum

Christiansen, Scott 15 June 2010 (has links)
Bovine colostrum collected within 12h of parturition was de-fatted, de-caseinated, and ultrafiltered (UF) using a 5 kDa cut-off membrane; the resulting UF permeate was freeze dried to create a powder with possible use as a functional food ingredient. Samples representative of five lots of this powdered “colostrum low molecular weight fraction” (CLMWF) were analyzed for chemical composition and nutrient profile. The average contents of fat, moisture, and ash were 0.6%, 1.7%, and 8.3% w/w, respectively. Carbohydrate analysis showed an average of 58.2% w/w lactose monohydrate with no monosaccharides, other disaccharides, trioses, or tetroses detected. The total nitrogen content averaged 1.13% w/w, with 74% of this in the non-protein nitrogen fraction, producing a true protein content of 1.9% w/w. A significant mass fraction of the material (~29% w/w) remains to be characterized. The CLMWF powders were found to contain significant quantities of the minerals calcium (average 870 mg/100g), magnesium, (311 mg/100g), phosphorus (1473 mg/100g), potassium (1705 mg/100g) and sodium (690 mg/100g), the nutrients taurine (average 26.5 mg/100g), L-carnitine (40.5 mg/100g), thiamine (648 mcg/100g) and riboflavin (6991 mcg/100g), and the nucleos(t)ides uridine (55.2 mg/100g) and 5’UMP (18.8 mg/100g), cytidine (3.33 mg/100g) and 5’CMP (4.83 mg/100g) and guanosine (3.45 mg/100g) and 5’GMP (3.57 mg/100g).
20

Dynamics and Transfers in two phase flows with phase change in normal and microgravity conditions

Trejo Peimbert, Esli 22 November 2018 (has links) (PDF)
Two-phase flows with or without phase change are present in terrestrial and space applications like thermal control of satellites, propellant supply for launchers, and waste water treatment for space exploration missions. Flow boiling experiment with HFE7000 were conducted in a heated tube in vertical upward flow on ground and in microgravity conditions to collect data on flow patterns, pressure drops, heat transfers, void fraction. Void fraction measurements allowed to measure mean gas velocity and the liquid film thickness in annular flow. In microgravity condition, the liquid film thickness and the interfacial shear stress are significantly lower than in normal gravity. A detail analysis of the film structure was performed by image processing. The impact of gravity and liquid and vapour superficial velocities on the disturbance waves velocities and frequencies was investigated. Two different measurement techniques were used and compared to determine the heat transfer coefficient. For quality values greater than 0.2, HTC is not sensitive to gravity and is in good agreement with classical correlations of the literature. For qualities smaller than 0.1, in the subcooled nucleate boiling regime HTC is significantly smaller in microgravityconditions.

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