Doctor of Philosophy

dissertationThis study examined patterns of change in the science teaching practice, beliefs, and content knowledge of 15 upper-elementary teachers from three Title I schools during their participation in a yearlong, reform-based science professional development program and during the year following the program. Further, this study sought to understand the school factors that hindered or supported these patterns in the year following the program. This study responds to calls for research on understanding teachers' continued learning within the context; of their classroom and school environment following professional development experiences. A mixed model design, integrating quantitative and qualitative data, was used. Quantitative data were used to examine changes in teachers' practices, beliefs, and physical science content knowledge across the 2 study years. Qualitative data were used to corroborate this data and provide additional insights into observed patterns. Both data types were used collaboratively to understand the barriers and supports in teachers' schools to their continued learning following professional development. The study findings indicated that scores in all three measures increased a statistically significant amount in Year 1. Scores continued to increase in Year 2, but only content knowledge scores increased significantly. Qualitative data corroborated the survey findings in teachers' beliefs and practices. A combination of school- and individual-level factors impacted the Year 2 changes. School-level factors were: (a) supportive same-grade teams and/or a mentor who advocated inquiry science and prioritized science as a subject, (b) principal prioritization of science, and (c) easy access to and training in the use of relevant materials. The individual-level factor was teachers' degree of willingness and readiness to change their beliefs in fundamental ways. The study results suggested that professional development, along with school and personal factors, impacted teacher change. These findings inform the education literature bases as well as professional development providers and school administrators about the types of support and resources that teachers require in the school context; in order to maintain or enhance professional development experiences. The decisions teachers make about whether and how to implement and sustain new practices, and the reasons for these decisions, ultimately determine the success of reform-based professional development in science education

A study of the structure and properties of certain aluminides

Experimental data are presented on the structure and heat resistance of the aluminides ZrAl3, Fe2Al5 and Co2Al9, considering sp. wt., type of combination, and resistance to oxidation at high temperatures. Co2Al9 possesses a relatively high heat of formation, attributed to its high heat resistance characteristics

Influence of the Outer Surface Layers of Crystals on the X-Ray Diffraction Intensity of Basal Reflections

International audienceThis study presents a mathematical formalism describing diffraction effects from periodic and mixed-layer minerals in which the outer surface layers of crystals differ from layers forming the core of the crystals. XRD patterns calculated for structure models of chlorite and irregular chlorite-smectites terminated on both sides of the crystals by either brucite-like or 2:1 layers show the strong influence that different outer surface layers make on the distribution of basal reflection intensities. Simulation of the experimental XRD patterns from two chlorite samples having different Fe-content shows that in these two samples the chlorite crystals were terminated by brucite-like layers on both sides. In contrast, crystals in a corrensite sample were terminated by water molecules and exchangeable cations. The nature of diffraction effects due to outer surface layers is discussed

Structure of birnessite obtained from decomposition of permanganate under soft hydrothermal conditions. I. Chemical and structural evolution as a function of temperature.

International audienceThe structure of a synthetic K-rich birnessite (KBi) prepared by hydrothermally reacting (4 days at 170°C) a finely ground KMnO4 powder in acidified water was determined. At room temperature the structure of KBi corresponds to a 3R - polytype which can be described as using the close-packing formalism. Assuming an orthogonal base-centered unit cell, KBi has a = b√3 = 4.923 A, b = 2.845 A, γ = 90° and c = 21.492 A. The layer charge deficit originates exclusively from the presence of vacant layer sites as only Mn AbC...BcACaBAbC c' b' a' c' a' b' 4+ cations are present in the octahedral layers, and the following structural formula can be proposed

Structure of Synthetic K-rich Birnessites Obtained by HighTemperature Decomposition of KMnO4. 2 Phase and Structural Heterogeneities

International audienceSynthetic K-rich birnessites (KBi) were prepared from the thermal decomposition of a fine-grained KMnO4 powder heated in air atmosphere at temperatures ranging from 2001000°C. The qualitative analysis of powder X-ray diffraction (XRD) patterns reveals a complex range of structural transformations from one metastable phase to the other, often through intermediate mixed-layer structures (MLSs). Phase and structural heterogeneities of KBi samples synthesized at 700°C, 800°C and 1000°C (referred to as KBi7, KBi8h and KBi10h) have been studied in details by chemical and thermal analysis and by simulation of the experimental powder XRD patterns. Two-layer orthogonal (2O), and hexagonal (2H) as well as three-layer rhombohedral (3R) polytypes were identified in these samples. The 2O structure consists of vacancy-free layers and their orthogonal symmetry is linked to the high content of layer Mn 3+ cations and to the unique azimuthal orientation of Mn3+ octahedra which are elongated because of Jahn-Teller distortion. In the 2H and 3R polytypes, the layers have a hexagonal symmetry as they contain only Mn 4+- and vacant octahedra. As a result, their interlayers have a heterogeneous cation composition, because of the migration of Mn 3+ from the layers to the interlayers. In addition to the periodic KBi polytypes, KBi7 and KBi8h contain MLSs in which layer pairs of the 2H polytype are interstratified at random with those of the 3R or of the 2O polytype. Interstratification of incommensurate 2O and 2H structural fragments leads to peculiar diffraction effects and represents a new type of structural disorder in birnessites. The increase of temperature from 700°C to 1000°C is associated with the replacement of 3R/2H, 2H, and 2O/2H mixed-layered structures by the more stable 2O polytype. KBi10h consists of a mixture of a minor 2H phase with three 2O varieties having slightly different layer unit-cell parameters. This phase heterogeneity results from the partial disorder in the orientation of Mn 3+ octahedra. The average structural formulae, K + 0.265Mn 3+ 0.145(Mn 4+ 0.82

Service Learning as an Instructional Strategy for the Preparation of Teachers

This paper addresses the strengths and challenges of university-based service learning projects, using preservice elementary teachers in an undergraduate social studies methods course as a model for implementing service learning in university courses. The goal of the project was to provide future teachers with the motivation and experience in facilitating service learning projects as a means of promoting student equity, social responsibility, and social justice. The carryover of this attitude and response to the first year of the teaching career is considered. Three cases of teachers are presented to share findings that focus on issues of context, teacher characteristics, understanding of the service learning pedagogy, and the responsiveness of students to the approach. Implications and recommendations for including service learning pedagogy in university courses are discussed

Investigation of smectite hydration properties by modeling experimental X-ray diffraction patterns. Part I. Montmorillonite hydration properties.

Hydration of the <1 μm size fraction of SWy-1 source clay (low-charge montmorillonite) was studied by modeling of X-ray diffraction (XRD) patterns recorded under controlled relative humidity (RH) conditions on Li-, Na-, K-, Mg-, Ca-, and Sr saturated specimens. The quantitative description of smectite hydration, based on the relative proportions of different layer types derived from the fitting of experimental XRD patterns, was consistent with previous reports of smectite hydration. However, the coexistence of smectite layer types exhibiting contrasting hydration states was systematically observed, and heterogeneity rather than homogeneity seems to be the rule for smectite hydration. This heterogeneity can be characterized qualitatively using the standard deviation of the departure from rationality of the 00l reflection series (ξ), which is systematically larger than 0.4 A when the prevailing layer type accounts for ~70% or less of the total layers (~25 of XRD patterns examined). In addition, hydration heterogeneities are not randomly distributed within smectite crystallites, and models describing these complex structures involve two distinct contributions, each containing different layer types that are randomly interstratifed. As a result, the different layer types are partially segregated in the sample. However, these two contributions do not imply the actual presence of two populations of particles in the sample. XRD profile modeling has allowed also the refinement of structural parameters, such as the location of interlayer species and the layer thickness corresponding to the different layer types, for all interlayer cations and RH values. From the observed dependence of the latter parameter on the cation ionic potential ( r/v , v = cation valency and r = ionic radius) and on RH, the following equations were derived: 36 37 Layer thickness (1W) = 12.556 + 0.3525 × ( r/v - 0.241) × (v × RH - 0.979) Layer thickness (2W) = 15.592 + 0.6472 × ( 38 r/v - 0.839) × (v × RH - 1.412) which allow the quantification of the increase of layer thickness with increasing RH for both 1W (one-water) and 2W (two-water) layers. In addition for 2W layers interlayer H2O molecules are probably distributed as a unique plane on each side of the central interlayer cation. This plane of H2O molecules is located at ~1.20 A from the central interlayer cation along the c* axis

Service Learning as an Instructional Strategy for the Preparation of Teachers

This paper addresses the strengths and challenges of university-based service learning projects, using preservice elementary teachers in an undergraduate social studies methods course as a model for implementing service learning in university courses. The goal of the project was to provide future teachers with the motivation and experience in facilitating service learning projects as a means of promoting student equity, social responsibility, and social justice. The carryover of this attitude and response to the first year of the teaching career is considered. Three cases of teachers are presented to share findings that focus on issues of context, teacher characteristics, understanding of the service learning pedagogy, and the responsiveness of students to the approach. Implications and recommendations for including service learning pedagogy in university courses are discussed

Diagenetic smectite-to-illite transition in clay-rich sediments: A reappraisal of X-ray diffraction results using the multi-specimen method

International audienceSmectite illitization is a common mineralogical reaction occurring during the burial diagenesis of clay-rich sediments and shales, and has thus attracted sustained interest over the last fifty years. Prior studies have concluded that smectite illitization proceeds through a steady set of homogeneous reactions involving intermediate mixed layers of varying compositions. In these intermediate structures, illite and smectite, or, more generally, expandable layers (I and Exp layers, respectively) coexist among the same crystallites giving rise to non-periodic structures (I-Exp) characterized by specific diffraction effects. Consistent with this model, reaction progress was characterized by the simultaneous increase in the illite content in I-Exp and in their stacking order leading to the following mineralogical sequence: smectite → randomly interstratified I-Exp with high smectite contents (> 50% Exp layers) → ordered I-Exp with high illite contents (> 50% I layers) → illite. Although reaction mechanisms have been extensively debated, this structural characterization has not been challenged, possibly due to a methodological bias. In the present study, X-ray diffraction patterns typical of the diagenetic illitization of smectite are interpreted using modern approaches involving profile fitting (multi-specimen method). Novel insights into the structure of intermediate reaction products are thus obtained. In particular, original clay parageneses are described including the systematic presence of illite, kaolinite, chlorite and a mixed layer containing kaolinite and expandable layers (K-Exp). In contrast to previous descriptions, the early stages of smectite illitization are characterized by the coexistence of discrete smectite and of a randomly interstratified I-Exp with a high content of illite layers (>50% I layers). Both the smectite and the I-Exp are authigenic and form under shallow burial, that is at low temperature conditions. With increasing burial depth, the relative proportion of I-Exp increases, essentially at the expense of discrete smectite, and the composition of I-Exp becomes slightly more illitic. In the second stage of smectite illitization, two illite-containing mixed layers are observed. They result from two parallel reaction mechanisms affecting the randomly interstratified I-Exp present in the shallow section of the series. The first reaction implies the dissolution of this randomly interstratified I-Exp and leads to the crystallization of an ordered I-Exp without significant illitization, possibly because of the low K-availability. The second reaction affecting the randomly interstratified I-Exp implies the growth of trioctahedral (Mg, Al) hydroxide sheets in Exp interlayers, thus developing di-trioctahedral chlorite layers (Ch layers) in the initial I-Exp to form an I-Exp-Ch. A layer-by-layer mechanism is hypothesized for this reaction. In this scheme, Mg cations released by the dissolution-recrystallization reaction of I-Exp likely represent the source of Mg for the formation of brucite-like sheets in expandable interlayers, and thus of the I-Exp-Ch. The reported structural characterization of smectite illitization intermediate products contradicts the conventional wisdom of a homogeneous reaction through a series of pure mixed layers of variable composition. In contrast, the coexistence of different phases implies a heterogeneous reaction via a sequence of intermediate phases and requires reassessing the reaction mechanisms proposed in the literature. The compositional range (relative proportion of the different layer types) of these phases is limited and smectite illitization proceeds essentially as relative proportions of the different phases vary. In addition, reaction kinetics and stability of the different intermediate products also need to be reconsidered

Structure of the Synthetic K-rich Phyllomanganate Birnessite Obtained by High-Temperature Decomposition of KMnO4. Substructures of K-rich Birnessite from 1000°C Experiment

International audienceThe structure of a synthetic potassium-rich birnessite prepared from the thermal decomposition of KMnO4 at 1000°C in air has been refined by Rietveld analysis of the powder X-ray diffraction (XRD) data, and the structure model shown to be consistent with extended X-ray absorption fine structure data. K-rich birnessite structure is a two-layer orthorhombic polytype (2O) with unit-cell parameters a = 5.1554(3) Ä, b = 2.8460(1) Ä, c = 14.088(1) Ä, α = β = γ = 90°, a/b = √3.281, and was refined in the Ccmm space group. The structure is characterized by the regular alternation of octahedral layers rotated with respect to each other by 180°. Octahedral layers are essentially devoid of vacant sites, the presence of 0.25 Mn 3+ layer cations within these layers being the main source of their deficit of charge, which is compensated for by interlayer K + cations. Mn3+ octahedra, which are distorted by the Jahn-Teller effect, are systematically elongated along the a axis (cooperative Jahn-Teller effect) to minimize steric strains, thus yielding an orthogonal layer symmetry. In addition, Mn 3+ octahedra are segregated in Mn3+-rich rows parallel to the b axis that alternate with two Mn 4+ rows according to the sequence ...-Mn3+-Mn4+-Mn4+-Mn3+-... along the a direction, thus leading to a A = 3a super-periodicity. At 350°C, the structure partially collapses due to the departure of interlayer H2O molecules and undergoes a reversible 2O-to-2H phase transition. This transition results from the relaxation of the cooperative Jahn-Teller effect, that is from the random orientation of elongated Mn 3+ octahedra