8,729 research outputs found

    Microstructure and growth of the lenses of schizochroal trilobite eyes

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    Lenses within the schizochroal eyes of phacopine trilobites are made principally of calcite and characterisation of them using light microscopy and high-resolution electron imaging and diffraction has revealed an array of microstructural arrangements that suggest a common original pattern across the suborder. The low convexity lenses of Odontochile hausmanni and Dalmanites sp. contain calcite fibres termed trabeculae. The c axis of trabecular calcite lies parallel to the lens axis, and adjacent trabeculae are distinguished by small differences in their a axis orientations. Despite the common alignment, the boundaries between trabeculae cross-cut the c axis as they fan out towards the lens base. Trabeculae are absent from the lens immediately beneath the visual surface and instead a radial fringe is present and is composed of micrometre-thick sheets of calcite whose c axes are oriented at a low angle to the visual surface. High convexity lenses are more common than those of lower convexity among the species studied, and they have a much thicker radial fringe. Beneath this fringe all of the lens calcite is oriented with its c axis parallel to the lens axis and it lacks trabeculae. We propose that both the high and low convexity lenses formed by rapid growth of calcite from a surface that migrated inwards from the cornea, and they may have had an amorphous calcium carbonate precursor. The trabeculae and radial fringes are unlikely to have had any beneficial effect on the transmission or focusing of light but rather are the outcomes of an elegant solution to the problem of how to construct a biconvex lens from a crystalline solid

    Do We Know What We Know? Self- Assessment Across the Lifespan

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    Self-knowledge can play a critical role in navigating physical, cognitive, and social changes in late life. To protect and preserve one\u27s sense of self against these changes, individuals may engage in self-enhancing and self-serving biases in areas important to self-esteem. The importance attached to these areas may change with age, and self-knowledge of these psychological processes may vary with age. We investigated self-enhancing biases and metacognitive awareness of abilities in adulthood. Participants ranging in age from 20 to 80 completed a series of tests assessing the better than average effect across a variety of age-relevant domains as well as objective memory and intelligence tests. Results yielded an overall better-than-average effect as well as higher positive biases in young, middle-aged, and older adults on age-congruent domains. Younger and older adults were accurate in their assessments of recall ability and processing speed, respectively. Differences between performance predictions and actual performance scores on four cognitive tasks were generally smaller after test than before, suggesting a preservation of monitoring accuracy in late life. Implications for task feedback and training programs for the elderly are discussed as well as the ability for individuals, even in late adulthood, to continue to self-make and grow in self-knowledge

    The Relationship Between Grouping Format Used For Reading Instruction and Fourth Grade Students\u27 Attitudes Toward Reading

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    The purpose of this study was to compare the reading attitude scores of fourth-grade students who are grouped homogeneously for reading instruction to those who are grouped heterogeneously. The null hypothesis stated that there would be no statistically significant differences between the mean reading attitude scores of students from the homogeneous or heterogeneous groups on the Elementary Reading Attitude Survey. The subjects were ninety-six fourth grade students from two different suburban area school districts located in western New York. Heterogeneous grouping was used for reading instruction in one school district while homogeneous grouping was used in the other district. Both school districts had been previously using their current instructional programs for reading, K-4 grades. During the beginning of the third quarter of the 1997-1998 school year, teachers of each classroom administered the Elementary Reading Attitude Survey to their students in accordance with the directions for administration given by the survey developers. These surveys were anonymously completed by the students and returned to the researcher by each teacher. Students were told that only the researcher would see their surveys. The researcher used a t test of independent means to analyze and compare results of the homogeneous reading group and of the heterogeneous reading group. The results showed that there was a significant difference between the mean reading attitude scores of the homogeneous group and the mean attitude scores of the heterogeneous group. The null hypothesis for this study had been rejected

    What are student inservice teachers talking about in their online Communities of Practice?:investigating student inservice teachers’ experiences in a double-layered CoP

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    This qualitative case study is the first phase of a large-scale design-based research project to implement a theoretically derived double-layered CoP model within real-world teacher development practices. The main goal of this first iteration is to evaluate the courses and test and refine the CoP model for future implementations. This paper demonstrates the potential synergies between two major approaches to teacher professional development practices: i) teachers’ CoPs development and ii) online teacher education courses. The double-layered CoP model could provide a practical integration of the two approaches by providing student inservice teachers in an online graduate course with meaningful opportunities to participate in two different teachers’ CoPs: i) an internal course CoP and ii) an external professional CoP. Our analysis of student inservice teachers’ CoPs experiences shows that the two layers of CoPs supported each other iteratively through the course period. Several design considerations for the second iteration of the online course design are also addressed
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