311 research outputs found
Evidence of dynamic recrystallization in polar firn
No full textMicrostructural analyses have been performed on polar firn from the European Project for Ice Coring in Antarctica drilling site in Dronning Maud Land, Antarctica. The results derived from images of the firn structure in microscopic resolution indicate that dynamic recrystallization is active in firn at all depths, and it dominates the evolution of the microstructure when the firn density exceeds a critical value of 730 kg/m3 (overburden snow load ∼0.2 MPa). At the firn-ice transition (density ∼820 kg/m3) the microstructure is characterized by many small grains and bulged or irregularly shaped grain boundaries. More than half of all grains show subgrain boundaries. Thus, strain-induced boundary migration is an essential feature to describe the irregular grain structure. In agreement with previous studies, significant grain growth has been observed with depth for the largest grains in the samples. However, our microscopic analysis reveals that the grain growth with depth in fact vanishes if all grains larger than 65 μm in diameter are taken into account. This result reflects the fact that the growth of the largest grains is counteracted by grain size reduction by shrinking and subdivision of old grains, as well as production of new grains. Consequently, previous conclusions that grain growth in polar firn is essentially analogous to normal grain growth in metallic and ceramic sinters and that the stored strain energy is small in comparison with grain boundary energy can no longer be supported. Additionally, our observations show that the incipience of dynamic recrystallization in polar ice sheets is not as sensitive to temperature as supposed so far. A discussion of the change of the mean grain size due to the measuring technique is imperative
Subgrain boundaries in Antarctic ice quantified by X-ray Laue diffraction
No full textIce in polar ice sheets undergoes deformation during its flow towards the coast.
Deformation and recrystallization microstructures such as subgrain boundaries can be observed and
recorded using high-resolution light microscopy of sublimation-edged sample surfaces (microstructure
mapping). Subgrain boundaries observed by microstructure mapping reveal characteristic shapes and
arrangements. As these arrangements are related to the basal plane orientation, full crystallographic
orientation measurements are needed for further characterization and interpretation of the subgrain
boundary types. X-ray Laue diffraction measurements validate the sensitivity of different boundary types
with sublimation used by microstructure mapping for the classification. X-ray Laue diffraction provides
misorientation values of all four crystal axes. Line scans across a subgrain boundary pre-located by
microstructure mapping can determine the rotation axis and angle. Together with the orientation of the
subgrain boundary this yields information on the dislocation types. Tilt and twist boundaries composed
of dislocations lying in the basal plane, and tilt boundaries composed of nonbasal dislocations were
found. A statistical analysis shows that nonbasal dislocations play a significant role in the formation of
all subgrain boundaries
Subgrain boundaries in Antarctic ice quantified by X-ray Laue diffraction
No full textIce in polar ice sheets undergoes deformation during its flow towards the coast. Deformation and recrystallization microstructures such as subgrain boundaries can be observed and recorded using high-resolution light microscopy of sublimation-edged sample surfaces (microstructure mapping). Subgrain boundaries observed by microstructure mapping reveal characteristic shapes and arrangements. As these arrangements are related to the basal plane orientation, full crystallographic orientation measurements are needed for further characterization and interpretation of the subgrain boundary types. X-ray Laue diffraction measurements validate the sensitivity of different boundary types with sublimation used by microstructure mapping for the classification. X-ray Laue diffraction provides misorientation values of all four crystal axes. Line scans across a subgrain boundary pre-located by microstructure mapping can determine the rotation axis and angle. Together with the orientation of the subgrain boundary this yields information on the dislocation types. Tilt and twist boundaries composed of dislocations lying in the basal plane, and tilt boundaries composed of nonbasal dislocations were found. A statistical analysis shows that nonbasal dislocations play a significant role in the formation of all subgrain boundaries
Subgrain boundaries and related microstructural features in EDML (Antarctica) deep ice core
No full textSubgrain boundaries revealed as shallow sublimation grooves on ice sample surfaces are a direct and easily observable feature of intracrystalline deformation and recrystallization. Statistical data obtained from the EPICA Dronning Maud Land (EDML) deep ice core drilled in East Antarctica cannot detect a depth region of increased subgrain-boundary formation. Grain-boundary morphologies show a strong influence of internal strain energy on the microstructure at all depths. The data do not support the classical view of a change of dominating recrystallization regimes with depth. Three major types of subgrain boundaries, reflecting high mechanical anisotropy, are specified in combination with crystal-orientation analysis.Deutsche Forschungsgemeinschaft (DFG) [FA 840/1-1]; European Unio
Subgrain boundaries and related microstructural features in EDML (Antarctica) deep ice core
No full textSubgrain boundaries revealed as shallow sublimation grooves on ice sample surfaces are a direct and easily observable feature of intracrystalline deformation and recrystallization. Statistical data obtained from the EPICA Dronning Maud Land (EDML) deep ice core drilled in East Antarctica cannot detect a depth region of increased subgrain-boundary formation. Grain-boundary morphologies show a strong influence of internal strain energy on the microstructure at all depths. The data do not support the classical view of a change of dominating recrystallization regimes with depth. Three major types of subgrain boundaries, reflecting high mechanical anisotropy, are specified in combination with crystal-orientation analysis.Deutsche Forschungsgemeinschaft (DFG) [FA 840/1-1]; European Unio
Author Correction: Reactive astrocytes function as phagocytes after brain ischemia via ABCA1-mediated pathway
No full textAbstractThe original version of this Article contained an error in the spelling of the author Nobuhiko Ohno, which was incorrectly given as Noubuhiko Ohno. This has now been corrected in both the PDF and HTML versions of the Article.</jats:p
Microstructure mapping: a new method for imaging deformation-induced microstructural features of ice on the grain scale
No full textThis work presents a method of mapping deformation-related sublimation patterns, formed on the surface of ice specimens, at microscopic resolution (3-4 gm pixel(-1)). The method is based on the systematic sublimation of a microtomed piece of ice, prepared either as a thick or a thin section. The mapping system consists of an optical microscope, a CCD video camera and a computer-controlled xy-stage. About 1500 images are needed to build a high-resolution mosaic map of a 4.5 x 9 cm section. Mosaics and single images are used to derive a variety of statistical data about air inclusions (air bubbles and air clathrate hydrates), texture (grain size, shape and orientation) and deformation-related features (subgrain boundaries, slip bands, subgrain islands and loops, pinned and bulged grain boundaries). The most common sublimation patterns are described, and their relevance for the deformation of polar ice is briefly discussed
Japanese middle schools' adaptation of the integrated studies: a case study
No full textIn 1998, Education Ministry of Japan announced the enactment of the periods of the Integrated Studies (IS) at all public school levels. The IS is defined as interdisciplinary, project-oriented learning activities which aim to promote students’ problem-solving abilities and self-learning skills. In spite of teachers' active involvement in the development of various educational activities for the periods, research indicated that teachers faced various barriers to implementing the IS. Generally, the middle school teachers were unsupportive to the IS due to their lack of resources for the curriculum development. Despite the constraints, how was the IS implemented in the middle schools? What kind of roles did the IS take in the curriculum? How did the teachers view the constraints to their implementation of the IS?
By taking "adaptation" perspective for educational policy implementation (McLaughlin, 1976b), this study examined the realities of the middle schools' implementation of the IS based on a multiple case study of three middle schools in Osaka. This study analyzed the data from my five months of field research in the schools, which included interviews with the teachers, observation of the teachers' implementation of the IS, survey of the teachers as well as collection of school documents.
The research findings are summarized as following. First, the analysis showed the IS periods assured the room for the schools' autonomous development of projects with specific sociocivic themes and increased the opportunities for various new learning styles (e.g., self-inquiry, presentation, and various hands-on activities). However, a large part of the IS periods was utilized for the schools' existing practices like career guidance or school events reflecting the middle schools' needs on sustaining its traditional curriculum. Consequently, the space for new learning styles was dispersed across the three years' curriculum, and tended to decrease in the higher grade.
Finally, the comparison of the three schools sheds light on the difference of the attitudes to the implementation of the IS across the schools. The analysis attributed this difference to some factors including shared pedagogy of the IS, longitudinal experience of collaboration, organizational context like school-size, and the degree of students' behavioral problems.Ph.D.Includes bibliographical references (p. 221-229)by Nobuhiko Hamamot
Recrystallization Diagram for Polar Ice
No full textIce is the most frequent mineral on the Earth’s surface, however experiences conditions comparable to silicate
minerals at high metamorphic grades. In all natural conditions ice is a hot material with homologous temperatures between 0.9 and 0.7 at least. Under such circumstances recrystallization plays a decisive role in governing the state and thus the behaviour of the material. This has been recognized and interpreted in many ice cores in the last decades (Faria et al. in press a) assigning recrystallization regimes to ice sheet depth ranges. This assignment made use of microstructure observations (mainly grain size) and estimated boundary conditions (temperature and stress/strain amounts) which change systematically with depth. To generalize the use of recrystallization regimes we decouple their occurrence from the ice sheet depth information and connect them directly to the activators and causes: strain rate and temperature (Faria et al. in press b).
References:
Faria, S. H.; Weikusat, I. & Azuma, N. The Microstructure of Polar Ice. Part I: Highlights from ice core research. Journal of Structural Geology , in press a, DOI: 10.1016/j.jsg.2013.09.010
Faria, S. H.; Weikusat, I. & Azuma, N. The Microstructure of Polar Ice. Part II: State of the Art. Journal of
Structural Geology , in press b, DOI: 10.1016/j.jsg.2013.11.00
<Articles PART I : BEYOND THE SELF>Heidegger, Ethics and Ontological Education : A Critical Response to Nobuhiko Itani's Paper 'Beyond the Self'
No full textFirst paragraph: Nobuhiko Itani's paper "'Beyond The Self' as a Goal of Education' (given at a conference held at the Institute of Education, London) marks an attempt to analyse previous theories of what the author calls 'ontological education' and, in so doing, clear the way for a new conception of ontological education that is more attuned to Heidegger's philosophy. During this process Itani makes some strong claims which, in part, derive from his attempt to locate a common ground that links previous Heideggerian contributions to the philosophy of education—he questions the validity of assumptions that make up that common ground. According to Itani such contributions are engaged in the 'deconstruction of education as utility' and 'share the concept of openness to Being itself. It is not so much that Itani disagrees with these aims, but feels that earlier studies suffer by dint of failing to address their 'naïve ethical evaluations'. For Itani, a true ontological education can only take place before/after ethics
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