Online Knowledge Communities as Student-Centered Open Learning Environments: How Likely Will They Be to Integrate Learners as New Members?

Using online knowledge communities (OKCs) from the Internet as studentcentered, open learning environments (SCOLEs) poses the question how likely these communities will be to integrate learners as new members. This premise of learning in SCOLEs is analyzed in the current study. Based on the approaches of voices interanimation and polyphony, a natural language processing tool was employed for dialog analysis in integrative vs. non-integrative blog-based OKCs. Three dialog dimensions were identified: participants’ individual content-oriented contribution, social contribution, and their position within the social network. Hierarchical clusters built upon these dimensions reflect sociocognitive structures including central, regular and peripheral OKC members. OKCs with a stronger layer of regular members appear more likely to integrate new members, whereas OKCs with a stronger layer of peripheral members appear less likely to do so. Consequently, the study suggests an automated prediction method of OKC integrativity that may sustain the educational use of OKCs

Plagioclase preferred orientation in layered mylonites : evaluation of flow laws for the lower crust

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2008We evaluate the applicability of plagioclase and gabbro flow laws by comparing predicted and observed deformation mechanisms in gabbroic shear zones. Gabbros and layered gabbro mylonites were collected from the Southwest Indian Ridge (SWIR), ODP Hole 735B. Deformation temperatures are constrained by two-pyroxene thermometry, stress is estimated from grain size, and deformation mechanisms are analyzed by microstructure and the presence or absence of a lattice preferred orientation (LPO). Our analyses indicate that mylonite layers deformed at a strain rate in the range of 10-12 to 10- 11 s-1, while coarse-grained gabbro deformed at a strain rate of approximately 10-14 to 10- 13 s-1. Plagioclase in pure plagioclase mylonite layers exhibit strong LPOs indicating they deform by dislocation creep. Plagioclase grain size in mixed plagioclase-pyroxene mylonite layers is finer than in pure plagioclase layers, and depends on the size and proportion of pyroxenes. Progressive mixing of pyroxene and plagioclase within gabbro mylonite layers is accompanied by weakening of the LPO indicating that phase mixing promotes a transition to diffusion creep processes that involve grain boundary sliding. Our results indicate that experimental flow laws are accurate at geologic strain rates, although the strain rate for diffusion creep of fine-grained gabbro may be underestimated. At the conditions estimated for the SWIR crust, our calculations suggest that strain localization leads to a factor of two to four decrease in lower crustal viscosity. Even so, the viscosity of lower gabbroic crust is predicted to be similar to that of dry upper mantle

Newcomer Integration in Online Knowledge Building Communities: Automated Dialogue Analysis in Integrative vs. Non-Integrative Blogger Communities

Online knowledge building communities (OKBC) reunite participants engaged in collaborative discourse. OKBCs can be made „smart“ by adding tools that predict how likely an OKBC is to integrate newcomers in existing dialogues and socio-cognitive structures. Starting from Bakhtin’s dialogical approach and polyphony theory, and building on the concept of inter- animation of voices, this study explores the relationship between newcomer integration and dialogue quality in OKBCs. The automated analysis tool “Important Moments” was employed to compare two dialogues, from an integrative and from a non-integrative blog-based OKBC. In the former, the concepts, lexical chains and inter-animation moments occurred more frequently than in the latter. Also, newcomer comments were linked to less lexical chains in the integrative community than in the non-integrative OKBC. These findings suggest close relationships between dialogue quality and newcomer integration, which can be used for designing smart OKBCs

Evolution of a polymineralic mantle shear zone and the role of second phases in the localization of deformation

The influence of second phases (e.g., pyroxenes) on olivine grain size was studied by quantitative microfabric analyses of samples of the Hilti massif mantle shear zone (Semail ophiolite, Oman). The microstructures range from porphyroclastic tectonites to ultramylonites, from outside to the center of the shear zone. Starting at conditions of ridge-related flow, they formed under continuous cooling leading to progressive strain localization. The dependence of the average olivine grain size on the second-phase content can be split into a second-phase controlled and a dynamic recrystallization-controlled field. In the former, the olivine grain size is related to the ratio between the second-phase grain size and volume fraction (Zener parameter). In the latter, dynamic recrystallization manifested by a balance between grain growth and grain size reduction processes yields a stable olivine grain size. In both fields the average olivine and second-phase grain size decreases with decreasing temperature. Combining the microstructural information with deformation mechanism maps suggests that the porphyroclastic tectonites (similar to 1100 degrees C) and mylonites (similar to 800 degrees C) formed under the predominance of dislocation creep. Since olivine-rich layers are intercalated with layer parallel, polymineralic bands in the mylonites, nearly equiviscous conditions can be assumed. In the ultramylonites, diffusion creep represents the major deformation mechanism in the polymineralic layers. It is this switch in deformation mechanism from dislocation creep to diffusion creep that forces strain to localize in the fine-grained polymineralic domains at low temperatures (<similar to 700 degrees C), underlining the role of the second phases on strain localization in cooling mantle rocks

Brittle and semibrittle creep of Tavel limestone deformed at room temperature

Deformation and failure mode of carbonate rocks depend on the confining pressure. In this study, the mechanical behavior of a limestone with an initial porosity of 14.7% is investigated at constant stress. At confining pressures below 55 MPa, dilatancy associated with microfracturing occurs during constant stress steps, ultimately leading to failure, similar to creep in other brittle media. At confining pressures higher than 55 MPa, depending on applied differential stress, inelastic compaction occurs, accommodated by crystal plasticity and characterized by constant ultrasonic wave velocities, or dilatancy resulting from nucleation and propagation of cracks due to local stress concentrations associated with dislocation pileups, ultimately causing failure. Strain rates during secondary creep preceding dilative brittle failure are sensitive to stress, while rates during compactive creep exhibit an insensitivity to stress indicative of the operation of crystal plasticity, in agreement with elastic wave velocity evolution and microstructural observations