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Several different conceptions of the relationship between learning and development are considered in this article. It is argued that dialectical and ecological developmental orientations might provide a useful basis for synthesizing the contrasting frameworks of the operant, information processing, learning theory, and knowledge acquisition models. (Author/DB)

Atomic structures of Ge25Sb15S60 and Ge35Sb5S60 glasses are investigated in the γ-irradiated and annealed after γ-irradiation states by means of high-energy synchrotron x-ray diffraction technique. The first sharp diffraction peak (FSDP) is detected at around 1.1 Å-1 in the structure factors of both alloys studied. The FSDP position is found to be stable for radiation/annealing treatment of the samples, while the FSDP intensity shows some changes between γ-irradiated and annealed states. The peaks in the pair distribution functions observed between 2 and 4 Å are related to the Ge–S, Ge–Sb, and Sb–Sb first neighbor correlations and Ge–Ge second neighbor correlations in the edge-shared GeS4/2 tetrahedra, and S–S and/or Ge–Ge second neighbor correlations in the corner-shared GeS4/2 tetrahedra. Three mechanisms of the radiation-/annealing-induced changes are discussed in the framework of coordination topological defect formation and bond-free solid angle concepts. [ABSTRACT FROM AUTHOR]

A pulsed mid-frequency magnetron sputtering technique was used to deposit MgO films. Atomic force microscopy, Rutherford backscattering, x-ray diffraction, and a diode discharge device were used to characterize surface morphology, oxygen content, crystalline structure, and the secondary electron emission (γ) coefficient of the films, respectively. The oxygen content (56 at. %) in all the films remained constant. However, surface morphology, crystalline structure, and the secondary electron emission properties of the films are strongly dependent on the O[sub 2] flow rate. As the O[sub 2] flow rate is increased from 3 to 10 sccm, a sudden decrease in the grain size and the y coefficient of the films can be observed, and the crystalline orientation evolves from a strong (200) preferred orientation continuously to a fully (220) preferred orientation. Further increase of O[sub 2] flow rate results in a slight change in the grain size and the crystalline orientation, but a considerable increase in the full width at half maximum of the x-ray diffraction peaks and a significant decrease in the y coefficient of the films. We found that preferred orientation and crystalline quality are the main factors that influence the secondary electron emission properties of the MgO films. [ABSTRACT FROM AUTHOR]