Browsing by Author "Assefa, Shimeles"

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    A Study on the Improvement of Surface Plasmon-Polariton (SPLP) Method for the Determination of Compelx Dielectric Permittivity € and Thickness of thin Metal Films.
    (Addis Ababa University, 1990-06) Assefa, Shimeles
    The existing SPLP method for the determination of the complex dielectric permittivity and the thickness of metal film .1.s reviewed. A close electrodynamic analysis of SPLP dispersion properties in very. thin metal films is made. The analysis is based on the numerical solution of the exact dispersion equation using the 'Downhill' method and subsequent selection of physically reasonable results. The selection is performed via the comparison of the power flows through the boundaries of the metal film in the transverse direction. The explicit expressions for the components of the power flo~1 in the Kretschmann Prism-Metal Film-Air configuration have been derived. Analysis made shovled that splitting of the classical dispersion equation into two branches (w - mode and w+ mode) known in li~erature for the case of symmetriC environment occurs also for the case of asymmetric environment, but the 0/ mode branch is represented by a number of discrete points only. It vias also shown that part of the IJj + mode branch known in 11 terature is physically unreal. In addition to the two branches mentioned a third 'side' branch have been found, which turned out to be physically unreal. The study of physically significant results revealed back-bending segments in the w- and w+ branches which demonstrate the phenomena of artificial anomalous dispersion The developed teclli1ique of the numerical solution of the exact dispersion equation allo~lS to extehd applicability of the SPLP method to the case of very thin metal films and puts no restrictions on the type of the environment
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    The Symmetrical-integral Model of Conceptual Change:The Case of Physical and Chemical Thermodynamics
    (AAU, 2012) Assefa, Shimeles; Asgedom, Amare PhD
    The purpose of this study is to develop and test the symmetrical-integral model of conceptual change Development of Conceptual change models is a growing area of research in science education.A survey of conceptual change research helped me develop a new model of conceptual change which I called . The spiral Cognitive-Sociocultural Model 0f Conceptual Change, This new conceptual change model was tested on Grade 12 physical thermodynamics and chemical thermodynamics units teaching dressed with my hybrid method of Reasoned persuasive Collaboration from a class of Critical Analytic pedagogies.This model,unlike previous models requires change in both rational/knowledge and extra rational or motivation, affection, and other s socio-cultural factors.