570 research outputs found

    A Study of Creative Imagination in Artistic Expression

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    In this investigation of the nature of artistic expression, creative imagination is studied through the medium of a model stage, appreciation of colored slides, and imaginative insight by abstract paintings

    Modeling And Experimental Determination Of Physical Properties Of Ge x Ga y Se 1-x-y Chalcogenide Glasses II: Optical And Thermal Properties

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    This study systematically analyzed the correlation between topological structure and chemical ordering on the optical and thermal properties of synthesized material in the glass forming region of the GexGaySe1-x-y ternary. A series of ten compositions from 5 to 30 mol% Ge and 5 to 15 mol% Ga were examined within the ternary, showing broadband infrared properties with transmission from 1 to 25 ÎŒm. Topological constraint theory applied to compositions examined exhibited sharp inflection at the average coordination number of = 2.67 defined as the chemical threshold where the glass network consists of tetrahedral Ge(Ga)Se2 units. These observations indicate that thermal and optical properties in these chalcogenide glasses are highly sensitive to the chemical ratio of homopolar versus heteropolar bonds, Ge to Ga ratio, as well as the dimensionality of the topological structure. Glass transition and crystallization temperature values compare well with previous literature on similar Ge–X–Se systems. This is a comprehensive study that systematically examined thermal conductivity, heat capacity, absorption coefficient, and refractive index within the GexGaySe1-x-y system, correlating these properties with structural network calculations. The presented methodology and findings will enable the compositional design of materials for infrared systems using GexGaySe1-x-y glasses with broadband transmission

    Situational Judgment Tests: An Overview of Development Practices and Psychometric Characteristics

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    Situational judgment tests (SJTs) are popular assessment methods often used for personnel selection and promotion. SJTs present problem scenarios to examinees, who then evaluate each response option for addressing the issue described in the scenario. As guidance for practitioners and researchers alike, this paper provides experience- and evidence-based best practices for developing SJTs: writing scenarios and response options, creating response instructions, and selecting a response format. This review describes scoring options, including key stretching and within-person standardization. The authors also describe research on psychometric issues that affect SJTs, including reliability, validity, group differences, presentation modes, faking, and coaching

    Modeling And Experimental Determination Of Physical Properties Of Ge x -Ga y -Se 1-x-y Chalcogenide Glasses I: Structure And Mechanical Properties

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    A series of ten GexGaySe1-x-y glasses within the topological constraint regime of = 2.3 to 2.8 were processed for physical property testing to compare measured to calculated property values enabling further understanding of structure-related mechanical property evolution. Average bond energies were calculated for each glass to elucidate structure and property relationships. Raman analysis was performed to correlate the topological constraint theory to experimentally determined structural units. Young\u27s modulus and Vickers hardness, respectively, were shown to increase with increasing coordination number from 14.42 GPa and 911 MPa at = 2.4 to 29.44 GPa and 2295 MPa at = 2.8. Poisson\u27s ratio decreased linearly with increasing coordination number from 0.2996 at = 2.4 for Ge0.15Ga0.05Se0.85 to 0.2477 at = 2.8 for Ge0.25Ga0.15Se0.60 . These properties indicate a strong dependence on the topological network of the glass, in which continued crosslinking and interconnectivity lead to a direct increase or decrease of the respective mechanical property. It was found that theoretical values were in good agreement with measured experiment values, elucidating the impact of the energy required to propagate a crack tip or alter bond lengths and atom positions

    Direct Reprogramming of Cardiac Fibroblasts to Repair the Injured Heart

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    Coronary heart disease is a leading cause of mortality and morbidity. Those that survive acute myocardial infarction are at significant risk of subsequent heart failure due to fibrotic remodelling of the infarcted myocardium. By applying knowledge from the study of embryonic cardiovascular development, modern medicine offers hope for treatment of this condition through regeneration of the myocardium by direct reprogramming of fibrotic scar tissue. Here, we will review mechanisms of cell fate specification leading to the generation of cardiovascular cell types in the embryo and use this as a framework in which to understand direct reprogramming. Driving expression of a network of transcription factors, micro RNA or small molecule epigenetic modifiers can reverse epigenetic silencing, reverting differentiated cells to a state of induced pluripotency. The pluripotent state can be bypassed by direct reprogramming in which one differentiated cell type can be transdifferentiated into another. Transdifferentiating cardiac fibroblasts to cardiomyocytes requires a network of transcription factors similar to that observed in embryonic multipotent cardiac progenitors. There is some flexibility in the composition of this network. These studies raise the possibility that the failing heart could one day be regenerated by directly reprogramming cardiac fibroblasts within post-infarct scar tissue

    Cu 2+ and Cu 3+ Acceptors in ÎČ-Ga 2 O 3 Crystals: A Magnetic Resonance and Optical Absorption Study

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    Electron paramagnetic resonance (EPR) and optical absorption are used to characterize Cu2+ (3d9) and Cu3+ (3d8) ions in Cu-doped ÎČ-Ga2O3. These Cu ions are singly ionized acceptors and neutral acceptors, respectively (in semiconductor notation, they are Cu− and Cu0 acceptors). Two distinct Cu2+ EPR spectra are observed in the as-grown crystals. We refer to them as Cu2+(A) and Cu2+(B). Spin-Hamiltonian parameters (a g matrix and a 63,65Cu hyperfine matrix) are obtained from the angular dependence of each spectrum. Additional electron-nuclear double resonance (ENDOR) experiments on Cu2+(A) ions give refined 63Cu and 65Cu hyperfine matrices and provide information about the nuclear electric quadrupole interactions. Our EPR results show that the Cu2+(A) ions occupy octahedral Ga sites with no nearby defect. The Cu2+(B) ions, also at octahedral Ga sites, have an adjacent defect, possibly an OH− ion, an oxygen vacancy, or an H− ion trapped within an oxygen vacancy. Exposing the crystals at room temperature to 275 nm light produces Cu3+ ions and reduces the number of Cu2+(A) and Cu2+(B) ions. The Cu3+ ions have an S = 1 EPR spectrum and are responsible for broad optical absorption bands peaking near 365, 422, 486, 599, and 696 nm. An analysis of loops observed in the Cu3+ EPR angular dependence gives 2.086 for the g value and 22.18, 3.31, and −25.49 GHz for the principal values of D (the fine-structure matrix). Thermal anneal studies above room temperature show that the Cu3+ ions decay and the Cu2+ ions recover between 75 and 375 °C
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