Browsing by Subject "Radiation absorption"

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    Radiation properties of sources inside photonic crystals
    (2003) Bulu, I.; Caglayan, H.; Özbay, Ekmel
    In this work, we have experimentally studied the emission of radiation from a monopole source embedded in a photonic crystal. We have demonstrated the enhancement of radiation at the band edges and at the cavity modes including coupled cavity modes. Moreover, we have shown that the emission of radiation from a source depends on the group velocities of the modes and on the electric field intensities of the modes at the source location.
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    Specific absorption rate reduction using nonlinear gradient fields
    (Wiley, 2013) Kopanoglu, E.; Yilmaz, U.; Gokhalk, Y.; Atalar, Ergin
    The specific absorption rate is used as one of the main safety parameters in magnetic resonance imaging. The performance of imaging sequences is frequently hampered by the limitations imposed on the specific absorption rate that increase in severity at higher field strengths. The most well-known approach to reducing the specific absorption rate is presumably the variable rate selective excitation technique, which modifies the gradient waveforms in time. In this article, an alternative approach is introduced that uses gradient fields with nonlinear variations in space to reduce the specific absorption rate. The effect of such gradient fields on the relationship between the desired excitation profile and the corresponding radiofrequency pulse is shown. The feasibility of the method is demonstrated using three examples of radiofrequency pulse design. Finally, the proposed method is compared with and combined with the variable rate selective excitation technique. © 2012 Wiley Periodicals, Inc.
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    Thermodynamic parameters of Cs+ sorption on natural clays
    (Akademiai Kiado Rt., 2002) Shahwan, T.; Erten, H. N.
    The sorption behavior of Cs+ on kaolinite, chlorite-illite, and bentonite clays as a function of time, cation concentration, and temperature was studied using the radiotracer method. Sorption data were well represented by Freundlich and Dubinin-Radushkevich type isotherms. Bentonite was found to have the highest sorption capacity and the highest exchange affinity to Cs+. In all three cases Cs+ sorption was found to be exothermic with ΔH° (kJ/mol) -13, -8, -19 and ΔS° (J/mol·K) -15, 31, and -3 for kaolinite, chlorite-illite, and bentonite, respectively. Negative ΔG° values were obtained in all cases, indicating the spontaneity of sorption. The magnitudes of ΔG° suggest that ion exchange is the primary sorption mechanism.