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Gallium K-edge x-ray absorption study on Mg-doped GaN (2001)

Pan, Y. C. ; Wang, S. F. ; Lee, W. H. ; [et al.]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 78 (2001), S. 31-33

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: Ga K-edge x-ray absorption measurements were employed to investigate Mg-doping effects in GaN samples. Strong polarization-dependent x-ray absorption near-edge structures become less pronounced with increasing doping concentration, indicating the formation of a mixing-phase structure of cubic and hexagonal phases. Analysis of the extended x-ray absorption region of the spectra revealed doping-related defects such as vacancies, substitutions, and interstitial occupations. They were formed anisotropically in the crystal c axis direction and its perpendiculars. Disorderliness arising from phase mix and defects is believed to have lowered the Debye temperature of the doped GaN films and caused the destructive interference of the absorption fine-structure oscillation functions. These effects were taken into account for the observed large coordination number reductions in our samples. © 2001 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1337636

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Role of Alkaloids in Resistance of Yellow Lupin to Red-Legged Earth Mite Halotydeus destructor (2000)

Wang, S. F. ; Liu, A. Y. ; Ridsdill-Smith, T. J. ; [et al.]

Springer

Journal of chemical ecology 26 (2000), S. 429-441

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ISSN: 1573-1561

Keywords: Lupinus luteus ; Halotydeus destructor ; plant resistance ; deterrent activity ; quinolizidine alkaloids ; ammodendrine

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology

Notes: Abstract Eleven varieties of Lupinus luteus were tested in choice and no-choice experiments for their resistance to feeding by the red-legged earth mite (Halotydeus destructor). Three were found to show resistance, and the alkaloid fraction from these varieties strongly deterred mites from feeding. The alkaloid components of the extracts, lupinine, a number of acyl derivatives of lupinine, and sparteine were tested for deterrent activity. Sparteine was the most potent, with significant activity at 0.001% concentration. Quantitation of the levels of nonpolar alkaloids in the cotyledons and leaves of the 11 varieties was by gas chromatography–mass spectrometry. An inverse correlation was found between the concentrations of these alkaloids and the damage caused by the mites; varieties with levels 〈100 μg/g (fresh wt) showed a high damage index. The involvement of sparteine and the bipiperidine alkaloid ammodendrine in the deterrence to mite feeding is discussed.