The Ca L 3,2 -edge XANES spectra of six calcium salts have been measured in both total electron and fluorescence yields using a high-resolution spherical grating monochromator. The compounds investigated were; CaF 2 , CaCO 3 , CaCl 2 ·2H 2 O, calcium phosphate, calcium glycerophosphate and calcium gluconate. We find that the fine structure of the Ca L 3,2 -edges for each compound is unique and relates to the local structure of the Ca atom. The implications of these results to the study of the structure of calcium binding sites in systems of biologically interest will be discussed.
Interferometric measurements of the linear thermal-expansion coefficients α∥ and α⊥ in the ``c'' and ``a'' axial directions of well-oriented pyrolytic graphite between approximately 20° and 270°K are reported. Grüneisen parameters γ∥ and γ⊥, defined for strain coordinates parallel and perpendicular to the ``c'' axis, respectively, have been calculated from the present thermal expansion coefficients and related data. Between 30° and 270°K γ∥ is positive, indicating the preponderance of longitudinal modes of vibration, while γ⊥ is negative, indicating the predominance of transverse modes. The quasiharmonic approximation has been applied to calculate the characteristic temperatures θ(n) corresponding to the maximum frequencies ωD(n) of the Debye distributions having the same nth moments 〈ωn〉 as the specimens, which vary between approximately 420° and 2270°K as n increases from −3 to +6. The dimensional dependence of the moments, defined by γ(n) =Σγjωjn /Σωjn corresponding to γ∥(n) and γ⊥(n), and their variations with n, are consistent with the existence of low-frequency modes of vibration between planes of atoms perpendicular to the ``c'' axis, and high-frequency modes within the planes, a result supported by calculations of the rms displacements of the atoms.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.