Absorption (logic)

About: Absorption (logic) is a research topic. Over the lifetime, 5733 publications have been published within this topic receiving 236302 citations.

X-Ray-Emission Microanalysis of Rock-Forming Minerals I. Experimental Techniques

Abstract: In order to provide a basis for calibration of X-ray-emission analyses, existing theories and experimental measurements on the generation, absorption, and fluorescence of X-rays produced by electron bombardment of mixed targets are reviewed and compared with new measurements for a variety of targets, principally common silicates. Theoretically, the efficiency of X-ray generation should depend strongly on the mean atomic number of a mixed target, and its variation is commonly described by a so-called atomic-number factor. Using hard radiation for which the absorption is trivial, measurements have shown that the Philibert factor (1 + h) varies too little with mean atomic number. A new empirical factor, $$[4.7 + 0.9 In (V_{0} - V_{k}) - In {\langle}Z{\rangle}] {\langle}Z/A {\rangle} R^{-1}$$ fits the data to within 2 per cent, except for $$V_{0}$$ close to $$V_{k}$$ ($$V_{0}$$is incident electron accelerating voltage in kilovolts, $$V_{k}$$ is ionization voltage for K-electrons, {\langle}Z{\rangle} is mean a...

K^- nuclear potentials from in-medium chirally motivated models

Abstract: A self-consistent scheme for constructing ${K}^{\ensuremath{-}}$ nuclear optical potentials from subthreshold in-medium $\overline{K}N$ $s$-wave scattering amplitudes is presented and applied to analysis of kaonic atoms data and to calculations of ${K}^{\ensuremath{-}}$ quasibound nuclear states. The amplitudes are taken from a chirally motivated meson-baryon coupled-channel model, both at the Tomozawa-Weinberg leading order and at the next to leading order. Typical kaonic atoms potentials are characterized by a real part $\ensuremath{-}\mathrm{Re}\phantom{\rule{0.222222em}{0ex}}{V}_{{K}^{\ensuremath{-}}}^{\mathrm{chiral}}=85\ifmmode\pm\else\textpm\fi{}5$ MeV at nuclear matter density, in contrast to half this depth obtained in some derivations based on in-medium $\overline{K}N$ threshold amplitudes. The moderate agreement with data is much improved by adding complex $\ensuremath{\rho}$- and ${\ensuremath{\rho}}^{2}$-dependent phenomenological terms, found to be dominated by ${\ensuremath{\rho}}^{2}$ contributions that could represent $\overline{K}NN\ensuremath{\rightarrow}YN$ absorption and dispersion, outside the scope of meson-baryon chiral models. Depths of the real potentials are then near 180 MeV. The effects of $p$-wave interactions are studied and found secondary to those of the dominant $s$-wave contributions. The in-medium dynamics of the coupled-channel model is discussed and systematic studies of ${K}^{\ensuremath{-}}$ quasibound nuclear states are presented.

The z=0.8596 Damped Lyman Alpha Absorbing Galaxy Toward PKS 0454+039

Abstract: We present {\it Hubble Space Telescope} and ground--based data on the $z_{abs}=0.8596$ metal line absorption system along the line of sight to PKS 0454+0356. The system is a moderate redshift damped Lyman alpha system, with ${\rm N(HI)}=(5.7\pm0.3)\times10^{20}$~cm$^{-2}$ as measured from the {\it Faint Object Spectrograph} spectrum. We also present ground--based images which we use to identify the galaxy which most probably gives rise to the damped system; the most likely candidate is relatively underluminous by QSO absorber standards ($M_B \sim -19.0$ for $q_0=0.5$ and $H_0=50$ \kms Mpc$^{-1}$), and lies $\sim 8.5h^{-1}$ kpc in projection from the QSO sightline. Ground--based measurements of Zn~II, Cr~II, and Fe~II absorption lines from this system allow us to infer abundances of [Zn/H]=$-1.1$, [Cr/H]=$-1.2$, and [Fe/H]=$-1.2$, indicating overall metallicity similar to damped systems at $z >2$, and that the depletion of Cr and Fe onto dust grains may be even {\it less} important than in many of the high redshift systems of comparable metallicity. Limits previously placed on the 21-cm optical depth in the $z=0.8596$ system, together with our new N(H~I) measurement, suggest a very high spin temperature for the H~I, $T_S >> 580$ K.

Fully ordered Sr 2 CrReO 6 epitaxial films: A high-temperature ferrimagnetic semiconductor

Abstract: We report growth of Sr${}_{2}$CrReO${}_{6}$ epitaxial films with 99$%$ Cr/Re ordering and crystalline perfection comparable to those of high-quality semiconductor films. The Sr${}_{2}$CrReO${}_{6}$ films show a Curie temperature of 508 K and a saturation magnetization of 1.29 ${\ensuremath{\mu}}_{\mathrm{B}}$ per formula unit, which confirms the presence of strong spin-orbit coupling. Unexpectedly, electrical transport and optical absorption measurements indicate that Sr${}_{2}$CrReO${}_{6}$ is a semiconductor with a band gap of 0.21 eV. The unique combination of high temperature ferrimagnetism and semiconductivity is both scientifically interesting and highly attractive for applications.

Structural relaxation around substitutional Cr3+ in MgAl2O4

Abstract: The structural environment of a substitutional ${\mathrm{Cr}}^{3+}$ ion in a $\mathrm{Mg}{\mathrm{Al}}_{2}{\mathrm{O}}_{4}$ spinel has been investigated by Cr $K$-edge extended x-ray absorption fine structure and x-ray absorption near edge structure (XANES) spectroscopies. First-principles computations of the structural relaxation and of the XANES spectrum have been performed, with a good agreement with the experiment. The Cr-O distance is close to that in $\mathrm{Mg}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$, indicating a full relaxation of the first neighbors, and the second shell of Al atoms relaxes partially. These observations demonstrate that Vegard's law is not obeyed in the $\mathrm{Mg}{\mathrm{Al}}_{2}{\mathrm{O}}_{4}\text{\ensuremath{-}}\mathrm{Mg}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$ solid solution. Despite some angular site distortion, the local ${D}_{3d}$ symmetry of the $B$ site of the spinel structure is retained during the substitution of Cr for Al. Here, we show that the relaxation is accommodated by strain-induced bond buckling, with angular tilts of the Mg-centered tetrahedra around the Cr-centered octahedron. By contrast, there is no significant alteration of the angles between the edge-sharing octahedra, which build chains aligned along the three fourfold axes of the cubic structure.