Absorption (logic)

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

L-edge x-ray absorption in fcc and bcc Cu metal: Comparison of experimental and first-principles theoretical results

Abstract: High resolution Cu ${\mathit{L}}_{2,3}$ x-ray absorption spectra of bulk fcc Cu metal are compared with those of thin Cu layers in Cu/Fe multilayers. Comparison of the measured fine structure with that obtained from a fully relativistic first-principles calculation for fcc and bcc Cu reveals that Cu is bcc in Cu(3 \AA{})/Fe(10 \AA{}) and fcc in Cu(10 \AA{})/Fe(3 \AA{}) multilayers. This result indicates that the thicker layer simply acts as a template for the structure of the thinner layer. The excellent agreement between experimental and theoretical spectra also demonstrates the validity of the theoretical approach. The theoretical spectra are discussed in terms of their angular momentum composition and the energy dependence of the radial transition matrix elements. \textcopyright{} 1996 The American Physical Society.

Electron spin magnetic moment in atomic hydrogen

Abstract: The ratio of the electron-spin $g$ factor to the proton $g$ factor has been measured in atomic hydrogen by a precision microwave magnetic resonance absorption technique. The result obtained is $\ensuremath{-}\frac{{g}_{s}}{{g}_{p}}=658.2277\ifmmode\pm\else\textpm\fi{}0.0002,$ where ${g}_{p}$ refers to protons in molecular hydrogen. The ratio is in good agreement with the atomic-beam result of Koenig, Prodell, and Kusch, and verifies their conclusions concerning the magnitude of the quantum electrodynamical contribution to ${g}_{s}$.

Impurity and Exciton Effects on the Infrared Absorption Edges of III-V Compounds

Abstract: The fundamental absorption edge of each of several III-V compounds has been examined for structure due to excitons and impurities using high resolution and sample temperatures down to 1.4\ifmmode^\circ\else\textdegree\fi{}K. The effects of an applied magnetic field were studied. The absorption edge of GaSb shows three sharp peaks ($\ensuremath{\alpha}$, $\ensuremath{\beta}$, $\ensuremath{\gamma}$) and a low-absorption tail. Under a magnetic field, the peaks ($\ensuremath{\alpha}$, $\ensuremath{\beta}$, $\ensuremath{\gamma}$) shift and split in a manner close to the expected behavior of the exciton. The peak $\ensuremath{\alpha}$ is shown to be the free-exciton peak and the peaks ($\ensuremath{\beta}$ and $\ensuremath{\gamma}$) are attributed to impurity-exciton complexes. The tail is found to be associated with electron transitions to the conduction band from impurity levels near the valence band. Absorption associated with impurity-valence-band transitions is also observed at low photon energies. Analysis of these results gives the energy gap, the electron $g$ factor, and the ionization energies of impurity levels. The absorption edge of InSb shows a step which is found to be due to ionized acceptors. Under a magnetic field, two peaks develop from the step absorption which behave like the impurity-exciton peaks in GaSb. The optical transitions involved appear to be related to the emission observed in the InSb laser. The electron $g$ factor and the ionization energies of impurity levels have been estimated from these results. Some studies on the impurity absorption near the intrinsic edge of other III-V compounds are reported.

Evidence for a proton halo in B 8 : Enhanced total reaction cross sections at 20 to 60 MeV/nucleon

Abstract: Total reaction cross sections ${\mathrm{\ensuremath{\sigma}}}_{\mathit{R}}$ for $^{8}\mathrm{B}$, $^{12}\mathrm{C}$, and $^{14}\mathrm{N}$ on $^{\mathrm{nat}}\mathrm{Si}$ were measured from about 20 to 60 MeV/nucleon. The ${\mathrm{\ensuremath{\sigma}}}_{\mathit{R}}$ for $^{12}\mathrm{C}$ and $^{14}\mathrm{N}$ compared reasonably well with conventional strong absorption and microscopic calculations. Measured ${\mathrm{\ensuremath{\sigma}}}_{\mathit{R}}$ for $^{8}\mathrm{B}$ were slightly larger than those for the two heavier nuclei, and notably larger than the conventional calculations. The $^{8}\mathrm{B}$ data were well reproduced by microscopic calculations using the same matter distribution used to explain the $^{8}\mathrm{B}$ quadrupole moment data, and therefore provide new evidence for the existence of a proton halo in $^{8}\mathrm{B}$.

The Chandra COSMOS Legacy Survey: Energy Spectrum of the Cosmic X-Ray Background and Constraints on Undetected Populations

Abstract: Using {\em Chandra} observations in the 2.15 deg$^{2}$ COSMOS legacy field, we present one of the most accurate measurements of the Cosmic X-ray Background (CXB) spectrum to date in the [0.3-7] keV energy band. The CXB has three distinct components: contributions from two Galactic collisional thermal plasmas at kT$\sim$0.27 and 0.07 keV and an extragalactic power-law with photon spectral index $\Gamma$=1.45$\pm{0.02}$. The 1 keV normalization of the extragalactic component is 10.91$\pm{0.16}$ keV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ keV$^{-1}$. Removing all X-ray detected sources, the remaining unresolved CXB is best-fit by a power-law with normalization 4.18$\pm{0.26}$ keV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ keV$^{-1}$ and photon spectral index $\Gamma$=1.57$\pm{0.10}$. Removing faint galaxies down to i$_{AB}\sim$27-28 leaves a hard spectrum with $\Gamma\sim$1.25 and a 1 keV normalization of $\sim$1.37 keV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ keV$^{-1}$. This means that $\sim$91\% of the observed CXB is resolved into detected X-ray sources and undetected galaxies. Unresolved sources that contribute $\sim 8-9\%$ of the total CXB show a marginal evidence of being harder and possibly more obscured than resolved sources. Another $\sim$1\% of the CXB can be attributed to still undetected star forming galaxies and absorbed AGN. According to these limits, we investigate a scenario where early black holes totally account for non source CXB fraction and constrain some of their properties. In order to not exceed the remaining CXB and the $z\sim$6 accreted mass density, such a population of black holes must grow in Compton-thick envelopes with N$_{H}>$1.6$\times$10$^{25}$ cm$^{-2}$ and form in extremely low metallicity environments $(Z_\odot)\sim10^{-3}$.