scispace - formally typeset
Search or ask a question
Topic

Absorption (logic)

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


Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, the multicomponent structure of the $3d$ x-ray photo-emission spectra of the light rare-earth metals is elucidated in terms of recent xray absorption and appearance-potential spectroscopy results for these materials.
Abstract: The multicomponent structure of the $3d$ x-ray photoemission spectra of the light rare-earth metals is elucidated in terms of recent x-ray absorption and appearance-potential spectroscopy results for these materials. Both multiplet splitting due to $3d\ensuremath{-}4f$ exchange and satellite structure due to two competing screening mechanisms are identified. The main component of the $3d$ line arises when the core hole is screened by $5d$ conduction electrons; the satellite from a $4{f}^{n}\ensuremath{\rightarrow}4{f}^{n+1}$ process. The satellites in the metals occur at lower binding energies because the empty $4f$ level falls below the Fermi energy. This interpretation is supported by an "equivalent cores" argument.

111 citations

Journal ArticleDOI
TL;DR: The hydrogen uptake kinetics in the ..cap alpha..-phase region are found to be rate limited by diffusion of atomic H into the bulk rather than by dissociative chemisorption of H/sub 2/ at the surface as previously reported.
Abstract: A coupled high-pressure--ultrahigh-vacuum technique is employed to make the first kinetic measurements of high-pressure hydrogen absorption through an atomically clean palladium surface, Pd(110). The hydrogen uptake kinetics in the \ensuremath{\alpha}-phase region are found to be rate limited by diffusion of atomic H into the bulk rather than by dissociative chemisorption of ${\mathrm{H}}_{2}$ at the surface as previously reported. Our findings strongly suggest that previous high-pressure measurements of hydrogen absorption by palladium may be suspect due to uncharacterized surface contamination. The bulk diffusivity of hydrogen in palladium determined in this study has an activation barrier of 5.39\ifmmode\pm\else\textpm\fi{}0.30 kcal/mol with a preexponential factor of (2.83\ifmmode\pm\else\textpm\fi{}0.05)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{cm}}^{2}$/s.

110 citations

Journal ArticleDOI
TL;DR: In this article, a spectroscopic study of electronic transitions from the ground state to several excited states in the potential well lying outside the free surface of liquid helium formed by the long-range attractive image potential and the short-range electron-atom repulsive potential was performed.
Abstract: We report a spectroscopic study of electronic transitions from the ground state to several excited states in the potential well lying outside the free surface of liquid helium formed by the long-range attractive-image potential and the short-range electron-atom repulsive potential. These electric dipole transitions were observed at frequencies from 130 to 220 GHz by measuring the microwave absorption derivative at fixed frequency as the splittings between states were tuned to resonance by an applied electric field $\mathcal{E}$. Transitions were observed between the ground state and the first through seventh excited states, and detailed measurements were made of the frequency versus $\mathcal{E}$ relation for transitions to the first and second excited states. Extrapolation of the respective data to $\mathcal{E}=0$ yields splittings of 125.9 \ifmmode\pm\else\textpm\fi{} 0.2 and 148.6 \ifmmode\pm\else\textpm\fi{} 0.3 GHz and initial Stark-tuning rates of 2.3 \ifmmode\pm\else\textpm\fi{} 0.1 and 5.9 \ifmmode\pm\else\textpm\fi{} 0.4 GHz/(V/cm). The data can be fit satisfactorily by variational calculations based on a simple model potential which takes the origin of the image potential to lie 1.04 \AA{} inside the liquid-helium surface. These calculations show the wave functions to be significantly compressed by the Stark-tuning fields; e.g., the second excited state is compressed at our highest fields to 1/2 of its original size. Measurements of the linewidth of the lowest transition as a function of the helium vapor density are reported. The peak-to-peak line width is 1.0 GHz at a vapor density of 5 \ifmmode\times\else\texttimes\fi{} ${10}^{18}$ atoms/${\mathrm{cm}}^{3}$ and increases approximately linearly with increasing vapor density. A phenomenological theory of several mechanisms contributing to the linewidth is discussed.

110 citations

Journal ArticleDOI
TL;DR: In this paper, an abstract approach based on the Limiting Absorption Principle has been proposed for the Boltzmann equation (1.1) for low-density flow of neutrons.
Abstract: Consider the Boltzmann equation {partial_derivative}/{partial_derivative}{sub t}u(t,x,v)=-v. {del}{sub x}u(t,x,v)-{sigma}{sub a}(x,v)u(t,x,v)+{integral}{sub v}k(x,v{prime},v)u(t,x,v{prime})dv{prime} in R{sup n} x V {such_that} (x,v), V being an open subset of R{sup n}, n {ge} 2. Equation (1.1) describes the dynamics of a flow of particles in R{sup n} under the assumption that the interaction between them is neglectable (no non-linear terms). This is the case for example for a low-density flow of neutrons. The term involving {sigma}{sub a} describes the loss of particles from (x,v) {epsilon} R{sup n} x V due to absorption or scattering into another point (x,v{prime}), while the last term in (1.1) involving k represents the production at x {epsilon} R{sup n} of particles with velocity v form particles with velocity v{prime}. The total rate of this production at (x,v{prime}) is given by {sigma}{sub p}(x,v{prime}) = {integral}{sub V} k (x,v{prime},v)dv. Following [RS] we say that the pair ({sigma}{sub a}, k) is admissible, if (i) O {le} {sigma}{sub a} {epsilon} L{sup {infinity}}(R{sup n} x V), (ii) O {le} k(x,v{prime}, {center_dot}) {epsilon} L{sup 1}(V) for a.e. (x,v{prime}) {epsilon} R{sup n} x V and {sigma}{sub p} {epsilon} L{sup {infinity}}(R{sup n} x V), (iii) There is an open bounded set X {contained_in} R{sup n}, such that k(x,v{prime},v) andmore » {sigma}{sub a}(x,v) vanish if x {epsilon} X. One can define the wave operators associated with T, T{sub O} by W{sub -} = s-lim/t{r_arrow}{infinity} U(t)U{sub O}(-t), W{sub +} = s-lim/t{r_arrow}{infinity} U(O)(-t)U(t). if W{sub -}, W{sub +} exist, then one can define the scattering operator S = W{sub +}W{sub -} as a bounded operator in L{sup 1}(R{sup n} x V). Scattering theory for (1.1) has been developed by other authors and we refer to these papers for sufficient conditions guaranteeing the existence of S. An abstract approach based on the Limiting Absorption Principle has been proposed. 22 refs.« less

110 citations

Journal ArticleDOI
TL;DR: In this article, the neutrino luminosities and spectra of all flavors are very similar and their difference even decreases during the deleptonization of the proto-neutron star.
Abstract: The neutrino-driven wind, which occurs after the onset of a core-collapse supernova explosion, has long been considered as the possible site for the synthesis of heavy $r$-process elements in the Universe. Only recently, it has been possible to simulate supernova explosions up to $\ensuremath{\sim}10\text{ }\text{ }\mathrm{seconds}$, based on three-flavor Boltzmann neutrino transport. These simulations show that the neutrino luminosities and spectra of all flavors are very similar and their difference even decreases during the deleptonization of the proto-neutron star. As a consequence, the ejecta are always proton rich which rules out the possible production of heavy $r$-process elements ($Zg56$). We perform a detailed analysis of the different weak processes that determine the neutrino spectra. Nonelectron flavor (anti)neutrinos are produced and interact only via neutral-current processes, while electron (anti)neutrinos have additional contributions from charge-current processes. The latter are dominated by ${\ensuremath{ u}}_{e}$-absorption on neutrons and ${\overline{\ensuremath{ u}}}_{e}$-absorption on protons. At early times, charge-current processes are responsible for spectral differences between ${\ensuremath{ u}}_{e}$, ${\overline{\ensuremath{ u}}}_{e}$ and ${\ensuremath{ u}}_{\ensuremath{\mu}/\ensuremath{\tau}}$. However, as the region of neutrino decoupling moves to higher densities during deleptonization, charge-current reactions are suppressed by final state Pauli blocking. ${\overline{\ensuremath{ u}}}_{e}$ absorption on protons is suppressed due to the continuously increasing chemical potential of the neutrons. ${\ensuremath{ u}}_{e}$ absorption on neutrons is blocked by the increasing degeneracy of the electrons. These effects result in negligible contributions from charge-current reactions on time scales on the order of tens of seconds, depending on the progenitor star. Hence, the neutrino spectra are mainly determined from neutral-current processes which do not distinguish between the different flavors and result in the convergence of the spectra. These findings are independent of the charge-current reaction rates used. It rules out the possibility of neutron-rich ejecta at late times and the production of heavy $r$-process elements from nonrotating and not magnetized proto-neutron stars.

110 citations


Network Information
Related Topics (5)
Type (model theory)
38.9K papers, 670.5K citations
86% related
Multimodal logic
6.1K papers, 178.8K citations
84% related
Dynamic logic (modal logic)
6.6K papers, 210.3K citations
84% related
Modal logic
5.9K papers, 143.6K citations
83% related
Decidability
9.9K papers, 205.1K citations
81% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2021290
2020249
2019220
2018230
2017162
2016163