159 research outputs found
Photoionization of the Ne-like Si4+ ion in ground and metastable states in the 110–184-eV photon energy range
We present measurements of the absolute photoionization cross section of the neonlike Si4+ ion over the 110–184 eV photon energy range. The measurements were performed using two independent merged-beam setups at the super-ACO and ASTRID synchrotron-radiation facilities, respectively. Signals produced in the photoionization of the 2p subshell of the Si4+ ion both from the 2p6 1S0 ground state and the 2p53s 3P0,2 metastable levels were observed. Calculations of the 2p photoionization cross sections were carried out using a multi-configuration Dirac-Fock code. They give results in good agreement with the measured spectra. Comparison with other available theoretical results is also presented
54. Diagnostic de néoplasie lobulaire in situ sur biopsies percutanées : considérations chirurgicales
Photoionization of the Be isoelectronic sequence: total cross sections
The photoionization of the four-electron beryllium-like isoelectronic series
from the neutral to Fe^{+22} has been studied for ground ^1S and metastable ^3P
initial states. The wave functions of the final-state (target) ions were built
using the CIV3 code. Both nonrelativistic LS-coupling R-matrix and relativistic
Breit-Pauli (BP) R-matrix methods were used to calculate the cross sections in
the photon-energy range between the first ionization threshold and the 1s^2
4f_{7/2} threshold for each ion. Our total cross sections compare well with
experiment which is available for Be, B^+, C^{+2}, N^{+3}, and O^{+4}. The
agreement between the present work and previous calculations is discussed in
detail. The importance of relativistic effects is seen by the comparison
between the LS and the BP results.Comment: 45 pages, 3 tables, 22 figure
Absolute photoionization cross sections and resonance structure of doubly ionized silicon in the region of the 2p-1 threshold: experiment and theory
We present the absolute photoionization cross section of doubly ionized silicon as a function of photon energy. These were obtained by merging a Si2+ ion beam generated in an electron cyclotron resonance source with monochromatized synchrotron radiation from an undulator. The photoion yield measurements were carried out in the photon energy range between 95 eV and 170 eV, i.e., the region corresponding to the excitation followed by the ionization (threshold ∼133.8eV) of an inner-subshell 2p electron. Resonance structure due to 2p excitation in the 2p63s3p3P metastable state was also observed with its contribution to the total cross section not exceeding 3%. Calculation of the 2p photoionization continuum cross section as a function of photon energy was carried out using the relativistic random-phase approximation (RRPA) and agreed very well with the corresponding measurements. The resonance structure in the 3s cross section below the 2p threshold was found to be in good agreement with the multiconfiguration atomic structure calculations of Sayyad et al. [J. Phys. B 28, 1715 (1995)], while the corresponding RRPA-RMQDT (relativistic multi-channel quantum-defect theory) calculations proved less successful
Secondary instability in drift wave turbulence as a mechanism for zonal flow and avalanche formation
The article reports on recent developments in the theory of secondary instability in drift-ion temperature gradient turbulence. Specifically, the article explores secondary instability as a mechanism for zonal flow generation, transport barrier dynamics and avalanche formation. These in turn are related to the space-time statistics of the drift wave induced flux, the scaling of transport with collisionality and β, and the spatio-temporal evolution of transport barriers
State-resolved valence shell photoionization of Be-like ions: experiment and theory
High-resolution photoionization experiments were carried out using beams of
Be-like C, N, and O ions with roughly equal populations of
the S ground-state and the P manifold of metastable components. The
energy scales of the experiments are calibrated with uncertainties of 1 to 10
meV depending on photon energy. Resolving powers beyond 20,000 were reached
allowing for the separation of contributions from the individual metastable
P, P, and P states. The measured data compare
favourably with semi-relativistic Breit-Pauli R-matrixComment: 23 figures and 3 table
Harmonisation, Mosaicing and Production of the Global Land Cover 2000 Database.
Abstract not availableJRC.H-Institute for environment and sustainability (Ispra
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