435 research outputs found
Arterial supply and venous drainage of the choroid plexus of the human lateral ventricle in the prenatal period as revealed by vascular corrosion casts and SEM
The topography of the arterial supply and venous drainage was visualised by
corrosion casting and scanning electron microscopy in the human foetal
(20 weeks) choroid plexus of the lateral ventricle. Although secondary villi were
not yet present at that developmental stage, the topography of the large arteries
and veins almost fully corresponded to that described in adult individuals. The
only major difference observed was a lack of the typical tortuosity of the lateral
branch of the anterior choroidal artery and of the superior choroidal vein, which
probably develops during further expansion of the vascular system associated
with the formation of secondary villi
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Dielectronic recombination data for dynamic finite-density plasmas II. The oxygen isoelectronic sequence
Dielectronic recombination (DR) and radiative recombination (RR) data for oxygen-like ions forming fluorine-like ions have been calculated as part of the assembly of a level-resolved DR and RR database necessary for modelling of dynamic finite-density plasmas (Badnell et al. 2003). Total DR and RR rate coefficients for F+ to Zn22+ are presented and the results discussed. By comparison between perturbative and R-matrix results, we find that RR/DR interference effects are negligible even for the lowest-charged F+ member. We also find that the 2→2 low-temperature DR (no change in the principal quantum number of the core electrons) does not scale smoothly with nuclear charge Z due to resonances straddling the ionization limit, thereby making explicit calculations for each ion necessary. These RR and DR data are suitable for modelling of solar and cosmic plasmas under conditions of collisional ionization equilibrium, photoionization equilibrium, and non-equilibrium ionization
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Dielectronic recombination data for dynamic finite-density plasmas VII. The neon isoelectronic sequence
Dielectronic recombination (DR) and radiative recombination (RR) data for neon-like ions forming sodium-like systems has been calculated as part of the assembly of a DR database necessary for modelling of dynamic and/or finite-density plasmas (Badnell et al. 2003). Dielectronic recombination coefficients for neon-like ions from Na+ to Zn20+, as well as Kr26+, Mo32+, Cd38+, and Xe44+, are presented and the results discussed
Dielectronic recombination data for dynamic finite-density plasmas : XIV. The aluminium isoelectronic sequence
Context. A comprehensive study of dielectronic recombination (DR) for the aluminum-like isoelectronic sequence has been completed. Aims. Total and final-state resolved DR rate coefficients for the ground and metastable initial levels of 17 ions between Si ii and Zn xviii are presented. Methods. Within an isolated-resonance, distorted-wave (IPIRDW) approximation, multiconfiguration Breit-Pauli (MCBP) calculations are carried out for the total and partial DR rate coefficients of Al-like ions. Both Δnc = 0 and Δnc = 1 core-excitations are included, using LS-coupled and intermediate-coupling (IC) schemes. Results. The inaccuracies of earlier empirical data and/or LS-coupling calculations, particularly at lower temperatures characteristic of photoionized plasmas, is demonstrated by comparison with present, state-of-the-art IC DR rate coefficients. Fine-structure effects are found to increase the DR rate coefficient at low temperatures and decrease it at high temperatures, rendering earlier LS calculations incomplete. Good agreement is found between present IC results and experimental measurements
Suppression of Dielectronic Recombination at Finite Densities
Density-dependent effective dielectronic recombination rate coefficients are determined in order to explore finite-density effects on the ionization balance of plasmas
Photoionization and recombination of Fe XIX
Photoionization cross sections and recombination rate coefficients are
presented for the L-shell ground state fine structure levels $2s^22p^4 \
^3P_{2,0,1}^3P_{2,0,1}$
levels are up to 50% higher than the LS rates at low temperarures but
comparable for higher temperatures; in contrast to the results of Donnelly et
al who obtained the LS rates to be higher than their BPRM results by about a
factor of 2. Reasons for these discrepancies are discussed.Comment: 7 pages, 3 figures, MNRAS, In Pres
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Dielectronic recombination data for dynamic finite-density plasmas II. The oxygen isoelectronic sequence
Mistakes in an earlier publication (Zatsarinny et al. 2003) have been discovered and are corrected below (in boldface). The first is a missing exponent in an equation, the second is some wrong fitting coefficients for several ions, the third and fourth are an incorrect caption and an incorrect label in a figure, and the fifth is an inaccuracy in high-temperature radiative recombination rate coefficients
Dielectronic Recombination of Ground-State and Metastable Li+ Ions
Dielectronic recombination has been investigated for Delta-n = 1 resonances
of ground-state Li+(1s^2) and for Delta-n = 0 resonances of metastable Li+(1s2s
^3S). The ground-state spectrum shows three prominent transitions between 53
and 64 eV, while the metastable spectrum exhibits many transitions with
energies < 3.2 eV. Reasonably good agreement of R-matrix, LS coupling
calculations with the measured recombination rate coefficient is obtained. The
time dependence of the recombination rate yields a radiative lifetime of 52.2
+- 5.0 s for the 2 ^3S level of Li+.Comment: Submitted to Phys. Rev. A; REVTeX, 4 pages, 3 figure
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Calculation of Atomic Data for NASA Missions
The interpretation of cosmic spectra relies on a vast sea of atomic data which are not readily obtainable from analytic expressions or simple calculations. Rather, their evaluation typically requires state-of-the-art atomic physics calculations, with the inclusion of weaker effects (spin-orbit and configuration interactions, relaxation, Auger broadening, etc.), to achieve the level of accuracy needed for use by astrophysicists. Our NASA-supported research program is focused on calculating data for three important atomic processes, 1) dielectronic recombination (DR), 2) inner-shell photoabsorption, and 3) fluorescence and Auger decay of inner-shell vacancy states. Some additional details and examples of our recent findings are given below
Deep inelastic scattering and "elastic" diffraction
We examine the total cross section of virtual photons on protons,
, at low and its
connection with ``elastic'' diffractive production in the two-gluon exchange dynamics for the virtual forward
Compton scattering amplitude. Solely based on the generic structure of
two-gluon exchange, we establish that the cross section is described by the
(imaginary part of the) amplitude for forward scattering of vector
states, . The
generalized vector dominance/color dipole picture (GVD/CDP) is accordingly
established to only rest on the two-gluon-exchange generic structure. This is
explicitly seen by the sum rules that allow one to directly relate the total
cross section to the cross section for elastic diffractive forward production,
, of vector states.Comment: 24 pages, latex file with three eps figures. BI-TP 2002/2
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