975 research outputs found
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
Electron-Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements. VII. Relativistic calculations for O VI and O VII for UV and X-ray modeling
Aimed at ionization balance and spectral analysis of UV and X-ray sources, we
present self-consistent sets of photoionization cross sections, recombination
cross sections, and rate coefficients for Li-like O VI and He-like O VII.
Relativistic fine structure is considered through the Breit-Pauli R-matrix
(BPRM) method in the close coupling approximation, implementing the unified
treatment for total electron-ion recombination subsuming both radiative and
di-electronic recombination processes. Self-consistency is ensured by using an
identical wavefunction expansion for the inverse processes of photoionization
and photo-recombination. Radiation damping of resonances, important for H-like
and He-like core ions, is included. Compared to previous LS coupling results
without radiative decay of low-n (<= 10) resonances, the presents results show
significant reduction in O VI recombination rates at high temperatures. In
addition to the total rates, level-specific photoionization cross sections and
recombination rates are presented for all fine structure levels n (lSLJ) up to
n <= 10, to enable accurate computation of recombination-cascade matrices and
spectral formation of prominent UV and X-ray lines such as the 1032,1038 A
doublet of O VI, and the `triplet' forbidden, intercombination, and resonance
X-ray lines of O VII at 22.1, 21.8, and 21.6 \ang respectively. Altogether,
atomic parameters for 98 levels of O VI and 116 fine structure levels of O VII
are theoretically computed. These data should provide a reasonably complete set
of photoionization and recombination rates in collisional or radiative
equilibrium.Comment: 33 pages, 8 figures, submitted to ApJ
[O II] line ratios
Based on new calculations we reconfirm the low and high density limits on the
forbidden fine structure line ratio [O II] I(3729)/I(3726): lim_{N_ e} --> 0} =
1.5 and lim_{N_ e} --> \infty} = 0.35. Employing [O II] collision strengths
calculated using the Breit-Pauli R-matrix method we rule out any significant
deviation due to relativistic effects from these canonical values. The present
results are in substantial agreement with older calculations by Pradhan (1976)
and validate the extensive observational analysis of gaseous nebulae by Copetti
and Writzel (2002) and Wang et al (2004) that reach the same conclusions. The
present theoretical results and the recent observational analyses differ
significantly from the calculations by MacLaughlin and Bell (1998) and Keenan
et al (1999). The new maxwellian averaged effective collision strengths are
presented for the 10 transitions among the first 5 levels to enable
computations of [O II] line ratios.Comment: Submitted to MNRAS (Letters), 4 pages, 2 figures, 1 tabl
K-shell dielectronic resonances in photoabsorption: differential oscillator strengths for Li-like C IV, O VI, and Fe XXIV
Recently X-ray photoabsorption in KLL resonances of O VI was predicted
[Pradhan, Astrophys.J. Lett. 545, L165 (2000)], and detected by the Chandra
X-ray Observatory [Lee et al, Astrophys. J. {\it Lett.}, submitted].
The required resonance oscillator strengths f_r, are evaluated in terms of
the differential oscillator strength df/de that relates bound and continuum
absorption. We present the f_r values from radiatively damped and undamped
photoionization cross sections for Li-like C,O, and Fe calculated using
relativistic close coupling Breit-Pauli R-matrix method. The KLL resonances of
interest here are: 1s2p (^3P^o) 2s [^4P^o_{1/2,3/2}, ^2P^o_{1/2,3/2}] and 1s2p
(^1P^o) 2s [^2P^o_{1/2,3/2}]. The KLL photoabsorption resonances in Fe XXIV are
fully resolved up to natural autoionization profiles for the first time. It is
demonstrated that the undamped f_r independently yield the resonance radiative
decay rates, and thereby provide a precise check on the resolution of
photoionization calculations in general. The predicted photoabsorption features
should be detectable by the X-ray space observatories and enable column
densities in highly ionized astrophysical plasmas to be determined from the
calculated f_r. The dielectronic satellites may appear as redward broadening of
resonances lines in emission and absorption.Comment: 9 pages, 2 figurs, Phys. Rev. A, Rapid Communication (submitted
Improved collision strengths and line ratios for forbidden [O III] far-infrared and optical lines
Far-infrared and optical [O III] lines are useful temeprature-density
diagnostics of nebular as well as dust obscured astrophysical sources. Fine
structure transitions among the ground state levels 1s^22s^22p^3 \ ^3P_{0,1,2}
give rise to the 52 and 88 micron lines, whereas transitions among the
levels yield the well-known optical lines 4363,
4959 and 5007 Angstroms. These lines are excited primarily by electron impact
excitation. But despite their importance in nebular diagnostics collision
strengths for the associated fine structure transitions have not been computed
taking full account of relativistic effects. We present Breit-Pauli R-matrix
calculations for the collision strengths with highly resolved resonance
structures. We find significant differences of up to 20% in the Maxwellian
averaged rate coefficients from previous works. We also tabulate these to lower
temperatures down to 100 K to enable determination of physical conditions in
cold dusty environments such photo-dissociation regions and ultra-luminous
infrared galaxies observed with the Herschel space observatory. We also examine
the effect of improved collision strengths on temperature and density sensitive
line ratios.Comment: Letter in press, Monthly Notices of Royal Astronomical Society, 5
pages, 6 figure
Atomic data from the Iron Project.XLIII. Transition probabilities for Fe V
An extensive set of dipole-allowed, intercombination, and forbidden
transition probabilities for Fe V is presented. The Breit-Pauli R-matrix (BPRM)
method is used to calculate 1.46 x 10^6 oscillator strengths for the allowed
and intercombination E1 transitions among 3,865 fine-structure levels dominated
by configuration complexes with n <= 10 and l <= 9. These data are complemented
by an atomic structure configuration interaction (CI) calculation using the
SUPERSTRUCTURE program for 362 relativistic quadrupole (E2) and magnetic dipole
(M1) transitions among 65 low-lying levels dominated by the 3d^4 and 3d^ 4s
configurations. Procedures have been developed for the identification of the
large number of fine-structure levels and transitions obtained through the BPRM
calculations. The target ion Fe VI is represented by an eigenfunction expansion
of 19 fine-structure levels of 3d^3 and a set of correlation configurations. Fe
V bound levels are obtained with angular and spin symmetries SL\pi and J\pi of
the (e + Fe VI) system such that 2S+1 = 5,3,1, L <= 10, J <= 8 of even and odd
parities. The completeness of the calculated dataset is verified in terms of
all possible bound levels belonging to relevant LS terms and transitions in
correspondence with the LS terms. The fine-structure averaged relativistic
values are compared with previous Opacity Project LS coupling data and other
works. The 362 forbidden transition probabilities considerably extend the
available data for the E2 and M1 transtions, and are in good agreement with
those computed by Garstang for the 3d^4 transitions.Comment: 19 pages, 1 figure. This paper marks the beginning of a large-scale
effort of ab initio atomic calculations that should eventually lead to
re-calculation of accurate iron opacities. Astron. Astrophys. Suppl. Ser. (in
press
Promoting physical activity in upper elementary children using multi-theory model (MTM) of health behavior change
Background: Physical activity and exercise offer numerous benefits to children and Centers for Disease Control and Prevention guidelines require that school children engage in at least 60 minutes of moderate to vigorous physical activity every day. Unfortunately, up to 30% elementary students do not meet these requirements and 79% elementary schools do not provide students with physical education classes every day. The transition from elementary to secondary school is particularly deleterious for levels of physical activity. Therefore, there is a need to develop educational interventions for upper elementary school children to promote physical activity. A new theory multi-theory model (MTM) of health behavior change can be utilized to develop such interventions.Objectives: The purpose of this article was to develop and introduce an instrument based on MTM for physical activity change in upper elementary school children and propose an approach for changing this behavior among sedentary students.Methods: A review of literature in MEDLINE, CINAHL, Google Scholar, and ERIC databases was conducted for physical activity in upper elementary children and multi-theory model of health behavior change to prepare this article. Results: An instrument with Flesch-Kincaid Grade level of 5.4 and the Flesch Reading Ease of 68 making it suitable for administration with upper elementary school children was developed. An approach utilizing the constructs of participatory dialogue, behavioral confidence and changes in physical environment to initiate physical activity and reifying the constructs of emotional transformation, practice for change and changes in social environment to sustain physical activity in upper elementary school children is presented.Conclusions: MTM offers potential to augment current educational efforts to promote physical activity in upper elementary school children
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