Oscillator strengths for dipole-allowed fine-structure transitions in Si II

An extensive dataset of oscillator strengths, line strengths, and Einstein A-coefficients has been calculated for a large number of dipole-allowed (ΔS=0) fine-structure transitions in Si II. The line strengths in LS coupling are obtained in an ab initio manner in the close-coupling approximation employing the R-matrix method. The fine-structure components are obtained through algebraic transformations of the LS multiplets. Observed spectroscopic energies are employed whenever available. A 12-state eigenfunction expansion of the core ion, Si III, is employed for the present calculations. This work presents the oscillator strengths of 1122 fine-structure transitions in Si II corresponding to 390 LS multiplets and provides a reasonably complete set of radiative transitions for this astrophysically important ion for the first time. Present results are of comparable accuracy to previous detailed calculations obtained for a small number of transitions and are in reasonably good agreement with the measured oscillator strengths and lifetimes.I thank Professor Anil K. Pradhan for comments and suggestions. This work was supported by NASA Grants NAGW-3315 and NAS-32643. The computational work was carried out on the Cray Y-MP at the Ohio Supercomputer Center

Electron-Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements. XI. N V-VI and F VII-VIII for Ultraviolet and X-Ray Modeling

Relevant data is available at: http://www.astronomy.ohio-state.edu/~nahar/nahar_radiativeatomicdata/index.htmlThe inverse processes of photoionization and electron-ion recombination for hv + N V ↔ N VI + e, hv + N VI ↔ N VII + e, hv + F VII ↔ F VIII + e, and hv + F VIII ↔ F IX + e are studied in detail using a self-consistent unified method for the total electron-ion recombination. The method enables calculation of the total and level-specific recombination rate coefficients α_R and α_R(i), subsuming both radiative and dielectronic recombination (RR and DR). The photoionization and recombination cross sections σ_PI and σ_RC are computed using an identical wave function expansion for both processes in the close coupling approximation using the R-matrix method. The results include total and partial photoionization cross sections and recombination rate coefficients for all fine-structure levels up to n ≤ 10, about 100 for Li-like N V and F VII with 1/2 ≤ J ≤ 17/2, and over 170 for He-like N VI and F VIII with 0 ≤ J ≤ 10. Level-specific σ_PI(nSLJ ) and α_R(T; nSLJ ) are calculated for the first time for these ions. The coupled-channel wave function expansions for N V and F VII consist of 17 levels of cores N VI and F VIII, respectively, and for N VI and F VIII consist of 16 levels of cores N VII and F IX, respectively. Relativistic fine structure is considered through the Breit-Pauli R-matrix method. The single-valued total α_R(T) is presented over an extended temperature range for astrophysical and laboratory plasma applications. Although the total unified α_R(T) for all ions agree well with the available published RR+DR rates, significant differences are noted at the DR peak for N v. Total α_RC(E) and α_R(E) as functions of photoelectron energy are presented for comparison with experiments. Total rates for H-like N VII and F IX are also given for completeness. The cross sections σ_PI and σ_RC include important atomic effects such as radiation damping, channel couplings, and interference of DR and RR, and should be accurate to within 10%-15%. The comprehensive data sets are applicable for ionization balance and recombination-cascade models for UV and X-ray lines.This work was supported partially by the NASA Astrophysical Theory Program and the Space Astrophysical Research and Analysis programs

Photoionization and electron-ion recombination of Cr I

Using the unified method, the inverse processes of photoionization and electron-ion recombination are studied in detail for neutral chromium, (Cr I + hv ↔ Cr II + e), for the ground and excited states. The unified method based on close-coupling approximation and R-matrix method (i) subsumes both the radiative recombination (RR) and dielectronic recombination (DR) for the total rate and (ii) provides self-consistent sets of photoionization cross sections σ_PI and recombination rates α_RC. The present results show in total photoionization of the ground and excited states an enhancement in the background at the first excited threshold, 3d^4 4s ^5D state of the core. One prominent phot-excitation-of-core (PEC) resonance due to one dipole allowed transition (^6S-^6P^0) in the core is found in the photoionization cross sections of most of the valence electron excited states. Structures in the total and partial photoionization, for ionization into various excited core states and ground state only, respectively, are demonstrated. Results are presented for the septet and quintet states with n ≤ 10 and l ≤ 9 of Cr I. These states couple to the core ground state ^6S and contribute to the recombination rates. State-specific recombination rates are also presented for these states and their features are illustrated. The total recombination rate shows two DR peaks, one at a relatively low temperature, at 630 K, and the other around 40,000 K. This can explain existence of neutral Cr in interstellar medium. Calculations were carried out in LS coupling using a close-coupling wave function expansion of 40 core states. The results illustrate the features in the radiative processes of Cr I and provide photoionization cross sections and recombination rates with good approximation for this astrophysically important ion.This work was partially supported by the NASA Astronomy and Physics Research Analysis Program. The computational work was carried out on Cray machines at the Ohio Supercomputer Center in Columbus Ohio

Oscillator strengths for dipole-allowed fine-structure transitions in Fe XIII

Oscillator strengths, line strengths, and transition probabilities for fine-structure levels in silicon-like iron, Fe XIII, are reported. The data obtained are for 1223 LS bound terms, 64,456 LS multiplets, and 307,863 fine-structure transitions. Calculations are carried out in LS coupling using the close coupling R-matrix approximation with a 14-term eigenfunction expansion. The fine-structure components are obtained through algebraic transformations. Present data considerably exceed the observed and the previously calculated data available, including those from the Opacity Project. Comparisons with previously measured and calculated values are made.I thank Professor Anil K. Pradhan for comments. This work was partially supported by a grant from the NSF for the Iron Project and by the NASA UV and Optical Astrophysical Program. Computations were carried out on the Cray T-94 at the Ohio Supercomputer Center

PHYSICOCHEMICAL PROPERTIES OF ATMOSPHERIC AEROSOLS AND THEIR EFFECT ON ICE CLOUD FORMATION

Atmospheric aerosols play a vital role in the Earth\u27s energy budget-directly by scattering and absorbing solar radiation and indirectly by acting as cloud condensation nuclei and ice-nucleating particles [1, 2]. The cloud formation potential of aerosol is driven by multiple factors, including surface properties, size distribution, composition, mixing state, phase state, and morphology [3]. The interaction of aerosols with clouds alters the aerosol\u27s physicochemical properties. Those properties can also evolve during transport due to atmospheric processing, in turn, affect the aerosol\u27s ice nucleation and cloud formation activities. This thesis presents experimental studies to understand the role of physicochemical properties of aerosol on the formation of ice. To get a detailed understanding of the aerosol effect on ice nucleation, we conducted controlled ice nucleation experiments on a known surface (muscovite mica) with controlled properties (e.g., surface cations) as well as ice nucleation experiments on complex atmospheric particles, which were characterized with multimodal microspectroscopic techniques. The results from controlled experiments suggest that the ice nucleation activity of a surface can be modified by simply changing the surface cations. In contrast, ice nucleation experiments with complex atmospheric particles indicates a more complicated dependence on the physicochemical properties

Multiliteracies Pedagogy in Second Language Learning: Examining How Canadian Elementary ESL Classrooms Can Empower Diverse English Language Learners

Canada\u27s socio-cultural landscape is changing every day due to the transitional migration of demographics from all over the world. The immigrant and refugee populations who enter Canadian society are mostly allophones who do not speak English or French- Canada\u27s two official languages as their mother tongue. The allophone students who belong to this migrator group must learn the official languages to get equal access to the country\u27s social and economic sectors. Thus, Canadian schools are entitled to provide adequate support in teaching English and French to these immigrant students to ensure their merging in broader society. But these immigrant students have diverse linguistic and cultural backgrounds. Therefore, they are essentially various in their second language learning needs. For this reason, it is challenging for educators to support these learners considering their linguistic and cultural diversity. The given research paper conducts a systematic literature review with authentic, peer-reviewed resources to examine how multiliteracies pedagogy can inform second language teaching and learning in elementary classrooms of Ontario, Canada. This study deals with the English language learning of multilingual and multicultural allophone English Language Learners (ELLs) in the English as a Second Language (ESL) programs of Ontario elementary schools. This research paper reflects upon different aspects of multiliteracies approaches. It concludes that multiliteracies pedagogy has numerous potentials to address ELL’s diversity and the educators of Ontario elementary ESL programs can offer a better English language learning environment to the ELLs by ensuring proper implementation of multiliteracies pedagogy in their teaching-learning process