Atomic Data for Permitted Resonance Lines of Atoms and Ions from H to Si, and S, Ar, Ca and Fe

We list vacuum wavelengths, energy levels, statistical weights, transition probabilities and oscillator strengths for permitted resonance spectral lines of all ions of 18 astrophysically important elements (H through Si, S, Ar, Ca, Fe). Using a compilation of experimental energy levels, we derived accurate wavelengths for 5599 lines of 1828 ground-term multiplets which have gf-values calculated in the Opacity Project. We recalculated the Opacity Project multiplet gf-values to oscillator strengths and transition probabilities of individual lines. For completeness, we added 372 resonance lines of NeI, ArI, FeI and FeII ions which are not covered by the Opacity Project. Intercombination and forbidden lines are not included in the present compilation.Comment: 6 pages of text, latex, 1 figure, 4 tables; tables in ASCII format available at ftp://asta.pa.uky.edu/dima/lines/ or at http://www.pa.uky.edu/~verner/atom.html Accepted by Atomic Data Nucl. Data Table

A Tale of Two Countries: Poverty among Immigrants in Denmark and Sweden since 1984

poverty, immigrants, panel data

Effective order strong stability preserving Runge–Kutta methods

We apply the concept of effective order to strong stability preserving (SSP) explicit Runge–Kutta methods. Relative to classical Runge–Kutta methods, effective order methods are designed to satisfy a relaxed set of order conditions, but yield higher order accuracy when composed with special starting and stopping methods. The relaxed order conditions allow for greater freedom in the design of effective order methods. We show that this allows the construction of four-stage SSP methods with effective order four (such methods cannot have classical order four). However, we also prove that effective order five methods—like classical order five methods—require the use of non-positive weights and so cannot be SSP. By numerical optimization, we construct explicit SSP Runge–Kutta methods up to effective order four and establish the optimality of many of them. Numerical experiments demonstrate the validity of these methods in practice

Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions

We present a complete set of analytic fits to the non-relativistic photoionization cross sections for the ground states of atoms and ions of elements from H through Si, and S, Ar, Ca, and Fe. Near the ionization thresholds, the fits are based on the Opacity Project theoretical cross sections interpolated and smoothed over resonances. At higher energies, the fits reproduce calculated Hartree-Dirac-Slater photoionization cross sections.Comment: 24 pages including Postscript figures and tables, uses aaspp4.sty, accepted for publication in Astrophysical Journal. Misprint in Eq.(1) is correcte

The Molecular Structure of Cyclobutane

The cyclobutane molecule has been found by electron diffraction to have the following bond distances and bond angles: C–C, 1.568±0.02A; C–H, 1.098±0.04A; ∠HCH, 114±8°. On the average the ring is nonplanar, with dihedral angle 20° (+10°, −20°), but the equilibrium symmetry may be either D_(2d) (puckered ring) or D_(4h) (planar ring with low rigidity leading to large amplitude of out‐of‐plane bending). This point is discussed in connection with earlier spectroscopic work. The long bond distances found in four‐membered rings are contrasted against the short distances in three‐membered rings, and the strain energies, bond distances, and HCH angles of cycloalkanes are discussed in terms of modern valence concepts. It is suggested that the potential energy arising from a repulsion of the nonbonded carbon atoms may contribute significantly to the apparently anomalously high strain energy of cyclobutane. The repulsive force associated with such a potential is shown to account satisfactorily for the long C–C distances

Photoexcited electron dynamics in Kondo insulators and heavy fermions

We have studied the photoexcited carrier relaxation dynamics in the Kondo insulator SmB6 and the heavy fermion metal YbAgCu4 as a function of temperature and excitation level. The dynamic response is found to be both strongly temperature dependent and nonlinear. The data are analyzed with a Rothwarf-Taylor bottleneck model, where the dynamics are governed by the presence of a narrow gap in the density of states near the Fermi level. The remarkable agreement with the model suggests that carrier relaxation in a broad class of heavy electron systems (both metals and insulators) is governed by the presence of a (weakly temperature dependent) hybridization gap.Comment: accepted for publication in Physical Review Letter

A Structure Containing Diastereomers, (2\u3ci\u3eS\u3c/i\u3e,4\u3ci\u3eR\u3c/i\u3e)-\u3ci\u3etrans\u3c/i\u3e- and (2\u3ci\u3eR\u3c/i\u3e,4\u3ci\u3eR\u3c/i\u3e)-\u3ci\u3ecis\u3c/i\u3e-2-hydroxy-2,4-dimethyl-3,4-dihydro-2\u3ci\u3eH\u3c/i\u3e,5\u3ci\u3eH\u3c/i\u3e-pyrano[3,2-\u3ci\u3ec\u3c/i\u3e][1]benzopyran-5-one, C\u3csub\u3e14\u3c/sub\u3eH\u3csub\u3e14\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e

Mr = 246·3, monoclinic, P21, a = 7·804 (3), b = 18·248 (8), c = 8·752 (5) Å, β = 99·59°, V = 1233 Å3, Z = 4 (2 molecules/asymmetric unit), Dx = 1·33 g cm-3, λ(Mo Kα) = 0·71067 Å, μ = 0·91 cm,-1, F(000) = 520, T = 293 K. Final R = 0·066 for 1123 observed independent intensities. The structure consists of diastereomers approximately inversionrelated through a pseudocenter of symmetry at x = 0·241 (4), z = 0·281 (3) except the 4-methyl groups. The dihydropyran rings are half chairs distorted towards the eƒ-diplanar conformation. Like molecules are hydrogen-bonded between hydroxyl and carbonyl groups along a, O···O distances being 2·781 (7) (trans) and 2· 780 (7) Å (cis)