We present the first reliable determination of chemical abundances in an AGN outflow. The abundances are extracted from the deep and simultaneous FUSE and HST/STIS observations of Mrk 279. This data set is exceptional for its high signal-to-noise, unblended doublet troughs and little Galactic absorption contamination. These attributes allow us to solve for the velocity-dependent covering fraction, and therefore obtain reliable column densities for many ionic species. For the first time we have enough such column densities to simultaneously determine the ionization equilibrium and abundances in the flow. Our analysis uses the full spectral information embedded in these high-resolution data. Slicing a given trough into many independent outflow elements yields the extra constraints needed for a physically meaningful abundances determination. We find that relative to solar the abundances in the Mrk 279 outflow are (linear scaling): carbon 2.2±0.7, nitrogen 3.5±1.1 and oxygen 1.6±0.8. Our UV-based photoionization and abundances results are in good agreement with the independent analysis of the simultaneous Mrk 279 X-ray spectra. This is the best agreement between the UV and X-ray analyses of the same outflow to date.

20Joint Inelastic Neutron and X Ray Scattering measurements have been performed on heavy water across the melting point. The spectra bear clear evidence of a low and a high frequency inelastic shoulders related to a transverse and a longitudinal mode, respectively. Upon increasing the momentum transfer, the spectral shape evolves from a viscoelastic regime, where the low frequency mode is clearly over-damped, towards an elastic one where its propagation becomes instead allowed.The crossover between the two regimes occurs whenever both the characteristic frequency and the line-width of the low frequency mode match the inverse of the structural relaxation time. Furthermore, we observe that the frequency of the transverse mode undergoes a discontinuity across the melting, whose extent reduces upon increasing the exchanged momentum. PACS numbers: 62.60.+v,25.40.Fq 1 I. INTRODUCTION 2The presence of a second, low-frequency and weakly dispersing mode in the THz spectrum of water is a common 3 finding of several Inelastic Neutron 1-4 and X Ray 5-9 Scattering (INS and IXS respectively) experiments. Its onset 4 was at first predicted in the mid-1970s by a molecular dynamics (MD) simulation 10 and more recently interpreted, by 5 similar computational methods, as the manifestation of a THz viscoelastic behavior 11 . This low-frequency excitation 6 appears in the spectrum of density fluctuations , S(Q, ω), when the exchanged momentum, Q, exceeds some 7 threshold value, Q T ≈ 4 nm −1 , and, according to a broadly accepted interpretation 7-9,11 , it arises from the coupling 8 of density fluctuations with shear waves 12 . This explanation stems from the analogy with ice, whose spectrum is 9 characterized by an optic transverse phonon at comparable frequencies 13 . Furthermore, it is supported by MD 10 results 8,11 demonstrating the presence of an analogous peak in the correlation function of transverse velocities. 11 12 In summary, the body of literature results on the S(Q, ω) of water outlines a rather coherent scenario: owing to the 13 lack of translational invariance typical of liquids, longitudinal and transverse modes become mutually intertwined and 14 their symmetry somehow ill-defined at distances shorter than some threshold ≈ Q −1 T . Such longitudinal-transverse 15 (L-T) coupling causes the onset of an inelastic transverse mode in the S(Q, ω), even if the latter, in principle, only 16 couples with longitudinal modes. 17 18It seems natural to ascribe the strength of the L-T coupling in water to the presence of a hydrogen bond network, 19 which enhances the correlations between the movements of molecules belonging to adjacent layers of the liquid, 20 thus fostering the propagation of shear waves. An L-T coupling has been demonstrated in other simulated network 21 systems such as glassy glycerol 14 and also experimentally observed in SiO 2 15 , GeO 2 16 and GeSe 2 17 , samples sharing 22 with water the property of a tetrahedral arrangement of local intermolecular structure. The circumstance that L-T 23 coupling was evi...

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We have investigated the accuracy of the 1s-vacancy fluorescence data base of Kaastra & Mewe (1993) resulting from the initial atomic physics calculations and the subsequent scaling along isoelectronic sequences. In particular, we have focused on the relatively simple Be-like and F-like 1s-vacancy sequences. We find that the earlier atomic physics calculations for the oscillator strengths and autoionization rates of singly-charged B II and Ne II are in sufficient agreement with our present calculations. However, the substantial charge dependence of these quantities along each isoelectronic sequence, the incorrect configuration averaging used for B II, and the neglect of spin-orbit effects (which become important at high-Z) all cast doubt on the reliability of the Kaastra & Mewe (1993) data for application to plasma modeling.