Dielectronic Recombination in Photoionized Gas. II. Laboratory Measurements for Fe XVIII and Fe XIX

In photoionized gases with cosmic abundances, dielectronic recombination (DR) proceeds primarily via nlj --> nl'j' core excitations (Dn=0 DR). We have measured the resonance strengths and energies for Fe XVIII to Fe XVII and Fe XIX to Fe XVIII Dn=0 DR. Using our measurements, we have calculated the Fe XVIII and Fe XIX Dn=0 DR DR rate coefficients. Significant discrepancies exist between our inferred rates and those of published calculations. These calculations overestimate the DR rates by factors of ~2 or underestimate it by factors of ~2 to orders of magnitude, but none are in good agreement with our results. Almost all published DR rates for modeling cosmic plasmas are computed using the same theoretical techniques as the above-mentioned calculations. Hence, our measurements call into question all theoretical Dn=0 DR rates used for ionization balance calculations of cosmic plasmas. At temperatures where the Fe XVIII and Fe XIX fractional abundances are predicted to peak in photoionized gases of cosmic abundances, the theoretical rates underestimate the Fe XVIII DR rate by a factor of ~2 and overestimate the Fe XIX DR rate by a factor of ~1.6. We have carried out new multiconfiguration Dirac-Fock and multiconfiguration Breit-Pauli calculations which agree with our measured resonance strengths and rate coefficients to within typically better than <~30%. We provide a fit to our inferred rate coefficients for use in plasma modeling. Using our DR measurements, we infer a factor of ~2 error in the Fe XX through Fe XXIV Dn=0 DR rates. We investigate the effects of this estimated error for the well-known thermal instability of photoionized gas. We find that errors in these rates cannot remove the instability, but they do dramatically affect the range in parameter space over which it forms.Comment: To appear in ApJS, 44 pages with 13 figures, AASTeX with postsript figure

Spectroscopic Observations of Fe XVIII in Solar Active Regions

The large uncertainties associated with measuring the amount of high temperature emission in solar active regions represents a significant impediment to making progress on the coronal heating problem. Most current observations at temperatures of 3 MK and above are taken with broad band soft X-ray instruments. Such measurements have proven difficult to interpret unambiguously. Here we present the first spectroscopic observations of the Fe XVIII 974.86 AA emission line in an on-disk active region taken with then SUMER instrument on SOHO. Fe XVIII has a peak formation temperature of 7.1 MK and provides important constraints on the amount of impulsive heating in the corona. Detailed evaluation of the spectra and comparison of the SUMER data with soft X-ray images from the XRT on Hinode confirm that this line is unblended. We also compare the spectroscopic data with observations from the AIA 94 AA channel on SDO. The AIA 94 AA channel also contains Fe XVIII, but is blended with emission formed at lower temperatures. We find that is possible to remove the contaminating blends and form relatively pure Fe XVIII images that are consistent with the spectroscopic observations from SUMER. The observed spectra also contain the Ca XIV 943.63 AA line that, although a factor 2 to 6 weaker than the Fe XVIII 974.86 AA line, allows us to probe the plasma around 3.5 MK. The observed ratio between the two lines indicates (isothermal approximation) that most of the plasma in the brighter Fe XVIII active region loops is at temperatures between 3.5 and 4 MK.Comment: 12 pages, 5 figures. Submitted as letter to Ap

Probing the QCD vacuum

Heavy quark bound states are used as significative probes of the QCD vacuum and the mechanism of confinement.Comment: 13 pages, sprocl.sty, 2 figures, Invited talk given at the XVIII Autumn School ``Topology of Strongly Correlated Systems'', Lisbon, Portugal, 8-13 October, 200

Review of Post-Theory: Reconstructing Film Studies, edited by David Bordwell and Noël Carroll (Madison, Wisconsin: the University of Wisconsin Press, 1996)

A review of Post-Theory: Reconstructing Film Studies, edited by David Bordwell and Noël Carroll (Madison, Wisconsin: the University of Wisconsin Press, 1996), xviii & 564 pages, $45.00 cloth,$17.95 paper, published on pages 492-494 of Philosophy & Literature, Vol. 21, No. 2 (October, 1997)

Single-top production with the POWHEG method

We describe briefly the POWHEG method and present results for single-top s- and t-channel production at hadron colliders.Comment: 5 pages, 2 figures. Submitted to the proceedings of the XVIII International Workshop on Deep-Inelastic Scattering and Related Subjects, DIS 2010, April 19-23, 2010, Firenze, Ital

Atmospheric neutrino results from Super-Kamiokande and Kamiokande - Evidence for nu_mu oscillations -

New atmospheric neutrino results from Super-Kamiokande are presented. Results from Kamiokande on upward going muons are also presented. All these data, together with the Kamiokande atmospheric neutrino data give evidence for neutrino oscillations. Two flavor nu_mu nu_tau oscillations, with large sin^2(2theta) and Delta-m^2 in the region of 10^-3 to 10^-2, explain all these data.Comment: 10 pages, 6 figures, to appear in the proceedings of XVIII International Conference on Neutrino Physics and Astrophysics (Neutrino'98), Takayama, Japan, June 199

Universal Properties in Low Dimensional Fermionic Systems and Bosonization

We analyze the universal transport behavior in 1D and 2D fermionic systems by following the unified framework provided by bosonization. The role played by the adiabatic transition between interacting and noninteracting regions is emphasized.Comment: 2 pages, RevTex, contribution for the Proceedings of the XVIII Autumn School `Topology of Strongly Correlated Systems', Lisbon, Portugal, October, 200