X-Ray Emission from the Warm Hot Intergalactic Medium

The number of detected baryons in the Universe at z<0.5 is much smaller than predicted by standard big bang nucleosynthesis and by the detailed observation of the Lyman alpha forest at red-shift z=2. Hydrodynamical simulations indicate that a large fraction of the baryons today is expected to be in a ``warm-hot'' (10^5-10^7K) filamentary gas, distributed in the intergalactic medium. This gas, if it exists, should be observable only in the soft X-ray and UV bands. Using the predictions of a particular hydrodynamic model, we simulated the expected X-ray flux as a function of energy in the 0.1-2 keV band due to the Warm-Hot Intergalactic Medium (WHIM), and compared it with the flux from local and high red-shift diffuse components. Our results show that as much as 20% of the total diffuse X-ray background (DXB) in the energy range 0.37-0.925keV could be due to X-ray flux from the WHIM, 70% of which comes from filaments at redshift z between 0.1 and 0.6. Simulations done using a FOV of 3', comparable with that of Suzaku and Constellation-X, show that in more than 20% of the observations we expect the WHIM flux to contribute to more than 20% of the DXB. These simulations also show that in about 10% of all the observations a single bright filament in the FOV accounts, alone, for more than 20% of the DXB flux. Red-shifted oxygen lines should be clearly visible in these observations.Comment: 19 pages, 6 figure

New markers and linkage data

New markers and linkage dat

New isogenic wild types in N. crassa

New isogenic wild types in N. crass

Strings And Non-Topological Solitons

We have numerically calculated topological andnon-topological solitons in two spatial dimensions with Chern-Simons term. Their quantum stability, as well as that of the Maxwell vortex, is analyzed by means of bounce instantons which involve three-dimensional strings and non-topological solitons.Comment: 12 pages. 5 figure

Frequency of the New HLA-B*2709 Allele in Ankylosing Spondylitis Patients and Healthy Individuals

We have recently described a new HLA-B27 subtype, named HLA-B*2709 (Del Porto et al. 1994). This allele is identical to the subtype most frequently found in Caucasoids, HLA-B*2705, except for a single amino acid substitution (Asp to His) in position 116. This residue, that is part of the F pocket of the molecule, has been shown to be relevant in determining which C-terminal amino acid of HLA-class I-binding peptides can be accomodated into the groove (Elliott, 1993). In nonamer peptides, this aminoacid corresponds to a primary anchor position (P9; Madden et al., 1992). Accordingly, we have previously shown that B2709 molecule hardly accepts nonamer peptides with an Arg or Tyr in P9, while the same amino acids represent good anchors for B2705 molecules (Fiorillo et al., 1995). Special attention is focused on HLA-B27 subtypes because of the strong association of B27 with ankylosing spondylitis (AS). More than 90% of AS patients are B27-positive and, conversely, about 4% of B27-positive individuals in the population are affected. This represents a relative risk over 100, that is the highest in HLA-disease associations. However, little is known on the pathogenic mechanisms of the disease. Following the hypothesis that an antigenic B27-binding peptide is involved in the disease (the so-called arthritogenic peptide), differential association with the different B27 subtypes may give a clue on the nature of such peptide. If two subtypes of partially overlapping peptide binding specificity are found to be both AS-associated, this would restrict the search for peptides that can be bound by both allelic products. Conversely, if a B27 subtype is found to be non AS-associated, this would be even more helpful in eliminating an array of peptides as possible candidates

Observed Limits on Charge Exchange Contributions to the Diffuse X-ray Background

We present a high resolution spectrum of the diffuse X-ray background from 0.1 to 1 keV for a ~1 region of the sky centered at l=90, b=+60 using a 36-pixel array of microcalorimeters flown on a sounding rocket. With an energy resolution of 11 eV FWHM below 1 keV, the spectrum's observed line ratios help separate charge exchange contributions originating within the heliosphere from thermal emission of hot gas in the interstellar medium. The X-ray sensitivity below 1 keV was reduced by about a factor of four from contamination that occurred early in the flight, limiting the significance of the results. The observed centroid of helium-like O VII is 568+2-3 eV at 90% confidence. Since the centroid expected for thermal emission is 568.4 eV while for charge exchange is 564.2 eV, thermal emission appears to dominate for this line complex, consistent with much of the high-latitude O VII emission originating in 2-3 x 10^6 K gas in the Galactic halo. On the other hand, the observed ratio of C VI Ly gamma to Ly alpha is 0.3+-0.2. The expected ratios are 0.04 for thermal emission and 0.24 for charge exchange, indicating that charge exchange must contribute strongly to this line and therefore potentially to the rest of the ROSAT R12 band usually associated with 10^6 K emission from the Local Hot Bubble. The limited statistics of this experiment and systematic uncertainties due to the contamination require only >32% thermal emission for O VII and >20% from charge exchange for C VI at the 90% confidence level. An experimental gold coating on the silicon substrate of the array greatly reduced extraneous signals induced on nearby pixels from cosmic rays passing through the substrate, reducing the triggered event rate by a factor of 15 from a previous flight of the instrument.Comment: 14 pages, 7 figures, to be published in Ap