X-ray absorption of cold gas: Simulating interstellar molecular clouds in the laboratory.

Galactic and extragalactic sources produce x-rays that are often absorbed by molecules and atoms in giant molecular clouds (GMCs), which provides valuable information about their composition and physical state. We mimic this phenomenon with a laboratory Z-pinch x-ray source, which is impinged on neutral molecular gas. This technique produces a soft x-ray pseudocontinuum using a pulsed-current generator. The absorbing gas is injected from a 1-cm-long planar gas-puff without any window or vessel along the line of sight. An x-ray spectrometer with a resolving power of λ/Δλ∼420, comparable to that of astrophysical space instruments, records the absorbed spectra. This resolution clearly resolves the molecular lines from the atomic lines, thus motivating the search for a molecular signature in astrophysical x-ray spectra. The experimental setup enables different gas compositions and column densities. K-shell spectra of CO_{2}, N_{2}, and O_{2} reveal a plethora of absorption lines and photoelectric edges measured at molecular column densities between ∼10^{16} and 10^{18} cm^{-2} typical of GMCs. We find that the population of excited states, contributing to the edge, increases with gas density.

Seed dispersal of wild radishes and its association with within-population spatial distribution.

BACKGROUND: The wild radishes, Raphanus raphanistrum and R. pugioniformis (Brassicaceae) are native to the East Mediterranean region. However, whereas R. raphanistrum is widely distributed worldwide, the endemic R. pugioniformis is limited to specific habitats. In R. raphanistrum the diaspores of the indehiscent fruits comprise glabrous, light, single-seeded segments, whereas the intact fruits of R. pugioniformis are heavy and covered with spiny backward-pointing trichomes. We aimed to investigate whether the structure of the diaspores was directly associated with long- and short-range dispersal in R. raphanistrum and R. pugioniformis, respectively. We further surveyed within-population spatial distributions, to test the hypothesis that short- and long-range dispersal contribute to a patchy vs. uniform distribution patterns of R. pugioniformis and R. raphanistrum, respectively. RESULTS: The results indicated that dispersal by wind and run-off water was substantially lower for diaspores of R. pugioniformis than for those of R. raphanistrum diaspores. Supporting the hypothesis that backward-pointing trichomes promote adherence to soil particles, the displacement on soil surface of R. pugioniformis fruits depended on their orientation relative to wind direction. Furthermore, trichome removal from fruits of R. pugioniformis significantly reduced wind velocity needed to remove fruits that were placed on soils typical of the species' natural habitats. The spatial-distribution survey results indicated a patchy distribution of R. pugioniformis populations as compared with the more uniform arrangement in the studied populations of R. raphanistrum; consistent with the unidirectional vs. homogeneous wind dispersal of the respective diaspores, with respect to wind direction. In addition, R. pugioniformis population sizes changed less between years than those of R. raphanistrum. CONCLUSIONS: Overall, our results indicate that fruit structure is strongly linked to dispersal ability and spatial distribution of the two closely related wild radish species. Whereas R. raphanistrum inhabits homogenous sandy soil habitats, the distribution range of R. pugioniformis includes heterogeneous environments in which growth niches are scarcer. We suggest that the different modes of dispersal have evolved as adaptive traits appropriate to the species' specific habitats.

GLIDER-A pulsed-current generator for laboratory astrophysics x-ray absorption experiments.

In the field of pulse-power, there has always been an interest on small and medium size pulsed-current generators (≤2 MA) which are affordable and of low maintenance. We developed the GLIDER, a compact and modular generator, that drives a gas-puff z-pinch load as a soft x-ray source (0.1-1 keV) for laboratory astrophysics absorption experiments. It comprises 48 bricks, tightly packed in a 1.7 m × 3.5 m × 0.8 m transformer oil container. Its compactness and reliability was enabled owing to unique multilayered oil-soaked insulators, and more than 100 post-hole convolutes. Its stripline includes interchangeable tiles for ease of construction and maintenance. Six triggering units enable current pulse shaping. The GLIDER was tested up to ±60 kV (34 kJ) and produced 2 MA in 450 ns rise time on a 5 nH load. We present grating spectra of K-shell absorption of neutral O and N proving the experimental concept and demonstrating column density and ionization measurements.

Galaxy evolution. Black hole feedback in the luminous quasar PDS 456.

The evolution of galaxies is connected to the growth of supermassive black holes in their centers. During the quasar phase, a huge luminosity is released as matter falls onto the black hole, and radiation-driven winds can transfer most of this energy back to the host galaxy. Over five different epochs, we detected the signatures of a nearly spherical stream of highly ionized gas in the broadband x-ray spectra of the luminous quasar PDS 456. This persistent wind is expelled at relativistic speeds from the inner accretion disk, and its wide aperture suggests an effective coupling with the ambient gas. The outflow's kinetic power larger than 10(46) ergs per second is enough to provide the feedback required by models of black hole and host galaxy coevolution.

Active galaxies. A fast and long-lived outflow from the supermassive black hole in NGC 5548.

Supermassive black holes in the nuclei of active galaxies expel large amounts of matter through powerful winds of ionized gas. The archetypal active galaxy NGC 5548 has been studied for decades, and high-resolution x-ray and ultraviolet (UV) observations have previously shown a persistent ionized outflow. An observing campaign in 2013 with six space observatories shows the nucleus to be obscured by a long-lasting, clumpy stream of ionized gas not seen before. It blocks 90% of the soft x-ray emission and causes simultaneous deep, broad UV absorption troughs. The outflow velocities of this gas are up to five times faster than those in the persistent outflow, and, at a distance of only a few light days from the nucleus, it may likely originate from the accretion disk.

Resonant and near-threshold photoionization cross sections of Fe14+.

Photoionization (PI) of Fe14+ in the range from 450 to 1100 eV was measured at the BESSY II storage ring using an electron beam ion trap achieving high target-ion area densities of 10(10) cm(-2). Photoabsorption by this ion is observed in astrophysical spectra and plasmas, but until now cross sections and resonance energies could only be provided by calculations. We reach a resolving power E/ΔE of at least 6500, outstanding in the present energy range, which enables benchmarking and improving the most advanced theories for PI of ions in high charge states.

Polymorphism of adhesion molecule CD31 and its role in acute graft-versus-host disease.

BACKGROUND: Graft-versus-host disease (GVHD) caused by poorly defined minor (i.e., other than HLA) histocompatibility antigens remains a serious problem in recipients of bone marrow transplants. We sought to determine whether the CD31 adhesion molecule is a minor alloantigen. METHODS: We directly sequenced samples of complementary DNA (cDNA) encoding CD31 molecules from 21 unrelated normal subjects. Sequence-specific primers were then designed to amplify alleles by the polymerase chain reaction, thereby permitting CD31 typing of genomic DNA from additional normal subjects. To assess the relevance of CD31 matching to bone marrow transplantation, we performed CD31 typing of 46 recipients of bone marrow (32 without GVHD and 14 with severe [grade III or IV] acute GVHD) and their HLA-identical sibling donors. The immunoreactivity of CD31 phenotypes with anti-CD31 monoclonal antibodies was compared by flow cytometry. RESULTS: Direct sequencing of cDNA for CD31 from the 21 normal subjects identified a single polymorphism, CTG-->GTG (Leu-->Val), at codon 125; we designated the resulting alleles CD31.L and CD31.V, respectively. The CD31 genotypes of these and 142 other unrelated subjects were of the expected frequencies. Among the transplant recipients, 71 percent of those with acute GVHD had CD31 genotypes that were not identical to the donor's genotype, as compared with 22 percent of the recipients without GVHD (P = 0.004). The binding of anti-CD31 monoclonal antibodies as measured by fluorescence-activated cell sorting correlated with the CD31 types of homozygous cell lines. CONCLUSIONS: The adhesion molecule CD31 is polymorphic. When donor and recipient genotypes are not identical, the risk of GVHD increases. Prospective CD31 typing may reduce the risk of acute GVHD.

Differential suppression activity induced by paternal leukocyte immunization in habitual abortion.

In order to investigate the possible role of suppressor cells in paternal leukocyte immunization to prevent recurrent miscarriages, peripheral blood lymphocytes from habitually aborting women before and after immunization were assessed. Immunization-induced suppressor activity as shown by (1) rise in CD8-positive cells and a decline in the CD4/CD8 ratio, (2) failure of cyclosporine A to inhibit the proliferation of phytohemagglutinin- and alloantigen-stimulated cells and (3) unresponsiveness to the immunizing spouses' antigen. These findings resembled those in normal pregnant women. Hence, paternal leukocyte immunization may induce specific and nonspecific T cell suppression which may induce the immune tolerance necessary to maintain pregnancy.

Lupus anti-DNA antibodies bearing the 8.12 idiotype appear to be somatically mutated.

Anti-DNA antibodies in systemic lupus erythematosus (SLE) sera were analyzed using an antiidiotype designated 8.12 which recognizes a determinant on lambda light chains highly expressed in SLE sera. Eight of ten normal individuals had peripheral blood lymphocytes which produced high-titered 8.12-positive antibodies, following transformation with Epstein Barr virus, implying that the 8.12-reactive sequence originates in the germline gene (GLG). Of 58 SLE sera, 32 contained elevated titers of 8.12-reactive antibodies. Twenty-three of these sera had 8.12-reactive anti-DNA antibodies, suggesting a strong correlation between 8.12 idiotype and DNA binding. Moreover, 20 of 26 8.12-reactive IgG antibodies and only 4 of 10 8.12-reactive IgM antibodies bound DNA (P less than 0.05). These observations strengthen our previous findings in myeloma sera that DNA binding is associated with IgG isotype in the 8.12 idiotype system and suggest that the acquisition of anti-DNA reactivity in antibodies bearing the GLG idiotype 8.12 is achieved by somatic mutation, a feature of an antigen-driven response.

Anti-idiotypic IgM antibodies to anti-HLA class I antibodies in habitual abortion.

In order to investigate the role of the idiotypic network in miscarriages, sera from 28 habitually aborting women undergoing paternal leukocyte immunization were studied for the presence of HLA antibodies and related anti-idiotypes. Sixty-eight percent of sera from preimmunized patients which did not contain anti-lymphocyte antibodies inhibited the activity of antibodies to the HLA class I antigens expressed by the spouse. This inhibitory activity could be assigned to IgM antibodies, which cross-inhibit antibodies of similar specificity. This suggests that they are anti-idiotypes for the binding site of HLA antibodies. Immune sera of successfully treated patients exhibited both cytotoxic IgG anti-HLA antibodies and inhibitory IgM anti-idiotypic antibodies. A possible role for an intact idiotypic network in maintaining pregnancy is suggested.