Resumption of mass accretion in RS Oph

The latest outburst of the recurrent nova RS Oph occurred in 2006 February. Photometric data presented here show evidence of the resumption of optical flickering, indicating re-establishment of accretion by day 241 of the outburst. Magnitude variations of up to 0.32 mag in V band and 0.14 mag in B band on time-scales of 600–7000 s are detected. Over the two-week observational period, we also detect a 0.5 mag decline in the mean brightness, from V≈ 11.4 to 11.9, and record B≈ 12.9 mag. Limits on the mass accretion rate of [inline image] are calculated, which span the range of accretion rates modelled for direct wind accretion and Roche lobe overflow mechanisms. The current accretion rates make it difficult for thermonuclear runaway models to explain the observed recurrence interval, and this implies average accretion rates are typically higher than seen immediately post-outburst

Experiment K-6-01. Distribution and biochemistry of mineral and matrix in the femurs of rats

Previous analyses of the composition of mineral and matrix in the bone of young rats following space flight has revealed deficits in calcium, phosphorus, and osteocalcin, a non-collagenous protein, without an associated decrease in collagen. To characterize the location and nature of this mineralization defect in a weight bearing long bone, the femur, researchers attempted to relate the spatial distribution of mineral in situ in the proximal, central and distal thirds of the femoral diaphysis to the biochemical composition of bone from the same area. Biochemical analyses revealed lower concentrations of calcium, phosphorus and osteocalcin but not collagen only in the central third of the diaphysis of the flight animals (F) compared to synchronous controls (S). Collagen concentration was reduced only in the proximal third of the diaphysis, where all 3 crosslinks, expressed as nM/mol collagen were higher in F than S. A new technique, x ray microtomography, with a resolution of 26 microns, was used to obtain semi-quantitative data on mineral distribution in reconstructed sections of wet whole bone. To improve the resolution of the mineral density distribution, images of the surfaces of cut sections were analyzed by backscattered electrons in a scanning electron microscope (BSE). There was good agreement between the results of the two stereochemical techniques which revealed distinct patterns of mineralization in transverse and longitudinal directions of the diaphysis. The novel methodology developed for this flight experiment shows considerable promise in elucidating the biochemical nature of what appear to be regional alterations in the mineralization of long bones of animals exposed to spaceflight

Probing the BLR in AGNs using time variability of associated absorption line

It is know that most of the clouds producing associated absorption in the spectra of AGNs and quasars do not completely cover the background source (continuum + broad emission line region, BLR). We note that the covering factor derived for the absorption is the fraction of photons occulted by the absorbing clouds, and is not necessarily the same as the fractional area covered. We show that the variability in absorption lines can be produced by the changes in the covering factor caused by the variation in the continuum and the finite light travel time across the BLR. We discuss how such a variability can be distinguished from the variability caused by other effects and how one can use the variability in the covering factor to probe the BLR.Comment: 12 pages, latex(aaspp4.sty), 2 figures, (To appear in ApJ

Plasmablast and plasma cell production and distribution in trout immune tissues

These studies describe the in vitro and ex vivo generation of plasmablasts and plasma cells in trout (Oncorhynchus mykiss) peripheral blood and splenic and anterior kidney tissues. Cells were derived either from naive trout and cultured with the polyclonal activator, Escherichia coli LPS, or from trout that had been immunized with trinitrophenyl-keyhole limpet hemocyanin. Hydroxyurea was used to resolve populations of replicating (plasmablast) and nonreplicating (plasma cell) Ab-secreting cells (ASC). Complete inhibition of Ig secretion was only observed within the PBL. Both anterior kidney and splenic lymphocytes possessed a subset of ASCs that were hydroxyurea resistant. Thus, in vitro production of plasma cells appears to be restricted to the latter two tissues, whereas peripheral blood is exclusively restricted to the production of plasmablasts. After immunization with trinitrophenyl-keyhole limpet hemocyanin, specific ASC could be isolated from all immune organs; however, the anterior kidney contained 98% of all ASC. Late in the response (\u3e 10 wk), anterior kidney ASC secreted specific Ab for at least 15 days in culture, indicating that they were long-lived plasma cells. Cells from spleen and peripheral blood lost all capacity to secrete specific Ab in the absence of Ag. Late in the Ab response, high serum titer levels are solely the result of Ig secretion from anterior kidney plasma cells

A novel recombinant antibody specific to full-length stromal derived factor-1 for potential application in biomarker studies

Background: Stromal derived factor-1α (SDF-1α/CXCL12) is a chemokine that is up-regulated in diseases characterised by tissue hypoxia, including myocardial infarction, ischaemic cardiomyopathy and remote ischaemic conditioning (RIC), a technique of cyclical, non-injurious ischaemia applied remote from the heart that protects the heat from lethal ischaemia-reperfusion injury. Accordingly, there is considerable interest in SDF-1α as a potential biomarker of such conditions. However, SDF-1α is rapidly degraded and inactivated by dipeptidyl peptidase 4 and other peptidases, and the kinetics of intact SDF-1α remain unknown. Methods & results: To facilitate investigation of full-length SDF-1α we established an ELISA using a novel recombinant human antibody we developed called HCI.SDF1. HCI.SDF1 is specific to the N-terminal sequence of all isoforms of SDF-1 and has a comparable KD to commercially available antibodies. Together with a detection antibody specific to the α-isoform, HCI.SDF1 was used to specifically quantify full-length SDF-1α in blood for the first time. Using RIC applied to the hind limb of Sprague-Dawley rats or the arms of healthy human volunteers, we demonstrate an increase in SDF-1α using a commercially available antibody, as previously reported, but an unexpected decrease in full-length SDF-1α after RIC in both species. Conclusions: We report for the first time the development of a novel recombinant antibody specific to fulllength SDF-1. Applied to RIC, we demonstrate a significant decrease in SDF-1α that is at odds with the literature and suggests a need to investigate the kinetics of full-length SDF-1α in conditions characterised by tissue hypoxia

Suppression of mitochondrial respiration through recruitment of p160 myb binding protein to PGC-1α : modulation by p38 MAPK

The transcriptional coactivator PPAR gamma coactivator 1 α (PGC-1α) is a key regulator of metabolic processes such as mitochondrial biogenesis and respiration in muscle and gluconeogenesis in liver. Reduced levels of PGC-1α in humans have been associated with type II diabetes. PGC-1α contains a negative regulatory domain that attenuates its transcriptional activity. This negative regulation is removed by phosphorylation of PGC-1α by p38 MAPK, an important kinase downstream of cytokine signaling in muscle and β-adrenergic signaling in brown fat. We describe here the identification of p160 myb binding protein (p160MBP) as a repressor of PGC-1α. The binding and repression of PGC-1α by p160MBP is disrupted by p38 MAPK phosphorylation of PGC-1α. Adenoviral expression of p160MBP in myoblasts strongly reduces PGC-1α's ability to stimulate mitochondrial respiration and the expression of the genes of the electron transport system. This repression does not require removal of PGC-1α from chromatin, suggesting that p160MBP is or recruits a direct transcriptional suppressor. Overall, these data indicate that p160MBP is a powerful negative regulator of PGC-1α function and provide a molecular mechanism for the activation of PGC-1α by p38 MAPK. The discovery of p160MBP as a PGC-1α regulator has important implications for the understanding of energy balance and diabetes

Complex X-ray Absorption and the Fe Kalpha Profile in NGC 3516

We present data from simultaneous Chandra, XMM-Newton and BeppoSAX observations of the Seyfert 1 galaxy NGC 3516, taken during 2001 April and Nov. We have investigated the nature of the very flat observed X-ray spectrum. Chandra grating data show the presence of X-ray absorption lines, revealing two distinct components of the absorbing gas, one which is consistent with our previous model of the UV/X-ray absorber while the other, which is outflowing at a velocity of ~1100 km/s has a larger column density and is much more highly ionized. The broad-band spectral characteristics of the X-ray continuum observed with XMM during 2001 April, reveal the presence of a third layer of absorption consisting of a very large column (~2.5 x 10E23 cm^-2) of highly ionized gas with a covering fraction ~50%. This low covering fraction suggests that the absorber lies within a few lt-days of the X-ray source and/or is filamentary in structure. Interestingly, these absorbers are not in thermal equilibrium with one another. The two new components are too highly ionized to be radiatively accelerated, which we suggest is evidence for a hydromagnetic origin for the outflow. Applying our model to the Nov dataset, we can account for the spectral variability primarily by a drop in the ionization states of the absorbers, as expected by the change in the continuum flux. When this complex absorption is accounted for we find the underlying continuum to be typical of Seyfert 1 galaxies. The spectral curvature attributed to the high column absorber, in turn, reduces estimates of the flux and extent of any broad Fe emission line from the accretion disk.Comment: 33 pages, 9 figures, accepted for publication in Ap

Variable UV Absorption in the Seyfert 1.5 Galaxy NGC 3516: The Case for Associated UV and X-ray Absorption

We present observations of the UV absorption lines in the Seyfert 1 galaxy NGC 3516, obtained at a resolution of $\lambda$/$\Delta\lambda$ $\approx$ 40,000 with the Space Telescope Imaging Spectrograph (STIS) on 2000 October 1. The UV continuum was $\sim$4 times lower than that observed during 1995 with the Goddard High Resolution Spectrograph (GHRS), and the X-ray flux from a contemporaneous {\it Chandra X-ray Observatory (CXO)} observation was a factor of $\sim$8 below that observed with {\it ASCA}. The STIS spectra show kinematic components of absorption in Ly$\alpha$, C IV, and N V at radial velocities of -376, -183, and -36 km s$^{-1}$ (components 1, 2, and 3+4, respectively), which were detected in the earlier GHRS spectra; the last of these is a blend of two GHRS components that have increased greatly in column density. Four additional absorption components have appeared in the STIS spectra at radial velocities of -692, -837, -994, and -1372 km s$^{-1}$ (components 5 through 8); these may also have been present in earlier low-flux states observed by the {\it International Ultraviolet Explorer (IUE)}. Based on photoionization models, we suggest that the components are arranged in increasing radial distance in the order, 3+4, 2, 1, followed by components 5 -- 8. We have achieved an acceptable fit to the X-ray data using the combined X-ray opacity of the UV components 1, 2 and 3+4. By increasing the UV and X-ray fluxes of these models to match the previous high states, we are able to match the GHRS C IV column densities, absence of detectable C IV absorption in components 5 through 8, and the 1994 {\it ASCA} spectrum. We conclude that variability of the UV and X-ray absorption in NGC 3516 is primarily due to changes in the ionizing flux.Comment: 7 figures (note that Fig6 is not referenced in the .Tex file and must be printed separately). There are 6 tables in the .tex file and an additional 8 tables included as separate .ps files. Accepted for Publication in the Astrophysical Journa