Eosinophilic aseptic arachnoiditis: A neurological complication in HIV-negative drug-addicts

Abstract.: The finding of an eosinophilic aseptic meningitis in IV drug abuse is usually suggestive of an opportunistic infection or an allergic reaction. However, HIV-negative patients are at lower risk for developing these complications. Two young HIV-negative patients, with previous intravenous polytoxicomany, developed cystic arachnoiditis over the spinal cord associated with eosinophilic meningitis. Histology of the meningeal spinal cord lesions revealed a vasculocentric mixed inflammatory reaction. In one patient prednisone led to marked clinical improvement. Since infection, vasculitis, sarcoidosis and previous myelography were ruled out, we believe that the syndrome of eosinophilic aseptic arachnoiditis may be related to an hyperergic reaction in the meniges toward drug-adulterants inoculated through the intravenous rout

About the initial mass function and HeII emission in young starbursts

We demonstrate that it is crucial to account for the evolution of the starburst population in order to derive reliable numbers of O stars from integrated spectra for burst ages t > 2 - 3 Myr. In these cases the method of Vacca & Conti (1992) and Vacca (1994) systematically underestimates the number of O stars. Therefore the current WR/O number ratios in Wolf-Rayet (WR) galaxies are overestimated. This questions recent claims about flat IMF slopes (alpha ~ 1-2) in these objects. If the evolution of the burst is properly treated we find that the observations are indeed compatible with a Salpeter IMF, in agreement with earlier studies. Including recent predictions from non-LTE, line blanketed model atmospheres which account for stellar winds, we synthesize the nebular and WR HeII 4686 emission in young starbursts. For metallicities 1/5 <= Z/Z_sun <= 1 we predict a strong nebular HeII emission due to a significant fraction of WC stars in early WR phases of the burst. For other metallicities broad WR emission will always dominate the HeII emission. Our predictions of the nebular HeII intensity agree well with the observations in WR galaxies and an important fraction of the giant HII regions where nebular HeII is detected. We propose further observational tests of our result.Comment: ApJ Letters, accepted. 8 pages LaTeX including 3 PostScript figures, uses AASTeX and psfig macros. PostScript file also available at ftp://ftp.stsci.edu/outside-access/out.going/schaerer/imf.p

New Models for Wolf-Rayet and O Star Populations in Young Starbursts

Using the latest stellar evolution models, theoretical stellar spectra, and a compilation of observed emission line strengths from Wolf-Rayet (WR) stars, we construct evolutionary synthesis models for young starbursts. We explicitly distinguish between the various WR subtypes (WN, WC, WO), and we treat O and Of stars separately. We provide detailed predictions of UV and optical emission line strengths for both the WR stellar lines and the major nebular hydrogen and helium emission lines, as a function of several input parameters related to the starburst episode. We also derive the theoretical frequency of WR-rich starbursts. We then discuss: nebular HeII 4686 emission, the contribution of WR stars to broad Balmer line emission, techniques used to derive the WR and O star content from integrated spectra, and explore the implications of the formation of WR stars through mass transfer in close binary systems in instantaneous bursts. The observational features predicted by our models allow a detailed quantitative determination of the massive star population in a starburst region (particularly in so-called "WR galaxies") from its integrated spectrum and provide a means of deriving the burst properties (e.g., duration, age) and the parameters of the initial mass function of young starbursts. (Abridged abstract)Comment: Accepted by ApJ Supplements. LaTeX using aasmp4, psfigs macros. 49 pages including 23 figures. Paper (full, or text/figures separated) and detailed model results available at http://www.stsci.edu/ftp/science/starburst/sv97.htm

Thick-Film Radial Position Sensor for High Temperature Active Magnetic Bearings

This paper presents the development of radial eddy-current position sensors for high temperature active magnetic bearing (AMB) applications. Thick-film technology was used to realize silver coils printed on ceramic substrates. Long term measurements showed a good stability of this technology at high temperature. However, silver migration was observed between the wire connections and countered with the use of dielectric pastes. An AC current source at 900 kHz and high impedance amplifiers enabled the sensor temperature compensation. The sensor response was measured from room temperature up to 600°C

The Rates of Hypernovae and Gamma-Ray Bursts: Implications for their Progenitors

A critical comparison of estimates for the rates of hypernovae (HNe) and gamma-ray bursts (GRBs) is presented. Within the substantial uncertainties, the estimates are shown to be quite comparable and give a Galactic rate of $10^{-6}$ -- $10^{-5}$yr$^{-1}$ for both events. These rates are several orders of magnitude lower than the rate of core-collapse supernovae, suggesting that the evolution leading to a HN/GRB requires special circumstances, very likely due to binary interactions. Various possible binary channels are discussed, and it is shown that these are generally compatible with the inferred rates.Comment: Accepted by Astrophysical Journal Letters. 12 page

On the formation and evolution of black-hole binaries

We present the results of a systematic study of the formation and evolution of binaries containing black holes and normal-star companions with a wide range of masses. We first reexamine the standard formation scenario for close black-hole binaries, where the spiral-in of the companion in the envelope of a massive star causes the ejection of the envelope. We estimate the formation rates for different companion masses and different assumptions about the common-envelope structure and other model parameters. We find that black-hole binaries with intermediate- and high-mass secondaries can form for a wide range of assumptions, while black-hole binaries with low-mass secondaries can only form with apparently unrealistic assumptions (in agreement with previous studies). We then present detailed binary evolution sequences for black-hole binaries with secondaries of 2 to 17 Msun and demonstrate that in these systems the black hole can accrete appreciably even if accretion is Eddington limited (up to 7 Msun for an initial black-hole mass of 10 Msun) and that the black holes can be spun up significantly in the process. We discuss the implications of these calculations for well-studied black-hole binaries (in particular GRS 1915+105), ultra-luminous X-ray sources and Cygnus X-1. Finally, we discuss how some of the assumptions in the standard model could be relaxed to allow the formation of low-mass, short-period black-hole binaries which appear to be very abundant in Nature. (Abstract abridged)Comment: 21 pages, 9 figures, accepted by MNRAS, Figs. 2a/2b and 5 in very reduced forma

Irradiation Pressure Effects in Close Binary Systems

We present a method for the calculation of the effects of external irradiation on the geometrical shape of the secondary in a close binary containing a compact star, the source of the radiation, and a normal companion star, where we include the possibility of shadowing by an accretion disc. The model is based on a simple modification of the standard Roche binary potential in which the radiation-pressure force is parameterised using the ratio of the radiation to the gravitational force. We have constructed numerical solutions of approximate 3-dimensional irradiated equipotential surfaces to demonstrate the main geometrical effects of external radiation pressure. For systems in which the inner Lagrangian point is irradiated directly and for sufficiently high irradiation fluxes, the critical condition for which the secondary fills its tidal lobe changes from an inner to an outer critical configuration, where the critical equipotential surface connects to one of the outer rather than the inner Lagrangian point. Such a situation may apply to evaporating binary pulsar systems (e.g. PSR 1957+20), stars orbiting supermassive black holes in AGN and some high-mass X-ray binaries (including Centaurus X-3). For systems containing an accretion disc, which shadows the inner Lagrangian point from the external irradiation, the presence of significant radiation pressure causes a non-axisymmetric deformation of the stellar surface. We have calculated modified Roche potentials to determine the main effects on the optical lightcurves and radial velocity curves for typical binary parameters. Compared to previous studies, the inclusion of irradiation-pressure effects results in changes in the derived system parameters (e.g. component masses, radial velocities) that may be as high as 30 per cent.Comment: 16 pages, 6 figures, submitted to MNRA

ATP-Dependent Unwinding of U4/U6 snRNAs by the Brr2 Helicase Requires the C Terminus of Prp8

The spliceosome is a highly dynamic machine requiring multiple RNA-dependent ATPases of the DExD/H-box family. A fundamental unanswered question is how their activities are regulated. Brr2 function is necessary for unwinding the U4/U6 duplex, a step essential for catalytic activation of the spliceosome. Here we show that Brr2-dependent dissociation of U4/U6 snRNAs in vitro is activated by a fragment from the C terminus of the U5 snRNP protein Prp8. In contrast to its helicase-stimulating activity, this fragment inhibits Brr2 U4/U6-dependent ATPase activity. Notably, U4/U6 unwinding activity is not stimulated by fragments carrying alleles of prp8 that in humans confers an autosomal dominant form of retinitis pigmentosa. Because Brr2 activity must be restricted to prevent premature catalytic activation, our results have important implications for fidelity maintenance in the spliceosome