N-Acetylation phenotype and genotype and risk of bladder cancer in benzidine-exposed workers

Several studies in subjects occupationally exposed to arylamine carcinogens have shown increased risks for bladder cancer associated with the slow acetylator phenotype. To follow up these reports, a case-control study of N-acetylation and bladder cancer risk was carried out among subjects occupationally exposed to benzidine, in benzidine dye production and use facilities in China. Thirty-eight bladder cancer cases and 43 controls from these factories were included for study of acetylation phenotype, by dapsone administration, and for polymorphisms in the NAT2 gene, by a polymerase chain reaction (PCR)-based test. In contrast to previous studies, no increase in bladder cancer risk was found for the slow N-acetylation phenotype (OR= 0.3; 95% CI = 0.1-1.3) or for slow N-acetylation-associated double mutations in NAT2 (OR = 0.5; 95% CI = 0.1-1.8). Examination of specific mutations and adjustment for age, weight, city and tobacco use did not alter the results. When examined by level of benzidine exposure in the cases, the bladder cancer risks associated with low (OR = 0.3, 95% CI = 0.0-2.2), medium (OR = 0.7, 95% CI = 0.1-4.5) and high (OR = 0.6, 95% CI = 0.1-3.5) exposure showed no interaction between genotype and benzidine exposure, within the range of exposures experienced by subjects in this study. This study, which is the first to incorporate phenotypic and genotypic analyses, provides evidence that the NAT2-related slow N-acetylation polymorphism is not associated with an increased risk of bladder cancer in workers exposed to benzidine, and may have a protective effec

X-ray Line Emission from Supernova Ejecta Fragments

We show that fast moving isolated fragments of a supernova ejecta composed of heavy elements should be sources of K_alpha X-ray line emission of the SN nuclear-processed products. Supersonic motion of the knots in the intercloud medium will result in a bow-shock/knot-shock structure creation. Fast nonthermal particles accelerated by Fermi mechanism in the MHD collisionless shocks diffuse through a cold metallic knot, producing the X-ray emission. We modeled the X-ray emission from a fast moving knot of a mass M ~ 10^{-3} \Msun, containing about 10^{-4} \Msun of any metal impurities like Si, S, Ar, Ca, Fe. The fast electron distribution was simulated using the kinetic description. We accounted for nonlinear effects of shock modification by the nonthermal particles pressure. The K_alpha line emission is most prominent for the knots propagating through dense molecular clouds. The bow shock should be a radiative wave with a prominent infrared and optical emission. In that case the X-ray line spectrum of an ejecta fragment is dominated by the low ionization states of the ions with the metal line luminosities reaching L_x \gsim 10^{31} erg/s. High resolution XMM and Chandra observations are able to detect the line emission from the knots at distances up to a few kpcs. The knots propagating through tenuous interstellar matter are of much fainter surface brightness but long-lived. The line spectra with higher ionization states of the ions are expected in that case. Compact dense knots could be opaque for some X-ray lines and that is important for their abundances interpretation. The ensemble of unresolved knots of galactic supernovae can contribute substantially to the iron line emission observed from the Galactic Center region and the Galactic ridge.Comment: 9 pages, 1 figure; Astronomy and Astrophysics (in press

Evolutionary synthesis models of starbursts IV. Soft X-ray emission

In this work we investigate the evolution of the X-ray emission of a cluster of single young massive stars with different metallicities. We have considered the X-ray contribution originated by the diffuse gas heated by the mechanical energy released by stellar winds and SN explosions as well as the X-ray contribution from SN remnants. The resulting ionizing spectrum (i.e. lambda < 912 A) has been used to compute the expected intensity of the nebular He II 4686 A. The observational ratio He II/Hbeta could be reproduced by the models assuming that a fraction of the mechanical energy produced by the star-formation episode is reprocessed by interaction with the ISM as soft X-ray radiation, contributing to the He ionization. However, the discreteness of the stellar populations affects the ionizing flux and may be responsible for the observed dispersion of the ratio. We have finally used the synthesis models to estimate the contribution of circumnuclear star-forming regions to the multiwavelength energy distribution in Active Galactic Nuclei, finding that the UV to soft X-ray continuum in many Seyfert 2 galaxies seems to be dominated by star-formation processes.Comment: 14 pages, 10 fig, A&A accepte

An Emerging Class of Bright, Fast-evolving Supernovae with Low-mass Ejecta

A recent analysis of supernova (SN) 2002bj revealed that it was an apparently unique type Ib SN. It showed a high peak luminosity, with absolute magnitude M_R -18.5, but an extremely fast-evolving light curve. It had a rise time of <7 days followed by a decline of 0.25 mag per day in B-band, and showed evidence for very low mass of ejecta (<0.15 M_Sun). Here we discuss two additional historical events, SN 1885A and SN 1939B, showing similarly fast light curves and low ejected masses. We discuss the low mass of ejecta inferred from our analysis of the SN 1885A remnant in M31, and present for the first time the spectrum of SN 1939B. The old environments of both SN 1885A (in the bulge of M31) and SN 1939B (in an elliptical galaxy with no traces of star formation activity), strongly support old white dwarf progenitors for these SNe. We find no clear evidence for helium in the spectrum of SN 1939B, as might be expected from a helium-shell detonation on a white dwarf, suggested to be the origin of SN 2002bj. Finally, the discovery of all the observed fast-evolving SNe in nearby galaxies suggests that the rate of these peculiar SNe is at least 1-2 % of all SNe.Comment: Additional analysis included. ApJ, in pres

Electrophysiologic actions of high plasma concentrations of propranolol in human subjects

The authors have previously shown that 40% of patients whose ventricular arrhythmias respond to propranolol require plasma concentrations in excess of those producing substantial beta-receptor blockade (> 150 ng/ml). However, the electrophysiologic actions of propranolol have only been examined in human beings after small intravenous doses achieving concentrations of less than 100 ng/ml. In this study, the electrophysiologic effects of a wider concentration range of propranolol was examined in nine patients. Using a series of loading and maintenance infusions, measurements were made at baseline, at low mean plasma propranolol concentrations (104 ± 17 ng/ml) and at high concentrations (472 ± 68 ng/ml). Significant (p < 0.05) increases in AH interval and sinus cycle length were seen at low concentrations of propranolol, with no further prolongation at the high concentrations; these effects are typical of those produced by beta-blockade. However, progressive shortening of the endocardial monophasic action potential duration and QTc interval were seen over the entire concentration range tested (p < 0.05). At high concentrations, there was significant (p < 0.05) further shortening of both the QTc and monophasic action potential duration beyond that seen at low propranolol concentrations, along with a progressive increase in the ratio of the ventricular effective refractory period to monophasic action potential duration. No significant changes were seen in HV interval, QRS duration or ventricular effective refractory period.In summary, the concentration-response relations for atrioventricular conductivity and sinus node automat-icity were flat above concentrations of 150 ng/ml. On the other hand, the durations of the monophasic action potential and the QTc interval shortened at high concentrations. It is concluded that propranolol, in addition to blocking beta-receptors, produces other beta-receptor independent electrophysiologic effects in human beings

Comparative evaluation of HERG currents and QT intervals following challenge with suspected torsadogenic and nontorsadogenic

Abstract word count: 243 Introduction word count: 75

X-ray emission from radiative shocks in Type II supernovae

The X-ray emission from the circumstellar interaction in Type II supernovae with a dense circumstellar medium is calculated. In Type IIL and Type IIn supernovae mass loss rates are generally high enough for the region behind the reverse shock to be radiative, producing strong radiation, particularly in X-rays. We present a model for the emission from the cooling region in the case of a radiative reverse shock. Under the assumption of a stationary flow, a hydrodynamic model is combined with time dependent ionization balance and multilevel calculations. The applicability of the steady state approximation is discussed for various values of the ejecta density gradient and different sets of chemical composition. We show how the emerging spectrum depends strongly on the reverse shock velocity and the composition of the shocked gas. We discuss differences between a spectrum produced by this model and a single-temperature spectrum. Large differences for especially the line emission are found, which seriously can affect abundance estimates. We also illustrate the effects of absorption in the cool shocked ejecta. The applicability of our model for various types of supernovae is discussed.Comment: 25 pages, 15 figures, 4 tables. Accepted for publication in A&

Supernova Remnants as Clues to Their Progenitors

Supernovae shape the interstellar medium, chemically enrich their host galaxies, and generate powerful interstellar shocks that drive future generations of star formation. The shock produced by a supernova event acts as a type of time machine, probing the mass loss history of the progenitor system back to ages of $\sim$ 10 000 years before the explosion, whereas supernova remnants probe a much earlier stage of stellar evolution, interacting with material expelled during the progenitor's much earlier evolution. In this chapter we will review how observations of supernova remnants allow us to infer fundamental properties of the progenitor system. We will provide detailed examples of how bulk characteristics of a remnant, such as its chemical composition and dynamics, allow us to infer properties of the progenitor evolution. In the latter half of this chapter, we will show how this exercise may be extended from individual objects to SNR as classes of objects, and how there are clear bifurcations in the dynamics and spectral characteristics of core collapse and thermonuclear supernova remnants. We will finish the chapter by touching on recent advances in the modeling of massive stars, and the implications for observable properties of supernovae and their remnants.Comment: A chapter in "Handbook of Supernovae" edited by Athem W. Alsabti and Paul Murdin (18 pages, 6 figures

Determining the location of Gamma-Ray Bursts through the evolution of their soft X-ray absorption

We investigate through dedicated numerical simulations the evolution of the soft X-ray absorption properties of a cloud surrounding a gamma-ray burst source. We show that the absorption properties of the material are strongly modified by the ionization induced by the intense burst flux. We derive the temporal evolution of the measured column density as a function of the density and size of the absorbing medium. Even if their statistical significance is not extremely compelling, we find that the detection in several bursts of variable absorption during the gamma-ray phase can be accounted for if these bursts are associated to overdense regions in molecular clouds with properties similar to those of star formation globules. We fit our model variable column density to the data of GRB 980329 and GRB 780506, showing that with this method the size, density and density distribution of the material surrounding a burst can be measured.Comment: 8 pages, 8 postscript figures, accepted for publication in MNRA