Relativistic Jets from Collapsars

We have studied the relativistic beamed outflow proposed to occur in the collapsar model of gamma-ray bursts. A jet forms as a consequence of an assumed energy deposition of $\sim 10^{50}- 10^{51}$ erg/s within a $30^{\circ}$ cone around the rotation axis of the progenitor star. The generated jet flow is strongly beamed (\la few degrees) and reaches the surface of the stellar progenitor (r $\approx 3 10^{10}$cm) intact. At break-out the maximum Lorentz factor of the jet flow is about 33. Simulations have been performed with the GENESIS multi-dimensional relativistic hydrodynamic code.Comment: 6 pages, 2 figures, to appear in the proceedings of the conference "Godunov methods: theory and applications", Oxford, October 199

Using the Active Collimator and Shield Assembly of an EXIST-Type Mission as a Gamma-Ray Burst Spectrometer

The Energetic X-ray Imaging Survey Telescope (EXIST) is a mission design concept that uses coded masks seen by Cadmium Zinc Telluride (CZT) detectors to register hard X-rays in the energy region from 10 keV to 600 keV. A partially active or fully active anti-coincidence shield/collimator with a total area of between 15 and 35 square meters will be used to define the field of view of the CZT detectors and to suppress the background of cosmic-ray-induced events. In this paper, we describe the use of a sodium activated cesium iodide shield/collimator to detect gamma-ray bursts (GRBs) and to measure their energy spectra in the energy range from 100 keV up to 10 MeV. We use the code GEANT4 to simulate the interactions of photons and cosmic rays with the spacecraft and instrument and the code DETECT2000 to simulate the optical properties of the scintillation detectors. The shield collimator achieves a nu-F-nu sensitivity of 3 x 10^(-9) erg cm^(-2) s^(-1) and 2 x 10^(-8) erg cm^(-2) s^(-1) at 100 keV and 600 keV, respectively. The sensitivity is well matched to that of the coded mask telescope. The broad energy coverage of an EXIST-type mission with active shields will constrain the peak of the spectral energy distribution (SED) for a large number of GRBs. The measurement of the SED peak may be key for determining photometric GRB redshifts and for using GRBs as cosmological probes.Comment: 20 pages, 10 Figures, Accepted May 19, 2006 A&

Evolution of protoplanetary disks: Constraints from DM Tauri and GM Aurigae

We present a one-dimensional model of the formation and viscous evolution of protoplanetary disks. The formation of the early disk is modeled as the result of the gravitational collapse of an isothermal molecular cloud. The disk's viscous evolution is integrated according to two parameterizations of turbulence: The classical $\alpha$ representation and a $\beta$ parameterization, representative of non-linear turbulence driven by the keplerian shear. We apply the model to DM Tau and GM Aur, two classical T-Tauri stars with relatively well-characterized disks, retrieving the evolution of their surface density with time. We perform a systematic Monte-Carlo exploration of the parameter space (i.e. values of the $\alpha$-$\beta$ parameters, and of the temperature and rotation rate in the molecular cloud) to find the values that are compatible with the observed disk surface density distribution, star and disk mass, age and present accretion rate. We find that the observations for DM Tau require $0.001<\alpha<0.1$ or $2\times 10^{-5}<\beta<5\times 10^{-4}$. For GM Aur, we find that the turbulent viscosity is such that $4\times 10^{-4}<\alpha<0.01$ or $2\times 10^{-6}<\beta<8\times 10^{-5}$. These relatively large values show that an efficient turbulent diffusion mechanism is present at distances larger than $\sim 10$AU. This is to be compared to studies of the variations of accretion rates of T-Tauri stars versus age that mostly probe the inner disks, but also yield values of $\alpha\sim 0.01$. We show that the mechanism responsible for turbulent diffusion at large orbital distances most probably cannot be convection because of its suppression at low optical depths.Comment: 24 pages, 22 figures, paper accepted for publication in A&

Chromatografia gazowa, analiza sensoryczna i nos elektroniczny w ocenie aromatu czarnuszki (Nigella sativa L.)

Essential oil composition of Nigella sativa L., the enantiomeric ratio of its chiral compounds as well as sensory characteristics were the subject of the study. The evaluation of several samples of N. sativa seeds purchased in retail was performed by gas chromatography, chiral gas chromatography, olfactometry, sensory profile analysis and the electronic nose. Eleven components were identified. Olfactometry revealed p-cymene, thymoquinone and carvacrol as the most important odorants. P-cymene occurred in all of the samples at highest amounts. Six pairs of enantiomers were isolated. All the components showed variability in their enantiomeric ratios, with exception of carvone, which was found with a stable optical purity of the (-)-isomer, not lower than 85%. The dominating attributes in the sensory profile were cardboard, herbal and spicy. Results of sensory profile analysis and the electronic nose, both interpreted by the Principal Component Analysis, gave similar, although not identical differentiation of the samples.Przedmiotem badań był skład związków zapachowych olejku eterycznego z nasion Nigella sativa L., stosunki enancjomerów związków chiralnych oraz charakterystyka sensoryczna. Ocenę kilku prób nasion czarnuszki pozyskanych na rynku wykonano z zastosowaniem chromatografii gazowej, spektrometrii mas, chiralnej chromatografii gazowej, olfaktometrii, profilowej analizy sensorycznej oraz nosa elektronicznego. Zidentyfikowano jedenaście składników aromatu. Analiza olfaktometryczna wykazała, że głównymi odorantami były p-cymen, tymochinon i karwakrol. Najwyższą zawartość we wszystkich próbach stwierdzono dla p-cymenu. Rozdzielono sześć par enancjomerów. Wszystkie te związki wykazywały zróżnicowanie stosunku enancjomerów w poszczególnych próbach, za wyjątkiem karwonu, który występował zawsze w formie lewoskrętnej (-)-karwon, o czystości optycznej nie mniejszej niż 85%. Dominującymi atrybutami w ocenie sensorycznej były zapachy kartonowy, ziołowy i korzenny. Sensoryczna analiza profilowa i nos elektroniczny wykazały podobne zróżnicowanie między próbami. Wyniki otrzymane obiema metodami były interpretowane z zastosowaniem Analizy Składowych Głównych (PCA)

The population of cataclysmic variable systems

About the Book: The book reviews recent observations of non-evolved and evolved binary populations in clusters and the field with special emphasis on statistical biases, incompleteness and distribution functions. Different binary types are considered: cataclysmic variables, super-soft X-ray sources, double degenerate binaries, Algol-type binaries, Be binaries, X-ray binaries, and Wolf-Rayet binaries. The observational part ends with a discussion on stellar winds in massive stars, on new results of massive starbursts and on the characteristics and the rates of the different types of supernovae. Population synthesis relies on stellar evolution. Recent results on single star and binary evolution are presented. We then compare theoretical models of population synthesis to observations. Much attention is given at population dynamics, spectral synthesis of starbursts, number synthesis of the binaries and supernova rates discussed in the first part of this book. Finally, the book highlights the possible effects of binaries on galactic chemical evolution