The supernova: A stellar spectacle

The life of a star, the supernova, related objects and their importance in astronomy and science in general are discussed. Written primarily for science teachers of secondary school chemistry, physics, and earth sciences, the booklet contains a glossary, reference sources, suggested topics for discussion, and projects for individual or group assignment

Comments on an association in Vela

Evidence for an association near the Vela pulsar rests on the H-R diagram. Definite bunching occurs around the mean line. However this evidence is not supported by correlation of proper motions in the region. If the Vela pulsar is a member of this association, a rather large mass is implied, about 10 solar masses

ADF95: Tool for automatic differentiation of a FORTRAN code designed for large numbers of independent variables

ADF95 is a tool to automatically calculate numerical first derivatives for any mathematical expression as a function of user defined independent variables. Accuracy of derivatives is achieved within machine precision. ADF95 may be applied to any FORTRAN 77/90/95 conforming code and requires minimal changes by the user. It provides a new derived data type that holds the value and derivatives and applies forward differencing by overloading all FORTRAN operators and intrinsic functions. An efficient indexing technique leads to a reduced memory usage and a substantially increased performance gain over other available tools with operator overloading. This gain is especially pronounced for sparse systems with large number of independent variables. A wide class of numerical simulations, e.g., those employing implicit solvers, can profit from ADF95.Comment: 24 pages, 2 figures, 4 tables, accepted in Computer Physics Communication

Solutions of evolution equations for medium-induced QCD cascades

In this paper we present solutions of evolution equations for inclusive distribution of gluons as produced by jet traversing quark-gluon plasma. We reformulate the original equations in such a form that the virtual and unresolved-real emissions as well as unresolved collisions with medium are resummed in a Sudakov-type form factor. The resulting integral equations are then solved most efficiently with use of newly developed Markov Chain Monte Carlo algorithms implemented in a dedicated program called MINCAS. Their results for a gluon energy density are compared with an analytical solution and a differential numerical method. Some results for gluon transverse-momentum distributions are also presented. They exhibit interesting patterns not discussed so far in the literature, in particular a departure from the Gaussian behaviour - which does not happen in approximate analytical solutions.Comment: 21 pages. Final versio

Thermonukleares Brennen und Mischen mit einer zeitabhängigen Konvektionstheorie in massereichen Population-III-Sternen

Die erste Generation von Sternen im Universum, die hypothetischen Population-III-Sterne, sollten sich aus reinem Wasserstoff-Helium-Gas frei von schweren Elementen gebildet haben. Die (quasi-)hydrostatische Entwicklung dieser Sterne wird im Massenbereich 15 Sonnenmassen bis 150 Sonnenmassen untersucht, angefangen von der Vorhauptreihe bis zum Ende des Hauptreihenstadiums. Wegen der anfaenglichen Abwesenheit von CNO-Elementen sowie der geringen Effizienz des pp-Brennens erreichen alle massereichen Population-III-Sterne die Hauptreihe im Vergleich zu 'normalen' Sternen als deutlich kompaktere und heissere Objekte. Population-III-Sterne mit Massen oberhalb von 30 Sonnenmassen kontrahieren bis zu Zentraltemperaturen von 100 Millionen Kelvin, produzieren im Drei-Alpha-Prozess Kohlenstoff und lassen sich im Modus des heissen CNO-Brennens auf der Hauptreihe nieder. Population-III-Sterne im Bereich 15 Sonnenmassen bis 30 Sonnenmassen erreichen die Hauptreihe im pp-Brennen, doch uebernimmt auch hier der CNO-Zyklus noch im Hauptreihenstadium die Energieproduktion. Die hohe Temperatur dieser Sterne fuehrt zur Koppelung der konvektiven Mischungszeitskala mit den Zeitskalen der Protoneneinfaenge und der Beta-Zerfaelle im CNO-Zyklus. Das Mischen kann nicht mehr als instantan innerhalb der Konvektionszonen angenommen werden. Ein neu entwickelter Sternentwicklungscode, der auf dem Softwarepaket LIMEX aufsetzt, integriert die Sternaufbaugleichungen zusammen mit einem zeitabhaengigen Kernreaktionsnetzwerk, zeitabhaengigem Mischen und einer zeitabhaengigen Konvektionstheorie erstmals vollstaendig gekoppelt und implizit. Die verbesserte Modellierung der Kernreaktionen und des Mischens wirkt sich nur in der raeumlichen Verteilung der CNO-Elemente aus, die 10 Prozent bis 20 Prozent von einer homogenen Durchmischung abweicht. Die verwendete zeitabhaengige Konvektionstheorie fuehrt in allen Modellen zu groesseren Konvektionszonen im Vergleich zu bestehe

Medium induced QCD cascades: broadening, entropy and rescattering during branching

We study evolution equations describing jet propagation through quark--gluon plasma (QGP). In particular we investigate the contribution of momentum transfer during branching and find that such a contribution is sizeable. Furthermore, we study various approximations, such as the Gaussian approximation and the diffusive approximation to the jet-broadening term. We notice that in order to reproduce the BDIM equation (without the momentum transfer in the branching) the diffusive approximation requires a very large value of the jet-quenching parameter $\hat q$. We also quantify the solutions by calculating time dependence of entropy associated with each of the distributions.Comment: 21 page

Chronic Multi-Electrode Electromyography in Snakes

Knowledge about body motion kinematics and underlying muscle contraction dynamics usually derives from electromyographic (EMG) recordings. However, acquisition of such signals in snakes is challenging because electrodes either attached to or implanted beneath the skin may unintentionally be removed by force or friction caused from undulatory motion, thus severely impeding chronic EMG recordings. Here, we present a reliable method for stable subdermal implantation of up to eight bipolar electrodes above the target muscles. The mechanical stability of the inserted electrodes and the overnight coverage of the snake body with a sleeping bag ensured the recording of reliable and robust chronic EMG activity. The utility of the technique was verified by daily acquisition of high signal-to-noise activity from all target sites over four consecutive days during stimulus-evoked postural reactions in Amazon tree boas and Western diamondback rattlesnakes. The successful demonstration of the chronic recording suggests that this technique can improve acute experiments by enabling the collection of larger data sets from single individuals

Space and Ground Based Pulsation Data of Eta Bootis Explained with Stellar Models Including Turbulence

The space telescope MOST is now providing us with extremely accurate low frequency p-mode oscillation data for the star Eta Boo. We demonstrate in this paper that these data, when combined with ground based measurements of the high frequency p-mode spectrum, can be reproduced with stellar models that include the effects of turbulence in their outer layers. Without turbulence, the l=0 modes of our models deviate from either the ground based or the space data by about 1.5-4.0 micro Hz. This discrepancy can be completely removed by including turbulence in the models and we can exactly match 12 out of 13 MOST frequencies that we identified as l=0 modes in addition to 13 out of 21 ground based frequencies within their observational 2 sigma tolerances. The better agreement between model frequencies and observed ones depends for the most part on the turbulent kinetic energy which was taken from a 3D convection simulation for the Sun.Comment: 13 pages, 7 figures, ApJ in pres