Ts-MARE VOLCANISM AND BASALT PETROGENESIS : " ASTOUNDING FUNDAMENTAL CONCEPTS ( AFC ) "-DEVELOPED OVER THE LAST FIFTEEN YEARS
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Lunar and Planetary Science XXIX 1305 . pdf
According to the idea of the triggered origin of the solar system, the formation of our planetary system was initiated by an interstellar shock wave generated by a nearby explosive stellar event, such as a supernova explosion [1] or ejection of a planetary nebula from an asymptotic giant branch star [2]. In addition to triggering the collapse of the molecular cloud core, the shock wave also deposited fresh radioactivities into the precollapse core, giving rise to the anomalous abundances of extinct radionuclides measured in primitive meteorites [3]. The viability of the scenario must be verified through numerical simulations. There are three questions the simulations must answer: i) can the collapse of a molecular cloud core be induced by an impact of an interstellar shock wave? ii) can radioactivities carried by the shock wave be injected into the collapsing system? iii) is the time scale for the process sufficiently short for the survival of the radioactivities? During the last few years, there have been several studies discussing assisted star formation (for a recent review see [4]) and its relation to the formation of the solar system (for reviews see [5][6]). Especially in the latter context, the problem has been examined by the two-dimensional piecewise-parabolic method (PPM) simulations of Foster and Boss [7][8][9] and the three-dimensional smoothed particle hydrodynamics (SPH) calculations of Vanhala and Cameron [5][10]. These studies concentrated on moderately slow (10-50 km/sec) shock waves impacting centrally condensed molecular cloud cores. Apart from the simulation methods themselves, the calculations also differed in their choice of thermodynamics: isothermal (PPM) vs. variable adiabatic index (SPH). The two sets of simulations agree on two of the three key issues mentioned above: molecular cloud cores can be triggered into collapse if the momentum of the shock wave is sufficiently high to compress the core significantly but not so large as to tear it apart. In terms of shock velocity, the benevolent range for assisted collapse is approximately 10-40 km/sec, depending on the evolutionary state of the pre-impact core [10]. The time scale for the collapse is 10 years, well below the limits set by the survival of the radioactivities, even if the material were carried from a supernova explosion occurring at a distance of a few parsecs [5]. The principal unresolved difference between the two sets of simulations is the injection of radioactivities into the collapsing system. The PPM calculations have found that an appreciable amount of shock wave material, 10-20%, can be injected into the system through Rayleigh-Taylor-like fingers [8][9], while the SPH simulations did not detect any evidence for injection in the cases leading to collapse [5][10]. The main purpose of the current study is to address this basic difference between the results. We used the 3D SPH code to study a problem similar to the standard case of Foster and Boss [7]. A spherically symmetric cloud was placed at the center of the three-dimensional coordinate system. The masses of the particles were varied in order to produce a configuration similar to the standard case of Foster and Boss: a marginally stable Bonnor-Ebert sphere joined smoothly to the surrounding medium. The cloud initially had a radius of 0.058 pc, temperature of 10 K, and central density of c = 6.2 10 19 g cm . The intercloud medium had Ticm = 10 K and icm = 7.3 10 22 g cm . The shock wave was represented by a top-hat model, in which the edge of the wave (thickness 0.003 pc) was given the velocity vedge = 20 km/sec, density edge = 7.3 10 20 g cm 3 and temperature Tedge = 10 K, while the wind behind the leading edge had wind = 7.3 10 22 g cm , Twind = 10 K and vwind = 0 km/sec. The simulation space extended to rxy = 0.150 pc and -0.15 pc < z < 0.15 pc, with the shock wave approaching from the +z direction and starting at z = 0.08. The boundary conditions were reflective on the cylindrical boundary and free inflow/outflow in the z direction. In accordance with the calculations of Foster and Boss, the value of the adiabatic index was kept constant at = 1.00001, instead of using the equation of state solver with a variable adiabatic index.
Proliferative kidney disease: first reported outbreak in North America
Abstract. Proliferative kidney disease (PKD) was diagnosed in rainbow trout, Salmo gairdneri Richardson, at the Hagerman, Idaho, State Fish Hatchery. Wild fish from Riley Creek, one of the hatchery water supplies, were infected with PKD organisms. Clinical signs, gross pathology and histopathology of affected fish were typical of those reported for PKD in salmonids from European hatcheries. In addition to lesions normally seen, we observed a severe vasculitis and occlusion of renal and hepatic vessels. Ultrastructure of the PKD organism and possible inclusion body production sites are described. The disease outbreak was complicated by the presence of other infectious diseases. This is the first recorded outbreak of PKD in North America.