The physical properties of an analytic model for a relativistic star

An exact solution of Einstein's equations for a static isentropic perfect fluid sphere is examined in detail. The analysis yields a strong indication that the model isstable with respect to infinitesimal radial pulsations. This means that the temperature is decreasing outwards. We prove that the adiabatic speed of sound is everywhere less than the speed of light if and only if the radius of the sphere is larger than 1.61 times its Schwarzschild radius. We further show that the strong energy condition is fulfilled everywhere if and only if the radius is larger than 1.76 times the Schwarzschild radius. The necessary and sufficient condition for the speed of sound to be decreasing outwards is given, and we find that this criterion is fulfilled if the fluid is causal. Taking the values of the pressure and the density to be somewhere given by the maximum values from Baymet al.'s equation of state, i.e., ₀=5.1×10¹⁴ g cm^–3 andp ₀=7.4×10³³ dyne cm^–2, we find the maximum mass of the fluid sphere to be 2.5 solar masses.Dedicated to the memory of the late George Cunliffe McVittie (1904–1988).     

S 235 B explained: an accreting Herbig Be star surrounded by reflection nebulosity

The intent of this study is to determine the nature of the star and associated nebulosity S 235 B, which are located in a region of active star formation still heavily obscured by the parent molecular cloud. Low-resolution  ( R = 400)  long-slit spectra of the star and nebulosity, and medium-  ( R = 1800)  and high-resolution  ( R = 60 000)  spectra of the central star are presented along with the results of Fabry–Perot interferometric imaging of the entire region. Based on the long-slit and Fabry–Perot observations, the nebulosity appears to be entirely reflective in nature, with the stellar component S 235 B★ providing most of the illuminating flux. The stellar source itself is classified here as a B1V star, with emission-line profiles indicative of an accretion disc. S 235 B★ thus belongs to the relatively rare class of early-type Hebrig Be stars. Based on the intensity of the reflected component, it is concluded that the accretion disc must be viewed nearly edge-on. Estimates of the accretion rate of S 235 B★ from the width of the Hα profile at 10 per cent of maximum intensity, a method which has been used lately for T Tauri stars and Brown Dwarfs, appear to be inconsistent with the mass outflow rate and accretion rate implied from previous infrared observations by Felli et al., suggesting this empirical law does not extend to higher masses.     

Ejecta formation and crater development of the Mjølnir impact

Abstract— Crater‐ejecta correlation is an important element in the analysis of crater formation and its influence on the geological evolution. In this study, both the ejecta distribution and the internal crater development of the Jurassic/Cretaceous Mjølnir crater (40 km in diameter; located in the Barents Sea) are investigated through numerical simulations. The simulations show a highly asymmetrical ejecta distribution, and underscore the importance of a layer of surface water in ejecta distribution. As expected, the ejecta asymmetry increases as the angle of impact decreases. The simulation also displays an uneven aerial distribution of ejecta. The generation of the central high is a crucial part of crater formation. In this study, peak generation is shown to have a skewed development, from approximately 50–90 sec after impact, when the peak reaches its maximum height of 1‐1.5 km. During this stage, the peak crest is moved about 5 km from an uprange to a downrange position, ending with a final central position which has a symmetrical appearance that contrasts with its asymmetrical development.     

Studies of granular velocities

Spectral observations of solar velocity fields made during a partial solar eclipse are described. Continuum intensity measurements at the lunar limb allow the modulation transfer function to be derived and the true spatial power spectrum of the velocity field to be reconstructed. The oscillatory and granular components are separated by applying spatial filters cutting off at 3.7. The oscillatory component values are in good agreement with those of Canfield (1976) but the granular component has substantially more power and a smaller height gradient. The discrepancy can be resolved by noting the uncertainties of the seeing corrections and of the separation into components in the work of Canfield.However on the basis of this limited material, we would go no further than to claim that the height dependence of the granular velocities remains an open question.Mitteilung aus dem Fraunhofer-Institut Nr. 157.     

Zur Interpretation eines Zirkulationskriteriums

Zusammenfassung Ein vonPhillips formuliertes und vonSmagorinsky umgeschriebenes Kriterium, das vor allem Aussagen über die Bedingungen gestattet, unter denen sich Störungen vom Typ der Rossby-Wellen entwickeln können, wird näher untersucht. Die Parameter, die in verschiedener Weise voneinander abhängen, sind die Zahl dieser Wellen, meriodionaler und vertikaler Gradient der potentiellen Temperatur und geographische Breite. Die Lage der planetarischen Hochdruckgürtel ist, worauf zuerstFlohn hingewiesen aht, bestimmbar in Abhängigkeit von den genannten Gradienten (Abb. 1). Ein funktionaler Zusammenhang zwischen Wellenzahl und Baroklinität besteht dann, wenn bei labilster Kombination von Wellenzahl, thermischer Schichtung und Breite gerade Indifferenz erreicht wird: beide Größen ändern sich dann entgegengesetzt (Abb. 2). Für thermische Schichtung und Wellenzahl kann ein solcher Zusammenhang bei fester Breite für beliebige Zustände exisitieren — bei Labilisierung der Schichtung vergrößert sich die Wellenzahl.

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Summary A baroclinic instability criterion is analysed in some detail which has been derived byPhillips, and has been rewritten bySmagorinsky. This criterion essentially permkits to make statements about the conditions by which disturbances of the Rossby-typemay develop. The parameters depending on one another in different ways are the wave number, the meridional and vertical gradients of potential temperature, and the latitude. The position of the planetary high pressure belts can be determined as a function of these gradients (Fig. 1), as has been demonstrated byFlohn. The wave number represents a function of the meridional temperature gradient by the condition that the most unstable combination of wave number, static stability, and latitude just leads to indifiference (in the sense of the criterion): both quantities are then varying in opposite directions (Fig. 2). At constant latitude and arbitary conditions otherwise the wave number is a function of static stability, or vice versa — the wave number increases if static, stability decreases.

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Résumé On examkine ici de plus près un critère formulé parPhillips et midifié parSmagorinsky, cirtère qui permet de déterminer les conditions initiales en partant desquelles des perturbations du type des ondes de Rossby peuvent se former. Les paramètres — dont l'interdépendance est complexe —sont: le nombre de ces ondes, les gradients méditional et vertical de la température potentielle et la latitude. La position des ceintures planétaires de haute pression, dont l'importance a àté signalée parFlohn — peutêtre déterminée à l'aide de ces gradients (Fig. 1). Un rapport fonctionnel entre le nombre d'ondullations et la baroclinité s'établit lorsque — par suite de la combinaison la moins stable du nombre d'ondulations, de l'étagement thermique et de la latitude —on obtient juste un état indifférent: ces deux grandeurs se modifient alors en sens inverse (Fig. 2). A une latitude donnée, un tel rapport entre l'étagement thermique et le nombre d'ondulations peut exister dans n'importe quelles conditions: si l'étagement devient moins stable, le nombre des ondulatiosn augmente.

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Mit 2 Textabbildungen     

Assessment and Control of Ore Dilution in Long Hole Mining: Case Studies

Unplanned ore dilution has a direct and large influence on the cost of a stope, and ultimately on the profitability of a mining operation. This paper presents the results of an examination of factors influencing ore dilution in a blasthole stoping environment. For the study, a comprehensive database was established, incorporating information related to the design, construction, excavation and cavity surveys of 172 sequentially mined long hole stope case histories from two orezones. Through a review of the case studies, it was demonstrated that, in addition to stope dimension, the amount of unplanned dilution differed according to stope type. Five stope types were identified, based on their position within a tabular blasthole mining sequence. Measured overbreak varies with stope type, with secondary stopes generating a greater volume of hanging-wall dilution than do primary stopes. Furthermore, a case study is presented to demonstrate the role cablebolts installed in the stope hanging-wall play to control ore dilution. The study illustrates relationships between measured hanging-wall overbreak, cablebolt orientation and stope type.     

Metamorphosis of Heteroxenia fuscescens planulae (Cnidaria: octocorallia) is inhibited by crude oil: a novel short term toxicity bioassay

By using TPA (12-tetra-decanoyl-phorbol-13-acetate) an artificial inducer for metamorphosis, it was possible to determine the effect of crude oil on settlement and metamorphosis of planulae of the soft coral Heteroxenia fuscescens. In the absence of crude oil, TPA induced metamorphosis in 97% of these planulae. The effect of crude oil on metamorphosis and appearance of deformed primary polyps was concentration dependent. Only 50% of the planulae grown in experimental vessels with crude oil at a concentration of 0.1 ppm covering the bottom and walls of the vessels underwent metamorphosis when triggered by TPA. Of those planulae exposed to 100 ppm of the pollutant only 3% metamorphosed after being induced by TPA. Furthermore, oil film on the water surface was less toxic to the larvae than the crude oil covering the bottom and walls of the experimental vessels. Some of the oil treated planulae died, while others remained viable, looked normal, but did not metamorphose after being presented with TPA. These findings suggest that even at very low concentrations crude oil affects larvae of H. fuscescens preventing their settlement and metamorphosis. Therefore it is possible that oil spills affect coral recruitment by decreasing the viability and the settlement of coral planulae. This assay represents a new sensitive bioindicator to detect the impact of oil pollution on tropical and subtropical marine environments.     

Diet composition and resource partitioning in two small flatfish species in the German Bight

Since the late 1980s, the small-sized non-commercial flatfish species solenette (Buglossidium luteum) and scaldfish (Arnoglossus laterna) have increased in abundance in the southern North Sea. Because these species are considered as possible competitors for prey of commercial flatfish, this study aimed at advancing knowledge of their feeding ecology.Between January 2009 and January 2010 stomach contents of solenette and scaldfish and benthic infauna were sampled seasonally in a study area in the German Bight. The objectives were to investigate the seasonal variability of feeding activity and diet composition of both flatfish species related to benthic prey availability.For both flatfish, the highest feeding activity was found in summer, at the same time that the highest prey densities occurred in the study area. A reduced feeding activity was observed during the winter of 2010, but not in the winter of 2009, probably related to higher 2009 water temperatures.In all seasons, diet composition of solenette was dominated by meiofauna, mainly harpacticoid copepods. Macrofauna prey species, namely juveniles of bivalves and echinoderms became important in spring. An increase in amphipods and cumaceans was found in the stomach contents during summer and autumn, simultaneously with their increased abundance in the benthic infauna. In contrast, polychaetes were rarely found in the diet, but dominated the infauna during all seasons.Diet composition of scaldfish was dominated by larger and mobile prey, and, during all seasons, was mainly comprised of crustaceans. Amphipods characterised the diet in both winters, while decapods such as Crangon spp. and Liocarcinus spp. were the dominant prey from spring to autumn. Additionally, juveniles of flatfish (Pleuronectids) and bivalves were found in the scaldfish diet in spring, replaced by cumaceans in summer. No dietary overlap between both flatfish species was found across seasons, indicating partitioning of prey resources between solenette and scaldfish. Their different feeding strategies and prey preferences, in turn were influenced by the seasonal variability of available prey.