On the Dynamics of the Jovian Ionosphere and Thermosphere: III. The Modelling of Auroral Conductivity     

George MillwardSteve Miller  Tom StallardAlan D. Aylward  Nicholas Achilleos 《Icarus》2002,160(1):95-107

Recent work has been concerned with calculating the three-dimensional ion concentrations and Pedersen and Hall conductivities within the auroral region of Jupiter for varying conditions of incident electron precipitation. Using the jovian ionospheric model, we present results that show the auroral ionospheric response to changing the incoming flux of precipitating electrons (for constant initial energy) and also the response to changing the initial energy (for both constant flux and constant energy flux). The results show that, for expected energy fluxes of precipitating particles, the average auroral integrated Pedersen conductivity attains values in excess of 1 mho. In addition, it is shown that electrons with an initial energy of around 60 keV are particularly effective at generating auroral conductivity: Particles of this energy penetrate most effectively to the layer of the jovian ionosphere at which the auroral conductivity is at a maximum.  相似文献   

First Results from Viper: Detection of Small-scale Anisotropy at 40 GHz     

Peterson JB  Griffin GS  Newcomb MG  Alvarez DL  Cantalupo CM  Morgan D  Miller KW  Ganga K  Pernic D  Thoma M 《The Astrophysical journal》2000,535(2):L83-L86

Using all available major samples of Seyfert galaxies and their corresponding closely matched control samples of nonactive galaxies, we find that the bar ellipticities (or axial ratios) in Seyfert galaxies are systematically different from those in nonactive galaxies. Overall, there is a deficiency of bars with large ellipticities (i.e., "thin" or "strong" bars) in Seyfert galaxies compared to nonactive galaxies. Accompanied with a large dispersion due to small number statistics, this effect is strictly speaking at the 2 sigma level. To obtain this result, the active galaxy samples of near-infrared surface photometry were matched to those of normal galaxies in type, host galaxy ellipticity, absolute magnitude, and, to some extent, redshift. We discuss possible theoretical explanations of this phenomenon within the framework of galactic evolution, and, in particular, of radial gas redistribution in barred galaxies. Our conclusions provide further evidence that Seyfert hosts differ systematically from their nonactive counterparts on scales of a few kiloparsecs.  相似文献   

A spatially and temporally adaptive solution of Richards’ equation     

Cass T. Miller  Chandra Abhishek  Matthew W. Farthing 《Advances in water resources》2006

Efficient, robust simulation of groundwater flow in the unsaturated zone remains computationally expensive, especially for problems characterized by sharp fronts in both space and time. Standard approaches that employ uniform spatial and temporal discretizations for the numerical solution of these problems lead to inefficient and expensive simulations. In this work, we solve Richards’ equation using adaptive methods in both space and time. Spatial adaption is based upon a coarse grid solve and a gradient error indicator using a fixed-order approximation. Temporal adaption is accomplished using variable order, variable step size approximations based upon the backward difference formulas up to fifth order. Since the advantages of similar adaptive methods in time are now established, we evaluate our method by comparison with a uniform spatial discretization that is adaptive in time for four different one-dimensional test problems. The numerical results demonstrate that the proposed method provides a robust and efficient alternative to standard approaches for simulating variably saturated flow in one spatial dimension.  相似文献   

Age of granite batholiths in the Anyui-Chukotka foldbelt     

S. M. Katkov  A. Strickland  E. L. Miller  J. Toro 《Doklady Earth Sciences》2007,414(1):515-518

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Paleolimnological significance of spinose and non-spinose morphs of Pyrgophorus hibbardi (Leonard and Franzen, 1944)     

Barry B. Miller  Michael J.S. Tevesz  Daniela C. Smith 《Journal of Paleolimnology》1998,20(1):99-102

The basal portion of the Ogallala Formation (=Laverne Formation) (Lower Pliocene) Beaver County, Oklahoma, contains an interesting assemblage of non-marine fossil molluscs that include both spinose and non-spinose forms of the aquatic gastropod species Pyrgophorus hibbardi. The origin and paleolimnological significance of the spinose morph has been a source of much conjecture that has influenced environmental reconstructions of this assemblage. In one hypothesis the spinose forms of P. hibbardi are assumed to be associated with brackish water conditions by analogy with some populations of a related hydrobiid Potamopyrgus jenkinsi. To test the hypothesis that the spinose forms lived under different water conditions than the non-spinose morphs, we analyzed 10 specimens each of the two varieties for stable oxygen and carbon isotope ratios in the shell aragonite.The mean isotope ratios for the smooth and spinose morphs show no significant difference (oxygen: t = 0.28, df = 18, P (T t) 0.78 n.s.; carbon: t = 0.96, df = 18, P (T t) 0.35 n.s). We conclude that the lack of a statistically significant difference between the means of the oxygen and carbon isotope values for the smooth and spinose morphs suggests that the two forms lived in waters having similar isotope signatures. The considerable range in oxygen isotope values recorded by both morphs of P. hibbardi, including values as high as 5–6, suggest that both morphs were associated with waters which were periodically evaporatively enriched in ¹⁸O.  相似文献   

Holocene environmental changes in the Whitefish Dunes Area, Door Peninsula, Northern Lake Michigan Basin, USA     

Barry B. Miller  J.S. Tevesz  John S. Carney 《Journal of Paleolimnology》1998,19(4):473-479

A two meter sediment core taken from an inter-dune pond in Whitefish Dunes State Park, Door Peninsula, Wisconsin, provides a record of paleoenvironmental changes in the area from approximately 3600 RCYBP to 5100 RCYBP. The hydrology of the Whitefish Dunes pond is now apparently dependent on ground water recharge from local precipitation that infiltrates into the dunes and from Clark Lane, making it very sensitive to low magnitude, short term climate fluctuations.Changes in lithology, molluscan species diversity, oxygen isotopes from gastropod shells, and sediment organic content permit division of the core into several intervals representing different environmental regimes. The basal sediments are older than 5130 RCYBP and resemble those of the Liberty Grove Member of the Pleistocene Horicon Formation. The oldest Holocene sediments recorded in the core are an organic rich layer dated at 5130 RCYBP, which accumulated in a depression on the surface of a sand bar. Continued rise in the local water table during the Nipissing Transgression produced paludal conditions in the area, which were followed by the onset of lacustrine conditions. During this interval, the area supported a diverse molluscan fauna. Minor, short term climate fluctuations are reflected in sediment and oxygen isotope changes which are absent from the record in deep water cores from Lake Michigan. This phase in the history of the area ended with the eutrophication of the pond and the development of dunes. Information from Whitefish Dunes pond and other onshore sites within the Lake Michigan basin are an important source of data for reconstructing the history of water levels and climate changes for this area of the Great Lakes drainage.  相似文献   

Are Q-stars a serious threat for stellar-mass black hole candidates?     

Miller  Shahbaz  & Nolan 《Monthly notices of the Royal Astronomical Society》1998,294(2):L25-L29

We examine the status of the threat posed to stellar-mass black hole candidates by the possible existence of Q-stars (compact objects with an exotic equation of state that might have masses well above the normally accepted maximum for standard neutron stars). We point out that Q-stars could be extremely compact (with radii less than 1.5 times the corresponding Schwarzschild radius) making it difficult to determine observationally that a given object is a black hole rather than a Q-star, unless there is direct evidence for the absence of a material surface. On the other hand, in order for a Q-star to have a mass as high as that inferred for the widely favoured black hole candidate V404 Cygni, it would be necessary for the Q-matter equation of state to apply already at densities an order of magnitude below that of nuclear matter and this might well be considered implausible on physical grounds. We also describe how rotation affects the situation and discuss the prospects for determining observationally that black hole candidates are not Q-stars.  相似文献   

The UVX quasar optical luminosity function and its evolution     

Pippa Goldschmidt  & Lance Miller 《Monthly notices of the Royal Astronomical Society》1998,293(1):107-112

The recently finished Edinburgh UVX quasar survey at B <18 is used together with other complete samples to estimate the shape and evolution of the optical luminosity function in the redshift range 0.3< z <2.2. There is a significantly higher space density of quasars at high luminosity and low redshift than previously found in the PG sample of Schmidt & Green, with the result that the shape of the luminosity function at low redshifts ( z <1) is seen to be consistent with a single power law. At higher redshifts the slope of the power law at high luminosities appears to steepen significantly. There does not appear to be any consistent break feature which could be used as a tracer of luminosity evolution in the population.  相似文献   

Oscillations in radiation-driven outflows     

Guy S. Miller  & Scott A. Grossman 《Monthly notices of the Royal Astronomical Society》1998,299(1):139-149

In this paper we investigate the dynamical behaviour of radiation-driven winds, specifically winds that arise when Compton scattering transfers momentum from the radiation field to the gas flow. Such winds occur during strong X-ray bursts from slowly accreting neutron stars, and also may be driven from the inner regions of a black hole or neutron star accretion disc when the mass transfer rate is very high. By linearizing the radiation hydrodynamic equations around steady spherical outflow, we evaluate the time-dependent response of these winds to perturbations introduced at their inner boundaries. We find that although radiation-driven winds are generally stable, they act as mechanical filters that should produce quasi-periodic oscillations or peaked noise in their radiation output when perturbations force them stochastically. This behaviour may underlie the photospheric oscillations observed in some strong Type I X-ray bursts.  相似文献   

Paläozoische und frühmesozoische Orogenesen am pazifischen Rand Gondwanas     

Prof. Dr. Hubert Miller 《International Journal of Earth Sciences》1981,70(2):519-528

Zusammenfassung In Südamerika, in der Antarktis und in Australien läßt sich gleichermaßen vom Kambrium bis in die Trias ein pazifikwärtiges Wandern der orogenen Aktivität beobachten. Aus der relativen Lage dieser Orogene ergibt sich, daß vor dem Jura die Antarktische Halbinsel westlich der Südspitze von Südamerika gelegen hat.

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In South America, Antarctica and Australia, from the Cambrian to the Triassic Pacificward shifting of the orogenic activity is observed. From the relative position of these orogenes is deduced that before the Jurassic the Antarctic Peninsula was situated west of the southern tip of South America.

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Resumen Tanto en Sudamérica como en la Antártida y en Australia desde el Cámbrico hasta el Triásico se observa una transposición continua de la actividad orogénica hacia el Pacífico. De la posición relativa de estos orógenos se concluye que antes del Jurásico la Península Antártica fue situada al Oeste de la punta Sur de Sudamérica.

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