Evaporation of Accretion Disks around Black Holes: The Disk-Corona Transition and the Connection to the Advection-dominated Accretion Flow

We apply the disk-corona evaporation model (Meyer & Meyer-Hofmeister) originally derived for dwarf novae to black hole systems. This model describes the transition of a thin cool outer disk to a hot coronal flow. The mass accretion rate determines the location of this transition. For a number of well-studied black hole binaries, we take the mass flow rates derived from a fit of the advection-dominated accretion flow (ADAF) model to the observed spectra (for a review, see Narayan, Mahadevan, & Quataert) and determine where the transition of accretion via a cool disk to a coronal flow/ADAF would be located for these rates. We compare this with the observed location of the inner disk edge, as estimated from the maximum velocity of the Halpha emission line. We find that the transition caused by evaporation agrees with this determination in stellar disks. We also show that the ADAF and the "thin outer disk + corona" are compatible in terms of the physics in the transition region.     

Inelastic dynamic analysis of tall buildings

The importance of inelastic action of frame structures subjected to strong ground motions has been recognized by engineers for many years. However, the dynamic analysis of buildings undergoing inelastic deformations requires the solution of many theoretical problems, as well as the development of computer software which makes such analyses economically feasible in a design office–in spite of the extraordinary amount of computation involved. In this paper, some of the principal theoretical problems are briefly described. These are the load-deformation relationship, yield capacity reduction, ductility, P– δ effect, viscous damping, panel zone distortions, numerical integration techniques, energy analysis and the effect of non-structural elements. Special consideration is given to questions associated with the practical implementation of this theory. These questions arose during the development of a computer program, called NLDYN, capable of analysing the non-linear dynamic behaviour of tall buildings in an engineering office environment. The capabilities of this computer program are illustrated with the results of the analysis of a 60 storey office building currently under construction in downtown Los Angeles.     

Phlogopite in calc-alkaline lamprophyres of Northern England

Summary Phlogopite mica is the major unaltered phase in minette and kersantite dikes in the Cross Fell and Taythes inliers in northwestern England. The compositional zonation trend in the micas from Mg-rich, Cr-bearing cores to Fe, Ti, Ba-rich, low Cr margins, or rims, is similar to that reported for micas from minettes and kersantites worldwide. Complex mantling and zoning trends suggest that the phenocrystal mica assemblage is a hybrid one formed by the mixing of magmas of broadly similar composition which have undergone different amounts of fractional crystallization. The magmas are considered to have beeen produced in a continuously replenished fractionating magma chamber. The lamprophyres have a common source and were probably derived by the extensive fractionation of a basic mantle-derived magma.

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Phlogopit in kalk-alkalischen lamprophyren von Nord-England

Zusammenfassung Phlogopit ist die wichtigste, unveränderte Phase in Minetten und kersantitischen Gängen in den Cross Fell and Taythes Gebieten von Nordwest-England. Die Zonierung der Zusammensetzung in den Glimmern von Mg-reichen, Cr-führenden Kernen zu Fe, Ti, Ba-reichen Rändern mit niedrigen Cr-Gehalten ist ähnlich der, die von Glimmern in Minetten und Kersantiten weltweit ermittelt wurde. Komplexe Ummantelung und Zonierung weisen darauf hin, daß die Glimmer-Vergesellschaftung, die weithin idiomorph ist, durch die Mischung von Magmen weithin ähnlicher Zusammensetzung entstanden ist, welche in verschiedenem Ausmaß von Kristallisationsfraktionierung betroffen waren. Die Magmen dürften in einer kontinuierlich aufgefüllten, fraktionierten Magmenkammer entstanden sein. Die Lamprophyre haben einen gemeinsamen Ursprung und gehen wahrscheinlich auf die extensive Fraktionierung eines basischen Magmas von Mantel-Herkunft zurück.

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With 5 Figures     

Torsional instability in structures

Torsional instability under harmonic excitation was detected in structures with cubic softening member stiffness. A variational procedure was introduced to perform the analysis for the general problem formulation. Single-storey structures with zero eccentricity were studied first; previous findings were checked and corrected, and the behaviour was examined in greater detail. Two-storey structures with large eccentricity were also examined, and further regions of torsional instability were detected. Time history analysis was then employed to quantify the behaviour of various typical structures. An unbounded growth in rotation or column displacement was not observed. Rather, the instability appeared to be related to the jump in response which exists in single degree-of-freedom softening oscillators subjected to harmonic excitation. The practical significance of torsional instability is therefore rather weak, although prudent practice would recommend its avoidance.     

Interstitial acid glass and chlorophaeite in Iceland basalts

Rhyolitic glass occurs as an interstitial phase in Tertiary basaltic dikes from northwestern Iceland forming up to 8% of the mode. Chlorophaeite occurs as globules within the glass as well as in interstitial vugs and vesicles. The existence and textural relations of these iron-rich globules in a silica-rich glass is suggestive of liquid immiscibility such as observed in synthetic systems. Trace element data on these naturally occurring phases is, however, inconsistent with experimentally determined partition coefficients for, for example, Ti, P, and Zr in immiscible liquids indicating that the chlorophaeite does not represent an immiscible phase and is more likely an alteration product. The similarity of the interstitial acid glasses to Iceland rhyolites is suggestive evidence of an origin for at least some Icelandic rhyolites by shallow-level fractional crystallization of basaltic magmas.     

Age of the last major scabland flood of the Columbia Plateau in eastern Washington

Pumice layers of set S from Mount St. Helens can be correlated with certain ash beds associated with young flood deposits of the channeled scabland. The correlation points to an age of about 13,000 ¹⁴C yr B.P. for the last major flood to have crossed the scabland. Until recently, the last major episode of flooding was thought to be closer to 20,000 yr B.P., an age inferred chiefly from the relation of the flood to glacial events of the northern Rocky Mountains. Several investigations within the last few years have suggested that the last major flood occurred well after 20,000 yr B.P. Tentative correlations of ash beds of the scabland with set S pumice layers, the relations of flood and glacial events along the northwestern margin of the Columbia Plateau, and a radiocarbon date from the Snake River drainage southeast of the plateau all indicate an age much younger than 20,000 yr. The postulated age of about 13,000 yr B.P. is further supported by a radiocarbon date in the Columbia River valley downstream from the scabland tract. Basal peat from a bog on the Portland delta of Bretz, which is a downvalley deposit of the last major scabland flood, has been dated as 13,080 ± 300 yr B.P. (W-3404).     

An iron-rich deposit from the Northeast Pacific

An iron-rich deposit dredged from the upper flank of Dellwood Seamount in the Northeast Pacific has been analyzed for major and trace elements, rare-earth contents and uranium isotopic composition. In terms of mineralogy and overall chemical composition, the deposit resembles other iron-rich deposits variously attributed to volcanic hydrothermal activity. Both the relative concentrations of the rare-earth elements and the isotopic composition of uranium rule out seawater as the sole source of elements in this deposit. The rare-earth element pattern indicates that these elements were derived from the underlying basalt. The²³⁴U/²³⁸U ratio is significantly higher than in seawater and can best be explained by preferential leaching of²³⁴U generated by decay from its parent²³⁸U in the underlying rock and subsequent redeposition of the excess²³⁴U together with the Fe and minor metals. These data are consistent with a model for the origin of submarine metal-rich solutions involving mobilization of elements from the interior of slowly cooling basalts by circulating seawater.     

Sulfide-oxide minerals in eclogite from Stockdale Kimberlite,Kansas

The opaque minerals in eclogite xenoliths from Stockdale Kimberlite are rutile, ilmenite, and a complex polysulfide assemblage. Rutile shows exsolutions of ilmenite and spinel. Discrete ilmenite contains up to 10 wt % MgO in solid solution and is a primary mineral, but not of kimberlitic origin. Pyrrhotite containing exsolved pentlandite is the major sulfide mineral, and is usually rimmed by chalcopyrite which may display exsolution of cubanite. A veneer of monosulfide solid solution (12 wt % Ni and 5 wt % Cu) forms a rim on the chalcopyrite-pyrrhotite masses. The simple model of sulfide liquid immiscibility within a silicate melt may account for the origin of the pyrrhotite-pentlandite-chalcopyrite assemblage, but it fails to explain the occurrence within one and the same sulfide globule of a monosulfide_ss rim, separated from an exsolved pyrrhotite core by chalcopyrite. The monosulfide_ss is probably a metastable phase produced by the partial melting of a preexisting sulfide assemblage of similar bulk chemical composition to that existing at present. The melting possibly took place instantaneously when the eclogite was incorporated into the rising hot kimberlitic magma. Fast cooling during the explosive ascent of the kimberlite could have led to the quenching of the monosulfide solid solution. Rutile in the eclogite xenolith was unaffected by the heating, but secondary amphibole and biotite may have possibly formed during this event.