Infrared imagery of a turbulent intrusion in a stratified environment

A time sequence of airborne infrared imagery provides a unique view of phenomena associated with a turbulent tidal intrusion into a stratified bay. During flood tide, cooler water from the Strait of Juan de Fuca is observed to penetrate Sequim Bay (Washington, U.S.V.) as a turbulent jet. After separating from the shoreline, the jet collapses into the stratified middle part of the bay, forming a mushroom-shaped head consisting of a semicircular plunge front and areas of recirculating flow. As the plunge front advances into the estuary, a set of nonlinear internal waves emerges and propagates toward the relatively stagnant southern part of the bay, where they are a potential source of vertical mixing. This range of phenomena is expected based on laboratory studies, but has not been seen previously in a natural setting.     

Impulsively generated MHD waves and their detectability in solar coronal loops

Impulsively generated magnetohydrodynamic waves in solar coronal loops, with arbitrary plasma , are studied numerically by a flux-corrected transport algorithm. Numerical results show that the total reflection which occurs in the region of low Alfvén speed leads to trapped fast kink magnetosonic waves. These waves propagate along the slab and exhibit periodic, quasi-periodic, and decay phases. As a consequence of the difference in wave propagation speeds, the time signatures of the slow magnetosonic waves are delayed in time in comparison to the time signatures of the fast magnetosonic and Alfvén waves. An interaction between the waves can generate a longer lasting and complex quasi-periodic phase of the fast wave. We discuss also the observational detectability of such MHD waves in optical, radio, and soft X-ray wavelenghts.     

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

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.     

Proximity and complexity in the emergence of high technology industry: The oxbridge comparison

This paper examines similarities and differences in the emergence of high-tech enterprise and the growth of associated industry in Cambridgeshire and Oxfordshire since the 1960s. These cases are viewed as instances of a generic phenomenon: the emergence and growth of the science-based ‘innovative milieu’. A conceptual scheme drawn from complexity studies is used to introduce explanatory coherence into the apparently scattered and disconnected factors relevant to the genesis of high-tech milieux.     

Observations of the SW Sextantis star UU Aquarii

We present 14 nights of medium resolution (1–2 Å) spectroscopy of the eclipsing cataclysmic variable UU Aquarii obtained during a high accretion state in 1995 August–October. UU Aqr appears to be an SW Sextantis (SW Sex) star, as noted by Baptista, Steiner & Horne, and we discuss its spectroscopic behaviour in the context of the SW Sex phenomenon. Emission-line equivalent width curves, Doppler tomography, and line profile simulation provide evidence for the presence of a bright spot at the impact site of the accretion stream with the edge of the disc, and a non-axisymmetric, vertically and azimuthally extended absorbing structure in the disc. The absorption has maximum depth in the emission lines around orbital phase 0.8, but is present from φ≈0.4 to φ≈0.95. An origin is explored for this absorbing structure (as well as for the other spectroscopic behaviour of UU Aqr) in terms of the explosive impact of the accretion stream with the disc.     

Chromospheric Ca II H and K emission among subdwarfs

Echelle spectra have been obtained of the Ca  II H and K lines for a sample of metal-poor subdwarf stars as well as for a number of nearby Population I dwarfs selected from among those included in the Mount Wilson HK survey. The main conclusion of this paper is that Ca  II H- and K-line emission does occur among subdwarfs. It is particularly notable among those subdwarfs with colours of B − V ≥0.75; all such stars observed exhibit chromospheric emission, although emission is observed among some subdwarfs bluer than this colour. The Ca  II K emission profile in most subdwarfs exhibits an asymmetry of V / R >1, similar to that seen in the integrated light of the solar disc. Two quantitative indicators of the contrast between the peaks in the emission profile and the neighbouring photospheric line profile are introduced. Measurements of these indicators show that the level of Ca  II emission among the subdwarfs is similar to that among low-activity Population I dwarfs.     

Magnetospheric accretion and pre-main-sequence stellar masses

We present a method of determining lower limits on the masses of pre-main-sequence (PMS) stars and so constraining the PMS evolutionary tracks. This method uses the redshifted absorption feature observed in some emission-line profiles of T Tauri stars, indicative of infall. The maximum velocity of the accreting material measures the potential energy at the stellar surface, which, combined with an observational determination of the stellar radius, yields the stellar mass. This estimate is a lower limit owing to uncertainties in the geometry and projection effects. Using available data, we show that the computed lower limits can be larger than the masses derived from PMS evolutionary tracks for M   0.5 M. Our analysis also supports the notion that accretion streams do not impact near the stellar poles but probably hit the stellar surface at moderate latitudes.     

The stable isotope geochemistry of Australian coals

D/H, ¹³C/¹²C, ¹⁸O/¹⁶O and ³⁴S/³²S ratios in the organic matrix and organic solvent extracts of Australian coals, and in the fluids and minerals associated with these coals, are reported and reviewed against similar isotopic data for coals from other regions.Where coals are immature, original isotopic differences between macrolithotypes, and between solvent extracts (lipid concentrates) and insoluble residues, are largely preserved. However, with increasing maturity these characteristic differences, particularly those between macrolithotypes, are rapidly erased. Conversely, where, as indicated by low total sulfur contents, coals of Cretaceous to Permian age were deposited under essentially freshwater conditions, δ³⁴S values^* for the organically-bound sulfur remain remarkably constant at +4 ± 3‰ relative to meteoritic sulfur. In similar, younger Tertiary coals, the organic sulfur is markedly enriched in ³⁴S.Five distinctive isotopic patterns, which may be interpreted in terms of the environment of sulfate reduction, can be recognized from ³⁴S/³²S ratio measurements on the various forms of sulfur in Australian coals.Isotopic studies of seam gas hydrocarbons collected in situ show these to be unexpectedly strongly depleted in the heavier isotopes of hydrogen and carbon relative to natural gases from proposed humic sources. Furthermore, no pronounced increase in the ¹³C content in methane with increase in rank of the parent coal was observed. In addition, several sources of associated carbon dioxide have been delineated, including normal maturation processes, invasion of the seams by magnetic carbon dioxide, and interaction of the coal with intrusive magma.Isotopic exchange between free seam gases is not accepted as an explanation for some unusual isotopic fractionations seen, rather the data suggest that these gases may be formed in a state approaching isotopic equilibrium. This argument also satisfactorily explains the isotopic compositions of primary siderite and secondary calcite associated with bituminous coal seams. However, where seams are invaded and permeated with externally derived carbon dioxide, usually of magnetic origin, carbonates are frequently absent, presumably as a result of the action of carbonic acid.     

Phanerozoic equal-area maps

This paper outlines a method used to make paleocontinental maps and outlines its limitations. 15 pairs of new Lambert equal-area paleocontinental maps are presented, drawn at 40 Ma intervals from the present-day back to 560 Ma (early Cambrian time).

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Zusammenfassung 15 Paare von paläoglobalen Karten werden hier nach einer Lambertschen flächengetreuen Projektion mit Hilfe eines Rechnerprogrammes dargestellt. Der Zeitabschnitt umfaßt in 40 Mill. Jahres-Schritten die letzten 560 Mill. Jahre seit dem Kambrium.

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Résumé Ce travail définit la méthode utilisée pour dresser des cartes paléocontinentales, ainsi que ses limitations. — 15 paires de cartes paléocontinentales sont présentées, dessinées à des intervalles de 40 M. a. depuis l'époque actuelle jusqu'à 560 M. a. (début du Cambrien).

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, , . 15 , , .. 560 , 40 .