Keimami Sa Vakila Na Liga Ni Kalou (Feeling the Hand of God): Human and Nonhuman Impacts on Pacific Island Environments By Patrick Nunn.     

Ian Owens 《New Zealand geographer》1998,54(2):53-53

  相似文献   

The breakdown of potassium feldspar at high water pressures   总被引：1，自引：0，他引：1  

Pauline Thompson  Ian Parsons  Colin M. Graham  Brian Jackson 《Contributions to Mineralogy and Petrology》1998,130(2):176-186

The equilibrium position of the reaction between sanidine and water to form “sanidine hydrate” has been determined by reversal experiments on well characterised synthetic starting materials in a piston cylinder apparatus. The reaction was found to lie between four reversed brackets of 2.35 and 2.50 GPa at 450 °C, 2.40 and 2.59 GPa at 550 °C, 2.67 and 2.74 GPa at 650 °C, and 2.70 and 2.72 GPa at 680 °C. Infrared spectroscopy showed that the dominant water species in sanidine hydrate was structural H₂O. The minimum quantity of this structural H₂O, measured by thermogravimetric analysis, varied between 4.42 and 5.85 wt% over the pressure range of 2.7 to 3.2 GPa and the temperature range of 450 to 680 °C. Systematic variation in water content with pressure and temperature was not clearly established. The maximum value was below 6.07 wt%, the equivalent of 1 molecule of H₂O per formula unit. The water could be removed entirely by heating at atmospheric pressure to produce a metastable, anhydrous, hexagonal KAlSi₃O₈ phase (“hexasanidine”) implying that the structural H₂O content of sanidine hydrate can vary. The unit cell parameters for sanidine hydrate, measured by powder X-ray diffraction, were a = 0.53366 (±0.00022) nm and c = 0.77141 (±0.00052) nm, and those for hexasanidine were a = 0.52893 (±0.00016) nm and c = 0.78185 (±0.00036) nm. The behaviour and properties of sanidine hydrate appear to be analogous to those of the hydrate phase cymrite in the equivalent barium system. The occurrence of sanidine hydrate in the Earth would be limited to high pressure but very low temperature conditions and hence it could be a potential reservoir for water in cold subduction zones. However, sanidine hydrate would probably be constrained to granitic rock compositions at these pressures and temperatures. Received: 6 May 1997 / Accepted: 2 October 1997  相似文献   

Sea level,climate change and coastal evolution in Morar,northwest Scotland     

Shennan  Ian  Tooley  Michael  Green  Frances  Innes  Jim  Kennington  Kevin  Lloyd  Jeremy  Rutherford  Mairead 《Geologie en Mijnbouw》1998,77(3-4):247-262

Analyses of geomorphologically contrasting sites in Morar, NW Scotland, describe the forcing mechanisms of coastal change. Isolation basins (i.e. basins behind rock sills and now isolated from the sea following isostatic uplift) accumulated continuous marine and freshwater sediments from c.12 to 2 ka BP. Raised dune, marsh and wetland sites register breaching, migration and stability of dunes from c. 9 to 2 ka BP. High-resolution methods designed to address issues of macroscale and microscale sea-level changes and patterns of storminess include 1-mm sampling for pollen, dinocyst and diatom analyses, infra-red photography, X-ray photography and thin-section analysis. The data enhance the record of relative sea-level change for the area. Major phases of landward migration of the coast occurred during the period of low sea-level rise in the mid-Holocene as the rate of rise decreased from c. 3 to < 1 mm/year. Relative sea-level change controls the broad pattern of coastal evolution at each site; local site-specific factors contribute to short-term process change. There is no record of extreme events such as tsunami. Within a system of dynamic metastable equilibrium, the Holocene records show that site-specific factors determine the exact timing of system breakdown, e.g. dune breaching, superimposed on regional sea-level rise. The global average sea-level rise of 3 to 6 mm/yr by AD 2050 predicted by IPCC would only partly be offset in the Morar area by isostatic uplift of about 1 mm/yr. A change from relative sea-level fall to sea-level rise, in areas where the regional rate of uplift no longer offsets global processes, is a critical factor in the management of coastal resources.  相似文献   

Transport and retention of suspended particulate matter and bacteria in the Humber-Ouse Estuary, United Kingdom, and their relationship to hypoxia and anoxia     

R. J. Uncles  Ian Joint  J. A. Stephens 《Estuaries and Coasts》1998,21(4):597-612

Data are presented on dissolved oxygen (DO) concentrations and their relationship to salinity, suspended particulate matter (SPM), concentrations, and the turbidity maximum in the Humber-Ouse Estuary, United Kingdom, during summer 1995. Measurements in the upper Humber during March 1995 showed DO in the range 82% to 87% of saturation. Suspended particulate matter concentrations were <5000 mg l^?1 and salinity was in the range 0.5 to 12. In contrast, a pronounced DO sag occurred in the upper reaches of the Ouse during medium and spring tide, summer conditions. The DO minimum was essentially an anoxic level and was associated with the location of the turbidity maximum, at salinities between about 0.4 and 1.5. SPM concentrations at 1 m beneath the surface reached 25,000 mg l^?1 in the turbidity maximum, between about 20 km and 40 km from the tidal limit. Suspended particulate matter concentrations were much lower at neap tides, although dense suspensions of SPM (>60,000 mg l^?1) occurred within 1 m of the bed in the turbidity maximum region. A spring-neap record showed a dramatic and tidally controlled decrease in DO at very low salinities as the tides progressed from neaps to springs. An anchor station located down-channel of the turbidity maximum showed that about 95% of the variance in DO, which varied from 28% at low-water slack to 67% at high-water slack, could be explained in terms of salinity variation. At the up-channel margins of the turbidity maximum, DO increased from zero (anoxia) near high water to 60% near low water slack, in contrast to the behavior down-channel of the turbidity maximum. About 82% of the variance in DO could be explained in terms of salinity variations alone. Only 43% of the DO variance could be explained in terms of SPM alone. Up-channel of the turbidity maximum, SPM concentrations were relatively low (<3000 mg l^?1) and DO levels varied from 48% of saturation near high water to 83% near low water slack. About 76% of the variance in DO could be explained in terms of salinity variations alone. Within the turbidity maximum region, DO varied from <2% saturation on the early flood and late ebb and maximized around 7% at high water slack. About 63% of the variance in DO could be explained in terms of salinity variation alone. This increased to 70% when suspended particulate matter was taken into account. Only 29% of the DO variance could be explained in terms of suspended particulate matter alone. Because bacteria were likely to have been the cause of the observed reduction in DO, the numbers of bacteria, both free-living and attached to particles, were measured in the turbidity maximum region. Numbers of free-living bacteria were low and most of the bacteria were attached to sediment particles. There was a linear correlation between total bacterial number and suspended particulate matter concentration, suggesting that the strong DO demand was exerted locally as a result of bacterial activity associated with increased suspended particulate matter concentrations. An order of magnitude analysis of DO consumption within the Ouse’s turbidity maximum, based on the premise that DO depletion was directly related to suspended particulate matter concentrations and that DO addition was due to reaeration, indicates that complete deoxygenation could have occurred with an oxygen depletion rate of ～0.01 mg DO h^?1/g suspended particulate matter during the residence time of waters within the turbidity maximum (～7 d). This rate was sufficiently fast that anoxic to aerobic conditions were able to develop a spring-neap periodicity within the turbidity maximum, but too slow to generate substantial intratidal fluctuations in DO. This is in accordance with the observations, which show that relatively little of the intratidal variance in DO could be explained in terms of suspended particulate matter fluctuations, whereas most of the variance could be explained in terms of salinity, which behaved as a surrogate measure for the proximity of the turbidity maximum.  相似文献   

Steady Convection in Deep Compressible Layers     

Ian W Roxburgh 《Astrophysics and Space Science》1998,261(1-4):55-56

  相似文献   

The Population of KPC-Scale Flat-Spectrum Radio Sources     

Pedro Augusto  Peter N. Wilkinson  Ian W.A. Browne 《Astrophysics and Space Science》1998,261(1-4):261-264

In this paper we present a subsample of 55 flat-spectrum radio sources dominated by (∼ 100 mas) kpc-scale structure, selected from a parent sample of 1665 VLA sources. Most are core-jets and 23 are CSO/MSO candidates. Properties of the subsample are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Helioseismic Constraints on Solar Structure and the Solar Neutrino Problem     

Ian W Roxburgh 《Astrophysics and Space Science》1998,261(1-4):57-58

  相似文献   

Observational limits to source confusion in the millimetre/submillimetre waveband     

A. W. Blain  R. J. Ivison  & Ian Smail 《Monthly notices of the Royal Astronomical Society》1998,296(3):L29-L33

The first observations to detect a population of distant galaxies directly in the submillimetre waveband have recently been made using the new Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT). The results indicate that a large number of distant galaxies are radiating strongly in this waveband. Here we discuss their significance for source confusion in future millimetre/submillimetre-wave observations of both distant galaxies and cosmic microwave background radiation (CMBR) anisotropies. Earlier estimates of such confusion involved significant extrapolation of the results of observations of galaxies at low redshifts; our new estimates do not, as they are derived from direct observations of distant galaxies in the submillimetre waveband. The results have important consequences for the design and operation of existing and proposed millimetre/submillimetre-wave telescopes: the Planck Surveyor survey will be confusion-limited at frequencies greater than 350 GHz, even in the absence of Galactic dust emission; a 1σ confusion noise limit of about 0.44 mJy beam⁻¹ is expected for the JCMT/SCUBA at a wavelength of 850 μm; and the subarcsecond resolution of large millimetre/submillimetre-wave interferometer arrays will be required in order to execute very deep galaxy surveys.  相似文献   

Magnetospheric accretion and pre-main-sequence stellar masses     

Ian A. Bonnell  Kester W. Smith  Michael R. Meyer  Christopher A. Tout  Daniel F. M. Folha  & James P. Emerson 《Monthly notices of the Royal Astronomical Society》1998,299(4):1013-1018

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.  相似文献   

Geochemical dispersion in wallrocks associated with the Norbec deposit, Noranda, Quebec     

Ian D. Pirie  Ian Nichol 《Journal of Geochemical Exploration》1981,15(1-3)

Increasing emphasis is being given to the search for blind mineral deposits and the presence of geochemical dispersion halos in wallrocks may significantly enhance the chances of exploration success. Accordingly, the nature of wallrock dispersion associated with the Lake Dufault Cu-Zn-Au-Ag massive sulphide deposit, Noranda, Quebec, was examined to see if any such patterns existed. On the basis of relatively well defined geology, the area offered an opportunity to establish the relation between geochemical alteration and metallogeny, texture, structure and mineralogy.Anomalous element contents spatially related to mineralization are confined to the stratigraphic footwall (Waite Rhyolite) where Na₂O, SiO₂ and possibly CaO depletions and total Fe₁ Mn and MgO enrichments can be related to the hydrothermal vent. Dispersion halos 150–500 m in diameter are at least twice as wide as the obvious mineralogical alteration halo. Cu, Zn, Ag and S distributions show roughly similar patterns which are not obviously related to the main alteration pipe but do reveal broad enrichment zones in the general area of mineralization.The dispersion appears to be partly controlled by texture. Because of greater primary permeability, the halos produced in rhyolite breccia are wider and better defined than those in more massive rhyolites. On a wider scale (10 km²) dispersion patterns are related to the fault and fracture systems of the area.As many as five stages of metamorphism have affected the area, altering all rocks to some extent. Samples can be classified petrographically into alteration groups, both related and unrelated to mineralization. Comparison of these groups reveals the inadequacy of certain elements for outlining alteration related to mineralization. For example, the range of K₂O in relatively unaltered rhyolite overlaps the composition of all other groups, including those related to mineralization. Similarly apparent is that the distribution of certain elements, e.g., Na₂O, may adequately define one part of an alteration zone such as the sericite-rich zone, but not another.It is concluded that careful use of lithogeochemistry in conjunction with detailed geological mapping and core logging can provide information otherwise obtainable only by time-consuming petrographic analysis. Thus it can be a potent weapon in the search for blind ore deposits.  相似文献