Joint geodynamical and seismic modelling of the Eifel plume     

U. Wüllner  U. R. Christensen  M. Jordan 《Geophysical Journal International》2006,165(1):357-372

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Interbasin groundwater flow and groundwater interaction with surface water in a lowland rainforest, Costa Rica: A review     

David P. Genereux  Michael Jordan   《Journal of Hydrology》2006,320(3-4):385-399

This paper reviews work related to interbasin groundwater flow (naturally occurring groundwater flow beneath watershed topographic divides) into lowland rainforest watersheds at La Selva Biological Station in Costa Rica. Chemical mixing calculations (based on dissolved chloride) have shown that up to half the water in some streams and up to 84% of the water in some riparian seeps and wells is due to high-solute interbasin groundwater flow (IGF). The contribution is even greater for major ions; IGF accounts for well over 90% of the major ions at these sites. Proportions are highly variable both among watersheds and with elevation within the same watershed (there is greater influence of IGF at lower elevations). The large proportion of IGF found in water in some riparian wetlands suggests that IGF is largely responsible for maintaining these wetlands. δ¹⁸O data support the conclusions from the major ion data. Annual water and major ion budgets for two adjacent watersheds, one affected by IGF and the other not, showed that IGF accounted for two-thirds of the water input and 92–99% of the major ion input (depending on the major ion in question) to the former watershed. The large (in some cases, dominating) influence of IGF on watershed surface water quantity and quality has important implications for stream ecology and watershed management in this lowland rainforest. Because of its high phosphorus content, IGF increases a variety of ecological variables (algal growth rates, leaf decay rate, fungal biomass, invertebrate biomass, microbial respiration rates on leaves) in streams at La Selva. The significant rates of IGF at La Selva also suggest the importance of regional (as opposed to small-scale local) water resource planning that links lowland watersheds with regional groundwater. IGF is a relatively unexplored and potentially critical factor in the conservation of lowland rainforest.  相似文献   

Dissolution kinetics of magnesite in acidic aqueous solution: a hydrothermal atomic force microscopy study assessing step kinetics and dissolution flux     

Steven R Higgins  Guntram Jordan  Carrick M Eggleston 《Geochimica et cosmochimica acta》2002,66(18):3201-3210

Magnesite (104) dissolution kinetics were studied in acidic aqueous solutions (2.0 < pH < 4.2) at temperatures between 60 and 90°C by atomic force microscopy (AFM). Comparison of dissolution fluxes obtained by AFM and chemical methods revealed six to seven times larger dissolution fluxes obtained by chemical analysis. Corresponding empirical activation energies were found to be 74 ±22 kJ/mol and 41 ± 4 kJ/mol (at pH 4.2) for the AFM and chemical methods, respectively. The empirical reaction order with respect to proton concentration was 0.36 ± 0.13 and 0.47 ± 0.03 for AFM and chemical methods, respectively. These comparisons suggest that the two experimental measurement methods differ as a result of the different sampling length scales associated with the methods. Negligible changes in step dissolution velocity with changes in bulk pH were found, suggesting that the principal source of increasing dissolution flux with decreasing pH is an increase in step density. However, the observed stable step orientation, which is dependent on pH, suggests that more than one proton adsorption equilibrium should be used to describe the surface chemistry of magnesite in acidic solution.  相似文献   

Photon scattering in the solar ultraviolet lines of He i and He ii     

C. Jordan  G. R. Smith  E. R. Houdebine 《Monthly notices of the Royal Astronomical Society》2005,362(2):411-423

Observations made with the Coronal Diagnostic Spectrometer (CDS) onboard the Solar and Heliospheric Observatory ( SOHO ) are used to investigate the behaviour of the intensities of the emission lines of He  i , He  ii and O  iii at the quiet Sun-centre and at  θ= 60°  towards the equatorial limb. The aim is to examine the possible effects of photon scattering on the spatial variation of the optically thick helium lines. At the quiet Sun-centre, we find that, in agreement with previous work, the ratios of the intensities of the He  i 584-Å and He  ii 304-Å lines to those of the O  iii 600-Å line decrease systematically as the intensity of the O  iii line increases. However, we find that the dependence of these ratios on the O  iii intensity is not unique, but differs between the individual regions studied. Similar results are found at  θ= 60°  . We have also used line intensities and intensity ratios to investigate limb-to-disc effects and variations across a sample of supergranulation cell boundaries and adjacent cell interiors at both locations. The results do not exclude photon scattering as the cause of the larger observed ratios in cell interiors. The differences between the apparent widths of boundaries in O  iii at Sun-centre and 60° show that the emitting material is extended in height, which will aid the process of scattering into cell interiors. Photon scattering could also account for the lack of oscillations in the He  i intensities in a cell interior studied by Pietarila & Judge. Three-dimensional radiative transfer calculations in chosen geometries are now needed to account for the observations in detail.  相似文献   

Probing the interior of asteroids and comets using radio reflection tomography     

A. Safaeinili  S. Gulkis  M. D. Hofstadter  R. L. Jordan 《Meteoritics & planetary science》2002,37(12):1953-1963

Abstract— Asteroids and comets are of great scientific interest: their interior structure and composition, which are poorly known, provide information about conditions and processes that occurred during the early stages of solar system development. They are also of interest for social and economic reasons. Their proximity to Earth and abundance in the solar system make them potential sources of raw materials as well as a threat, as evidenced by past catastrophic impacts. Information on their composition and structure is therefore important to assess both the potential benefit of these objects and mitigate the potential risk they pose. This paper describes the use of radio reflection tomography for studying the interiors of asteroids and comets. We discuss technical issues regarding benefits and challenges of implementing a radio reflection tomography instrument and present potential solutions. This paper addresses a range of topics including (1) data collection scenarios, (2) data processing and inversion, and (3) instrument implementation. A “strawman” instrument capable of imaging the full interior of an asteroid or a comet with dimensions of a few kilometers is presented. Such an instrument can play a significant role in studying the near‐Earth objects, both for scientific and socio‐economic purposes.  相似文献   

Distribution and cycling of dimethylsulfide,dimethylsulfoniopropionate, and dimethylsulfoxide during spring and early summer in the Southern Ocean south of New Zealand     

Ronald P. Kiene  David J. Kieber  Doris Slezak  Dierdre A. Toole  Daniela A. del Valle  John Bisgrove  Jordan Brinkley  Alison Rellinger 《Aquatic Sciences - Research Across Boundaries》2007,69(3):305-319

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Long-term timing observations of 374 pulsars     

G. Hobbs  A. G. Lyne  M. Kramer  C. E. Martin  C. Jordan 《Monthly notices of the Royal Astronomical Society》2004,353(4):1311-1344

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Photogrammetric application of viking orbital photography     

Sherman S.C Wu  A.A Elassal  Raymond Jordan  F.J Schafer 《Planetary and Space Science》1982,30(1):45-55

Special techniques are described for the photogrammetric compilation of topographic maps and profiles from stereoscopic photographs taken by the two Viking Orbiter spacecraft. These techniques were developed because the extremely narrow field of view of the Viking cameras precludes compilation by conventional photogrammetric methods. The techniques adjust for internal consistency the Supplementary Experiment Data Record (SEDR—the record of spacecraft orientation when photographs were taken) and the computation of geometric orientation parameters of the stereo models. A series of contour maps of Mars is being compiled by these new methods using a wide variety of Viking Orbiter photographs, to provide the planetary research community with topographic information.  相似文献   

A procedure for estimating lateral variations from low-frequency eigenspectra data     

Thomas H. Jordan 《Geophysical Journal International》1978,52(3):441-455

Summary. Expressions are derived for the zeroth and first moments of an isolated normal mode multiplet in the presence of rotational anisotropy, lateral heterogeneity and attenuation. It is demonstrated that, to first order, the zeroth moment is independent of the heterogeneity and the first moment is a linear functional of the heterogeneity. The location of the multiplet, defined in terms of the ratio of the first moment to the zeroth moment, is used to set up a linear inverse problem for lateral variations. The approximations employed in deriving the differential kernels are uniformly valid for all angular orders. In addition, formula for the differential kernels asymptotically valid in the limit of large angular order are developed, and the correspondence between these formulae and the geometrical optics approximation is established. It is shown that, in the limit of weak heterogeneity and large angular order, the location of the multiplet is the average of the local perturbation to the eigenfrequency over the great circular path containing the source and receiver.  相似文献   

Wucherungen von Cyanophyceen an den Ufern des Zürichsees und deren Ursachen     

PD. Dr. E. A. Thomas 《Aquatic Sciences - Research Across Boundaries》1961,23(1):225-235

Ohne Zusammenfassung Nach einem Referat, gehalten am I. Internationalen Cyanophyceen-Symposium in Luzern, Kastanienbaum, 29.8.-3.9. 60.  相似文献