Useful properties of the system matrix for a homogeneous anisotropic visco-elastic solid     

L. Neil Frazer  Gerard J. Fryer 《Geophysical Journal International》1989,97(1):173-177

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Abundance of brown trout as related to littoral zone gradient in Lakes Te Anau and Manapouri,New Zealand     

Rick J. Stoffels  Gerard P. Closs 《新西兰海洋与淡水研究杂志》2013,47(2):455-458

Adult brown trout (Salmo trutta L.) in lakes are primarily littoral/benthic foragers. We predicted that the distribution of adult brown trout in lakes would be shaped by foraging demands, and that they would be more abundant in gently sloping littoral areas, that is, littoral areas that have a greater space available to support benthic foraging habitats. To address this hypothesis, we measured abundance of brown trout among littoral areas with different gradients in Lakes Te Anau and Manapouri. There was a significant negative relationship between littoral zone gradient and relative abundance (CPUE) of adult brown trout. This result supports the hypothesis that brown trout aggregate in littoral areas with greater amounts of foraging habitat in Fiordland lakes.  相似文献   

Organizing social resilience in the context of natural hazards: a research note     

Gerard Hutter 《Natural Hazards》2013,67(1):47-60

Organizational scholars increasingly use the term “resilience” to analyze options of dealing with uncertain context conditions. What do these scholars have to offer to researchers in the field of natural hazards? This research note makes three suggestions. First, the research note frames social resilience—in contrast to a rigid response to radical change—as a process of broadening information-based activities, loosening formal controls, and using slack resources of organizational members. Second, the research note argues to leave the meaning of social resilience undefined at the outset of a research project with the aim of building theory about resilience. It is expected that a useful definition emerges in empirical research. Third, organizational studies highlight specific social structures and processes of social resilience, for instance, small groups of individuals in organizational and interorganizational contexts. Organizing becomes a crucial factor for dealing with natural hazards.  相似文献   

Laser-induced time-resolved luminescence spectroscopy of minerals: a powerful tool for studying the nature of emission centres     

Michael Gaft  Gerard Panczer 《Mineralogy and Petrology》2013,107(3):363-372

The paper summarises new data and results referring to the characterization of the nature of luminescence centres in minerals that were published during the last 8 years. Besides well-established luminescence centres, such as Mn²⁺, Fe³⁺, Cr³⁺, divalent and trivalent rare-earth elements, S₂ ^?, and Pb²⁺, several other centres were proposed and substantiated, such as Mn³⁺, Mn⁴⁺, V²⁺, Ni²⁺, Pb⁺, Mn³⁺, Sb³⁺, Tl⁺, and radiation-induced centres. Also, a relatively new type of luminescence excitation mechanism is discussed briefly, namely plasma-induced luminescence. Here, the emission takes place when the matrix, where the formation of plasma is caused by irradiation with a beam of laser light, is capable to luminescence and contains luminescence centres.  相似文献   

Enceladus: A hypothesis for bringing both heat and chemicals to the surface     

Dennis L. Matson  Julie C. Castillo-Rogez  Ashley Gerard Davies  Torrence V. Johnson 《Icarus》2012,221(1):53-62

The eruptive plumes and large heat flow (～15 GW) observed by Cassini in the South Polar Region of Enceladus may be expressions of hydrothermal activity inside Enceladus. We hypothesize that a subsurface ocean is the heat reservoir for thermal anomalies on the surface and the source of heat and chemicals necessary for the plumes. The ocean is believed to contain dissolved gases, mostly CO₂ and is found to be relatively warm (～0 °C). Regular tidal forces open cracks in the icy crust above the ocean. Ocean water fills these fissures. There, the conditions are met for the upward movement of water and the dissolved gases to exsolve and form bubbles, lowering the bulk density of the water column and making the pressure at its bottom less than that at the top of the ocean. This pressure difference drives ocean water into and up the conduits toward the surface. This transportation mechanism supports the thermal anomalies and delivers heat and chemicals to the chambers from which the plumes erupt. Water enters these chambers and there its bubbles pop and loft an aerosol mist into the ullage. The exiting plume gas entrains some of these small droplets. Thus, nonvolatile chemical species in ocean water can be present in the plume particles. A CO₂ equivalent-gas molar fraction of ～4 × 10^?4 for the ocean is sufficient to support the circulation. A source of heat is needed to keep the ocean warm at ～0 °C (about two degrees above its freezing point). The source of heat is unknown, but our hypothesis is not dependent on any particular mechanism for producing the heat.  相似文献   

Phillipsite formation in nephelinitic rocks in response to hydrothermal alteration at Mount Etinde,Cameroon     

Jacques Etame  Che Emmanuel Suh  Martine Gerard  Paul Bilong 《Chemie der Erde / Geochemistry》2012,72(1):31-37

Fresh nephelinitic rocks and hydrothermally altered rocks at Mount Etinde (Cameroon Volcanic Line, West Africa) have been studied by combined whole rock geochemistry (ICP-MS), mineralogy and mineral chemistry (SEM-EDS, WDS, XRD) techniques. The nephelinites have feldspathoids, clinopyroxene, perovskite and titanomagnetite as the principal minerals in the mode with subsidiary apatite and sphene. The mineralogy of their hydrothermally altered counterparts includes phillipsite, calcite and analcime which are secondary phases developed in response to hydrothermal fluid events. Correspondingly, the bulk rock geochemical data show elevated SiO₂, CaO, Na₂O and K₂O concentrations with increasing alteration and Al₂O₃ and Fe₂O₃ depletion while MgO, MnO and TiO₂ concentrations are largely unaffected. The nephelinites also have high concentrations of LILLE, HFSE and REE and upon hydrothermal alteration they show an enrichment of LREE and MREE over HREE. Phillipsite is the principal alteration mineral in the rocks and it occurs along cracks, vesicles and also forms alteromorphs after feldspathoids. The Ce content of these categories of phillipsite varies. Phillipsite along cracks is richer in Ce while phillipsite associated with calcite has lower Ce concentration and the phillipsite alteromorphs very little or no Ce. Various stages of fluid circulation are proposed hereby to explain the variations in phillipsite generation and composition.  相似文献   

Influence of temporal fluctuations and spatial heterogeneity on pollution transport in porous media   总被引：1，自引：1，他引：0  

Amro M. M. Elfeki  Gerard Uffink  Sophie Lebreton 《Hydrogeology Journal》2012,20(2):283-297

The combined influence of temporal fluctuations and spatial heterogeneity on non-reactive solute transport mechanisms in porous media can be understood by performing simulations of steady and unsteady flow and transport in heterogeneous media. The study focuses on issues such as the degree of heterogeneity, correlation length, separation of the combined effects of temporal and spatial variations, and ergodicity conditions under unsteady flow conditions. It is shown that the effect of temporal variations on solute transport is masked by the strong effect of spatial heterogeneity. There is no obvious difference in plume shape between steady and unsteady flow conditions; the first and the second spatial moments of the plume of the unsteady-state flow condition fluctuate around the steady-state flow condition with the same period of oscillations as the input signal at small storage coefficient (S????0.001). At a relatively high standard deviation in hydraulic conductivity and a small storage coefficient, the unsteady flow condition sharpens the temporal variations in macrodispersion coefficients. The magnitude of the longitudinal macrodispersion coefficient under unsteady flow condition is almost doubled at the maximum values. However, the transverse macrodispersion coefficient fluctuates around zero. The Kubo number and Peclet number ranges are 1.2?C64 and 10?C250, respectively.  相似文献   

Do Planetary Motions Drive Solar Variability?   总被引：1，自引：0，他引：1  

Cornelis?De?JagerEmail author  Gerard?J.?M.?Versteegh 《Solar physics》2005,229(1):175-179

We examine the occasionally forwarded hypothesis that solar activity originates by planetary Newtonian attraction on the Sun. We do this by comparing three accelerations working on solar matter at the tachocline level: Those due to planetary tidal forces, to the motion of the Sun around the planetary system's centre of gravity, and the observed accelerations at that level. We find that the latter are by a factor of about 1000 larger than the former two and therefore cannot be caused by planetary attractions. We conclude that the cause of the dynamo is purely solar.  相似文献   

Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: II. Geochronologies and mass sedimentation rates based on <Superscript>14</Superscript>C and <Superscript>210</Superscript>Pb data     

Brent?A.?McKeeEmail author  Andrew?S.?Cohen  David?L.?Dettman  Manuel?R.?Palacios-Fest  Simone?R.?Alin  Gerard?Ntungumburanye 《Journal of Paleolimnology》2005,34(1):19-29

We established sediment geochronologies for cores from eight deltaic areas in Lake Tanganyika (the Lubulungu, Kabesi, Halembe, Malagarasi, Nyasanga/Kahama, Mwamgongo, Nyamusenyi, and Karonge/Kirasa River deltas), recording a range of watershed disturbance histories from the eastern margin of this African rift valley lake. Cores from currently disturbed sites on the central Tanzanian coast display remarkably uniform and low rates of sediment accumulation from the 18th century until the early 1960s, when a synchronous and dramatic rise in rates occurs. Through this same time interval sedimentation rates offshore from undisturbed Tanzanian watersheds either remain unchanged or decline. Further north, at disturbed sites along the northern Tanzania and Burundi coasts, the pattern of sedimentation rate increase is more complex. Although a mid-late 20th century increase is also evident in these sites, indications of earlier periods of increasing sediment erosion, dating from the mid-late 19th century, are also evident. Synchronous changes in sediment accumulation rates dating from the early 1960s may be the result of exceptionally wet years triggering an increase in the discharge of previously eroded and unconsolidated alluvium and stream/beach terrace deposits, previously accumulated in the deltas and stream valleys of impacted watersheds. Sedimentation rate impacts of deforestation on lake ecosystems are likely modulated by short-term climatic forcing events, which can impact the specific timing and location of sediment discharge to lakes.  相似文献   

Organic matter mineralization in sediment of a coastal freshwater lake and response to salinization   总被引：1，自引：0，他引：1  

Richard W. Canavan  Caroline P. Slomp  Philippe Van Cappellen  Gerard A. van den Berg 《Geochimica et cosmochimica acta》2006,70(11):2836-2855

Solid phase and pore water chemical data collected in a sediment of the Haringvliet Lake are interpreted using a multi-component reactive transport model. This freshwater lake, which was formed as the result of a river impoundment along the southwestern coast of the Netherlands, is currently targeted for restoration of estuarine conditions. The model is used to assess the present-day biogeochemical dynamics in the sediment, and to forecast possible changes in organic carbon mineralization pathways and associated redox reactions upon salinization of the bottom waters. Model results indicate that oxic degradation (55%), denitrification (21%), and sulfate reduction (17%) are currently the main organic carbon degradation pathways in the upper 30 cm of sediment. Unlike in many other freshwater sediments, methanogenesis is a relatively minor carbon mineralization pathway (5%), because of significant supply of soluble electron acceptors from the well-mixed bottom waters. Although ascorbate-reducible Fe(III) mineral phases are present throughout the upper 30 cm of sediment, the contribution of dissimilatory iron reduction to overall sediment metabolism is negligible. Sensitivity analyses show that bioirrigation and bioturbation are important processes controlling the distribution of organic carbon degradation over the different pathways. Model simulations indicate that sulfate reduction would rapidly suppress methanogenesis upon seawater intrusion in the Haringvliet, and could lead to significant changes in the sediment’s solid-state iron speciation. The changes in Fe speciation would take place on time-scales of 20-100 years.  相似文献