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131.
Nyamboge Chacha Karoli N. Njau George V. Lugomela Alfred N. N. Muzuka 《Hydrogeology Journal》2018,26(8):2693-2706
The continuous abstraction of groundwater from Arusha aquifers in northern Tanzania has resulted in a decline in water levels and subsequent yield reduction in most production wells. The situation is threatening sustainability of the aquifers and concise knowledge on the existing groundwater challenge is of utmost importance. To gain such knowledge, stable isotopes of hydrogen and oxygen, and radiocarbon dating on dissolved inorganic carbon (DIC), were employed to establish groundwater mean residence time and recharge mechanism.14C activity of DIC was measured in groundwater samples and corrected using a δ13C mixing method prior to groundwater age dating. The results indicated that groundwater ranging from 1,400 years BP to modern is being abstracted from deeper aquifers that are under intensive development. This implies that the groundwater system is continuously depleted due to over-pumping, as most of the sampled wells and springs revealed recently recharged groundwater. High 14C activities observed in spring water (98.1?±?7.9 pMC) correspond with modern groundwater in the study area. The presence of modern groundwater suggests that shallow aquifers are actively recharged and respond positively to seasonal variations. 相似文献
132.
We use records from the East Thuringian Seismic Network (OTSN, Ostthüringer Seismisches Netzwerk) to characterize the site response for each station, and to analyze the scope and limits of the Rayleigh modeling for H/V spectral ratio. The stations considered in this work can be classified by their seismic response as hard rock sites or as sites with some site effect. From these results we propose velocity models based on Rayleigh modeling (theoretical Rayleigh wave ellipticity).Our results show that for locations affected by site effects the H/V spectral ratio can be modeled by the theoretical ellipticity of layered velocity models. For hard rock sites the spectral ratio is rather flat and the modeling with the theoretical ellipticity was not very clear. This may be explained by the fact that for hard rock sites the conditions for a clear fundamental frequency associated with S-wave resonance, and therefore with Rayleigh wave ellipticity, are not fulfilled. 相似文献
133.
Abstract This paper explores magnetic equilibria which could result from the kink instability in a cylindrical magnetic flux tube. We examine a variety of cylindrical magnetic equilibria which are susceptible to the kink, and simulate its evolution in a frictional fluid. We assume that the evolution takes place under conditions of helical symmetry, so the problem becomes effectively two-dimensional. The initial cylindrical equilibrium field is specified in terms of its twist function k(r) = B θ/(rBz ) and for a variety of k(r) functions we calculate linear growth rates for the kink instability, assuming that it develops under helical symmetry with pitch τ. We find that the growth rate is sensitive to the value of τ. We simulate nonlinear evolution of the kink using a Lagrangian frictional code which constrains the field to have helical symmetry of a given pitch τ. Ideal MHD is assumed and the plasma pressure is taken to be small in order to mimic conditions in the solar corona. In some cases the flux tube evolves to a new smooth helically symmetric equilibrium which involves a relatively small change in the maximum electric current. In other cases there is evidence of current-sheet formation. 相似文献
134.
Wilson M. Khaemba Alfred Stein 《International journal of geographical information science》2013,27(8):833-853
This paper applies generalised linear statistical techniques in a GIS to analyse wildlife data from a Kenyan wildlife reserve and its surrounding areas. Attention focuses on the spatial distribution of elephant during nine successive surveys, analysing their temporal and spatial relationship to 12 environmental covariates. A principal component analysis identifies five major determining factors, thereby reducing dimensionality in the data, while a simple spatial analysis procedure, suitable for wildlife data obtained from airborne surveys, quantfies clustering for different animal species. The number of explanatory variables appearing in abundance models is found to be subject to large variations during successive surveys with a minimum and maximum of four and eight variables, respectively. Species from highly clustered populations are found to have over 20 times more observations within short distances compared to the rest. The study concludes that a combination of generalised linear modelling and GIS gives deeper insight into the dynamics of wildlife species in and around well-defined nature reserves. 相似文献
135.
Numerical and multivariate stochastic approaches to characterize flow in a constructed wetland basin 总被引:1,自引:1,他引:0
Xiaohua Wei Anand K. Plappally Alfred B. O. Soboyejo Bin Dong Zhi Mao Larry C. Brown 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(4):545-556
Reduction in specific and viscous dissipation rate in surface waters by flow control and contaminant removal are the goals
of constructed wetlands. A two-dimensional simulation study on surface flow through a constructed wetland in Guilin, China
is performed. The flow through the wetland is modeled and dynamically simulated by distinct case studies by varying both inlet
width and inflow rate. Nonlinear increase in peak dynamic pressure and specific dissipation rates as a function of increasing
inflow rate is reported for the different cases studied. The results of the numerical models confirm an increase in viscous
dissipation, shear stress and dynamic pressure within the wetland with increase in inflow rate. These modeling results are
used as inputs for performing a statistical data analysis. Further, a multivariate stochastic statistical framework has been
proposed for the prediction of dissipation as a function of variables including inflow rate, inlet geometry and wall shear
stress. Multivariate and variance analysis is performed to validate the appropriateness of the theoretical models proposed.
Results provide simplified meaningful suggestions to constructed wetland design and related applications. 相似文献
136.
Anozie Ebigbo Rainer Helmig Alfred B. Cunningham Holger Class Robin Gerlach 《Advances in water resources》2010
The concentration of greenhouse gases – particularly carbon dioxide (CO2) – in the atmosphere has been on the rise in the past decades. One of the methods which have been proposed to help reduce anthropogenic CO2 emissions is the capture of CO2from large, stationary point sources and storage in deep geological formations. The caprock is an impermeable geological layer which prevents the leakage of stored CO2, and its integrity is of utmost importance for storage security. Due to the high pressure build-up during injection, the caprock in the vicinity of the well is particularly at risk of fracturing. Biofilms could be used as biobarriers which help prevent the leakage of CO2 through the caprock in injection well vicinity by blocking leakage pathways. The biofilm could also protect well cement from corrosion by CO2-rich brine. 相似文献
137.
138.
Alfred Bögli 《International Journal of Earth Sciences》1968,58(2):395-408
Zusammenfassung Über die Gebundenheit der Karsthydrographie an Klüfte oder Schichtfugen herrschen je nach den Sprachgebieten unterschiedliche Meinungen vor. Allgemein ging man jedoch an der Tatsache vorbei, daß das Wasser bei Druckfließen, also unter phreatischen Bedingungen, kein aggressives CO2 mehr zur Verfügung hat und daher nicht korrodieren kann. Korrosion war daher nur für die vadose Zone erklärbar, und auch nur dann, wenn das Wasser den Gleichgewichtskalkgehalt von 60 bis 90 mg/Liter, je nach Höhenlage, nicht erreicht, was unter bedecktem Karst kaum jemals der Fall ist. Genaue Untersuchungen im 100 km langen Hölloch (Schweiz) (Bögli 1953, 1960, 1966, 1968) und an andern, vor allem französischen Höhlen (Chevalier 1944), ergeben, daß sich das unterirdische Gewässernetz zum größeren Teil anfänglich unter phreatischen Bedingungen entwickelt, was aber nur durch Mischungskorrosion (Bögli 1963 b, 1964 a, 1964 b) möglich ist, die nicht auf eine CO2-Zufuhr von außen angewiesen ist. Durch Inkasion (Nachbruch, Einsturz), die an der primären Hohlraumbildung meist nicht beteiligte Kluftflächen herausarbeitet, wird die schichtgebundene Entstehung meist verdeckt, was zu falschen Folgerungen führt. In der vadosen Zone folgt das Wasser vorwiegend offenen Klüften oder einer undurchlässigen Schicht und fließt auf kürzestem Weg dem Karstwasserkörper zu.
Up to now the connection between the hydrology of karst and joints on the one and bedding planes on the other hand is much discussed. But in every case the corrosion of limestone appeared impossible in the phreatic zone because free CO2 is missing in waterfilled galleries. Intensive investigations in the 62.2 miles of galleries in the Hölloch (Switzerland,Bögli 1953, 1960, 1966, 1968) and in many other caves, in particular in France (Chevalier 1944), demonstrate that on the base of corrosion by mixed water the pattern of underground watercourses is predominantly formed under phreatic conditions in pressure flows and on bedding planes. This fact is frequently masked by incasion (roof fall, lat. incadere = to break down in a cavity) removing joints and fractures which have never participated on the primary forming of galleries. In the vadose zone the underground watercourses generally follow open joints and flow on the nearest way to the groundwater.
Résumé Le rapport entre l'hydrographie karstique et soit les diaclases d'une part, soit les joints de stratification de l'autre est une question assez discutée, surtout en dehors de la France. Mais en tout cas on ne se rend normalement pas compte qu'en conduit forcé l'eau n'emporte pas du CO2 aggressif plus loin que quelques mètres à l'intérieur de la terre, sauf dans les réseaux déjà assez élargis. L'élargissement demande alors d'une part des conditions vadoses, c'est-à-dire la présence de l'air avec du CO2, de l'autre de l'eau qui n'a pas encore atteint la concentration d'équilibre de 60 à 90 mg CO3Ca par litre selon l'altitude. Mais les recherches avancées dans les 100 km du Hölloch (Muotatal, Suisse,Bögli 1953, 1960, 1966, 1968) et dans maintes autres cavernes, surtout en France (Chevalier 1944), prouvent, que les réseaux souterrains se développent au contraire primairement en grandes parties dans la zone noyée en conduit forcé et sur des joints de stratification. Cela demande alors un autre type de corrosion, la corrosion par mélange des eaux qui ne dépend pas de l'adduction de CO2 d'en dehors de l'eau (Bögli 1963 b, 1964 a, 1964 b). La naissance des galeries sur des joints de stratification est très souvent cachée par incasion (lat. incadere = s'effondrer dans une cavité) qui fait ressortir des diaclases et le clivage qui ne participent en rien à la naissance de la galerie souterraine, ce qui a provoqué des conclusions eronnées.
(; 100 ) , . ., , , . , , . , . , .相似文献
139.
Volcanism in the Sumisu Rift, I. Major element, volatile, and stable isotope geochemistry 总被引:2,自引:0,他引:2
Alfred G. Hochstaedter James B. Gill Minoru Kusakabe Sally Newman Malcolm Pringle Brian Taylor Patty Fryer 《Earth and Planetary Science Letters》1990,100(1-3)
A bimodal volcanic suite with KAr ages of 0.05–1.40 Ma was collected from the Sumisu Rift using alvin. These rocks are contemporaneous with island arc tholeiite lavas of the Izu-Ogasawara arc 20 km to the east, and provide a present day example of volcanism associated with arc rifting and back-arc basin initiation. Major element geochemistry of the basalts is most similar to that of basalts found in other, more mature back-arc basins, which indicates that back-arc basins need not begin their magmatic evolution with lavas bearing strong arc signatures.Volatile concentrations distinguish Sumisu Rift basalts from island arc basalts and MORB. H2O contents, which are at least four times greater than in MORB, suppress plagioclase crystallization. This suppression results in a more mafic fractionating assemblage, which prevents Al2O3 depletion and delays the initiation of Fe2O3(tot) and TiO2 enrichment. However, unlike arc basalts,Fe3+/ΣFe ratios are only slightly higher than in MORB and are insufficient to cause magnetite saturation early enough to suppress Fe2O3(tot) and TiO2 enrichment. Thus, major element trends are more similar to those of MORB than arcs.H2O, CO2 and S are undersaturated relative to pure phase solubility curves, indicating exsolution of an H2O-rich mixed gas phase. HighH2O/S, highδD, and low (MORB-like)δ34S ratios are considered primary and distinctive of the back-arc basin setting. 相似文献
140.
Anisotropy in the continental upper mantle: possible evidence from explosion seismology 总被引:1,自引:0,他引:1
Alfred Hirn 《Geophysical Journal International》1977,49(1):49-58
Summary. Peculiarities of propagation in the upper mantle of western Europe are documented by profiles of stations recording body waves generated by explosions. Azimuthal variations of travel times and amplitudes of P waves and possible birefringence of S waves may be associated with an anisotropic layer at depths where the lithosphere-asthenosphere transition is supposed to be. 相似文献