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1.
Bank failure and erosion on the Ohio river 总被引：1，自引：0，他引：1
River bank erosion has benn the focus of recent concern surrounding construction and operation of navigation dams along the Ohio River. Such factors as navigation pool levels, pool fluctuations, and towboat traffic have been alleged to be the cause of severe erosion of Ohio River banks. In this paper available information on Ohio River bank erosion is examined from an historical perspective and from the perspective of recent comprehensive investigations. Historical illustrations, photographs, and published reports indicate a history of significant bank erosion for more than 150 years on the Ohio River. Results of field bank condition reconnaissance studies suggest that construction of navigation dams on the Ohio River has not significantly accelerated or intensified bank erosion. Analysis of erosional mechanisms indicates that bank failure and erosion on the Ohio River are complex and episodic phenomena; however, the principal erosional mechanisms appear to be bank material removal by current tractive forces during flood events and internal erosion of bank materials by bank discharge following floods. It is concluded that waves generated by tow and recreational vessels have little impact on bank stability, but land use changes may affect slope stability and bank erosion. 相似文献
2.
Santiago Hernández-León Lutz Postel Javier Arístegui May Gómez María Fernanda Montero Santiago Torres Carlos Almeida Eugen Kühner Ullrich Brenning Eberhard Hagen 《Journal of Oceanography》1999,55(4):471-482
Plankton biomass and indices of metabolism and growth [electron transport system (ETS), glutamate dehydrogenase (GDH) and aspartate transcarbamylase (ATC) activities] were studied over a 2,800 km east-west section of the tropical North Atlantic Ocean (21°N) in <200, 200–500 and >;500 µm size classes. On the large-scale, zooplankton (>;200 µm) enzymatic activities increased westward in the study section, where large cyanobacteria chains (Trichodesmium spp.) were observed. Parallel to it, an increase in medium calanoids (1–2 mm length) was observed towards the western part of the transect, whereas small calanoids (<1 mm) were dominant throughout the boundary area of the subtropical gyre. Microplankton ETS and mesoplankton ETS and ATC activities seemed to match the wave length of low frequency waves. Our results suggest that such waves are related to the observed enhancement of metabolic activity of micro- and mesoplankton. The large-scale and mesoscale variability observed give evidence of the inadequacy of assuming a steady-state picture of the euphotic zone of tropical and subtropical waters. 相似文献
3.
Chemical weathering of marbles has greatly increased during the past decades. The gaseous pollutants generated mainly by combustion of automobile, domestic, and industrial fuels have contributed significantly towards this increase. The weathering affects marble gradationally from outside inwards, producing three distinct zones. The success of a technique developed to provide cohesion to reduced and dislodged calcite crystals in the zone of weathering, by impregnation with resins which even permeate the inter-crystalline boundaries in the non-weathered region, is tested. As these weathered layers are quite thin and easily destructible, direct measurement of compressive strength is impossible. This property is, therefore, determined indirectly via Shore scleroscope hardness and specific gravity.
The impregnation increased the strength of the weathered zone up to 59% and of the unweathered region up to 24%. Corresponding values for permeability and capillarity, relative to untreated specimens, change inversely to strength changes as the pores receive relatively larger amounts of resin in the outer weathered region than in the unweathered region in depth. This phenomenon is substantiated by scanning electron microscopy (S.E.M.). 相似文献
4.
Angela Ullrich Ronald Miletich Tonci Balic-Zunic Lars Olsen Fabrizio Nestola Manfred Wildner Haruo Ohashi 《Physics and Chemistry of Minerals》2010,37(1):25-43
A compressional study of (Na,Ca)(Ti3+,Mg)Si2O6-clinopyroxenes was carried out at high pressures between 10−4 and 10.2 GPa using in situ single-crystal X-ray diffraction, Raman spectroscopy and optical absorption spectroscopy. Compressional
discontinuities accompanied by structural changes, in particular, the appearance of two distinct Ti3+–Ti3+ distances within the octahedral chains at 4.37 GPa, provide evidence for the occurrence of a phase transition in NaTi3+Si2O6. Equation-of-state parameters are K
0 = 115.9(7) GPa with K′ = −0.9(3) and K
0 = 102.7(8) GPa with K′ = 4.08(5) for the low- and high-pressure range, respectively. The transition involves a C2/c–P
[`1] \overline{1} symmetry change, which can be confirmed by the occurrence of new modes in Raman spectra. Since no significant discontinuity
in the evolution of the unit-cell volume with pressure has been observed, the transition appears to be second-order in character.
The influence of the coupled substitution Na+Ti3+↔Ca2+Mg2+ on the static compression behavior and the structural stability has been investigated using a sample of the intermediate
composition (Na0.54Ca0.46)(Mg0.46Ti0.54)Si2O6. No evidence for a deviation from continuous compression behavior has been found, neither in lattice parameter nor in structural
data and the fit of a third-order Birch–Murnaghan equation-of-state to the pressure–volume data yields a bulk modulus of K
0 = 109.1(5) GPa and K′ = 5.02(13). Raman and polarized absorption spectra have been compared to NaTiSi2O6 and reveal major similarities. The main driving force for the phase transition in NaTi3+Si2O6 is the localization of the Ti3+
d-electron and the accompanying distortion, which is suppressed in the (Na,Ca)(Ti3+,Mg)Si2O6-clinopyroxene. 相似文献
5.
Ewald Brückl Johanna Brückl Werner Chwatal Christian Ullrich 《Swiss Journal of Geoscience》2010,103(3):329-344
Results from geophysical explorations of three deep valleys, selected from different tectonic regimes in the Eastern Alps (Ötz-, Oichten-, and Drau Valley), are presented and discussed. Ongoing tectonic deformation may use tectonic structures related to these valleys. However, seismic activity is low there. During the Würm ice age, the thickness of the ice cover ranged between 300 and 1,500 m above present ground elevation. The geophysical investigations comprised reflection seismology, gravity- and resistivity surveys. The maximum depth down to the erosional base of the valleys varies from ~340 to 700 m. Distinct layer packages of the valley-infill at depths greater than 250 m were termed “old valley-fill”. Geophysical parameters and a comparison with the reflection seismic image of an intermediate layer at the recent Pasterze glacier suggest that the top of the “old valley-fill” represents the glacier bed during the decay of the Würm glaciation. Deep erosion is not related to high basal shear stress. The confluence of tributary glaciers is apparently not a significant factor for deep erosion in our examples of deep alpine valleys. We conclude that deep erosion may be related to high water pressure at the glacier bed, supported by specific processes of tectonic weakening. 相似文献
6.
7.
Effect of water residence time on annual export and denitrification of nitrogen in estuaries: A model analysis 总被引：1，自引：0，他引：1
Edward H. Dettmann 《Estuaries and Coasts》2001,24(4):481-490
A simple model of annual average response of an estuary to mean nitrogen loading rate and freshwater residence time was developed
and tested. It uses nitrogen inputs from land, deposition from the atmosphere, and first-order calculations of internal loss
rate and net export to perform a steady-state analysis over a yearly cycle. The model calculates the fraction of total nitrogen
input from land and the atmosphere that is exported and the fraction that is denitrified or lost to other processes within
the estuary. The model was tested against data from the literature for 11 North American and European estuaries having a wide
range of physical characteristics, nitrogen loading rates, and geographical and climatic settings. The model shows that the
fraction of nitrogen entering an estuary that is exported or denitrified can be predicted from the freshwater residence time.
The first-order rate constant for nitrogen loss within an estuary, as a fraction of total nitrogen in the water column, is
0.30 mo−1. Denitrification typically accounts for 69–75% of the total annual net nitrogen removal from the water column by processes
within the estuary. The model makes explicit the dependence of nitrogen concentration in the water column on the loading rate
of nitrogen, water residence time, estuary volume, and the rate constant for loss within the estuary. 相似文献
8.
K.-H. Mittenzwey S. Breitwieser J. Penig A. A. Gitelson G. Dubovitzkii G. Garbusov S. Ullrich V. Vobach A. Müller 《洁净——土壤、空气、水》1991,19(1):1-15
Ship-based experiments around Berlin and laboratory tests were carried out in order to develop spectroscopic methods for the in-situ determination of chlorophyll a (Chla) and chemical oxygen demand (CODcr) of surface waters. The regression analysis of spectroscopic data (reflectance (R); laser-stimulated and conventional fluorescence (IF)) and chemical-biological data yielded correlations of a relatively good quality. 相似文献
9.
Temperature dependence of the polarized electronic absorption spectra of olivines. Part I – fayalite
Polarized electronic absorption spectra of orthorhombic fayalite, Fe2SiO4, [E || a(|| Z),E || b(|| X), E || c(|| Y)], space group Pbnm, have been studied in the temperature range 293 ≤T/K ≤ 1273. The spectra were analysed into component bands originating from spin-allowed dd transitions of iron(II) at the different sites, M1 and M2, in the structure. The assignments of bands, made on the basis
of the polarization dependence of the spectra and considerations of transition energies, were confirmed by the analysis of
the temperature-dependent spectra. The temperature dependencies of integral intensities, half band widths and energy positions
of absorptions bands caused by Fe2+ on the different octahedral sites, M1 and M2, were evaluated for the individual transitions. Independent of the site symmetry,
absorption bands shift to lower energies and half band widths increase on rising temperature. The temperature dependence of
band intensities depends on site symmetry. The integral intensities are found to increase with temperature for the transition
metal ion on a centrosymmetric site, or remain constant when the site is missing an inversion centre. This is consistent with
the general conclusion of Taran et al. (1994).
Received: 11 October 2001 / Accepted: 17 January 2002 相似文献
10.
J. Escuder Viruete A. Díaz de Neira P.P. Herniz Huerta J. Monthel J. García Senz M. Joubert E. Lopera T. Ullrich R. Friedman J. Mortensen A. Prez-Estaún 《Lithos》2006,90(3-4):161-186
Located in the Cordillera Oriental of the Dominican Republic, the Early Cretaceous Los Ranchos Fm (LRF) comprises a > 3-km thick sequence of volcanic and volcaniclastic rocks with variable geochemical characteristics, which is intruded by tonalite batholiths, minor gabbro/diorite plutons and mafic dykes. From top to bottom, three main stratigraphic units have been mapped: upper basaltic, intermediate rhyodacitic and lower basaltic. Combined detailed mapping, stratigraphy, geochemistry, Rb–Sr/Sm–Nd isotopic studies and U–Pb/Ar–Ar geochronology show that the mafic rocks of the LRF include boninites and LREE-depleted island arc tholeiites (IAT) in the lower unit, both which appear genetically related, whereas normal IAT occur in the upper unit. The source for these rocks is thought to reflect variably depleted mantle, overprinted by a subduction zone component. Contemporaneous Aptian U–Pb zircon ages were obtained for a rhyodacite from the intermediate unit (116.0 ± 0.8 Ma) and a tonalite of the Zambrana batholith (115.5 ± 0.3 Ma) that intrudes the LRF. The similarity of trace element signatures in both units argues for genetic link between the felsic volcanics of the LRF and the tonalite plutonism. Low-K rhyolites and tonalite batholiths are interpreted as products of secondary melting at the base of thickened early arc crust. 40Ar/39Ar plateau ages of hornblende in most tonalites are Albian (109–106 Ma) and interpreted as final cooling ages, prior to unroofing and growth of unconformable overlying reef limestones of the Hatillo Fm (112–100 Ma). The LREE-depleted IAT and boninites of lower basaltic unit are interpreted to have formed during subduction zone initiation in the Caribbean Island arc, and the normal IAT of the upper unit are thought to represent the subsequent establishment of the volcanic front. 相似文献