Assessment of micro‐aggregation using laser diffractometry     

L. Beuselinck  G. Govers  J. Poesen 《地球表面变化过程与地形》1999,24(1):41-49

In order to evaluate the influence of the measuring technique on the determination of (micro‐)aggregation in soil and sediment samples, results of grain size distributions of undispersed silty soil samples obtained by the sieve‐pipette method are compared with those obtained using a laser diffraction grain size analyser, the Coulter LS‐100. Reduced major axis relationships are calculated which may be used to convert Coulter LS‐100 results to those obtained by the sieve‐pipette method. The relationships obtained are very similar to the reduced major axis relationships established for dispersed silty soil samples. The results also show that the Coulter LS measurements have a systematic bias compared to the sieve‐pipette data. This implies that, if the percentage of (micro‐)aggregation is determined, the (interpretation of the) results will be strongly dependent on the measurement technique used. Using the calibration relationships that were established, nomographs can be developed to predict the level of sieve‐pipette (micro‐) aggregation from Coulter LS‐100 data. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Sediment transport by overland flow over an area of net deposition     

L. Beuselinck  G. Govers  A. Steegen  T. A. Quine 《水文研究》1999,13(17):2769-2782

Flume studies were conducted in order to evaluate the influence of slope, sediment size, discharge and inflow sediment concentration on sediment deposition by overland flow. Additionally, experiments were carried out to measure transport capacity of overland flow at low slopes, using a wide range of discharges. The experimental data show that the hydraulic conditions where net deposition occurs can be divided into two domains. The first domain is characterized by hydraulic conditions where transport capacity is not significant. In the second domain net deposition still occurs but transport capacity is significant. The size of the latter domain is dependent on the sediment size distribution, on the hydraulic roughness and on the inflow sediment concentration. The experiments clearly indicate the necessity of incorporating a threshold value in any deposition equation. These experiments demonstrate that shear stress is a valuable threshold for deposition modelling. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Harmonizing North Sea policy in the Netherlands     

Henk van Hoorn  Gerard Peet  Koos Wieriks 《Marine Policy》1985,9(1):53-61

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Measuring surface-layer fluxes of heat and momentum using optical scintillation   总被引：2，自引：1，他引：2  

Reginald J. Hill  Gerard R. Ochs  James J. Wilson 《Boundary-Layer Meteorology》1992,58(4):391-408

An experiment is described showing that an optical scintillation instrument gives reliable values of heat and momentum fluxes in the surface layer, subject to the usual restrictions of homogeneity and steady state. This instrument measures the turbulence inner scale and refractive-index structure parameter, which are used to obtain the fluxes from Monin-Obukhov similarity relationships. The instrument gives space-averaged values over a propagation path that can range in length from tens to hundreds of meters. The history of the use of optical propagation to estimate fluxes is reviewed.  相似文献   

Detection of Cracking Levels in Brittle Rocks by Parametric Analysis of the Acoustic Emission Signals     

Zabihallah Moradian  Herbert H. Einstein  Gerard Ballivy 《Rock Mechanics and Rock Engineering》2016,49(3):785-800

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Schwankungen der Sonnenstrahlung seit 18000 Jahren     

Gerard De Geer  G. Steinmann 《International Journal of Earth Sciences》1928,18(6):417-454

Ohne Zusammenfassung  相似文献   

Sodium fluoride ion-pairs in seawater     

Gerard R. Miller  Dana R. Kester 《Marine Chemistry》1976,4(1):67-82

Laboratory investigations were conducted on the formation of NaF° ion-pairs at the ionic strength of seawater using specific ion electrodes. Sodium and fluoride ion electrodes produced results which are consistent with the ion-pairing model for these ionic interactions. The stoichiometric association constant for NaF°, $\text{K}{}^1{}_{\mathrm{<mtext>NaF</mtext>}}$, was determined at 15, 25, and 35°C. It was assumed that $\text{K}{}^1{}_{\mathrm{<mtext>NaF</mtext>}}$ was a function of temperature, pressure, and ionic strength but not of solution composition. The value for $\text{K}{}^1{}_{\mathrm{<mtext>NaF</mtext>}}$ at 25°C and I = 0.7 m is 0.045 ± 0.006. $\text{K}{}^1{}_{\mathrm{<mtext>NaF</mtext>}}$ increased with decreasing temperature. This result was used to recompute values of $\text{K}{}^1{}_{\mathrm{<mtext>MgF</mtext>}}$ and $\text{K}{}^1{}_{\mathrm{<mtext>CaF</mtext>}}$ accounting for the presence of NaF° ion-pairs. The value for $\text{K}{}^1{}_{\mathrm{<mtext>NaF</mtext>}}$ indicates that 1.1% of the fluoride in seawater is ion-paired with sodium at 25°C and 35‰ salinity. This fraction increases to approximately 2% at the lower temperatures found in the deep ocean. The percentage of free fluoride in natural seawater was measured at 15, 25, and 35°C to verify the speciation calculated from equilibrium constants.  相似文献   

A pilot tagging experiment on European hake (Merluccius merluccius): methodology and preliminary results     

de Pontual  Helene; Bertignac  Michel; Battaglia  Andre; Bavouzet  Gerard; Moguedet  Philippe; Groison  Anne-Laure 《ICES Journal of Marine Science》2003,60(6):1318-1327

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Assessment of population size and migration routes of silver eel in the River Rhine based on a 2-year combined mark-recapture and telemetry study     

Breteler  Jan Klein; Vriese  Tim; Borcherding  Jost; Breukelaar  Andre; Jorgensen  Lothar; Staas  Stefan; de Laak  Gerard; Ingendahl  Detlev 《ICES Journal of Marine Science》2007,64(7):1450-1456

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Early diagenesis in rapidly accumulating sediments on the Alboran slope, ODP site 976     

Stefano M. Bernasconi  Philip A. Meyers  Gerard O&#;Sullivan 《Geo-Marine Letters》1999,18(3):209-214

 The oxidation and reduction that occur during early diagenesis of sediments has been studied in the interstitial waters of a rapidly accumulating sedimentary sequence from the Mediterranean margin of Spain. A series of reactions that are mediated by progressively lower free energy derived from oxidation of organic matter is evident in the sedimentary sequence. Iron and manganese are rapidly reduced. Phosphate and alkalinity maxima at a subbottom depth of 15 m indicate maximal organic matter degradation. Methane first appears at ∼20 m subbottom after sulfate is depleted, and its concentrations quickly climb. Received: 27 October 1997 / Revision received: 4 March 1998  相似文献