Une controverse que l'on croyait oubliée     

Jacques Touret 《Comptes Rendus Geoscience》2004,336(2):167

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Effet de la teneur en eau d'un sol sur la réduction bactérienne d'oxydes de fer     

Sébastien J. Stemmler  Stéphanie Loyaux-Lawniczak  Jacques Berthelin 《Comptes Rendus Geoscience》2004,336(13):1171-1179

Iron-reducing activity of autochthonous bacteria from two temporary hydromorphic soils is evaluated by the study of iron reductive dissolution, as a function of water content. The release of ferrous iron in solution is coupled to the mineralization of soil organic carbon. Water soil saturation is not necessary for iron reductive dissolution, since the highest dissolution is obtained for a wet, but not water-saturated soil (100% of water holding capacity WHC), and dissolution is also very high in a soil at 75% WHC. To cite this article: S.J. Stemmler et al., C. R. Geoscience 336 (2004).  相似文献   

The Elusive AD 1826 Tsunami, South Westland, New Zealand   总被引：1，自引：0，他引：1  

James R. Gofr Andrew Wells  Catherine Chagu‐Goff  Scott L. Nichol  Robert J.N. Devoy 《New Zealand geographer》2004,60(2):28-39

In AD 1826 sealers reported earthquake and tsunami activity in Fiordland, although, contemporary or near‐contemporary accounts of tsunami inundation at the time are elusive. A detailed analysis of recent sediments from Okarito Lagoon builds on contextual evidence provided by earlier research concerning past tsunami inundation. Sedimentological, geochemical, micropalaeontological and geochronological data are used to determine palaeoenvironments before, during and after what was most probably tsunami inundation in AD 1826. The most compelling chronological control is provided fry a young cohort of trees growing on a raised shoreline bench stranded fry a drop in the lagoon water level following tsunami inundation.  相似文献   

MTBE in Drinking Water Production – Occurrence and Efficiency of Treatment Technologies     

Christine Baus  HsuWen Hung  Frank Sacher  Michael Fleig  Heinz‐Jürgen Brauch 《洁净——土壤、空气、水》2005,33(2):118-132

In Germany, the gasoline additive methyl tert‐butyl ether (MTBE) is almost constantly detected in measurable concentrations in surface waters and is not significantly removed during riverbank filtration. The removal of MTBE from water has been the focus of many studies that mostly were performed at high concentration levels and centred in understanding the mechanisms of elimination. In order to assess the performance of conventional and advanced water treatment technologies for MTBE removal in the low concentration range further studies were undertaken. Laboratory experiments included aeration, granulated activated carbon (GAC) adsorption, ozonation and advanced oxidation processes (AOP). The results show that the removal of MTBE by conventional technologies is not easily achieved. MTBE is only removed by aeration at high expense. Ozonation at neutral pH values did not prove to be effective in eliminating MTBE at all. The use of ozone/H₂O₂ (AOP) may lead to a partly elimination of MTBE. However, the ozone/H₂O₂ concentrations required for a complete removal of MTBE from natural waters is much higher than the ozone levels applied nowadays in waterworks. MTBE is only poorly adsorbed on activated carbon, thus GAC filtration is not efficient in eliminating MTBE. A comparison with real‐life data from German waterworks reveals that if MTBE is detected in the raw water it is most often found in the corresponding drinking water as well due to the poor removal efficiency of conventional treatment steps.  相似文献   

Short‐term intertidal bar mobility on a ridge‐and‐runnel beach,Merlimont, northern France     

E. J. Anthony  F. Levoy  D. Monfort  C. Degryse‐Kulkarni 《地球表面变化过程与地形》2005,30(1):81-93

Digital elevation models and topographic pro?les of a beach with intertidal bar and trough (ridge‐and‐runnel) morphology in Merlimont, northern France, were analysed in order to assess patterns of cross‐shore and longshore intertidal bar mobility. The beach exhibited a pronounced dual bar–trough system that showed cross‐shore stationarity. The bars and troughs were, however, characterized by signi?cant longshore advection of sand under the in?uence of suspension by waves and transport by strong tide‐ and wind‐driven longshore currents. Pro?le changes were due in part to the longshore migration of medium‐sized bedforms. The potential for cross‐shore bar migration appears to be mitigated by the large size of the two bars relative to incident wave energy, which is modulated by high vertical tidal excursion rates on this beach due to the large tidal range (mean spring tidal range = 8·3 m). Cross‐shore bar migration is also probably hindered by the well‐entrenched troughs which are maintained by channelled high‐energy intertidal ?ows generated by swash bores and by tidal discharge and drainage. The longshore migration of intertidal bars affecting Merlimont beach is embedded in a regional coastal sand transport pathway involving tidal and wind‐forced northward residual ?ows affecting the rectilinear northern French coast in the eastern English Channel. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

An automated salt‐tracing gauge for flow‐velocity measurement     

Olivier Planchon  Norbert Silvera  Raphael Gimenez  David Favis‐Mortlock  John Wainwright  Yves Le Bissonnais  Gerard Govers 《地球表面变化过程与地形》2005,30(7):833-844

This article introduces the SVG (salt‐velocity gauge), a novel automated technique for measuring flow velocity by means of salt tracing. SVG allows a high measuring rate (up to one every 2 seconds), short control section length (down to 10 cm), high accuracy (+[sol ]?1·5 cm s^?1), and unbiased calculation of the mean velocity in experimental conditions with turbulent, supercritical flow. A few cubic centimetres of saturated salt solution (NaCl) are injected into the flow at regular time intervals using a programmable solenoid valve. The tracer successively passes two conductivity probes placed a short distance downstream. The transformation of the signal between the two probes is modelled as a one‐dimensional diffusion wave equation. Model calibration gives an estimation of the mean velocity and the diffusion for each salt plume. Two implementations of the SVG technique are described. The first was an outdoors simulated rainfall experiment in Senegal (conductivity probes at 40 cm apart, 8 Hz measurement rate, salt injections at 10 second intervals). Mean velocity was estimated to range between 0·1 and 0·3 m s^?1. The second was a laboratory‐based flume experiment (conductivity probes at 10 cm apart, 32 Hz, salt injections at 2 second intervals). Another SVG with probes at 34 cm apart was used for comparison. An acoustic Doppler velocimeter (ADV) was also used to give an independent assessment of velocity. Using the 10 cm salt gauge, estimated mean velocity ranged from 0·6 to 0·9 m s^?1 with a standard deviation of 1·5 cm s^?1. Comparisons between ADV, 10 cm SVG and 34 cm SVG were consistent and demonstrated that the salt‐tracing results were unbiased and independent of distance between probes. Most peaks were modelled with r² > 90 per cent. The SVG technology offers an alternative to the dye‐tracing technique, which has been severely criticized in the literature because of the wide interval of recommended values for the correction factor α to be applied to the timings. This article demonstrates that a fixed value of α is inappropriate, since the correction factor varies with velocity, diffusion and the length of the control section. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Probabilistic approach for active control of structures: experimental verification     

Jae‐Seung Hwang  Kyung‐Won Min  Sang‐Hyun Lee  Hongjin Kim 《地震工程与结构动力学》2005,34(3):207-225

In our previous study (Earthquake Engineering and Structural Dynamics 2003; 32 :2301), we have developed a probabilistic algorithm for active control of structures. In the probabilistic control algorithm, the control force is determined by the probability that the structural energy exceeds a specified target critical energy, and the direction of a control force is determined by the Lyapunov controller design method. In this paper, an experimental verification of the proposed probabilistic control algorithm is presented. A three‐story test structure equipped with an active mass driver (AMD) has been used. The effectiveness of the control algorithm has been examined by exciting the test structure using a sinusoidal signal, a scaled El Centro earthquake and a broadband Gaussian white noise; and, especially, experiments on control have been performed under different conditions to that of system identification in order to prove the stability and robustness of the proposed control algorithm. The experimental results indicate that the probabilistic control algorithm can achieve a significant response reduction under various types of ground excitations even when the modeling error exists. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Delayed geochemical hazard: Concept, digital model and case study     

CHEN Ming  FENG Liu  Jacques Yvon 《中国科学D辑(英文版)》2005,48(Z2)

Delayed Geochemical Hazard (DGH briefly) presents the whole process of a kind of serious ecological and environmental hazard caused by sudden reactivation and sharp release of long-term accumulated pollutant from stable species to active ones in soil or sediment system due to the change of physical-chemical conditions (such as temperature, pH, Eh, moisture, the concentrations of organic matters, etc.) or the decrease of environment capacity. The characteristics of DGH are discussed. The process of a typical DGH can be expressed as a nonlinear polynomial. The points where the derivative functions of the first and second orders of the polynomial reach zero, minimum and maximum are keys for risk assessment and harzard pridication.The process and mechanism of the hazard is due to the transform of pollutant among different species principally. The concepts of "total releasable content of pollutant", TRCP, and "total concentration of active specie", TCAS, are necessarily defined to describe the mechanism of DGH. The possibility of the temporal and spatial propagation is discussed. Case study shows that there exists a transform mechanism of "gradual release" and "chain reaction" among the species of the exchangeable and the bounds to carbonate, iron and manganese oxides and organic matter, thus causing the delayed geochemical hazard.  相似文献   

Interannual Variability in Pollen Dispersal and Deposition on the Tropical Quelccaya Ice Cap*     

Carl A. Reese  Kam‐biu Liu 《The Professional geographer》2005,57(2):185-197

Pollen collected from snow samples on the Quelccaya Ice Cap in 2000 and 2001 reveals significant interannual variability in pollen assemblage, concentration, and provenance. Samples from 2000, a La Niña year, contain high pollen concentrations and resemble samples from the Andean forests (Yungas) to the east. Samples from 2001, an El Niño year, contain fewer pollen and resemble those from the Altiplano. We suggest that varying wind patterns under different El Niño/Southern Oscillation (ENSO) conditions may affect the processes of pollen transport over the Altiplano and on the ice cap, although confounding variables such as flowering phenology and sublimation should also be considered  相似文献   

Land tenure type as an underrated legal constraint on the conservation management of coastal dunes: examples from Ireland     

John McKenna  Michael MacLeod  rew Cooper  Anne Marie O'Hagan†  James Power‡ 《Area》2005,37(3):312-323

Legal factors play an underrated but significant role as constraints on conservation management. In this paper, based on observations in both Northern Ireland and the Republic of Ireland, mode of land tenure is assessed to determine its influence on the conservation management of coastal dunes. The tenure types considered are: private ownership, corporate private ownership, tenancy, secured tenancy, leasing, common (joint) ownership, uncertain ownership, public ownership and its subset military ownership. It is suggested that multiple private ownership is least likely to favour effective conservation management. Public ownership by a statutory conservation authority and corporate private ownership by a conservation-orientated NGO are regarded as the optimum tenure types for conservation management of coastal dunes.  相似文献