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   

Turbulent flow over a dune: Green River,Colorado     

Jeremy G. Venditti  Bernard O. Bauer 《地球表面变化过程与地形》2005,30(3):289-304

Detailed echo‐sounder and acoustic Doppler velocimeter measurements are used to assess the temporal and spatial structure of turbulent flow over a mobile dune in a wide, low‐gradient, alluvial reach of the Green River. Based on the geometric position of the sensor over the bedforms, measurements were taken in the wake, in transitional flow at the bedform crest, and in the internal boundary layer. Spatial distributions of Reynolds shear stress, turbulent kinetic energy, turbulence intensity, and correlation coefficient are qualitatively consistent with those over fixed, two‐dimensional bedforms in laboratory flows. Spectral and cospectral analysis demonstrates that energy levels in the lee of the crest (i.e. wake) are two to four times greater than over the crest itself, with minima over the stoss slope (within the developing internal boundary layer). The frequency structure in the wake is sharply defined with single, dominant peaks. Peak and total spectral and cross‐spectral energies vary over the bedform in a manner consistent with wave‐like perturbations that ‘break’ or ‘roll up’ into vortices that amalgamate, grow in size, and eventually diffuse as they are advected downstream. Fluid oscillations in the lee of the dune demonstrate Strouhal similarity between laboratory and field environments, and correspondence between the peak frequencies of these oscillations and the periodicity of surface boils was observed in the field. Copyright © 2005 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   

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   

Analysis of rock structure stability in coal mines   总被引：1，自引：0，他引：1  

Yi‐Shan Pan  Zhong‐Hua Li 《国际地质力学数值与分析法杂志》2005,29(10):1045-1063

In this paper, the theory of limit point instability is used to analyse the stability of rock structures in coal mines. A general method of analysing stability of rock structures is put forward and a uniform instability condition of rock structures is set up. Some instability phenomena, such as rock bursts in circular roadways, pillars and long walls, and the outburst of coal and gas from circular roadways, are discussed analytically. At a later stage, the critical point of rock structure instability is determined. The influence of relative parameters (such as the mechanical properties of rock, coal, and the geometric sizes) on the stability of the rock structures is carefully analysed. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Challenges for Sustainable Mineral Resources Development in the 21st Century*     

Jeremy P. Richards 《Resource Geology》2005,55(2):131-137

Abstract. The modern minerals industry is more environmentally responsible and socially aware than at any time in the past, and yet faces increasing challenges to improve its performance in these areas still further. Some of these expectations are reasonable and achievable, but others are unrealistic (e.g., “zero impact”) if real development is to continue. Moreover, because society is the ultimate beneficiary of the industry's products, it should be prepared to pay for the improvements it demands. Currently externalized costs, such as many environmental and social impacts, should be internalized into prices, and higher royalties should be charged on gross revenue to ensure effective capture of value of non‐renewable resources by host countries. Such costs to consumers could be offset by higher recycling value, leasing, or deposit‐return schemes. NGOs have an important role to play in working with industry to convince society to accept such changes.  相似文献   

Potentiometric titrations of Bacillus subtilis cells to low pH and a comparison of modeling approaches     

Jeremy B. Fein  Jean-François Boily  Drew Gorman-Lewis 《Geochimica et cosmochimica acta》2005,69(5):1123-1132

To provide constraints on the speciation of bacterial surface functional groups, we have conducted potentiometric titrations using the gram-positive aerobic species Bacillus subtilis, covering the pH range 2.1 to 9.8. Titration experiments were conducted using an auto-titrator assembly, with the bacteria suspended in fixed ionic strength (0.01 to 0.3 M) NaClO₄ solutions. We observed significant adsorption of protons over the entire pH range of this study, including to the lowest pH values examined, indicating that proton saturation of the cell wall did not occur under any of the conditions of the experiments. Ionic strength, over the range studied here, did not have a significant effect on the observed buffering behavior relative to experimental uncertainty. Electrophoretic mobility measurements indicate that the cell wall is negatively charged, even under the lowest pH conditions studied. These experimental results necessitate a definition of the zero proton condition such that the total proton concentration at the pH of suspension is offset to account for the negative bacterial surface charge that tends towards neutrality at pH <2.The buffering intensity of the bacterial suspensions reveals a wide spread of apparent pKa values. This spread was modeled using three significantly different approaches: a Non-Electrostatic Model, a Constant Capacitance Model, and a Langmuir-Freundlich Model. The approaches differ in the manner in which they treat the surface electric field effects, and in whether they treat the proton-active sites as discrete functional groups or as continuous distributions of related sites. Each type of model tested, however, provides an excellent fit to the experimental data, indicating that titration data alone are insufficient for characterizing the molecular-scale reactions that occur on the bacterial surface. Spectroscopic data on the molecular-scale properties of the bacterial surface are required to differentiate between the underlying mechanisms of proton adsorption inherent in these models. The applicability and underlying conceptual foundation of each model is discussed in the context of our current knowledge of the structure of bacterial cell walls.  相似文献   

Fracture mechanics analysis of multiple cracks in anisotropic media     

Chia‐Huei Tu  C.‐S. Chen  T.‐T. Yu 《国际地质力学数值与分析法杂志》2011,35(11):1226-1242

This paper presents a single‐domain boundary element method (BEM) for linear elastic fracture mechanics analysis in the two‐dimensional anisotropic material. In this formulation, the displacement integral equation is collocated on the un‐cracked boundary only, and the traction integral equation is collocated on one side of the crack surface only. A special crack‐tip element was introduced to capture exactly the crack‐tip behavior. A computer program with the FORTRAN language has been developed to effectively calculate the stress intensity factors of an anisotropic material. This BEM program has been verified having a good accuracy with the previous researches. Furthermore, by analyzing the different anisotropic degree cracks in a finite plate, we found that the stress intensity factors of crack tips had apparent influence by the geometry forms of cracks and media with different anisotropic degrees. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Chronology and stratigraphy of the Magdalen Islands archipelago from the last glaciation to the early Holocene: new insights into the glacial and sea‐level history of eastern Canada          下载免费PDF全文

Audrey M. Rémillard  Guillaume St‐Onge  Pascal Bernatchez  Bernard Hétu  Jan‐Pieter Buylaert  Andrew S. Murray  Benoit Vigneault 《Boreas: An International Journal of Quaternary Research》2016,45(4):604-628

  相似文献