Exhumation during crustal folding in the Namche-Barwa syntaxis   总被引：6，自引：0，他引：6  

Jean-Pierre Burg  Philippe Davy  Peter Nievergelt  Felix Oberli  Diane Seward  Zhizhong Diao  Martin Meier 《地学学报》1997,9(2):53-56

Geological observation in the eastern end of the Himalaya shows that the Asia/India Suture is folded. Metamorphic rocks derived from India occur structurally below the suture, in the core of a regional antiform. Isotopic and fission track dating establish cooling-exhumation of rocks from c.30 km depth within the last 4 Myr. We argue that exhumation is caused by ～ 10 mm yr^-1 erosion coeval with crustal scale folding.  相似文献   

A Simple Temporal and Spatial Analysis of Flow in Complex Terrain in the Context of Wind Energy Modelling   总被引：1，自引：0，他引：1  

Keith W. Ayotte  Robert J. Davy  Peter A. Coppin 《Boundary-Layer Meteorology》2001,98(2):275-295

A simple temporal and spatial analysisis done on wind speed and direction data from a number ofmeteorological towers separated by distances between roughly 1 and 100 kilometres. The analysis is done in the context of expected model error in wind energy calculations. The study first uses single point statistics to show the evolution of mean values with time. It is shown that strong seasonal signals are present and that stable means are achieved only after averaging periods of a year or more. The study then uses discrete Fourier transforms to show that significant amounts of spectral energy reside in modes with periods of a few days to less than a day. Frequency dependent cross correlation values are then derived and used to show how correlation between towers diminishes with increasing frequency. The mechanism responsible for this diminished correlation is shown through the comparison of cross-correlation phase as a function of frequency and its relationship to distance between towers. Error in wind energy estimates are shown to be strongly related to correlation and therefore distance over which the prediction is made. In summary, much of the inaccuracy in modelling flow in the context of wind energy calculations is due to a lack of scale separation between the deterministic part of the flow, which is well modelled, and that part of the flow that is stochastic at the length and time scales modelled.  相似文献   

Morphometric analysis using remote sensing techniques in the chaka sub-basin, purulia district, West Bengal     

SK Nag 《Journal of the Indian Society of Remote Sensing》1998,26(1-2):69-76

Remote sensing techniques using satellite imagery have proved to be an indispensible tool in morphometric analysis and groundwater studies. In the present area, morphometric analysis using temote sensing techniques have been carried out in Chaka river sub-basin of Manbazar Block, Purulia district, West-Bengal, which is one of the most drought affected area in West-Bengal. The parameters worked out include Bifurcation ratio (R_b), Stream length (L_u). Form factor (R_f), Circulatory ratio (R_c), and Drainage density. The morphometric analysis suggests that the area is covered by fractured, resistant, permeable rocks, the drainage network not so affected by tectonic disturbances. Using satellite imageries of LANDSAT and IRS, different hydrogeomorphological units have been delineated. The study shows that moderately weathered pediplains and valley fills are good prospective zones for groundwater exploration.  相似文献   

Experimental study and constitutive modelling of elasto‐plastic damage in heat‐treated mortar     

Xiao‐Ting Chen  J. F. Shao  C. A. Davy  F. Skoczylas 《国际地质力学数值与分析法杂志》2010,34(4):357-382

This study investigates the effect of a heat‐treatment upon the thermo‐mechanical behaviour of a model cement‐based material, i.e. a normalized mortar, with a (w/c) ratio of 0.5. First, a whole set of varied experimental results is provided, in order to either identify or validate a thermo‐mechanical constitutive model, presented in the second paper part. Experimental responses of both hydraulic and mechanical behaviour are given after different heating/cooling cycling levels (105, 200, 300, 400^°C). The reference state, used for comparison purposes, is taken after mass stabilization at 60^°C. Typical uniaxial compression tests are provided, and original triaxial deviatoric compressive test responses are also given. Hydraulic behaviour is identified simultaneously to triaxial deviatoric compressive loading through gas permeability K_gas assessment. K_gas is well correlated with volumetric strain evolution: gas permeability increases hugely when ε_v testifies of a dilatant material behaviour, instead of contractile from the test start. Finally, the thermo‐mechanical model, based on a thermodynamics approach, is identified using the experimental results on uniaxial and triaxial deviatoric compression. It is also positively validated at residual state for triaxial deviatoric compression, but also by using a different stress path in lateral extension, which is at the origin of noticeable plasticity. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Environmental limitations on recruitment from seed in invasive Spartina densiflora on a southern European salt marsh     

Enrique Mateos-Naranjo  Susana Redondo-Gmez  Carlos J. Luque  Eloy M. Castellanos  Anthony J. Davy  M. Enrique Figueroa 《Estuarine, Coastal and Shelf Science》2008,79(4):727-732

The South American cordgrass, Spartina densiflora, has invaded a range of different habitats that can support different native species assemblages on salt marshes in the Gulf of Cadiz, Spain. Little is known about the mechanisms of invasion. We examined the potential for seed germination and recruitment in a field transplant experiment, representing a wide range of environments, on elevational gradients across marshes with muddy and sandy sediments. The biotic resistance of native, perennial vegetation (where present) to recruitment of the alien was also investigated. Spartina densiflora seeds were able to germinate over a greater than 2-m range of elevation in the tidal frame. Germination success on unvegetated muddy sediments was related to sediment redox potential, with poor germination at strongly negative redox potentials on the lower sites. On sandy, well-drained sediments, germination was apparently constrained by water availability at the highest elevations. Comparison of vegetated and cleared plots on the upper marsh showed that there was a negative relationship between the presence of Atriplex portulacoides and germination on the muddy sediments. Recruitment (survival of seedlings for 12 weeks) was seen only on unvegetated muddy sediments at the highest elevation. Hence the invasive success and wide elevational tolerance of S. densiflora on the marshes of the Gulf of Cadiz are not reflected in its short-term ability to become established from its prolific seed production. Colonization of sub-optimal habitats may be largely by vegetative propagules and clonal growth.  相似文献   

Mental maps and travel behaviour: meanings and models     

Els Hannes  Diana Kusumastuti  Maikel León Espinosa  Davy Janssens  Koen Vanhoof  Geert Wets 《Journal of Geographical Systems》2012,14(2):143-165

In this paper, the “mental map” concept is positioned with regard to individual travel behaviour to start with. Based on Ogden and Richards’ triangle of meaning (The meaning of meaning: a study of the influence of language upon thought and of the science of symbolism. International library of psychology, philosophy and scientific method. Routledge and Kegan Paul, London, 1966) distinct thoughts, referents and symbols originating from different scientific disciplines are identified and explained in order to clear up the notion’s fuzziness. Next, the use of this concept in two major areas of research relevant to travel demand modelling is indicated and discussed in detail: spatial cognition and decision-making. The relevance of these constructs to understand and model individual travel behaviour is explained and current research efforts to implement these concepts in travel demand models are addressed. Furthermore, these mental map notions are specified in two types of computational models, i.e. a Bayesian Inference Network (BIN) and a Fuzzy Cognitive Map (FCM). Both models are explained, and a numerical and a real-life example are provided. Both approaches yield a detailed quantitative representation of the mental map of decision-making problems in travel behaviour.  相似文献   

Statistical Downscaling of Wind Variability from Meteorological Fields   总被引：1，自引：0，他引：1  

Robert J. Davy  Milton J. Woods  Christopher J. Russell  Peter A. Coppin 《Boundary-Layer Meteorology》2010,135(1):161-175

Measurements show that on numerous occasions the low-level wind is highly variable across a large portion of south-eastern Australia. Under such conditions the risk of a large rapid change in total wind power is increased. While variability tends to increase with mean wind speed, a large component of wind variability is not explained by wind speed alone. In this work, reanalysis fields from the US National Centers for Environmental Prediction (NCEP) are statistically downscaled to model wind variability at a coastal location in Victoria, Australia. In order to reduce the dimensionality of the problem, the NCEP fields are each decomposed using empirical orthogonal function (EOF) techniques. The downscaling technique is applied to two periods in the seasonal cycle, namely (i) winter to early spring, and (ii) summer. In each case, data representing 2 years are used to form a model that is then validated using independent data from another year. The EOFs that best predict wind variability are examined. To allow for non-linearity and complex interaction between variables, all empirical models are built using random forests. Quantitatively, the model compares favourably with a simple regression of wind variability against wind speed, as well as multiple linear regression models.  相似文献   

The effects of suspended sediment on brown trout (Salmo trutta) feeding and respiration after macrophyte control     

MJC Greer  SK Crow  AS Hicks  GP Closs 《新西兰海洋与淡水研究杂志》2013,47(2):278-285

Sediment resuspension during and after mechanical excavation of macrophytes may have a significant impact on resident fish populations. Unfortunately, little is known about the influence of this sediment on the respiratory performance and feeding abilities of fishes in New Zealand waterways. We examined the effects of suspended sediment (SS) concentrations previously observed after a large-scale macrophyte removal operation on oxygen consumption (MO₂) and feeding rates of brown trout (Salmo trutta). MO₂ at 0 mg L^?1, 150 mg L^?1, 300 mg L^?1, 450 mg L^?1 and 600 mg L^?1 of SS was measured using semi-closed respirometry. Feeding rates at the same SS concentrations were also measured using laboratory tank experiments. Results suggest that SS concentrations up to 600 mg L^?1 have no effect on MO₂. Conversely, feeding rates were significantly reduced at 450 mg L^?1 (22% reduction) and 600 mg L^?1 (31% reduction), indicating that sediment concentrations above 450 mg L^?1 may negatively affect brown trout populations.  相似文献   

Modeling patterns of coral bleaching at a remote Central Pacific atoll     

Gareth J. Williams  Ingrid S. Knapp  Simon K. Davy 《Marine pollution bulletin》2010,60(9):1467-1476

A mild bleaching event (9.2% prevalence) at Palmyra Atoll occurred in response to the 2009 ENSO, when mean water temperature reached 29.8-30.1 °C. Prevalence among both abundant and sparse taxa varied with no clear pattern in susceptibility relating to coral morphology. Seven taxon-specific models showed that turbidity exacerbated while prior exposure to higher background temperatures alleviated bleaching, with these predictors explaining an average 16.3% and 11.5% variation in prevalence patterns, respectively. Positive associations occurred between bleaching prevalence and both immediate temperature during the bleaching event (average 8.4% variation explained) and increased sand cover (average 3.7%). Despite these associations, mean unexplained variation in prevalence equalled 59%. Lower bleaching prevalence in areas experiencing higher background temperatures suggests acclimation to temperature stress among several coral genera, while WWII modifications may still be impacting the reefs via shoreline sediment re-distribution and increased turbidity, exacerbating coral bleaching susceptibility during periods of high temperature stress.  相似文献   

Statistical characteristics of flow as indicators of channeling in heterogeneous porous and fractured media     

R. Le Goc  J.-R. de Dreuzy  P. Davy 《Advances in water resources》2010

We introduce two new channeling indicators D_ic and D_cc based on the Lagrangian distribution of flow rates. On the basis of the participation ratio, these indicators characterize the extremes of both the flow-tube width distribution and the flow rate variation along flow lines. The participation ratio is an indicator biased toward the larger values of a distribution and is equal to the normalized ratio of the square of the first-order moment to the second-order moment. Compared with other existing indicators, they advantageously provide additional information on the flow channel geometry, are consistently applicable to both porous and fractured media, and are generally less variable for media generated using the same parameters than other indicators. Based on their computation for a broad range of porous and fracture permeability fields, we show that they consistently characterize two different geometric properties of channels. D_ic gives a characteristic scale of low-flow zones in porous media and a characteristic distance between effectively flowing structures in fractured cases. D_cc gives a characteristic scale of the extension of high-flow zones in porous media and a characteristic channel length in fractured media. D_ic is mostly determined by channel density and permeability variability. D_cc is, however, more affected by the nature of the correlation structure like the presence of permeability channels or fractures in porous media and the length distribution in fracture networks.  相似文献