Quantifying engineering parameters of expansive soils from their reflectance spectra   总被引：2，自引：0，他引：2  

Fekerte Arega Yitagesu  Freek van der Meer  Harald van der Werff  Wolter Zigterman 《Engineering Geology》2009,105(3-4):151-160

Occurrence of expansive soils in construction sites has serious implications on planning, design, construction, maintenance, and overall performance especially of lightweight engineering infrastructures. Such soils are particularly susceptible to large volume changes in response to moisture content fluctuations following seasonal climatic variations. This can lead to deformation of structures built up on them. For this study, soil samples were collected from the eastern part of Addis Ababa. Specific expansive soil engineering parameters namely; Atterberg limits (LL, PL and PI), free swell and cation exchange capacity were measured in a soil mechanics laboratory. Reflectance spectra of each soil sample were acquired in a remote sensing laboratory using ASD fieldspec full range spectrometer. A multivariate calibration method, partial least squares regression (PLSR) analysis, through simple wavelength approach, was used to construct empirical prediction models for estimating engineering parameters of expansive soils from their respective reflectance spectra. Correlation coefficients of 0.90, 0.87, 0.71, 0.81 and 0.71 for CEC, LL, PL, PI and FS respectively were obtained. The correlation coefficients showed that large portion of variations in engineering parameters of expansive soils could be accounted for by spectral parameters. Apart from these high correlation coefficients, small root mean square errors of calibration (RMSEC) and prediction (RMSEP), standard error of calibration (SEC) and prediction (SEP) and minimum bias were obtained. The results indicate potential of spectroscopy in deriving engineering parameters of expansive soils from their respective reflectance spectra and hence, its potential applicability in supporting geotechnical investigations of such soils.  相似文献   

Characterisation of rock aggregate breakage properties using realistic texture‐based modelling     

Hongyuan Liu  Per‐Arne Lindqvist  Urban Åkesson  Shaoquan Kou  Jan‐Eric Lindqvist 《国际地质力学数值与分析法杂志》2012,36(10):1280-1302

Realistic texture‐based modelling methods, that is microstructural modelling and micromechanical modelling, are developed to simulate the rock aggregate breakage properties on the basis of the rock actual microstructure obtained using microscopic observations and image analysis. The breakage properties of three types of rocks, that is Avja, LEP and Vandle taken from three quarries in Sweden, in single aggregate breakage tests and in inter‐aggregate breakage tests are then modelled using the proposed methods. The microstructural modelling directly integrates the microscopic observation, image analysis and numerical simulation together and provides a valuable tool to investigate the mechanical properties of rock aggregates on the basis of their microstructure properties. The micromechanical modelling takes the most important microstructure properties of rock aggregates into consideration and can model the major mechanical properties. Throughout this study, it is concluded that in general, the microstructure properties of rock aggregate work together to affect their mechanical properties, and it is difficult to correlate a single microstructure property with the mechanical properties of rock aggregates. In particular, for the three types of rock Avja, LEP and Vandle in this study, crack size distribution, grain size and grain perimeter (i.e. grain shape and spatial arrangement) show good correlations with the mechanical properties. The crack length and the grain size negatively affect the mechanical properties of Avja, LEP and Vandle, but the perimeter positively influences the mechanical properties. Besides, the modelled rock aggregate breakage properties in both single aggregate and inter‐aggregate tests reveal that the aggregate microstructure, aggregate shape and loading conditions influence the breakage process of rock aggregate in service. For the rock aggregate with the same microstructure, the quadratic shape and good packing dramatically improve its mechanical properties. During services, the aggregate is easiest to be fragmented under point‐to‐point loading condition, and then in the sequence of multiple‐point, point‐to‐plane and plane‐to‐plane loading conditions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Diurnal dynamics of streamflow in an upland forested micro‐watershed during short precipitation‐free periods is altered by tree sap flow          下载免费PDF全文

Jan Deutscher  Petr Kupec  Peter Dundek  Ladislav Holík  Martin Machala  Josef Urban 《水文研究》2016,30(13):2042-2049

Diurnal variations in streamflow are becoming acknowledged as a way of analysing how changing climatic conditions and land use affects watersheds but also as a way to understand watersheds as a whole. Yet not many studies from uplands below 900 mm mean annual precipitation zone are available from European countries. During the 2012 growing season, a sampling campaign took place in an upland forested micro‐watershed, Czech Republic (65 ha). Tree sap flow, rainfall and temperature were measured continuously, while streamflow at the discharge point and soil moisture were estimated from short‐term measurements. Short precipitation‐free periods lasting several days were identified for evaluation of trends in diurnal dynamics of both sap flow and streamflow. The results demonstrated that during these periods, the main factor altering streamflow was almost exclusively tree sap flow. A decrease in streamflow was observed during the day and an increase at night. The decline in sap flow after sunset was accompanied by a continuous increase in streamflow throughout the night up to its initial maximum in the morning. The amplitude in diurnal variations reached 18%. The observed time lag between the diurnal variations of sap flow and streamflow was approximately 2 h. Relatively low changes in diurnal dynamics of streamflow pointed out a strong regulatory role of the forest in buffering water discharge from the catchment. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Bias,variance and computational properties of Kijko’s estimators of the upper limit of magnitude distribution,M<Subscript>max</Subscript>     

Stanisław Lasocki  Paweł Urban 《Acta Geophysica》2011,59(4):659-673

It is often assumed in probabilistic seismic hazard analysis that the magnitude distribution has an upper limit M _max, which indicates a limitation on event size in specific seismogeneic conditions. Accurate estimation of M _max from an earthquake catalog is a matter of utmost importance. We compare bias, dispersion and computational properties of four popular M _max estimators, introduced by Kijko and others (e.g., Kijko and Sellevoll 1989, Kijko and Graham 1998, Kijko 2004) and we recommend the ones which can be the most fruitful in practical applications. We provide nomograms for evaluation of bias and standard deviation of the recommended estimators for combinations of sample sizes and distribution parameters. We suggest to use the bias nomograms to correct the M _max estimates. The nomograms of standard deviation can be used to determine minimum sample size for a required accuracy of M _max.  相似文献   

TIGRE: A new robotic spectroscopy telescope at Guanajuato,Mexico     

J. H. M. M. Schmitt  K.‐P. Schrder  G. Rauw  A. Hempelmann  M. Mittag  J. N. Gonzlez‐Prez  S. Czesla  U. Wolter  D. Jack  P. Eenens  M. A. Trinidad 《Astronomische Nachrichten》2014,335(8):787-796

TIGRE is a new robotic spectroscopy telescope located in central Mexico at the La Luz Observatory of the University of Guanajuato. The 1.2 m telescope is fiber‐coupled to an ´echelle spectrograph with a spectral resolving power exceeding 20000 over most of the covered spectral range between 3800 Å and 8800 Å, with a small gap of 130 Å around 5800 Å. TIGRE operates robotically, i.e. it (normally) carries out all observations without any human intervention, including, in particular, the target selection in any given observing night. In this paper we describe the properties of the TIGRE instrumentation and its technical realization, as well as our first operational experience with the performance and efficiency of the overall system. Finally, we present some examples of recent TIGRE observations. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

BeppoSAX observations of 1-Jy BL Lacertae objects – I     

Paolo Padovani †‡  Luigi Costamante  Paolo Giommi  Gabriele Ghisellini  rea Comastri  Anna Wolter  Laura Maraschi  Gianpiero Tagliaferri  C. Megan Urry 《Monthly notices of the Royal Astronomical Society》2001,328(3):931-943

We present new BeppoSAX observations of seven BL Lacertae objects selected from the 1-Jy sample plus one additional source. The collected data cover the energy range     (observer's frame), reaching ∼50 keV for one source (BL Lac). All sources characterized by a peak in their multifrequency spectra at infrared/optical energies (i.e., of the low-energy peaked BL Lac type, LBL) display a relatively flat     X-ray spectrum, which we interpret as inverse Compton emission. Four objects (two-thirds of the LBLs) show some evidence for a low-energy steepening, which is probably due to the synchrotron tail merging into the inverse Compton component around ∼     . If this were generally the case with LBLs, it would explain why the     ROSAT spectra of our sources are systematically steeper than the BeppoSAX ones     . The broad-band spectral energy distributions fully confirm this picture, and a synchrotron inverse Compton model allows us to derive the physical parameters (intrinsic power, magnetic field, etc.) of our sources. Combining our results with those obtained by BeppoSAX on BL Lacs covering a wide range of synchrotron peak frequency, ν _peak, we confirm and clarify the dependence of the X-ray spectral index on ν _peak originally found in ROSAT data.  相似文献   

On the compact nature of the most luminous ULX in the Cartwheel ring     

Anna Wolter  Ginevra Trinchieri  Monica Colpi 《Monthly notices of the Royal Astronomical Society》2006,373(4):1627-1632

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Simulating Oxygen Intrusion into Highly Heterogeneous Fractured Media Using High Performance Computing     

Paolo Trinchero  Jorge Molinero  Hedieh Ebrahimi  Ignasi Puigdomenech  Björn Gylling  Urban Svensson  Dirk Bosbach  Guido Deissmann 《Mathematical Geosciences》2018,50(5):549-567

Fractured crystalline rocks are under consideration by several countries as host formations for high-level nuclear waste repositories. The redox evolution in these host rock formations is an important issue for the stability and safety of these disposal sites. If, for example, during a glaciation/deglaciation event, oxygen-rich glacial meltwater penetrates to the depth of the planned repository, some of the engineered barriers would be adversely affected. Moreover, oxidizing conditions would increase the solubility and mobility of many radionuclides. Reactive transport simulations, which are typically used to assess the redox buffering capacity of these host rock formations, are computationally demanding, and thus, calculations for the evaluation of oxygen penetration are usually carried out over simplified geometries and the heterogeneity of the site, both physical (e.g., variability in the groundwater flow field and the kinematic porosity) and mineralogical (e.g., variability in the abundance of Fe(II)-bearing minerals), is usually represented in a simplified fashion. Here, it is shown how a recently developed numerical framework, combined with high performance computing technologies, allows the full geometrical, physical and mineralogical complexity of the site under study to be efficiently included in these types of reactive transport calculations. A synthetically generated realistic three-dimensional fractured medium is used to assess oxygen penetration patterns and their dependence on both the hydrogeological conditions and the availability of Fe(II)-bearing minerals. The results of the calculations point out the significant influence of both physical and mineralogical heterogeneity on the oxygen penetration patterns, thus highlighting the importance of a model parameterisation consistent with the site complexity.  相似文献   

Improvement of the Integrating Velocity-Azimuth Process Single-Doppler Radar Wind-Retrieval Method     

LIANG Xudong 《Acta Meteorologica Sinica》2010,24(6):721-731

Among the single-Doppler radar wind analysis methods,the velocity-azimuth display(VAD),velocityazimuth process(VAP),and uniform wind(UW) methods are widely used because of their simplicity.A general form of the VAD,VAP,and UW methods is the integrating VAP(IVAP) method,which is based on the azimuth uniform-wind assumption.In this study,the IVAP method is improved by applying the method along natural coordinates. The natural coordinates can be chosen to ensure that the tangential and radial winds are unif...  相似文献   

A new passive synthetic aperture technique for towed arrays     

Stergiopoulos  S. Urban  H. 《Oceanic Engineering, IEEE Journal of》1992,17(1):16-25

An algorithm that synthesizes apertures in the beam domain using FFT transformations and performs coherent processing of subaperture signals at successive time intervals is presented. Experimental tests of the algorithm show that for ocean environments with spatial coherence longer than the synthetic aperture length and for signals with temporal coherence longer than the required acquisition time, a synthetic array gain is achieved which roughly corresponds to the length of an equivalent fully populated array. In the experiments, transducer generated CW with phase stability and pseudorandom signals were used. Limitations on the spatial and temporal coherence were introduced only by the medium, the temporal coherence of the pseudorandom signal, and the shape and stability of the line array used  相似文献