This paper presents a laboratory investigation of electric resistivity parameter for samples subject to loading in automatic press of INOVA type. The procedure of automatic quasi-continuous measurements of resistivity is briefly outlined. The distribution of mini-electrodes within the sample is described. Also shown is the manner in which reliability can be improved by increasing the repetition of resistivity measurements (every 7–16 s). 相似文献
Heavy metals are constantly emitted into the environment and pose a major threat to human health, particularly in urban areas. The threat is linked to the presence of Cd, Cr, Cu, Ni, Pb, and Zn in street dust, which consists of mineral and organic particles originating from the soil, industrial emitters, motor vehicles, and fuel consumption. The study objective was to determine the level of street dust contamination with trace metals in Lublin and to indicate their potential sources of origin. The analyses were carried out with an energy-dispersive X-ray fluorescence spectrometer. The sampling sites (49) were located within the city streets characterised by varying intensity of motor traffic. The following mean content values and their variation (SD) were determined: Cd: 5.1?±?1.7 mg kg?1, Cr: 86.4?±?23.3 mg kg?1, Cu: 81.6?±?69.2 mg kg?1, Ni: 16.5?±?3.9 mg kg?1, Pb: 44.1?±?16.4 mg kg?1, and Zn: 241.1?±?94.6 mg kg?1. The level of pollution was assessed with several widely used geochemical indices (geoaccumulation index, enrichment factor, pollution index, index of ecological risk, and potential ecological risk index). For most of the indices, the mean (median) values are arranged in the following manner: Zn?>?Cu(or Cd)?>?Pb?>?Ni?>?Cr. In general, street dust in Lublin does not show pollution with Cr, Ni, and Pb. Igeo and EF indices show moderate levels for Cu, Cd, and Zn; their presence in street dust is linked with anthropogenic factors (motor traffic). A significant threat is posed by Cd, and more than half of the samples show considerable pollution with cadmium (median for the index of ecological risk: 151). The spatial pattern of indices and the results of statistical analyses (CA, PCA) indicate three groups of elements: (1) Cr and Ni: natural origin; (2) Pb: mixed origin; and (3) Cd, Cu, and Zn: anthropogenic origin (mainly motor vehicle traffic). Higher content values for metals of anthropogenic origin in street dust indicate that it is a source of pollution of soil and air in the city. 相似文献
Gilbert‐type deltas are sensitive recorders of short‐term base‐level changes, but the delta‐front record of a base‐level rise tends to be erased by fluvial erosion during a subsequent base‐level fall, which renders the bulk record of base‐level changes difficult to decipher from the delta‐front deposits. The present detailed study of three large Pleistocene Gilbert‐type deltas uplifted on the southern coast of the Gulf of Corinth, Greece, indicates a genetic link between the delta‐front morphodynamic responses to base‐level changes and the delta‐slope sedimentation processes. Sigmoidal delta‐brink architecture signifies a base‐level rise and is accompanied by a debrite‐dominated assemblage of delta foreset deposits, thought to form when the aggrading delta front stores sediment and undergoes discrete gravitational collapses. Oblique delta‐brink architecture tends to be accompanied by a turbidite‐dominated assemblage of foreset deposits, which are thought to form when the delta‐front accommodation decreases and the sediment carried by hyperpycnal effluent bypasses the front. This primary signal of the system response to base‐level changes combines further with the secondary ‘noise’ of delta autogenic variation and possible allogenic fluctuations in fluvial discharge due to regional climatic conditions. Nevertheless, the evidence suggests that the facies trends of delta foreset deposits may be used to decipher the delta ‘hidden’ record of base‐level changes obliterated by fluvial topset erosion. Early‐stage bayhead deltas may be an exception from the hypothetical model, because their narrow front tends to be swept by river floods irrespective of base‐level behaviour and their subaqueous slope deposits are thus mainly turbidites. 相似文献
The stress–dilatancy relation is of critical importance for constitutive modelling of geomaterial. A novel fractional-order stress–dilatancy equation had been developed for granular soil, where a nonlinear stress–dilatancy response was always predicted. However, it was experimentally observed that after a certain extent of shearing, an almost linear response between the stress ratio and the dilatancy ratio, rather than the nonlinear response, usually existed. To capture such stress–dilatancy behaviour, a new fractional stress–dilatancy model is developed in this study, where an apparent linear response of the stress–dilatancy behaviour of soil after sufficient shearing is obtained via analytical solution. As the fractional order varies, the derived stress–dilatancy curve and the associated phase transformation state stress ratio keep changing. But, unlike existing researches, no other specific parameters, except the parameter related to fractional order, concerning such shift are required. Then, the developed stress–dilatancy model is applied to constitutive modelling of granular soil and soil–structure interface, for further validation. A series of test results of different granular soils and soil–structure interfaces under different loading conditions are simulated and compared, where a good model performance is observed.
The paper discusses the performance and robustness of the Bayesian (probabilistic) approach to seismic tomography enhanced by the numerical Monte Carlo sampling technique. The approach is compared with two other popular techniques, namely the damped least-squares (LSQR) method and the general optimization approach. The theoretical considerations are illustrated by an analysis of seismic data from the Rudna (Poland) copper mine. Contrary to the LSQR and optimization techniques the Bayesian approach allows for construction of not only the “best-fitting” model of the sought velocity distribution but also other estimators, for example the average model which is often expected to be a more robust estimator than the maximum likelihood solution. We demonstrate that using the Markov Chain Monte Carlo sampling technique within the Bayesian approach opens up the possibility of analyzing tomography imaging uncertainties with minimal additional computational effort compared to the robust optimization approach. On the basis of the considered example it is concluded that the Monte Carlo based Bayesian approach offers new possibilities of robust and reliable tomography imaging. 相似文献
A mathematical model that produces curves for predicting the expansion of granular activated carbon (GAC) filter beds has been developed and applied to several widely used commercial GAC products. Initially, the hydraulic load required to produce a given bed expansion was assumed to be inversely proportional to the viscosity. This assumption was then modified by assuming a power law for the dependence on viscosity. The errors were sufficiently small to allow practical application of the formulae presented in this paper. The potential for application of the method was tested and is illustrated by an example. 相似文献
Acta Geotechnica - The stress–strain response of sand was observed to depend on its material state, i.e., pressure and density. Successful modelling of such state-dependent response of sand... 相似文献