Uniaxial compression and tension tests of anthracite and loading rate dependence of peak strength

The mechanical characteristics of coal under uniaxial compressive stress and uniaxial tensile stress are key factors in investigations of the stability of galleries and coal faces, and are vital considerations for the efficient design of coalmines, disaster prevention, and environmental preservation. These mechanical characteristics have long been a topic of research, but remain insufficiently understood. In this study we performed uniaxial compression tests and uniaxial tension tests on coal, with particular attention to two concerns. The first was to measure the loading rate dependence of the peak strength of coal. Coal shows high sample-to-sample scatter in strength; test methods that are successful in comparatively homogeneous rock types cannot be used for coal. We therefore used an alternative test method that was recently developed by the authors. Anthracite samples were subjected to alternating slow and fast strain rates. Measured variations in stress during this process were used to estimate the loading rate dependence of peak strength. The second objective was to obtain complete stress–strain curves for coal under uniaxial tensile stress. It is difficult to hold samples secure during a tensile test; consequently, such curves have yet to be obtained. This study presents a successful application of the authors' method to the analysis of coal samples, yielding a complete stress–strain curve under tensile stress. The two methods presented here hold promise for application not only to anthracite but also to a wide variety of coals. It is possible to derive the values of the constants used in constitutive equations from the obtained experimental results. Once these equations are determined, they can be incorporated into finite-element software to investigate various time-dependent behaviors of coal and aid in the efficient design of coalmines and the prevention of subsidence and mine disasters.     

On the Importance of Geolithological Features for the Estimate of the Site Response: The Case of Catania Metropolitan Area (Italy)

The evaluation of seismic site response in the urban area of Catania was tackled by selecting test areas having peculiar lithological and structural features, potentially favourable to large local amplifications of ground motion. The two selected areas are located in the historical downtown and in the northern part of Catania where the presence of a fault is evident. Site response was evaluated using spectral ratio technique taking the horizontal- to-vertical component ratio of ambient noise. Inferences from microtremor measurements are compared with results from synthetic accelerograms and response spectra computed at all drillings available for this area. Such method is particularly suitable in urban areas where the nature of the outcropping geological units is masked by city growth and anthropic intervention on the surface geology. The microtremor H/V spectral ratios evaluated at soft sites located within the downtown profile tend to be smaller than that usually reported in the literature for such soils. A tendency for amplifications to peaks near 2 Hz is observed only in some sites located on recent alluvial deposits. Evidences for amplifications of site effects (frequency range 4–8 Hz) were observed in the sampling sites located on the fault, with a rapid decrease of spectral amplitude just a few tenths of metres away from the discontinuity. Numerical simulations evidenced the importance of geolithological features at depth levels even greater than 20–30 m. Besides this, the results strongly confirm the importance of the subsurface geological conditions, in the estimate of seismic hazard at urban scale.     

Assessing the Vibrational Frequencies of the Cathedral of Cologne (Germany) by Means of Ambient Seismic Noise Analysis

Ambient seismic noise measurements were conducted inside the Cathedral of Cologne (Germany) for assessing its frequencies of vibration and for checking whether these occur in the range where soil amplification is expected. If this is the case, damages may increase in case of an earthquake due to an increased structural response of the building. Analysis of the ratio between the horizontal and vertical components of the spectra recorded at stations located inside the building as well as the ratio between the corresponding components of the spectra recorded simultaneously inside the building and at a reference station placed in the basement of the cathedral indicated several modes of vibration. Facilitated by these results an assessment of the seismic vulnerability was attempted for a 2D ground motion scenario using the finite element method.     

Site Effects Study in the Serravalle Village (NE Italy) by Means of Spectral Ratios Analyses Relatively to Multiple Reference Sites

The area of Serravalle, sited in the northern part of the town of Vittorio Veneto (TV), NE Italy, has been the target of a seismic microzonation campaign. 10 seismic stations have been deployed for a 7 months period to record in continuous mode. Three stations were installed on bedrock outcrops and seven on sedimentary sites with variable cover thickness. Spectral analyses have been performed on the collected data-set using the Generalized Inversion Technique (GIT, e.g. Andrews, 1986). In particular, spectral ratios have been calculated for each station relatively to the average of the three reference, bedrock sites. The spectral ratios provide quantitative estimates of the seismic motion amplifications which occur in each of the monitored sites. Two sites show high values of amplification, 5 times larger than signal amplitude at the reference sites, in correspondence of well discernible peak frequencies of 5 Hz. Results for the other stations show smaller amounts of site amplification spreading over a broad range of frequencies. Sites where the highest amplifications were recorded all lie on the left bank of the Meschio River and in areas farther away from its outlet into the plain correlating with the presence of thick layers of Quaternary deposits.     

Spherical Slepian functions and the polar gap in geodesy

The estimation of potential fields such as the gravitational or magnetic potential at the surface of a spherical planet from noisy observations taken at an altitude over an incomplete portion of the globe is a classic example of an ill-posed inverse problem. We show that this potential-field estimation problem has deep-seated connections to Slepian's spatiospectral localization problem which seeks bandlimited spherical functions whose energy is optimally concentrated in some closed portion of the unit sphere. This allows us to formulate an alternative solution to the traditional damped least-squares spherical harmonic approach in geodesy, whereby the source field is now expanded in a truncated Slepian function basis set. We discuss the relative performance of both methods with regard to standard statistical measures such as bias, variance and mean squared error, and pay special attention to the algorithmic efficiency of computing the Slepian functions on the region complementary to the axisymmetric polar gap characteristic of satellite surveys. The ease, speed, and accuracy of our method make the use of spherical Slepian functions in earth and planetary geodesy practical.     

Spectral Simulation and Conditioning to Local Continuity Trends in Geologic Modeling

Spectral simulation has gained application in building geologic models due to the advantage of better honoring the spatial continuity of petrophysical properties, such as reservoir porosity and shale volume. Distinct from sequential simulation methods, spectral simulation is a global algorithm in the sense that a global density spectrum is calculated once and the inverse Fourier transform is performed on the Fourier coefficient also only once to generate a simulation realization. The generated realizations honor the spatial continuity structure globally over the whole field instead of only within a search neighborhood, as with sequential simulation algorithms. However, the disadvantage of global spectral simulation is that it traditionally cannot account for the local information such as the local continuity trends, which are often observed in reservoirs and hence are important to be accounted for in geologic models. This disadvantage has limited wider application of spectral simulation in building geologic models. In this paper, we present ways of conditioning geologic models to the relevant local information. To account for the local continuity trends, we first scale different frequency components of the original model with local-amplitude spectrum ratios that are specific to the local trend. The sum of these scaled frequency components renders a new model that displays the desired local continuity trend. The implementation details of this new method are discussed and examples are provided to illustrate the algorithm.     

二维地震观测系统合理性的论证方法

已知勘查区深度范围前提下,最大炮检X和道间距ΔX,不可以太大也不可以太小,施工前能够计算出它的允许值范围。     

基于高光谱卫星遥感数据的UPDM分析方法

提出了一种用于处理多高光谱卫星数据的UPDM分析方法。研究结果证明．该方法应用干Landsat／TM(ETM^-)、Terra／MODIS和ADEOS—II／GLI等高光谱卫星传感器时．光谱重构均方根误差小于0．029适用于研究高光谱卫星遥感数据。     

高光谱遥感数据三次光滑样条滤噪

分析了高光谱遥感数据噪声滤波的作用和现状，实现了一种基于三次光滑样条函数的高光谱遥感数据噪声滤波算法，解决了目前高光谱遥感数据噪声滤波算法自适应效果不理想的问题。通过对AVIRIS数据试验，证明此方法简单易行，计算精度高，具有良好的局部自适应拟合能力，并能有效地滤除数据中的噪声，改善数据质量。