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Number of results: 8
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Abstract

The sodium expansion and creep strain of semi-graphitic cathodes are investigated using a modified Rapoport apparatus. To further understanding of the sodium and bath penetration damage processes, the impact of external stress fluence on the carbon cathode microstructure has been defined with XRD analysis, Raman spectroscopy and scanning electron microscope (SEM). Graphite atoms fracture into smaller fragments that are less directional than the pristine platelets, which allows for a possible filling of the cracks that thus develop by the sodium and bath during aluminum electrolysis. The average microcrystalline size (calculated by Raman spectroscopy) is reduced by the deformation. The decreased intensity and widened ‘G’ and ‘D’ peaks in the analysis indicate the poor order of the sheets along the stacking direction while the consistent layered graphite structure is sustained.
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Abstract

In multi-axis motion control systems, the tracking errors of single axis load and the contour errors caused by the mismatch of dynamic characteristics between the moving axes will affect the accuracy of the motion control system. To solve this issue, a biaxial motion control strategy based on double-iterative learning and cross-coupling control is proposed. The proposed control method improves the accuracy of the motion control system by improving individual axis tracking performance and contour tracking performance. On this basis, a rapid control prototype (RCP) is designed, and the experiment is verified by the hardware and software platforms, LabVIEW and Compact RIO. The whole design shows enhancement in the precision of the motion control of the multiaxis system. The performance in individual axis tracking and contour tracking is greatly improved.
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Abstract

With the rise of coal mine underground reservoir engineering in the Shendong Mining Area, the space time dynamic evolution prediction of storage coefficient is becoming one of the critical technical problems for long-term reservoir operation. This coefficient directly determines the storage capacity and the comprehensive benefits of the operation of a coal mine underground reservoir. To this end, the proposed underground reservoir in Daliuta coal mine (No. 22616 working face) is selected in this study for the development and application of an experimental device to measure the storage coefficient. Rock and coal fragments from similar materials are prepared, which are filled and loaded according to the caving rock nature as well as the lumpiness and accumulation mode characteristics pertaining to No. 22616 working face. Subsequently, the measured storage coefficient under circulating water injection conditions revealed a four-dimensional spatial and temporal pattern. It followed the law of storage coefficient under joint interaction of water-rock and stress. The results showed that, prior to the experiment, rock and coal fragments made from similar materials had good water resistance when the paraffin content was set at 8%. The three stress zones were defined based on a theoretical analysis, which were applied on the corresponding loads. During the experiments, significant regional differences were found in the top surface with persisting subsidence of each stress loading zone. Hence, compared with its initial state, the maximum subsidence in the stress stability zone, the stress recovery zone, and the low-stress zone was 7.89, 5.8, and 1.83 mm, respectively. While the storage capacity and the storage coefficient gradually decreased, the former ranged from 0.2429 to 0.2397 m3, and the latter ranged from 0.270 to 0.266. The experimental results are verified by drainage engineering tests in the Shendong Mining Area. In essence, the storage coefficient had remarkable spatial distribution characteristics and a time-varying effect. In space, the storage coefficient increased with height along the vertical direction of the coal mine underground reservoir. However, it decreased with the distance from the boundary of the dam body in the horizontal direction. With time, the storage coefficient decreased dynamically. This study provides a new way of predicting the storage coefficient of a coal mine underground reservoir.
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Abstract

Correct incipient identification of an analog circuit fault is conducive to the health of the analog circuit, yet very difficult. In this paper, a novel approach to analog circuit incipient fault identification is presented. Time responses are acquired by sampling outputs of the circuits under test, and then the responses are decomposed by the wavelet transform in order to generate energy features. Afterwards, lower-dimensional features are produced through the kernel entropy component analysis as samples for training and testing a one-against-one least squares support vector machine. Simulations of the incipient fault diagnosis for a Sallen-Key band-pass filter and a two-stage four-op-amp bi-quad low-pass filter demonstrate the diagnosing procedure of the proposed approach, and also reveal that the proposed approach has higher diagnosis accuracy than the referenced methods.
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Abstract

In this paper, the different mechanical behaviors of layered rocks with different bedding angles during uniaxial compression tests are studied. Numerical simulation models of layered rock are validated based on laboratory tests, and uniaxial compression tests are conducted by using Particle Flow Code (PFC). Using these simulations, the uniaxial compressive strength, failure patterns, development of micro-cracks, and displacement of meso particles are analyzed. When the bedding angle is similar to the failure angle, the macro failure planes develop directly along the beddings, the bedding behavior dictates the behavior of the layered rock, reducing the compressive strength.
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Abstract

Lower Carboniferous limestone has been extracted in the “Czatkowice” open-pit hill-slope quarry in southern Poland since 1947, for the needs of metallurgical and building industries, as well as farming. We can distinguish two aquifers in the Czatkowice area: the Quaternary porous aquifer and the Carboniferous fissure-porous one. Two vertical zones representing different hydrodynamic characteristics can be indentified in the Carboniferous formations. One is a weathering zone and the other one the zone of fissures and interbedding planes. Groundwater inflows into the quarry workings have been observed at the lowest mining level (+315 m above the sea level (asl)) for over 30 years. This study concerns two hypotheses of the sources of such inflows originating either from (a) the aeration zone or from (b) the saturation zone. Inflows into the quarry combine into one stream flowing gravitationally to the doline under the pile in the western part of the quarry. This situation does not cause a dewatering need. Extending eastward mining and lowering of the exploitation level lead to increased inflows.
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Abstract

The objective of this paper is to evaluate the self- healing properties of a commercially-available geosynthetic clay liner (GCL) using flexible-wall permeameter. The GCLs are produced by the same factory, but the contents of bentonite are different. Also the hydraulic conductivities (HC) of GCLs with no defect are different. In this study, specimens were completely saturated under the backpressure of 20 kPa before the test. Permeability tests were performed on GCL specimens with penetrating flaw and also on specimens permeated with distilled water and CaCl2 solutions. The test results were presented and discussed. Experimental results showed that the GCL with penetrating flaw did not exhibit complete self-healing in the case of flaw. After 120 days, the hydraulic conductivity increased by approximately an order of magnitude. In addition, CaCl2 solutions had a significant influence on the hydraulic conductivity. The research findings might be of interest to researchers and engineers who design liners for landfills and other liquid containment facilities
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