Characterization of a fluvial aquifer at a range of depths and scales: the Triassic St Bees Sandstone Formation, Cumbria, UK

Fluvial sedimentary successions represent porous media that host groundwater and geothermal resources. Additionally, they overlie crystalline rocks hosting nuclear waste repositories in rift settings. The permeability characteristics of an arenaceous fluvial succession, the Triassic St Bees Sandstone Formation in England (UK), are described, from core-plug to well-test scale up to ~1 km depth. Within such lithified successions, dissolution associated with the circulation of meteoric water results in increased permeability (K~10−1–100 m/day) to depths of at least 150 m below ground level (BGL) in aquifer systems that are subject to rapid groundwater circulation. Thus, contaminant transport is likely to occur at relatively high rates. In a deeper investigation (> 150 m depth), where the aquifer has not been subjected to rapid groundwater circulation, well-test-scale hydraulic conductivity is lower, decreasing from K~10−2 m/day at 150–400 m BGL to 10−3 m/day down-dip at ~1 km BGL, where the pore fluid is hypersaline. Here, pore-scale permeability becomes progressively dominant with increasing lithostatic load. Notably, this work investigates a sandstone aquifer of fluvial origin at investigation depths consistent with highly enthalpy geothermal reservoirs (~0.7–1.1 km). At such depths, intergranular flow dominates in unfaulted areas with only minor contribution by bedding plane fractures. However, extensional faults represent preferential flow pathways, due to presence of high connective open fractures. Therefore, such faults may (1) drive nuclear waste contaminants towards the highly permeable shallow (< 150 m BGL) zone of the aquifer, and (2) influence fluid recovery in geothermal fields

Generating Bessel beams with broad depth-of-field by using phase-only acoustic holograms

[EN] We report zero-th and high-order acoustic Bessel beams with broad depth-of-field generated using acoustic holograms. While the transverse field distribution of Bessel beams generated using traditional passive methods is correctly described by a Bessel function, these methods present a common drawback: the axial distribution of the field is not constant, as required for ideal Bessel beams. In this work, we experimentally, numerically and theoretically report acoustic truncated Bessel beams of flat-intensity along their axis in the ultrasound regime using phase-only holograms. In particular, the beams present a uniform field distribution showing an elongated focal length of about 40 wavelengths, while the transverse width of the beam remains smaller than 0.7 wavelengths. The proposed acoustic holograms were compared with 3D-printed fraxicons, a blazed version of axicons. The performance of both phase-only holograms and fraxicons is studied and we found that both lenses produce Bessel beams in a wide range of frequencies. In addition, high-order Bessel beam were generated. We report first order Bessel beams that show a clear phase dislocation along their axis and a vortex with single topological charge. The proposed method may have potential applications in ultrasonic imaging, biomedical ultrasound and particle manipulation applications using passive lenses.This work was supported by the Spanish Ministry of Economy and Innovation (MINECO) through Project TEC2016-80976-R. NJ and SJ acknowledge financial support from Generalitat Valenciana through grants APOSTD/2017/042, ACIF/2017/045 and GV/2018/11. FC acknowledges financial support from Agencia Valenciana de la Innovacio through grant INNCON00/18/9 and European Regional Development Fund (IDIFEDER/2018/022).Jiménez-Gambín, S.; Jimenez, N.; Benlloch Baviera, JM.; Camarena Femenia, F. (2019). 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Gradient based edge operator in multispectral images

In this paper, a novel scheme for multispectral edge operator is presented. The dichromatic model proposed by Shafer [1] is used to describe the object reflection properties in HSV spectral space. Under the properties and white illustration assumption, the specular reflection from the color image that mainly cause false edge result can be removed. The scheme is designed to detect the color boundary and the shading edge on a uniform color object as well as downward compatible to grey intensity image

Enhanced hit rate simulated annealing in codebook training

Codebook generation and optimization in the Vector Quantization system is a high dimensional and nonlinear optimization process. Lloyd's algorithm aims at the finding of the least mean square between the training vectors and their centroids. The major problem of this method is ''local optimal state''. Therefore Simulated Annealing (SA) is applied in the optimization of the codebook in VQ system. In the existing SA scheme, the successful rate of each generation, especially in the end of the process, would be very low. In this paper, novel schemes (Local Region Searching and Least Frequently Hit) are suggested to enhanced the performance and arise the hit rate of the generation of the existing SA algorithms. From the experimental result, the hit rate is arise by over 100 times of existing method. Improvement is found in both the fidelity testing and perception testing on the decoded image

A novel Predictive Vector Quantization system in color image coding

Predictive Vector Quantization (PVQ) is the combination scheme of Predictive Coding (PC) and Vector Quantization (VQ). The performance of the PVQ system would be projected from complexity of the predictor and fidelity of the decoded image. In this paper, three novel predictors are suggested to enhance the performance of existing PVQ system. Different schemes would be compared among their coding fidelity of the decoded image. The improvement in both the quantitative and qualitative qualities is significance in the color image coding