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The use of high-voltage electrical pulse (HVEP) technology for improving the rate of penetration in deep, complex formations has been reported; however, its rock fragmentation mechanism is not fully understood, and the parametric design of electric drilling tools is not perfect. This research paper realized the whole process of single-pulse HVEP rock-breaking by using the electric breakdown model, combining circuit parameter coupling, Kirchhoff’s law, electric breakdown criterion, heat transfer process, and solid mechanical field. The sensitivity simulation of HVEP rock-breaking parameters, which considers the structural parameters of pulse power supply, the deterioration of rock during the electrical breakdown process, the correlation between dynamic dielectric strength of rock and time, and rock heterogeneity, is analyzed. The simulation results indicate that the shape of the plasma channel has little relationship with the pulse peak voltage, and the rock-breaking volume of a single pulse is positively related to the pulse peak voltage; the electrode spacing is positively correlated with the breakdown voltage of the rock in a first-order function shape and has a positive correlation with the failure volume; large electrode spacing can promote HVEP rock-breaking; electrode tilt has little effect on the minimum breakdown voltage and failure volume, and its optimal design should be combined with the flow field analysis of the electric bit structure; the heterogeneity index of granite results in breakdown voltage amplitudes within 3 kV and differences in the fragmentation effect of HVEP. The research results can be used as theoretical support for optimizing HVEP matching drilling tools.

High-voltage electric pulse (HVEP) is an innovative low-energy and high-efficiency technique. However, the underlying physics of the electrical breakdown within the rock, and the coupling mechanism between the various physical fields involved in HVEP still need to be further understood. In this study, we establish a 2D numerical model of multi-physical field coupling of the electrical breakdown of porous rock with randomly distributed pores to investigate the effect of pore characteristics (porosity, pore media composition) on the partial electrical breakdown of rock (i.e. the generation of a plasma channel inside the rock). Our findings indicate that the generation of a plasma channel is directionally selective and extends in the direction of a weak electrical breakdown intensity. As the porosity of the rock increases, so does the intensity of the electric field in the ‘electrical damage’ region—the greater the porosity, the greater the effectiveness of rock-breaking. As the fraction of pore fluid (S water/S air) gradually declines, the generation time of the plasma channel decreases, and the efficacy of rock-breaking by HVEP increases. In addition, in this study, we conducted an indoor experiment utilizing an electric pulse drill to break down the rock in order to recreate the growth mode of the plasma channel in the rock. Moreover, the experimental results are consistent with the simulation results. In addition, the development of this type of partial electrical breakdown is confirmed to be related to electrode polarity and pore characteristics via the experiment of the symmetrical needle-needle electrode arrangement, which further demonstrates the mechanism of partial electrical breakdown. This research is significant for comprehending the process of electric impulse rock-breaking and gives theoretical guidance and technological support for advancing electric impulse drilling technology.

Positron emission tomography (PET) imaging plays an indispensable role in early disease detection and postoperative patient staging diagnosis. However, PET imaging requires not only additional computed tomography (CT) imaging to provide detailed anatomical information but also attenuation correction (AC) maps calculated from CT images for precise PET quantification, which inevitably demands that patients undergo additional doses of ionizing radiation. To reduce the radiation dose and simultaneously obtain high-quality PET/CT images, in this work, we present an alternative based on deep learning that can estimate synthetic attenuation corrected PET (sAC PET) and synthetic CT (sCT) images from non-attenuation corrected PET (NAC PET) scans for whole-body PET/CT imaging. Our model consists of two stages: the first stage removes noise and artefacts in the NAC PET images to generate sAC PET images, and the second stage synthesizes CT images from the sAC PET images obtained in the first stage. Both stages employ the same deep Wasserstein generative adversarial network and identical loss functions, which encourage the proposed model to generate more realistic and satisfying output images. To evaluate the performance of the proposed algorithm, we conducted a comprehensive study on a total of 45 sets of paired PET/CT images of clinical patients. The final experimental results demonstrated that both the generated sAC PET and sCT images showed great similarity to true AC PET and true CT images based on both qualitative and quantitative analyses. These results also indicate that in the future, our proposed algorithm has tremendous potential for reducing the need for additional anatomic imaging in hybrid PET/CT systems or the need for lengthy MR sequence acquisition in hybrid PET/MRI systems.

Oil and gas development at home and abroad face the problem of low natural productivity of low permeability reservoirs. As it can effectively improve the recovery rate and reserve utilization rate of low permeability reservoirs, the multi-stage segmented fracturing technology today is one of the important means for the development of unconventional reservoirs. The fracturing sleeve is the core tool of multi-stage segmented technology. Major foreign companies have launched target-specific research and achieved many advanced results. In spite of a latecomer in this field, some domestic experts and scholars have proposed some characteristic techniques and tools. The author of this paper is poised to analyze the key technical principle of domestic and foreign fracturing sleeve and discuss the advantages and applicability of various relevant tools and processes with the purpose of laying a foundation for the development of fracturing sleeves in China.

The cosine-model analysis (CMA) method and the small angle x-ray scattering (SAXS) method are two major types of information retrieval algorithms, commonly utilized in x-ray phase-contrast imaging with a grating interferometer. However, there are significant differences between the two methods in algorithm implementation, and the existing literature has not completely revealed their intrinsic relationship. In this paper, we theoretically derive and experimentally verify the intrinsic connections between CMA and SAXS, and it is seen that SAXS can be interpreted well by the cosine-model assumption of CMA. To validate our analysis of the scattering distribution when applying the cosine model to the convolution used in SAXS, we applied a deconvolution process into CMA before using the Fourier transform to get the three contrasts. Furthermore, the principal component analysis (PCA) is introduced in this work, and two PCA-based retrieval algorithms are presented in order to simplify the iteration process of deconvolution in SAXS or to obtain absorption and dark-field signals instead of the Fourier transform in CMA. Applying a quantitative structural similarity (SSIM) index and a profile analysis to the results of an ex vivo mammography, it is proved that retrieved images via CMA and SAXS are consistent with each other (SSIM values are 1.0000, 0.9845 and 0.9767 respectively), and that the extra deconvolution process applied into CMA shows a good performance and our analytical analysis of the scattering distribution is valid when applying the cosine model to the convolution used in SAXS. Besides, it is concluded that PCA shows almost the same performance with the Fourier transform (SSIM values are 1.0000 for both absorption and dark-field images), and the simplified SAXS-analogous method works well with higher efficiency in computation and better stability relative to the original SAXS, while maintaining the similar level of image quality (SSIM values are 1.0000, 0.9839 and 0.9781 respectively).