Development of Downhole Motor Drilling Test Platform

AbstractThe Downhole motor is a kind of important rotary or percussive power drilling tool driven by high pressure mud. Drilling using downhole motor can reduce the energy consumption caused by the friction between long drill string and borehole, and reduce drill pipe wear. In this paper, some important drilling simulation experimental devices around the world have been studied, especially, two kind of drilling simulation experimental devices, the conventional bottom hole experimental device and high temperature and high pressure experimental devices have been analyzed respectively. At home and abroad, the typical drilling simulation devices include ZM-35, LST-10, LMT-I, M150, and Terra Tek, etc.. The characters, structures, principles and experimental methods of these typical simulation devices had been introduced in detail, which provides a reference for developing downhole motor testing and drilling process testing

Encoding inductive invariants as barrier certificates: synthesis via difference-of-convex programming

A barrier certificate often serves as an inductive invariant that isolates an unsafe region from the reachable set of states, and hence is widely used in proving safety of hybrid systems possibly over an infinite time horizon. We present a novel condition on barrier certificates, termed the invariant barrier-certificate condition, that witnesses unbounded-time safety of differential dynamical systems. The proposed condition is the weakest possible one to attain inductive invariance. We show that discharging the invariant barrier-certificate condition -- thereby synthesizing invariant barrier certificates -- can be encoded as solving an optimization problem subject to bilinear matrix inequalities (BMIs). We further propose a synthesis algorithm based on difference-of-convex programming, which approaches a local optimum of the BMI problem via solving a series of convex optimization problems. This algorithm is incorporated in a branch-and-bound framework that searches for the global optimum in a divide-and-conquer fashion. We present a weak completeness result of our method, namely, a barrier certificate is guaranteed to be found (under some mild assumptions) whenever there exists an inductive invariant (in the form of a given template) that suffices to certify safety of the system. Experimental results on benchmarks demonstrate the effectiveness and efficiency of our approach.Comment: To be published in Inf. Comput. arXiv admin note: substantial text overlap with arXiv:2105.1431

Effects of Constructivist and Transmission Instructional Models on Mathematics Achievement in Mainland China: A Meta-Analysis

The innovation of teaching and learning methods has been a common theme among these meta-analyses in the field of mathematics education. However, no published study has reviewed the effects of teaching models on mathematics achievement in mainland China. This review is intended to examine effects of constructivist instructional models and improved transmission instructional models on mathematics performance in mainland China. Using rigorous inclusion criteria, we identified 89 studies for constructivist instruction and 25 studies for improved transmission instruction in grades 1–12. Compared with traditional transmission instruction, the weighted mean effect sizes of constructivist instruction and improved transmission instruction were +0.55 and +0.63, respectively. These two effect sizes were not significantly different. Of the included studies, inquiry-based learning (N = 26, d = +0.52), problem-based learning (N = 21, d = +0.58), cooperative learning (N = 14, d = +0.67), autonomous learning (N = 8, d = +0.43), and script-based learning (N = 12, d = +0.47) were frequently used constructivist models, and grouping teaching (N = 10, d = +0.57) and variation teaching (N = 7, d = +0.49) were frequently used improved transmission models. All seven models had significant effects on improving mathematics achievement. Our findings implicate that the traditional transmission teaching model needs to be changed in mainland China but the constructivist model is not the only promising approach. The impact of study features and the limitations of this review were also discussed

Stiffness characteristic comparison between metal-rubber and rubber isolator under sonic vibration

Stiffness of rubber and metal rubber (MR) changes nonlinearly. Based on hysteretic damping theory and energy conservation equations, a unified stiffness model is developed. The ring type of isolators made from rubber and metal rubber are studied. The isolator samples are tested on the electro-hydraulic loading system, which is fixed by a clamping device. We aim to study the deformations under different loading rates, loading forces and other quasi-static loading states. The dynamic stiffness affected by the preload and vibration frequency is studied on the sonic drilling processing. It can be concluded that the metal rubber isolators deform larger plastic than the rubber. The damping, plastic deformation and elastic deformation of the metal rubber and rubber material are inversely proportional to the loading rate. The total deformation of the rubber is larger than the metal rubber, no matter when the load increases or decreases. The dynamic stiffness of the metal rubber isolator is proportional to the vibration frequency. However, the dynamic stiffness of the rubber remains the same under different preloads, while decreases when the preload increases

Unlocking opportunities for migrant workers in China: Analyzing the impact of health insurance on hukou switching intentions

The Chinese urban–rural binary health insurance structure has contributed to a significant urban–rural segmentation and regional fragmentation, which will affect labor mobilization and urbanization. The purpose of this research is to study whether and how urban–rural binary health insurance impacts the intentions of migrant workers to switch between rural and urban hukou. Pooled data were drawn from China Migrants Dynamic Survey, collected by the National Health Commission of China. The study applied the instrument variable model due to the existence of the endogeneity; and the IVprobit model to conduct the empirical analysis. Our findings are as follows: (1) the urban–rural binary health insurance affects migrant workers’ intentions to switch to urban hukou significantly. (2) The negative impact of originally rural health insurance on migrant workers’ intention of switching to urban hukou is relatively large for low-education-level migrant workers. (3) Compared with new generation of migrant workers, old migrant workers have higher health insurance dependency levels. Finally, our research suggested several policy implications, such as accelerating the establishment of a unified urban–rural health insurance system, increasing the urban health insurance participation rate of migrant workers in their working cities, and including migrant workers in the scope of equal access to urban public services, etc. All the policy suggestions are essential in order to accelerate the citizenization of migrant workers, improve the quality of urbanization, and promote the construction of a unified national labor market.Web of Science158art. no. 699

The effect of various pressure of pneumatic uterine bracket by using saccule sterine external stent on incidence of supine hypotensive syndrome

Objectives: The saccule uterine external stent with a pneumatic uterine bracket reportedly prevents the incidence of supine hypotension syndrome (SHS) during cesarean section under combined spinal — epidural anesthesia (CSEA). However, the preventive effect is affected by the pressure within pneumatic uterine bracket. This study aims to explore the optimal pressure.Material and methods: One hundred forty-eight pregnant women were selected and randomly divided into three groups: Group A (the control group, n = 49), Group B (n = 49), and Group C (n = 50). The pressure within pneumatic uterine bracket was set at 240 mmHg, 260mmHg, and 280mmHg, respectively, during cesarean section under CSEA for participants in groups A, B and C. The intraoperative comfort rate and incidence of SHS were recorded.Results: No significant difference in the anesthetic efficacy was observed among the three groups (p > 0.05). However, there was a significant difference in the occurrence of SHS, with a reduction of 30 mmHg in blood pressure. The incidence of SHS belong the three groups showed significant differences (36.73% in Group A, 18.37% in Group B and 18.00% in Group C, p < 0.05). In addition, significant differences (p < 0.05) in the intraoperative comfort rate were also found among the three groups, with the comfort rate of 69.39% in group A, 91.84% in group B and 90.00% in Group C.Conclusions: The optimal pressure within pneumatic uterine bracket for preventing SHS hypotension is about 260 mmHg. These findings might contribute to the prevention of SHS

The Qitai Radio Telescope

This study presents a general outline of the Qitai radio telescope (QTT) project. Qitai, the site of the telescope, is a county of Xinjiang Uygur Autonomous Region of China, located in the east Tianshan Mountains at an elevation of about 1800 m. The QTT is a fully steerable, Gregorian type telescope with a standard parabolic main reflector of 110 m diameter. The QTT has adopted an um-brella support, homology-symmetric lightweight design. The main reflector is active so that the deformation caused by gravity can be corrected. The structural design aims to ultimately allow high-sensitivity observations from 150 MHz up to 115 GHz. To satisfy the requirements for early scientific goals, the QTT will be equipped with ultra-wideband receivers and large field-of-view mul-ti-beam receivers. A multi-function signal-processing system based on RFSoC and GPU processor chips will be developed. These will enable the QTT to operate in pulsar, spectral line, continuum and Very Long Baseline Interferometer (VLBI) observing modes. Electromagnetic compatibility (EMC) and radio frequency interference (RFI) control techniques are adopted throughout the system design. The QTT will form a world-class observational platform for the detection of low-frequency (nanoHertz) gravitational waves through pulsar timing array (PTA) techniques, pulsar surveys, the discovery of binary black-hole systems, and exploring dark matter and the origin of life in the universe.Comment: 12 pages, 11 figures, accepted for publication in Science China Physics, Mechanics & Astronom