Detection of low-dimensional chaos in drill bit torsional vibration time series

The near-bit strap-down measurement-while-drilling (MWD) system has been developed in this paper. By means of triaxial magnetometers, calculation method for bit rotational velocity was developed to monitor the drill bit torsional vibration. A number of techniques were applied to perform a nonlinear analysis of the experimental data of torsional vibration. Estimate delay time with mutual information and calculated the embedding dimension through Cao’s method, after reconstruct the phase space, the chaotic characteristics of the system were analyzed by calculating the correlation dimension and the largest Lyapunov exponent. We show that the largest Lyapunov exponent is positive and the correlation dimension is more than two, which is a strong indicator for the chaotic behaviour of the system. We also found that chaotic characteristics of the drill bit torsional vibration even existed in the whole drilling process, and thus the techniques based on phase space dynamics can be used to analyze and to predict drill bit torsional vibration. The results of this paper are of interest to applied and theoretical mechanics and petroleum engineering

Numerical Studies of Scattering Properties of Leaves and Leaf Moisture Influences on the Scattering at Microwave Wavelengths

This study uses 3-dimensional finite difference time domain method to accurately calculate single-scattering properties of randomly orientated leaves and evaluate the influences of vegetation water content (VWC) on these properties at 19 and 37 GHz frequencies. The studied leaves are assumed to be thin elliptic disks with two different sizes and have various VWC values. Although the leaf moisture produces considerable absorption during scattering processes, the effective efficiencies of extinction and scattering of leaves still near-linearly increase with VWC. Calculated asymmetry factors and phase functions indicate that there are significant amounts of scattering at large scattering angles in microwave wavelengths, which provides good opportunities for off-nadir microwave remote sensing of forests. This study lays a basic foundation in future quantifications of the relations between satellite measurements and physical properties of vegetation canopies

Ferroelectric-driven tunable magnetism in ultrathin platinum films

Electric control of magnetism in magnetoelectric (ME) multiferroics is expected to have a significant impact on a wide range of technological applications. Here, we predict the modulation of magnetism in ultrathin platinum films due to the ferroelectric polarization of the BaTiO3 substrate, which along with biaxial strain changes the density of states at the Fermi energy. We demonstrate that both the magnitude and direction of the magnetization depend strongly on the polarization direction and/or strain. This leads to an unprecedented ME effect involving a giant change of magnetocrystalline anisotropy under polarization switching due to the large spin-orbit coupling of Pt. These findings pave the way of an alternative strategy for the design of nonvolatile and ultralow power spintronics and magnetic memory storage devices

Detection of low-dimensional chaos in drill bit torsional vibration time series

The near-bit strap-down measurement-while-drilling (MWD) system has been developed in this paper. By means of triaxial magnetometers, calculation method for bit rotational velocity was developed to monitor the drill bit torsional vibration. A number of techniques were applied to perform a nonlinear analysis of the experimental data of torsional vibration. Estimate delay time with mutual information and calculated the embedding dimension through Cao’s method, after reconstruct the phase space, the chaotic characteristics of the system were analyzed by calculating the correlation dimension and the largest Lyapunov exponent. We show that the largest Lyapunov exponent is positive and the correlation dimension is more than two, which is a strong indicator for the chaotic behaviour of the system. We also found that chaotic characteristics of the drill bit torsional vibration even existed in the whole drilling process, and thus the techniques based on phase space dynamics can be used to analyze and to predict drill bit torsional vibration. The results of this paper are of interest to applied and theoretical mechanics and petroleum engineering

Stochastic evolutionary game analysis of food cooperation among countries along the Belt and Road from the perspective of food security

IntroductionIn recent years, the combination of the public health crisis and the climate crisis has greatly weakened the resilience of food systems. The Belt and Road food cooperation will make outstanding contributions to consolidate food security and reduce global poverty in countries along the Belt and Road.MethodsThis paper constructs a three-party stochastic evolutionary game model from the perspective of food security, distinguishes the difference between large and small countries by calculating the cereal self-sufficiency rate, which studies the cooperation strategy with the Belt and Road cereal large countries, cereal small countries and regulatory committees as the object. In addition, we introduce the Gaussian white noise characteristics to characterize the stochastic disturbance of the game system. Then we combine the mathematical derivation of the stochastic evolutionary game analysis with the simulation method, examine the effect of the stochastic disturbance factors on the cooperation, and find out the factors that affect the cooperation. And finally verifies the model and proves the reasonableness and practicability of the model.ResultsThe stochastic evolutionary game model analyzes the interaction of stochastic disturbance and influencing factors from a dynamic perspective, and the stability of evolution is related to the strength of Gaussian white noise. The level of effort of large cereal countries and the incentives of regulatory committees can have a positive impact, but high income in small cereal countries can lead to instability in the strategic choices of other players.DiscussionTaking the countries along the Belt and Road as the research object, Gaussian white noise is introduced to describe the stochastic external environment, discriminate the stability of the game system through stochastic differential equations, and analyze the influencing factors of the dynamic behavioral strategies of the parties in combination with simulation methods. To improve the capacity of national food security governance and help improve the resilience of the world food system

Exercise intervention to reduce mobile phone addiction in adolescents: a systematic review and meta-analysis of randomized controlled trials

BackgroundThe growing problem of adolescent mobile phone addiction has attracted significant attention, underscoring the importance of identifying approaches to address it. Exercise has been found to reduce adolescent mobile phone addiction; however, its mechanism remains unclear. This review aims to elucidate the potential moderating factors between exercise and mobile phone addiction based on previous studies to provide a reference for adolescents to effectively participate in exercise to reduce mobile phone addiction.MethodsArticles were searched in the CNKI, Web of Science, Scopus, Cochrane, PsycINFO, and PubMed databases according to the inclusion criteria and followed the Preferred Reporting Items for Systematic Assessment and Meta-analysis (PRISMA). The quality of the literature was assessed by two independent reviewers using the Cochrane Collaboration Risk of Bias tool for methodological quality assessment. Meta-analysis was performed using Stata 15.1 software for Meta-analysis, standardized mean difference (SMD) was combined using a random effects model, and subgroup analysis was used to explore heterogeneity.ResultsA total of 12 studies, 17 samples, and 861 subjects were included in the meta-analysis, and all studies were randomized controlled trials. The findings revealed that the exercise intervention significantly reduced mobile phone addiction in adolescents (SMD = −3.11; 95% CI: −3.91, −2.30; p < 0.001). The intervention effect was moderated by multiple variables, such as the measurement tools, exercise intervention types, cycles, frequency, and duration of a single exercise intervention.ConclusionOur findings suggest that exercise could serve as an effective strategy for preventing or ameliorating mobile phone addiction in adolescents. Based on the results of this study, we encourage mobile phone-addicted adolescents to engage in a single exercise using a mix of skills for 30–60 min three or more times weekly for more than eight consecutive weeks

Diagnostic performance and clinical impact of blood metagenomic next-generation sequencing in ICU patients suspected monomicrobial and polymicrobial bloodstream infections

IntroductionEarly and effective application of antimicrobial medication has been evidenced to improve outcomes of patients with bloodstream infection (BSI). However, conventional microbiological tests (CMTs) have a number of limitations that hamper a rapid diagnosis.MethodsWe retrospectively collected 162 cases suspected BSI from intensive care unit with blood metagenomics next-generation sequencing (mNGS) results, to comparatively evaluate the diagnostic performance and the clinical impact on antibiotics usage of mNGS.Results and discussionResults showed that compared with blood culture, mNGS detected a greater number of pathogens, especially for Aspergillus spp, and yielded a significantly higher positive rate. With the final clinical diagnosis as the standard, the sensitivity of mNGS (excluding viruses) was 58.06%, significantly higher than that of blood culture (34.68%, P<0.001). Combing blood mNGS and culture results, the sensitivity improved to 72.58%. Forty-six patients had infected by mixed pathogens, among which Klebsiella pneumoniae and Acinetobacter baumannii contributed most. Compared to monomicrobial, cases with polymicrobial BSI exhibited dramatically higher level of SOFA, AST, hospitalized mortality and 90-day mortality (P<0.05). A total of 101 patients underwent antibiotics adjustment, among which 85 were adjusted according to microbiological results, including 45 cases based on the mNGS results (40 cases escalation and 5 cases de-escalation) and 32 cases on blood culture. Collectively, for patients suspected BSI in critical condition, mNGS results can provide valuable diagnostic information and contribute to the optimizing of antibiotic treatment. Combining conventional tests with mNGS may significantly improve the detection rate for pathogens and optimize antibiotic treatment in critically ill patients with BSI

Associations of HLA-DP Variants with Hepatitis B Virus Infection in Southern and Northern Han Chinese Populations: A Multicenter Case-Control Study

) locus has been reported to be associated with hepatitis B virus (HBV) infection in populations of Japan and Thailand. We aimed to examine whether the association can be replicated in Han Chinese populations. = 0.097∼0.697 and 0.198∼0.615 in northern Chinese population, respectively). loci were strongly associated with HBV infection in southern and northern Han Chinese populations, but not with HBV progression