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

Research on Low Density Cementing Technology of Coalbed Methane Well

The pressure of the coalbed methane (CBM) reservoir is relatively low, there is serious loss circulation, andlow mechanical strength of the coal, which seriously influence the cementing quality. In this paper, according to the characteristics of coal in southern Qinshui basin, an ultra-low density cement slurry system and a foamed cement slurry system are designed and developed to reduce the density of cement slurry by adding lightening admixture and foaming agent through the experimental method. An appropriate bridging type preflush system is also researched and developed. Considering the drilling conditions, the operation technologies are put forward.The ultra-low density cement slurry system has good rheological performance, small API filter loss (≤ 45 mL/ (30 min·6.9 MPa)), excellent sedimentation stability, suitable thickening time and higher early strength. Foamed cement slurry systemhas good rheological performance, excellent sedimentation stability andsuitable thickening time, and can satisfy the compressive strength requirements for the cementing of CBM wells. The fluid loss of the bridging type preflush system is small under the medium or high pressure, withgood rheological performance,andexcellent plugging ability. The ultra-low density cement slurry system and foamed cement slurry system were applied in 14 and 11 CBM wells respectively, and good results have been achieved

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

Analysis of Fracture Initiation Pressure of Horizontal Well at Anisotropic Formation Using Boundary Element Method

With the influence of bedding plane, the mechanical properties of bedded rocks, such as shale and coal rock at vertical and parallel bedding direction show comparatively significant difference. Therefore, compared with homogeneous rocks, bedded rocks exhibit obvious anisotropic mechanical properties. Currently, most fracture initiation pressure prediction models simplify rock to homogeneous dielectric elastomer, which is inapplicable to calculate wellbore fracture initiation pressure at bedded stratums. Given that the mechanical properties of bedded rocks at bedding plane direction are the same, this paper established a calculation model of horizontal well fracture initiation pressure in the anisotropic formation and set up a numerical solution method of circumferential stress around the borehole by means of using boundary element method. In addition, a calculation method for fracture initiation pressure based on tensile strength criterion and simplex algorithm was also proposed. The research results indicate that: In the case of high elasticity modulus anisotropy ratio, the wellbore fracture initiation pressure is low; when the elasticity modulus at vertical bedding direction is greater than that at parallel bedding direction, fracture initiation pressure decreases with the increase of bedding dip angle; the shape of wellbore has imposed an significant influence on fracture initiation pressure. For non-circular wellbore, fracture initiation pressure increases with the increase of length-width ratio in the case of smaller ovality. When wellbore shape transforms from equiaxial circle to long and narrow ellipse, fracture initiation pressure decreases with the increase of stress concentration level. Thus, this paper performed calculation and comparison with classical solutions for particular cases similar to isotropic body of stratum using the model established which verified the validity of the proposed theory. According to the research results, a new method for precise calculation of fracture initiation pressure of horizontal well at bedded stratum was provided

Rationally designed α-conotoxin analogues maintained analgesia activity and weakened side effects

A lack of specificity is restricting the further application of conotoxin from Conus bullatus (BuIA). In this study, an analogue library of BuIA was established and virtual screening was used, which identified high α7 nicotinic acetylcholine receptor (nAChR)-selectivity analogues. The analogues were synthesized and tested for their affinity to functional human α7 nAChR and for the regulation of intracellular calcium ion capacity in neurons. Immunofluorescence, flow cytometry, and patch clamp results showed that the analogues maintained their capacity for calcium regulation. The results of the hot-plate model and paclitaxel-induced peripheral neuropathy model indicated that, when compared with natural BuIA, the analgesia activities of the analogues in different models were maintained. To analyze the adverse effects and toxicity of BuIA and its analogues, the tail suspension test, forced swimming test, and open field test were used. The results showed that the safety and toxicity of the analogues were significantly better than BuIA. The analogues of BuIA with an appropriate and rational mutation showed high selectivity and maintained the regulation of Ca2+ capacity in neurons and activities of analgesia, whereas the analogues demonstrated that the adverse effects of natural α-conotoxins could be reduced

Structural Basis for Calmodulin as a Dynamic Calcium Sensor

Calmodulin is a prototypical and versatile Ca2+ sensor with EF-hands as its high-affinity Ca2+ binding domains. Calmodulin is present in all eukaryotic cells, mediating Ca2+-dependent signaling. Upon binding Ca2+, calmodulin changes its conformation to form complexes with a diverse array of target proteins. Despite a wealth of knowledge on calmodulin, little is known on how target proteins regulate calmodulin’s ability to bind Ca2+. Here, we take advantage of two splice variants of SK2 channels, which are activated by Ca2+-bound calmodulin, but show different sensitivity to Ca2+ for their activation. Protein crystal structures and other experiments show that depending on which SK2 splice variant it binds to calmodulin adopts drastically different conformations with different affinities for Ca2+ at its C-lobe. Such target protein induced conformational changes make calmodulin a dynamic Ca2+ sensor, capable of responding to different Ca2+ concentrations in cellular Ca2+ signaling

Structural Basis for Calmodulin as a Dynamic Calcium Sensor

Calmodulin is a prototypical and versatile Ca2+ sensor with EF-hands as its high-affinity Ca2+ binding domains. Calmodulin is present in all eukaryotic cells, mediating Ca2+-dependent signaling. Upon binding Ca2+, calmodulin changes its conformation to form complexes with a diverse array of target proteins. Despite a wealth of knowledge on calmodulin, little is known on how target proteins regulate calmodulin’s ability to bind Ca2+. Here, we take advantage of two splice variants of SK2 channels, which are activated by Ca2+-bound calmodulin, but show different sensitivity to Ca2+ for their activation. Protein crystal structures and other experiments show that depending on which SK2 splice variant it binds to calmodulin adopts drastically different conformations with different affinities for Ca2+ at its C-lobe. Such target protein induced conformational changes make calmodulin a dynamic Ca2+ sensor, capable of responding to different Ca2+ concentrations in cellular Ca2+ signaling

Metagenomic next-generation sequencing for detecting lower respiratory tract infections in sputum and bronchoalveolar lavage fluid samples from children

Lower respiratory tract infections are common in children. Bronchoalveolar lavage fluid has long been established as the best biological sample for detecting respiratory tract infections; however, it is not easily collected in children. Sputum may be used as an alternative yet its diagnostic accuracy remains controversial. Therefore, this study sought to evaluate the diagnostic accuracy of sputum for detecting lower respiratory tract infections using metagenomic next-generation sequencing. Paired sputum and bronchoalveolar lavage fluid samples were obtained from 68 patients; pathogens were detected in 67 sputum samples and 64 bronchoalveolar lavage fluid samples by metagenomic next-generation sequencing, respectively. The combined pathogen-detection rates in the sputum and bronchoalveolar lavage fluid samples were 80.90% and 66.2%, respectively. For sputum, the positive predictive values (PPVs) and negative predictive values (NPVs) for detecting bacteria were 0.72 and 0.73, respectively, with poor Kappa agreement (0.30; 95% confidence interval: 0.218–0.578, P < 0.001). However, viral detection in sputum had good sensitivity (0.87), fair specificity (0.57), and moderate Kappa agreement (0.46; 95% confidence interval: 0.231–0.693, P < 0.001). The PPVs and NPVs for viral detection in sputum were 0.82 and 0.67, respectively. The consistency between the sputum and bronchoalveolar lavage fluid was poor for bacterial detection yet moderate for viral detection. Thus, clinicians should be cautious when interpreting the results of sputum in suspected cases of lower respiratory tract infections, particularly with regards to bacterial detection in sputum. Viral detection in sputum appears to be more reliable; however, clinicians must still use comprehensive clinical judgment

Challenges and benefits of implementing DIBH for breast cancer radiotherapy: Experiences from Guangzhou Concord Cancer Center

Radiation therapy is used for breast cancer treatments to improve local control and overall survival but may also lead to unwanted complications such as cardiac toxicity and pneumonitis. Deep inspirational breath hold (DIBH) has been used to reduce doses to the heart and other organs near the treatment target to lower the risk of radiation-induced complications. In this study, we present our experience on the clinical implementation and application of DIBH for breast cancer patients, its dosimetric benefits in heart and other organ sparing based on comparisons with free breathing plans, effects on the treatment efficiency as represented by treatment imaging, and beam delivery times, as well as challenges during implementation and clinical application at our center