Search

Purpose The purpose of this paper is to study the control strategy of transition mode of the stopped-rotor (SR) aircraft under the condition of redundant control and complex aerodynamic characteristics. Design/methodology/approach This paper first proposes a transition strategy for the conversion between helicopter mode and fixed-wing mode. Then, aiming at the redundancy of the two control systems in the transition process, a control model is proposed, which greatly simplifies the control in conversion mode. Then, to facilitate the design of the control system, the Takagi-Sugeno model of the SR aircraft in transition mode is established. Finally, an explicit model tracking and tuning parameter stability augmentation control system is designed, so that the SR aircraft has a good stability during the transition process. Then, the outer loop control system of transition flight is designed. Findings The simulation results show that the control strategy proposed in this paper can realize the mode conversion well. It lays a solid foundation for the subsequent engineering flight test for the SR aircraft. Originality/value The work done in this paper provides ideas and methods for the flight control system design of SR aircraft in transition mode. The method of designing control model to solve the coordination of redundant control system is also applicable for other multimode aircraft, which provides a simple and convenient method for the multimode aircraft control.

Purpose This study aims to deal with the problem of trajectory tracking control for the quadrotor under external environmental disturbance and variable payloads. Design/methodology/approach In the field of unmanned aerial vehicle (UAV) control, external environmental disturbance and internal variable payloads as two major interference factors lead to control performance degradation or even instability, thus a trajectory tracking controller which innovatively combines sliding mode control technology and model-free control technique is proposed. The proposed controller is constructed with a learning rate-based sliding mode controller and an ultra-local model. Based on the proposed controller, the nonlinear system model of variable load quadrotor is locally estimated and the system’s uncertainties and disturbances can be compensated. Findings The simulation and actual test results demonstrate the satisfactory control performance and the robustness of the proposed controller compared with the PID and Backstepping controller under external environmental disturbance and variable payloads. Moreover, the proposed controller solves the trajectory tracking control problem not only when payloads change at the center of gravity but also when the position of load variation deviates from the center of gravity. Practical implications In both military and civilian domains, the quadrotor may encounter such situations that the payloads change, such as transporting goods, aerial refueling and so on. As a large internal interference factor, variable load tends to lead to unstable control. The research results provide theoretical guidance and technical support for trajectory tracking control of quadrotor under variable payloads. Originality/value The proposed controller combines learning rate-based sliding mode controller and model-free control technique to achieve a more efficient and accurate trajectory control of the quadrotor when considering system uncertainties and the load variation that happens in the unknown location.

The method of using unmanned aerial vehicle (UAV) to obtain aerial image information of target scene has the characteristics of wide coverage, strong mobility and high efficiency, which is widely used in urban traffic monitoring, vehicle detection, oil pipeline inspection, regional survey and other aspects. Aiming at the difficulties of the object to be detected in the process of aerial image object detection, such as multiple orientations, small image pixel size and UAV body vibration interference, a novel aerial image object detection model based on the rotation-invariant deep denoising auto encoder is proposed in this paper. Firstly, the interest region of the aerial image is extracted by the selective search method, and the radial gradient of interest region is calculated. Then, the rotation invariant feature descriptor is obtained from the radial gradient feature, and the noise in the original data is filtered out by the deep denoising automatic encoder and the deep feature of the feature descriptors is extracted. Finally, the experimental results show that this method can achieve high accuracy for aerial image target detection and has good rotation invariance.

The aerodynamic layout of the Canard Rotor/Wing (CRW) aircraft in helicopter flight mode differs significantly from that of conventional helicopters. In order to study the flight dynamics characteristics of CRW aircraft in helicopter mode, first, the aerodynamic model of the main rotor system is established based on the blade element theory and wind tunnel test results. The aerodynamic forces and moments of the canard wing, horizontal tail, vertical tail and fuselage are obtained via theoretical analysis and empirical formula. The flight dynamics model of the CRW aircraft in helicopter mode is developed and validated by flight test data. Next, a method of model trimming using an optimization algorithm is proposed. The flight dynamics characteristics of the CRW are investigated by the method of linearized small perturbations via Simulink. The trim results are consistent with the conventional helicopter characteristics, and the results show that with increasing forward flight speed, the canard wing and horizontal tail can provide considerable lift, which reflects the unique characteristics of the CRW aircraft. Finally, mode analysis is implemented for the linearized CRW in helicopter mode. The results demonstrate that the stability of majority modes increases with increasing flight speed. However, one mode that diverges monotonously, and the reason is that the CRW helicopter mode has a large vertical tail compared to the conventional helicopter. The results of the dynamic analysis provide optimization guidance and reference for the overall design of the CRW aircraft in helicopter mode, and the model developed can be used for control system design. Keywords: Canard rotor/wing aircraft, Dynamics analysis, Flight dynamics, Helicopter, Linearization, Model building

Model uncertainties, unknown disturbances, and sensors measurement noises affect the attitude tracking control performance of quadrotors. In this article, a novel robust adaptive recursive sliding mode control (ARSMC) strategy is proposed for the quadrotor to improve the attitude tracking performance and disturbance rejection. Firstly, recursive sliding mode control is introduced, including a two-layer sliding surface, an integral sliding surface, and a fast nonsingular terminal sliding surface, which are recursive. Both sliding surfaces converge to zero in turn. And the initial value of the integral sliding surface is designed to eliminate the reaching phase. Besides, the adaptive gain adjustment method is presented to make an estimate of the unknown upper bound of disturbances. It is proved that the attitude control system has the finite-time convergence and the attitude tracking error will converge to zero. A quadrotor attitude test platform is built to evaluate the proposed algorithm. For comparison, twisting controller (TC), cascade PID, and active disturbance rejection control (ADRC) algorithms are introduced. Ultimately, the efficiency and feasibility of the proposed algorithm are verified by simulation and experimental results.

The aerodynamic layout of the fixed-wing mode of Canard Rotor/Wing (CRW) aircraft is quite different from that of the conventional fixed-wing aircraft. This study will focus on the flight dynamics characteristics and control in the fixed-wing mode of the CRW aircraft. First, aiming at the complicated aerodynamic interference in the fixed-wing mode of CRW aircraft, the flight dynamics model of the fixed-wing mode is established by combining CFD and engineering estimation. Then, by trimming at the different forward flight speeds, it is found that the minimum thrust is required when only the canard control surface is operated for longitudinal control. The linearized results show that the stability of most modes are good, and nevertheless only the Dutch roll mode diverges. It is found that the Dutch roll mode divergence is results from the unique three-wing aerodynamic layout of CRW aircraft. Finally, an explicit model tracking control system is designed to enhance the stability of the fixed-wing mode of CRW aircraft, which contributes for the future engineering application.

Background Type 4C myocardial infarction (MI) is a special type of myocardial infarction related to restenosis without thrombosis. There is a lack of relevant data on this new classification of acute MI (AMI). This study set out to examine the prognosis and treatment of type 4C MI in patients with non-ST-segment elevation MI (NSTEMI). Methods With reference to the NSTEMI cohort study database, we enrolled 1,032 cases of type 1 MI and 42 cases of type 4C MI from the period January 01, 2018 to August 31, 2018. All cases were followed up for 1 year. The outcome was major cardiovascular adverse events (including all-cause deaths, nonfatal MI, heart failure necessitating hospitalization, uncontrollable angina pectoris, and revascularization of the target vessels). Risk ratios (RR) were calculated using the generalized linear model. Cox multivariate analysis was performed to analyze the prognostic effects of drug-coated balloon (DCB) angioplasty or drug-eluting stent (DES) implantation in patients with type 4C MI. Results Compared with type 1 MI, type 4C MI was associated with a higher incidence of major adverse cardiovascular events (MACEs) [21.43% vs. 5.14%; adjusted RR: 3.725, 95% confidence interval (CI): 1.937-7.164]. Type 4C MI also showed a higher 1-year mortality rate than type 1 MI (7.14% vs. 1.55%; unadjusted RR: 4.607, 95% CI: 1.395-15.212). However, after adjusting for covariates, no statistical difference was noted (adjusted RR: 2.515, 95% CI: 0.768-8.233). Multiple adjustments to the Cox multivariate models revealed that neither DCB nor DES affected the clinical outcomes. Conclusions Type 4C MI has a poorer prognosis than type 1 MI. DCB angioplasty and DES implantation show similar efficacy in the treatment of type 4C MI.

Background Modern pharmacological studies have demonstrated that Baihe–Zhimu decoction (BZD) has antidepressant effects. However, the complex composition and lack of clear evaluation standards for BZD make it less likely to be understood and accepted than evidence-based active natural compounds. Methods In this study, an effective method for the identification of antidepressant components was demonstrated and applied to BZD. The first step was to evaluate the efficacy of BZD by the forced swimming test (FST) and the tail suspension test (TST), followed by successive quantitative analyses of the absorbed constituents at different stages, such as before hepatic disposition, liver distribution, after hepatic disposition and brain distribution after the oral administration of BZD. Finally, the compounds detected in the brain were confirmed by activity testing. Results Our investigation observed that timosaponin BII and timosaponin BIII were accurately determined in the brain after oral administration of BZD, and they were further confirmed to reduce the immobility time in the FST and TST. As described above, timosaponin BII and timosaponin BIII were used to scientifically and reasonably explain the effective chemical basis of the effect of BZD on depression. Conclusions This research affords an effective method to discover lead molecules for antidepressants from traditional Chinese medicine.

In this paper, a T-S fuzzy model of helicopter transition and hover is established as the dynamic characteristics of the helicopter vary with decline of height and decrease of speed. Based on the performance index requirement of automatic transition and hover, the pole assignment method is used to determine the feedback control parameters and regulating controller in full envelope of the automatic transition and hover is designed according to the theory of parallel distributed compensation. Eventually the sliding mode control law is designed. The simulation results show that the designed system in this paper is feasible and effective.

The complete sequence of transferrin has been cloned from cypermethrin-resistant strain of Culex pipiens pallens(Cr-C strain). Quantitative reverse transcription PCR analysis indicated that the transferrin transcription level was 12.6 times higher in Cr-C strain than in susceptible strain at fourth instar larvae. The transferrin expression was also found to be consistently higher throughout the life cycle of Cr-C strain. A protein of predicted size 90.8 kDa has been detected by Western blotting in transferrin-transfected mosquito C6/36 cells. These transferrin-transfected cells also showed enhanced cypermethrin resistance compared to null-transfected or plasmid vector-transfected cells as determined by methyl tritiated thymidine((3)H-TdR) incorporation. These results indicate that transferrin is expressed at higher levels in Cr-C strain and may confer some insecticide resistance in C. pipiens pallens.

Some expansion joints bellows used in buried gas pipeline in east China cities cracked after 1∼2 years service, the cracks usually located at top of the bellows, they expand nearly 48% of total circumference and the whole thickness. The material of the bellows was austenitic stainless steel plate. In order to research the crack causes, one typical failure bellows was chosen in this work, the specimen cut near the crack were analyzed by the macro-analysis, micro-analysis, chemical composition analysis, optical microscopy and electron microanalysis. The results showed that the chloride ion and sulfide in water of pipeline well and the high additional stress due to deviation of alignment of the two side pipeline ends were the main causes, the interaction effects of aggressive and high stress lead to stress corrosion crack of the top of bellows.Copyright © 2011 by ASME

The stress corrosion cracking susceptibilities of type 16MnR low-alloy steel in simulated oil refining environment were investigated by slow strain rate test. Many research works have been done to study the single solution parameter effect on the stress corrosion cracking, such as H2 S concentration or Cl− content, but less had been done for the interactive effect of the multiparameter. In this work, the separate and interactive effects of H2 S concentration, Cl− content, temperature and pH value on stress corrosion cracking susceptibilities were studied. By stepwise regression analysis of test results, the effect notabilities of medium parameters on stress corrosion cracking susceptive index were revealed. It could be conclude that the effect of H2 S concentrations was most notable to susceptive indexes, there was no notable correlativity between Cl− content and susceptive indexes, temperature and H2 S played interactive role on the susceptive indexes.Copyright © 2011 by ASME

People usually take the machining of elements with super- smooth surfaces just as a polishing process. But occasionally super-smooth polishing cannot be accomplished even conducted under a succeeded polishing procedure, resulting in the failure of obtaining super-smooth surfaces repeatedly. A concept of super-smooth surfaces machining 'process technology' is proposed which takes super-smooth surfaces machining as a system in general, not merely a polishing process. We take the machining of super-smooth surfaces as a chain consisted of some key nodes. The failure at any node will result in the failure of the final surfaces. The nodes in the process technology system refer to a series of key sub- items, such as sample material selection, pre-machining, and super-smooth surface evaluation, et al. With the aid of polishing experiments, the effects of some key sub-items are discussed.

Ultrasmooth optical surfaces are of important application due to low-loss and low-scauer properties. Especially, in soft X-ray region, the surface roughness of substrates of multilayered mirrors is demanded to be below 1 nm rms. Furthermore, the excellent reflectors usually take advantage of the surface roughness less than 0. 1 nm rms. Polishing by a tin plate is one of the remarkable methods for fabricating mirror surfaces. We studied the tin polisher forpolishing ultrasmooth surfaces. The characteristic of tin as a polisher material is presented. Non-contact, direct-contactand selfweight polishing states are studied Polishing experiments on many materials are carried out with perfect surfacequality. Surface roughness around 0.5 nm rms is obtained on BK7 glass, Zerodur, and sapphire plates. This paper submits a profile of the work on superpolishing with a tin pusher.Keywords: ultraprecision, ultrasmooth surface, superpolishing, polishing, low-loss, low-scatter, soft X-ray optics

Background Insecticide resistance jeopardizes the control of mosquito populations and mosquito-borne disease control, which creates a major public health concern. Two-dimensional electrophoresis identified one protein segment with high sequence homology to part of Aedes aegypti iron-responsive element binding protein (IRE-BP). Method RT-PCR and RACE (rapid amplification of cDNA end) were used to clone a cDNA encoding full length IRE-BP 1. Real-time quantitative RT-PCR was used to evaluate the transcriptional level changes in the Cr-IRE strain Aedes aegypti compared to the susceptible strain of Cx. pipiens pallens. The expression profile of the gene was established in the mosquito life cycle. Methyl tritiated thymidine (3H-TdR) was used to observe the cypermethrin resistance changes in C6/36 cells containing the stably transfected IRE-BP 1 gene of Cx. pipiens pallens. Results The complete sequence of iron responsive element binding protein 1 (IRE-BP 1) has been cloned from the cypermethrin-resistant strain of Culex pipiens pallens (Cr-IRE strain). Quantitative RT-PCR analysis indicated that the IRE-BP 1 transcription level was 6.7 times higher in the Cr-IRE strain than in the susceptible strain of 4th instar larvae. The IRE-BP 1 expression was also found to be consistently higher throughout the life cycle of the Cr-IRE strain. A protein of predicted size 109.4 kDa has been detected by Western blotting in IRE-BP 1-transfected mosquito C6/36 cells. These IRE-BP 1-transfected cells also showed enhanced cypermethrin resistance compared to null-transfected or plasmid vector-transfected cells as determined by 3H-TdR incorporation. Conclusion IRE-BP 1 is expressed at higher levels in the Cr-IRE strain, and may confer some insecticide resistance in Cx. pipiens pallens.