Parameter effects on high-speed UAV ground directional stability using bifurcation analysis

A loss of ground directional stability can trigger a high-speed Unmanned Aerial Vehicle(UAV)to veer off the runway.In order to investigate the combined effects of the key structural and operational parameters on the UAV ground directional stability from a global perspective,a fully parameterized mathematical high-speed UAV ground nonlinear dynamic model is developed considering several nonlinear factors.The bifurcation analysis procedure of a UAV ground steering system is introduced,following which the simulation efficiency is greatly improved comparing with the time-domain simulation method.Then the numerical continuation method is employed to investigate the influence of the nose wheel steering angle and the global stability region is obtained.The bifurcation parameter plane is divided into several parts with different stability properties by the saddle nodes and the Hopf bifurcation points.We find that the UAV motion states will never cross the bifurcation curve in the nonlinear system.Also,the dual-parameter bifurcation analyses are presented to give a complete description of the possible steering performance.It is also found that BT bifurcation appears when the UAV initial rectilinear velocity and the tire frictional coefficient vary.In addition,results indicate that the influence of tire frictional coefficient has an opposite trend to the influence of initial rectilinear velocity.Overall,using bifurcation analysis method to identify the parameter regions of a UAV nonlinear ground dynamic system helps to improve the development efficiency and quality during UAV designing phase.

Safety and efficacy of Compound Huangdai Tablets combined with all-trans retinoic acid for treatment of acute promyelocytic leukemia:Clinical evidence and potential mechanisms

Objective:To evaluate the safety and efficacy of Compound Huangdai Tablets(Realgar-Indigo Naturalis formula,RIF)combined with all-trans retinoic acid(ATRA)to treat acute promyelocytic leukemia(APL).Methods:This study was registered in PROSPERO(CRD42018108118).The relevant literatures on RIF treatment of APL were systematically searched in the following databases:China National Knowledge Infrastructure,Wanfang,VIP Medical Information System,Chinese Biomedical Database,EMBASE,Cochrane Library,and PubMed.The quality of the included studies was evaluated and Review Manager 5.3 software and Stata 13.0 software were used to perform the Meta-analysis.In addition,this study used the method of network pharmacology to conduct a preliminary exploration of the mechanism of RIF on APL.Results:The study included 12 studies involving 775 APL patients.The Meta-analysis showed that there was no significant difference(P>0.05)between the RIF group and the arsenic trioxide(ATO)group for primary outcomes,secondary outcomes apart from liver dysfunction.The incidence of liver dysfunction(P=0.006)in the RIF group were significantly lower than those in the ATO group.In addition,the cost of maintenance therapy in the RIF group was significantly lower(P<0.05)than the ATO group.Besides,the active ingredients in RIF mainly act on targets proteins such as ACHE,NCOA2,RXRA,and then play a role in the treatment of APL through regulating multiple molecular mechanisms,such as TP53 regulates transcription of cell cycle genes,nuclear receptor transcription pathway.Conclusion:There was no significant difference in efficacy of oral RIF combined with ATRA compared with intravenous ATO combined with ATRA for the treatment of APL.The oral RIF exposed patients to less risk,offered more convenience and had lower prices.RIF can treat APL by multi-target and multipathway interventions that inducing apoptosis of APL cells and inhibiting the proliferation of APL cells,and so on.Therefore,oral RIF in the treatment of APL is worthy of further research and development.

Study on modal characteristics and vibration reduction of an aircraft rotor–stator brake-induced squeal system

Based on the modal coupling theory,the rotor and stator contact stiffness and axial relative velocity are considered to build an electric aircraft brake dynamic system model in this study.Both the complex modal analysis and transient dynamic analysis methods are used to study the aircraft brake squeal performance and vibratory mechanism.The unstable vibration modes indicate that the out-of-plane vibration plays an important role and the feed-in energy is larger than the output energy in the brake rotor–stator module so that brake squeal takes place.Then the influences of the contact stiffness,friction damping and frictional coefficient on the brake squeal system are carried out,laying the foundation for the three proposed vibration suppression methods.Results show that the coefficient negative-slope condition will intensify the vibration.Also,a linear relationship between the squeal factor and the frictional coefficient is obtained to provide a guidance to predict squeal stability under more conditions.Vibration reduction design shows that adding a damping layer to the brake mechanism and chamfering the edge of braking stators both can reduce brake squeal effectively,while slotting braking stators is invalid in aircraft braking system.