Modelling and dynamic analysis of spline-connected multi-span rotor system

Meccanica - Self-excited oscillation induced by the internal frictions of spline joints is a major cause of rotor system instability. In this study, the dynamic equations of spline-connected...     

三轴转台速率的数字实现

本文针对用22位绝对式的光电编码器同时形成速率和位置信号的任务,设计了一种实用数字测速方法.从原理上进行了分析,并设计了硬件电路和软件程序.该方法使转台结构紧凑,增加了数字化程度.实践证明了其工程有效性.     

转台数字锁相系统最高极限速率的确定方法

数字锁相速率系统实质是一个非线性系统。确定其最高速率极限是设计者十分关心的问 题。本文采用求锁相环非线性系统极限环频率的方法确定了系统的速率极限，并给出了计算公 式。用该方法对某转台速率系统进行了计算，结果证明了此方法的有效性。     

Visible-Light-Promoted C(sp3)−H Alkylation by Intermolecular Charge Transfer: Preparation of Unnatural α-Amino Acids and Late-Stage Modification of Peptides

Disclosed herein is the visible-light-promoted deaminative C(sp³)−H alkylation of glycine and peptides using Katritzky salts as electrophiles. Simple reaction conditions and excellent functional-group tolerance provide a general strategy for the efficient preparation of unnatural α-amino acids and precise modification of peptides with unnatural α-amino-acid residues. Mechanistic studies suggest that visible-light-promoted intermolecular charge transfer within a glycine–Katritzky salt electron donor-acceptor (EDA) complex induces a single-electron transfer process without the assistance of photocatalyst.     

Visible‐Light‐Promoted C(sp3)−H Alkylation by Intermolecular Charge Transfer: Preparation of Unnatural α‐Amino Acids and Late‐Stage Modification of Peptides

Disclosed herein is the visible‐light‐promoted deaminative C(sp³)?H alkylation of glycine and peptides using Katritzky salts as electrophiles. Simple reaction conditions and excellent functional‐group tolerance provide a general strategy for the efficient preparation of unnatural α‐amino acids and precise modification of peptides with unnatural α‐amino‐acid residues. Mechanistic studies suggest that visible‐light‐promoted intermolecular charge transfer within a glycine–Katritzky salt electron donor‐acceptor (EDA) complex induces a single‐electron transfer process without the assistance of photocatalyst.     

Responses of dopaminergic, serotonergic and noradrenergic networks to acute levo-tetrahydropalmatine administration in naïve rats detected at 9.4 T

Aim

The aim of this study was to understand the neuropharmacological characteristics of levo-tetrahydropalmatine (l-THP), a recently found potential treatment for drug addiction, and discover its neural correlates and sites of action.

Methods

High-field pharmacological magnetic resonance imaging (phMRI) was used to detect activation induced by acute l-THP administration in the naïve rat brain at dose levels of 5, 10, 20 and 40 mg/kg.

Results

Interestingly, the pharmacological profile of l-THP selectively binds to the receptors of the dopaminergic, serotonergic and noradrenergic systems. Using the phMRI method, it was demonstrated that l-THP selectively activated the key brain regions of the dopaminergic, serotonergic and noradrenergic systems in a dose-dependent manner.

Conclusion

Numerous studies suggest a critical role of monoamines in the behavioral, pharmacological and addictive properties of psychostimulants. It is suggested that l-THP holds great potential to be a therapeutic medication for drug addiction.     

Stochastic optimal control of flexible aircraft taxiing at constant or variable velocity

Active control landing gears are used to alleviate vibration during aircraft taxiing. A nonlinear stochastic dynamics model is established, considering the aircraft body pitch movement and elastic vibration excited by the random runway. The equivalent linearization method is adopted to ensure the model linearity near the balance point, and the Gaussian random process of the runway is generated from the Gaussian white noise using a shape filter. Based on the stochastic optimal control theory, the LQG controller is designed along with weighted quadratic performance index for a better ride comfort, shock absorption, road holding and least energy expenditure. The algebraic Riccati and Lyapunov equations are solved to obtain stationary response while taxiing aircraft at a constant velocity and the differential Riccati and Lyapunov equations are solved to obtain the nonstationary response while taxiing aircraft at a variable velocity. The aircraft dynamic responses are obtained through the runway random process modeled by Monte Carlo method. Simulation results show that active control landing gear can give a better ride comfort, shock absorption and road holding performance no matter whether taxiing is at constant or variable velocity.     

感应同步器测角系统误差分析及补偿

本文讨论了提高感应同步器精度的硬件方法和软件方法。硬件方法即根据误差来源，针对不同谐波成分误差，用电路调节的方法消除误差。软件方法就是采用计算机通过误差曲线拟合来减小误差。     

直升机弹性多支点传动轴的主共振分析

传动轴主共振的最大振幅、稳定性、振幅突变性是其主要特性。在根据质心运动定理、Galer-kin法和Dirac函数求得非惯性移动系下直升机的倾斜弹性多支点传动轴的弯曲运动方程基础上,用多尺度法求得稳态下主共振的一次近似定常解,再分析了主共振的最大振幅、支点的位置及数量对主共振的影响、主共振的稳定性及振幅突变性等。弹性中间支点有提高传动轴的运动稳定性、增大相邻阶主共振之间的频率范围及限幅器的功用。提出通过减小偏心距、降低主共振的阶数、加大传动轴中及中间支点处的阻尼减小主共振的最大振幅及消除振幅突变。