FIXED-DESIGN REGRESSION FOR LINEARTIME SERIES

This paper obtains asymptotic normality for double array sum of linear time series zeta(t), and gives its application in the regression model. This generalizes the main results in [1].

Fixed time integral sliding mode controller and its application to the suppression of chaotic oscillation in power system

Chattering phenomenon and singularity are still the main problems that hinder the practical application of sliding mode control. In this paper, a fixed time integral sliding mode controller is designed based on fixed time stability theory, which ensures precise convergence of the state variables of controlled system, and overcomes the drawback of convergence time growing unboundedly as the initial value increases in finite time controller. It makes the controlled system converge to the control objective within a fixed time bounded by a constant as the initial value grows, and convergence time can be changed by adjusting parameters of controllers properly. Compared with other fixed time controllers, the fixed time integral sliding mode controller proposed in this paper achieves chattering-free control, and integral expression is used to avoid singularity generated by derivation. Finally, the controller is used to stabilize four-order chaotic power system. The results demonstrate that the controller realizes the non-singular chattering-free control of chaotic oscillation in the power system and guarantees the fixed time convergence of state variables, which shows its higher superiority than other finite time controllers.

Time-and Frequency-Domain Analysis of Ice-Induced Displacement Responses Offshore Fixed Platforms

On the basis of ice- induced forced vibration model, ice- induced displacement responses of offshore fixed platforms are investigated in both time domain and frequency domain. The relationships of ice-induced displacement responses with ice breaking modes, ice acting directions and platform structures are analyzed and determined. The results lead to an important conclusion obtained for the first time that ice breaking frequency and the natural frequency of the first mode of the platform are the two main factors that dominate the degree of vibration. The present work provides a firm basis for both design and operation of fixed platforms against ice loading.

Robust controller design for compound control missile with fixed bounded convergence time

A robust controller for bank to turn(BTT) missiles with aerodynamic fins and reaction jet control system(RCS) is developed based on nonlinear control dynamic models comprising couplings and aerodynamic uncertainties. The fixed time convergence theory is incorporated with the sliding mode control technique to ensure that the system tracks the desired command within uniform bounded time under different initial conditions. Unlike previous terminal sliding mode approaches, the bound of settling time is independent of the initial state, which means performance metrics like convergence rate can be predicted beforehand. To reduce the burden of control design in terms of robustness, extended state observer(ESO) is introduced for uncertainty estimation with the output substituted into the controller as feedforward compensation. Cascade control structure is employed with the proposed control law and therein the compound control signal is obtained.Afterwards, control inputs for two kinds of actuators are allocated on the basis of their inherent characteristics. Finally, a number of simulations are carried out and demonstrate the effectiveness of the designed controller.

Observer-based multivariable fixed-time formation control of mobile robots

This paper proposes a multivariable fixed-time leaderfollower formation control method for a group of nonholonomic mobile robots, which has the ability to estimate multiple uncertainties. Firstly, based on the state space model of the leader-follower formation, a multivariable fixed-time formation kinematics controller is designed. Secondly, to overcome uncertainties existing in the nonholonomic mobile robot system, such as load change,friction, external disturbance, a multivariable fixed-time torque controller based on the fixed-time disturbance observer at the dynamic level is designed. The designed torque controller is cascaded with the formation controller and finally realizes accurate estimation of the uncertain part of the system, the follower tracking of reference velocity and the desired formation of the leader and the follower in a fixed-time. The fixed-time upper bound is completely determined by the controller parameters, which is independent of the initial state of the system. The multivariable fixed-time control theory and the Lyapunov method are adopted to ensure the system stability.Finally, the effectiveness of the proposed algorithm is verified by the experimental simulation.

FIXED-DESIGN SEMIPARAMETRIC REGRESSION FOR LINEAR TIME SERIES

This article studies parametric component and nonparametric component estimators in a semiparametric regression model with linear time series errors; their r-th mean consistency and complete consistency are obtained under suitable conditions. Finally, the author shows that the usual weight functions based on nearest neighbor methods satisfy the designed assumptions imposed.

ANN-Time Varying GARCH Model for Processes with Fixed and Random Periodicity

Financial Time Series Forecasting is an important tool to support both individual and organizational decisions. Periodic phenomena are very popular in econometrics. Many models have been built aiding capture of these periodic trends as a way of enhancing forecasting of future events as well as guiding business and social activities. The nature of real-world systems is characterized by many uncertain fluctuations which makes prediction difficult. In situations when randomness is mixed with periodicity, prediction is even much harder. We therefore constructed an ANN Time Varying Garch model with both linear and non-linear attributes and specific for processes with fixed and random periodicity. To eliminate the need for time series linear component filtering, we incorporated the use of Artificial Neural Networks (ANN) and constructed Time Varying GARCH model on its disturbances. We developed the estimation procedure of the ANN time varying GARCH model parameters using non parametric techniques.

Fixed-time Consensus for Leader-follower Second-order Multi-agent Systems

We analyse the fixed-time consensus problem for multi-agent systems with leaderfollower mode. Based on a follower’s observation structure for the leader’s information, it is proved that the estimation errors can be converged to zero at a fixed time. From this stability and a sliding mode structure, we derive a control input of followers, which provides a critical support for fixed-time consensus. The simulation results demonstrate that this control approach does conduce to the implementation of the fixed-time synchronization.

Pregnancy outcome of lactating dairy cows assigned for Presynch-Ovsynchsynchronization program and inseminated either at detected standing heat or at scheduled fixed time

Objective: To determine if insemination at standing heat results in a similar or higher pregnancy rate compared with fixed time artificial insemination, and to study some factors affecting the pregnancy rate. Methods: A total of 8944 inseminations were included in this study, from which 6823 inseminations were done in Holstein cows and 2121 inseminations were performed in Simmental cows. All cows were subjected to a Presynch-Ovsynch protocol. Cows detected in estrus (n=7424) were artificially inseminated, whereas cows not observed in estrus (n=1520) were submitted to fixed time artificial insemination. Results: The overall pregnancy rate of cows inseminated on the basis of the detected standing heat was comparable to that recorded for cows receiving fixed time artificial insemination. A higher pregnancy rate was recorded for cows during cold months than that recorded during hot months (P=0.000). A higher pregnancy rate was recorded for Simmental compared with that recorded for Holstein cows (P=0.001). Regarding parity, significant differences in the pregnancy rate were detected between primiparous and multiparous cows (P=0.040). In addition, artificial insemination technicians had no sigificant effect on pregnancy rate (P>0.05). Meanwhile, the used artificial insemination sires significantly (P=0.000) impacted the pregnancy rate. Conclusions: Insemination of cows detected in standing heat prior to predetermined fixed time results in similar pregnancy outcome and decreases days to the first service compared with insemination at the scheduled fixed time at the end of the Presynch-Ovsynch synchronization program. The overall pregnancy outcome is not affected by the breeding program, but it is highly impacted by cow's breed, parity, artificial insemination sire and breeding season.

A novel robust fixed time synchronization of complex network subject to input nonlinearity in the presence of uncertainties and external disturbances

This paper studies the global fixed time synchronization of complex dynamical network,including non-identical nodes with disturbances and uncertainties as well as input nonlinearity.First,a novel fixed time sliding manifold is constructed to achieve the fixed time synchronization of complex dynamical network with disturbances and uncertainties.Second,a novel sliding mode controller is proposed to realize the global fixed time reachability of sliding surfaces.The outstanding feature of the designed control is that the fixed convergence time of both reaching and sliding modes can be adjusted to the desired values in advance by choosing the explicit parameters in the controller,which does not rest upon the initial conditions and the topology of the network.Finally,the effectiveness and validity of the obtained results are demonstrated by corresponding numerical simulations.

Pregnancy Rate of Bunaji Cows in a Fixed Time AI Synchronization Protocol Using Ovatide

This study accessed the reproductive performance of Bunaji cows in an Ovsynch protocol involving ovatide.Bunaji cows(n=16)aged 4-6 years and weighing between 250-350 kg with body condition scores(BCS)of 2.5-3.5 were used.There were two treatment groups for synchronization of ovulation.Treatment group 1 comprising Bunaji(n=8)received 50μg of gonadotropin releasing hormone(GnRH)(Cystorelin)and 25 mg of PGF2α.While,treatment group 2 comprising Bunaji(n=8)received 50μg of ovatide and 25 mg of PGF2α.All cows from both treatment groups were inseminated at 16 h after each second GnRH or ovatide injections.Cows that showed mucus discharge from the vagina on the day of artificial insemination(AI)were recorded as well as those that had patent cervix.Cervical dilation was measured by taking note of the cows that had mid cervix insemination due to non-passage of the AI gun through the cervix.Transrectal palpation was conducted twice at a month interval to select cycling cows within 5-12 d of the estrous cycle before initiating Ovsynch protocol.It was repeated on day 45 post AI to confirm pregnancies in animals.Results showed that the rate of mucus discharge from the vagina was 37.5%and 87.5%for ovatide and Cystorelin,respectively;while the rate of cervical dilation were 75%and 87.5%for ovatide and Cystorelin,respectively(p>0.05),and pregnancy rates were 0%and 12.5%for ovatide and Cystorelin,respectively.There were no significant differences between the two groups.It was concluded that treatment of Bunaji cows with 50μg ovatide in Ovsynh protocol has heat and ovulation synchronization potentials and zero pregnancy rate.It was recommended that further studies be carried out using graded doses of 50,100 and 150μg of ovatide in a fixed time AI synchronization protocol in Bunaji cows,to tap the potentials of the hormone in manipulation of bovine reproduction.

Fixed-Time and Finite-Time Synchronization for a Class of Output-Coupling Complex Networks via Continuous Control

This paper mainly investigates the finite-time and fixed-time synchronization problem for a class of general output-coupling complex networks with output feedback nodes. The fixed-time and finite-time synchronization protocols are presented based on continuous controller strategies which can efficaciously eliminate chattering phenomenon existing in some previous results. Several sufficient conditions ensuring fixed-time and finite-time synchronization are derived by employing Lyapunov stability theory, linear matrix inequality (LMI) and adaptive technique. Furthermore, aimed at the model of this article, we study the problem of adaptive coupling strength in fixed-time synchronization which is rarely involved in previous results. Finally, several numerical examples are given to illustrate the effectiveness of our results.

Fixed Time Control of Dynamic Positioning Ship with Unknown Interference

This paper proposes a fixed-time control scheme to ensure that the dynamic positioning can accurately reach the specified position under external interference. A fixed-time state observer was developed to accurately estimate the total external unknown interference. Based on the dynamic positioning ship motion model, the inversion design method is used to ensure the stability of the system and eliminate various uncertain effects. A fixed-time backstepping sliding mode controller is designed. Finally, the simulation results show that the method has good performance and advantages.

Some Further Results on Fixed-Time Synchronization of Neural Networks with Stochastic Perturbations

In this paper, fixed-time (FXT) synchronization issue of a type of neural networks (NNs) with stochastic perturbations is considered. First, we obtained some novel sufficient criteria to guarantee the FXT synchronization of considered networks via introducing two types of controllers and employing some inequality techniques. Lastly, our theoretical results are verified via giving two numerical examples with their Matlab simulations.

旋翼飞行机械臂固定时间滑模控制

针对旋翼飞行机械臂轨迹跟踪控制中的不确定性和扰动问题,提出了一种基于固定时间滑模观测器的滑模控制算法。首先,在广义坐标系下建立了旋翼飞行机械臂运动学与动力学模型,并设计出固定时间观测器对模型参数不确定性与外部扰动进行估计,通过在滑模中引入分段函数和饱和函数抑制固定时间观测器的抖振,加快其收敛速度。随后,将旋翼飞行机械臂划分为位置、姿态以及机械臂3个子系统,基于固定时间理论,分别对3个子系统设计了新型固定时间滑模控制器,并设计自适应趋近律以抑制滑模控制器的抖振。与传统滑模控制器相比,该控制器具有更快的收敛速度与更好的跟踪性能。利用Lyapunov稳定性理论证明了系统的稳定性。最后通过仿真实验验证了所提算法的有效性,该算法对旋翼飞行机械臂轨迹跟踪控制具有较好效果。

色纺纱用黏胶纤维的连续染色工艺与染色性能

采用散纤维连续染色技术对黏胶散纤维进行连续浸渍染色后再冷堆固色,然后进行连续式水洗。分析了固色时间对黏胶纤维外观形貌、色泽指标及力学性能的影响,并对染色黏胶纤维成品的色牢度、pH和甲醛含量进行测试。结果表明:连续浸渍染色后的黏胶纤维,经冷堆24 h固色后,可获得较好的匀染性;染色黏胶纤维的力学性能略有下降,其中强度下降约15%,断裂伸长率下降约16%;染色黏胶纤维的各项色牢度、pH和甲醛含量均符合要求。

基于干扰观测器的多航天器固定时间姿态协同跟踪控制

针对受扰动下的多航天器系统姿态一致性跟踪问题,提出一种基于干扰观测器与固定时间理论的分布式姿态协同控制策略。多航天器系统在空间中易受太阳光压、重力梯度与地磁力等外部干扰影响而导致控制精度下降,此外航天器内部惯量不确定性带来的影响也不可忽视,因此设计一种基于二阶积分滑模的干扰观测器对复合干扰进行快速精确估计,且该观测器无需任何干扰先验信息。利用观测器获得的估计值,结合领导跟随法,提出一种分布式固定时间姿态协同控制器,实现系统固定时间收敛,收敛时间可通过控制参数进行调节。利用Lyapunov函数证明了系统的固定时间稳定性。仿真与对比试验结果表明,干扰观测器能在较快时间内实现对复合干扰准确估计,协同控制器能在固定时间内实现对期望姿态鲁棒跟踪,与自适应有限时间方法相比,该控制策略精度更高、收敛速度更快和燃油消耗更少。

一种求解混合变分不等式的带有扰动项的神经网络方法

通过构建带有干扰项的新型神经网络求解混合变分不等式问题.主要将已有的固定时间收敛的前向-后向-前向神经动力学网络进行推广,构建出带有扰动项的神经网络模型.证明了所构建的神经网络的平衡点是固定时间稳定的,并给出了稳定时间的上界.最后通过数值实验证明了该方法的有效性.

数字化转型助力津门老字号企业品牌发展研究

数字经济改变着人们的生活与工作方式,历史底蕴和文化价值深厚的老字号品牌如何在数字经济时代传承创新、改革发展已成为研究热点。基于2011—2021年天津老字号企业面板数据,构建时间、个体双向固定效应模型和中介效应模型,探究企业数字化转型对品牌竞争力的影响及其作用机制。结果表明,老字号企业数字化转型能够显著提升品牌竞争力,企业创新水平对数字化转型提升品牌竞争力具有中介作用。基于此,对老字号企业转型发展提出相关对策建议,促进老字号企业利用数字化转型推动品牌发展,提升竞争力。

复合风场影响下RLV着陆段固定时间控制

本文针对垂直起降的可重复使用运载器(RLV)返回着陆段面临多类型复合风场干扰影响导致的姿态跟踪控制收敛时间上界与初始状态强耦合及跟踪性能严重下降等问题,提出一种基于双幂次固定时间稳定理论的快速高精度控制方法。首先,对可重复使用运载器返回着陆段所受的自然风场进行分类建模,并分析风场对着陆段姿态控制的影响;其次,基于反步法框架,设计高低幂次加权多项式形式的趋近律,以保证系统状态误差在固定时间内收敛,且收敛时间和上界与初始状态无关;同时,为降低风场扰动对着陆段控制系统性能的影响,保证着陆段控制性能的稳定性及着陆安全性,引入固定时间扩张状态观测器对风场扰动进行估计和补偿;最后基于Lyapunov理论,证明了所设计的控制律可使RLV返回着陆段姿态控制误差在固定时间内收敛;多组数值仿真验证了所提方法的有效性。