Extensions in adaptive model tracking with mitigated passivity conditions

Feasibility of nonlinear and adaptive control methodologies in multivariable linear timeinvariant systems with state space realization {A, B, C} has apparently been limited by the standard strict passivity (or positive realness) conditions that imply that the product CB must be positive definite symmetric. More recently the symmetry condition has been mitigated, requiring instead that the not necessarily symmetric matrix CB be diagonalizable and with positive real eigenvalues. However, although the mitigated conditions are useful in proving pure stabilizability with Adaptive Controllers, the Model Tracking question has remained open and counterexamples seem to demonstrate total divergence of standard model reference adaptive controllers when the regular passivity conditions are not fully satisfied. Therefore, this paper further extends the previous results, showing that the new passivity conditions do guarantee stability with adaptive model tracking. Examples show how the new conditions solve the case of flexible structures with unknown parameters when perfect collocation is not possible. Also, the so-called counterexamples become simple, well-behaved, examples.     

Bayesian edge detector for SAR imagery using discontinuity-adaptive Markov random feld modeling

Synthetic aperture radar（SAR）image is severely affected by multiplicative speckle noise,which greatly complicates the edge detection.In this paper,by incorporating the discontinuityadaptive Markov random feld（DAMRF）and maximum a posteriori（MAP）estimation criterion into edge detection,a Bayesian edge detector for SAR imagery is accordingly developed.In the proposed detector,the DAMRF is used as the a priori distribution of the local mean reflectivity,and a maximum a posteriori estimation of it is thus obtained by maximizing the posteriori energy using gradient-descent method.Four normalized ratios constructed in different directions are computed,based on which two edge strength maps（ESMs）are formed.The fnal edge detection result is achieved by fusing the results of two thresholded ESMs.The experimental results with synthetic and real SAR images show that the proposed detector could effciently detect edges in SAR images,and achieve better performance than two popular detectors in terms of Pratt＇s fgure of merit and visual evaluation in most cases.     

基于二项分布的优化序贯截尾检验方法分析计算

基于二项分布的优化截尾序贯检验法能降低平均试验数,可有效用于导弹试验检验方案中,但该方法存在实际风险计算不准确的特点。文章在深入分析该算法基础上,提出采用马尔科夫链的方法计算试验风险,给出了试验方案制定步骤,并用实例计算说明该方法的正确性及可行性。     

基于故障树与马尔科夫分析模型的发动机系统安全性评估

安全性评估是发动机适航验证的重要方法之一,故障树与马尔科夫分析方法是安全性评估常用的方法,两种方法在安全性评估的不同时机具有各自的特点。针对故障树与马尔科夫在安全性评估中的应用时机行了深入的研究,分析结果表明:对于失效率为常数的顺序相关的系统,若部件是主动失效部件(即λ×t较小),应用故障树与马尔科夫分析方法均可准确评估系统的失效概率,采用故障树可以减少运算的复杂性;若部件是潜在失效部件,由于部件暴露时间较长(即λ×t较大),使用马尔科夫的分析方法可以更精确的评估系统的安全性。     

FC-AE-1553数据总线的特点及在航天领域的应用

MIL-STD-1553B总线被广泛运用于许多嵌入式系统,例如飞机、轮船、导弹、卫星等。但是随着科学技术的发展,当前的航空航天系统,武器系统的互连子系统的数量和复杂性不断增加,系统对高带宽、低延时数据需求愈发迫切,而光纤天然具有的高带宽、低延时的特点能够很好解决上述需求。除此之外,用光纤搭建的通信网络还具有灵活的拓扑结构、较远的传输距离、高抗电磁干扰等优点。FC-AE-1553的通信介质采用光纤,其各个节点之间的通信协议与MIL-STD-1553B高度相似,因此采用FC-AE-1553通信协议的新设备能够较好地兼容MIL-STD-1553B协议的传统设备。     

Adaptive flow control of low-Reynolds number aerodynamics using dielectric barrier discharge actuator

Aerodynamic performance of low-Reynolds number flyers, for a chord-based Reynolds number of 10⁵ or below, is sensitive to wind gusts and flow separation. Active flow control offers insight into fluid physics as well as possible improvements in vehicle performance. While facilitating flow control by introducing feedback control and fluidic devices, major challenges of achieving a target aerodynamic performance under unsteady flow conditions lie on the high-dimensional nonlinear dynamics of the flow system. Therefore, a successful flow control framework requires a viable as well as accessible control scheme and understanding of underlying flow dynamics as key information of the flow system. On the other hand, promising devices have been developed recently to facilitate flow control in this flow regime. The dielectric barrier discharge (DBD) actuator is such an example; it does not have moving parts and provides fast impact on the flow field locally. In this paper, recent feedback flow control studies, especially those focusing on unsteady low-Reynolds number aerodynamics, are reviewed. As an example of an effective flow control framework, it is demonstrated that aerodynamic lift of a high angle-of-attack wing under fluctuating free-stream conditions can be stabilized using the DBD actuator and an adaptive algorithm based on general input–output models. System nonlinearities and control challenges are discussed by assessing control performance and the variation of the system parameters under various flow and actuation conditions. Other fundamental issues from the flow dynamics view point, such as the lift stabilization mechanism and the influence on drag fluctuation are also explored. Both potentiality and limitation of the linear modeling approach are discussed. In addition, guidelines on system identification and the controller and actuator setups are suggested.     

基于Markov的察打无人机数据链时延建模与补偿研究

为了改善在数据链时延情况下察打无人机的性能,对造成时延的因素及影响进行了分析,在此基础上对数据链时延进行了合理的假设和简化。并对无人机整个控制回路的各个节点的响应方式,提出了一种时间-事件-事件-时间驱动方式,使得无人机数据链的时延序列具有Markov性,同时给出了状态转移矩阵的求取方法。为了改善无人机的响应特性,采用最优控制的方法对时延进行了补偿,并基于某无人机平台验证了补偿方法的有效性。仿真结果表明,该方法的引入使得无人机的动态响应特性有了显著提高。     

Soybean cultivation for Bioregenerative Life Support Systems (BLSSs): The effect of hydroponic system and nitrogen source

Soybean [Glycine max (L.) Merr.] is one of the plant species selected within the European Space Agency (ESA) Micro-Ecological Life Support System Alternative (MELiSSA) project for hydroponic cultivation in Biological Life Support Systems (BLSSs), because of the high nutritional value of seeds. Root symbiosis of soybean with Bradirhizobium japonicum contributes to plant nutrition in soil, providing ammonium through the bacterial fixation of atmospheric nitrogen. The aim of this study was to evaluate the effects of two hydroponic systems, Nutrient Film Technique (NFT) and cultivation on rockwool, and two nitrogen sources in the nutrient solution, nitrate (as Ca(NO₃)₂ and KNO₃) and urea (CO(NH₂)₂), on root symbiosis, plant growth and seeds production of soybean. Plants of cultivar ‘OT8914’, inoculated with B. japonicum strain BUS-2, were grown in a growth chamber, under controlled environmental conditions.     

Predictive Space Weather: An information theory approach

It is rather well recognized that the global dynamics of the Sun–Earth relationship involves complex nonlinear phenomena. Here we present a preliminary attempt to characterize the influence and the timing of the solar magnetic activity on the near-Earth environment, based on quite novel tools based on concepts from information theory.