Ptolemy – an Instrument to Measure Stable Isotopic Ratios of Key Volatiles on a Cometary Nucleus

A fundamental goal of cometary studies is to determine the exact relationship between these bodies and the Solar System – the question(s) can be summarised as follows: did comets originate during the same events that spawned the Sun and planets, are they more primitive bodies that record a pre-solar history, or are they interstellar materials collected in relatively more recent times? Now, whatever the origin of comets, it is entirely possible that they could, in part, contain interstellar or pre-solar components – indeed, it seems rather likely in light of the fact that primitive meteorites contain such entities. These particular components are likely to be refractory (dust, macromolecular organic complexes, etc.). Of more relevance to the issues above are the volatile constituents, which make up the bulk of a comet's mass. Since these materials, by their very nature, volatilise during perihelion passage of a comet they can, in some instances, be detected and measured spectroscopically. Perhaps the most useful species for isotopic investigations are C₂, HCN and CN. Unfortunately, spectroscopic measurements can only currently be made with accuracies of ±10 to ±20%. As such it is very often not practical to conclude anything further than the fact that isotopic measurements are compatible with ‘`solar’' values, which tends to imply an origin from the margins of the solar accretion disk. But there is another problem with the spectroscopic measurements – since these are made on gaseous species in the coma (and relatively minor species at that) it is impossible to be certain that these represent the true nuclear values. In other words, if the processes of sublimation, active jetting, and photochemistry in the coma impart isotopic fractionation, the spectroscopic measurements could give a false impression of the true isotope ratios. What is required is an experiment capable of measuring isotopic ratios at the very surface of a comet. Herein we describe the Ptolemy instrument, which is included on the Philae lander as part of the Rosetta mission to 67P/Churyumov-Gerasimenko. The major objective of Ptolemy is a detailed appraisal of the nature and isotopic compositions of all materials present at the surface of a comet.     

基于神经网络的导弹稳定控制回路设计方法

基于径向基函数神经网络（RBFNN）的学习能力和逼近特性，将传统方法中的局部/整体构架蕴涵于神经网络内部，对导弹稳定控制律进行局部（定点）/整体（拟合）设计，以简化计算步骤，提高设计方法的通用性和自动化程度，以防空导弹侧向稳定控制回路设计为背景，对所提出的稳定控制回路设计方法进行了仿真，验证了该方法的可行性和有效性。     

星载激光雷达高精高稳探测卫星系统保证技术

激光雷达探测精度高,具备全天时工作和垂直探测能力,在大气环境天基遥感领域应用广泛。基于CO_2柱线浓度激光遥感探测原理,分析了积分路径差分吸收星载激光雷达测量系统的激光波长、能量精度和稳定性及光轴指向精度等关键指标要求和功能模块配置,重点开展了星载激光雷达光机头部稳定安装、良好机热环境保障及星敏载荷一体化布局等整星层面系统设计保证,仿真结果初步表明设计方案可行。同时,提出了激光雷达波长、能量精度及稳定性实时监测、卫星对地光轴指向高精度测定和星地载荷光轴指向测量误差标定的地面试验验证要求,以确保系统设计的有效性,为激光雷达遥感卫星的研制提供了技术参考。     

航空惯性稳定装置的齿隙误差实验平台设计

设计了航空惯性稳定装置的齿隙误差实验平台。该平台通过更换不同尺寸的齿轮和调节齿轮中心距,实现齿隙微调,用于研究不同传动比和不同齿隙情况下的齿隙误差特性,为航空惯性稳定装置的齿隙误差建模与补偿工作奠定了基础。     

知识互动中的知识交换行为进化博弈分析

利用博弈理论,研究动态知识交互系统中知识个体的知识交换行为特征。引入动态进化博弈链结构，建立知识团队中持续的动态知识交互行为的进化博弈分析模型，在此基础上讨论其可能的演变趋势。最后通过仿真数据分析识别了该行为进化稳定策略（ESS），ESS稳定性特征有利于在知识管理过程中激励员工进行知识交互、把撮知识共享活动中可能的演进规则。     

Precise Decoupling Tracking of Airspeed and Altitude for UAV Based on Causal Solution of Stable Inversion

Use stable inversion to accomplish precise decoupling tracking of airspeed and altitude for conventional takeoff and landing of unmanned aerial vehicles (UAVs) is in essence a non-minimum phase output tracking problem. The main contribution of this article is that a new method to calculate the causal solution of stable inversion is proposed by introducing a well defined perturbed signal to the system's unstable internal dynamics. It is helpful to overcome the pitfalls resulting from non-causality in existing methods. Different from the mathematically accurate offline non-causal solution, the causal solution is an approximation with asymptotically convergent errors. The important merits are: It obviates the needs for the output trajectory to be pre-known time parameterized functions, hence broadening the application of stable inversion; The low computational workload is much more suitable for and beneficial to real-time applications than any existing method based on stable inversion. The output tracking problem is then converted into a state tracking problem based on the causal solution of stable inversion. Precise decoupling tracking of airspeed and altitude is realized by using a feedback controller. Simulations are carried out to verify the viability and low computational workload of the method.     

8米×6米风洞直升机旋翼机身组合模型试验台的动态特性测试及初步分析

本文介绍了8米×6米风洞直升机旋翼机身组合模型试验台的动态特性测试,给出了试验台在不同工况下的固有频率及振型。并在试验的基础上,进行了试验台安装 BO-105旋翼模型时的地面共振问题的分析计算,确定了旋翼临界稳定转速。同时,初步分析了有关参数对试验台动态特性的影响。     

脉冲噪声下微弱信号相似度检测方法及应用

实际中采集的信号常常含有脉冲性噪声且信噪比偏低,这时用相关函数来表示信号之间的相似度时,会出现精度不高、鲁棒性不强的问题。提出了一种脉冲噪声下微弱信号的相似度检测方法,即非线性变换法。该方法采用Alpha稳定分布描述脉冲噪声信号,首先将采集的带噪信号进行Sigmoid映射,削弱脉冲噪声对信号相似度检测的干扰;接着对映射后的信号求取相关函数,得到信号之间相似度的信息。该方法简洁、计算量小,没有调整参数,能较好地减弱脉冲噪声对信号相似度估计的不利影响。该方法可以应用于定位系统中信号到达时差的估计。比较脉冲噪声低信噪比条件下计算机仿真结果显示,非线性变换相关法的估计精度高于共变法。实验结果表明:非线性变换相关法不仅可以用于高斯噪声环境下微弱信号相似度的检测,也可以用于强脉冲噪声环境下信号相似度的检测,具有较宽的适用范围和较好的鲁棒性。     

基于正余弦耦合的三轴速率平台控制结构优化

针对三轴速率平台进行三自由度的动态摇摆时出现的平台台体线性漂移问题,提出了一种基于正余弦耦合的三轴速率平台稳定回路控制结构优化方法。当三轴平台进行三自由度摇摆运动时,由于框架间角运动激励的物理耦合和角运动解耦激励的数学耦合,平台台体会产生动态漂移。首先建立三轴平台的角运动输出模型,再根据传递特性将平台基座上的角运动代入到台体伺服控制回路中得到交叉耦合误差项。其次,对比三轴速率陀螺平台和三轴位置陀螺平台在稳定回路控制结构上的异同,分析动态摇摆条件下造成平台台体出现正余弦耦合误差和台体大漂移率误差的形成机理,根据误差源进一步对三轴速率平台的稳定回路控制结构进行了设计优化。最后通过仿真和三自由度转台摇摆试验可见,摇摆过程中不再出现框架角的较大线性漂移,验证了稳定回路结构优化的正确性。     

一类受扰不确定系统的渐近镇定控制

 实际工程中的许多被控系统（如航天器,机器人,飞机等）几乎都处在一种变化的环境中,用精确的数学模型描述这类系统是不现实的。因此,研究考虑了这种不确定性的系统控制问题,在理论和应用中都有重要意义。 考虑用下述状态方程描述的不确定系统 （?）=（A₀+△A（r,s））X+（B₀+△B（r,s）u） （1）其中,X∈Rⁿ,系统状态,n为系统阶数,u∈R^m,控制信号,A₀,B₀是适当维数的常值阵,r,s分别为p维和q维未知参数矢量,△A（r,s）,△B（r,s）分别是与A₀,B₀同维的不确定矩阵。