Distributed clock skew and offset estimation from relative measurements in mobile networks with Markovian switching topology

We analyze a distributed algorithm for the estimation of scalar parameters belonging to nodes in a mobile network from noisy relative measurements. The motivation comes from the problem of clock skew and offset estimation for the purpose of time synchronization. The time variation of the network was modeled as a Markov chain. The estimates are shown to be mean square convergent under fairly weak assumptions on the Markov chain, as long as the union of the graphs is connected. Expressions for the asymptotic mean and correlation are also provided.     

Robust linear output feedback controller for autonomous landing of a quadrotor on a ship deck

Ship deck landing control of a quadrotor requires certain robustness with respect to ship heave motion. Typical systems only provide relative height, therefore do not have relative heave rate information. In this paper, a linear output feedback control consisting of a full state feedback controller and a Luenberger observer is formulated. Invariant ellipsoid method is used to formulate an estimation of a bound on the response of a linear output feedback-controlled system subjected to external disturbances and measurement noise. The gains that result in a minimum bound are optimized using a gradient descent iterative approach proposed in this paper where the invariant ellipsoid condition is linearized into a tractable LMI condition. This approach is applied to a simulation of a quadrotor landing on a ship deck and results are compared with other gains. The gains selected using the proposed approach exhibits improved robustness to external disturbances and measurement noise.     

Effects of actuator and sensor bandwidths in intelligent cruise control of autonomous vehicles. Part II: performance

We analyse disturbance rejection for a platoon of vehicles with intelligent cruise control, both for the spatially discrete model and the continuum model with open and periodic boundary conditions. By explicitly calculating the eigenmodes for both the discrete and the continuum models, we derive the dynamic response of an individual discrete mode, as well as the response of a single vehicle to disturbances generated through either boundary vehicles or vehicles within the platoon. It is shown that if the biasing is small then the n-mode truncated continuum model and the spatially discrete model predict same qualitative responses to disturbances for the lower order modes. In the case of periodic boundary conditions, the two types of models predict quantitatively the same responses to disturbances for a range of feedback gains.     

Chosen plaintext attack on a cryptosystem with discretized skew tent map

An encryption system with discretized skew tent map has been proposed recently by N. Masuda . However, there is a fundamental weakness with this chaotic cryptographic scheme. In this paper, a chosen plaintext attack requiring only two plaintexts is proposed. An improved version of this attack that narrows the key space need to be searched is also suggested. The test results demonstrate that this encryption cryptosystem is easily broken under the proposed chosen plaintext attack.     

集成U-Net方法的无人机影像胡杨树冠提取和计数

塔里木河流域的胡杨林是该荒漠区域典型的森林资源,胡杨树冠大小和株数信息对塔里木河流域森林资源监测、生态保护和恢复具有重要意义。由于该流域乔灌草植物群落分布的复杂性,传统方法很难实现胡杨树冠的精准分割和大范围的株数提取。以塔里木河中游胡杨林为研究区,选取几块典型胡杨林区域,提出集成深度学习和分水岭分割的处理方法,对密集胡杨树冠的精准分割和单株胡杨的提取进行了深入探讨。首先,将无人机影像（空间分辨率0.16 m）无缝拼接生成正射影像;采用U-Net卷积神经网络对胡杨树冠覆盖区域进行精准分割;在U-Net模型分割的基础上使用标记分水岭方法对密集胡杨树冠进行自动再分割和单株计数,计算出所选研究区的胡杨株数并精准定位。结果表明U-Net卷积神经网络对胡杨的所有树冠区域提取的平均精度可达94.1%,在胡杨树冠覆盖区域识别分割的基础上,用标记分水岭分割方法对胡杨单木计算总体精度为93.3%。研究认为,结合深度学习和标记分水岭方法为自动化大范围森林资源监测提供了新思路和借鉴经验。     

Compact dual‐band printed quadrifilar helix antenna for practical hand‐held devices

This paper proposes a compact dual‐band printed quadrifilar helix antenna (QHA) operating at GPS‐L1 (1575 ± 2 MHz) and L2 (1228 ± 2 MHz) bands. To generate the dual operating bands, two interconnected lines with unequal lengths are introduced as a radiating element. The closely allocated radiators resonate in quarter‐wavelength mode, which significantly miniaturizes antenna's size. Four shunt capacitors are loaded near ports to manipulate the mutual coupling between each two radiators, so that satisfactory matching condition with minimum active reflection at two target bands can be obtained simultaneously. Then, a compact feeding network consisting of on‐chip hybrid couplers is designed and connected to the QHA. Measured results show that the compact proposed antenna achieves peak gains of 1.5 dBic and 2.6 dBic at 1575 MHz and 1228 MHz, respectively. The axial ratios (ARs) at L1 and L2 bands are both below 2.5 dB, and the half‐power‐beamwidths (HPBWs) are as wide as 130° and 116°, respectively. As compared with reported works, the proposed antenna can achieve much more compact size (0.11 × 0.21 λ₀²) and dual‐band radiation at the same time.     

实时内存数据库分区模糊检验点策略

检验点技术是实时内存数据库恢复的关键技术之一.在分析实时内存数据库数据特征基础上,给出了综合考虑数据和事务定时约束的数据检验点优先级计算方法.然后,结合内存数据库段式存储结构,讨论了一种基于数据段检验点优先级的分区模糊检验点策略PFCS-SCP. 通过性能测试,表明所提出的检验点策略能减低超截止期事务比率.     

智能化分布式医学图像管理

一般的图像归档和通信系统（PACS）的管理缺乏智能性,存储及查询图像效率低。在广东石龙人民医院的PACS中,采用多级分布式存储体系,引入基于图像内容的查询和图像理解专家系统技术。通过显示工作站图像访问时间评估,采用智能化体系后,在存储管理、查询速度及灵活性上都有了较大的提高。     

河口坝砂体储层非均质性及剩余油分布

运用非均质综合指数,以胜坨油田坨28断块沙二段8,9砂层组为例,对河口坝砂体储层的层间、层内、平面非均质性进行了定量表征,并分析了非均质性与剩余油分布之间的关系。认为河口坝储层层间非均质性弱,而层内、平面非均质性以中等-弱为主,非均质综合指数与含油饱和度有良好的对应关系,剩余油主要分布在非均质性中等的区域内。     

裁剪曲面的三角化及图形显示

结合自主版权的超人ＣＡＤ／ＣＡＭ系统的开发，本文提出了一种适合于裁剪曲面图形显示的曲面三角化算法，该算法将曲面的三角化转化为曲面参数域的三角化，并将二维图形的集合运算与Ｄｅｌａｕｎａｙ三角剖分应有和于曲面参数域边界的处理，从而使裁剪曲面在边界上的三角形分布均匀。