基于P2P覆盖树网络的流媒体传输技术优化研究

PeerCast是一个基于P2P网络的流媒体传输系统,各节点被组织成树状来进行数据的分发.但没有一个有效的机制来维护树的平衡和保证所选取的父节点是最佳的节点.在此基础上,对该系统进行优化,在媒体数据包上加一个字节用来标识当前节点与根节点的距离,并对节点间响应消息进行优化.实验结果表明,这些优化措施能够有效的维护树的平衡和降底数据传输时延.     

基于嵌入式技术的开关寿命测试仪的设计

为了对开关的寿命进行快速准确地测试,设计了开关寿命测试仪。设计过程如下:首先设计了测试仪的硬件,该硬件使用LPC2138CPU芯片采集开关触头对应的开关量,并与TG12864液晶模块接口输出提示信息;其次设计了判断开关好坏算法和识别坏触头算法;最后根据算法给出了测试仪软件的流程图。应用表明,用这种设计方法实现的测试仪工作可靠、容易使用,适合在开关生产行业推广应用。     

离轴式拖车移动机器人的任意路径跟踪控制

离轴式拖车移动机器人属于非完整系统,当车头线速度随时间变化且过零变号时,难以用一个控制器实现系统对期望路径的跟踪.本文研究离轴式拖车移动机器人系统的任意路径跟踪问题.首先由系统和虚拟小车的运动学方程得到误差状态模型,线性化后用坐标变换将其化为标准型,然后基于Lyapunov方法构造出一种跟踪控制律.只要车头的运动线速度有界且不趋于零,其导数有界,则所设计的控制律就可以保证系统跟踪任意的期望路径,且跟踪误差最终一致有界,最终界的大小与期望路径的曲率变化率成比例.当期望路径的曲率变化率为零或趋于零时,所设计的控制律可以保证拖车移动机器人指数收敛到期望路径.仿真结果证实了控制律的有效性.     

电容式倾角传感器在底盘悬挂系统中的应用

以P89V51RD2FN单片机为控制核心,采用电容式倾角传感器实时测量车辆底盘的倾斜角,并用光电传感器检测车辆最终运动姿态和车速。光电传感器和倾角传感器将实时测量信号馈送至单片机,并采用增量式PID控制算法确保车辆能够达到平衡。利用CANBUS 2.0将数据传输至车载电脑来达到智能化车姿控制。实验结果表明:系统响应时间快,精度高,性能稳定。     

坑道水核磁共振探测激发磁场计算与测试方法研究

提出一种测量激发场垂直于地磁场分量的测量方法：应用固定线圈电磁感应法测量激发场,应用磁通门传感器测量地磁场,通过矢量运算求解激发场垂直于地磁场的分量。制作了激发场测量装置,通过对比激发场的径向分量和轴向分量的理论计算值和实测值,验证测量装置有效性。分析固定点处激发场垂直于地磁场的分量受线圈布设方向的影响,推导出固定点处激发场垂直于地磁场的分量取最大值时线圈布设角度求解方法,为实际探测线圈布设方向提供理论指导。     

Edge location to subpixel values in digital imagery

A new method for locating edges in digital data to subpixel values and which is invariant to additive and multiplicative changes in the data is presented. For one-dimensional edge patterns an ideal edge is fit to the data by matching moments. It is shown that the edge location is related to the so-called ``Christoffel numbers.' Also presented is the study of the effect of additive noise on edge location. The method is extended to include two-dimensional edge patterns where a line equation is derived to locate an edge. This in turn is compared with the standard Hueckel edge operator. An application of the new edge operator as an edge detector is also provided and is compared with Sobel and Hueckel edge detectors in presence and absence of noise.     

Structuring formal specifications—a lesson relearned

Specifications written in the formal specification language Z often make use of a form of decomposition that is novel to programmers. A published Z specification is rewritten using the form of decomposition familiar to programmers. Whenever decomposition is used, there must be some strategy for deciding what is to go in one component and what is to go in another. At the highest level, the strategy underlying the rewritten specification is the well-known strategy of separating user interface issues from deeper system functionality issues. The effectiveness of the strategy is put to a simple test by showing how a modification to the interface can be supported by a modification to only part of the specification. The conclusions drawn are that care over decomposition is important in specifications, just as it is in programs, and that lessons learned from programming about effective decomposition strategies can be applicable at the specification level, too. In particular, the lesson relearned is that it is important to separate information about a system's functionality from information about how this functionality is presented to users.     

Persistent caching: an implementation technique for complex objectswith object identity

Many recent complex object database systems support the concepts of object identity and object identifier. Following an object identifier to access the referenced object is called navigation operation and is an essential operation in dealing with complex objects. Navigation operation is a difficult operation to implement efficiently since every navigation operation inherently causes one disk access operation. A scheme to notably accelerate the navigation operation among a sea of complex objects, by increasing the effective number of objects in one disk page is proposed. The main concept of the presented technique is threefold. The first idea is to store a cached value within a complex object that is referencing another complex object. The second is that when the referenced object is to be updated the update propagation is delayed until the time when the cached value is referenced. The third is to utilize a hashed table on main memory to efficiently validate the consistency between the cached values and the original values     

主题爬行中的隧道穿越技术

由于网络环境的复杂性和网页内容的多主题性,要想得到更多的特定主题相关网页,就要穿越那些主题不相关网页来获取更多的主题相关网页,即隧道穿越.将隧道穿越分为灰色隧道穿越和黑色隧道穿越.对于灰色隧道,在爬行过程中,将一个多主题Web页面分割成数量不多的内容块分别处理来避免由于网页整体主题不相关给该块所带来的影响.对于黑色隧道的穿越,将隧道中主题不相关网页根据其父亲页面的主题相关性赋予一个深度值,然后根据其深度值的大小进行取舍,来达到扩展主题爬行区域的目的.实验结果显示,这两种方法都达到了预期效果,所以方法是有效、稳健和实用的.     

基于使用剖面的软件可靠性测试用例生成方法

为了获得软件的可靠性指标,需要设计操作剖面来仿真用户实际使用软件的情况,并基于操作剖面来进行可靠性测试.传统的基于操作剖面的可靠性测试方法难以适用于航天软件,为了解决此问题,描述了一种具有层次化网络体系结构特征的使用剖面的形式化定义,阐述了构造这种使用剖面的系统化方法,给出了根据使用剖面生成用于软件可靠性测试操作序列的算法,以及基于操作序列生成可靠性测试用例的方法.提出的方法经过实验验证表明是可行的.     

Constrained clustering as an optimization method

A deterministic annealing approach to clustering is derived on the basis of the principle of maximum entropy. This approach is independent of the initial state and produces natural hierarchical clustering solutions by going through a sequence of phase transitions. It is modified for a larger class of optimization problems by adding constraints to the free energy. The concept of constrained clustering is explained, and three examples are are given in which it is used to introduce deterministic annealing. The previous clustering method is improved by adding cluster mass variables and a total mass constraint. The traveling salesman problem is reformulated as constrained clustering, yielding the elastic net (EN) approach to the problem. More insight is gained by identifying a second Lagrange multiplier that is related to the tour length and can also be used to control the annealing process. The open path constraint formulation is shown to relate to dimensionality reduction by self-organization in unsupervised learning. A similar annealing procedure is applicable in this case as well     

Monitoring Smoothly Degrading Systems for Increased Dependability

A strategy is presented for determining when it is advantageous to take some action to restore a system to full capacity. A determination is made of the types of data that need to be collected and circumstances under which the strategy is likely to be useful. Production traffic data is presented for a very large industrial telecommunications project, and the strategy is applied. An investigation is made of when the application of the strategy leads to increased system availability and decreased packet loss experienced by users.     

一种新的删除AVL树的结点的算法

所有传统的删除AVL树的结点的算法的主要思想都是先删除结点再自下而上处理某些子树,涉及自下而上的后退。提出一种新的删除AVL树的结点的算法,其主要思想是先自上而下处理某些子树再删除结点,不涉及自下而上的后退。举例说明新算法的执行过程。证明新算法是正确的。与目前通常采用的Foster的算法相比,新算法不涉及辅助栈的使用。设n是AVL树的结点的个数。新算法的时间复杂性是O(log2n),与Foster的算法相同。实验结果表明新算法的平均执行时间比Foster的算法的短。新算法的空间复杂性是O(1),比Foster的算法的低。     

A Hybrid Bayesian-Frequentist Approach to SLAM

A hybrid Bayesian/ frequentist approach is presented for the Simultaneous Localization and Mapping Problem (SLAM). A frequentist approach is proposed for mapping a dense environment when the robotic pose is known and then extended to the case when the pose is uncertain. The SLAM problem is then solved in two steps: 1) the robot is localized with respect to a sparse set of landmarks in the map using a Bayes filter and a belief on the robot pose is formed, and 2) this belief on the robot pose is used to map the rest of the map using the frequentist estimator. The frequentist part of the hybrid methodology is shown to have complexity linear (constant time complexity under the assumption of bounded noise) in the map components, is robust to the data association problem and is provably consistent. The complexity of the Bayesian part is kept under control owing to the sparseness of the features, which also improves the robustness of the technique to the issue of data association. The hybrid method is tested on standard datasets on the RADISH repository.     

Control performance assessment for multivariable systems based on a modified relative variance technique

In this paper, a new technique is presented which enables the relative performance of both single and multiple loop control systems to be determined. The technique is based on the relative variance index technique which has been proposed recently for monitoring single loop control systems. This technique provides a control loop performance metric that considers the performance of the control system relative to both minimum variance and open-loop control. A major limitation with this technique is that it requires a highly restrictive assumption to be made regarding the structure of the disturbance to the process and the extension of the technique to multiple loop systems is not straight forward. The technique proposed in this paper does not require any assumptions to be made regarding the structure of the disturbance and can be extended to multiple loop situations with relative ease. The ability of the proposed technique to assess the performance of controllers applied to two simulated systems and also an industrial process is examined and it is shown that the proposed approach is superior to alternative techniques. A further benefit of the proposed technique is that it is able to provide an estimate of the potential improvement to the performance of the control loop that is achievable if the control system is retuned or redesigned.     

提高测量可靠性的多传感器数据融合有偏估计方法

为了提高测量数据可靠性,多传感器数据融合在过程控制领域得到了广泛应用. 本文基于有偏估计能够减小最小二乘无偏估计方差的思想,提出采用多传感器有偏估计数据融合改善测量数据可靠性的方法. 首先,基于岭估计提出了有偏测量过程,并给出了测量数据可靠性定量表示方法,同时证明了有偏测量可靠度优于无偏测量可靠度. 其次,提出了多传感器有偏估计数据融合方法,证明了现有集中式与分布式无偏估计数据融合之间的等价性. 最后,证明了多传感器有偏估计数据融合收敛于无偏估计数据融合. 实例应用验证了方法的有效性.     

一种基于分支覆盖的测试数据自动生成算法

通过构造新的程序流图，利用Fibonacci法优化选取路径．为指定的分支生成测试数据。提出了路径测试数据生成代价的概念，并给出了代价的计算方法。当所选路径的分支谓词均为线性表达式时，直接求解线性约束集即可生成测试数据，或判定路径不可行；当分支谓词含有非线性表达式时，利用均差近似导数将非线性函数线性化，通过简单的迭代，亦能容易生成测试数据或判定路径在很大程度上不可行。若所选路径不可行或在很大程度上不可行，则选取新的路径，重复以上过程，直至求出所期望的数据，或无新的路径被选取，给定分支不可达。实例和实验表明，算法可行、有效。     

近景数码影像中墙面纹理自动拼接方法的研究

影像拼接是从近景数码影像中生成墙面纹理需要解决的问题。然而由于现有的拼接软件通常不适用于处理几何变形大的近景影像,但通过对从近景数码影像中自动拼接墙面纹理的方法进行的研究发现,在相机的位置离建筑物相对较远,且大致沿一条直线进行拍摄时,当原始影像预先纠正到同一个铅垂面上后,由于各影像之间的大小比例接近于1,因此对于此种情况的拼接而言,就只需要通过选取拼接点来确定相邻影像之间沿X轴和Y轴方向的平移量,即可实现拼接。然而对于比较狭窄的街道(如步行街)来说,则由于摄站与建筑物之间的距离比较小,使影像的倾角增大,导致影像的几何变形增大,所以不适于采用选取拼接点的方法进行拼接。针对此种情况的拼接,提出了一种类似于航带法生成正射影像的条带法,用来进行墙面纹理的自动拼接,并且结合影像间同名水平直线的约束和加密匹配同名点两种方法来对拼接结果进行优化。最后针对地面实拍的序列影像进行了实验。实验结果证明,该方法能够显著消除相邻影像间的几何差异,从而真正实现了影像的无缝拼接。     

自顶向下聚集型代数多重网格预条件的健壮性与参数敏感性研究

本文针对自顶向下聚集型代数多重网格预条件,进行了健壮性与参数敏感性研究。对从各向同性与各向异性偏微分方程边值问题离散所得的多种稀疏线性方程组,首先对问题规模敏感性进行了研究,并与基于强连接的经典聚集型算法进行了系统比较,发现虽然对沿不同坐标轴具有强各向异性的问题,基于坐标分割的自顶向下聚集型算法不如基于强连接的经典聚集算法,但对其它所有情形,自顶向下聚集型算法都具有明显优势,特别是在采用Jacobi光滑时,优势更加显著。之后,对最粗网格层的分割数与每次每个子图进行分割时的分割数这两个参数进行了敏感性分析,发现在采用Jacobi光滑求解五点差分离散所得的稀疏线性方程组时,自顶向下聚集型算法对这两个参数存在敏感性,虽然大部分情形下,迭代次数比较稳定,但在少量几种情形下,迭代次数明显增加。而对从九点差分离散得到的稀疏线性方程组,以及在采用Gauss-Seidel光滑的情况下,算法对这两个参数的选取不再具有敏感性,迭代次数都比较稳定。综合分析表明,自顶向下聚集型代数多重网格预条件具有较好的健壮性,特别是在采用Gauss-Seidel光滑,或采用九点差分离散时,健壮性表现更加充分。     

光纤Bragg光栅损伤检测系统

损伤会导致结构局部刚度的下降,结果使损伤部位邻域的应变场分布发生显著变化。光纤Bragg光栅（FBG）传感器具有很高的灵敏度并能组成传感网络,适合于检测应变场的变化。通过应变场的变化也可以对失效螺钉进行定位。分布在结构表面的FBG传感器检测的应变数据组成向量,其单位向量定义为“模式”,该模式与载荷大小无关,与加载点位置有关,因此,能用于描述应变场。如果损伤前后模式的相关系数小于1,则加载点附件的螺钉可以判定为损伤。该方法在机翼盒段螺钉失效检测实验得到应用。