The fractional Fourier transform and quadratic field magnetic resonance imaging

The fractional Fourier transform (FrFT) is revisited in the framework of strongly continuous periodic semigroups to restate known results and to explore new properties of the FrFT. We then show how the FrFT can be used to reconstruct Magnetic Resonance (MR) images acquired under the presence of quadratic field inhomogeneity. Particularly, we prove that the order of the FrFT is a measure of the distortion in the reconstructed signal. Moreover, we give a dynamic interpretation to the order as time evolution of a function. We also introduce the notion of ρ-α space as an extension of the Fourier or k-space in MR, and we use it to study the distortions introduced in two common MR acquisition strategies. We formulate the reconstruction problem in the context of the FrFT and show how the semigroup theory allows us to find new reconstruction formulas for discrete sampled signals. Finally, the results are supplemented with numerical examples that show how it performs in a standard 1D MR signal reconstruction.     

Detection and characterization of defects using GMR probes and artificial neural networks

This work presents an eddy-current testing system based on a giant magnetoresistive (GMR) sensing device. Non-destructive tests in aluminum plates are applied in order to extract information about possible defects: cracks, holes and other mechanical damages. Eddy-current testing (ECT) presents major benefits such as low cost, high checking speed, robustness and high sensitivity to large classes of defects. Coil based architecture probes or coil-magnetoresistive probes are usually used in ECT. In our application the GMR sensor is used to detect a magnetic field component parallel to a plate surface, when an excitation field perpendicular to the plate is imposed. A neural network processing architecture, including a multilayer perceptron and a competitive neural network, is used to classify defects using the output amplitude of the eddy-current probe (ECP) and its operation frequency. The crack detection, classification and estimation of the geometrical characteristics, for different classes of defects, are described in the paper.     

Study of magnetic ranging technology in horizontal directional drilling

Intersection technology plays a key role in long-distance horizontal directional drilling (HDD). Magnetic ranging technology is an effective way to realize the intersection. A three-dimensional magnetic field model suitable for the cylindrical magnet connected with drilling bit was established. New formulae of magnetic induction intensity were deduced from the fundamental formulae to suit to the new magnetic ranging method. Based on the new formulae, a curve fitting model was established to complete the ranging. The whole process is simple and effective. The result of the experiment proved the feasibility of the new method and the accuracy is high enough for HDD.     

A systematic mapping study of software product lines testing

Context

In software development, Testing is an important mechanism both to identify defects and assure that completed products work as specified. This is a common practice in single-system development, and continues to hold in Software Product Lines (SPL). Even though extensive research has been done in the SPL Testing field, it is necessary to assess the current state of research and practice, in order to provide practitioners with evidence that enable fostering its further development.

Objective

This paper focuses on Testing in SPL and has the following goals: investigate state-of-the-art testing practices, synthesize available evidence, and identify gaps between required techniques and existing approaches, available in the literature.

Method

A systematic mapping study was conducted with a set of nine research questions, in which 120 studies, dated from 1993 to 2009, were evaluated.

Results

Although several aspects regarding testing have been covered by single-system development approaches, many cannot be directly applied in the SPL context due to specific issues. In addition, particular aspects regarding SPL are not covered by the existing SPL approaches, and when the aspects are covered, the literature just gives brief overviews. This scenario indicates that additional investigation, empirical and practical, should be performed.

Conclusion

The results can help to understand the needs in SPL Testing, by identifying points that still require additional investigation, since important aspects regarding particular points of software product lines have not been addressed yet.     

Generating asynchronous test cases from test purposes

Context

Input/output transition system (IOTS) models are commonly used when next input can arrive even before outputs are produced. The interaction between the tester and an implementation under test (IUT) is usually assumed to be synchronous. However, as the IUT can produce outputs at any moment, the tester should be prepared to accept all outputs from the IUT, or else be able to block (refuse) outputs of the implementation. Testing distributed, remote applications under the assumptions that communication is synchronous and actions can be blocked is unrealistic, since synchronous communication for such applications can only be achieved if special protocols are used. In this context, asynchronous tests can be more appropriate, reflecting the underlying test architecture which includes queues.

Objective

In this paper, we investigate the problem of constructing test cases for given test purposes and specification input/output transition systems, when the communication between the tester and the implementation under test is assumed to be asynchronous, performed via multiple queues.

Method

When issuing verdicts, asynchronous tests should take into account a distortion caused by the queues in the observed interactions. First, we investigate how the test purpose can be transformed to account for this distortion when there are a single input queue and a single output queue. Then, we consider a more general problem, when there may be multiple queues.

Results

We propose an algorithm which constructs a sound test case, by transforming the test purpose prior to composing it with the specification without queues.

Conclusion

The proposed algorithm mitigates the state explosion problem which usually occurs when queues are directly involved in the composition. Experimental results confirm the resulting state space reduction.     

Low-complexity joint transmit and receive antenna selection for MIMO systems

In this paper, we present a low-complexity algorithm for real-time joint transmit and receive antenna selection in MIMO systems. The computational complexity of exhaustive search in this problem grows exponentially with the number of transmit and receive antennas. We apply Binary Particle Swarm Optimization (BPSO) to the joint transmit and receive antenna selection problem. In addition, applying the general BPSO to joint antenna selection, we also present a specific improvement to this population-based heuristic algorithm, namely, we feed cyclically shifted initial population so that the average convergence time (the number of iterations until reaching an acceptable solution) is reduced. The proposed BPSO for joint antenna selection problem has a low computational complexity, and its effectiveness is verified through simulation results.     

基于改进PSO算法的测试数据自动生成研究

为了提高软件测试中测试数据自动生成的效率,提出了一种基于改进PSO算法的测试数据自动生成的方法。通过在标准的PSO算法中引入人工免疫的思想,保持了群体的多样性,从而有效避免标准PSO算法易陷入局部最优的问题,提高了算法全局搜索的能力,增强了算法的整体性能。实验结果表明,利用改进后的PSO算法寻找最优解所需的迭代次数和时间明显少于标准粒子群算法,生成测试数据的速度快、效率高。     

基于序列分析的僵尸网络检测模型

现有的IRC botnet检测技术不适合控制命令交互不频繁的botnet检测。为了实现小规模隐秘僵尸网络的检测,提出了一种基于序列分析的僵尸网络检测模型,对现有的被动检测技术进行补充。讨论了几种探测技术和检测算法,根据客户端响应类型选择检测算法,分析了平均检测轮数,只须观察少量的命令控制交互,能够对单个或多个IRC僵尸主机进行检测。实验结果表明,在保证误报率和漏报率的前提下该方法能在预定检测轮数内完成判定。     

动态节点质心定位改进算法

为降低无线传感器网络的定位误差,提高动态节点的定位精度和定位覆盖度,使节点定位能够应用于动态环境下,基于传统的定位算法,提出了一种新的动态节点定位改进算法。该算法通过未知节点接收、保存的分组信息来循环组成虚拟三角形,同时依靠内点测试方法来判断未知节点自身位置,最后根据质心算法来进行最终定位。将仿真结果与传统算法进行比较,结果表明,改进算法可以大大提高无线传感器网络的定位精度和覆盖度。