Novel ultra‐compact two‐dimensional waveguide‐based metasurface for electromagnetic coupling reduction of microstrip antenna array

A novel ultracompact two‐dimensional (2D) waveguide‐based metasurface is proposed herein and applied for the first time to reduce mutual coupling in antenna array for multiple‐input multiple‐output applications. The unit cell of the proposed 2D waveguide‐based metasurface is ultracompact (8.6 mm × 4.8 mm, equal to λ₀/14.2 × λ₀/25.5) mainly due to the symmetrical spiral lines etched on the ground. The metasurface exhibits a bandgap with two transmission zeros attributing to the negative permeability in the vicinity of magnetic resonance and the negative permittivity in the vicinity of electric resonance. Taking advantage of these two features, a microstrip antenna array is then designed, fabricated, and measured by embedding an 8 × 1 array of the well‐engineered 2D waveguide‐based metasurface elements between two closely spaced (9.2 mm, equal to λ₀/13.3) H‐plane coupled rectangular patches. There is good agreement between the simulated and measured results, indicating that the metasurface effectively reduces antenna mutual coupling by more than 11.18 dB and improves forward gain. The proposed compact structure has one of the highest reported decoupling efficiencies among similar periodic structures with comparable dimensions. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:789–794, 2015.     

Bright-field scanning confocal electron microscopy using a double aberration-corrected transmission electron microscope

Scanning confocal electron microscopy (SCEM) offers a mechanism for three-dimensional imaging of materials, which makes use of the reduced depth of field in an aberration-corrected transmission electron microscope. The simplest configuration of SCEM is the bright-field mode. In this paper we present experimental data and simulations showing the form of bright-field SCEM images. We show that the depth dependence of the three-dimensional image can be explained in terms of two-dimensional images formed in the detector plane. For a crystalline sample, this so-called probe image is shown to be similar to a conventional diffraction pattern. Experimental results and simulations show how the diffracted probes in this image are elongated in thicker crystals and the use of this elongation to estimate sample thickness is explored.     

Spatial and functional relationships between air conduits and blood capillaries in the pulmonary gas exchange tissue of adult and developing chickens

The documented data regarding the three-dimensional structure of the air capillaries (ACs), the ultimate sites of gas exchange in the avian lung is contradictory. Further, the mode of gas exchange, described as cross-current has not been clearly elucidated. We studied the temporal and spatial arrangement of the terminal air conduits of the chicken lung and their relationship with the blood capillaries (BCs) in embryos as well as the definitive architecture in adults. Several visualization techniques that included corrosion casting, light microscopy as well as scanning and transmission electron microscopy were used. Two to six infundibulae extend from each atrium and give rise to numerous ACs that spread centrifugally. Majority of the ACs are tubular structures that give off branches, which anastomose with their neighboring cognates. Some ACs have globular shapes and a few are blind-ending tapering tubes. During inauguration, the luminal aspects of the ACs are characterized by numerous microvillus-like microplicae, which are formed during the complex processes of cell attenuation and canalization of the ACs. The parabronchial exchange BCs, initially inaugurated as disorganized meshworks, are reoriented via pillar formation to lie predominantly orthogonal to the long axes of the ACs. The remodeling of the retiform meshworks by intussusceptive angiogenesis essentially accomplishes a cross-current system at the gas exchange interface in the adults, where BCs form ring-like patterns around the ACs, thus establishing a cross-current system. Our findings clarify the mode of gas exchange in the parabronchial mantle and illuminate the basis for the functional efficiency of the avian lung.     

不同有机物组分对膜污染影响的中试研究

采用粉末活性炭、混凝沉淀和超滤膜联用的技术对某低浊湖水进行中试研究。试验结果表明,采用的超滤膜及其工艺系统不仅能有效地去除浊度及悬浮颗粒,还可将CODMn由4.17mg/L降至3mg/L以下。试验将有机物分离为强疏水、弱疏水、极性亲水和中性亲水四种组分,研究不同组分对膜污染的影响。试验结果显示,预处理和超滤膜能有效去除疏水性和极性亲水性有机物,但对中性亲水性有机物的去除效果较差。反冲洗能有效清除累积在膜内的疏水性和极性亲水性有机物,但难以清洗中性亲水性组分。药剂清洗可有效去除中性亲水性有机物。疏水组分造成膜的可逆污染,而中性亲水组分导致膜的不可逆污染。三维荧光分析表明,造成不可逆污染的有机物主要在Ex238/Em345区域响应。     

子空间聚类在入侵检测中的应用

在高维数据聚类中,受维度效应的影响,现有的算法聚类效果不佳。在分析现有软子空间聚类算法不足的基础上,引入子空间差异的概念,结合簇内紧凑度的信息来设计新的目标优化函数,提出了一种新的k-means型软子空间聚类算海针对目前入侵检测实时性和准确性的要求,将离群点扫描技术嵌入新算法中。在KDDCup1999数据集上的试验表明,该算法能进行高效的特征选择,提高入侵检测的检测精度。     

高维数据的相似性度量研究

数据间的相似性度量是进一步分析数据集整体特性的一个重要基础。针对高维数据的相似性度量问题,提出了一种基于子空间的相似性度量方法。该方法先将高维空间进行基于网格的划分,然后在划分后的子空间内计算数据间的相似性。理论分析表明,在合理选定网格划分参数的前提下,该方法可有效减小维度灾难对高维数据相似性度量的影响。     

子空间聚类改进算法研究综述

高维数据聚类是聚类技术的难点和重点,子空间聚类是实现高维数据集聚类的有效途径。CLIQUE算法是最早提出的基于密度和网格的子空间聚类算法,自动子空间聚类算法的实用性和高效性,带来了子空间聚类算法的空前发展。深入分析CLIQUE算法的优点和局限性;介绍了一些近几年提出的子空间聚类算法,并针对CLIQUE算法的局限性作了改进,聚类的效率和精确性得到了提高;最后对子空间聚类算法的发展趋势进行了讨论。     

A new graphical visualization of n-dimensional Pareto front for decision-making in multiobjective optimization

New challenges in engineering design lead to multiobjective (multicriteria) problems. In this context, the Pareto front supplies a set of solutions where the designer (decision-maker) has to look for the best choice according to his preferences. Visualization techniques often play a key role in helping decision-makers, but they have important restrictions for more than two-dimensional Pareto fronts. In this work, a new graphical representation, called Level Diagrams, for n-dimensional Pareto front analysis is proposed. Level Diagrams consists of representing each objective and design parameter on separate diagrams. This new technique is based on two key points: classification of Pareto front points according to their proximity to ideal points measured with a specific norm of normalized objectives (several norms can be used); and synchronization of objective and parameter diagrams. Some of the new possibilities for analyzing Pareto fronts are shown. Additionally, in order to introduce designer preferences, Level Diagrams can be coloured, so establishing a visual representation of preferences that can help the decision-maker. Finally, an example of a robust control design is presented - a benchmark proposed at the American Control Conference. This design is set as a six-dimensional multiobjective problem.     

Maximal versus strong solution to algebraic Riccati equations arising in infinite Markov jump linear systems

We deal with a perturbed algebraic Riccati equation in an infinite dimensional Banach space which appears, for instance, in the optimal control problem for infinite Markov jump linear systems (from now on iMJLS). Infinite or finite here has to do with the state space of the Markov chain being infinite countable or finite (see, e.g., [M.D. Fragoso, J. Baczynski, Optimal control for continuous time LQ—problems with infinite Markov jump parameters, SIAM J. Control Optim. 40(1) (2001) 270–297]). By using a certain concept of stochastic stability (a sort of L₂-stability), we have proved in [J. Baczynski, M.D. Fragoso, Maximal solution to algebraic Riccati equations linked to infinite Markov jump linear systems, Internal Report LNCC, no. 6, 2006] existence (and uniqueness) of maximal solution for this class of equations. As it is noticed in this paper, unlike the finite case (including the linear case), we cannot guarantee anymore that maximal solution is a strong solution in this setting. Via a discussion on the main mathematical hindrance behind this issue, we devise some mild conditions for this implication to hold. Specifically, our main result here is that, under stochastic stability, along with a condition related with convergence in the infinite dimensional scenario, and another one related to spectrum—weaker than spectral continuity—we ensure the maximal solution to be also a strong solution. These conditions hold trivially in the finite case, allowing us to recover the result of strong solution of [C.E. de Souza, M.D. Fragoso, On the existence of maximal solution for generalized algebraic Riccati equations arising in stochastic control, Systems Control Lett. 14 (1990) 233–239] set for MJLS. The issue of whether the convergence condition is restrictive or not is brought to light and, together with some counterexamples, unveil further differences between the finite and the infinite countable case.     

一种适合于复杂电磁环境下短波跳频信号的检测方法

分析短波波段复杂电磁环境下跳频信号检测存在的难点,并根据短波通信信号的特点,提出一种时间、频谱和幅度关联的检测方法,称之为时频幅三维关联法.文章主要结合商空间粒度分析理论,提出改进的覆盖聚类算法,并对截获的海量复杂数据进行预处理,消除了噪声,然后运用时频幅三维关联法,排除定频信号、突发信号等.实验结果说明该方法能够有效地检测出跳频信号,验证了方法的实效性.