Characteristics of microwave filters based on microstrip photonic bandgap ring structures

We study the characteristics of microstrip ring exhibiting photonic band gap properties. Since the stop band is caused by the reflection of electromagnetic waves at the narrow gap introduced in the ring, the geometry of the ring can influence on the characteristics of stop band. The center frequency of the stop band is determined mainly by the outer ring radius when the line width of the circular ring is rather narrow. But it is determined mainly by the mean ring radius when the ring is not a circular form or the line width of circular ring is wide. The frequency range of the stop band can be varied by a reactive component mounted on the gap. The presence of capacitor (inductor) on the gap decreases (increases) the center frequency and the frequency range of the stop band. Moreover, the stop band can be widened by modifying the geometry of ring. These properties can be useful in the applications to the compact microwave circuits, tunable filters and microwave switches.     

Protograph bit-interleaved coded modulation: A bandwidth-efficient design paradigm for 6G wireless communications

Bit-interleaved coded modulation (BICM) has attracted considerable attention from the research community in the past three decades, because it can achieve desirable error performance with relatively low implementation complexity for a large number of communication and storage systems. By exploiting the iterative demapping and decoding (ID), the BICM is able to approach capacity limits of coded modulation over various channels. In recent years, protograph low-density parity-check (PLDPC) codes and their spatially-coupled (SC) variants have emerged to be a pragmatic forward-error-correction (FEC) solution for BICM systems due to their tremendous error-correction capability and simple structures, and found widespread applications such as deep-space communication, satellite communication, wireless communication, optical communication, and data storage. This article offers a comprehensive survey on the state-of-the-art development of PLDPC-BICM and its innovative SC variants over a variety of channel models, e.g., additive white Gaussian noise (AWGN) channels, fading channels, Poisson pulse position modulation (PPM) channels, and flash-memory channels. Of particular interest is code construction, constellation shaping, as well as bit-mapper design, where the receiver is formulated as a serially-concatenated decoding framework consisting of a soft-decision demapper and a belief-propagation decoder. Finally, several promising research directions are discussed, which have not been adequately addressed in the current literature.     

Quantitative investigation of resolution increase of free-flow electrophoresis via simple interval sample injection and separation

Interval free‐flow zone electrophoresis (FFZE) has been used to suppress sample band broadening greatly hindering the development of free‐flow electrophoresis (FFE). However, there has been still no quantitative study on the resolution increase of interval FFZE. Herein, we tried to make a comparison between bandwidths in interval FFZE and continuous one. A commercial dye with methyl green and crystal violet was well chosen to show the bandwidth. The comparative experiments were conducted under the same sample loading of the model dye (viz. 3.49, 1.75, 1.17, and 0.88 mg/h), the same running time (viz. 5, 10, 15, and 20 min), and the same flux ratio between sample and background buffer (= 10.64 × 10^?3). Under the given conditions, the experiments demonstrated that (i) the band broadening was evidently caused by hydrodynamic factor in continuous mode, and (ii) the interval mode could clearly eliminate the hydrodynamic broadening existing in continuous mode, greatly increasing the resolution of dye separation. Finally, the interval FFZE was successfully used for the complete separation of two‐model antibiotics (herein pyoluteorin and phenazine‐1‐carboxylic acid coexisting in fermentation broth of a new strain Pseudomonas aeruginosa M18), demonstrating the feasibility of interval FFZE mode for separation of biomolecules.     

Nonparametric Approach to Analysis of Space-Time Data on Earthquake Occurrences

Abstract

As an alternative to traditional, parametric approaches, we suggest nonparametric methods for analyzing spatial and temporal data on earthquake occurrences. Nonparametric techniques are particularly adaptive to anomalous behavior in the data and provide a new way of accessing a variety of different types of information about the way in which both intensity and magnitude of events evolve in time. They can be employed to estimate the spatial trajectory of event clusters as a function of time, and to define quiescent and active periods. The latter application suggests new approaches to forecasting high magnitude events. Our methods are founded on multivariate techniques for curve and surface estimation, particularly in contexts where curves or surfaces are unbounded at points or along lines.     

Nonparametric Estimation of Hazard Rate Under the Constraint of Monotonicity

This article shows how to smoothly “monotonize” standard kernel estimators of hazard rate, using bootstrap weights. Our method takes a variety of forms, depending on choice of kernel estimator and on the distance function used to define a certain constrained optimization problem. We confine attention to a particularly simple kernel approach and explore a range of distance functions. It is straightforward to reduce “quadratic” inequality constraints to “linear” equality constraints, and so our method may be implemented using little more than conventional Newton–Raphson iteration. Thus, the necessary computational techniques are very familiar to statisticians. We show both numerically and theoretically that monotonicity, in either direction, can generally be imposed on a kernel hazard rate estimator regardless of the monotonicity or otherwise of the true hazard rate. The case of censored data is easily accommodated. Our methods have straightforward extension to the problem of testing for monotonicity of hazard rate, where the distance function plays the role of a test statistic.     

Correction of chemical shift misregistration by images from two different bandwidths

One major effect caused by the different chemical shift frequencies of water and fat is the misregistration between the two components in MR images. Methods to correct misregistration are required in clinical MRI for accurate localization and artifact reduction. One of the methods uses the images scanned at opposite readout gradients to separate water and fat signal in the k-space. Its signal-to-noise ratio (SNR) achieves maximum when misregistration is around 0.9 pixels and deteriorates rapidly as the misregistration gets larger. In this work, we proposed a method to correct the chemical shift misregistration by using two data sets acquired at two different bandwidths. It is more generalized and flexible than the former method of opposite readout gradients and covers the former one as a special case. In both simulation and experiment, the new method is proved to be capable of correcting large chemical shift misregistration and maintain a good SNR.     

Characterization of Er-doped fluoride glass ceramics waveguides containing LaF3 nanocrystals

Highly Er³⁺-doped fluoride glass ceramics planar waveguides containing LaF₃ nanocrystals have been fabricated by physical vapor deposition (PVD). The solubility of Er³⁺ in the segregated nanocrystals can reach 30 mol% which is much larger than the value found in LaF₃-oxide glass ceramics. A quantitative analysis of the photoluminescence of the 1.54 μm emission band of Er³⁺ ions has demonstrated that erbium ions are partitioned in both crystals and vitreous phase. The short lifetime (2.2 ms) measured for erbium incorporated in LaF₃ crystal lattice is a consequence of concentration quenching while the lifetime is close to 10 ms in the glassy phase. The emission bandwidth has been found to be greater than that of the precursor glass (71 nm at the half-height width). The high Er³⁺ concentration and spectral width could make this nanostructured fluoride material suitable for planar amplifier in the C telecommunication band.     

平显全息组合镜的衍射特性研究

给出了平显用全息组合镜的衍射效率、水平选择角和带宽的实验测量结果,并运用耦合波理论进行了分析.测试结果表明,DCG是一种制作体积全息图的优良材料,由其制作的全息组合镜具有优良的透过率和衍射特性.     

基于波段带宽的谱段测温法的测温范围分析

基于窄波段内普适性的线性发射率模型,将三波长（单色）辐射温度测量拓展到谱段辐射温度测量。在谱段测量中,为实现非失真的有效测量,文中结合传感器的动态范围及最低灵敏度等特性参数 ,考虑多路信号的耦合关系,讨论了有效温度测量的相应限制条件。从而针对具有已知辐射物性的被测物体,通过数值模拟给出谱段测温的有效测温范围相对于传感器的波段带宽的变化趋势。理论上明确 了实现有效温度范围测量对传感器的波段带宽的要求。文章分析将为辐射传感器的设计提供必要的理论指导。     

Causality study on a feedforward active noise control headset with different noise coming directions in free field

A systematic analysis is proposed to predict the performance of a typical feedforward single channel ANC headset in terms of the delay, especially the non-causal delay caused by different noise coming directions. First, the performance of a non-causal feedforward system for a band-limited noise is analyzed by using a simplified pure delay model, where it is found that the noise reduction bandwidth is narrowed and the maximum noise reduction is decreased with the increase of the non-causal delay. Second, a systematic method is developed, which can be used to predict the system performance with measured primary and secondary path transfer functions in most practical sound fields and to study the effects of the control filter length and the path delay on the performance. Then, the causality of a typical feedforward active noise control headset with the primary source at 0° and 90° positions in an anechoic chamber is analyzed, and the performance for the two locations predicted by the systematic analysis is shown in good agreements with the experiment results. Finally, an experiment of a typical feedforward active noise control headset in a reverberation chamber is carried out, which shows the validity of the proposed systematic analysis for other more practical sound fields.