Algebraic foundations of split hypercomplex nonlinear adaptive filtering

A split hypercomplex learning algorithm for the training of nonlinear finite impulse response adaptive filters for the processing of hypercomplex signals of any dimension is proposed. The derivation strictly takes into account the laws of hypercomplex algebra and hypercomplex calculus, some of which have been neglected in existing learning approaches (e.g., for quaternions). Already in the case of quaternions, we can predict improvements in performance of hypercomplex processes. The convergence of the proposed algorithms is rigorously analyzed. Copyright © 2012 John Wiley & Sons, Ltd.     

X射线相衬成像技术应用于高能量密度物理条件下内爆靶丸诊断

内爆压缩过程中多层球壳靶丸变化规律的研究是惯性约束聚变的核心内容. 利用相衬成像技术可以提高低Z材料分界面成像衬度的特点在神光Ⅱ大型激光装置上开展了相关研究. 实验通过激光打Ti靶和针孔点背光的方式产生4.75 keV的X射线微点源, 针对内爆压缩过程中的靶丸样品投影成像获得了清晰的多层球壳靶丸图像, 空间分辨率优于10 μm.同时利用一维流体力学数值模拟程序分析了球壳运动的过程, 实验结果与数值模拟结果符合较好.表明了X射线相衬成像技术在高能量密度物理环境下仍然能够提高低Z材料分界面的衬度,获得高质量的物理图像,能够广泛应用于可控聚变能源、 天体物理等前沿科学领域.     

飞秒激光用多层介质膜脉宽压缩光栅的设计

以薄膜光学的干涉理论和衍射光学的傅里叶模式理论为基础，给出了0.8μm飞秒激光器用多层介质膜脉宽压缩光栅的理论设计；设计采用H3L(HL)^9H0.5L2.4H的多层介质膜为基底，当刻蚀后表面浮雕结构的占宽比为0.35，线密度为1480线/mm，槽深为0.2μm，顶层HfO₂的剩余厚度为0.15μm时，对于Littrow角度(36.7°)和TE波模式入射的衍射光栅其-1级衍射效率达到95％以上. 关键词： 飞秒激光 脉宽压缩光栅 多层介质膜     

A non-horizontal multi-layer numerical model for the flow in natural rivers

A non-horizontal multi-layer element model is developed for the simulation for the flow in natural rivers. Either Cartesian coordinates or sigma coordinates will experience difficulties in dealing with the water surface and irregular bed topography of natural rivers. To create the surface-fitting and non-deformed cells, the newly developed model divides the water column into several layers with non-horizontal interfaces which are nearly parallel to the water surface. The irregular bed topography is also represented by the layered integration between non-horizontal interfaces. Two case studies for the flow in a straight channel and the flow in an S-shaped meander channel are conducted with good agreement between the numerical predictions and the analytical or experimental results. The model is further applied for the investigation of the flow in a 12-km-long and 3.46-m-drop reach of the Yangtze River with the water surface evaluation and the stream-wise velocity satisfactory accordance with the observed data.     

色散吸收一维光学系统中光场量子起伏的功率谱

利用格林函数方法量子化色散吸收介质中的电磁场,针对由三层色散吸收介质组成的一维光学系统,研究其中光场的量子理论,借助起伏一耗散定理给出色散吸收介质光腔中光场量子起伏的功率谱,并通过数值计算结果分析和讨论介质的色散吸收性质对光学器件工作性能的影响。结果表明,系统的工作状态与所选光场频率密切相关,并且每一区域中介质的色散吸收性不但影响自身区域的电场起伏功率谱,而且明显地连带另一侧介质中电场起伏功率谱的变化行为。此结果对于研究复杂的介质分布与结构体系在光通信、现代光学工程、微波技术等领域中的实际应用有着重要的指导意义。     

直流磁控溅射镀膜实验条件的选择

介绍一台改制的直流以磁控溅射镀膜机用于溅射镀膜实验,选择实验条件,观察实验现象,得到多层薄膜。     

多层膜界面结构探测技术

分别以丙醇锆和正硅酸乙酯为原料,采用溶胶-凝胶工艺制备了性能稳定的ZrO2和Si O2溶胶。用旋转镀膜法在K9玻璃上分别制备了Si O2单层膜、ZrO2单层膜和ZrO2/Si O2/ZrO2三层膜。采用椭偏仪测量薄膜的厚度与折射率,用紫外-可见分光光度计测量了薄膜的透过率,利用TFCalc_Demo模系设计软件,采用三层理论模型对薄膜的透过率进行模拟,用扫描电镜(SEM)观察了三层膜的断面结构,用X射线光电子能谱仪(XPS)测量了薄膜的成分随深度方向的变化,进一步验证了ZrO2/Si O2/ZrO2三层膜之间的渗透关系,同时对多层膜的界面结构探测方法起到了借鉴作用。     

Polar interface and surface optical vibration spectra in multi-layer wurtzite quantum wires： transfer matrix method

The polar interface optical （IO） and surface optical （SO） phonon modes and the corresponding Froehlich electron phonon-interaction Hamiltonian in a freestanding multi-layer wurtzite cylindrical quantum wire （QWR） are derived and studied by employing the transfer matrix method in the dielectric continuum approximation and Loudon＇s uniaxial crystal model. A numerical calculation of a freestanding wurtzite GaN/AlN QWR is performed. The results reveal that for a relatively large azimuthal quantum number m or wave-number kz in the free z-direction, there exist two branches of IO phonon modes localized at the interface, and only one branch of SO mode localized at the surface in the system. The degenerating behaviours of the IO and SO phonon modes in the wurtzite QWR have also been clearly observed for a small kz or m. The limiting frequency properties of the IO and SO modes for large kz and m have been explained reasonably from the mathematical and physical viewpoints. The calculations of electron-phonon coupling functions show that the high-frequency IO phonon branch and SO mode play a more important role in the electron phonon interaction.     

Active Online Learning in the Binary Perceptron Problem

The binary perceptron is the simplest artificial neural network formed by N input units and one output unit, with the neural states and the synaptic weights all restricted to ±1 values. The task in the teacher-student scenario is to infer the hidden weight vector by training on a set of labeled patterns. Previous efforts on the passive learning mode have shown that learning from independent random patterns is quite inefficient. Here we consider the active online learning mode in which the student designs every new Ising training pattern. We demonstrate that it is mathematically possible to achieve perfect(error-free) inference using only N designed training patterns, but this is computationally unfeasible for large systems. We then investigate two Bayesian statistical designing protocols, which require 2.3N and 1.9N training patterns, respectively, to achieve error-free inference. If the training patterns are instead designed through deductive reasoning, perfect inference is achieved using N + log_2N samples. The performance gap between Bayesian and deductive designing strategies may be shortened in future work by taking into account the possibility of ergodicity breaking in the version space of the binary perceptron.     

Bispectral Analysis of Heart Rate Variability to Characterize and Help Diagnose Pediatric Sleep Apnea

Pediatric obstructive sleep apnea (OSA) is a breathing disorder that alters heart rate variability (HRV) dynamics during sleep. HRV in children is commonly assessed through conventional spectral analysis. However, bispectral analysis provides both linearity and stationarity information and has not been applied to the assessment of HRV in pediatric OSA. Here, this work aimed to assess HRV using bispectral analysis in children with OSA for signal characterization and diagnostic purposes in two large pediatric databases (0–13 years). The first database (training set) was composed of 981 overnight ECG recordings obtained during polysomnography. The second database (test set) was a subset of the Childhood Adenotonsillectomy Trial database (757 children). We characterized three bispectral regions based on the classic HRV frequency ranges (very low frequency: 0–0.04 Hz; low frequency: 0.04–0.15 Hz; and high frequency: 0.15–0.40 Hz), as well as three OSA-specific frequency ranges obtained in recent studies (BW1: 0.001–0.005 Hz; BW2: 0.028–0.074 Hz; BWRes: a subject-adaptive respiratory region). In each region, up to 14 bispectral features were computed. The fast correlation-based filter was applied to the features obtained from the classic and OSA-specific regions, showing complementary information regarding OSA alterations in HRV. This information was then used to train multi-layer perceptron (MLP) neural networks aimed at automatically detecting pediatric OSA using three clinically defined severity classifiers. Both classic and OSA-specific MLP models showed high and similar accuracy (Acc) and areas under the receiver operating characteristic curve (AUCs) for moderate (classic regions: Acc = 81.0%, AUC = 0.774; OSA-specific regions: Acc = 81.0%, AUC = 0.791) and severe (classic regions: Acc = 91.7%, AUC = 0.847; OSA-specific regions: Acc = 89.3%, AUC = 0.841) OSA levels. Thus, the current findings highlight the usefulness of bispectral analysis on HRV to characterize and diagnose pediatric OSA.