Analysis of dynamic of two-phase flow in small channel based on phase space reconstruction combined with data reduction sub-frequency band wavelet

A new method of nonlinear analysis is established by combining phase space reconstruction and data reduction sub-frequency band wavelet. This method is applied to two types of chaotic dynamic systems(Lorenz and Rssler) to examine the anti-noise ability for complex systems. Results show that the nonlinear dynamic system analysis method resists noise and reveals the internal dynamics of a weak signal from noise pollution. On this basis, the vertical upward gas–liquid two-phase flow in a 2 mm × 0.81 mm small rectangular channel is investigated. The frequency and energy distributions of the main oscillation mode are revealed by analyzing the time–frequency spectra of the pressure signals of different flow patterns. The positive power spectral density of singular-value frequency entropy and the damping ratio are extracted to characterize the evolution of flow patterns and achieve accurate recognition of different vertical upward gas–liquid flow patterns(bubbly flow:100%, slug flow: 92%, churn flow: 96%, annular flow: 100%). The proposed analysis method will enrich the dynamics theory of multi-phase flow in small channel.

Reconstruction of sub cross-correlation cancellation technique for unambiguous acquisition of BOC(kn, n) signals

In order to solve the problem of ambiguous acquisition of BOC signals caused by its property of multiple peaks,an unambiguous acquisition algorithm named reconstruction of sub cross-correlation cancellation technique(RSCCT)for BOC(kn,n)signals is proposed.In this paper,the principle of signal decomposition is combined with the traditional acquisition algorithm structure,and then based on the method of reconstructing the correlation function.The method firstly gets the sub-pseudorandom noise(PRN)code by decomposing the local PRN code,then uses BOC(kn,n)and the sub-PRN code cross-correlation to get the sub cross-correlation function.Finally,the correlation peak with a single peak is obtained by reconstructing the sub cross-correlation function so that the ambiguities of BOC acquisition are removed.The simulation shows that RSCCT can completely eliminate the side peaks of BOC(kn,n)group signals while maintaining the narrow correlation of BOC,and its computational complexity is equivalent to sub carrier phase cancellation(SCPC)and autocorrelation side-peak cancellation technique(ASPeCT),and it reduces the computational complexity relative to BPSK-like.For BOC(n,n),the acquisition sensitivity of RSCCT is 3.25 dB,0.81 dB and 0.25 dB higher than binary phase shift keying(BPSK)-like,SCPC and ASPeCT at the acquisition probability of 90%,respectively.The peak to average power ratio is 1.91,3.0 and 3.7 times higher than ASPeCT,SCPC and BPSK-like at SNR=–20 dB,respectively.For BOC(2n,n),the acquisition sensitivity of RSCCT is 5.5 dB,1.25 dB and 2.69 dB higher than BPSK-like,SCPC and ASPeCT at the acquisition probability of 90%,respectively.The peak to average power ratio is 1.02,1.68 and 2.12 times higher than ASPeCT,SCPC and BPSK-like at SNR=–20 dB,respectively.

Common (π,π) Band Folding and Surface Reconstruction in Fe As-Based Superconductors

High resolution angle-resolved photoemission spectroscopy(ARPES)measurements are carried out on CaKFe_4 As_4,KCa_2 Fe_4 As_4 F_2 and(Ba_(0.6)K_(0.4))Fe_2 As_2 superconductors.Clear evidence of band folding between the Brillouin zone center and corners with a(π,π)wave vector has been found from the measured Fermi surface and band structures in all the three kinds of superconductors.A dominant √2×√2 surface reconstruction is observed on the cleaved surface of CaKFe_4As_4 by scanning tunneling microscopy(STM)measurements.We propose that the commonly observed √2×√2 reconstruction in the FeAs-based superconductors provides a general scenario to understand the origin of the(π,π)band folding.Our observations provide new insights in understanding the electronic structure and superconductivity mechanism in iron-based superconductors.

OMP-BASED MULTI-BAND SIGNAL RECONSTRUCTION FOR ECOLOGICAL SOUNDS RECOGNITION

The paper proposes a new method of multi-band signal reconstruction based on Orthogonal Matching Pursuit(OMP),which aims to develop a robust Ecological Sounds Recognition(ESR)system.Firstly,the OMP is employed to sparsely decompose the original signal,thus the high correlation components are retained to reconstruct in the first stage.Then,according to the frequency distribution of both foreground sound and background noise,the signal can be compensated by the residual components in the second stage.Via the two-stage reconstruction,high non-stationary noises are effectively reduced,and the reconstruction precision of foreground sound is improved.At recognition stage,we employ deep belief networks to model the composite feature sets extracted from reconstructed signal.The experimental results show that the proposed approach achieved superior recognition performance on 60 classes of ecological sounds in different environments under different Signal-to-Noise Ratio(SNR),compared with the existing method.

Sub-band ICA with selection criterion for BBS of dependent mages

Because of the correlation of images,the efficiency of the standard ICA is not satisfied in the blind source separation (BSS) of image.Therefore,a new method of sub-band ICA with selection criterion is proposed for this problem.Firstly,the sub-bands of the new method are made up of the wavelet packets (WP) coefficients.Secondly,the selection criterion of the new method is a combination of the mutual information (MI),kurtosis and sparsity.One sub-band or a sub-bands group obtained from the new method are more suitable as the inputs parameters of the algorithm of ICA than mixed images.The new method has been applied into the BSS of partially dependent images and highly dependent images successfully.According to the separation experiments,it is shown that the separation efficacy of the new method is more accurate and robust.

Feature Conditioning Based on DWT Sub-Bands Selection on Proposed Channels in BCI Speller

In this paper, we present a novel and efficient scheme for detection of P300 component of the event-related potential in the Brain Computer Interface (BCI) speller paradigm that needs significantly less EEG channels and uses a minimal subset of effective features. Removing unnecessary channels and reducing the feature dimension resulted in lower cost and shorter time and thus improved the BCI implementation. The idea was to employ a proper method to optimize the number of channels and feature vectors while keeping high accuracy in classification performance. Optimal channel selection was based on both discriminative criteria and forward-backward investigation. Besides, we obtained a minimal subset of effective features by choosing the discriminant coefficients of wavelet decomposition. Our algorithm was tested on dataset II of the BCI competition 2005. We achieved 92% accuracy using a simple LDA classifier, as compared with the second best result in BCI 2005 with an accuracy of 90.5% using SVM for classification which required more computation, and against the highest accuracy of 96.5% in BCI 2005 that used SVM and much more channels requiring excessive calculations. We also applied our proposed scheme on Hoffmann’s dataset to evaluate the effectiveness of channel reduction and achieved acceptable results.

Tunning the Band Gap of 1T’-WTe2 by Uniaxial Strain

The QSH edge channels can be used to connect dissipationless nanoelectronic devices, when the topological edge states and the bulk states have the perfectly spaced. But the monolayer 1T’-WTe2 bulk state is metallic nature, with edge channel lengths around 100 nm, which hinders its further study. By simulating the different terminational edge states, using the GGA-1/2 method to calculate, we found a stable terminational edge state. And under strain engineering, fixed the a-axis, the band gap gradually increases with the b-axis tensile. When the tensile to 2.9%, the band gap increases to 245 meV. It greatly improves the application of 1T’-WTe2. During the phase transition of the material from half-metal to insulator, the topology of edge states remains unchanged, showing strong robustness. Thus introducing strain can make 1T’-WTe2 a suitable material for fundamental research or topological electronic devices.

Video Compression USING a New Active Mesh Based Motion Compensation Algorithm in Wavelet Sub-Bands

In this paper, a new mesh based algorithm is applied for motion estimation and compensation in the wavelet domain. The first major contribution of this work is the introduction of a new active mesh based method for motion estimation and compensation. The proposed algorithm is based on the mesh energy minimization with novel sets of energy functions. The proposed energy functions have appropriate features, which improve the accuracy of motion estimation and compensation algorithm. We employ the proposed motion estimation algorithm in two different manners for video compression. In the first approach, the proposed algorithm is employed for motion estimation of consecutive frames. In the second approach, the algorithm is applied for motion estimation and compensation in the wavelet sub-bands. The experimental results reveal that the incorporation of active mesh based motion-compensated temporal filtering into wavelet sub-bands significantly improves the distortion performance rate of the video compression. We also use a new wavelet coder for the coding of the 3D volume of coefficients based on the retained energy criteria. This coder gives the maximum retained energy in all sub-bands. The proposed algorithm was tested with some video sequences and the results showed that the use of the proposed active mesh method for motion compensation and its implementation in sub-bands yields significant improvement in PSNR performance.

Information Hiding Method Based on Block DWT Sub-Band Feature Encoding

For realizing of long text information hiding and covert communication, a binary watermark sequence was obtained firstly from a text file and encoded by a redundant encoding method. Then, two neighboring blocks were selected at each time from the Hilbert scanning sequence of carrier image blocks, and transformed by 1-level discrete wavelet transformation (DWT). And then the double block based JNDs (just noticeable difference) were calculated with a visual model. According to the different codes of each two watermark bits, the average values of two corresponding detail sub-bands were modified by using one of JNDs to hide information into carrier image. The experimental results show that the hidden information is invisible to human eyes, and the algorithm is robust to some common image processing operations. The conclusion is that the algorithm is effective and practical.

基于FullSubNet的单通道实时语音增强算法

针对语音实时通信场景,本文提出一种基于循环神经网络的单通道实时语音增强方案。通过模型层面融合全频带和子频带特征以同时捕获全频带信息和局部语谱特征,并且基于循环神经网络的内在时序性,实现了按帧推理实时输出的要求。实验结果显示,在DNS-Challenge InterSpeech 2020的测试集上,本文按帧输出方式的模型可以取得2.85的pesq值。在系统固定延时32 ms的情况下,使用NVidia GeForce RTX 3060 GPU处理16 ms一帧长度的数据耗时1.5 ms;如果将模型转为onnx格式,在Intel i7@2.7GHz CPU上处理一帧数据耗时3.8 ms。

面向Sub 6G终端设备的三频天线设计

为满足我国现行5G通信要求,设计了一款工作在三个频段的终端设备天线。该天线采用平面单极子结构,辐射贴片上设置两个枝节实现高频和中频覆盖,并对中频长枝节进行了Z型弯折,高频枝节采用了L型弯折。同时在地板上增加了一个倒L型枝节,谐振在更低频段。天线刻蚀在FR4介质基板上,对天线进行了仿真加工与测试。结果表明,天线尺寸为25 mm×25 mm×0.8 mm,工作频段为2.38~2.68 GHz(共300 MHz),3.25~3.63 GHz(共380 MHz),以及4.45~5.26 GHz(共810 MHz),在三个中心频点处的增益分别为1.51,2.77和3.55 dBi。三个频点处的方向图近似圆形,具有较好的全向性。该三个频段能够覆盖我国目前为移动运营商分配的Sub 6G中n41/n78/n79频段,天线能够满足Sub 6G终端设备的通信需求。

基于双向Sub-G芯片的无线MESH软件系统开发

目前物联网智能设备种类繁多,但设备性能缺乏统一标准,对多物联网终端互联与控制造成了一定困难。因此提出MCMI与双路径并发的自动跳频Mesh组网方案,结合用户控制端,设计基于双向Sub-G的无线MESH智能家居控制系统。Mesh结构为3层终端间通信,第一层与第二层构成星形拓扑,第二层与第三层构成多连接树形,较之一般Mesh结构,更加简洁且降低了硬件要求。通过MCMI与双路径并发的信号传输方式,消除了无线网络信道干扰,信号稳定性提高50%。为应对各厂商协议不统一难以成为一个完整系统的问题,设计上层专有协议以克服技术差异化。该系统经过测试,运行稳定、性能优秀、可信赖度高,并且协议还预留自定义接口,拥有一定的拓展能力。

High Sensitivity of Porous Cu-Doped SnO2 Thin Films to Methanol

Porous Cu-doped SnO2 thin films were synthesized by the sol-gel dip-coating method for enhancing methanol sensing performance. The effect of Cu doping concentration on the SnO2 sensibility was investigated. XRD data confirm that the fabricated SnO2 films are polycrystalline with tetragonal rutile crystal structure. AFM and SEM micrographs confirmed the roughness and the porosity of SnO2 surface, respectively. UV-Vis spectrum shows that SnO2 thin films exhibit high transmittance in the visible region ~95%. The band gap (3.80 - 3.92 eV) and the optical thickness (893 - 131 nm) of prepared films were calculated from transmittance data. The sensing results demonstrate that SnO2 films have a high sensitivity and a fast response to methanol. In particular, 3% Cu-SnO2 films have a higher sensitivity (98%), faster response (10-2 s) and shorter recovery time (18 s) than other films.

Sub-1G和2.4G超低功耗双频段无线系统设计与应用

介绍了一种基于CC1350的超低功耗双频段无线系统设计。该系统除了具有灵活的供电模式外,还具有很低的有源RF电流消耗和系统电流消耗,既支持了使用小型纽扣电池供电的远距离应用和各种信号采集应用,还保证了卓越的电池使用寿命。本文所述系统可以被集成到另一个系统中,并展示了如何将设备通过无线网络连接到互联网云的过程。

Required CIGS and CIGS/Mo Interface Properties for High-Efficiency Cu(In, Ga)Se<SUB>2</SUB>Based Solar Cells

In this work, we have modeled and simulated the electrical performance of CIGS thin-film solar cell using one-dimensional simulation software (SCAPS-1D). Starting from a baseline model that reproduced the experimental results, the properties of the absorber layer and the CIGS/Mo interface have been explored, and the requirements for high-efficiency CIGS solar cell were proposed. Simulation results show that the band-gap, acceptor density, defect density are crucial parameters that affect the performance of the solar cell. The best conversion efficiency is obtained when the absorber band-gap is around 1.2 eV, the acceptor density at 1016 cm−3 and the defect density less than 1014 cm−3. In addition, CIGS/Mo interface has been investigated. It appears that a thin MoSe2 layer reduces recombination at this interface. An improvement of 1.5 to 2.5 mA/cm2 in the current density (Jsc) depending on the absorber thickness is obtained.

Comprehensive Analysis of CuIn_1-xGa_xSe₂Based Solar Cells with Zn_1-yMg_yO Buffer Layer

The development of cadmium-free CIGS solar cells with high conversion efficiency is crucial due to the toxicity of cadmium. Zinc-based buffer layers seem to be the most promising. In this paper, a numerical analysis using SCAPS-1D software was used to explore the Zn(Mg,O) layer as an alternative to the toxic CdS layer. The effect of several properties such as thickness, doping, Mg concentration of the Zn(Mg,O) layer on the current-voltage parameters was explored and their optimal values were proposed. The simulation results reveal that the optimal value of the ZMO layer thickness is approximately 40 nm, the doping at 1017 cm-3 and an Mg composition between 0.15 and 0.2. In addition, the effect of Gallium (Ga) content in the absorber as well as the Zn(Mg,O)/CIGS interface properties on the solar cell’s performance was examined. The results show that contrary to the CdS buffer layer, the best electrical characteristics of the ZMO/CIGS heterojunction are obtained using a Ga-content equal to 0.4 and high interface defect density or unfavorable band alignment may be the causes of poor performances of Zn(Mg,O)/CIGS solar cells in the case of low and high Mg-contents.

基于特征值的动态数字信道化子带检测算法

动态数字信道化接收结构通过检测所有子带,判断信号是否存在,为综合滤波器组处理提供依据,因此子带检测在接收结构中起着关键作用。针对传统检测算法存在低信噪比(signal-to-noise ratio,SNR)下检测性能不高的问题,依据随机矩阵理论,提出了基于最大最小特征值之差与平均特征值之比的检测算法,利用平均特征值和最小特征值的极限分布规律来推导算法的检测门限。其次,根据所有子带数据获取的特征值信息对所提算法进行了优化。最后,在动态数字信道化接收结构中,分析不同因素下算法的性能,表明了所提算法能够克服低SNR的影响,子带检测的性能更好。

匹配控制构网型直驱风电场经LCC-HVDC送出系统的次同步振荡特性及机理分析

在“沙戈荒”地区风电经电网换相高压直流输电(line-commutated-converter based high voltage direct current,LCC-HVDC)外送系统中,采用基于匹配控制的构网型直驱风机(matching control permanent magnet synchronous generator,MC-PMSG)可以提升送端电网的稳定性。然而,当MC-PMSG位于LCC-HVDC整流站近区时,系统的次同步振荡(sub-synchronous oscillation,SSO)特性尚未明确。针对上述问题,该文采用模块化建模法建立MC-PMSG经LCC-HVDC送出系统的小信号模型,通过特征值法研究MC-PMSG与LCC-HVDC对系统各SSO模态的参与情况与系统运行方式变化对次同步振荡阻尼特性的影响,通过阻尼重构法分析LCC-HVDC并网对系统振荡风险的影响机理。研究结果表明,系统存在匹配控制型风机主导、LCC-HVDC参与的SSO模态,MC-PMSG与LCC-HVDC间的次同步交互作用为SSO提供负阻尼;当混合型风电场中的MC-PMSG占比增大、MC-PMSG风电场容量增大或短路比减小、LCC-HVDC定电流控制器的比例系数增大、风机网侧换流控制器外环积分系数减小、直流电容增大时,SSO阻尼增大。通过PSCAD/EMTDC电磁暂态仿真证明理论分析结果的有效性。

F波段宽带分谐波混频器设计

针对大带宽、低损耗的应用场景,研制了一款覆盖整个F波段(90~140GHz)的分谐波混频器。混频器采用国产分立二极管器件,以波导-石英混合集成电路形式实现。混频电路中所涉及的耦合探针、紧凑谐振滤波等结构均集成于厚度为127μm的单片石英基片上,通过设计高鲁棒性的直流接地回路以及紧凑谐振滤波单元,实现了整个石英基片的紧凑化及宽带混频特性。测试结果表明,所设计的分谐波混频器在12dBm本振功率激励下,可在90~140GHz频率范围内实现12~16d B的单边带变频损耗,本振和中频工作带宽分别为45~70GHz以及DC~15GHz,可以用于频谱扩展测量系统中。

基于子带谐波一致性的语音转换反取证框架研究

语音转换任务指的是在保持语言内容不变的情况下,将一个说话者的声音身份转换为另一个说话者.然而现有工作很少考虑针对音频取证机器分类模型进行抗检测研究,转换音频极容易被取证模型所识别.本文提出了一种具有3个子带频谱鉴别器设计的语音转换反取证框架HADV-GAN,其合成音频在具有高保真度的前提下,对语音欺骗取证模型具有反取证能力.此外,HADV-GAN无需训练额外的声码器,可以直接以原始音频波形作为输入,并以声学特征重建语音,因此可以避免使用声码器所导致的特征不匹配问题.实验结果表明,本文所提出的方法在3种主流的语音欺骗取证模型LFCC-GMM、MCG-Res2Net以及AASIST上,对比基线模型NVC-Net,在合成音频质量相当的条件下,拥有更好的反取证能力.