基于 MPDE-EEMD 及自适应共振解调的轴承故障特征提取方法

针对滚动轴承振动信号具有非线性、非平稳性和非高斯性,并且故障特征往往淹没于系统噪声之中而难于识别的问题, 提出了以多种群差分进化(multiple population differential evolution, MPDE) 算法来改进集合经验模式分解( ensemble empirical mode decomposition, EEMD) 的 MPDE-EEMD 消噪方法,并与自适应共振解调技术( adaptive resonance demodulation technique, ARDT)相结合实现故障特征提取。 首先,为了解决 EEMD 中加入参数依靠人工选择且难以准确获取的问题,建立极值点分布 特性评价函数,利用 MPDE 来寻优获取最佳白噪声幅值,实现 EEMD 自适应分解。 然后,采用峭度与相关性相结合的准则对分 解后的 IMF 分量进行自动筛选,将满足条件的有效信号进行重构,实现对原始振动信号的降噪处理。 最后,采用 ARDT 自动确 定对消噪信号进行带通滤波的带宽和中心频率,再通过包络解调提取出滤波信号的特征频率。 将轴承仿真故障信号与实际故 障信号用于算法的验证,结果表明 MPDE-EEMD+ARDT 能有效提取出轴承故障特征。     

1D ZnFe2O4 nanorods coupled with plasmonic Ag,Ag2S nanoparticles and Co-Pi cocatalysts for efficient photoelectrochemical water splitting

Improving the absorption of visible light, accelerating the separation of carries and reducing the recombination of electron-hole pairs are critical to enhance photoelectrochemical (PEC) performance of ZnFe₂O₄. Herein, the ZnFe₂O₄/Ag/Ag₂S films are firstly prepared with a photocurrent density of 0.91 mA/cm² at 1.23 V vs. RHE, which is 9.10 times higher than that of pristine ZnFe₂O₄ (0.10 mA/cm² at 1.23 V vs. RHE). On the basis, Co-Pi cocatalyst is deposited on ZnFe₂O₄/Ag/Ag₂S to further optimize PEC performance of ZnFe₂O₄, the photocurrent density of ZnFe₂O₄/Ag/Ag₂S/Co-Pi is 1.18 mA/cm² at 1.23 V vs. RHE. The improved PEC performance of ZnFe₂O₄/Ag/Ag₂S/Co-Pi films could be attributed to: (i) fast transmission of electron-hole pairs owing to 1D ZnFe₂O₄ NRs; (ii) surface plasmon resonance (SPR) effect of Ag nanoparticles; (ⅲ) visible light absorption is improved by sensitization of Ag₂S nanoparticles; (ⅳ) Co-Pi cocatalyst decreases the recombination of electron-hole pairs by capturing holes. This work provides new insights for metal plasmas, sensitizers and cocatalysts synergistically modify photoanodes for efficient PEC water splitting.     

Highly broadband plasmonic Cu film modified Cu2O/TiO2 nanotube arrays for efficient photocatalytic performance

To develop an efficient photocatalyst electrode for solar energy harvesting and photocatalysis application in the visible region, broadband plasmonic Cu film combined with Cu₂O/TiO₂ nanotube arrays heterojunction (Cu film/Cu₂O/TiNT) has been successfully fabricated by anodization combined with electrodeposition method. Interestingly, linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and UV–Vis diffuse reflectance spectroscopy reveal that the combined consequence of both Cu film and Cu₂O in the as-synthesized ternary composite considerably enhances light absorption in the visible spectral. This activity is attributed to the more efficient charge separation/transportation and the presence of Cu film with strong plasmon resonance (SPR) effect. Moreover, the combined effects of both Cu film and Cu₂O on TiNT approved highest catalytic current density and highest photocatalytic activity on methylene blue (MB). The efficiency and the rate of MB photodegradation over the Cu film/Cu₂O/TiNT were found to be triple compared to TiNT. Within only 30 min of reaction time, the photodegradation of MB reaches nearly 100%.     

Effects of Sr2+ substitution on the crystal structure,Raman spectra,bond valence and microwave dielectric properties of Ba3-xSrx(VO4)2 solid solutions

The effects of Sr²⁺ substitution for Ba²⁺ on microwave dielectric properties and crystal structure of Ba_3-xSr_x(VO₄)₂ (0 ≤ x ≤ 3, BSVO) solid solution were investigated. Such Sr²⁺ substitution contributes to significant reduction in sintering temperature from 1400 °C to 1150 °C. Both permittivity (∑_r) and quality factor (Q × f) values decreased with increasing x value, which was determined to be related with the descending values of average polarizability and packing fraction, whereas the increase in τ_f value was explained by the decreased average VO bond length, A-site bond valence. BSVO ceramics possessed encouraging dielectric performances with ∑_r = 12.2–15.6 ± 0.1, Q × f = 44,340 - 62,000 ± 800 GHz, and τ_f = 24.5–64.5 ± 0.2 ppm/°C. Low-temperature sintering was manipulated by adding B₂O₃ as sintering additive for the representative Sr₃V₂O₈ (SVO) ceramic and only 1 wt.% B₂O₃ addition successfully contributed to a 21.7% decrease in sintering temperature to 900 °C, showing good chemical compatibility with silver electrodes, which render BSVO series and SVO ceramics potential candidates in multilayer electronic devices fabrication.     

Tailorable Dynamics in Nonlinear Optical Metasurfaces

Controlling light with light is essential for all-optical switching, data processing in optical communications and computing. Until now, all-optical control of light has relied almost exclusively on nonlinear optical interactions in materials. Achieving giant nonlinearities under low light intensity is essential for weak-light nonlinear optics. In the past decades, such weak-light nonlinear phenomena have been demonstrated in photorefractive and photochromic materials. However, their bulky size and slow speed have hindered practical applications. Metasurfaces, which enhance light–matter interactions at the nanoscale, provide a new framework with tailorable nonlinearities for weak-light nonlinear dynamics. Current advances in nonlinear metasurfaces are introduced, with a special emphasis on all-optical light controls. The tuning of the nonlinearity values using metasurfaces, including enhancement and sign reversal is presented. The tailoring of the transient behaviors of nonlinearities in metasurfaces to achieve femtosecond switching speed is also discussed. Furthermore, the impact of quantum effects from the metasurface on the nonlinearities is introduced. Finally, an outlook on the future development of this energetic field is offered.     

CO2驱沥青质沉积对致密储层的伤害机理——以鄂尔多斯盆地延长组长8储层为例

为了揭示CO2驱替过程中沥青质沉积对致密储层的伤害机理,文中基于岩心核磁共振T2谱测试原理,开展了CO2注入压力下的岩心驱替实验,研究了沥青质在岩心中的沉积特征,评价了沥青质沉积对储层的伤害程度。实验结果表明:沥青质沉积量和渗透率伤害率随着CO2注入压力的升高呈现先快速上升后趋于平缓的趋势;在CO2注入过程中,沥青质主要沉积在弛豫时间大于10 ms的大、中孔隙,导致大、中孔隙占比下降,微细、小孔隙占比增加,且随着CO2注入压力的升高,大、中孔隙占比下降幅度增大,微细、小孔隙占比上升幅度增大;此外,沥青质沉积会引起润湿性发生反转,随着沥青质沉积量的增加,润湿反转指数增大,岩心润湿性不断向强油湿方向转变。     

Electron Paramagnetic Resonance and Magnetic Circular Dichroism Spectra of the Nitrogenase M Cluster Precursor Suggest Sulfur Migration upon Oxidation: A Proposal for Substrate and Inhibitor Binding

The active site of the nitrogen-fixing enzyme Mo-nitrogenase is the M cluster ([MoFe₇S₉C ⋅ R-homocitrate]), also known as the FeMo cofactor or FeMoco. The biosynthesis of this highly complex metallocluster involves a series of proteins. Among them, NifB, a radical-SAM enzyme, is instrumental in the assembly of the L cluster ([Fe₈S₉C]), a precursor and all-iron core of the M cluster. In the absence of sulfite, NifB assembles a precursor form of the L cluster called the L* cluster ([Fe₈S₈C]), which lacks the final ninth sulfur. EPR and MCD spectroscopies are used to probe the electronic structures of the paramagnetic, oxidized forms of both the L and L* clusters, labeled L^Ox and [ L* ] ^Ox . This study shows that both L^Ox and [ L* ] ^Ox have nearly identical EPR and MCD spectra, thus suggesting that the two clusters have identical structures upon oxidation; in other words, a sulfur migrates away from L^Ox following oxidation, thereby rendering the cluster identical to [ L* ] ^Ox . It is proposed that a similar migration could occur to the M cluster upon oxidation, and that this is an instrumental part of both M cluster formation and nitrogenase substrate/inhibitor binding.     

Numerical study on the loss of fast ions produced by minority ion cyclotron resonance heating in EAST

The classical prompt loss of fast ions produced by minority ion cyclotron resonance heating(ICRH)is studied by a guiding center orbit following code in the Experimental Advanced Superconducting Tokamak(EAST).It is found that the loss of fast ions produced by ICRH mainly appears in both ends of the resonance layer,while the loss of fast ions in the middle resonance layer is very small.The dominant fast loss comes from trapped ions,rather than from passing ions.Controlling the location of resonance layer at the plasma core may be more beneficial to the EAST tokamak ICRH.In addition,the loss distribution of fast ions is studied.The results show that the fast ions are mainly lost near the midplane in the poloidal direction,but almost uniformly in the toroidal direction.Moreover,we investigate the dependence of fast ion loss on the ICRH power.The simulation results show that the loss fraction of fast ions in both ends of the resonance region increases with the ion cyclotron range of frequencies(ICRF)power,but barely affects the loss of fast ions in the middle region.     

Customizing MRI-Compatible Multifunctional Neural Interfaces through Fiber Drawing

Fiber drawing enables scalable fabrication of multifunctional flexible fibers that integrate electrical, optical, and microfluidic modalities to record and modulate neural activity. Constraints on thermomechanical properties of materials, however, have prevented integrated drawing of metal electrodes with low-loss polymer waveguides for concurrent electrical recording and optical neuromodulation. Here, two fabrication approaches are introduced: 1) an iterative thermal drawing with a soft, low melting temperature (T_m) metal indium, and 2) a metal convergence drawing with traditionally non-drawable high T_m metal tungsten. Both approaches deliver multifunctional flexible neural interfaces with low-impedance metallic electrodes and low-loss waveguides, capable of recording optically-evoked and spontaneous neural activity in mice over several weeks. These fibers are coupled with a light-weight mechanical microdrive (1 g) that enables depth-specific interrogation of neural circuits in mice following chronic implantation. Finally, the compatibility of these fibers with magnetic resonance imaging is demonstrated and they are applied to visualize the delivery of chemical payloads through the integrated channels in real time. Together, these advances expand the domains of application of the fiber-based neural probes in neuroscience and neuroengineering.