基于FFT盲辨识的肌电信号建模及模式识别

针对表面肌电信号(Electromyographic signal,sEMG)产生原理复杂、易受人体自身及外界因素影响的特点,采用基于快速傅里叶变换(Fast Fourier transform,FFT)的盲辨识方法建立肌电信号模型.该方法通过计算即可确定信道阶次,无需人为凭借经验设定,且计算简单、易于实现、运算速度快.其利用输出信道间的相互关系特性,实现信号的频域盲辨识,建立数学模型.此方法适用于小样本信号建模,非常适合易受肌肉疲劳影响的表面肌电信号.将模型系数作为改进的BP神经网络的输入,实现多运动模式识别,与其他盲辨识方法比较,此方法识别效果较好.     

pH-responsive smart superwetting Fe foam for efficient in situ on-demand oil/water separation

Journal of Materials Science - Confronted with the increasing oily wastewater and oil leakage accidents, it is urgent to seek effective strategies to separate water/oil mixtures or clean spilt oil....     

A new method for the investigation of fluid-fluid mass transfer—II. Mass transfer in liquid-liquid systems

A new dynamic electrochemical method for the determination of liquid-liquid mass-transfer coefficients in a stirred cell and in a mixer cell is described. Current transients are recorded for different flow conditions and evaluated applying a non-linear regression analysis. The resulting mass-transfer coefficients correlate linearly with the stirring rate but the mean values over a long time period are considerably low. The extent of the investigated initial time dependence of the mass-transfer coefficient decreases with increasing electrolyte concentration.     

The effects of pre-existing grain boundary cavities on the creep rupture life of a copper-antimony alloy

• 1.1. The pre-creep and sintering technique was used to implant cavities onto grain boundaries of a CuSb alloy. The rupture times of this material were ten times longer than those of OFHC Cu after a similar treatment. This difference can be explained by the differences in grain size, cavity structure and creep rate.
• 2.2. The creep conditions in this study fall in a range where both the creep properties of the material and interfacial self-diffusion contribute to cavity growth. The coupled diffusion and creep controlled cavity growth model can explain the rupture behavior of this material.
• 3.3. The presence of Sb in Cu does not appear to influence the cavity growth mechanism except to slow the creep rate.
• 4.4. The nucleation of new cavities during creep has not been eliminated by the implanted cavities. However, their influence on the rupture time is probably small.

     

A Biomimetic Structural Material with Adjustable Mechanical Property for Bone Tissue Engineering

The development of cellular materials with adjustable mechanical properties, total porosity (Tp), and elastic modulus (E) similar to those of natural bone are eternal pursuits in the field of bone implants. Designing and manufacturing an implant that fulfills all these requirements is a challenging task. In this study, inspired by the trabecular structure of natural bone and developed a biomimetic structural material. Laser powder bed fusion (L-PBF) is utilized to create the biomimetic structural material. Comprehensive valuations of both the natural trabecular bone and biomimetic structural material are conducted using micro-CT scanning, nanoindentation testing, finite element (FE) analysis, and compression testing. The results demonstrate that the mechanical properties of the developed biomimetic structural material have excellent controllability. The rod-plate-like trabecular (RPT) biomimetic structural material exhibited significantly superior mechanical load-bearing performance compared to the natural bone trabeculae while maintaining the natural bone's Tp (83.1%) and E (798.1 MPa). The biomimetic structural material effectively balances the combination of strength and E, providing a design template for the next generation of medical implants. It has great potential as a bone repair material for clinical applications, and its adjustable mechanical properties also make it highly promising in the field of tissue engineering.     

合并分割块的点云语义分割方法

随着激光雷达等三维点云获取工具的快速发展,点云的语义信息在计算机视觉、智能驾驶、遥感测绘、智慧城市等领域更具重要意义。针对基于分割块特征匹配的点云语义分割方法无法处理过分割和欠分割点云块、行道树和杆状物的语义分割精度低等问题,提出了一种基于分割块合并策略的行道树和杆状物点云语义分割方法,该方法可对聚类分割后感兴趣的分割块进行合并,通过计算其多维几何特征实现对合并后的物体分类,并使用插值优化算法对分割结果进行优化,最终实现城市道路环境下行道树和杆状物的语义分割。实验结果表明,所提方法可将城市道路环境下的行道树、杆状物等点云数据的召回率和语义分割精度平均提升至89.9%以上。基于分割块合并的语义分割方法,可以很好地解决城市道路下行道树和杆状物语义分割精度低等问题,该方法对于三维场景感知等问题的研究具有重要意义。     

A combinatorial approach for automotive friction materials: Effects of ingredients on friction performance

Raw materials used in automotive friction formulations were classified using a combinatorial approach into two groups in accordance with their ability to improve the wear properties of the mixture by two-phase friction composites. Components of group one, which improved the wear resistance, include softer additives (graphite, MoS₂, and Twaron), harder additives (Al₂O₃ and steel wool), and organic binder (benzoxazine). Softer additives have low friction coefficient (μ), low wear, and easily transferred debris to the surface of disc. Harder additives have intermediate wear, intermediate μ, and formed iron-containing surface layer transferred from cast iron disc to friction material pad. Benzoxazine has high wear and high μ and there is no transferred layer formed either on disc or pad in the case of benzoxazine used as pad. The wear of two-phase friction materials can be improved by adding Al₂O₃, graphite, MoS₂, steel wool, and Twaron to benzoxazine and four wear improvement mechanisms were proposed: (1) lubrication mechanism (graphite and MoS₂); (2) abrasive mechanism (Al₂O₃); (3) friction layer mechanism (steel wool); (4) reinforced mechanism (Twaron). Components of group two, which produced poor wear resistance, include BaSO₄, BN, B₂O₃, brass chips, CaCO₃, Ca(OH)₂, cashew, copper chips, CuS, Cu₂S, H₃BO₃, iron powder, MgO, oxidized PAN fiber, PMF (SiO₂ + CaO), Sb₂S₃, Ultrafibe (CaSiO₃), and ZrSiO₄.     

Influences of tensile pre-strain and bending pre-deflection on bending and tensile behaviors of an extruded AZ31B magnesium alloy

This paper focused on the influences of tensile pre-strain and bending pre-deflection on the three point bending and uniaxial tensile properties of an extruded AZ31B magnesium alloy. The influences of pre-strain/deflection on bending/tensile curves could be divided into three stages. The results show that: (1) In the elastic stage, considering the variation of specimen’s cross sectional area, the pre-strain/deflection did not affect the measured elastic modulus obtained from both bending and tensile tests. (2) In the transition hardening stage, the specimen presented obvious hardening behaviors on basis of the pre-strain/deflection, the phenomenon was mainly caused by the strain hardening effects produced from previous uniaxial tensile and bending processes. (3) In the large plastic deformation stage/necking stage, as the accumulation of plastic deformations caused by pre-strain/deflection were significant, the specimen’s ability to resist plastic deformation was weakened. Specially, as the tensile pre-strain increased, the bending load decrement rate gradually decreased, and as the bending pre-deflection increased, both the tensile strength and elongation sharply decreased, the accumulated irreversible plastic work promoted the damage process of the magnesium alloy. The influences of tensile pre-strain on the bending behaviors of the magnesium alloy were also analyzed via finite element method.     

Gas–Solid Erosive Wear of Biomimetic Pattern Surface Inspired from Plant

Gas–solid erosive wear is a phenomenon in which serious mechanical damage is caused by the impact of solid particles on a wall. In this study, we investigated the erosive wear characteristics and mechanism of biomimetic groove surfaces in gas–solid erosive wear. Orthogonal experimental results showed that the order of the factors that influenced the erosive wear of the biomimetic groove surface was morphology > space > feature size. The V-shaped groove surface exhibited the best erosive wear resistance over the smooth, square, and U-shaped groove surfaces. The surface microstrain calculated by X-ray diffraction lines was used to study the mechanism of erosive wear resistance enhancement of the biomimetic surface. The microstructure of the eroded surface was analyzed by scanning electron microscopy. The appearance of ribs on the biomimetic groove surface increased the erosive wear of the surface in a distal position with respect to the ribs themselves. This article shows more opportunities for bionic application in improving the anti-erosion performance of moving parts that work under dirt and sand particle environments.     

Direct Laser Writing of Superhydrophobic PDMS Elastomers for Controllable Manipulation via Marangoni Effect

Direct light‐to‐work conversion enables manipulating remote devices in a contactless, controllable, and continuous manner. Although some pioneering works have already proven the feasibility of controlling devices through light‐irradiation‐induced surface tension gradients, challenges remain, including the flexible integration of efficient photothermal materials, multifunctional structure design, and fluidic drag reduction. This paper reports a facile one‐step method for preparing light‐driven floating devices with functional surfaces for both light absorption and drag reduction. The direct laser writing technique is employed for both arbitrary patterning and surface modification. By integrating the functional layer at the desired position or by designing asymmetric structures, three typical light‐driven floating devices with fast linear or rotational motions are demonstrated. Furthermore, these devices can be driven by a variety of light sources including sunlight, a filament lamp, or laser beams. The approach provides a simple, green, and cost‐effective strategy for building functional floating devices and smart light‐driven actuators.