Wearable flexible sensors are being increasingly designed for monitoring human health states. In this study, we optimized the preparation process of paper-based graphene and designed amplifier filter circuit to sense weak pulse signals with high sensitivity (0~300Pa) and fast response time (<1ms). We further used a convolutional neural network (CNN) as the recognition method to analyze the collected pulse signals. We successfully achieved the recognition and classification of three signals (Cun, guan, chi, and Sport) with an accuracy of 85.79% in the training set and an accuracy of 80% in the testing set. Our research offers new possibilities for the wide application of paper-based graphene sensors in medical diagnosis and health monitoring.

Here, the mechanical properties of single layer graphene oxide (GO) doped woven carbon fibers (CFs)/epoxy (EP) system with two preparation methods are investigated by uniaxial longitudinal static tensile experiments and metallographic images analysis. Mechanical characterizations indicate the optimal GO-doped fabrics of woven CFs/EP (CFs-GO/EP) specimen demonstrates 12.5, 15.7, and 16.2% increase respectively in tensile strength (433.4 MPa), elastic modulus (11.8 GPa) and elongated strain at break (4.3%) compared to the undoped system. And the GO-doped matrix of woven CFs/EP (CFs/GO-EP) specimen shows similar mechanical behavior to CFs-GO/EP specimens with better mechanical properties. The highest tensile strength is 495.2 MPa at 0.2 wt % GO, 14.3% higher than the optimal CFs-GO/EP specimen at 0.1 wt % GO. The maximum elastic modulus and elongated strain at break are 11.9 GPa and 4.5%. With metallographic images, the dominant tensile damage is interface decohesion (fiber-matrix debonding and matrix fracture). We find that without any previous treatment, the GO sheets strongly attached to the CF fabric surface and minimized grooves, voids and defects, improving the interface rough between fibers and matrix, and the interfacial adhesion, which is responsible for the intrinsic improved interlaminar properties and leads to superior mechanical properties. The surface of CFs/GO-EP specimen has much more granular nanofillers between the interfacial region surrounding the fiber surface. The present work provides significant guidelines and in-depth understanding for the effective use of GO in strain engineering applications and as protective coating.

The study of wave power generation is more and more popular in modern science and technology for the new renewable energy, in recent years. Designing wave power generation devices with high conversion efficiency and stability, and improving the technical level for commercialization are both scientifically interesting and potentially useful. Here we achieve the stability of wave generation equipment by establishing one nodding duck energy conversion system in a wave tank. Equipped with ultrasonic distance sensor, combining screw slide and stepper motor as draft self-regulation feedback system, our device is always in the best working performance under the single-chip microcomputer STM32 auto-measuring system. The good conversion efficiency performance can be 43%. The ARDUINO module and the Labview host computer interface are equipped to real-time visualize and characterize the parameters of the device and calculate the optimal power generation efficiency. Our designed device can resist damage validly with high conversion efficiency and stability.

仿形涡流检测技术因其耦合性好可有效抑制检测过程晃动而特别适合对大曲率叶片前缘快速检测.针对涡轮叶片前缘仿形涡流检测建立前缘及仿形线圈有限元模型,运用有限元方法分析叶片前缘凹坑、长裂纹、边沿凹坑3种典型缺陷在内外两种激励、不同内径线圈、不同频率等模式下的检测信号特征.仿真结果表明:大曲率前缘实施仿形涡流检测,检测区域可有效覆盖整个前缘区域,检测频率越高,检测灵敏度越高.双线圈检测模式下,外激励内接收比内激励外接收灵敏高,当内检测线圈尺寸大于缺陷的尺度时,内接收线圈内径越小,其相对灵敏度越高.结合仿真结论,制作前缘缺陷试块,采用锁相放大及图形化编程技术,设计前缘仿形涡流检测系统,试验结果表明,仿形线圈可有效检出前缘典型缺陷,检测幅值相位输出结果与仿真结论相似.研究成果可用于指导大曲率叶片前缘的工程实践检测.

When implementing eddy current testing for carbon fiber reinforced polymer (CFRP), it is usually necessary to apply a higher testing frequency and analyze the voltage amplitude and phase changes of the output signal of the testing coil to identify defects. In this paper, a three-point capacitive resonance circuit is designed to identify artificial defects of carbon fiber reinforced polymer by detecting changes in the frequency of the output signal. The research in this paper has the following conclusions: 1. Through the change of resonant frequency, artificial defects with groove width of 0.50mm, groove depth of 0.50mm, 1.00mm, and 1.50mm can be effectively identified; 2. When the lift-off distance is less than 1.00mm, the resonance frequency does not change much; 3. Compared with the traditional analysis of voltage amplitude and phase changes to identify defects, the resonance frequency method can use a data acquisition card with a lower sampling frequency to realize the identification of the signal frequency (defect); 4. The detection sensitivity of the disc coil is higher than that of the rectangular coil; 5. The greater the inductance of the disc coil, the higher the resonance frequency and the higher the detection sensitivity.

Reduced friction with increasing normal load in the adhesive regime is revealed by vdW-corrected DFT calculations of various rigid junction models such as Graphene/Graphene, h-BN/h-BN, and Graphene/h-BN. The origin of the friction–load relationship arises from the decreased sliding potential corrugation with increased normal load in the attractive regime of the interfacial separation above its equilibrium. The “negative” coefficient of friction behavior, which is mainly dominated by van der Waals attraction, is expected to appear in many interfaces without significant deformation. However, the friction behavior presented here may be inaccessible to atomic forces microscope (AFM) due to the intrinsic instability. The instruments such as interfacial forces microscope with force-feedback sensor or quartz tuning forks with large stiffness are proposed to measure friction behaviors in the entire attractive region.

As a distinct member of layered structure transition metal dichalcogenides, the anisotropic response of rhenium disulphide (ReS2) is important for the potential applications in flexible devices, while the atomic bonding structure determined mechanical properties underlying the distorted low symmetry remains to be well understood. The objective of the present work is to disentangle the atomic-scale structure determined anisotropic mechanical properties of ReS2. The elastic constants of ReS2 are studied by first-principles calculations. Based on the calculated elastic constants, the mechanical properties, such as bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio are obtained via Hill’s approximations. While having a higher in-plane elastic modulus C22 and C33 values, the layered structure has a low-strength shearing elastic constants C55 and C66, making ReS2 more flexible than most studied common transition metal dichalcogenides such as MoS2. Projected phonon density of states (PDOS) along different directions, the electronic density charge distribution as well as the Mulliken charge population are calculated underlying the anisotropic atomic bonding mechanism of this low symmetry structure, which provides an interpretation of the anisotropic mechanical properties.

本论文对单轴压应力条件下的碳纤维材料进行了拉曼光谱实验探究,实验结果显示碳纤维的D峰和G峰对拉应变/应力存在响应,且它们的变化在一定范围内呈线性或正比关系,表明拉曼光谱法可用于碳纤维及其复合材料的检测,在工业无损检测领域很有发展潜能.

Since the fast development of prefabricated building industry facilitate the light thin – walled steel application in both low residential building and fast construction, better understanding of the labour intensive fabrication of connection indicates the problems of optimized connection design and reduced manufacturing cost can be addressed. Several parameters such as number of screws and configurations of the screw layout were varied to study the impact on shear strength. Since the connection strength governs the structural behavior of the truss system which is the main part of modern thin – walled steel structure, the connection strength is calculated according to the American Iron and Steel Institute (AISI), Euro code, and Chinese specification respectively. The main failure mode occurred in self – drilling screw connections are found to be the tilting and bearing failure based on 84 single lap shear test. All testing specimens have experience four stages. When the spacing is fixed to certain number and the screw is less than six, the effect of configuration patter on the resistance capacity is very limited. In contrast, if the screw number is more than six, certain patter layout could lead to better overall strength compare with normal layout patter and the group effect factor is becoming as a constant. The strength of connection can be increased by enlarging the screw spacing with certain range.

研究了碳纤维布,碳纤维布浸渍胶单层和碳纤维布浸渍胶双层的拉曼光谱,测试了碳纤维布加热处理下的拉曼光谱,分析了温度对碳纤维布内应力的影响,同时测试了单轴压应力条件下的碳纤维布拉曼光谱.结果显示:碳纤维的D峰和G峰对浸渍固化、温度、外应力存在响应,可以用于探究碳纤维界面以及内部存在的残余应力,表明拉曼光谱可用于碳纤维及其复合材料的检测,在工业无损检测领域具有发展潜力.

Voids, which considerably degrade mechanical performance, are the most common and dangerous type of flaw found in composite materials. In this study, a smart acoustic attenuation model was proposed to estimate porosity (ie void content) in carbon fibre composite materials. The attenuation model was developed using a priori knowledge, which consisted of determining porosity using a metalloscope and estimating the corresponding acoustic attenuation via ultrasonic testing. A Hilbert transform-based processing method was introduced to process ultrasonic echoes, which were used to compute acoustic attenuation. Several textile glass fibre laminates and unidirectional carbon fibre laminates used in the AVIC Leadair AG300 aircraft (a whole fuselage composite aircraft built in China) were selected as specimens. Experimental results indicated that the porosity estimated using the acoustic attenuation model agreed well with the results obtained using the destructive method of metallography.

文章报导了基于涡流悬浮原理的可控磁悬浮小车的设计,介绍了它的悬浮基本原理,并提出了将涡流磁悬浮和传统的永磁悬浮结合在一起的一种新型磁悬浮方式,还较为详细地介绍了它的装置设计,同时也描述了小车各组件的选择.可控磁悬浮小车在设计的过程中应用了二轴(或四轴)的结构,解决了电机这一特定物体在悬浮时定子会逆着转子旋转方向转动的问题.本文最后记录了小车目前的测试结果,经观察小车悬浮高度为11mm,运行速度最大值为0.51m/s,能完全悬浮,证实了本文章的设计方案确实可行,文章最后展望了小车的应用前景.

We study the conventional electron-phonon mediated superconducting properties of hole-doped black phosphorus by density functional calculations and get quite a large electron-phonon coupling (EPC) constant λ ~ 1.0 with transition temperature T C ~ 10 K, which is comparable to MgB2 when holes are doped into the degenerate and nearly flat energy bands around the Fermi level. We predict that the softening of low-frequency [Formula: see text] optical mode and its phonon displacement, which breaks the lattice nonsymmorphic symmetry of gliding plane and lifts the band double degeneracy, lead to a large EPC. These factors are favorable for BCS superconductivity.

The isostructural phase transitions such as in compressed molybdenum disulfide (MoS2) are ubiquitous in nature, but surprisingly, how and why the vertical compression driven lateral interlayer sliding are still open questions of interest. Here, we address the tribological determination of the pressure-driven interlayer sliding for the structural and electric tuning in compressed MoS2 bilayer by using ab initio calculations. The density functional calculations demonstrate the pressure-driven evolution of interlayer potential energy landscape, providing the preferred sliding pathway for initiating mutual sliding of crystal faces between MoS2 bilayers. Interestingly, even though the 2H a stacking becomes more stable than the 2H c stacking at a load of about 9.2 GPa, a spontaneous slippage would take place only around 30.1 GPa, when the sliding barrier of saddle stacking vanishes as a consequence of the load-driven modification of the potential energy surface. The structural transition from 2H c -MoS2 to 2H a -MoS2 is thus triggered, which allows for the semiconductor–metal transition of the bilayer under pressure. These results agree with recent experimental and dynamics observations of the transition occurring almost completely at 28–30 GPa in bulk crystals. By elucidating these criteria, we suggest that the study may be thus extended to understand the macroscopic properties of the bulk layered crystals such as the possible occurrence of phase transitions taking place at solid interfaces from the atomistic sliding mechanisms at the microscopic scale.

Tungsten ditelluride has attracted intense research interest due to the recent discovery of its large unsaturated magnetoresistance up to 60 T. Motivated by the presence of a small, sensitive Fermi surface of 5d electronic orbitals, we boost the electronic properties by applying a high pressure, and introduce superconductivity successfully. Superconductivity sharply appears at a pressure of 2.5 GPa, rapidly reaching a maximum critical temperature (T-c) of 7 K at around 16.8 GPa, followed by a monotonic decrease in T-c with increasing pressure, thereby exhibiting the typical dome-shaped superconducting phase. From theoretical calculations, we interpret the low-pressure region of the superconducting dome to an enrichment of the density of states at the Fermi level and attribute the high-pressure decrease in T-c to possible structural instability. Thus, tungsten ditelluride may provide a new platform for our understanding of superconductivity phenomena in transition metal dichalcogenides.

Lattice structure and symmetry of two-dimensional (2D) layered materials are of key importance to their fundamental mechanical, thermal, electronic and optical properties. Raman spectroscopy, as a convenient and nondestructive tool, however has its limitations on identifying all symmetry allowing Raman modes and determining the corresponding crystal structure of 2D layered materials with high symmetry like graphene and MoS2. Due to lower structural symmetry and extraordinary weak interlayer coupling of ReS2, we successfully identified all 18 first-order Raman active modes for bulk and monolayer ReS2. Without van der Waals (vdW) correction, our local density approximation (LDA) calculations successfully reproduce all the Raman modes. Our calculations also suggest no surface reconstruction effect and the absence of low frequency rigid-layer Raman modes below 100 cm-1. Combining with Raman and LDA thus provides a general approach for studying the vibrational and structural properties of 2D layered materials with lower symmetry.

Raman spectra of few-layer phosphorene have been systematically studied using density functional theory calculations. We find that due to the interlayer van der Waals interactions, the low-frequency rigid layer Ag breathing mode and B1g shear mode can shift by as much as 45.1 cm−1 and 38.5 cm−1, respectively, as the layer numbers increase from 2L to 5L. In addition, a typical characteristic for the experimentally observable mode (∼460 cm−1 in bulk) is identified. Interestingly, this mode changes from coupled in-plane and out-of-plane vibrations in single layer to pure in-plane vibrations in a few layers and the corresponding frequencies vary by as much as over 10 cm−1. We argue that this Raman frequency variation might be used to experimentally characterize the thickness of this intriguing 2D layered material.

Semiconducting two-dimensional transition metal dichalcogenides are emerging as top candidates for post-silicon electronics. While most of them exhibit isotropic behaviour, lowering the lattice symmetry could induce anisotropic properties, which are both scientifically interesting and potentially useful. Here we present atomically thin rhenium disulfide (ReS 2 ) flakes with unique distorted 1T structure, which exhibit in-plane anisotropic properties. We fabricated monolayer and few-layer ReS 2 field-effect transistors, which exhibit competitive performance with large current on/off ratios (∼10 7 ) and low subthreshold swings (100 mV per decade). The observed anisotropic ratio along two principle axes reaches 3.1, which is the highest among all known two-dimensional semiconducting materials. Furthermore, we successfully demonstrated an integrated digital inverter with good performance by utilizing two ReS 2 anisotropic field-effect transistors, suggesting the promising implementation of large-scale two-dimensional logic circuits. Our results underscore the unique properties of two-dimensional semiconducting materials with low crystal symmetry for future electronic applications.