Deflection Estimation of Truss Structures Using Inverse Finite Element Method.

It is well recognized that strain and deflection data are important indexes to judge the safety of truss structures. Specifically, the shape sensing technology can estimate the deformation of a structure by exploiting the discrete strain data without considering the material property conditions. To fill the gap in which most of the methods in SHM (structural health monitoring) cannot be directly used to predict the displacement field, this paper proposed a novel inverse finite element method (iFEM) algorithm based on the equivalent stiffness theory. A deflection sensor is fabricated to focus on predicting the distributed deflection variation of the truss structure. The performance of the deflection sensor was evaluated by a calibration test and a stability test. Finally, it was applied to distributed deflection monitoring in the testing of truss structures. Results of all tests verify that the deflection sensor based on the i-FEM algorithm can predict the distributed deflection variation of the truss structure accurately, in real time, and dynamically.

A Strain Transfer Model for Detection of Pitting Corrosion and Loading Force of Steel Rebar with Distributed Fiber Optic Sensor.

Steel rebar corrosion is one of the predominant factors influencing the durability of marine and offshore reinforced concrete structures, resulting in economic loss and the potential threat to human safety. Distributed fiber optic sensors (DFOSs) have gradually become an effective method for structural health monitoring over the past two decades. In this work, a strain transfer model is developed between a steel rebar and a DFOS, considering pitting-corrosion-induced strain variation in the steel rebar. The Gaussian function is first adopted to describe the strain distribution near the corrosion pit of the steel rebar and then is substituted into the governing equation of the strain transfer model, and the strain distribution in the DFOS is analytically obtained. Tensile tests are also conducted on steel rebars with artificially simulated corrosion pits, which are used to validate the developed model. The results show that the Gaussian function can be used to describe the strain variation near a corrosion pit with a depth less than 50% of the steel rebar diameter, and the strain distribution in the DFOS analytically determined based on the developed strain transfer model agrees well with the tensile test results. The corrosion pit depth and loading force in the steel rebars estimated based on the proposed model agree well with the actual values, and therefore, the developed strain transfer model is effective in detecting pitting corrosion and loading force in steel rebars.

Bayesian-Inference Embedded Spline-Kerneled Chirplet Transform for Spectrum-Aware Motion Magnification.

The ability to discern subtle image changes over time is useful in applications such as product quality control, civil engineering structure evaluation, medical video analysis, music entertainment, and so on. However, tiny yet useful variations are often combined with large motions, which severely distorts current video amplification methods bounded by external constraints. This paper presents a novel use of spectra to make motion magnification robust to large movements. By exploiting spectra, artificial limitations and the magnification of small motions are avoided at similar frequency levels while ignoring large ones at distinct spectral pixels. To achieve this, this paper constructs spline-kerneled chirplet transform (SCT) into an empirical Bayesian paradigm that applies to the entire time series, giving powerful spectral resolution and robust performance to noise in nonstationary nonlinear signal analysis. The important advance reported is Bayesian-rule embedded SCT (BE-SCT); two numerical experiments show its superiority over current approaches. For applying to spectrum-aware motion magnification, an elaborate analytical framework is established that captures global motion, and use of the proposed BE-SCT for dynamic filtering enables a frequency-based motion isolation. Our approach is demonstrated on real-world and synthetic videos. This approach shows superior qualitative and quantitative results with less visual artifacts and more local details over the state-of-the-art methods.

A Novel Embeddable Tubular Piezoceramics-Based Smart Aggregate for Damage Detection in Two-Dimensional Concrete Structures.

Due to their multiple advantages, piezoceramic materials have been widely used in structural health monitoring (SHM). Piezoceramic patch-based smart aggregate (SA) and spherical piezoceramic-based smart aggregate (SSA) have been developed for damage detection of concrete structures. However, the stress waves generated by these two types of transducers are limited by their geometry and are unsuitable for use in two-dimensional concrete structures (e.g., shear walls, floors and cement concrete pavements). In this paper, a novel embeddable tubular smart aggregate (TSA) based on a piezoceramic tube was designed, fabricated and tested for use in two-dimensional (2D) structures. Due to its special geometry, radially uniform stress waves can be generated, and thus the TSA is suitable for damage detection in planar structures. The suitability of the transducer for use in structural health monitoring was investigated by characterizing the ability of the transducer to transmit and measure stress waves. Three experiments, including impedance analysis, time of arrival analysis and sweep frequency analysis, were conducted to test the proposed TSA. The experimental results show that the proposed TSA is suitable for monitoring the health condition of two-dimensional concrete structures.

Looseness Monitoring of Bolted Spherical Joint Connection Using Electro-Mechanical Impedance Technique and BP Neural Networks.

The bolted spherical joint (BSJ) has wide applications in various space grid structures. The bar and the bolted sphere are connected by the high-strength bolt inside the joint. High-strength bolt is invisible outside the joint, which causes the difficulty in monitoring the bolt looseness. Moreover, the bolt looseness leads to the reduction of the local stiffness and bearing capacity for the structure. In this regard, this study used the electro-mechanical impedance (EMI) technique and back propagation neural networks (BPNNs) to monitor the bolt looseness inside the BSJ. Therefore, a space grid specimen having bolted spherical joints and tubular bars was considered for experimental evaluation. Different torques levels were applied on the sleeve to represent different looseness degrees of joint connection. As the torque levels increased, the looseness degrees of joint connection increased correspondingly. The lead zirconate titanate (PZT) patch was used and integrated with the tubular bar due to its strong piezoelectric effect. The root-mean-square deviation (RMSD) of the conductance signatures for the PZT patch were used as the looseness-monitoring indexes. Taking RMSD values of sub-frequency bands and the looseness degrees as inputs and outputs respectively, the BPNNs were trained and tested in twenty repeated experiments. The experimental results show that the formation of the bolt looseness can be detected according to the changes of looseness-monitoring indexes, and the degree of bolt looseness by the trained BPNNs. Overall, this research demonstrates that the proposed structural health monitoring (SHM) technique is feasible for monitoring the looseness of bolted spherical connection in space grid structures.

A Fiber Bragg Grating (FBG)-Enabled Smart Washer for Bolt Pre-Load Measurement: Design, Analysis, Calibration, and Experimental Validation.

A washer is a common structural element that is directly used along the loading path of a bolted connection. Pre-load on a bolted connection directly impacts its load bearing capacity and pre-load monitoring is an important aspect of structural health monitoring (SHM). With the change of the pre-load on a bolted connection, the loading force on the washer will change and, therefore, the outer diameter and outer circumferential length of the washer will change. Taking advantage of the high sensitivity and the small size of a Fiber Bragg Grating (FBG) sensor, we propose an innovative smart washer encircled by an FBG sensor that can directly measure the circumferential strain change and, therefore, the pre-load on the washer. For protection, the FBG is embedded in a pre-machined groove along the circumferential surface of the washer. A theoretical approach is used to derive the linear relationship between the applied load and the circumferential strain of the washer. To validate the functionality of the FBG-enabled smart sensor for in situ bolt pre-load monitoring, a simple but effective testing apparatus is designed and fabricated. The apparatus involves a bolt, the FBG-enabled washer, a metal plate, and a nut. The bolt has an embedded FBG along its axial direction for precise axial strain and, therefore, force measurement. With the calibrated axial force measuring bolt, in situ experiments on the FBG-enabled smart washers are conducted. Experimental results reveal the linear relationship between the pre-load and the wavelength of the FBG sensor encircling the washer. Both analytical and experimental results demonstrate that the proposed novel approach is sensitive to the bolt pre-load and can monitor in real time the bolt looseness in the entire loading range.

Health Monitoring of Bolted Spherical Joint Connection Based on Active Sensing Technique Using Piezoceramic Transducers.

Bolted spherical joints are widely used to form space steel structures. The stiffness and load capacity of the structures are affected by the looseness of bolted spherical joint connections in the structures. The looseness of the connections, which can be caused by fabrication error, low modeling accuracy, and "false twist" in the installation process, may negatively impact the load capacity of the structure and even lead to severe accidents. Furthermore, it is difficult to detect bolted spherical joint connection looseness from the outside since the bolts connect spheres with rods together from the inside. Active sensing methods are proposed in this paper to monitor the tightness status of the bolted spherical connection using piezoceramic transducers. A triangle-on-triangle offset grid composed of bolted spherical joints and steel tube bars was fabricated as the specimen and was used to validate the active sensing methods. Lead Zirconate Titanate (PZT) patches were used as sensors and actuators to monitor the bolted spherical joint tightness status. One PZT patch mounted on the central bolted sphere at the upper chord was used as an actuator to generate a stress wave. Another PZT patch mounted on the bar was used as a sensor to detect the propagated waves through the bolted spherical connection. The looseness of the connection can impact the energy of the stress wave propagated through the connection. The wavelet packet analysis and time reversal (TR) method were used to quantify the energy of the transmitted signal between the PZT patches by which the tightness status of the connection can be detected. In order to verify the effectiveness, repeatability, and consistency of the proposed methods, the experiments were repeated six times in different bolted spherical connection positions. The experimental results showed that the wavelet packet analysis and TR method are effective in detecting the tightness status of the connections. The proposed active monitoring method using PZT transducers can monitor the tightness levels of bolted spherical joint connections efficiently and shows its potential to guarantee the safety of space steel structures in construction and service.

Structural Health Monitoring for a Z-Type Special Vehicle.

Nowadays there exist various kinds of special vehicles designed for some purposes, which are different from regular vehicles in overall dimension and design. In that case, accidents such as overturning will lead to large economical loss and casualties. There are still no technical specifications to follow to ensure the safe operation and driving of these special vehicles. Owing to the poor efficiency of regular maintenance, it is more feasible and effective to apply real-time monitoring during the operation and driving process. In this paper, the fiber Bragg grating (FBG) sensors are used to monitor the safety of a z-type special vehicle. Based on the structural features and force distribution, a reasonable structural health monitoring (SHM) scheme is presented. Comparing the monitoring results with the finite element simulation results guarantees the accuracy and reliability of the monitoring results. Large amounts of data are collected during the operation and driving progress to evaluate the structural safety condition and provide reference for SHM systems developed for other special vehicles.

Dynamic Modelling of Embeddable Piezoceramic Transducers.

Embedded Lead Zirconate Titanate (PZT) transducers have been widely used in research related to monitoring the health status of concrete structures. This paper presents a dynamic model of an embeddable PZT transducer with a waterproof layer and a protecting layer. The proposed model is verified by finite-element method (FEM). Based on the proposed model, the factors influencing the dynamic property of the embeddable PZT transducers, which include the material and thickness of the protecting layer, the material and thickness of the waterproof layer, and the thickness of the PZT, are analyzed. These analyses are further validated by a series of dynamic stress transfer experiments on embeddable PZT transducers. The results show that the excitation frequency can significantly affect the stress transfer of the PZT transducer in terms of both amplitude and signal phase. The natural frequency in the poling direction for the PZT transducer is affected by the material properties and the thickness of the waterproof and protecting layers. The studies in this paper will provide a scientific basis to design embeddable PZT transducers with special functions.

Study on dynamic response measurement of the submarine pipeline by full-term FBG sensors.

The field of structural health monitoring is concerned with accurately and reliably assessing the integrity of a given structure to reduce ownership costs, increase operational lifetime, and improve safety. In structural health monitoring systems, fiber Bragg grating (FBG) is a promising measurement technology for its superior ability of explosion proof, immunity to electromagnetic interference, and high accuracy. This paper is a study on the dynamic characteristics of fiber Bragg grating (FBG) sensors applied to a submarine pipeline, as well as an experimental investigation on a laboratory model of the pipeline. The dynamic response of a submarine pipeline under seismic excitation is a coupled vibration of liquid and solid interaction. FBG sensors and strain gauges are used to monitor the dynamic response of a submarine pipeline model under a variety of dynamic loading conditions and the maximum working frequency of an FBG strain sensor is calculated according to its dynamic strain responses. Based on the theoretical and experimental results, it can be concluded that FBG sensor is superior to strain gauge and satisfies the demand of dynamic strain measurement.

Bone Marrow Mesenchymal Stem Cell Extracellular Vesicle-derived miR-27b- 3p activates the Wnt/Β-catenin Pathway by Targeting SMAD4 and Aggravates Hepatic Ischemia-reperfusion Injury.

BACKGROUND: To investigate the roles of extracellular vesicles (EVs) secreted from bone marrow mesenchymal stem cells (BMSCs) and miR-27 (highly expressed in BMSC EVs) in hepatic ischemia‒ reperfusion injury (HIRI). APPROACHES AND RESULTS: We constructed a HIRI mouse model and pretreated it with an injection of agomir-miR-27-3p, agomir-NC, BMSC-EVs or control normal PBS into the abdominal cavity. Compared with the HIRI group, HIRI mice preinjected with BMSC-EVs had significantly decreased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels and alleviated liver necrosis (P<0.05). However, compared with HIRI+NC mice, HIRI+miR-27b mice had significantly increased ALT and AST levels, aggravated liver necrosis, and increased apoptosis-related protein expression (P<0.05). The proliferation and apoptosis of AML-12 cells transfected with miR-27 were significantly higher than the proliferation and apoptosis of AML-12 cells in the mimic NC group (P<0.01) after hypoxia induction. SMAD4 was proven to be a miR-27 target gene. Furthermore, compared to HIRI+NC mice, HIRI+miR-27 mice displayed extremely reduced SMAD4 expression and increased levels of wnt1, ß-catenin, c-Myc, and Cyclin D1. CONCLUSION: Our findings reveal the role and mechanism of miR-27 in HIRI and provide novel insights for the prevention and treatment of HIRI; for example, EVs derived from BMSCs transfected with antimiR- 27 might demonstrate better protection against HIRI.

BMSC-exosomes miR-25-3p Regulates the p53 Signaling Pathway Through PTEN to Inhibit Cell Apoptosis and Ameliorate Liver Ischemia‒reperfusion Injury.

BACKGROUND: Hepatic ischemia‒reperfusion injury (HIRI) is a pathological phenomenon during liver surgery, and bone marrow-mesenchymal stem cell (BMSC) exosomes (BMSC-Exos) regulate cell apoptosis and reduce ischemia‒reperfusion injury. We aimed to investigate the roles of BMSC-Exos and miR-25b-3p (enriched in BMSC-Exos) in HIRI and elucidate the underlying mechanisms. APPROACHES AND RESULTS: An HIRI mouse model was constructed and preinjected with BMSC-Exos, agomir-miR-25, agomir-miR-NC, or PBS via the tail vein. Compared with mice with HIRI, mice with HIRI preinjected with BMSC-Exos had significantly decreased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels and alleviated liver necrosis (P < 0.05). Quantitative hepatic transcriptomics showed that mice with HIRI preinjected with BMSC-Exos exhibited increased cell division, hematopoietic or lymphoid organ development and metabolic processes. miRNA sequencing of BMSC-Exos revealed that miR-25, which is related to I/R injury, was enriched in the exosomes. Compared with HIRI + NC mice, HIRI + miR-25b-3p mice had significantly increased miR-25b-3p expression, decreased ALT/AST levels and apoptosis-related protein expression (P < 0.05), and alleviated liver necrosis. The proliferation of AML-12 cells transfected with miR-25b-3p was significantly higher than that in the mimic NC group (P < 0.01) after hypoxia induction, and the apoptosis rate of cells was significantly lower than that in the NC group (P < 0.01). PTEN was identified as a miR-25b-3p target gene. PTEN expression was significantly diminished in miR-25b-3p-transfected AML12 cells (P < 0.05). HIRI + agomir-miR-25 mice displayed reduced PTEN expression and decreased p53 and cleaved caspase 3 levels compared to HIRI + NC mice. CONCLUSIONS: We revealed the roles and underlying mechanisms of BMSC-Exos and miR-25 in HIRI, contributing to the prevention and treatment of HIRI.

Noise smoothing for structural vibration test signals using an improved wavelet thresholding technique.

In structural vibration tests, one of the main factors which disturb the reliability and accuracy of the results are the noise signals encountered. To overcome this deficiency, this paper presents a discrete wavelet transform (DWT) approach to denoise the measured signals. The denoising performance of DWT is discussed by several processing parameters, including the type of wavelet, decomposition level, thresholding method, and threshold selection rules. To overcome the disadvantages of the traditional hard- and soft-thresholding methods, an improved thresholding technique called the sigmoid function-based thresholding scheme is presented. The procedure is validated by using four benchmarks signals with three degrees of degradation as well as a real measured signal obtained from a three-story reinforced concrete scale model shaking table experiment. The performance of the proposed method is evaluated by computing the signal-to-noise ratio (SNR) and the root-mean-square error (RMSE) after denoising. Results reveal that the proposed method offers superior performance than the traditional methods no matter whether the signals have heavy or light noises embedded.

Effect of Particle Size on Microstructure and Element Diffusion at the Interface of Tungsten Carbide/High Strength Steel Composites.

The microstructure and micro-hardness of tungsten carbide/high strength steel (WC/HSS) composites with different particle sizes were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), ultra-high temperature laser confocal microscopy (UTLCM) and micro-hardness testing. The composites were prepared by cold pressing and vacuum sintering. The results show that WC density tends to increase as the average grain size of WC decreases and the micro-hardness of WC increases with the decrease of WC particle size. The micro-hardness of WC near the bonding interface is higher than that in other regions. When the particle size of WC powder particles is 200 nm, a transition layer with a certain width is formed at the interface between WC and HSS, and the combination between the two materials is metallurgical. The iron element in the HSS matrix diffuses into the WC structure in contact with it, resulting in a fusion layer of a certain width, and the composite interface is relatively well bonded. When the average particle size of WC powder is 200 nm, W, Fe and Co elements significantly diffuse in the transition zone at the interface. With the increase of WC particle size, the trend of element diffusion decreases.

A Hierarchical Copper Oxide-Germanium Hybrid Film for High Areal Capacity Lithium Ion Batteries.

Self-supported electrodes represent a novel architecture for better performing lithium ion batteries. However, lower areal capacity restricts their commercial application. Here, we explore a facial strategy to increase the areal capacity without sacrificing the lithium storage performance. A hierarchical CuO-Ge hybrid film electrode will not only provide high areal capacity but also outstanding lithium storage performance for lithium ion battery anode. Benefiting from the favorable structural advance as well as the synergic effect of the Ge film and CuO NWs array, the hybrid electrode exhibits a high areal capacity up to 3.81 mA h cm-2, good cycling stability (a capacity retention of 90.5% after 150 cycles), and superior rate performance (77.4% capacity remains even when the current density increased to 10 times higher).

Field Validation of a Magnetic Sensor to Monitor Borehole Deviation during Tunnel Excavation.

In this article, a magnetic sensor is proposed to monitor borehole deviation during tunnel excavation. It is made by piling four super-strong N42 NdFeB cylinder magnets and then encasing them in an aluminum alloy hollow cylinder. The distribution of the magnetic field produced by the magnetic sensor and its summation with the geomagnetic field (GMF) in a global coordinate system are derived based on the theory of magnetic fields. An algorithm is developed to localize the position of the magnetic sensor. The effect of the GMF variation on the effective monitoring range of the magnetic sensor is also studied numerically. Field validation tests are conducted at Jinzhai Pumped-Storage hydroelectric power station, during the excavation of an inclined tunnel in Anhui Province of China. Test results show that the algorithm and the magnetic sensor are used successfully to detect the deviation of the borehole with an estimated error of approximately 0.5 m. The errors are mainly from the measurement errors of the coordinates, of both the test and the measurement points. The effective monitoring range of the magnetic sensor is dependent on the direction of the magnetic sensor as well as the variation of the GMF.

Biodegradation of two organophosphorus pesticides in whole corn silage as affected by the cultured Lactobacillus plantarum.

Biodegradation of the pesticides is considered as one of the safest and cheapest ways. The aim of the present study was to reveal if the inoculated Lactic acid bacteria widely used in silage could provide beneficial safety to guarantee dairy feedstuffs and fresh milk. Organophosphorus pesticides (OPPs) degradation in whole corn silage was investigated. Two OPPs, chlorpyrifos and phorate, were added to the whole corn, which was inoculated with L. plantarum 1.0315, L. plantarum 1.0624, L. plantarum 1.0622 and their combination at room temperature for 10 weeks. OPPs residues in the whole corn silage at different weeks were analyzed by gas chromatography after OPPs extraction and purification. The degradation rate constants were calculated according to the OPPs residues results at different fermentation stage. The data showed that the inoculated microorganisms and strain combination exhibited obvious acceleration on OPPs degradation as the wild microorganisms did, and resulted in decreased levels of OPPs from 24.9 to 33.4 %. Strains combination brought about greater OPPs degradation than single strain or the wild microorganisms. Compared to phorate, clorpyrifos had lower degradation rate constants (0.0274-0.0381 vs. 0.0295-0.0355 week-1) and was more stable. The present result indicates safety benefit of lactic acid bacteria on corn silage besides lactic acid fermentation.

π-π stacking, spin density and magnetic coupling strength.

The π-π stacking interaction, one of the main intermolecular forces, sometimes leads to amazing magnetic properties. Although the concept has been raised that spin density is one of the main factors that contribute to the magnetic coupling strength in intermolecular magnetic coupling systems, it has not been confirmed either experimentally or theoretically to date. Herein we present a study on the magnetostructural data of seven unpublished Cu(II) complexes and ten reported radicals. It is confirmed for the first time that the spin density on short contact atoms is a major factor that contributes to the π-π stacking magnetic coupling strength. Based on the reported data to date, when the short contact distance is larger than the default contact radius, medium or relatively strong magnetic coupling strength could be obtained only if the spin density on the short contact atoms is greater than 0.1350; when the C···C short contact is less than the default contact radius of 3.4 Å, but not less than 3.351 Å, and the spin density is less than 0.1, neither medium nor strong magnetic coupling strength could be observed. Further, when the short contact distance decreases with a temperature drop, the spin densities on the relevant short contact atoms increase. In the complexes reported the small spin densities on the relevant short contact atoms are the major factors that result in the weak π-π magnetic coupling strength.

Fiber Bragg grating displacement sensor for movement measurement of tendons and ligaments.

Biomechanical studies often involve measurements of the strains developed in tendons or ligaments in posture or locomotion. Fiber-optic sensors present an attractive option for the measurement of strains in tendons and ligaments because of their low cost, ease of implementation, and increased accuracy compared with other implantable transducers. A new displacement sensor based on a fiber Bragg grating and shape memory alloy technology is proposed for the monitoring of tendon and ligament strains in different postures and in locomotion. After sensor calibration in the laboratory, a comparison of the fiber sensors and traditional camera displacement sensors was carried out to evaluate the performance of the fiber sensor during the application of tension to the Achilles tendon. Additional experiments were performed in cadaver knees to assess the suitability of these fiber sensors to measure ligament deformation in a variety of simulated postures. The results demonstrate that the proposed fiber Bragg grating sensor is a highly accurate, easily implantable, and minimally invasive method of measuring tendon and ligament displacement.