Search

This paper presents a novel control strategy to compensate hysteretic nonlinearity and achieve precise positioning control of a cell puncture mechanism driven by a piezoelectric actuator (PEA). A dynamic model of the cell puncture mechanism is developed based on the Bouc–Wen model. Parameters of the nonlinear model are identified by particle swarm optimization. The strategy of feedforward (FF) control and sliding mode feedback (FB) control based on the Bouc–Wen inverse model is further developed to position the cell puncture mechanism. Zebrafish embryo is used as the validation object, wherein a cell micropuncture experiment is successfully performed. Proportional-integral sliding mode FB control plus FF control has a simple structure and exhibits excellent performance. Thus, this method can be easily extended to other micro-or nanopositioning mechanisms based on PEAs and adopted in practical applications. [ABSTRACT FROM AUTHOR]

Probabilistic site characterization is the cornerstone of data-centric geotechnics, which underpins the digitalization in geotechnical engineering. The essential aspect of probabilistic site characterization is to reasonably infer the probability density distributions of geotechnical parameters, based on field and laboratory data. In this paper, a clay property database, SZ-CLAY/11/5130, was established by collecting geotechnical investigation reports from 52 engineering projects in Shenzhen city. This SZ-CLAY/11/5130 database was first compared with the global clay database CLAY/10/7490 and the Shanghai clay database SH-CLAY/11/4051, in terms of their sample ranges, correlations, and scatter plots. Then, the multivariate probability distribution of eight clay parameters was established using the training records selected from SZ-CLAY/11/5130, to characterize the generic correlations between multiple clay parameters. Based on Bayesian theory, the posterior distributions of clay mechanical parameters from a construction site in Shenzhen city were updated using both the site-specific correlations and the generic correlations given by SZ-CLAY/11/5130. The constructed multivariate probability density distribution is necessary for this updating step. [ABSTRACT FROM AUTHOR]

• A medaka embryo development monitoring method using differential EIS is proposed. • The proposed method has merits of eliminating the effect of EDL. • The extracted electrical characteristics reflect physiological changes of embryo well. A medaka embryo development monitoring method using differential Electrical Impedance Spectroscopy (EIS) is proposed. Impedance difference between measurement system with and without embryo is innovatively introduced to analyze embryo's development. Electrical characteristics of embryo are extracted from differential EIS. The proposed method has merits of eliminating the effect of electrical double layer (EDL) between electrodes and suspension. Besides relaxation frequency and its corresponding real/imaginary values of embryo, relaxation models and their fitting parameters are also extracted as properties of embryo in different developmental stages. In simulation, models of medaka embryo in 13 developmental stages from zygote stage to hatching stage are built, the extracted electrical characteristics reflect morphological and physiological changes of embryo well. In experiment, the proposed method is used to monitor medaka embryo's development from neurula stage to hatching stage. It also show that the electrical characteristics reflect physiological properties of embryo sensitively. [ABSTRACT FROM AUTHOR]

The avoidance of singularities is critical to design and control of parallel robots. This paper aims at efficient determination of the maximal singularity-free joint space and workspace of a class of six-DOF parallel robots with six kinematic chains of same type. We represent the singularity-free joint space by a 6-cube and determine it firstly. The singularity-free workspace is generated by continuous motion of all active joints in the singularity-free joint space. As a result, the boundary of the workspace can be obtained with simultaneous consideration of position and orientation of the mobile platform. The size relation between the maximal singularity-free joint space and workspace is discussed. To efficiently determine the singularity-free joint space and workspace, we propose dual quaternion-based Jacobian matrices and construct an efficient algorithm. The algorithm detects singularities in a given joint space and simultaneously calculates its corresponding workspace. The computational costs of the proposed algorithm and the traditional one are compared using a 6-U P S parallel robot, leading to 9 seconds and 458 seconds respectively. Finally, both the maximal singularity-free joint space and workspace of a 6- P US parallel robot are determined to further demonstrate the effectiveness of the new approach. [ABSTRACT FROM AUTHOR]

We report a novel electrostatic self-excited resonator that achieves frequency jump and mode transition under DC voltage powering and control. By gradually increasing the DC voltage by 10%, the frequency output can suddenly jump to 5 times of its original value with the oscillation mode transitioning from the first-order to the second-order. Further, by implementing an artificial insect wing on the resonator, we also present a dual-mode flapping-wing actuator with dramatic increases in lift force and power output after a frequency jump. The frequency jump and mode transition due to small voltage variations have great potential in the field of multi-mode propulsion devices for high-mobility micro-robots. [ABSTRACT FROM AUTHOR]

the six-axis vibration isolation system is essential for high-precision space systems. Its architecture is always designed based on the cubic-configuration Stewart platform, whose six flexible modes generally have different natural frequencies resulting in multiple resonances at various frequencies such that a uniform capability of vibration isolation cannot be achieved for the six flexible modes. To solve this problem, the dynamic isotropic design of the isolator is studied to make the six nonzero natural frequencies identical. The free-floating state of the isolator is taken into account and six design criteria of the dynamic isotropy are obtained. The internal relation between the dynamic isotropy and the kinematic isotropy is revealed and discussed. A decentralized active controller is then investigated for the isolator of dynamic isotropy. The controller decouples the six-axis vibration control into six identical control of a single-axis vibration isolator. The same control gains in each single-axis isolator reaches the optimum simultaneously for all the flexible modes such that a best performance of vibration isolation can be achieved. Finally, we present an example of an isolator of dynamic isotropy. With the proportional plus integral compensator, the uniform corner frequency and optimal active damping can eventually be achieved. [ABSTRACT FROM AUTHOR]

The forward kinematics is the basis of the design and control of the parallel robots. This paper aims to provide an efficient solution to the forward kinematics of a class of six-degrees-of-freedom parallel robots for real-time applications. With a unit dual quaternion used as the generalized coordinates of the robot system, the forward kinematic equations are derived to be a set of quadratic ones. An efficient algorithm is proposed to get the actual solution to them. The convergence and singularity problems of the new algorithm have been discussed. We have provided a convergence strategy and revealed the internal relation of the singularity with that of the parallel robot, proving the feasibility of the algorithm and giving the working condition in the practical applications. The new algorithm have been compared to the Newton's method for an 8-U P S parallel robot, resulting in the time consumptions of 0.2187 milliseconds and 14.25 milliseconds respectively. And then we perform a simulation of the state-feedback control for an 8- P US parallel robot. The two examples present the applications of the new algorithm and demonstrate its validity and efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Nogo-A is a major form of growth inhibitory molecule (growth-IM) which inhibits axonal regeneration and neurite regrowth after neural injury. Bone marrow stromal cells (MSCs) have been shown to inhibit Nogo-A expression in vitro and in cerebral ischemic animal models. The present study was designed to investigate the effects of treatment with human MSCs (hMSCs) impregnated into collagen scaffolds on the expression of Nogo-A and axonal plasticity after traumatic brain injury (TBI). Adult male Wistar rats were injured with controlled cortical impact and treated either with saline, hMSCs-alone or hMSCs impregnated into collagen scaffolds (scaffold+hMSC) transplanted into the lesion cavity 7 days after TBI. Rats were sacrificed 14 days after TBI and brain tissues were harvested for immunohistochemical studies, Western blot analysis, laser capture microdissections and qRT-PCR to evaluate axonal density and Nogo-A protein and gene expressions. Our data showed that treatment of TBI with scaffold+hMSC significantly decreased TBI-induced Nogo-A protein expression and increased axonal density compared to saline and hMSC-alone treatments. In addition, scaffold+hMSC transplantation decreased Nogo-A transcription in oligodendrocytes after TBI. Scaffold+hMSC treatment was superior to hMSC-alone treatment in suppressing Nogo-A expression and enhancing axonal regeneration after TBI. Our data suggest that transplanting hMSCs with scaffolds down-regulates Nogo-A transcription and protein expression which may partially contribute to the enhanced axonal regeneration after TBI. [Copyright &y& Elsevier]

Abstract: The beneficial effects of simvastatin on experimental traumatic brain injury (TBI) have been demonstrated in previous studies. In this study, we investigated the effects of simvastatin on axonal injury and neurite outgrowth after experimental TBI and explored the underlying mechanisms. Wistar rats were subjected to controlled cortical impact or sham surgery. Saline or simvastatin was administered for 14 days. A modified neurological severity score (mNSS) test was performed to evaluate functional recovery. Immunohistochemistry studies using synaptophysin, neurofilament H (NF-H) and amyloid-β precursor protein (APP) were performed to examine synaptogenesis and axonal injury. Primary cortical neurons (PCNs) were subjected to oxygen glucose deprivation (OGD) followed by various treatments. Western blot analysis was utilized to assess the activation of phosphatidylinositol-3 kinase (PI-3K)/Akt/mammalian target of rapamycin (mTOR) and glycogen synthase kinase 3β (GSK-3β)/adenomatous polyposis coli (APC) pathways. Simvastatin decreased the density of APP-positive profiles and increased the density of NF-H -positive profiles. Simvastatin reduced mNSS, which was correlated with the increase of axonal density. Simvastatin treatment stimulated the neurite outgrowth of PCNs after OGD, which was attenuated by LY294002 and enhanced by lithium chloride (LiCl). Simvastatin activated Akt and mTOR, inactivated GSK-3β and dephosphorylated APC in the injured PCNs. Our data suggest that simvastatin reduces axonal injury, enhances neurite outgrowth and promotes neurological functional recovery after experimental TBI. The beneficial effects of simvastatin on neurite outgrowth may be mediated through manipulation of the PI-3K/Akt/mTOR and PI-3K/GSK-3β/APC pathways. [Copyright &y& Elsevier]

Abstract: Technology absorption, assimilation and re-creation can be fulfilled by reverse engineering and re-creation. In the two steps, design knowledge base plays a very important role. The effects knowledge base is a powerful tool in solving technical problems and can inspire designers more effectively for creative design. This paper explores the use of the effects knowledge base to aid technology absorption, assimilation and re-creation. In the reverse engineering, the effects knowledge base is used to identify the appropriate function concept, solution principle to gain the design intent of the existing product. And then the effects knowledge base facilitates designers to generate the alternative solutions from the viewpoint of function, effect, principle, and structure for re-creation. [Copyright &y& Elsevier]

• A novel position measurement approach of a single particle using EIS is proposed. • A general expression is proposed to fit impedance distribution of different position. • SVR is innovatively introduced to tackle the inverse problem of position estimation. A novel position measurement approach for a single particle in a channel using Electrical Impedance Spectroscopy (EIS) only with two pairs of electrodes is proposed. The proposed approach is label-free, non-invasive and is very accurate in measurement domain by using machine learning method. Relationship between the single particle's position and the measured impedances is described by a set of nonlinear equations showing excellent fitting performance with R-square reaching 0.9999. Finding accurate analytical solution of the particle's position is the inverse problem, it is tackled by a well-trained Support Vector Regression (SVR) model with the help of multi-frequency EIS. The proposed approach is evaluated by simulation models with a single particle in 100 different positions. The results show that the approach performs an outstanding position measurement accuracy to reach 99.25%. Comparing with EIT, it has more simple structure, less measurement time and more accurate measurement results. [ABSTRACT FROM AUTHOR]

Abstract A new carbazole-based naked-eye colorimetric and fluorescent sensor CPPB with aggregation induced emission (AIE) effect was successfully synthesized. The solid powder of CPPB emitted intense yellow fluorescence, and its emission wavelength and fluorescence intensity in DMSO/H 2 O solution varied with the percentage of water (f w). Nano-aggregates of CPPB molecules were prepared by increasing f w of DMSO/H 2 O solution, and the optimal aggregation state of CPPB was reached in 99% aqueous DMSO solution with the maximum fluorescence intensity. Moreover, CPPB displayed high selectivity and sensitivity toward cyanide anions (CN−) in 99% aqueous DMSO solution even in the presence of other competitive anions (CN−, F−, Cl−, AcO−, NO 3 −, I−, CO 3 2−, HCO 3 −, HSO 3 −, SO 4 2−, S2−, HS−, OH−, H 2 PO 4 − and HPO 4 2−) and the reactive oxygen species (H 2 O 2 , O 2 ·−, 1O 2 , t-BuOOH and ·OH). The sensing mechanism for CN− was confirmed by optical spectral studies, 1H NMR titration, HRMS spectra, Job's plot analyses and DFT calculations. Sensor CPPB for CN− detection revealed extremely low detection limit (67.4 nM), high anti–interference ability, wide pH response range (3.0–10.0) as well as the immediate response (15 s). Furthermore, the CPPB -based test strips were applied to detect CN− qualitatively and quantitatively in 100% aqueous solution. Graphical abstract We have successfully developed sensor CPPB, which exhibited distinct aggregation induced emission (AIE) effect, and detected CN− based on naked-eye colorimetric and fluorescent sensing with high selectivity and great sensitivity. Image 1 Highlights • Carbazole-based sensor CPPB was designed and synthesized, which exhibited obvious aggregation induced emission (AIE) effect. • Sensor CPPB detected CN− in 99% aqueous DMSO solution, and the test strips of CPPB recognized CN− in 100% aqueous solution. • The detection limit of CPPB for CN− were at nanomolar level in 99% aqueous DMSO solution. • Colorimetric responses of CPPB toward CN− were visible with the naked eyes under sunlight and UV lamp (365 nm). [ABSTRACT FROM AUTHOR]

Background We conducted this prospective nested case–control study for the hepatic artery and portal vein hemodynamic changes after orthotopic liver transplantation. Methods A total 128 cases of orthotropic liver transplantation were analyzed, including 25 cases of ischemic type biliary lesions (ITBL). The portal vein and hepatic artery flow velocities were detected by ultrasound on days 28, 42, and 84 after liver transplantation. In the GLM analysis of Lg(S/D), the P values of Group Effect, Time Effect, and Time × Group were 0.014, 0.376, and 0.008, respectively. Conclusion Our results show a relatively reduced hepatic artery S/D in ITBL, especially in extrahepatic ITBL. [ABSTRACT FROM AUTHOR]

• A soft wearable exoskeleton with compliance tendon-sheath actuation is developed for elbow assistance. • A neural-network-enhanced torque estimation controller is proposed to improve assistance efficiency. • The effectiveness is validated by dumbbell-lifting experiments with various weights and frequencies. • The results are compared with proportional control strategy and sEMG-based assistive control strategy. Soft wearable exoskeletons are a new approach for the applications of power assistance and rehabilitation training. In the present work, a neural-network-enhanced torque estimation controller (NNETEC) is proposed for a soft wearable elbow assistance exoskeleton with compliant tendon-sheath actuator. A comprehensive overview for the major components of the soft exoskeleton is introduced. The locations of anchor points are optimized via the maximum-stiffness principle. The NNETEC strategy is developed by fusing the feedback signals from surface electromyography (sEMG) sensors, inertial measurement units, force sensors, and motor encoder. It consists of a joint torque estimation module to identify the elbow torque of wearer based on Kalman filter, a neural-network adjustment module to recognize human motion intention, and a proportional-integral-derivative controller with hybrid position/torque feedbacks. Further experimental investigations are carried out by five volunteers to validate the effectiveness of the proposed soft elbow exoskeleton and control strategy. The results of the dumbbell-lifting experiments with various weights and frequencies demonstrate that, when compared with the proportional control strategy and the sEMG-based assistive control strategy without neural-network adjustment, the developed NNETEC method can achieve higher power assistance efficiency. [ABSTRACT FROM AUTHOR]

Abstract Motor dysfunction has become a serious threat to the health of older people and the patients with neuromuscular impairment. The application of exoskeleton to motion assistance has received increasing attention due to its promising prospects. The major contribution of this paper is to develop a joint torque estimation control strategy for a soft elbow exoskeleton to provide effective power assistance. The surface electromyography signal (sEMG) from biceps is utilized to estimate the motion intension of wearer and map into the real-time elbow joint torque. Moreover, the control strategy fusing the estimated joint torque, estimated joint angle from inertial measurement unit and encoder feedback signal is proposed to improve motion assistance performance. Finally, further experimental investigations are carried out to compare the control effectiveness of the proposed intention-based control strategy to that of the proportional control strategy. The experimental results indicate that the proposed control strategy provides better performance in elbow assistance with different loads, and the average efficiency of assistance with heavy load is about 42.66%. Highlights • A soft elbow exoskeleton suit is developed to provide effective power assistance. • A sEMG-based elbow joint torque estimation control strategy is proposed. • The proposed control strategy is more efficient and stable than proportional strategy. • The average efficiency of power assistance with heavy load is about 42.66%. [ABSTRACT FROM AUTHOR]

The patients of paralysis with motion impairment problems require extensive rehabilitation programs to regain motor functions. The great labor intensity and limited therapeutic effect of traditional human-based manual treatment have recently boosted the development of robot-assisted rehabilitation therapy. In the present work, a neural-fuzzy adaptive controller (NFAC) based on radial basis function network (RBFN) is developed for a rehabilitation exoskeleton to provide human arm movement assistance. A comprehensive overview is presented to describe the mechanical structure and electrical real-time control system of the therapeutic robot, which provides seven actuated degrees of freedom (DOFs) and achieves natural ranges of upper extremity movement. For the purpose of supporting the disable patients to perform repetitive passive rehabilitation training, the RBFN-based NFAC algorithm is proposed to guarantee trajectory tracking accuracy with parametric uncertainties and environmental disturbances. The stability of the proposed control scheme is demonstrated through Lyapunov stability theory. Further experimental investigation, involving the position tracking experiment and the frequency response experiment, are conducted to compare the control performance of the proposed method to those of cascaded proportional-integral-derivative controller (CPID) and fuzzy sliding mode controller (FSMC). The comparison results indicate that the proposed RBFN-based NFAC algorithm is capable of obtaining lower position tracking error and better frequency response characteristic. [ABSTRACT FROM AUTHOR]

To ensure satisfactory control performance for the cable-driven manipulators under complex lumped uncertainties, a new continuous fractional-order nonsingular terminal sliding mode (CFONTSM) control scheme based on time delay estimation (TDE) is proposed and studied in this paper. The proposed control scheme contains three elements, a TDE element adopted to suitably cancel out the unknown lumped dynamics with purposely time-delayed signals of the closed-loop control system, a newly proposed FONTSM manifold adopted to realize finite-time convergence in the sliding mode phase and a fast-TSM-type reaching law adopted to ensure finite-time convergence in the reaching phase. The proposed control scheme is model-free and no longer needs system dynamics benefiting from TDE, which is very suitable and easy to use in practical applications. Meanwhile, high precision, fast convergence and good robustness against lumped uncertainties are ensured thanks to the newly proposed FONTSM manifold and adopted fast-TSM-type reaching law. Integrated stability analysis of the closed-loop control system is presented based on Lyapunov stability theory. Finally, the effectiveness of our proposed control scheme is demonstrated by comparative 2-DoFs (degrees-of-freedom) simulation and experiments. [ABSTRACT FROM AUTHOR]

Performing search and rescue tasks in the ruins after disasters demand rescue robots with slender and compliant structure to accommodate the complicated configurations under debris. This paper presents the structural design and system composition of a novel tendon-sheath actuated compliant rescue manipulator with slender and flexible body. The proposed robot can drill into the narrow space where rescuers and traditional rigid robots cannot get in because of size limitation or toxic environment. The self-sensing calibration, dynamic modeling, and hybrid force/position control trajectory of the compliant gripper with integrated position and force monitoring capabilities are analyzed and discussed. With the aim of regulating the gripper displacement and clamping force during operation, a hybrid force/position control strategy is proposed based on a cascaded proportional-integral-derivative (PID) controller and a fuzzy sliding mode controller (FSMC). Experimental setups mainly consisting of servo motor, tendon sheath transmission components, compliant gripper, and real-time control system are established to calibrate the strain gauge sensors and identify the dynamic model parameters. Further experimental investigations involving force tracking experiments, position tracking experiments, and object grasping experiments are carried out. The experimental results demonstrate the effectiveness of the developed self-sensing approach and control strategies during rescue operation. [ABSTRACT FROM AUTHOR]

MgAl-LDH/(BiO) 2 CO 3 p-n heterojunction nanocomposite was prepared using a hydrothermal method. The as-prepared MgAl-LDH/(BiO) 2 CO 3 composites were characterized through XRD, SEM&EDX, TEM, FT-IR, XPS, as well as UV–vis DRS. The photodegradation activity of MgAl-LDH/(BiO) 2 CO 3 was examined through the degradation of tetracycline under visible light irradiation. The maximum degradation efficiency (97.2%) was achieved among the heterostructures when the percentage of MgAl-LDH was 15%. Moreover, the degradation efficiency of MgAl-LDH/(BiO) 2 CO 3 still reached 88% after five successive cycles. Furthermore, a photocatalytic mechanism involved was proposed by exploring its energy band structure. In this study, a novel method for photocatalytic degradation of tetracycline was proposed. [Display omitted] • Synthesized a novel p–n junction photocatalyst MgAl-LDH/(BiO)2CO3. • The MgAl-LDH/(BiO) 2 CO 3 showed the higher degradation efficiency, reaching 97.2% in 105 min. • The catalyst has high catalytic stability, which still with 88% degradation efficiency after 5 cycles. • The study provides new insights into the photocatalytic degradation of antibiotics under visible light irradiation. [ABSTRACT FROM AUTHOR]

Abstract: We have previously demonstrated that human marrow stromal cells (hMSCs) embedded in collagen I scaffolds significantly enhance the restorative therapeutic effect of hMSCs after traumatic brain injury (TBI). In this study, we test the hypothesis that the collagen scaffold alters gene expression in hMSCs and that hMSCs impregnated into scaffolds increase the astrocytic expression of vascular endothelial growth factor (VEGF) in the injured brain. Following TBI induced by controlled cortical impact injury, scaffold with hMSCs (3.0×106), hMSCs-only and saline were implanted into the lesion cavity one week after brain injury (n =8/each group). Morris water maze and modified neurological severity scores were performed to evaluate the spatial learning and sensorimotor functions, respectively. Lesion volume and expression of VEGF were measured one week after different treatments. In vitro, total RNA from hMSCs was extracted one week after culture with or without collagen I scaffold for evaluation of gene microarrays. Furthermore, an RT-PCR study on a select subgroup of genes was performed to identify the changes of expression between the culturing hMSCs with collagen scaffolds and hMSCs only. The treatment of TBI with collagen scaffold impregnated with hMSCs significantly decreases the functional deficits from TBI within 7days after treatment, and significantly enhances the VEGF expression of astrocytes in the injured brain compared to the hMSCs-only group. In vitro data indicate that collagen scaffolds stimulate hMSCs to express multiple factors which may contribute to hMSC survival, tissue repair and functional recovery after TBI. [ABSTRACT FROM AUTHOR]

• Propose a novel robust control with feedforward compensation. • Prove the stability of the closed-loop control system considering the proposed dynamics. • Demonstrate the validity of proposed method through both simulations and experiments. For the trajectory tracking purpose of cable-driven robots, a novel robust control method is proposed and investigated in this paper. The proposed method consists of three elements, i.e. a time-delay estimation (TDE) element and a nonsingular fast terminal sliding mode (NFTSM) control element and a feedforward compensation. The TDE technique is utilized to estimate the lumped system dynamics in a simple but effective way, and then ensures an attractive model-free control scheme. The NFTSM control element is adopted to guarantee precise and robust control performance with continuous and singularity-free control efforts. Moreover, the feedforward compensation is also utilized to further enhance the control performance by taking advantages of the system dynamics. Due to this feedforward compensation element, higher control performance has been ensured compared with the traditional TDE-based control. Thanks to above three elements, the proposed method is practical to use and highly accurate and strongly robust. Comparative simulations and experiments were conducted to verify the effectiveness and superiorities of our proposed control method over the recently proposed one. [ABSTRACT FROM AUTHOR]

Artificial tendon is a kind of bionic actuation system capable of imitating the transmission characteristics of skeleton tendon. This paper presents a new compliant single-tendon-sheath artificial tendon actuator inspired by Hill-type muscle model. The proposed artificial tendon can perform variable compliance properties with two linear springs applying onto the tendon-sheath element. Detailed development and modeling of the actuation system is given, and transmission characteristics are analyzed and validated via simulations and experiments. Then, a bending angle measurement method is developed to compensate the variation of tendon-sheath configuration during transmission process. A model-based inverse control strategy with bending angle compensation is developed for displacement and force control without distal feedback. Trajectory tracking experiments are conducted to verify the effectiveness of the proposed control strategy. Experimental results indicate that the control errors of displacement and force control without distal feedback could be limited within 7.07% and 13.62%, respectively. [ABSTRACT FROM AUTHOR]