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We present a reconfigurable elastic metasurface design composed of an array of zigzag-folded sheets with parallel corrugations to control the wavefront of the refracted A0 Lamb mode wave. The performance of this origami-inspired metasurface can be tuned by tailoring the thickness and folding angles of the sheets. Zigzag-folded sheets exhibit dynamic properties depending on their thicknesses and folding angles, yielding different phase profiles required for wavefront control via the metasurface. The transmission characteristics and phase modulation capability of the metasurface units are studied through numerical models and utilized to inform the metasurface design reconfiguring for different wave functions, such as wave focusing and deflecting at different frequencies. The design frameworks and the applicability of the reconfigurable metasurface are validated using a full-scale experimental setup. Overall, the proposed metasurface can accomplish distinct wavefront controls at adjustable geometrical parameters, developing new potentials for designing intelligent systems adaptable to different environments.

Male fetal Leydig cells in the testis secrete androgen and insulin-like 3, determining the sexual differentiation. The abnormal development of fetal Leydig cells could lead to the reduction of androgen and insulin-like 3, thus causing the male reproductive tract anomalies in male neonates, including cryptorchidism and hypospadias. Environmental pollutants, such as phthalic acid esters (phthalates), can perturb the development and differentiated function of Leydig cells, thereby contributing to the reproductive toxicity in the male. Here, we review the epidemiological studies in humans and experimental investigations in rodents of various phthalates. Most of phthalates disturb the expression of various genes encoded for steroidogenesis-related proteins and insulin-like 3 in fetal Leydig cells and the dose-additive effects are exerted after exposure in a mixture.

Accurate position control of pneumatic artificial muscle actuated systems has always been difficult due to their inherent nonlinear hysteresis characteristics. This article designs a bio-inspired semi-active robotic joint that is synergistically driven by a pneumatic artificial muscle and an extension spring by imitating the mechanism of energy storage and return in animals and then studies its position tracking control with hysteresis compensation. To simplify the derivation of the inverse hysteresis model which functions as hysteresis compensator, a novel approach termed as direct inverse hysteresis modeling is adopted. With this method, the inversion of the asymmetric angle–pressure hysteresis of the semi-active joint is modeled directly from experimental measurements by a modified Prandtl–Ishlinskii model. On the basis, a closed-loop position tracking controller composed of forward hysteresis compensation and conventional proportional–integral–derivative control is designed for the joint. Experimental results indicate that the proposed controller can track the reference position signals with high accuracy.

Rescue robots that can penetrate into narrow gaps in the rubble, create and maintain spaces for rescuers after earthquakes are urgently needed in search and rescue missions. This paper proposes two novel rescue robots, including a cutting robot and a jack robot, which are used to cut obstacles and jack up heavy debris in hazardous locations and in narrow spaces, where rescuers cannot work or approach. Firstly, a multi-linked tracked, or snake-like rescue robot platform is designed, which is composed of modular crawler vehicles connected by active and passive joints with three degrees of freedom. This rescue robot platform has high mobility on irregular terrains and the ability to move into narrow collapsed structures. Then, portable rescue tools including an electric cutter and a novel electric screw jack are designed. In order to perform operations to the tools, manipulators with multi degrees of freedom are also developed. Consequently, the cutting robot and jack robot are realized by equipping the corresponding rescue tool and manipulator in the rescue robot platform. Finally, field tests of the two rescue robots operating on different terrains and performing rescue missions are carried out in the national training base for urban search and rescue. The results validated the mobility, cutting and lift-up capacity of the two rescue robots. The experiments show that they might play some role in rescue operations.

Walking on rough terrains still remains a challenge that needs to be addressed for biped robots because the unevenness on the ground can easily disrupt the walking stability. This paper proposes a novel foot system with passively adjustable stiffness for biped robots which is adaptable to small-sized bumps on the ground. The robotic foot is developed by attaching eight pneumatic variable stiffness units to the sole separately and symmetrically. Each variable stiffness unit mainly consists of a pneumatic bladder and a mechanical reversing valve. When walking on rough ground, the pneumatic bladders in contact with bumps are compressed, and the corresponding reversing valves are triggered to expel out the air, enabling the pneumatic bladders to adapt to the bumps with low stiffness; while the other pneumatic bladders remain rigid and maintain stable contact with the ground, providing support to the biped robot. The performances of the proposed foot system, including the variable stiffness mechanism, the adaptability on the bumps of different heights, and the application on a biped robot prototype are demonstrated by various experiments.

The under-actuated foot rotation that the heel of the stance leg lifts off the ground and the body rotates around the stance toe is an important feature in human walking. However, it is absent in the realized walking gait for the majority of biped robots because of the difficulty and complexity in the control it brings about. In this paper, a hybrid control approach aiming to integrate the main characteristics of human walking into a simulated seven-link biped robot is presented and then verified with simulations. The bipedal robotic gait includes a fully actuated single support phase with the stance heel supporting the body, an under-actuated single support phase, with the stance toe supporting the body, and an instantaneous double support phase when the two legs exchange their roles. The walking controller combines virtual force control and foot placement control, which are applied to the stance leg and the swing leg, respectively. The virtual force control assumes that there is a virtual force which can generate the desired torso motion on the center of mass of the torso link, and then the virtual force is applied through the real torques on each actuated joint of the stance leg to create the same effect that the virtual force would have created. The foot placement control uses a path tracking controller to follow the predefined trajectory of the swing foot when walking forward. The trajectories of the torso and the swing foot are generated based on the cart-cable model. Co-simulations in Adams and MATLAB show that the desired gait is achieved with a biped robot under the action of the proposed method.

Tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular beam sampling mass spectrometry techniques were used for examining a fuel-lean laminar premixed methylmethacrylate (MMA)/oxygen/argon flame at 2.6kPa with an equivalence ratio of 0.75. Results suggest the identification of 43 compounds formed in the MMA flame.

The under-actuated foot rotation that the heel of the stance leg lifts off the ground and the body rotates around the stance toe is an important feature in human walking. However, it is absent in the realized walking gait for the majority of biped robots because of the difficulty and complexity in the control it brings about. In this paper, a hybrid control approach aiming to integrate the main characteristics of human walking into a simulated seven-link biped robot is presented and then verified with simulations. The bipedal robotic gait includes a fully actuated single support phase with the stance heel supporting the body, an under-actuated single support phase, with the stance toe supporting the body, and an instantaneous double support phase when the two legs exchange their roles. The walking controller combines virtual force control and foot placement control, which are applied to the stance leg and the swing leg, respectively. The virtual force control assumes that there is a virtual force which can generate the desired torso motion on the center of mass of the torso link, and then the virtual force is applied through the real torques on each actuated joint of the stance leg to create the same effect that the virtual force would have created. The foot placement control uses a path tracking controller to follow the predefined trajectory of the swing foot when walking forward. The trajectories of the torso and the swing foot are generated based on the cart-cable model. Co-simulations in Adams and MATLAB show that the desired gait is achieved with a biped robot under the action of the proposed method. [ABSTRACT FROM AUTHOR]

BACKGROUND: High-performance position control of pneumatic artificial muscles is limited by their inherent nonlinearity and hysteresis. OBJECTIVE: This study aims to model the length/pressure hysteresis of a single pneumatic artificial muscle and to realize its accurate position tracking control with forward hysteresis compensation. METHODS: The classical Prandtl--Ishlinskii model is widely used in hysteresis modelling and compensation. But it is only effective for symmetric hysteresis. Therefore, a modified Prandtl--Ishlinskii model is built to characterize the asymmetric length/pressure hysteresis of a single pneumatic artificial muscle, by replacing the classical play operators with two more flexible elementary operators to independently describe the ascending branch and descending branch of hysteresis loops. On the basis, a position tracking controller, which is composed of cascade forward hysteresis compensation and simple proportional pressure controller, is designed for the pneumatic artificial muscle. RESULTS: Experiment results show that theMPI model can reproduce the length/pressure hysteresis of the pneumatic artificial muscle, and the proposed controller for the pneumatic artificial muscle can track the reference position signals with high accuracy. CONCLUSION: By modelling the length/pressure hysteresis with the modified Prandtl--Ishlinskii model and using its inversion for compensation, precise position control of a single pneumatic artificial muscle is achieved. [ABSTRACT FROM AUTHOR]

Pneumatic artificial muscles have been widely used in various fields owing to their inherent compliance and high power-to-weight ratio. However, the natural hysteresis nonlinearity including length/pressure hysteresis and force/pressure hysteresis degrades their performance in precise tracking control, making it necessary to build a mathematical hysteresis model for hysteresis compensation. This paper deals with the modelling of length/pressure hysteresis of pneumatic artificial muscles. The length/pressure hysteresis loops measured by the isotonic test are found to be asymmetric and independent of the external load when the load is small. Considering that the classical Prandtl-Ishlinskii model is only effective for symmetric hysteresis, a modified Prandtl-Ishlinskii model is proposed to describe the length/pressure hysteresis behaviour. The developed model utilizes two asymmetric operators with simple mathematical forms to independently model the ascending branch and descending branch of hysteresis loops. The model parameters are identified using the recursive least square algorithm. Comparisons between simulation results and experimental measurements demonstrate that the proposed model can characterize the asymmetric major hysteresis loop and minor hysteresis loops with high accuracy. [ABSTRACT FROM AUTHOR]

This study was designed to estimate the human risk to polybrominated diphenyl ethers (PBDEs) exposure via two main exposure routes (dust and diet) in an e-waste recycling area in southern China. A total of 134 dust samples and 129 food samples were analyzed by gas chromatography/mass spectrometry (GC/MS). The mean concentration of ΣPBDE in in-house dust (38,685ng/g dw) was higher than that in out-house dust (24,595ng/g). For food samples, the highest concentration of ΣPBDE was found in fish and shellfish (2755ng/kg ww), followed in descending order by eggs (2423ng/kg), cereals (2239ng/kg) and meat (1799ng/kg). The estimated total daily dietary intake of PBDEs was 1671ng/day for adults and 952ng/day for children. The present study indicated that dust intake was the dominant PBDE exposure route for children, and the dietary intake was the dominant PBDE exposure route for adults. Our findings revealed high PBDE concentrations in dust and food samples collected at the center of e-waste recycling area, raising significant health concerns for residents in this particular region, especially for children. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Triphenyltin delays stem Leydig cell regeneration. • Triphenyltin lowers Leydig cell number. • Triphenyltin down-regulates steroidogenic gene expression. • Triphenyltin lowers AKT and ERK1/2 phosphorylation. • Triphenyltin delays spermatogenesis. Abstract Triphenyltin (TPT) is an organotin compound and may be an endocrine disruptor, impairing the male reproductive system. However, the effect of short-term TPT exposure on stem Leydig cell regeneration later on remains unknown. Here, we show that TPT affects stem Leydig cell regeneration in the adult rat testis. Adult male Sprague Dawley rats were gavaged with TPT (0, 0.5, 1.0, 2.0 mg/kg body weight/day) for 10 days, followed by a single intraperitoneal injection of ethane dimethane sulfonate (EDS, 75 mg/kg body weight) to eliminate Leydig cells. Testis parameters and hormone levels were investigated on post-EDS days 21, 35, and 56. TPT significantly reduced serum testosterone levels, decreased Leydig cell number and cell size, and down-regulated its specific gene and protein expression at 1.0 and 2.0 mg/kg even 56 days after cession of treatment. TPT lowered PCNA-labeling index of progenitor Leydig cells on post-EDS day 21. TPT also lowered AKT1 and AKT2, and ERK1/2 phosphorylation on post-EDS day 56. This study reveals that a short-term exposure to TPT blocks stem Leydig cell regeneration in the long term thus delaying spermatogenesis. [ABSTRACT FROM AUTHOR]