CPG Human Motion Phase Recognition Algorithm for a Hip Exoskeleton with VSA Actuator

Due to the dynamic stiffness characteristics of human joints, it is easy to cause impact and disturbance on normal movements during exoskeleton assistance. This not only brings strict requirements for exoskeleton control design, but also makes it difficult to improve assistive level. The Variable Stiffness Actuator (VSA), as a physical variable stiffness mechanism, has the characteristics of dynamic stiffness adjustment and high stiffness control bandwidth, which is in line with the stiffness matching experiment. However, there are still few works exploring the assistive human stiffness matching experiment based on VSA. Therefore, this paper designs a hip exoskeleton based on VSA actuator and studies CPG human motion phase recognition algorithm. Firstly, this paper puts forward the requirements of variable stiffness experimental design and the output torque and variable stiffness dynamic response standards based on human lower limb motion parameters. Plate springs are used as elastic elements to establish the mechanical principle of variable stiffness, and a small variable stiffness actuator is designed based on the plate spring. Then the corresponding theoretical dynamic model is established and analyzed. Starting from the CPG phase recognition algorithm, this paper uses perturbation theory to expand the first-order CPG unit, obtains the phase convergence equation and verifies the phase convergence when using hip joint angle as the input signal with the same frequency, and then expands the second-order CPG unit under the premise of circular limit cycle and analyzes the frequency convergence criterion. Afterwards, this paper extracts the plate spring modal from Abaqus and generates the neutral file of the flexible body model to import into Adams, and conducts torque-stiffness one-way loading and reciprocating loading experiments on the variable stiffness mechanism. After that, Simulink is used to verify the validity of the criterion. Finally, based on the above criterions, the signal mean value is removed using feedback structure to complete the phase recognition algorithm for the human hip joint angle signal, and the convergence is verified using actual human walking data on flat ground.

Sandwiching Sulfur into the Dents Between N,O Co-Doped Graphene Layered Blocks with Strong Physicochemical Confinements for Stable and High-Rate Li-S Batteries

The development of lithium-sulfur batteries(LSBs)is restricted by their poor cycle stability and rate performance due to the low conductivity of sulfur and severe shuttle effect.Herein,an N,O co-doped graphene layered block(NOGB)with many dents on the graphene sheets is designed as effective sulfur host for high-performance LSB s.The sulfur platelets are physically confined into the dents and closely contacted with the graphene scaffold,ensuring structural stability and high conductivity.The highly doped N and O atoms can prevent the shuttle effect of sulfur species by strong chemical adsorption.Moreover,the micropores on the graphene sheets enable fast Li^+transport through the blocks.As a result,the obtained NOGB/S composite with 76 wt%sulfur content shows a high capacity of 1413 mAh g^-1 at 0.1 C,good rate performance of 433 mAh g^-1 at 10 C,and remarkable stability with 526 mAh g^-1 at after 1000 cycles at 1 C(average decay rate:0.038%per cycle).Our design provides a comprehensive route for simultaneously improving the conductivity,ion transport kinetics,and preventing the shuttle effect in LSBs.

Precise and controllable tandem strategy triggering boosted oxygen reduction activity

The development of efficient and cost‐effective metal‐free electrocatalysts for oxygen reduction reaction(ORR)has become crucial for electrochemical energy systems.However,reasonably validating and precisely regulating the active sites for designing optimized materials are still challenging.Herein,we report a precise and controllable tandem strategy to boost the ORR activity based on metal‐free covalent organic frameworks(MFCOFs)comprising imine‐N,thiophene‐S,or triazine‐N.Among these MFCOFs,post‐tandem BTT‐TAT‐COF structure displayed a more positive catalytic capability and excellent electrochemical stability,indicating that the synergistic catalysis of multiple active sites induced the ORR catalytic activity through the conjugated skeleton of the structure.Density‐functional theory calculations suggest that the series‐connected backbone contained highly effective electrocatalytic active centers and provided synergistic catalysis.More importantly,this strategy highlights new opportunities for the advancement of efficient COF‐based metal‐free ORR catalysts.

Novel design and synthesis of 1D bamboo-like CNTs@Sn_(4)P_(3)@C coaxial nanotubes for long-term sodium ion storage

In this work,a novel bamboo-like carbon nanotubes@Sn4P3@carbon(BLCNTs@Sn_(4)P_(3)@C)coaxial nanotubes are designed and prepared using a newly developed hydrothermal method followed by a phophidation process.The prepared Sn_(4)P_(3) nanoparticles are uniformly coated and wrapped on the one-dimensional(1D)bamboo-like CNTs,which is covered by a uniform carbon layer to form a sandwich-like structure with Sn_(4)P_(3) in between.The inner CNT and outer carbon can effectively maintain the structural stability and serve as the good electron conductors.Additionally,the outer carbon coating layer can effectively keep BLCNTs@Sn_(4)P_(3)@C nanotubes separate each other,preventing aggregation of Sn_(4)P_(3) during charge/discharge when this material is used as anode for sodium ion batteries.The anode of BLCNTs@Sn_(4)P_(3)@C shows excellent reversible capacity and a long cycling of over 2000 cycles.The unique design of coaxial nanotubes is greatly beneficial to the electrochemical performance of Sn_(4)P_(3) for sodium ion storage.

Toward the Design of High-performance Supercapacitors by Prussian Blue, its Analogues and their Derivatives

Supercapacitors(SCs)with high power output have attracted increasing attention as efficient and environmentally friendly energy storage devices.Prussian blue and its analogues(PB/PBAs)are simple coordination polymers with tunable chemical compositions and open framework.Prussian blue can act as electrode materials in its pristine form and has also been utilized to derive various metallic nanostructures for electrochemical applications due to their simple fabrication process,non-toxic characteristics,and low price.Here,we firstly describe the charge storage mechanisms of SCs briefly followed by an introduction of the fabrication methods of PB/PBAs and their derivatives.Then,a comprehensive review on recent studies of the use of PB/PBAs and their derivatives as the electrode materials for SCs are given with a focus on strategies to improve their electrochemical performances.Finally,we discuss critical challenges in this research area and propose some general ideas for future research.

Recent Progress of Catalytic Cathodes for Lithium-oxygen Batteries

Lithium-oxygen batteries are among the most promising electrochemical energy storage systems,which have attracted significant attention in the past few years duo to its far more energy density than lithium-ion batteries.Lithium oxygen battery energy storage is a reactive storage mechanism,and the discharge and charge processes are usually called oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).Consequently,complex systems usually create complex problems,lithium oxygen batteries also face many problems,such as excessive accumulation of discharge products(Li_(2)O_(2))in the cathode pores,resulting in reduced capacity,unstable cycling performance and so on.Cathode catalyst,which could influence the kinetics of OER and ORR in lithium oxygen(Li-O_(2))battery,is one of the decisive factors to determine the electrochemical performance of the battery,so the design of cathode catalyst is vitally important.This review discusses the catalytic cathode materials,which are divided into four parts,carbon based materials,metals and metal oxides,composite materials and other materials.

Freestanding film formed with Sb-nanoplates embedded in flexible porous carbon nanofibers as a binder-free anode for high-performance wearable potassium-ion battery

Antimony-based materials are considered as promising anodes for potassium ion batteries due to their high theoretical capacity and low electrode potential. However, the aggregation and bulk expansion of Sb particles in cycling will cause capacity attenuation and poor rate performance. In this paper, Sb nanoplates were designed to be embedded in flexible porous N-dopped carbon nanofibers(Sb@PCNFs)by a simple electrospinning deposition(ESD) method. In this structural design, Sb nanoplates of high capacity were employed as active materials, N-dopped carbon nanofibers were used to improve conductivity and structural stability. The introduction of pore-forming agent enables the nanofibers to possess porous structure, thus buffering the huge volume change and promoting the transfer of electrolyte/ions.More importantly, the freestanding film can be directly used as a working electrode, reducing the redundancy in the battery and the cost. Benefitting from the favorable structure, the freestanding flexible Sb@PCNFs electrode shows excellent potassium storage performance with a capacity of 314 m Ah/g after 2000 cycles at 500 m A/g. This strategy of employing active material with high capacity in porous and conductive flexible nanofibers represents an effective method of achieving binder-free electrode with good electrochemical performance towards wearable energy storage devices.

Half‑Power Prediction and Its Application on the Energy Management Strategy for Fuel Cell City Bus

The fuel cell hybrid powertrain is a potential power supply system for fuel cell vehicles.The underlying problem is that the fuel cell vehicles encounter exhaustive hydrogen consumption.To effectively manage hydrogen consumption,the aim is to propose fuel cell city bus power and control system.The underlying idea is to determine the target power of fuel cell through simulation study on fuel cell and battery energy management strategy and road test verifications.A half-power prediction energy management strategy is implemented to predict the target power of the fuel cell in the current time step based on the demand power of the vehicle and the state of charge(SOC)of the battery in the previous time steps.This offers better understanding of the correlation between fuel cell power and vehicle drive cycle for enabling effective power supply management.The research results show that the half-power prediction energy management strategy effectively reduces the hydrogen consumption of the vehicle by 7.1%and the number of battery cycle by 6.0%,compared to the stepped manage-ment strategy of battery SOC.When applied to a 12-m fuel cell city bus—F12,specially designed and manufactured for the Winter Olympic Games in 2022—the fuel economy of 3.7 kg/100 km is achieved in urban road conditions.This study lays a foundation for providing the powertrain configuration and energy management strategy of fuel cell city bus.

The effect of aerobic dancing on physical fitness and cognitive function in older adults during the COVID-19 pandemic-a natural experiment

During the Coronavirus disease(COVID-19),the physical activity of older adults is at a lower level.The study aimed to examine the effectiveness of aerobic dancing on physical fitness and cognitive function in older adults.We conducted a randomized controlled trial with 34 older adults who were assigned into an aerobic dancing group and a control group.Three dance sessions weekly for 60min were scheduled for the aerobic dancing group for a total of 12 weeks.Physical fitness,blood pressure,lipids,glucose,cognitive function were assessed before and after the intervention.Baseline adjusted Analysis of Covariance(ANCOVA)was used to determine whether outcome variables varied between groups at pre-test and post-test.Effect size(Cohen's d)was calculated to determine the differences between groups from baseline to post-test.After 12 weeks,we found that the aerobic dancing group showed significant improvement in memory(portrait memory:F=10.45,p=0.003,d=1.18).The Limit of Stability(LOS)parameters in the aerobic dancing group displayed a significant increase after the intervention(right angle:F=5.90,p=0.022,d=0.60;right-anterior angle:F=4.23,p=0.049,d=0.12).Some beneficial effects were found on flexibility,grip strength,balance and subjective well-being(sit and reach:F=0.25,p=0.62,d=−0.40;grip strength:F=3.38,p=0.08,d=0.89;one-legged standing with eyes closed:F=1.26,p=0.27,d=0.50)in the aerobic dancing group.Aerobic dancing training was effective in improving memory and balance ability in older adults during the COVID-19 pandemic in China.In the future,aerobic dancing is a promising tool to encourage physical activity in older adults.