Model Parameters Identification and Backstepping Control of Lower Limb Exoskeleton Based on Enhanced Whale Algorithm

Exoskeletons generally require accurate dynamic models to design the model-based controller conveniently under the human-robot interaction condition.However,due to unknown model parameters such as the mass,moment of inertia and mechanical size,the dynamic model of exoskeletons is difficult to construct.Hence,an enhanced whale optimization algorithm(EWOA)is proposed to identify the exoskeleton model parameters.Meanwhile,the periodic excitation trajectories are designed by finite Fourier series to input the desired position demand of exoskeletons with mechanical physical constraints.Then a backstepping controller based on the identified model is adopted to improve the human-robot wearable comfortable performance under cooperative motion.Finally,the proposed Model parameters identification and control are verified by a two-DOF exoskeletons platform.The knee joint motion achieves a steady-state response after 0.5 s.Meanwhile,the position error of hip joint response is less than 0.03 rad after 0.9 s.In addition,the steady-state human-robot interaction torque of the two joints is constrained within 15 N·m.This research proposes a whale optimization algorithm to optimize the excitation trajectory and identify model parameters.Furthermore,an enhanced mutation strategy is adopted to avoid whale evolution’s unsatisfactory local optimal value.

Biochar induced trade-offs and synergies between ecosystem services and crop productivity

Biochar amendment offers a chance for sustainable agriculture.However,the effectiveness of biochar relies on its physical and chemical properties,which are heavily affected by biochar production conditions and management practices.Therefore,substantial uncertainties regarding the use of biochar exist in agricultural systems globally.This study provides the first quantitative evaluation of the impacts of biochar characteristics and management practices on key ecosystem services by performing a second-order meta-analysis based on 34,628 paired observations in biochar-amended and unamended systems.Overall,biochar enhances phytotoxicity alleviation,physiology regulation,soil remediation and carbon sequestration,and microbial functional gene abundance.However,some prominent trade-offs exist between crop productivity and ecosystem service deliveries including for nutrient cycling,microbial function,climate change mitigation,and the soil microbial community.The adoption of low C:N biochar produced at high pyrolysis temperatures from sewage sludge-derived feedstock,in combination with a moderate application rate and inorganic fertilizer input,shows potential for achieving synergistic promotion of crop productivity and ecosystem services.These outcomes highlight the need for judicious implementation of biochar-based solutions to site-specific soil constraints.The quantified synergy and tradeoff relationships will aid the establishment of a sustainable biochar development framework that strengthens necessary ecosystem services commensurate with food security assurance.

构筑高效耐腐蚀的碳铠甲层包覆Co_(9)Se_(8)电催化剂用于海水基锌空气电池

得益于较高的理论能量密度、环境友好性和丰富的海水储量,海水基锌-空气电池(S-ZABs)被认为是一种极具应用前景的储能和能源转换装置,是解决能源短缺和环境污染问题的能源装置之一。然而对于S-ZABs而言,构筑在海水中具有高耐氯离子腐蚀性与高性能的阴极氧还原反应电催化剂仍然具有挑战性。因此,我们通过高温硒化策略,在氮掺杂介孔碳材料上设计了超薄碳铠甲层封装的Co_(9)Se_(8)纳米颗粒高效ORR电催化剂(命名为NMC-Co_(9)Se_(8))。外部的超薄碳铠甲层不仅可以改善催化过程中的电子转移过程,抑制纳米颗粒的团聚,而且可以作为盔甲保护内部活性位点免受Cl^(-)吸附和腐蚀。得益于这种独特的结构,NMC-Co_(9)Se_(8)在0.1 mol·L^(-1)KOH海水电解质中表现出优异的ORR性能,其起始电位为0.904V,半波电位为0.860 V。更重要的是,基于NMC-Co_(9)Se_(8)催化剂的S-ZABs可提供172.4 m W·cm^(-2)的功率密度和超过150h的优异长期放电稳定性,均高于基于Pt/C的S-ZABs性能。这项工作为开发用于海水基锌-空气电池和其他能源转换技术具有耐氯离子腐蚀且高效的ORR催化剂提供了新思路。

Exponentially Convergent Multiscale Finite Element Method

We provide a concise review of the exponentially convergent multiscale finite element method(ExpMsFEM)for efficient model reduction of PDEs in heterogeneous media without scale separation and in high-frequency wave propagation.The ExpMsFEM is built on the non-overlapped domain decomposition in the classical MsFEM while enriching the approximation space systematically to achieve a nearly exponential convergence rate regarding the number of basis functions.Unlike most generalizations of the MsFEM in the literature,the ExpMsFEM does not rely on any partition of unity functions.In general,it is necessary to use function representations dependent on the right-hand side to break the algebraic Kolmogorov n-width barrier to achieve exponential convergence.Indeed,there are online and offline parts in the function representation provided by the ExpMsFEM.The online part depends on the right-hand side locally and can be computed in parallel efficiently.The offline part contains basis functions that are used in the Galerkin method to assemble the stiffness matrix;they are all independent of the right-hand side,so the stiffness matrix can be used repeatedly in multi-query scenarios.

A distinctive HPHT platform with different types of large-volume press subsystems at SECUF

Large-volume presses(LVPs)providing large volumes,liquid media,deformation capability,jump compression,and in situ measurements are in great demand for high-pressure research,particularly in the fields of geoscience,condensed matter physics,material science,chemistry,and biology.A high-pressure and high-temperature(HPHT)platform with different LVP subsystems,both solid-state and liquid environments,and nonequilibrium subsystems,has been constructed at the Synergetic Extreme Condition User Facility,Jilin University.This article describes the construction of the different subsystems and provides an overview of the capabilities and characteristics of the different HPHT subsystems.A large sample volume(1000 mm^(3))at 20 GPa is achieved through the use of a belt-type apparatus in the solid-state subsystem.HPHT conditions(1.8 GPa and 1000 K)are realized in the liquid subsystem through the use of a piston-cylinder-type LVP with optical diamond windows for in situ spectroscopic measurements.A maximum pressure jump to 10.2 GPa can be reached within 20 ms in the nonequilibrium subsystem with the use of an improved bladder-pressurization jump press.Some typical results obtained with different LVPs are briefly reviewed to illustrate the applications and advantages of these presses.In summary,the platform described here has the potential to contribute greatly to high-pressure research and to innovations in high-pressure technology.

Simulation Method and Feature Analysis of Shutdown Pressure Evolution During Multi-Cluster Fracturing Stimulation

Multistage multi-cluster hydraulic fracturing has enabled the economic exploitation of shale reservoirs,but the interpretation of hydraulic fracture parameters is challenging.The pressure signals after pump shutdown are influenced by hydraulic fractures,which can reflect the geometric features of hydraulic fracture.The shutdown pressure can be used to interpret the hydraulic fracture parameters in a real-time and cost-effective manner.In this paper,a mathematical model for shutdown pressure evolution is developed considering the effects of wellbore friction,perforation friction and fluid loss in fractures.An efficient numerical simulation method is established by using the method of characteristics.Based on this method,the impacts of fracture half-length,fracture height,opened cluster and perforation number,and filtration coefficient on the evolution of shutdown pressure are analyzed.The results indicate that a larger fracture half-length may hasten the decay of shutdown pressure,while a larger fracture height can slow down the decay of shutdown pressure.A smaller number of opened clusters and perforations can significantly increase the perforation friction and decrease the overall level of shutdown pressure.A larger filtration coefficient may accelerate the fluid filtration in the fracture and hasten the drop of the shutdown pressure.The simulation method of shutdown pressure,as well as the analysis results,has important implications for the interpretation of hydraulic fracture parameters.

Generation of induced pluripotent stem cells from human β-thalassemia fibroblast cells

Dear Editor, Induced pluripotent stem （iPS） cells have recently been generated by directly introducing several transcription factors into differentiated human somatic cells, and these iPS cells show great similarities to embryo-derived ES cells. Moreover, patient-specific iPS cells have recently been generated, and these studies provided hopes for patients with genetic and degenerative diseases . β-thalassemia is an inherited blood disorder that is characterized by reduced synthesis of hemoglobin subunit beta （hemoglobin β-chain）. Individuals with thalassemia major （also called Cooley＇s anemia） have severe anemia and hepatosplenomegaly; without treatment, affected children have severe failure to thrive and a shortened life expectancy. Even with transfusion and chelation therapy treatments, the life span of patients with thalassemia major can only be extended for a limited time.

Methods to Evaluate and Measure Power of Pneumatic System and Their Applications

Pneumatic system has been widely used throughout industry, and it consumes more than billions kW h of electricity one year all over the world. So as to improve the efficiency of pneumatic system, its power evaluation as well as measurement methods should be proposed, and their applicability should be validated. In this paper, firstly, power evaluation and measurement methods of pneumatic system were introduced for the first time. Secondly, based on the proposed methods, power distributions in pneumatic system was analyzed. Thirdly, through the analysis on pneumatic efficiencies of typical compressors and pneumatic components, the applicability of the proposed methods were validated. It can be concluded that, first of all, the proposed methods to evaluation and measurement the power of pneumatic system were efficient. Furthermore, the pneumatic power efficiencies of pneumatic system in the air production and cleaning procedure are respectively about 35%–75% and 85%–90%. Moreover, the pneumatic power efficiencies of pneumatic system in the transmission and consumption procedures are about 70%–85% and 10%–35%. And the total pneumatic power efficiency of pneumatic system is about 2%–20%, which varies largely with the system configuration. This paper provides a method to analyze and measure the power of pneumatic system, lay a foundation for the optimization and energy-saving design of pneumatic system.

New strategy of S,N co‐doping of conductive‐copolymer‐derived carbon nanotubes to effectively improve the dispersion of PtCu nanocrystals for boosting the electrocatalytic oxidation of methanol

Efficacious regulation of the geometric and electronic structures of carbon nanomaterials via the introduction of defects and their synergy is essential to achieving good electrochemical performance.However,the guidelines for designing hybrid materials with advantageous structures and the fundamental understanding of their electrocatalytic mechanisms remain unclear.Herein,superfine Pt and PtCu nanoparticles supported by novel S,N‐co‐doped multi‐walled CNT(MWCNTs)were prepared through the innovative pyrolysis of a poly(3,4‐ethylenedioxythiophene)/polyaniline copolymer as a source of S and N.The uniform wrapping of the copolymer around the MWCNTs provides a high density of evenly distributed defects on the surface after the pyrolysis treatment,facilitating the uniform distribution of ultrafine Pt and PtCu nanoparticles.Remarkably,the Pt_(1)Cu_(2)/SN‐MWCNTs show an obviously larger electroactive surface area and higher mass activity,stability,and CO poisoning resistance in methanol oxidation compared to Pt/SN‐MWCNTs,Pt/S‐MWCNTs,Pt/N‐MWCNTs,and commercial Pt/C.Density functional theory studies confirm that the co‐doping of S and N considerably deforms the CNTs and polarizes the adjacent C atoms.Consequently,both the adsorption of Pt1Cu2 onto the SN‐MWCNTs and the subsequent adsorption of methanol are enhanced;in addition,the catalytic activity of Pt_(1)Cu_(2)/SN‐MWCNTs for methanol oxidation is thermodynamically and kinetically more favorable than that of its CNT and N‐CNT counterparts.This work provides a novel method to fabricate high‐performance fuel cell electrocatalysts with highly dispersed and stable Pt‐based nanoparticles on a carbon substrate.

Gas Leakage Detection and Pressure Difference Identification by Asymmetric Differential Pressure Method

Currently,the measurement methods for pneumatic system leakage include bubbling,ultrasonic,and pressure detection methods.These methods are sensitive to high-precision sensors,long detection times,and stable external environments.The traditional differential pressure method involves severe differential pressure fluctuations caused by environmental pressure fluctuations or electromagnetic noise interference of sensors,leading to inaccurate detection.In this paper,a differential pressure fitting method for an asymmetric differential pressure cylinder is proposed.It overcomes the limitation of the detection efficiency caused by the asynchronous temperature recovery of the two chambers in the asymmetric differential pressure method and uses the differential pressure substitution equation to replace the differential calculation of the differential pressure.The improved differential pressure method proposes an innovation based on the detection principle and calculation method.Additionally,the influence of the parameters in the differential pressure substitution equation on the leakage calculation results was simulated,and the specific physical significance of the parameters of the differential pressure substitution equation was explained.The experiments verified the fitting effect and proved the accuracy of this method.Compared with the traditional differential pressure method,the maximum leakage deviation of inhibition was 0.5 L/min.Therefore,this method can be used to detect leaks in air tanks.

The soybean PLATZ transcription factor GmPLATZ17 suppresses drought tolerance by interfering with stress-associated gene regulation of GmDREB5

Plant AT-rich sequence and zinc binding(PLATZ)transcription factors are a class of plant specific zincdependent DNA-binding proteins that function in abiotic stress response and plant development.In this study,31 GmPLATZ genes were identified in soybean.GmPLATZ17 was down-regulated by drought and exogenous abscisic acid.Transgenic Arabidopsis and soybean hairy roots overexpressing GmPLATZ17 showed drought sensitivity and inhibition of stress-associated gene transcription.In contrast,suppressed expression of GmPLATZ17 led to increased drought tolerance in transgenic soybean hairy roots.The GmPLATZ17 protein was verified to interact physically with the GmDREB5 transcription factor,and overexpression of GmDREB5 increased drought tolerance in soybean hairy roots.Interaction of GmPLATZ17 with GmDREB5 was shown to interfere with the DRE-binding activity of GmDREB5,suppressing downstream stress-associated gene expression.These results show that GmPLATZ17 inhibits drought tolerance by interacting with GmDREB5.This study sheds light on PLATZ transcription factors and the function of GmPLATZ17 in regulating drought sensitivity.

Interlayer environment engineered MXene: Pre-intercalated Zn^(2+)ions as intercalants renders the modulated Li storage

The intercalation of foreign species into MXene, as an approach of tuning the interlayer environment, is employed to improve electrochemical ion storage behaviors. Herein, to understand the effect of confined ions by the MXene layers on the performance of electrochemical energy storage, Zn^(2+) ions were employed to intercalate into MXene via an electrochemical technique. Zn^(2+) ions induced a shrink of the adjacent MXene layers. Meaningfully, a higher capacity of lithium ion storage was obtained after Zn^(2+) preintercalation. In order to explore the roles of the intercalated Zn^(2+) ions, the structural evolution, and the electronic migration among Zn, Ti and the surface termination were investigated to trace the origination of the higher Li^(+) storage capacity. The pre-intercalated Zn^(2+) ions lost electrons, meanwhile Ti of MXene obtained electrons. Moreover, a low-F surface functional groups was achieved. Contrary to the first shrink, after 200 cycles, a larger interlayer distance was monitored, this can accelerate the ion transport and offer a larger expansile space for lithium storage. This may offer a guidance to understand the roles of the confined ion by two-dimensional(2D) layered materials.

Phosphine-free synthesis of FeTe2 nanoparticles and self-assembly into tree-like nanoarchitectures

Manipulating the self-assembly of transition metal telluride nanocrystals(NCs) creates opportunities for exploring new properties and device applications. Iron ditelluride(FeTe2) has recently emerged as a new class of magnetic semiconductor with three-dimensional(3D) magnetic ordering and narrow band gap structure, yet the self-assembly of FeTe2 NCs has not been achieved. Herein, the tree-like FeTe2 nanoarchitectures with orthorhombic crystal structure have been successfully synthesized by hot-injection solvent thermal approach using phosphine-free Te precursor. The morphology, size, and crystal structure have been investigated using transmission electron microscopy(TEM), high-resolution TEM(HRTEM),and powder x-ray diffraction(XRD). We study the formation process of tree-like FeTe2 NCs according to trace the change of the sample morphology with the reaction time. It was found that the FeTe2 nanoparticles show oriented aggregation and self-assembly behavior with the increase of reaction time, which is attributed to size-dependent magnetism properties of the samples. The magnetic interaction is thought to be the driving force of nanoparticle self-organization.

Dimensionless Study on Secretion Clearance of a Pressure Controlled Mechanical Ventilation System with Double Lungs

A pressure controlled mechanical ventilator with an automatic secretion clearance function can improve secretion clearance safely and efficiently.Studies on secretion clearance by pressure controlled systems show that these are suited for clinical applications.However,these studies are based on a single lung electric model and neglect the coupling between the two lungs.The research methods applied are too complex for the analysis of a multi-parameter system.In order to understand the functioning of the human respiratory system,this paper develops a dimensionless mathematical model of doublelung mechanical ventilation system with a secretion clearance function.An experiment is designed to verify the mathematical model through comparison of dimensionless experimental data and dimensionless simulation data.Finally,the coupling between the two lungs is studied,and an orthogonal experiment designed to identify the impact of each parameter on the system.

Vote-Based Feature Selection Method for Stratigraphic Recognition in Tunnelling Process of Shield Machine

Shield machines are currently the main tool for underground tunnel construction. Due to the complexity and variability of the underground construction environment, it is necessary to accurately identify the ground in real-time during the tunnel construction process to match and adjust the tunnel parameters according to the geological conditions to ensure construction safety. Compared with the traditional method of stratum identifcation based on staged drilling sampling, the real-time stratum identifcation method based on construction data has the advantages of low cost and high precision. Due to the huge amount of sensor data of the ultra-large diameter mud-water balance shield machine, in order to balance the identifcation time and recognition accuracy of the formation, it is necessary to screen the multivariate data features collected by hundreds of sensors. In response to this problem, this paper proposes a voting-based feature extraction method (VFS), which integrates multiple feature extraction algorithms FSM, and the frequency of each feature in all feature extraction algorithms is the basis for voting. At the same time, in order to verify the wide applicability of the method, several commonly used classifcation models are used to train and test the obtained efective feature data, and the model accuracy and recognition time are used as evaluation indicators, and the classifcation with the best combination with VFS is obtained. The experimental results of shield machine data of 6 diferent geological structures show that the average accuracy of 13 features obtained by VFS combined with diferent classifcation algorithms is 91%;among them, the random forest model takes less time and has the highest recognition accuracy, reaching 93%, showing best compatibility with VFS. Therefore, the VFS algorithm proposed in this paper has high reliability and wide applicability for stratum identifcation in the process of tunnel construction, and can be matched with a variety of classifer algorithms. By combining 13 features selected from shield machine data features with random forest, the identifcation of the construction stratum environment of shield tunnels can be well realized, and further theoretical guidance for underground engineering construction can be provided.

Research on the Pressure Regulator Effect on a Pneumatic Vibration Isolation System

The pneumatic vibration isolator(PVI)plays an increasingly important role in precision manufacturing.In this paper,aiming to detect the performance of the pressure regulator in the PVI system,a PVI testing system with a pressure regulator is designed and developed.Firstly,the structure of the pneumatic spring is presented and analyzed,and the nonlinear stiffness is obtained based on the ideal gas model and material mechanics.Then,according to the working principle and continuity equations of ideal airflow,a dynamic model of the PVI system with a pressure regulator is established.Through the simulation analysis,the vibration isolation performance is improved with the efficient and precise pressure regulator.The average values of both the vibration velocity and transmission rate decrease when the vibration is set to 4,10,20 and 40 Hz,respectively.The experiments demonstrate the reliability and effectiveness of the pressure regulator.This achievement will become an important basis for future research concerning precision manufacturing.

Modeling and Simulation of an Invasive Mild Hypothermic Blood Cooling System

Nowadays,mild hypothermia is widely used in the fields of post-cardiac arrest resuscitation,stroke,cerebral hemorrhage,large-scale cerebral infarction,and craniocerebral injury.In this paper,a locally mixed sub-low temperature device is designed,and the cold and hot water mixing experiment is used to simulate the human blood transfer process.To set a foundation for the optimization of the heat transfer system,the static characteristics are analyzed by building the mathematic model and setting up the experimental station.In addition,the affection of several key structure parameters is researched.Through experimental and simulation studies,it can be concluded that,firstly,the mathematical model proved to be effective.Secondly,the results of simulation experiments show that 14.52℃ refrigeration can reduce the original temperature of 33.42℃ to 32.02℃,and the temperature of refrigerated blood rises to 18.64℃,and the average error is about 0.3℃.Thirdly,as the thermal conductivity of the vascular sheath increases,the efficiency of the heat exchange system also increases significantly.Finally,as the input cold blood flow rate increases,the mass increases and the temperature of the mixed blood temperature decreases.It provides a research basis for subsequent research on local fixed-point sub-low temperature control technology.

Information Theoretic Weighted Fuzzy Clustering Ensemble

In order to improve performance and robustness of clustering,it is proposed to generate and aggregate a number of primary clusters via clustering ensemble technique.Fuzzy clustering ensemble approaches attempt to improve the performance of fuzzy clustering tasks.However,in these approaches,cluster(or clustering)reliability has not paid much attention to.Ignoring cluster(or clustering)reliability makes these approaches weak in dealing with low-quality base clustering methods.In this paper,we have utilized cluster unreliability estimation and local weighting strategy to propose a new fuzzy clustering ensemble method which has introduced Reliability Based weighted co-association matrix Fuzzy C-Means(RBFCM),Reliability Based Graph Partitioning(RBGP)and Reliability Based Hyper Clustering(RBHC)as three new fuzzy clustering consensus functions.Our fuzzy clustering ensemble approach works based on fuzzy cluster unreliability estimation.Cluster unreliability is estimated according to an entropic criterion using the cluster labels in the entire ensemble.To do so,the new metric is dened to estimate the fuzzy cluster unreliability;then,the reliability value of any cluster is determined using a Reliability Driven Cluster Indicator(RDCI).The time complexities of RBHC and RBGP are linearly proportional with thnumber of data objects.Performance and robustness of the proposed method are experimentally evaluated for some benchmark datasets.The experimental results demonstrate efciency and suitability of the proposed method.

Correlation Between ASI and Yield and Drought Resistance of Maize Inbred

Maize is the main grain crop and important forage crop in China. The correlation between ASI and yield of maize inbred lines and whether ASI and the ASI extension time(Dct) of maize inbred lines could be used as a direct indicator of drought resistance of maize inbred lines were explored. The results showed that the goodness of fit of ASI and Dct with DI were 0.478 and 0.829, respectively, and the ASI had an extremely significant negative correlation with yield per plant. ASI and Dct could be used as a parameter to evaluate drought resistance of maize inbred lines, but Dct was more effective than ASI in determining drought resistance index(DI) of maize inbred lines.

温度驱动的相变润滑剂灌注表面用于可持续抗垢

润滑剂灌注表面(LIS)能够减少来自不同来源的污染(包括细菌、冰和水垢).然而,润滑剂的液体特性经常导致这类表面在恶劣环境中流失,从而无法防止污垢的沉积.本文报道了一种相变润滑剂灌注的表面,实现了长期高效抗水垢.当温度在润滑剂的熔点以下时,润滑剂为固态,展示出了高的稳定性.当温度在润滑剂的熔点以上时,液态润滑剂利用其光滑的表面形貌和水垢黏附的降低,实现了抗水垢.本文对于处理实际应用中结垢问题,特别是在温度变化场景下的结垢问题,提供了一种可行方法.