Introduction
Individuals with lower limb loss experience an increased risk of falls partly due to the lack of sensory feedback from their missing foot. It is possible to restore plantar sensation ...perceived as originating from the missing foot by directly interfacing with the peripheral nerves remaining in the residual limb, which in turn has shown promise in improving gait and balance. However, it is yet unclear how these electrically elicited plantar sensation are integrated into the body’s natural sensorimotor control reflexes. Historically, the H-reflex has been used as a model for investigating sensorimotor control. Within the spinal cord, an array of inputs, including plantar cutaneous sensation, are integrated to produce inhibitory and excitatory effects on the H-reflex.
Methods
In this study, we characterized the interplay between electrically elicited plantar sensations and this intrinsic reflex mechanism. Participants adopted postures mimicking specific phases of the gait cycle. During each posture, we electrically elicited plantar sensation, and subsequently the H-reflex was evoked both in the presence and absence of these sensations.
Results
Our findings indicated that electrically elicited plantar sensations did not significantly alter the H-reflex excitability across any of the adopted postures.
Conclusion
This suggests that individuals with lower limb loss can directly benefit from electrically elicited plantar sensation during walking without disrupting the existing sensory signaling pathways that modulate reflex responses.
•A new approach of using computationally cheap surrogate models for optimization of SMB chromatography is presented.•Two different types of surrogate models are developed to replace the detailed but ...expensive full-order SMB model for optimization.•The trust-region framework is proposed to implement an efficient and reliable management of both types of surrogates.•The results show that the new scheme not only converges to the optimum obtained with the full-order system, but also yields significant computational advantages.
A new approach of using computationally cheap surrogate models for efficient optimization of simulated moving bed (SMB) chromatography is presented. Two different types of surrogate models are developed to replace the detailed but expensive full-order SMB model for optimization purposes. The first type of surrogate is built through a coarse spatial discretization of the first-principles process model. The second one falls into the category of reduced-order modeling. The proper orthogonal decomposition (POD) method is employed to derive cost-efficient reduced-order models (ROMs) for the SMB process. The trust-region optimization framework is proposed to implement an efficient and reliable management of both types of surrogates. The framework restricts the amount of optimization performed with one surrogate and provides an adaptive model update mechanism during the course of optimization. The convergence to an optimum of the original optimization problem can be guaranteed with the help of this model management method. The potential of the new surrogate-based solution algorithm is evaluated by examining a separation problem characterized by nonlinear bi-Langmuir adsorption isotherms. By addressing the feed throughput maximization problem, the performance of each surrogate is compared to that of the standard full-order model based approach in terms of solution accuracy, CPU time and number of iterations. The quantitative results prove that the proposed scheme not only converges to the optimum obtained with the full-order system, but also provides significant computational advantages.
A new improvement based on outlet fractionation and feedback has been developed for simulated moving bed (SMB) chromatography. In this contribution, this fractionation and feedback SMB (FF-SMB) ...concept is extended to the general scenario which integrates a simultaneous fractionation of both outlet streams. A model-based optimization approach, previously adopted to investigate single fractionation, is extended to consider this flexible fractionation policy. Quantitative optimization studies based on a specific separation problem reveal that the double fractionation is the most efficient operating scheme in terms of maximum feed throughput, while the two existing single fractionation modes discussed in our previous study are also significantly superior to the conventional SMB operation. The advantages of the double fractionation extension are further demonstrated in terms of several more detailed performance criteria. In order to evaluate the applicability of the fractionation and feedback modification, the effect of product purity, adsorption selectivity, column efficiency and column number on the relative potential of FF-SMB over SMB is examined.
This paper presents new multistage optimal startup and shutdown strategies for simulated moving bed (SMB) chromatographic processes. The proposed concept allows to adjust transient operating ...conditions stage-wise, and provides capability to improve transient performance and to fulfill product quality specifications simultaneously. A specially tailored decomposition algorithm is developed to ensure computational tractability of the resulting dynamic optimization problems. By examining the transient operation of a literature separation example characterized by nonlinear competitive isotherm, the feasibility of the solution approach is demonstrated, and the performance of the conventional and multistage optimal transient regimes is evaluated systematically. The quantitative results clearly show that the optimal operating policies not only allow to significantly reduce both duration of the transient phase and desorbent consumption, but also enable on-spec production even during startup and shutdown periods. With the aid of the developed transient procedures, short-term separation campaigns with small batch sizes can be performed more flexibly and efficiently by SMB chromatography.
A novel modification of simulated moving bed (SMB) technology, referred to as fractionation and feedback SMB (FF-SMB), has been introduced recently. This concept is based on fractionating one or both ...outlet streams and feeding the off-spec fractions back into the unit alternatingly with the original feed mixture. In this paper, the optimization problem of FF-SMB realizing one outlet fractionation is considered. A mathematical optimization framework based on a detailed process model is presented which allows to evaluate quantitatively the potential of this operating scheme. Detailed optimization studies have been carried out for a difficult separation characterized by small selectivity and low column efficiency. The results reveal that the proposed fractionation and feedback regime can be significantly superior to the classical SMB chromatography, in terms of both feed throughput and desorbent consumption. The effect of the feeding sequence on the performance of FF-SMB is also examined.
Microplastics (MPs) have recently attracted much attention due to their widespread distribution in the aquatic environment. Microplastics can act as a vector of heavy metals in the aquatic ...environment, causing a potential threat to aquatic organisms and human health. This review mainly summarized the occurrence of microplastics in the aquatic environment and their interaction with heavy metals. Then, we considered the adsorption mechanisms of MPs and heavy metals, and further critically discussed the effects of microplastics properties and environmental factors (e.g., pH, DOM, and salinity) on the adsorption of heavy metals. Finally, the potential risks of combined exposure of MPs and heavy metals to aquatic biota were briefly evaluated. This work aims to provide a theoretical summary of the interaction between MPs and heavy metals, and is expected to serve as a reference for the accurate assessment of their potential risks in future studies.
•Microplastics serve as vectors of heavy metals in the aquatic environment.•The possible mechanisms of heavy metal adsorption by microplastics are complex.•Microplastics properties and environmental factors affect heavy metal adsorption.•Co-exposure of microplastics and heavy metals may have different effects on aquatic biota.
In this study, the adsorption behavior of Pb(II) on natural-aged and virgin microplastics in different electrolyte solutions was investigated. The results demonstrated that natural-aged microplastics ...exhibited higher adsorption capacity for Pb(II) compared to virgin ones, and the addition of CaCl2 strongly inhibited the adsorption amount of Pb(II). The adsorption kinetics of Pb(II) adsorption were better fitted by the pseudo-second order model and Elovich equation, and were slowed down greatly at higher ionic strength. The rate-limiting steps of adsorption process were dominated by intra-particle diffusion. The adsorption isotherm of Pb(II) onto microplastics affected by salt ions can be well described by Freundlich model, the greater adsorption efficiency of natural-aged microplastics proved that adsorption process was multilayer and heterogeneous. In addition, pH significantly influenced the adsorption of Pb(II) due to the changes electrostatic interactions. The effect of fulvic acid in the electrolyte solutions was also revealed and attributed to the complexation with Na+ and Ca2+. Furthermore, the higher pH and ionic strength in different environmental water dramatically decreased adsorption capacity onto microplastics. Finally, it’s confirmed that the adsorption mechanisms affected by salt ions mainly involve electrostatic interaction, surface complexation, and ionic exchange. These findings indicate that salt ions exert an important influence on the adsorption of heavy metals for MPs, which should be further concerned.
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•The adsorption capacity of Pb(II) on natural-aged microplastics was higher than virgin ones.•Divalent Ca2+ markedly inhibited the sorption of Pb(II) compared to monovalent Na+.•The pH and fulvic acid affected the Pb(II) sorption in different electrolyte solutions.•Competition and complexation interactions played great roles in the adsorption process.
•A novel method of electrospinning was employed to enhance quorum quenching hydrogel.•QQ-ECHB performs excellent physical stability and environmental-tolerance.•Stable and long-lasting quorum ...quenching can be effected at low dosage of QQ-ECHB.•MBR biofouling greatly mitigated and extended service cycle with QQ media addition.
Bacterial quorum quenching (QQ) is an effective strategy for controlling biofouling in membrane bioreactor (MBR) by interfering the releasing and degradation of signal molecules during quorum sensing (QS) process. However, due to the framework feature of QQ media, the maintenance of QQ activity and the restriction of mass transfer threshold, it has been difficult to design a more stable and better performing structure in a long period of time. In this research, electrospun fiber coated hydrogel QQ beads (QQ-ECHB) were fabricated by using electrospun nanofiber coated hydrogel to strengthen layers of QQ carriers for the first time. The robust porous PVDF 3D nanofiber membrane was coated on the surface of millimeter-scale QQ hydrogel beads. Biocompatible hydrogel entrapping quorum quenching bacteria (sp.BH4) was employed as the core of the QQ-ECHB. In MBR with the addition of QQ-ECHB, the time to reach transmembrane pressure (TMP) of 40 kPa was 4 times longer than conventional MBR. The robust coating and porous microstructure of QQ-ECHB contributed to keeping a lasting QQ activity and stable physical washing effect at a very low dosage (10g beads/5L MBR). Physical stability and environmental-tolerance tests also verified that the carrier can maintain the structural strength and keep the core bacteria stable when suffering long-term cyclic compression and great fluctuations in sewage quality.
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•Introduing N defects over g-C3N4 significantly increased photocatalytic activity.•An IEF was built to further strengthened the transport of photoexcited carriers.•The excellent O2 ...adsorption capacity promoted H2O2 production via 2e− ORR.•A possible H2O2 generation pathway formed via 1O2 was proposed.
The development of photocatalysts for the efficient generation of hydrogen peroxide (H2O2) and degradation of antibiotic pollutants is a mutual-beneficial solution to the chemical resource demands and environmental remediation. Herein, efficient visible-light-driven H2O2 production and antibiotic degradation are achieved by using nitrogen-deficient modified polymeric carbon nitride (g-C3N4) to facilitate the reduction of dioxygen. The N defects modified g-C3N4 reached an excellent H2O2 generation rate of 623.5 μmol g−1h−1 without O2 bubbling. The structural features and entire photocatalytic conversion process were systematically studied via experiments and theoretical calculations. It was found that the N defects in the framework constructed a giant internal electric field (IEF), which effectively inhibited carrier recombination. Revealed the neglected H2O2 production via 1O2 pathway, which effectively promoting the selective 2e− oxygen reduction reaction (ORR). More interestingly, the N defects structure greatly improved the O2 adsorption ability and O2 production ability of the material, while inhibiting the in situ generated H2O2 from being decomposed and maintaining high efficiency of H2O2 production under air conditions. This study thoroughly revealed the synergistic effects of the terminal cyano group and nitrogen vacancies over g-C3N4 for efficient H2O2 photogeneration photosynthesis.
Due to the mass production and daily use of plastic products, the potential toxicity of microplastics to the water environment has attracted worldwide attention. In this work, the effect of typical ...microplastics (PET) on the performance of activated sludge from membrane bioreactors (MBR) was evaluated. The impacts on biological removal efficiency were unconspicuous with continuous dosing of 60 particles/L. However, further investigations revealed that PET particle accumulation caused adverse impacts on settleability and dewaterability. The SVI value increased from 53.3 ml/g MLSS to 69.9 ml/g MLSS and the CST in the PET reactor increased by 22%. Nevertheless, hydrophobicity was reduced by 49.2%. Mechanism studies exposed that the PET microplastics accumulation improved extracellular polymeric substances (EPS) from 116.96 mg/L to 138.70 mg/L and caused cell membrane damage. The abundance and diversity of microbial community reduced in activated sludge in PET reactor compared with control reactor. These phenomena revealed a possible hypothesis that the microplastic particles increased EPS and cytotoxicity of activated sludge. However, the rate of transmembrane pressure (TMP) build-up was significantly mitigated in PET-MBR compared to that in a control-MBR (1.27 folds), which attributes that physical scour of particles may still alleviate membrane contamination in MBR.
•Membrane biofouling was alleviated due to physical scouring of PET particles.•The physicochemical properties of sludge were changed after long-term PET exposure.•Accumulation of PET particles caused EPS secretion and cell membrane damage.•Long-term exposure to PET changed the microbial community of MBR system.
