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Various backdrivable lower limb exoskeletons have demonstrated the electromechanical capability to assist volitional motions of able-bodied users and people with mild to moderate gait disorders, but there does not exist a control framework that can be deployed on any joint(s) to assist any activity of daily life in a provably stable manner. This article presents the modular, multitask optimal energy shaping (M-TOES) framework, which uses a convex, data-driven optimization to train an analytical control model to instantaneously determine assistive joint torques across activities for any lower limb exoskeleton joint configuration. The presented modular energy basis is sufficiently descriptive to fit normative human joint torques (given normative feedback from signals available to a given joint configuration) across sit-stand transitions, stair ascent/descent, ramp ascent/descent, and level walking at different speeds. We evaluated controllers for four joint configurations (unilateral/bilateral and hip/knee) of the modular backdrivable lower limb unloading exoskeleton (M-BLUE) exoskeleton on eight able-bodied users navigating a multiactivity circuit. The two unilateral conditions significantly lowered overall muscle activation across all tasks and subjects (p $\mathbf {\lt }$ 0.001). In contrast, bilateral configurations had a minimal impact, possibly attributable to device weight and physical constraints.

The study explores the adsorption behavior of unmodified natural clay as an ecologically acceptable procedure in the treatment of toxic elements such as Cr6+in wastewater. Batch experiments were conducted by stirring 30 ml of a Cr6+solution and natural clay for 3 h at different temperatures, pH, Cr6+loadings, and concentrations. Characterization of natural clay before and after adsorption was studied by XRD, FTIR, and BET for surface area, SEM, and EDX for surface topography. The Cr6+content was analyzed by UV–visible spectrophotometer further, the mechanism of the process was illustrated by isotherm and kinetic studies. Cr6+maximum sorption capacity obtained was 12.3 mg/g at pH 3. The overall process followed the Langmuir model elucidating monolayer adsorption as a major, in addition kinetics study (pseudo-2nd-order) describes accurately that chemisorption is a rate-controlling stage. Thermodynamics measurements indicated a spontaneous and endothermic process involved throughout the adsorption. Therefore, the study highlights the efficacy of unmodified natural clay as an efficient adsorbent for the elimination of Cr6+from aqueous solution.

The study on removal of fluoride from water is performed by using two anion exchangers and two modified cation exchangers by varying contact time, resin dosage, pH, and initial concentration of fluoride ions. Maximum fluoride removal is possible in the pH range of 4.0–10.0 and removal efficiency reaches maximum, within 60 min for anion exchangers and 120 min for cation exchangers. Among Langmuir and Freundlich isotherms, adsorption data fit well in Freundlich isotherm. The kinetic study suggests adsorption process follows pseudo-second-order reaction kinetics. Among two anion exchangers used for the removal of fluoride Tulsion A-10X (MP) has better fluoride removal efficiency than Amberlyst A-21(MP). However, in the case of modified cation exchangers, Al+3forms of resins have better fluoride removal efficiency than Fe+3forms. It clearly indicates that modified resins can be useful for the removal of fluoride. Desorption study is also carried out on all the resins using 0.1 N NaOH and 0.1 N HCl.

Thiocyanate (SCN–) enters into water bodies through several industrial processes. The removal of thiocyanate from water is essential as it is toxic to aquatic organisms and humans. The kinetics and equilibrium study of removing thiocyanate from water was investigated using two microporous anion exchangers having different resin matrices namely Tulsion A-10X (TUL-10) of acrylic matrix and Amberlyst A-21 (AMB-21) of styrene divinyl benzene matrix. The effect of pH, thiocyanate concentration, temperature, contact time and resin dosage was studied on both the resins. Different kinetic models were applied to understand adsorption mechanism. Adsorption of thiocyanate follows pseudo-second-order kinetic model and fits into Langmuir and Freundlich isotherms. The adsorption capacities of the resins from the Langmuir isotherm are 153.19 and 142.87 mg g–1for TUL-10 and AMB-21 resins, respectively. The experimental data indicates that AMB-21 with styrene divinyl benzene matrix has removal efficiency of 90% at adsorption dosage of 150 mg with 350 mg L–1thiocyanate concentration at 303 K, whereas TUL-10 resin having acrylic matrix shows 75% removal efficiency at same conditions. The adsorption is exothermic in nature and does not show significant change in internal structure of the resin. Fourier transform infrared spectroscopy spectra of resins after adsorption confirm the presence of thiocyanate. Desorption study indicates NaOH is more efficient desorbent for AMB-21 showing 99.61% desorption efficiency.

The adsorption studies of chromium (VI) in aqueous and aqueous-organic solvents mixed media is carried out using weak base anion exchangers Tulsion A-10 X (MP) and Amberlyst A-21 (MP) by batch process. Adsorption of chromium (VI) is investigated by varying contact time, chromium (VI) concentration, resin dosage, temperature and pH. The effect of solvent on adsorption of chromium (VI) was also studied at different solvent compositions. The percentage of chromium (VI) removal was found faster on Amberlyst A-21 (MP) than Tulsion A-10X (MP) due to the difference in resin structure. However, the percentage removal of chromium (VI) is up to 99% on both the resins. Chromium (VI) removal is maximum in the pH range 2.0 to 5.0 with a resin dosage of 150 mg and initial chromium (VI) concentration 350 mg·L–1. The equilibrium sorption data was analysed with Freundlich and Langmuir isotherms. The data fits well in Langmuir model indicating monolayer adsorption of chromium (VI) on the resin. Adsorption process follows pseudo-second order kinetic equation and is controlled by intra-particle diffusion. The desorption study indicates that NaOH is better desorbent for resin Amberlyst A-21(MP) than Tulsion A-10X(MP). Thermodynamic parameters were evaluated by applying Van’t Hoff equation to the adsorption process.

AbstractThe sorption of hexavalent chromium from water and water–organic solvents onto an ion exchange resin Tulsion A-23(Gel) is reported under various experimental conditions such as initial metal concentration, contact time, temperature, pH, and dielectric constant of the medium. The batch ion-exchange process was relatively fast and it reached equilibrium after 110 min of contact. The ion-exchange process, which is pH dependent, showed maximum removal of chromium(VI) in the pH range 7.0–9.0 for an initial chromium(VI) concentration of 0.0011 M. The equilibrium related to Tulsion A-23(Gel) ion-exchange capacity and the total amounts of the ion exchange were obtained using plots of the Langmuir and Freundlich adsorption isotherms. Various thermodynamic parameters have also been evaluated, including differential adsorption enthalpy and entropy.

ABSTRACTThe kinetics, thermodynamic, and adsorption studies on removal of chromium(VI) from aqueous and in presence of industrial solvents 2-methoxyethanol and 2-ethoxyethanol with macroporous resin Tulsion A-27 was studied at varying concentration of Cr(VI), adsorbent dosage, pH, contact time, and temperature. Batch shaking sorption experiments were carried out to evaluate the performance of Tulsion A-27(MP) anion exchange resin in the removal of Cr(VI) from aqueous and mixed aqueous solvents, 2-methoxyethanol and 2-ethoxyethanol. The concentrations of Cr(VI) in aqueous and mixed aqueous solvents were determined by UV-Visible spectrophotometer. As the adsorption process is pH dependent, it showed maximum removal efficiency of Cr(VI) in the pH range of 5–6 for an initial chromium concentration of 0.0011 M. Effect of temperature on the equilibrium constant was studied and the thermodynamic parameters were evaluated. Kinetic experiments revealed the dominance of adsorption. The sorption models, Langmuir and Freundlich adsorption isotherms, were discussed on amount of Cr(VI) uptake. The resin was analyzed by infrared spectroscopy and scanning electron microscopy before and after the adsorption process. The sorption of Cr(VI) by the anion exchange resin was reversible and so it has good potential for the removal/recovery of Cr(VI) from aqueous and mixed aqueous solvents. The anion exchange resin can be used for the efficient removal of Cr(VI) from water and wastewater.

The antibiotic caerulomycin is shown to be 4-methoxy-2,2′-dipyridyl-6-syn-aldoxime (I) by chemical and spectroscopic studies.