Optimal time-varying potential profile for electro-hydro-dimerization reactions

Optimal time-varying potential profile for batch electrochemical reactor is evaluated for a major industrial electro-organic synthesis, the electro-hydro-dimerization of acrylonitrile to adiponitrile. The control vector iteration technique is used for computing the optimal profiles. As the technique is continuous on both state and adjoint variables, it can give more accurate profile with no need for any polynomial approximation. A heterogeneous model of the reactor is uniquely used for the formulation of dynamic optimization problem statements by expressing the differential constraints in terms of concentration variations in bulk as well as at the electrode surface. In addition to taking an account of surface concentration variations, the separation of total current as faradic and non-faradic currents is also considered as an additional equality constraint. A path constraint on the electrode potential is imposed for safe reactor function and economical operation. The results of optimum time-varying potential profile are compared with those of applying a steady potential.     

A novel approach for computing tertiary current distributions based on simplifying assumptions

A novel yet efficient method for the computation of simplified tertiary current density and surface concentration distributions in electrochemical processes is presented. The method is rooted in the important physiochemical property that the activation potential is constant and uniform for given electrode material during the electrolysis. The technique is attractive because it involves a single iterative procedure against the conventional doubly iterative procedure. The initial assumption of current distribution along the electrode is also not necessary, as it involves only an assumption of a suitable power series to solve steady state laminar convective diffusion. Accordingly the method is relevant only for electrodes of constant activation polarization, but this holds good for situations where the electrode configurations are such that the primary current density distribution is almost uniform and for situations where the Wagner number is high. To illustrate the utility of the technique the procedure is applied to some realistic problems encountered in electrochemical engineering such as the current distribution either in plane-parallel plate electrode with electrolyte flowing between them or a moving electrode with the electrolyte stationary.     

Poly(1-vinyl-2-pyrrolidinone) hydrogels as vitreous substitutes: histopathological evaluation in the animal eye

A homopolymer of 1-vinyl-2 pyrrolidinone and its copolymer with 2-hydroxyethyl methacrylate, both cross-linked with divinyl glycol, were produced as possible substitutes for the vitreous body of the eye. The hydrated polymers behaved like viscoelastic gels, displaying excellent physical and optical properties. The sterile gels (0.7-1.5 ml) were injected into the vitreous cavity of rabbits, which previously underwent gas-mediated vitrectomy. Clinically, the eyes were quiet, with the exception of transient opacities in the vitreous. After 4 weeks, the operated eyes were enucleated and subjected to histopathological analysis using light and transmission electron microscopy. The common feature in all sections was the invasion of inflammatory cells. Vacuoles containing granular material, assumed to be polymer, were seen in the intercellular spaces of the neural retina, in the retinal pigment epithelium cells, and in macrophages. These findings indicated the fragmentation and phagocytosis of synthetic gels. It appeared that the biodegradation of the internalized polymers did not proceed further, however, the fate of polymers and their usefulness as vitreous substitutes should be investigated through long-term experiments.     

Preliminary evaluation of a hydrogel core-and-skirt keratoprosthesis in the rabbit cornea

BACKGROUND: We developed a core-and-skirt keratoprosthesis, with both components made from poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels. The identical chemical nature of both spongy skirt and transparent core assures a permanent union between them. We have previously shown that PHEMA sponges, within a certain range of pore size, can support cellular invasion and neovascularization when implanted into the rabbit cornea. The present study is the first to evaluate the behavior of the whole prosthesis after implantation into the rabbit cornea. METHODS: Hydrogel keratoprostheses were inserted intrastromally into the corneas of seven rabbits and histologically examined by light microscopy in five eyes enucleated at 8, 12, and 14 weeks. RESULTS: None of the implants extruded over this period. Both clinical and histopathologic examination showed that the keratoprostheses were well tolerated by the host tissue. The porous skirt was fully integrated into the stroma by fibrovascular invasion, and no capsule formed around the implants. Stromal melting anterior to the implant occurred in two cases, but this did not affect the fixation of the keratoprostheses. CONCLUSIONS: This study indicates that our keratoprosthesis can prevent extrusion in the short term when inserted into an intrastromal pocket of the rabbit eye.     

Cell viability and inflammatory response in hydrogel sponges implanted in the rabbit cornea

In the quest for the development of a functional keratoprosthesis, the biocompatibility of the porous skirt material in the Chirila keratoprosthesis (KPro) was investigated. The population of live and dead cells within, and the inflammatory response to, a tissue-integrating poly(2-hydroxyethyl methacrylate) (PHEMA) sponge were studied. Samples of the hydrogel sponge were implanted in rabbit corneas and explanted at predetermined time points up to 12 weeks. The explanted sponges were subjected to cell viability assay using two types of fluoroprobes, 5-chloromethylfluorescein diacetate and ethidium homodimer-1. A semiquantitative analysis was performed to assess the number of dead cells within the sponge and in the area of corneal stroma proximal to the sponge. Five rabbits were used for each end point (2, 4 and 12 weeks). To investigate the inflammatory response to the sponge, immunocytochemistry, using specific antibodies to rabbit macrophages, enzyme histochemistry of chloroacetate esterase (to detect neutrophils) and transmission electron microscopy (TEM) were also employed at 24 h, 2, 4 and 12 weeks after implantation. Four weeks after implantation, fewer viable cells were observed in the sponge when compared to the 2-week implant. However, the proportion of viable cells increased dramatically by 12 weeks. The proportion of nonviable cells decreased gradually with time; central sponge contained 34+/-11 % dead cells after 2 weeks, and 15+/-4.3% after 12 weeks. The staining of inflammatory cells demonstrated the presence of macrophages and neutrophils up to 12 weeks after implantation. TEM confirmed the presence of these cell types and others. including eosinophils and myofibroblasts, as well as blood capillaries. The presence of a significant number of viable cells at each time point and the uniform reduction of the nonviable cell proportion with time suggests that the sponge is a conducive environment supporting a prolific, viable cellular colonization. Dead cells observed in the first instance indicate a normal injury pattern. However, the presence of a small but significant proportion of invading inflammatory cells 12 weeks after implantation confirms a characteristic pattern of wound healing within the sponges.     

Melanin-containing hydrogel intraocular lenses: a histopathological study in animal eyes

Poly(2-hydroxyethyl methacrylate) hydrogel intraocular lenses, containing adrenochrome-melanin, were manufactured and implanted in animal eyes in order to assess the effect of melanin upon (a) biocompatibility of implants with the eye tissues, and (b) fibrous proliferation of lens epithelium responsible for the opacification of the posterior capsular membrane. An equal number of control lenses were also implanted. The animals were followed up for durations up to two years, and a detailed histopathological examination of the eyes was performed subsequent to their enucleation. The postoperative complications were minor and probably caused by surgical trauma. The study failed to give any indication of the postulated antiproliferative activity of adrenochrome-melanin since minimal capsular opacification occurred in the operated eyes, regardless of the presence of melanin.     

Computation of Current Distributions using FEMLAB

An efficient method for the computation of current density and surface concentration distributions in electrochemical processes is analyzed using the commercial mathematical software FEMLAB. To illustrate the utility of the software, the procedure is applied to some realistic problems encountered in electrochemical engineering, such as current distribution in a continuous moving electrode, parallel plate electrode, hull cell, curvilinear hull cell, thin layer galvanic cell, through‐hole plating, and a recessed disc electrode. The model equations of the above cases are considered and their implementations into the software, FEMLAB, are analyzed. The technique is attractive because it involves a systematic way of coupling equations to perform case studies.     

Evaluation of optimal discharge current profile for planar electrodes to maximize the utilization

In this paper, optimization of operating conditions for electrochemical energy sources is attempted using a dynamic optimization approach. This rigorous approach is demonstrated using a nonlinear diffusion equation that governs the mass transport limitation from/to the planar electrode. The resulting differential-algebraic model is solved using piecewise constant control vector iteration method that uses vectorized discharge current. The results obtained using the optimal control profile is compared with constant current discharge method and also with another trial and error approach that uses linear current control. It is found that the optimal control method achieves 12% more state of discharge against constant current discharge method with better energy efficiency and battery use. The proposed approach can be extended to complex systems such as operating electrochemical energy sources in hybrid environments that require proper control of energy distribution among the hybrid components.     

Towards real-time (milliseconds) parameter estimation of lithium-ion batteries using reformulated physics-based models

In this paper, transport and kinetic parameters of lithium-ion batteries are estimated using a rigorous porous electrode theory based model. The rigorous model used in this investigation is reformulated using advanced mathematical techniques. Since batteries and other electrochemical devices are used in hybrid environments, which include devices with time constants less than a second (like supercapacitor), we need to develop parameter estimation codes with computation time less than a second or a few milliseconds. In this investigation, the computation time for parameter estimation measures between 100 and 300 ms since a reformulated battery model is devised especially for these purposes. Obtaining the numerical solution for battery model equations is very difficult towards the end of discharge and is usually neglected for parameter estimation purposes. However, in this paper the estimation takes into account the entire discharge data ranging from an initial potential of 4.2 V to a cut-off potential of 2.5 V. It is found from this investigation that the reformulated lithium-ion battery model is efficient and accurate in estimating parameters.     

An Efficient Clustering and Deep Learning Based Resource Scheduling for Edge Computing to Integrate Cloud-IoT

Wireless Personal Communications -