Constrained unscented recursive estimator for nonlinear dynamic systems

Nonlinear constrained state estimation is an important task in performance monitoring, online optimization and control. There has been recent interest in developing estimators based on the idea of unscented transformation for constrained nonlinear systems. One of these approaches is the unscented recursive nonlinear dynamic data reconciliation (URNDDR) method. The URNDDR approach follows the traditional predictor-corrector framework. Constraints are handled in the prediction step through a projection algorithm and in the correction step through an optimization formulation. It has been shown that URNDDR produces very accurate estimates at the cost of computational expense. However, there are two issues that need to be addressed in the URNDDR framework: (i) URNDDR approach was primarily developed to handle bound constraints and needs to be enhanced to handle general nonlinear equality and inequality constraints, and (ii) computational concerns in the application of the URNDDR approach needs to be addressed. In this paper, a new estimation technique named constrained unscented recursive estimator (CURE) is proposed, which eliminates these disadvantages of URNDDR, while providing estimates with almost the same accuracy.     

Perovskite-based electrocatalyst discovery and design using word embeddings from retrained SciBERT language model

With the ever-increasing volume of scientific literature, there is a strong need to develop methods that allow rigorous information identification. In this contribution, a state-of-the-art natural language processing (NLP) model was used to select perovskite materials for electrocatalytic applications from literature. This was accomplished by obtaining word embeddings for perovskite materials from the NLP model and subsequently designing downstream tasks to discover perovskite-based electrocatalyst materials. However, embeddings could be obtained only for materials available in the literature. Consequently, a novel methodology was devised to generate embeddings for newly designed materials. Results from the analysis showed that the computed embeddings could be used to rank materials for their suitability for electrocatalytic applications. Further, the word embeddings were also employed as features in predicting the electrocatalytic activity of perovskite-based electrocatalysts. The analysis demonstrated that the fidelity of regression models increased when the embeddings were used as features.     

Step response analysis of phosphoric acid fuel cell (PAFC) cathode through a transient model

Transient state response analysis of phosphoric acid fuel cell (PAFC) cathode is important to understand various competitive processes like diffusion, reaction and product back diffusion occurring at various layers of the composite cathode. A two-dimensional unsteady state model for simulating PAFC cathode is developed as an extension of the previously developed steady-state model [S. Roy Choudhury, M.B. Deshmukh, R. Rengaswamy, A two-dimensional steady-state model for phosphoric acid fuel cells (PAFC), J. Power sources 112 (2002) 137–152]. The transient model is solved to study the impact of various parameters such as Tafel slope, diffusivity etc on the step response of the fuel cell. The effect of partial pressure variation in bulk gas for large sized PAFC cathode is also analysed. Trend analysis based on the model output is also experimentally verified using a small unit cell setup. The effect of various parameters on the settling time of the cathode, as revealed in this study, suggests possible development of a diagnostic tool employing such transient model.     

Effect of prior damage on the performance of cement based coatings on rebar: macrocell corrosion studies

The performance of any rebar coating system depends upon its resistance to corrosion in the presence of chloride contaminated concrete. It also mainly depends upon its tolerance towards damage that may occur during handling, transporting and concreting. The severe corrosion of epoxy coated reinforcing steel in long key bridge and other structures in Florida gave raise to the concern over the influence of damages in the coating system [R.J. Kessler, P.G. Powers, Interim report on corrosion evaluation of substructure in Long key bridge, Corrosion Report No. 87-9A, Florida Department of Transportation, Florida, 1987]. The performance of rebar coating such as galvanizing and epoxy based coating with prior surface damage has been evaluated and reported. [J. Hartley, Concrete Jan/Feb (1994) 12–15; A. Sagues, Performance of galvanized rebars in marine substructure service, Project ZE-418, Part I, October, 1994]. To date, the performance of cement based coatings with prior damages has not been widely studied and reported. In the present investigation the effect of prior damage produced during concrete pouring has been studied on inhibited cement slurry coating. To simulate the marine substructure environment, macrocell corrosion has been created via a chloride ion concentration gradient. Test conditions and method of macrocell current measurement as described in ASTM G 109-92 have been followed. The above investigation revealed that the cement based coating appears to have better tolerance towards defects in chloride contaminated concrete as compared to epoxy based coating system. The performance of the coating is independent of the height of concrete pouring.     

Representation of thermodynamic properties of quaternary systems using interaction parameters

Integral excess free energy of a quaternary system has been expressed in terms of the MacLaurin infinite series. The series is subjected to appropriate boundary conditions and each of the derivatives correlated to the corresponding interaction coefficients. The derivation of the partial functions involves extensive summation of various infinite series pertaining to the first order and quaternary parameters to remove any truncational error. The thermodynamic consistency of the derived partials has been established based on the Gibbs-Duhem relations. The equations are used to interpret the thermodynamic properties of the Fe-Cr-Ni-N system.     

Integration of machine learning and first principles models

Model building and parameter estimation are traditional concepts widely used in chemical, biological, metallurgical, and manufacturing industries. Early modeling methodologies focused on mathematically capturing the process knowledge and domain expertise of the modeler. The models thus developed are termed first principles models (or white-box models). Over time, computational power became cheaper, and massive amounts of data became available for modeling. This led to the development of cutting edge machine learning models (black-box models) and artificial intelligence (AI) techniques. Hybrid models (gray-box models) are a combination of first principles and machine learning models. The development of hybrid models has captured the attention of researchers as this combines the best of both modeling paradigms. Recent attention to this field stems from the interest in explainable AI (XAI), a critical requirement as AI systems become more pervasive. This work aims at identifying and categorizing various hybrid models available in the literature that integrate machine-learning models with different forms of domain knowledge. Benefits such as enhanced predictive power, extrapolation capabilities, and other advantages of combining the two approaches are summarized. The goal of this article is to consolidate the published corpus in the area of hybrid modeling and develop a comprehensive framework to understand the various techniques presented. This framework can further be used as the foundation to explore rational associations between several models.     

Design and material analysis for prototyping of four arm mechanical microgripper with self-locking and anti-slipping capability

Microsystem Technologies - In this work, a mechanically actuated microgripper is designed with the COMSOL Multiphysics and its analysis is discussed. The mechanical microgripper is having a...     

Modelling of Chevron electrothermal actuator and its performance analysis

Microsystem Technologies - In this work, a Chevron electrothermal actuator is designed and its analytical model is developed. Chevron actuator works on the principle of Joules heating effect and...