In this work, we analyze the kinetics of the entanglement–disentanglement process of complex fluids coupled to a rheological constitutive equation of state within an irreversible thermodynamics ...framework. In the context of the coupling between the kinetics and the mechanical phenomena, we assume that the rate constants are functions of the affinities that contain the chemical potentials, which are themselves functions of the extended Gibbs free energy containing the irreversible dissipation terms. Although the derived model has a simple mathematical structure, it is able to predict complex flow behaviors, including shear‐thickening, shear‐thinning, and more complex flow histories such as shear‐banding. As special case, we derive the constitutive equations of the Bautista–Manero–Puig (BMP) model in which the material constants have a thermodynamic basis and have been successfully used for the last two decades to predict the behavior of complex fluids such as the ones examined here.
Anaerobic digestion (AD) is an efficient wastewater bioprocess, suitable for treating agroindustrial residues with high organic loads and characterized by both a low environmental impact and energy ...generation. This process is conformed by several chemical and biological reactions in an oxygen free atmosphere, that degrades high molecular weight organic compounds into carbon dioxide and methane mainly but also into traces of hydrogen and ammonia. This process is potentially unstable to volatile fatty acids (VFA), and the alkalinity. variations and is satisfactorily described by the non-linear AM2 model. In this contribution, the AM2 model is modified to include a more general expression for the pH, a cheap and continuous measurement, and also to add more detail in the interactions of the VFA, bicarbonates, and the alkalinity, key factors in the process stability. The stability of the AM2 modified model is explored through a rigorous bifurcation analysis that identifies unstable operation zones and viability of operation trajectories as a function of the dilution rate. Finally, an experimental validation is carried out to show the feasibility and accuracy of the proposed modifications.
Esterification is the first step in the biodiesel production process from low cost feedstock, which is typically characterized by its high content (>5%) of free fatty acids (FFAs). Although multiple ...attempts have been made to describe the kinetics of the esterification process for this feedstock, there is no consensus regarding which model is the most suitable. In this paper, two models were evaluated as candidates to describe the esterification of grease trap wastes, a synthetic mixture of tallow fat and canola oil, and oleic acid, which all have a high degree of acidity. The first model considers a pseudo‐first order reaction, whereas the second model considers the reversibility of the reaction. All parameters involved in these models are structurally identifiable and are estimated with the Levenberg–Marquardt method. A statistical analysis based on Akaike's weights show that the reversible model provides the best fit for all experimental runs compared to the first order model. This result was obtained from variations in catalyst loading and moisture content. Practical applications: The design and implementation of monitoring algorithms or robust control laws for a process carried out in a continuous stirred tank reactor (CSTR) require the knowledge of its dynamical mathematical model that contains a kinetic term. In the particular case of the esterification reactions for feedstock with high content of FFAs developed in the presence of homogeneous acid catalyst, there exists a discrepancy on the mathematical structure of such kinetic term. In this study we perform some batch experiments, considering industrial reagent grade alcohols, to deduce which model (among the two simplest kinetic models) better describes the esterification of oleic acid, grease trap wastes and a mixture of tallow fat and canola oil. Then, the results obtained from this basic research could be applied if monitoring‐regulation tasks are required for the esterification of the feedstock considered herein when such esterification be carried out in a CSTR under industrial conditions. Low cost feedstock has been esterified under variations in catalyst loading and initial moisture content. Two kinetic models were used to fit experimental data and a structural identifiability analysis has been conducted for each parameter contained in these models. According with Akaike's weights, the kinetic model that considers the reversibility of the esterification reaction provides the best fit for all experimental runs.
Assessing the viability of a blastosyst is still empirical and non-reproducible nowadays. We developed an algorithm based on artificial vision and machine learning (and other classifiers) that ...predicts pregnancy using the beta human chorionic gonadotropin (b-hCG) test from both the morphology of an embryo and the age of the patients. We employed two high-quality databases with known pregnancy outcomes (n = 221). We created a system consisting of different classifiers that is feed with novel morphometric features extracted from the digital micrographs, along with other non-morphometric data to predict pregnancy. It was evaluated using five different classifiers: probabilistic bayesian, Support Vector Machines (SVM), deep neural network, decision tree, and Random Forest (RF), using a k-fold cross validation to assess the model's generalization capabilities. In the database A, the SVM classifier achieved an F1 score of 0.74, and AUC of 0.77. In the database B the RF classifier obtained a F1 score of 0.71, and AUC of 0.75. Our results suggest that the system is able to predict a positive pregnancy test from a single digital image, offering a novel approach with the advantages of using a small database, being highly adaptable to different laboratory settings, and easy integration into clinical practice.
The aim of this work is to propose and to validate a dynamical model for an esterification reaction that was carried out in a relatively new configuration for biodiesel production process: a packed ...bed reactor with input, output, and recycle. More specifically, the reagents of the esterification process were free fatty acids (FFA) contained in canola oil and low cost methanol (LCM), whereas a commercial cation exchange resin (Purolite CT725) was used as a solid-acid catalyst. The effects of both the LCM volumetric inflow rate and the inflow FFA molar fraction were investigated. The dynamical model was built considering the following assumptions: 1) the reactor was modeled as a CSTR due to the high ratio of recycling volumetric flow to reactor volumetric inflow and 2) the kinetic expression in the model is written in terms of activity coefficients in the light of the non-ideal behavior of the esterification reaction. A satisfactory agreement between the experimental data and the proposed model was obtained. Thus, the resulting model may be advised as a valuable tool for the analysis, control, and optimization of continuous packed bed reactors where the esterification of FFA in the presence of solid acid catalyst is carried out to produce biodiesel.
This is the second part of a two-part manuscript focused on the analysis of electronic circuits employing extended irreversible thermodynamics. In this contribution, internal entropy production is ...used as a Lyapunov function for a thermodynamically consistent model of Chua’s circuit to address stability properties of an isolated, isothermal system containing it. In order to achieve this, simpler electronic circuits are first analyzed with an increasing complexity in construction. Here an RC-nonlinear resistor circuit and an RLC-nonlinear resistor circuit are considered as a preamble of the study of Chua’s circuit. In this manner, the entropy production approach allows conservative and dissipative phenomena and their interactions to be identified and contrasted with those of simpler study cases. Identification of recurrent terms in the dynamics of the entropy production function leads to the description of elemental interactions among electronic components. Analytical results are supported with numerical simulations at specific conditions. Chaos and other complex behaviors, like limit cycles, are analyzed and described with entropic and energetic perspectives. Apart from the determination of their stability, entropic descriptions for nodes, saddles and foci observed in the study cases and their vicinities are presented. It is observed through an extended Gibbs free energy analysis that the dissipation in limit cycles equals the build-up of energy. On the contrary, the behavior of changes of the state variables in a strange attractor is energetically asynchronous and unbalanced.
Sliding modes control (SMC) is a nonlinear control method with a systematic design procedure that allows to obtain a explicit solution for the control input. This method has some advantages, such as ...robustness against external disturbances and unpredictable parametric variations. On this work, two conventional SMC techniques, one using the error and other using the error integral, are designed and validated in a heat exchange system composed of a single pass circulation electric heater, whose control objective is to regulate the output temperature of the fluid, under the influence of external disturbances, such as variations in the flow and inflow temperature, manipulating the electric current passing through the heater resistance. The two SMC algorithms are analyzed using numerical simulations and their performance is compared through the integral absolute error and the integral absolute control input, selecting the best one to be tested experimentally. The experimental results indicate that the SMC is capable of fulfilling the control objective with satisfactory performance.
Keywords: Conventional sliding modes control; heat exchange system; nonlinear control.
This work is the second in a series of articles that deal with analytical solutions of nonlinear dynamical systems under oscillatory input that may exhibit harmonic frequencies. Frequency response ...techniques of nonlinear dynamical systems are usually analyzed with numerical methods, because in most cases analytical solutions such as the harmonic balance series solution turn out to be difficult, if not impossible, as they are based on an infinite series of trigonometric functions with harmonic frequencies. The key contribution of the analytic matrix methods reported in the present series of articles is to work with the invariant submanifold of the problem and to propose the solution as infinite power series of the oscillatory input; this procedure is a direct one that speeds up the computations compared to traditional series solution methods. The method reported in the first contribution of this series allows for the computation of the analytical solution only for small and medium amplitudes of the oscillatory input, because these series may diverge when large amplitudes are applied. Therefore, the analytic matrix method reported here, which is a reconfiguration of the method proposed in the first contribution in this series, allows the solving of problems in the regime of large-amplitude oscillations where the contributions of the high order harmonics affect the amplitudes of the low order harmonics, leading to amplitude- and frequency-dependent coefficients for the infinite series of trigonometric function expansion.
Grease trap wastes have been recently considered as an alternative feedstock for biodiesel production due to its relatively low cost and availability. These wastes are characterized by a high content ...of free fatty acids (FFA) and then, its processing towards biodiesel requires an esterification. In this paper, a dynamical model for the esterification of grease trap wastes was constructed. Specifically, this process has been conducted within a continuous stirred tank reactor. Almost all the parameters contained in the dynamical model were deduced from a series of batch temperature-controlled esterification experiments and from thermodynamic essays. The rest of the model parameters have been successfully estimated by means of a proposed algorithm that combines the notion of sensitivity with the Levenberg–Marquardt procedure. This regression procedure provides the estimates in spite of load and temperature variations and processing low-cost measurements. Finally, the proposed dynamical model has been validated with the runs test.
•A dynamical model for biodiesel production was proposed.•The biodiesel was produced via the esterification of grease trap wastes within a CSTR.•The esterification runs were conducted under load and temperature variations.•Esterification data were fitted to the model with a proposed regression algorithm.•The proposed model has been validated with the runs test using low-cost measurements.
Breast cancer ranks among the most commonly diagnosed cancers worldwide and bears the highest mortality rate. As an integral component of cancer treatment, mastectomy entails the complete removal of ...the affected breast. Typically, breast reconstruction, involving the use of silicone implants (augmentation mammaplasty), is employed to address the aftermath of mastectomy. To mitigate postoperative risks associated with mammaplasty, such as capsular contracture or bacterial infections, the functionalization of breast implants with coatings of cyclodextrin polymers as drug delivery systems represents an excellent alternative. In this context, our work focuses on the application of a mathematical model for simulating drug release from breast implants coated with cyclodextrin polymers. The proposed model considers a unidirectional diffusion process following Fick's second law, which was solved using the orthogonal collocation method, a numerical technique employed to approximate solutions for ordinary and partial differential equations. We conducted simulations to obtain release profiles for three therapeutic molecules: pirfenidone, used for preventing capsular contracture; rose Bengal, an anticancer agent; and the antimicrobial peptide KR-12. Furthermore, we calculated the diffusion profiles of these drugs through the cyclodextrin polymers, determining parameters related to diffusivity, solute solid-liquid partition coefficients, and the Sherwood number. Finally, integrating these parameters in COMSOL multiphysics simulations, the unidirectional diffusion mathematical model was validated.
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