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Featured Application: In this work, cheese whey, which is a by-product of the cheese industry, was used to obtain lactic acid by biotechnological processes (using strains isolated from the same cheese whey). Lactic acid has several uses in the cosmetic, food, medical, textile, and manufacturing industries. Therefore, while lactic acid can have multiple uses, we want to use it as a raw material for biopolymers for the manufacturing of bioplastics in future research. Cheese whey is a byproduct of the cheese industry that causes high levels of pollution in the environment, but its high lactose content means that it can be used as a source to obtain lactic acid. In this study, two strains, one belonging to a yeast and the other one to a bacteria (Kluyveromyces lactis and Enterococcus faecalis), were isolated from cheese whey and molecularly characterized, and the optimal growth conditions were determined. Then, using proteinized and deproteinized cheese whey, batch fermentation was carried out with the strains arranged in suspension and immobilized. The consumption of lactose and the production of lactic acid were measured through Brix degrees and acidity analysis. Afterwards, the lactic acid was purified, and its yield and physical and chemical characteristics were determined. It was proven that there were differences between each of the strains; arranged in free or encapsulated cells, the proteinized and deproteinized cheese wheys, under the same purification conditions, achieved different yields, colors, and densities of lactic acid. Immobilized Enterococcus faecalis had the highest yield (50.61 ± 34.94 g/L) using the deproteinized cheese whey compared to the immobilized Kluyveromyces lactis (35.70 ± 0.15 g/L) using the proteinized cheese whey. [ABSTRACT FROM AUTHOR]

We present a novel finite element method to solve the thermal variables in welding problems. The mathematical model is based on the enthalpy formulation of the energy conservation law, which is simultaneously valid for the solid, liquid, and mushy regions. Both isothermal and non-isothermal melting models are considered to relate the enthalpy with the temperature. Quadratic triangular elements with local anisotropic mesh adaptation are employed for the space discretization of the governing equation, and a second-order backward differentiation formula is employed for the time discretization. The resulting non-linear discretized system is solved with a simple Newton algorithm with two versions: the  θ -Newton algorithm, which considers the temperature as the main unknown variable, as in most works in the literature, and the h-Newton algorithm, which considers the enthalpy, which is the main novelty of the present work. Then, we show via numerical experiments that the h-Newton method is robust and converges well to the solution, both for isothermal and non-isothermal melting. However, the  θ -method can only be applied to the case of non-isothermal melting and converges only for a sufficiently large melting temperature range or sufficiently small time step. Numerical experiments also confirm that the method is able to adequately capture the discontinuities or sharp variations in the solution without the need for any kind of numerical dissipation. [ABSTRACT FROM AUTHOR]

Textile effluents derived from azo-reactive dyeing processes represent a severe problem for aquatic ecosystems and human health. The large amounts of water used in this process and the poor quality of the discharges urge the need to develop treatment systems that involve reusing treated water. In this research, we present the optimization of a feasible, simple, and efficient treatment system that improves the quality of the effluents from the cotton fabric dyeing process. Through the characterization of the influents and effluents, we have identified seven parameters that have allowed the optimization of the treatment. Analytical techniques, such as nephelometry, EDTA, gravimetry, and BOD5, among others, and specialized equipment, such as the spectrophotometer, have been used for these purposes. The results showed that using combustion gases in the neutralization stage and new flocculant-coagulant reagents improved parameters, such as pH, total solids, hardness, and conductivity. The quality of the effluents thus obtained allowed their reuse only in the stages before the dyeing bath without affecting the final quality of the cotton fabrics in dark colors. This effort implies savings in water and supplies, and opens the door to future research on the treatment of textile effluents that help improve the environmental conditions of our region. [ABSTRACT FROM AUTHOR]

Theoretical predictions and numerical simulations are used to determine the transition to bubble and conical vortex breakdown in low-Mach-number laminar axisymmetric variable-density swirling jets. A critical value of the swirl number S for the onset of the bubble (S∗B) and the cone (S∗C) is determined as the jet-to-ambient density ratio Λ is varied, with the temperature dependence of the gas density and viscosity appropriate to that of air. The criterion of failure of the slender quasi-cylindrical approximation predicts S∗B that decreases with increasing values of Λ for a jet in solid-body rotation emerging sharply into a quiescent atmosphere. In addition, a new criterion for the onset of conical breakdown is derived from divergence of the initial value of the radial spreading rate of the jet occurring at S∗C, found to be independent of Λ, in an asymptotic analysis for small distances from the inlet plane. To maintain stable flow in the unsteady numerical simulations, an effective Reynolds number Reeff, defined employing the geometric mean of the viscosity in the jet and ambient atmosphere, is fixed at Reeff = 200 for all Λ. Similar to the theoretical predictions, numerical calculations of S∗B decrease monotonically as Λ is increased. The critical swirl numbers for the cone, S∗C, are found to depend strongly on viscous effects; for Λ = 1/5, the low jet Reynolds number (51) at Reeff = 200 delays the transition to the cone, while for Λ = 5 at Reeff = 200, the large increase in kinematic viscosity in the external fluid produces a similar trend, significantly increasing S∗C. [ABSTRACT FROM AUTHOR]

This numerical study uses a Lagrangian–Eulerian formulation employing the point-source approximation to investigate nonpremixed axisymmetric spray diffusion flames stabilized between a stream of hot air and a stream of nitrogen carrying a monodisperse spray of fuel droplets injected at a distance zl from the stagnation plane. The computations consider moderately large values of the relevant thermal Peclet number, such that the thickness of the mixing layer separating both streams is much smaller than zl. A one-step irreversible reaction is assumed between the fuel vapor and the oxygen of the air. Most of the computations consider the thermochemical, vaporization, and transport properties of dodecane, with additional results for the properties of methanol used to assess effects of higher fuel volatility. The analysis considers moderately small values of the liquid mass loading ratio at the injection plane, consistent with the stoichiometric value of the fuel-to-air mass ratio of the global oxidation reaction of typical hydrocarbon and alcohol fuels. Attention is mainly focused on inertial droplets with associated Stokes numbers St of order unity or larger, for which the droplets penetrate far into the oxidizer stream, vaporizing over distances of order zl and leading to combustion occurring outside the mixing layer. In this inertial regime, besides solutions involving a diffusion flame separating the fuel and oxygen with a well-defined peak temperature of the order of the adiabatic flame temperature, the analysis reveals, for the first time, the existence of flameless solutions with distributed combustion and small temperature increments from the air-side value. The two solutions are found to exist for the same sets of boundary conditions. Integrations for increasing values of St identify a value of the Stokes number St2 above which the vaporization rate is too small to support a diffusion-flame solution, while integrations for decreasing St lead to the identification of another value of the Stokes number St1 < St2 below which a distributed reaction cannot occur. In the intermediate hysteretic range St1 ≤ St ≤ St2 where two different steady solutions may exist, the type of solution encountered depends on the initial conditions imposed. The preliminary results suggest that future efforts targeting quantification of the flameless regime, which is found to be relevant in applications with larger droplets, would benefit from consideration of different possible gas-phase chemical kinetics, including cool-flame chemistry. [ABSTRACT FROM AUTHOR]

This computational study addresses deflagration initiation of lean, stoichiometric, and moderately rich hydrogen–air mixtures by the sudden discharge of a hot planar jet of its adiabatic combustion products. The objective is to determine the minimum slot size required for ignition, a relevant quantity of interest for safety and technological applications concerning the accidental ignition of hydrogen. For sufficiently small jet velocities, the numerical solution of the problem requires integration of the two-dimensional Navier–Stokes equations for chemically reacting ideal-gas mixtures, supplemented by standard descriptions of the molecular transport terms and a reduced chemical–kinetic mechanism suitable for hydrogen–air combustion. The computations provide the variation of the critical slot size for hot-jet ignition with both the jet Reynolds number and the equivalence ratio of the mixture. In particular, it is seen that, while the Reynolds number exerts only a relatively weak effect on the ignition process, the influence of the equivalence ratio is much more pronounced, with the smallest slot widths found for stoichiometric or slightly-rich conditions. The numerical results show three different ignition modes, with the flame developing from a clearly identified ignition kernel located either at the core of the leading vortex pair (mode 1), at the symmetry plane near the leading edge of the starting jet (mode 2), or at the jet stem connecting the jet exit with the starting vortex (mode 3). [ABSTRACT FROM AUTHOR]

Thanks to its very simple recursive computing scheme, exponential smoothing has become a popular technique to forecast time series. In this work, we show the advantages of its multivariate version and present some properties of the model, which allows us to perform a dynamic factor analysis. This analysis leads to a simple methodology to reduce the number of parameters (useful when the dimension of observations is large) via a linear transformation that decomposes the multivariate process into independent univariate exponential smoothing processes, characterized by a single smoothing parameter that goes from zero (white-noise process) to one (random walk process). A computer implementation of the expectation-maximization (EM) algorithm has been built for the maximum likelihood estimation of the models. The practicality of the method is demonstrated by its application to hourly electricity price predictions in some day-ahead markets, such as Omel, Powernext, and Nord Pool markets, whose forecasts are given as examples. This article has supplementary material online. [ABSTRACT FROM AUTHOR]

We propose in this paper an anisotropic, adaptive, finite element algorithm for steady, linear advection-diffusion-reaction problems with strong anisotropic features. The error analysis is based on the dual weighted residual methodology, allowing us to perform "goal-oriented" adaptation of a certain functional J(u) of the solution and derive an "optimal" metric tensor for local mesh adaptation with linear and quadratic finite elements. As a novelty, and to evaluate the weights of the error estimator on unstructured meshes composed of anisotropic triangles, we make use of a patchwise, higher-order interpolation recovery readily extendable to finite elements of arbitrary order. We carry out a number of numerical experiments in two dimensions so as to prove the capabilities of the goal-oriented adaptive method. We compute the convergence rate and the effectivity index for a series of output functionals of the solution. The results show the good performance of the algorithm with linear as well as quadratic finite elements. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the Expectation Maximization algorithm (EM) applied to operational modal analysis of structures. The EM algorithm is a general-purpose method for maximum likelihood estimation (MLE) that in this work is used to estimate state space models. As it is well known, the MLE enjoys some optimal properties from a statistical point of view, which make it very attractive in practice. However, the EM algorithm has two main drawbacks: its slow convergence and the dependence of the solution on the initial values used. This paper proposes two different strategies to choose initial values for the EM algorithm when used for operational modal analysis: to begin with the parameters estimated by Stochastic Subspace Identification method (SSI) and to start using random points. The effectiveness of the proposed identification method has been evaluated through numerical simulation and measured vibration data in the context of a benchmark problem. Modal parameters (natural frequencies, damping ratios and mode shapes) of the benchmark structure have been estimated using SSI and the EM algorithm. On the whole, the results show that the application of the EM algorithm starting from the solution given by SSI is very useful to identify the vibration modes of a structure, discarding the spurious modes that appear in high order models and discovering other hidden modes. Similar results are obtained using random starting values, although this strategy allows us to analyze the solution of several starting points what overcome the dependence on the initial values used. [Copyright &y& Elsevier]

A computational fluid dynamics software (DynamFluid) based on the application of the finite element method with the characteristic-based-split algorithm is presented and validated. The software is used to numerically integrate the steady and unsteady Navier–Stokes equations for both constant-density and Boussinesq non-isothermal flows. Benchmark two-dimensional computations carried out with DynamFluid show good agreement with previous results reported in the literature. Test cases used for validation include (i) the lid-driven cavity flow, (ii) mixed convection flow in a vertical channel with asymmetric wall temperatures, (iii) unsteady incompressible flow past a circular cylinder, and (iv) steady non-isothermal flow past a circular cylinder with negligible buoyancy effects. The new software is equipped with a graphical user interface that facilitates the definition of the fluid properties, the discretization of the physical domain, the definition of the boundary conditions, and the post-processing of the computed velocity, pressure and temperature fields. [ABSTRACT FROM AUTHOR]