A singular value decomposition entropy approach to assess the impact of Covid-19 on the informational efficiency of the WTI crude oil market.

This work investigates the impact of the Covid-19 outbreak on crude oil market efficiency. The approach is based on the singular value decomposition (SVD) entropy. Iso-distributional surrogate data test was used to contrast the results against random patterns, and phase randomization based on Fourier transform was used to assess nonlinearities. The analysis considered the WTI market and focused on the Covid-19 pandemic period January 2020-November 2021 and contrasted with the long preceding period from January 2000 to date. It was found that the crude oil market was informationally efficient most of the time with small sporadic deviations from efficiency in the pre-Covid-19 years. The Covid-19 period exhibited the largest deviations from efficiency, mainly in the first months of the outbreak, accompanied by a marked reduction of nonlinear components. The analysis was conducted for different scales, and the results showed that the deviations from efficiency were more pronounced for quarterly scales. For the sake of comparison, the analysis was also carried out on the trading volume dynamics and the results showed that the market activity is not fully random. The dynamics of the trading volume exhibited significant deviations from the randomness behavior when the crude oil market was efficient, and a behavior that was consistent with nonlinear patterns. The opposite behavior was noted for stages when the crude oil market showed strong deviations from efficiency. Overall, the findings of this study suggest an increasing opportunity for crude oil price predictions and abnormal returns during the Covid-19 pandemic.

On-line optimization of biomethane production in continuous AD processes via model-based ESC approach.

This paper is aimed at designing a class of model based extremum-seeking feedback controllers (ESC) for the on-line optimization of biomethane production rate in continuous anaerobic digestion (AD) processes. The ESC scheme is based on the modelling error compensation approach coupled with a first-order gradient estimator. The feedback control law is able to keep the concentration of volatile fatty acids (VFAs) near the unknown optimal setpoint while the methane production rate is maximized. Unlike other ESC algorithms applied to AD processes, the proposed control scheme includes a continuous uncertain estimator and avoids excessive oscillations in the control action. Numerical simulations compare the performance of the proposed ESC controller with traditional perturbation-based and sliding mode based approaches.

Effect of nopal mucilage addition on physical, barrier and mechanical properties of citric pectin-based films.

This study considered the effect of the nopal mucilage (NM) fraction on the physical, barrier and mechanical properties of citric pectin-based (CP) films. Pectin aqueous dispersion 75 mL (2.0 g/100 g water) were mixed with 5 mL of glycerol and 20 mL of NM aqueous dispersions at different concentrations; namely, 5, 10, 12, 14 16, 18 and 20 g/100 g water. Films containing the highest NM content (20 g/100 g water) exhibited improved thermal stability. The addition of NM at relatively low concentration (0-10 g/100 g water) led to important modifications of mechanical properties, including elongation to break, tensile strength, and elasticity. Microstructural analysis showed that films containing between 14 and 20 g/100 g water of NM presented rough and fractured surfaces. As mucilage concentration in films was increased, the vapor water permeability decreased as result of better internal cohesiveness of components. The modification of the physical properties in CP films resulted from molecular and physical interaction of its components. In general, the combination of NM and CP for forming edible films led to enhanced thermal stability and higher water vapor permeability, which are prescribed properties for applications as food packaging.

Thermodynamic sorption analysis and glass transition temperature of faba bean (Vicia faba L.) protein.

Freeze-dried faba bean (Vicia faba L.) protein adsorption isotherms were determined at 25, 35 and 40 °C and fitted with the Guggenheim-Anderson-de Boer model. The pore radius of protein was in the range of 0.87-6.44 nm, so that they were considered as micropores and mesopores. The minimum integral entropy ranged between 4.33 and 4.44 kg H2O/100 kg d.s., was regarded as the point of maximum of stability. The glass transition temperature of the protein equilibrated at the different conditions of storage was determined, showing that the protein remained in glassy state for all cases. The protein showed compact and rigid structures, evidenced by microscopy analysis.

Effect of gelatinized flour fraction on thermal and rheological properties of wheat-based dough and bread.

This work considered gelatinized wheat flour fraction with properties similar to hydrocolloid to enhance the strength of dough network by improving water retention and rheological characteristics. The gelatinized (90 °C) fraction of the wheat flour was incorporated in the dough formulation at different levels (5, 10, and 20% w/w). The effects of the gelatinized flour (GF) fraction on the dough rheology and thermal properties were studied. The incorporation of GF induced a moderate increase of dough viscoelasticity and reduced the freezing and melting enthalpies. On the other hand, the changes in bread textural properties brought by incorporation of GF were insignificant, indicating that the gelatinized fraction acted as a binder that enhanced water trapping in the structure. SEM images showed a more heterogeneous crumb microstructure (e.g., gas cells, porous, etc.) bread prepared using GF. Drying kinetics obtained from TGA indicated that the water diffusivity decreased with the incorporation of GF, which suggested that the bread had a compact microstructure.

Monitoring anaerobic sequential batch reactors via fractal analysis of pH time series.

Efficient monitoring and control schemes are mandatory in the current operation of biological wastewater treatment plants because they must accomplish more demanding environmental policies. This fact is of particular interest in anaerobic digestion processes where the availability of accurate, inexpensive, and suitable sensors for the on-line monitoring of key process variables remains an open problem nowadays. In particular, this problem is more challenging when dealing with batch processes where the monitoring strategy has to be performed in finite time, which limits the application of current advanced monitoring schemes as those based in the proposal of nonlinear observers (i.e., software sensors). In this article, a fractal time series analysis of pH fluctuations in an anaerobic sequential batch reactor (AnSBR) used for the treatment of tequila vinasses is presented. Results indicated that conventional on-line pH measurements can be correlated with off-line determined key process variables, such as COD, VFA and biogas production via some fractality indexes.

Effective diffusivity through arrays of obstacles under zero-mean periodic driving forces.

We perform a numerical investigation of the transport of Brownian particles driven by a zero-mean periodic force across two-dimensional arrays of obstacles with finite length. By applying axial and transversal driving forces relative to the diffusion transport direction, the effective diffusivity is determined as function of the array geometry and the driving frequency, finding excess diffusion peaks at certain frequency ranges. The results indicate that a suitable selection of the axial and transversal frequencies yields enhanced diffusion transport along the axial direction. Symmetric and asymmetric arrays are considered, showing that the asymmetry has a detrimental effect in the magnitude of the excess diffusion peaks. This suggests that enhanced diffusion is obtained because the oscillatory driving force exploits preferential transport channels, whose effective obstacle spacing is maximized under symmetric configurations.

Diffusion in one-dimensional channels with zero-mean time-periodic tilting forces.

We investigate the motion of overdamped Brownian particles in a one-dimensional channel under a zero-mean time-periodic tilting force F(t). By introducing a simple harmonic signal, strong enhancement of diffusion is possible for relatively large values of the Peclet number. Direct numerical simulations over the corresponding Fokker-Planck equation show that the diffusion enhancement is induced by a type of nonlinear resonance effect involving the tilting force and the density gradient.

A fractal scaling analysis of the SARS-CoV-2 genome sequence.

An approach based on fractal scaling analysis to characterize the organization of the SARS-CoV-2 genome sequence was used. The method is based on the detrended fluctuation analysis (DFA) implemented on a sliding window scheme to detect variations of long-range correlations over the genome sequence regions. The nucleotides sequence is mapped in a numerical sequence by using four different assignation rules: amino-keto, purine-pyrimidine, hydrogen-bond and hydrophobicity patterns. The originally reported sequence from Wuhan isolates (Wuhan Hu-1) was considered as a reference to contrast the structure of the 2002-2004 SARS-CoV-1 strain. Long-range correlations, quantified in terms of a scaling exponent, depended on both the mapping rule and the sequence region. Deviations from randomness were attributed to serial correlations or anti-correlations, which can be ascribed to ordered regions of the genome sequence. It was found that the Wuhan Hu-1 sequence was more random than the SARS-CoV-1 sequence, which suggests that the SARS-CoV-2 possesses a more efficient genomic structure for replication and infection. In general, the virus isolated in the early 2020 months showed slight correlation differences with the Wuhan Hu-1 sequence. However, early isolates from India and Italy presented visible differences that led to a more ordered sequence organization. It is apparent that the increased sequence order, particularly in the spike region, endowed some early variants with a more efficient mechanism to spreading, replicating and infecting. Overall, the results showed that the DFA provides a suitable framework to assess long-term correlations hidden in the internal organization of the SARS-CoV-2 genome sequence.

Analysis of starch digestograms using Monte Carlo simulations.

Monte Carlo dynamics were used to simulate the enzymatic starch digestion. Enzyme and starch molecules were distributed on a periodic grid and allowed to stochastically interact according to the kinetics scheme S + E â†’ P + E. Digestion of gelatinized dispersions was simulated by assuming limited mobility of starch and complete mobility of enzymes and products. The results showed that the starch conversion kinetics follows the exponential model X(t) = X∞(1 -  exp (-kHt)). On the other hand, the simulation of native granular starch digestion considered non-mobile aggregates of starch molecules hydrolyzed to products by mobile enzyme molecules. The results showed the presence of bi-phasic digestion patterns, which were linked to the transition from a regular to an irregular (fractal-like) granule morphology as a consequence of the erosion of the granule surface by the enzyme action. The simulation results were contrasted qualitatively with experimental results for gelatinized and granular starch digestion.

Enhanced diffusion in conic channels by means of geometric stochastic resonance.

Geometric stochastic resonance of Brownian particles diffusing across a converging conic channel subject to oscillating forces is studied in this paper. Conic channel geometries have been previously considered as a model for transport of particles in biological membranes, zeolites, and nanostructures. For this system, a broad excess peak of the effective diffusion above the free diffusion limit is exhibited over a wide range of frequencies, suggesting a synchronization effect in the confining geometry as particles respond to the periodic modulation of the external force. This indicates that the geometric stochastic resonance effect with unbiased ac forces can be exploited for improving the transport of particles in complex geometries.

Effects of dry heat treatment temperature on the structure of wheat flour and starch in vitro digestibility of bread.

The effects of the dry heat treatment (DHT) temperature (20, 50, 100, 150, 200 °C) on the structure of wheat flour and on the texture and in vitro starch digestibility of breads were investigated. X-ray diffraction and FTIR showed that increasing temperatures produced reduction of the hydrated starch structures, increased crystallinity and molecular order of starch chains, and had important effects on the gluten secondary structure. High treatment temperatures produced significant reductions in rapidly digestible starch (RDS) (53.21% at 20 °C, 22.24% at 200 °C), and the slowly digestible starch fraction tended to increase (26.12% at 20 °C, 31.48% at 200 °C). On the other hand, bread hardness showed a significant increase from 11.25 N at 20 °C to 49.53 N at 200 °C, the latter value being similar to that reported for bread crusts. Principal component analysis results showed that the flour and bread characteristics were drastically changed by the DHT, with 100 °C representing a critical temperature. Below 100 °C, breads showed textural characteristics close to that of the control bread, with reduced RDS fractions, while at temperatures above 100 °C, hardness was boosted.

Morphological, barrier, and mechanical properties of banana starch films reinforced with cellulose nanoparticles from plantain rachis.

The main aim of the present study was to characterize banana starch films reinforced with nanoparticles from plantain rachis. Nanoparticles were obtained by acid hydrolysis and sonication, exhibiting a mean hydraulic diameter of about 60 nm. Scanning electron microscopy micrographs showed that the nanoparticle thickness ranged between 9.8 and 22.3 nm. The thermal gravimetric analysis showed that nanoparticles are thermally stable for temperatures up to 340 °C. Films were made for different fractions of nanoparticles (0.0, 1.75, 2.5, and 4.0%) relative to total solids, and glycerol was used as a plasticizer. The influence of the addition of nanoparticles to starch films on the morphology, water vapor permeability (WVP), and mechanical properties of the nanocomposites films was explored. Cellulose nanoparticles reduced the WVP, and increased the tensile strength and flexibility of the starch films. FTIR analysis of films was used to show that nanoparticles improved the molecular organization of starch chains. It was proposed that nanoparticles acted as a crosslinked for starch chains via hydrogen bonding effects.

Gaining insights into α­amylase inhibition by glucose through mathematical modeling and analysis of the hydrolysis kinetics of gelatinized corn starch dispersions.

The inhibitory effect of glucose on the activity of α­amylase used for starch hydrolysis was explored in this study. Four gelatinized corn starch dispersions (5 g/100 mL) containing different glucose concentrations (0.5, 1.0, 2.0 and 4.0 g/100 mL) and a control without added glucose were subjected to enzymatic hydrolysis with α­amylase (0.33 IU/mL) for 2 h. The hydrolysis kinetics showed that the limiting hydrolysis advance was reduced as glucose concentration increased. A Michaelis-Menten scheme was used for developing a mathematical model of the hydrolysis kinetics. The mathematical model predicted that the maximum hydrolysis value was consequence of the inhibition of the enzyme activity by the initial glucose load added to the gelatinized starch dispersions and by the glucose produced by amylolytic action. FTIR analysis of the Amide I band showed that glucose disrupted the secondary structure of the α­amylase, an effect that could be related to the inhibition of the enzymatic activity.

A multiscale kinetics model for the analysis of starch amylolysis.

Simple exponential decaying functions are commonly used for fitting the kinetics of starch digested by amylolytic enzymes. A common assumption is that a sole exponential function can account for the kinetics of the whole digestible starch. Recent studies using logarithm-of-slope (LOS) plots showed that digestion kinetics can exhibit multi-scale behavior, an effect reflecting starch fractions with different digestion characteristics. This work proposed an extension of the widely used Goñi et al.'s model to account for two starch fractions; one fraction linked with fast digestion rate and other with slow digestion rates. The fitting of experimental data was carried out by solving numerically a nonlinear least-squares problem. The estimated parameters have a straightforward interpretation in terms of reaction rates and digestible/resistant starch fractions. Two experimental examples were used for illustrating the performance of the multi-exponential function.

ECG scaling properties of cardiac arrhythmias using detrended fluctuation analysis.

We applied detrended fluctuation analysis to characterize at very short time scales during episodes of cardiac arrhythmias the raw electrocardiogram (ECG) waveform, aiming to get a global insight into its dynamical behaviour in patients who experienced sudden death. We found that in 15 recordings involving different types of arrhythmias (taken from PhysioNet's Sudden Cardiac Death Holter Database), the ECG waveform, besides showing a less-random dynamics, becomes more regular during bigeminy, ventricular tachycardia or even atrial fibrillation and ventricular fibrillation. The ECG waveform scaling properties thus suggest that reduced complexity dominates the underlying mechanisms of arrhythmias. Among other explanations, this may result from shorted or restricted (i.e. less diverse) pathways of conduction of the electrical activity within ventricles.

Thermodynamic criteria analysis for the use of taro starch spherical aggregates as microencapsulant matrix.

Spherical aggregates can be obtained from taro starch by spray-drying without using bonding agents. Accurate information about thermal issues of spherical aggregates can provide valuable information for assessing the application as encapsulant. Spherical aggregates of taro starch were obtained by spray-drying and analyzed using dynamic vapour sorption. The use of the Guggenheim, Anderson and de Boer (GAB) model indicated a Type II isotherm pattern with weaker interactions in the multilayer region. Differential enthalpy and entropy estimates reflected a mesoporous microstructure, implying that energetic mechanisms dominate over transport mechanisms in the sorption process. The limitation by energetic mechanisms was corroborated with enthalpy-entropy compensation estimates. The diffusivity coefficient was of the order of 10-8 m2·s-1, which is in line with results obtained for common materials used for encapsulation purposes. The thermodynamic properties and the lack of a bonding agent indicated the viability of spherical aggregates of taro starch for encapsulation of biocompounds.

Potential of taro starch spherical aggregates as wall material for spray drying microencapsulation: Functional, physical and thermal properties.

Taro starch spherical aggregates have been considered as wall material for the microencapsulation of bioactive compounds. The distribution of particle size, morphology, stability, glass transition temperature, ζ-potential, physical properties and flowability and compression indexes, and functional properties (water, oil and dye retention capacity) were measured. The average diameter was 17.5 ±â€¯0.3 µm. Aggregates formed by a relatively high number of starch granules were observed. The residual protein in the aggregates was in the periphery of the starch granules, favoring the aggregation and the stability under aqueous stirring conditions. The ζ-potential was -21.8 ±â€¯0.3 mV. The value of the glass transition temperature was in the range from 176.8 to 75.4 °C, with 5% and excess water, respectively. The Hausner ratio and Carr index were 1.06 and 14.7, respectively. The oil holding capacity was 1.2 ±â€¯0.01 g of oil·g-1 of dry solid. Overall, the functional, physical and thermal properties of the spherical aggregates of taro starch granules showed that this material offers good potential for the microencapsulation of bioactive compounds.

Thermodynamic analysis for assessing the physical stability of core materials microencapsulated in taro starch spherical aggregates.

Taro starch has the ability of producing spherical aggregates under spray-drying without the addition of binding agents. This property makes taro starch suitable for microencapsulation of dietary compounds. This study addressed the physical stability of hydrophilic and hydrophobic core materials microencapsulated by spray-drying into taro starch spherical aggregates determined from a thermodynamic standpoint via vapor adsorption isotherms. Ascorbic acid and almond oil were used as compound models. Encapsulation efficiency, GAB sorption parameters, differential and integral thermodynamic properties, Gibb's free energy, entropy-enthalpy compensation, spreading pressure, effective diffusion rate, activation energy and critical water activity were determined. The encapsulation efficiency of ascorbic acid and almond oil was 99% and 56%, respectively. Monolayer moisture content was relatively low for ascorbic acid microcapsules. The adsorption process was driven by entropic mechanisms. The physical stability of taro starch spherical aggregates microcapsules with different core material was guaranteed for a range of water activities and temperatures.

In vitro digestibility of normal and waxy corn starch is modified by the addition of Tween 80.

Aqueous dispersions of normal and waxy corn starch (3% w/w) were mixed with Tween 80 (0, 7.5, 15, 22.5 and 30 g/100 g of starch), and gelatinized (90 °C, 20 min). Optical microscopy of the gelatinized starch dispersions (GSDx; x = Tween 80 concentration) revealed that the microstructure was characterized by a continuous phase of leached amylose and amylopectin entangled chains, and a dispersed phase of insoluble remnants, called ghosts, on whose surface small granules were observed, imputed to Tween 80. The apparent viscosity of the GSDx decreased as the concentration of Tween 80 increased (up to about 70-90%). FTIR analysis of dried GSDx indicated that Tween 80 addition decreased short-range ordering. The content of rapidly digestible starch (RDS) and resistant starch (RS) fractions tended to increase significantly, at the expense of a significant decrease of slowly digestible starch (SDS) fraction, an effect that may be attributed to the increase of amorphous structures and starch chain-surfactant complexes. The RDS and RS increase was more pronounced for normal than for waxy corn starch, and the significance of the increase was dependent on Tween 80 concentration. Overall, the results showed that surfactant can affect largely the digestibility of starch chains.