Stabilization of a chaotic oscillator via a class of integral controllers under input saturation.

This work presents the straightforward design of an integral controller with an anti-windup structure to prevent undesirable behavior when actuator saturation is considered, and the proposed controller improves the performance of the closed-loop dynamics of a class of nonlinear oscillators. The proposed integral controller has an adaptive control gain, which includes the absolute value of the named control error to turn off the integral action when it is saturated. Closed-loop stability analysis is performed under the Lyapunov theory framework, where it can be concluded that the system behaves in an asymptotically stable way. The proposed methodology is successfully applied to a Rikitake-type oscillator, considering a single input-single output (SISO) structure for regulation and tracking trajectory purposes. For comparison, an equivalent fixed gain integral controller is also implemented to analyze the corresponding anti-windup properties of the proposed control structure. Numerical experiments are conducted, showing the superior performance of the proposed controller.

A novel kinetic model for a cocoa waste fermentation to ethanol reaction and its experimental validation.

A non-segregated kinetic model is proposed to describe a fermentation process of agro-industrial residues derived via cocoa (mucilage juice) by Pichia kudriavzevii. The novel proposed hybrid model is based on a multiple coupling reaction mechanisms (structured) to describe the kinetics of substrate consumption, biomass, carbon dioxide, and ethanol, coupled to an unstructured model for the activity enzyme. The parameters of the kinetic model are estimated by non-linear least-squares curve fitting using the Marquardt-Levenberg algorithm. In addition, numerical simulations were compared with the experimental data via residual graphs. The effectiveness of the model was statistically evaluated using dimensionless efficiency coefficients under different initial conditions. A global sensitivity analysis was applied (Fisher's information matrix). The experimental results of the batch reactor showed a maximum ethanol concentration of 29 g/L, with a yield of 0.48 g-ethanol/g-glucose and a productivity of 0.30 g/L h. The method determined that the cell formation coefficient and the specific substrate consumption rate (θ1 and θ2) directly influence most of the states of our system. The proposed scheme is particularly suitable to assist in the rational design of cell factory properties or fermentation processes because it can represent the complex biochemistry in more detail and under different initial experimental conditions; the above reveals that the generated model is robust and can be considered for control and optimization purposes.

Bioremediation of an agricultural saline soil contaminated with endosulfan and Escherichia coli by an active surface agent induced in a Penicillium crustosum culture.

This study evaluates the production of a biological active surface agent (BASA) through its surface tension (ST) and emulsifying activity (E24) for endosulfan degradation (ED) and Escherichia coli growth inhibition (EcGI) in an agricultural saline soil. The fungus, identified as Penicillium crustosum was isolated from the Citrus sinensis peel (CsP), then the surface properties were evaluated in 9 culture media through a Taguchi L9 experimental design. The culture conditions included: stirring speed, pH, carbon (C) and nitrogen (N) sources; being glucose, NH4N03, 120 rpm and pH of 5, the most significant parameters in the BASA production. The BASA identified as a lipopeptide type, showed a ST = 38 mN m-1 and E24=71%. Both properties were stable at 80 °C, while ST presented stability in the pH range of 2 - 12, and a saline concentration of 200 g L-1; E24 was also stable at a pH between 8-12. Further application of BASA and fungal inoculum to a contaminated agricultural saline soil presented an EcGI of 99.8% on the 8th day, and ED of 92.9 ± 4.7% in 30 days, respectively; being the first report that uses this fungus for pesticide and bacteria elimination from an agricultural saline soil.

High Kanamycin Concentration as Another Stress Factor Additional to Temperature to Increase pDNA Production in E. coli DH5α Batch and Fed-Batch Cultures.

Plasmid DNA (pDNA) vaccines require high supercoiled-pDNA doses (milligrams) to achieve an adequate immune response. Therefore, processes development to obtain high pDNA yields and productivity is crucial. pDNA production is affected by several factors including culture type, medium composition, and growth conditions. We evaluated the effect of kanamycin concentration and temperature on pDNA production, overflow metabolism (organic acids) and metabolic burden (neomycin phosphotransferase II) in batch and fed-batch cultures of Escherichia coli DH5α-pVAX1-NH36. Results indicated that high kanamycin concentration increases the volumetric productivity, volumetric and specific yields of pDNA when batch cultures were carried out at 42 °C, and overflow metabolism reduced but metabolic burden increased. Micrographs taken with a scanning electron microscope (SEM) were analyzed, showing important morphological changes. The high kanamycin concentration (300 mg/L) was evaluated in high cell density culture (50 gDCW/L), which was reached using a fed-batch culture with temperature increase by controlling heating and growth rates. The pDNA volumetric yield and productivity were 759 mg/L and 31.19 mg/L/h, respectively, two-fold greater than the control with a kanamycin concentration of 50 mg/L. A stress-based process simultaneously caused by temperature and high kanamycin concentration can be successfully applied to increase pDNA production.

Removal of phenanthrene in aqueous solution containing photon competitors by TiO2-C-Ag film supported on fiberglass.

Surface interactions with pollutants and photons are key factors that affect the applications of TiO2 in environmental remediation. In this study, the solubilizing agents dimethylsulfoxide and polyoxyethylene sorbitan monooleate, which act as photon competitors, had no effect on the photocatalytic activity of TiO2-C-Ag film in phenanthrene (PHE) removal. Fiberglass with TiO2-C-Ag coating removed 91.1 ± 5.2 and 99.7 ± 0.4% of PHE in treatments using UVA (365-465 nm) and UVC (254 nm) irradiation, respectively. The use of fiberglass as a support increased the superficial area, thus allowing PHE sorption. C and Ag, which are electrically active impurities in TiO2, enhanced its photocatalytic activity and thus the attraction of the pollutant to its surface. The use of high-frequency UV light (UVC) decreased the amount of carbon species deposited on the TiO2CAg film surface. X-ray photoelectron spectroscopy of the TiO2-C-Ag film revealed extensive oxidation of the carbon deposited on the film under UVC light and loss of electrons from Ag clusters by conversion of Ag0 to Ag3+.

A New Finite-Time Observer for Nonlinear Systems: Applications to Synchronization of Lorenz-Like Systems.

This paper proposes a synchronization methodology of two chaotic oscillators under the framework of identical synchronization and master-slave configuration. The proposed methodology is based on state observer design under the frame of control theory; the observer structure provides finite-time synchronization convergence by cancelling the upper bounds of the main nonlinearities of the chaotic oscillator. The above is showed via an analysis of the dynamic of the so called synchronization error. Numerical experiments corroborate the satisfactory results of the proposed scheme.

Effect of Cd⁺² on phosphate solubilizing abilities and hydrogen peroxide production of soil-borne micromycetes isolated from Phragmites australis-rhizosphere.

The aims of this work were to evaluate the phosphate-solubilization and hydrogen peroxide (H2O2) production by the soil-borne micromycetes, Aspergillus japonicus, Penicillium italicum and Penicillium dipodomyicola, isolated from Phragmites australis rhizosphere and to study the effect of several concentrations of Cadmium (Cd(2+)) on both variables. Our results showed that P. italicum achieved a higher P-solubilization and H2O2 production than A. japonicus and P. dipodomyicola, as only P. italicum showed a positive correlation (R(2) = 0.71) between P-solubilization and H2O2 production. In dose-response assays, P. italicum was also more tolerant to Cd(2+) (0.31 mM) in comparison to A. japonicus (0.26 mM). Analysis of the 2(4) factorial experimental design showed that P-solubilization by P. italicum was negatively affected by increases in Cd(2+) (p = 0.04) and yeast extract (p = 0.02) in the culture medium. The production of H2O2 was positively affected only by glucose (p = 0.002). Fungal biomass production was reduced significantly (p = 0.0009) by Cd(2+) and increased (p = 0.0003) by high glucose concentration in the culture medium. The tolerance and correlation between P-solubilization and H2O2 production in the presence of Cd(2+) was strain and species dependent. The effects of Cd(2+), glucose, ammonium sulfate and yeast extract on those variables were evaluated through a two-level factorial design. P. italicum is promising for P-solubilization in soils contaminated with Cd(2+) and may be an alternative for manufacture of biofertilizers to replace chemical fertilizers.

Evaluation of hydrocarbons and organochlorine pesticides and their tolerant microorganisms from an agricultural soil to define its bioremediation feasibility.

The concentrations of hydrocarbons and organochlorine pesticides (OCPs), nutrients and tolerant microorganisms in an agricultural soil from a locality in Tepeaca, Puebla, Mexico, were determined to define its feasibility for bioremediation. The OCPs detected were heptachlor, aldrin, trans-chlordane, endosulfán I, endosulfán II, 1,1,1-bis-(4-chlorophenyl)-2,2-trichloroethane (4,4'-DDT), 1,1-bis-(4-chlorophenyl)-2,2-dichloroethene (4,4'-DDE) and endrin aldehyde, with values of 0.69-30.81 ng g(-1). The concentration of hydrocarbons in the soil of Middle Hydrocarbons Fraction (MHF), C10 to C28, was 4608-27,748 mg kg(-1) and 1117-19,610 mg kg(-1) for Heavy Hydrocarbons Fraction (HHF), C28 to C35, due to an oil spill from the rupture of a pipeline. The soil was deficient in nitrogen (0.03-0.07%) and phosphorus (0 ppm), and therefore it was advisable to fertilize to bio-stimulate the native microorganisms of soil. In the soil samples, hydrocarbonoclast fungi 3.72 × 10(2) to 44.6 × 10(2) CFU g(-1) d.s. and hydrocarbonoclast bacteria (0.17 × 10(5) to 8.60 × 10(5) CFU g(-1) d.s.) were detected, with a tolerance of 30,000 mg kg(-1) of diesel. Moreover, pesticideclast fungi (5.13 × 10(2) to 42.2 × 10(2) CFU g(-1) d.s.) and pesticideclast bacteria (0.15 × 10(5) to 9.68 × 10(5) CFU g(-1) d.s.) were determined with tolerance to 20 mg kg(-1) of OCPs. Fungi and bacteria tolerant to both pollutants were also quantified. Therefore, native microorganisms had potential to be stimulated to degrade hydrocarbons and pesticides or both pollutants. The concentration of pollutants and the microbial activity analyzed indicated that bioremediation of the soil contaminated with hydrocarbons and pesticides using bio-stimulation of native microorganisms was feasible.

Multisynchronization of chaotic oscillators via nonlinear observer approach.

The goal of this work is to synchronize a class of chaotic oscillators in a master-slave scheme, under different initial conditions, considering several slaves systems. The Chen oscillator is employed as a benchmark model and a nonlinear observer is proposed to reach synchronicity between the master and the slaves' oscillators. The proposed observer contains a proportional and integral form of a bounded function of the synchronization error in order to provide asymptotic synchronization with a satisfactory performance. Numerical experiments were carried out to show the operation of the considered methodology.

Monitoring in a predator-prey systems via a class of high order observer design.

The goal of this work is the monitoring of the corresponding species in a class of predator-prey systems, this issue is important from the ecology point of view to analyze the population dynamics. The above is done via a nonlinear observer design which contains on its structure a high order polynomial form of the estimation error. A theoretical frame is provided in order to show the convergence characteristics of the proposed observer, where it can be concluded that the performance of the observer is improved as the order of the polynomial is high. The proposed methodology is applied to a class of Lotka-Volterra systems with two and three species. Finally, numerical simulations present the performance of the proposed observer.