This paper presents the results of investigating the dynamics of an economic system with chaotic behavior and a suboptimal control proposal to suppress the chaotic behavior. Numerical results using ...phase portraits, bifurcation diagrams, Lyapunov exponents, and 0-1 testing confirmed chaotic and hyperchaotic behavior. The results also proved the effectiveness of the control, showing errors below 1%, even in cases where the control design is subject to parametric errors. Additionally, an investigation of the system in fractional order is included, demonstrating that the system has periodic, constant, or chaotic behavior for specific values of the order of the derivative.
This paper investigates, through numerical simulations, the application of piezoelectric materials in energy generation. The mathematical model describes a U-shaped portal frame system, excited by an ...engine with unbalanced mass and coupled to a nonlinear energy sink (NES), which is used as a passive vibration absorber. The influence of the piezoelectric material parameters used in the energy collection and the dimensioning parameters of the NES system is deeply analyzed in this paper. Numerical simulations are presented considering all combinations of the parameters of the piezoelectric material model and the NES. The system dynamics were analyzed through phase diagrams and the 0–1 test. The estimation of energy collection was carried out by calculating the average power. The numerical results show that a more significant potential for energy generation is obtained for certain combinations of parameters, as well as chaotic behavior in some cases.
The present work explored the adsorptive capacity and catalytic activity of rock powders from basaltic and granitic rocks in the discoloration of synthetic and industrial effluents containing the ...yellow dye Basic Yellow 96. The rock powders were characterized with scanning electron microscopy associated with energy-dispersive spectroscopy, photoacoustic spectroscopy, N2 physisorption and X-ray diffraction, the latter confirming the abundant presence of silica in the four materials studied. The basaltic powders presented specific surface areas between 7 and 10 times greater than those of granitic materials, which allowed up to 92% removal of the dye in 3 h of test using the basaltic powder. Despite the smaller area, the granitic materials showed considerable photocatalytic activity in 3 h, 94%, the same as that of the basaltic materials in the photocatalysis. Granitic and basaltic photocatalysts proved to be efficient in the discoloration of synthetic and industrial effluents, although TOC analyses indicated that it was not possible to promote the pollutant mineralization in the industrial effluent. Both artificial light and sunlight were effective in the photocatalysis of the dye, although the former was slightly faster.
The present work proposes the use of a hybrid controller combining concepts of a PID controller with LQR and a feedforward gain to control the positioning of a 2 DOF robotic arm with flexible joints ...subject to non-ideal excitations. To characterize the performance of the controls, two cases were studied. The first case considered the positioning control of the two links in fixed positions, while the second case considered the situation in which the second link is in rotational movement and the first one stays in a fixed position, representing a system with a non-ideal excitation source. In addition to the second case, the sensitivity of the proposed controls for changes in the length and mass of the second link in the rotational movement was analyzed. The results of the simulations showed the effectiveness of the controls, demonstrating that the PID control combined with feedforward gain provides the lowest error for both cases studied; however, it is sensitive to variations in the mass of the second link, in the case of rotational movements. The numerical results also revealed the effectiveness of the PD control obtained by LQR, presenting results similar to the PID control combined with feedforward gain, demonstrating the importance of the optimal control design.
In this paper, a mathematical model was developed to describe the dynamic behavior of a bioreactor in which a fermentation process takes place. The analysis took into account the bioreactor ...temperature controlled by the refrigerant fluid flow through the reactor jacket. An optimal LQR control acting in the water flow through a jacket was used in order to maintain the reactor temperature during the process. For the control design, a reduced-order model of the system was considered. Given the heat transfer asymmetry observed in reactors, a model considering the fractional order heat exchange between the reactor and the jacket using the Riemann–Liouville differential operators was proposed. The numerical simulation demonstrated that the proposed control was efficient in maintaining the temperature at the desired levels and was robust for disturbances in the inlet temperature reactor. Additionally, the proposed control proved to be easy to apply in real life, bypassing the singularity problem and the difficulty of initial conditions for real applications that can be observed when considering Riemann–Liouville differential operators.
In recent years, the number of motor vehicles in circulation has increased in proportion to Brazil’s economic growth, resulting in an increase in emissions of toxic gases from combustion, such as ...nitrogen oxide, particulate matter, carbon dioxide and volatile organic compounds, among other polluting compounds. This type of pollution has its impacts potentiated in large cities, accumulating due to the configuration of streets and buildings in large urban centers, and can even penetrate indoor environments, having harmful effects on the health of residents. To minimize the emission of these gases, catalytic converters can be used in the vehicle exhausts. Catalytic converters are a promising technology used to reduce exhaust emissions from the engine. In this context, this paper presents an overview of the emission of toxic gases by heavy transport powered by diesel oil and the influence of the use of automotive catalysts in reducing the emission of toxic gases. Additionally, a proposal for monitoring the useful life of automotive catalysts is presented through an electronic sensing system, which makes it possible to determine the catalyst efficiency and the appropriate point for its reactivation or replacement.
Chlorophyll Sensitization of TiO2: A Mini-Review Fuziki, Maria E. K.; Tusset, Angelo M.; dos Santos, Onélia A. A. ...
Reactions (Basel, Switzerland),
12/2023, Volume:
4, Issue:
4
Journal Article
Peer reviewed
Open access
Recent studies have shown that chlorophyll sensitization can improve the performance of semiconductors like TiO2 in photocatalytic reactions and light-harvesting technologies, such as solar cells. ...Faced with the search for renewable energy sources and sustainable technologies, the application of this natural pigment has been gaining prominence. The present work addresses some of the main possibilities of chlorophyll-TiO2 combination, presenting the most relevant aspects affecting chlorophyll extraction and TiO2 sensitization.
TiO2-based semiconductors are formidable photocatalysts for redox reaction applications. Although N-doped TiO2-Nb2O5 catalysts have already been explored in the literature, studies on their ...antioxidant activity are scarce, and systematic investigations on the effects of synthesis parameters over a wide range of %Nb and NH4OH concentrations are limited. In addition, the relationship between optimal pH and %Nb has not yet been adequately explored. In the present work, the sol–gel synthesis of N-doped TiO2-Nb2O5 catalysts was optimized using a design of experiments approach focused on photocatalysis, adsorption, and antioxidant applications. The samples were characterized by TGA, SEM/EDS, XRD, PZC tests, photoacoustic spectroscopy, and N2-adsorption/desorption experiments. The salicylic acid (SA) degradation tests and DPPH radical scavenging assays demonstrated the superior photocatalytic activity (up to 72.9% SA degradation in 30 min, pH 5) and antioxidant capacity (IC50 = 88.9 μg mL−1) of pure TiO2 compared to the N-doped TiO2-Nb2O5 catalysts. The photocatalytic activity, however, proved to be intensely dependent on the pH and %Nb interaction, and at pH 3, the 25Nb-1N-400 catalyst promoted more significant SA degradation (59.9%) compared to pure TiO2 (42.8%). In the methylene blue (MB) adsorption tests, the catalysts N-doped TiO2-Nb2O5 showed removals at least seven times greater than TiO2 catalysts without Nb.
In this work, a comparison was made between the synthesis of niobium-based materials (Nb2O5), both in terms of material characterization and catalytic performance. The methods used were chemical ...mixtures: modified sol-gel and Pechini. The materials were calcined at different temperatures (753, 873 and 993K) and characterized by the following techniques: photoacousticspectroscopy (PAS), zero charge point (pHPZC), scanning electron microscopy (SEM/EDS), thermogravimetric analysis (TGA/DTG) and X-ray diffraction (XRD). The photocatalytic process was carried out to evaluate the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under UV radiation (250 W mercury vapor lamp) and different experimental conditions. In addition, to better understand the influence of parameters such as pH, catalyst concentration (0.2, 0.5 and 0.8 g L
−1
) and calcination temperature, a Design of Experiments (DoE) was used. The results indicated that despite having similar structures and phases in the XRD analysis, the morphology presents two distinct surfaces, due to the preparation method. Differences in the synthesis method affected the catalytic activity in the parameters studied. Although the zero charge point values are close (6.18-6.36), we observed differences in the band gap depending on the calcination temperature. In the optimal condition studied, the catalyst prepared by the sol-gel method obtained the best results.
This study describes the synthesis of Cu/Nb
2
O
5
, Fe/Nb
2
O
5
, and Cu-Fe/Nb
2
O
5
catalysts obtained by incorporating copper and/or iron metals into niobium pentoxide (Nb
2
O
5
). The new ...materials were characterized by the following techniques: Thermogravimetric Analysis (TA), surface and pore analysis, X-ray diffractometry (XRD), and Fourier Transform Infrared Spectroscopy (FT-IR). The catalyst was applied in the photocatalytic degradation of salicylic acid (SA). The influence of different parameters (calcined temperature, pH, and metal addition) on the photocatalytic reaction was evaluated. The results indicated that catalysts containing copper were more active and pH influenced the SA degradation process. SA removal results indicated that Cu/Nb
2
O
5
photocatalyst presented a 1.5 fold higher degradation after 120 min in comparison to Cu-Fe/Nb
2
O
5
and 4.6 fold higher than Fe/Nb
2
O
5
catalyst, all them calcined at 400 °C. In tests carried out in the presence of formic acid, increasing the pH from about 3 to 7 allowed an almost 3.4-fold increase in SA degradation for the Cu-Fe/Nb
2
O
5
catalyst calcined at 400 °C.
