Arrhenius Model Research Articles

Construction of Co-doped Fe2O3/carbonized melamine foam heterogeneous catalyst for enhanced degradation of organic pollutants through peroxymonosulfate activation

Co-doped Fe2O3/carbonized melamine foam heterogeneous catalyst (CMF/Co-Fe2O3) was prepared by hydrothermal method. Rhodamine B (RhB) degradation was employed as a model test for evaluating peroxymonosulfate (PMS) activation. The degradation efficiency of RhB can reach 97 % in the catalyst dosage (50 mg/L), PMS concentration (100 mg/L), pH = 7 and RhB initial concentration (10 mg/L) after 60 min reaction. The reaction rate constant is 10 times higher than that of CMF/Fe2O3 and the activation ability of PMS is greatly improved. The degradation efficiency of RhB can be inhibited by increasing the initial mass concentration of RhB and pH value. The effect of temperature on the degradation rate of RhB conforms to the Arrhenius model, and the degradation process is a surface reaction controlled process. The results of free radical capture experiments and electron paramagnetic resonance (EPR) experiments showed that SO4¯ was the main active free radical for RhB degradation. After four cycles, the degradation efficiency of RhB still maintains 80 % with CMF/10 %Co-Fe2O3 catalyst. The heterogeneous catalyst exhibited potential application in the field of degradation of dye wastewater due to its excellent cycling stability.

A Study on Drying Characteristics, Color, and Vitamin C Preservation of Green Banana Slices Using a Vacuum Heat Pump System

Abstract This study aimed to evaluate the characteristics related to the removal of moisture from green banana slices and the effect of the drying conditions on color and vitamin C preservation using a drying system based upon the use of a vacuum heat pump. The green banana slices underwent drying at 40, 50, and 60°C with vacuum pressure levels of 0, 40, and 80 kPa. The average drying time decreased by 18.9% and 32.7% as the vacuum pressure and temperature increased, respectively. Six thin-layer models underwent assessment to explain the kinetic process involved in moisture removal using the vacuum heat pump set to provide differing experimental circumstances, and fitted to experimental data. Results showed that the characteristics of moisture removal from the green banana slices could most appropriately be explained by the Page model. There is in increase in effective moisture diffusivity, which ranged from 1.1658×10−10 to 1.9717×10−10 m2·s−1, with increases in temperature and vacuum pressure. Energy of activation ranged from 15.99 to 19.73 kJ·mol−1, which was explained by an exponential expression based on the Arrhenius models. The drying temperature of 50°C under a vacuum pressure of 80 kPa could preserve the vitamin C content by a maximum of 55.9%, which is the optimal drying condition for obtaining good product quality.

Luminescence properties and Judd-Ofelt analysis of Tb3+ doped Sr2YTaO6 double perovskite phosphors for white LED applications.

A series of Tb3+-doped Sr2YTaO6 double perovskite phosphors (SYT:Tb3+) were synthesized using a conventional solid-state reaction method. A strong green emission was observed in the SYT:Tb3+ phosphors, and the optimal doping concentration of Tb3+ was confirmed to be 5 mol%. The electric dipole-dipole interaction was ascribed to be the main mechanism for the luminescence concentration quenching. Analysis of the concentration-dependent fluorescence decay confirmed that the self-generated quenching model holds for the dynamic process of Tb3+ decays in SYT. Furthermore, the internal quantum efficiencies, non-radiative transition rates, and energy transfer rates of the 5D4 level for the SYT:Tb3+ samples were estimated, respectively. The luminescence thermal stability of the sample was also evaluated based on the Arrhenius model. The chromaticity shift of the SYT:5 mol% Tb3+ phosphor was examined to be 0.013 when the sample temperature was increased from 303 to 483 K, thus indicating excellent chromaticity shifting resistance under high temperature conditions. Moreover, the Judd-Ofelt parameters were calculated from the emission spectra of SYT:Tb3+ to be Ω2 = 0.29 × 10-20, Ω4 = 0.45 × 10-20, and Ω6 = 0.72 × 10-20 cm2, respectively. The fluorescence branching ratios and radiative transition rates for the 5D4 level were calculated based on the obtained Judd-Ofelt parameters. Finally, a white light-emitting diode (LED) prototype was assembled using a 310 nm LED chip combined with a prepared green SYT:Tb3+ phosphor and two other commercial blue and red phosphors. The obtained warm white light exhibits good chromaticity coordinates (0.32, 0.32) and a high color rendering index of 96.1. Based on the above results, it can be known that the prepared SYT:Tb3+ phosphors have a potential application as green emitting phosphors in white LEDs.

Determination Of The Shelf Life Of Tamban Fish Choux Pastry (Sardinella Lemuru) Using The Accelerated Shelf Life Testing (Aslt) Method

Choux pastry is a light snack characterized by its small size, softness, volume, and yellow-brown color. The choux pastry product has been diversified with the addition of tamban fish. The fat content and moisture content in the tamban fish choux pastry are 37.77% fat and 8.41% moisture, respectively. Finding the ideal shelf life for tamban fish choux pastry (Sardinella lemuru) is the aim of this investigation. The Arrhenius model and the ASLT method are used to calculate the tamban fish choux pastry's shelf life. The product is kept in three different temperature ranges: 30˚, 40˚, and 50˚C, with moisture content tests conducted every 10 days on days 0, 10, 20, and 30 of storage. The total plate count (TPC) test results show the highest value on day 30 at 30˚C storage temperature, which is 2.5 x 10^3 CFU/ml. The hedonic test results show that the color of the choux pastry has an average score 2.34-2.81, aroma has an average score of 1.93-2.68, and texture has an average score of 2.28-2.76. Shelf determination life is based on critical parameters, specifically the TPC and hedonic. The results show that the tamban fish choux pastry 33 days at 30˚C, 35 days at 40˚C, and 33 days at 50˚C are the product's shelf lives.

Determining The Shelf Life of Tamban Fish Choux Pastry (Sardinella Lemuru) Using Aluminum Foil Packaging using The Aslt Method

Choux pasty is known as sus, which is defined as a cake that has a dry, hollow and light texture so that it can be filled with various variations. Tamban fish meat is less popular with the public because it has many spines, so it can be used as raw material for making choux pastry which is capable of containing quality, added product value and good nutritional content. Apart from that, it can produce products with a delicious taste. Aluminum foil type plastic packaging is one type of plastic that is widely used in making food because it is the best type of plastic which is able to prevent chemical reactions and has heat resistant properties. Aluminum foil type plastic packaging in the form of a standing pouch has excellent air and light barrier capabilities and has a locking clip. This method uses environmental conditions that can accelerate the reaction of decreasing product quality. The use of the Arrhenius model on dry products can predict the rate of chemical reactions resulting in damage or changes in product quality at various storage temperatures. My research used 3 different temperatures, namely, temperature 30, temperature 40 and temperature 50. The shelf life parameters used in my research are peroxide value, hedonic test, water content and total plate number. The data contained in the research carried out on day 0 is: Water content is the ratio between the weight of water contained in a product and the weight of dry ingredients. Water content can be used to determine the quality and shelf life of products and foam to determine humidity. The initial water content value on day 0 was 3.78.

Assessment of Reaction Kinetics for the Dehydrogenation of Perhydro-Dibenzyltoluene Using Mg- and Zn-Modified Pt/Al2O3 Catalysts

The catalysts utilized for the dehydrogenation of dibenzyltoluene-based liquid organic hydrogen carriers (LOHCs) remain crucial. The state-of-the-art catalyst for dehydrogenation of dibenzyltoluene-based LOHC still suffers from deactivation and by-product formation. This is crucial in terms of the efficiency of the industrial dehydrogenation plant for hydrogen production, cyclability as well as the cost of replacing the catalyst. The development of catalysts with optimum performance, minimum deactivation and low by-product formation is required to attain the full benefits of the LOHC technology. Therefore, in this study, the effect of Mg and Zn modification on Pt/Al2O3 catalyst is investigated for the catalytic dehydrogenation of perhydro-dibenzyltoluene (H18-DBT). In addition, an assessment of reaction kinetics is also conducted. High dehydrogenation performance was obtained for Mg-doped Pt/Al2O3 using a batch reactor at 300 °C and 6 h reaction time. In this case, the degree of dehydrogenation (dod), productivity and conversion obtained are 100%, 1.84 gH2/gPt/min and 99.9%, respectively. Moreover, the Mg-doped catalyst has resulted in a high turnover frequency (TOF) of 586 min−1 compared to the Zn-doped catalyst (269 min−1) and the undoped catalyst (202 min−1) at the reaction temperature of 300 °C. The amount of by-products increased with an increase in the catalytic activity, with the Pt/Mg-Al2O3 catalyst possessing the highest amount of by-products. The dehydrogenation of H18-DBT followed first-order reaction kinetics. In addition, the activation energy obtained using the Arrhenius model is 102, 130 and 151 kJ/mol for Pt/Al2O3, Pt/Zn-Al2O3 and Pt/Mg-Al2O3, respectively. Although the Mg-doped Pt/Al2O3 shows high activation energy, the higher performance of the catalyst suggests that mass transfer limitations have no major effect on the dehydrogenation reaction under the conditions used.

Machine Learning Tabulation Scheme for Fast Chemical Kinetics Computation

<div>This study proposes a machine learning tabulation (MLT) method that employs deep neural networks (DNNs) to predict ignition delay and knock propensity in spark ignition (SI) engines. The commonly used Arrhenius model and Livengood–Wu integral for fast knock prediction are not accurate enough to account for residual gas species and may require adjustments or modifications to account for specific engine characteristics. Detailed kinetics modeling is computationally expensive, so the MLT approach is introduced to solve these issues. The MLT method uses precalculated thermochemical states of the mixture that are clustered based on a combustion progress variable. Hundreds of DNNs are trained with the stochastic Levenberg–Marquardt (SLM) optimization algorithm, reducing training time and memory requirements for large-scale problems. MLT has high interpolation accuracy, eliminates the need for table storage, and reduces memory requirements by three orders of magnitude. The proposed MLT approach can operate across a wider range of conditions and handle a variety of fuels, including those with complex reaction mechanisms. MLT computational time is independent of the reaction mechanism’s size. It demonstrates a remarkable capability to reduce computation time by a factor of approximately 300 when dealing with complex reaction mechanisms comprising 621 species. MLT has the potential to significantly advance our understanding of complex combustion processes and aid in the design of more efficient and environmentally friendly combustion engines. In summary, the MLT approach has acceptable accuracy with less computation cost than detailed kinetics, making it ideal for fast model-based knock detection. This article presents a detailed description of the MLT method, including its workflow, challenges involved in data generation, pre-processing, data classification and regression, and integration into the engine cycle simulation. The results of the study are summarized, which includes validation against kinetics for ignition delay and engine simulation for knock angle prediction. The conclusions are presented along with future work.</div>

BPANN modified constitutive descriptions for flow behavior and softening mechanism in the α+β phase region of Ti-55511 alloy with equiaxed microstructure

The deformation behavior of Ti-55511 alloy was investigated by hot compression tests conducted at deformation temperatures of 993∼1113 K and strain rates of 0.001–1 s−1. To eliminate the effects of friction and adiabatic temperature rise on the flow stresses, the flow curves were corrected. Subsequently, a strain compensated Arrhenius (SCA) model was developed and further modified using the back propagation artificial neural network (BPANN) method. The modified model exhibits significant improvements compared to the SCA model. The average absolute relative error (AARE) decreases from 4.895 % to 0.756 %, while the relative error (δ) range decreases from −14.75 %–17.99 % to −4.78 %–8.01 %. Moreover, cross-validation also confirms the modified model has higher generalization ability and prediction accuracy than the SCA model. Microstructural characterization reveals dynamic recrystallization (DRX) of the α phase and dynamic recovery (DRV) of the β phase are the main mechanisms responsible for softening, and their volume fractions increase with decreasing strain rate and increasing deformation temperature. The equiaxed α phase undergoes elongation first, followed by gradual migration and transformation of grain boundaries. Finally, the β phase wedges into the α phase until the α phase separates. The continuous dynamic recrystallization (CDRX) of β phase accompanies its DRV, which is mainly characterised by progressive sub-grain rotation. The α grains aggregated by dislocations promote CDRX of the β phase.

Effects of Premixed and Diffusion Conditions on the Iso-Octane/ammonia and Iso-Octane/ethanol Flames

ABSTRACT The combustion engines fueled by liquid hydrocarbon fuel significantly release emissions such as CO, CO2, and soot. Renewable fuels such as zero-carbon fuel and biofuel mitigate these emissions of IC engines when used with liquid hydrocarbon fuel. Previously, ammonia and ethanol were used in IC engines and also studied fundamentally, but these fuels were tested separately. In the current study, a comparative effect of these renewable fuels on the emission characteristics of hydrocarbon fuel was made on premixed and diffusion flame conditions. A kinetic mechanism was prepared by adding the sub-mechanisms of ammonia combustion, soot precursors formation and nitrogen oxide emissions to the detailed mechanism of iso-octane flame. The combustion conditions of premixed flow flame, counterflow flame and coflow flame were adopted. The Arrhenius model with soot surface reaction pathways was used in the premixed flow flame and counterflow flame analysis. The Moss-Brooke model with soot surface reaction pathways was added in OpenFOAM Solver to study the soot formation in normal and inverse coflow flames. The results tell that a higher reduction in peak combustion temperature was observed in premixed flame instead of diffusion flame thanks to alternative fuels. Ethanol greatly reduced the peak temperature of the premixed flame rather than ammonia. The impact of carbon-free fuel on total reduction in CO and CO2 emissions was higher than that of biofuel at premixed and diffusion flame conditions. Ethanol impact on total reduction in benzene formation was stronger than ammonia at premixed and normal coflow flames. Pyrene was reduced highly by ammonia rather than ethanol at diffusion flame conditions. The study suggests that biofuel can be used from 0% to 90% in iso-octane fuel, and better results may be achieved when its fraction is ≥ 70%. In contrast, the use of ammonia with iso-octane may be better if its fraction is < 70% because a higher reduction in burning velocity will occur with higher NO2 emissions at NH3 ≥70%.

High shear reactor for glycerolysis—Interesterification palm stearin‐olein blend: Reaction kinetics and physical properties

AbstractStructured lipids containing high monoacylglycerol (MAG) and diacylglycerol (DAG) (SLs‐MDAG) were synthesized by chemical glycerolysis‐interesterification using sodium metasilicate as the catalyst in High Shear Reactor (HSR). The objective of this research was to investigate the effect of temperature on the glycerolysis‐interesterification kinetics at relatively low temperatures in an HSR and the physical product properties. The reaction was performed using immiscible and highly viscous reactants at various temperatures (80–120°C) and a mixing rate of 2000 rpm for 5 h. Results showed that the reaction rate constant exponentially increased as temperature increased. Triacylglycerol (TAG) conversion was 2.5 fold greater at 110 and 120°C compared to lower reaction temperatures (80 and 90°C). MAG and DAG increased by about 18.3% and 13.4%, respectively, as the reaction temperature increased from 80 to 120°C. The product's melting point, hardness, and color were also improved by increasing temperature. In summary, SLs‐MDAG could be produced at a relatively low temperature (110°C) using HSR. The glycerolysis‐interesterification kinetic displayed an exponential relationship, even though it did not precisely fit the Arrhenius model.

Hot Deformation Behavior and Microstructural Evolution of the As-rolled 7050Al Alloy

The hot deformation behavior of the as-rolled 7050 aluminum alloy was investigated using isothermal hot compression experiments with temperatures ranging from 300 to 460 °C and strain rates ranging from 0.001 to 1 s−1, up to a total strain of 1.1. A strain-compensated Arrhenius (SCA) model was established based on the experimental flow stress data. The predictive accuracy of the model was numerically evaluated using the Correlation Coefficients (R) and the Average Absolute Relative Error (AARE). Electron backscatter diffraction (EBSD) was used to characterize the effects of strain rate and compressive temperature on the microstructure evolution and recrystallization behavior. The results indicated that the geometric dynamic recrystallization (GDRX) occurred at high strain rates or low temperatures, while continuous dynamic recrystallization (CDRX) became the dominant recrystallization mechanism with increasing deformation temperature and decreasing strain rate. The work hardening effect was enhanced during the later stage of deformation, and discontinuous dynamic recrystallization (DDRX) became the main recrystallization mechanism.

Interval models for uncertainty analysis and degradation prediction of the mechanical properties of rubber

Abstract As rubber is a hyperelastic material, its nonlinear deformation behavior during aging is significantly influenced by various factors, including the material characteristics, demonstrating a significant uncertainty. Most of the existing uncertain prediction methods of rubber nonlinear property degradation are based on the probability density function, which requires a large number of samples to obtain the probability distribution and requires a lot of work. Therefore, the interval model is used in this study to characterize the uncertainty. However, the traditional interval constitutive models ignore the correlation between interval variables, and the prediction results have large errors. In order to minimize prediction errors and improve prediction accuracy, an interval Mooney–Rivlin (M–R) correlation model that considers the correlation between parameters was established. To address the influence of uncertainties, an interval Arrhenius model was constructed. The M–R model requires multiple fittings of stress–strain curves to obtain the model parameters, and the prediction process is relatively complex. Therefore, combing the two proposed models, the relationship equations of rubber tensile stress with aging temperature and aging time were first established by interval Arrhenius, and then the interval M–R model was used to obtain the variation ranges of parameters C 10 {C}_{10} and C 01 {C}_{01} . By contrasting this with the measured rubber aging information, the effectiveness of the proposed model was confirmed. Compared with the prediction model based on the average value, the maximum error of prediction of this model is reduced by about 60%. Compared with the traditional interval model, the prediction region is significantly reduced, which further improves the prediction accuracy. The above results indicate that this interval aging lifetime prediction model is suitable for characterizing the nonlinear stress–strain behavior of rubber-like elastomers.

Constitutive Modeling for Flow Stress and Processing Maps of a 0.2C–2.0Mn–0.5Cr Microalloyed Steel

Low‐carbon microalloyed steel with the microstructure of bainite is frequently utilized to produce automotive parts. The systematic investigation of the hot deformation behavior can serve as a reference for the optimization of deformation process parameters. The hot deformation of 0.2C–2.0Mn–0.5Cr microalloyed steel is studied. Based on the stress–strain curve, an Arrhenius model with strain compensation is established. The correlation coefficient R2 and the average absolute relative error calculated according to this model are 0.962 and 4.871%. The microstructure evolution at the strain of 0.90 is studied. In the stable region with substantial power dissipation, the microstructure is uniformly fine. The strain rate is high in the stable region with low‐power dissipation, and the room‐temperature microstructure after deformation retains a large amount of deformation storage energy and fine substructures. During deformation, the banded structures are formed in the instable region. The difference in dislocation density between the band structure and the nearby regions promotes the formation of necklace microstructures. Therefore, the 0.2C–2.0Mn–0.5Cr microalloyed steel has an ideal deformation process window in the range of a hot deformation temperature of 880–920 °C and a strain rate of 0.1–0.3 s−1.

Performance degradation and reliability analysis of a MEMS flow sensor with accelerated degradation testing

In this article, we research the performance degradation of a MEMS flow sensor with accelerated degradation testing (ADT). The degradation of temperature stress (Ts) on sensor is studied. Based on the performance in the aging test, resistance degradation ∆R is selected as a more suitable degradation characteristic parameter. Furthermore, the degradation process of the characteristic parameter results from resistivity decreases, in which Ts leads to stress relief within the bulk of the resistor. By implementing the Constant-stress accelerated degradation test (CSADT), we estimate the lifetime of this MEMS flow sensor based on the Arrhenius model. The calculated lifetime is 6.833 years for the 120°C group, 3.942 years for the150°C group, and 2.492 years for the180°C group. In addition, using statistics analysis, the Weibull distribution (WD) is proved to be the better mode for the MEMS flow sensor acceleration life with the Anderson-Darling (AD) being 235.910. The scale and shape of WD was evaluation. On the other hand, to verify the rationality of the distribution, the Standard residual error method and the Cox-Snell residual error method have been used separately, to perform the Goodness-of-fit tests. The AD value of Standard residual error and Cox-Snell residual error is 3.476. It proves that the selected life distribution model of this MEMS flow sensor is befitting. Finally, in this research the CSADT results are original and novelty. The lifetime distribution results reveal that considering the Goodness-of-fit tests can significantly improve the accuracy of reliability analysis of this MEMS flow sensor. Based on those results, a reliability method for this MEMS flow sensor is established.

Release kinetic modeling of Satureja Khuzestanica Jamzad essential oil from fish gelatin/succinic anhydride starch nanocomposite films: The effects of temperature and nanocellulose concentration

Fish gelatin (FG) and octenyl succinic anhydride starch (OSAS) composite films loaded with 1, 2, 3 and 4 wt% bacterial nanocellulose (BNC) and Satureja Khuzestanica Jamzad essential oil (SKEO) were achieved successfully and their physicochemical and release properties were investigated. The results revealed that incorporation of BNC improved the tensile strength which was associated with FE-SEM, FTIR and XRD. Moreover, this study focused on the release modeling of SKEO in 4, 25 and 37 °C from nanocomposite films using different release kinetic and Arrhenius models. Also, analysis of variance-simultaneous component analysis (ASCA) and exploratory data visualization by principal component analysis (PCA) were carried out to investigate the effects of two controlled factors. Consequently, the Peleg model showed the best fitting of experimental data. The activation energies decreased by increasing the BNC concentration. This research demonstrated the nanocomposite film containing SKEO would be a suitable candidate for active food packaging.

Tailoring frequency/temperature independent colossal dielectric constant in Zn-doped Fe3O4/Fe2O3@C/PANI using phase co-existence approach

Introducing doped binary oxides to polymers offers a promising way towards advancement of charge density/energy storage materials with colossal dielectric constant. However, the origin of colossal dielectric constant explored in terms of conduction mechanism with a deeper understanding of the coexistence of phases/interfaces in these materials still requires much attention. In this context, we synthesised Zn-doped Fe3O4/Fe2O3@C/PANI composite that exhibits frequency and temperature independent colossal dielectric constant over a broad range, 1 Hz to 10 MHz and 93 K to 333 K, respectively. We analyzed the impedance data using an equivalent circuit model and Cole-Cole fitting to gain insight into the colossal dielectric response and low dielectric loss. The relaxation phenomenon corresponding to a highly stable electroactive region is validated by the distribution of relaxation time (DRT). Furthermore, the composite exhibited a non-relaxor-like behavior due to diffuse phase transition near semiconductor-to-metallic transition (SMT), observed at 303 K. The charge carriers follow the variable range hopping (VRH) and Arrhenius models yielding localization length of 3 Å and activation energy of 35 meV, which supports the charge transport mechanism between like cation interfaces. This detailed analysis covering the frequency and temperature independent dielectric constant along with the understanding of relaxation and conduction phenomena could provide a viable approach towards producing charge density/energy storage devices for practical applications.

Estimation of Shelf Life of Pegagan Tea (Centella asiatica (L) Urban) using Accelerated Shelf Life Testing (ASLT) Method with Arrhenius Model

This research aimed to evaluate the shelf life of pegagan (Centella asiatica (L) Urban) tea using the Accelerated Shelf Life Testing (ASLT) method by applying the Arrhenius Model since its widely known for its various health benefits, including its ability to enhance cognitive function and exhibit antioxidant effects. The ASLT method was employed to accelerate the chemical and physical changes in the product, thereby enabling a shorter estimation of shelf life compared to conventional methods. In this research, samples of pegagan tea were packaged in paper sacks, aluminum foil, and vacuum-sealed plastic and stored at temperatures of 15, 30, and 45 °C for 28 days, with observations conducted every 7 days. The Arrhenius Model was utilized to predict the rate of chemical reactions in the product, taking into account the temperature's influence on these changes. The data were analyzed using Analysis of Variance (ANOVA) at a 5% confidence level. If the ANOVA results showed significant differences, Duncan Multiple Range Test (DMRT) was further conducted. The results of the observations indicated that storage temperature and packaging type significantly influenced the yield value and pH value, but had no significant effect on the moisture content of pegagan tea. The estimated shelf life of pegagan tea for 28 days using paper sack packaging at temperatures of 15, 30, and 45 °C was 173, 616, and 195 days, respectively. For aluminum foil packaging, the estimated shelf life was 189, 661, and 205 days at the same temperatures. As for vacuum-sealed plastic packaging, the estimated shelf life was 551, 192, and 597 days at the respective temperatures. The findings of this research are expected to provide valuable information for manufacturers and consumers regarding the shelf life of pegagan Tea. Additionally, the research aims to offer a scientific basis for appropriate packaging and storage practices to better maintain the product's quality.

Study on the Flow Behavior of 5052 Aluminum Alloy over a Wide Strain-Rate Range with a Constitutive Model Based on the Arrhenius Model Extension

The formability at room temperature and low speed limits the application of aluminum alloy, while high strain rates positively improve the formability of materials. The constitutive behaviors of materials under high strain rates or impact loadings are significantly different from those under quasi-static conditions, while few constitutive models consider the effect of the mobile dislocation and forest dislocation evolution on the dynamic strain aging (DSA) over a wide strain-rate range. The 5052 aluminum alloy, of which the primary source of strain-hardening is dislocation–dislocation interaction, is widely used in manufacturing automotive covering parts and is considered one of the most promising alloys. Therefore, this study conducts uniaxial tensile tests on AA5052-O under conditions of temperatures ranging from 293 K to 473 K and strain rates ranging from 0.001 s−1 to 3000 s−1, and compares the stress–strain relationships of AA5052-O under different conditions to illustrate the constitutive relationship affected by the dislocation evolution over a wide strain-rate range. The Arrhenius model based on the thermal activation mechanism is modified and extended by considering the effects of dynamic strain aging (DSA), drag stress, and the evolution of mobile dislocation and forest dislocation. Thus, a new physics-based constitutive model for AA5052-O is proposed, which can well reflect the change in strain-rate sensitivity with the strain rate increasing. The mobile dislocation density and total dislocation density are predicted with a modified Kubin–Estrin (KE) model, and the influences of variable mobile dislocation on DSA and dislocation drag are discussed as well. In order to verify the reliability of the new constitutive model, the dislocation densities of the specimens before and after deformation are obtained with TEM and XRD, which are in good agreement with the predicted values. This study also compares the newly proposed model with classic constitutive models using multiple statistical evaluation methods, which shows that the new physics-based constitutive model has not only more clear physical meanings for its parameters but also has a higher prediction accuracy.

Thermal degradation kinetics of cynatratoside-C and its antiparasitic efficacy after being stored in sterile water and aquaculture water

Cynatratoside-C (CyC), a C-21 steroidal saponin isolated from Cynanchum atratum, is a promising candidate for treating freshwater fish infected with the ciliated parasite Ichthyophthirius multifiliis. To promote the drug development process of CyC, the present study investigated the stability of CyC under heating, sterile water, and aquaculture water treatments. An accelerated stability test demonstrated that the thermal degradation kinetics followed a first-order reaction with a predicted half-life (t0.5) of 3472 days (9.5 years) at a temperature of 25 °C. According to the Arrhenius model, the activation energy Ea of CyC was calculated as 91.7 kJ/mol. When CyC was stored in sterile water for 3 years, the mortality rates of theronts and nonencysted tomonts were decreased significantly in the low CyC concentration treatment group, and the minimum concentration that inhibited the production of encysted tomonts increased from 0.06 mg/L to 0.125 mg/L. When CyC was stored in sterile water for 6 years, it showed a nearly complete loss of antiparasitic efficacy, indicating that water may promote the degradation of CyC. When CyC was stored in aquaculture water, the antiparasitic efficacy of CyC against theronts and tomonts was decreased significantly at 2 days post-storage, indicating that microorganisms in aquaculture water could absorb and degrade CyC. The present study provides important information concerning the stability of CyC and the drug approval process.

A kinetic study on carrot juice treated by dielectric barrier discharge (DBD) cold plasma during storage

This study aimed to investigate the efficacy of DBD cold plasma (CP) on carrot juice quality maintenance and develop suitable shelf life models based on carotenoid degradation and total mesophilic bacteria (TMB) growth. The physicochemical, microbial, and sensory properties of carrot juice treated with CP (8, 10, and 12 kV for 3 min) and heat (80 °C for 7 min) were evaluated during storage at 4 °C for 21 days. Results showed carrot juice treatment with the lowest voltage (8 kV) better preserved the physicochemical properties (ascorbic acid and total phenol), color changes, microbial growth, and sensory deterioration. The temperature effect on TMB growth was modeled using the Baranyi and Roberts model, followed by the Arrhenius and square root models. The Q10 and activation energy (Ea) values of TMB growth were higher than those for carotenoid degradation, proposing that bacterial growth could be a more reliable marker in the self life prediction of carrot juice treated by DBD cold plasma.