Search

A combined experimental and molecular dynamic simulation approach was used to examine the structure and interfacial properties of solute-saturated micelles. The properties of dodecylbenzenesulfonate (DBS) micelles were examined in dodecane and benzene hydrocarbon systems. Pyrene fluorescence was used to determine the aggregation number of surfactant monomers in the micelle systems. Molecular dynamic (MD) simulations using energy minimization applying the CHARMm force field with the TIP3P model for water. Comparison of the DBS/benzene and DBS/Dodecane micelles equilibrium structures via radial distribution function (RDF) and probability distribution function (PDF) analysis indicates that the area per head group for the DBS/Benzene micelle interface is significantly larger than that of the DBS/Dodecane at the interface. It was also determined that benzene molecules can move freely within the micelle while dodecane is strictly confined in the core of the micelle. The increased interfacial area per monomer caused by the insertion of benzene also reduces the effectiveness of the surfactant, which has implications for use in various environmental applications. However, the DBS/benzene micelle can solubilize many more hydrocarbon molecules in one micelle with less surfactant monomer (i.e., lower aggregation number) per micelle due to the increased available packing positions within the micelle. This, in turn, increases the efficiency of the surfactant in real-world applications which is consistent with previous laboratory results. Understanding the differing solubilization characteristics of surfactants against various classes of hydrocarbons in single solute systems is a necessary step to beginning to understand their solubilization properties in the mixed waste systems prevalent in most surfactant enhanced remediation (SEAR) strategies. [ABSTRACT FROM AUTHOR]

• Novel CRB vibration model considering contact stiffness and natural frequency characteristics. • The outer raceway spalling fault with varying sizes is simulated in this paper, considering spalling defect extents and load distribution. • This paper showed that the effects of contact stiffness variation on natural frequency characteristics by the statistical distribution of fault feature signals. The modeling of early spalling defects in cylindrical roller bearings (CRB) is a challenging problem in fault diagnosis. Due to the absence of prominent "drop-in" excitation, accurately describing the signal characteristics of the early failure mechanism model for CRBs becomes difficult. In this paper, the failure of cylindrical roller bearings due to spalling caused by fatigue is a frequent occurrence. The previous defect models have been centered on sharp-edge impact between the roller and spalling defects. However, they have not provided an adequate depiction of the variation in contact stiffness caused by roller-fault interaction. In this paper, a novel CRB vibration model that takes into account contact stiffness and natural frequency characteristics is proposed. The model considers both the load redistribution and contact stiffness variation caused by spalling defects. This new model provides a spring-damper system based on contact stiffness between the roller and raceway, enabling an estimation of the CRB system's natural frequency characteristics. The outer raceway spalling fault with varying sizes is simulated in this paper, taking into account spalling defect extents and load distribution. The vibration response of the fault signal model is investigated. The simulation results show that the load and contact stiffness will change as the roller passes through the defect zone. Furthermore, the statistical distribution of fault feature signals demonstrates the effects of contact stiffness variation on natural frequency characteristics. The experiments given in this paper have verified the simulation results of the proposed signal model. [ABSTRACT FROM AUTHOR]

• To reduce the occurrence of alarm floods, improved rationalization strategies are introduced to evaluate the quality and effectiveness of multivariate alarm systems developed in recent research. • Strategies demonstrated on an exothermic CSTR result in a significant reduction in nuisance alarms. • Real-time risk of the rationalized alarm systems were evaluated using dynamic risk assessment by estimating their failure probabilities using multiple dynamic simulations. • The posterior distribution, constructed for the exothermic CSTR using Bayesian statistics, had much lower variance as compared to one developed using a flat prior. In this paper, improved alarm rationalization strategies are introduced to evaluate the quality of the multivariate alarm systems developed in previous work – with the alarm thresholds and response actions modified appropriately, based on key statistical metrics. For an exothermic CSTR, our strategies resulted in a significant reduction in the number of nuisance alarms, focusing on only quality alarms, which, if ignored, are more likely to result in an abnormal shift in operation to the undesirable regions. Next, their real-time performance is evaluated using dynamic risk analysis (DRAn), in which, the associated risk is analyzed by estimating the failure probabilities of the multivariate alarm systems using Bayesian statistics, based on multiple dynamic simulations for the process, inclusive of control, alarms and response actions. As expected, the failure probability distribution developed for the exothermic CSTR has a much lower variance as compared to one developed using a flat prior distribution. [ABSTRACT FROM AUTHOR]

• A CA-based model of slope soil erosion was constructed to simulate complex spatiotemporal dynamic behaviors and processes. • A simulation model was developed for the transition between various types of soil erosion intensity. • To predict the development trend of soil erosion in different regions under different rainfall conditions. • Based on transition probability matrix and suitability map, the future trend of slope soil erosion intensity was simulated. The study of soil erosion is significant to soil and water conservation and ecological construction planning. CA, a dynamic modeling method, has been widely used to simulate the future changes of soil erosion intensity. In this study, three slopes with different vegetation patterns (uniform distribution, aggregated distribution, and random distribution) and a bare slope in the Baojiagou watershed in the Pisha sandstone area were taken as the study objects. Based on the soil erosion intensity grade maps of slopes with different vegetation patterns under the three periods of rainfall, the soil erosion intensity grade maps of the four slopes were simulated by combining multi-criteria evaluation (MCE) and Markov chain (CA-Markov). Through tests, the Kappa coefficients of the simulated maps of uniform distribution, random distribution, aggregated distribution and a bare slope reached 80.15%, 75.41%, 75.92% and 76.48%, respectively. The results revealed that the soil erosion types on slopes with different vegetation patterns were transferred differently, and fewer erosion areas were generally transferred into highly eroded ones, with moderately and slightly eroded areas as the main transfer flows. After simulating the grade map of soil erosion intensity on slopes with different vegetation patterns, it was found that the slopes with uniform and random vegetation distribution primary displayed the transfer from highly eroded areas to less eroded ones, and the sedimentary area was enlarged, while the slope with aggregated vegetation distribution and the bare slope mainly presented the transfer from less eroded areas to highly eroded ones. The sedimentary area was diminished. Therefore, compared with the bare slope, the slopes with uniform and random vegetation distribution exerted a better inhibitory effect on the soil erosion degree of hydraulically eroded slopes, and the inhibitory effect of aggregated vegetation distribution-type slope was the weakest. The study results provide critical information for planning and implementing soil conservation measures in the study area. [ABSTRACT FROM AUTHOR]