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•SFR variation of alginate complexes with PACl dosage showed a unimodal pattern.•Alginate gel at PACl dosage of 100 mg/L had an ultra-high value of 1.40 × 1015 m−1 kg−1.•Unimodal ...pattern of SFR was caused by morphology transition from gel to floc.•Morphology transition was caused by the coordination order of Al3+with COOH.•Ultra-high gel SFR could be interpreted by Flory–Huggins lattice theory.
While polyaluminum chloride (PACl) coagulation- microfiltration (MF) process is one of the most popular methods for surface water treatment, the fouling mechanism underlying this process has not well explored. In this study, sodium alginate (SA) was used as the model organic matter. It was interestingly found that, specific filtration resistance (SFR) of alginate-aluminum complexes initially increased to an ultra-high value of 1.40 × 1015 m−1 kg−1, and then sharply declined to rather low level of 3.85 × 1012 m−1 kg−1 with the increase in PACl dosage from 0 to 500 mg/L. A series of characterizations of the foulant samples showed that the alginate-aluminum complexes suffered a morphology transition from gel form to floc/cake form with the PACl dosage increase. Density functional theory (DFT) calculation indicated the preferential coordination of aluminum ions with the terminal carboxyl groups of the alginate chains at low PACl level, facilitating homogeneous gel formation. The ultra-high SFR of gel was interpreted by the Flory-Huggins lattice theory. High PACl level resulted in the coordination of aluminum ions with the non-terminal carboxyl groups and reduced the surface charge, and thus, caused gel collapse and floc formation, corresponding to rather low SFR values. Preferential coordination combined with the Flory-Huggins lattice theory revealed in this study offered a molecular level fouling mechanism in the coagulation- microfiltration (MF) process for water treatment.
In order to suppress the external disturbances existing in the trajectory tracking process of the 3-CRU parallel robot, a trajectory tracking control method based on PD+robust controller is proposed ...in this paper. The kinematic model of the 3-CRU parallel robot is established to solve the kinetic energy and potential energy of the system. The basic dynamic model of the 3-CRU parallel robot is obtained based on Lagrangian formulation, and the complete dynamic model of the parallel robot is established by introducing Coulomb and viscous friction. Based on the analysis of the factors affecting the stability of PD controller, a trajectory tracking control method based on PD+robust controller is proposed, and it is proved theoretically that the system converges stably and has a good external disturbance suppression effect. The method has the characteristics of easy implementation and strong applicability of PD controller and strong robustness of robust controller. Experimental results prove the effectiveness of this method.
Ni-base superalloys operate in harsh service conditions where cyclic heating and cooling introduce deformation fields that need to be investigated in detail. We used the high-angular-resolution ...electron backscatter diffraction method to study the evolution of internal stress fields and dislocation density distributions in carbides, dendrites, and notch tips. The results indicate that the stress concentrations decay exponentially away from the notch, and this pattern of distribution was modified by the growth of cracks and the emission of dislocations from the crack tip. Crack initiation follows crystallographic traces and is weakly correlated with carbides and dendrites. Thermal cycles introduce local plasticity around carbides, the dendrite boundary, and cracks. The dislocations lead to higher local stored energy than the critical value that is often cited to induce recrystallization. No large-scale onset of recrystallization was detected, possibly due to the mild temperature (800 °C); however, numerous recrystallized grains were detected in carbides after 50 and 80 cycles. The results call for a detailed investigation of the microstructure-related, thermally assisted recrystallization phenomenon and may assist in the microstructure control and cooling channel design of turbine blades.
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•The Ni-Co base dual-phase superalloy is welded successfully at a broad range of temperatures by hot-compression bonding.•The interfacial healing mechanism of superalloys at different ...temperatures involves two main recrystallization mechanisms.•The deformation mechanism of primary γ′ phase changes with increasing deformation temperature.•Heterogeneous epitaxial recrystallization is induced by diffusion of Cr elements and DDRX is induced by strain gradients.
Hot-compression bonding (HCB) as an advanced technique for preparation of large-size homogenized components is widely applied. Despite the fact that interfacial healing mechanisms during HCB have been extensively investigated, the interfacial healing mechanisms in duplex superalloys still need to be clarified. This article investigates effect of deformation temperature on multiple interface (γ′-γ′, γ-γ, γ-γ′) healing mechanism of dual-phase superalloys. The healing mechanism of γ-γ interface at different temperatures involves a necklace-like distribution of discontinuous dynamic recrystallization (DDRX) grains occupying original interface. With increasing deformation temperature, the healing mechanism of γ′-γ′ interface transforms from DDRX to diffusion bonding due to weakening of strain concentration. Simultaneously, as deformation temperature increases, the deformation mechanism of primary γ′ phase transforms from shearing by stacking fault to dislocation pairs. At deformation temperature 1100 °C, the healing mechanism of γ′-γ interface is heterogeneous epitaxial recrystallization (HERX) induced by primary γ′ phase driven by diffusion of Cr element in dislocation pairs. However, as deformation temperature decreases, healing mechanism in γ′-γ interface transforms into DDRX. Although interfacial healing mechanism is transformed at different deformation temperatures, the synergistic action of different recrystallization mechanisms ensures that mechanical properties of joints reached the same level as those of base material.
Microplastics, which have been frequently detected worldwide, are strong adsorbents for organic pollutants and may alter their environmental behavior and toxicity in the environment. To completely ...state the risk of microplastics and their coexisting organics, the adsorption behavior of microplastics is a critical issue that needs to be clarified. Thus, the microplastic/water partition coefficient (log
) of organics was investigated by in silico method here. Five log
predictive models were developed for the partition of organics in polyethylene/seawater, polyethylene/freshwater, polyethylene/pure water, polypropylene/seawater, and polystyrene/seawater. The statistical results indicate that the established models have good robustness and predictive ability. Analyzing the descriptors selected by different models finds that hydrophobic interaction is the main adsorption mechanism, and π-π interaction also plays a crucial role for the microplastics containing benzene rings. Hydrogen bond basicity and cavity formation energy of compounds can determine their partition tendency. The distinct crystallinity and aromaticity make different microplastics exhibit disparate adsorption carrying ability. Environmental medium with high salinity can enhance the adsorption of organics and microplastics by increasing their induced dipole effect. The models developed in this study can not only be used to estimate the log
values, but also provide some necessary mechanism information for the further risk studies of microplastics.
Polycyclic aromatic hydrocarbons (PAHs) and their halogenated derivatives (X-PAHs), which generally produced from photochemical and thermal reactions of parent PAHs, widely exist in the environment. ...They are semi-volatile organic chemicals (SVOCs) and the partitioning between gas/particulate phases affects their environmental migration, transformation and fate, which further impacts their toxicity and health risk to human. However, there is a large data missing of the experimental distribution ratio in the atmospheric particulate phase (f), especially for X-PAHs. In this study, we first checked the correlation between experimental f values of 53 PAH derivatives and their octanol-air partitioning coefficients (log KOA), which is frequently used to characterize the distribution of chemicals in organic phase, and yielded R2 = 0.803. Then, quantum chemical descriptors derived from molecular structural optimization by M06–2X/6–311 +G (d,p) method were further employed to develop Quantitative Structure-Property Relationship (QSPR) model. The model contains two descriptors, the average molecular polarizability (α) and the equilibrium parameter of molecular electrostatic potential (τ), and yields better performance with R2 = 0.846 and RMSE = 0.122. The mechanism analysis and validation results by different strategies prove that the model can reveal the molecular properties that dominate the distribution between gas and particulate phases and it can be used to predict f values of other PAHs/X-PAHs, providing basic data for their environmental ecological risk assessment.
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•QSPR models for the distribution of PAHs derivatives in atmospheric particles (f) were developed.•The molecular polarizability and the surface electrostatic potential significantly affect the f values.•The model has good regression performance, robustness and predictive ability.•The model can be applied to predict the f values of PAH derivatives.
Polycyclic aromatic hydrocarbons (PAHs) and their oxygen/nitrogen derivatives released into the atmosphere can alternate between a gas phase and a particulate phase, further affecting their ...environmental behavior and fate. The gas/particulate partition coefficient (KP) is generally used to characterize such partitioning equilibrium. In this study, the correlation between log KP of fifty PAH derivatives and their n-octanol/air partition coefficient (log KOA) was first analyzed, yielding a strong linear correlation (R2 = 0.801). Then, Gaussian 09 software was used to calculate quantum chemical descriptors of all chemicals at M062X/6-311+G (d,p) level. Both stepwise multiple linear regression (MLR) and support vector machine (SVM) methods were used to develop the quantitative structure-property relationship (QSPR) prediction models of log KP. They yield better statistical performance (R2 > 0.847, RMSE < 0.584) than the log KOA model. Simulation external validation and cross validation were further used to characterize the fitting performance, predictive ability, and robustness of the models. The mechanism analysis shows intermolecular dispersion interaction and hydrogen bonding as the main factors to dominate the distribution of PAH derivatives between the gas phase and particulate phase. The developed models can be used to predict log KP values of other PAH derivatives in the application domain, providing basic data for their ecological risk assessment.
Organic chemicals in the aquatic ecosystem may inhibit algae growth and subsequently lead to the decline of primary productivity. Growth inhibition tests are required for ecotoxicological assessments ...for regulatory purposes. In silico study is playing an important role in replacing or reducing animal tests and decreasing experimental expense due to its efficiency. In this work, a series of theoretical models was developed for predicting algal growth inhibition (log EC50) after 72 h exposure to diverse chemicals. In total 348 organic compounds were classified into five modes of toxic action using the Verhaar Scheme. Each model was established by using molecular descriptors that characterize electronic and structural properties. The external validation and leave-one-out cross validation proved the statistical robustness of the derived models. Thus they can be used to predict log EC50 values of chemicals that lack authorized algal growth inhibition values (72 h). This work systematically studied algal growth inhibition according to toxic modes and the developed model suite covers all five toxic modes. The outcome of this research will promote toxic mechanism analysis and be made applicable to structural diversity.
•Verhaar Scheme based toxicity predictive models for algae were developed.•Molecular descriptors that characterize electronic and structural properties were used.•The models were validated to be mechanistically explainable and statistically robust.•The model can predict log EC50 values for algal growth inhibition (72 h).
This paper proposes a 3-PPRU parallel mechanism (PM) with a completely/partially/non constant Jacobian matrix. Based on screw theory and selecting actuating components theory, the reasonability of ...the actuating input selection is analyzed. By different actuating selection, the Jacobian matrix of the PM can realize completely/partially/non constant. The direct, inverse and combined kinematic singularities of the PM with three different Jacobian matrices are discussed. The velocity, payload and stiffness performance of the PM are discussed and compared. A new index, as auxiliary evaluation index, is proposed first.
Biotransformation of organophosphorus flame retardants (OPFRs) mediated by cytochrome P450 enzymes (CYPs) has a potential correlation with their toxicological effects on humans. In this work, we ...employed five typical OPFRs including tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), tris(1-chloro-2-propyl) phosphate (TCIPP), tri(2-chloroethyl) phosphate (TCEP), triethyl phosphate (TEP), and 2-ethylhexyl diphenyl phosphate (EHDPHP), and performed density functional theory (DFT) calculations to clarify the CYP-catalyzed biotransformation of five OPFRs to their diester metabolites. The DFT results show that the reaction mechanism consists of Cα-hydroxylation and O-dealkylation steps, and the biotransformation activities of five OPFRs may follow the order of TCEP ≈ TEP ≈ EHDPHP > TCIPP > TDCIPP. We further performed molecular dynamics (MD) simulations to unravel the binding interactions of five OPFRs in the CYP3A4 isoform. Binding mode analyses demonstrate that CYP3A4-mediated metabolism of TDCIPP, TCIPP, TCEP, and TEP can produce the diester metabolites, while EHDPHP metabolism may generate para-hydroxyEHDPHP as the primary metabolite. Moreover, the EHDPHP and TDCIPP have higher binding potential to CYP3A4 than TCIPP, TCEP, and TEP. This work reports the biotransformation profiles and binding features of five OPFRs in CYP, which can provide meaningful clues for the further studies of the metabolic fates of OPFRs and toxicological effects associated with the relevant metabolites.