The flow stress of face-centered cubic (FCC) metals exhibits a rapid increase near a strain rate of 104 s−1 under fixed-strain conditions. However, many existing constitutive models either fail to ...capture the mechanical characteristics of this plastic deformation or use piecewise strain-rate hardening models to describe this phenomenon. Unfortunately, these piecewise models may suffer from issues such as discontinuity of physical quantities and difficulties in determining segment markers, and struggle to reflect the underlying physical mechanisms that give rise to this mutation phenomenon. In light of this, this paper proposes that the abrupt change in flow stress sensitivity to strain rate in FCC metals can be attributed to microstructural evolution characteristics. To address this, a continuous semiempirical physical constitutive model for FCC metals is established based on the microstructural size evolution proposed by Molinari and Ravichandran and the dislocation motion slip mechanism. This model effectively describes the mutation behavior of strain-rate sensitivity under fixed strain, particularly evident in an annealed OFHC. The predicted results of the model across a wide range of strain rates (10−4–106 s−1) and temperatures (77–1096 K) demonstrate relative errors generally within ±10% of the experimental values. Furthermore, the model is compared with five other models, including the mechanical threshold stress (MTS), Nemat-Nasser–Li (NNL), Preston–Tonks–Wallace (PTW), Johnson–Cook (JC), and Molinari–Ravichandran (MR) models. A comprehensive illustration of errors reveals that the proposed model outperforms the other five models in describing the plastic deformation behavior of OFHC. The error results offer valuable insights for selecting appropriate models for engineering applications and provide significant contributions to the field.
•This paper verifies the applicability of BSMPM, GIMP, and CPDI in mesoscale simulating the SCJs.•BSMPM based on cubic and quartic splines is most suitable for mesoscale simulating, whose SCJs are in ...great continuity with little cavity and small surface roughness.•For SCJs material, the strain evolution is hierarchical and the particle trajectories can be classified as a laminar layer, transition layer, and turbulent layer from outer to the axis, consistent with the grain size evolution.
Shaped charge (SC) generates a fluid-like high-speed jet (SCJ) undergoing extremely large ductile stretching without fracture. It is a formidable challenge to accurately track and monitor the mesoscale deformation characteristics of materials using fluid simulation algorithms. To address this issue, the Material Point Method (MPM) is introduced as an efficient particle-based method that discretizes the continuum into Lagrangian particles moving through a fixed Eulerian grid. By possessing all material properties, these particles facilitate tracking throughout the deformation process and enable the implementation of history-dependent constitutive models. Regrettably, the utilization of MPM in the study of SCJ formation is restricted. The objective of this study is to assess the capability of 2D-axisymmetric MPMs in modeling SCJ formation and free flight at the mesoscale, thereby providing valuable guidelines for their application in SCJs. The MPMs employed in this study are based on the B-spline (BSMPM) and domain interpolations (generalized and convected particle domain interpolations in MPM). The numerical results indicate that BSMPM with cubic and quartic splines is the most suitable method for calculating SCJs due to its exceptional continuity and alignment with the experimental data. The mesoscale evolution of particles reveals that the material undergoes impact crushing and tensile tearing, transforming into a low-speed slug and a high-speed jet. The equivalent plastic strain (EPS) in SCJs exhibits a radial expansion from the exterior to the axis in a layered manner. Particles in the outer layer with a thickness of approximately 1/2 exhibit a 'laminar' distribution, while particles near the axis exhibit 'turbulent' distribution and undergo severe deformation. The hierarchical progression of EPS and particle motion traces provides insight into the underlying causes of mesoscale experimental phenomena, such as the axial elongation of voids in the SCJ slug and the radial distribution of the material in three concentric circles.
A photocatalyst based on the integration of reduced graphene oxide (rGO) with Bi4O5Br2 nanosheets was facilely prepared and was confirmed by transmission electron microscope, scanning electron ...microscope, X-ray diffraction and Raman spectroscopy. The integration of rGO can effectively improve the adsorption and the photocatalytic properties of Bi4O5Br2 nanosheets towards the target antibiotics under visible light irradiation. rGO/Bi4O5Br2 nanocomposite containing 1.0 wt% of rGO exhibits the optimal adsorption and photocatalytic activity towards ciprofloxacin (CIP), norfloxacin (NOR) and tetracycline (TC). The removal efficiencies of CIP, NOR and TC are 97.6%, 80.7% and 98.7%, which are higher than that obtained with Bi4O5Br2 nanosheets. The capture experiments and ESR data show that ·O2−, OH· and h+ are the main active species that participated in the photodegradation system. This work provides a simple strategy to integrate rGO with BixOyXz (X = Cl, Br, I) nanosheets to construct effective photocatalysts for the degradation of antibiotics.
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•Reduced graphene oxide (rGO) integrated with Bi4O5Br2 nanosheets was facilely prepared.•rGO/Bi4O5Br2 nanocomposites were employed as photocatalyst for degradation of antibiotics.•Photodegradation activity and mechanism of rGO/Bi4O5Br2 towards antibiotics was demonstrated.
Stability of colloidal particles contributes to the turbidity in the water column, which significantly influences water quality and ecological functions in aquatic environments especially shallow ...lakes. Here we report characterization, origin and aggregation behavior of aquatic colloids, including natural colloidal particles (NCPs) and total inorganic colloidal particles (TICPs), in a highly turbid shallow lake, via field observations, simulation experiments, ultrafiltration, spectral and microscopic, and light scattering techniques. The colloidal particles were characterized with various shapes (spherical, polygonal and elliptical) and aluminum-, silicon-, and ferric-containing mineralogical structures, with a size range of 20–200 nm. The process of sediment re-suspension under environmentally relevant conditions contributed 78–80% of TICPs and 54–55% of NCPs in Lake Taihu, representing an important source of colloids in the water column. Both mono- and divalent electrolytes enhanced colloidal aggregation, while a reverse trend was observed in the presence of natural organic matter (NOM). The influence of NOM on colloidal stability was highly related to molecular weight (MW) properties with the high MW fraction exhibiting higher stability efficiency than the low MW counterparts. However, the MW-dependent aggregation behavior for NCPs was less significant than that for TICPs, implying that previous results on colloidal behavior using model inorganic colloids alone should be reevaluated. Further studies are needed to better understand the mobility/stability and transformation of aquatic colloids and their role in governing the fate and transport of pollutants in natural waters.
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•Characterization, origin and aggregation behavior of shallow-lake colloids were studied.•Aquatic colloids had Al-, Si- and Fe-containing mineralogical structures with diverse conformation.•Sediment re-suspension contributed 78–80% of TICPs and 54–55% of NCPs in lake waters.•HMW-NOM greatly enhanced colloidal stability of TICPs compared to LMW-NOM.•Colloidal behavior analyses based on model inorganic colloids and bulk NOM should be reevaluated.
Colloidal particles are omnipresent in lake sediments and substantially influence the retention, transportation, and fate of contaminants in lake ecosystems. In this study, the abundance, chemical ...composition and adsorption behavior of sedimentary colloids (including total and inorganic colloids) from different ecological regions, were for the first time investigated via ultrasonic extraction, spectral analysis and batch absorption experiments. Results showed that the extraction efficiencies of sedimentary colloids showed an ultrasonic energy-dependent enhancement, and the algae-dominated area contained comparable colloidal abundance with the macrophyte-dominated area (i.e., 198.5 vs. 183.3 mg/g). Despite the different ecosystems, these sedimentary colloids usually had a wide size distribution of 30–200 nm, and were characterized with montmorillonite-, kaolin-, volkonskoite-, and quartz-rich chemical compositions. Batch experiment showed that the total pristine colloids exhibited higher adsorption capacity for Pb(II) than the inorganic colloids both for the macrophyte- and algae-dominated sediments, and the adsorption process followed pseudo-second-order kinetics and Langmuir isotherm, irrespective of different colloidal types. Thus, sedimentary colloids can immobilize the heavy metals in sediment and decrease their release into the water column, which can be considered as a sink for contaminants. This study highlighted the significance of sedimentary colloids in determining the physicochemical properties of lake sediments and in evaluating the environmental behavior and fate of contaminants in lake ecosystems.
•Abundance, composition and adsorption properties of sedimentary colloids were studied.•The ultrasonic-induced extraction efficiency enhancement was related to colloidal composition and sediment type.•Sedimentary colloids had Fe-, Al- and Si-containing mineralogical structures with various conformations.•Total colloids exhibited higher adsorption capacity for Pb(II) than the inorganic colloids.•Langmuir isotherm, pseudo-second-order kinetics, and chemical mechanism accounted for the adsorption process.
With the fast development of modern industries, scarcity of freshwater resources caused by heavy metal pollution (i.e., Hg2+) has become a severe issue for human beings. Herein, a 3D-MoS2 sponge as ...an excellent absorbent is fabricated for mercury removal due to its multidimensional adsorption pathways, which decreases the biomagnification effect of methylmercury in water bodies. Furthermore, a secondary water purification strategy is employed to harvest drinkable water with the exhausted adsorbents, thus alleviating the crisis of drinking water shortage. Compared to the conventional landfill treatment, the exhausted MoS2 sponge absorbents are further functionalized with a poly(ethylene glycol) (PEG) layer to prevent the heavy metals from leaking and enhance the hydrophilicity for photothermal conversion. The fabricated evaporator displays excellent evaporation rates of ∼1.45 kg m–2 h–1 under sunlight irradiation and produces freshwater with Hg2+ under the WHO drinking water standard at 0.001 mg L–1. These results not only assist in avoiding the biodeposition effect of mercury in water but also provide an environment-friendly strategy to recycle hazardous adsorbents for water purification.
•A theoretical model of the hole evolution on the inclined thin target impacted by a shaped charge jet is derived, and the influence of the inclined angle on the initial pressure distribution and the ...final radii of the crater is discussed.•The modified equation of target resistance strength as a function of the inclined angle is proposed.•It is theoretically verified that the major axis and minor axis increase with the increase of the oblique angle.•Interestingly, the offset between the minor axis and the geometric center of G is gradually significant with the increase of the oblique angle.•The most important thing is that the radius in the downstream direction is greater than that in the upstream direction for oblique penetration, and the difference between them is more and more obvious with the increases of the oblique angle.
In the armor design field, the asymmetric interaction between various hypervelocity penetrators and the inclined targets is an important topic. However, most existing studies overlook the influence of asymmetry on the expansion of the initial penetration hole. A modified theoretical model for predicting the hole radii of hypervelocity penetrator impacting an inclined thin plate was derived in this research. According to a set of experimental results, the empirical parameters of the resistance strength term as a function of the oblique angle in this model were obtained. The theoretical predictions have excellent agreement with a series of simulation results as performed with an ANSYS/AUTODYN solver.
Colloidal particles in lake waters interact inevitably with cyanobacterial extracellular polymeric substance (EPS), which will change their behavior and fate. Quantitative prediction of the effects ...of cyanobacterial EPS on colloidal behavior is difficult due to its variability and heterogeneity. To explore the effects of molecular weight (MW) fractions and chemical properties of cyanobacterial EPS on aggregation kinetics of colloidal particles, time-series cyanobacterial samples were collected in Lake Taihu, China, from April to November (during blooming and maintenance period), with the bulk EPS matrix fractionating into low MW (LMW–, <1 nm) and high MW (HMW–, 1 nm–0.45 μm) fractions. HMW–EPS was generally characterized with higher absorbance and predominant distribution of protein-like substances, while LMW–EPS contained mainly the humic- and fulvic-like substances. The absorbance, molecular size, and humification degree for each MW fraction consistently increased from April to November, showing obvious temporal variations from blooming period to maintenance period. As for the MW-dependent aggregation behaviors, the HMW–EPS provided better stability against aggregation than the LMW–EPS, and the bulk EPS matrix that consisted of HMW– and LMW–fractions exhibited the effects intermediate between that of each fraction alone. Regardless of MW fractions, the effects of EPS-induced stability enhancement were more evident in maintenance period than in blooming period. Further analysis showed that the colloidal stability was correlated positively with SUVA254 (R2 = 0.82–0.93) but negatively with Slope275–295 (R2 = 0.53–0.91) of UV–Vis absorption spectra, indicating that aromaticity and MWs were two critical parameters controlling colloidal aggregation. Therefore, cyanobacterial EPS can exhibit variable effects on colloidal stability, and characterization of MW distribution is strongly required in predicating the behavior and fate of colloidal particles in water environments.
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•Effects of MWs and chemical properties of cyanobacterial EPS on colloidal stability were studied.•The concentration and chemical properties in each MW fraction showed obvious temporal variations.•HMW–EPS provided better stability against aggregation than bulk and LMW–EPS.•Colloidal stability was positively correlated with aromaticity and MWs for each MW fraction.•Characterization of MW distribution was required in future studies on colloidal stability.
The low quantum yield and weak catalytic ability of bismuth oxyhalides retard their applications in photocatalytic degradation. To promote the performances of bismuth oxyhalides in photodegradation ...of antibiotics, a series of BiOBr/β-Bi2O3 nanocomposites was synthesized via a facile solvothermal process in which one-pot strategy was adopted to accomplish the purpose by adjusting the mole ratio of the bismuth and bromine. The formation of heterojunction at the BiOBr/β-Bi2O3 surface boundary was confirmed by XRD, PL, DRS, XPS and HR-TEM. The photocatalytic properties of these BiOBr/β-Bi2O3nanocomposites were evaluated by the photodegradation of norfloxacin under simulated sunlight irradiation. The BiOBr/β-Bi2O3 nanocomposites obtained at the molar ratio of 3:1 (Bi:Br) exhibit the best photodegradation activity. The photocurrent density of BiOBr/β-Bi2O3 nanocomposites (Bi:Br = 3:1) is twice higher than that of the pristine BiOBr, indicating the in-situ generating Bi2O3 on the BiOBr surface can effectively promote the separation of photogenerated electron-hole pairs and thus improving the photocatalytic performance. Furthermore, the photocatalytic mechanism was investigated using trapping experiments and ESR study. The results reveal that the matched energy band structure between BiOBr and Bi2O3 was able to facilitate the charge transfer and reduce the recombination of the photogenerated carriers. This work supplies a simple procedure for the in-situ growing Bi2O3 on Bi-based photocatalysts and an effective measurement for degrading norfloxacin.
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•Facile synthesis of BiOBr/β-Bi2O3 nanocomposites via one-pot hydrothermal method.•In-situ formation of β-Bi2O3 on BiOBr surface thorough adjusting the molar ratio of Bi3+/Br− precursors.•BiOBr/β-Bi2O3 identified as efficient photocatalyst for norfloxacin degration under simulated solar irradiation.•Mechanism for enhancing photocatalytic activity of BiOBr/β-Bi2O3 was illuminated.
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•A rhodamine-based CDs (CDs-Rho) ratiometric nanosensor was fabricated.•CDs-Rho displayed a selective, sensitive and a low limit detection towards Hg2+.•Cellulose hydrogel slices with ...CDs-Rho (CCR) were continuously prepared by microtomy.•CCR hydrogel showed over 95% uptake efficiency and good detection ability for Hg2+.•The purified water after treated with CCR hydrogel exhibited good biocompatibility.
Mercury ions are one of the most toxic heavy metals and as such they can cause serious risk to the human body and environmental ecosystem. To effectively detect and remove Hg2+ from contaminated water, a new cellulose-based fluorescent hydrogel has been fabricated using a ratiometric probe with carbon dots as energy donor and rhodamine moiety as energy acceptor (CDs-Rho). The probe exhibits a sensitive and linear response to Hg2+ over a wide range from 0–100 μM with a limit detection of 2.19 × 10−9 M and exhibits high selectivity for Hg2+ over other cations. In addition, a series of cellulose-based fluorescent hydrogel slices containing CDs-Rho are continuously prepared using microtomy of a hydrogel, facilitating the large-scale fabrication of functionalized hydrogel slices with controlled thickness. The cellulose-based CDs-Rho (CCR) hydrogel exhibits good sensitivity and excellent adsorption capacity for Hg2+ with ~95% removal efficiency, meeting the requirements for sewage discharge. Moreover, the purified water is successfully used for cell culture and animal growth, demonstrating excellent biocompatibility. Our approach is expected to offer a novel concept for the construction of biocompatible fluorescent hydrogels for the detection of various metal ions and removal by simply swapping the current probe with suitable replacements for a variety of relevant applications.
