Search

Understanding the fate and transport of polystyrene nanoparticles (PSNPs) in porous media under various conditions is necessary for evaluating and predicting environmental risks caused by microplastics. The transport kinetics of PSNPs are investigated by column experiment and numerical model. The surface of DLVO interaction energy is calculated to analyze and predict the adsorption and aggregation of PSNPs in porous media, which the critical ionic strength of PSNPs can be accurately investigated. The results of the DLVO energy surface suggest that when the concentration of Na+ increases from 1 mM to 50 mM, the DLVO energy barrier of PSNPs-silica sand (SS) decreases from 78.37 kT to 5.46 kT. As a result, PSNPs are easily adsorbed on the surface of SS and the mobility of PSNPs is reduced under the condition of a high concentration of Na+ (PSNPs recovery rate decreases from 62.16% to 3.65%). When the concentration of Ca2+ increases from 0.1 mM to 5 mM, the DLVO energy barrier of PSNPs-SS decreases from 12.10 kT to 1.90 kT, and PSNPs recovery rate decreases from 82.46% to 4.27%. Experimental and model results showed that PSNPs mobility is enhanced by increasing initial concentration, flow velocity and grain size of SS, while the mobility of PSNPs with larger particle diameter is lower. Regression analysis suggests that kinetic parameters related to PSNPs mobility are correlated with DLVO energy barriers. The environmental behavior and mechanism of PSNPs transport in porous media are further investigated in this study, which provides a scientific basis for the systematic and comprehensive evaluation of the environmental risk and ecological safety of nano-plastic particles in the groundwater system. [Display omitted] • The critical ionic strength of PSNPs can be accurately quantified by DLVO energy surface. • k , S max and PSNPs recovery rate are correlated with initial concentration, flow velocity, grain sizes of PSNPs and SS. • Divalent cations have a stronger charge shielding effect on PSNPs than monovalent cations. • The kinetic parameters related to PSNPs mobility are correlated with DLVO energy barriers. [ABSTRACT FROM AUTHOR]

Column experiments were conducted to investigate the effects of ion type, ion strength, humic acid (HA), and nanometer alumina (NA) particles on the transport of hexavalent chromium (HC) in saturated porous media. A one-dimensional model is developed to simulate the migration of HC affected by NA particles. The results show that nano-alumina particles would enhance the mobility of HC in saturated porous media. However, the influence of NA on the migration of HC in porous media is complex. When the concentration of NA reaches 30 mg/L, HC has minimum retention parameter and best mobility. The transport of HC also is affected by ion strength and ion type. Higher ionic strength would decrease the retention of HC and enhance its mobility. Compared with sodium ion, calcium ion has larger effects on the transport of HC. Moreover, HA can improve the mobility of HC in saturated porous media, but the corresponding promoting effect decreases with the increase of HA concentration. As nanometer contaminants and HC come into the subsurface environment, findings from this study elucidate the key factors and processes controlling the transport of HC in porous media, which can promote the prediction and assessment of HC in the groundwater system. [Display omitted] • Nano-alumina (NA) significantly affects the mobility of hexavalent chromium (HC) in porous media. • High ionic strength decreases the retention of HC and enhances its mobility. • Divalent cations enhance the mobility of HC more than monovalent cations. • One-site kinetic deposition model can simulate and predict the effect of NA on HC migration. • Fitted equations of HC transport parameters and mass recovery rate are achieved. [ABSTRACT FROM AUTHOR]

Abstract: Metal oxide and oxyhydroxide nanoparticles are important components of natural aqueous systems and have application in photocatalysis. Uncoated (oxyhydr)oxide nanoparticles can form charge-stabilized colloids in water, but the precise regimes of dispersion and aggregation have been determined for very few nanomaterials. We studied the colloidal behavior of ∼6 nm nanoparticles of iron oxyhydroxide (FeOOH), a common natural nanoscale colloid, and found that these nanoparticles formed stable suspended clusters under a range of aqueous conditions. Light and X-ray scattering methods show that suspended fractal nanoclusters are formed between pH 5 and 6.6 with well-defined maximum diameters that can be varied from 25 nm to approximately 1000 nm. The nanoclusters retain a very high surface area, and persist in suspension for at least 10 weeks in solution. The process is partially reversible because optically transparent suspensions are regained when nanoparticles that aggregated and settled at pH >7 are adjusted to pH 4 without stirring. However, completely redispersed nanoparticles are not obtained even after one month. Because nanocluster formation is controlled predominantly by surface charge, we anticipate that many metal oxide and other inorganic nanoparticles will exhibit equivalent cluster-forming behavior. Our results indicate that natural nanoparticles could form stable nanoclusters in groundwater that are likely to be highly mobile, with implications for the long-range transport of surface sorbed contaminants. [Copyright &y& Elsevier]

• SE in children was a cost intensive disease in China. • The median inpatient medical cost of children with SE was $1175.5 (665.1–2320.6). • Cost-driving factors including LOS, etiology and examinations, and treatments. • PFS and idiopathic/cryptogenic epilepsy were associated with a lower cost. To describe the inpatient medical cost during hospitalization in children with status epilepticus (SE) and identify factors associated with the cost by a nationwide, multicenter study in China. We retrospectively identified pediatric inpatients with SE form Hospital Information System (HIS) of 44 hospitals in 27 provinces in China between 2013 and 2015. Inpatient medical cost and factors associated with the cost were analyzed. A total of 4041 children diagnosed with SE with inpatient medical cost were enrolled in the present study. The median age at admission was 2.9 (range 0.1–18) years, and 2271 patients were male (56.2%). The median inpatient medical cost of children with SE was $1175.5 (665.1–2320.6). The median inpatient medical cost was $3865.6 (1837.4–8210.4) in children with SRSE and $1048.6 (619.8–1865.4) in those with N-SRSE (p < 0.0001). Children with length of hospital stay (LOS) > 7 showed a much higher inpatient medical cost than those with LOS ≤ 7 day ($2300.7 vs. $767.2, p < 0.0001). Regarding different etiologies, children with acute symptomatic etiology showed the highest median inpatient medical cost of $1681.1 (901.0–3699.6), in which children with central nervous system (CNS) infection reported $2606.0 (1380.0–5016.1) and prolonged febrile seizures (PFS) reported $909.8 (649.3–1322.0). Additionally, children with idiopathic/cryptogenic etiology reported a medical cost of $923.2 (548.9–1534.5). Multiple linear regression analysis of cost-driving factors revealed LOS > 7, examinations, treatment equipment and procedures, and treatment medicines were independently associated with a higher inpatient medical cost (R 2 = 60.91). In addition, PFS and idiopathic/cryptogenic epilepsy etiology were independently associated with a lower cost. SE in children was a cost intensive disease in China with a median inpatient medical cost of $1175.5. LOS, etiology and examinations, treatment equipment and procedures, and treatment medicines were significantly associated with inpatient medical cost. [ABSTRACT FROM AUTHOR]

A piecewise linear vibration isolator used to isolate the rocket launch vibration is proposed and investigated in this paper. The dynamic characteristics of the piecewise linear vibration isolator are analyzed theoretically and experimentally. Assuming base excitation from the rocket, the dynamic equation is established and the response is solved by using averaging method. The influence of the system parameters such as stiffness ratio and clearance distance on the system performance is discussed. The jumping phenomenon and frequency shift are observed. The vibration isolation performance of the isolator is tested by using vibration table to simulate the launch vibration loads according to certain criterion. The theoretical and experimental results are compared and are in good accordance. The results show that the piecewise linear vibration isolation system can lower the response for large amplitude vibration excitation at launch. The results present here can be a useful guideline when design such kind of vibration isolator. Image 1 • The piece-wise linear isolator can both isolate the micro-vibration on-orbit and large vibration at launch phase. • The second stage stiffness can shift the resonance to higher frequency which leads to relatively small displacement. • The experimental results show jump phenomenon and frequency shifts which is in accordance with the theoretical results. [ABSTRACT FROM AUTHOR]