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Water transport is an essential process in proton exchange membrane fuel cells (PEMFC). For the novel metal foam flow fields, water transport is difficult to be visualized and still remains inadequately understood. In this work, for the first time, the two-phase flows in the metal foam flow fields of a transparent PEMFC was visualized by using an artificial intelligence (AI) image recognition method. In order to distinguish water from the metal foam ligaments, a scoring system was developed, which effectively solved the problem of inconsistent reflectance of liquid water between the ligament and the gas diffusion layer. According to the state of liquid water, the scoring system categorized the local images into three labels of waterless state, wet state, and slug state for AI image recognition network training. The trained AI image recognition model was then used to visualize the liquid water state in the metal foam flow fields under different operating conditions of relative humidity (RH), temperature, and inlet flow rate. Results show that, since the porous structure of the metal foam provides flexible transport paths, the PEMFC can operate effectively in a wide range of wet states. Even a 25% difference in the wet-state percentage between different operating conditions yields an almost consistent voltage. The increased slugs in the flow fields are the primary reason for the performance degradation of the PEMFC. At a high current density of 2 A/cm2, the voltage is as low as 0.03 V when the slug state occupies 35% of the flow fields (100% RH, 60 °C, 1.0 SLPM cathode inlet flow rate), and as high as 0.56 V when the slug state is absent in the flow fields (100% RH, 60 °C, 2.0 SLPM cathode inlet flow rate). The present work provides a novel approach for the studies of water transport in PEMFC. • Water transportin the metal foam flow fields of atransparent PEMFC is visualized by using an AI image recognition method. • Ascoring system is developed to distinguish water from the metal foam ligaments. • The trained AI image recognition modelshowsgood performance in recognizingwater state. • The water state under different operating conditions issystematically studied. [ABSTRACT FROM AUTHOR]

Gas diffusion layers (GDLs) play a crucial role for the performance of proton exchange membrane fuel cells (PEMFCs). The utilization of composite foam-rib flow fields (CFRFFs) can alter the reactant gas transfer pattern, hence improving the efficiency of under-rib reactant gas transfer and water drainage. The impact of the cathode and anode GDL thicknesses (h c , GDL and h a,GDL) on the performance of CFRFF design is investigated by three-dimensional multiphase non-isothermal numerical simulation in this study. The results indicate that for the conventional rib flow field (CRFF) design, there is an optimal h c,GDL for optimal cell performance, while for the CFRFF design, as h c,GDL becomes thinner, the cell performance increases, and the trend is dominated by the variation of the oxygen concentration. Under a thin GDL, the rib width of the CRFF design should be as small as possible to minimize concentration polarization loss, while the rib width of the CFRFF design can be slightly larger. Furthermore, by decreasing the thickness of h a,GDL in both the CRFF and CFRFF designs, there is an increase in the dissolved water content in the ionomer of the cathode CL and a subsequent decrease in the Ohmic polarization loss. • The effects of the GDL thickness on PEMFC performance are studied by simulations. • Composite foam-rib (CFRFF) and conventional rib flow fields (CRFF) are compared. • There is an optimal GDL thickness for the optimal performance of the CRFF design. • Cell performance of the CFRFF design increases as cathode GDL thickness decreases. • Rib width of CFRFF can be designed slightly larger at a thin cathode GDL thickness. [ABSTRACT FROM AUTHOR]

The electric power distribution system (PDS) and the water distribution system (WDS) are coupled with each other through electricity-driven water facilities (EdWFs), such as pumps, water desalination plants, and wastewater treatment facilities. However, they are generally owned and operated by different utilities, and there does not exist an operator that possesses full information of both systems. As a result, centralized methods are not applicable for coordinating the operation of the two systems. This paper proposes a decentralized framework where the PDS and WDS operators solve their own operation problems, respectively, by sharing only limited information. Nevertheless, the boundary variables (i.e., the variables shared between two systems) are discontinuous due to their dependence on the on/off nature of EdWFs. Unfortunately, mature decentralized/distributed optimization algorithms like the alternating direction method of multipliers (ADMM) cannot guarantee convergence and optimality for a case like this. Therefore, this paper develops a novel algorithm that can guarantee convergence and optimality for the decentralized optimization of PDS and WDS based on a recently developed algorithm called the SD-GS-AL method. The SD-GS-AL method is a combination of the simplicial decomposition (SD), gauss–seidel (GS), and augmented Lagrangian (AL) methods, which can guarantee convergence and optimality for mixed-integer programs (MIPs) with continuous boundary variables. Nonetheless, the original SD-GS-AL algorithm does not work for the PDS-WDS coordination problem where the boundary variables are discontinuous. This paper modifies and improves the original SD-GS-AL algorithm by introducing update rules to discontinuous boundary variables (called the Auxiliary Variables Update step). The proposed mixed-integer boundary compatible (MIBC) SD-GS-AL algorithm has the following benefits: (1) it is capable of handling cases whose boundary variables are discontinuous with convergence and optimality guaranteed for mild assumptions, and (2) it only requires limited information exchange between PDS and WDS operators, which will help preserve the privacy of the two utilities and reduce the investment in building additional communication channels. Simulations on two coupled PDS and WDS test cases (Case 1: IEEE-13 node PDS and 11-node WDS, and Case 2: IEEE-37 node PDS and 36-node WDS) show that the proposed MIBC algorithm converges to the optimal solutions while the original SD-GS-AL does not converge for both test cases. The ADMM does not converge for the first test case while it converges to a sub-optimal solution, 63 % more than the optimal solution for the second test case. • We propose a decentralized optimization of the water-energy nexus. • The proposed algorithm handles mixed-integer boundary variables. • The optimality and convergence of the proposed algorithm are guaranteed. • Outperforms mature distributed algorithms like ADMM. [ABSTRACT FROM AUTHOR]

The Zn–Co double metal cyanide (DMC) complex is regarded as a promising catalyst for the copolymerization of CO 2 and propylene epoxide (PO). Various methods have been adopted to improve the catalytic performance of DMC. In this study, polyvinylpyrrolidone (PVP), as a co-complexing agent, was innovatively used to modify DMC and applied to the synthesis of poly(ether–carbonate) polyols from CO 2 , PO, and a chain transfer agent. The modified catalysts exhibited higher catalytic activity than the catalysts prepared by conventional methods, with a nearly 10 % increase in PO conversion. The most critical breakthrough was a reduction of nearly 5 wt% in the byproduct propylene–carbonate. The results confirmed that amide groups in PVP could coordinate with active center Zn2+, providing the modified catalysts with advantages such as low-symmetry structure, high specific surface area, and strong acidity. Moreover, the dual effects of PVP coordination and dispersion led to dramatic differences in the microstructure and activity of the catalysts when added during different preparation processes of DMC. The coordination effect of PVP was dominant in the nucleation stages which affected the crystal structure and morphology, whereas, the dispersion effect was dominant in the aging stages which prevented the catalyst particles from growing and thus a higher specific surface area. This is critical for paving the way towards exploring the introduction of groups with high steric hindrance into Zn–Co complex catalysts. In addition, a detailed and in-depth insight into the structure–activity relationship of DMC for poly(ether–carbonate) polyols synthesis was summarized. [Display omitted] • Polyvinylpyrrolidone (PVP) was first used to modify double metal cyanide catalysts. • PVP added in different preparing stages affected crystal structure of the catalyst. • PVP-modified catalysts showed low symmetry, high surface area, and strong acidity. • N of PVP coordinated to Zn2+ helped to activate CO 2 and epoxide. • Modified catalysts showed higher activity and selectivity for CO 2 copolymerization. [ABSTRACT FROM AUTHOR]

We study unbendable rational curves, i.e., nonsingular rational curves in a complex manifold of dimension n with normal bundles isomorphic to O P 1 (1) ⊕ p ⊕ O P 1 ⊕ (n − 1 − p) for some nonnegative integer p. Well-known examples arise from algebraic geometry as general minimal rational curves of uniruled projective manifolds. After describing the relations between the differential geometric properties of the natural distributions on the deformation spaces of unbendable rational curves and the projective geometric properties of their varieties of minimal rational tangents, we concentrate on the case of p = 1 and n ≤ 5 , which is the simplest nontrivial situation. In this case, the families of unbendable rational curves fall essentially into two classes: Goursat type or Cartan type. Those of Goursat type arise from ordinary differential equations and those of Cartan type have special features related to contact geometry. We show that the family of lines on any nonsingular cubic 4-fold is of Goursat type, whereas the family of lines on a general quartic 5-fold is of Cartan type, in the proof of which the projective geometry of varieties of minimal rational tangents plays a key role. [ABSTRACT FROM AUTHOR]

• Composite foam-rib flow field structure is proposed to improve fuel cell performance. • The composite design is simulated by using a 3D homogeneous non-isothermal model. • The composite design can improve the oxygen transfer and water removal capabilities. • The composite design can improve the cell performance under different conditions. • Optimal metal foam filling ratio and porosity of the composite design are obtained. Mass transfer capability of reactants and hydrothermal management is important for the performance and durability of proton exchange membrane fuel cells. In the conventional rib flow field, the oxygen transport is affected by the accumulation of under-rib liquid water which causes excessive concentration loss and limits cell performance. To improve the cell performance, a composite foam-rib flow field structure is proposed by combining the metal foam flow field and the conventional rib flow field. The proposed design is simulated by using a three-dimensional homogeneous non-isothermal numerical model. The results show that the composite foam-rib flow field, by improving the oxygen transfer and water removal capabilities under the ribs, can improve the oxygen concentration and current density without increasing the pumping power, thus improving the cell performance under different conditions. The key parameters of the composite foam-rib flow field are optimized. With the optimal metal foam filling ratio of 0.75 and porosity of 0.85, the peak power density and the limiting current density for the composite foam-rib flow field are higher than the conventional rib flow field by 5.20% and 22.68%. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the efficacy of surgical revascularization versus conservative treatment and different surgical modalities, in order to provide evidence for the patient with moyamoya disease (MMD) to choose the appropriate treatment. We comprehensively searched PubMed, Embase, Web of Science, and the Cochrane Library for articles published regarding MMD treatment. If the I 2 value, which evaluated the heterogeneity, was <50%, a fixed-effect model was used; if not, a random effect model was applied. Twenty-seven articles were included in the meta-analysis. The surgery group is more advantageous in reducing the risk of future stroke events than conservative treatment in MMD patients (odds ratio [OR] 0.26, 95% confidence interval [CI] 0.20–0.33, P < 0.001). In addition, the surgical group also had an advantage in terms of increased cerebral perfusion (OR 7.16, 95% CI 3.28–15.64, P < 0.001) and death due to rebleeding (OR 0.27, 95% CI 0.10–0.72, P < 0.01). Direct surgery showed a significant efficacy over indirect surgery (OR 2.03, 95% CI 1.32–3.13, P < 0.01). No obvious difference was found between the direct and indirect bypass subset (OR 0.76, 95% CI 0.51–1.14, P = 0.185). Angiographic results in patients undergoing direct bypass surgery are more pronounced (OR 0.20, 95% CI 0.06–0.67, P < 0.01). In patients with symptomatic moyamoya disease, bypass surgery is more effective than conservative treatment to prevent future strokes. In surgical patients, direct bypass seems to reduce the risk of stroke more than an indirect bypass. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A series of CO 2 derived amino-alcohol compounds were synthesized. • Structures of amino-alcohol compounds influenced the properties of adhesives. • PU adhesives from the synthesized amino-alcohol compounds showed excellent adhesion properties. • CO 2 derived adhesives showed other considerable properties. Abstract A series of novel amino-alcohol curing agents for PU adhesives were synthesized from CO 2 , glycidyl ether and diamine through carbonation and amination reactions. By physically evaluating the compounds through FT-IR and 1H NMR spectroscopy and mechanically analyzing the adhesives through T-peel strength tests, the raw materials have successfully been transformed into curing agents and the curing agents were found to endow the adhesives with specific structures and unique properties. For PVC bonding, compared to the traditional curing agents HDA and HDO, the T-peel strength and medium resistance from the novel amino-alcohol compounds improved. Further analysis revealed distinction in mechanical properties for different curing agents, the trifunctional curing agent exhibited the largest tensile strength and hardness. Moreover, thermal analysis of the adhesives demonstrated the considerable thermal stability to those prepared from HDA and HDO. [ABSTRACT FROM AUTHOR]

Abstract Perfluoroalkyl acids (PFAAs) have been widely detected and pose potential risks to both human and ecosystem health. Since the probation of perfluorooctane sulfonate (PFOS) by the Stockholm Convention, perfluorooctanoate (PFOA) has frequently been used as a chemical intermediate and processing aid. Owing to a lack of effective treatment technologies for PFOA, surrounding environments have been highly affected. Previous studies by our group have reported elevated PFOA levels in the Xiaoqing River, which receives sewage from a major fluorochemical manufacturer in northern China. To further explore the transport, flux, and ecological risk of the perfluorooctanoate in the river, this study conducted a 2-year sampling campaign of surface water from 2014 to 2015. An extremely high PFOA concentration (mean: 62.3 μg L−1) was observed for the Xiaoqing River in comparison with other studies. The highest average concentration and flux of PFOA were recorded in the autumn and summer, respectively. With data on selected hydrological parameters and cross-sections, PFOA concentrations were modeled using DHI MIKE 11. To explore the current loads and environmental capacity of PFOA, two scenarios (i.e., emissions based on observed concentrations and on the predicted no-effects concentration, PNEC) were set. The simulation results based on observed data showed that PFOA loads in the Xiaoqing River were 11.4 t in 2014, and 12.5 t in 2015. Based on the PNEC, the environmental carrying capacity of PFOA was estimated to be 13.9 t in 2014, and 13.8 t in 2015. The current loads of PFOA were found to approach the maximum environmental carrying capacity. Relatively high risks around both the fluorine industrial park (FIP) and estuary area were identified. In comparison with other suggested guidelines, threats to the ecological status of the river would be severe, which suggests that stringent management and emission criteria are needed for this industry. Graphical abstract Unlabelled Image Highlights • PFOA transport process simulation and risk assessment were conducted using a hydrological dynamic model. • Extremely high PFOA level (average: 62.28 μg L−1) in Xiaoqing River was found through a 2-year sampling campaign. • PFOA emission loads from a major fluorine manufacturer were approaching the local aquatic environmental capacity. • High level of ecological risks by PFOA was observed around both the fluorine industrial park and estuary area. [ABSTRACT FROM AUTHOR]

Highlights • Study effect of nanovoid on grain boundary migration and disclinated cracking. • Analytic solutions of energy changes characterizing these processes are derived. • Discuss theoretically energy and critical conditions for initiating these processes. • Characterize effect of microstructure interactions on predominant mechanism Abstract The greatest objective in the design of nanocrystalline materials (NCMs) is to improve their strength while maintain ductility. Therefore, from both fundamental and applied viewpoints, to reveal the causes of the improved damage tolerance of NCMs, there is large interest in the advancement of an understanding of the fundamental micromechanisms for the competition/interaction between plastic deformation and fracture process in NCMs. In doing so, this paper develops a theoretical model to describe the energy and critical conditions of the tilt GB migration and then the disclinated TJ nanocrack nucleation and growth processes near a nanovoid at the triple junctions (TJs) of GBs in plastically deformed NCM. The analytic solutions of the total energy changes that characterize these processes are derived quantitatively by the complex variable method. The results show that the stress-driven tilt GB migration near a nanovoid is energetically favorable and effective in relieving high local stresses near a nanovoid, which is crucially significant for stopping further nanovoid growth and enhancing the ductility of the plastically deformed NCMs. On the other hand, GB disclination storage is capable of causing the stress concentration, and consequent generation and growth of nanocracks at the TJs near a nanovoid, thereby decreasing their ductility. The predominant mechanism controlling plasticity deformation and fracture process in NCMs is closely related with nanovoid, GB configuration and geometry. [ABSTRACT FROM AUTHOR]

Abstract The production of polychlorinated biphenyls (PCBs) has been banned globally for decades, but PCB concentrations in environmental media remain relatively high, especially in urban areas. Emissions estimates, studies of soil gradients between urban and rural areas, and quantitative identification of regional sources of PCBs in soils are necessary for understanding the environmental behavior of PCBs. In this study, regional PCB emissions were estimated at a resolution of 10 km × 10 km, and the spatial distribution of soil PCBs from urban to rural areas was studied along the Bohai and Yellow Sea regions. Compared with rural areas, mean PCB concentrations in urban soils (20.7 ng/g) were found to be higher, and concentrations decreased with distance from the city. Across both latitude and longitude directions, high PCB emissions in urban areas matched the distribution of total PCB concentrations in soils. The concentrations of the pollutants PCB28, PCB52, PCB101, PCB118, PCB138, PCB153, and PCB180 in soils originated from 5-year emissions, and accounted for 97%, 95%, 84%, 81%, 58%, 57%, and 27% of the total emissions, respectively. Unintentionally produced PCB (UP-PCB) emissions, which are mainly derived from cement (42%), pig iron (37%), crude steel (18%), and rolled steel (3%) industries, are the major contributors to PCBs in soils. Further identification of the sources and fates of PCBs requires a combination of field, laboratory, and modeling efforts. Graphical abstract Image 1 Highlights • Ln PCB concentrations linearly decrease with distances from the city. • PCB emission inventory in the Bohai and Yellow Sea Rim was estimated. • Quantitative source identification was conducted using fugacity model method. • Low-chlorine PCBs in soils mainly came from recent 5-year emissions. • Unintentionally produced PCB emissions are the major contributors to PCBs in soils. Quantitative PCB source identification and impacts of regional PCB emission inventories on spatial distribution and urban-rural PCB gradients were explored. [ABSTRACT FROM AUTHOR]

Methodology to quantify and distinguish the spatial distribution of the risks from multiple pollutants within the region was developed in this paper. An integrated quantitative risk assessment was conducted by utilizing a large amount of information available to explore spatial distribution of risk by single and multiple pollutants, and the magnitude of the overall risk from multiple pollutants based on the current concentrations of pollutants and toxicity data. Two target criteria levels – level I (NOEC/LOEC based) and level II (LC/EC/IC 50 based) – were employed, and thus, the regional and sub-regional risks were evaluated according to these two levels. The risk of multiple toxic metals (As, Cd, Cr, Hg and Pb) to a terrestrial ecosystem for the region around the Bohai Sea and the Yellow Sea were evaluated as a case. The total overall ecological risks from heavy metals in the region for level I and level II were 21.73% and 12.53%, respectively. The risks were ranked in the order of Cr > As > Pb > Cd > Hg with Cr posing the greatest ecological risk, which was 61.12% for level I. The top three cities according to the level II ecological risk were Cangzhou > Lianyungang > Panjin, while the top three cities of level I ecological risk were Cangzhou > Panjin > Lianyungang. This method provides a quantitative risk assessment with multiple and clear protection levels for risk management. [ABSTRACT FROM AUTHOR]

Xiaoqing River, located in the Laizhou Bay of Bohai Sea, is heavily polluted by various pollutants including heavy metals, polycyclic aromatic hydrocarbons (PAHs), hexachlorocyclohexanes (HCHs), perfluoroalkyl acids (PFAAs), bisphenol A (BPA) and pharmaceutical and personal care products (PPCPs). The aim of this study is to identify the relative risks of such contaminants that currently affect the coastal ecosystem. The median and highest concentrations of PFAAs and perfluorooctanoic acid (PFOA) were 3.23 μg L −1 and 325.28 μg L −1 , and 0.173 μg L −1 and 276.24 μg L −1 , respectively, which were ranked higher when compared with global level concentrations. To assess the relative risk levels of perfluorooctane sulfonic acid (PFOS), PFOA, and other contaminants in the upstream and downstream of the Xiaoqing River and in its tributary, a risk ranking analysis was carried out. Copper (Cu), Zinc (Zn), and arsenic (As) showed the highest risk values in the Xiaoqing River, while the relative risks of PFOA and PFOS differed across the various segments. The risk ranking of PFOA was the second highest in the tributary and the fourth highest in the downstream portion of the river, whereas the PFOS was found to be the lowest in all the segments. Heavy metals and PFOA are the main chemicals that should be controlled in the Xiaoqing River. The results of the present study provide a better understanding of the potential ecological risks of the contaminants in Xiaoqing River. [ABSTRACT FROM AUTHOR]

Coastal zone is of great importance in the provision of various valuable ecosystem services. However, it is also sensitive and vulnerable to environmental changes due to high human populations and interactions between the land and ocean. Major threats of pollution from over enrichment of nutrients, increasing metals and persistent organic pollutants (POPs), and climate change have led to severe ecological degradation in the coastal zone, while few studies have focused on the combined impacts of pollution and climate change on the coastal ecosystems at the global level. A global overview of nutrients, metals, POPs, and major environmental changes due to climate change and their impacts on coastal ecosystems was carried out in this study. Coasts of the Eastern Atlantic and Western Pacific were hotspots of concentrations of several pollutants, and mostly affected by warming climate. These hotspots shared the same features of large populations, heavy industry and (semi-) closed sea. Estimation of coastal ocean capital, integrated management of land-ocean interaction in the coastal zone, enhancement of integrated global observation system, and coastal ecosystem-based management can play effective roles in promoting sustainable management of coastal marine ecosystems. Enhanced management from the perspective of mitigating pollution and climate change was proposed. [ABSTRACT FROM AUTHOR]

Between 1945 and 1983, China was the world's largest producer of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs), and the second largest producer of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs). The provinces of Liaoning, Hebei, Tianjin, Shandong, and Jiangsu around the Yellow and Bohai Seas have a long history of production and usage of OCPs and PCBs. To investigate their residual concentration, distribution, risk level, and temporal degradation, 7 OCPs and 7 indicator PCBs were determined in surface soils collected around the Yellow and Bohai Seas. Residues of the 7 OCPs and 7 PCBs were in the range of 5.89–179.96 ng g −1 dry weight (dw) and non-detectable (ND)–385.67 ng g −1 dw, respectively. Tianjin and Hebei provinces recorded the highest concentrations of OCPs and PCBs, respectively. Moreover, OCPs residues had a significant relationship with agriculture and orchard land-use types, whereas PCBs residues occurred more in wasteland. Lifetime carcinogenic and non-carcinogenic risks of OCPs and PCBs through ingestion, inhalation, and dermal contact indicated that OCPs and PCBs residues in surface soils are at a low risk level. [ABSTRACT FROM AUTHOR]