[en] Highlights: • A novel three-dimensional waved flow field is proposed and investigated. • The waved flow filed can introduce forced convection at the through-plane direction. • The waved flow filed significantly improves the water management and PEMFC net power. - Abstract: It has been well recognized that both the performance and operation stability of proton exchange membrane fuel cells (PEMFCs) are closely associated with water transport and accumulation behaviors in the membrane electrode assembly. Therefore, an optimal water management is highly desired. Conventional serpentine flow field (CSFF) can effectively facilitate water removal and prevent water flooding. However, CSFF would cause a high pressure drop from the inlet to outlet, thus resulting in large parasitic power loss. In this study, a novel three-dimensional flow field (WSFF), patterned with waved serpentine flow channels, is designed and analyzed by combing the simulating method with experimental method. A three-dimensional, multi-phase, steady, isothermal, laminar simulation model is firstly established based on FLUENT PEM fuel cell module, and this model reveals that WSFF is overall better than CSFF in promoting oxygen transport though the diffusion layer and removing liquid water accumulated in microstructure. Its periodic waved structure introduces cyclical variation of local flow direction, local flow velocity and local pressure, thus leading to enhanced forced-convection. The superior performance of WSFF has also been experimentally verified, proving that WSFF not only enables a lower pressure drop over the entire current density range, but also improves the cell performance in comparison to CSFF at high current density region. Specifically, there is a 17.8% increment in the peak power density due to the use of WSFF.

[en] The natural circulation test of CAP1400 passive residual heat removal heat exchanger system (PRHR) is one of the first plant only tests and the major plant transient tests during the commissioning. During the natural circulation test, the temperature, pressure, liquid level and other parameters of the reactor primary circuit change dramatically, which increase the test risk and propose higher requirements for the operation control of the unit. Based on the AP1000 commissioning test practice, it is proposed to perform the PRHR natural circulation test using real decay heat generated following the reactor operation from the perspective of reducing test risk. At the same time, it analyzes the safety risks caused by the drastic changes in the parameters of the primary loop pressure, temperature, pressurizer level and the external source range detectors of the reactor during the test, and formulates corresponding countermeasures to provide the strong support for the safety implementation of subsequent CAP1400 PRHR natural tests. (authors)

[en] The base-excision repair enzyme uracil-DNA glycosylase (UDG) plays a crucial role in the maintenance of genome integrity. The authors describe a fluorometric method for the detection of the activity of UDG. It is making use of (a) a 3’-FAM-labeled hairpin DNA probe with two uracil deoxyribonucleotides in the self-complementary duplex region of its hairpin structure, (b) exonuclease I (Exo I) that catalyzes the release of FAM from the UDG-induced stretched ssDNA probe, and (c) graphene oxide that quenches the green FAM fluorescence of the intact hairpin DNA probe in the absence of UDG. If Exo I causes the release of FAM from the hairpin DNA probe, the fluorescence peaking at 517 nm is turned off in the absence of UDG but turned on in its presence. The resulting assay has a wide linear range (0.008 to 1 U·mL⁻¹) and a detection limit as low as 0.005 U·mL⁻¹. It has good specificity for UDG over potentially interfering enzymes and gave satisfactory results when applied to biological samples. Conceivably, the method may be used in a wide range of applications such as in diagnosis, drug screening, and in studying the repair of DNA lesions.

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[en] The spatial chirp generated in the Ti:sapphire multipass amplifier is numerically investigated based on the one-dimensional (1D) and two-dimensional (2D) Frantz–Nodvik equations. The simulation indicates that the spatial chirp is induced by the spatially inhomogeneous gain, and it can be almost eliminated by utilization of proper beam profiles and spot sizes of the signal and pump pulses, for example, the pump pulse has a top-hatted beam profile and the signal pulse has a super-Gaussian beam profile with a relatively larger spot size. In this way, a clear understanding of spatial chirp mechanisms in the Ti:sapphire multipass amplifier is proposed, therefore we can effectively almost eliminate the spatial chirp and improve the beam quality of a high-power Ti:sapphire chirped pulse amplifier system. (paper)

[en] This paper presents a study on selecting electricity contracts for a large-scale chemical production plant, which requires electricity importation, under demand uncertainty. Two common types of electricity contracts are considered, time zone (TZ) contract and loading curve (LC) contract. A multi-period linear probabilistic programming model is adopted for the contract selection and optimization. Hence, by using the probabilistic programming, a solution procedure is proposed that allow users to determine the best electricity contract according to their desired confident level of the uncertainties. In addition, due to the fact that the demand of product is uncertain, if one considers the overage and shortage of the products in the market as well, an interesting result can be obtained. The methodology is explained in the paper. (author)

[en] As structure-directing agents, the molecular structure of surfactants is critical for determining the properties of prepared mesoporous materials. Using dehydroabietic acid as a starting material, a series of rosin-based Gemini surfactants (abbreviated as R-n-R, n = 3, 6, 8 and 10, indicating the carbon atom number contained in the spacer) were synthesized and applied as templates in the preparation of ordered mesoporous silica. The structures and morphologies of the samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope and N₂ adsorption–desorption. The R-n-R surfactants feature rigid tricyclic hydrophobic groups with large volumes, which are beneficial for the formation of a three-dimensional cubic phase. Furthermore, the spacer length was found to have a tremendous effect on the structure of the prepared mesoporous silica materials. The head group of R-3-R, which has a short spacer, is excessively charged, leading to silica nanoparticles with an irregular morphology and a rather low BET surface area. With longer spacer lengths, R-6-R, R-8-R and R-10-R are conducive to generating silica nanoparticles with a novel dumbbell-like morphology and with higher BET surface areas of 1171, 1096 and 1186 m² g⁻¹, respectively. The results demonstrate the particularities of the Gemini surfactant structure in the preparation of mesoporous silica nanoparticles with novel morphologies, and the details of the molecular interactions that occur in the condensation of silicate anions are also revealed.

[en] Highlights: • Sewer biofilms related to sewer safety and public health are illustrated. • Sewer biofilms are influenced by operation mode, sewage character, and shear stress. • Transformation of organics, sulfur, and nitrogen in sewer biofilms are clarified. • Biomarkers, ARGs, and ENs might be well-controlled via their fate in sewer. -- Abstract: With rapid urbanization, sewer systems are extensively being constructed for the collection and transportation of sewage to minimize the severe environmental and health issues, especially relating to the spread diseases. The existence of abundant biofilms on the inner walls of sewers could lead to potential risks such as sewer explosions, poisonous gas leaks, and pipe corrosions with the transformations of various kinds of pollutants. Therefore, it is urgent to clarify their inner mechanisms to safely govern sewer systems. In this study, the characteristics of sewer biofilms including their structure, influencing factors, and substance transformations were analyzed in-depth. The results reveal that sewer biofilms (1.0 mm depth approximately) consist of large quantities of inorganic and some organic substances, while the abundant functional genus of the bacteria and archaea are summarized. Sewer biofilms influencing factors were determined to be sewer operation mode, sewage characteristics, and shear stress. Further, the transformation of organics, sulfur, and nitrogen as well as emerging micropollutants (such as, biomarkers, antibiotic resistance genes, and engineered nanoparticles) was investigated to guarantee sewer security and public health. Therefore, the current review could be considered as guidance for researchers and decision-makers.

[en] Highlights: • Obvious succession of bacteria, SRB, and MA existed in rural sewer biofilms. • Biofilm thickness variation in rural sewers was different with municipal sewers. • SRB number was much higher than MA and MA were eliminated in rural sewer biofilms. • Rural sewers sulfide accumulation was the main problem rather than CH₄ accumulation. Rural sewers are applied widely to collect rural sewage and biofilm characteristics in rural sewers may be different with municipal sewers. The succession of bacteria communities, sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) need to be studied since rural sewers have a potential risk of sulfide and methane accumulation. In this study, lab-scale rural sewer facilities were established to analyze the characteristics of sewer biofilm and the generation of sulfide and methane. The results indicate that the variation tendency of biofilm thickness in rural sewers was different with municipal sewers. Time-based bacterial succession existed in rural sewer biofilms and the predominant genus was changed from Acinetobacter (approximately 19.10%) to Pseudomonas (approximately 12.61%). SRB (mean 1.49 × 10⁶ dsrA copies/cm²) were abundant than MA (mean 2.57 × 10⁵ mcrA copies/cm²) while MA were eliminated gradually in rural sewer biofilms. The tendency of sulfide and methane generation was similar with the number variation of SRB and MA, indicating sulfide accumulation might be more serious trouble than methane accumulation in a long-run rural sewer. Overall, this study deeply analyzed the succession of rural sewer biofilms and found that MA and methane were automatically inhibited in rural sewers.

[en] Highlights: • PM_2.5 concentrations have shown a sharply decreasing trend during the period from 2013 to 2017 in China. • The premature mortality associated with PM_2.5 concentrations dropped from 1,078,800 in 2014 to 962,900 in 2017. • The health cost avoided in 2017 as a result of the reduction of PM_2.5 concentrations amounted to 1.58% of the national GDP. • The mortality density in dense urban areas is much higher than that in rural area. • The urban migration can increase the premature mortality caused by PM_2.5 indirectly. -- Abstract: In this study, the trend of PM_2.5 concentrations and its adverse health effects in China from 2001 to 2017 are estimated utilizing 1-km high-resolution annual satellite-retrieved PM_2.5 data. PM_2.5 concentrations for most of the provinces/cities remained stable from 2001 to 2012; however, following the issue of the Air Pollution Prevention and Control Action Plan (APPCAP) by the central government of China, a dramatic decrease in PM_2.5 concentrations from 2013 to 2017 occurred. Premature mortality caused by PM_2.5 dropped from 1,078,800 in 2014 to 962,900 in 2017. The PM_2.5 caused 17-year average mortality ranges from 3800 in Hainan Province to 124,800 in Henan Province. The health cost benefits gained by the reduction of PM_2.5 pollution amounted to US $193,800 in 2017 (compared to the costs due to PM_2.5 concentrations in 2013), amounting to 1.58% of the total national GDP. The impacts of urbanization on PM_2.5 concentration and mortality are analyzed. The PM_2.5 concentration and its induced mortality density in dense urban areas are much higher than those in rural areas. The aggravation of PM_2.5 associated premature mortality in urban areas is mainly due to the larger amount of emissions and to urban migration, and 6500 deaths in 2014 could have been avoided were the population ratios in dense-urban/normal-urban/rural areas to be reversed to the ones in 2001. It is recommended that people with respiratory-related diseases live in rural areas, where the pollutant concentration is relatively low.

[en] Mid-infrared (MIR) pulsed lasers operating at 2-5 µm have important applications in communication, sensing, and medicine. However, the lack of robust MIR saturable absorbers (SAs) remains a major obstacle. Here, a semiconductor material cadmium oxide (CdO) film with high laser-induced damage threshold (800 nm, 134 mJ cm${}^{-<!--\; ???\; -->2}$) and broadband saturable absorption (2.0-3.9 µm) is investigated. The effective tuning of the nonlinear optical response of CdO is demonstrated by adjusting the carrier concentration via a tungsten (W)-doping scheme. The saturable absorption is improved and carrier relaxation process is accelerated after increasing the W-dopant level. Based on these findings, the robust CdO-SAs with customizable parameters are realized and Q-switched lasers with decreasing pulse width from 372 to 254.3 ns are obtained at 2 µm. The design flexibility provided by CdO opens up a large parameter space that enables the continuous improvement of compact and high-performance MIR ultrafast lasers. (© 2023 Wiley‐VCH GmbH)