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In this paper, the health monitoring of Al 7075 friction stir welded structure was carried out, including elastic and plastic deformation during stretching and bending. A thin film sensor composed of MXene and single-walled carbon nanotubes was developed by simple mixing and vacuum filtration. This flexible MXene/SWCNT thin film sensor combining the sensitivity of MXene with the stability of carbon nanotubes and can be pasted on the surface of Al 7075 FSW joints through polyimide encapsulation to achieve structural health monitoring. The experimental results show that the MXene/SWCNT sensors encapsulated in polyimide can effectively capture the micro strain of different areas during stretching and bending. When the strain of the welded structure is less than 3000, only elastic deformation occurs in different regions of the welded structure, and the sensors located in different regions show the same resistance change rate. When the strain is greater than 3000, the resistance change rate of the sensors in the thermal-mechanical affected zone and heat affected zone obviously, and when the external force is released, there is residual resistance, which proves that the plastic deformation occurs in the welded structure at this time. By comparing the resistance change rate of the sensors in different regions, it can be inferred whether plastic deformation occurs. As the strain further increases, the resistance change rate of the sensor further increases and make a stable response until the structure breaks. This sensor can be used to track the whole process monitoring of welded structure before fracture. [Display omitted] • Thin film sensors composed of SWCNT and MXene were prepared by vacuum filtration. • The MXene/SWCNT sensor can monitor different strain with different aera of welding structure in real-time. • The MXene/SWCNT sensor adopted by polyimide package has good sensitivity and synchronization to cyclic load. • The MXene/SWCNT sensor can be used to follow the entire strain of welding structure till end-of-life. [ABSTRACT FROM AUTHOR]

• Ultralow-concentration emulsion-based ink (5.882 mg mL−1) of MXene was prepared due to the enhanced binding of MXene and GO by ODA. • The MX/rGO architectures with macroscopic (hierarchical lattice) and microscopic (porous) structure were constructed by DIW technology. • The synergistic effect of macroscopic (hierarchical lattice) and microscopic (porous) structure enables 3D MX/rGO architectures to achieve high sensitivity (166.957 kPa−1), wide sensing range (∼100 kPa), and excellent cyclic stability (10500 cycles). 3D direct ink writing technology based on two-dimensional (2D) MXene nanomaterial inks receives attention in the field of pressure sensing for simplicity of fabrication, programmable geometry with controllable function and performance. However, it is still a huge challenge to print excellent macro-structure with ultralow-concentration MXene inks, attributed to its weak gelation ability. Herein, we construct a MXene/reduced graphene oxide (MX/rGO) architecture (0.012 g cm−3) with macroscopic (hierarchical lattice) and microscopic (porous) structure by using ultralow-concentration emulsion-based inks of MXene (5.882 mg mL−1). The introduction of octadecylamine enhances the bonding between the MXene and GO, significantly improving the gelation ability of the ink with low-concentration 2D nanomaterials. More importantly, the MX/rGO pressure sensor achieves a high sensitivity (166.957 kPa−1), wide sensing range (0.028∼100 kPa), and excellent cyclic stability (10500 cycles) due to its 3D hierarchical lattice porous structure. These sensing capabilities enable the sensor to detect various human motions, such as pulse beating, vocal cord vibration, facial expressions, different joint movements and pressure distribution. Undoubtedly, this work provides a broad development prospect for the customized flexible pressure sensors based on MXene ink 3D printing technology. [ABSTRACT FROM AUTHOR]

The fatigue load has become an increasingly prominent problem affecting the damage tolerance and service life of wind turbine blades. The damage monitoring of repaired blades is a challenging task. The purpose of this study was to use buckypaper (BP) sensors to monitor the structural health of the repaired composite specimens in fatigue environments. First, the quasi-static tensile failure test and the graded loading and unloading experiment verified the feasibility of using BP sensors to monitor the specimens. Then, the BP sensors were used to systematically monitor the axial fatigue of the repaired and reinforced composite specimens. The cumulative damage caused by fatigue was visualised through the Δ R / R 0 response change in the BP sensors. The analysis results of the sensors were compared with the actual damage of the specimens, and a non-destructive inspection chart was used for auxiliary verification, further verifying the feasibility of using the BP sensor to monitor damage on wind turbine blades. The method of monitoring the repaired composite structure damage using BP sensors can be used to study the damage behaviour of the repaired wind turbine blade under fatigue. [Display omitted] [ABSTRACT FROM AUTHOR]

Recently, owing to the high theoretical capacity and safety, zinc-ion energy storage devices have been known as one of the most prominent energy storage devices. However, the lack of ideal electrode materials remains a crucial hindrance to developing zinc-ion energy storage devices. MXene is an ideal electrode material due to its ultra-high conductivity, particular sheet structure and unique physical and chemical properties, and it has shown excellent performance in practical applications. Therefore, this review briefly introduces the basic information about MXenes and details the applications of MXene in zinc-ion batteries and zinc-ion hybrid capacitors in recent years. Finally, the application characteristics of MXene in zinc-ion energy storage devices are summarized and an outlook is given. This paper highlights the features and advantages of zinc-ion energy storage devices more by comparing them with other energy storage devices, to provide a comprehensive reference for scholars in this field. [ABSTRACT FROM AUTHOR]

Composite pressure vessels (COPV) are widely used in the aerospace field, where they experience a wide range of unpredictable operating conditions. However, the recent work remains at monitoring the structural health of the whole COPV without considering lamination. This article introduces a kind of buckypaper (BP) sensor that can be put into COPV for structural health monitoring without requiring their removal from service. Simultaneously, the introduction of a flexible printed circuit enables the omnidirectional BP sensor to monitor strain state changes in two directions at one time. It can also form a matrix monitoring area with fewer sensors and increase the survival rate. Before being applied to COPV, tensile experiments and fatigue cycle experiments were carried out. At hydraulic pressure tests, the BP sensor is embedded in the COPV to perform real-time strain monitoring in both the bile layer and fiber layer. The experimental result shows that the BP sensor can maintain a good response and response consistency for a long time. Therefore, the BP sensor can be used for health monitoring of COPV. [ABSTRACT FROM AUTHOR]

In this paper, lifetime health monitoring of composites was conducted, included manufactured monitoring and structural health monitoring. A thin film sensor composed of multi-walled carbon nanotubes (MWCNTs) and MXene was developed through simple mixing and spray vacuum filtration. This highly flexible and susceptible MXene/CNT film sensor can be embedded in polymer composites to monitor the phase change of the resin and the determination of the gel point during the preparation of the composite in real-time. The MXene/CNT film sensors were embedded and arrayed in fiber-reinforced composites, which can be used for resin curing monitoring, then continued structural health monitoring. Experimental results show that the MXene/CNT film sensor embedded in the composite laminates can effectively capture the change of the resin phase, that characterized by resistance. MXene/CNT films have a good ability to respond to changes in the resin state. The gel point of resin obtained from the MXene/CNT film sensor is 134 °C, which is consistent with 137 °C from the DMA results. The accurate gel point can optimize the curing system and improve the quality of composite products. Then the tensile, bending, and fatigue tests of fiber-reinforced composite laminates embedded with MXene/CNT film sensors were carried out. MXene/CNT film sensor can keep good response and response consistency for a long time. As a novel sensor, the MXene/CNT film sensor has the advantages of high response sensitivity, solid real-time performance, and long service time. The MXene/CNT film sensor has great potential to establish and optimize manufacturing processes and to improve the cure quality of fiber-based resin composites. This sensor can be used to follow the entire life cycle of a composite from fabrication till end-of-life. The 3D structure of the MXene/CNT film sensor can be used for life-long health monitoring of fiber-reinforced composite materials [Display omitted] • Thin film sensors composed of MWCNTs and MXene were prepared by mixing and spray vacuum filtration. • The MXene / CNT film sensor, which has good compatibility with resin, can monitor the phase change of resin during curing. • The MXene/CNT film sensor can monitor gel spots with different positions and thickness in real-time. • The MXene/CNT film sensor embedded in fiber reinforced composites has good sensitivity and synchronization to bending. • The MXene/CNT film sensor can be used to follow the entire life cycle of a composite from fabrication till end-of-life. [ABSTRACT FROM AUTHOR]

[Display omitted] • The pressure monitoring range of mxene sensor reaches MPa level. • A distributed pressure measurement scheme for bolt structure interface is proposed. • Early warning monitoring of bolt looseness was achieved in vibration environment. • The results provide a reliable solution for industrial applications. Mxenes can be used in a variety of applications due to their multifunctional chemical properties. It has received increasing attention as a piezoresistive sensor. However, the stability and pressure monitoring range of the reported MXene sensors are limited, thereby limiting these scalability and effectiveness. In contrast, this paper presents a conductive MXene/FPC based pressure sensor overcomes the aforementioned shortcoming in that its pressure monitoring range and stability are improved by one order of magnitude. Therefore, this study aims to validate the use of MXene sensor for detecting bolt loosening. First, the mechanical properties of MXene were tested, including pressure test, vibration test and so on. The mechanical parameters of MXene are obtained. Secondly, the bolt structure embedded with MXene sensor is tested by torque loading and bolt looseness monitoring under vibration environment. The experimental results show that it has a linear pressure monitoring range of 0−120Mpa, the sensitivity of the sensor is up to 1.3 Mpa −1, and can remain stable after more than 63,000 cycles. Through monitoring the change of resistance ΔR/R 0 , the pressure of bolt pre tightening force transmitted to the joint surface can be accurately sensed. In the vibration environment, when the excitation frequency is 20 Hz, the bolt structure resonates, and ΔR/R 0 increases from 0.28 to 0.6; when the bolt looses in about 100 s, the ΔR/R 0 increases from 0.3 to 0.68 indicates that MXene can respond to bolt loosening in time. Thus, the sensor can be used in the whole life health monitoring of bolted structure completely. [ABSTRACT FROM AUTHOR]

Repair of composite materials is an important cost savings for the aviation industry, and it is also very important to monitor the repaired structure. In this paper, a novel micro-nano sensor which is combined with Flexible Printed Circuit and Buckypaper (BP) sensor is introduced, and has the characteristics of multidirectional, real time and high sensitivity. These sensors are used to monitor the strain at different positions on the composite repair structure. The piezoresistive response of BP sensor is obtained and the main working mechanism of BP sensor is explained. Experiments show that this sensor can preliminarily judge the damage position and degree of the repaired structure, and monitor whether it reaches the strength limit. And it can judge the loading history of the structure. This ensures the safety of the repaired structure in the process of continuous service to a certain extent. [ABSTRACT FROM AUTHOR]

Preparation and sensing properties of the MXene/ink nanocomposite sensor for health monitoring. • A new strain sensor based on MXene film and printing ink encapsulated with nylon fabric, which can be manufactured by simple spraying-coated technique to meet the needs of mass production. • The unique sheet structure of MXene makes it easier to form a stable conductive network. The surface of Ti3C2Tx prepared by etching in LiF-HCl solution has a large amount of oxygen and hydroxyl groups, which are easy to disperse in aqueous solution and contribute to the improvement of strain sensing performance. The effect of different mxene ratio on ink conductivity was discussed, and a low permeability threshold was found. MXene/ink based strain sensor exhibited excellent sensitivity , low detection limit and stable sensing performance after 2950 cycles at 20% strain. • The designed MXene/ink strain sensor encapsulated with nylon fabric could be used to detect different movement behaviors and physiological signals of human body, showing a wide application prospect in the field of new flexible multi-functional sensors. Flexible strain sensors still face great challenges in combining high sensitivity, wide detection range, good mechanical stability and simple manufacturing processes into sensors. Herein, this paper reports a simple and low cost strain sensor fabricating method based on two-dimensional (2D) material (MXene) and ink, which can be large-scale fabricated into multiduty sensors with high sensitivity and excellent durability by spray-coated process and wrapped by nylon fabric. Owing to the fact that MXene has excellent dispersion in printing ink material, the sensor obtains low percolation threshold of 3.6 wt% and a percolation network based on Ti 3 C 2 T x MXene/ink composites was precisely designed. The migration of the MXene lamination leads to a large change in resistance, while the ink coating restricts the large displacement of the nanometer lamella to maintain the connectivity of the conductive path in the large strain region. The strain sensing test shows that the MXene/ink encapsulated by nylon fabric strain sensor exhibits a high sensitivity (gauge factor of 27.2 and 170.9 under 0 %–25 % and 25 %–29.7 % strain, respectively), good linearity (R-Square >0.967), and excellent reliability and stability (>2950 cycles). The as-developed MXene/ink strain sensor was demonstrated to monitor real-time both tiny and large human activities, showing that it has great potential in the field of wearable strain sensor. [ABSTRACT FROM AUTHOR]

This work developed a facile approach to fabricate highly sensitive and flexible polyurethane/graphene platelets composite film for wearable strain sensor. The composite film was fabricated via layer-by-layer laminating method which is simple and cost-effective; it exhibited outstanding electrical conductivity of 1430 ± 50 S/cm and high sensitivity to strain (the gauge factor is up to 150). In the sensor application test, the flexible strain sensor achieves real-time monitoring accurately for five bio-signals such as pulse movement, finger movement, and cheek movement giving a great potential as wearable-sensing device. In addition, the developed strain sensor shows response to pressure and temperature in a certain region. A multifaceted comparison between reported flexible strain sensors and our strain sensor was made highlighting the advantages of the current work in terms of (1) high sensitivity (gauge factor) and flexibility, (2) facile approach of fabrication, and (3) accurate monitoring for body motions. [ABSTRACT FROM AUTHOR]

The properties of polymer nanocomposites depend greatly on the dispersion of nanoparticles in the polymer matrix. To improve the dispersion of single-walled carbon nanotubes (SWCNTs) in bismaleimide (BMI) resin, this paper developed a feasible method for non-covalent modification of SWCNTs by using polyvinylpyrrolidone (PVP). Moreover, the effect of functionalized SWCNTs on the properties of BMI composites was systematically investigated. The results showed that it was very effective for PVP as a surface modifier for the dispersion of SWCNTs in BMI resin. As a consequence, the electrical conductivity and mechanical properties of the SWCNT/BMI composites were all improved by the incorporation of SWCNTs at a low content. The study also presented that the heat resistance and thermal stability of SWCNT/BMI composites were simultaneously enhanced. [Display omitted] • A simple and feasible dispersion method for SWCNTs in BMI resin was developed. • The threshold percolation of SWCNTs/BMI composites was less than 0.01 wt%. • The mechanical properties of the composites increased substantially with a very low SWCNTs content. [ABSTRACT FROM AUTHOR]

The traditional wearable sensor has the problem of insufficient sensing coefficient and sensing range. In order to solve these problems, this paper innovatively prepared CNTs and MXene monodisperse waterborne slurry mixed with waterborne thermoplastic polyurethane and nanocellulose to prepare composite ink. The monodisperse CNTs and MXene have good conductive network construction ability, so that when the content of CNTs and MXene in the ink is as low as 0.08%, a stable sensing conductive network can still be formed (conductivity 127s/cm). The low addition of nanomaterials are cost saving along with the influence in conductivity which made the experiment to implement the bonding strength and viscous attributes of the inkjet in printing. The mechanical properties of the composite ink film sensor assembled by ink and medical fabric can be carried out by digital spraying printing technology. The results show that the sensitivity of the MXene/CNTs/WPU/CNFs ink sensor in the tensile test is up to 43.61, and the sensor resistance still shows a linear change under the strain of 0–89%. At the same time, after 2100 fatigue tests, the sensor resistance change remains stable. Finally, the MXene/CNTs/WPU/CNFs ink sensor has also been successful in human monitoring. From monitoring small changes such as finger bending and cervical spine bending to monitoring large movements such as arm flexion and knee bending, the corresponding electrical response can be obtained in time respectively. Therefore, the MXene/CNTs/WPU/CNFs ink sensor has the characteristics of high sensitivity, real-time monitoring and recording, which shows that the research has broad application prospects in the future development. [ABSTRACT FROM AUTHOR]

Due to the increasing demand for portability of electronic devices in society, flexible and lightweight shielding materials have received greater attention. There is an urgent need for ultra-thin, flexible, and highly conductive materials with excellent electromagnetic interference shielding performance, especially for the preparation of stretchable shielding materials in practical applications such as wearable and foldable electronics. Herein, the microwave and hydroiodic acid reduced graphene oxide (M-HIRGO) was obtained through the combination of the two reduction methods. Three-layer and five-layer M-HIRGO/PES-C composite films with sandwich structure were prepared in the form of PES-C|RGO|PES-C laminates. In the five-layer structure, the electromagnetic shielding of M-HIRGO/PES-C composite film with a middle PES-C layer thickness of 122 μm in the X-band was 46.73 dB. And the shielding mechanism is mainly due to absorption. Meanwhile, the obtained M-HIRGO/PES-C composite films had a tensile strength of 23.43 MPa. This study may provide a simple and effective approach to achieve new EMI shielding materials, especially for absorption-dominated EMI shielding. [Display omitted] • A rapid microwave irradiation method was used for the reduction of graphene oxide. • Composite films with sandwich structure give the good EMI shielding performance. • The EMI shielding values increase with the increase of PES-C interlayer thickness. • The PES-C provides good thermal resistance and tensile properties for the composite film. • The prepared composite films are an absorption-dominated EMI shielding materials. [ABSTRACT FROM AUTHOR]

A new type of embedded composite material health monitoring nano-sensor is designed to ensure that the unique material advantages of nanofillers can be maximized. The carbon nanotubes (CNTs)/polysulfone (PSF)/polyimide (PI) thin film sensor in this paper is obtained by the self-assembly of a PSF/PI asymmetric porous membrane which is prepared by a phase inversion method through vacuum filtration of SWCNTs. It is a new structure for a practical CNT sensor that can take into account both 'composite health monitoring and damage warning' and 'composite mechanical enhancement'. The new structure of the CNTs/PSF/PI film sensor is divided into two parts. The upper part consists of small-aperture finger-like holes filled with SWCNTs (the SWCNT content is 0.0127 mg cm -2 ). The lower part consists of large-aperture cavities conducive to resin infiltration, which enhance the interface bonding force between the sensor and the composite material. This unique structure allows the CNTs/PSF/PI film sensor to change the influence of the embedded sensor from 'introducing defects' to 'local enhancement', and the mechanical strength of the enhanced specimen can reach up to 1.68 times that of the original specimen, and the service interval can reach 2.01 times that of the original specimen. In addition, the CNTs/PSF/PI film sensor also has good sensitivity (GF = 2.54) and extremely high linearity ( R 2 = 0.9995), and has excellent follow-up and interface bonding ability. It can also maintain excellent fatigue resistance and stability over 46 500 vibration cycles, which provides new research ideas and research methods for the field of composite-life monitoring sensors.

To uncover the internal mechanisms of various drought stress intensities affecting the soluble sugar content in organs and its regulation by endogenous abscisic acid (ABA), we selected the saplings of Platycladus orientalis , a typical tree species in the Beijing area, as our research subject. We investigated the correlation between tree soluble sugars and endogenous ABA in the organs (comprised of leaf, branch, stem, coarse root, and fine root) under two water treatments. One water treatment was defined as T1, which stopped watering until the potted soil volumetric water content (SWC) reached the wilting coefficient and then rewatered the sapling. The other water treatment, named T2, replenished 95% of the total water loss of one potted sapling every day and irrigated the above-mentioned sapling after its SWC reached the wilt coefficients. The results revealed that (1) the photosynthetic physiological parameters of P. orientalis were significantly reduced ( p < 0.05) under fast and slow drought processes. The photosynthetic physiological parameters of P. orientalis in the fast drought-rehydration treatment group recovered faster relative to the slow drought-rehydration treatment group. (2) The fast and slow drought treatments significantly ( p < 0.05) increased the ABA and soluble sugar contents in all organs. The roots of the P. orientalis exhibited higher sensitivity in ABA and soluble sugar content to changes in soil moisture dynamics compared to other organs. (3) ABA and soluble sugar content of P. orientalis showed a significant positive correlation ( p < 0.05) under fast and slow drought conditions. During the rehydration stage, the two were significantly correlated in the T2 treatment ( p < 0.05). In summary, soil drought rhythms significantly affected the photosynthetic parameters, organ ABA, and soluble sugar content of P. orientalis . This study elucidates the adaptive mechanisms of P. orientalis plants to drought and rehydration under the above-mentioned two water drought treatments, offering theoretical insights for selecting and cultivating drought-tolerant tree species.

Designing flexible wearable sensors with a wide sensing range, high sensitivity, and high stability is a vulnerable research direction with a futuristic field to study. In this paper, Ti 3 C 2 T x MXene/carbon nanotube (CNT)/thermoplastic polyurethane (TPU)/polysulfone (PSF) composite films with excellent sensor performance were obtained by self-assembly of conductive fillers in TPU/PSF porous films with an asymmetric structure through vacuum filtration, and the porous films were prepared by the phase inversion method. The composite films consist of the upper part with finger-like "cavities" filled by MXene/CNTs, which reduces the microcracks in the conductive network during the tensile process, and the lower part has smaller apertures of a relatively dense resin cortex assisting the recovery process. The exclusive layer structure of the MXene/CNTs/TPU/PSF film sensor, with a thickness of 46.95 μm, contains 0.0339 mg/cm 2 single-walled carbon nanotubes (SWNTs) and 0.348 mg/cm 2 MXene only, providing functional range (0-80.7%), high sensitivity (up to 1265.18), and excellent stability and durability (stable sensing under 2300 fatigue tests, viable to the initial resistance), endurably cycled under large strains with serious damage to the conductive network. Finally, the MXene/CNTs/TPU/PSF film sensor is usable for monitoring pulse, swallow, tiptoe, and various joint bends in real time and distributing effective electrical signals. This paper implies that the MXene/CNTs/TPU/PSF film sensor has broad prospects in pragmatic applications.

To explore whether there were differences among the patterns of response of grasslands with different levels of degradation to extreme drought events and nitrogen addition, three grasslands along a degradation gradient (extremely, moderately, and lightly degraded) were selected in the Bashang area of northern China using the human disturbance index (HDI). A field experiment with simulated extreme spring drought, nitrogen addition, and their interaction was conducted during the growing seasons of 2020 and 2021. The soil moisture, aboveground biomass, and composition of the plant community were measured. The primary results were as follows. (1) Drought treatment caused soil drought stress, with moderately degraded grassland being the most affected, which resulted in an 80% decrease in soil moisture and a 78% decrease in aboveground biomass. The addition of nitrogen did not mitigate the impact of drought. Moreover, the aboveground net primary production (ANPP) in 2021 was less sensitive to spring drought than in 2020. (2) The community composition changed after 2 years of drought treatment, particularly for the moderately degraded grasslands with annual forbs, such as Salsola collina , increasing significantly in biomass proportion, which led to a trend of exacerbated degradation (higher HDI). This degradation trend decreased under the addition of nitrogen. (3) The variation in drought sensitivities of the ANPP was primarily determined by the proportion of plants based on the classification of degradation indicators in the community, with higher proportions of intermediate degradation indicator species exhibiting more sensitivity to spring drought. These findings can help to provide scientific evidence for the governance and restoration of regional degraded grassland under frequent extreme weather conditions.

More and more studies have shown that Branched chain amino acid transaminase 1 (BCAT1) is involved in the occurrence and development of a variety of tumors. However, the mechanism of its occurrence and development in hepatocellular carcinoma (HCC) remains unclear. Here, we demonstrated the relationship between BCAT1 and AKT signaling pathway, as well as EMT, and the clinical significance of BCAT1 by using BCAT1 expression in 5 cell lines and 113 liver cancer and non-liver cancer tissue samples. The results showed that the expression of AKT was positively correlated with BCAT1 in HCC tissues, and BCAT1 could promote the progression of HCC cells through the AKT signaling pathway. Clinical analysis and Bioinformatics technology analysis revealed that BCAT1 was correlated with poor prognosis, and BCAT1 expression in the HCC tissues was evidently correlated with tumor number, vascular invasion, Edmondson grade and TNM stage (P < 0.05). In vitro studies showed that BCAT1 increased the invasion and migration of in MHCC-97H cells a d Huh7 cells. By inhibiting the expression of the BCAT1 gene, we detected the corresponding changes in the expression levels of Twist, E-cadherin and Vimentin, confirming that BCAT1 may promote the invasion and migration of HCC cells through epithelial-mesenchymal transformation (EMT). Overall, BCAT1 can activate AKT signaling pathway and EMT to promote the development and metastasis of HCC cells. this study may provide new ideas and directions for cancer diagnosis and treatment., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

Air pollution caused by PM 2.5 particles is a critical issue for public health that adversely affects people living in urban cities. Short-term Mega-events such as international meetings, sports tournaments, and traditional festivals can profoundly influence the local air quality. However, the extent of these influences and their role in improving or deteriorating the local air quality is still unclear. By collecting relative research from 75 publications based on more than 37 cities worldwide, we conducted a systematic review and meta-analysis. We calculated the log response ratio (RR) of the treatment (during) and control periods (before and after) of the Mega-events. The short-term policy control measures enacted during the Mega-Events consisting of meetings caused a significant decline (by -44.06%) in the ambient PM 2.5 concentration. The mean daily PM 2.5 concentration reduced from more than 100.00 μg/m 3 before the events to 60.39 μg/m 3 , which is below the WHO (World Health Organization) interim target - 1 (75 μg/m 3 ). On the contrary, setting off fireworks during the festival increased the ambient PM 2.5 concentrations by 89.57% on average, with a mean daily value of 254.22 μg/m 3 . The variations in the effects of all event types on the air quality were primarily influenced by the background PM 2.5 concentrations, with a negative correlation throughout. Moreover, the impact of events with policy control measures was also influenced by the year of the event, level of control, and location (suburban/urban) of the monitoring sites. Our findings provide evidence of the potential of human intervention on PM 2.5 pollution reduction. We further highlight the crucial role of background pollution level in implementing policies during the Mega-events, which can benefit the environmental governance of developing countries., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Facing the relative lag of forest ecosystem service and estimation in China, this paper proposed to quickly carry out the research on the evaluation of forest ecosystem service. On the basis of the classification of forest ecosystem types in China, the service of artificial and semi-artificial forest ecosystems was investigated, which was divided into eight types, i.e., timber and other products, recreation and eco-tourism, water storage, C fixation and O2 release, nutrient cycling, air quality purifying, erosion control, and habitat provision. According to the assessment index system for global ecosystem service proposed by Costanza et al., a series of assessment index system suitable for Chinese forest ecosystem service was set up, by which, the total value of forest ecosystem service in China was estimated to be 30 601.20 x 10(8) yuan x yr(-1), including direct and indirect economic value about 1 920.23 x 10(8) and 28 680.97 x 10(8) yuan x yr(-1), respectively. The indirect value was as 14.94 times as the direct one. The research aimed to bring natural resources and environment factors into the account system of national economy quickly, and to realize the green GDP at last, which would be helpful to realize sustainable development and environment protection.