Retrieval of Suspended Sediment Concentration from Bathymetric Bias of Airborne LiDAR.

In addition to depth measurements, airborne LiDAR bathymetry (ALB) has shown usefulness in suspended sediment concentration (SSC) inversion. However, SSC retrieval using ALB based on waveform decomposition or near-water-surface penetration by green lasers requires access to full-waveform data or infrared laser data, which are not always available for users. Thus, in this study we propose a new SSC inversion method based on the depth bias of ALB. Artificial neural networks were used to build an empirical inversion model by connecting the depth bias and SSC. The proposed method was verified using an ALB dataset collected through Optech coastal zone mapping and imaging LiDAR systems. The results showed that the mean square error of the predicted SSC based on the empirical model of ALB depth bias was less than 2.564 mg/L in the experimental area. The proposed method was compared with the waveform decomposition and regression methods. The advantages and limits of the proposed method were analyzed and summarized. The proposed method can effectively retrieve SSC and only requires ALB-derived and sonar-derived water bottom points, eliminating the dependence on the use of green full-waveforms and infrared lasers. This study provides an alternative means of conducting SSC inversion using ALB.

Does the Application of ICTs Improve the Efficiency of Agricultural Carbon Reduction? Evidence from Broadband Adoption in Rural China.

Based on the Environmental Kuznets Curve (EKC) hypothesis, this paper examines whether rural broadband adoption affects agricultural carbon reduction efficiency (ACRE), using panel data from 30 Chinese provinces from 2011 to 2019. This paper achieves a measurement of ACRE by taking the carbon sink of agricultural as one of the desired outputs and using a Slacks-Based Measure (SBM) model and the global Malmquist-Luenberger (GML) index. The results show that: (1) Rural broadband adoption has a positive effect on ACRE. The relationship between the income of rural residents and ACRE was an inverted U-shaped, which confirms the EKC hypothesis. (2) Land transfer has a significant promoting effect on the relationship between rural broadband adoption and ACRE. When the land transfer rate is high, the positive effect of broadband adoption is obvious. (3) The positive effect of broadband adoption on ACRE was more obvious when farmers invested more in production equipment, that is to say, it has a significant positive moderating effect. As farmers in many developing countries suffer from increasingly frequent and severe extreme weather events, we believe that the results of this study also have implications for the implementation of agricultural carbon reduction and smart agricultural equipment roll-out in many countries.

Honeycomb-Inspired Robust Hygroscopic Nanofibrous Cellular Networks.

Mimicking nature is a highly efficient and meaningful way for designing functional materials. However, constructing bioinspired nanofibrous 3D cellular networks with robust mechanical features is extremely challenging. Herein, a biomimetic, super-flexible, highly elastic, and tough nanofibrous membrane (NFM)-based water harvester is reported with a highly ordered honeycomb-inspired gradient network structure, self-assembled from electrospun spider-silk-like humped nanofibers. The resultant NFM exhibits super flexibility, high tensile strength (2.9 MPa), superior elasticity, and decent toughness (3.39 MJ m-3 ), allowing it to be used as the framework of hygroscopic materials. The resulting hygroscopic NFM displays excellent moisture absorption performance, which can be used as an efficient water harvester with a superhigh equilibrium moisture absorption capacity of 4.60 g g-1 at 95% relative humidity for 96 h, fast moisture absorption and transport rates, and long-term durability, achieving directional transport and collection of tiny water droplets. This work paves the way for the design and development of multifunctional NFMs with a honeycomb-inspired gradient network structure.

Background noise reduction for airborne bathymetric full waveforms by creating trend models using Optech CZMIL in the Yellow Sea of China.

Raw full waveforms of green lasers used in airborne LiDAR bathymetry (ALB) are contaminated by background and random noise related to the environment and ALB devices. Traditional thresholding methods have been widely used to reduce background noise in raw full waveforms on the basis of the assumption of constant background noise. However, background noise that is mainly related to background solar radiation and detector dark current changes over time. Thresholding methods perform poorly on the full waveforms with a wide variation range of background noise. A background noise reduction method considering its wide variation is proposed to decrease the background noise by creating trend models. First, each green full waveform is divided into two parts: pulse- and non-pulse-return waveforms. Second, a linear interpolation is conducted on the non-pulse-return waveform to impute the missing noise. Third, a low-pass filter is used to filter the random noise with high frequency in the imputed non-pulse-return waveform and obtain the trend model of background noise of the full waveform. Finally, the derived background noise model is used to decrease the background noise in the pulse-return waveform. The proposed method is applied to decrease the background noise in raw green full waveforms collected by the Optech coastal zone mapping and imaging LiDAR (CZMIL). The mean and standard deviation of residual noise in the CZMIL waveform reduced by the trend model of background noise are -0.03 and 3.5 digitizer counts, respectively. The proposed background noise reduction method is easy to apply and can reduce the background noise to a significantly low level. This method is recommended for preprocessing the raw full waveforms of green lasers collected by Optech CZMIL for ALB.

One-step fabrication of multi-scaled, inter-connected hierarchical fibrous membranes for directional moisture transport.

HYPOTHESIS: Functional textiles engineered for maintaining body comfort by fast sweat release using the directional moisture transport concept are in high demand. However, designing these functional textiles remains a critical job and generally requires multi-step complex fabrication routes. In this regard, developing one-step strategy to fabricate multi-scaled, inter-connected nonwoven-nanofiber/nets hierarchical fibrous composite membranes with asymmetric wettability for enhanced directional moisture transport would be a very fruitful approach. EXPERIMENT: Composite membranes were fabricated by the rational combination of commercial polyethylene terephthalate nonwoven (CNW) as hydrophobic layer, and polyamide and silver nanoparticles (PA-Ag) nanofiber/nets as hydrophilic layer via one-step electrospinning process. FINDINGS: The resultant CNW/PA-Ag nanofiber/net composite membranes were carefully investigated for water vapor transport, moisture management performance, and antibacterial activity. The subsequent membranes not only exhibit exceptionally high one-way moisture transport index (1253%), considerably high water vapor transport rate (11.45 Kg m-2d-1), and overall moisture management capacity (0.91), but also offer high resistance of 16.9 cm H2O to prohibit the moisture drive in the opposite way, and considerable antibacterial activity against Escherichia coli and Staphylococcus aureus. The effective one-step fabrication of such fascinating directional moisture transport membranes with decent antibacterial activity opens a new intuition into the designing of novel functional materials for rapid sweat release and personal drying applications.

Impact of dissolved O2 on phenol oxidation by δ-MnO2.

Although redox reactions of organic contaminants with manganese oxides have been extensively studied, the role of dissolved O2 in these processes has largely been overlooked. In this study, the oxidative degradation of phenol by δ-MnO2 was investigated under both oxic and anoxic conditions. Dissolved O2 inhibited phenol degradation due to its promoting role in the reoxidation and precipitation of reduced Mn(ii) to Mn(iii) on the δ-MnO2 surface, resulting in partial transformation of δ-MnO2 to "c-disordered" H+-birnessite at pH 5.5 and feitknechtite, manganite, and hausmannite at pH 7.0 and 8.5. The reformed Mn(iii) phases could reduce phenol oxidation by blocking reactive sites of δ-MnO2. In addition, dissolved O2 caused a higher degree of particle agglomeration and a more severe specific surface area decrease, and hence lower reactivity of δ-MnO2. These findings revealed that after reductive dissolution by phenol and reoxidation by dissolved O2 throughout continuous redox cycling, δ-MnO2 became less reactive rather than being regenerated. These results can provide new insights into the understanding of the oxidation of organic contaminants by manganese oxides in the natural environment.

Sorption of Non-ionic Aromatic Organics to Mineral Micropores: Interactive Effect of Cation Hydration and Mineral Charge Density.

The influence of K+ and Ca2+ on the sorption of non-ionic aromatic contaminants (1,4-dinitrobenzene and p-xylene) on a series of microporous zeolite minerals (HZSM-5) with various surface charge densities was investigated. For zeolites with high or low charge density (>1.78 or <0.16 sites/nm2), K+ and Ca2+ had negligible influence on the sorption of organics, which mainly occurred at the hydrophobic nanosites. For zeolites with charge density in the moderate range (0.16-1.78 sites/nm2), the sorption of organics was strongly dependent upon the cation hydration effect. K+ with a lower hydration free energy greatly favored sorption of organics to the micropores compared to Ca2+. Differential scanning calorimetry and X-ray photoelectron spectroscopy results indicated that K+ can reduce the water affinity and promote specific sorption of organics in the zeolites with moderate charge density. The above mechanisms were successfully applied to explain the retention of 1,4-dinitrobenzene and p-xylene on four natural minerals (smectite, illite, kaolinite, and mordenite). This study shed new insights on how cation hydration influences sorption interactions of non-ionic aromatic contaminants at mineral-water interfaces as a function of the mineral charge density.

Dual Alkali Solvent System for CO2 Capture from Flue Gas.

A novel two-aqueous-phase CO2 capture system, namely the dual alkali solvent (DAS) system, has been developed. Unlike traditional solvent-based CO2 capture systems in which the same solvent is used for both CO2 absorption and stripping, the solvent of the DAS system consists of two aqueous phases. The upper phase, which contains an organic alkali 1-(2-hydroxyethyl) piperazine (HEP), is used for CO2 absorption. The lower phase, which consists of a mixture of K2CO3/KHCO3 aqueous solution and KHCO3 precipitate, is used for CO2 stripping. Only a certain kind of amine (such as HEP) is able to ensure the phase separation, satisfactory absorption efficiency, effective CO2 transfer from the upper phase to the lower phase, and regeneration of the upper phase. In the meantime, due to the presence of K2CO3/KHCO3 in the lower phase, HEP in the upper phase is capable of being regenerated from its sulfite/sulfate heat stable salt, which enables the simultaneous absorption of CO2 and SO2/SO3 from the flue gas. Preliminary experiments and simulations indicate that the implementation of the DAS system can lead to 24.0% stripping energy savings compared to the Econamine process, without significantly lowering the CO2 absorption efficiency (∼90%).

Low-Resistance Dual-Purpose Air Filter Releasing Negative Ions and Effectively Capturing PM2.5.

The fatal danger of pollution due to particulate matter (PM) calls for both high-efficiency and low-resistance air purification materials, which also provide healthcare. This is however still a challenge. Herein, a low-resistance air filter capable of releasing negative ions (NIs) and efficiently capturing PM2.5 was prepared by electrospinning polyvinylidene fluoride (PVDF) fibers doped with negative ions powder (NIPs). The air-resistance of fibrous membranes decreased from 9.5 to 6 Pa (decrease of 36%) on decreasing the average fiber diameter from 1.16 to 0.41 µm. Moreover, the lower rising rate of air-resistance with reduction in pore size, for fibrous membranes with thinner fiber diameter was verified. In addition, a single PVDF/NIPs fiber was provided with strong surface potentials, due to high fluorine electronegativity, and tested using atomic force microscopy. This strong surface potential resulted in higher releasing amounts of NIs (RANIs). Interestingly, reduction of fiber diameter favored the alleviation of the shielding effects on electric field around fibers and promoted the RANIs from 798 to 1711 ions cc-1. Moreover, by regulating the doping contents of NIPs, the RANIs increased from 1711 to 2818 ions cc-1. The resultant fibrous membranes showed low air resistance of 40.5 Pa. Field-tests conducted in Shanghai showed stable PM2.5 purification efficiency of 99.99% at high RANIs, in the event of haze.

Cleanable Air Filter Transferring Moisture and Effectively Capturing PM2.5.

The lethal danger of particulate matter (PM) pollution on health leads to the development of challenging individual protection materials that should ideally exhibit a high PM2.5 purification efficiency, low air resistance, an important moisture-vapor transmission rate (MVTR), and an easy-to-clean property. Herein, a cleanable air filter able to rapidly transfer moisture and efficiently capture PM2.5 is designed by electrospinning superhydrophilic polyacrylonitrile/silicon-dioxide fibers as the adsorption-desorption vector for moisture-vapor, and hydrophobic polyvinylidene fluoride fibers as the repellent components to avoid the formation of capillary water under high humidity. The desorption rate of water molecules increases from 10 to 18 mg min-1 , while the diameters of polyacrylonitrile fibers reduce from 1.02 to 0.14 µm. Significantly, by introducing the hydroxyl on the surface of polyacrylonitrile nanofibers, rapid adsorption-desorption of the water molecules is observed. Moreover, by constructing a hydrophobic to super-hydrophilic gradient structure, the MVTR increases from 10 346 to 14 066 g m-2 d-1 . Interestingly, the prepared fibrous membranes is easy to clean. More importantly, benefiting from enhanced slip effect, the resultant fibrous membranes presented a low air resistance of 86 Pa. A field test in Shanghai shows that the air filter maintains stable PM2.5 purification efficiency of 99.99% at high MVTR during haze event.

Slip-Effect Functional Air Filter for Efficient Purification of PM2.5.

Fabrication of air filtration materials (AFM) that allow air to easily flow through while retaining particles is a significant and urgent need due to the harmful airborne particulate matter pollution; however, this is still a challenging research area. Herein, we report novel slip-effect functional nanofibrous membranes with decreased air resistance (reduction rate of 40%) due to the slip flow of air molecules on the periphery of nanofibers. This was achieved through careful control over the diameters of electrospun polyacrylonitrile fibers and aperture size of fiber assembly. Fiber assembly with 86% of fiber diameters between 60-100 nm was found to be most effective for slip flow, as these diameters are close to the mean free path of air molecules (65.3 nm). Significantly, an equilibrium factor τ = df/d2 has been introduced to elucidate the effect of distance of adjacent fibers on the drag force of airflow. Furthermore, the most effective aperture size (>3.5 µm) for slip-effect has been determined. Ultimately, the new material displayed low air resistance of 29.5 Pa, high purification efficiency of 99.09%, good transmittance of 77%, and long service life. The successful fabrication of such materials can facilitate the development of high-performance AFMs for various applications.

Electret Polyvinylidene Fluoride Nanofibers Hybridized by Polytetrafluoroethylene Nanoparticles for High-Efficiency Air Filtration.

Airborne particulate matter (PM) pollution has become a severe environmental concern calling for electret fibrous materials with high filtration efficiency and low pressure drop. However, restraining the dissipation of the electric charges in service to ensure the stabilized electrostatic force of the fibers for effectively adsorbing particles is extremely important and also challenging. Herein, we report novel electret nanofibrous membranes with numerous charges and desirable charge stability using polyvinylidene fluoride (PVDF) as the matrix polymer and polytetrafluoroethylene nanoparticles (PTFE NPs) as an inspiring charge enhancer through the in situ charging technology of electrospinning. Benefiting from the employment of PTFE NPs and optimized injection energy, the fibrous membranes are endowed with elevated surface potentials from 0.42 to 3.63 kV and reduced decrement of charges from 75.4 to 17.5%, which contribute to the ameliorative stability of filtration efficiency. Significantly, an electret mechanism is proposed, while deepened depth of the energy level and incremental polarized dipole charges with increasing PTFE NP concentrations and injection energy have been confirmed through the measurement of open-circuit thermally stimulated discharge and surface potential decay. Ultimately, the resultant fibrous membrane exhibited a high filtration efficiency of 99.972%, a low pressure drop of 57 Pa, a satisfactory quality factor of 0.14 Pa(-1), and superior long-term service performance. The successful fabrication of such an intriguing material may provide a new approach for the design and development of electret materials for PM2.5 governance.