Impact of High-Speed Rail Construction on the Environmental Sustainability of China’s Three Major Urban Agglomerations

Under the background of global warming, it is of great significance to explore how to realize environmentally sustainable development. This paper takes China’s three major urban agglomerations as the research objects: Yangtze River Delta, Beijing–Tianjin–Hebei, and Pearl River Delta. Generally, we use carbon emission efficiency to represent the sustainable development of the environment. Then we use the city-level panel data of the three urban agglomerations from 2006 to 2019 to construct the slacks-based measure integrating data envelopment (SBM-DEA) model for calculating each city’s carbon dioxide emission efficiency. Finally, we construct the spatial difference-in-differences (SDID) model to explore the impact of high-speed rail construction on each urban agglomeration’s carbon dioxide emission efficiency and its internal mechanism. The findings are as follows: (1) On the whole, high-speed rail construction improves urban agglomerations’ carbon dioxide emission efficiency. Meanwhile, it has a positive spatial spillover effect on surrounding areas. (2) In terms of urban agglomerations, high-speed rail construction has significantly promoted carbon emission efficiency in the Beijing–Tianjin–Hebei region. However, it has had negative external effects on the surrounding areas. (3) From the perspective of mechanism analysis, the construction of high-speed rail has promoted manufacturing agglomeration in the Pearl River Delta region and, at the same time, has had a negative impact on the local carbon dioxide emission efficiency. This study has strong policy implications for promoting the sustainable development of the three major urban agglomerations

Predicting a novel two-dimensional BN material with a wide band gap

Based on density functional theory, a new two-dimensional boron nitride, Pmma BN, is proposed and studied in detail for the first time. The stability of Pmma BN is demonstrated using phonon spectra, ab initio molecular dynamics simulations at 300 and 500 K, and in-plane elastic constants. The orientation dependences of the Young’s modulus and Poisson’s ratio show that Pmma BN has large mechanical anisotropy. Pmma BN is an indirect band gap semiconductor material with a band gap of 5.15 eV and the hole and electron effective masses have high anisotropy. The electron carrier mobilities of Pmma BN along the x and y directions are similar, while the hole carrier mobility along the y direction is more than double that along the x direction. The band gap of Pmma BN remains indirect under the effect of uniaxial tensile strain and its adjustable range reaches 0.64 eV when the uniaxial strain is applied along the x direction. When uniaxial strain is applied along the y direction, the positions of the conduction band minimum and valence band maximum change. Pmma BN under uniaxial strain shows strong optical absorption capacity in the ultraviolet region. To explore its potential clean energy applications, the thermoelectric properties of Pmma BN are also investigated

Using Particle Residence Time Distributions as an Experimental Approach for Evaluating the Performance of Different Designs for a Pilot-Scale Spray Dryer

The performances of four different designs for a pilot-scale spray dryer have been evaluated and compared based on experimentally measured particle residence time distributions (RTD), recovery rates and physical properties of spray-dried fresh skim milk. The RTDs have been measured using a dye pulse injection method, and the measurements have been fitted to models using continuous stirred-tank reactors in series (CSTR-TIS) for quantitative performance evaluation and comparison. Conical drying chambers and a box connection design have been used in the latest dryer design to reduce the amount of wall deposition and provide a smoother gas flow pattern. The particle-to-gas mean residence time ratio for the latest design is significantly closer to unity (1.6 s/s to 1.0 s/s) compared with earlier designs (2.6 s/s to 1.5 s/s). The latest design has a wider spread of RTD (n = 5–8) compared with earlier designs (n = 13–18), which may be linked to the recirculation zone in the box connection. Although the latest design has a wider spread of RTD, the conical design has shown promising results compared with a cylindrical drying chamber in terms of overall wall deposition behaviours

Theoretical Treatment of CH3NH3PbI3 Perovskite Solar Cells

Hybrid halide perovskite solar cells (PSCs) giving over 22% power conversion efficiencies (PCEs) have attracted considerable attention. Although perovskite plays a significant role in the operation of PSCs, the fundamental theories associated with perovskites have not been resolved in spite of the increase in research. In this Minireview, we assess the current understanding, based on the first-principles calculations, of structural and electronic properties, defects, ionic diffusion, and shift current for CH3NH3PbI3 perovskite, and the effect of ionic transport on the hysteresis of current-voltage curves in PSCs. The shift current connected to the possible presence of ferroelectricity is also discussed. The current state-of-the-art and some open questions regarding PSCs are also highlighted, and the benefits, challenges, and potentials of perovskite for use in PSCs are stressed

Modulation of cadmium-induced phytotoxicity in Cabomba caroliniana by urea involves photosynthetic metabolism and antioxidant status

Urea is a widespread organic pollutant, which can be a nitrogen source, playing different roles in the growth of submerged macrophytes depending on concentrations, while high cadmium (Cd) concentrations are often toxic to macrophytes. In order to evaluate the combined effect of urea and Cd on a submerged macrophyte, Cabomba caroliniana, the morphological and physiological responses of C. caroliniana in the presence of urea and Cd were studied. The results showed that high concentrations of urea (400 mg L-1) and Cd (500 mot L-1) had negative effects on C. carolinicuza. There were strong visible symptoms of toxicity after 4 days of exposure under Cd-alone, 400 mg L-1 urea, and Cd + 400 mg L-1 urea treatments. In addition, 400 mg L-1 urea and Cd had adverse effects on C. caroliniana's pigment system. Significant losses in chlorophyll fluorescence and photosynthetic rates, as well as Rubisco activity were also observed under Cd-alone, 400 mg L-1 urea, and Cd + 400 mg L-1 urea treatments. 400 mg L-1 urea markedly enhanced Cd toxicity in C. caroliniana, reflected by a sharp decrease in photosynthetic activity and more visible toxicity symptoms. The results of thiobarbituric acid reactive substances (TBARS) pointed to extreme oxidative stress in C. caroliniana induced under Cd or 400 mg L-1 urea exposure. Exogenous ascorbate (AsA) protected C. caroliniana from adverse damage in 400 mg L-1 urea, which further corroborated the oxidative stress claim under 400 mg L-1 urea. However, results also demonstrated that lower urea concentration (10 mg L-1) alleviated Cd-induced phytotoxicity by stimulating chlorophyll synthesis and photosynthetic activity, as well as activating the activity of catalase (CAT) and glutathione-S-transferase (GST), which may explain the alleviating effect of urea on C. caroliniana under Cd stress