Donor–Acceptor Fluorophores for Energy-Transfer-Mediated Photocatalysis

Triplet–triplet energy transfer (EnT) is a fundamental activation pathway in photocatalysis. In this work, we report the mechanistic origins of the triplet excited state of carbazole-cyanobenzene donor–acceptor (D–A) fluorophores in EnT-based photocatalytic reactions and demonstrate the key factors that control the accessibility of the 3LE (locally excited triplet state) and 3CT (charge-transfer triplet state) via a combined photochemical and transient absorption spectroscopic study. We found that the energy order between 1CT (charge transfer singlet state) and 3LE dictates the accessibility of 3LE/3CT for EnT, which can be effectively engineered by varying solvent polarity and D–A character to depopulate 3LE and facilitate EnT from the chemically more tunable 3CT state for photosensitization. Following the above design principle, a new D–A fluorophore with strong D–A character and weak redox potential is identified, which exhibits high efficiency for Ni(II)-catalyzed cross-coupling of carboxylic acids and aryl halides with a wide substrate scope and high selectivity. Our results not only provide key fundamental insight on the EnT mechanism of D–A fluorophores but also establish its wide utility in EnT-mediated photocatalytic reactions

Higher Dietary Se Intake Is Associated With the Risk of New-Onset Fracture: A National Longitudinal Study for 20 Years

Background: The association between dietary selenium (Se) intake and osteoporosis-related fractures remains inconsistent. We aimed to examine the dose relationship between Se intake and incident fracture among Chinese adults. Methods: The dietary data were retrieved from the China Health and Nutrition Survey conducted between 1991 and 2011, and 17,150 participants aged above 20 were included. A 3-day, 24-h recall of food intake was performed to assess cumulative average dietary Se intake. The fracture was based on self-report in each survey between 1997 and 2011. The association between Se intake and fracture was tested by Cox regression, and the non-linear association was examined by restricted cubic splines (RCS). Results: There were 976 fracture cases during a mean of 10.2 years follow-up. In a fully adjusted Cox model, across the quartiles of Se intake, the hazard ratios (HRs) for fracture were 1.07 (95% CI .86–1.33), 1 (reference), 1.25 (95% CI 1.02–1.53), and 1.33 (95% CI 1.07–1.65). RCS showed a parabolic association (P non-linear = 0.037) between Se and fracture for men as well as a U-shape dose-response (P non-linear = 0.04) between Se and fracture for subjects living in highly urbanized areas. Conclusion: In conclusion, there is a non-linear association between selenium intake and fracture, with higher intake associated with increased risk. The shape of the association varies by gender and urbanization level

Analyzing the characteristics and reason for the ground collapse hazard in Shenzhen

To ascertain the causes of ground collapse in Shenzhen and put forward prevention and control measures, this paper collects ground collapse accidents in Shenzhen between 2016 and 2020 and analyses the spatial and temporal distribution, hazard degree of ground collapse, and causes of ground collapse through field investigation, statistical data analysis and GIS spatial analysis. The results show that ground collapse disasters in Shenzhen are in a stage of continuous growth, most of which are small-scale ones, and most of which occur in the rainy season, especially from May to August. The disaster sites of ground collapse are mainly in Futian District, Luohu District and Guangming District, and the main sites of ground collapse are municipal roads and sidewalks. The main reason for ground collapse disasters is damage to water pipelines, damage to culverts, improper construction, rainwater erosion, settlement of soft soil, excessive vehicle loads and so on. Among them, water pipeline damage and improper construction are the main causes of ground collapse. The research results can provide some reference for the prevention and control of ground collapse in Shenzhen and other similar cities

Drought-Modulated Boreal Forest Fire Occurrence and Linkage with La Nina Events in Altai Mountains, Northwest China

Warming-induced drought stress and El Nino-associated summer precipitation failure are responsible for increased forest fire intensities of tropical and temperate forests in Asia and Australia. However, both effects are unclear for boreal forests, the largest biome and carbon stock over land. Here, we combined fire frequency, burned area, and climate data in the Altai boreal forests, the southmost extension of Siberia’s boreal forest into China, and explored their link with El Nino–Southern Oscillation (ENSO). Surprisingly, both summer drought severity and fire occurrence showed significant (p < 0.05) correlation with La Nina events of the previous year and therefore provide an important reference for forest fire prediction and prevention in Altai. Despite a significant warming trend, the increased moisture over Altai has largely offset the effect of warming-induced drought stress and led to an insignificant fire frequency trend in the last decades, resulting in largely reduced burned area since the 1980s. The reduced burned area can also be attributed to fire suppression efforts and greatly increased investment in fire prevention since 1987

Analytical and numerical investigation of trapped ocean waves along a submerged ridge

Based on the linear shallow-water equations, new analytical solutions are derived for trapped waves over a ridge with a hyperbolic-cosine squared cross-sectional profile which may be used to idealize many real-world ocean ridges. In the new analytical formulation, the free surface of the trapped waves is described using the combination of the first and second kinds of the associated Legendre functions, which is further analysed to reveal the existence of both symmetrical and anti-symmetrical trapped waves on the ridge under consideration. New algebraic equations are also derived to depict the wave dispersion relationships, allowing explicit quantification of their sensitivity to the topographic profile. Furthermore, a ray-tracing method is applied to interpret the propagation paths of trapped waves over the ridge and better understand the excitation mechanisms. Finally, an extensively validated Boussinesq wave model is used to conduct numerical experiments for trapped waves induced by tsunamis. The numerical predictions are consistent with the new analytical solutions, which effectively confirms the validity of the new analytical framework for trapped waves over a more general type of oceanic ridges

Effects of Temperature and Ytterbium Sensitizing on Upconversion Characteristics in Erbium-doped Tellurite Glasses

International audienceTellurite glasses 75TeO2-20ZnO-(4.6-x)La2O3-0.4Er2O3-xYb2O3 (x=0, 0.4, 0.8, 2.0, 3.2, 4.0) were prepared by conventional melt-quenching method. The effects of temperature (8-300K) and the ytterbium concentration on upconversion characteristics were investigated. When the Yb3+ concentration is 2mol%, the upconversion emission intensities around 545nm and 657nm present 6-fold and 4-fold enhancement, respectively, compared with Er3+-doped glass at room temperature. The green emission intensities around 530nm present monotonic increase with increasing temperature from 8K to 300K. The green emission intensities around 545nm increase with increasing temperature from 8K to 80K and reach the maximum at around 80K, then decrease with increasing temperature from 80K to 300K. The characteristics of the red emission intensity around 657nm are similar to the green emission intensity around 545nm. The effects of temperature and concentration of ytterbium on upconversion characteristics are analyzed by rate equations in details, which match well with the experiment results