In natural forests at a demographic equilibrium state, the size frequency distribution (SFD) of trees is linked with their size-dependent growth and mortality rates. While the mean growth rate (MGR) of each size class is generally used for determining the SFD, the variance in the growth rate (VGR) has always been ignored. Here, based on the analyses with Kolmogorov forward equation, we show that in general, the VGR can flatten the slope of the SFD and, in particular, can address the contradiction between the size-dependent MGR and the −2 power-law SFD in the metabolic scaling theory. We traced the origin of the VGR to the intrinsic stochasticity in the allometric growth coefficients of trees and deduced its functional form based on variance propagation. Using the forest censuses data from Barro Colorado Island, we verified the prediction of the VGR and indicated its indispensability in the theory of forest size-structure formation.
The variations in physicochemical properties of airborne particles collected during a typical transition from haze to dust were investigated using single particle analysis with transmission and scanning electron microscopes combined with online measurement of chemical compositions of airborne particles in Beijing in February 2013. The transition was divided into three phases based on the weather condition. During haze pollution (Phase 1), gaseous and particle pollutants enhanced gradually. Results from single particle analysis showed that more coatings and more anthropogenic elements (e.g., S) appeared on the surface of fine and coarse particles, which was probably caused by efficient aqueous-phase reactions under high humidity (70%) condition. Phase 2 was dust intrusion episode. PM10 reached over 1000 mu g m(-3). Larger fractions of mineral particles and bare-like soot particles were observed in fine particles, while the fraction of secondary particles with coatings decreased. The proportion of black carbon in submicron particles also increased. Photochemical oxidation in gas phase likely dominated in secondary formation under high O-3 concentration. After the dust episode (Phase 3), secondary formation enhanced obviously. Soot aged quickly and had a larger mode of 0.45 mu m than the other phases. The size modes of airborne fine particles during Phases 1 and 3 were 0.35 mu m, which were a bit larger than that during Phase 2 (0.24 mu m). These results indicate that dust plumes accompanied with strong wind brought mineral particles in both fine and coarse modes and freshly emitted particles with smaller sizes, and swept away pre-presence air pollutants. This study could provide detailed information on the physicochemical properties of airborne particles during typical severe pollution processes in a short time. Such short-term change should be taken into account in order to more accurately assess the environmental, climatic and health-related effects of airborne particles.
A catalytic system to synthesize α-amino amides from isocyanates and ketimines has been developed using visible light iridium photoredox catalysis via umpolung reactivity of ketimines. Cross-couplings between diverse ketimine and isocyanate substrates have been evaluated, affording the desired α-amino amide products in good yields. In addition, a metal-free catalytic system using perylene and N,N-diisopropylethylamine has been developed. Finally, single-step synthesis of the psychoactive drug benzodiazepine-2-one analogue from one of the coupling products has been achieved, indicating the great application potential of the synthetic method developed herein.
Protected areas (PAs) play a pivotal role in maintaining viable populations of species and minimizing their habitat loss. Globally, there are currently over 200,000 PAs that cover approximately 15% of land area. The post-2020 global biodiversity framework aims to expand this coverage to 30% by 2030. However, focusing only on the percentage coverage of PAs without evaluating their effectiveness may fail to achieve conservation goals. Here, we use a multidimensional approach incorporating species, climate and anthropogenic vulnerabilities to assess the threat levels in over 2500 PAs in China. We identify nearly 10% of PAs as the most threatened PAs in China and about one-fifth PAs as hotspots of climate and anthropogenic vulnerabilities. We also find high climate instability in species vulnerability hotspots, suggesting an elevated likelihood of species' extirpation therein. Our framework could be useful in assessing resiliency of global protected lands and also in selecting near optimal areas for their future expansion.
As a major constituent of aromatic compounds, toluene exists widely in environmental aqueous phases. This research investigated the aqueous-phase OH oxidation of toluene to determine how liquid water changes the radical chemistry of ring-cleavage pathways. Results show that ring-cleavage pathways through the C7 bicyclic peroxy radical (BPR) account for about 70% of total aqueous-phase oxidation pathways, which is similar to that in the gas-phase oxidation. However, detailed ring-cleavage pathways in the aqueous phase change significantly compared with those in the gas phase as shown by the decreased production of glyoxal and methylglyoxal and the enhanced production of formic acid and acetic acid as primary products, which can be attributed to the presence of liquid water. Water facilitates the formation of the BPR whose structure is different from that in the gas-phase oxidation and results in different ring-cleavage pathways through hydrogen-shift reactions. Furthermore, water helps the hydration of acyl radicals formed by the BPR to produce organic acids. With the suggested ring-cleavage mechanisms, a box model can simulate aqueous-phase product distributions better than that with the classical ring-cleavage mechanisms. Given the influence of water on reaction mechanisms, aqueous-phase oxidation of hydrophobic organic compounds may be more important than previously assumed.
Luminophores with tunable emission properties are appealing due to various applications. Among those properties, thermally activated delayed fluorescence (TADF) has been attracting enormous research interests. Herein, we synthesized a 9,9'-spirobifluorene based homo-conjugated molecule 1, which connects a diphenylamino moiety as electron donor and a naphthalimide group as electron acceptor via 2,2'-positions of spirofluorene. Compound 1 displays dual emission behaviour with both blue and orange fluorescence. The one orange fluorescence around 555 nmshows sensitivity to oxygen and a prolonged lifetime of 284 ns in degassed toluene. Such characteristics imply TADF nature for this emission from a charge-transfer excited state. The other emission at 440 nm with blue colour displayed resistance to oxygen quenching and a normal fluorescence lifetime of 1.5 ns. Compared with control molecule, this emission band is assigned as conventional fluorescence from a localized excited state. In addition, dual emission property allows molecule 1 to be modulated to emit white photoluminescence in thin film with a CIE color coordinate of (0.25, 0.33).
This study revisits the association between bilateral relations and trade based on rare-event data from Integrated Data for Event Analysis (IDEA). Our results suggest that a country imports more from another if the two countries are friendlier. We further argue that states face two constraints when attempting to manipulate trade. First, they are constrained by domestic institutions such as elections and Congress. Second, they are constrained by international institutions such as the World Trade Organization (WTO). Our results show that the imports of authoritarian countries follow the flag of politics, but democratic countries' imports are less likely to be affected by bilateral relations. Moreover, WTO membership can gradually restrict democratic states from intervening on imports but has little impact on authoritarian governments.
The identification and characterization of lead-bearing and associated minerals in scales on lead pipes are essential to understanding and predicting the mobilization of lead into drinking water. Despite its long-recognized usefulness in the unambiguous identification of crystalline and amorphous solids, distinguishing between polymorphic phases, and rapid and non-destructive analysis on the micrometer spatial scale, the Raman spectroscopy (RS) technique has been applied only occasionally in the analysis of scales in lead service lines (LSLs). This article illustrates multiple applications of RS not just for the identification of phases, but also compositional and structural characterization of scale materials in harvested lead pipes and experimental pipe-loop/recirculation systems. RS is shown to be a sensitive monitor of these characteristics through analyses on cross-sections of lead pipes, raw interior pipe walls, particulates captured in filters, and scrapings from pipes. RS proves to be especially sensitive to the state of crystallinity of scale phases (important to their solubility) and to the specific chemistry of phases precipitated upon the introduction of orthophosphate to the water system. It can be used effectively alone as well as in conjunction with more standard analytical techniques. By means of fiber-optic probes, RS has potential for in situ, real-time analysis within water-filled pipes.