Most previous studies exploit the discontinuity in children's school entry age around the enrolment cut-off to identify the effect of delayed school entry on child learning. However, the effect so ...identified is only relevant to children who were 'forced' to enter school late because of being born slightly after the enrolment cut-off. In developing countries, many children voluntarily start school late regardless of their birthdates, for whom the commonly-used discontinuity-based strategy fails to identify the effect relevant to their delayed enrolment. This study exploits community peer effects to estimate the impact of voluntary delay in school entry, using older peers' school entry age to instrument one's own school entry age. Analysing data on nearly 4,000 children from rural northwestern China, we found that while both types of delay in school entry raise the incidence of first-grade repetition, the effect of voluntary delay is much larger than that of forced delay. More specifically, one year of voluntary delay increases a child's likelihood of first-grade retention by 12.4 percentage points, which is more than twice the effect of forced delay.
Conspectus Nanosized supramolecular metallocages have a unique self-assembly process that allows chemists to both understand and control it. In addition, well-defined cavities of such supramolecular ...aggregates have various attractive applications including storage, separation, catalysis, recognition, drug delivery, and many others. Coordination-driven self-assembly of nanosized supramolecular metallocages is a powerful methodology to construct supramolecular metallocages with considerable size and desirable shapes. In this Account, we summarize our recent research on controllable coordination-driven assembly of supramolecular metallocages and infinite cage-based frameworks. To this end, we have chosen flexible ligands that can adopt various conformations and metal ions with suitable coordination sites for the rational design and assembly of metal–organic supramolecular ensembles. This has resulted in various types of metallocages including M3L2, M6L8, M6L4, and M12L8 with different sizes and shapes. Because the kinds of metal geometries are limited, we have found that we can replace single metal ions with metal clusters to alternatively increase molecular diversity and complexity. There are two clear-cut merits of this strategy. First, metal clusters are much bigger than single metal ions, which helps in the construction and stabilization of large metallocages, especially nanosized cages. Second, metal clusters can generate diverse assembly modes that chemists could not synthesize with single metal ions. This allows us to obtain a series of unprecedented supramolecular metallocages. The large cavities and potential unsaturated coordination sites of these discrete supramolecular cages offer opportunities to construct infinite cage-based frameworks. This in turn can offer us a new avenue to understand self-assembly and realize certain various functionalities. We introduce two types of infinite cage-based frameworks here: cage-based coordination polymers and cage-based polycatenanes, which we can construct through coordination bonds and mechanical bonds, respectively. Through either directly linking the unsaturated coordination sites of metallocages or replacing the labile terminal ligands with bridging ligands, we can produce infinite cage-based frameworks based on coordination bonds. We introduce several interesting cage-based coordination polymers, including a single-crystal-to-single-crystal transformation from a M6L8 cage to an infinite cage-based chain. Compared with discrete metallocages, these kinds of materials can give us higher structural stability and complexity, favoring the applications of metallocages. In addition, we discuss how we can use mechanical bonds, such as interlocking and interpenetrating, to construct extended cage-based frameworks. So far, study in this field has focused on polycatenanes constructed from M6L4 and M12L8 cages, as well as a controllable and dynamic self-assembly based on M6L4 metallocages. We also discuss cage-based polycatenanes, which can give dynamic properties to discrete metallocages. We hope that our investigations will bring new insights to the world of the supramolecular metallocages by enlarging its breadth and encourage us to devote more effort to this blossoming field in the future.
Abstract
Many countries have undertaken large and high-profile payment-for-ecosystem-services (PES) programs to sustain the use of their natural resources. Nevertheless, few studies have ...comprehensively examined the impacts of existing PES programs. Grassland Ecological Compensation Policy (GECP) is one of the few pastorally focused PES programs with large investments and long duration, which aim to improve grassland quality and increase herder income. Here we present empirical evidence of the effects of GECP on grassland quality and herder income. Through a thorough and in-depth econometric analysis of remote sensing and household survey data, we find that, although GECP improves grassland quality (albeit to only a small extent) and has a large positive effect on income, it exacerbates existing income inequality among herders within their local communities. The analysis demonstrates that the program has induced herders to change their livestock production behavior. Heterogeneity analysis emphasizes the importance of making sure the programs are flexible and are adapted to local resource circumstances.
Considering the rapid increase of CO
emission, especially from power plants, there is a constant need for materials which can effectively eliminate post-combustion CO
(the main component: CO
/N
= ...15/85). Here, we show the design and synthesis of a Cu(II) metal-organic framework (FJI-H14) with a high density of active sites, which displays unusual acid and base stability and high volumetric uptake (171 cm
cm
) of CO
under ambient conditions (298 K, 1 atm), making it a potential adsorbing agent for post-combustion CO
. Moreover, CO
from simulated post-combustion flue gas can be smoothly converted into corresponding cyclic carbonates by the FJI-H14 catalyst. Such high CO
adsorption capacity and moderate catalytic activity may result from the synergistic effect of multiple active sites.
Gluons may converge to a stable state at a critical momentum in hadrons. This gluon condensation is predicted by a nonlinear QCD evolution equation. We review the understanding of the gluon ...condensation and present a clear physical picture that produces the gluon condensation from the colour glass condensate. We summarize the applications of the GC effect in the p−p(A) collisions and predict that the p−Pb and Pb−Pb collisions at the LHC are close to the energy region of the gluon condensation. We warn that for the next generation of hadron colliders with the increasing of the collision energy, the extremely strong gamma-rays will be emitted in a narrow space of the accelerator due to the gluon condensation effect. Such artificial mini gamma-ray bursts in the laboratory may damage the detectors.
This article estimates the causal effect of primary school entry age on children's cognitive development in rural northwestern China, using data on nearly 1,800 primary school aged children from the ...Gansu Survey of Children and Families. Instrumental variable estimates, exploiting the discontinuity structure in children's school entry age around the enrolment cut-off date, indicate that a 1-year delay in school entry reduces children's scores on a cognitive ability test administered when they were aged 9-12 by 0.11-0.16 standard deviations (of the distribution of test scores). The negative late-school-entry effect is significantly larger in villages with no preprimary schools. It also persists as children advance to higher grades. These findings suggest that delayed school entry, even if it may be rural parents' rational response to resource constraints, can be harmful for children's cognitive development in developing areas with underdeveloped preprimary school systems.
Abstract In the construction of tunnels under existing stations, it is necessary to control their settlement. When there is a pile foundation in the existing station, the pile cutting has a ...significant impact on the settlement of the existing station. To determine the influence of existing piles on the settlement of subway stations, a reasonable pile-cutting time is proposed. Based on the Chengdu Metro Line 9 underpassing the existing Line 1 hatchery station, the settlement law of the tunnel underpassing the existing Line 1 station is analysed via a numerical simulation. Furthermore, the deformation and stress characteristics of the existing piles, pipe roofs, and tunnel linings and the supporting effect on the existing station are discussed. It is concluded that the cutting of existing piles causes a change in the tunnel bearing system, thus resulting in a certain deformation of the station. The influence of different pile cutting times on the settlement of the existing station is then analysed, and it is clarified that the tunnel support stiffness is significantly enhanced after the construction of the secondary lining. At this time, the settlement of the existing pile station is significantly reduced. Finally, through a field investigation, the effect of surface grouting, pipe shed, and multilayer lining on the settlement control of the existing station while the existing pile foundation exists is determined. This research can provide a reference for the settlement control and foundation underpinning of existing stations at ultra-small distances in underground excavation tunnels.
An extraordinary metal-organic framework
with high adsorption and selectivity for the reversible uptake of Cd(ii) has been developed. Further research indicates that such high absorption results from ...an unusual synergy from active sites and the confined cavity. In addition, fast detection of Cd(ii) at low concentrations down to 10 ppm and
reconstruction of the used framework into a fresh one have also been successfully achieved.
The efficient and accurate selection of primary drought-driving factors as the independent variables of drought prediction model is critical in improving drought prediction accuracy. In this study, a ...novel feature selection method based on information changing rate and conditional mutual information (ICR-CMIFS) was proposed and evaluated by the comparison with other feature selection methods from feature selection, simulation, and classification aspects; two artificial intelligence drought prediction models, which treated the factors selected by ICR-CMIFS, correlation analysis (CA) and mutual information maximum (MIM) respectively as independent variables and standardized precipitation evapotranspiration index (SPEI) in 3/6/12-month time scales as dependent variables, were established; the superiority of ICR-CMIFS over CA and MIM methods in the selection of primary climatic drought-driving factors in Yunnan-Guizhou Plateau (YGP) was tested by the performance of the two models. The results revealed: the ICR-CMIFS was superior to the other feature selection methods; both artificial intelligence drought prediction models with the independent variables selected by ICR-CMIFS performed better in terms of correlation coefficient, Nash–Sutcliffe coefficient, root-mean square error and model computing time than by the MIM and CA methods. The outputs can provide an innovative approach in selecting primary drought-driving factors and improving drought prediction accuracy.
•Using students’ home-to-school distance as an instrumental variable to estimate impacts of boarding on primary school students’ mental health.•Boarding has a significantly negative effect (0.455 ...SDs) on their mental health status.•The negative effects of boarding on mental health are larger for students with relatively advantageous backgrounds.
This paper estimates the impacts of boarding on primary school students’ health outcomes, using data on 7606 students from rural areas of two northwestern provinces (Qinghai and Ningxia) of China. Exogenous variations in students’ home-to-school distance are exploited to address potential endogeneity in their boarding status. Instrumental variable estimates suggest that while boarding has little impact on students’ physical health (measured by height-for-age and BMI-for-age z-scores and hemoglobin concentration levels), it has a significantly detrimental effect on their mental health status, amounting to 0.455 standard deviations (SDs) of the distribution of scores on a Mental Health Test (a modified version of the Children’s Manifest Anxiety Scale). The effect of boarding is more pronounced for students with relatively advantageous backgrounds. For example, boarding boys scored 0.544 SDs higher on the Mental Health Test (suggesting more anxiety problems) than nonboarding boys, and boarders from relatively wealthier families scored 0.754 SDs higher than wealthier nonboarders. ‘
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