The first highly enantioselective CuI‐catalyzed azide‐alkyne cycloaddition (CuAAC) of tertiary alcohols and their kinetic resolution is reported. This approach allows facile access to multifunctional ...tertiary alcohols featuring an α‐ethynyl or α‐triazole moiety, and represents the first successful kinetic resolution of racemates with a tetrasubstituted carbon stereocenter via CuAAC. Newly developed pyridinebisoxazoline (PYBOX) ligands with a C4 phosphonate group play a key role.
Preparation of multifunctional tertiary alcohols featuring an α‐ethynyl or α‐triazole moiety is described via enantioselective CuI‐catalyzed azide‐alkyne cycloaddition (CuAAC) of tertiary alcohols in the presence of phosphonate‐functionalized pyridinebisoxazoline (PYBOX) ligands. The method achieves kinetic resolution of racemates with a tetrasubstituted carbon stereocenter.
Understanding the drivers behind urban floods is critical for reducing its devastating impacts to human and society. This study investigates the impacts of recent urban development on hydrological ...runoff and urban flood volumes in a major city located in northern China, and compares the urbanization impacts with the effects induced by climate change under two representative concentration pathways (RCPs 2.6 and 8.5). We then quantify the role of urban drainage system in mitigating flood volumes to inform future adaptation strategies. A geo-spatial database on landuse types, surface imperviousness and drainage systems is developed and used as inputs into the SWMM urban drainage model to estimate the flood volumes and related risks under various urbanization and climate change scenarios. It is found that urbanization has led to an increase in annual surface runoff by 208 to 413%, but the changes in urban flood volumes can vary greatly depending on performance of drainage system along the development. Specifically, changes caused by urbanization in expected annual flood volumes are within a range of 194 to 942%, which are much higher than the effects induced by climate change under the RCP 2.6 scenario (64 to 200%). Through comparing the impacts of urbanization and climate change on urban runoff and flood volumes, this study highlights the importance for re-assessment of current and future urban drainage in coping with the changing urban floods induced by local and large-scale changes.
The study is set in a major city located in Northern China with a focus on comparing the impacts of recent urbanization and future climate change on urban runoff and flood volumes, in particular taking into account the role of urban drainage. Display omitted
•Investigate changes in landuse and drainage systems to assess urbanization impacts•Projections of climate change based on 5 bias-corrected GCMs under RCP 2.6 and 8.5•Evaluate hydrological runoff and total flood volume using SWMM drainage modeling•Compare effects of climate change and urbanization on urban flood volume and risk•Assess the role of urban drainage in mitigating urban flood volume
In this paper, we propose a switchable bi-functional metamaterial device based on a hybrid gold-vanadium dioxide (VO
) nanostructure. Utilizing the property of a metal-to-insulator transition in VO
, ...perfect absorption and asymmetric transmission (AT) can be thermally switched for circularly polarized light in the near-infrared region. When VO
is in the metallic state, the designed metamaterial device behaves as a chiral-selective plasmonic perfect absorber, which can result in an optical circular dichroism (CD) response with a maximum value ∼ 0.7. When VO
is in the insulating state, the proposed metamaterial device exhibits a dual-band AT effect. The combined hybridization model and electromagnetic field distributions are presented to explain the physical mechanisms of chiral-selective perfect absorption and AT effect, respectively. The influences of structure parameters on CD response and AT effect are also discussed. Moreover, the proposed switchable bi-functional device is robust against the incident angle for obtaining perfect absorption and strong CD response as well as the AT effect. Our work may provide a promising path for the development of multifunctional optoelectronic devices, such as thermal emitters, optical modulators, CD spectroscopy, optical isolator, etc.
Medium-entropy alloys strengthened by the L12-type coherent precipitates were recently proposed, whereas the mechanical property still needs to be improved. Here, we demonstrated a strategy for ...notably improving the strength of the representative (CoCrNi)94Ti3Al3 alloy, in which the refinement of grain structures and the promotion of precipitation were concurrently achieved by pre-strain followed by aging. A refined grain structure containing incoherent σ-precipitates and a large number of coherent L12-precipitates was formed, which enhances the yield strength and ultimate tensile strength up to 1431 MPa and 1683 MPa respectively. Furthermore, decreasing pre-strain temperature or increasing strain further aids the enhancement. The present study opens an avenue for fabricating high-performance precipitation-strengthened alloys.
Export of mRNA from the nucleus to the cytoplasm is a critical process for all eukaryotic gene expression. As mRNA is synthesized, it is packaged with a myriad of RNA‐binding proteins to form ...ribonucleoprotein particles (mRNPs). For each step in the processes of maturation and export, mRNPs must have the correct complement of proteins. Much of the mRNA export pathway revolves around the heterodimeric export receptor yeast Mex67•Mtr2/human NXF1•NXT1, which is recruited to signal the completion of nuclear mRNP assembly, mediates mRNP targeting/translocation through the nuclear pore complex (NPC), and is displaced at the cytoplasmic side of the NPC to release the mRNP into the cytoplasm. Directionality of the transport is governed by at least two DEAD‐box ATPases, yeast Sub2/human UAP56 in the nucleus and yeast Dbp5/human DDX19 at the cytoplasmic side of the NPC, which respectively mediate the association and dissociation of Mex67•Mtr2/NXF1•NXT1 onto the mRNP. Here we review recent progress from structural studies of key constituents in different steps of nuclear mRNA export. These findings have laid the foundation for further studies to obtain a comprehensive mechanistic view of the mRNA export pathway.
Nuclear export of mRNA, in the form of ribonucleoprotein particles (mRNPs), is governed by the highly regulated alterations in mRNP protein composition known as mRNP remodeling. Central to mRNP remodeling are two DEAD‐box ATPases, Sub2 and Dbp5, which respectively mediate the assembly of export‐competent mRNPs in the nucleus and the release of mRNPs into the cytoplasm. Here we provide an overview on structural studies of key steps in mRNA export.
Molybdenum sulfides are very attractive noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) from water. The atomic structure and identity of the catalytically active sites ...have been well established for crystalline molybdenum disulfide (c-MoS2) but not for amorphous molybdenum sulfide (a-MoSx), which exhibits significantly higher HER activity compared to its crystalline counterpart. Here we show that HER-active a-MoSx, prepared either as nanoparticles or as films, is a molecular-based coordination polymer consisting of discrete Mo3S13(2-) building blocks. Of the three terminal disulfide (S2(2-)) ligands within these clusters, two are shared to form the polymer chain. The third one remains free and generates molybdenum hydride moieties as the active site under H2 evolution conditions. Such a molecular structure therefore provides a basis for revisiting the mechanism of a-MoSx catalytic activity, as well as explaining some of its special properties such as reductive activation and corrosion. Our findings open up new avenues for the rational optimization of this HER electrocatalyst as an alternative to platinum.
This study aims to enhance conventional vibration energy harvesting systems (VEHs) by repositioning the piezoelectric patch (PZT) in the middle of a fixed–fixed elastic steel sheet instead of the ...root, as is commonly the case. The system is subjected to an axial simple harmonic force at one end to induce transversal vibration and deformation. To further improve power conversion, a baffle is strategically installed at the point of maximum deflection, introducing a slapping force to augment electrical energy harvesting. Employing the theory of nonlinear beams, the equation of motion for this nonlinear elastic beam is derived, and the method of multiple scales (MOMS) is used to analyze the phenomenon of parametric excitation. This study demonstrates through experiments and theoretical analysis that the second mode yields better power generation benefits than the first mode. Additionally, the voltage generation benefits of the enhanced system with the added baffle (slapping force) surpass those of traditional VEH systems. Overall, the proposed model proves feasible and holds promising potential for efficient vibration energy harvesting applications in various industrial sectors.
To better understand the creep mechanical behavior of salt rock under very long-term tests and more accurately predict the long-term deformation of the salt caverns, a series of long-term uniaxial ...creep tests lasting for 21000 h (875 days) were carried out. The results show that the creep strain and creep rate of salt rock increase with the increase of axial stress. The initial creep stage under lower stresses lasted for 4.3–8.3 months, which was much higher than that under high stresses. Predicting the true creep rate of the salt cavern based on the test results of the creep rate in this paper is more accurate than the existing research results. A new nonlinear creep-damage constitutive model is proposed by introducing the nonlinear damage body and using the fractional derivative theory. Using the presented model and the classic creep constitutive models to fit the experimental data, it is found that the presented model best characterizes the creep evolution characteristics of salt rock. The fitting function obtained from the experimental data at different times predicts the final creep results, revealing that the longer the test duration, the more accurate the predicted results. The research in this paper provides the necessary basis for intensive investigation and prediction of the long-term creep mechanical behavior of salt storage caverns.
Many workers who just arrived at the third line had ideological problems such as fear of hardship, fatigue, difficulty, and not settling down to work. The Party committees and political departments ...in third line regions immediately carried out in-depth ideological education. Through education on the situation and task of preparing for war, the strategic idea of constructing third line rooted in workers’ hearts deeply. The Workers, with a posture of facing war, were working against time to engage in construction. Through class education that recalled sufferings in old society and contrasted them with happiness in new society, workers carried out construction with strong class emotions, swearing to protect Socialist New China. By lively learning and utilizing Chairman Mao’s writings, workers improved their thinking, defied difficulties, and dared to fight tough battles, striving to become good workers of Chairman Mao. The effective ideological education made third line construction team quickly become strong, which played a powerful arming thought role in the generation of hardworking and pioneering spirit.
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