1,2‐Bisphosphines have been identified as one class of important and powerful chiral ligands in asymmetric catalysis with transition metals. Herein, a copper(I)‐catalyzed asymmetric ...hydrophosphination of α,β‐unsaturated phosphine sulfides was developed with the assistance of “soft–soft” interaction between copper(I)‐catalyst and the phosphine sulfide moiety, which afforded 1,2‐bisphosphine derivatives with diversified electronic nature and steric hindrance in high to excellent yields with high to excellent enantioselectivity. Moreover, the challenging catalytic asymmetric hydrophosphination/protonation reaction was achieved with excellent enantioselectivity. Strikingly, the dynamic kinetic resolution of racemic diarylphosphines was also successfully carried out with high to excellent diastereo‐ and enantioselectivities. Interestingly, the nucleophilic copper(I)‐diphenylphosphide species was characterized by 31P NMR spectrum and mass spectrum. At last, three products were transformed to chiral 1,2‐bisphosphines, which were employed as ligands in Rh‐catalyzed asymmetric hydrogenation of α‐amino‐α,β‐unsaturated ester. The α‐amino acid derivative was produced in high enantioselectivity, which demonstrated the utility of the present methodology.
A catalytic asymmetric conjugate hydrophosphination of α,β‐unsaturated phosphine sulfides with diarylphosphines allows rapid construction of chiral 1,2‐bisphosphine derivatives with diversified electronic nature and steric hindrance. This reaction is facilitated by the “soft–soft” interaction between copper(I) catalysts and phosphine sulfides.
Despite much research on probabilistic key predistribution schemes for wireless sensor networks over the past decade, few formal analyses exist that define schemes' resilience to node-capture attacks ...precisely and under realistic conditions. In this paper, we analyze the resilience of the q-composite key predistribution scheme, which mitigates the node capture vulnerability of the Eschenauer-Gligor scheme in the neighbor discovery phase. We derive scheme parameters to have a desired level of resiliency, and obtain optimal parameters that defend against different adversaries as much as possible. We also show that this scheme can be easily enhanced to achieve the same "perfect resilience" property as in the random pairwise key predistribution for attacks launched after neighbor discovery. Despite considerable attention to this scheme, much prior work explicitly or implicitly uses an incorrect computation for the probability of link compromise under node-capture attacks and ignores the real-world transmission constraints of sensor nodes. Moreover, we derive the critical network parameters to ensure connectivity in both the absence and presence of node-capture attacks. We also investigate node replication attacks by analyzing the adversary's optimal strategy.
Security is an important issue in wireless sensor networks (WSNs), which are often deployed in hostile environments. The q-composite key predistribution scheme has been recognized as a suitable ...approach to secure WSNs. Although the q-composite scheme has received much attention in the literature, there is still a lack of rigorous analysis for secure WSNs operating under the q-composite scheme in consideration of the unreliability of links. One main difficulty lies in analyzing the network topology, whose links are not independent. Wireless links can be unreliable in practice due to the presence of physical barriers between sensors or because of harsh environmental conditions severely impairing communications. In this paper, we resolve the difficult challenge and investigate topological properties related to node degree in WSNs operating under the q-composite scheme with unreliable communication links modeled as independent ON/OFF channels. Specifically, we derive the asymptotically exact probability for the property of minimum degree being at least k, present the asymptotic probability distribution for the minimum degree, and demonstrate that the number of nodes with a fixed degree is in distribution asymptotically equivalent to a Poisson random variable. We further use the theoretical results to provide useful design guidelines for secure WSNs. Experimental results also confirm the validity of our analytical findings.
Support Vector Machine(SVM) algorithm has the advantages of complete theory, global optimization, strong adaptability, and good generalization ability because of it on the basis of Statistical ...Learning Theory's(SLT). It is a new hot spot in machine learning research. This article first systematically studies some basic concepts of SVM and the optimization of SVM. In addition, this article also discusses the application of SVM in modern machining, protein prediction and face detection. Through these applications, the performance characteristics and advantages of SVM can be reflected. At the end of the article, some shortcomings of SVM are introduced, and the development trend of subsequent SVM is pointed out accordingly.
Circular RNAs (circRNAs) are long, non-coding RNAs that result from the non-canonical splicing of linear pre-mRNAs. However, the characteristics and the critical role of circRNA in ...co-/post-transcriptional regulation were not well recognized until the "microRNA sponge" function of circRNA is discovered. Recent studies have mainly been devoted to the function of the circular RNA sponge for miR-7 (ciRS-7) and sex-determining region Y (SRY) by targeting microRNA-7 (miR-7) and microRNA-138 (miR-138), respectively. In this review, we illustrate the specific role of circRNAs in a wide variety of cancers and in regulating the biological behavior of cancers via miR-7 or miR-138 regulation. Furthermore, circRNA, together with its gene silencing ability, also shows its potential in RNA interference (RNAi) therapy by binding to target RNAs, which provides a novel perspective in cancer treatment. Thus, this review concerns the biogenesis, biological function, oncogenesis, progression and possible therapies for cancer involving circRNAs.
The South China Craton consists of the Yangtze and Cathaysia blocks that were welded together along the Jiangnan Fold Belt in the Neoproterozoic. The Neoproterozoic magmatism in the western and ...northern margins of the Yangtze Block is characterized by voluminous volcano-sedimentary strata, numerous felsic intrusions and many mafic-ultramafic plutons which provide a good opportunity to examine the geodynamics and tectonic evolution of the South China Craton during the assembly and breakup of Rodinia. Based on the geochronological and geochemical data, our study shows that the Neoproterozoic igneous rocks in the western and northern margins of the Yangtze Block were formed in subduction- and rift-related tectonic settings, respectively.
In the western margin of the Yangtze Block, the Neoproterozoic mafic and ultramafic rocks show arc-affinity trace elemental compositions that are indicative of mantle sources enriched by slab fluids. High-δ18O mafic rocks (850–780 Ma) were derived from mantle wedges that were modified by sediment melts, whereas low-δ18O mafic rocks (750–740 Ma) were formed by partial melting of mantle sources further enriched by altered oceanic crust melts. The widespread calc-alkaline I-type granitoids in this region, generated between 870 and 750 Ma, show negative to positive whole rock εNd (−4.9 to +4.8) and variable zircon εHf values (−1.9 to +10.6), similar to those of the contemporary mafic-ultramafic rocks, suggesting that they were produced by melting of the juvenile crust. The 780–750 Ma adakitic granitoids are characterized by high Sr/Y (19–318) and low Y (1.78–17.9 ppm) and have relatively constant εNd (−2.1 to +2.9) and εHf (+4.3 to +7.1) and mantle-like δ18O values (3.40‰ to 6.86‰), suggesting that they were partial melts of a subducted oceanic slab. These three types of igneous rocks demonstrate that the Neoproterozoic magmatism in the western margin of the Yangtze Block was controlled by a continuous subduction system.
However, Neoproterozoic magmatism in the South Qinling Belt at the northern margin of the Yangtze Block generated both arc- and rift-related igneous rocks. The arc-like mafic-ultramafic rocks are thought to have been derived from a subduction-modified lithospheric mantle source, whereas the MORB-affinity mafic rocks were probably sourced from an asthenosphere mantle. Associated Neoproterozoic granitoids were produced by melting of the juvenile mafic crust, except minor felsic rocks derived from the ancient basement. Widespread 800–700 Ma volcano-sedimentary sequences and 650 Ma mafic dike swarms suggest an extensional environment. Neoproterozoic magmatic zircons from felsic volcanic rocks and HP/UHP metamorphic rocks preserve low-δ18O values that were inherited from their protolith which underwent high temperature hydrothermal interaction in a rift setting. On the basis of these observations, the Neoproterozoic magmatism in the South Qinling Belt is proposed to have been controlled by a subduction-transform edge propagator (STEP) in relation to the continuous subduction system at the western margin of the Yangtze Block.
Considering the potential relationship between the digital economy and energy transition, we investigate the effect of the digital economy on the structure of renewable energy consumption and ...generation by employing panel data of 72 countries covering the period 2003–2019. We also investigate the mediating effect of government governance, asymmetry, and heterogeneity between the digital economy and energy transition, and draw several results. First, the digital economy positively affects energy transition; in other words, a 1% increase in the digital economy will boost the renewable energy consumption structure by 0.021% and renewable energy generation structure by 0.106%. Moreover, the digital economy stimulates the renewable energy transition by promoting governments’ governance capabilities. In addition, according to the asymmetric check, the positive effect of the digital economy on energy transition is stronger at higher quantiles. Finally, heterogeneity results indicate that the digital economy positively contributes to renewable energy transition in the high-income countries, and there are regional heterogeneities in the impact of the digital economy on energy transition. These research findings offer valuable policy implications for governments and scholars.
•This paper explores the effects of the digital economy on energy transition.•We further discuss the mediating mechanism, asymmetry, and heterogeneity.•The digital economy positively affects the transition of renewable energy consumption and generation.•Government governance has a positive impact on the relationship between the digital economy and energy transition.•The impact of the digital economy on energy transition is asymmetric and heterogeneous.
This paper investigates the problem of adaptive neural tracking control via output-feedback for a class of switched uncertain nonlinear systems without the measurements of the system states. The ...unknown control signals are approximated directly by neural networks. A novel adaptive neural control technique for the problem studied is set up by exploiting the average dwell time method and backstepping. A switched filter and different update laws are designed to reduce the conservativeness caused by adoption of a common observer and a common update law for all subsystems. The proposed controllers of subsystems guarantee that all closed-loop signals remain bounded under a class of switching signals with average dwell time, while the output tracking error converges to a small neighborhood of the origin. As an application of the proposed design method, adaptive output feedback neural tracking controllers for a mass-spring-damper system are constructed.
Background/Aims: Treatment of breast cancer remains a clinical challenge. This study aims to validate exosomal microRNA-1246 (miR-1246) as a serum biomarker for breast cancer and understand the ...underlying mechanism in breast cancer progression. Methods: The expression levels of endogenous and exosomal miRNAs were examined by real time PCR, and the expression level of the target protein was detected by western blot. Scanning electron and confocal microscopy were used to characterize exosomes and to study their uptake and transfer. Luciferase reporter plasmids and its mutant were used to confirm direct targeting. Furthermore, the functional significance of exosomal miR-1246 was estimated by invasion assay and cell viability assay. Results: In this study, we demonstrate that exosomes carrying microRNA can be transferred among different cell lines through direct uptake. miR-1246 is highly expressed in metastatic breast cancer MDA-MB-231 cells compared to non-metastatic breast cancer cells or non-malignant breast cells. Moreover, miR-1246 can suppress the expression level of its target gene, Cyclin-G2 (CCNG2), indicating its functional significance. Finally, treatment with exosomes derived from MDA-MB-231 cells could enhance the viability, migration and chemotherapy resistance of non-malignant HMLE cells. Conclusions: Together, our results support an important role of exosomes and exosomal miRNAs in regulating breast tumor progression, which highlights their potential for applications in miRNA-based therapeutics.
The exploration of high nuclearity molecular metal oxide clusters and their reactivity is a challenge for chemistry and materials science. Herein, we report an unprecedented giant molecular ...cerium–bismuth tungstate superstructure formed by self‐assembly from simple metal oxide precursors in aqueous solution. The compound, {W14CeIV6O61(W3Bi6CeIII3(H2O)3O14B‐α‐BiW9O333)2}34− was identified by single‐crystal X‐ray diffraction and features 104 metal centers, a relative molar mass of ca. 24 000 and is ca. 3.0×2.0×1.7 nm3 in size. The cluster anion is assembled around a central {Ce6} octahedron which is stabilized by several molecular metal oxide shells. Six trilacunary Keggin anions (B‐α‐BiW9O339−) cap the superstructure and limit its growth. In the crystal lattice, water‐filled channels with diameters of ca. 0.5 nm are observed, and electrochemical impedance spectroscopy shows pronounced proton conductivity even at low temperature.
A giant cerium–bismuth tungstate cluster featuring more than 100 metal ions and a relative molar mass of approximately 24 000 is structurally characterized. The cluster anions form a highly 3D‐porous crystalline lattice featuring water‐filled channels. Proton conductivity measurements show high proton mobility within the framework.
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