The fast and living ring‐opening polymerization (ROP) of propylene oxide (PO) by metal‐free catalysis is reported. By using triethyl borane (TEB) and organic Lewis bases (LBs, e.g.: phosphazene base, ...amidine and guanidine) as the catalysts, various alkyl alcohols can effectively initiate the ROP of PO, yielding tailor‐made poly(propylene oxide)s (PPOs) with high regioregularity, predictable molecular weights, and narrow dispersity approaching Poisson distribution. The TEB/LB catalysts present unprecedentedly high activity (turnover frequency of up to 7500 h−1) and a truly living character for the polymerization, as evidenced by kinetic studies that showed fast initiation and growth, unobserved chain‐transfer to PO, chain extension reactions, and the synthesis of various PPO‐based block copolymers with narrow dispersities (Đ<1.1).
Poisson project: The metal‐free, fast, and living ring‐opening polymerization of propylene oxide is performed by a unique masking anion strategy, yielding tailor‐made poly(propylene oxide)s with unprecedented activity, high regioregularity, predictable molecular weights, and narrow dispersity approaching Poisson distribution.
Exotic massless fermionic excitations with nonzero Berry flux, other than the Dirac and Weyl fermions, could exist in condensed matter systems under the protection of crystalline symmetries, such as ...spin-1 excitations with threefold degeneracy and spin-3/2 Rarita-Schwinger-Weyl fermions. Herein, by using the ab initio density functional theory, we show that these unconventional quasiparticles coexist with type-I and type-II Weyl fermions in a family of transition metal silicides, including CoSi, RhSi, RhGe, and CoGe, when spin-orbit coupling is considered. Their nontrivial topology results in a series of extensive Fermi arcs connecting projections of these bulk excitations on the side surface, which is confirmed by (001) surface electronic spectra of CoSi. In addition, these stable arc states exist within a wide energy window around the Fermi level, which makes them readily accessible in angle-resolved photoemission spectroscopy measurements.
In recent years, natural and anthropogenic geohazards have occured frequently all over the world, and field monitoring is becoming an increasingly important task to mitigate these risks. However, ...conventional geotechnical instrumentations for monitoring geohazards have a number of weaknesses, such as low accuracy, poor durability, and high sensitivity to environmental interferences. In this aspect, fiber Bragg grating (FBG), as a popular fiber optic sensing technology, has gained an explosive amount of attention. Based on this technology, quasi-distributed sensing systems have been established to perform real-time monitoring and early warning of landslides, debris flows, land subsidence, earth fissures and so on. In this paper, the recent research and development activities of applying FBG systems to monitor different types of geohazards, especially those triggered by human activities, are critically reviewed. The working principles of newly developed FBG sensors are briefly introduced, and their features are summarized. This is followed by a discussion of recent case studies and lessons learned, and some critical problems associated with field implementation of FBG-based monitoring systems. Finally the challenges and future trends in this research area are presented.
•Carbon nanoparticles derived from 3-hydroxybenzoic acid were achieved.•Lanthanide was incorporated into the nanosystem.•An “off-on” change was discovered in the presence of GSH.
Selective ...determination of targets in live cells and the real-time detection of active species will be highly valuable in biological field. Integration of 3-hydroxybenzoic acid and europium ions under hydrothermal conditions would lead to the formation of regular carbon nanoparticles with the size of 10–20 nm. This novel nanostructure possessed striking blue luminescence and no effective lanthanide signals were detected. In the presence of glutathione (GSH), the europium incorporated nanoparticles showed intensive red luminescence and an “off-on” change was observed. It has been accepted that GSH acts as an antioxidant to protect cell via entrapping free radicals and it controls oxidative stress within living systems. The abnormal levels of GSH will be closely related to a variety of diseases. Therefore, the bio-distribution and in vitro detection of GSH were investigated in this study. The biocompatibility and cytotoxicity of the europium incorporated nanoparticles were also evaluated by MTT assay and flow cytometry. This new system will be essential to monitor the concentration of important biological compounds in living organisms.
•Low cycle fatigue and creep-fatigue behaviors are systematically explored.•Cracking modes and damage mechanisms under different loading waveforms are investigated.•Σ3 CSLBs show great resistance of ...intergranular damage.•The present model addresses fatigue, creep and oxidation on life prediction.
The low cycle fatigue (LCF) and creep-fatigue behaviors of Ni-based GH4169 superalloy are investigated by uniaxial strain-controlled fully-reversed testing at 650 °C. Compared with LCF tests, the effects of tensile and compressive strain hold times on creep-fatigue lifetimes are experimentally explored with varying total strain ranges in the present work. In order to elucidate the damage mechanisms under complex loading waveforms, an additional series of tests with both tensile and compressive hold times are carried out at a given total strain range of 2.0%. Posterior to the cyclic tests, main-crack-failure modes and secondary cracking modes are studied via optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) techniques. Main-crack failure mechanisms are examined by the fracture appearance observations. Cracking modes are explored through quantitative characterization on the distributions of secondary cracks in the longitudinal cross sections under different loading waveforms. Moreover, a generalized life model based on linear damage summation (LDS) framework and energy dissipation criterion (EDC) is elaborated to estimate the damage mechanisms of fatigue, creep and oxidation. The prediction results can well establish the correlations between the reductions of numbers of cycles to failure and the presences of different damage mechanisms under respective loading waveforms.
Abstract
Ultrasonic surface deep rolling (USDR), oxygen boost diffusion (OBD), and their combination (USDR-OBD) were all used to improve the surface hardening of pure titanium. The microstructure, ...microhardness, and fatigue life of pure titanium treated by USDR, OBD, and USDR-OBD methods were analyzed. USDR treatment induced a severe deformation area, while OBD treatment produced a brittle oxygen diffusion zone. The USDR-OBD treated samples approached the highest hardness in comparison with other treated samples. The fatigue lives of USDR treated samples were improved, which was due to the high compressive residual stress and refined grains. However, the fatigue lives of both OBD treated samples and USDR-OBD treated samples were decreased due to premature crack initiation and rapid propagation in the oxygen diffusion zone. Finally, the fatigue fracture mechanisms of different samples were proposed.
Synaptic pruning during adolescence is important for appropriate neurodevelopment and synaptic plasticity. Aberrant synaptic pruning may underlie a variety of brain disorders such as schizophrenia, ...autism and anxiety. Dopamine D2 receptor (Drd2) is associated with several neuropsychiatric diseases and is the target of some antipsychotic drugs. Here we generate self-reporting Drd2 heterozygous (SR-Drd2
) rats to simultaneously visualize Drd2-positive neurons and downregulate Drd2 expression. Time course studies on the developing anterior cingulate cortex (ACC) from control and SR-Drd2
rats reveal important roles of Drd2 in regulating synaptic pruning rather than synapse formation. Drd2 also regulates LTD, a form of synaptic plasticity which includes some similar cellular/biochemical processes as synaptic pruning. We further demonstrate that Drd2 regulates synaptic pruning via cell-autonomous mechanisms involving activation of mTOR signaling. Deficits of Drd2-mediated synaptic pruning in the ACC during adolescence lead to hyper-glutamatergic function and anxiety-like behaviors in adulthood. Taken together, our results demonstrate important roles of Drd2 in cortical synaptic pruning.
The anomalous Hall effect is a fundamental transport process in solids arising from the spin-orbit coupling. In a quantum anomalous Hall insulator, spontaneous magnetic moments and spin-orbit ...coupling combine to give rise to a topologically nontrivial electronic structure, leading to the quantized Hall effect without an external magnetic field. Based on first-principles calculations, we predict that the tetradymite semiconductors Bi₂Te₃, Bi₂Se₃, and Sb₂Te₃ form magnetically ordered insulators when doped with transition metal elements (Cr or Fe), in contrast to conventional dilute magnetic semiconductors where free carriers are necessary to mediate the magnetic coupling. In two-dimensional thin films, this magnetic order gives rise to a topological electronic structure characterized by a finite Chern number, with the Hall conductance quantized in units of e²/h (where e is the charge of an electron and h is Planck's constant).
Reactive oxygen species (ROS) are byproducts of aerobic metabolism and potent agents that cause oxidative damage. In oxygenic photosynthetic organisms such as cyanobacteria, ROS are inevitably ...generated by photosynthetic electron transport, especially when the intensity of light-driven electron transport outpaces the rate of electron consumption during CO₂ fixation. Because cyanobacteria in their natural habitat are often exposed to changing external conditions, such as drastic fluctuations of light intensities, their ability to perceive ROS and to rapidly initiate antioxidant defences is crucial for their survival. This review summarizes recent findings and outlines important perspectives in this field.
Vertical deformation can be revealed by various techniques such as precise leveling, satellite imagery, and extensometry. Despite considerable effort, recording detailed subsurface deformation using ...traditional extensometers remains challenging when attempting to detect localized deformation. Here we introduce distributed fiber optic sensing based on Brillouin scattering as a geophysical exploration method for imaging distributed profiles of vertical deformation. By examining fiber optic cable‐soil interaction we found a threshold in confining pressure to achieve a strong cable‐soil coupling, thus validating data collected from a borehole‐embedded fiber optic cable deployed in Shengze, southern Yangtze Delta, China. Clear‐cut strain profiles acquired from November 2014 to December 2016 allowed us to pinpoint where compaction or rebound was actively occurring and examine strain responses at various locations along the entire cable length. We suggest that distributed fiber optic sensing can complement with extensometry and remote sensing techniques for improved monitoring of vertical deformation.
Plain Language Summary
Recording detailed subsurface deformation using traditional methods (e.g., extensometers) is sometimes difficult due to limited measuring points. This dilemma may be overcome by using the emerging distributed fiber optic sensing technology, which transforms common telecommunication fiber optic cables into sensors capable of making distributed strain measurements. We report the use of this technology for monitoring distributions of vertical deformation resulting from groundwater ion in Shengze, southern Yangtze Delta, China. An evaluation of the performance of a borehole‐embedded fiber optic cable helps us to validate the in situ strain data. The advantage of using this technology for vertical deformation sensing is the ability to locate any strata undergoing compaction or rebound and look at strain responses at any depth of interest. Moreover, recording subsurface changes in this fashion may also be useful in other geophysical and engineering applications that require refined monitoring of the media.
Key Points
Distributed fiber optic sensing with Brillouin scattering provides a clear subsurface strain profile using a single fiber optic cable
We find a threshold in confining pressure to achieve a strong fiber optic cable‐soil coupling
Distributed fiber optic sensing can complement with existing techniques for improved monitoring of vertical deformation
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