The controlled synthesis of calcium carbonate particles surface-functionalized with azido groups and its subsequent copper-catalyzed alkyne-azide cycloaddition (CuAAC) reactions with organocatalysts bearing alkyne anchors allowed the preparation of novel catalytic materials. A calcium carbonate-supported α,α-diarylprolinol silyl ether prepared in this manner catalyzes Michael addition of aldehydes to trans-β-nitrostyrenes with very high diastereo- and enantioselectivity. The immobilized catalyst can be recovered by simple decantation and reused. In addition, this heterogeneous catalytic system can also be adapted to continuous-flow operation, affording a five-fold productivity increase in comparison with the batch process.
Compared with previous studies focused on the effect of CNTs or antibiotics on aquatic organisms, our efforts were mainly devoted to the combined effect of CNTs and antibiotics on cyanobacterium Synechocystis sp. PCC 6803 to reveal the influencing mechanism of CNTs on the toxicity of antibiotics. CNTs exhibited an additive effect with CAP but an antagonistic effect with TC. Moreover, this study provides direct evidence for the molecular mechanisms of proteomic perturbations in Synechocystis sp. exposed to CNTs and/or antibiotics. This study provides a new insight into the molecular mechanisms of combined toxicity of multiple pollutants to cyanobacterium.
On-chip tunneling electron sources have wide potential applications in miniature vacuum electronic devices, and emission efficiency is one of their performance benchmarks. A cascade electron source (CES) based on series metal–insulator–metal horizontal tunneling junctions (HTJs) is proposed, where free electrons are additively extracted from each tunneling junction. A CES with $n$ HTJs shows a theoretical emission efficiency of approximately $η ( n )=1-( 1-η _0 )^n$ , with $η _0$ being the efficiency of a single tunneling junction. Experimentally, a CES with three Si–SiOx–Si tunneling junctions is demonstrated, achieving an emission efficiency of as high as 47.6%. This work provides a new way of realizing highly efficient on-chip tunneling electron sources.
Tin and tungsten are important metals for the industrializing society. Deciphering the origin and evolution of hydrothermal fluids responsible for their formation is critical to underpin genetic models of ore formation. Traditional approaches obtain isotopic information mainly from bulk analysis of both ore and gangue minerals, or less frequently from in situ analysis of gangue minerals, which either bear inherited complexities and uncertainties or are indirect constraints. Hence, directly obtaining isotopic information from ore minerals such as cassiterite by in situ techniques is warranted. However, this has been hampered by challenges from both analytical and applicational aspects. In this study, we first demonstrate a lack of crystallographic orientation effects during cassiterite ion microprobe oxygen isotope analysis. Along with our newly developed matrix-matched reference material, the Yongde-Cst, which has a recommended delta O-18 value of 1.36 +/- 0.16 parts per thousand (VSMOW) as defined by gas source isotope ratio mass spectrometry, in situ oxygen isotope analysis of cassiterite now is possible. We further refine the oxygen isotope fractionation (1000 ln alpha) for quartz-cassiterite by first-principles calculations, which is given by the equation of 1.259 x 10(6)/T-2 + 8.15 x 10(3)/T - 4.72 (T is temperature in Kelvin). The 1000 ln alpha for quartz-cassiterite has a sensitive response to temperature, and makes cassiterite-quartz an excellent mineral pair in oxygen isotope thermometry, as described by the equation of T (celcius) = 2427 x (delta O-18(qtz) - delta O-18(cst))(-0.4326) - 492.4. Using the well-established 1000 ln alpha of quartz-water, 1000 ln alpha of cassiterite-water is derived as 2.941 x 10(6)/T-2 - 11.45 x 10(3)/T + 4.72 (T in Kelvin), which shows a weak response to temperature. This makes cassiterite an ideal mineral from which to derive delta O-18 of fluids as robust temperature estimates are no longer a prerequisite. We have applied oxygen isotope analysis to cassiterite samples from six Sn(-W) deposits in China. The results show considerable variability in delta O-18 values both within a single deposit and among studied deposits. Combining the delta O-18 of cassiterite samples and the equilibrium oxygen isotope fractionation, we find that the delta O-18 values of ore-forming fluids show a strong magmatic affinity with variable but mostly no to low degree involvements (similar to 0-10%) of meteoric water, hence our results invite a reassessment on the extent and role of meteoric water in Sn-W mineralization. This study demonstrates that in situ oxygen isotope analysis of cassiterite is a promising tool to refine sources of ore-forming fluids, and to decode hydrothermal dynamics controlling tin and tungsten mineralization.
Clinical trials may often be encountered with truncation-by-death problem, where subjects enrolled in the experiment dies before their outcomes are collected. It is worth noting that truncation by death is a totally different concept from censoring. Censoring refers to the cases that subjects do have an outcome (such as time to recovery), but this outcome is masked by loss of follow-up, while truncation by death leaves the outcome undefined. In this article, we address the truncation-by death issue by reviewing two clinical trials on remdesivir for COVID-19, and provide some instructions to deal with the truncation-by-death problem.
Metal-organic frameworks (MOFs) are innovative porous structures consisting of metal ions and organic ligands, which have been verified for extraordinary applications in nanomedicine and pharmaceuticals. PCN-224 is a type of Zr-based MOFs, which has recently emerged as one of the most attractive nanomaterials for various applications, such as drug delivery, bioimaging and cancer therapy due to its favorable and fascinating physical-chemical properties. However, the safety evaluation and the potential toxicological properties remain unclear. In this study, the general cytotoxicity of PCN-224 were examined in both human hepatocytes L-02 cells and mouse macrophages RAW264.7. Furthermore, the effect of inflammation and autophagy were measured in L-02 cells. The results indicated that PCN-224 was engulfed in L-02 cells and subsequently resulted in morphological changes, cell membrane destruction, and oxidative stress in L-02 cells. PCN-224 might trigger inflammation by promoting the secretion of inflammatory factors such as Tumor necrosis factors (TNF-alpha) and Interleukin (IL-6). PCN-224 might induce autophagosome accumulation and subsequently autophagic dysfunction. Additionally, PCN-224 induced cytotoxicity in RAW264.7 cells and increased the protein levels of the inflammasome component NLR Family Pyrin Domain Containing 3 (NLRP3) molecular, which indicated its cellular effects in different cell types. All of these results will support the reasonable use of PCN-224.
With deep peak-load regulations, utility boilers are frequently operated under variable/low load conditions. However, their hydrodynamics, combustion and NOx emission characteristics are uncertain and relevant theoretical guidance are lacking. For this purpose, a comprehensive CFD model including flow, coal combustion and NOx formation is established for a 630 MW tangentially fired pulverized-coal boiler, aiming at solving the problem of decreasing combustion stability and increasing NOx emission in low-load operation. Based on the grid independence and model validation, the flow field, temperature profile, species concentration profile and NOx emission are predicted, and the influences of angle/arrangement of burners are further evaluated. Simulation results indicate that under low-load conditions, residual airflow rotation still persists at the top of boiler regardless of how to adjust the angle/arrangement of burners. With tilting the burner angle upward, flame is more concentrated, combustion becomes more stable, and heat flux rises in the upper zone; the burner arrangement of ABDE gives more uniform temperature distribution in the combustion zone. CO species shows higher content in the combustion zone; the 0° tilt angle gives maximum CO content, followed by the 15° angle, and finally the −15° angle; compared to the ACDE and ABCE arrangement, the ABDE arrangement mode gives much lower CO contents. Burner tilt angle of −15° benefits for lower NOx emission (183 mg/m3) but goes against stable combustion; the burner arrangement mode of ABDE is optimal for the present boiler, which ensures both stable combustion and lower NOx emission (209 mg/m3).
The Internet of Things (IoT) is an interface with the physical world that usually operates in random-sparse-event (RSE) scenarios. This article discusses main challenges of IoT chips: power consumption, power supply, artificial intelligence (AI), small-signal acquisition, and evaluation criteria. To overcome these challenges, many works recently aimed at IoT system design have emerged. This work reviews the architecture and circuit innovations that have contributed to IoT developments. This paper does not cover security of IoT. Event-driven architectures and nonuniform sampling ADCs significantly reduce the long-term average power. Besides, embedding AI engines in IoT nodes (AIoT) is one critical trend. The computing-in-memory technique improves the energy efficiency of the AI engine. Asynchronous spike neural networks (ASNNs) AI engines show low power potential. In addition to data processing, small-signal acquisition is also critical. The charge-domain analog-front-end (AFE) techniques such as floating inverter-based amplifiers improve energy efficiency. In addition to the above low power and high energy efficiency technologies, energy harvesting can also enhance the lifetime of AIoT devices. This article discusses recent ambient RF and natural energy harvesting approaches and high-efficiency DC-DC with a wide load range. Finally, novel evaluation criteria are introduced to establish benchmark standards for AIoT chips.