Oximation reaction induced reduced graphene oxide gas sensor for formaldehyde detection

High-performance gas sensors can offer great potentials for monitoring and detection ofvolatile organic compounds (VOCs) in both domestic and industrial environment. In the presentwork, a new HCHO gas sensor was constructed with reduced graphene oxide (RGO) induced bythe oximation reaction. The gas-sensing performance test results suggested that the RGO hydrox-ylamine hydrochloride (RGO/HA-HCl) sensor presented a high response of 75% at 16 ppm HCHOat room temperature, and a high selectivity for HCHO suffering little interference with high concen-trations of volatile organic compounds, including methanol, ethanol, and methylbenzene, dichlor-omethane and water. Additionally, the RGO/HA-HCl sensor also showed a good long-termstability with RSD of 5.83% for a 15-day continuous sensing test, and the detection limit (DL)could reach 0.023 ppm under ambient conditions. Moreover, the mechanism for the high sensitivityand selectivity of formaldehyde was further established by in-situ gas chromatography mass spec-trometry (GC–MS). This work would provide a reliable new HCHO gas sensor which could be usedfor monitoring and forewarning the emission of HCHO for a better protection and improvement ofour environment

CTAB Enhanced Room-Temperature Detection of NO2 Based on MoS2-Reduced Graphene Oxide Nanohybrid

A new NO2 nanohybrid of a gas sensor (CTAB-MoS2 /rGO) was constructed for sensitive room-temperature detection of NO2 by 3D molybdenum disulfide (MoS2 ) and reduced graphene oxide (rGO), assisted with hexadecyl trimethyl ammonium bromide (CTAB). In comparison with MoS2 and MoS2 /rGO, the BET and SEM characterization results depicted the three-dimensional structure of the CTAB-MoS2 /rGO nanohybrid, which possessed a larger specific surface area to provide more active reaction sites to boost its gas-sensing performance. Observations of the gas-sensing properties indicated that the CTAB-MoS2 /rGO sensor performed a high response of 45.5% for 17.5 ppm NO2, a remarkable selectivity of NO2, an ultra-low detection limit of 26.55 ppb and long-term stability for a 30-day measurement. In addition, the response obtained for the CTAB-MoS2 /rGO sensor was about two to four times that obtained for the MoS2 /rGO sensor and the MoS2 sensor toward 8 ppm NO2, which correlated with the heterojunction between MoS2 and rGO, and the improvement in surface area and conductivity correlated with the introduction of CTAB and rGO. The excellent performance of the CTAB-MoS2 /rGO sensor further suggested the advantage of CTAB in assisting a reliable detection of trace NO2 and an alternative method for highly efficiently detecting NO2 in the environment

GeoGauss: Strongly Consistent and Light-Coordinated OLTP for Geo-Replicated SQL Database

Multinational enterprises conduct global business that has a demand for geo-distributed transactional databases. Existing state-of-the-art databases adopt a sharded master-follower replication architecture. However, the single-master serving mode incurs massive cross-region writes from clients, and the sharded architecture requires multiple round-trip acknowledgments (e.g., 2PC) to ensure atomicity for cross-shard transactions. These limitations drive us to seek yet another design choice. In this paper, we propose a strongly consistent OLTP database GeoGauss with full replica multi-master architecture. To efficiently merge the updates from different master nodes, we propose a multi-master OCC that unifies data replication and concurrent transaction processing. By leveraging an epoch-based delta state merge rule and the optimistic asynchronous execution, GeoGauss ensures strong consistency with light-coordinated protocol and allows more concurrency with weak isolation, which are sufficient to meet our needs. Our geo-distributed experimental results show that GeoGauss achieves 7.06X higher throughput and 17.41X lower latency than the state-of-the-art geo-distributed database CockroachDB on the TPC-C benchmark

Larmor precession: observation and utilization for boosting the signal intensity of radio frequency glow discharge mass spectrometry

A novel magnet array system was constructed to use Larmor precession for boosting the signal intensity of rf-GD-MS. The enhancement mechanism with four magnet array devices of single block magnet and 2×2, 3×2, and 3×4 magnet arrays was simulated and studied by COMSOL Multiphysics Software 5.4.0 (COMSOL) to determine if the electrons in the discharge plasma could perform Larmor precession along the direction perpendicular to the magnetic field. Induced by Larmor precession, inelastic collisions between the primary electrons and sample produced numerous secondary electrons and further improved the ionization efficiency. Moreover, the fuzzy synthetic evaluation result predicted that the device with 3×2 magnet array would display the greatest enhancement effect among the four devices. Based on these theoretical studies, a magnet array system with four magnet array devices was fabricated and utilized for studies of two scintillation crystals BGO and PWO. The observations indicated that the signal intensities obtained for 209Bi and 208Pb with the magnet array system were 630-3600 times of that obtained without magnet, and were enhanced by a factor of 1.5-2.8 compared with a previously reported stacked magnetic device. Two NIST samples were used to validate the method, and the results suggested that relative errors were less than 10% and the lowest detection limit for the 3×2 magnet array could reach 0.0032μg•g−1. Furthermore, the magnet array enhancement system with Larmor precession offers an efficient and sensitive approach for the direct analysis of non-conducting materials

Studies of dopamine oxidation process by atmospheric pressure glow discharge mass spectrometry

An atmospheric pressure glow discharge ionisation source was constructed and utilized to study the dopamine (DA) oxidation process coupling with mass spectrometry. During the DA oxidation process catalysed by polyphenol oxidase (PPO), six cationic intermediates were directly detected by the atmospheric pressure glow discharge mass spectrometry (APGD-MS). Combined with tandem mass spectrometry, the structures of the dopamine o-semiquinone radical (DASQ) and leukodopaminochrome radical (LDAC●) intermediates and structures of the isomers of dopaminochrome (DAC) and 5,6-dihydroxyindole (DHI) were further characterised with the introduction of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and deuterium oxide (D2O) to APGD-MS. Meanwhile, UV–Vis studies confirmed the important role of PPO in catalyzing the DA oxidation reaction. Based on APGD-MS studies, a possible mechanism could be proposed for DA oxidation catalysed by PPO. Furthermore, APGD-MS could provide possibilities for the effective detection and characterisation of short-lived intermediates, even in complicated systems

Antimicrobial peptide temporin derivatives inhibit biofilm formation and virulence factor expression of Streptococcus mutans

IntroductionTemporin-GHa obtained from the frog Hylarana guentheri showed bactericidal efficacy against Streptococcus mutans. To enhance its antibacterial activity, the derived peptides GHaR and GHa11R were designed, and their antibacterial performance, antibiofilm efficacy and potential in the inhibition of dental caries were evaluated.MethodsBacterial survival assay, fluorescent staining assay and transmission electron microscopy observation were applied to explore how the peptides inhibited and killed S. mutans. The antibiofilm efficacy was assayed by examining exopolysaccharide (EPS) and lactic acid production, bacterial adhesion and cell surface hydrophobicity. The gene expression level of virulence factors of S. mutans was detected by qRT-PCR. Finally, the impact of the peptides on the caries induced ability of S. mutans was measured using a rat caries model.ResultsIt has been shown that the peptides inhibited biofilm rapid accumulation by weakening the initial adhesion of S. mutans and reducing the production of EPS. Meanwhile, they also decreased bacterial acidogenicity and aciduricity, and ultimately prevented caries development in vivo.ConclusionGHaR and GHa11R might be promising candidates for controlling S. mutans infections

Development and application of a porous cage carrier method for detecting trace elements in soils by direct current glow discharge mass spectrometry

The accurate and reliable determination of trace elements in soil still remains a big challenge for glow discharge mass spectrometry due to the poor conductive nature of soils. In the present work, a porous cage carrier was developed and used in the analysis of soils. The investigation results suggested that the carrier with a circular cross-sectional area in the range from 20 to 38 mm2, length from 15 to 17 mm and diameter of hole size from 1.5 mm to 2.0 mm could obtain good signals. Then the porous cage carrier method was systematically evaluated by analysing three types of soil reference materials. The discharge process was kept stable for more than 100 minutes, which was much longer than the boric acid method and indium sheet method. The investigations suggested that the internal precision was obtained within 16%, the external precision was better than 20% and the relative error was in the range from 0.7% to 17%. The detection limit of Tb could reach 0.014 μg g−1, which indicated that the new method qualified for the analysis of trace elements in soils. Compared to traditional tablet-pressed methods, the porous cage carrier method was not only convenient for sample preparation, but also showed good stability, reproducibility and better detection limits for trace elements. Furthermore, this method was proved to promote the potential application of GD-MS in the environmental field

Metal–Organic Cages: Applications in Organic Reactions

Supramolecular metal–organic cages, a class of molecular containers formed via coordination-driven self-assembly, have attracted sustained attention for their applications in catalysis, due to their structural aesthetics and unique properties. Their inherent confined cavity is considered to be analogous to the binding pocket of enzymes, and the facile tunability of building blocks offers a diverse platform for enzyme mimics to promote organic reactions. This minireview covers the recent progress of supramolecular metal–organic coordination cages for boosting organic reactions as reaction vessels or catalysts. The developments in the utilizations of the metal–organic cages for accelerating the organic reactions, improving the selectivity of the reactions are summarized. In addition, recent developments and successes in tandem or cascade reactions promoted by supramolecular metal–organic cages are discussed

Metal–Organic Cages: Applications in Organic Reactions

Supramolecular metal–organic cages, a class of molecular containers formed via coordination-driven self-assembly, have attracted sustained attention for their applications in catalysis, due to their structural aesthetics and unique properties. Their inherent confined cavity is considered to be analogous to the binding pocket of enzymes, and the facile tunability of building blocks offers a diverse platform for enzyme mimics to promote organic reactions. This minireview covers the recent progress of supramolecular metal–organic coordination cages for boosting organic reactions as reaction vessels or catalysts. The developments in the utilizations of the metal–organic cages for accelerating the organic reactions, improving the selectivity of the reactions are summarized. In addition, recent developments and successes in tandem or cascade reactions promoted by supramolecular metal–organic cages are discussed

Review on Motion and Load-Bearing Characteristics of the Planetary Roller Screw Mechanism

Studying the motion and load-bearing characteristics of the planetary roller screw mechanism is the basis for the structural design and performance optimisation of the mechanism. The mechanical structures and working principles of different kinds of planetary roller screw mechanisms are summarised. Published papers on kinematic, load-bearing and dynamic models of the planetary roller screw mechanism are reviewed. Based on the slip state in point contacts at the screw–roller and the nut–roller interfaces, the kinematic models are divided into three types. The finite element method and numerical theory are the two main methods used to develop the load-bearing models. Current dynamic models differ mainly concerning whether they take the rotation of the screw into consideration. In this work, each kind of model is presented in detail along with relevant literature. The main conclusions for each type of model are discussed, and an overview of the future evolution of motion and load-bearing characteristics of the planetary roller screw mechanism are given