Flux measurements in the near surface layer over a non-uniform crop surface in China

International audienceEddy covariance measurements were conducted on fluxes of moisture, heat and CO2 in a near-surface layer over a non-uniform crop surface in an agricultural ecosystem in the central plain of China from 10 June to 20 July 2002. During this period, the mean canopy height was about 0.50 m. The study site consisted of grass (10% of area), bean (15%), corn (15%) and rice (60%). Based on footprint analysis, we expected >90% of the measured flux (at a height of 4 m above ground surface) to occur within the nearest 600 m of upwind area. We examined interdiurnal variations in the components of the surface energy balance and in CO2 flux. Results show that the pattern of energy partition had no obvious variation during the season. Daytime absorption of CO2 flux by the crop canopy suddenly increased after thunderstorm events. We examined the energy budget closure and found it to be around 0.85. We compared energy partitioning for all rain-free days, and found energy imbalance was more significant for the 1~3 days after rainy events and energy components almost achieve balance for the other rain-free days. It indicated that the cold or warm rainwater infiltrating into soil made problems

A comparison of the local spiral structure from Gaia DR2 and VLBI maser parallaxes

Context. The Gaia mission has released the second data set (Gaia DR2), which contains parallaxes and proper motions for a large number of massive, young stars. Aims. We investigate the spiral structure in the solar neighborhood revealed by Gaia DR2 and compare it with that depicted by VLBI maser parallaxes. Methods. We examined three samples with different constraints on parallax uncertainty and distance errors and stellar spectral types: (1) all OB stars with parallax errors of less than 10%; (2) only O-type stars with 0.1 mas errors imposed and with parallax distance errors of less than 0.2 kpc; and (3) only O-type stars with 0.05 mas errors imposed and with parallax distance errors of less than 0.3 kpc. Results. In spite of the significant distance uncertainties for stars in DR2 beyond 1.4 kpc, the spiral structure in the solar neighborhood demonstrated by Gaia agrees well with that illustrated by VLBI maser results. The O-type stars available from DR2 extend the spiral arm models determined from VLBI maser parallaxes into the fourth Galactic quadrant, and suggest the existence of a new spur between the Local and Sagittarius arms.Comment: 4 pages, 3 figures, 1 table, accepted for publication in A&

Strategies and reaction systems for solar-driven CO2 reduction by water

Solar driven CO2 conversion into high-value-added chemicals and energy-rich fuels is one of the promising strategies to tackle global warming and to address the energy-supply crisis. Even though enormous effort has been devoted to exploring all sorts of homogeneous and heterogeneous photocatalysts, the current efficiency and more importantly selectivity to valuable chemicals are still rather moderate, thus it is desired to develop high-efficiency photocatalytic system toward CO2 reduction with excellent selectivity. In this review, fundamental aspects of photocatalytic CO2 reduction by pure water, the reaction systems and the reliable method for detection of the products are firstly described. Thereafter the recent advances of the main strategy for improving the photocatalytic CO2 reduction from the perspective of promoting the CO2 adsorption and activation, accelerating the kinetics of water oxidation, and modulating charge separation are overviewed. The prospects and challenges on precise designing heterogeneous catalysts for CO2 photoreduction are proposed at the end, indicating the significance for the further development of photocatalytic systems with high CO2 conversion efficiency and product selectivity

Synthesis of Silicate-Bridged Heterojunctional SnO2/BiVO4 Nanoplates as Efficient Photocatalysts to Convert CO2 and Degrade 2,4-Dichlorophenol

Bismuth vanadate (BiVO4) is a promising visible‐light responsive photocatalyst, whose photocatalytic activity can be significantly improved by increasing its surface area and utilizing its high‐energy‐level photogenerated electrons effectively. In this work, 2D BiVO4 nanoplates with large specific surface area are successfully fabricated by hydrothermal conversion with the pre‐prepared BiOCl nanosheets as precursors. To improve the photogenerated charge separation, resulted BiVO4 nanoplates are further coupled with nanocrystalline SnO2 to construct heterojunctions, then silicate bridges are introduced between the interfaces of BiVO4 and SnO2. The amount‐optimized silicate‐bridged SnO2/BiVO4 nanocomposite exhibit exceptional visible‐light photocatalytic activities, by ≈7‐time and 4‐time enhancements for CO2 conversion to CH4 and for 2,4‐dichlorophenol degradation, respectively, compared to bare BiVO4 nanoparticles. The significantly enhanced charge separation is verified by steady‐state and time‐resolved surface photovoltage responses and produced hydroxyl radical amounts. Moreover, it is deduced through designed photo‐electrochemical experiments that the introduced SnO2 acts as a proper‐energy platform capable of accepting the photogenerated electrons of BiVO4 nanoplates, and the constructed silicate bridges further facilitate the electron transfer between BiVO4 and SnO2. This work opens up a feasible route to synthesize visible‐light‐driven 2D bismuth‐based nano‐photocatalysts with high photocatalytic activities for efficient fuel production and environmental remediation

Energy Platform for Directed Charge Transfer in the Cascade Z-Scheme Heterojunction: CO2 Photoreduction without a Cocatalyst

A universal strategy is developed to construct a cascade Z-scheme system, in which an effective energy platform is a core to direct charge transfer and separation, blocking the unexpected type-II charge transfer pathway. The dimension-matched (001)TiO 2 -g-C 3 N 4 /BiVO 4 nanosheet heterojunction (T-CN/BVNS) is the first such model. The optimized cascade Z-scheme exhibits ~19-fold photoactivity improvement for CO 2 reduction to CO in the absence of cocatalysts and costly sacrificial agents under visible-light irradiation, compared with BVNS, which is also superior to other reported Z-scheme systems even with noble metals as mediators. The experimental results and DFT calculations based on Van der Waals structural models on the ultrafast timescale reveal the introduced T as the platform could not only prolong the lifetimes of spatially separated electrons and holes but also did not compromise their reduction and oxidation potentials

Validation of an algorithm to evaluate the appropriateness of outpatient antibiotic prescribing using big data of Chinese diagnosis text

OBJECTIVE: We aimed to evaluate the validity of an algorithm to classify diagnoses according to the appropriateness of outpatient antibiotic use in the context of Chinese free text. SETTING AND PARTICIPANTS: A random sample of 10 000 outpatient visits was selected between January and April 2018 from a national database for monitoring rational use of drugs, which included data from 194 secondary and tertiary hospitals in China. RESEARCH DESIGN: Diagnoses for outpatient visits were classified as tier 1 if associated with at least one condition that 'always' justified antibiotic use; as tier 2 if associated with at least one condition that only 'sometimes' justified antibiotic use but no conditions that 'always' justified antibiotic use; or as tier 3 if associated with only conditions that never justified antibiotic use, using a tier-fashion method and regular expression (RE)-based algorithm. MEASURES: Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the classification algorithm, using classification made by chart review as the standard reference, were calculated. RESULTS: The sensitivities of the algorithm for classifying tier 1, tier 2 and tier 3 diagnoses were 98.2% (95% CI 96.4% to 99.3%), 98.4% (95% CI 97.6% to 99.1%) and 100.0% (95% CI 100.0% to 100.0%), respectively. The specificities were 100.0% (95% CI 100.0% to 100.0%), 100.0% (95% CI 99.9% to 100.0%) and 98.6% (95% CI 97.9% to 99.1%), respectively. The PPVs for classifying tier 1, tier 2 and tier 3 diagnoses were 100.0% (95% CI 99.1% to 100.0%), 99.7% (95% CI 99.2% to 99.9%) and 99.7% (95% CI 99.6% to 99.8%), respectively. The NPVs were 99.9% (95% CI 99.8% to 100.0%), 99.8% (95% CI 99.7% to 99.9%) and 100.0% (95% CI 99.8% to 100.0%), respectively. CONCLUSIONS: The RE-based classification algorithm in the context of Chinese free text had sufficiently high validity for further evaluating the appropriateness of outpatient antibiotic prescribing