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A non-equiatomic high entropy alloy (HEA) Ti40Nb25Zr25Ta5Mo5 (at.%) was designed by replacing 5% Ta with 5% Mo in a precursor Ti40Nb25Zr25Ta10 HEA for improved mechanical properties and reduced density. The Ti40Nb25Zr25Ta5Mo5 HEA fabricated by copper mould casting exhibited a nearly equiaxed grain structure (grain size: 96 ± 16 μm), but within each equiaxed grain, dendritic structures are discernible in the backscattered electron imaging mode. These dendrites are enriched in Ta, Nb and Mo, while the inter-dendritic regions contain higher Zr and Ti. The as-cast HEA achieved tensile yield strength (σ0.2) of 976 ± 8 MPa and strain to fracture (εf) of 16.80 ± 1.86%, well above the minimum requirements of σ0.2 and εf for medical-grade titanium alloy Ti–6Al–4V (759 MPa and 10%). The formation of microscale and nanoscale shear bands and the presence of significant dislocations in the shear band boundary region played a key role in allowing this as-cast HEA to achieve the excellent combination of tensile strength and ductility. Furthermore, the HEA exhibited a lower wear rate, lower coefficient of friction and much higher corrosion resistance in Hank's solution (electrochemical assessments) than Ti–6Al–4V, making it a promising alternative biomedical alloy.

Abstract Heterotrophic activity, primarily driven by sulfate-reducing prokaryotes, has traditionally been linked to nitrogen fixation in the root zone of coastal marine plants, leaving the role of chemolithoautotrophy in this process unexplored. Here, we show that sulfur oxidation coupled to nitrogen fixation is a previously overlooked process providing nitrogen to coastal marine macrophytes. In this study, we recovered 239 metagenome-assembled genomes from a salt marsh dominated by the foundation plant Spartina alterniflora, including diazotrophic sulfate-reducing and sulfur-oxidizing bacteria. Abundant sulfur-oxidizing bacteria encode and highly express genes for carbon fixation (RuBisCO), nitrogen fixation (nifHDK) and sulfur oxidation (oxidative-dsrAB), especially in roots stressed by sulfidic and reduced sediment conditions. Stressed roots exhibited the highest rates of nitrogen fixation and expression level of sulfur oxidation and sulfate reduction genes. Close relatives of marine symbionts from the Candidatus Thiodiazotropha genus contributed ~30% and ~20% of all sulfur-oxidizing dsrA and nitrogen-fixing nifK transcripts in stressed roots, respectively. Based on these findings, we propose that the symbiosis between S. alterniflora and sulfur-oxidizing bacteria is key to ecosystem functioning of coastal salt marshes.

The generation of energetic particles in the Universe is an important topic in astrophysical and space physics. Although the diffusive shock acceleration has been acknowledged to play an essential role in particle acceleration, the injection problem has not been well resolved yet. Using measurements from the Magnetospheric Multiscale spacecraft, we report unexpected spiky enhancements of energetic electron flux in the upstream region of the Earth’s bow shock. Such enhancements are then demonstrated to result from the accelerated electron population by shock reflection. Meanwhile, the magnetic field exhibits no variations except an increase in radius of curvature. Based on the results above, we uncover the underlying acceleration scenario. When the interplanetary magnetic field with a proper curvature approaches the bow shock, the two ends of a magnetic field line may touch the shock front earlier than its middle part. Magnetic mirror points form at the two field-line-shock intersections. The solar wind electrons are therefore trapped and bounce between two mirror points. Eventually, these electrons undergo fast Fermi reflection several times and gain substantial energies. The spacecraft observation of accelerated electrons is reproduced with a numerical method based on the reflection model. Such an acceleration process may be a potential solution to the injection problem.

Non-Helicobacter pylori Helicobacters (NHPHs) represent a group of bacteria distinct from H. pylori. They are commonly found in the gastrointestinal tracts of animals, such as poultry, swine, and domestic pets. Recent studies have demonstrated that these organisms have implications beyond animal hosts, indicating a potential role in human gastric diseases and raising concerns about the possibility of zoonotic transmission. Different NHPH species can cause gastritis, ulcerations, and even systemic effects like bacteremia in human individuals. A comprehensive literature search protocol on MEDLINE (PubMed) from the last twelve months was employed, resulting in the identification of 24 articles and case studies on NHPHs in animals and 12 in humans, respectively. Furthermore, we conducted a search for Helicobacter species other than H. pylori that are referenced individually in the National Library of Medicine database. The most recent studies have focused on the clinical manifestations and diagnostic challenges of NHPHs-related diseases in animal models and human cases. An important subject was the transmission of disease between different species, particularly those associated with livestock farming. The results suggest that NHPHs, especially H. pullorum, H. suis, and H. cinaedi, may be a significant contributing factor in the development of gastrointestinal diseases in humans, particularly in instances where H. pylori is not present. Although there has been a significant improvement in the overall awareness regarding NHPH infections, it remains a challenge to identify new species and distinguish between low and high pathogenicity levels. Further research is needed to understand how NHPH impacts human health, with a focus on improved diagnostic tools and treatment strategies.

Robot-assisted rehabilitation has proven to improve a subject's upper-extremity motor function. However, it is still challenging to control the robot to provide minimal assistance based on the subject's performance. This paper proposes a motion-trend-based assistance control strategy to solve this problem. The control strategy provides the corresponding normal and tangential forces by constructing an adaptive virtual assistance force field around a predetermined training trajectory. In the normal direction, a performance function based on the position-tracking error and normal motion trend is established to adjust the normal assistance force field strength in real time; in the tangential direction, a performance function based on the tangential interaction force and tangential motion trend is established to adjust the tangential assistance force field strength in real time. Additionally, good motion trends can quickly reduce the assistance force field. The normal motion trend represents the state of the subject moving toward the target trajectory, and the tangential motion trend represents the state of increasing tangential interaction force. Finally, the performance of this control strategy was evaluated by training experiments with eight healthy subjects. Preliminary experiments showed that the normal assist force in the active movement phase was 92.48 % smaller than that in the poor phase, and the tangential assist force was 90.73 % smaller than that in the slack phase. And the normal assist force and tangential assist force will become zero within 0.2 s when the subject has a good tendency to move. This shows that the control strategy proposed in this paper can quickly adjust the assistance according to the subject's motor performance. In addition, the assistance can be quickly reduced when the subject has a good movement trend. Future work will incorporate OpenSim (muscle and bone simulation software) to develop a pathway suitable for the subject's arm rehabilitation.

When patients with lower limb dyskinesia use robots for rehabilitation training, gait parameters are of great significance for disease diagnosis and rehabilitation evaluation. Gait measurement is usually carried out by using optical motion capture systems, pressure plates and so on. However, it is difficult to apply these systems to lower limb rehabilitation robots due to their high price, limited scope and wearing requirements. At the same time, most of the current applications in robots focus on the basic gait parameters (such as step length and step speed) for robot control or user intention recognition. Therefore, this paper proposes an online gait analysis algorithm for lower limb rehabilitation robots, which uses a lidar sensor as the gait data acquisition sensor. The device is installed on the lower limb rehabilitation robot, which not only avoids the problems of decline in the detection accuracy and failure of leg tracking caused by lidar placement on the ground, but it also calculates seven gait parameters, such as step length, stride length, gait cycle and stance time, with high precision in real time. At the same time, the walking track of the patient may not be straight, and the lidar coordinate system is also changed due to the movement of the lower limb rehabilitation robot when the patient moves forward. In order to overcome this situation, a spatial parameter-splicing algorithm based on a time series is proposed to effectively reduce the error impact on gait spatiotemporal parameters. The experimental results show that the gait analysis algorithm proposed in this paper can measure the gait parameters effectively and accurately. Except for the swing time and double support time, which are calculated with large relative errors due to their small values, the relative errors of the remaining gait parameters are kept below 8 %, meeting the requirements of clinical applications.

Summary: Macrophages populate the embryo early in gestation, but their role in development is not well defined. In particular, specification and function of macrophages in intestinal development remain little explored. To study this event in the human developmental context, we derived and combined human intestinal organoid and macrophages from pluripotent stem cells. Macrophages migrate into the organoid, proliferate, and occupy the emerging microanatomical niches of epithelial crypts and ganglia. They also acquire a transcriptomic profile similar to that of fetal intestinal macrophages and display tissue macrophage behaviors, such as recruitment to tissue injury. Using this model, we show that macrophages reduce glycolysis in mesenchymal cells and limit tissue growth without affecting tissue architecture, in contrast to the pro-growth effect of enteric neurons. In short, we engineered an intestinal tissue model populated with macrophages, and we suggest that resident macrophages contribute to the regulation of metabolism and growth of the developing intestine.

The electron temperature fluctuation-induced dynamo electric field has been measured in the core of high-temperature EAST tokamak plasmas by Faraday-effect polarimetry and electron cyclotron emission. It is found that a dynamo electric field primarily arises from the coherent interaction between radial magnetic-field fluctuations and electron temperature fluctuations associated with the internal kink instability, acting to self-regulate the current profile to prevent sawtooth magnetic reconnection.

David McKellar et al. integrate single-cell and -nuclear transcriptomic analyses of mouse skeletal muscle in homeostatic conditions or following injury. The resulting transcriptomic model of myogenesis identified rare, transitional states and cell subtypes that are poorly represented in individual datasets, providing a valuable resource for the field.

A 6-year-long high-resolution Chinese air quality reanalysis (CAQRA) dataset is presented in this study obtained from the assimilation of surface observations from the China National Environmental Monitoring Centre (CNEMC) using the ensemble Kalman filter (EnKF) and Nested Air Quality Prediction Modeling System (NAQPMS).This dataset contains surface fields of six conventional air pollutants in China (i.e. PM2.5, PM10, SO2, NO2, CO, and O3) for the period 2013–2018 at high spatial (15 km×15 km) and temporal (1 h) resolutions. This paper aims to document this dataset by providing detailed descriptions of the assimilation system and the first validation results for the above reanalysis dataset. The 5-fold cross-validation (CV) method is adopted to demonstrate the quality of the reanalysis. The CV results show that the CAQRA yields an excellent performance in reproducing the magnitude and variability of surface air pollutants in China from 2013 to 2018 (CV R2=0.52–0.81, CV root mean square error (RMSE) =0.54 mg/m3 for CO, and CV RMSE =16.4–39.3 µg/m3 for the other pollutants on an hourly scale). Through comparison to the Copernicus Atmosphere Monitoring Service reanalysis (CAMSRA) dataset produced by the European Centre for Medium-Range Weather Forecasts (ECWMF), we show that CAQRA attains a high accuracy in representing surface gaseous air pollutants in China due to the assimilation of surface observations. The fine horizontal resolution of CAQRA also makes it more suitable for air quality studies on a regional scale. The PM2.5 reanalysis dataset is further validated against the independent datasets from the US Department of State Air Quality Monitoring Program over China, which exhibits a good agreement with the independent observations (R2=0.74–0.86 and RMSE =16.8–33.6 µg/m3 in different cities). Furthermore, through the comparison to satellite-estimated PM2.5 concentrations, we show that the accuracy of the PM2.5 reanalysis is higher than that of most satellite estimates. The CAQRA is the first high-resolution air quality reanalysis dataset in China that simultaneously provides the surface concentrations of six conventional air pollutants, which is of great value for many studies, such as health impact assessment of air pollution, investigation of air quality changes in China, model evaluation and satellite calibration, optimization of monitoring sites, and provision of training data for statistical or artificial intelligence (AI)-based forecasting. All datasets are freely available at https://doi.org/10.11922/sciencedb.00053 (Tang et al., 2020a), and a prototype product containing the monthly and annual means of the CAQRA dataset has also been released at https://doi.org/10.11922/sciencedb.00092 (Tang et al., 2020b) to facilitate the evaluation of the CAQRA dataset by potential users.

An innovative divertor concept, the fish tail divertor, is proposed in this paper, aimed at reducing the surface temperature on the tokamak divertor plate as well as that due to the edge localized modes. This new concept has been implemented in experiments to demonstrate its capability of strike point sweeping on the plate at a frequency range from 10 to 100 Hz by using an oscillating magnetic field. A strike point movement of 5–6 cm is achieved by applying a coil current of several percent of plasma current, leading to a significant reduction of divertor surface temperature. The result indicates a possible application in a fusion reactor.

We study the influence of the baryon chemical potential μ B on the properties of the Quark−Gluon−Plasma (QGP) in and out-of equilibrium. The description of the QGP in equilibrium is based on the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation-of-state of the partonic system above the deconfinement temperature T c from lattice Quantum Chromodynamics (QCD). We study the transport coefficients such as the ratio of shear viscosity η and bulk viscosity ζ over entropy density s, i.e., η / s and ζ / s in the ( T , μ ) plane and compare to other model results available at μ B = 0 . The out-of equilibrium study of the QGP is performed within the Parton−Hadron−String Dynamics (PHSD) transport approach extended in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections based on the DQPM and the evaluated at actual temperature T and baryon chemical potential μ B in each individual space-time cell where partonic scattering takes place. The traces of their μ B dependences are investigated in different observables for symmetric Au + Au and asymmetric Cu + Au collisions such as rapidity and m T -distributions and directed and elliptic flow coefficients v 1 , v 2 in the energy range 7.7 GeV ≤ s N N ≤ 200 GeV.

Although much effort has been put into studying air pollution, our knowledge of the mechanisms of frequently occurring intense haze episodes in China is still limited. In this study, using 3 years of measurements of air pollutants at three different height levels on a 325 m Beijing meteorology tower, we found that a positive aerosol–boundary layer feedback mechanism existed at three vertical observation heights during intense haze polluted periods within the mixing layer. This feedback was characterized by a higher loading of PM2.5 with a shallower mixing layer. Modelling results indicated that the presence of PM2.5 within the boundary layer led to reduced surface temperature, relative humidity and mixing layer height during an intensive haze episode. Measurements showed that the aerosol–boundary layer feedback was related to the decrease in solar radiation, turbulent kinetic energy and thereby suppression of the mixing layer. The feedback mechanism can explain the rapid formation of intense haze episodes to some extent, and we suggest that the detailed feedback mechanism warrants further investigation from both model simulations and field observations.

The characteristics of ozone variations and the impacts of synoptic and local meteorological factors in northern China were quantitatively analyzed during the warm season from 2013 to 2017 based on multi-city in situ ozone and meteorological data as well as meteorological reanalysis. The domain-averaged maximum daily 8 h running average O3 (MDA8 O3) concentration was 122±11 µg m−3, with an increase rate of 7.88 µg m−3 yr−1, and the three most polluted months were closely related to the variations in the synoptic circulation patterns, which occurred in June (149 µg m−3), May (138 µg m−3) and July (132 µg m−3). A total of 26 weather types (merged into five weather categories) were objectively identified using the Lamb–Jenkinson method. The highly polluted weather categories included the S–W–N directions (geostrophic wind direction diverts from south to north), low-pressure-related weather types (LP) and cyclone type, which the study area controlled by a low-pressure center (C), and the corresponding domain-averaged MDA8 O3 concentrations were 122, 126 and 128 µg m−3, respectively. Based on the frequency and intensity changes of the synoptic circulation patterns, 39.2 % of the interannual increase in the domain-averaged O3 from 2013 to 2017 was attributed to synoptic changes, and the intensity of the synoptic circulation patterns was the dominant factor. Using synoptic classification and local meteorological factors, the segmented synoptic-regression approach was established to evaluate and forecast daily ozone variability on an urban scale. The results showed that this method is practical in most cities, and the dominant factors are the maximum temperature, southerly winds, relative humidity on the previous day and on the same day, and total cloud cover. Overall, 41 %–63 % of the day-to-day variability in the MDA8 O3 concentrations was due to local meteorological variations in most cities over northern China, except for two cities: QHD (Qinhuangdao) at 34 % and ZZ (Zhengzhou) at 20 %. Our quantitative exploration of the influence of both synoptic and local meteorological factors on interannual and day-to-day ozone variability will provide a scientific basis for evaluating emission reduction measures that have been implemented by the national and local governments to mitigate air pollution in northern China.

Abstract Degradation mechanisms leading to deterioration in the battery performance is an inevitable phenomenon. Although there are detailed physics and equivalent circuit based models to predict the losses incurred due to degradation in estimating the health of the battery, they are either incomplete, computationally expensive or both. In this study, we present a very simple and elegant, chemistry independent mathematical analysis, which accurately calculates resistive and capacitive components of cycle-life related losses in a battery system. We demonstrate that discharge profiles obtained at any given degradation state of the battery can be represented by an analytical function, with its origin lying at the heart of battery dynamics, using simple parameter fitting. The model parameters relate to the battery electrochemical potential, resistance and capacity. We first validate our protocol using simulated cycling data from a degrading lithium-ion battery system modeled with detailed electrochemical thermal calculations and show that the estimates of capacity and power fades are >99% accurate using our method. Further, we construct a unique phase space plot of normalized energy, power that gives a compact representation of quantitative and qualitative trend of the degradation state of the system, as well as available power and energy.

The problem of ecology of a soul in the works by V. Astafyev and modern Chinese writer Zhang Wei is considered. Their common views on the ecological crisis in the spiritual sphere are established. Two lines of the artistic embodiment of the problem of ecology of a soul in the works of Russian and Chinese authors are revealed: an appeal to the motives and images of spiritual wandering and the creation of an ecological utopia. Special attention is paid to the artistic principles of creating an ecological utopia. The difference between these concepts is revealed: Astafyev’s ecological ideal is embodied in the life of the village Boganida (“King-Fish”), while Zhang Wei’s ideal can be comprehended through the philosophical concept of “entering the wild territory.” The relevance of the study is due, first, to the special role of V. Astafyev’s work in Chinese literature of the new era (after the Cultural revolution), including Zhang Wei’s works; secondly, to the importance of the problem of the ecology of a soul for society. The novelty of the study is due to the fact that for the first time the influence of Astafiev’s works on the work of Zhang Wei is analyzed in such detail. The authors come to conclusion that Zhang Wei, largely following the artistic principles of Astafyev in solving the problem of the ecology of a soul, created - on the basis of the tradition of the Russian author - original works taking into account his national culture.

Few-mode fiber (FMF) based mode division multiplexing (MDM) transmission system has been considered as a potential candidate for future backbone network, unfortunately, the mode-dependent loss (MDL) in MDM system remains to be a tough issue in high speed transmission application. Recently, the optimal maximum-likelihood (ML) detection has demonstrated its potential ability and efficiency in suppressing the capacity-limiting MDL. However, this ML detector employed at the receiver of MDM system achieves the optimal performance at the sacrifice of the exponential growth in complexity. Inspired by the fact that probabilistic data association (PDA) is able to offer near-ML performance without introducing the enormous computational complexity, in this paper, a soft-decision aided PDA detector is proposed for MDM system detection, in which the probabilities of the potential candidate symbols are iteratively estimated by using the approximation of the Bayesian theorem. In addition, only those high reliability symbols are detected to save the computational effort. To validate the proposed scheme, both weakly and strongly coupled modes have been considered. Simulation results show that the proposed PDA based detector can achieve a flexible trade-off between the BER performance and the computational complexity when compared with the optimal ML detection in FMF-based MDM system.

A novel planar artificial magnetic conductor (AMC) structure is presented for ultra-wideband radar cross section reduction (RCSR). The structure consists of three different AMC tiles in a quadruple triangle-type chessboard configuration. By precise design, a 180°±30° reflection phase difference between every two of the three units nearly covers from 3.98GHz to 18.84GHz to broaden the RCSR bandwidth. By this means, the scattered energy is redirected into several lobes and the measured RCSR for over -6dB is achieved nearly from 3.62GHz to 18GHz with a relative bandwidth of 133.02% for both polarizations. Both full-wave simulation and measurement results verify the capability and potentiality of the proposed design for ultra-wideband RCSR.

To investigate the spatiotemporal variability of the mixing layer height (MLH) on the North China Plain (NCP), multi-site and long-term observations of the MLH with ceilometers at three inland stations (Beijing, BJ; Shijiazhuang, SJZ; Tianjin, TJ) and one coastal site (Qinhuangdao) were conducted from 16 October 2013 to 15 July 2015. The MLH of the inland stations in the NCP were highest in summer and lowest in winter, while the MLH on the coastal area of Bohai was lowest in summer and highest in spring. As a typical site in southern Hebei, the annual mean of the MLH at SJZ was 464 ± 183 m, which was 15.0 and 21.9 % lower than that at the BJ (594 ± 183 m) and TJ (546 ± 197 m) stations, respectively. Investigation of the shear term and buoyancy term in the NCP revealed that these two parameters in southern Hebei were 2.8 times lower and 1.5 times higher than that in northern NCP within 0–1200 m in winter, respectively, leading to a 1.9-fold higher frequency of the gradient Richardson number > 1 in southern Hebei compared to the northern NCP. Furthermore, combined with aerosol optical depth and PM2.5 observations, we found that the pollutant column concentration contrast (1.2 times) between these two areas was far less than the near-ground PM2.5 concentration contrast (1.5 times). Through analysis of the ventilation coefficient in the NCP, the near-ground heavy pollution in southern Hebei mainly resulted from the lower MLH and wind speed. Therefore, due to the importance of unfavorable weather conditions, heavily polluting enterprises should be relocated and strong emission reduction measures should be introduced to improve the air quality in southern Hebei.

A novel design of aperture-coupled microstrip antenna with ultra-wideband low radar cross section (RCS) is proposed. Hybrid frequency selective surface (FSS) structures consisting of two kinds of polarization-dependent folded split ring resonators (PDFSRRs) and square patches are utilized to replace the conventional metallic ground. By orthogonally arranging the PDFSRRs in a chessboard-like configuration, the band-stop characteristic contributes to the gain enhancement, while the zero degree points of reflection phase and wave-transmission characteristic are utilized to achieve RCS reduction both in-band and out-of-band. Furthermore, with square patches periodically etched on the bottom of FSS structure, a new zero degree reflection phase is introduced to enhance the effect of RCS reduction. Full wave simulations and measurements demonstrate that the proposed antenna achieves RCS reduction from 1 GHz to 18 GHz and gain enhancement compared with traditional microstrip antenna.

The data shown in this article are related to the research article entitled “Characterization of Sgo1 expression pattern in developing and adult mouse” (Song et al., 2017) [3]. The article provides novel data on Sgo1 gene expression pattern utilizing Sgo1_LacZ_Knock in mouse line and immunohistochemistry in wild type mice. The data presents Sgo1 expression pattern during development, and in post-developmental proliferative and quiescent tissue. The article describes following tissues: developing heart, neural tube, adult colon, cerebellum, cerebral cortex, liver, and testis. Keywords: Heart development, Intestinal development, Retinal development, SGO1, CAID syndrome, Cohesin

MnCoGe1-xVx (x = 0.005, 0.01, 0.015, 0.02, 0.03, and 0.04) compounds were synthesized and investigated in view of the effect of transition metals on main-group-element sites to the magnetostructural transition. A small amount of V doping results in a decrease of the martensitic transformation temperature, while a further increase of V disturbs the Co-Ge bonds hence destabilizing the MM’X phase. Therefore, the transformation temperature returns to high temperature, and the expected Curie temperature window becomes incomplete. Accordingly, a large magnetic entropy change of about 10 J/kg·K and a refrigerant capacity of about 129.5 J/kg is obtained in the series.

Additive manufacturing & 3D printing has almost no limitation in realizing any geometry due to its layer-by-layer manufacturing manner, while producing small-sized, interconnected pores is one of its major challenges. In this study, we report that, by creatively combining additive manufacturing with foaming agent, interconnected pores (~26 vol.% porosity) with pore size of 2–30 μm have been successfully achieved. One of the most important applications of such unique structure is for developing the so-called breathable mould steel. Breathability is rather demanding for the mould industry, since it is capable to eliminate the trapped, detrimental gas during injection moulding and therefore much improve the quality of as-injected parts. It will be revealed by the study that, due to a good selection of the foaming agent (i.e. CrNx), the as-printed breathable steel has a great combination of compressive strength (~1.3 GPa), strain (~26%), microhardness (~360 HV) and corrosion resistance, along with sufficient breathability. These mechanical properties are even superior to the commercial PM-35 breathable steel. Based on detailed microstructural characterization, the affecting factors to the pore forming are studied, and the importance of the novel approach developed by the current study has been addressed. Keywords: Breathable mould steel, Selective laser melting, Foaming agent, Gas permeability, Microstructure and mechanical property

This study investigates a cross-variable ozone data assimilation (DA) method based on an ensemble Kalman filter (EnKF) that has been used in the companion study to improve ozone forecasts over Beijing and surrounding areas. The main purpose is to delve into the impacts of the cross-variable adjustment of nitrogen oxide (NOx) emissions on the nitrogen dioxide (NO2) forecasts over this region during the 2008 Beijing Olympic Games. A mixed effect on the NO2 forecasts was observed through application of the cross-variable assimilation approach in the real-data assimilation (RDA) experiments. The method improved the NO2 forecasts over almost half of the urban sites with reductions of the root mean square errors (RMSEs) by 15–36 % in contrast to big increases of the RMSEs over other urban stations by 56–239 %. Over the urban stations with negative DA impacts, improvement of the NO2 forecasts (with 7 % reduction of the RMSEs) was noticed at night and in the morning versus significant deterioration during daytime (with 190 % increase of the RMSEs), suggesting that the negative data assimilation impacts mainly occurred during daytime. Ideal-data assimilation (IDA) experiments with a box model and the same cross-variable assimilation method confirmed the mixed effects found in the RDA experiments. In the same way, NOx emission estimation was improved at night and in the morning even under large biases in the prior emission, while it deteriorated during daytime (except for the case of minor errors in the prior emission). The mixed effects observed in the cross-variable data assimilation, i.e., positive data assimilation impacts on NO2 forecasts over some urban sites, negative data assimilation impacts over the other urban sites, and weak data assimilation impacts over suburban sites, highlighted the limitations of the EnKF under strong nonlinear relationships between chemical variables. Under strong nonlinearity between daytime ozone concentrations and NOx emissions uncertainties (with large biases in the a priori emission), the EnKF may come up with inefficient or wrong adjustments to NOx emissions. The present findings reveal that bias correction is essential for the application of the EnKF in dealing with the data assimilation problem over strong nonlinear system.

The mixing layer is an important meteorological factor that affects air pollution. In this study, the atmospheric mixing layer height (MLH) was observed in Beijing from July 2009 to December 2012 using a ceilometer. By comparison with radiosonde data, we found that the ceilometer underestimates the MLH under conditions of neutral stratification caused by strong winds, whereas it overestimates the MLH when sand-dust is crossing. Using meteorological, PM2.5, and PM10 observational data, we screened the observed MLH automatically; the ceilometer observations were fairly consistent with the radiosondes, with a correlation coefficient greater than 0.9. Further analysis indicated that the MLH is low in autumn and winter and high in spring and summer in Beijing. There is a significant correlation between the sensible heat flux and MLH, and the diurnal cycle of the MLH in summer is also affected by the circulation of mountainous plain winds. Using visibility as an index to classify the degree of air pollution, we found that the variation in the sensible heat and buoyancy term in turbulent kinetic energy (TKE) is insignificant when visibility decreases from 10 to 5 km, but the reduction of shear term in TKE is near 70 %. When visibility decreases from 5 to 1 km, the variation of the shear term in TKE is insignificant, but the decrease in the sensible heat and buoyancy term in TKE is approximately 60 %. Although the correlation between the daily variation of the MLH and visibility is very poor, the correlation between them is significantly enhanced when the relative humidity increases beyond 80 %. This indicates that humidity-related physicochemical processes is the primary source of atmospheric particles under heavy pollution and that the dissipation of atmospheric particles mainly depends on the MLH. The presented results of the atmospheric mixing layer provide useful empirical information for improving meteorological and atmospheric chemistry models and the forecasting and warning of air pollution.

The heat dissipation of surrounding rock of a non-circular roadway is computed using an equivalent circular roadway approach under three circumstances when the area, perimeter, or hydraulic diameter of the circular roadway is equal to the non-circular roadway to obtain the optimal equivalent radius. The differential equations of heat conduction for unstable surrounding rock are established in cylindrical and rectangular coordinate systems using dimensionless analysis method. The calculation formulas of heat dissipation capacity and heat transfer resistance are derived from differential equations. Based on the method of equivalent radius, the similarities and differences between non-circular and circular roadways in calculating the heat dissipation of surrounding rock are discussed. Using the finite volume method, the calculation models for non-circular and circular roadways in the heat dissipation of surrounding rock are also established, among the non-circular roadways including three circumstances, namely, trapezoid, rectangle, and arch. The relation errors of heat dissipation of the surrounding rock of the three equivalent circular roadway methods are investigated for the three non-circular roadways. Results show that the calculation approach with equal perimeters is the best for the heat dissipation of surrounding rock of non-circular roadways.