Long-term air pollution data with high temporal and spatial resolutions are needed to support the research of physical and chemical processes that affect the air quality, and the corresponding health ...risks. However, such datasets were not available in China until recently. For the first time, this study examines the spatial and temporal variations of PM2.5, PM10, CO, SO2, NO2, and 8h O3 in 31 capital cities in China between March 2013 and February 2014 using hourly data released by the Ministry of Environmental Protection (MEP) of China. The annual mean concentrations of PM2.5 and PM10 exceeded the Chinese Ambient Air Quality Standards (CAAQS), Grade I standards (15 and 40μg/m3 for PM2.5 and PM10, respectively) for all cities, and only Haikou, Fuzhou and Lasa met the CAAQS Grade II standards (35 and 70μg/m3 for PM2.5 and PM10, respectively). Observed PM2.5, PM10, CO and SO2 concentrations were higher in cities located in the North region than those in the West and the South-East regions. The number of non-attainment days was highest in the winter, but high pollution days were also frequently observed in the South-East region during the fall and in the West region during the spring. PM2.5 was the largest contributor to the air pollution in China based on the number of non-attainment days, followed by PM10, and O3. Strong correlation was found between different pollutants except for O3. These results suggest great impacts of coal combustion and biomass burning in the winter, long range transport of windblown dust in the spring, and secondary aerosol formation throughout the year. Current air pollution in China is caused by multiple pollutants, with great variations among different regions and different seasons. Future studies should focus on improving the understanding of the associations between air quality and meteorological conditions, variations of emissions in different regions, and transport and transformation of pollutants in both intra- and inter-regional contexts.
•Temp-spatial variations of air pollutants in 31 Chinese cities were analyzed.•Major cities in China experience severe air pollution.•Significant temp-spatial differences in criteria air pollutants were observed.•Strong correlation was found between different pollutants except for O3.•China’s pollution is caused by multi-pollutants with temp-spatial variations.
This paper first analyzes the causes of phonological and lexical changes in English linguistics and discusses the main manifestations of English phonological changes and phonological and lexical ...changes. Then, it constructs the evaluation model of English linguistics using the dominant correlation method based on the entropy value, approximation ideal, and gray correlation methods. Finally, data on phonological and lexical changes are analyzed about the development of English linguistics in the past sixty years. From the analysis of factors affecting English vocabulary change, the historical factor responsible for vocabulary change is the development of human society, and the factor value currently stands at 0.428. In comparison, the social, psychological, cultural and foreign language factor values reach 0.654, 0.458, 0.512 and 0.461, respectively.
The North China Plain (NCP) and the Yangtze River Delta (YRD) in China have been experiencing severe particulate matter (PM) pollution problems associated with the rapid economic growth and the ...accelerated urbanization. In this study, hourly mass concentrations of PM2.5 and PM10 during June 1st–August 31st, 2013 were collected in 13 cities located in or adjacent to the NCP region and 20 cities located in the YRD region. The overall average PM2.5 and PM10 concentrations were 77.0 μg/m3 and 136.2 μg/m3 in the NCP region, respectively, and 42.8 μg/m3 and 74.9 μg/m3 in the YRD region, respectively. The frequencies of occurrence of concentrations exceeding the China's Ambient Air Quality Standard (AAQS) (BG3095-12) Grade I standards were 83% for PM2.5 and 93% for PM10 in the NCP region, and 51% for PM2.5 and 66% for PM10 in the YRD region. Strong temporal correlation for both PM2.5 and PM10 between cities within 250 km was frequently observed. PM2.5 was found to be negatively associated with wind speed. On the PM2.5 episode days (when the 24 h PM2.5 concentration is greater than 75 μg/m3), average PM2.5 concentrations were 2–4 times greater compared to the non-episode days. The PM2.5 to PM10 ratio increased from 0.50 (0.57) on the non-episode days to 0.64 (0.64) on the episode days in the NCP (YRD) region. No distinct weekday/weekend difference was observed for PM2.5, PM10, and other gaseous pollutants (CO, SO2, NO2, and O3) in all cities. The results presented in this paper will serve as an important basis for future regional air quality modeling and source apportionment studies.
•Summertime PM2.5 and PM10 in the NCP and YRD regions of China were analyzed.•Average PM2.5 and PM10 concentrations are 77.0 and 136.2 μg/m3 in the NCP region.•Average PM2.5 and PM10 concentrations are 42.8 and 74.9 μg/m3 in the YRD region.•Strong temporal correlation between cities within 250 km is found.•PM2.5 concentrations on episode days are 2–4 times greater than non-episode days.
One year-long criteria air pollutants data collected in Beijing were analyzed in this paper, which can support the research on formation, transport and human health effects of air pollutants. This is ...the first time to study the spatial and temporal variations of criteria pollutants in Beijing using hourly observational data from 12 sites between June 2014 and May 2015 released by the Ministry of Environmental Protection (MEP) of China. Beijing is facing tremendous air pollution as the daily averaged PM2.5 (particulate matter with aerodynamic diameter less than 2.5µm) concentrations in all sites exceeding the Chinese Ambient Air Quality Standards (CAAQS) Grade I & II standards (15 and 35µg/m3). Slightly differences in PM2.5 and ozone (O3) were observed between sites at the urban and rural areas. Pearson correlation coefficients show that most pollutants are temporally correlated in Beijing except for O3. The coefficients of divergence (COD) indicate that PM2.5 is associated at most sites with only one rural site (Dingling) having observable difference and one site may be insufficient for monitoring surrounding area. The 8h peak O3 (O3-8h) also correlates at different sites but with one urban site (Haidianquwanliu) different from others. In addition, an extreme PM2.5 event (hourly average concentration exceeding 300μg/m3 for ~40h) was examined with the consideration of meteorological conditions. Southerly wind with low speed and high relative humidity allow the accumulation of pollutants while northerly wind with high speed and low relative humidity result in good air quality.
•One year-long concentrations of criteria air pollutants in Beijing were analyzed.•Air pollution in Beijing is severe with PM2.5 exceeding CAAQS standards.•Major pollutants in Beijing are spatially and temporally correlated.•Meteorological conditions play significant role in extreme PM2.5 event.
The adoption of geothermal energy in space conditioning of buildings through utilizing ground source heat pump (GSHP, also known as geothermal heat pump) has increased rapidly during the past several ...decades. However, one problem in operating GSHPs is that collection or rejection heat from the ground alters the ground temperature, which can adversely affect the coefficient of performance (COP). In turn, the amount of heat that must be exchanged with the ground increases in order to satisfy a given heating or cooling load. This paper presents a novel model to calculate the soil temperature distribution and the COP of GSHP. Different scenarios were simulated to quantify the impact of different factors on the GSHP performance, including seasonal balance between heat collection and heat rejection, daily running mode, and spacing between boreholes. Our results show that greater loads and smaller distances between boreholes cause changes in soil temperature large enough to adversely affect the GSHP performance, even resulting in COPs less than those commonly achieved with air source heat pumps. However, shifting from heating to cooling on a seasonal basis can, in part, mitigate this problem. Long boreholes, additional space between boreholes and intermittent running mode could also improve the performance of GSHP, but large initial investment is required.
•A novel model was developed to calculate GSHP COP and soil temperatures.•GSHP is suitable for buildings with balanced seasonal cooling and heating loads.•Intermittent operation modes can facilitate the soil temperature recovery.•Long boreholes with large spacing can improve the GSHP performance.
Ambient PM2.5 pollution is a substantial threat to public health in global megacities. This paper reviews the PM2.5 pollution of 45 global megacities in 2013, based on mass concentration from ...official monitoring networks and composition data reported in the literature. The results showed that the five most polluted megacities were Delhi, Cairo, Xi'an, Tianjin and Chengdu, all of which had an annual average concentration of PM2.5 greater than 89μg/m3. The five cleanest megacities were Miami, Toronto, New York, Madrid and Philadelphia, the annual averages of which were less than 10μg/m3. Spatial distribution indicated that the highly polluted megacities are concentrated in east-central China and the Indo-Gangetic Plain. Organic matter and SNA (sum of sulfate, nitrate and ammonium) contributed 30% and 36%, respectively, of the average PM2.5 mass for all megacities. Notable seasonal variation of PM2.5 polluted days was observed, especially for the polluted megacities of China and India, resulting in frequent heavy pollution episodes occurring during more polluted seasons such as winter. Marked differences in PM2.5 pollution between developing and developed megacities require more effort on local emissions reduction as well as global cooperation to address the PM2.5 pollution of those megacities mainly in Asia.
•PM2.5 pollution in 45 megacities in 2013 was compared.•The megacities in east-central China and the Indo-Gangetic Plain were most polluted.•Organic matter and sulfate, nitrate and ammonium dominated the composition of PM2.5 of global megacities.•Heavy polluted days occurred in winter and in Asia megacities.
Early oxidation behavior of a Nb-Stabilizing heat-resistant steel in water vapor at 700 °C for 336 h was investigated. Micro-characterization methods including in-depth XPS, SEM/EDS, FIB were ...employed to acquire the composition and distribution of oxidation products. The results showed that the oxidation kinetics of this heat-resistant steel almost followed a parabolic law at 700 °C, indicating the oxidation was controlled by the ion diffusion. Surfaces of oxidation products on TP347HFG were gradually from compact to loose with a longer exposure. Oxide scales were mainly composed of layered (Mn, Fe)Cr2O4 and Cr2O3 and scattered Nb2O5. Contents of Mn at the surface were much higher than other positions, confirming that Mn diffuse much faster than Fe and Cr. During the initial oxidation stage, NbC was transformed into Nb2O5, which was covered by Fe–Cr oxide scales. The growth of oxide scales on TP347HFG is suggested.
•Early oxidation behavior of TP347HFG in water vapor at 700 °C was investigated.•Oxide scales were mainly composed of layered (Mn, Fe)Cr2O4 and Cr2O3 and scattered Nb2O5.•The growth of oxide scales on TP347HFG at the early stage is suggested.
Cancer stem cells play a critical role in colorectal cancer (CRC) progression. Myeloid‐derived suppressor cells (MDSCs) promote tumor progression through multiple mechanisms in CRC. The roles of ...MDSCs in CRC cell stemness are unclear. MDSC‐derived exosomes are proposed to act as intercellular messengers. Herein, it is reported that granulocytic MDSCs (G‐MDSCs) promote CRC cell stemness and progression in mice through exosomes. It is found that S100A9, is highly expressed in G‐MDSC‐derived exosomes, and its blockade suppresses CRC cell stemness and the susceptibility of mice to AOM/DSS‐induced colitis‐associated colon cancer. Hypoxia induces G‐MDSCs to secrete more exosomes in a hypoxia‐inducible factor 1α (HIF‐1α)‐dependent manner, and respiratory hyperoxia can reduce CRC cells stemness through the inhibition of GM‐Exo production. Study‐based CRC patients also show that human MDSCs enhance CRC cell stemness and growth via exosomal S100A9, and plasma exosomal S100A9 level in CRC patients is markedly higher than that in healthy subjects. Thus, this study suggests that G‐MDSCs promote CRC cell stemness and growth through exosomal S100A9. Moreover, respiratory hyperoxia may be a beneficial strategy to reduce CRC cells stemness through the inhibition of GM‐Exo production. MDSCs exosomal S100A9 may be a marker for predicting the development of CRC.
Granulocytic myeloid‐derived suppressor cells (G‐MDSCs) exhibit the function of promoting colorectal cancer (CRC) cell stemness through exosomal S100A9. Hypoxia induces G‐MDSCs to secrete more exosomes by stimulating HIF‐1α‐dependent Rab27a expression. Exosomal S100A9 increases ROS production with phosphorylation of STAT3 and NF‐κB resulting in enhanced stemness of CRC cells.
•An accurate surrogate model for addressing flow maldistribution effectively.•High-temperature zones result primarily from the lowest coolant channel velocity.•An innovative index to ensure the ...lowest velocity and temperature maldistribution.•Optimized structure minimizes flow maldistribution and eliminates the hot zones.
Flow maldistribution significantly impacts the performance and operation of microchannel heat sinks, which are extensively utilized across various industries. This study develops a surrogate model to address the flow maldistribution in microchannel heat sinks, employing a combination of genetic algorithm backpropagation neural networks and numerical simulations. Genetic algorithms optimize the microchannel heat sink manifold, involving five variables. The optimized manifold reduces the flow maldistribution factor by 38 % at a coolant inlet velocity of 0.1 m/s compared to that of the conventional structure. The mechanisms of this improvement are explored through comparative analyses of the manifold shape and pressure distribution. However, addressing the flow maldistribution alone proves insufficient in eliminating local hot zones within the microchannel heat sink. Consequently, this study introduces the concept of a corrected maldistribution factor and establishes a new structure guided by this factor as the optimization index. The results indicate a 47 % reduction in the maximum-to-minimum channel flow velocity ratio compared to that of the conventional structure at a coolant inlet velocity of 2 m/s. Furthermore, the maximum temperature drops by 20 K, significantly enhancing the flow and temperature distribution within the microchannel heat sink.
In this study, the tomography of dynamic stress coefficient (TDSC) was established based on a mechanical model of stress wave propagation in bedding planes and a mathematical model of the stress wave ...attenuation in rock masses. The reliability of the TDSC was verified by a linear bedding plane model and field monitoring. Generally, the TDSC in the dynamic stress propagation of bedding planes increases with the following conditions: (1) the increase of the normal stiffness of the bedding plane, (2) the increase of the incident angle of the stress wave, (3) the decrease of the incident frequency of the stress wave, or (4) the growth of three ratios (the ratios of rock densities, elastic moduli, and the Poisson’s ratios) of rocks on either side of bedding planes. The additional stress weakens TDSC linearly and slowly during the stress wave propagation in bedding planes, and the weakening effect increases with the growth of the three ratios. Besides, the TDSC decreases exponentially in the rock mass as propagation distance increases. In a field case, the TDSC decreases significantly as vertical and horizontal distances increase and its wave range increases as vertical distance increases in the sedimentary rock layers.
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