期刊文献+
共找到100,649篇文章
< 1 2 250 >
每页显示 20 50 100
Terahertz wave generation from ring-Airy beam induced plasmas and remote detection by terahertz-radiation- enhanced-emission-of-fluorescence: a review
1
作者 Kang LIU Pingjie HUANG Xi-Cheng ZHANG 《中国光电子学前沿:英文版》 EI CSCD 2019年第2期117-147,共31页
With the increasing demands for remote spectroscopy in many fields ranging from homeland security to environmental monitoring, terahertz (THz) spectroscopy has drawn a significant amount of attention because of its ca... With the increasing demands for remote spectroscopy in many fields ranging from homeland security to environmental monitoring, terahertz (THz) spectroscopy has drawn a significant amount of attention because of its capability to acquire chemical spectral signatures non-invasively. However, advanced THz remote sensing techniques are obstructed by quite a few factors, such as THz waves being strongly absorbed by water vapor in the ambient air, difficulty to generate intense broadband coherent THz source remotely, and hard to transmit THz waveform information remotely without losing the signal to noise ratio, etc. In this review, after introducing different THz air-photonics techniques to overcome the difficulties of THz remote sensing, we focus mainly on theoretical and experimental methods to improve THz generation and detection performance for the purpose of remote sensing through tailoring the generation and detection media, air-plasma. For the THz generation part, auto-focusing ring-Airy beam was introduced to enhance the THz wave generation yield from two-color laser induced air plasma. By artificially modulated exotic wave packets, it is exhibited that abruptly auto-focusing beam induced air-plasma can give an up to 5.3-time-enhanced THz wave pulse energy compared to normal Gaussian beam induced plasma under the same conditions. At the same time, a red shift on the THz emission spectrum is also observed. A simulation using an interference model to qualitatively describe these behaviors has be developed. For the THz detection part, the results of THz remote sensing at 30 m using THz-radiation-enhanced-emission- of-fluorescence (THz-REEF) technique are demonstrated, which greatly improved from the 10 m demonstration last reported. The THz-REEF technique in the counter-propagation geometry was explored, which is proved to be more practical for stand-off detections than co-propagation geometry. We found that in the counter- propagating geometry the maximum amplitude of the REEF signal is comparable to that in the 展开更多
关键词 ultrafast TERAHERTZ (THz) techniques THZ air- photonics ring-Airy beams THz-radiation-enhanced-emis- sion-of-fluorescence (THz-REEF) of air-plasma in co- propagation geometry THz-REEF of air-plasma in coun-ter-propagation geometry
Vietnam Economic Situation and Its Impacts on Three Natural Resources: Air, Water, and Soil 预览
2
作者 Le Dieu Linh Nguyen 《管理研究:英文版》 2019年第6期582-587,共6页
The current economic development is the process of improving the physical and spiritual living conditions for people through the production of material wealth and the improvement of social relations as well as the imp... The current economic development is the process of improving the physical and spiritual living conditions for people through the production of material wealth and the improvement of social relations as well as the improvement of cultural quality.In recent years,Vietnam showed robust growth in terms of economic development,along with the fast pace of urbanization and population increase.However,the economic growth has led to serious problems relating to the environment,such as the pollution of the air,water,and soil,which hugely affected the quality of human life.The Environmental Kuznets Curve(EKC)implied that a country with strong economic background shifting to industrialization or mechanization of agriculture will have positive GDP and the environmental damage level will decrease.The analysis and assessment showed that the environmental problems caused by economic activities are:air pollution in the urban area still maintained at high level;water pollution in rivers and limited fresh water supply;and the soil pollution and declining water supply underneath soil are developing. 展开更多
关键词 SOCIO-ECONOMIC development EKC AIR WATER SOIL AIR POLLUTION WATER POLLUTION SOIL POLLUTION
在线阅读 下载PDF
In-situ emb e dding zeolitic imidazolate framework derived Co–N–C bifunctional catalysts in carbon nanotube networks for flexible Zn–air batteries 预览
3
作者 Bo Lv Sha Zeng +6 位作者 Wei Yang Jian Qiao Chao Zhang Chengfeng Zhu Minghai Chen Jiangtao Di Qingwen Li 《能源化学:英文版》 SCIE EI CAS CSCD 2019年第11期170-176,共7页
Recently, the development of high-performance bifunctional oxygen catalysts integrated with flexible conductive scaffolds f or rechargeable metal-air batteries has attracted considerable interest, driving by fastgrowi... Recently, the development of high-performance bifunctional oxygen catalysts integrated with flexible conductive scaffolds f or rechargeable metal-air batteries has attracted considerable interest, driving by fastgrowing wearable electronics. Herein, we report a flexible bifunctional oxygen catalyst thin film consisting of Co–N–C bifunctional catalysts embedding in carbon nanotube(CNT) networks. The catalyst is readily prepared by pyrolysis of cobalt-based zeolitic imidazolate frameworks(ZIF-67) that are in-situ synthesized in CNT networks. Such catalyst film demonstrates very high catalytic activities for oxygen reduction(onset potential: 0.91 V, and half-wave potential: 0.87 V vs. RHE) and oxygen evolution(10 m Acm^-2 at 1.58 V) reactions, high methanol tolerance property, and long-term stability(97% current retention). Moreover, our integrated catalyst film shows very good structure flexibility and robustness. Based on the obtained film air electrodes, flexible Zn–air batteries demonstrate low charging and discharging overpotentials(0.82 V at 1 m A cm^-1) and excellent structure stability in the bending tests. These results indicate that presently reported catalyst films are potential air electrodes for flexible metal–air batteries. 展开更多
关键词 Air electrodes Carbon nanotube films Bifunctional catalysts Zn-air batteries Zeolitic imidazolate framework
在线阅读 下载PDF
Efficient molecular model for squeeze-film damping in rarefied air
4
作者 陆存豪 李普 方玉明 《中国物理B:英文版》 SCIE EI CAS CSCD 2019年第9期367-372,共6页
Based on the energy transfer model(ETM) proposed by Bao et al.and the Monte Carlo(MC) model proposed by Hutcherson and Ye, this paper proposes an efficient molecular model(MC-S) for squeeze-film damping(SQFD) in raref... Based on the energy transfer model(ETM) proposed by Bao et al.and the Monte Carlo(MC) model proposed by Hutcherson and Ye, this paper proposes an efficient molecular model(MC-S) for squeeze-film damping(SQFD) in rarefied air by releasing the assumption of constant molecular velocity in the gap.Compared with the experiment data, the MC-S model is more efficient than the MC model and more accurate than ETM.Besides, by using the MC-S model, the feasibility of the empirical model proposed by Sumali for SQFD of different plate sizes is discussed.It is proved that, for various plate sizes, the accuracy of the empirical model is relatively high.At last, the SQFD of various vibration frequencies is discussed, and it shows that, for low vibration frequency, the MC-S model is reduced to ETM. 展开更多
关键词 micro-electro-mechanical system(MEMS) squeeze-film AIR DAMPING rarefied AIR MOLECULAR model
Approach for air-to-air confrontment based on uncertain interval information conditions 预览
5
作者 LI Qiuni YANG Rennong +1 位作者 FENG Chao LIU Zongcheng 《系统工程与电子技术:英文版》 SCIE EI CSCD 2019年第1期100-109,共10页
Model combat information conditions are always uncertain and varied, the uncertain interval theory is therefore introduced into the research of multiple fighters suppressing the integrated air defense system (IADS) pr... Model combat information conditions are always uncertain and varied, the uncertain interval theory is therefore introduced into the research of multiple fighters suppressing the integrated air defense system (IADS) problem. Considering that the combat information conditions are uncertain intervals, the payoff function of the game for multiple fighters suppressing the IADS is modeled. Using the operation rules for interval numbers and the possibility degree, an improved chaotic particle swarm optimization (CPSO) is designed to solve the proposed model so as to obtain the optimal game solution. Comparison simulations are performed to analyze the influence of the weapons consumption and the distances of non-escaped zone and jamming on air combat result. Simulation results suggest that Nash equilibrium is achieved and verify the effectiveness of the proposed method. 展开更多
关键词 INTERVAL information integrated AIR defense system (IADS) AIR COMBAT CHAOTIC particle SWARM optimization (CPSO) game.
在线阅读 下载PDF
Air-vent layouts and water-air flow behaviors of a wide spillway aerator 预览
6
作者 James Yang Penghua Teng Chang Lin 《力学快报:英文版》 CAS CSCD 2019年第2期130-143,共14页
A spillway aerator should guarantee favorable flow conditions in the coupled water-air system even if the aerator is unconventionally wide. Eight air-vent configurations are devised and incorporated into a 35-m wide c... A spillway aerator should guarantee favorable flow conditions in the coupled water-air system even if the aerator is unconventionally wide. Eight air-vent configurations are devised and incorporated into a 35-m wide chute aerator for a generalized study. Computational fluid dynamics (CFD) simulations are performed to explore their effects on water-jet and air-cavity features. The Re-normalisation group (RNG) k-ε turbulence model and the two-fluid model are combined to predict the two-phase flow field. The results demonstrate appreciable influences of the vent layouts on the water-air flow. The air vents stir the air motion and re-distribute the cavity air pressure. Once the vent layout is modified, reciprocal adjustments exist between the jet behavior and air-pressure field in the cavity, thus leading to considerable differences in air-flow rate, jet-trajectory length, vent air-flow distribution across the chute, etc. The large width plays a discernable role in affecting the aerated flow. Telling differences exist between the near-wall region and the central part of the chute. To improve the duct pressure propagation, a gradual augment of the vent area should be assigned towards the chute center. Relative to single-slot vents across the flow, the layouts with segregated vents gain by comparison. A designer should see to it that a vented aerator operates satisfactorily for a given range of flow discharges. 展开更多
关键词 SPILLWAY WIDE AERATOR AIR ENTRAINMENT Air-vent layout Jet trajectory CFD
在线阅读 下载PDF
THE INTERACTION OF HURRICANE MICHAEL WITH AN UPPER TROUGH LEADING TO INTENSIFICATION RIGHT UP TO LANDFALL
7
作者 Jeff Callaghan 《热带气旋研究与评论(英文版)》 2019年第2期101-108,共8页
Hurricane Michael was intensifying as it made landfall devastating areas of the Florida Panhandle including the small town of Mexico Beach. The structure of the hurricane is examined using radar wind data made availab... Hurricane Michael was intensifying as it made landfall devastating areas of the Florida Panhandle including the small town of Mexico Beach. The structure of the hurricane is examined using radar wind data made available from aircraft reconnaissance missions. This showed a dominant warm air advection configuration(winds turning in direction in an anticyclonic fashion with height) around the core of the hurricane. Conventional radiosonde data was also used to study the warm air advection environment east of a deep layered tough system which Michael moved into and which appeared to favour such strong intensification. The structure of this deep trough is also examined and compared with a situation where Hurricane Dennis in 2005 weakened as it approached the coast in much the same region. It appears that the thermal structure of the upper trough at low to middle levels is critical to whether the hurricane intensifies or weakens with the presence of strong cold air advection associated with weakening. 展开更多
关键词 INTENSIFICATION warm AIR advection cold AIR advection upper OUTFLOW deep TROUGH
Thermodynamic Modeling and Simulation of Air System Control Device 预览
8
作者 FU Jiangfeng LI Huacong +1 位作者 LIU Xianwei HONG Linxiong 《南京航空航天大学学报:英文版》 EI CSCD 2019年第3期517-526,共10页
This paper aims to obtain the thermodynamic characteristics of the air system control device sealing part in different compressor bleed air and ambient temperature.On the basis of considering the main factors affectin... This paper aims to obtain the thermodynamic characteristics of the air system control device sealing part in different compressor bleed air and ambient temperature.On the basis of considering the main factors affecting the heat exchange process and simplifying the physical model of the air system control device,the thermodynamic model of air system control device is established based on the basic theory of laminar flow heat transfer and heat conduction theory.Then the piston motion characteristics and the thermodynamic characteristics of the air system control device seal are simulated.The simulation results show that the valve actuation dynamic time of piston is about 0.13 s in the actual working conditions,and the temperature effect on the dynamic response of the piston rod is only 5 ms when the inlet air temperature at 300 ℃ and 370 ℃.The maximum temperature of the air system control device sealing part is not more than 290 ℃ under long time working condition of compressor air entraining.The highest temperature of the sealing part can reach up to 340 ℃ when the air flow temperature reaches the limit temperature of 370 ℃,and the longest duration working temperature limit is not more than 14 s.Therefore,the selection of control device sealing material should consider the work characteristic of instantaneous temperature limit. 展开更多
关键词 AEROENGINE AIR system AIR bleed CONTROL DEVICE THERMODYNAMIC analysis
在线阅读 下载PDF
Citizens and Air Quality: The Results of the First Survey Carried Out in the Po River Basin (Northern Italy) 预览
9
作者 Enrico Cancila Irene Sabbadini +2 位作者 Marco Ottolenghi Marco Deserti Sara Tessitore 《大气污染开放期刊(英文)》 2019年第3期69-79,共11页
The air quality survey investigated the level of perception and awareness of citizens on the air quality in the 42 cities (provincial capitals) of the Po basin in the north west of Italy. This study means that percept... The air quality survey investigated the level of perception and awareness of citizens on the air quality in the 42 cities (provincial capitals) of the Po basin in the north west of Italy. This study means that perceptions could then be compared between in the Po basin and other parts of Italy and Europe. This research was carried out as part of the Life15 IPE IT 013 PREPAIR Project (Po Regions Engaged to Policies of Air), which involves 18 national and international partners, and includes all the regions of the Po Basin. The survey involved around 7331 citizens that live in the Po basin that includes 42 cities (provincial capitals) and a total of 6.5 million inhabitants. A multivariate analysis was applied to identify the main citizens’ profiles concerning the topic of air quality and the availability to implement virtuous behaviours to reduce air pollution. Four different profiles emerge from the cluster analysis: “Committed and proactive”, “Willing but …”, “Hesitant”, “Not willing”. 展开更多
关键词 PERCEPTION Air POLLUTION Quality CITIZENS
在线阅读 免费下载
Safety assessment of approximate segregated parallel operation on closely spaced parallel runways
10
作者 Fei LIU Xinze LIU +1 位作者 Mingjiang MOU Zhiqiang WEI 《中国航空学报:英文版》 SCIE EI CAS CSCD 2019年第2期463-476,共14页
With the continuous growth of air traffic flow, some airports in China or other countries begin to construct Closely Spaced Parallel Runways(CSPR) to meet the capacity requirement of civil aviation. In this paper, the... With the continuous growth of air traffic flow, some airports in China or other countries begin to construct Closely Spaced Parallel Runways(CSPR) to meet the capacity requirement of civil aviation. In this paper, the simulation and calculation method of flight trajectory is developed,as well as the collision risk calculation method and wake vortex encounter risk calculation method.New methods for departure and go-around procedures are proposed to achieve approximate segregated parallel operation in an attempt to obtain approximately the same results on closely spaced parallel runways as on widely spaced parallel runways. By comparing with the independent parallel departure and segregated parallel operation in ICAO Doc. 9643, it is found that the lateral separation between aircraft in this proposal is not less than the separations in the other two cases. Based on the simulation calculation of flight trajectories under different conditions, the probabilities of collision conflict and encountering wake vortex are lower than those in current operation plan.The proposed plan has no special requirements in pilot operation, control command procedures,airport facilities, or meteorological observation and prediction, so it is convenient to promote and implement at the airports with closely spaced parallel runways. 展开更多
关键词 AIR traffic control AIR transportation Closely spaced PARALLEL runways Segregated PARALLEL operation WAKE VORTEX ENCOUNTER WAKE VORTEX separation standards
Degradation of p-nitrophenol(PNP)in aqueous solution by mFe/Cu-air-PS system
11
作者 Heng Zhang Qingqing Ji +2 位作者 Leiduo Lai Gang Yao Bo Lai 《中国化学快报:英文版》 SCIE CAS CSCD 2019年第5期1129-1132,共4页
In this study,batch experiments were conducted to investigate the performance of microscale Fe/Cu bimetallic particles-air-persulfate system(mFe/Cu-air-PS)for p-nitrophenol(PNP)treatment in aqueous solution.First,the ... In this study,batch experiments were conducted to investigate the performance of microscale Fe/Cu bimetallic particles-air-persulfate system(mFe/Cu-air-PS)for p-nitrophenol(PNP)treatment in aqueous solution.First,the optimal operating parameters(i.e.,aeration rate of 1.0 L/min,theoretical Cu mass loading(TMLCu)of 0.110 g Cu/g Fe,mFe/Cu dosage of 15 g/L,PS total dosage of 15 mmol/L,feeding times of PS of 5,initial pH 5.4)were obtained successively by single-factor experiments.Under the optimal conditions,high COD and TOC removal efficiencies(71.0%,65.8%)were obtained after 60 min treatment.Afterword,compared with control experiments(i.e.,mFe/Cu,air,PS,mFe/Cu-air,mFe/Cu–PS,air-PS and mFe-air-PS),mFe/Cu-air-PS system exerted superior performance for pollutants removal due to the synergistic effect between mFe/Cu,air and PS.In addition,the results of control experiments and radical quenching experiments indicate this reinforcement by feeding of PS was greater than by aeration in m Fe/Cu-air-PS system.Furthermore,the degradation intermediates of PNP in mFe/Cu-air-PS process were identified and measured by HPLC.Based on the detected intermediates,the degradation pathways of PNP were proposed comprehensively,which revealed that toxic and refractory PNP in aqueous solution could be decomposed effectively and transformed into lower toxicity intermediates.As a result,m Fe/Cu-air-PS system with the performance of oxidation combined reduction can be also a potential technology for the treatment of toxic and refractory PNP contained wastewater. 展开更多
关键词 p-Nitrophenol(PNP) Microscale Fe/Cu bimetallic particles(mFe/Cu) Persulfate(PS) AIR aeration mFe/Cu-air-PS system
Experimental Study of Air Layer Drag Reduction with Bottom Cavity for A Bulk Carrier Ship Model 预览
12
作者 WU Hao OU Yong-peng 《中国海洋工程:英文版》 CSCD 2019年第5期554-562,共9页
Air lubrication by means of a bottom cavity is a promising method for ship drag reduction. The characteristics of the bottom cavity are sensitive to the flow field around the ship hull and the effect of drag reduction... Air lubrication by means of a bottom cavity is a promising method for ship drag reduction. The characteristics of the bottom cavity are sensitive to the flow field around the ship hull and the effect of drag reduction, especially the depth of the bottom cavity. In this study, a ship model experiment of a bulk carrier is conducted in a towing tank using the method of air layer drag reduction (ALDR) with different bottom cavity depths. The shape of the air layer is observed, and the changes in resistance are measured. The model experiments produce results of approximately 20% for the total drag reduction at the ship design speed for a 25-mm cavity continuously supplied with air at Cq = 0.224 in calm water, and the air layer covers the whole cavity when the air flow rate is suitable. In a regular head wave, the air layer is easily broken and reduces the drag reduction rate in short waves, particularly when λ/Lw1 is close to one;however, it still has a good drag reduction effect in the long waves. 展开更多
关键词 AIR LAYER drag reduction BULK CARRIER model test DEPTH of CAVITY AIR LAYER shape
在线阅读 下载PDF
Challenges in Civil Aviation for the New Brazilian Government 预览
13
作者 Flademir Candido da Silva 《交通与运输工程:英文版》 2019年第1期13-19,共7页
After a cycle of management that began with President Luis Inácio Lula da Silva,the inauguration of Jair Bolsonaro bringing a new period of management in the Federative Republic of Brazil.In addition to macroecon... After a cycle of management that began with President Luis Inácio Lula da Silva,the inauguration of Jair Bolsonaro bringing a new period of management in the Federative Republic of Brazil.In addition to macroeconomic issues and various other national interests,the new government will have to analyze the legacies and will have new challenges in the civil aviation sector.Using an evolutionary historical perspective,this article briefly points out some alternatives for the implementation of viable projects for the development of this important sector for the country’s development. 展开更多
关键词 AVIATION planning AIR NAVIGATION ATC(air traffic control)
在线阅读 下载PDF
苯甲醛衍生-高效液相色谱法测定工作场所空气中肼
14
作者 崔师伟 闫慧芳 《中国职业医学》 CAS 北大核心 2019年第1期78-82,共5页
目的建立工作场所空气中肼的苯甲醛衍生-高效液相色谱测定方法。方法采用硫酸溶液浸渍过的玻璃纤维滤膜采集空气样品,经磷酸二氢钠-乙二胺四乙酸二钠缓冲液洗脱,体积分数为1.00%的苯甲醛-乙腈溶液衍生,并经C18液相色谱柱分离,二极管阵... 目的建立工作场所空气中肼的苯甲醛衍生-高效液相色谱测定方法。方法采用硫酸溶液浸渍过的玻璃纤维滤膜采集空气样品,经磷酸二氢钠-乙二胺四乙酸二钠缓冲液洗脱,体积分数为1.00%的苯甲醛-乙腈溶液衍生,并经C18液相色谱柱分离,二极管阵列检测器检测。结果肼在质量为12.50~150.00μg时线性关系良好,相关系数为0.999 7。肼的平均洗脱效率为89.28%~95.52%,批内、批间相对标准偏差分别为1.09%~1.86%和3.63%~4.00%;样品在4℃冰箱内至少可保存25 d。结论本方法灵敏度高,精密度好,样品前处理简单,可用于工作场所空气中肼的测定。 展开更多
关键词 工作场所 空气 衍生化 液相色谱
Spatial-temporal Analysis of Daily Air Quality Index in the Yangtze River Delta Region of China During 2014 and 2016 预览
15
作者 YE Lei OU Xiangjun 《中国地理科学:英文版》 SCIE CSCD 2019年第3期382-393,共12页
Urban air pollution is a prominent problem related to the urban development in China, especially in the densely populated urban agglomerations. Therefore, scientific examination of regional variation of air quality an... Urban air pollution is a prominent problem related to the urban development in China, especially in the densely populated urban agglomerations. Therefore, scientific examination of regional variation of air quality and its dominant factors is of great importance to regional environmental management. In contrast to traditional air pollution researches which only concentrate on a single year or a single pollutant, this paper analyses spatiotemporal patterns and determinants of air quality in disparate regions based on the air quality index(AQI) of the Yangtze River Delta region(YRD) of China from 2014 to 2016. Results show that the annual average value of the AQI in the YRD region decreases from 2014 to 2016 and exhibit a basic characteristic of ‘higher in winter, lower in summer and slightly high in spring and autumn’. The attainment rate of the AQI shows an apparently spatial stratified heterogeneity, Hefei metropolitan area and Nanjing metropolitan area keeping the worst air quality. The frequency of air pollution occurring in large regions was gradually decreasing during the study period. Drawing from entropy method analysis, industrialization and urbanization represented by per capita GDP and total energy consumption were the most important factors. Furthermore, population agglomeration is a factor that cannot be ignored especially in some mega-cities. Limited to data collection, more research is needed to gain insight into the spatiotemporal pattern and influence mechanism in the future. 展开更多
关键词 air quality index(AQI) spatial-temporal evolution contributing FACTORS YANGTZE RIVER Delta(YRD)
在线阅读 下载PDF
黑河流域气温的稳定性与长程相关性
16
作者 杨静 苏凯 叶思菁 《地理学报:英文版》 SCIE CSCD 2019年第9期1462-1474,共13页
Air temperature(AT) is a subsystem of a complex climate.Long-range correlation(LRC) is an important feature of complexity.Our research attempt to evaluate AT’s complexity differences in different land-use types in th... Air temperature(AT) is a subsystem of a complex climate.Long-range correlation(LRC) is an important feature of complexity.Our research attempt to evaluate AT’s complexity differences in different land-use types in the Heihe River Basin(HRB) based on the stability and LRC.The results show the following:(1) AT’s stability presents differences in different land-use types.In agricultural land,there is no obvious variation in the trend throughout the year.Whereas in a desert,the variation in the trend is obvious: the AT is more stable in summer than it is in winter,with Ta ranges of [8,20]°C and SD of the AT residual ranges of [0.2,0.7],respectively.Additionally,in mountainous areas,when the altitude is beyond a certain value,AT’s stability changes.(2) AT’s LRC presents differences in different land-use types.In agricultural land,the long-range correlation of AT is the most persistent throughout the year,showing the smallest difference between summer and winter,with the Hs range of [0.8,1].Vegetation could be an important factor.In a desert,the long-range correlation of AT is less persistent,showing the greatest difference between summer and winter,with the Hs range of [0.54,0.96].Solar insolation could be a dominant factor.In an alpine meadow,the long-range correlation of AT is the least persistent throughout the year,presenting a smaller difference between summer and winter,with the Hs range of [0.6,0.85].Altitude could be an important factor.(3) Usually,LRC is a combination of the Ta and SD of the AT residuals.A larger Ta and smaller SD of the AT residual would be conducive to a more persistent LRC,whereas a smaller Ta and larger SD of the AT residual would limit the persistence of LRC.A larger Ta and SD of the AT residual would create persistence to a degree between those of the first two cases,as would a smaller Ta and SD of the AT residual.In addition,the last two cases might show the same LRC. 展开更多
关键词 Heihe RIVER BASIN air temperature LONG-RANGE CORRELATION stability GEOGRAPHICAL environment
冶炼行业大气排放对周边土壤重金属污染的贡献率研究 预览
17
作者 姚娜 张萌 +1 位作者 刘足根 赵龙 《江西科学》 2019年第5期750-754,共5页
以某工业园为例,采用排放因子法估算2010-2016年园区冶炼企业大气重金属的年平均排放量,从污染物种类、时间变化2个方面分析了冶炼企业大气重金属的排放特征,并揭示了其与周边土壤污染的相关性。结果表明:2010-2016年间,冶炼企业大气砷... 以某工业园为例,采用排放因子法估算2010-2016年园区冶炼企业大气重金属的年平均排放量,从污染物种类、时间变化2个方面分析了冶炼企业大气重金属的排放特征,并揭示了其与周边土壤污染的相关性。结果表明:2010-2016年间,冶炼企业大气砷、铅、镉共累积排放649.29 kg,年均增长达44.60%。大气降尘造成土壤中砷、铅、镉年增加值分别占土壤标准值的1.01%、1.02%和3.77%,以此推算,大气降尘造成土壤镉、砷、铅超标的累积时间分别为16 a、31 a、60 a以上;大气砷和铅之间有显著正相关性,土壤中砷-铅、镉-铅、镉-砷之间均具有显著正相关性,说明它们的同源性很高。 展开更多
关键词 重金属 土壤 大气 排放
在线阅读 下载PDF
中国中小学校日常室内空气质量监测和管理现况
18
作者 戴洁 胡佩瑾 +4 位作者 李艳辉 陶然 温勃 赵海萍 马军 《中国学校卫生》 CAS 北大核心 2019年第8期1224-1226,共3页
目的了解中国中小学校日常室内空气质量监测和管理现况,为制定学习生活环境的卫生标准提供科学依据。方法采用分层抽样的方法抽取中国17个省(区、市)2 400所学校,通过问卷调查的方式对学校相关负责人进行日常通风换气情况的资料收集,采... 目的了解中国中小学校日常室内空气质量监测和管理现况,为制定学习生活环境的卫生标准提供科学依据。方法采用分层抽样的方法抽取中国17个省(区、市)2 400所学校,通过问卷调查的方式对学校相关负责人进行日常通风换气情况的资料收集,采用χ2检验分析不同学校类型间通风换气情况。结果 317所学校(占13.2%)检测过空气环境中CO2浓度。CO2日常检测情况城区学校优于乡镇学校,在寄宿/非寄宿分层中,非寄宿学校优于寄宿学校,差异均有统计学意义(χ^2值分别为72.06,21.89,P值均<0.01)。日常检测过CO、可吸入颗粒物和可挥发性污染物的学校比例依次为6.5%,7.5%,9.3%。在参与调查的学校中,80.8%有日常通风换气制度,其中在寒冷季节每天换气累计时间在90 min以上的学校有925所,占38.5%;少于30 min的学校有331所,占13.8%。结论卫生和教育等相关部门应完善针对教室空气质量监测的规定和标准。建议由疾病预防控制中心等有资质的检测机构进行检测,并加强学校管理力度,为中小学生营造健康的学习生活环境。 展开更多
关键词 空气 质量指标 卫生保健 环境监测 组织和管理
Effect of angular misalignment on the static characteristics of rotating externally pressurized air journal bearing
19
作者 SHI JiangHai CAO HongRui CHEN XueFeng 《中国科学:技术科学英文版》 SCIE EI CAS CSCD 2019年第9期1520-1533,共14页
This paper studies the effect of angular misalignment on the static characteristics of rotating externally pressurized air journal bearing with four degrees of freedom(4-DOF). A clearance function is used to describe ... This paper studies the effect of angular misalignment on the static characteristics of rotating externally pressurized air journal bearing with four degrees of freedom(4-DOF). A clearance function is used to describe the film thickness of air journal bearings with angular misalignment along two perpendicular directions. The finite different method(FDM) and an iterative procedure are applied to solve the Reynolds equation and obtain the air film pressure distribution. Various eccentricity ratios and rotating speeds are taken into considerations for the comparisons of static performances of the air journal bearing under different tilt angles. The results show that the air film thickness, load capacity, stiffness, load moment, attitude angle and volume flow rate are affected greatly by the angular misalignment. 展开更多
关键词 ANGULAR MISALIGNMENT STATIC characteristics AIR journal bearing finite different method
Discharge characteristics of different lightning air terminals under composite voltages
20
作者 庄池杰 王泽众 +5 位作者 曾嵘 刘磊 李特 李敏 催英哲 何金良 《等离子体科学与技术:英文版》 SCIE EI CAS CSCD 2019年第5期1-4,共4页
Different types of lightning air terminals have been designed over the years.Concern regarding the effect of different types of air terminals,especially the early streamer emission(ESE)-type,remains controversial.This... Different types of lightning air terminals have been designed over the years.Concern regarding the effect of different types of air terminals,especially the early streamer emission(ESE)-type,remains controversial.This paper describes the discharge characteristics of different types of air terminals,two of which are quite similar to the ESE-type dynasphere,and concludes that the tested non-standard air terminals have discharge characteristics similar to those of Franklin rods and that their lightning protection performance should be similar. 展开更多
关键词 air tenninal LIGHTNING protection DISCHARGE characteristics COMPOSITE VOLTAGE LEADER
上一页 1 2 250 下一页 到第
使用帮助 返回顶部 意见反馈