Ambient logics have been proposed to describe properties for mobile agentswhich may evolve over time as well as space. This paper takes a predicate-based approach toextending an ambient logic with recursion, yielding ...Ambient logics have been proposed to describe properties for mobile agentswhich may evolve over time as well as space. This paper takes a predicate-based approach toextending an ambient logic with recursion, yielding a predicate μ-calculus in which fixpointformulas are formed using predicate variables. An algorithm is developed for model checkingfinite-control mobile ambients against formulas of the logic, providing the first decidabilityresult for model checking a spatial logic with recursion.展开更多
The maximum rise-height,zero-buoyancy height,thickness of the spreading layer,minimum dilution and the height of the lower edge of the spreading layer are the important characteristic quantities of buoyant jets in str...The maximum rise-height,zero-buoyancy height,thickness of the spreading layer,minimum dilution and the height of the lower edge of the spreading layer are the important characteristic quantities of buoyant jets in stratified ambients.The scaling law is derived by the dimensional analysis of the influence factor on a buoyant jet.The characteristic quantities are found to converge to a single line under the unified scaling law.The correlation of the predicted results and experimental data is given.展开更多
We apply ambient noise tomography to significant seismic data resources in a region including the northeastern Tibetan plateau, the Ordos block and the Sichuan basin. The seismic data come from about 160 stations of t...We apply ambient noise tomography to significant seismic data resources in a region including the northeastern Tibetan plateau, the Ordos block and the Sichuan basin. The seismic data come from about 160 stations of the provincial broadband digital seismograph networks of China. Ambient noise cross-correlations are performed on the data recorded between 2007 and 2009 and high quality inter-station Rayleigh phase velocity dispersion curves are obtained between periods of 6 s to 35 s. Resulting Rayleigh wave phase velocity maps possess a lateral resolution between 100 km and 200 kin. The phase velocities at short periods （〈20 s） are lower in the Sichuan basin, the northwest segment of the Ordos block and the Weihe graben, and outline sedimentary deposits. At intermediate and long periods （〉25 s）, strong high velocity anomalies are observed within the Ordos block and the Sichuan basin and low phase velocities are imaged in the northeastern Tibetan plateau, reflecting the variation of crustal thickness from the Tibetan plateau to the neighboring regions in the east. Crustal and uppermost mantle shear wave velocities vary strongly between the Tibetan plateau, the Sichuan basin and the Ordos block. The Ordos block and the Sichuan basin are dominated by high shear wave velocities in the crust and uppermost mantle. There is a triangle-shaped low velocity zone located in the northeastern Tibetan plateau, whose width narrows towards the eastern margin of the plateau. No low velocity zone is apparent beneath the Qinling orogen, suggesting that mass may not be able to flow eastward through the boundary between the Ordos block and the Sichuan basin in the crust and uppermost mantle.展开更多
Ambient benzene homologues were measured at a site in the northeastern urban area of Beijing, China, from August 24 to September 4, 2012 by SUMMA canister sampling followed by laboratory determination using cryogenic ...Ambient benzene homologues were measured at a site in the northeastern urban area of Beijing, China, from August 24 to September 4, 2012 by SUMMA canister sampling followed by laboratory determination using cryogenic cold trap pre-concentration-GC-MS/FID, and their health risks were also assessed. Daily total benzene homologues ranged from 0.99 to 49.71 μg/m3 with an average of 11.98 μg/m3. Benzene homologues showed higher concentrations in the morning and evening than that at noontime. Comparison with previous studies revealed a trend of decrease for ambient benzene homologues probably due to the effective emission control in Beijing in recent years. Vehicular exhaust was the main source while volatilization of paints and solvents also made substantial contributions. Health risk assessment showed that BTEX （benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene） and styrene had no appreciable adverse non-cancer health risks for the exposed population, while benzene has potential cancer risk of 1.34E-05. Available data from cities in China all implied that benzene imposes relatively higher cancer risk on the exposed populations and therefore strict control measures should be taken to further lower ambient benzene levels in China.展开更多
Following the M w 7.9 Wenchuan earthquake, the M w 6.6 Lushan earthquake is another devastating earthquake that struck the Longmenshan Fault Zone (LFZ) and caused severe damages. In this study, we collected continuous...Following the M w 7.9 Wenchuan earthquake, the M w 6.6 Lushan earthquake is another devastating earthquake that struck the Longmenshan Fault Zone (LFZ) and caused severe damages. In this study, we collected continuous broadband ambient noise seismic data and earthquake event data from Chinese provincial digital seismic network, and then utilized ambient noise tomography method and receiver function method to obtain high resolution shear wave velocity structure, crustal thickness, and Poisson ratio in the earthquake source region and its surroundings. Based on the tomography images and the receiver function results, we further analyzed the deep seismogenic environment of the LFZ and its neighborhood. We reveal three main findings: (1) There is big contrast of the shear wave velocities across the LFZ. (2) Both the Lushan earthquake and the Wenchuan earthquake occurred in the regions where crustal shear wave velocity and crustal thickness change dramatically. The rupture faults and the aftershock zones are also concentrated in the areas where the lateral gradients of crustal seismic wave speed and crustal thickness change significantly, and the focal depths of the earthquakes are concentrated in the transitional depths where shear wave velocities change dramatically from laterally uniform to laterally non-uniform. (3) The Wenchuan earthquake and its aftershocks occurred in low Poisson ratio region, while the Lushan earthquake sequences are located in high Poisson ratio zone. We proposed that the effect of the dramatic lateral variation of shear wave velocity, and the gravity potential energy differences caused by the big contrast in the topography and the crustal thickness across the LFZ may constitute the seismogenic environment for the strong earthquakes in the LFZ, and the Poisson ratio difference between the rocks in the south and north segments of the Longmenshan Fault zone may explain the 5 years delay of the occurrence of the Lushan earthquake than the Wenchuan earthquake.展开更多
Intelligence at either the material or metamaterial level is a goal that researchers have been pursuing.From passive to active,metasurfaces have been developed to be programmable to dynamically and arbitrarily manipul...Intelligence at either the material or metamaterial level is a goal that researchers have been pursuing.From passive to active,metasurfaces have been developed to be programmable to dynamically and arbitrarily manipulate electromagnetic(EM)wavefields.However,the programmable metasurfaces require manual control to switch among different functionalities.Here,we put forth a smart metasurface that has self-adaptively reprogrammable functionalities without human participation.The smart metasurface is capable of sensing ambient environments by integrating an additional sensor(s)and can adaptively adjust its EM operational functionality through an unmanned sensing feedback system.As an illustrative example,we experimentally develop a motion-sensitive smart metasurface integrated with a three-axis gyroscope,which can adjust self-adaptively the EM radiation beams via different rotations of the metasurface.We develop an online feedback algorithm as the control software to make the smart metasurface achieve single-beam and multibeam steering and other dynamic reactions adaptively.The proposed metasurface is extendable to other physical sensors to detect the humidity,temperature,illuminating light,and so on.Our strategy will open up a new avenue for future unmanned devices that are consistent with the ambient environment.展开更多
To investigate the relationship between velocity structure and earthquake activity on the southeastern front of the Tibetan Plat- eau, we make use of continuous observations of seismic ambient noise data obtained at 5...To investigate the relationship between velocity structure and earthquake activity on the southeastern front of the Tibetan Plat- eau, we make use of continuous observations of seismic ambient noise data obtained at 55 broadband stations from the regional Yunnan Seismic Network. These data are used to compute Rayleigh wave Green＇s Functions by cross-correlating between two stations, extracting phase velocity dispersion curves, and finally inverting to image Rayleigh wave phase velocity with periods between 5 and 34 s by ambient noise tomography. The results tie structures in the studied region. Phase velocity anomalies show significant lateral variations in crustal and uppermost man- at short periods （5-12 s） are closely related to regional tectonic features such as sediment thickness and the depth of the crystalline basement. The Sichuan-Yunnan rhombic block, enclosed by the Honghe, Xiaojiang and Jianchuan faults, emerges as a large range of low-velocity anomalies at periods of 16-26 s, that in- verts to high-velocity anomalies at periods of 30-34 s. The phase velocity variation in the vicinity of the Sichuan-Yunnan rhombic block suggests that the low-velocity anomaly area in the middle-lower crust may correspond to lower crustal channel- ized flow of the Tibetan Plateau. The spatial distribution of strong earthquakes since 1970 reveals that the Yunnan region is inhomogeneous and shows prominent characteristics of block motion. However, earthquakes mostly occur in the upper crust, with the exception of the middle-Yunnan block where earthquakes occur at the interface zone between high and low velocity as well as in the low-velocity zones, with magnitudes being generally less than 7. There are few earthquakes of magnitude 5 at the depths of 15-30 km, where gather earthquakes of magnitude 7 or higher ones which mainly occur in the interface zone between high and low velocities with others extending to the high-velocity abnormal zone.展开更多
We determine the three-dimensional shear wave velocity structure of the crust and upper mantle in China using Green＇s functions obtained from seismic ambient noise cross-correlation. The data we use are from the Chin...We determine the three-dimensional shear wave velocity structure of the crust and upper mantle in China using Green＇s functions obtained from seismic ambient noise cross-correlation. The data we use are from the China National Seismic Network, global and regional networks and PASSCAL stations in the region. We first acquire cross-correlation seismograms between all possible station pairs. We then measure the Rayleigh wave group and phase dispersion curves using a frequency-time analysis method from 8 s to 60 s. After that, Rayleigh wave group and phase velocity dispersion maps on 1°by 1°spatial grids are obtained at different periods. Finally, we invert these maps for the 3-D shear wave velocity structure of the crust and upper mantle beneath China at each grid node. The inversion results show large-scale structures that correlate well with surface geology. Near the surface, velocities in major basins are anomalously slow, consistent with the thick sediments. East-west contrasts are striking in Moho depth. There is also a fast mid-to-lower crust and mantle lithosphere beneath the major basins surrounding the Tibetan plateau （TP） and Tianshan （Junggar, Tarim, Ordos, and Sichuan）. These strong blocks, therefore, appear to play an important role in confining the deformation of the TP and constraining its geometry to form its current triangular shape. In northwest TP in Qiangtang, slow anomalies extend from the crust to the mantle lithosphere. Meanwhile, widespread, a prominent low-velocity zone is observed in the middle crust beneath most of the central, eastern and southeastern Tibetan plateau, consistent with a weak （and perhaps mobile） middle crust.展开更多
In China, the health risk from overexposure to particles is becoming an important public health concern. To investigate daily exposure characteristics to PM 2.5 with high ambient concentration in urban area, a persona...In China, the health risk from overexposure to particles is becoming an important public health concern. To investigate daily exposure characteristics to PM 2.5 with high ambient concentration in urban area, a personal exposure study was conducted for school children, and office workers in Beijing, China. For all participants （N = 114）, the mean personal 24-hr exposure concentration was 102.5, 14.7, 0.093, 0.528, 0.934, 0.174 and 0.703 μg/m 3 for PM 2.5 , black carbon, Mn, Al, Ca, Pb, and Fe. Children’s exposure concentrations of PM 2.5 were 4–5 times higher than those in related studies. The ambient concentration of PM 2.5 （128.5 μg/m 3 ） was significantly higher than the personal exposure concentration （P 0.05）, and exceed the reference concentration （25 μg/m 3 ） of WHO air quality guideline. Good correlation relationships and significant differences were identified between ambient concentration and personal exposure concentration. The relationships indicate that the ambient concentration is the main factor influencing personal exposure concentration, but is not a good indicator of personal exposure concentration. Outdoor activities （commute mode, exposure to heating, workday or weekend travel） influenced personal exposure concentrations significantly, but the magnitude of the influence from indoor activities （exposure to cooking） was masked by the high ambient concentrations.展开更多
The rapid development in Beijing, the capital of China, has resulted in serious air pollution problems. Meanwhile great efforts have been made to improve the air quality, especially since 1998. The variation in air qu...The rapid development in Beijing, the capital of China, has resulted in serious air pollution problems. Meanwhile great efforts have been made to improve the air quality, especially since 1998. The variation in air quality under the interaction of pollution and control in this mega city has attracted much attention. We analyzed the changes in ambient air quality in Beijing since the 1980’s using the Daniel trend test based on data from long-term monitoring stations. The results showed that different pollutants displayed three trends： a decreasing trend, an increasing trend and a flat trend. SO2, dustfall, B[a]P, NO2 and PM10 fit decreasing trend pattern, while NOx showed an increasing trend, and CO, ozone pollution, total suspended particulate （TSP）, as well as Pb fit the flat trend. The cause of the general air pollution in Beijing has changed from being predominantly related to coal burning to mixed traffic exhaust and coal burning related pollution. Seasonally, the pollution level is typically higher during the heating season from November to the following March. The interaction between pollution sources change and implementation of air pollution control measures was the main driving factor that caused the variation in air quality. Changes of industrial structure and improved energy effciency, the use of clean energy and preferred use of clean coal, reduction in pollution sources, and implementation of advanced environmental standards have all contributed to the reduction in air pollution, particularly since 1998.展开更多
The structural damage alarming method based on wavelet packet energy spectrum (WPES) for long-span cable-stayed bridges is presented through combination of ambient vibration test and wavelet packet analysis. The envir...The structural damage alarming method based on wavelet packet energy spectrum (WPES) for long-span cable-stayed bridges is presented through combination of ambient vibration test and wavelet packet analysis. The environmental variability in the measured WPES and damage alarming indices ERVD of the Runyang Cable-stayed Bridge are discussed in detail using the wavelet packet analysis of the measured acceleration responses of the bridge under daily environmental conditions. The analysis results reveal that the actual environmental conditions including traffic loadings, environmental temperature and typhoon loadings have remarkable correlations with the measured WPES. The changes of environmental temperature have a long-term trend influence on the WPES, while the influences of traffic and typhoon loadings on the measured WPES of the bridge present instantaneous changes because of the nonstationary properties of the loadings. The analysis results of the measured responses further reveal that the damage alarming indices ERVD can sensitively reflect the influences of environmental temperature and typhoon loadings on the dynamic properties of Runyang Cable-stayed Bridge. Therefore, the proposed structural damage alarming indices ERVD under ambient vibrations are suitable for real-time damage alarming for long-span cable-stayed bridges.展开更多
Objective To investigate the association between ambient air pollution and hospital emergency admissions in Beijing. Methods In this study, a semi-parametric generalized additive model （GAM） was used to evaluate the...Objective To investigate the association between ambient air pollution and hospital emergency admissions in Beijing. Methods In this study, a semi-parametric generalized additive model （GAM） was used to evaluate the specific influences of air pollutants （PM10, SO2, and NO2） on hospital emergency admissions with different lag structures from 2009 to 2011, the sex and age specific influences of air pollution and the modifying effect of seasons on air pollution to analyze the possible interaction. Results It was found that a 10μg/m3 increase in concentration of PMlo at lag 03 day, SO2 and NO2 at lag 0 day were associated with an increase of 0.88%, 0.76%, and 1.82% respectively in overall emergency admissions. A 10 lag/m3 increase in concentration of PM10, SO2 and NO2 at lag 5 day were associated with an increase of 1.39%, 1.56%, and 1.18% respectively in cardiovascular disease emergency admissions. For lag 02, a 10 μg/m3 increase in concentration of PM10, SO2 and NO2 were associated with 1.72%, 1.34%, and 2.57% increases respectively in respiratory disease emergency admissions. Conclusion This study further confirmed that short-term exposure to ambient air pollution was associated with increased risk of hospital emergency admissions in Beijing.展开更多
The Tan-Lu fault zone is a large NNE-trending fault zone in eastern China.Investigations of the structures of the fault zone and its surrounding areas have attracted much attention.In this study,we used dense-array am...The Tan-Lu fault zone is a large NNE-trending fault zone in eastern China.Investigations of the structures of the fault zone and its surrounding areas have attracted much attention.In this study,we used dense-array ambient noise tomography to construct a threedimensional shear wave velocity model of shallow crust in an area about 80km×70km in Lujiang,Anhui Province,eastern China.For approximately one month we collected continuous ambient noise signals recorded by 90 short-period seismographs in the region,and obtained the short-period Rayleigh wave empirical Green's functions between stations by the cross-correlation method;we also extracted 0.5–8 s fundamental mode Rayleigh wave group velocity and phase velocity dispersion curves.Based on the direct surface wave tomography method,we jointly inverted the group velocity and phase velocity dispersion data of all paths and obtained the 3-D shear wave velocity structure in the depth range of 0–5 km.The results revealed important geological structural features of the study area.In the north region,the sedimentary center of the Hefei Basin—the southwestern part of the Chaohu Lake—shows a significant low-velocity anomaly to a depth of at least 5 km.The southwestern and southeastern regions of the array are the eastern margin of the Dabie orogenic belt and the intrusion area of Luzong volcanic rocks,respectively,and both show obvious high-speed anomalies;the sedimentary area within the Tan-Lu fault zone(about 10 km wide)shows low-velocity anomalies.However,the volcanic rock intrusion area in the fault zone is shown as high velocity.Our shallow crustal imaging results reflect the characteristics of different structures in the study area,especially the high-speed intrusive rocks in the Tan-Lu fault zone,which were probably partially derived from the magmatic activity of Luzong volcanic basin.From the Late Cretaceous to Early Tertiary,the Tan-Lu fault zone was in a period of extensional activity;the special stress environment and the fractured fault zone morphology展开更多
As a noncontact strategy with flexible tools and high efficiency,laser precision engineering is a significant advanced processing way for high-quality micro-/nanostructure fabrication,especially to achieve novel funct...As a noncontact strategy with flexible tools and high efficiency,laser precision engineering is a significant advanced processing way for high-quality micro-/nanostructure fabrication,especially to achieve novel functional photoelectric structures and devices.For the microscale creation,several femtosecond laser fabrication methods,including multiphoton absorption,laserinduced plasma-assisted ablation,and incubation effect have been developed.Meanwhile,the femtosecond laser can be combined with microlens arrays and interference lithography techniques to achieve the structures in submicron scales.Down to nanoscale feature sizes,advanced processing strategies,such as near-field scanning optical microscope,atomic force microscope,and microsphere,are applied in femtosecond laser processing and the minimum nanostructure creation has been pushed down to~25 nm due to near-field effect.The most fascinating femtosecond laser precision engineering is the possibility of large-area,high-throughput,and far-field nanofabrication.In combination with special strategies,including dual femtosecond laser beam irradiation,~15 nm nanostructuring can be achieved directly on silicon surfaces in far field and in ambient air.The challenges and perspectives in the femtosecond laser precision engineering are also discussed.展开更多
文摘Ambient logics have been proposed to describe properties for mobile agentswhich may evolve over time as well as space. This paper takes a predicate-based approach toextending an ambient logic with recursion, yielding a predicate μ-calculus in which fixpointformulas are formed using predicate variables. An algorithm is developed for model checkingfinite-control mobile ambients against formulas of the logic, providing the first decidabilityresult for model checking a spatial logic with recursion.
文摘The maximum rise-height,zero-buoyancy height,thickness of the spreading layer,minimum dilution and the height of the lower edge of the spreading layer are the important characteristic quantities of buoyant jets in stratified ambients.The scaling law is derived by the dimensional analysis of the influence factor on a buoyant jet.The characteristic quantities are found to converge to a single line under the unified scaling law.The correlation of the predicted results and experimental data is given.
基金supported by Chinese Academy of Sciences grant kzcx2-yw-142 and Y009021002National Natural Science Foundation of China under grant No. 40974034+1 种基金NSF-EAR award 0944022NSF-OISE 0730154 at the University of Colorado at Boulder
文摘We apply ambient noise tomography to significant seismic data resources in a region including the northeastern Tibetan plateau, the Ordos block and the Sichuan basin. The seismic data come from about 160 stations of the provincial broadband digital seismograph networks of China. Ambient noise cross-correlations are performed on the data recorded between 2007 and 2009 and high quality inter-station Rayleigh phase velocity dispersion curves are obtained between periods of 6 s to 35 s. Resulting Rayleigh wave phase velocity maps possess a lateral resolution between 100 km and 200 kin. The phase velocities at short periods （〈20 s） are lower in the Sichuan basin, the northwest segment of the Ordos block and the Weihe graben, and outline sedimentary deposits. At intermediate and long periods （〉25 s）, strong high velocity anomalies are observed within the Ordos block and the Sichuan basin and low phase velocities are imaged in the northeastern Tibetan plateau, reflecting the variation of crustal thickness from the Tibetan plateau to the neighboring regions in the east. Crustal and uppermost mantle shear wave velocities vary strongly between the Tibetan plateau, the Sichuan basin and the Ordos block. The Ordos block and the Sichuan basin are dominated by high shear wave velocities in the crust and uppermost mantle. There is a triangle-shaped low velocity zone located in the northeastern Tibetan plateau, whose width narrows towards the eastern margin of the plateau. No low velocity zone is apparent beneath the Qinling orogen, suggesting that mass may not be able to flow eastward through the boundary between the Ordos block and the Sichuan basin in the crust and uppermost mantle.
基金supported by the Special Research Project for the National Environmental Protection Public Welfare Industry of China(No.201009032)the Strategic Pilot Science and Technology Project of Chinese Academy of Sciences(Class B)(No.XDB05010200)the Project of National Natural Science Foundation of China(No.41175111)
文摘Ambient benzene homologues were measured at a site in the northeastern urban area of Beijing, China, from August 24 to September 4, 2012 by SUMMA canister sampling followed by laboratory determination using cryogenic cold trap pre-concentration-GC-MS/FID, and their health risks were also assessed. Daily total benzene homologues ranged from 0.99 to 49.71 μg/m3 with an average of 11.98 μg/m3. Benzene homologues showed higher concentrations in the morning and evening than that at noontime. Comparison with previous studies revealed a trend of decrease for ambient benzene homologues probably due to the effective emission control in Beijing in recent years. Vehicular exhaust was the main source while volatilization of paints and solvents also made substantial contributions. Health risk assessment showed that BTEX （benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene） and styrene had no appreciable adverse non-cancer health risks for the exposed population, while benzene has potential cancer risk of 1.34E-05. Available data from cities in China all implied that benzene imposes relatively higher cancer risk on the exposed populations and therefore strict control measures should be taken to further lower ambient benzene levels in China.
基金supported by National Natural Science Foundation of China (Grant Nos.41074052,41174086,40974034)Key project from Institute of Geodesy and Geophysics,Chinese Academy of Sciences,and Foundation for Innovative Research Groups of the National Science Foundation of China (Grant No.41021003)
文摘Following the M w 7.9 Wenchuan earthquake, the M w 6.6 Lushan earthquake is another devastating earthquake that struck the Longmenshan Fault Zone (LFZ) and caused severe damages. In this study, we collected continuous broadband ambient noise seismic data and earthquake event data from Chinese provincial digital seismic network, and then utilized ambient noise tomography method and receiver function method to obtain high resolution shear wave velocity structure, crustal thickness, and Poisson ratio in the earthquake source region and its surroundings. Based on the tomography images and the receiver function results, we further analyzed the deep seismogenic environment of the LFZ and its neighborhood. We reveal three main findings: (1) There is big contrast of the shear wave velocities across the LFZ. (2) Both the Lushan earthquake and the Wenchuan earthquake occurred in the regions where crustal shear wave velocity and crustal thickness change dramatically. The rupture faults and the aftershock zones are also concentrated in the areas where the lateral gradients of crustal seismic wave speed and crustal thickness change significantly, and the focal depths of the earthquakes are concentrated in the transitional depths where shear wave velocities change dramatically from laterally uniform to laterally non-uniform. (3) The Wenchuan earthquake and its aftershocks occurred in low Poisson ratio region, while the Lushan earthquake sequences are located in high Poisson ratio zone. We proposed that the effect of the dramatic lateral variation of shear wave velocity, and the gravity potential energy differences caused by the big contrast in the topography and the crustal thickness across the LFZ may constitute the seismogenic environment for the strong earthquakes in the LFZ, and the Poisson ratio difference between the rocks in the south and north segments of the Longmenshan Fault zone may explain the 5 years delay of the occurrence of the Lushan earthquake than the Wenchuan earthquake.
基金supported in part by the National Key Research and Development Program of China(2017YFA0700201,2017YFA0700202,and 2017YFA0700203)in part by the National Natural Science Foundation of China(61631007,61571117,61501112,61501117,61522106,61731010,61735010,61722106,61701107,and 61701108)+1 种基金in part by the 111 Project(111-2-05)in part by the Fund for International Cooperation and Exchange of the National Natural Science Foundation of China(61761136007).
文摘Intelligence at either the material or metamaterial level is a goal that researchers have been pursuing.From passive to active,metasurfaces have been developed to be programmable to dynamically and arbitrarily manipulate electromagnetic(EM)wavefields.However,the programmable metasurfaces require manual control to switch among different functionalities.Here,we put forth a smart metasurface that has self-adaptively reprogrammable functionalities without human participation.The smart metasurface is capable of sensing ambient environments by integrating an additional sensor(s)and can adaptively adjust its EM operational functionality through an unmanned sensing feedback system.As an illustrative example,we experimentally develop a motion-sensitive smart metasurface integrated with a three-axis gyroscope,which can adjust self-adaptively the EM radiation beams via different rotations of the metasurface.We develop an online feedback algorithm as the control software to make the smart metasurface achieve single-beam and multibeam steering and other dynamic reactions adaptively.The proposed metasurface is extendable to other physical sensors to detect the humidity,temperature,illuminating light,and so on.Our strategy will open up a new avenue for future unmanned devices that are consistent with the ambient environment.
基金supported by National Natural Science Foundation of China(Grant No.41174042)China National Special Fund for Earthquake Scientific Research in Public Interest(Grant No.201008001)
文摘To investigate the relationship between velocity structure and earthquake activity on the southeastern front of the Tibetan Plat- eau, we make use of continuous observations of seismic ambient noise data obtained at 55 broadband stations from the regional Yunnan Seismic Network. These data are used to compute Rayleigh wave Green＇s Functions by cross-correlating between two stations, extracting phase velocity dispersion curves, and finally inverting to image Rayleigh wave phase velocity with periods between 5 and 34 s by ambient noise tomography. The results tie structures in the studied region. Phase velocity anomalies show significant lateral variations in crustal and uppermost man- at short periods （5-12 s） are closely related to regional tectonic features such as sediment thickness and the depth of the crystalline basement. The Sichuan-Yunnan rhombic block, enclosed by the Honghe, Xiaojiang and Jianchuan faults, emerges as a large range of low-velocity anomalies at periods of 16-26 s, that in- verts to high-velocity anomalies at periods of 30-34 s. The phase velocity variation in the vicinity of the Sichuan-Yunnan rhombic block suggests that the low-velocity anomaly area in the middle-lower crust may correspond to lower crustal channel- ized flow of the Tibetan Plateau. The spatial distribution of strong earthquakes since 1970 reveals that the Yunnan region is inhomogeneous and shows prominent characteristics of block motion. However, earthquakes mostly occur in the upper crust, with the exception of the middle-Yunnan block where earthquakes occur at the interface zone between high and low velocity as well as in the low-velocity zones, with magnitudes being generally less than 7. There are few earthquakes of magnitude 5 at the depths of 15-30 km, where gather earthquakes of magnitude 7 or higher ones which mainly occur in the interface zone between high and low velocities with others extending to the high-velocity abnormal zone.
基金supported by National Science Foundation of United States (EAR-0838188) and Department of Geology, UIUCsupported by NSF-EAR award 0944022 and a sub-award from NSF-OISE 0730154
文摘We determine the three-dimensional shear wave velocity structure of the crust and upper mantle in China using Green＇s functions obtained from seismic ambient noise cross-correlation. The data we use are from the China National Seismic Network, global and regional networks and PASSCAL stations in the region. We first acquire cross-correlation seismograms between all possible station pairs. We then measure the Rayleigh wave group and phase dispersion curves using a frequency-time analysis method from 8 s to 60 s. After that, Rayleigh wave group and phase velocity dispersion maps on 1°by 1°spatial grids are obtained at different periods. Finally, we invert these maps for the 3-D shear wave velocity structure of the crust and upper mantle beneath China at each grid node. The inversion results show large-scale structures that correlate well with surface geology. Near the surface, velocities in major basins are anomalously slow, consistent with the thick sediments. East-west contrasts are striking in Moho depth. There is also a fast mid-to-lower crust and mantle lithosphere beneath the major basins surrounding the Tibetan plateau （TP） and Tianshan （Junggar, Tarim, Ordos, and Sichuan）. These strong blocks, therefore, appear to play an important role in confining the deformation of the TP and constraining its geometry to form its current triangular shape. In northwest TP in Qiangtang, slow anomalies extend from the crust to the mantle lithosphere. Meanwhile, widespread, a prominent low-velocity zone is observed in the middle crust beneath most of the central, eastern and southeastern Tibetan plateau, consistent with a weak （and perhaps mobile） middle crust.
基金supported by the National Natural Science Foundation of China(No.50778100) funded in part by Afton Chemical Corporation
文摘In China, the health risk from overexposure to particles is becoming an important public health concern. To investigate daily exposure characteristics to PM 2.5 with high ambient concentration in urban area, a personal exposure study was conducted for school children, and office workers in Beijing, China. For all participants （N = 114）, the mean personal 24-hr exposure concentration was 102.5, 14.7, 0.093, 0.528, 0.934, 0.174 and 0.703 μg/m 3 for PM 2.5 , black carbon, Mn, Al, Ca, Pb, and Fe. Children’s exposure concentrations of PM 2.5 were 4–5 times higher than those in related studies. The ambient concentration of PM 2.5 （128.5 μg/m 3 ） was significantly higher than the personal exposure concentration （P 0.05）, and exceed the reference concentration （25 μg/m 3 ） of WHO air quality guideline. Good correlation relationships and significant differences were identified between ambient concentration and personal exposure concentration. The relationships indicate that the ambient concentration is the main factor influencing personal exposure concentration, but is not a good indicator of personal exposure concentration. Outdoor activities （commute mode, exposure to heating, workday or weekend travel） influenced personal exposure concentrations significantly, but the magnitude of the influence from indoor activities （exposure to cooking） was masked by the high ambient concentrations.
基金supported by the State Key Program of National Natural Science Foundation of China (No.41030744)the Specialized Research Fund of State Key Laboratory of Urban and Regional Ecology
文摘The rapid development in Beijing, the capital of China, has resulted in serious air pollution problems. Meanwhile great efforts have been made to improve the air quality, especially since 1998. The variation in air quality under the interaction of pollution and control in this mega city has attracted much attention. We analyzed the changes in ambient air quality in Beijing since the 1980’s using the Daniel trend test based on data from long-term monitoring stations. The results showed that different pollutants displayed three trends： a decreasing trend, an increasing trend and a flat trend. SO2, dustfall, B[a]P, NO2 and PM10 fit decreasing trend pattern, while NOx showed an increasing trend, and CO, ozone pollution, total suspended particulate （TSP）, as well as Pb fit the flat trend. The cause of the general air pollution in Beijing has changed from being predominantly related to coal burning to mixed traffic exhaust and coal burning related pollution. Seasonally, the pollution level is typically higher during the heating season from November to the following March. The interaction between pollution sources change and implementation of air pollution control measures was the main driving factor that caused the variation in air quality. Changes of industrial structure and improved energy effciency, the use of clean energy and preferred use of clean coal, reduction in pollution sources, and implementation of advanced environmental standards have all contributed to the reduction in air pollution, particularly since 1998.
基金the National Hi-Tech Research and Development Program of China (Grant No. 2006AA04Z416)the National Natural Science Foundation of China (Grant No. 50538020)
文摘The structural damage alarming method based on wavelet packet energy spectrum (WPES) for long-span cable-stayed bridges is presented through combination of ambient vibration test and wavelet packet analysis. The environmental variability in the measured WPES and damage alarming indices ERVD of the Runyang Cable-stayed Bridge are discussed in detail using the wavelet packet analysis of the measured acceleration responses of the bridge under daily environmental conditions. The analysis results reveal that the actual environmental conditions including traffic loadings, environmental temperature and typhoon loadings have remarkable correlations with the measured WPES. The changes of environmental temperature have a long-term trend influence on the WPES, while the influences of traffic and typhoon loadings on the measured WPES of the bridge present instantaneous changes because of the nonstationary properties of the loadings. The analysis results of the measured responses further reveal that the damage alarming indices ERVD can sensitively reflect the influences of environmental temperature and typhoon loadings on the dynamic properties of Runyang Cable-stayed Bridge. Therefore, the proposed structural damage alarming indices ERVD under ambient vibrations are suitable for real-time damage alarming for long-span cable-stayed bridges.
基金supported by the Gong-Yi Program of China Meteorological Administration(GYHY201106034)the Fundamental Research Funds for the Central Universities(lzuibky-2013-m03)+2 种基金National Natural Science Foundation of China(41075103)National Natural Science Foundation of China(41075102)National Natural Science Foundation of China(41305105)
文摘Objective To investigate the association between ambient air pollution and hospital emergency admissions in Beijing. Methods In this study, a semi-parametric generalized additive model （GAM） was used to evaluate the specific influences of air pollutants （PM10, SO2, and NO2） on hospital emergency admissions with different lag structures from 2009 to 2011, the sex and age specific influences of air pollution and the modifying effect of seasons on air pollution to analyze the possible interaction. Results It was found that a 10μg/m3 increase in concentration of PMlo at lag 03 day, SO2 and NO2 at lag 0 day were associated with an increase of 0.88%, 0.76%, and 1.82% respectively in overall emergency admissions. A 10 lag/m3 increase in concentration of PM10, SO2 and NO2 at lag 5 day were associated with an increase of 1.39%, 1.56%, and 1.18% respectively in cardiovascular disease emergency admissions. For lag 02, a 10 μg/m3 increase in concentration of PM10, SO2 and NO2 were associated with 1.72%, 1.34%, and 2.57% increases respectively in respiratory disease emergency admissions. Conclusion This study further confirmed that short-term exposure to ambient air pollution was associated with increased risk of hospital emergency admissions in Beijing.
基金the National Natural Science Foundation of China(project 41790464)the China Postdoctoral Fund(BH2080000099).
文摘The Tan-Lu fault zone is a large NNE-trending fault zone in eastern China.Investigations of the structures of the fault zone and its surrounding areas have attracted much attention.In this study,we used dense-array ambient noise tomography to construct a threedimensional shear wave velocity model of shallow crust in an area about 80km×70km in Lujiang,Anhui Province,eastern China.For approximately one month we collected continuous ambient noise signals recorded by 90 short-period seismographs in the region,and obtained the short-period Rayleigh wave empirical Green's functions between stations by the cross-correlation method;we also extracted 0.5–8 s fundamental mode Rayleigh wave group velocity and phase velocity dispersion curves.Based on the direct surface wave tomography method,we jointly inverted the group velocity and phase velocity dispersion data of all paths and obtained the 3-D shear wave velocity structure in the depth range of 0–5 km.The results revealed important geological structural features of the study area.In the north region,the sedimentary center of the Hefei Basin—the southwestern part of the Chaohu Lake—shows a significant low-velocity anomaly to a depth of at least 5 km.The southwestern and southeastern regions of the array are the eastern margin of the Dabie orogenic belt and the intrusion area of Luzong volcanic rocks,respectively,and both show obvious high-speed anomalies;the sedimentary area within the Tan-Lu fault zone(about 10 km wide)shows low-velocity anomalies.However,the volcanic rock intrusion area in the fault zone is shown as high velocity.Our shallow crustal imaging results reflect the characteristics of different structures in the study area,especially the high-speed intrusive rocks in the Tan-Lu fault zone,which were probably partially derived from the magmatic activity of Luzong volcanic basin.From the Late Cretaceous to Early Tertiary,the Tan-Lu fault zone was in a period of extensional activity;the special stress environment and the fractured fault zone morphology
基金support from Academic Research Fund Tier 2,Ministry of Education-Singapore(MOE2019-T2-2-147).
文摘As a noncontact strategy with flexible tools and high efficiency,laser precision engineering is a significant advanced processing way for high-quality micro-/nanostructure fabrication,especially to achieve novel functional photoelectric structures and devices.For the microscale creation,several femtosecond laser fabrication methods,including multiphoton absorption,laserinduced plasma-assisted ablation,and incubation effect have been developed.Meanwhile,the femtosecond laser can be combined with microlens arrays and interference lithography techniques to achieve the structures in submicron scales.Down to nanoscale feature sizes,advanced processing strategies,such as near-field scanning optical microscope,atomic force microscope,and microsphere,are applied in femtosecond laser processing and the minimum nanostructure creation has been pushed down to~25 nm due to near-field effect.The most fascinating femtosecond laser precision engineering is the possibility of large-area,high-throughput,and far-field nanofabrication.In combination with special strategies,including dual femtosecond laser beam irradiation,~15 nm nanostructuring can be achieved directly on silicon surfaces in far field and in ambient air.The challenges and perspectives in the femtosecond laser precision engineering are also discussed.
