Metamaterials are artificial structures that are usually described by effective medium parameters on the macroscopic scale,and these metamaterials are referred to as‘analog metamaterials’.Here,we propose‘digital me...Metamaterials are artificial structures that are usually described by effective medium parameters on the macroscopic scale,and these metamaterials are referred to as‘analog metamaterials’.Here,we propose‘digital metamaterials’through two steps.First,we present‘coding metamaterials’that are composed of only two types of unit cells,with 0 and p phase responses,which we name‘0’and‘1’elements,respectively.By coding‘0’and‘1’elements with controlled sequences(i.e.,1-bit coding),we can manipulate electromagnetic(EM)waves and realize different functionalities.The concept of coding metamaterials can be extended from 1-bit coding to 2-bit coding or higher.In 2-bit coding,four types of unit cells,with phase responses of 0,p/2,p,and 3p/2,are required to mimic the‘00’,‘01’,‘10’and‘11’elements,respectively.The 2-bit coding has greater freedom than 1-bit coding for controlling EM waves.Second,we propose a unique metamaterial particle that has either a‘0’or‘1’response controlled by a biased diode.Based on this particle,we present‘digital metamaterials’with unit cells that possess either a‘0’or‘1’state.Using a field-programmable gate array,we realize digital control over the digital metamaterial.By programming different coding sequences,a single digital metamaterial has the ability to manipulate EM waves in different manners,thereby realizing‘programmable metamaterials’.The above concepts and physical phenomena are confirmed through numerical simulations and experiments using metasurfaces.展开更多
State-of-the-art technologies such as the Internet of Things(IoT),cloud computing(CC),big data analytics(BDA),and artificial intelligence(AI)have greatly stimulated the development of smart manufacturing.An important ...State-of-the-art technologies such as the Internet of Things(IoT),cloud computing(CC),big data analytics(BDA),and artificial intelligence(AI)have greatly stimulated the development of smart manufacturing.An important prerequisite for smart manufacturing is cyber-physical integration,which is increasingly being embraced by manufacturers.As the preferred means of such integration,cyber-physical systems(CPS)and digital twins(DTs)have gained extensive attention from researchers and practitioners in industry.With feedback loops in which physical processes affect cyber parts and vice versa,CPS and DTs can endow manufacturing systems with greater efficiency,resilience,and intelligence.CPS and DTs share the same essential concepts of an intensive cyber-physical connection,real-time interaction,organization integration,and in-depth collaboration.However,CPS and DTs are not identical from many perspectives,including their origin,development,engineering practices,cyber-physical mapping,and core elements.In order to highlight the differences and correlation between them,this paper reviews and analyzes CPS and DTs from multiple perspectives.展开更多
This paper studies two kinds of nonlinear transformations, namely the higher-dimensional Arnold transformation and the higher-dimensional Fibonacci Q-transformation and discusses the scrambling action of the two trans...This paper studies two kinds of nonlinear transformations, namely the higher-dimensional Arnold transformation and the higher-dimensional Fibonacci Q-transformation and discusses the scrambling action of the two transformations focusing on the phase space of the digital images. A sufficient and necessary condition that a matrix transformation of digital image has periodicity is given. The results show that the two transformations have potential application in the storage and transportation of image information for the purpose of information security.展开更多
World-wide urbanization has significantly modified the landscape, which has important climatic implications across all scales due to the simultaneous removal of natural land cover and introduction of urban materials. ...World-wide urbanization has significantly modified the landscape, which has important climatic implications across all scales due to the simultaneous removal of natural land cover and introduction of urban materials. This resulted in a phenomenon known as an urban heat island(UHI). A study on the UHI in Xiamen of China was carried out using remote sensing technology. Satellite thermal infrared images were used to determine surface radiant temperatures. Thermal remote sensing data were obtained from band 6 of two Landsat TM/ETM\++ images of 1989 and 2000 to observe the UHI changes over 11-year period. The thermal infrared bands were processed through several image enhancement technologies. This generated two 3-dimension-perspective images of Xiamen's urban heat island in 1989 and 2000, respectively, and revealed heat characteristics and spatial distribution features of the UHI. To find out the change of the UHI between 1989 and 2000, the two thermal images were first normalized and scaled to seven grades to reduce seasonal difference and then overlaid to produce a difference image by subtracting corresponding pixels. The difference image showed an evident development of the urban heat island in the 11 years. This change was due largely to the urban expansion with a consequent alteration in the ratio of sensible heat flux to latent heat flux. To quantitatively compare UHI, an index called Urban-Heat-Island Ratio Index(URI) was created. It can reveal the intensity of the UHI within the urban area. The calculation of the index was based on the ratio of UHI area to urban area. The greater the index, the more intense the UHI was. The calculation of the index for the Xiamen City indicated that the ratio of UHI area to urban area in 2000 was less than that in 1989. High temperatures in several areas in 1989 were reduced or just disappeared, such as those in old downtown area and Gulangyu Island. For the potential mitigation of the UHI in Xiamen, a long-term heat island reduction strategy of planting shade trees and usin展开更多
The geospatial sciences face grand information technology(IT)challenges in the twenty-first century:data intensity,computing intensity,concurrent access intensity and spatiotemporal intensity.These challenges require ...The geospatial sciences face grand information technology(IT)challenges in the twenty-first century:data intensity,computing intensity,concurrent access intensity and spatiotemporal intensity.These challenges require the readiness of a computing infrastructure that can:(1)better support discovery,access and utilization of data and data processing so as to relieve scientists and engineers of IT tasks and focus on scientific discoveries;(2)provide real-time IT resources to enable real-time applications,such as emergency response;(3)deal with access spikes;and(4)provide more reliable and scalable service for massive numbers of concurrent users to advance public knowledge.The emergence of cloud computing provides a potential solution with an elastic,on-demand computing platform to integrateobservation systems,parameter extracting algorithms,phenomena simulations,analytical visualization and decision support,and to provide social impact and user feedbackthe essential elements of the geospatial sciences.We discuss the utilization of cloud computing to support the intensities of geospatial sciences by reporting from our investigations on how cloud computing could enable the geospatial sciences and how spatiotemporal principles,the kernel of the geospatial sciences,could be utilized to ensure the benefits of cloud computing.Four research examples are presented to analyze how to:(1)search,access and utilize geospatial data;(2)configure computing infrastructure to enable the computability of intensive simulation models;(3)disseminate and utilize research results for massive numbers of concurrent users;and(4)adopt spatiotemporal principles to support spatiotemporal intensive applications.The paper concludes with a discussion of opportunities and challenges for spatial cloud computing(SCC).展开更多
基金This work was supported in part by the National High Tech(863)Projects(2012AA030402 and 2011AA010202)in part by the National Science Foundation of China(61138001,60990320 and 60990324)in part by the 111 Project(111-2-05)and in part by the Joint Research Center on Terahertz Science.
文摘Metamaterials are artificial structures that are usually described by effective medium parameters on the macroscopic scale,and these metamaterials are referred to as‘analog metamaterials’.Here,we propose‘digital metamaterials’through two steps.First,we present‘coding metamaterials’that are composed of only two types of unit cells,with 0 and p phase responses,which we name‘0’and‘1’elements,respectively.By coding‘0’and‘1’elements with controlled sequences(i.e.,1-bit coding),we can manipulate electromagnetic(EM)waves and realize different functionalities.The concept of coding metamaterials can be extended from 1-bit coding to 2-bit coding or higher.In 2-bit coding,four types of unit cells,with phase responses of 0,p/2,p,and 3p/2,are required to mimic the‘00’,‘01’,‘10’and‘11’elements,respectively.The 2-bit coding has greater freedom than 1-bit coding for controlling EM waves.Second,we propose a unique metamaterial particle that has either a‘0’or‘1’response controlled by a biased diode.Based on this particle,we present‘digital metamaterials’with unit cells that possess either a‘0’or‘1’state.Using a field-programmable gate array,we realize digital control over the digital metamaterial.By programming different coding sequences,a single digital metamaterial has the ability to manipulate EM waves in different manners,thereby realizing‘programmable metamaterials’.The above concepts and physical phenomena are confirmed through numerical simulations and experiments using metasurfaces.
基金This work is financially supported by the National Key Research and Development Program of China(2016YFB1101700)the National Natural Science Foundation of China(51875030)the Academic Excellence Foundation of BUAA for PhD Students.
文摘State-of-the-art technologies such as the Internet of Things(IoT),cloud computing(CC),big data analytics(BDA),and artificial intelligence(AI)have greatly stimulated the development of smart manufacturing.An important prerequisite for smart manufacturing is cyber-physical integration,which is increasingly being embraced by manufacturers.As the preferred means of such integration,cyber-physical systems(CPS)and digital twins(DTs)have gained extensive attention from researchers and practitioners in industry.With feedback loops in which physical processes affect cyber parts and vice versa,CPS and DTs can endow manufacturing systems with greater efficiency,resilience,and intelligence.CPS and DTs share the same essential concepts of an intensive cyber-physical connection,real-time interaction,organization integration,and in-depth collaboration.However,CPS and DTs are not identical from many perspectives,including their origin,development,engineering practices,cyber-physical mapping,and core elements.In order to highlight the differences and correlation between them,this paper reviews and analyzes CPS and DTs from multiple perspectives.
文摘This paper studies two kinds of nonlinear transformations, namely the higher-dimensional Arnold transformation and the higher-dimensional Fibonacci Q-transformation and discusses the scrambling action of the two transformations focusing on the phase space of the digital images. A sufficient and necessary condition that a matrix transformation of digital image has periodicity is given. The results show that the two transformations have potential application in the storage and transportation of image information for the purpose of information security.
文摘World-wide urbanization has significantly modified the landscape, which has important climatic implications across all scales due to the simultaneous removal of natural land cover and introduction of urban materials. This resulted in a phenomenon known as an urban heat island(UHI). A study on the UHI in Xiamen of China was carried out using remote sensing technology. Satellite thermal infrared images were used to determine surface radiant temperatures. Thermal remote sensing data were obtained from band 6 of two Landsat TM/ETM\++ images of 1989 and 2000 to observe the UHI changes over 11-year period. The thermal infrared bands were processed through several image enhancement technologies. This generated two 3-dimension-perspective images of Xiamen's urban heat island in 1989 and 2000, respectively, and revealed heat characteristics and spatial distribution features of the UHI. To find out the change of the UHI between 1989 and 2000, the two thermal images were first normalized and scaled to seven grades to reduce seasonal difference and then overlaid to produce a difference image by subtracting corresponding pixels. The difference image showed an evident development of the urban heat island in the 11 years. This change was due largely to the urban expansion with a consequent alteration in the ratio of sensible heat flux to latent heat flux. To quantitatively compare UHI, an index called Urban-Heat-Island Ratio Index(URI) was created. It can reveal the intensity of the UHI within the urban area. The calculation of the index was based on the ratio of UHI area to urban area. The greater the index, the more intense the UHI was. The calculation of the index for the Xiamen City indicated that the ratio of UHI area to urban area in 2000 was less than that in 1989. High temperatures in several areas in 1989 were reduced or just disappeared, such as those in old downtown area and Gulangyu Island. For the potential mitigation of the UHI in Xiamen, a long-term heat island reduction strategy of planting shade trees and usin
基金We thank Drs.Huadong Guo and Changlin Wang for inviting us to write this definition and field review paper.Research reported is partially supported by NASA(NNX07AD99G and SMD-09-1448),FGDC(G09AC00103)Environmental Informatics Framework of the Earth,Energy,and Environment Program at Microsoft Research Connection.We thank insightful comments from reviewers including Dr.Aijun Chen(NASA/GMU),Dr.Thomas Huang(NASA JPL),Dr.Cao Kang(Clark Univ.),Krishna Kumar(Microsoft),Dr.Wenwen Li(UCSB),Dr.Michael Peterson(University of Nebraska-Omaha),Dr.Xuan Shi(Geogia Tech),Dr.Tong Zhang(Wuhan University),Jinesh Varia(Amazon)and an anonymous reviewer.This paper is a result from the collaborations/discussions with colleagues from NASA,FGDC,USGS,EPA,GSA,Microsoft,ESIP,AAG CISG,CPGIS,UCGIS,GEO,and ISDE.
文摘The geospatial sciences face grand information technology(IT)challenges in the twenty-first century:data intensity,computing intensity,concurrent access intensity and spatiotemporal intensity.These challenges require the readiness of a computing infrastructure that can:(1)better support discovery,access and utilization of data and data processing so as to relieve scientists and engineers of IT tasks and focus on scientific discoveries;(2)provide real-time IT resources to enable real-time applications,such as emergency response;(3)deal with access spikes;and(4)provide more reliable and scalable service for massive numbers of concurrent users to advance public knowledge.The emergence of cloud computing provides a potential solution with an elastic,on-demand computing platform to integrateobservation systems,parameter extracting algorithms,phenomena simulations,analytical visualization and decision support,and to provide social impact and user feedbackthe essential elements of the geospatial sciences.We discuss the utilization of cloud computing to support the intensities of geospatial sciences by reporting from our investigations on how cloud computing could enable the geospatial sciences and how spatiotemporal principles,the kernel of the geospatial sciences,could be utilized to ensure the benefits of cloud computing.Four research examples are presented to analyze how to:(1)search,access and utilize geospatial data;(2)configure computing infrastructure to enable the computability of intensive simulation models;(3)disseminate and utilize research results for massive numbers of concurrent users;and(4)adopt spatiotemporal principles to support spatiotemporal intensive applications.The paper concludes with a discussion of opportunities and challenges for spatial cloud computing(SCC).
