Planar and ultrathin liquid crystal(LC)polarization optical elements have found promising applications in augmented reality(AR),virtual reality(VR),and photonic devices.In this paper,we give a comprehensive review on ...Planar and ultrathin liquid crystal(LC)polarization optical elements have found promising applications in augmented reality(AR),virtual reality(VR),and photonic devices.In this paper,we give a comprehensive review on the operation principles,device fabrication,and performance of these optical elements.Optical simulations methods for optimizing the device performance are discussed in detail.Finally,some potential applications of these devices in AR and VR systems are illustrated and analyzed.展开更多
Mixed reality(MR)technology is a new digital holographic image technology,which appears in the field of graphics after virtual reality(VR)and augmented reality(AR)technology,a new interdisciplinary frontier.As a new g...Mixed reality(MR)technology is a new digital holographic image technology,which appears in the field of graphics after virtual reality(VR)and augmented reality(AR)technology,a new interdisciplinary frontier.As a new generation of technology,MR has attracted great attention of clinicians in recent years.The emergence of MR will bring about revolutionary changes in medical education training,medical research,medical communication,and clinical treatment.At present,MR technology has become the popular frontline information technology for medical applications.With the popularization of digital technology in the medical field,the development prospects of MR are inestimable.The purpose of this review article is to introduce the application of MR technology in the medical field and prospect its trend in the future.展开更多
Guidance problems with flight time constraints are considered in this article. A new virtual leader scheme is used for design of guidance laws with time constraints. The core idea of this scheme is to adopt a virtual ...Guidance problems with flight time constraints are considered in this article. A new virtual leader scheme is used for design of guidance laws with time constraints. The core idea of this scheme is to adopt a virtual leader for real missiles to convert a guidance problem with time constraints to a nonlinear tracking problem,thereby making it possible to settle the problem with a variety of control methods. A novel time-constrained guidance （TCG） law, which can control the flight time of missiles to a prescribed time,is designed by using the virtual leader scheme and stability method. The TCG law is a combination of the well-known proportional navigation guidance（PNG） law and the feedback of flight time error. What＇ s more, this law is free of singularities and hence yields better performances in comparison with optimal guidance laws with time constraints. Nonlinear simulations demonstrate the effectiveness of the proposed law.展开更多
Resources over Internet have such intrinsic characteristics as growth, autonomy and diversity, which have brought many challenges to the efficient sharing and comprehensive utilization of these resources. This paper p...Resources over Internet have such intrinsic characteristics as growth, autonomy and diversity, which have brought many challenges to the efficient sharing and comprehensive utilization of these resources. This paper presents a novel approach for the construction of the Internet-based Virtual Computing Environment （iVCE）, whose sig- nificant mechanisms are on-demand aggregation and autonomic collaboration. The iVCE is built on the open infrastructure of the Internet and provides harmonious, transparent and integrated services for end-users and applications. The concept of iVCE is presented and its architectural framework is described by introducing three core concepts, i.e., autonomic element, virtual commonwealth and virtual executor. Then the connotations, functions and related key technologies of each components of the architecture are deeply analyzed with a case study, iVCE for Memory.展开更多
Virtual reality （VR） is a scientific method and technology created during the exploration of the nature by human beings to understand, simulate, and better adapt and use the nature. Based on the analysis on the whol...Virtual reality （VR） is a scientific method and technology created during the exploration of the nature by human beings to understand, simulate, and better adapt and use the nature. Based on the analysis on the whole process of VR, this paper presents different categories of VR problems and a type of theoretical expression, and abstracts three kinds of scientific and technical problems in VR field. On the basis of foresaid content, this paper also studies current major research objectives, research results and development trend of VR in the aspects of VR modeling method, VR representation technology, human-machine interaction and devices, VR development suites and supporting infrastructure, as well as VR applications. Finally, several theoretical and technical problems that need to be further studied and solved are addressed.展开更多
Tracheoesophageal fistula （TEF） or bronchoesophageal fistula may be congenital, inflammatory, neoplastic, or secondary to trauma. Congenital TEF or bronchoesophageal fistula is usually associated with esophageal atr...Tracheoesophageal fistula （TEF） or bronchoesophageal fistula may be congenital, inflammatory, neoplastic, or secondary to trauma. Congenital TEF or bronchoesophageal fistula is usually associated with esophageal atresia and is readily diagnosed in infancy. But if it is not associated with esophageal atresia, it may persist until adulthood. Some theories have been proposed to explain this delay in diagnosis. We present a case of a 70-year-old man with congenital TEF. The TEF was successfully diagnosed by multidetector-row CT esophagography.展开更多
Three-dimensional geological modeling （3DGM） assists geologists to quantitatively study in three-dimensional （3D） space structures that define temporal and spatial relationships between geological objects. The 3D ...Three-dimensional geological modeling （3DGM） assists geologists to quantitatively study in three-dimensional （3D） space structures that define temporal and spatial relationships between geological objects. The 3D property model can also be used to infer or deduce causes of geological objects. 3DGM technology provides technical support for extraction of diverse geoscience information, 3D modeling, and quantitative calculation of mineral resources. Based on metallogenic concepts and an ore deposit model, 3DGM technology is applied to analyze geological characteristics of the Tongshan Cu deposit in order to define a metallogenic model and develop a virtual borehole technology; a BP neural network and a 3D interpolation technique were combined to integrate multiple geoscience information in a 3D environment. The results indicate： （1） on basis of the concept of magmatic-hydrothermal Cu polymetallic mineraliza- tion and a porphyry Cu deposit model, a spatial relational database of multiple geoscience information for mineralization in the study area （geology, geophysics, geochemistry, borehole, and cross-section data） was established, and 3D metallogenic geological objects including mineralization stratum, granodiorite, alteration rock, and magnetic anomaly were constructed; （2） on basis of the 3D ore deposit model, 23,800 effective surveys from 94 boreholes and 21 sections were applied to establish 3D orebody models with a kriging interpolation method; （3） combined 23,800 surveys involving 21 sections, using VC＋＋ and OpenGL platform, virtual borehole and virtual section with BP network, and an improved inverse distance interpolation （IDW） method were used to predict and delineate mineralization potential targets （Cu-grade of cell not less than 0.1%）; （4） comparison of 3D ore bodies, metallogenic geological objects of mineralization, and potential targets of mineralization models in the study area, delineated the 3D spatial and temporal relationship and causal processes among th展开更多
Digital farming is the practice of modern technologies such as sensors,robotics,and data analysis for shifting from tedious operations to continuously automated processes.This paper reviews some of the latest achievem...Digital farming is the practice of modern technologies such as sensors,robotics,and data analysis for shifting from tedious operations to continuously automated processes.This paper reviews some of the latest achievements in agricultural robotics,specifically those that are used for autonomous weed control,field scouting,and harvesting.Object identification,task planning algorithms,digitalization and optimization of sensors are highlighted as some of the facing challenges in the context of digital farming.The concepts of multi-robots,human-robot collaboration,and environment reconstruction from aerial images and ground-based sensors for the creation of virtual farms were highlighted as some of the gateways of digital farming.It was shown that one of the trends and research focuses in agricultural field robotics is towards building a swarm of small scale robots and drones that collaborate together to optimize farming inputs and reveal denied or concealed information.For the case of robotic harvesting,an autonomous framework with several simple axis manipulators can be faster and more efficient than the currently adapted professional expensive manipulators.While robots are becoming the inseparable parts of the modern farms,our conclusion is that it is not realistic to expect an entirely automated farming system in the future.展开更多
By applying a regional integrated environmental model system (RIEMS), a virtual numerical experiment is implemented to study the impacts of recovering natural vegetation on the regional climate and environmental condi...By applying a regional integrated environmental model system (RIEMS), a virtual numerical experiment is implemented to study the impacts of recovering natural vegetation on the regional climate and environmental conditions. The results show that recovering the natural vegetation in large scale could have significant influence on summer climate in East Asia. Not only would it be able to change the surface climate, but also to modify to certain extent the intensity of monsoon circulation. Although this is a virtual experiment at an extremely ideal condition, the implication of the simulating results is that the on-going nation-wide activities to recover the crop land for forest and pasture must be managed according to the local natural climate, hydrological and soil conditions. Only under such a condition, would the recovering of natural vegetation bring about significant climate and environmental benefits at regional scale.展开更多
通过对国内外Living Library的考察,结合Web2.0和社会性网络SNS的发展,提出了一个基于SNS的Living Library虚拟社区模型:Virtual Living Library(简称VLL),并就VLL的概念模型的构建、实践和评价等方面进行了论述,讨论了VLL的建设可能性...通过对国内外Living Library的考察,结合Web2.0和社会性网络SNS的发展,提出了一个基于SNS的Living Library虚拟社区模型:Virtual Living Library(简称VLL),并就VLL的概念模型的构建、实践和评价等方面进行了论述,讨论了VLL的建设可能性和发展前景。展开更多
This paper investigates the use of a virtual synchronous generator(VSG) to improve frequency stability in an autonomous photovoltaic-diesel microgrid with energy storage. VSG control is designed to emulate inertial re...This paper investigates the use of a virtual synchronous generator(VSG) to improve frequency stability in an autonomous photovoltaic-diesel microgrid with energy storage. VSG control is designed to emulate inertial response and damping power via power injection from/to the energy storage system. The effect of a VSG with constant parameters(CP-VSG) on the system frequency is analyzed. Based on the case study, self-tuning algorithms are used to search for optimal parameters during the operation of the VSG in order to minimize the amplitude and rate of change of the frequency variations. The performances of the proposed self-tuning(ST)-VSG, the frequency droop method, and the CP-VSG are evaluated by comparing their effects on attenuating frequency variationsunder load variations. For both simulated and experimental cases, the ST-VSG was found to be more efficient than the other two methods in improving frequency stability.展开更多
文摘Planar and ultrathin liquid crystal(LC)polarization optical elements have found promising applications in augmented reality(AR),virtual reality(VR),and photonic devices.In this paper,we give a comprehensive review on the operation principles,device fabrication,and performance of these optical elements.Optical simulations methods for optimizing the device performance are discussed in detail.Finally,some potential applications of these devices in AR and VR systems are illustrated and analyzed.
文摘Mixed reality(MR)technology is a new digital holographic image technology,which appears in the field of graphics after virtual reality(VR)and augmented reality(AR)technology,a new interdisciplinary frontier.As a new generation of technology,MR has attracted great attention of clinicians in recent years.The emergence of MR will bring about revolutionary changes in medical education training,medical research,medical communication,and clinical treatment.At present,MR technology has become the popular frontline information technology for medical applications.With the popularization of digital technology in the medical field,the development prospects of MR are inestimable.The purpose of this review article is to introduce the application of MR technology in the medical field and prospect its trend in the future.
基金National Natural Science Foundation of China(60674103,60975073)National High-tech Research and Develop-ment Program of China (2006AA04Z260)+1 种基金Research Foundation forDoctoral Program of Higher Education of China (20091102110006 )Aeronautical Science Foundation of China(2008ZC13011)
文摘Guidance problems with flight time constraints are considered in this article. A new virtual leader scheme is used for design of guidance laws with time constraints. The core idea of this scheme is to adopt a virtual leader for real missiles to convert a guidance problem with time constraints to a nonlinear tracking problem,thereby making it possible to settle the problem with a variety of control methods. A novel time-constrained guidance （TCG） law, which can control the flight time of missiles to a prescribed time,is designed by using the virtual leader scheme and stability method. The TCG law is a combination of the well-known proportional navigation guidance（PNG） law and the feedback of flight time error. What＇ s more, this law is free of singularities and hence yields better performances in comparison with optimal guidance laws with time constraints. Nonlinear simulations demonstrate the effectiveness of the proposed law.
文摘Resources over Internet have such intrinsic characteristics as growth, autonomy and diversity, which have brought many challenges to the efficient sharing and comprehensive utilization of these resources. This paper presents a novel approach for the construction of the Internet-based Virtual Computing Environment （iVCE）, whose sig- nificant mechanisms are on-demand aggregation and autonomic collaboration. The iVCE is built on the open infrastructure of the Internet and provides harmonious, transparent and integrated services for end-users and applications. The concept of iVCE is presented and its architectural framework is described by introducing three core concepts, i.e., autonomic element, virtual commonwealth and virtual executor. Then the connotations, functions and related key technologies of each components of the architecture are deeply analyzed with a case study, iVCE for Memory.
基金Supported by the National Basic Research Program of China (Grant No. 2009CB320805)the National Natural Science Foundation of China(Grant Nos. 60533070, 60503066)the National High-Tech Research & Development Program of China (Grant Nos. 2006AA01Z333,2006AA01Z311)
文摘Virtual reality （VR） is a scientific method and technology created during the exploration of the nature by human beings to understand, simulate, and better adapt and use the nature. Based on the analysis on the whole process of VR, this paper presents different categories of VR problems and a type of theoretical expression, and abstracts three kinds of scientific and technical problems in VR field. On the basis of foresaid content, this paper also studies current major research objectives, research results and development trend of VR in the aspects of VR modeling method, VR representation technology, human-machine interaction and devices, VR development suites and supporting infrastructure, as well as VR applications. Finally, several theoretical and technical problems that need to be further studied and solved are addressed.
文摘Tracheoesophageal fistula （TEF） or bronchoesophageal fistula may be congenital, inflammatory, neoplastic, or secondary to trauma. Congenital TEF or bronchoesophageal fistula is usually associated with esophageal atresia and is readily diagnosed in infancy. But if it is not associated with esophageal atresia, it may persist until adulthood. Some theories have been proposed to explain this delay in diagnosis. We present a case of a 70-year-old man with congenital TEF. The TEF was successfully diagnosed by multidetector-row CT esophagography.
基金supported by the National Basic Research Program of China(Grant No.1212010881001 )the National Scicnce of the 12th "Five-Year Technology Support Program"(Grant No.2010BAE00281-6)+1 种基金the National Natural Science Foundation of China(Grant Nos.40772157,40972232, 41072070)the State Key Laboratory of Geological Processes and Mineral Resources(Grant Nos.GPMR0941,200624)
文摘Three-dimensional geological modeling （3DGM） assists geologists to quantitatively study in three-dimensional （3D） space structures that define temporal and spatial relationships between geological objects. The 3D property model can also be used to infer or deduce causes of geological objects. 3DGM technology provides technical support for extraction of diverse geoscience information, 3D modeling, and quantitative calculation of mineral resources. Based on metallogenic concepts and an ore deposit model, 3DGM technology is applied to analyze geological characteristics of the Tongshan Cu deposit in order to define a metallogenic model and develop a virtual borehole technology; a BP neural network and a 3D interpolation technique were combined to integrate multiple geoscience information in a 3D environment. The results indicate： （1） on basis of the concept of magmatic-hydrothermal Cu polymetallic mineraliza- tion and a porphyry Cu deposit model, a spatial relational database of multiple geoscience information for mineralization in the study area （geology, geophysics, geochemistry, borehole, and cross-section data） was established, and 3D metallogenic geological objects including mineralization stratum, granodiorite, alteration rock, and magnetic anomaly were constructed; （2） on basis of the 3D ore deposit model, 23,800 effective surveys from 94 boreholes and 21 sections were applied to establish 3D orebody models with a kriging interpolation method; （3） combined 23,800 surveys involving 21 sections, using VC＋＋ and OpenGL platform, virtual borehole and virtual section with BP network, and an improved inverse distance interpolation （IDW） method were used to predict and delineate mineralization potential targets （Cu-grade of cell not less than 0.1%）; （4） comparison of 3D ore bodies, metallogenic geological objects of mineralization, and potential targets of mineralization models in the study area, delineated the 3D spatial and temporal relationship and causal processes among th
文摘Digital farming is the practice of modern technologies such as sensors,robotics,and data analysis for shifting from tedious operations to continuously automated processes.This paper reviews some of the latest achievements in agricultural robotics,specifically those that are used for autonomous weed control,field scouting,and harvesting.Object identification,task planning algorithms,digitalization and optimization of sensors are highlighted as some of the facing challenges in the context of digital farming.The concepts of multi-robots,human-robot collaboration,and environment reconstruction from aerial images and ground-based sensors for the creation of virtual farms were highlighted as some of the gateways of digital farming.It was shown that one of the trends and research focuses in agricultural field robotics is towards building a swarm of small scale robots and drones that collaborate together to optimize farming inputs and reveal denied or concealed information.For the case of robotic harvesting,an autonomous framework with several simple axis manipulators can be faster and more efficient than the currently adapted professional expensive manipulators.While robots are becoming the inseparable parts of the modern farms,our conclusion is that it is not realistic to expect an entirely automated farming system in the future.
基金This work was supported by the National Key Basic Research Development Program of the Ministry of Science and Technology of China (Grant No. 1999-2004).
文摘By applying a regional integrated environmental model system (RIEMS), a virtual numerical experiment is implemented to study the impacts of recovering natural vegetation on the regional climate and environmental conditions. The results show that recovering the natural vegetation in large scale could have significant influence on summer climate in East Asia. Not only would it be able to change the surface climate, but also to modify to certain extent the intensity of monsoon circulation. Although this is a virtual experiment at an extremely ideal condition, the implication of the simulating results is that the on-going nation-wide activities to recover the crop land for forest and pasture must be managed according to the local natural climate, hydrological and soil conditions. Only under such a condition, would the recovering of natural vegetation bring about significant climate and environmental benefits at regional scale.
文摘通过对国内外Living Library的考察,结合Web2.0和社会性网络SNS的发展,提出了一个基于SNS的Living Library虚拟社区模型:Virtual Living Library(简称VLL),并就VLL的概念模型的构建、实践和评价等方面进行了论述,讨论了VLL的建设可能性和发展前景。
基金supported by National High Technology Research and Development Program of China(863Program)(No.2015AA050607)the National key Research and Development Program of China(No.2016YFB0900300)the Science and Technology project of SGCC(No.NYB17201700151)
文摘This paper investigates the use of a virtual synchronous generator(VSG) to improve frequency stability in an autonomous photovoltaic-diesel microgrid with energy storage. VSG control is designed to emulate inertial response and damping power via power injection from/to the energy storage system. The effect of a VSG with constant parameters(CP-VSG) on the system frequency is analyzed. Based on the case study, self-tuning algorithms are used to search for optimal parameters during the operation of the VSG in order to minimize the amplitude and rate of change of the frequency variations. The performances of the proposed self-tuning(ST)-VSG, the frequency droop method, and the CP-VSG are evaluated by comparing their effects on attenuating frequency variationsunder load variations. For both simulated and experimental cases, the ST-VSG was found to be more efficient than the other two methods in improving frequency stability.
