It is widely used for the rotational parallel mechanism in the field of spatial orientation. While owing to the existence of coupling, the forward kinematic solution and the control of the general rotational parallel ...It is widely used for the rotational parallel mechanism in the field of spatial orientation. While owing to the existence of coupling, the forward kinematic solution and the control of the general rotational parallel mechanism are especially difficult. If decoupling can be realized, the kinematic analysis of the mechanism will be very simple. Presently, the research of the parallel mechanism is focused on the inverse solution and structure optimization, and there is a lack of rotation decoupled parallel mechanisms （DPMs）. So this paper proposes a family of 2 degree of freedom （DOF） rotational DPMs based on the four-bar linkage mechanism, and performs a characteristic analysis. This family of DPMs is composed of a moving platform, a fixed base and three limbs. Taking U_RRU SPU DPM as an example, the motion feature of this DPM is analyzed with the constraint screw method, and its mobility is calculated by using the Modified Kutzbach-Grtibler criterion. The inverse and forward displacement problems of the proposed parallel mechanism are solved. The decoupled feature of the proposed parallel mechanism is validated by the deduction of the expression of the Jaeobian matrix. Three kinds of singularity conditions of this DPM are discussed, and the atlases of the output parameter concerning different geometric parameters are plotted with the theory of the physical model of the solution space. The proposition and characteristic analysis of the novel rotational DPMs in this paper should be useful for further research and application of the parallel mechanisms.展开更多
Chang＇e-3 （CE-3） landed on the Mare Imbrium basin in the east part of Sinus Iridum （19.51°W, 44.12°N）, which was China＇s first soft landing on the Moon and it started collecting data on the lunar surfa...Chang＇e-3 （CE-3） landed on the Mare Imbrium basin in the east part of Sinus Iridum （19.51°W, 44.12°N）, which was China＇s first soft landing on the Moon and it started collecting data on the lunar surface environment. To better understand the environment of this region, this paper utilizes the available high-resolution topography data, image data and geological data to carry out a detailed analysis and research on the area surrounding the landing site （Sinus Iridum and 45 km×70 km of the landing area） as well as on the topography, landform, geology and lunar dust of the area surrounding the landing site. A general topographic analysis of the surrounding area is based on a digital elevation model and digital elevation model data acquired by Chang＇e-2 that have high resolution; the geology analysis is based on lunar geological data published by USGS; the study on topographic factors and distribution of craters and rocks in the surrounding area covering 4km^4km or even smaller is based on images from the CE-3 landing camera and images from the topographic camera; an analysis is done of the effect of the CE-3 engine plume on the lunar surface by comparing images before and after the landing using data from the landing camera. A comprehensive analysis of the results shows that the landing site and its surrounding area are identified as typical lunar mare with flat topography. They are suitable for maneuvers by the rover, and are rich in geological phenomena and scientific targets, making it an ideal site for exploration.展开更多
Background Chordomas of the upper cervical spine are rare and present unique surgical challenge.This study aimed to describe the clinical characteristics and surgical management of patients with chordomas of the upper...Background Chordomas of the upper cervical spine are rare and present unique surgical challenge.This study aimed to describe the clinical characteristics and surgical management of patients with chordomas of the upper cervical spine.Methods Twenty-one patients with chordomas of the upper cervical spine who were treated in Peking University Third Hospital from January 1999 to October 2012 were retrospectively analyzed.Survival was calculated by the Kaplan-Meier method and was compared between groups using the log-rank test.Results The postoperative diagnosis was classical chordoma in 20 cases and chondroid chordoma in one case.The mean operative time was 9.5 hours （range 6-17 hours）,and the mean blood loss was 2 812 ml （range 700-4 800 ml）.There were two postoperative deaths.Unilateral vertebral artery ligation was performed in six patients,cervical nerve roots were cut in six patients,and the external branch of the superior laryngeal nerve was repaired after being cut in one case.Two patients developed postoperative velopharyngeal incompetence,and loosening of the occipitocervical screws was observed in one patient.The recurrence rate was 66.7% （10/15） after a mean follow-up period of 46.8 months （range 14-150 months）.The 5-and 10-year overall survival rates were （39.8±13.1）% and （31.9±12.7）%,respectively.There was a significant difference in survival rate between patients who underwent surgery and those who did not.Conclusion In spite of the high rates of recurrence and complications after surgical treatment of chordomas of the upper cervical spine,intralesional resection combined with adjuvant radiotherapy remains the optimal treatment to prolong survival.展开更多
A number of spectroscopic surveys have been carried out or are planned to study the origin of the Milky Way. Their exploitation requires reliable automated methods and softwares to measure the fundamental parameters o...A number of spectroscopic surveys have been carried out or are planned to study the origin of the Milky Way. Their exploitation requires reliable automated methods and softwares to measure the fundamental parameters of the stars. Adopting the ULySS package, we have tested the effect of different resolutions and signal-to- noise ratios （SNR） on the measurement of the stellar atmospheric parameters （effective temperature Teff, surface gravity log g, and metaUicity [Fe/H]）. We show that ULySS is reliable for determining these parameters with medium-resolution spectra （R ～2000）. Then, we applied the method to measure the parameters of 771 stars selected in the commissioning database of the Guoshoujing Telescope （LAMOST）. The results were compared with the SDSS/SEGUE Stellar Parameter Pipeline （SSPP）, and we derived precisions of 167 K, 0.34dex, and 0.16dex for Teff, logg and [Fe/H] respectively. Furthermore, 120 of these stars are selected to construct the primary stellar spectral template library （Version 1.0） of LAMOST, and will be deployed as basic ingredients for the LAMOST automated parametrization pipeline.展开更多
A six-axis force sensor with parallel 8/4-4 structure is introduced and its measurement principle is analyzed.Based on condition numbers of Jacobian matrix spectral norm of the sensor,the relationship between the forc...A six-axis force sensor with parallel 8/4-4 structure is introduced and its measurement principle is analyzed.Based on condition numbers of Jacobian matrix spectral norm of the sensor,the relationship between the force and moment isotropy and some structural parameters is deduced.Orthogonal test methods are used to determine the degree of primary and secondary factors that have significant effect on sensor characteristics.Furthermore,the relationship between each performance index and the structural parameters of the sensor is analyzed by the method of the atlas,which lays a foundation for structural optimization design of the force sensor.展开更多
Generalized geothermal data was used to produce two electronic atlases for Asian Russia,Geothermal Atlas of Siberia（GAS）（1995-2000） and Geothermal Atlas for Siberia and Russian Far East（GASRFE）（2009-2012）.The ...Generalized geothermal data was used to produce two electronic atlases for Asian Russia,Geothermal Atlas of Siberia（GAS）（1995-2000） and Geothermal Atlas for Siberia and Russian Far East（GASRFE）（2009-2012）.The atlases include heat flow maps,temperatures at depths of 0.5,1,2,3,5 km and lower boundary of permafrost.Quantitative values of parameters are presented as isolines（GAS） and symbols（GASRFE）.GAS website is located at the Trofimuk Institute（www.ipgg.sbras.ru/ru/institute/structure/geophysics/natural-fields）.GASRFE provides the most complete geothermal data on Asian Russia,which has been growing for the last 50 years,and is published on the Internet at http：//maps.nrcgit.ru/geoterm.In this atlas,data about the depth of permafrost lower boundary（ ＂zero＂ isotherm） are presented for the first time.展开更多
Sky brightness is an essential topic in the field of astronomy, especially for optical astronom- ical observations that need very clear and dark sky conditions. This study presents the spatial model of sky brightness ...Sky brightness is an essential topic in the field of astronomy, especially for optical astronom- ical observations that need very clear and dark sky conditions. This study presents the spatial model of sky brightness magnitude in Langkawi Island, Malaysia. Two types of Sky Quality Meter （SQM） manu- factured by Unihedron are used to measure the sky brightness on a moonless night （or when the Moon is below the horizon）, when the sky is cloudless and the locations are at least 100 m from the nearest light source. The selected locations are marked by their GPS coordinates. The sky brightness data obtained in this study were interpolated and analyzed using a Geographic Information System （GIS）, thus producing a spatial model of sky brightness that clearly shows the dark and bright sky areas in Langkawi Island. Surprisingly, our results show the existence of a few dark sites nearby areas of high human activity. The sky brightness of 21.45 mag arcsec-2 in the Johnson-Cousins V-band, as the average of sky brightness equivalent to 2.8 × 10-4cd m-2 over the entire island, is an indication that the island is, overall, still relatively dark. However, the amount of development taking place might reduce the number in the near future as the island is famous as a holiday destination.展开更多
This paper describes the development of cybercartography since the introduction of the term in 1997.Although the origins of cybercartography were largely conceptual in nature,the evolution of cybercartography to date ...This paper describes the development of cybercartography since the introduction of the term in 1997.Although the origins of cybercartography were largely conceptual in nature,the evolution of cybercartography to date has been an iterative process reflecting the creative interplay between theory and practice.A major step forward was made in 2002 when the Geomatics and Cartographic Research Centre at Carleton University received a$2.5 million grant from the Social Sciences and Humanities Research Council of Canada to explore the utility of cybercartography to what was described as the New Economy.By 2006,the interaction between theory and practice had led to considerable advances in cybercartography as a holistic,location-based concept and two new cybercartographic products,the Cybercartographic Atlas of Antarctica and the Cybercartographic Atlas of Canada’s Trade with the World,were produced.Between 2006 and 2009,cybercartography was further developed as a result of interaction with indigenous communities,especially in Canada’s north and new interactive atlases such as the Kitikmeot Place Names Atlas and the Community Atlas of Arctic Bay were created in cooperation with the communities involved.The Nunaliit Cybercartographic Atlas Framework,built using open source software and open specifications and standards,was developed to facilitate direct input to these atlases.Cybercartography is now entering a new phase in both theory and practice building on a recently completed prototype atlas of Indigenous Perspectives and Knowledge.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 50875227)
文摘It is widely used for the rotational parallel mechanism in the field of spatial orientation. While owing to the existence of coupling, the forward kinematic solution and the control of the general rotational parallel mechanism are especially difficult. If decoupling can be realized, the kinematic analysis of the mechanism will be very simple. Presently, the research of the parallel mechanism is focused on the inverse solution and structure optimization, and there is a lack of rotation decoupled parallel mechanisms （DPMs）. So this paper proposes a family of 2 degree of freedom （DOF） rotational DPMs based on the four-bar linkage mechanism, and performs a characteristic analysis. This family of DPMs is composed of a moving platform, a fixed base and three limbs. Taking U_RRU SPU DPM as an example, the motion feature of this DPM is analyzed with the constraint screw method, and its mobility is calculated by using the Modified Kutzbach-Grtibler criterion. The inverse and forward displacement problems of the proposed parallel mechanism are solved. The decoupled feature of the proposed parallel mechanism is validated by the deduction of the expression of the Jaeobian matrix. Three kinds of singularity conditions of this DPM are discussed, and the atlases of the output parameter concerning different geometric parameters are plotted with the theory of the physical model of the solution space. The proposition and characteristic analysis of the novel rotational DPMs in this paper should be useful for further research and application of the parallel mechanisms.
基金Supported by the National Natural Science Foundation of China
文摘Chang＇e-3 （CE-3） landed on the Mare Imbrium basin in the east part of Sinus Iridum （19.51°W, 44.12°N）, which was China＇s first soft landing on the Moon and it started collecting data on the lunar surface environment. To better understand the environment of this region, this paper utilizes the available high-resolution topography data, image data and geological data to carry out a detailed analysis and research on the area surrounding the landing site （Sinus Iridum and 45 km×70 km of the landing area） as well as on the topography, landform, geology and lunar dust of the area surrounding the landing site. A general topographic analysis of the surrounding area is based on a digital elevation model and digital elevation model data acquired by Chang＇e-2 that have high resolution; the geology analysis is based on lunar geological data published by USGS; the study on topographic factors and distribution of craters and rocks in the surrounding area covering 4km^4km or even smaller is based on images from the CE-3 landing camera and images from the topographic camera; an analysis is done of the effect of the CE-3 engine plume on the lunar surface by comparing images before and after the landing using data from the landing camera. A comprehensive analysis of the results shows that the landing site and its surrounding area are identified as typical lunar mare with flat topography. They are suitable for maneuvers by the rover, and are rich in geological phenomena and scientific targets, making it an ideal site for exploration.
文摘Background Chordomas of the upper cervical spine are rare and present unique surgical challenge.This study aimed to describe the clinical characteristics and surgical management of patients with chordomas of the upper cervical spine.Methods Twenty-one patients with chordomas of the upper cervical spine who were treated in Peking University Third Hospital from January 1999 to October 2012 were retrospectively analyzed.Survival was calculated by the Kaplan-Meier method and was compared between groups using the log-rank test.Results The postoperative diagnosis was classical chordoma in 20 cases and chondroid chordoma in one case.The mean operative time was 9.5 hours （range 6-17 hours）,and the mean blood loss was 2 812 ml （range 700-4 800 ml）.There were two postoperative deaths.Unilateral vertebral artery ligation was performed in six patients,cervical nerve roots were cut in six patients,and the external branch of the superior laryngeal nerve was repaired after being cut in one case.Two patients developed postoperative velopharyngeal incompetence,and loosening of the occipitocervical screws was observed in one patient.The recurrence rate was 66.7% （10/15） after a mean follow-up period of 46.8 months （range 14-150 months）.The 5-and 10-year overall survival rates were （39.8±13.1）% and （31.9±12.7）%,respectively.There was a significant difference in survival rate between patients who underwent surgery and those who did not.Conclusion In spite of the high rates of recurrence and complications after surgical treatment of chordomas of the upper cervical spine,intralesional resection combined with adjuvant radiotherapy remains the optimal treatment to prolong survival.
基金Supported by the National Natural Science Foundation of China(Grant Nos. 10973021, 10778626 and 10933001)the National Basic Research Development Program of China (Grant No. 2007CB815404)the China Scholarship Council (CSC) (Grant No. 2007104275)
文摘A number of spectroscopic surveys have been carried out or are planned to study the origin of the Milky Way. Their exploitation requires reliable automated methods and softwares to measure the fundamental parameters of the stars. Adopting the ULySS package, we have tested the effect of different resolutions and signal-to- noise ratios （SNR） on the measurement of the stellar atmospheric parameters （effective temperature Teff, surface gravity log g, and metaUicity [Fe/H]）. We show that ULySS is reliable for determining these parameters with medium-resolution spectra （R ～2000）. Then, we applied the method to measure the parameters of 771 stars selected in the commissioning database of the Guoshoujing Telescope （LAMOST）. The results were compared with the SDSS/SEGUE Stellar Parameter Pipeline （SSPP）, and we derived precisions of 167 K, 0.34dex, and 0.16dex for Teff, logg and [Fe/H] respectively. Furthermore, 120 of these stars are selected to construct the primary stellar spectral template library （Version 1.0） of LAMOST, and will be deployed as basic ingredients for the LAMOST automated parametrization pipeline.
基金supported by the Open Foundation of Graduate Innovation Base(Laboratory)of Nanjing University of Aeronautics and Astronautics (No.kfjj20170512)the National Natural Science Foundation of China(No. 51175263)
文摘A six-axis force sensor with parallel 8/4-4 structure is introduced and its measurement principle is analyzed.Based on condition numbers of Jacobian matrix spectral norm of the sensor,the relationship between the force and moment isotropy and some structural parameters is deduced.Orthogonal test methods are used to determine the degree of primary and secondary factors that have significant effect on sensor characteristics.Furthermore,the relationship between each performance index and the structural parameters of the sensor is analyzed by the method of the atlas,which lays a foundation for structural optimization design of the force sensor.
基金The Project VIII.70.2.3 of IPGG SB RAS and Project 7.1 of Department of Earth Sciences of Russian Academy of Sciences (Program 7) were supported this work
文摘Generalized geothermal data was used to produce two electronic atlases for Asian Russia,Geothermal Atlas of Siberia（GAS）（1995-2000） and Geothermal Atlas for Siberia and Russian Far East（GASRFE）（2009-2012）.The atlases include heat flow maps,temperatures at depths of 0.5,1,2,3,5 km and lower boundary of permafrost.Quantitative values of parameters are presented as isolines（GAS） and symbols（GASRFE）.GAS website is located at the Trofimuk Institute（www.ipgg.sbras.ru/ru/institute/structure/geophysics/natural-fields）.GASRFE provides the most complete geothermal data on Asian Russia,which has been growing for the last 50 years,and is published on the Internet at http：//maps.nrcgit.ru/geoterm.In this atlas,data about the depth of permafrost lower boundary（ ＂zero＂ isotherm） are presented for the first time.
基金Langkawi National Observatory,Space Science Research Unit,National Space Agency and East Coast Environmental Research Institute(ESERI)Universiti Sultan Zainal Abidin under university grant(RACE/F1/ST1/UNISZA/15-RR118)
文摘Sky brightness is an essential topic in the field of astronomy, especially for optical astronom- ical observations that need very clear and dark sky conditions. This study presents the spatial model of sky brightness magnitude in Langkawi Island, Malaysia. Two types of Sky Quality Meter （SQM） manu- factured by Unihedron are used to measure the sky brightness on a moonless night （or when the Moon is below the horizon）, when the sky is cloudless and the locations are at least 100 m from the nearest light source. The selected locations are marked by their GPS coordinates. The sky brightness data obtained in this study were interpolated and analyzed using a Geographic Information System （GIS）, thus producing a spatial model of sky brightness that clearly shows the dark and bright sky areas in Langkawi Island. Surprisingly, our results show the existence of a few dark sites nearby areas of high human activity. The sky brightness of 21.45 mag arcsec-2 in the Johnson-Cousins V-band, as the average of sky brightness equivalent to 2.8 × 10-4cd m-2 over the entire island, is an indication that the island is, overall, still relatively dark. However, the amount of development taking place might reduce the number in the near future as the island is famous as a holiday destination.
文摘This paper describes the development of cybercartography since the introduction of the term in 1997.Although the origins of cybercartography were largely conceptual in nature,the evolution of cybercartography to date has been an iterative process reflecting the creative interplay between theory and practice.A major step forward was made in 2002 when the Geomatics and Cartographic Research Centre at Carleton University received a$2.5 million grant from the Social Sciences and Humanities Research Council of Canada to explore the utility of cybercartography to what was described as the New Economy.By 2006,the interaction between theory and practice had led to considerable advances in cybercartography as a holistic,location-based concept and two new cybercartographic products,the Cybercartographic Atlas of Antarctica and the Cybercartographic Atlas of Canada’s Trade with the World,were produced.Between 2006 and 2009,cybercartography was further developed as a result of interaction with indigenous communities,especially in Canada’s north and new interactive atlases such as the Kitikmeot Place Names Atlas and the Community Atlas of Arctic Bay were created in cooperation with the communities involved.The Nunaliit Cybercartographic Atlas Framework,built using open source software and open specifications and standards,was developed to facilitate direct input to these atlases.Cybercartography is now entering a new phase in both theory and practice building on a recently completed prototype atlas of Indigenous Perspectives and Knowledge.
