The present paper introduces the concepts of exergy and treats it applications to analysis of the gain in exergy efficiency between one-step and multi-step thermal processes. The analysis, which is carried out with th...The present paper introduces the concepts of exergy and treats it applications to analysis of the gain in exergy efficiency between one-step and multi-step thermal processes. The analysis, which is carried out with the Excel-based SEPE program, is exemplified with the comparison between single-step and two-steps heat pump setup for providing heat to a floor heating system and for domestic hot water. The paper discusses the use of the concept of exergy efficiency as a measure of success for design of a heat pump application and how the use of information on exergy destruction and temperature levels in different parts of the system add a new perspective to the analysis and the evaluation of the system performance. The paper shows how this information can be used to improve the system configuration and also the operation of the system for given boundary conditions. This is especially useful when the energy from the low temperature sources can be utilized at different temperature or quality levels such as for space heating and domestic hot water.展开更多
The Niagara Escarpment,a 440-million-year-old landform,cuts through a property owned by the University of Toronto in Caledon,Ontario in Canada.The property juxtaposes impacts from historical quarrying activity which b...The Niagara Escarpment,a 440-million-year-old landform,cuts through a property owned by the University of Toronto in Caledon,Ontario in Canada.The property juxtaposes impacts from historical quarrying activity which burrowed directly into the Escarpment’s slope,the greater context of the region’s urban development demands,and the Escarpment’s identity as an ancient geological formation,ecological refugium,and old-growth forest housing ancient species such as Thuja occidentalis.This project explores the university’s responsibility in advocating for the protection of the Escarpment’s unique ecologic conditions,including the distinct cliff ecosystems and the novel successional plant communities evolving on sites of former quarry activities.Interventions on the trail system,cave bridges and lookouts,and the boardwalk and path system,along with guidance of signage and trail markers,will bring visitors to areas where former quarry activities sculptured the Escarpment’s limestone faces and are now reclaimed by a system of lush novel wetlands and habitats in evolutionary stages.Connecting to a system of existing public trails,this project leverages the university’s educational and recreational objectives to form new strategic partnerships with local conservancy groups,aiming at monitoring and managing access and habitat protection.展开更多
To control the growth of space debris in the geostationary earth orbit （GEO）, a novel solution of net capture and tether-tugging reorbiting is proposed. After capture, the tug （i.e., active spacecraft）, tether, ne...To control the growth of space debris in the geostationary earth orbit （GEO）, a novel solution of net capture and tether-tugging reorbiting is proposed. After capture, the tug （i.e., active spacecraft）, tether, net, and target （i.e., GEO debris） constitute a rig- id-flexible coupled tethered combination system （TCS）, and subsequently the system is transported to the graveyard orbit by a thruster equipped on the tug. This paper attempts to study the dynamics of tether-tugging leorbiting after net capture. The net is equivalent to four flexible bridles, and the tug and target are viewed as rigid bodies. A sophisticated mathematical model is developed, taking into account the system orbital motion, relative motion of two spacecraft and spacecraft attitude motion. Given the complexity of the model, the numerical method is adopted to study the system dynamics characteristics. Particular attention is given to the investigation of the possible risks such as tether slack, spacecraft collision, tether rupture, tether-tug intertwist and destabilizing of the rug＇s attitude. The influence of the initial conditions and the magnitudes of the thrust are studied.展开更多
A method of correlation analysis to determine the correlation between two too-short arcs is presented to monitor geosynchro- nous earth orbit objects on a space-based surveillance system. The necessary condition for a...A method of correlation analysis to determine the correlation between two too-short arcs is presented to monitor geosynchro- nous earth orbit objects on a space-based surveillance system. The necessary condition for a geosynchronous earth orbit object to be observed by a space-based visible sensor in two successive orbital periods is derived, and the principle for the selection of search fence parameters is proposed. The processing procedure of the correlation analysis for the two too-short arcs as well as two correlation judgment methods is given and the selection of the threshold value for the judgment is analyzed. Finally, a simulation is performed to demonstrate the applicability of the presented methods. Simulation results ir^dicate that a surveil- lance system can acquire two observation arcs in two successive orbital periods by selecting the suitable search fence parame- ters, and that the two correlation judgment methods and the selected threshold are valid. The initial orbit of the uncorrelated objects can be determined by two observation arcs, and the accuracy of the initial orbit meets the requirements of re-acquiring the object.展开更多
Satellite-station two-way time comparison is a typical design in Beidou System(BDS)which is significantly different from other satellite navigation systems.As a type of two-way time comparison method,BDS time synchron...Satellite-station two-way time comparison is a typical design in Beidou System(BDS)which is significantly different from other satellite navigation systems.As a type of two-way time comparison method,BDS time synchronization is hardly influenced by satellite orbit error,atmosphere delay,tracking station coordinate error and measurement model error.Meanwhile,single-way time comparison can be realized through the method of Multi-satellite Precision Orbit Determination(MPOD)with pseudo-range and carrier phase of monitor receiver.It is proved in the constellation of 3GEO/2IGSO that the radial orbit error can be reflected in the difference between two-way time comparison and single-way time comparison,and that may lead to a substitute for orbit evaluation by SLR.In this article,the relation between orbit error and difference of two-way and single-way time comparison is illustrated based on the whole constellation of BDS.Considering the all-weather and real-time operation mode of two-way time comparison,the orbit error could be quantifiably monitored in a real-time mode through comparing two-way and single-way time synchronization.In addition,the orbit error can be predicted and corrected in a short time based on its periodic characteristic.It is described in the experiments of GEO and IGSO that the prediction accuracy of space signal can be obviously improved when the prediction orbit error is sent to the users through navigation message,and then the UERE including terminal error can be reduced from 0.1 m to 0.4 m while the average accuracy can be improved more than 27%.Though it is still hard to make accuracy improvement for Precision Orbit Determination(POD)and orbit prediction because of the confined tracking net and the difficulties in dynamic model optimization,in this paper,a practical method for orbit accuracy improvement is proposed based on two-way time comparison which can result in the reflection of orbit error.展开更多
With the approaching of the 24th solar cycle peak year （2012-2014）, the impacts of super solar storms on the geospace envi- ronment have drawn attentions. Based on the geomagnetic field observations during Carringto...With the approaching of the 24th solar cycle peak year （2012-2014）, the impacts of super solar storms on the geospace envi- ronment have drawn attentions. Based on the geomagnetic field observations during Carrington event in 1859, we estimate the interplanetary solar wind conditions at that time, and investigate the response of the magnetosphere-ionosphere system to this extreme solar wind conditions using global 3D MHD simulations. The main findings include： l） The day-side magnetopause and bow shock are compressed to 4.3 and 6.0 Re （Earth radius）, and their flanks are also strongly compressed. The magneto- pause shifts inside the geosynchronous orbit, exposing geosynchronous satellites in the solar wind in the magnetosheath. 2） During the storm, the region-1 current increases by about 60 times, and the cross polar potential drop increases by about 80 times; the reconnection voltage is about 5 to 6 times larger than the average storms, which means a larger amount of the solar wind energy enters the magnetosphere, resulting in strong space weather phenomena.展开更多
文摘The present paper introduces the concepts of exergy and treats it applications to analysis of the gain in exergy efficiency between one-step and multi-step thermal processes. The analysis, which is carried out with the Excel-based SEPE program, is exemplified with the comparison between single-step and two-steps heat pump setup for providing heat to a floor heating system and for domestic hot water. The paper discusses the use of the concept of exergy efficiency as a measure of success for design of a heat pump application and how the use of information on exergy destruction and temperature levels in different parts of the system add a new perspective to the analysis and the evaluation of the system performance. The paper shows how this information can be used to improve the system configuration and also the operation of the system for given boundary conditions. This is especially useful when the energy from the low temperature sources can be utilized at different temperature or quality levels such as for space heating and domestic hot water.
文摘The Niagara Escarpment,a 440-million-year-old landform,cuts through a property owned by the University of Toronto in Caledon,Ontario in Canada.The property juxtaposes impacts from historical quarrying activity which burrowed directly into the Escarpment’s slope,the greater context of the region’s urban development demands,and the Escarpment’s identity as an ancient geological formation,ecological refugium,and old-growth forest housing ancient species such as Thuja occidentalis.This project explores the university’s responsibility in advocating for the protection of the Escarpment’s unique ecologic conditions,including the distinct cliff ecosystems and the novel successional plant communities evolving on sites of former quarry activities.Interventions on the trail system,cave bridges and lookouts,and the boardwalk and path system,along with guidance of signage and trail markers,will bring visitors to areas where former quarry activities sculptured the Escarpment’s limestone faces and are now reclaimed by a system of lush novel wetlands and habitats in evolutionary stages.Connecting to a system of existing public trails,this project leverages the university’s educational and recreational objectives to form new strategic partnerships with local conservancy groups,aiming at monitoring and managing access and habitat protection.
基金supported by the National Natural Science Foundation of China(Grant No.11272345)
文摘To control the growth of space debris in the geostationary earth orbit （GEO）, a novel solution of net capture and tether-tugging reorbiting is proposed. After capture, the tug （i.e., active spacecraft）, tether, net, and target （i.e., GEO debris） constitute a rig- id-flexible coupled tethered combination system （TCS）, and subsequently the system is transported to the graveyard orbit by a thruster equipped on the tug. This paper attempts to study the dynamics of tether-tugging leorbiting after net capture. The net is equivalent to four flexible bridles, and the tug and target are viewed as rigid bodies. A sophisticated mathematical model is developed, taking into account the system orbital motion, relative motion of two spacecraft and spacecraft attitude motion. Given the complexity of the model, the numerical method is adopted to study the system dynamics characteristics. Particular attention is given to the investigation of the possible risks such as tether slack, spacecraft collision, tether rupture, tether-tug intertwist and destabilizing of the rug＇s attitude. The influence of the initial conditions and the magnitudes of the thrust are studied.
文摘A method of correlation analysis to determine the correlation between two too-short arcs is presented to monitor geosynchro- nous earth orbit objects on a space-based surveillance system. The necessary condition for a geosynchronous earth orbit object to be observed by a space-based visible sensor in two successive orbital periods is derived, and the principle for the selection of search fence parameters is proposed. The processing procedure of the correlation analysis for the two too-short arcs as well as two correlation judgment methods is given and the selection of the threshold value for the judgment is analyzed. Finally, a simulation is performed to demonstrate the applicability of the presented methods. Simulation results ir^dicate that a surveil- lance system can acquire two observation arcs in two successive orbital periods by selecting the suitable search fence parame- ters, and that the two correlation judgment methods and the selected threshold are valid. The initial orbit of the uncorrelated objects can be determined by two observation arcs, and the accuracy of the initial orbit meets the requirements of re-acquiring the object.
基金supported by the National Natural Science Foundation of China(Grant No.11103064)the Basic Research Foundation Program of Education Ministry Key Laboratory for Earth Space Environment and Geodetic survey,China(Grant No.11-01-06)
文摘Satellite-station two-way time comparison is a typical design in Beidou System(BDS)which is significantly different from other satellite navigation systems.As a type of two-way time comparison method,BDS time synchronization is hardly influenced by satellite orbit error,atmosphere delay,tracking station coordinate error and measurement model error.Meanwhile,single-way time comparison can be realized through the method of Multi-satellite Precision Orbit Determination(MPOD)with pseudo-range and carrier phase of monitor receiver.It is proved in the constellation of 3GEO/2IGSO that the radial orbit error can be reflected in the difference between two-way time comparison and single-way time comparison,and that may lead to a substitute for orbit evaluation by SLR.In this article,the relation between orbit error and difference of two-way and single-way time comparison is illustrated based on the whole constellation of BDS.Considering the all-weather and real-time operation mode of two-way time comparison,the orbit error could be quantifiably monitored in a real-time mode through comparing two-way and single-way time synchronization.In addition,the orbit error can be predicted and corrected in a short time based on its periodic characteristic.It is described in the experiments of GEO and IGSO that the prediction accuracy of space signal can be obviously improved when the prediction orbit error is sent to the users through navigation message,and then the UERE including terminal error can be reduced from 0.1 m to 0.4 m while the average accuracy can be improved more than 27%.Though it is still hard to make accuracy improvement for Precision Orbit Determination(POD)and orbit prediction because of the confined tracking net and the difficulties in dynamic model optimization,in this paper,a practical method for orbit accuracy improvement is proposed based on two-way time comparison which can result in the reflection of orbit error.
基金supported by National Natural Science Foundation of China (Grant Nos. 40921063, 40974106,40831060)the special fund for State Key Laboratory of Ministry of Science and Technology
文摘With the approaching of the 24th solar cycle peak year （2012-2014）, the impacts of super solar storms on the geospace envi- ronment have drawn attentions. Based on the geomagnetic field observations during Carrington event in 1859, we estimate the interplanetary solar wind conditions at that time, and investigate the response of the magnetosphere-ionosphere system to this extreme solar wind conditions using global 3D MHD simulations. The main findings include： l） The day-side magnetopause and bow shock are compressed to 4.3 and 6.0 Re （Earth radius）, and their flanks are also strongly compressed. The magneto- pause shifts inside the geosynchronous orbit, exposing geosynchronous satellites in the solar wind in the magnetosheath. 2） During the storm, the region-1 current increases by about 60 times, and the cross polar potential drop increases by about 80 times; the reconnection voltage is about 5 to 6 times larger than the average storms, which means a larger amount of the solar wind energy enters the magnetosphere, resulting in strong space weather phenomena.
