To investigate the effects of sudden change in wind loads on the running performance of trains on the bridge in crosswinds,a highway-railway one-story bridge was taken as the research object.Aerodynamic coefficients o...To investigate the effects of sudden change in wind loads on the running performance of trains on the bridge in crosswinds,a highway-railway one-story bridge was taken as the research object.Aerodynamic coefficients of the train and the bridge were measured in a series of train-bridge system segment models through wind tunnel tests when two trains passed each other on the bridge and when a train entered and left the wind barrier section of the bridge.Based on the improved SIMPACK and ANSYS rigid-flexible coupling simulation method,a wind-double train-track-bridge system coupled vibration model was established.The dynamic responses of the train were analyzed under the effects of sudden change in wind loads caused by two trains passing each other and a train entering and leaving the wind barrier section of the bridge.The results show that the effects of sudden wind load change caused by the trains passing each other had less effects on the running safety of the leeward-side train than the wind shielding effect caused by the windward-side train in the wind speed range of 10−25 m/s.With the decrease in the porosity of wind barriers,the effects of the sudden wind load change played an increasingly important role in the running safety and comfort of the train.With the increase in wind speed,the lateral response of the train increased obviously because of the effects of sudden wind load change,which affects both the lateral running stability and the comfort of the train.展开更多
We present a comparison of changes in large and sharp solar wind dynamic pressure, observed by several spacecraft, with fast disturbances in the magnetospheric magnetic field, measured by the geosynchronous satellites...We present a comparison of changes in large and sharp solar wind dynamic pressure, observed by several spacecraft, with fast disturbances in the magnetospheric magnetic field, measured by the geosynchronous satellites. More than 260 changes in solar wind pressure during the period 1996-2003 are selected for this study. Large statistics show that an increase （a decrease） in dynamic pressure always results in an increase （a decrease） in the magnitude of geosynchronous magnetic field. The amplitude of response to the geomagnetic field strongly depends on the location of observer relative to the noon meridian, the value of pressure before disturbance, and the change in amplitude of pressure.展开更多
In this paper, a Wind Direction Change Index (WI), which can describe four-dimensional spatiotemporal changes of the atmospheric circulation objectively and quantitatively, is defined to study its evolution and season...In this paper, a Wind Direction Change Index (WI), which can describe four-dimensional spatiotemporal changes of the atmospheric circulation objectively and quantitatively, is defined to study its evolution and seasonal variation. The first four modes can be obtained by EOF expansion of the zonally averaged WI. The first mode reveals the basic spatial distribution of the annually averaged WI. The second mode reflects the quasi-harmonic parts of the WI deviations. Tropical, subtropical and extratropical monsoon areas can be clearly reflected by this mode. The third mode reflects the non-harmonic parts of the WI deviations. It shows the so-called February reverse in stratospheric atmosphere as well as the asymmetric seasonal changes from spring to fall and from fall to spring due to both the land-sea distribution contrast between the Northern and Southern Hemispheres and the nonlinear effect of atmospheric and ocean fluids. The fourth mode reveals the northward advancing of the global reversed wind fields from spring to summer and their southward withdrawal from summer to autumn.展开更多
BY all accounts the only people surprised by the results of South Africa＇s local government elections in August were those in the ANC ruling party. For the first time since coming to power in 1994, the ANC saw its n...BY all accounts the only people surprised by the results of South Africa＇s local government elections in August were those in the ANC ruling party. For the first time since coming to power in 1994, the ANC saw its national support drop to below 60 percent. The party of legendary freedom struggle icons like Oliver Tambo and Nelson Mandela was handed a rude awakening by voters.展开更多
THE winds of change were discerned in Botswana when Festus Mogae, former president of the southern African nation from 1998-2008, expressed his support for gay rights in Africa.
THERE＇S a revolution blowing along the highlands about 95 km southeast of Addis Ababa, Ethiopia＇s capital. Standing high up on the Great Rift Valley, row upon row of giant white wind turbines spin freely, churning o...THERE＇S a revolution blowing along the highlands about 95 km southeast of Addis Ababa, Ethiopia＇s capital. Standing high up on the Great Rift Valley, row upon row of giant white wind turbines spin freely, churning out valuable green energy to supple- ment the nation＇s grid.展开更多
The United States takes an active new approach on climate change,but more still needs to be done Nearly a year after entering the Oval Office,U.S.President Barack Obama has shown a clear commitment to reversing Americ...The United States takes an active new approach on climate change,but more still needs to be done Nearly a year after entering the Oval Office,U.S.President Barack Obama has shown a clear commitment to reversing America’s soiled reputation on展开更多
Researcher Peng Weixue from the Institute of Taiwan Studies of the Chinese Academy of Social Sciences,and also Executive Editor in Chief of Taiwan Weekly,a publication affiliated to the research institute,comments on ...Researcher Peng Weixue from the Institute of Taiwan Studies of the Chinese Academy of Social Sciences,and also Executive Editor in Chief of Taiwan Weekly,a publication affiliated to the research institute,comments on the outcome of the recently concluded"legislature"election in Taiwan and its impacts on relations across the Taiwan Straits.展开更多
The newly born Republic of Nepal has gone a long way to transform its political system more than three months after it became arepublic, Nepal will hopefully have a new government soon, with the election for prime min...The newly born Republic of Nepal has gone a long way to transform its political system more than three months after it became arepublic, Nepal will hopefully have a new government soon, with the election for prime minister slated for August 15. The Constituent Assembly declared Nepal to展开更多
Flux adjustable permanent magnet machines(FAPMMs)are a novel type of permanent magnet(PM)machines which are able to flexibly adjust the field excitation flux linkage and offer the distinctive advantages of high power ...Flux adjustable permanent magnet machines(FAPMMs)are a novel type of permanent magnet(PM)machines which are able to flexibly adjust the field excitation flux linkage and offer the distinctive advantages of high power density and high efficiency.They have attracted ever-increasing interests and are promising candidate machines for electric vehicle,machine-tool and aircraft applications.In this paper,the state-of-the-art of various FAPMMs are comprehensively reviewed according to three means of flux-adjustment,i.e.electrically adjusted by either auxiliary field windings or armature winding change,mechanically adjusted magnetic reluctances of flux paths,and memory machines by magnetizing/demagnetizing PMs.The corresponding flux-adjustable principles and electromagnetic characteristics are systematically elaborated and quantitatively compared.Their merits and demerits are highlighted,together with their recent developments.展开更多
基金Projects(51822803,51878080,51778073) supported by the National Natural Science Foundation of ChinaProjects(2020JJ3035,2018JJ3538) supported by the Hunan Provincial Natural Science Foundation of China。
文摘To investigate the effects of sudden change in wind loads on the running performance of trains on the bridge in crosswinds,a highway-railway one-story bridge was taken as the research object.Aerodynamic coefficients of the train and the bridge were measured in a series of train-bridge system segment models through wind tunnel tests when two trains passed each other on the bridge and when a train entered and left the wind barrier section of the bridge.Based on the improved SIMPACK and ANSYS rigid-flexible coupling simulation method,a wind-double train-track-bridge system coupled vibration model was established.The dynamic responses of the train were analyzed under the effects of sudden change in wind loads caused by two trains passing each other and a train entering and leaving the wind barrier section of the bridge.The results show that the effects of sudden wind load change caused by the trains passing each other had less effects on the running safety of the leeward-side train than the wind shielding effect caused by the windward-side train in the wind speed range of 10−25 m/s.With the decrease in the porosity of wind barriers,the effects of the sudden wind load change played an increasingly important role in the running safety and comfort of the train.With the increase in wind speed,the lateral response of the train increased obviously because of the effects of sudden wind load change,which affects both the lateral running stability and the comfort of the train.
基金Project supported by the Russian Foundation for Basic Researches （Grant Nos 04-02-16152 and 04-02-39004）, the International Association for the Promotion of Co-operation with Scientists from the New Independent States of the Former Soviet Union （Grant Nos 03-51-3738 and MK-2267.2004.2） and the National Natural Science Foundation of China （Grand Nos 40325010 and 40574069）.
文摘We present a comparison of changes in large and sharp solar wind dynamic pressure, observed by several spacecraft, with fast disturbances in the magnetospheric magnetic field, measured by the geosynchronous satellites. More than 260 changes in solar wind pressure during the period 1996-2003 are selected for this study. Large statistics show that an increase （a decrease） in dynamic pressure always results in an increase （a decrease） in the magnitude of geosynchronous magnetic field. The amplitude of response to the geomagnetic field strongly depends on the location of observer relative to the noon meridian, the value of pressure before disturbance, and the change in amplitude of pressure.
文摘In this paper, a Wind Direction Change Index (WI), which can describe four-dimensional spatiotemporal changes of the atmospheric circulation objectively and quantitatively, is defined to study its evolution and seasonal variation. The first four modes can be obtained by EOF expansion of the zonally averaged WI. The first mode reveals the basic spatial distribution of the annually averaged WI. The second mode reflects the quasi-harmonic parts of the WI deviations. Tropical, subtropical and extratropical monsoon areas can be clearly reflected by this mode. The third mode reflects the non-harmonic parts of the WI deviations. It shows the so-called February reverse in stratospheric atmosphere as well as the asymmetric seasonal changes from spring to fall and from fall to spring due to both the land-sea distribution contrast between the Northern and Southern Hemispheres and the nonlinear effect of atmospheric and ocean fluids. The fourth mode reveals the northward advancing of the global reversed wind fields from spring to summer and their southward withdrawal from summer to autumn.
文摘BY all accounts the only people surprised by the results of South Africa＇s local government elections in August were those in the ANC ruling party. For the first time since coming to power in 1994, the ANC saw its national support drop to below 60 percent. The party of legendary freedom struggle icons like Oliver Tambo and Nelson Mandela was handed a rude awakening by voters.
文摘THE winds of change were discerned in Botswana when Festus Mogae, former president of the southern African nation from 1998-2008, expressed his support for gay rights in Africa.
文摘THERE＇S a revolution blowing along the highlands about 95 km southeast of Addis Ababa, Ethiopia＇s capital. Standing high up on the Great Rift Valley, row upon row of giant white wind turbines spin freely, churning out valuable green energy to supple- ment the nation＇s grid.
文摘The United States takes an active new approach on climate change,but more still needs to be done Nearly a year after entering the Oval Office,U.S.President Barack Obama has shown a clear commitment to reversing America’s soiled reputation on
文摘Researcher Peng Weixue from the Institute of Taiwan Studies of the Chinese Academy of Social Sciences,and also Executive Editor in Chief of Taiwan Weekly,a publication affiliated to the research institute,comments on the outcome of the recently concluded"legislature"election in Taiwan and its impacts on relations across the Taiwan Straits.
文摘The newly born Republic of Nepal has gone a long way to transform its political system more than three months after it became arepublic, Nepal will hopefully have a new government soon, with the election for prime minister slated for August 15. The Constituent Assembly declared Nepal to
文摘Flux adjustable permanent magnet machines(FAPMMs)are a novel type of permanent magnet(PM)machines which are able to flexibly adjust the field excitation flux linkage and offer the distinctive advantages of high power density and high efficiency.They have attracted ever-increasing interests and are promising candidate machines for electric vehicle,machine-tool and aircraft applications.In this paper,the state-of-the-art of various FAPMMs are comprehensively reviewed according to three means of flux-adjustment,i.e.electrically adjusted by either auxiliary field windings or armature winding change,mechanically adjusted magnetic reluctances of flux paths,and memory machines by magnetizing/demagnetizing PMs.The corresponding flux-adjustable principles and electromagnetic characteristics are systematically elaborated and quantitatively compared.Their merits and demerits are highlighted,together with their recent developments.
