In this study,the transmission capacity of VANETs in a highway scenario is analysed on the basis of a 1D line model and the carrier sense multiple access with collision avoidance(CSMA/CA)protocol.We describe the CSMA/...In this study,the transmission capacity of VANETs in a highway scenario is analysed on the basis of a 1D line model and the carrier sense multiple access with collision avoidance(CSMA/CA)protocol.We describe the CSMA/CA protocol used in IEEE802.11 p from the perspective of the geometric relationship amongst simultaneous transmitters.The desired channel and interfering channels are assumed to experience the same amount of path-loss and Rayleigh fading.On the basis of the proposed model,we analyse the attempted transmission probability of each road segment and the maximum intensity of active transmitters,including their theoretical values.Then,we employ the physical model to obtain the outage probability and derive the upper bound of the transmission capacity of a VANET,which is defined as the average spatial density of successful transmissions in the network.Simulation results indicate that the theoretical value offers a good bound on network capacity.展开更多
1.General reviewThe first 330 kV transmission line in Northwest China fromLiujiaxia Hydro Power Station through Qinan Substation to TangyuSubstation was commissioned in 1972.In the seventies,accompany-ing the commissi...1.General reviewThe first 330 kV transmission line in Northwest China fromLiujiaxia Hydro Power Station through Qinan Substation to TangyuSubstation was commissioned in 1972.In the seventies,accompany-ing the commissioning of Hancheng and Qinling Thermal PowerPlants in Shaanxi Province,the 330 kV transmission lines展开更多
It is a common practice in China to use an insulated silk jack lad-der in the live-line work to enter the 500 kV EHV electric field.Wuhan High Voltage Research Institute has successfully carried outsuch operating perf...It is a common practice in China to use an insulated silk jack lad-der in the live-line work to enter the 500 kV EHV electric field.Wuhan High Voltage Research Institute has successfully carried outsuch operating performance at the meeting of ESMO-90 in Canada.(Fig.1) The operating procedure is now recommended asfollows.展开更多
During two years odd period from Dec.1987 to Feb.1990,there had been repeatedly pollution-flashoverfailures on our 500 kV transmission lines,resulting in a wide scopeblackout.There were eleven 500 kV lines altogether ...During two years odd period from Dec.1987 to Feb.1990,there had been repeatedly pollution-flashoverfailures on our 500 kV transmission lines,resulting in a wide scopeblackout.There were eleven 500 kV lines altogether in North-east,East and North China power grids,where pollution-flashover failureshappened one after another on 36 transmission line towers (poles).Since 500 kV transmission lines are the main trunks of high展开更多
Anorectal emergencies refer to anorectal disorders presenting with some alarming symptoms such as acute anal pain and bleeding which might require an immediate management. This article deals with the diagnosis and man...Anorectal emergencies refer to anorectal disorders presenting with some alarming symptoms such as acute anal pain and bleeding which might require an immediate management. This article deals with the diagnosis and management of common anorectal emergencies such as acutely thrombosed external hemorrhoid, thrombosed or strangulated internal hemorrhoid, bleeding hemorrhoid, bleeding anorectal varices, anal fissure, irreducible or strangulated rectal prolapse, anorectal abscess, perineal necrotizing fasciitis(Fournier gangrene), retained anorectal foreign bodies and obstructing rectal cancer. Sexually transmitted diseases as anorectal non-surgical emergencies and some anorectal emergencies in neonates are also discussed. The last part of this review dedicates to the management of early complications following common anorectal procedures that may present as an emergency including acute urinary retention, bleeding, fecal impaction and anorectal sepsis. Although many of anorectal disorders presenting in an emergency setting are not life-threatening and may be successfully treated in an outpatient clinic, an accurate diagnosis and proper management remains a challenging problem for clinicians. A detailed history taking and a careful physical examination, including digital rectal examination and anoscopy, is essential for correct diagnosis and plan of treatment. In some cases, some imaging examinations, such as endoanal ultrasonography and computerized tomography scan of whole abdomen, are required. If in doubt, the attending physicians should not hesitate to consult an expert e.g., colorectal surgeon about the diagnosis, proper management and appropriate follow-up.展开更多
基金supported in part by the National Natural Science Foundation of China under Grant No.61271184 and 61571065
文摘In this study,the transmission capacity of VANETs in a highway scenario is analysed on the basis of a 1D line model and the carrier sense multiple access with collision avoidance(CSMA/CA)protocol.We describe the CSMA/CA protocol used in IEEE802.11 p from the perspective of the geometric relationship amongst simultaneous transmitters.The desired channel and interfering channels are assumed to experience the same amount of path-loss and Rayleigh fading.On the basis of the proposed model,we analyse the attempted transmission probability of each road segment and the maximum intensity of active transmitters,including their theoretical values.Then,we employ the physical model to obtain the outage probability and derive the upper bound of the transmission capacity of a VANET,which is defined as the average spatial density of successful transmissions in the network.Simulation results indicate that the theoretical value offers a good bound on network capacity.
文摘1.General reviewThe first 330 kV transmission line in Northwest China fromLiujiaxia Hydro Power Station through Qinan Substation to TangyuSubstation was commissioned in 1972.In the seventies,accompany-ing the commissioning of Hancheng and Qinling Thermal PowerPlants in Shaanxi Province,the 330 kV transmission lines
文摘It is a common practice in China to use an insulated silk jack lad-der in the live-line work to enter the 500 kV EHV electric field.Wuhan High Voltage Research Institute has successfully carried outsuch operating performance at the meeting of ESMO-90 in Canada.(Fig.1) The operating procedure is now recommended asfollows.
文摘During two years odd period from Dec.1987 to Feb.1990,there had been repeatedly pollution-flashoverfailures on our 500 kV transmission lines,resulting in a wide scopeblackout.There were eleven 500 kV lines altogether in North-east,East and North China power grids,where pollution-flashover failureshappened one after another on 36 transmission line towers (poles).Since 500 kV transmission lines are the main trunks of high
文摘Anorectal emergencies refer to anorectal disorders presenting with some alarming symptoms such as acute anal pain and bleeding which might require an immediate management. This article deals with the diagnosis and management of common anorectal emergencies such as acutely thrombosed external hemorrhoid, thrombosed or strangulated internal hemorrhoid, bleeding hemorrhoid, bleeding anorectal varices, anal fissure, irreducible or strangulated rectal prolapse, anorectal abscess, perineal necrotizing fasciitis(Fournier gangrene), retained anorectal foreign bodies and obstructing rectal cancer. Sexually transmitted diseases as anorectal non-surgical emergencies and some anorectal emergencies in neonates are also discussed. The last part of this review dedicates to the management of early complications following common anorectal procedures that may present as an emergency including acute urinary retention, bleeding, fecal impaction and anorectal sepsis. Although many of anorectal disorders presenting in an emergency setting are not life-threatening and may be successfully treated in an outpatient clinic, an accurate diagnosis and proper management remains a challenging problem for clinicians. A detailed history taking and a careful physical examination, including digital rectal examination and anoscopy, is essential for correct diagnosis and plan of treatment. In some cases, some imaging examinations, such as endoanal ultrasonography and computerized tomography scan of whole abdomen, are required. If in doubt, the attending physicians should not hesitate to consult an expert e.g., colorectal surgeon about the diagnosis, proper management and appropriate follow-up.
