Considerable changes have taken place in commercial passenger air transport since the enactment of the 1978 Airline Deregulation Act in the US and the deregulation of airline networks that has occurred elsewhere. The ...Considerable changes have taken place in commercial passenger air transport since the enactment of the 1978 Airline Deregulation Act in the US and the deregulation of airline networks that has occurred elsewhere. The commercial and operational freedoms have led most of the larger carriers to develop hub-and-spoke networks, within which certain cities or metropolitan areas emerge as key nodes possessing tremendous advantages over other locations in the air transport system. This paper examines the nature of hub-and-spoke operations in air transportation services, and the benefits that accrue to a city or geographical region that is host to an airline hub. In particular, it looks into linkages between the air service hub and local economic development. Four potential types of impact of airports on the regional economy are defined and discussed. As an example, the assessment of the economic impacts of Cincinnati-Northern Kentucky International Airport (CVG), a major Delta Airlines hub, is introduced.展开更多
On the basis of analyzing the history and characteristics of the undergroundspace exploitation and the urban space development in Guangzhou, and making a thorough study on theunderground space exploitation based on th...On the basis of analyzing the history and characteristics of the undergroundspace exploitation and the urban space development in Guangzhou, and making a thorough study on theunderground space exploitation based on the subway building, this paper points out some mam problemsin the exploitation of underground space in Guangzhou, and emphasizes that Guangzhou must developthe underground space on a large scale with the aid of the subway building, and puts forward aproposal on the urban space coordinate development between on-ground and underground in GuangzhouCity.展开更多
The tourist industry, as global mass phenomenon, is inextricably linked to the evolution of air transport systems and air carriers, in turn, depends on tourism to ensure stability in routes and prices. Therefore, both...The tourist industry, as global mass phenomenon, is inextricably linked to the evolution of air transport systems and air carriers, in turn, depends on tourism to ensure stability in routes and prices. Therefore, both sectors must face the new challenges together, the transport industry is heading a problem of energy and cost overruns, that inevitably will affect tourism in the short term. The first energy crisis that they are starting to live, has been mitigated by changes in three parameters： （1） the international regulation of commercial aviation; （2） the connectivity and business （birth of low cost companies） models; and （3） the new policies for climate change and gas emission. So far, the rapid growth of the tourist industry has being held on a fast and cheap access to transport energy resources based on the false belief of unlimited access to energy. The article is a review of the state of the art, and the research papers published on air transportation, relating to tourism and the emergence of low cost airlines, in order to give a global vision for the decision makers of mass destinations, as it is the case of the Canary Islands that we will use as a reference.展开更多
We first propose fundamental solutions of wave propagation in dispersive chain subject to a localized initial perturbation in the displacement. Analytical solutions are obtained for both second order nonlinear dispers...We first propose fundamental solutions of wave propagation in dispersive chain subject to a localized initial perturbation in the displacement. Analytical solutions are obtained for both second order nonlinear dispersive chain and homogenous harmonic chain using stationary phase approximation. Solution is also compared with numerical results from molecular dynamics （MD） simulations. Locally dominant phonon modes （k-space） are introduced based on these solutions. These locally defined spatially and temporally varying phonon modes k（x, t） are critical to the concept of the local thermodynamic equilibrium （LTE）. Wave propagation accompanying with the nonequilibrium dynamics leads to the excitation of these locally defined phonon modes. It is found that the system energy is gradually redistributed among these excited phonons modes （k-space）. This redistribution process is only possible with nonlinear dispersion and requires a finite amount of time to achieve a steady state distribution. This time scale is dependent on the spatial distribution （or frequency content） of the initial perturbation and the dispersion relation. Sharper and more concentrated perturbation leads to a faster energy redistribution and dissipation. This energy redistribution generates localized phonons with various frequencies that can be important for phonon-phonon interaction and energy dissipation in nonlinear systems. Depending on the initial perturbation and temperature, the time scale associated with this energy distribution can be critical for energy dissipation compared to the Umklapp scattering process. Ballistic type of heat transport along the harmonic chain reveals that at any given position, the lowest mode （k = O） is excited first and gradually expanding to the highest mode （km^（x,t））, where km^（x,t） can only asymptotically approach the maximum mode kB of the first Brillouin zone （kmax（x,t） --~ kB）. NO energy distributed into modes with k_max（x,t） 〈 k 〈 k^B demonstrates that the local thermodynamic equilibrium cannot be established in harmonic chain. Energy is shown to be uniformly distributed in all available phonon modes k ≤ _max（x, t） at any position with heat transfer along the harmonic chain. The energy flux along the chain is shown to be a constant with time and proportional to the sound speed （ballistic transport）. Comparison with the Fourier＇s law leads to a time-dependent thermal conductivity that diverges with time.展开更多
基金Under the auspices of Intramural Research Incentive Grant from the Office of the Senior Vice President for Research atUniversity of Louisville
文摘Considerable changes have taken place in commercial passenger air transport since the enactment of the 1978 Airline Deregulation Act in the US and the deregulation of airline networks that has occurred elsewhere. The commercial and operational freedoms have led most of the larger carriers to develop hub-and-spoke networks, within which certain cities or metropolitan areas emerge as key nodes possessing tremendous advantages over other locations in the air transport system. This paper examines the nature of hub-and-spoke operations in air transportation services, and the benefits that accrue to a city or geographical region that is host to an airline hub. In particular, it looks into linkages between the air service hub and local economic development. Four potential types of impact of airports on the regional economy are defined and discussed. As an example, the assessment of the economic impacts of Cincinnati-Northern Kentucky International Airport (CVG), a major Delta Airlines hub, is introduced.
文摘On the basis of analyzing the history and characteristics of the undergroundspace exploitation and the urban space development in Guangzhou, and making a thorough study on theunderground space exploitation based on the subway building, this paper points out some mam problemsin the exploitation of underground space in Guangzhou, and emphasizes that Guangzhou must developthe underground space on a large scale with the aid of the subway building, and puts forward aproposal on the urban space coordinate development between on-ground and underground in GuangzhouCity.
文摘The tourist industry, as global mass phenomenon, is inextricably linked to the evolution of air transport systems and air carriers, in turn, depends on tourism to ensure stability in routes and prices. Therefore, both sectors must face the new challenges together, the transport industry is heading a problem of energy and cost overruns, that inevitably will affect tourism in the short term. The first energy crisis that they are starting to live, has been mitigated by changes in three parameters： （1） the international regulation of commercial aviation; （2） the connectivity and business （birth of low cost companies） models; and （3） the new policies for climate change and gas emission. So far, the rapid growth of the tourist industry has being held on a fast and cheap access to transport energy resources based on the false belief of unlimited access to energy. The article is a review of the state of the art, and the research papers published on air transportation, relating to tourism and the emergence of low cost airlines, in order to give a global vision for the decision makers of mass destinations, as it is the case of the Canary Islands that we will use as a reference.
文摘We first propose fundamental solutions of wave propagation in dispersive chain subject to a localized initial perturbation in the displacement. Analytical solutions are obtained for both second order nonlinear dispersive chain and homogenous harmonic chain using stationary phase approximation. Solution is also compared with numerical results from molecular dynamics （MD） simulations. Locally dominant phonon modes （k-space） are introduced based on these solutions. These locally defined spatially and temporally varying phonon modes k（x, t） are critical to the concept of the local thermodynamic equilibrium （LTE）. Wave propagation accompanying with the nonequilibrium dynamics leads to the excitation of these locally defined phonon modes. It is found that the system energy is gradually redistributed among these excited phonons modes （k-space）. This redistribution process is only possible with nonlinear dispersion and requires a finite amount of time to achieve a steady state distribution. This time scale is dependent on the spatial distribution （or frequency content） of the initial perturbation and the dispersion relation. Sharper and more concentrated perturbation leads to a faster energy redistribution and dissipation. This energy redistribution generates localized phonons with various frequencies that can be important for phonon-phonon interaction and energy dissipation in nonlinear systems. Depending on the initial perturbation and temperature, the time scale associated with this energy distribution can be critical for energy dissipation compared to the Umklapp scattering process. Ballistic type of heat transport along the harmonic chain reveals that at any given position, the lowest mode （k = O） is excited first and gradually expanding to the highest mode （km^（x,t））, where km^（x,t） can only asymptotically approach the maximum mode kB of the first Brillouin zone （kmax（x,t） --~ kB）. NO energy distributed into modes with k_max（x,t） 〈 k 〈 k^B demonstrates that the local thermodynamic equilibrium cannot be established in harmonic chain. Energy is shown to be uniformly distributed in all available phonon modes k ≤ _max（x, t） at any position with heat transfer along the harmonic chain. The energy flux along the chain is shown to be a constant with time and proportional to the sound speed （ballistic transport）. Comparison with the Fourier＇s law leads to a time-dependent thermal conductivity that diverges with time.
