A study of the accessibility of a city’s scenic spots via different travel modes can contribute to optimization of tourism-related transportation while improving tourists’ travel-related satisfaction levels and adva...A study of the accessibility of a city’s scenic spots via different travel modes can contribute to optimization of tourism-related transportation while improving tourists’ travel-related satisfaction levels and advancing tourism. We systematically analyzed the accessibility of 56 scenic spots in Xi’an City, China, via car and public transport travel modes using the real-time travel function of the Baidu Maps API(Application Programming Interface) along with spatial analysis methods and the modal accessibility gap index of scenic spots. We obtained the following results. First, maximum and minimum travel times using public transport exceeded those using cars. Moreover, the accessibility of scenic spots via cars and public transport presented a circular spatial pattern of increasing travel time from the center to the periphery. Contrasting with travel by public transport, car travel showed a clear time-space compression effect. Second, accessibility of the scenic spots via cars and public transport showed some spatial heterogeneity, with no clear advantages of car accessibility in the central urban area. However, advantages of car accessibility were increasingly evident moving from the center to the periphery. Third, whereas the correlation of the modal accessibility gap index of scenic spots in Xi’an with global space was significantly positive, local spatial interdependence was only evident in some inner city areas and in marginal areas. Moreover, spatial heterogeneity was evident in two regions but was insignificant in other areas, indicating that the spatial interdependence of the modal accessibility gap index in most scenic spots was not apparent in terms of the overall effect of public transport routes, road networks, and the distribution of scenic spots. The improvement of public transport coverage in marginal areas and the optimization of public transport routes in central urban areas are essential tasks for improving travel using public transport in the future.展开更多
In this paper, the zero voltage switching (ZVS) region of a dual active bridge (DAB) converter with wide band-gap (WBG) power semiconductor device is analyzed. The ZVS region of a DAB converter varies depending on out...In this paper, the zero voltage switching (ZVS) region of a dual active bridge (DAB) converter with wide band-gap (WBG) power semiconductor device is analyzed. The ZVS region of a DAB converter varies depending on output power and voltage ratio. The DAB converters operate with hard switching at light loads, it is difficult to achieve high efficiency. Fortunately, WBG power semiconductor devices have excellent hard switching characteristics and can increase efficiency compared to silicon (Si) devices. In particular, WBG devices can achieve ZVS at low load currents due to their low parasitic output capacitance (C<sub>o,tr</sub>) characteristics. Therefore, in this paper, the ZVS operating resion is analyzed based on the characteristics of Si, silicon carbide (SiC) and gallium nitride (GaN). Power semiconductor devices. WBG devices with low C<sub>o,tr</sub> operate at ZVS at lower load currents compared to Si devices. To verify this, experiments are conducted and the results are analyzed using a 3 kW DAB converter. For Si devices, ZVS is achieved above 1.4 kW. For WBG devices, ZVS is achieved at 700 W. Due to the ZVS conditions depending on the switching device, the DAB converter using Si devices achieves a power conversion efficiency of 91% at 1.1 kW output. On the other hand, in the case of WBG devices, power conversion efficiency of more than 98% is achieved under 11 kW conditions. In conclusion, it is confirmed that the WBG device operates in ZVS at a lower load compared to the Si device, which is advantageous in increasing light load efficiency.展开更多
Timely response to earthquake characterization can facilitate earthquake emergency rescue and further scientific investigations.On June 1,2022,M_(W) 5.9 earthquake occurred in the southern area of the Longmenshan faul...Timely response to earthquake characterization can facilitate earthquake emergency rescue and further scientific investigations.On June 1,2022,M_(W) 5.9 earthquake occurred in the southern area of the Longmenshan fault zone.This event also happened at the south end of the Dayi seismic gap and is the largest earthquake that has occurred in this seismic gap since the 1970 M 6.2 event.The slip-distribution model constrained by the seismic waveforms suggests a thrust-dominated faulting mechanism.The main slip occurs at a depth of~14 km,and the cumulative energy is released in the first 6 s.The variations of Coulomb stress caused by the mainshock show a positive change in the southwest area of the Dayi seismic gap,indicating possible activation of future earthquakes.In addition,we emphasize the importance of rapid estimation of deformation for near-field hazard delineation,especially when interferometric radar fails to image coseismic deformation in a high relief terrain.展开更多
中国工业存在较为严重的资源错配问题已经成为学界共识,但资源错配在行业间还是行业内更为严重依旧悬而未决,行业间和行业内错配对总量生产率损失的影响如何也亟需深入了解。文章以Hsieh and Klenow(2009)模型框架为主体,引入Aoki(2008...中国工业存在较为严重的资源错配问题已经成为学界共识,但资源错配在行业间还是行业内更为严重依旧悬而未决,行业间和行业内错配对总量生产率损失的影响如何也亟需深入了解。文章以Hsieh and Klenow(2009)模型框架为主体,引入Aoki(2008)的研究逻辑,建立一个同时分解行业间和行业内资源错配的分析框架,采用1999—2013年中国工业企业数据库为样本,实证分析了行业间和行业内资源错配对行业TFP以及总量生产率的损失。研究发现:(1)资源错配指数和产出、生产率增长潜力在不同的行业部门间差异较大。在资源错配指数和TFP改善潜力上:重工业>轻工业;高技术型行业>低技术型行业>中等技术型行业;技术密集型行业>劳动密集型行业>资本密集型行业;下游行业>上游行业;垄断性行业>竞争性行业。(2)要素错配降低了工业整体产出或TFP,即使不增加投入,通过有效消除行业间以及行业内企业间的资源配置扭曲,可使得工业产出提高21.5%。(3)资源错配使得工业TFP(对数值)损失了3.79,行业间的效率损失要高于行业内企业间的效率损失,行业间效率损失占总效率损失的53.08%,行业内企业间的效率损失占46.92%。研究明确了行业间与行业内的资源错配对工业总产出损失的影响大小,为中国工业界资源错配的论断提供了微观依据,也为中国工业企业供给侧结构性改革提供了经验证据和理论指导。展开更多
基金Under the auspices of National Natural Science Foundation of China(No.41831284,41501120)Special Scientific Research Project of Education Department of Shaanxi Provincial Government(No.18JK0649)Scientific Research Project of Xi’an International Studies University(No.18XWC24)
文摘A study of the accessibility of a city’s scenic spots via different travel modes can contribute to optimization of tourism-related transportation while improving tourists’ travel-related satisfaction levels and advancing tourism. We systematically analyzed the accessibility of 56 scenic spots in Xi’an City, China, via car and public transport travel modes using the real-time travel function of the Baidu Maps API(Application Programming Interface) along with spatial analysis methods and the modal accessibility gap index of scenic spots. We obtained the following results. First, maximum and minimum travel times using public transport exceeded those using cars. Moreover, the accessibility of scenic spots via cars and public transport presented a circular spatial pattern of increasing travel time from the center to the periphery. Contrasting with travel by public transport, car travel showed a clear time-space compression effect. Second, accessibility of the scenic spots via cars and public transport showed some spatial heterogeneity, with no clear advantages of car accessibility in the central urban area. However, advantages of car accessibility were increasingly evident moving from the center to the periphery. Third, whereas the correlation of the modal accessibility gap index of scenic spots in Xi’an with global space was significantly positive, local spatial interdependence was only evident in some inner city areas and in marginal areas. Moreover, spatial heterogeneity was evident in two regions but was insignificant in other areas, indicating that the spatial interdependence of the modal accessibility gap index in most scenic spots was not apparent in terms of the overall effect of public transport routes, road networks, and the distribution of scenic spots. The improvement of public transport coverage in marginal areas and the optimization of public transport routes in central urban areas are essential tasks for improving travel using public transport in the future.
文摘In this paper, the zero voltage switching (ZVS) region of a dual active bridge (DAB) converter with wide band-gap (WBG) power semiconductor device is analyzed. The ZVS region of a DAB converter varies depending on output power and voltage ratio. The DAB converters operate with hard switching at light loads, it is difficult to achieve high efficiency. Fortunately, WBG power semiconductor devices have excellent hard switching characteristics and can increase efficiency compared to silicon (Si) devices. In particular, WBG devices can achieve ZVS at low load currents due to their low parasitic output capacitance (C<sub>o,tr</sub>) characteristics. Therefore, in this paper, the ZVS operating resion is analyzed based on the characteristics of Si, silicon carbide (SiC) and gallium nitride (GaN). Power semiconductor devices. WBG devices with low C<sub>o,tr</sub> operate at ZVS at lower load currents compared to Si devices. To verify this, experiments are conducted and the results are analyzed using a 3 kW DAB converter. For Si devices, ZVS is achieved above 1.4 kW. For WBG devices, ZVS is achieved at 700 W. Due to the ZVS conditions depending on the switching device, the DAB converter using Si devices achieves a power conversion efficiency of 91% at 1.1 kW output. On the other hand, in the case of WBG devices, power conversion efficiency of more than 98% is achieved under 11 kW conditions. In conclusion, it is confirmed that the WBG device operates in ZVS at a lower load compared to the Si device, which is advantageous in increasing light load efficiency.
基金the National Natural Science Foundation of China(No.42174023)。
文摘Timely response to earthquake characterization can facilitate earthquake emergency rescue and further scientific investigations.On June 1,2022,M_(W) 5.9 earthquake occurred in the southern area of the Longmenshan fault zone.This event also happened at the south end of the Dayi seismic gap and is the largest earthquake that has occurred in this seismic gap since the 1970 M 6.2 event.The slip-distribution model constrained by the seismic waveforms suggests a thrust-dominated faulting mechanism.The main slip occurs at a depth of~14 km,and the cumulative energy is released in the first 6 s.The variations of Coulomb stress caused by the mainshock show a positive change in the southwest area of the Dayi seismic gap,indicating possible activation of future earthquakes.In addition,we emphasize the importance of rapid estimation of deformation for near-field hazard delineation,especially when interferometric radar fails to image coseismic deformation in a high relief terrain.
文摘中国工业存在较为严重的资源错配问题已经成为学界共识,但资源错配在行业间还是行业内更为严重依旧悬而未决,行业间和行业内错配对总量生产率损失的影响如何也亟需深入了解。文章以Hsieh and Klenow(2009)模型框架为主体,引入Aoki(2008)的研究逻辑,建立一个同时分解行业间和行业内资源错配的分析框架,采用1999—2013年中国工业企业数据库为样本,实证分析了行业间和行业内资源错配对行业TFP以及总量生产率的损失。研究发现:(1)资源错配指数和产出、生产率增长潜力在不同的行业部门间差异较大。在资源错配指数和TFP改善潜力上:重工业>轻工业;高技术型行业>低技术型行业>中等技术型行业;技术密集型行业>劳动密集型行业>资本密集型行业;下游行业>上游行业;垄断性行业>竞争性行业。(2)要素错配降低了工业整体产出或TFP,即使不增加投入,通过有效消除行业间以及行业内企业间的资源配置扭曲,可使得工业产出提高21.5%。(3)资源错配使得工业TFP(对数值)损失了3.79,行业间的效率损失要高于行业内企业间的效率损失,行业间效率损失占总效率损失的53.08%,行业内企业间的效率损失占46.92%。研究明确了行业间与行业内的资源错配对工业总产出损失的影响大小,为中国工业界资源错配的论断提供了微观依据,也为中国工业企业供给侧结构性改革提供了经验证据和理论指导。
