ABSTRACT Contrary to the predictions of the basic spatial equilibrium model, the long‐run distribution of population across rural U.S. counties with high‐valued natural amenities has become relatively more concentrated versus dispersed. We provide an explanation by developing a two‐region model with mobile labor, production externalities and endogenous natural amenities. We find that strong preferences for natural amenities generally foster population dispersion. However, such preferences can also lead to population concentration when ecological degradation is low and man‐made capital is a relatively scarce input into natural amenity production. Investments that enhance natural amenities are found to reduce the divergence between the steady state and optimal outcomes. 相似文献
This article investigates the ductility reduction factors for RC eccentric frame structures subjected to pulse-like ground motions. The structural models are with the strength eccentricities which are much disadvantageous than the stiffness eccentricities during the inelastic response range. A method to determine the ductility reduction factors of the strength eccentric structures is suggested by modifying those of reference symmetric structures through an eccentricity modification factor. The four factors of strength eccentricity ratio, ductility ratio, story number and velocity pulse of ground motions, are investigated to gain insight into this modification factor. It shows that the ductility reduction factors of the eccentric structures are clearly smaller than those of the symmetric structures. The eccentricity modification factor is mainly affected by the strength eccentricity and the ductility ratio, decreasing with the increment of the eccentricity or the decrement of the ductility ratio in a medium eccentricity range. The earthquake pulse-like effect and the eccentricity have coupling influence on the modification factor, while the effect of story number is not apparent. Based on the results of a comprehensive statistical study a simplified expression is suggested, which can estimate the eccentricity modification factors for both pulse-like and nonpulse-like ground motion cases. 相似文献
Ground motions recorded in the epicentral region of an earthquake often have a strong vertical component with dominant high frequencies. Damage to bridges in near-source regions due to strong vertical ground motion has been reported. The beneficial effects of footing uplift on structural performance in form of reduction of seismic response of structural members have been confirmed in previous research. The uplift of bridge piers has been utilised in a very limited number of bridge structures, e.g., the South Rangitikei railway bridge in New Zealand. However, the near-fault seismic behaviour of bridges with footing uplift has been even less addressed. In this study shake table investigations were carried out on the response of a single-span bridge model with footing uplift subjected to simultaneous vertical and horizontal excitations. Near-fault ground motions recorded in the Canterbury earthquake sequences of 2010 and 2011 were used. The experimental results show that inclusion of vertical ground motions produce stronger axial force in the pier and larger bending moment in the deck. Concurrent horizontal and vertical excitations may also cause more frequent footing uplift than the solely horizontal excitations. 相似文献
This article is built upon the author's previous attempt to review Sino–Israel relations from the Chinese perspective, where it is argued that the relationship is at a crossroads because China is increasingly more proactively involved in the international arena, which will inevitably lead to a more assertive role in trying to facilitate a solution to the Israel–Palestinian conflicts. The author also affirmed that China is more supportive of the Palestinians. In this article, the author will further analyze China's pro‐Palestine stance, give empirical evidence of this preference by Chinese intelligentsia, and provide insight into the decision‐making mechanisms of the Chinese government in terms of its diplomatic policies. The author also wants to demonstrate that, despite the evident pro‐Palestine tendency of Chinese scholars and consequently the government, little has been done to implement this preference. The Israelis still have a sizable time window to achieve a fair and just peace agreement with the Palestinians. In the long run, China's pro‐Palestine inclination will work more and more against Israel, in contrast to the strong pro‐Israel inclination of the United States. 相似文献
Taxonomic restudy of Early Darriwilian graptolites from the Yangtze region, Chiadam and Alxa, has enabled a precise correlation of the Undulograptus austrodentatus Zone (including two subzones) across the three regions, and with the Darriwilian GSSP at Huangnitang in the Jiangshan-Changshan-Yushan (JYC) area. Based on specimens from 17 localities in the Yangtze region, the Exigraptus clavus and Undulograptus austrodentatus zones are recognised as replacements respectively of the Undulograptus sinodentatus (Lower) and U. austrodentatus (Upper) zones of Mu et al. (1979). The U. sinicus Subzone, the upper subzone of the U. austrodentatus Zone, is also recognised from the Sichuan-Guizhou area of the Yangtze region. Two subzones of the U. austrodentatus Zone have also been identified from the Chiadam region with more diverse graptolite fauna. The U. austrodentatus Zone fauna also occurs in the Alxa region. A general pattern of changing graptolite diversity from platform through basinal slope to deep basin is proposed, based on early Darriwilian bio- and lithofacies changes from the Yangtze Platform through the Jiangnan belt to the Zhujiang basin. The graptolite diversity increased with water depth and more off-shore setting. Key graptolite species are illustrated. 相似文献
The Late Devonian (Famennian) brachiopod Yunnanella is reported from the western Junggar Basin, northern Xinjiang, on the basis of Yunnanella hanburii (Davidson) and Yunnanella sp. 相似文献
O’Gorman, J.P. &; Gasparini, Z., 2013. Revision of Sulcusuchus erraini (Sauropterygia, Polycotylidae) from the Upper Cretaceous of Patagonia, Argentina. Alcheringa 37, 161–174. ISSN 0311-5518. Sulcusuchus erraini, from the upper Campanian–lower Maastrichtian of Patagonia, Argentina, is the only polycotylid from the Southern Hemisphere for which the skull and mandible are known. The diagnosis of the species and genus is emended based on new observations. Sulcusuchus is characterized by the following autapomorphies: (1) deep and broad rostral and mandibular grooves and (2) a wide notch on the posterior margin of the pterygoids that are combined with a part of the body of the basioccipital, forming a wide plate. Several hypotheses about the identity of the structures that could have been housed in the rostral and mandibular grooves are evaluated. Only two of several hypotheses were not discarded. The first is that the grooves may have accommodated oral glands (supralabial and sublabial), but the biological role of such glands could not be inferred. The second hypothesis is the presence of special structures of an electrosensitive and/or mechanosensitive nature, which might allow the detection of infaunal or semi-infaunal food in soft substrates, as is represented in modern analogues, such as dolphins. José P. O’Gorman [joseogorman@fcnym.unlp.edu.ar] and Zulma Gasparini [zgaspari@fcnym.unlp.edu.ar], División Paleontología Vertebrados, Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n., B1900FWA La Plata, Argentina. Also affiliated with Consejo Nacional de Investigaciones Científicas y Técnicas, Av. Rivadavia 1917 (C1033AAJ), Ciudad Autónoma de Buenos Aires, Argentina and CONICET: Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina Received 5.6.2012; revised 31.7.2012; accepted 4.9.2012.相似文献
LU, J.-F., QIE, W.-Q. & CHEN, X.-Q., July 2016. Pragian and lower Emsian (Lower Devonian) conodonts from Liujing, Guangxi, South China. Alcheringa 40, xxx–xxx. ISSN 0311-5518.
Lower Devonian (Pragian and Emsian) conodonts are described from the Liujing section in Guangxi, South China, highlighting the phylogeny of early polygnathids and establishing the basis for faunal correlations with deposits throughout the world. Records of Eognathodus kuangi sp. nov. and E. nagaolingensis Xiong increase the biodiversity of the Pragian eognathodids in South China and represent intermediate stages and probably the latest eognathodids in the evolutionary succession from Eognathodus to Polygnathus. During this evolutionary succession, the degeneration of the sulcus (or the flattening of the upper platform surface) is the most important morphological change, especially in the eognathodid lineage. Polygnathus trilinearis, P. pireneae and P. sokolovi are recognized together for the first time in South China. The contemporaneous occurrences of the kitabiformis and sokoloviformis morphs of P. pireneae with P. sokolovi and their respective similarities to P. kitabicus and P. sokolovi suggest that the latter two species are phylogenetically linked with P. pireneae. Evidence from the Liujing section also favours Polygnathus probably having evolved from Eognathodus in a tropical or subtropical area.
Jian-feng Lu* [lujfivan@sina.cn] and Xiu-qin Chen [xqchen@nigpas.ac.cn], Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, PR China; Wen-Kun Qie [wkqie@nigpas.ac.cn], Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, 39 East Beijing Road, Nanjing 210008, PR China. *Also affiliated with University of Chinese Academy of Sciences, Beijing 100049, PR China.相似文献