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111.
Hanna Maoh Kevin Gingerich Rahaf Husein William Anderson 《The Professional geographer》2018,70(3):350-362
Land borders connecting Canada and the United States are vital transportation facilities for the two countries. Truck crossing times at these facilities can have a significant impact on the performance of the economy. To date, knowledge about border crossing times has been limited due to lack of detailed data on the Canadian border. This article explores and models the patterns of crossing times at the three major land crossings connecting Canada to the United States: Ambassador Bridge, Blue Water Bridge, and Peace Bridge. The analysis is based on 387,775 border crossing truck trips that were generated between Canada and the United States over a course of twelve months. Seemingly unrelated regression (SUR) models are estimated to evaluate the seasonal and hourly crossing times of Canada- and U.S.-bound trips on each border crossing, controlling for traffic intensity in the models. The SUR modeling approach is chosen to control for potential cross-model correlations. The results suggest that crossing times at the border vary by season and hour of the day. Crossing times also vary by direction of traffic and by type of day (i.e., weekday vs. weekend). Traffic intensity has a significant influence on crossing times at two of the crossings but not the Blue Water Bridge. Finally, crossing times are more variable during the summer season and tend to be higher during the late evening hours and past midnight. 相似文献
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Vincent J. Del Casino Jr. Andrew J. Grimes Stephen P. Hanna John Paul Jones III 《Geoforum》2000,31(4):523-538
In this paper, we present three methodological frameworks for the geographic study of organizations. These are situated within three meta-theoretical perspectives in human geography: spatial science, critical realism, and post-structuralism. Each framework offers a different theorization of organizations, and each prompts different research questions that can be used to guide their geographic study. The research questions we offer are general, and are pertinent to all types of organizations. To supplement the methodological contributions of this paper, we suggest how each of these frameworks might inform empirical investigations of Appalshop, a media arts organization located in Whitesburg, Kentucky. 相似文献
116.
Daniel T. Britt Kevin M. Cannon Kerri Donaldson Hanna Joanna Hogancamp Olivier Poch Pierre Beck Dayl Martin Jolantha Escrig Lydie Bonal Philip T. Metzger 《Meteoritics & planetary science》2019,54(9):2067-2082
A set of high‐fidelity simulated asteroid materials, or simulants, was developed based on the mineralogy of carbonaceous chondrite meteorites. Three varieties of simulant were developed based on CI1 chondrites (typified by Orgueil), CM2 chondrites (typified by Murchison), and CR2/3 chondrites (multiple samples). The simulants were designed to replicate the mineralogy and physical properties of the corresponding meteorites and anticipated asteroid surface materials as closely as is reasonably possible for bulk amounts. The simulants can be made in different physical forms ranging from larger cobbles to fine‐grained regolith. We analyzed simulant prototypes using scanning electron microscopy, X‐ray fluorescence, reflectance spectroscopy at ambient conditions and in vacuum, thermal emission spectroscopy in a simulated asteroid environment chamber, and combined thermogravimetry and evolved gas analysis. Most measured properties compare favorably to the reference meteorites and therefore to predicted volatile‐rich asteroid surface materials, including boulders, cobbles, and fine‐grained soils. However, there were also discrepancies, and mistakes were made in the original mineral formulations that will be updated in the future. The asteroid simulants are available to the community from the nonprofit Exolith Lab at UCF, and the mineral recipes are freely published for other groups to reproduce and modify as they see fit. 相似文献
117.
Natural Hazards - Emergency support is often delayed after a disaster. Despite the importance of being prepared to deal with the immediate aftermath of disasters, not everyone prepares effectively.... 相似文献
118.
The influence of late Quaternary sedimentation on vegetation in an Amazonian lowland megafan 下载免费PDF全文
Dilce F. Rossetti Rogério Gribel Hanna Tuomisto Carlos L.O. Cordeiro Sonia H. Tatumi 《地球表面变化过程与地形》2018,43(6):1259-1279
The largest areas of white‐sand vegetation in northern Amazonia are confined to Late Pleistocene–Holocene megafan depositional systems, which suggest a relationship between the two. The aim of this work is to determine: (i) the relative role of sedimentary history and recent ecological processes to explaining the mosaic of white‐sand forest patches, grasslands and shrublands in a wetland area of northern Amazonia; and (ii) the long‐term successional trajectory that led to the establishment of the white‐sand forest patches. Facies analysis was used to reconstruct the megafan paleoenvironment; δ13C, total organic carbon and carbon/nitrogen from sedimentary organic matter to reconstruct the past vegetation; and floristic inventories to characterize the modern vegetation. The results revealed that the Viruá megafan consists of various sandy sub‐environments, including aeolian sand dunes and sheets developed mostly in the Holocene after the megafan turned inactive as a depositional site. Dune margins and tops are colonized by white‐sand trees mixed with a few generalist rain‐forest species, whereas adjacent lower‐lying areas, which are affected by seasonal flooding, are covered by graminoid plants and/or shrubs. The latter initiated their development over the megafan surface in different times of the Holocene due to hydrological gradients imposed by the topography of the various megafan depositional environments, while the white‐sand forest became dominant only on sand dunes over the last few centuries. We suggest that the late Quaternary sedimentary history was crucial in creating morphologies that now determine topographic gradients responsible for different vegetation physiognomies over the Amazonian lowlands. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
119.
A comparison of streamflow,salt and water balances in adjacent farmland and forest catchments in south‐western Victoria,Australia 下载免费PDF全文
S. Michael Adelana P. Evan Dresel Peter Hekmeijer Hanna Zydor John A. Webb Michael Reynolds Matthew Ryan 《水文研究》2015,29(6):1630-1643
A study of the hydrologic effects of catchment change from pasture to plantation was carried out in Gatum, south‐western Victoria, Australia. This study describes the hydrologic characteristics of two adjacent catchments: one with 97% grassland and the other one with 62% Eucalyptus globulus plantations. Streamflow from both catchments was intermittent during the 20‐month study period. Monthly streamflow was always greater in the pasture‐dominated catchment compared with the plantation catchment because of lower evapotranspiration in the pasture‐based catchment. This difference in streamflow was also observed even during summer 2010/2011 when precipitation was 74% above average (1954–2012) summer rainfall. Streamflow peaks in the plantation‐based catchment were smaller than in the pasture‐dominated system. Flow duration curves show differences between the pasture and plantation‐dominated catchments and affect both high‐flow and low‐flow periods. Groundwater levels fell (up to 4.4 m) in the plantation catchment during the study period but rose (up to 3.2 m) in the pasture catchment. Higher evapotranspiration in the plantation catchment resulted in falling groundwater levels and greater disconnection of the groundwater system from the stream, resulting in lower baseflow contribution to streamflow. Salt export from each catchment increases with increasing flow and is higher at the pasture catchment, mainly because of the higher flow. Reduced salt loading to streams due to tree planting is generally considered environmentally beneficial in saline areas of south‐eastern Australia, but this benefit is offset by reduced total streamflow. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
120.
Seven sites within the mountain region of Abisko, northern Sweden, were selected for measurement of solifluction movement rates and correlation with the local environmental factors. Grids with sizes from 20 m × 30 m to 50 m × 100 m included both solifluction landforms and adjacent ground. Positions of movement markers and the terrain were recorded and the grid areas were digitally reconstructed. This allowed topography, vegetation and soil texture (fraction of fine material) surfaces to be interpolated and used together with data on soil moisture in statistical analyses. Significant correlations differ from site to site indicating that environmental factors have varying importance and inter‐relations depending on the local setting. Geomorphic work was also assessed within the grids. The results indicate measurable geomorphic work where no landforms are present. These areas may make larger contributions to sediment displacement than where solifluction landforms exist. Solifluction is an important denudational agent in the region and has its greatest impact on landscape development in the western part of the region. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献