A set modified equinoctial orbit elements     

M. J. H. Walker  B. Ireland  Joyce Owens 《Celestial Mechanics and Dynamical Astronomy》1985,36(4):409-419

Modified equinoctial elements are introduced which are suitable for perturbation analysis of all kinds of orbit. Equations of motion in Lagrangian and Gaussian forms are derived. Identities connecting the partial derivatives of the disturbing function with respect to equinoctial elements are established. Numerical comparisons of the evolution of a perturbed, highly eccentric, elliptic orbit analysed in equinoctial elements and by Cowell's method show satisfactory agreement.  相似文献   

Major and trace element chemistry of Boulder 1 at Station 2, Apollo 17     

Douglas P. Blanchard  Larry A. Haskin  Jeffrey W. Jacobs  Joyce C. Brannon  Randy L. Korotev 《Earth, Moon, and Planets》1975,14(3-4):359-371

Twenty-seven samples of matrix and clast materials from Boulder 1 at Station 2, Apollo 17 have been analyzed for major and trace elements as part of the study of this boulder by Consortium Indomitabile. Both unusual and common types of material have been characterized. Gray and black competent breccia (GCBx and BCBx) and anorthositic breccia (AnBx) have compositions which are common at the Apollo 17 site and were common at the site of boulder formation. Light friable breccias (LFBx) have compositions which are not found at the Apollo 17 site other than in the boulder. Pigeonite basalt is a new type of lunar rock and has characteristics that would be expected of a highland volcanic rock. It is associated with LFBx material, and like LFBx material it is exotic to the Apollo 17 site. Coarse norite is an old primitive rock which is no longer (if ever) found as millimeter fragments at the Apollo 17 site. It was, however, present as millimeter fragments associated with GCBx and BCBx materials at the site and time of boulder formation. Therefore the boulder-forming process combined materials from at least two different localities or vertical strata; at least one of these (LFBx) has not been previously sampled and analyzed.  相似文献   

Geovisualization of Human Hybrid Activity-Travel Patterns   总被引：4，自引：0，他引：4  

Fang Ren  Mei-Po Kwan 《Transactions in GIS》2007,11(5):721-744

While GIS‐based geovisualization techniques have been fruitfully employed in a wide range of fields, they have not been applied to explore human hybrid activity‐travel patterns (i.e. the patterns of people's activities and/or travel in both the physical and virtual worlds). This study develops two geovisualization approaches using 3D and 2D GIS techniques to address the difficulties faced by past studies. First, the notions of information cube and hybrid 3D space‐time paths are developed to accommodate cyberspatial activities in exploratory data analysis. Second, a new representation of 2D space‐time paths that incorporates parallel coordinate plots is developed for exploring the multiple attributes of people's Internet and physical activities. These two methods were implemented using ArcObjects and the Visual Basic for Applications environment in ArcGIS. They were used to visualize a complex Internet‐activity diary dataset collected in Columbus (Ohio, USA). The study shows that the 3D and 2D geovisualization methods developed allow us to uncover important patterns in hybrid human activity‐travel behavior.  相似文献   

Spatial and temporal dynamics of epiphytic microalgae on the cordgrassSpartina alterniflora in North Inlet Estuary, South Carolina     

Gabriella Jackson  Richard Zingmark  Alan J. Lewitus  Raphael G. Tymowski  Joyce Stuckey 《Estuaries and Coasts》2006,29(6):1212-1221

Epiphytic microbial biomass (as chlorophylla) was measured monthly in North Inlet Estuary, South Carolina, for 16 months on spatially distinct stem sections (bottom and middle) of dead and livingSpartina alterniflora growth forms (tall, medium, and short) exposed at low tide. The highest biomass was located on the bottom section of tall plants, presumably due to their relatively longer contact with creek water and associated phytoplankton, and their closer proximity to marsh sediments with associated benthic microalgae, both recruitment sources for epiphytes. Dead plants left standing from the previous year’s growth cycle had higher epiphytic biomass than living plants, which occurred mostly in late spring through fall. Epiphytic biomass was highest in the winter (mean of 1.77 mg chla (m² marsh)⁻¹) and lowest in the summer (mean of 0.34 mg chla (m² marsh)⁻¹). Because phytoplankton andSpartina production are lowest in the winter, the results emphasize the relative importance of epiphytes to growth of herbivores in this season.  相似文献   

Performance of ethylene-vinyl acetate foam as cushioning material for rigid debris-resisting barriers     

Carlos Lam  Julian S. H. Kwan  Y. Su  Clarence E. Choi  Charles W. W. Ng 《Landslides》2018,15(9):1779-1786

This paper reports an investigation on the performance of ethylene-vinyl acetate (EVA) foam when used as a cushion layer for rigid barriers used to resist debris flow. Large-scale pendulum impact tests were conducted to study the effects of layer thickness on cushion performance under six successive impacts. Results show that for the first impact at 70 kJ, the peak contact force with the EVA foam thickness of 500 mm is about twice larger compared to that of 1000 mm. Results also reveal that the cushion mechanism of elastic collapse of cell walls in the EVA foam results in peak contact forces and maximum transmitted loads that are up to 30 and 50% lower compared to gabions for the first impact at 70 kJ, respectively. The elastic behavior of EVA foam provides consistent cushioning efficiency. Furthermore, EVA foam is found to be susceptible to degradation by ultraviolet light so that a suitable coating layer is required for outdoor use. Polyurea was identified as a suitable coating material and a small-scale coating trial was performed to confirm this. Findings presented in this paper will have direct implications on the future design of cushion layers for rigid barriers used to intercept debris flows.  相似文献   

Present-day regional climate simulation over Malaysia and western Maritime Continent region using PRECIS forced with ERA40 reanalysis     

Meng Sei Kwan  Fredolin T. Tangang  Liew Juneng 《Theoretical and Applied Climatology》2014,115(1-2):1-14

This study examines the performance of the regional climate model, PRECIS, in reproducing the historical seasonal mean climatology over the Malaysian region. The performance of the model in simulating the seasonal climate pattern of the temperature, precipitation and large-scale circulation was reasonably good. The biases of temperature are less than 2 °C in general, while the seasonal cycles match the observed pattern despite some differences in certain regions. However, the biases for precipitation were greater, particularly over the mountainous areas. These biases could be associated with the deficiencies of the model physics, related to the misrepresentation of the land–surface interaction and convective scheme. Furthermore, the model fails to simulate the mean sea-level pressure over the interior part of Borneo with a significant low-pressure centre. A higher magnitude of the moisture convergence and divergence simulated by the model also contributed to the biases of precipitation over Malaysia.  相似文献   

Multi-scale groundwater flow modeling during temperate climate conditions for the safety assessment of the proposed high-level nuclear waste repository site at Forsmark,Sweden     

Steven Joyce  Lee Hartley  David Applegate  Jaap Hoek  Peter Jackson 《Hydrogeology Journal》2014,22(6):1233-1249

Forsmark in Sweden has been proposed as the site of a geological repository for spent high-level nuclear fuel, to be located at a depth of approximately 470 m in fractured crystalline rock. The safety assessment for the repository has required a multi-disciplinary approach to evaluate the impact of hydrogeological and hydrogeochemical conditions close to the repository and in a wider regional context. Assessing the consequences of potential radionuclide releases requires quantitative site-specific information concerning the details of groundwater flow on the scale of individual waste canister locations (1–10 m) as well as details of groundwater flow and composition on the scale of groundwater pathways between the facility and the surface (500 m to 5 km). The purpose of this article is to provide an illustration of multi-scale modeling techniques and the results obtained when combining aspects of local-scale flows in fractures around a potential contaminant source with regional-scale groundwater flow and transport subject to natural evolution of the system. The approach set out is novel, as it incorporates both different scales of model and different levels of detail, combining discrete fracture network and equivalent continuous porous medium representations of fractured bedrock.  相似文献   

Mechanisms driving polymagmatic activity at a monogenetic volcano, Udo, Jeju Island, South Korea   总被引：3，自引：1，他引：2  

Marco Brenna  Shane J. Cronin  Ian E. M. Smith  Young Kwan Sohn  Karoly Németh 《Contributions to Mineralogy and Petrology》2010,160(6):931-950

High-resolution, stratigraphically ordered samples of the Udo tuff cone and lava shield offshore of Jeju Island, South Korea, show complex geochemical variation in the basaltic magmas that fed the eruption sequence. The eruption began explosively, producing phreatomagmatic deposits with relatively evolved alkali magma. The magma became more primitive over the course of the eruption, but the last magma to be explosively erupted had shifted back to a relatively evolved composition. A separate sub-alkali magma batch was subsequently effusively erupted to form a lava shield. Absence of weathering and only minor reworking between the tuff and overlying lava implies that there was no significant time break between the eruptions of the two magma batches. Modelling of the alkali magma suggests that it was generated from a parent melt in garnet peridotite at c. 3 to 3.5 GPa and underwent mainly clinopyroxene + olivine ± spinel fractionation at c. 1.5 to 2 GPa. The sub-alkali magma was, by contrast, generated from a chemically different peridotite with residual garnet at c. 2.5 GPa and evolved through olivine fractionation at a shallower level compared to its alkali contemporary. The continuous chemostratigraphic trend in the tuff cone, from relatively evolved to primitive and back to evolved, is interpreted to have resulted from a magma batch having risen through a single dyke and erupted the batch’s head, core and margins, respectively. The alkali magma acted as a path-opener for the sub-alkali magma. The occurrence of the two distinct batches suggests that different magmatic systems in the Jeju Island Volcanic Field have interacted throughout its history. The polymagmatic nature of this monogenetic eruption has important implications for hazard forecasting and for our understanding of basaltic field volcanism.  相似文献   

Gender and Individual Access to Urban Opportunities: A Study Using Space–Time Measures     

Mei-Po Kwan 《The Professional geographer》1999,51(2):210-227

Conventional accessibility measures based on the notion of locational proximity ignore the role of complex travel behavior and space–time constraints in determining individual accessibility. As these factors are especially significant in women's everyday lives, all conventional accessibility measures suffer from an inherent “gender bias.” This study conceptualizes individual accessibility as space–time feasibility and provides formulations of accessibility measures based on the space–time prism construct. Using a subsample of European Americans from a travel diary data set collected in Franklin County, Ohio, space–time accessibility measures are implemented with a network-based GIS method. Results of the study indicate that women have lower levels of individual access to urban opportunities when compared to men, although there is no difference in the types of opportunities and areas they can reach given their space–time constraints. Further, individual accessibility has no relationship with the length of the commute trip, suggesting that the journey to work may not be an appropriate measure of job access.  相似文献   

Graph distance and feature-guided multi-view clustering: A novel method for clustering urban buildings     

Lin Yang  Ruolin Yang  Zejun Zuo  Mei-Po Kwan  Shunping Zhou 《Transactions in GIS》2023,27(8):2127-2158

Urban buildings are an integral component of urban space, and accurately identifying their spatial configurations and grouping them is vital for various urban applications. However, most existing building clustering methods only utilize the original spatial and nonspatial features of buildings, disregarding the potential value of complementary information from multiple perspectives. This limitation hinders their effectiveness in scenarios with intricate spatial configurations. To address this, this article proposes a novel multi-view building clustering method that captures cross-view information from spatial and nonspatial features. Drawing inspiration from both spatial proximity characteristics and nonspatial attributes, three views are established, including two spatial distance graphs (centroid distance graph and the nearest outlier distance graph) and a building attribute graph (multiple-attribute graph). The three graphs undergo iterative cross-diffusion processes to amplify similarities within each predefined graph view, culminating in their fusion into a unified graph. This fusion facilitates the comprehensive correlation and mutual enhancement of spatial and nonspatial information. Experiments were conducted using 10 real-world community-building datasets from Wuhan and Chengdu, China. The results demonstrate that our approach achieves 21.27% higher accuracy and 22.28% higher adjusted rand index in recognizing diverse complex arrangements compared to existing methods. These findings highlight the importance of leveraging complementary and consensus information across different feature dimensions for improving the performance of building clustering.  相似文献