Some thoughts on spatial data and structure analysis     

Yee Leung 《Journal of Geographical Systems》2000,2(1):107-110

The discussion is structured around two themes, namely spatial data analysis and spatial structure/process analysis. With respect to spatial data analysis, I concentrate on the issues related to geographical information systems (GIS), as well as spatial data mining and knowledge discovery in databases. With reference to spatial structure/process analysis, the emphasis is placed on the analysis of complex systems.  相似文献   

Helium-volume dynamics of Upper Freeport coal powder and lumps     

Vyacheslav Romanov  Yee Soong 《International Journal of Coal Geology》2009,77(1-2):10-15

Exposure to 7 MPa of helium at room temperature alters the texture of Upper Freeport coal in a lump form. The differences in texture and porosity between coal powder and lumps may affect the transport and interaction of fluids and coal. In this work, the information about the coal texture and micro- and meso-porosity was obtained via the BET, BJH, and Dubinin–Astakhov analyses. We further investigated the free-fluid-phase volume (free-volume) effects due to helium interaction with the powder and the lumps. During the manometric experiment, helium penetration into the dry coal matrix resulted in slow relaxation of pressure. After exposure of coal to helium, there have been no significant changes of the macroscopic dimensions observed and the relaxation process can be attributed to microscopic ‘free-volume’ effects. Evolution of the sorption–desorption rates indicates that exposure to helium may change the texture and apparent (helium) density of dry coal.  相似文献   

Theory for Reconstruction of an Unknown Number of Contaminant Sources using Probabilistic Inference   总被引：1，自引：0，他引：1  

Eugene Yee 《Boundary-Layer Meteorology》2008,127(3):359-394

We address the inverse problem of source reconstruction for the difficult case of multiple sources when the number of sources is unknown a priori. The problem is solved using a Bayesian probabilistic inferential framework in which Bayesian probability theory is used to derive the posterior probability density function for the number of sources and for the parameters (e.g., location, emission rate, release time and duration) that characterize each source. A mapping (source–receptor relationship) that relates a multiple source distribution to the concentration measurements made by an array of detectors is formulated based on a forward-time Lagrangian stochastic model. A computationally efficient methodology for determination of the likelihood function for the problem, based on an adjoint representation of the source–receptor relationship and realized in terms of a backward-time Lagrangian stochastic model, is described. An efficient computational algorithm based on a parallel tempered Metropolis-coupled reversible-jump Markov chain Monte Carlo (MCMC) method is formulated and implemented to draw samples from the posterior probability density function of the source parameters. This methodology allows the MCMC method to initiate jumps between the hypothesis spaces corresponding to different numbers of sources in the source distribution and, thereby, allows a sample from the full joint posterior distribution of the number of sources and the parameters for each source to be obtained. The proposed methodology for source reconstruction is tested using synthetic concentration data generated for cases involving two and three unknown sources.  相似文献   

Application of extended Dempster–Shafer theory of evidence in accident probability estimation for dangerous goods transportation     

Leung  Yee  Li  Rongrong  Ji  Nannan 《Journal of Geographical Systems》2017,19(3):249-271

Journal of Geographical Systems - Transportation of dangerous goods (DGs) is generally associated with significant levels of risk. In the context of DG transportation, risk refers to the likelihood...  相似文献   

Multi-objective route planning for dangerous goods using compromise programming   总被引：2，自引：1，他引：1  

Rongrong Li  Yee Leung 《Journal of Geographical Systems》2011,13(3):249-271

The transportation of dangerous goods (DG) can significantly affect the human and natural environment if accidents occur during the transportation process. Hong Kong is a large city with high population density and narrow streets. Due to the land constraints, vehicles carrying DG inevitably have to pass through densely populated areas or their vicinities. Therefore, safe DG transportation is of paramount importance. There is thus an urgent need to review and improve the way trucks carrying DG are being routed on the road networks. Routing of such vehicles should consider not only the operating cost, but also the safety of travelers in the network, the population potentially exposed, and the possible damage inflicted to the surrounding properties and facilities in the event of a DG incident. This research develops a novel methodology for the determination of optimal routes for DG transportation under conflicting objectives by means of the compromise programming approach. With the support of geographical information system (GIS), a case study is carried out for the transportation of DG in the road network of Hong Kong. The experimental results confirm the effectiveness of the proposed approach.  相似文献   

Comparing Two Implementations of a Micromixing Model. Part I: Wall Shear-Layer Flow     

John?V.?PostmaEmail author  John?D.?Wilson  Eugene?Yee 《Boundary-Layer Meteorology》2011,140(2):207-224

A Lagrangian stochastic (LS) micromixing model is used for estimating concentration fluctuations in plumes of a passive, non-reactive tracer dispersing from elevated and ground-level compact sources into a neutral wall shear-layer flow. SPMMM (for sequential particle micromixing model) implements the familiar IECM (interaction by exchange with the conditional mean) micromixing scheme. The parametrization of the scalar micromixing time scale is identical to that proposed in a previously reported LS–IECM model (Cassiani et al., Atmos Environ 39:1457–1469, 2005a). However, while SPMMM is mathematically equivalent to the previously reported model, it differs in its numerical implementation: SPMMM releases N independent particles sequentially, whereas the previously reported model releases N independent particles simultaneously. In both implementations, the trajectories of the N particles are governed by single-point velocity statistics. The sequential particle implementation is computationally efficient, but cannot be applied to the case of reacting species. Results from both implementations are compared to experimental wind-tunnel dispersion data and to each other.  相似文献   

Temporal changes of polyphenols and enzyme activities in seedlings of Kandelia obovata under lead and manganese stresses     

Yan ZZ  Tam NF 《Marine pollution bulletin》2011,63(5-12):438-444

The temporal responses of peroxidase (POD), superoxide dismutase (SOD), total polyphenols (TP), extractable condensed tannins (ECT) to different levels of lead (Pb) or manganese (Mn) stress, as well as the metal accumulation, in seedlings of Kandelia obovata were investigated. Both stress time and stress intensity had significant effects with significant accumulation of Pb and Mn in roots at Day 1. Pb and Mn showed no significant effects on root or leaf TP and ECT at Day 1. Prolonged exposure to metals caused significant drops of root TP and ECT but increased in leaves at Days 7 and 49. POD activities decreased in both roots and leaves at Day 1, while POD and SOD both increased under moderate levels of Pb and Mn at Day 7. The present study showed that antioxidative enzyme activities were more sensitive indicators to Pb or Mn stresses than phenolic compounds.  相似文献   

Geomicrobiology of selenium: Life and death by selenite     

Nathan Yee 《Applied Geochemistry》2011

Selenite oxyanions are readily assimilated by microorganisms for the synthesis of selenoproteins. However, at elevated concentrations, selenite becomes highly toxic due to the intracellular formation of reactive oxygen species. Remarkably, some microorganisms have evolved the ability to not only survive toxic levels of selenite, but to flourish in its presence. The cultivation and genomic sequencing of dissimilatory selenite-respiring Bacteria and Archaea have begun to help elucidate the molecular mechanisms of selenite respiration.  相似文献   

Foil X-ray mirrors     

Peter J. Serlemitsos  Yang Soong 《Astrophysics and Space Science》1996,239(2):177-196

Nested thin foil reflectors have made possible light weight, inexpensive and fast grazing incidence X-ray mirrors for astronomical spectroscopy over a broad band. These mirrors were developed at Goddard for the US Shuttle program and were flown on NASA's shuttleborne Astro-l mission in December 1990. Presently, the Japan/US collaborative spectroscopic mission ASCA, nearing its third year of successful operation in earth orbit, carries, four such mirrors, weighing less than 40 kg and giving total effective areas of 1200 and 420 cm² at l and 8 keV respectively. The 420 kg observatory is the best possible example of how conical foil mirrors opened areas of research that could not have been otherwise addressed with available resources. In this paper, we will briefly review the development and performance of our first generation foil mirrors. We will also describe progress toward improving their imaging capability to prime them for use in future instruments. Such a goal is highly desirable, if not necessary for this mirror technology to remain competitive for future applications.  相似文献   

The force-restore method revisited     

Samuel Y. K. Yee 《Boundary-Layer Meteorology》1988,43(1-2):85-90

The so-called ‘force-restore method’ has been used with considerable success in numerical weather prediction models to simulate diurnal variations of ground temperature. This note demonstrates that the force-restore equation is no more nor less than an approximation to the surface-energy-balance equation. The applicability of the method to the case of multi-component heating functions and to the case in which the soil is covered by a litter layer is discussed.  相似文献