Finding least-cost paths across a continuous raster surface with discrete vector networks     

Yosoon Choi  Jeong-Gi Um  Myong-Ho Park 《制图学和地理信息科学》2013,40(1):75-85

The problem of finding the least-cost path from a source point to a destination point can be dealt with by routing across a continuous surface or routing along a discrete network. The solutions within these two contexts are linked to the use of a raster- or a vector-based least-cost path algorithm. This study presents a technique which integrates raster- and vector-based least-cost path algorithms for determining the least-cost path across a continuous raster surface with discrete vector networks. The technique incorporates ancillary vector data sets that are required to examine the travel cost at each link, connections between nodes, and the representation of intersecting links in the discrete vector network into raster-based least-cost path analysis. The integrated technique presented here is applicable to all-terrain vehicle navigation where a continuous raster surface and discrete vector networks need to be considered simultaneously in order to find least-cost paths. This paper describes the concept behind, and details of, the integrated technique. Applications of the technique with synthetic and real-world data sets are also presented. They provide proof that the technique is effective in finding least-cost paths across a continuous raster surface with discrete vector networks.  相似文献   

Relationships between variations of the land–ocean–atmosphere system of northeastern Asia and northwestern North America     

John E. Walsh  Hotaek Park  William L. Chapman  Tetsuo Ohata 《Polar Science》2013,7(2):188-203

This study is a broad-scale synthesis of information on climate changes in two Arctic terrestrial regions, eastern Siberia and the Alaska–Yukon area of North America. Over the past 60 years (1951–2010), the trends of temperature and precipitation in the two regions are broadly similar in their seasonality. However, atmospheric advection influences the two regions differently during winter. The differential advective effects are much weaker in the other seasons. The Pacific Decadal Oscillation is the strongest correlator with interannual variability in the two regions, followed by the Arctic Oscillation and the El Niño/Southern Oscillation.Projected changes by the late 21st Century are qualitatively similar to the changes that have been ongoing over the past 60 years, although the rate of change increases modestly under mid-range forcing scenarios (e.g., the A1B scenario). The greatest warming is projected to occur farther north over the Arctic Ocean in response to sea ice loss. Precipitation is projected to increase by all models, although increases in evapotranspiration preclude conclusions about trends toward wetter or drier land surface conditions. A notable feature of the future climate simulations is a strong maximum of pressure decreases in the Bering Sea region, implying further advective changes.  相似文献   

Imaging Spectroscopy of a Solar Filament Using a Tunable Hα Filter   总被引：1，自引：0，他引：1  

Jongchul Chae  Young-Deuk Park  Hyung-Min Park 《Solar physics》2006,234(1):115-134

Observations using a narrow band Hα filter still remain one of the best ways to investigate the fine structures and internal dynamics of solar filaments. Hα observations, however, have been usually carried out with the peak response of the filter fixed at a single wavelength, usually at the centerline, in which the investigation is limited to the Hα morphology and its time evolution. In this paper, we demonstrate that the Hα spectroscopy that takes Hα images successively at several wavelengths is a useful tool in the study of solar filaments on the solar disk. Our observation of a filament was carried out on August 3, 2004 at Big Bear Solar Observatory using the 10-inch refractor. The Lyot Hα filter was successively tuned to five wavelengths: ?0.6, ?0.3, 0.0, +0.3, and +0.6 Å from the Hα line center. Each set of wavelength scan took 15 s. After several steps of data reduction, we have constructed a five-wavelength spectral profile of intensity contrast at every spatial point. The contrast profile at each spatial point inside the filament was reasonably well fit by the cloud model as far as the contrast is high enough, and allowed us to construct the maps of τ₀, v, Δ λ_D and S in the filament. We also found that the line center method that is often used, always yields line-of-sight velocities that are systematically lower than the cloud model fit. Our result suggests that taking Hα images at several wavelengths using a tunable filter provides an effective way of deriving physically meaningful parameters of solar filaments. Particularly constructing the time sequence of v maps appears to be a useful tool for the study of internal dynamics, like counterstreaming, in filaments.  相似文献   

Equations of general relativistic radiation hydrodynamics from a tensor formalism     

Myeong-Gu Park 《Monthly notices of the Royal Astronomical Society》2006,367(4):1739-1745

Radiation interacts with matter via exchange of energy and momentum. When matter is moving with a relativistic velocity or when the background space–time is strongly curved, rigorous relativistic treatment of hydrodynamics and radiative transfer is required. Here, we derive fully general relativistic radiation hydrodynamic equations from a covariant tensor formalism. The equations can be applied to any three-dimensional problems and are rather straightforward to understand compared to the comoving frame-based equations. The current approach is applicable to any space–time or coordinates, but in this work we specifically choose the Schwarzschild space–time to show explicitly how the hydrodynamic and the radiation moment equations are derived. Some important aspects of relativistic radiation hydrodynamics and the difficulty with the radiation moment formalism are discussed as well.  相似文献   

Clay minerals and geochemistry of the bottom sediments in the northwestern East China Sea   总被引：1，自引：0，他引：1  

Jeungsu YOUN Shouye YANG Yong Ahn PARK 《中国海洋湖沼学报》2007,25(3):235-246

Clay minerals of 34 sediments collected from the northwestern continental shelf of the East China Sea have been determined by X-ray diffraction analysis. The clay mineral distribution is mainly controlled by the sediment source and the dominant circulation pattern. The predominant clay mineral in our study area is illite comprising more than 67% of the whole clay fraction. The highest concentration of illite (>68%) is found in the southeastern offshore parts beyond the reach of terrigenous input from the Jeju Island. It means that these illites are largely transported by the Kuroshio Current from the South China Sea (SCS). Smectite is highly concentrated in the northwest middle part and in the outer-shelf mud patch. It seems to be due to the high supply of smectite transported from China where fine-grained sediments are discharged from modern and ancient Huanghe (Yellow) River. The relatively high abundant kaolinite is likely derived from the Changjiang (Yangtze) River via the Taiwan Warm Current. In contrast, large amounts of chlorite and high chlorite/kaolinite ratios occur in the northwestern area, reflecting the transportation by the Yellow Sea Coastal Current from the southern Yellow Sea. The discrimination diagrams clearly show that the sediments in the northwestern East China Sea are ultimately sourced from Chinese rivers, especially from the Huanghe River, whereas the sediment in the northeast part might come from the Jeju Island. The muddy sediments of the Changjiang River’s submerged delta have much lower 87Sr/86Sr ratios (0.716 2–0.718 0) than those of the Shandong Peninsular mud wedge (0.721 6–0.724 9), which are supposed to be originated from the Huanghe River, suggesting the distribution pattern of 87Sr/86Sr ratios as a new tracer to discriminate the provenance of shelf sediments in the study area. The 87Sr/86Sr ratios of the outer-shelf muddy sediments ranged from 0.7169 to 0.7216 in a wide range and was between those of the Huanghe River and Changjiang River sediments, suggesting multiple sources of the sediment in the area.  相似文献   

Density Measurements of Shock Compressed Matter Using Short Pulse Laser Diagnostics     

M. Koenig  A. Ravasio  A. Benuzzi-Mounaix  B. Loupias  N. Ozaki  M. Borghesi  C. Cecchetti  D. Batani  R. Dezulian  S. Lepape  P. Patel  H. S. Park  D. Hicks  A. Mckinnon  T. Boehly  A. Schiavi  E. Henry  M. Notley  R. Clark  S. Bandyopadhyay 《Astrophysics and Space Science》2007,307(1-3):257-261

In this paper, experimental results on X-ray and proton radiography of shock compressed matter are presented. It has been performed at the Rutherford Appleton Laboratory (RAL) using three long pulse beams to generate a shock wave in a multi-layer foil and a short pulse beam to create either an X-ray or protons source for a transverse radiography. Depending on the probe material (aluminium or carbon foam) a Molybdenum Kα source or a proton beam are used. Density data of the shocked aluminium, in the multimagabar regime are presented.  相似文献   

Hydroclimatic controls on dissolved organic matter (DOM) characteristics and implications for trace metal transport in Hwangryong River Watershed,Korea, during a summer monsoon period     

Ji‐Hyung Park  Ji‐Ho Lee  Seo‐Young Kang  Sei‐Young Kim 《水文研究》2007,21(22):3025-3034

Frequent heavy rainfalls during the East Asian summer monsoon drastically increase water flow and chemical loadings to surface waters. A solid understanding of hydroclimatic controls on watershed biogeochemical processes is crucial for water quality control during the monsoon period. We investigated spatio‐temporal variations in the concentrations and spectroscopic properties of dissolved organic matter (DOM) and the concentrations of trace metals in Hwangryong River, Korea, during a summer period from the relatively dry month of June through the following months with heavy rainfall. DOM and its spectroscopic properties differed spatially along the river, and also depended on storm and flow characteristics around each sampling time. At a headwater stream draining a forested watershed, the concentrations (measured as dissolved organic carbon (DOC)), aromaticity (measured as specific UV absorbance at 254 nm), and fulvic acid‐ and protein‐like fluorescence of DOM were higher in stormflow than in baseflow waters. DOC concentrations and fluorescence intensities increased along the downstream rural and urban sites, in which DOC and fluorescence were not higher in stormflow waters, except for the ‘first flush’ at the urban site. The response of DOM in reservoir waters to monsoon rainfalls differed from that of stream and river waters, as illustrated by storm‐induced increases in DOM aromaticity and fulvic‐like fluorescence, and no significant changes in protein‐like fluorescence. The results suggest that surface water DOM and its spectroscopic properties differentially respond to changes in hydroclimatic conditions, depending on watershed characteristics and the influence of anthropogenic organic matter loadings. DOC concentrations and intensities of spectroscopic parameters were positively correlated with some of the measured trace metals (As, Co, and Fe). Further research will be needed to obtain a better understanding of climate effects on the interaction between DOM and trace metals. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Colour change measurements of gravitational microlensing events by using the difference image analysis method     

Cheongho Han  Seong-Hong Park 《Monthly notices of the Royal Astronomical Society》2001,320(1):41-48

Detecting colour changes of a gravitational microlensing event induced by the limb-darkened extended source effect is important for obtaining useful information about both the lens and the source star. However, precise measurements of the colour changes are hampered by blending, which also causes colour changes of the event. In this paper, we show that although the colour change measured from the subtracted image by using the recently developed photometric method of the 'difference image analysis' (DIA) differs from the colour change measured by using the conventional method based on the extraction of the individual source stars' point spread functions, the curve of the colour changes (colour curve) constructed by using the DIA method enables one to obtain the same information about the lens and source star, but with significantly reduced uncertainties due to the absence of blending. We investigate the patterns of the DIA colour curves for both single lens and binary lens events by constructing colour change maps.  相似文献   

Determination of magnetic helicity content of solar active regions from SOHO/MDI magnetograms     

Jongchul Chae  Yong-Jae Moon  Young-Deuk Park 《Solar physics》2004,223(1):39-55

Chae (2001) first proposed a method of self-consistently determining the rate of change of magnetic helicity using a time series of longitudinal magnetograms only, such as taken by SOHO/MDI. Assuming that magnetic fields in the photosphere are predominantly vertical, he determined the horizontal component of velocity by tracking the displacements of magnetic flux fragments using the technique of local correlation tracking (LCT). In the present paper, after briefly reviewing the recent advance in helicity rate measurement, we argue that the LCT method can be more generally applied even to regions of inclined magnetic fields. We also present some results obtained by applying the LCT method to the active region NOAA 10365 under emergence during the observable period, which are summarized as follows. (1) Strong shearing flows were found near the polarity inversion line that were very effective in helicity injection. (2) Both the magnetic flux and helicity of the active region steadily increased during the observing period, and reached 1.2 × 10²² Mx and 8 ×10⁴² Mx², respectively, 4.5 days after the birth of the active region. (3) The corresponding ratio of the helicity to the square of the magnetic flux, 0.05, is roughly compatible with the values determined by other studies using linear-force-free modeling. (4) A series of flares took place while the rate of helicity injection was high. (5) The choice of a smaller window size or a shorter time interval in the LCT method resulted in a bigger value of the LCT velocity and a bigger value of the temporal fluctuation of the helicity rate. (6) Nevertheless when averaged over a time period of about one hour or longer, the average rate of helicity became about the same within about 10%, almost irrespective of the chosen window size and time interval, indicating that short-lived, fluctuating flows may be insignificant in transferring magnetic helicity. Our results suggest that the LCT method may be applied to 96-minute cadence full-disk MDI magnetograms or other data of similar kind, to provide a practically useful, if not perfect, way of monitoring the magnetic helicity content of active regions as a function of time.  相似文献   

Non-Gaussian signatures in the temperature fluctuation observed by the Wilkinson Microwave Anisotropy Probe     

Chan-Gyung Park 《Monthly notices of the Royal Astronomical Society》2004,349(1):313-320

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