Baryonic fraction in the cold plus hot dark matter universe

The observational infrared spectra of a number of Wolf–Rayet stars of WC8–9 spectral classes are shown to be quite satisfactorily explained by making use of the detailed theoretical model of a dust shell made up of spherical amorphous carbon grains, the dynamics, growth–destruction, thermal and electrical charge balance of which are taken into account. The dust grains acquire mainly positive electrical charge, move with suprathermal drift velocities and may grow up to 100–200 Å as a result of implantation of impinging carbon ions. For most of the stars the fraction of condensed carbon does not exceed 1 per cent. While the nature of the grain nucleation remains unknown, the condensation distances and the grain seed production can be estimated by fitting the observational spectra with theoretical ones.     

Tectonic and stratigraphic significance of the Middle Ordovician carbonate breccias in the Ogcheon Belt, South Korea

Abstract Carbonate breccias occur sporadically in the Lower–Middle Ordovician Maggol Limestone exposed in the Taebacksan Basin in the northeastern part of the northeast–southwest‐trending Ogcheon Belt, South Korea. These carbonate breccias have been previously interpreted as intraformational or fault‐related breccias. Thus, little attention has been focused on tectonic and stratigraphic significance of these carbonate breccias. The present study, however, indicates that the majority of these carbonate breccias are solution–collapse breccias, which are causally linked to paleokarstification. Carbonate facies analysis in conjunction with conodont biostratigraphy suggests that an overall regression toward the top of the Maggol Limestone probably culminated in subaerial exposure of platform carbonates during the early Middle Ordovician (earliest Darriwilian). Extensive subaerial exposure of platform carbonates resulted in paleokarst‐related solution–collapse breccias in the upper Maggol Limestone. This subaerial exposure event is manifested as a major paleokarst unconformity at the Sauk–Tippecanoe sequence boundary elsewhere beneath the Middle Ordovician succession and its equivalents, most notably North America and North China. Due to its global extent, this paleokarst unconformity has been viewed as a product of second‐ or third‐order eustatic sealevel drop during the early Middle Ordovician. Although a paleokarst breccia zone is recognized beneath the Middle Ordovician succession in South Korea, the Sauk–Tippecanoe sequence boundary appears to be a conformable transgressive surface on the top of the paleokarst breccia zone in the upper Maggol Limestone. The paleokarst breccia zone beneath the conformable transgressive surface is represented by a thinning‐upward stack of exposure‐capped tidal flat‐dominated cycles that are closely associated with multiple occurrences of paleokarst‐related solution–collapse breccias. This paleokarst breccia zone was a likely consequence of repeated fourth‐ and fifth‐order sealevel fluctuations. It suggests that second‐ and third‐order eustatic sealevel drop may have been significantly tempered by substantial tectonic subsidence near the end of the Maggol deposition. The tectonic subsidence in the basin is also evidenced by the occurrence of coeval off‐platform lowstand siliciclastic quartzite lenses as well as debris flow carbonate breccias (i.e. the Yemi Breccia). With the continued tectonic subsidence, subsequent rise in the eustatic cycle caused drowning and deep flooding of carbonate platform, forming a transgressive surface on the top of the paleokarst breccia zone. This tectonic implication contrasts notably with the slowly subsiding carbonate platform model for the basin as has been previously interpreted. Thus, it is proposed that the Taebacksan Basin in the northeastern part of the Ogcheon Belt evolved from a slowly subsiding carbonate platform to a rapidly subsiding intracontinental rift basin during the early Middle Ordovician. The proposed tectonic model in the basin gives much better insight to unravel the stratigraphic response to tectonic evolution of the Ogcheon Belt, which remains an enigmatic feature in formulating a tectonic framework of the Korean peninsula. The present study also provides a good example that the falling part of the eustatic sealevel cycle may not produce a significant event in a rapidly subsiding basin where the rate of eustatic fall always remained lower than the rate of subsidence.     

Monitoring of suspended sediment variation using Landsat and MODIS in the Saemangeum coastal area of Korea

Suspended sediment concentration (SS) is an important indicator of marine environmental changes due to natural causes such as tides, tidal currents, and river discharges, as well as human activities such as construction in coastal regions. In the Saemangeum area on the west coast of Korea, construction of a huge tidal dyke for land reclamation has strongly influenced the coastal environment. This study used remotely sensed data to analyze the SS changes in coastal waters caused by the dyke construction. Landsat and MODIS satellite images were used for the spatial analysis of finer patterns and for the detailed temporal analysis, respectively. Forty Landsat scenes and 105 monthly composite MODIS images observed during 1985-2010 were employed, and four field campaigns (from 2005 to 2006) were performed to verify the image-derived SS. The results of the satellite data analyses showed that the seawater was clear before the dyke construction, with SS values lower than 20 g/m(3). These values increased continuously as the dyke construction progressed. The maximum SS values appeared just before completion of the fourth dyke. Values decreased to below 5 g/m(3) after dyke construction. These changes indicated tidal current modification. Some eddies and plumes were observed in the images generated from Landsat data. Landsat and MODIS can reveal that coastal water turbidity was greatly reduced after completion of the construction.     

Changes in topography and surface sediments by the Saemangeum dyke in an estuarine complex,west coast of Korea

The effects of a giant offshore dyke, Saemangeum, have been of special interest on both scientific and environmental aspects. Without any rival worldwide with regard to the ample scale and estuarine setting, the Saemangeum dyke and its vicinity (Saemangeum Area) should be an unprecedented experimental site for monitoring the consequence of the estuarine developments with dykes. In order to unravel geologic changes caused by the Saemangeum dyke, we collected a number of surface sediment samples and bathymetric profiles from a full coverage of the Saemangeum Area, and compared topography and sediment phase on the inter-annual (2002–2006, post-construction) and decadal (1982–2002, between pre- and post-construction) timescales.     

Factors controlling groundwater chemistry in an agricultural area with complex topographic and land use patterns in mid‐western South Korea

Shallow and bedrock groundwater from granitic aquifers were investigated for the hydrogeochemistry of major and minor constituents in an agricultural area. Nitrate concentrations were observed up to 49 mg/l as NO₃‐N, with 22% of samples exceeding the drinking water standard, which could pose a significant threat because most residents rely on groundwater as their drinking water source. Principal component analysis revealed three principal components (PCs): (1) nitrate contamination, contributed by major cations, Cl^?, SO and NO , (2) reduction processes positively involving Fe, Mn and B, and negatively involving dissolved oxygen and NO and (3) natural mineralization, involving HCO and F^?. Cluster analysis, performed on the PC scores, resulted in seven sample groups, which were successfully identified by total depth, elevation and land use. The nitrate‐contaminated groups had mixed land uses, with locally concentrated residential areas. Uncontaminated groundwater groups were found in the natural environment, including high‐altitude spring water and bedrock groundwater with a higher degree of natural mineralization. Shallow groundwater groups in paddy fields in lowlands were affected by reducing environments, of which one group was characterized by high Fe, Mn and B, and negligible nitrate. Groundwater with intermediate nitrate and lower Cl^? and SO was found primarily in hilly terrains with orchards and vegetable gardens, indicating lower contaminant loadings than lowland areas. Higher concentrations of F^? and nitrate were observed in the nitrate‐contaminated water, which seemed unlikely to be explained by groundwater mixing. The strong acidity generated from nitrification may infiltrate deeper into the aquifer, induce accelerated weathering of bedrock and result in the coexistence of F^? and nitrate, which may be an evidence of intense nitrate loading, leading to soil acidification. Multivariate statistical analysis successfully delineated hydrochemical characteristics of groundwater attained by natural and anthropogenic processes in an agriculturally stressed area with complex topographic land use patterns. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of radiation amplification factor of atmospheric aerosol from the surface UV irradiance measurement at Gwangju, Korea

Summary This study investigated the impact of atmospheric aerosols on surface ultraviolet (UV) irradiance at Gwangju, Korea (35°13′N, 126°50′E). Data analyzed included surface UV irradiance measured by UV radiometers from June 1998 to April 2001 and the aerosol optical depth (AOD) in the visible range determined from a rotating shadow-band radiometer (RSR). The radiation amplification factor (RAF) of ozone for UV-B (280–315 nm) at Gwangju was 1.32–1.62. Values of the RAF of aerosols (RAF_AOD) for UV-A and UV-B were 0.18–0.20 and 0.22–0.26, respectively. Authors’ addresses: Jeong Eun Kim, Advanced Environmental Monitoring Research Center (ADEMRC), Gwangju Institute of Science and Technology (GIST) and Korea Meteorological Administration (KMA); Seong Yoon Ryu, Advanced Environmental Monitoring Research Center (ADEMRC), Gwangju Institute of Science and Technology (GIST) and Division of Metrology, Korea Research Institute of Standards and Science (KRISS); Young Joon Kim, Advanced Environmental Monitoring Research Center (ADEMRC) Gwangju Institute of Science and Technology (GIST), 1 Oryong-dong, Buk-gu, Gwangju 500-712, Republic of Korea.     

Computational Fluid Dynamics Modelling of the Diurnal Variation of Flow in a Street Canyon

Urban surface and radiation processes are incorporated into a computational fluid dynamics (CFD) model to investigate the diurnal variation of flow in a street canyon with an aspect ratio of 1. The developed CFD model predicts surface and substrate temperatures of the roof, walls, and road. One-day simulations are performed with various ambient wind speeds of 2, 3, 4, 5, and 6 ms⁻¹, with the ambient wind perpendicular to the north–south oriented canyon. During the day, the largest maximum surface temperature for all surfaces is found at the road surface for an ambient wind speed of 3 ms⁻¹ (56.0°C). Two flow regimes are identified by the vortex configuration in the street canyon. Flow regime I is characterized by a primary vortex. Flow regime II is characterized by two counter-rotating vortices, which appears in the presence of strong downwind building-wall heating. Air temperature is relatively low near the downwind building wall in flow regime I and inside the upper vortex in flow regime II. In flow regime II, the upper vortex expands with increasing ambient wind speed, thus enlarging the extent of cool air within the canyon. The canyon wind speed in flow regime II is proportional to the ambient wind speed, but that in flow regime I is not. For weak ambient winds, the dependency of surface sensible heat flux on the ambient wind speed is found to play an essential role in determining the relationship between canyon wind speed and ambient wind speed.     

The Application of Artificial Neural Networks to Landslide Susceptibility Mapping at Janghung, Korea

The purpose of this study was to develop techniques for landslide susceptibility using artificial neural networks and then to apply these to the selected study area at Janghung in Korea. Landslide locations were identified from interpretation of satellite images and field survey data, and a spatial database of the topography, soil, forest, and land use. Thirteen landslide-related factors were extracted from the spatial database. These factors were then used with an artificial neural network to analyze landslide susceptibility. Each factor's weight was determined by the back-propagation training method. Five different training sets were applied to analyze and verify the effect of training. Then the landslide susceptibility indices were calculated using the back-propagation weights, and susceptibility maps were constructed from Geographic Information System (GIS) data for the five cases. Landslide locations were used to verify results of the landslide susceptibility maps and to compare them. The artificial neural network proved to be an effective tool for analyzing landslide susceptibility.