Holocene climate and environmental changes inferred from sediment characteristics and diatom assemblages in a core from Hwajinpo Lagoon,Korea

Hwajinpo is the largest lagoon in Korea and is located along the east coast of the country. It possesses Holocene sediments that provide an important record of past climate change. We studied the evolution of Hwajinpo Lagoon using grain size data and diatom assemblages in an 11.0-m core (HJ02), which was obtained at the mouth of a small river that drains into the lagoon. Core chronology was established with accelerator mass spectrometry ¹⁴C dates and optically stimulated luminescence dates. Diatom assemblages and grain size analysis revealed that estuarine conditions in the inner lagoon area transitioned to an open embayment ca. 8 ka as a result of sea-level rise. Around 7.8 ka, the open bay became a semi-closed bay as a consequence of development of a sand barrier. After the bay was semi-closed, marine water inflow was increasingly restricted as the sand barrier developed, and the semi-closed bay became a completely enclosed, low-salinity, brackish lagoon around 6 ka. There was an erosional hiatus between 5.5 and 1.7 ka (7.0 m depth), likely caused by river flooding and a switch in the location of drainage along the delta. The lagoon became oligohaline around 1.6 ka, likely because of increasing precipitation associated with an intensified Asian summer monsoon. This increase in precipitation resulted in expansion of the sand bar by sediment inflow, driven by agricultural development in the area. About 1000 years ago, the diatom assemblage was similar to the modern assemblage, suggesting the lagoon’s current geomorphic conditions had been established.     

Isolation and Identification of Lactic Acid Bacteria Isolated from a Traditional Jeotgal Product in Korea

Seventeen lactic acid bacterial strains (LAB) were isolated using MRS agar medium from Jeotgal, a Korean fermented food, purchased at the Jukdo market of Pohang. To identify the strains isolated, they were tested by examining their cell morphologies, gram-staining, catalase activity, arginine hydrolase activity, D-L lactate form and carbohydrate fermentation. According to the phenotypic characteristics, three strains were tent atively identified asLactobacillus spp., ten wereEnterococcus spp. (orStreptococcus spp., orPediococcus spp.) and the rest were Leuconostoc spp. (orWeissella spp.). Five strains among 17 were chosen by preliminary bacteriocin activity test. Four bacterial strains which inhibited both indicator microorganisms were identified by 16S rRNA sequencing. The results are as follows; Leuconostoc mesenteroides (HK 4),Leuconostoc mesenteroides (HK 5),Leuconostoc mesenteroides(HK 11),Streptococcus salivarius(HK 8). In order to check LAB which are showing a high survival rate in gut, we investigated three strains inhibiting both indicator microorganisms in artificial gastric acid and bile juice -all except HK8. The three strains mentioned above grew in extreme low acid conditions.     

A Wind-tunnel Study of Atmospheric Boundary-Layer Flow over Vegetated Surfaces to Suppress PM10 Emission on Owens (dry) Lake

Dust storms on Owens (dry) Lake located 200 milesnortheast of Los Angeles, California, U.S.A., havecaused serious PM₁₀ emission problems. Alaboratory-based experimental study was conducted toinvestigate the efficiency of 'vegetation cover' onthe playa to suppress dust emission rates as part ofa mitigation plan.Erodible lakebed material and field vegetation (saltgrass) taken from Owens (dry) Lake were placed in awind tunnel to simulate near-surface wind flow in theatmospheric boundary layer. Vertical wind-speedprofiles and vertical PM₁₀-concentration profileswere measured over six different levels of surfacevegetation cover. In order to understand the mechanismof aeolian particle transport and dust injection intothe atmosphere, the roughness parameter, z₀, thefriction velocity, u_*, and the surface dragcoefficient, C_D, were carefully determined.An empirical equation was developed to predictPM₁₀ emission rates as a function of wind speedand level of vegetation coverage for Owens (dry) Lake.Although the current results apply only to theeffectiveness of vegetation cover to suppressPM₁₀ emissions at Owens playa, the procedure canbe employed for any arid area or region that mightutilize added vegetation as a mitigation measure.     

Ultimate load capacities of mooring bollards and hull foundation structures

CSRs (Common Structural Rules for bulker and tanker), which came into effect in 2006, invoke the concept of the ultimate strength of hull girders. While numerous studies associated with the ultimate capacities regarding global hull girders and stiffened panels have been carried out, there are few application cases of the ultimate strengths for deck machineries and their supporting structures. In the present study, nonlinear finite element analyses have been performed to obtain ultimate capacities for a size 450 DIN type bollard including hull foundation structures for which elastic strength assessments based on allowable stress analyses were jointly carried out by a Mooring Fitting SWL Standardization Committee consisting of four major Korean shipbuilders (DSME, HHI, HHIC, and SHI) in 2003. The plastic hardening property is identified from a comparison of the results of ultimate strength simulations and a bollard tension tests performed by the committee. It is assumed that the ultimate load is the corresponding load point when the deformation slope of the bollard column reaches the critical slip angle. It is concluded that the reinforcements appear to be effective with respect to the allowable stress criterion, but are not substantially effective from the point of view of ultimate capacities. In other words, structural reinforcements based on allowable stress analyses may noticeably increase production costs, but do not remarkably raise the ultimate capacities.     

The effects of the M/V Sea Prince accident on maritime safety management in Korea

The Sea Prince accident was the first VLCC accident in Korea and a shock to the general public and government. Before the accident, any oil-spill management plan, such as National contingency plan (NCP) and regional contingency plans (RCPs), was not available and the resources for oil spills were lacking for the Sea Prince accident. About 5000 tons of oil spilled, polluting large areas of southern coastal waters, damaging the fisheries, including aquaculture. After the Sea Prince accident, Korea's government established various alternatives for dealing with oil spills, such as the NCP, RCPs, Typhoon Refuge Management Plan, and resources for oil-spill response. However, port safety management in emergency situations such as typhoons has not been solved.     

Three-dimensional imaging of subsurface structures using resistivity data

We have developed a three-dimensional inverse scheme for carrying out DC resistivity surveys, incorporating complicated topography as well as arbitrary electrode arrays. The algorithm is based on the finite-element approximation to the forward problem, so that the effect of topographic variation on the resistivity data is effectively evaluated and incorporated in the inversion. Furthermore, we have enhanced the resolving power of the inversion using the active constraint balancing method. Numerical verifications show that a correct earth image can be derived even when complicated topographic variation exists. By inverting the real field data acquired at a site for an underground sewage disposal plant, we obtained a reasonable image of the subsurface structures, which correlates well with the surface geology and drill log data.     

Geotechnical parameter estimation in tunnelling using relative convergence measurement

Accurate estimation of geotechnical parameters is an important and difficult task in tunnel design and construction. Optimum evaluation of the geotechnical parameters have been carried out by the back‐analysis method based on estimated absolute convergence data. In this study, a back‐analysis technique using measured relative convergence in tunnelling is proposed. The extended Bayesian method (EBM), which combines the prior information with the field measurement data, is adopted and combined with the 3‐dimensional finite element analysis to predict ground motion. By directly using the relative convergence as observation data in the EBM, we can exclude errors that arise in the estimation of absolute displacement from measured convergence, and can evaluate the geotechnical parameters with sufficient reliability. The proposed back‐analysis technique is applied and validated by using the measured data from two tunnel sites in Korea. Copyright © 2005 John Wiley & Sons, Ltd.     

Application of CASI Hyperspectral Image to Analysis of the Distribution of Hydrogen-Fluoride-Damaged Vegetation in Gumi,Korea

On the night of 27th Sept 2012, a hydrogen fluoride (HF) storage tank exploded in the industrial area of Gumi, Korea. In this study, an attempt was made to detect the damaged vegetation using a hyperspectral image. Assuming that HF was the most significant stressor of vegetation near the blast site, our results indicated that the difference in reflectance values between the 786 and 801 nm wavelengths became negative (?) and fluctuated from ?5 to ?160 in the affected vegetation. On the other hand, positive (+) values were found in the non-affected vegetation. The combination of normalized difference vegetation index (NDVI) and simple ratio (SR) was used [named combined vegetation index (CVI) in this study] to assess the accuracy of these measurements. Among 150,965 pixels that were defined as damaged vegetation, about 2.8 % were analyzed incorrectly in this study. As a result, factors such as wind direction, distance from the accident spot, elevation, and aspect were shown to affect damage distribution.     

Practical modified scheme of linear shallow-water equations for distant propagation of tsunamis

A simple but practical numerical model describing a distant propagation of tsunamis is newly proposed by introducing an additional term to the existing modified scheme. The numerical dispersion of the proposed model is manipulated to replace the physical dispersion of the linear Boussinesq equations without any limitation. The new model developed in this study is applied to propagation of a Gaussian hump over a constant water depth and the predicted free surface displacements are compared with available analytical solutions. A very reasonable agreement is observed.