Long-term behavior of particulate matters at urban roadside and background locations in Seoul,Korea

The concentrations of particulate matter, PM_2.5, PM₁₀, and TSP at an urban roadside and an urban background station are analyzed. Data collected over a 10 year period are analyzed. The concentrations of the particulates measured at the urban site are systematically larger than at the background station. The mean PM values at the former also exhibit a slight fall over the decade unlike those at the background station. Overall, the particulate matters at both locations are in an intermediate range of global level, e.g., approximately two times lower than those in other Asian regions but higher than in Europe.     

Computational investigation of cavitation on a semi-spade rudder

This article examines noncavitating and cavitating flow fields around a semi-spade rudder in the ship wake and propeller slipstream based on a computational method. The article seeks to explain the erosion that can occur around the gap due to cavitation; such erosion has been reported to occur while a ship is at sea. Another area of research is the effect of the gap size and shape. The effects of erosion-evading devices such as elongated gap edges, an increased edge radius, flow control projections, and vertical and horizontal guide plates were also studied.     

Using Electronic Toll Collection Data to Understand Traffic Demand

In this study, we explored the potential of using electronic toll collection (ETC)-derived data that are a part of intelligent transport systems (ITS). Dynamic origin–destination (OD) traffic volumes were estimated using ETC data on the Hanshin Expressway. A dynamic OD estimation model that was suggested in a previous study was used, and abundant ETC data were input to improve the estimation accuracy. The results of OD estimation were analyzed to understand traffic demand and its variation. External factors were clarified that have an influence on variances in the OD flows, and statistical analysis methods for the variations were proposed depending on the factors. Moreover, the improvements in traffic simulation accuracy and performance as a result of using ETC data as input variables in the simulation models were discussed. According to the results of this study, ETC data have potential to assist in understaningd traffic demand and its variation, and the results can be applied to network management.     

Effect of Sea Level Rise and Offshore Wave Height Change on Nearshore Waves and Coastal Structures

In 1994, Townend proposed a method to calculate the relative changes in various wave characteristics and structure-related parameters due to sea level rise for regular waves. The method was extended to irregular waves by Cheon and Suh in 2016. In this study, this method is further extended to include the effect of future change in offshore wave height and the sea level rise. The relative changes in wavelength, refraction coefficient, shoaling coefficient, and wave height in nearshore area are presented as functions of the relative changes in water depth and offshore wave height. The calculated relative changes in wave characteristics are then used to estimate the effect of sea level rise and offshore wave height change on coastal structures by calculating the relative changes in wave run-up height, overtopping discharge, crest freeboard, and armor weight of the structures. The relative changes in wave characteristics and structure-related parameters are all expressed as a function of the relative water depth for various combinations of the relative changes in water depth and offshore wave height.     

An integrated measure of accessibility and reliability of mass transit systems

The growth of a city or a metropolis requires well-functioning transit systems to accommodate the ensuing increase in travel demand. As a result, mass transit networks have to develop and expand from simple to complex topological systems over time to meet this demand. Such an evolution in the networks’ structure entails not only a change in network accessibility, but also a change in the level of network reliability on the part of stations and the entire system as well. Network accessibility and reliability are popular measures that have been widely applied to evaluate the resilience and vulnerability of a spatially networked system. However, the use of a single measure, either accessibility or reliability, provides different results, which demand an integrated measure to evaluate the network’s performance comprehensively. In this paper, we propose a set of integrated measures, named ACCREL (Integrated Accessibility and Reliability indicators) that considers both metrics in combination to evaluate a network’s performance and vulnerability. We apply the new measures for hypothetical mass transit system topologies, and a case study of the metro transit system in Seoul follows, highlighting the dynamics of network performance with four evolutionary stages. The main contribution of this study lies in the results from the experiments, which can be used to inform how transport network planning can be prepared to enhance the network functionality, thereby achieving a well-balanced, accessible, and reliable system. Insights on network vulnerability are also drawn for public transportation planners and spatial decision makers.     

Interannual variability of the shelf-slope front position between 75° and 50° W

The shelf-slope front (SSF) is a continuous shelf-break front running from the Tail of the Grand Banks to Cape Hatteras, North Carolina, separating colder and less-saline continental shelf waters from warmer and more saline slope waters. Time series containing mean monthly SSF positions were produced along each of 26 longitude lines between 75° and 50°W by workers located at Bedford Institute of Oceanography by digitizing individual frontal charts and computing mean monthly latitudinal positions over a 29-year (1973–2001) period. After removing seasonal variability at each longitude, interannual variability (IAV) of the SSF position at each longitude was computed as the annual mean of all monthly SSF position anomalies for each year over the 29-year period. Despite some missing data, a longitude-time plot reveals alternating bands of offshore (late-1970s, late-1980s, late-1990s) and onshore (early-1980s, early-1990s, early-2000s) annual mean SSF anomaly values, exhibiting a period of approximately 10 years. Annual mean SSF anomaly amplitudes are largest in the east, with maxima of O (± 100 km) located east of 60° W for years when data are available. Empirical orthogonal function (EOF) modes 1–4 (accounting for > 90% of the variance) form a set of basis functions that describe the SSF anomaly data and allow reconstruction of the entire data set since missing data are relatively few (14%). A complex empirical orthogonal function (CEOF) analysis using the “reconstructed” data reveals a wavelength scale of approximately 20° of longitude, a distance nearly equal to the entire study domain, along with steady, westward phase propagation of SSF anomalies over approximately the same distance. Speed calculations for the westward-propagating features yield a value of approximately 1.2 to 2.4 cm s^− 1 (1 to 2 km d^− 1), with annual mean SSF anomalies thus requiring about 4 years to propagate from the Tail of the Grand Banks in the east to Cape Hatteras, North Carolina, in the west. This propagation speed and the timing of the SSF positional anomalies at the Tail of the Grand Banks for the 29-year study period are in agreement with speeds computed for the propagation of quasi-decadal salinity anomalies through the Labrador Sea and the time of their arrival at the Tail of the Grand Banks. The small westward SSF anomaly propagation speed is an order of magnitude smaller than the associated currents, in agreement with a highly damped flow-through system originating from both Davis Strait and the West Greenland Current as discussed by other workers. Observations from both southern and northern portions of the study domain, within both continental shelf and slope waters, show that interannual changes in the volume of shelf water along with shelf water bulk properties exhibit a strong relationship with IAV of the SSF position over long time periods.     

Recent observations in the straits of the East/Japan Sea: A review of hydrography, currents and volume transports

Recent observations of hydrography, currents and volume transports in the straits of the East/Japan Sea are reviewed. It is newly found that bottom cold water in the Korea/Tsushima Strait originating from the northern region of the East/Japan Sea appears not only in summer and autumn but also in winter. Intensive observations in the Korea/Tsushima Strait revealed two distinct cores of northeastward currents in the upper layer of the western and eastern channels. Mean volume transport through the Korea/Tsushima Strait is calculated as 2.5 ± 0.5 Sv from four-year direct and indirect measurements. As continuous monitoring has started in the Tsugaru and Soya Straits, understanding of temporal variability of currents and volume transports through the straits is in progress. For the first time, simultaneous time series of volume transports are available in the Korea/Tsushima and Tsugaru Straits during the winter of 1999–2000. Ouflow through the Tsugaru Strait accounts for about 70% of inflow through the Korea/Tsushima Strait for this period.     

Temporal stability of travelers' activity choice and home-stay duration: Some empirical evidence

This paper explores the temporal stability of activity type-choice models and models of travelers' home-stay duration. To empirically evaluate this stability, a nested logit model of activity-type choice and a proportional hazards model of home-stay duration are estimated using data from two-day travel diaries collected in the fall of 1989 and again, from the same individuals, in the fall of 1990. The results show that the models are not temporally stable over the one year time period separating the two travel-diary samples. A number of possible reasons for this instability are discussed.     

Enhancing the competitiveness of Korea’s container shipping industry through structural improvements

ABSTRACT

After the collapse of Hanjin Shipping in 2016, Korea faced the task of reconstructing its container shipping industry by enhancing the competitiveness of its shipping companies in a rapidly evolving market environment. Responding to this need for policy design, this study first attempts to understand the industry based on the shipping ecosystem, which comprises the following four areas: shipping finance, collection of cargo, acquisition of ships, and partnership among carriers. Second, it lists the structural problems, along with the remedial policy alternatives, that were identified after conducting in-depth interviews with industry experts, which included mid-level managers. Third, it conducts an importance-performance analysis to classify problems according to their importance and performance, followed by an analytic hierarchy process analysis to define the priorities of policy alternatives. Finally, drawing on the empirical results, the paper concludes with suggestions on an integrated policy package for the container shipping industry.     

Effects of split injection,oxygen enriched air and heavy EGR on soot emissions in a diesel engine

The effects of split injection, oxygen enriched air, and heavy exhaust gas recirculation (EGR) on soot emissions in a direct injection diesel engine were studied using the KIVA-3V code. When split injection is applied, the second injection of fuel into a cylinder results in two separate stoichiometric zones, which helps soot oxidation. As a result, soot emissions are decreased. When oxygen enriched air is applied together with split injection, a higher concentration of oxygen causes higher temperatures in the cylinder. The increase in temperature promotes the growth reaction of acetylene with soot. However, it does not improve acetylene formation during the second injection of fuel. As more acetylene is consumed in the growth reaction with soot, the concentration of acetylene in the cylinder is decreased, which leads to a decrease in soot formation and thus soot emissions. A combination of split injection, a high concentration of oxygen, and a high EGR ratio shows the best results in terms of diesel emissions. In this paper, the split injection scheme of 75.8.25, in which 75% of total fuel is injected in the first pulse, followed by 8°CA of dwell time, and 25% of fuel is injected in the second pulse, with an oxygen concentration of 23% in volume and an EGR ratio of 30% shows a 45% reduction in soot emissions, with the same NOx emissions as in single injection.