• Geomechanics and Engineering
• /
• v.2 no.4
• /
• pp.321-335
• /
• 2010

This article describes a laboratory research on stabilizing tropical peat using ordinary Portland cement (OPC) as a binding agent, and polypropylene and steel fibres as chemically inert additives. California bearing ratio (CBR) and unconfined compressive strength (UCS) tests were carried out to evaluate the increase in the strength of the stabilized samples compacted at their optimum moisture contents and air cured for up to 90 days. The results show that the UCS values of stabilized peat samples increased by as high as 748.8% by using OPC (5%), polypropylene fibres (0.15%), and steel fibres (2%). The CBR values of the samples stabilized with OPC (5%), polypropylene fibres (0.15%), and steel fibres (4%) showed an increase of as high as 122.7%. The stabilized samples showed a shrinkage in volume upon air curing and this shrinkage was measured by an index called, volume shrinkage index (VSI). The highest VSI recorded was 36.19% for peat without any additives; and the minimum was 0% for the sample containing 30% OPC, 0.15% polypropylene fibres and 2% steel fibres. The technique of stabilizing peat with OPC, polypropylene and fibres, coupled with air curing, appears to be cost-effective compared with other frequently used techniques.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.29 no.2
• /
• pp.106-110
• /
• 2021

In this study, the main factors affecting the number of passengers and cargo volume transported by air between Korea, China and Japan over the past 20 years are to be identified. For the analysis, data from three countries' GDP and per capita as well as exchange rates and international oil prices were used, and OLS multiple regression analysis and fixed effect analysis were performed. As a result of the analysis, both the number of passengers and cargo volume transported by air showed a negative (-) direction for GDP, which represents the country's economic power, and a positive (+) direction, for per capita GDP, which represents income level. And the increase in the exchange rate between China and Japan acted in a positive (+) direction on the increase in the number of passengers, and the effect of oil prices was found to be limited.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.17 no.2
• /
• pp.576-590
• /
• 2023

Machine learning is widely used in various academic fields, and recently it has been actively applied in the medical research. In the medical field, machine learning is used in a variety of ways, such as speeding up diagnosis, discovering new biomarkers, or discovering latent traits of a disease. In the respiratory field, a relative regional air volume change (RRAVC) map based on quantitative inspiratory and expiratory computed tomography (CT) imaging can be used as a useful functional imaging biomarker for characterizing regional ventilation. In this study, we seek to predict RRAVC using various regular machine learning models such as extreme gradient boosting (XGBoost), light gradient boosting machine (LightGBM), and multi-layer perceptron (MLP). We experimentally show that MLP performs best, followed by XGBoost. We also propose several relative coordinate systems to minimize intersubjective variability. We confirm a significant experimental performance improvement when we apply a subject's relative proportion coordinates over conventional absolute coordinates.

• Journal of the Korean Institute of Gas
• /
• v.3 no.3 s.8
• /
• pp.23-28
• /
• 1999

Variation of explosion characteristics by the blocks in closed vessel was investigated to analyse the effect of the block volume(volume blockage) and the surface area of the blocks(ratio of block surface area to vessel volume). Volume and surface area of blocks in explosion vessel were changed by the combination of blocks. The volume of explosion vessels was 270 liter, and the LPG-air or NG-air mixtures were ignited by the electric spark. Explosion pressure was measured with the strain type pressure transducer. From the experimental results, explosion pressure was decreased by the increase of the volume blockage and the block surface area. And the decrease of explosion pressure was more affected by the volume blockage than the surface area.

• Journal of the Society of Naval Architects of Korea
• /
• v.56 no.4
• /
• pp.361-372
• /
• 2019

The flow pattern of air layers and skin-friction drag reduction by air injection are investigated to find the suitable multiphase flow model using unstructured finite-volume CFD solver for the Reynolds-averaged Navier-Stokes equations. In the present computations, two different multiphase flow modeling approaches, such as the Volume of Fluid (VOF) and the Eulerian Multi-Phase (EMP), are adopted to investigate their performances in resolving the two-phase flow pattern and in estimating the frictional drag reduction. First of all, the formation pattern of air layers generated by air injection through a circular opening on the bottom of a flat plate are investigated. These results are then compared with those of MMkiharju's experimental results. Subsequently, the quantitative ratios of skin-friction drag reduction including the behavior of air layers, within turbulent boundary layers in large scale and at high Reynolds number conditions, are investigated under the same conditions as the model test that has been conducted in the US Navy's William B. Morgan Large Cavitation Channel (LCC). From these results, it is found that both VOF and EMP models have similar capability and accuracy in capturing the topology of ventilated air cavities so called'air pockets and branches'. However, EMP model is more favorable in predicting quantitatively the percentage of frictional drag reduction by air injection.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.11 no.1
• /
• pp.117-124
• /
• 1999

In this study, three different supply diffuser types(desktop, floor and ceiling) are compared in view of their ability to distribute supply air to the workstation breathing zone. The measurements on the age of air and the air change effectiveness using the tracer gas method are carried out to analyze the ventilation performance for provision of fresh air between the diffusers. The desktop diffuser type could deliver air directly to the occupants breathing zone with a high degree of effectiveness. The measured local air change effectiveness of the desktop diffuser in the breathing zone was usually 1.13 to 1.23 times greater than that of ceiling and floor diffusers. When the minimum outside air change rate as specified using ASHRAE Standard 62R is supplied with a desktop diffuser type, the volume of outside air can be reduced 13 to 23%, resulting in a commensurate in ventilation energy use.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.3 no.3
• /
• pp.129-139
• /
• 1995

This study investigates the combustion characteristics of methane-hydrogen-air premixture in a constant volume combustion chamber. Primary factors of the combustion characteristics of methane- hydrogen-air premixture are the equivalence ratio and hydrogen supplement rate. In the case of $\phi$= 1.1, maximum combustion pressure and heat release rate have peaks, and they increase as the initial pressure and hydrogen supplement rate increase. The total burning time is also the shortest at the $\phi$= 1.1, it shorten by lowering the initial pressure and by increasing the hydrogen supplement rate. The maximum flame temperature is shown at the $\phi$= 1.0, and increasing the initial pressure and hydrogen supplement rate, it increases. The concentration of NO reveals the highest value at the $\phi$= 0.9, and it increases by increasing the initial pressure and hydrogen supplement rate. It is also found that the limit of lean inflammability of methane-hydrogen-air premixture is greatly widened by increasing the hydrogen supplement rate.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.24 no.4
• /
• pp.53-61
• /
• 2016

Air Traffic Controllers (ATC) are also essential to the efficiency of airports and the airline industry. With the increasing volume of traffic, managing flights is a complex and sometimes very stressful job. ATC is using radar and other technology to track planes 'en route' between airports and keep in touch with pilots. Alternatively, ATCs are liaising with the planes on approach. However, ATC's working condition is getting more stressful, as the volume of air traffic increases. Thus this paper tried to research cognitive emotional regulation, job satisfaction, and job involvement and organizational committment of ATCs under the stressful work condition, taking care of safety of a couple of hundreds passengers per plane. Using CERQ survey sheet (Cognitive Emotional Regulation Questionnaire), it was found out that positive thinking and acceptance of self-blame have a significant impact on job satisfaction, work absorption and organizational Loyalty.

• Journal of Environmental Impact Assessment
• /
• v.16 no.6
• /
• pp.485-494
• /
• 2007

Air pollution and traffic noise from roads distributed near residential area has been a major social problem. In this study, an environmental pollution map for a residential area of Shihung-city was made by an expectation model based on hourly traffic volume change. Using the result from the model, a plan to reduce population in the residential area was established. The result of the modelling is summarized as follows: 1. At peak traffic hours (18 o'clock), 301-500 degree in hazardous and $d_{25}$ degree (25% of the residents are suffering extremely from the noise) in noise pollution were predicted in Jeongwang Main Road in Shihung city. 2. The calculated critical pollutant standard index, PSI showed the air pollution level, especially PM-10 high enough to require re-entrainment. 3. It was expected air pollution would extensively extend over the area distribution of each degree. However, noise pollution problem was limited to the area near roads.

• Journal of environmental and Sanitary engineering
• /
• v.14 no.4
• /
• pp.158-164
• /
• 1999

This study was carried out to investigate total suspended particulates (TSP) in Iksan area collected by nine stages Anderson air sampler and High volume air sampler from Jul. 1996 to Jul. 1998.The results are as follows1. The average of TSP concentration to be collected by Anderson air sampler and High volume air sampler in Iksan city are $59{\mu}g/m^3$, $67{\mu}g/m^3$. It was below the level of environmental standard. 2. The average of TSP concentration by measured method are HVAS > AS > Gov. 3. The average of TSP concentration on seasonal change are higher spring than winter. It were $65.5{\mu}g/m^3$ of Spring, $57{\mu}g/m^3$ of Summer, $52.5{\mu}g/m^3$ of Fall, $61{\mu}g/m^3$ of Winter. 4. Particle size 3istribution of atmospheric particulate was divided into two groups, coarse group was made by particles larger than $1.1-2.1{\mu}m$ in diameter and fine groups smaller than $1.1-2.1{\mu}m$ in diameter. about 50% of total suspended particle measured by Anderson air sampler during the sampling period was coarse particle.