• Membrane and Water Treatment
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• v.10 no.4
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• pp.307-311
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• 2019

The ejector type microbubble generator, which is the method to supply air to water by using cavitation in the nozzle, does not require any air supplier so it is an effective and economical. Also, the distribution of the size of bubbles is diverse. Especially, the size of bubbles is smaller than the bubbles from a conventional air diffuser and bigger than the bubbles from a pressurized dissolution type microbubble generator so it could be applied to the aeration tank for wastewater treatment. However, the performance of the ejector type microbubble generator was affected by hydraulic pressure and MLSS(Mixed Liquor Suspended Solid) concentration so many factors should be considered to apply the generator to aeration tank. Therefore, this study was performed to verify effects of hydraulic pressure and MLSS concentration on oxygen transfer of the ejector type microbubble generator. In the tests, the quantity of sucked air in the nozzle, dissolved oxygen(DO) concentration, oxygen uptake rate(OUR), oxygen transfer coefficient were measured and calculated by using experimental results. In case of the MLSS, the experiments were performed in the condition of MLSS concentration of 0, 2,000, 4,000, 8,000 mg/L. The hydraulic pressure was considered up to $2.0mH_2O$. In the results of experiments, oxygen transfer coefficient was decreased with the increase of MLSS concentration and hydraulic pressure due to the increased viscosity and density of wastewater and decreased air flow rate. Also, by using statistical analysis, when the ejector type microbubble generator was used to supply air to wasterwater, the model equation of DO concentration was suggested to predict DO concentration in wastewater.

• Journal of Environmental Health Sciences
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• v.17 no.2
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• pp.48-53
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• 1991

This study was carried out to investigate age, noise intensity, work period, hearing loss at frequencies, hypertension and to examine correlation of the total quantity of noise exposure(Dose) and blood pressure (Response) in the auto industry during May 1987-December 1987. To perform this study 65 workers were tested. Results of this study were as follows: 1. In frequency analysis, the CS-dip phenomenon occurred around 4000 Hz. 2. Between under of ten years group and over of ten years group, average hearing loss value was statitically significant (P < 0.05). 3. The prevalence of hypertension of 65 workers was 7.84% . 4. At 90dB(A) over and 10 years under and workers in the 20's group, the total quantity of noise exposure (Dose) and systolic blood pressure (Response) were statistically significant (P < 0.05). 5. At under 10 years of work period group, the total quantity of noise exposure(Dose) and diastolic blood pressure (Response) were statistically significant(r =0.234, P < 0.1).

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.274-281
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• 2004

In this paper, the existing Stokoe type torsional shear equipment is modified to saturate the specimen and measure excess pore water pressure during undrained testing. Two types of sands, Geumgang and Toyoura sands, were collected and TS tests were performed at various densities drainage conditions, and confining pressures. The cyclic threshold shearing strains were estimated based on the variations of shear modulus, material damping ratio and pore pressures with loading cycles. The effects of relative density, confining pressure, and drainage condition on the cyclic threshold shearing strains were investigated.

• Journal of Korean Society of Water and Wastewater
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• v.29 no.6
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• pp.617-623
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• 2015

In this study, determination methods of monitoring location in water distribution system were suggested and applied to real test bed. Small block of Gwangtan water distribution system is consisted of 582 pipes, 564 junctions, 1 reservoir, and 1 pump station. Small block of Ho Chi Minh water distribution system is consisted of 162 pipes, 148 junctions, and 1 reservoir. Two small block water distribution systems were analyzed by pressure contribution analysis method to determine the optimum monitoring locations. The pressure change was estimated at each junctions by the additional demand at a junction. From the results, the optimum monitoring location can be determined by rank of pressure contribution index at each junctions due to demand change at a junction.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.6 no.1
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• pp.38-54
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• 1996

Respirator fit testing is required before entering specific work environmentals to ensure that the respirator worn satisfies a minimum of fit and that the user knows when the respirator fits properly. The fit of a respirator can be determined by qualitative (QLFT) or quantitative fit test (QNFT). The QNFT, having been universally accepted more than the QLFT, provide an objective and numerical basis by measuring a fit factor (FF). Until a few years age, only one QNFT technigue was available and accepted by U.S. Occupational Safety and Health Administration (OSHA) regulations. In the 1980's and 1990's, several new and fundamentally different QNFT methods were developed. Two of the newer methods are commercially availale and are accepted by OSHA as suitable alternatives. In this articles, the principle of operation of each ONFT technique is explained and each technique's major advantages and disadvantages are pointed out. Emphasis is given to negative-pressure air-purifying respirators, as they are in most frequent use today. The requirements and recommendations for fit testing positive-pressure respirators are discussed as well. Finally, the presently available QNFT standards and regulations are summarized to assist the user in making fit testing decisions.

• Environmental Analysis Health and Toxicology
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• v.20 no.4 s.51
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• pp.303-309
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• 2005

Essential hypertension has been considered as multifactorial disease resulted from the interaction of both environmental and genetic factors. The renin-angiotensin system (RAS) plays an important role in the regulation of blood pressure homeostasis. Recently, a homologue of angiotensin I converting enzyme, ACE2 has been focused on as a candidate gene of essential hypertension in the experiments using animal model and human being. In this study, we carried out an association study in order to clarify the relationship between the A 1075G polymorphism in the ACE2 gene and essential hypertension in Korean subjects. Because this polymorphism is located on human chromosome X, the statistical analysis for each gender was performed separately. There were no significant differences in allele distribution of the A 1075G polymorphism in the ACE2 gene between normotensives and hypertensives in the both gender groups, respectively. However, this polymorphism was significantly associated with systolic blood pressure (SBP) and diastolic blood pressure (DBP) values in only female groups (P< 0.05). Thus, these results may suggest the probable role of ACE2 gene in the inter-individual susceptibility of female group to blood pressure variability.

• Structural Engineering and Mechanics
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• v.68 no.1
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• pp.95-101
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• 2018

The low rate of penetration and short lifetime of drilling bit served as the most common problems encountered in hard formation drilling, thus leading to severe restriction of drilling efficiency in oil and gas reservoir. This study developed a new local impact drilling method to enhance hard formation drilling efficiency. The limitation length formulas of radial/lateral cracks under static indentation and dynamic impact are derived based on the experimental research of Marshall D.B considering the mud column pressure and confining pressure. The local impact rock breaking simulation model is conducted to investigate its ROP raising effect. The results demonstrate that the length of radial/lateral cracks will increase as the decrease of mud pressure and confining pressure, and the local impact can result in a damage zone round the impact crater which helps the rock cutting, thus leading to the ROP increase. The numerical results also demonstrate the advantages of local impact method for raising ROP and the vibration reduction of bit in hard formation drilling. This study has shown that the local impact method can help raising the ROP and vibration reduction of bit, and it may be applied in drilling engineering.

• Wind and Structures
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• v.20 no.2
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• pp.327-347
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• 2015

This paper investigates the effects of Reynolds number (Re) on the aerodynamic characteristics of a twin-deck bridge. A 1:36 scale sectional model of a twin girder bridge was tested using the Wall of Wind (WOW) open jet wind tunnel facility at Florida International University (FIU). Static tests were performed on the model, instrumented with pressure taps and load cells, at high wind speeds with Re ranging from $1.3{\times}10^6$ to $6.1{\times}10^6$ based on the section width. Results show that the section was almost insensitive to Re when pitched to negative angles of attack. However, mean and fluctuating pressure distributions changed noticeably for zero and positive wind angles of attack while testing at different Re regimes. The pressure results suggested that with the Re increase, a larger separation bubble formed on the bottom surface of the upstream girder accompanied with a narrower wake region. As a result, drag coefficient decreased mildly and negative lift coefficient increased. Flow modification due to the Re increase also helped in distributing forces more equally between the two girders. The bare deck section was found to be prone to vortex shedding with limited dependence on the Re. Based on the observations, vortex mitigation devices attached to the bottom surface were effective in inhibiting vortex shedding, particularly at lower Re regime.

• Journal of Korean Association for Spatial Structures
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• v.17 no.4
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• pp.167-174
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• 2017

The F3D(Free-Form Formwork 3D Printer) technology that manufactures EPS(Expanded Polystyrene) formworks for irregular-shaped concrete structures by 3D printers was developed to reduce the cost and time. Because of weak strength and low elastic modulus of the EPS, structural performance including lateral pressure by fresh concrete of the formwork that consisted of EPS should be investigated. In order to calculate lateral pressures acting on formwork, several variables including sizes, shapes of formwork, tangential force(fricition) between fresh concrete and formwork, and material properties of fresh concrete should be considered. However, current regulations have not considered the properties of concrete, only focused on vertical formwork. Galleo introduced 3-dimensional finite element analysis models to calculate lateral pressure on formwork. Thus, proposed finite element analysis model based on previous studies were verified for vertical formwork and irregular-shaped formwork. The test results were compared with those by FEM analysis. As a result, the test agrees well with the analysis.

• Journal of the Korean GEO-environmental Society
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• v.11 no.2
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• pp.53-60
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• 2010

Considering environmental issues and lack of space, it is a necessity to minimize the amount of excavation. Various types of excavation methods are being used in practice. This study proposes a reasonable method for estimating the earth pressure acting on a reinforced wall in front of a excavated slope. The measured data in the field and numerical analyses were used. Results of the study shows that the earth pressure acting on the excavated wall is less than that estimated by Rankine's equations. It was shown that when the excavated slope is used with the reinforced wall, the pressures acting on the reinforced wall can be greatly reduced.