• Journal of Korean Society on Water Environment
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• v.40 no.5
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• pp.215-228
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• 2024

Lakes are one of major sources of methane gas due to anaerobic decomposition of organic matter in sediments. Since methane released from lakes is a greenhouse gas, it is necessary to investigate factors affecting methane production of lakes. This study conducted field and incubation experiments in Lake Asan in August and October to determine effects of thermal stratification and sediment organic matter characteristics on methane production. Field experiments measured temperature and dissolved oxygen to determine the formation of thermal stratification of lakes. Methane and organic matter characteristics were analyzed using gas chromatography, Total Organic Carbon (TOC) analyzers, and fluorescence spectroscopy. Incubation experiments under anaerobic conditions used sediment and water samples from the same site. Field results showed higher methane fluxes in August and increased Dissolved Organic Carbon (DOC) concentration closer to Asan Bay seawall. Elevated methane fluxes and DOC concentration resulted from intensified anaerobic decomposition formed by thermal stratification. Incubation results indicated that sediment organic matter characteristics influenced methane flux between sites. Statistical analysis revealed that thermal stratification could be a primary factor affecting methane production of lakes. Characteristics of sediment organic matter with respect to quantity and quality could be factors influencing methane production of lakes. Results of this study can serve as fundamental data for predicting methane emissions from lakes due to climate change and for mitigating lake's contributions to global warming.

• Journal of Biomedical Engineering Research
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• v.35 no.4
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• pp.105-110
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• 2014

For the combination of MRI and magnetic particle hyperthermia(MPH), we investigated the relative heating efficiency with respect to the strength of the static magnetic field under which the magnetic nanoparticles are to be heated by RF magnetic field. We performed nanoparticle heating experiments at the fringe field of 3T MRI magnet with applying the RF magnetic field perpendicularly to the static magnetic field. The static field strengths were 0T, 0.1T, 0.2T, and 0.3T. To prevent the coil heat from conducting to the nanoparticle suspension, we cooled the heating solenoid coil with temperature-controlled water with applying heat insulators between the solenoid coil and the nanoparticle container. We observed significant decrease of heat generation, up to 6% at 0.3T(100% at 0T), due to the magnetic saturation of the nanoparticles of 15 nm diameter under the static field. We think MPH is still feasible at low magnetic field lower than 0.3T if stronger RF magnetic field generation is permitted.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.742-747
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• 2001

A study on the ultrasonic effect for turbulence enhancement is carried out in the horizontal flow field of a coaxial circular pipe. A large transparent acryl tank is made to perform several experiments for the above research. The front flow field from jet exit is divided as 4 measuring regions to observe characteristics of the above flow field according to those with and without ultrasonic. An ultrasonic transducer with 2MHz high frequency is used to give them the ultrasonic forcing. Characteristics such as the velocity distribution, the kinetic energy and the turbulence intensity are visualized, observed, examined and considered at Re No. 2000. In results, it is clarified that the ultrasonic increases the turbulence enhancement. And the optimum and harmonious intensity suited to the power of flow is needed to maximize the turbulence enhancement.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.04a
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• pp.18-21
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• 2002

Phytoremediation which uses plants to enhance the bioremediation through stimulation of microbial activity and root uptake, has been a topic of increasing interest. Mathematical model were developed that can be applied to various bioremediation methods in the unsaturated zone, especially phytoremediation, for simulating the fate and transport of contaminants under field conditions. A 2-year field study was conducted using 72 (1.5m long and 0.1 m diameter) column lysimeters with four treatments: Johnsongrass; wild rye grass; a rotation of Johnsongrass and wild rye grass; and unplanted fallow conditions. The developed model represented the fate and transport of contaminant both in vegetated and unplanted soils satisfactorily for field applications. Parameters related to the contaminant concentration in the water phase were the main parameters determining the contaminant fate in the vadose zone and indicated that the bioavailability can be the most important factor in the success of phytoremediation as well as bioremediation applications.

• KIEAE Journal
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• v.1 no.1
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• pp.27-33
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• 2001

There are many research Papers and experiments indicating that the geomagnetic field affects the people and living organism. People grow up and build up most of their character through living in dwelling space and have relax and refresh at home. Creating healthy dwelling space is being considered very important in architectural planning and design for providing comfortable living environment and improving quality of life. Therefore. it is necessary to investigate the geomagnetic field and people's response in living space. In this study the vertical component(Z value) of geomagnetic field in detached houses was measured, evaluated by related evaluation criteria, compared with interview survey.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.9
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• pp.407-411
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• 2003

The purpose of this paper is to study the removal of nitrogen oxide(NOx) using a wire-plate type plasma reactor with magnet attached for indoor air purification. In order to produce a more effective reactor, we conducted magnetic field simulations. The results of the magnetic field simulations show that NOx can be removed more effectively. The results from the magnetic field simulation show that when 7 magnets were applied to the reactor, the magnetic flux density was at its highest amount than when using 0, 3, or 5 magnets. From the data obtained by the simulation results a plasma reactor was made and thus, several experiments were conducted. The best removal efficiency was obtained with 14 W AC power to the reactor with 5 magnets.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.124-125
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• 2000

We introduce a scheme with a maximized efficiency of detecting atoms passing through an optical standing-wave mode cavity. Consider a standing-wave optical cavity illuminated by a weak probe beam through one of its mirrors where the transmission through the other mirror is monitored by a photodetector. If an atom is put in the cavity, the atom-cavity coupling shifts the resonance frequency of the system via the so-called normal mode splitting, and thereby the transmission power will drop. In fact, this type of atom detection scheme has been used in recent single atom trap experiments In practice, however, the field in a standing-wave mode will have a geometrical structure having nodes and antinodes that when the atom traverses the cavity through one of the nodes, there will be no such effect of atom-field interaction. (omitted)

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.1
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• pp.12-20
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• 2002

To control the noise of an enclosed sound field, we built a state space model using the acoustic modal parameter description. Using the state space model, we can investigate the controllability and observability, and find an appropriate position of control speaker and microphone to control sound field of the enclosed space. We implemented LQR(linear quadratic regulator) controller and reduced order observer to reduce the first acoustic mode. Experiments showed satisfactory results of 4∼10 dB reduction of magnitude of the first acoustic mode, and support the feasibility of the proposed scheme to lightly damped acoustic field.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.444-446
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• 1995

This paper deals with semisphere-type sensor fo measuring the electric field waveforms by lightning discharges. The theoretical principle and design rule of the device are introduced, and also the calibration and application investigations are carried out. From the calibration experiments, the frequency bandwidth of the semisphere-type electric field measuring device ranges from 200 [Hz] to 1.56 [MHz], and the sensitivity of sensor is 0.96 [mV/V/m]. The electric field waveforms produced by lightning discharges were observed for June and August 1995. It is shown that the electric field waveforms produced at the distance of more than 50 [km] include only radiation component.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.462-464
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• 1995

In this paper, experiments were carried out to study the decrease of NOx in simulated flue gases (initial concentration of NO 1000, 750, 400 ppm, : $N_2$ balance gas). Characteristics of NOx reduction are measured and analysed in corona discharge of multi needles to plane electrode structure and magnetic field. The best characteristics of NO reduction is measured when electric and magnetic field were supplied to reactor, at same time. Consumption power applied electric and magnetic field were higher than that of discharge applied only electric field.