• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.9 no.4
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• pp.1-7
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• 2013

This study is to compare energy consumption of air-source, ground-source and dual-source heat pump systems during intermediate season using dynamic simulation. Ground-source heat pump has higher COP than that of air-source but requires additional power consumption of auxiliary equipment such as circulation pump. During intermediate season when the outdoor air temperature is favorable, total COP of air-source heat pump may be greater than that of ground-source when circulation pump power consumption is included. Dual-source heat pump which selects the more favorable heat source is compared with air-source only and ground-source only heat pumps for total power consumption. Results show that power consumption of dual-source heat pump is lower than that of ground-source only by 0.73%.

• Journal of Power Electronics
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• v.18 no.2
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• pp.395-406
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• 2018

Marine controlled-source electromagnetic transmitters (MCSETs) are important in marine electromagnetic exploration systems. They play a crucial role in the exploration of solid mineral resources, marine oil, and gas and in marine engineering evaluation. A DC-DC controlled-source circuit is typically used in traditional MCSETs, but using this circuit in MCSETs causes several problems, such as large voltage ringing of the high-frequency diode, heating of the insulated-gate bipolar transistor (IGBT) module, high temperature of the high-frequency transformer, loss of the duty cycle, and low transmission efficiency of the controlled-source circuit. This paper presents a clamping-diode circuit for MCSET (CDC-MCSET). Clamping diodes are added to the controlled-source circuit to reduce the loss of the duty ratio and the voltage peak of the high-frequency diode. The temperature of the high-frequency diode, IGBT module, and transformer is decreased, and the service life of these devices is prolonged. The power transmission efficiency of the controlled-source circuit is also improved. Saber simulation and a 20 KW MCSET are used to verify the correctness and effectiveness of the proposed CDC-MCSET.

• Journal of Korean Vacuum Science & Technology
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• v.4 no.4
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• pp.93-96
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• 2000

Microchannel plates (MCPs) have been developed by introducing new materials and process technologies. Main body was made of alumina by programmable punching, laminating, and firing. The channel walls of pore arrays of an MCP were deposited with thin films by electroless copper plating and sol-gel process. Our MCP has advantages such as easy fabrication, durability, high temperature endurance, and applicability to the large size comparing with the conventional MCPs. Experiments on the brightness of an MCP incorporated FED revealed that the FED with a MCP is three to four times brighter than a conventional FED. Moreover, the focusing in a FED is improved. Incorporating an MCP into a FED is one of promising methods to enhance the characteristics of the FED. In addition, amplification yield of the MCP is measured for varying the aspect ratio and the input current.

• Proceedings of the Korean Vacuum Society Conference
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• 1992.07a
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• pp.113-114
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• 1992

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.1028-1031
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• 2002

Ga-based semiconductor nanowires (GaN, GaP) were synthesized by the reaction of Ga metal and GaN/GaP powder with a $NH_3/Ar$ gas using thermal chemical vapor deposition. The field emission and emission stability under oxygen and argon environments were investigated. Field emission energy distributions of electrons from these nanowires revealed that field emission mechanism of the semiconductor nanowires were different from carbon nanotubes.

• Journal of Korea Technology Innovation Society
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• v.7 no.1
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• pp.1-20
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• 2004

In this paper, we try to explore the nature of open source software development process. The process involves peculiar characteristics which seem to defy the traditional economic reasoning for technology policy. Based upon the comparative case study of open source software development process with the two innovation processes adopted from literature on economic history, we argue that technology policy should strike the balance between provision of innovation incentives and voluntary disclosure of information.

• Journal of Technology Innovation
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• v.14 no.2
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• pp.117-141
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• 2006

The paper describes the status and context of the Chinese Open Source Software (OSS) industry and ecosystem based on the analysis of the components of the China OSS Promotion Union. The analysis involves comparisons of several main Chinese developers of Linux operating system and makers of open source counterpart of the popular Microsoft Office package as well as several main Chinese OSS communities. Comparisons concern the technological and business aspect. The findings reveal peculiarities of the divergence of innovative activities of Chinese companies, as well as indicate that the strong government support may at the same time limit the technology selection under rigid competition, especially as foreign open source companies are found to be more focused on hobbyist developers and are able to maintain larger independent communities. Implications of the paper include the need to coordinate global development efforts and adjust science & technology policies in order to stimulate both the development and the diffusion of open source among Chinese companies and individual hobbyists.

• The Journal of the Acoustical Society of Korea
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• v.23 no.2E
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• pp.56-67
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• 2004

Despite abundant research outcomes of blind source separation (BSS) in many types of simulated environments, their performances are still not satisfactory to be applied to the real environments. The major obstacle may seem the finite filter length of the assumed mixing model and the nonlinear sensor noises. This paper presents a two-step speech enhancement method with multiple microphone inputs. The first step performs a frequency-domain BSS algorithm to produce multiple outputs without any prior knowledge of the mixed source signals. The second step further removes the remaining cross-channel interference by a spectral cancellation approach using a probabilistic source absence/presence detection technique. The desired primary source is detected every frame of the signal, and the secondary source is estimated in the power spectral domain using the other BSS output as a reference interfering source. Then the estimated secondary source is subtracted to reduce the cross-channel interference. Our experimental results show good separation enhancement performances on the real recordings of speech and music signals compared to the conventional BSS methods.

• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.3030-3038
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• 2023

Nowadays, mobile robots have been used to search for uncontrolled radioactive source in indoor environments to avoid radiation exposure for technicians. However, in the indoor environments, especially in the presence of obstacles, how to make the robots with limited sensing capabilities automatically search for the radioactive source remains a major challenge. Also, the source search efficiency of robots needs to be further improved to meet practical scenarios such as limited exploration time. This paper proposes an automatic source search strategy, abbreviated as ACA: the location of source is estimated by a convolutional neural network (CNN), and the path is planned by the A-star algorithm. First, the search area is represented as an occupancy grid map. Then, the radiation dose distribution of the radioactive source in the occupancy grid map is obtained by Monte Carlo (MC) method simulation, and multiple sets of radiation data are collected through the eight neighborhood self-avoiding random walk (ENSAW) algorithm as the radiation data set. Further, the radiation data set is fed into the designed CNN architecture to train the network model in advance. When the searcher enters the search area where the radioactive source exists, the location of source is estimated by the network model and the search path is planned by the A-star algorithm, and this process is iterated continuously until the searcher reaches the location of radioactive source. The experimental results show that the average number of radiometric measurements and the average number of moving steps of the ACA algorithm are only 2.1% and 33.2% of those of the gradient search (GS) algorithm in the indoor environment without obstacles. In the indoor environment shielded by concrete walls, the GS algorithm fails to search for the source, while the ACA algorithm successfully searches for the source with fewer moving steps and sparse radiometric data.

• Journal of Information Display
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• v.2 no.4
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• pp.23-28
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• 2001

Field emission characteristics of carbon nanotubes(CNTs) on four kinds of metallic substrates have been investigated under the irradiation of a laser. The field emission measurement reveals that after laser irradiation the current was increased and new humps at the field emission current was found. The current enhancement was thought to have occurred due to the fact that the electrical contact between CNTs and metals was improved due to the irradiation of the laser.