• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2091-2093
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• 2005

Five model coils of 6.6kV motor were manufactured with several defects. These stator coils have artificial defects such as void of groundwall insulation, removal of semi-conductive coating and damage of strand insulation. Epoxy-mica coupler(80 pF) was connected to five model coil terminals, respectively The voltage applied to the coils was 3.81kV, 4.76kV, 6.0kV and 6.6kV. Partial discharge(PD) tests performed in the laboratory and shield room. Digital PD detector (PDD) and turbine generator analyzer(TGA) were used to measure PD activity. TGA summarizes each plot with two quantities such as the normalized quantity number(NQN) and the peak PD magnitude(Qm). The PD levels in pC were measured with PDD. PD patterns of model coils were indicated the internal and slot discharges. PD patterns coincide with both PDD and TGA.

• Journal of electromagnetic engineering and science
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• v.13 no.2
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• pp.113-119
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• 2013

We developed a transformed, symmetrical, mushroom-like surface without via holes in cells focused on a 2.4-GHz WLAN band. Each slot in the novel type structure plays a key role in modeling at the desired frequencies. The designed artificial magnetic conductor (AMC) has several advantages, including a small size, a wider bandwidth, a short reflecting distance to the antenna, and easy fabrication because there are no via holes. Overall dimensions of the AMC cell are 21 mm $(Width){\times}21mm$ $(Height){\times}2.6mm$ (Thickness), and the bandwidth is about three times wider (11.7%) compared to that of a conventional AMC (4.0%). For evaluating the performance of the proposed structure, a reflector, which periodically consists of the designed AMC cells, was developed. The antenna with the investigated AMC reflector not only works within a quarter of the wavelength because of the extremely high wave impedance generated by the AMC cells on the surface of the structure but also reduces the specific absorption rate (SAR). Electromagnetic field (EMF) exposure to a human phantom was analyzed by applying the designed reflector to the 2.4-GHz dipole antenna in a tablet PC. The calculated peak SAR averaged over 1 g was 0.125 W/kg when the input power was 1 W and the antenna was located at 20 cm from the human phantom. However, the SAR value was only 0.002 W/kg (i.e., 98.4% blocked) when the designed reflector was inserted in front of the antenna.

• The korean journal of orthodontics
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• v.37 no.5
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• pp.341-350
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• 2007

The purpose of this study was to evaluate how the friction that occurs during the sliding movement of the archwire through esthetic brackets is differently affected by bracket materials, slot designs, and tip angulations of the archwire. Methods: Eight types of brackets with 0.018 inch slots (composite: Brillant (BR); composite with metal slot: Spirit MB (SP); ceramic: Inspire (IN), Signature (SI), Cristaline V (CR); ceramic with metal slot: Clarity (CL), Luxi II (LU); and metal bracket: Integra (IT)), and placed into groups of 20 brackets in each group, were tested in artificial saliva with 0.018 inch stainless steel wire. The wire tip angulations were given as 0, 4 and 8 degrees. Results: CR group significantly showed the lowest frictional force with all wire tip angulations of 0,4, and 8 degrees. IN significantly showed the highest frictional force (p < 0.001). BR (polyoxymethylene) had significantly less frictional force than SP (polycarbonate) (p < 0.001) and showed no significant difference between metal brackets. Friction was increased as the wire tip angulations were increased, but no notches were observed on any parts of the archwire. Conclusions: According to the results of this study, esthetic brackets are superior or similar to 55 brackets from a frictional point of view.

• Journal of the Korean Society of Industry Convergence
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• v.20 no.2
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• pp.169-176
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• 2017

Dental implants are required to have biomechanical functions and biostability in order to perform authoring, pronunciation, and aesthetic functions in the oral cavity. In terms of biostability, pure titanium for medical have good biostability and no rejection in the alveolar bone. with appropriate strength in terms of strength as well as biocompatibility. In recent years, various surgical methods and devices have been developed to improve the convenience and safety of the procedure. However, as the number of procedures increases, the screw loosening of the abutment screw connecting the artificial root and the abutment There are many reports of artificial root and abutment fracture. Fig. 1 is an example of a case where the upper part of the abutment screw is arbitrarily modified to remove the abutment by the abutment fracture due to the loosening of the abutment screw. The fundamental cause of abduction of the abutment screw is caused by the slight movement due to the lowering of the retention force of the abutment screw. It is necessary to minimize loosening of the abutment screw to avoid problems such as fracture during the period of using the implant. The purpose of this study is to investigate the structure of the abutment screw to prevent the loosening of the abutment screw by forming 0.5mm slot.

• The Korean Journal of Air & Space Law and Policy
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• v.9
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• pp.445-488
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• 1997

In the forthcoming 21st century new technical and scientific developments in outer space demands new approaches towards the problems arising in several fields of the use and exploitation of outer space including practical applications. The main purposes of this study are to analyze the legal problems of geostationary orbital position, telecommunication, direct television broadcasting by uses of artificial satellites. Communication via artificial Earth satellites was one of the first applications of space technology and is now one of the most developed field. From the technical and economic standpoints the advantages of world-wide satellites communication system are too all obvious. However, as the practical uses of space technology become more freguent, the legal conflicts among nations have become more divisive. One of the problem grown in uses of artificial satellites is that of the increasing shortage of suitable orbital slot positions for satellites, especially in geostationary orbit. Legal status of geostationary orbit as a limited resourece have to be reviewed in consideration of the side effect of the "First use, first-served" principle. The geostationary orbit is to be used for the benifits of all mankind and to be guaranteed for each state institutionaly in order to have eguitable access to the use of the orbit. Rapid increase of satellites broadcasting system in not only developed countries but also in developing countries opened up new possibilities with one another's scientific and cultural achievements. But there is also a potential danger that this powerful new instrument of influencing public opinion will be abused. Such a danger incudes spill-over or harmful interference. This controversial issue brings about the question whether prior consent from the receiver nation is needed to broadcast across international boundaries. Some states have rejected prior consent because it interfere with the free flow of information. Many other countries have opposed that opinion as an invasion and violation of sovereignty and as a violation of the 1967 Treaty and the UN Charter. Since declaration of the First Year of Outer Space in 1985, our country have promoted the plan of launching communication and broadcasting satellites. With the Koreasat launched in 1995 as the start, a real satellite-telecommunication era was opened in korea. According to this new development of our country, there will also rise various legal problems related to satellite broadcasting and telecommunication such as the inflow of foreign programs, the permeation of culture and the infringement of program copyright. Consequently the effective reactions to these problems in satellite-communication era should be tried including international cooperation. It is therefore to take into careful consideration the legal issues which may arise in outer space activities and to formulate positive policy on international cooperation with surrounding or advanced countries and international organization concerned. For this purpose the United Nations also prepares the UNISPACE III in 1999, to enable the international community to meet a more promising 21st century.

• Journal of the Korean Chemical Society
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• v.44 no.2
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• pp.102-108
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• 2000

Relative retention times (RRTs) of RAH molecules in HPLC are trained and predicted intesting sets using a multiple linear regression (NLR) and an artificial neural network (ANN). The maindescriptors in QSRR are molecular connectivity ($^1X_v,\;^2X_v$), the length-to-breadth ratios (L/B), and molecular dipole moment(D). L/B which is related with slot model is a good descripter in ANN, but isn't in MLR. Varainces which show the accuracy of prediction times in testing sets are 0.0099, 0.0114 for ANN and MLR, respectively. It was shown that ANN can exceed the MLR in prediction accuracy.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.9
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• pp.52-59
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• 2009

In this paper, the planar waveguide slotted array antenna is presented, which has the 3-layered structure of feeding networks for a high gain. Due to the ionosphere which generates 'Faraday rotation', the skew is happened between the signal radiated from an artificial satellite and the receiving antenna. This causes a polarization loss. In this paper, to remove this polarization loss, the dumbbell shaped linear polarizer using a single layer film is proposed. The gain of proposed antenna is 29.4dB.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.3
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• pp.1377-1399
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• 2020

In search and rescue mission, micro aerial vehicles (MAVs) are typically used to capture image and video from an aerial perspective and transfer the data to the ground station. Because of the power limitation, a cluster of MAVs are required for a large search area, hence an ad-hoc wireless network must be maintained to transfer data more conveniently and fast. However, the unstable link and the intermittent connectivity between the MAVs caused by MAVs' movement may challenge the packet forwarding. This paper proposes a delay tolerant packet forwarding algorithm based on location estimation for MAV networks, called DTN_est algorithm. In the algorithm, ferrying MAVs are used to transmit data between MAVs and the ground station, and the locations of both searching MAVs and ferrying MAVs are estimated to compute the distances between the MAVs and destination. The MAV that is closest to the destination is selected greedy to forward packet. If a MAV cannot find the next hop MAV using the greedy strategy, the packets will be stored and re-forwarded once again in the next time slot. The experiment results show that the proposed DTN_est algorithm outperforms the typical DTN_geo algorithm in terms of packet delivery ratio and average routing hops.

• Journal of Electrical Engineering and Technology
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• v.3 no.4
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• pp.571-575
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• 2008

Stator insulation quality assessment for high voltage motors is a major issue for the reliable maintenance of industrial and power plants. To assess the condition of stator insulation, nondestructive tests were performed on the sixty coil groups of twelve motors. After completing the nondestructive tests, the AC voltage applied to the stator winding was gradually increased until insulation failure in order to obtain the breakdown voltage. The stator winding of each motor was classified into five coil groups; one group with healthy insulation and four groups with four different types of artificial defects. To analyze the breakdown voltage statistically, Weibull distribution was employed for the tests on the fifty coil groups of ten motors. The 50th percentile values of the measured breakdown voltages based on the statistical data of the five coil groups of ten motors were 26.1kV, 25.0kV, 24.4kV, 26.7kV and 30.5kV, respectively. Almost all of the failures were located in the line-end coil at the exit of the core slot. The breakdown voltages and the types of defects showed strong relation to the stator insulation tests such as in the case of dissipation factor and ac current. It is shown that the condition of the motor insulation can be determined from the relationship between the probability of failure and the type of defect.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1612-1614
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• 2003

80pF capacitive couplers were connected to six 6.6kV motor model coil terminals. The voltage applied to the coils were 3.81kv, 4.76 kV and 6.6kV, respectively. These stator coils have various types of artificial insulation defects such as large voids, semi-conductive coating damage and strand insulation fault. Digital PD detector(PDD) and turbine generator analyzer(TGA) were used to measure PD activity. TGA summarizes each plot with two quantities such as the normalized quantity number(NQN) and the peak PD magnitude(Qm). The PD levels in PD were measured with a conventional digital PD detector. Most of the defect mechanism of large motor stator winding can be associated with PD patterns such as internal and slot discharges. PD patterns coincide with PDD and TGA. These instruments have an input bandwidth of 40-400kHz and 0.1-350MHz. Surge testing detects faults in inter-turn winding of high voltage motor model coils.