• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.10 s.101
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• pp.1003-1009
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• 2005

In this paper, small-size high-power single pole double throw(SPDT) switch with defected pound structure(DGS) is presented for wireless broadband internet application. To reduce the circuit size using slow-wave characteristic, the DGS is applied to ${\lambda}/4$ transmission line of the switch and the measured results are compared with them of conventional switch. To secure high degree of isolation, the switch with the DGS is composed of shunt-connected PIN diodes and shows insertion loss of 0.8 dB and isolation more than 50 dB at 2.3 GHz. The size of the switch is reduced about $50\%$ only with the DGS patterns while it has very similar performance to the conventional shunt-type switch.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.146-150
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• 1996

A thermal micro actualtor has been fabricated using surface micromachining techniques. It consists of doped ploysilicon as a moving part and TEOS(Tetra Ethyl Ortho Silicate) as a sacrificial layer. The polysilicon was annealed for the reduction of residual stress which is the main cause to its deformation such as bending and buckling. And the newly developed HF VPE(vapor phase etching)process was also used as an effective release method for the elimination of sacrificaial layer. With noliquid involved during any of the steps for relasing, unlike other reported relase techniques, the HF VPE pocess has produced polysilicon microstructures with virtually no process-induced stiction problem. The actuation is incured by the thermal expasion due to current flow in active polysilicon cantilever, which motion is amplified bylever mechanism. The thickness of pllysilicon is 2 .mu. m and the length of active and passive polysilicon cantilever are 500 .mu. m, respectively. The moving distance of polysilicon actuator was experimentally conformed as large as 21 .mu. m at the input voltage level of 10 V and 50Hz square wave. These micro actuator technology can be utilized for the fabrication of MEMS (microlectromechanical system) such as microrelay, which requires large displacement or contact force but relatively slow response.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.997-1008
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• 1994

Heat transfer by laminar oscillating flow in a circular pipe has been studied analytically. The general solution with respect to the arbitrary wall boundary condition is obtained by superposing the fluid temperatures with the sinusoidal wall temperature distributions. The fulid temperature distributions are two dimensional, but uniform flow assumption is used to simplify the velocity distribution. The heat transfer characteristics in the thermally developing regions are analyzed by applying the general solution to the two cases of thermal boundary conditions in which the wall temperature and wall heat flux distributions have a square-wave form, respectively. The results show that the length of the thermally developing region becomes larger in proportion to the oscillation frequency at slow oscillation and eventually approaches to the value comparable to the swept distance as the frequency increases. The time and cross-section averaged Nusselt number in the developing region is inversely proportional to the square root of the distance from the position where the wall boundary condition is changed suddenly. In the developed region, Nusselt number is only determined by the oscillation frequency.

• Journal of Power System Engineering
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• v.11 no.3
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• pp.29-34
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• 2007

Existent researches about indoor thermal environment have been focused on to seek human's comfort in daytime. Also researches about thermal comfort during the sleeping time that is important for resting and recharging to modern people have been seldom existed. At present, as global warming phenomenon is being continued, most people are going through inconvenience by sultriness during the sleeping hours in sweltering summer night. Therefore we need another control method of an air conditioner to keep human's thermal comfort. Ambient temperature is a common factor of the environment, but analysis of its effect on human body physiology is still unknown. The effect of ambient temperature on human sleep has been increasingly studied in the last decade. This research investigated about optimal indoor temperature to maintain proper skin temperature and comfortable sleep when indoor air is cooled by an air conditioner in sweltering summer night.

• Journal of the Institute of Convergence Signal Processing
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• v.10 no.1
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• pp.1-6
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• 2009

Propagation of electromagnetic wave in the water or underground is very difficult because of the conductivity of the propagation materials. In this case, we usually use acoustic signal as ultrasonic but, it is not easy to transfer long distance with coherent method because of time varying multipath, doppler effect, and attenuations. So, we use noncoherent method as FSK to communicate between long distances. But, as the propagation speed of acoustic sound is very slow, the BW of the channel is narrow. It is very hard to guaranty the enough speed of communication like digital image data. In this paper, we proposed a new data communication protocol which can transmit multi-bit digital data with every single ping, and improve the data communication speed in the water.

• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.3
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• pp.73-79
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• 2010

In the present study, the loading frequency dependencies of cyclic shear strength and elastic shear modulus of reconstituted clay were examined by performing undrained cyclic triaxial tests and undrained cyclic triaxial tests to determine deformation properties. The result of undrained cyclic triaxial test of reconstituted and saturated clay shows that a faster frequency leads to higher stress amplitude ratio, but when the frequency becomes fast up to a certain point, the stress amplitude ratio will reach its maximum limit and the frequency dependence becomes insignificant. And also, the result of undrained cyclic triaxial deformation test shows a fact that a faster loading frequency leads to higher equivalent shear modules and smaller hysteresis damping ratio, and confirms the frequency dependence of cohesive soil. Meanwhile, the result of the creep test shows that continuing creep is created in the undrained cyclic triaxial test with slow loading frequency rate, and since loading rate becomes slower at the vicinity of the maximum and the minimum deviator stress due to sine wave loading, the vicinity of the maximum and the minimum deviator stress shall be more influenced by creep.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.5 s.182
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• pp.190-196
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• 2006

Transparent materials are widely used in the fields of optic parts and bio industry. We have experiment to find out the characteristics of the micromachining inside transparent materials using femtosecond laser pulses. With its non-linear effects by very high peak intensity, filament (plasma channel) was formed by the cause of the self-focusing and the self-defocusing. Physical damage could be found when the intensity is high enough to give rise to the thermal stress or evaporation. At the vicinity of the power which makes the visible damage or modification, the structural modification occurs with the slow scanning speed. According to the polarization direction to the scanning direction, the filament quality is quite different. There is a good quality when the polarization direction is parallel to the scanning direction. For fine filament, we could suggest the conditions of the high numerical aperture lens, the short shift of focusing point, the low scanning speed and the low power below 20 mW. As the examples of optics parts, we fabricated the fresnel zone plate with the $225{\mu}m$ diameter and Y-bend optical wave guide with the $5{\mu}m$ width.

• Clinical and Experimental Pediatrics
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• v.50 no.8
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• pp.711-717
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• 2007

Sleep is a vital, highly organized process regulated by complex systems of neuronal networks and neurotransmitters. Normal sleep comprises non-rapid eye movement (NREM) and REM periods that alternate through the night. Sleep usually begins in NREM and progresses through deeper NREM stages (2, 3, and 4 stages), but newborns enter REM sleep (active sleep) first before NREM (quiet sleep). A period of NREM and REM sleep cycle is approximately 90 minutes, but newborn have a shorter sleep cycle (50 minutes). As children mature, sleep changes as an adult pattern: shorter sleep duration, longer sleep cycles and less daytime sleep. REM sleep is approximately 50% of total sleep in newborn and dramatically decreases over the first 2 years into adulthood (20% to 25%). An initial predominant of slow wave sleep (stage 3 and 4) that peaks in early childhood, drops off abruptly after adolescence by 40% from preteen years, and then declines over the life span. The hypothalamus is recognized as a key area of brain involved in regulation of sleep and wakefulness. The basic function of sleep largely remains elusive, but it is clear that sleep plays an important role in the regulation of CNS and body physiologic processes. Understanding of the architecture of sleep and basic mechanisms that regulate sleep and wake cycle are essential to evaluate normal or abnormal development of sleep pattern changes with age. Reduction or disruption of sleep can have a significant impact on daytime functioning and development, including learning, growth, behavior, and emotional regulation.

• Journal of the Korean Operations Research and Management Science Society
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• v.26 no.3
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• pp.21-37
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• 2001

Riding on the wave of the information technology revolution, a slow of internet venture businesses (IVB) came into being. Hence, one of the recent developments in Korean capital market has been the proliferation of IVB, which is in accordance with the worldwide trend of ‘new economy’. Although the fair valuation is crucial for the nourishment of IVB, it is difficult to apply traditional valuation methods to these firms without reservation. It is due to the facts that most venture firms have little records of performance, grow unprecedently fast, and have highly uncertain future. The main purpose of this study is to suggest performance evaluation system of IVB and to develop KPE (Key Performance Indicators). Our empirical study is based upon Kaplan & Norton’s Balance Scorecard (BSC) approach. Specifically, our research has been conducted by the following two subsequent procedures: Firstly, seven internet venture firms have been selected and their executives have been interviewed by FGI(Focus Group Interview) method. Based upon these results, performance indicators have been developed. Secondly, by using the above mentioned BSC items (i.e., financial perspective, customer perspective, internal perspective and innovation & learning perspective), questionnaires have been constructed and sent to IVB through e-mail as well as over the Fax. Among the collected 110 samples, reliable 106 samples have been used to build BSC model and to draw our conclusion. In the future study, it would be much better to consider the role of strategy in IVB and the causal relationship among Key Performance Indicators of BSC.

• Sleep Medicine and Psychophysiology
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• v.4 no.1
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• pp.89-95
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• 1997

The authors studied 5 cases of idiopathic CNS hypersomnia who visited Division of Sleep Studies, Seoul National University Hospital in 1995. Detailed medical history was taken and nocturnal polysomnography(NPSG), multiple sleep latency test(MSLT) and human leukocyte antigen(HLA) typing were performed. Neither cataplexy nor hypnagogic hallucination was reported in all cases and in NPSGs, there were tendencies of increased sleep period time and decreased slow wave sleep time. In MSLT, all the subjects showed average sleep latencies less than 8 minutes without sleep-onset rapid eye movement period(SOREMP). In HLA typing, some correlation between idiopathic CNS hypersomnia and HLA DR4 was observed. In contrast to previous reports, overall treatment response with methylphenidate was remarkable. Therefore, the authors suggest that patients suspected of idiopathic CNS hypersomnia be actively evaluated and treated with rather optimistic perspective.