• Proceedings of the Korean Information Science Society Conference
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• 2012.06a
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• pp.227-229
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• 2012

한국해양연구원에서 개발하고 있는 해저보행로봇 CR200은 6개의 다리를 이용하여 해저면에서 보행으로 이동하며 정밀 해저탐사 및 작업을 수행할 수 있는 로봇이다. 운용자는 선상제어실에서 유선으로 연결된 CR200을 원격으로 모니터링하거나 제어한다. 특히 안정적인 보행을 위해서는 100Hz의 주기로 CR200의 상태 정보가 선상제어실로 전송되고, 선상제어실에서는 전송된 정보를 기반으로 제어 명령을 산출하여 CR200으로 전송해야 한다. 이러한 주기적인 실시간 제어를 위해서는 일반적으로 실시간 운영체제를 사용하지만, 본 논문에서는 실시간 운영체제를 사용하지 않고 시스템 시간 기반의 백그라운드 프로세스로 동작하는 소프트웨어 타이머를 사용하여 실시간 제어를 하는 방법을 제안하고, 성능 평가 결과를 제시한다. 제안한 방법의 실시간 속성을 검증하기 위하여, 현재 설계에서 운영체제로 고려하고 있는 우분투 10.04와 윈도우즈 7을 CR200에 탑재되는 Advantech 사의 PCM-3362 보드에 설치하여 소프트웨어 타이머의 성능을 10ms부터 100ms까지 각각 실험하였다. 실험결과에 따르면, 두 운영체제에서 모두 누락이 없이 타이머 동작이 수행되었으며, 10ms 간격으로 타이머를 동작하였을 때에 우분투에서는 평균 오차가 $41{\mu}s$이었고 윈도우즈 7에서는 7.7ms였다. 윈도우즈 7에서의 오차는 100Hz 제어 주기에 사용하기에 적합하지 않지만, 우분투에서의 오차는 제어 주기 간격의 0.41%에 불과하기 때문에 해저보행로봇의 실시간 제어에 영향을 주지 않는 오차이다. 따라서 CR200의 임베디드 컴퓨터와 선상제어실의 원격제어 컴퓨터는 우분투 운영체제 상에서 소프트웨어 타이머를 이용하여 상호 연동되도록 구현할 예정이다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.346.1-346.1
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• 2016

본 연구에서는 열처리(Thermal Dewetting Process)와 빗각 증착(Oblique angle deposition)을 이용하여 비주기 서브파장 구조물을 마이크로 렌즈 형태의 유리 기판 상부에 제작하였다. 먼저 $2{\times}2cm2$ 크기의 유리 기판에 기존 리소그래피 공정으로 원기둥 형태의 감광액을 형성한다. 이후 Hot-plate로 $180^{\circ}C$에서 90초간 열을 가해 지름이 $20{\mu}m$인 반구형태로 변형시킨 뒤 반응성이온식각 공정을 진행하여 마이크로 렌즈를 제작한다. 렌즈의 표면에 나방 눈 구조를 형성하기 위해 전자빔 증착으로 15nm의 은 박막을 쌓은 뒤 $500^{\circ}C$에서 1분간 열처리 공정을 진행하였다. 열이 가해졌을 때 은 박막은 표면자유에너지를 최소화하기 위해 나노 크기의 덩어리진 입자 형태로 변화한다. 여기서 형성되는 나노입자의 크기가 렌즈 표면 중심에서 가장자리로 갈수록 작아진다는 것을 주사전자현미경을 통해 확인하였다. 증착 각도가 증가할수록 열처리 공정 후의 은 나노입자의 크기가 점점 작아진다는 것을 검증하기 위해 은 박막의 증착 각도를 $0^{\circ}$, $35^{\circ}$, $55^{\circ}$, $70^{\circ}$로 증착 후 열처리 공정을 진행하여 확인하였다. 비스듬하게 증착되어 형성된 박막은 다공형태로 낮은 밀도를 가지는데 이는 박막 두께 감소를 일으킨다. 따라서 증착 각도가 증가할수록 열처리 공정 후의 은 나노입자의 크기는 점점 작아진다. 이후 은 나노입자를 마스크로 하여 다시 반응성이온식각 공정을 진행하였으며 식각 후 나머지 은 나노입자들은 HNO3용액에서 1분간 처리하여 제거하였다. 제작된 구조물의 평균 직경과 크기는 각각 ~220nm 및 ~250nm인 것으로 확인하였다. 위와 같은 공정을 통해 다양한 크기를 가진 비주기 서브파장 구조물을 제작할 수 있다. 구조물의 주기가 파장 길이보다 짧을 경우 분산이 최소화되며 넓은 파장 대역에서 무반사 효과를 얻을 수 있다. 이 공정은 마스크를 통한 리소그래피의 한계를 극복할 수 있으며 여러 곡면형 표면에 적용가능한 장점이 있다. 또한 프리즘, 렌즈, 광섬유와 같은 광소자의 광투과율을 향상시키는데 이용될 수 있다.

• Journal of Korean Society of Forest Science
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• v.89 no.4
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• pp.463-469
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• 2000

Douglas-fir (Pseudotsuga menziesd Mirb. Franco) is highly regarded as a commercial timber species throughout the world in part due to its fast growth relative to many other species. In this study, basal area per hectare equation for Douglas-fir plantations in Southland of New Zealand has been developed based on medium measurement cycles of permanent sample plots data set. The function was developed using the algebraic difference equation method, and various sigmoid-shaped projection equations were used. Parameter estimation was obtained by non-linear routine of the SAS. As a result, of the functions tested a variant of the Schumacher polymorphic function including site index and thinning term as predictor variables showed the higher precision of the fitting. The results indicate that site index is positively correlated with basal area growth. And the thinning term was found to be useful to increase precision of the model.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.6
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• pp.1380-1386
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• 2015

Recently, the importance of users' geographic location information has been highlighted with a rapid increase of online social network services. In this paper, by utilizing geo-tagged tweets that provides high-precision location information of users, we first identify both Twitter users' exact location and the corresponding timestamp when the tweet was sent. Then, we analyze a relationship between the tweet frequency and the average user velocity. Specifically, we introduce a tweet-frequency computing algorithm, and show analysis results by country and by city. As a main result, it is shown that the tweet frequency according to user velocity follows a power-law distribution (i.e., Zipf' distribution or a Pareto distribution). In addition, by performing a comparison between the United States and Japan, one can see that the exponent of the distribution in Japan is smaller than that in the United States.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.9 no.6
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• pp.591-598
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• 2016

For the mobile healthcare environment, it is important to measure the exact biomedical signals in real time, and another key point is to design mobile healthcare devices with low power consumption. In this paper, we propose a method in which the piezo film sensor(PFS), having a low power characteristic, is used to measure the pulse signal synchronized with the heart rate from the radial artery. The critical issue in the bio-signal processing is the existence of the motion artifacts. To dissolve this problem, we have applied the periodic moving average filter using the quasi-periodicity of the pulse signal in addition to the conventional method of the adaptive filtering using the reference signal. Results of simulation and experiments are presented to confirm that the quasi-periodicity of the PFS signal can be used to eliminate completely the motion artifacts which still appears after the adaptive filtering.

• Journal of Korea Multimedia Society
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• v.10 no.3
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• pp.348-357
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• 2007

One of the major issues in recent researches on wireless sensor networks is to reduce energy consumption of sensor nodes operating with limited battery power, in order to lengthen their lifespan. Among the researches, we are interested in the schemes in which a sensor node periodically turns on and off its radio and requires information on the time when its neighbors will wake up (or turn on). Clock synchronization is essential for wakeup scheduling in such schemes. This paper proposes three methods based on the asynchronous averaging algorithm for clock synchronization in sensor nodes which periodically wake up: (1) a fast clock synchronization method during an initial network construction period, (2) a periodic clock synchronization method for saving energy consumption, and (3) a decision method for switching the operation mode of sensor nodes between the two clock synchronization methods. Through simulation, we analyze maximum clock difference and the number of messages required for clock synchronization.

• Fire Science and Engineering
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• v.32 no.4
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• pp.35-41
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• 2018

The purpose of study intends to investigate effects of repetitive work and workload for body while wearing firefighting protective clothing in hot conditions and to provide the basic data for the safety of firefighter. The experimental temperature is WBGT $30^{\circ}C$ and the work intensity is 3, 9 METs. The experiment is processed 15 minutes (Ex1), 15 minutes rest (Rest), 15 minutes (Ex2) in order of time. A comparative experiment was carried out for firefighting school students(9 persons; $24.3{\pm}0.71$ years old) wearing firefighting protective clothing. When workload is increased from 3 METs to 9 METs, mean skin temperature change (33.3%), tympanic temperature change (242.9%), heart rate (36.2%), respiration rate (53.9%), RPE (81.6%), thermal Sensation (20.8%), weight loss (60.0%), glucose (-4.4%), lactate (41.7%) are statistically significantly higher. As a result, it is considered that repetitive work and workload have a strong effect on the body when wearing firefighting protective clothing in hot conditions.

• Korean Journal of Environment and Ecology
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• v.29 no.6
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• pp.947-951
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• 2015

This study presents proper irrigation interval for the soil condition of green roof system and the smooth growth of the landscaping herbaceous plants available and reveal the need for irrigation in rooftop conditions. Twenty kinds of greenery plants are tested on ground paved wood panels where rain and wind shielder is installed. Before test, irrigation is conducted fully to experimental plants and then soil moisture in pot is measured after every ten minutes. In conclusion, it is suggested that the irrigation has to be carried out every 4~5 days in order to minimize water and heat stress of plants. Also, irrigation management is an essential prerequisite for good condition and the smooth growth of plants and environmental effects in green roof system.

• Journal of Korea Water Resources Association
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• v.47 no.1
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• pp.37-47
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• 2014

This study examines the processes and the behaviour characteristics of forcing bars in channels with periodic variable width in the alternate and braided regimes by using a two dimensional numerical model. The wavelength and the migration speed decrease as the amplitude of variable width increases. The forcing effects of the width variation on the alternate bars is stronger than those on the braided bars. The bar migration speed increases as the dimensionless amplitude in the braided regime is 0.25. However, the migration speed is abruptly decreased as the amplitude in it was larger than 0.25. The bar migration speed increases in the alternates bar regime as the dimensionless wavelength increases. However, the migration speed decreases around 1 of the wavelength. As the bar wavelength and the variable width wavelength coincide, the bars don't migrate downstream by the strong forcing effects on the bars due to the suppression by the width variation.

• Journal of KIISE:Databases
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• v.31 no.4
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• pp.422-431
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• 2004

In recent years, different models in data delivery have been explored in mobile computing systems. Particularly, there were a lot of research efforts in the periodic push model where the server repetitively disseminates information without explicit request. However, average waiting time per data operation highly depends on the length of a broadcast cycle and different access pattern among clients may deteriorate the response time considerably. In this case, clients are preferably willing to send a data request to the server explicitly through backchannel in order to obtain optimal response time. We call the broadcast model supporting backchannel as hybrid broadcast. In this paper, we devise a new transaction processing algorithm(O-PreH) in hybrid broadcast environments. The data objects which the server maintains are divided into Push_Data for periodic broadcasting and Pull_Data for on-demand processing. Clients tune in broadcast channel or demand the data of interests according to the data type. Periodic invalidation reports from the server support maintaining transactional consistency. If one or more conflicts are found, conflict orders are determined not to violate the consistency(pre-reordering) and then the remaining operations have to be executed pessimistically. Through extensive simulations, we demonstrate the improved throughput of the proposed algorithm.