• 한국안전학회지
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• 제36권3호
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• pp.50-59
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• 2021

The main purpose of accident analysis is to identify the causal factors and the mechanisms of those factors leading to the accident. However, current accident analysis techniques focus only on finding the factors related to the accident without providing more insightful results, such as structures or mechanisms. For this reason, preventive actions for safety management are concentrated on the elimination of causal factors rather than blocking the connection or chain of accident processes. This greatly reduces the effectiveness of safety management in practice. In the present study, a technique to model the correlational structure of accident risk factors is proposed by using the co-occurrence keyword network analysis technique. To investigate the effectiveness of the proposed technique, a case study involving a portable ladder fall accident is conducted. The results indicate that the proposed technique can construct the correlational structure model of the risk factors of a portable ladder fall accident. This proves the effectiveness of the proposed technique in modeling the correlational structure of accident risk factors.

• 한국과학교육학회지
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• 제17권1호
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• pp.45-53
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• 1997

The purpose of this study was to investigate the instructional effects of a problem solving model on students' achievement, science process skills, and perceptions of science activities. The problem solving model was developed on the basis of the SSCS (Search, Solve, Create, Share) problem solving model while considering Korean educational situations under a national curriculum. The model developed is composed of 4 stages; identify, solve, create, and share. In this research, the treatment and control groups (6 classes) were selected from a middle school in Seoul and taught about the separation of mixture for four weeks. Prior to instruction, the Group Assessment of Logical Thinking and the Learning Approach Questionnaire were administered, and their scores were used as covariate and blocking variable, respectively. During instruction, classroom observations for each group were conducted with a researcher-made checklist. Immediately following the instructions, students' achievement, science process skills, and perceptions of science activities were measured by a researcher-made achievement test, the Middle Grades Integrated Science Process Skills Test(MIPT), and the Perceptions of Science Activities Questionnaire, respectively. The results indicated that students in the treatment group achieved significantly better than those in the control group. Although students in the treatment group were found to use more science process skills correctly during their science activities, the MIPT scores of the treatment group were not significantly higher than those of the control group. No interaction with students' learning approach was found for both students' achievement and science process skills. On the questionnaire of students' perceptions of science activities, the treatment group showed more positive perceptions and interest than the control group. Educational implications are discussed.

• Geomechanics and Engineering
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• 제14권5호
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• pp.467-477
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• 2018

Estimation of hydraulic parameters is a critical step during design of foundation dewatering works. When many piles are installed in an aquifer, estimation of the hydraulic conductivity should consider the blocking of groundwater seepage by the piles. Based on field observations during a dewatering project in Shanghai, hydraulic conductivities are back-calculated using a numerical model considering the actual position of each pile. However, it is difficult to apply the aforementioned model directly in field due to requirement to input each pile geometry into the model. To develop a simple numerical model and find the optimal hydraulic conductivity, three scenarios are examined, in which the soil mass containing the piles is considered to be a uniform porous media. In these three scenarios, different sub-regions with different hydraulic conductivities, based on either automatic inverted calculation, or on effective medium theory (EMT), are established. The results indicate that the error, in the case which determines the hydraulic conductivity based on EMT, is less than that determined in the automatic inversion case. With the application of EMT, only the hydraulic conductivity of the soil outside the pit should be inverted. The soil inside the pit with its piles is divided into sub-regions with different hydraulic conductivities, and the hydraulic conductivity is calculated according to the volume ratio of the piles. Thus, the use of EMT in numerical modelling makes it easier to consider the effect of piles installed in an aquifer.

• 대기
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• 제24권1호
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• pp.17-27
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• 2014

In this study, the observational environment for sunshine duration at Seoul and Daegu Automated Synoptic Observing Systems (ASOSs) was analyzed using a numerical model. In order to analyze the effects of topography and buildings on observational environment for sunshine duration, the model domains including the elevated building and mountainous areas around Seoul and Daegu ASOSs were considered. Three dimensional topography and buildings used as input data for the numerical model were constructed using a geographic information system (GIS) data. Solar azimuth and altitude angles calculated for the analysis period (one-week for each season in 2008) in this study were validated against those by Korea Astronomy and Space Science Institute (KASI). The starting and ending times of sunshine duration observed at ASOSs largely differed from the respective sunrise and sunset times simply calculated using solar angles and information of ASOSs' latitude and longitude, because uneven topography and elevated buildings around ASOSs cut off sunshine duration right after the sunrise and right before the sunset. The model produced the sunshine indices for Seoul and Daegu ASOSs with the time interval of one minute and the period of one week for each season and we compared the hourly averaged indices with those observed at the ASOSs. One week of which the cloudiness is lowest for each season is selected for analysis. Not only the adjacent buildings but also distant buildings and mountain cut off sunshine duration right after the sunrise and right before the sunset. The buildings and topography cutting off sunshine duration were found for each analyzing date. It was suggested that, in order to evaluate the observational environment for sunshine duration, we need to consider even the information of topography and/or building far away from ASOSs. This study also showed that the analyzing method considering the GIS data is very useful for evaluation of observational environment for sunshine duration.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권9호
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• pp.2073-2085
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• 2012

Recently, the International Telecommunication Union allocated the 470-862 MHz band to the digital broadcasting (DB) service. Moreover, the 790-862 MHz sub-band will be allocated to the next-generation mobile system, known as the International Mobile Telecommunication - Advanced (IMT-A), and to the DB on a co-primary basis in the year 2015. Currently, two candidate technologies are available to represent the IMT-A system; the Mobile WiMAX and Long Term Evolution - Advanced (LTE-A). One of the main criteria of the IMT-A candidate is to not cause additional interference to the primary service (i.e., DB). In this paper, we address the spectrum sharing issue between the IMT-A candidates and the DB service. More precisely, we investigate the interference effect between the DB service and the mobile network, which could be either LTE-A or WiMAX. Our study proposes a spectrum sharing model to take into account the impact of interference and evaluates the spectrum sharing requirements such as frequency separation and separation distance. This model considers three spectrum sharing scenarios: co-channel, zero guard band, and adjacent channel. A statistical analysis is performed, by considering the interferer spectrum emission mask and victim receiver blocking techniques. The interference-to-noise ratio is used as an essential spectrum sharing criterion between the systems. The model considers the random distribution of the users, antenna heights, and the bandwidth effect as well as the deployment environment in order to achieve spectrum sharing. The results show that LTE-A is preferable to WiMAX in terms of having less interference impact on DB; this can eventually allow the operation of both services without performance degradation and thus will lead to efficient utilization of the radio spectrum.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제2권2호
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• pp.63-81
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• 2008

WiMAX has been introduced as a competitive alternative for metropolitan broadband wireless access technologies. It is connection oriented and it can provide very high data rates, large service coverage, and flexible quality of services (QoS). Due to the large number of connections and flexible QoS supported by WiMAX, the uplink access in WiMAX networks is very challenging since the medium access control (MAC) protocol must efficiently manage the bandwidth and related channel allocations. In this paper, we propose and investigate a cost-effective WiMAX bandwidth management scheme, named the WiMAX partial sharing scheme (WPSS), in order to provide good QoS while achieving better bandwidth utilization and network throughput. The proposed bandwidth management scheme is compared with a simple but inefficient scheme, named the WiMAX complete sharing scheme (WCPS). A maximum entropy (ME) based analytical model (MEAM) is proposed for the performance evaluation of the two bandwidth management schemes. The reason for using MEAM for the performance evaluation is that MEAM can efficiently model a large-scale system in which the number of stations or connections is generally very high, while the traditional simulation and analytical (e.g., Markov models) approaches cannot perform well due to the high computation complexity. We model the bandwidth management scheme as a queuing network model (QNM) that consists of interacting multiclass queues for different service classes. Closed form expressions for the state and blocking probability distributions are derived for those schemes. Simulation results verify the MEAM numerical results and show that WPSS can significantly improve the network’s performance compared to WCPS.

• 한국정보처리학회논문지
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• 제6권4호
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• pp.1058-1070
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• 1999

이 논문은 이동통신 시스템의 제어국에 순간적으로 가해지는 다량의 입력 메시지에 대하여 효율적이고 신뢰성 있는 제어를 위하여 입력 메시지를 메시지 특성에 따라 분리한 다음 다중 프로세서를 사용하여 제어하는 모델을 제안한다. 제안 모델의 성능 개선에 필요한 요소들의 특성을 사전에 파악하기 위하여 M/M/c/K 큐잉 모델을 이용한다. 이 결과를 토대로 SLAM II를 이용한 시뮬레이션에 의해 입력 메시지에 대한 손실확률, 큐의 평균점유 길이의 분포, 프로세서 관리기(서버)의 점유율, 큐에서의 평균 대기 시간에 대하여 제안 모델과 기존 모델의 성능을 비교한다. 또한 과도한 입력 메시지로 인하여 과부하가 발생할 경우 두 입력 메시지에 대한 부하 제어 기능을 추가한 모델을 제안하고, 시뮬레이션에 의해 성능을 분석한다.

• 상하수도학회지
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• 제35권6호
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• pp.425-436
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• 2021

In this study, chemically enhanced steam cleaning(CESC) was applied as a novel and efficient method for the control of organic and inorganic fouling in ceramic membrane filtration. The constant filtration regression model and the resistance in series model(RISM) were used to investigate the membrane fouling mechanisms. For total filtration, the coefficient of determination(R²) with an approximate value of 1 was obtained in the intermediate blocking model which is considered as the dominant contamination mechanism. In addition, most of the coefficient values showed similar values and this means that the complex fouling was formed during the filtration period. In the RISM, R _c/R _f increased about 4.37 times in chemically enhanced steam cleaning compared to physical backwashing, which implies that the internal fouling resistance was converted to cake layer resistance, so that the membrane fouling hardly to be removed by physical backwashing could be efficiently removed by chemically enhanced steam cleaning. The results of flux recovery rate showed that high-temperature steam may loosen the structure of the membrane cake layer due to the increase in diffusivity and solubility of chemicals and finally enhance the cleaning effect. As a consequence, it is expected that chemically enhanced steam cleaning can drastically improve the efficiency of membrane filtration process when the characteristics of the foulant are identified.

• 한국HCI학회:학술대회논문집
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• 한국HCI학회 2008년도 학술대회 2부
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• pp.158-164
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• 2008

본 논문은 모바일폰의 사용성 연구에 있어서 모바일폰의 사용 특성을 충분히 반영할 수 있도록 추후 연구를 돕기 위한 목적으로 진행되었다. 모바일폰의 사용 특성은 무엇보다 컨텍스의 영향에 매우 민감하다는 것과, 1인 1디바이스로서 개인적인 라이프 패턴을 많은 부분 수용한다는 것이다. 이러한 전제로부터 모바일폰이 사용되는 컨텍스트를 정의하였다. 특별히 컨텍스트의 정의에 있어서 상황적 컨텍스트(situational context)라는 정의를 도입하였으며, 모바일폰으로 할 수 있는 다양한 task 중 특별히 situational context의 영향을 직접적으로 받는 task를 contextual task로 이름하였다. 연구 결과물로써 contextual task의 모델을 제작하였다. 이는 디자인 종사자들과 타 업계의 종사자들이 모두 사용자의 실제적 행태를 이해할 수 있도록 하여 동일한 컨셉을 가지고 사용자 중심의 디자인을 진행할 수 있도록 한다. 또한, 이러한 사용자 사용 행태에 대한 통일한 컨셉은 디자인을 위한 서로의 의사전당에도 효과적일 젓이다. 수집된 사용자 task 들은 3가지 모델로 그 패턴을 정의할 수 있다. 사용자의 공간 확장과 관련되어 다양한 패턴을 구조화한 Extend Model, 기능의 컨버전스로 인해서 각 기능의 충돌을 최소화하여 사용성을 높일 수 있는 기회를 제공하기 위해 이와 관련된 task 들의 패턴을 구조화한 Synchronize Model, 마지막으로 사용자의 라이프 패턴을 반영하여 기존의 object를 대체하는 결과를 가져오는 task들의 패턴을 구조화한 Replace Model 로 Contextual Task를 정의하였다. 마지막으로 각 모델의 구체적 용도를 보이기 위해 Context 를 반영한 Interview 를 시행할 수 있는 질문지 제작을 진행하였다.

• Spatial Information Research
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• 제21권3호
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• pp.45-53
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• 2013

웹GIS는 수년 동안 사용자들에게 효율적이고 정확한 공간정보를 제공하기 위해 최신 웹기술을 기반으로 발전해왔다. 또한 웹GIS 서버는 클라이언트의 요청을 빠르게 연산 처리하고 공간정보 서비스를 제공하기 위해 성능개선을 지속해왔다. 본 연구에서는 서버 개발에 자바스크립트(JavaScript)를 사용하는 이벤트 기반의 비동기식 I/O 처리가 가능한 프레임웍 기술인 Node.js를 활용하여 NodeMap이라고 이름붙인 웹GIS 서버를 설계하고 구현하였다. NodeMap은 기본적으로 OGC 표준 인터페이스를 지원하는 웹GIS 서버이다. 이를 위해 공간 인덱스 및 표준 공간쿼리 함수를 지원하는 DBMS를 활용하여 GIS 데이터를 처리하도록 하였다. 그리고 공간 정보를 타일 맵 위에 렌더링 하기 위해 HTML5 Canvas를 지원하는 Node-Canvas 모듈을 활용하였다. 마지막으로 Node.js의 가장 많이 쓰이는 커넥트 모듈 기반의 프레임웍인 Express 모듈을 활용하였다. 구현된 NodeMap은 성능테스트를 통해 향 후 웹GIS 서버개발기술로서 Node.js의 활용 가능성을 확인하였다. 본 연구를 통해 기존 서버 개발 기술과 차별화된 기술인 Node.js를 웹GIS 서버 구현에 우선적용 함으로서 향 후 인터넷 GIS 서비스에서의 활용 가능성을 제시하였다.