• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권2호
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• pp.901-923
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• 2017

Efficient key distribution and management mechanisms as well as lightweight ciphers are the main pillar for establishing secure wireless sensor networks (WSN). Several symmetric based key distribution protocols are already proposed, but most of them are not scalable, yet vulnerable to a small number of compromised nodes. In this paper, we propose an efficient and scalable key management and distribution framework, named KMMR, for large scale WSNs. The KMMR contributions are three fold. First, it performs lightweight local processes orchestrated into upward and downward tiers. Second, it limits the impact of compromised nodes to only local links. Third, KMMR performs efficient secure node addition and revocation. The security analysis shows that KMMR withstands several known attacks. We implemented KMMR using the NesC language and experimented on Telosb motes. Performance evaluation using the TOSSIM simulator shows that KMMR is scalable, provides an excellent key connectivity and allows a good resilience, yet it ensures both forward and backward secrecy. For a WSN comprising 961 sensor nodes monitoring a 60 hectares agriculture field, KMMR requires around 2.5 seconds to distribute all necessary keys, and attains a key connectivity above 96% and a resilience approaching 100%. Quantitative comparisons to earlier work show that KMMR is more efficient in terms of computational complexity, required storage space and communication overhead.

• 한국물환경학회지
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• 제31권4호
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• pp.418-427
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• 2015

This study was carried out to evaluate the performance of a lab-scale novel septic tank system for improving the conventional septic tank in the developing countries of water shortages. The lab-scale novel septic tank system consists of sepetic tank, aeration tank with HBC-ring, and sand filter. Optimum HRT was reguired about 1.5days to get a total COD removal efficiency of 90%, COD, BOD and SS removal efficiency was about 70%, 60%, and 85% in sepetic tank only. The structure of sepetic tank with two stages results in the high removal efficiency of organic matter. When sepetic tank, aeration tank, and sand filter were more than HRT 1.5days, 18hrs, and 12hrs, respectively, final effluent was less than 20 mg/L of BOD, 14 mg/L of SS, so that there is a high potential of its use for reusing water in flush toilet. There is no significant effect of HRT change on nutrient removal. Total nitrogen removal efficiency was about 40%, final effluent was 30~40 mg/L of TN, total phosphorus removal efficiency was about 11~25%, final effluent was 9~12 mg/L of TP. Because there is very small amounts of organic nitrogen and phosphorus in effluent, it was possible to reuse water for agricultural use.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.1455-1471
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• 2009

In order to investigate on the effect of stabilization methods for rice paddies contaminated by heavy metals, a series of lab-scale model test was carried out by applying the characteristics of submerged Paddy soil. To perform the lab-scale model test, columns were made by acrylic with the dimension of diameter=10cm, thickness=0.5cm and were filled with soils which was contaminated were mixed with stabilization agents(lime stone 5% and steel refining slag 5% respectively). To manipulate the reduction condition, soils in the columns were submerged with distilled water. And then soil water and subsurface water in each column were sampled in the regular term and analysed the various physical and chemical properties.

• 자원리싸이클링
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• 제26권3호
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• pp.69-78
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• 2017

최근 국내 자동차부품 및 전자기기 산업에서 마그네슘 금속의 수요가 증가하고 있다. 마그네슘 제련은 크게 용융염전해법과 열환원법 두 가지로 대별할 수 있는데, 본 고에서는 마그네슘 금속 제련에 관하여 원료 광석인 마그네사이트로부터 무수염화마그네슘 제조를 거쳐 용융염전해법에 의한 금속 마그네슘 제조까지 실험실 규모로 전해 마그네슘을 제조한 내용을 요약 보고하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.386-392
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• 2010

상용 전산유체해석 프로그램을 사용하여 오리피스형 분사기에서 수직분사 액체 제트의 다상유동을 해석하였다. 본 연구의 목적은 오리피스형 분사기 분무 특성을 이해하고 연소기 내부 위치에 따른 유동조건와 항력계수와의 관계식을 구하는 것이다. 수치해석 결과 모형 램젯 연소기에서 수직분사 유동해석은 난류점성모델인 Realizable $k-{\varepsilon}$ 모델과 다상유동모델인 DPM 모델이 유효함을 확인하였다. 또한 오리피스형 분사기에서 레이저 흡수법을 사용하여 측정한 실험결과(증기농도분포)는 수치해석 결과와 잘 일치하였다.

• 대한기계학회논문집B
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• 제32권8호
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• pp.574-581
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• 2008

The characteristics of combustion and flow for a lean premixed flame in lab-scale gas turbine combustor was studied through experiment and numerical analysis. From the experiment, flame structure and heat release rate were obtained from OH emission spectroscopy. Qualitative comparisons were made line-integrated OH chemiluminescence image and abel-transformed one. NOx analyzer was implemented to get the characteristic of NOx exhaust from the combustor. From the numerical analysis, the thermal distribution and characteristic of recirculation zone with the change of fuel-air mixing degree, the characteristic of methane distribution with equivalence ratio in the combustor respectively. Total heat release rate is increased with increasing equivalence ratio. Thermal Nox is reduced with increasing fuel-air mixing degree. Increasing equivalence ratio results in the decrease of the size of reaction zone and alteration of the position of the reaction zone into the entrance of the combustor.

• Structural Engineering and Mechanics
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• 제31권4호
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• pp.439-451
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• 2009

The paper deals with the problem related to the modelling of riveted assemblies for crashworthiness analysis of full-scale complete aircraft structures. Comparisons between experiments and standard FE computations on high-energy accidental situations onto aluminium riveted panels show that macroscopic plastic strains are not sufficiently localised in the FE shells connected to rivet elements. The main reason is related to the structural embrittlement caused by holes, which are currently not modelled. Consequently, standard displacement FE models do not succeed in initialising and propagating the rupture in sheet metal plates and along rivet rows as observed in the experiments. However, the literature survey show that it is possible to formulate super-elements featuring defects that both give accurate singular strain fields and are compatible with standard displacement finite elements. These super-elements can be related to the displacement model of the hybrid-Trefftz principle of the finite element method, which is a kind of domain decomposition method. A feature of hybrid-Trefftz finite elements is that they are mainly used for elastic computations. It is thus proposed to investigate the possibility of formulating a hybrid displacement finite element, including the effects of a hole, dedicated to crashworthiness analysis of full-scale aeronautic structures.

• 상하수도학회지
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• 제20권2호
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• pp.273-280
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• 2006

The sludge settleability is a key factor for operating activated sludge process as well as BNR (biological nutrient removal) process, because the poor sludge settling causes an increase of suspended solid in the effluent. In order to improving the sludge settleability, a settling agent such as iron dust can be applied. In this study, the effect of sludge settleability on the performance of DNR (Daewoo nutrient removal) process was investigated with GPS-X, which is the popular wastewater treatment process model program, and the result of modeling was verified with operating lab-scale DNR process. As a result, if the sludge blanket keeps stable in the secondary settling tank, the effluent quality is similar in spite of different SVI values. And in case of the good sludge settleability, short HRT or long SRT increased the biomass concentration in the bioreactor, and improved the pollutant removal efficiency. In spite of daily influent changing, the good sludge settleability also guaranteed the stable effluent quality. And the results of the lab-scale DNR process experiment could support the simulated results.

• Journal of the Korean Wood Science and Technology
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• 제43권2호
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• pp.186-195
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• 2015

This study aims at modeling the rotary drying of wood chips in co-current mode and estimating the drying time of larch (Larix kaemferi) wood chip. Drying data were obtained in a lab. scale fixed bed dryer operating with an air velocity of 1 m/sec. and at hot air inlet temperatures of $100^{\circ}C$, $200^{\circ}C$, and $300^{\circ}C$. The lab. scale fixed-bed drying rates for small, medium and large size larch wood chips that had been dried from 40% wet-based moisture content (MC) to 10% MC at $200^{\circ}C$ drying temperature were 17.3 %/min., 10.2 %/min. and 5.5 %/min., respectively. It was predicted that larch large size wood chips could be dried from 40% MC to 10% MC in about 23.0, 34.6, and 44.7 minutes at $300^{\circ}C$, $200^{\circ}C$ and $150^{\circ}C$, respectively. Expected drying times for medium size chips were about 8.6, 11.2 and 13.2 minutes and those for small size chips were 4.3, 5.5 and 6.4 minutes, respectively.

• 한국정밀공학회지
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• 제17권8호
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• pp.165-171
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• 2000

In this study the 4-way spool valve characteristics are clearly defined and clearly defined and proposed new type of spool valve. This paper presents governing equations of the flow through clearances between sleeve and spool as a model of orifice flow for null characteristics analysis and programmed analysis software of it. This software is possible to basically analysis that not only which case of open center closed center or critical center but _ -displacement of spool lab position boundary region and spool opening of the valve and to estimate the pressure variation in the spool and external leak flow variation. We are convinced that the scale of load pressure difference is changed as lab condition of valve and this scale is changed with boundary point on the annular clearance. It is vary useful to designer and user of spool valve with this design data and analysis software.