• Journal of Educational Research in Mathematics
• /
• v.20 no.3
• /
• pp.275-292
• /
• 2010

In this study, we discussed the way to teach algebra earlier through investigating to research trends of Early Algebra and researching about nature of subject involving algebra. There is a strong view that arithmetic and algebra have analogous forms and that algebra is on extension to arithmetic. Nevertheless, it is also possible to present a perspective that the fundamental goal and role of symbols and letters are difference between arithmetic and algebra. And, we could recognize that geometry was starting point of algebra trough historical perspectives. To consider these, we extracted some of possible directions to approaches to teach algebra earlier. To access to teaching algebra earlier, following ways are possible. (1) To consider informal strategy of young children. (2) Arithmetic reasoning considered of the algebraic relation. (3) Starting to algebraic reasoning in the context of geometrical problem situation. (4) To present young students to tool of letters and formular.

• School Mathematics
• /
• v.14 no.4
• /
• pp.445-468
• /
• 2012

This study is tried in order to link informal arithmetic reasoning to formal algebraic reasoning. In this study, we investigated elementary school student's non-formal algebraic reasoning used in algebraic problem solving. The result of we investigated algebraic reasoning of 839 students from grade 1 to 6 in two schools, Korea, we could recognize that they used various arithmetic reasoning and pre-formal algebraic reasoning which is the other than that is proposed in the text book in word problem solving related to the linear systems of equation. Reasoning strategies were diverse depending on structure of meaning and operational of problems. And we analyzed the cause of failure of reasoning in algebraic problem solving. Especially, 'quantitative reasoning', 'proportional reasoning' are turned into 'non-formal method of substitution' and 'non-formal method of addition and subtraction'. We discussed possibilities that we are able to connect these pre-formal algebraic reasoning to formal algebraic reasoning.

• Journal of Environmental Policy
• /
• v.14 no.2
• /
• pp.73-99
• /
• 2015

A subsidy policy on early scrapping of old diesel vehicles has been activated to improve air pollution in Seoul metropolitan area. The benefit-cost analysis on this policy evidently shows cost effective as benefit is greater than cost. The policy currently provides 80% of old diesel vehicle's worth within the maximum amount capped which limited the effects on increasing the level of subsidy. Therefore, to induce more old diesel vehicles scrapped, it is needed to consider that the level of subsidy and the maximum amount are raised at the same time. Meanwhile, taking account of insufficient subsidy amount, granting older vehicles more subsidy would be a good way of extending the policy effect.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.18 no.9
• /
• pp.1295-1303
• /
• 1993

We present an 1-out-of-n noninteractive OT(Oblivious Transfer) protocol based on the Diffle-Hellman assumption and a new fair exchange scheme of secret information among multi-users. Using the noninteractive OT protocol and the fair exchange scheme, we also present a new digital multisignature scheme based on Fiat-Shamir signature scheme and analyze its security. Owing to its concurrency, viability, and dishonesty detectablility, the proposed digital multisignature scheme is applicable to electronic multi-user contract systems.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39B no.1
• /
• pp.29-37
• /
• 2014

In this paper we show that a dynamic ID authentication scheme using smart cards proposed by Tsai et al. is not secure against DoS attack and insider attack. Further we claim that their scheme may raise a security problem when a user changes his/her password. Then we come up with a security-enhanced version only with small additional computational cost. Our scheme is based on the security of cryptographic hash function and the infeasibility assumption of discrete logarithm problem. In addition, we provide details of security and computational cost analysis.

• Journal of the Korean Society of Groundwater Environment
• /
• v.7 no.1
• /
• pp.8-14
• /
• 2000

The present day, interest in low flow statistics has been increased, primarily because of the increase in water demands and the contamination of water quality and the limitation of water resource development and the annual water supply stability. The model for estimating low flow statistics is points of this study chosen catchments in the Youngsan basin. For the purpose of this study. the low-flow discharge at 23 points, where absent gauging station is unmeasured and the data is used for the model. Finally, the regional formula to estimate the low flow statistics at the unmeasured point is proposed.

• 한국신재생에너지학회:학술대회논문집
• /
• 2009.11a
• /
• pp.571-571
• /
• 2009

지열은 날씨와 기온 등에 영향을 받지 않고 연중 가동할 수 있어 기저부하를 담담할 수 있는 유일한 신재생에너지 자원이므로 이에 대한 기술개발이 시급하다. 우리나라는 비화산지대이며 지중 온도가 가장 높은 지역의 5km에서 약 $170^{\circ}C$ 내외이므로 외국에 비해 지온경사도가 크지 않은 편이다. 그리고 3km 이상에서는 지하대수층이 거의 존재하지 않기 때문에 지열발전을 위해서는 EGS 기법을 도입할 수 밖에 없는 실정이다. 그리고 지열수를 확보할 수 있는 온도범위가 약 $100{\sim}150^{\circ}C$ 정도이므로 이에 적합한 지열발전 플랜트를 선정할 필요가 있다. 일반적으로 지열발전에 적용되는 플랜트는 건증기 지열발전, 플래쉬증기 지열발전, 바이너리 사이클 지열발전으로 분류할 수가 있으나 국내 여건에 맞는 방식으로서 바이너리 사이클 발전으로서 ORC 플랜트 또는 Kalina 사이클 플랜트가 적합하므로 이에 대한 기술 개발이 적극적으로 이루어져야 한다. 따라서 국내 지열발전의 기술개발에 있어서 핵심요소는 심부천공 및 EGS를 위한 인공파쇄기술과 지상 플랜트로서 저온지열 발전 플랜트의 기술확보가 필요한 실정이다. 이와 같은 기술개발이 완성되면 발전 뿐만아니라 집단지역난방, 온실 및 양어장 등에도 열공급이 가능한 열병합발전이 가능하게 될 것이다. 또한, EGS 기술로서 상업적 성공을 이룬 것은 세계적으로 2~3개 사례에 불과한 신기술로서, EGS 기술의 국내 조기 실현으로 기술 선점 및 해외 수출을 모색할 필요가 있다. 그리고 심부 지열자원은 국내 어디에나 부존하는 ubiquitous 자원이며 이산화탄소 배출이 전무한 청정 국산 에너지 자원이나, 이의 개발에는 높은 초기 투자비와 risk를 요하므로 민간 업체의 투자가 제약을 받는다. 따라서 정부의 적극적인 지원하에 산.학.연 중심으로 시범보급이 우선 이루어진 후 민간의 자발적 투자를 통한 지열 개발을 유도할 필요가 있다.

• The Journal of Engineering Geology
• /
• v.29 no.1
• /
• pp.51-68
• /
• 2019

This study performs to evaluate adaptability of seashore filtering type seawater-intake which adapts dua1 filter well alternative for direct seawater-intake. This study varies filter condition of seashore free surface aquifer which is composed of sand layer then installs real size dual filter well and single filter well to evaluate water permeability and proper pumping amount according to filter condition. According to result of step aquifer test, it is analysed that 110.3% synergy effect of water permeability coefficient is happened compare to single filter since dual filter well has better improvement. dual filter has higher water permeability coefficient compare to same pumping amount, this means dual filter has more improved water permeability than single filter. According to analysis result of continuous aquifer test, it is evaluated that dual filter well (SD1200) has higher water permeability than single filter well (SS800) by analysis of water permeability coefficient using monitoring well and gauging well, it is also analysed dual filter has 110.7% synergy effect of water permeability coefficient. As a evaluation result of pumping amount according to analysis of water level dropping rate, it is analysed that dual filter well increased 122.8% pumping amount compare to single filter well when water level dropping is 2.0 m. As a result of calculating proper pumping amount using water level dropping rate, it is analysed that dual filter well shows 136.0% higher pumping amount compare to single filter well. It is evaluated that proper pumping amount has 122.8~160% improvement compare to single filter, pumping amount improvement rate is 139.6% compare to averaged single filter. In other words, about 40% water intake efficiency can be improved by just installation of dual filter compare to normal well. Proper pumping amount of dual filter well using inflection point is 2843.3 L/min and it is evaluated that daily seawater intake amount is about $4,100m^3/day$ (${\fallingdotseq}4094.3m^3/day$) in one hole of dual filter well. Since it is possible to intake plenty of water in one hole, higher adaptability is anticipated. In case of intaking seawater using dual filter well, no worries regarding damages on facilities caused by natural disaster such as severe weather or typhoon, improvement of pollution is anticipated due to seashore sand layer acts like filter. Therefore, It can be alternative of environmental issue for existing seawater intake technique, can save maintenance expenses related to installation fee or damages and has excellent adaptability in economic aspect. The result of this study will be utilized as a basic data of site demonstration test for adaptation of riverside filtered water of upcoming dual filter well and this study is also anticipated to present standard of well design and construction related to riverside filter and seashore filter technique.

• The Journal of the Korea Contents Association
• /
• v.20 no.11
• /
• pp.38-48
• /
• 2020

The domestic AI speaker market is growing into a full-fledged early audience market beyond the innovative consumer market with 3 million domestic supply units at the end of 2018, but the reality is that for various reasons, we are not satisfied with the use. There are many previous papers on AI Speaker, but the majority of research so far tends to be biased towards the acceptance of the device's own performance. Many changes are being made, such as OTT providers trying to secure the market through collaboration with AI speaker providers. This study tried to identify the priorities for content services, which can be another major selection factor for AI speakers, excluding the factors of unsatisfactory technology. First, this study identified the priorities among AI speaker selection factors using AHP (Analytic Hierarchy Process), based on the AI speaker selection factors derived through literature research. The most important hierarchical factor are Concierge Service, Education Service, and Entertainment Service order in AI speaker selection, and the primary content among the individual factors was the one that ranked weather/temperature/fine dust (11.6%) and child caring content was in the second place (10.8%), and then music service was in the third place (9.8%). The three top priorities were derived from the items in the top tier 1, 2 and 3 priorities. Of the total 15 individual services, 6 sub-layers of Concierge Service (weather/temperature/fine dust, news, voice schedule notification) and Education Service (foreign language, toddler, reading books) were in the top 8, and two of the Entertainment Service Music service and movie service ranked third and sixth.

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.16 no.4
• /
• pp.359-367
• /
• 2014

Drought index can be used to implement an early warning system for drought and to operate a drought monitoring service. In this study, an approach was examined to determine agricultural drought index (ADI) at high spatial resolution, e.g., 270 m. The value of ADI was calculated based on soil water balance between supply and demand of water. Water supply is calculated by the cumulative effective precipitation with the application of the weight to the precipitation from two months ago. Water demand is derived from the actual evapotranspiration, which was calculated applying a crop coefficient to the reference evapotranspiration. The amount of surface runoff on a given soil type was also used to calculate soil residual moisture. Presence of drought was determined based on the probability distribution in the given area. In order to assess the reliability of this index, the amount of residual moisture, which represents severity of drought, was compared with measurements of soil moisture at three experimental between July 2012 and December 2013. As a result, the ADI had greater correlation with measured soil moisture compared with the standardized precipitation index, which suggested that the ADI would be useful for drought warning services.