• Journal of the Korean Society for Precision Engineering
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• v.10 no.3
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• pp.31-40
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• 1993

The vibration-proof material normally used in structural components of precision machinery or measuring instruments requires higher damping in vibration and better characteristics in dimensional stability and rigidity to accomplish the quality assurance of the products. In this study the ferrite-resin material, which is the mixture of epoxy resin and the oxidized steel (Fe$_{3}$O$_{4}$: ferrite) in consideration of characteristics of aggregator and binder, is developed and investigated as one of vibration-proof materials. Four kinds of composite plates for experiments are made by adding another filler materials such as steel powder, granite powder and carbon-fiber sheet to the basic ferrite-resin matrix. Their characteristics are compared with a cast iron specimen which has the same bending rigidity as other specimens. The ferrite-resin material gives the best damping effect in the motor-induced vibration test. Therefore, the material can be applied to the manufacturing industry for vibration damping of machine elements.

• Communications of Mathematical Education
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• v.22 no.4
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• pp.471-487
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• 2008

Inventive mathematical thinking, original mathematical problem solving ability, mathematical invention and so on are core concepts, which must be emphasized in all branches of mathematical education. In particular, Polya(1981) insisted that inventive thinking must be emphasized in a suitable level of university mathematical courses. In this paper, the author considered two cases of inventive problem solving ability shown by his many students via real analysis courses. The first case is about the proof of the problem "what is the derived set of the integers Z?" Nearly all books on mathematical analysis sent the question without the proof but some books said that the answer is "empty". Only one book written by Noh, Y. S.(2006) showed the proof by using the definition of accumulation points. But the proof process has some mistakes. But our student Kang, D. S. showed the perfect proof by using The Completeness Axiom, which is very useful in mathematical analysis. The second case is to show the infinite countability of NxN, which is shown by informal proof in many mathematical analysis books with formal proofs. Some students who argued the informal proof as an unreasonable proof were asked to join with us in finding the one-to-one correspondences between NxN and N. Many students worked hard and find two singled-valued mappings and one set-valued mapping covering eight diagrams in the paper. The problems are not easy and the proofs are a little complicated. All the proofs shown in this paper are original and right, so the proofs are deserving of inventive mathematical thoughts, original mathematical problem solving abilities and mathematical inventions. From the inventive proofs of his students, the author confirmed that any students can develope their mathematical abilities by their professors' encouragements.

• Fire Science and Engineering
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• v.24 no.1
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• pp.95-102
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• 2010

The combustion characteristics of roof 'Jucsim' structure was analysed using real scale fire test on wooden structure heritage building. the fire test model was made to consider roof timberling internal structure for a Sunglemun. Structure of test body layed lime, soil, 'Jucsin' and ceiling board excepting roof tile to find heat propagation process by setting thermocouples. The first test to find fire growth and heat propagation process in the part of ceiling. The second test organized to find the efficiency of fire proof paint between ceiling board and inside of Jucsim structure. The third test try to get the performance level of fire proof fabric with the same manner. The result showed from the test proof the heavy smoke exposure with limited effect of fire proof paint however, reliable fire resistance effect showed in case of fire proof fabric.

• The Journal of Bigdata
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• v.7 no.1
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• pp.1-14
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• 2022

The proof-of-work consensus algorithm used by most blockchains is causing a massive waste of computing resources in the form of mining. A useful proof-of-work consensus algorithm has been studied to reduce the waste of computing resources in proof-of-work, but there are still resource waste and mining centralization problems when creating blocks. In this paper, the problem of resource waste in block generation was solved by replacing the relatively inefficient computation process for block generation with distributed artificial intelligence model learning. In addition, by providing fair rewards to nodes participating in the learning process, nodes with weak computing power were motivated to participate, and performance similar to the existing centralized AI learning method was maintained. To show the validity of the proposed methodology, we implemented a blockchain network capable of distributed AI learning and experimented with reward distribution through resource verification, and compared the results of the existing centralized learning method and the blockchain distributed AI learning method. In addition, as a future study, the thesis was concluded by suggesting problems and development directions that may occur when expanding the blockchain main network and artificial intelligence model.

• Journal of the Korean Society of Safety
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• v.35 no.1
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• pp.1-11
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• 2020

Article 325 (Prevention of Fire Explosion due to Electrostatic) of the Rule for Occupational Safety and Health Standard specifies that in order to prevent the risk of disasters caused by static electricity, fire, explosion and static electricity in the production process, However, in order to do this, it is absolutely necessary to use a pre-detection technology and a detector for antistatic discharge prediction, which is a precautionary measure by static electricity in a fire / explosion hazard place, but in Korea, And there is no technical standard for the application of the technology of the explosion proof structure of the related equipment. Research methods include domestic and overseas electrostatic discharge detection technology and literature investigation of related equipment explosion proofing technology, domestic and foreign electrostatic discharge detection device production and use situation investigation, advanced foreign technology data analysis and benchmarking. In particular, we sought to verify the results of empirical experiments using electrostatic discharge detection technology through sample purchase and analysis of related major products, development of optimization technology through prototype production, evaluation, and supplementation, and expert knowledge through expert consultation. The results of this study were developed and fabricated two prototypes of electrostatic discharge detector based on the technology / standard related to electrostatic discharge detection technology in Korea and abroad through development of electrostatic discharge detection technology and development and production of detector. In addition, based on the development of electrostatic discharge detection technology, we developed an intrinsic safety explosion proof ib class explosion proof technology applicable to the process of using and handling flammable gas and flammable liquid vapor and combustible dust. In the case of the over voltage and minimum voltage are supplied to the explosion-proof structure ESD detector, check the state of the circuit and the transient and transient currents generated by the coil and capacitor elements during the input and standby of the signal pulse voltage. Explosion-proof equipment-Part 11: Intrinsically safe explosion proof structure The comparative evaluation with the reference curve in Annex A of "i" confirms that the characteristics of the intrinsically safe explosion protection structure are met.

• Journal of Educational Research in Mathematics
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• v.24 no.3
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• pp.359-374
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• 2014

Students' difficulties and errors in relation to mathematical proofs are worth while to say one of the dilemmas in mathematics education. The potential elements of their difficulty are scattered over the process of proving in geometry as well as algebra. This study aims to investigate whether middle school students understand the context of algebraic proof including literal expressions. We applied 24 third-grade middle school students a test item which shows a proof including a literal expression and missing the conclusion. Over the half of them responded wrong answers based on only the literal expression without considering its context. Three of them were interviewed individually to show their thinking. As a result, we could find some characteristics of their thinking including the perspective on proof as checking the validity of algebraic expression and the gap between proving and understanding of proof etc. From these, we also discussed about several didactical implications.

• The Journal of the Korea Contents Association
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• v.19 no.9
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• pp.637-645
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• 2019

The RFID group proof is an extension of the yoking proof proving that multiple tags are scanned by a reader simultaneously. Existing group proof schemes provide only delayed tag loss detection which detects loss of tag response in a verification phase. However, delayed tag loss detection is not suitable for real-time applications where tag loss must be detected immediately. In this study, I propose a tag response loss detection scheme which detects loss of tag response in the proof generation process quickly. In the proposed scheme, the tag responds with the sequence number assigned to the tag group, and the reader detects the loss of the tag response through the sequence number. Through an experiment for indistinguishability, I show that the sequence number is secure against an analyzing message attack to distinguish between specific tags and tag groups. In terms of efficiency, the proposed scheme requires fewer transmissions and database operations than existing techniques to determine which tags response is lost.

• School Mathematics
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• v.14 no.4
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• pp.469-493
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• 2012

The purpose of this study is find the relation between students' concept and types of proof construction. For this, four undergraduate students majored in mathematics education were evaluated to examine how they understand mathematical concepts and apply their concepts to their proving. Investigating students' proof with their concepts would be important to find implications for how students have to understand formal concepts to success in proving. The participants' proof productions were classified into syntactic proof productions and semantic proof productions. By comparing syntactic provers and semantic provers, we could reveal that the approaches to find idea for proof were different for two groups. The syntactic provers utilized procedural knowledges which had been accumulated from their proving experiences. On the other hand, the semantic provers made use of their concept images to understand why the given statements were true and to get a key idea for proof during this process. The distinctions of approaches to proving between two groups were related to students' concepts. Both two types of provers had accurate formal concepts. But the syntactic provers also knew how they applied formal concepts in proving. On the other hand, the semantic provers had concept images which contained the details and meaning of formal concept well. So they were able to use their concept images to get an idea of proving and to express their idea in formal mathematical language. This study leads us to two suggestions for helping students prove. First, undergraduate students should develop their concept images which contain meanings and details of formal concepts in order to produce a meaningful proof. Second, formal concepts with procedural knowledge could be essential to develop informal reasoning into mathematical proof.

• Journal of the Korean Society of Safety
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• v.21 no.3 s.75
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• pp.22-30
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• 2006

On this study, we developed the electrostatic eliminator for charged particles in manufacturing process. The characteristics of the electrostatic eliminator were investigated, which is two kinds. The first one is Electrical Corona Discharged Type Ionizer. The second one is Photo Ionizer in using soft X-ray. From the experiment, we have obtained the following results. In case of Electrical Corona Discharged Ionizer, neutralization efficiency of charged particles were approximately saturated to 98% over 6.0kV, but as it is non-explosion proof, can not be used in flammable particle treatment process. While in case of photo Ionizer in using soft X-Ray, neutralization efficiency of charged particles were approximately 95%, and more its structure is explosion proof, could be used in flammable particle treatment process.

• Journal of Korea Society of Digital Industry and Information Management
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• v.4 no.2
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• pp.57-66
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• 2008

There have been proposed various copyright protection protocols in network-based digital multimedia distribution framework. However, most of conventional copyright protection protocols are focused on the stability of copyright information embedding/extracting and the access control to data suitable for user's authority but overlooked the privacy of copyright owner and user in authentication process of copyright and access information. In this paper, we propose a solution that builds a privacy-preserving proof of copyright ownership of digital contents in conjunction with keyword search scheme. The appeal of our proposal is three-fold: (1) content providers maintain stable copyright ownership in the distribution of digital contents; (2) the proof process of digital contents ownership is very secure in the view of preserving privacy; (3) the proposed protocol is the copyright protection protocol added by indexing process but is balanced privacy and efficiency concerns for its practical use.