• International Journal of Highway Engineering
• /
• v.15 no.4
• /
• pp.65-73
• /
• 2013

PURPOSES : As a research to develop a cement treated base course for an airport pavement which can enhance its drainage, this paper investigated the strength, infiltration performance and durability of the pervious concrete with respect to maximum coarse aggregate sizes and compaction methods. METHODS : This study measured compressive strength, infiltration rate, continuous porosity and freeze-thaw resistance of pervious concrete specimens, which were fabricated with five different compaction methods and different maximum aggregate sizes. In addition, in order to reduce the usage of Portland cement content and to enhance environment-friendliness, a portion of the cement was replaced with Ground Granulated Blast Furnace Slag (GGBS). RESULTS: Compressive strength requirement, 5 MPa at 7 days, was met for all applied compaction methods and aggregate sizes, except for the case of self-compaction. Infiltration rate became increased as the size of aggregate increased. The measured continuous porosities varied with the different compaction methods but the variation was not significant. When GGBS was incorporated, the strength requirement was successfully satisfied and the resistance to freezing-thawing was also superior to the required limit. CONCLUSIONS: The infiltration rate increased as the maximum size of aggregate increased but considering construct ability and supply of course aggregate, its size is recommended to be 25mm. With the suggested mix proportions, the developed pervious concrete is expected to successfully meet requirements for strength, drainage and durability for cement treated base or subbase course of an airport pavement.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.468-468
• /
• 2011

Carbon nanotubes (CNTs) have been considered as one of the promising candidate for next-generation field emitters because of their unique properties, such as high field enhancement factor, good mechanical strength, and excellent chemical stability. So far, a lot of researchers have been interested in field emission properties of CNT itself. However, it is necessary to study proper field emitter shapes, as well as the fundamental properties of CNTs, to apply CNTs to real devices. For example, specific applications, such as x-ray sources, e-beam sources, and microwave amplifiers, need to get a focused electron beam from the field emitters. If we use planar-typed CNT emitters, it will need several focal lenses to reduce a size of electron beam. On the other hand, the point-typed CNT emitters can be an effective way to get a focused electron beam using a simple technique. Here, we introduce a fabrication of CNT fibers with nanoscale point tips which can be used as a point-typed emitter. The emitter made by the CNT fibers showed very low turn-on electric field, high current density, and large enhancement factor. In addition, it showed stable emission current during long operation period. The high performance of CNT point emitter indicated the potential e-beam source candidate for the applications requiring small electron beam size.

• Membrane Journal
• /
• v.16 no.3
• /
• pp.196-203
• /
• 2006

A flue gas emission known to cause an acid rain, containing sulfur dioxide, is tightly controlled by a regulation. The membrane contactor could be one of the alternatives which might be useful technologies for better performance of desulfurization. The fundamental sulfur dioxide separation data were obtained by a flat membrane contactor so that they could be utilized for the full scale membrane contactor. The separation of sulfur dioxide was measured in terms of the concentration of NaOH absorbent, the concentration of sulfur dioxide, the feed flow rate and different membrane materials. As the concentration of absorbent increased, the removal efficiency increased. By increasing the concentration of sulfur dioxide, the removal efficiency decreased. As the feed flow rate increased, it was observed that the removal efficiency decreased. Finally, the effect of the membrane material on separation was found to be negligible.

• School Mathematics
• /
• v.9 no.1
• /
• pp.45-64
• /
• 2007

The primary purposes of this study were to investigate how sixth graders would react to the types of tasks with regard to the comprehension of graphs and what differences might be among the kinds of graphs, and to raise issues about instructional methods of graphs. A descriptive study through pencil-and-paper tests was conducted. The tests consisted of 48 questions with 4 types of tasks (reading the data, reading between the data, reading beyond the data, and understanding the situations) and 6 kinds of graphs. The conclusions drawn from the results obtained in this study were as follows: First, it is necessary to foster the ability of interpreting the data and understanding the situation in graphs as well as that of reading the data and finding out the relationships in the data. Second, it is informative for teachers to know students' difficulties and thinking processes. Third, in order to develop understanding of graphs, it is important that students solve different types of tasks beyond simple question-answer tasks. Fourth, teachers need to pay attention to teach fundamental factors such as reading the data with regard to line graphs and stem-and-leaf plots Finally, graph type and task type interact to determine graph-comprehension performance. Therefore, both learning all kinds of graphs and being familiar with multiple types of tasks are important.

• Applied Chemistry for Engineering
• /
• v.27 no.6
• /
• pp.555-564
• /
• 2016

In recent years, methanol has attracted much attention since it can be cleanly manufactured by the combined use of atmospheric $CO_2$ recycling and water splitting via renewable energy. For the concept of "methanol economy", an active methanol synthesis catalyst should be prepared in a sophisticated manner rather than by empirical optimization approach. Even though Cu/ZnO-based catalysts prepared by coprecipitation are well known and have been extensively investigated even for a century, fundamental understanding on the precipitation chemistry and catalyst nanostructure has recently been achieved due to complexity of the necessary preparation steps such as precipitation, ageing, filtering, washing, drying, calcination and reduction. Herein we review the recent reports regarding the effects of various synthesis variables in each step on the physicochemical properties of materials in precursor, calcined and reduced states. The relationship between these characteristics and the catalytic performance will also be discussed because many variables in each step strongly influence the final catalytic activity, called "chemical memory". All discussion focuses on how to prepare a highly active Cu/ZnO-based catalyst for methanol synthesis. Furthermore, the preparation strategy we deliver here would be utilized for designing other coprecipitation-derived supported metal or metal oxide catalysts.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.43 no.1
• /
• pp.23-32
• /
• 2015

Modeling of fighter pilots, which is a fundamental technology for war games using defense M&S (Modeling & Simulation) becomes one of the prominent research issues as the importance of defense M&S increases. Especially, the recent accumulation of combat logs makes it possible to adopt statistical learning methods to pilot modeling, and an HMM (Hidden Markov Model) which is able to utilize the sequential characteristic of combat logs is suitable for the modeling. However, since an HMM works only by using one type of features, discrete or continuous, to apply an HMM to heterogeneous features, type integration is required. Therefore, we propose a dPCA-HMM method, where dPCA (Discrete Principal Component Analysis) is combined with an HMM for the type integration. From experiments conducted on combat logs acquired from a simulator furnished by agency for defense development, the performance of the proposed model is evaluated and was satisfactory.

• Journal of Internet Computing and Services
• /
• v.9 no.2
• /
• pp.35-42
• /
• 2008

Mobile IP is a solution to support mobile nodes, however, it does not handle NEtwork MObility (NEMO). The NEMO Basic Support (NBS) protocol ensures session continuity for all the nodes in the mobile network. Since the protocol is based on Mobile IP, it inherits the same fundamental problem such as tunnel convergence, when supporting the multicast for NEMO. In this paper, we propose the multicast route optimization scheme for NEMO environment. We assume that the Mobile Router (MR) has a multicast function and the Nested Mobile Router Information (NeMRI) table. The NeMRI is used to record o list of the CoAs of all the MRs located below it. And it covers whether MRs desire multicast services. Any Route Optimization (RO) scheme can be employed here for pinball routing. Therefore, we achieve optimal routes for multicasting based on the given architecture. We also propose cost analytic models to evaluate the performance of our scheme. We observe significantly better multicast cost in NEMO compared with other techniques such as Bi-directional Tunneling, Remote Subscription, and Mobile Multicast based on the NBS protocol.

• The Journal of the Korea Contents Association
• /
• v.7 no.11
• /
• pp.43-51
• /
• 2007

Access control techniques should be flexible enough to support all protection granularity levels. Since access control policies are very likely to be specified in relation to document types, it is necessary to properly manage a situation in which documents fail to be dealt with by the existing access control policies. The existing access control has not taken information structures and semantics into full account due to the fundamental limitations of HTML. In addition, access control for XML documents allows only read operations, and there exists the problem of slowing down system performance due to the complex authorization evaluation process. In order to resolve this problem, this paper designs a XML Access Control Management System which is capable of making fined-grained access control. And then, in developing an access control system, it describes the subject and object policies of authorization for XML document on which authorization levels should be specified and which access control should be performed.

• Convergence Security Journal
• /
• v.10 no.4
• /
• pp.31-37
• /
• 2010

The risks and threats in IT security systems to protect, prevent damage and Risk should be minimized. Context of information security products such as information processing, storage, delivery, and in the process of information system security standards, That is the basic confidentiality, availability, integrity and secondary clarity, potential evidence, detection, warning and defense capabilities, to ensure sufficient and should be. Web services are the most important elements in the security, the web nature of port 80 for the service to keep the door open as a structure, Web applications, web sources and servers, networks, and to hold all the elements are fundamental weaknesses. Accordingly, these elements through a set of Web application development errors and set-up errors and vulnerabilities in Web applications using their own home pages and web servers to prevent hacking and to improve the efficiency of Web services is proposed methodology performs security BMT.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.42 no.1
• /
• pp.268-278
• /
• 2017

In this paper, we propose two novel detection schemes with low-complexity based on the unified receiver architecture which minimizes a fundamental tradeoff at rate-energy region in SWIPT system. The proposed detection schemes are twofold: The two-stage detection scheme and Euclidean distance combination detection scheme. The two-stage detection scheme detects amplitude information of symbols from rectified signals for energy harvesting. In the sequel, it detects symbols based on phase information of baseband signals for information decoding. The Euclidean distance combination detection scheme detects symbols using linear positive-weighted sum of two metrics: Euclidean distance based on baseband signals for information decoding and Euclidean distance based on rectified signals for energy harvesting. For numerical results, we confirm that the proposed detection scheme can achieve better performance than the conventional scheme in terms of symbol error rate, symbol success rate-energy region and achievable rate-energy region.