• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.2
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• pp.8-15
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• 2021

This study presents post-installed anchors whose heads and extension sleeves are improved. The optimal lengths of the extension sleeves and headers were analytically determined by simulations. As a result of analysis using Finite element method (FEM), 9.0mm and 3.0mm were determined as the optimal lengths of sleeves and headers respectively. In pull-out tests using the improved post-installed anchors, all specimens satisfied the coefficient of variation of 15%. Comparing the pull-out strengths of existing anchors and the improved anchors, it was increased by 1.25 times for anchors embedded with a depth of 50mm, and 1.54 times for 70mm. In the cases of high-strength concrete, the strengths were increased by 1.28 and 1.55 times for 50mm and 70mm respectively. Moreover, as a result of shear tests, the improved anchors perform the greater strength of 1.38 times than the existing anchors.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.6
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• pp.1076-1085
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• 2004

Recently, the demands for real-time service and multimedia data are rapidly increasing. There are significant redundancies between header fields both within the same packet header and in consecutive packets belonging to the same packet stream. And there are many overheads in using the current UDP/IP protocol. Header compression is considered to enhance the transmission efficiency for the payload of small size. By sending the static field information only once initially and by utilizing dependencies and predictability for other fields, the header size can be significantly reduced for most packets. This work describes an implementation for header compression of the headers of IP/UDP protocols to reduce the overhead on Ethernet network. Typical UDP/IP Header packets can be compressed down to 7 bytes and the header compression system is designed and implemented in Linux environment. Using the Header compression system designed between a server and clients provides have the advantage of effective data throughput in network. Since the minimum packet size in Ethernet is 64 bytes, the amount of reduction by header compression in practical chatting environment was 6.6 bytes.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.440-459
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• 2021

Roadheaders have begun to be adopted in Korean tunneling sites. The performance prediction models proposed by the manufacturer are used by Korean construction companies. The models use UCS (uniaxial compressive strength) value to predict the net cutting rate, but the rock specimens conducted for the uniaxial compression test have 1.0 of the diameter to length ratio. It has been reported that the specimen shape generally influences the rock strength. The previous references studying the shape effect were cited, and the UCS data of Korean rocks are also updated to analyze the shape effect on UCS. The cause of effect was discussed by previous theory. The change amount of UCS values of Korean rocks was estimated by the data, and the modified prediction model for NCR was finally suggested.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.1
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• pp.76-87
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• 2005

In this paper, we propose a new profile, ROHC(RObust Header Compression) profile 7, for SCTP with ROHC for applying robust header compression SCTP, which is a transport layer protocol. The proposed new profile 7 adds a new field of 1 or 2 byte size on the existing SCTP packet header, which can make the SCTP stream to be diveded into acknowledgement stream and data stream. In addition, the classification of the stream can be used for recovering fault context. Consequently, in the case of using proposed ROHC-SCTP, it is possible to reduce the SCTP header overhead rate and also can be saved bandwidth.

• Journal of Korea Multimedia Society
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• v.11 no.10
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• pp.1359-1365
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• 2008

The portion of header in H.264 gets higher than those of previous standards instead of its better compression efficiency. Therefore, this paper proposes a new technique to compress the header of H.264. Unifying a sentence elementary in H.264, H.264 does not consider the distribution of element which be encoded and uses existing Exp-Golomb method, but it is uneffective for variable length coding. Most of the header are block type(s) and motion vector difference(s), and there are redundancies in the header of H.264. The redundancies in the header of H.264 which are analyzed in this paper are three. There are frequently appearing symbols and non-frequently appearing symbols in block types. And when mode 8 is selected in macroblock, all of four sub-macroblock types are transferred. At last, same values come in motion vector difference, especially '0.' This paper proposes the algorithm using type code and quadtree, and with them presents the redundant information of header in H.264. The type code indicates shape of the macroblock and the quadtree does the tree structured motion compensation. Experimental results show that proposed algorithm achieves lower total number of encoded bits over JM12.4 up to 32.51% bit reduction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.11
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• pp.444-449
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• 2016

The main objective of this work is to experimentally investigate the effect of angle variation and intrusion depth of channels on the distribution of two-phase flow at header-channel junctions. The dimensions of the header and the channels in cross-section were fixed at $16mm{\times}16mm$ and $12mm{\times}1.8mm$, respectively. Air and water were used as the test fluids. Two different header-channel positions were tested : a vertical header with horizontal channels (case VM-HC) and a horizontal header with horizontal channels (case HM-HC). In all cases, the intrusion depths of the channels are 0 mm, 2 mm, and 4 mm. For the case of the intrusion depth of VM-HC, the flow distribution became more uniform. However, the intrusion depth negatively affected the flow distribution for the case of HM-HC because liquid separation delay occurred.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.04a
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• pp.353-356
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• 2014

역공학 방지 기법이 적용되지 않은 어플리케이션은 악의적인 역공학에 취약할 수밖에 없다. 악의적인 역공학은 사회적으로 여러가지 손실을 가져온다. 그러므로 역공학 방지 기법을 적용하여 어플리케이션을 보호해야 한다. 역공학 방지 기법은 다양하며, 크게 자바 소스 난독화, Smali 코드 조작, Dex 파일 포맷 조작, 그리고 Zip 파일 포맷 조작 기법으로 나눌 수 있다. 자바 소스 난독화는 코드의 가독성을 떨어트려 안드로이드 어플리케이션의 역공학을 어렵게 하는 기법이다. Smali 코드 조작 기법은 Goto 문 추가, 예외 처리 재귀 기법 등을 통하여 역공학을 막는 기법이다. Dex 파일 포맷 조작 기법에는 클래스명 길이 변경, 헤더 크기 변경 등을 통해 역공학을 어렵게 만드는 기법이다. Zip 파일 포맷 조작 기법은 Zip 파일 포맷에서 헤더 값을 조작하여 마치 암호화된 것처럼 보이도록 만드는 기법이다. 본 논문에서는 이러한 다양한 기법들에 대해서 설명하고 이를 비교 분석한다.

• Proceedings of the Korea Multimedia Society Conference
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• 2002.11b
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• pp.194-197
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• 2002

본 논문은 리눅스 환경에서 IEEE1394의 동시 전송 프로토콜을 이용하는 멀티미디어 스트리밍 시스템의 구현에 대해 기술한다. 구현된 시스템은 DV 데이터의 스트리밍과 재생, 저장은 물론 로컬 재생과 장치 제어 기능을 갖는 사용자 프로그램과 dv1394 디바이스 드라이버로 구성된다. 스트리밍을 위한 메모리할당, 버퍼관리, 전송 데이터 형식 선언, IEEE1394 헤더 및 CIP 처리기능을 가진 dv1394 드라이버를 사용하여 드라이버와 OHCI1394 카드 사이의 스트리밍에 대한 투명성을 제공함으로써 기존의 스트리밍 시스템이 가졌던 응용 프로그램 개발의 복잡성을 줄였다. 이 시스템은 실시간 원격 모니터링이나 화상 회의 시스템, 그리고 비선형 비디오 편집 시스템에 응용될 수 있다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.10
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• pp.51-58
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• 2003

In this paper, we propose a group scheduling scheme to efficiently utilize network resources for core nodes in optical burst switching networks. This scheme schedules multiple bursts utilizing an interval graph to obtain the maximum stable set using the information such as arrival times and burst lengths from the collected header packets. Simultaneous scheduling of multiple bursts in a scheduling window results in lower burst loss probability and increased channel utilization than those proposed previously using one-to-one mapping. Simulation results for both cases of variable and fixed burst sizes show that the group scheduling scheme is better than the immediate scheduling, so called Latest Available Unused Channel with Void Filling, scheme in both performance metrics above mentioned.

• Tunnel and Underground Space
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• v.33 no.5
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• pp.414-424
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• 2023

In this study, a total of 326 data on a variety of geometric parameters of pick cutters and the corresponding cuttable rock conditions were collected and built as a database. Statistical analysis of the database showed that there is a significant positive correlation between the parameters that define the geometry of a pick cutter, especially between the parameters related to the length of a pick cutter and the geometry of a tungsten carbide insert. The diameter of a pick cutter shaft was also strongly correlated with the geometry of the inserts. On the other hand, it was difficult to find a clear correlation between the parameters for the rock conditions defined by the four conditions and the geometric parameters of pick cutters, which may be due to the uncertainty of the rock mass and the fact that the application of a pick cutter is presented as a range rather than a numerical single value. However, the mean values of geometric parameters of pick cutters tend to increase as a rock mass becomes harder. However, the pick length parameters are found to decrease as a rock mass becomes harder, which may be a way to reduce the moments that can occur when using long pick cutters in a hard rock condition.