• Journal of Internet Computing and Services
• /
• v.8 no.5
• /
• pp.141-150
• /
• 2007

This paper proposes new Steganographic model for VoIP that has very effective method using low bit encoding. Most of Steganographic models using Low bit Encoding have two disadvantages; one is that the existence of hidden secret message can be easily detected by auditory, the other is that the capacity of stego data is low. To solve these problems, this method embed more than one bit in inaudible range, so this method can improve the capacity of the hidden message in cover data. The embedding bit position is determined by using a pseudo random number generator which has seed with remaining message length, so it is hard to detect the stego data produced by the proposed method. This proposed model is able to use not only to communicate wave file with hidden message in VoIP environment but also to hide vary information which is user basic information, authentication system, etc.

• Journal of Energy Engineering
• /
• v.8 no.1
• /
• pp.189-201
• /
• 1999

범용 열가소성 플라스틱(polyethylene(PE), polypropylene(PP), polystyrene(PS), polyethylene-terephthalate(PET), acrylonitrile-butandiene-styrene(ABS))과 폐윤활유의 동시처리 열분해반응 실험을 수행하였다. 반응실험은 40$m\ell$ 용량의 회분식 미분반응기(microreactor)를 이용한 실험과 1리터 용량의 autoclave를 이용한 실험의 두 가지로 구분하여 행하였다. 전자의 경우는 통계적 실험적계획법(statistical experimental design)의 하나인 회전계획실험(rotatable design experiments)으로서 오각형 실험계획(pentagonal experimental design)에 의거한 반응변수 실험을 수행한 후 반응표면(response surface)을 회기분석법에 의하여 분석함으로써 최대의 오일 수율을 얻을 수 있는 최적 반응조건을 추적, 결정하였다. Autoclave 반응실험의 기본적인 목적은 실제 연속공정에 있어서 열분해 반응기 거동을 모사하기 위한 전초단계로서 충분한 시료의 확보를 통하여 이 때 생성된 연로유의 체계적인 분석(비등점분포특성, 진공증류, 기체분석, 원소분석, 발열량, 비중 등)을 행함으로써 연료유 수율 및 품질을 모사하고자 하였다. 미분반응기 실험에 있어서 주 범용열가소성수지인 PE, PP 그리고 PS는 각각의 최적반응조건하에서 거의 100%에 가깝게 오일로 전환되었지만 응축수지인 PET와 그래프트공중합수지인 ABS의 오일수율은 각기 78% 및 90%로서 상대적으로 낮게 나타났다. Autoclave를 이용한 실험의 경우 혼합플라스틱을 폐유에 대하여 40wt% 혼합하여 열분해하였을 때, 80wt% 오일, 15wt% 코우크, 그리고 나머지 5wt%는 탄화수소기체(C1-C6)로 전환되었다. 진공증류(252$^{\circ}C$,2 torr) 결과, 기/액-분리도는 3으로서 이는 생성오일의 75wt%가 경질연료유(가솔린, 등유, 경유)로 회수 가능하였다.

• The KIPS Transactions:PartC
• /
• v.8C no.1
• /
• pp.75-87
• /
• 2001

The Conditional Access System is the complete system for ensuring that broadcasting services are only accessible to those who are entitled to receive them. Four major parts to this system are scrambling, descrambling, authentication and encryption. For the proper operation, which means hard-to- break and uninterrupted service, secure key management and efficient delivery mechanism are very important design factors to this system. Performance analysis is another important factor to this system that is used in massive subscriber environment. In this thesis, one of the secure and efficient key management mechanisms is proposed. For the secrecy of this mechanism, hierarchical stacking of keys and key generation matrix are proposed. For the proof of efficient delivery of those keys, simulation results and performance analysis. which is based on queuing analysis, are presented. Lastly, optimal key generation and delivery period, maximal and minimal key deliver time, and communication capacity for data collection are presented for various subscriber volume.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.18 no.1
• /
• pp.28-35
• /
• 2004

$N_2$ has been one of the most useful gases in industrial application, for example, plasma ashing, surface cleaning and decomposition of pollution gases. In order to clarify $N_2$ plasma properties and increase practical applications, many experimental and theoretical investigations have been carried out until now on. In this papa, we examined the characteristics of $N_2$ RF Plasmas using one-dimensional fluid model. $N_2$ plasmas showed a double-layer structure in both sheath regions as the power source voltage becomes higher. Generally, a double-layer structure should be showed in electro-negative plasmas, but not in electro-postive plasmas such as $N_2$ discharge. However, most electrons in $N_2$ plasmas lost their energy by many excitation reactions in the near of both electrodes where electron collisions were actively executed and such continuous reactions during an RF period made this structure strong with increase of the power source voltage. The dependence of $N_2$ plasma properties on pressure was also discussed.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.7B
• /
• pp.642-651
• /
• 2006

In ad-hoc network, the most of existing packet scheduling schemes provides throughput-based fairness. To provide throughput-based fairness, it basically supposes that the channel capacity is fixed. But, the supposing that the channel capacity is fixed is not appropriate because IEEE 802.11b and 802.11g which are normally used for organizing ad-hoc network can provide various data rate according to channel conditions. So, we define time-based fairness for each flow to consider multi-rate and suggest the MRADPS reaching the defined time-based fairness. Simulation result shows that MRADPS improves the total network throughput in ad-hoc network with providing time-based fairness to each flow.

• Polymer(Korea)
• /
• v.31 no.6
• /
• pp.479-484
• /
• 2007

In this study, the hybrid ion exchange fibers (HIEF) were prepared by using web spraying muthod with hot melt adhesive. Characteristics of HIEF and their adsorption properties for ammonia gas were investigated. The ion exchange capacity (IEC) of HIEF was increased with increasing the resin contents and their values were higher than those of pure resin and ion exchange fabrics. The removal efficiency for ammonia gas increased with an increase in packing density of hybrid ion exchange fabrics in the column. The adsorption breakthrough time was 270 min, which was slower than those of the resin and fibers. The maximum value of adsorption for ammonia gas was 94%. The breakthrough time was also increased with increasing the concentration and flow rate of ammonia gas. The reaction constant(k) for ammonia gas was increased with increasing the concentration and flow rate of the gas, while it was decreased an the mass was increased.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.21 no.2
• /
• pp.143-151
• /
• 2010

In this paper, a novel rectangular patch antenna is proposed to have Zeroth Order Resonance(ZOR) generated based on the Metamaterial Complosite Right- and Left-Handed(CRLH) structure. Making the in-phase electric field over the entire antenna other than a half-wavelength as the fundamental resonance mode of a standard microstrip patch or its positive multiple, the metallic patch is suggested to be capacitively coupled with only one surrounding rectangular ring, different from the previous 1D ZOR antennas commonly having several metal cells in line. The performance of the proposed antenna is simulated by a 3D field solver that inputs the sizes of the physical structure corresponding to the equivalent circuit designed to have ZOR at 2.4 GHz. Consequently, the resonance frequency, the gain and the antenna efficiency are observed 2.4 GHz, 5 dB and 98%, respectively. Besides, the important property of the proposed antenna is addressed as the combination of the low profile as an advantage of microstrip patch antennas, and the omni-directional field pattern typical of monopole antennas.

• Journal of Korean Society of Transportation
• /
• v.21 no.6
• /
• pp.27-42
• /
• 2003

The basis for planning airport development is the specific demand at peak hour among various aviation demands. The demand at peak hour is regarded to be the source which enables us to estimate the size requirement and capacity of an airport facility. The distribution type of peak hour-operation depends on the difference of aircraft route, geographical location of airport, passengers and cargo. The demand at peak hour is calculated with peak hour factor. So far, the features of peak hour adopted for domestic airport construction plan have been based on the foreign research results. However, it is officially unconfirmed whether the various peak hour characteristics or peak hour factor suggested from foreign studies can be compatible with Korean state or not. In this study, the aircraft operation pattern and the peak hour characteristics are analyzed with hourly data using the operation schedule of an airport for the last 5 years and the actual result statistics of Korean air transportation by airport through the recent 10 Years. After the peak hour factor of the airports is calculated and compared with existing research results, peak hour factor by annual operation frequency is suggested for Korean airports.

• The KIPS Transactions:PartC
• /
• v.11C no.7 s.96
• /
• pp.905-916
• /
• 2004

Self-organizing hierarchical ad hoc network (SOHAN) is a new ad-hoc network architecture designed to improve the scalability properties of conventional 'flat' ad hoc networks. This network architecture consists of three tiers of ad-hoc nodes, i.e.. access points, forwarding nodes and mobile nodes. This paper presents a topology discovery and routing protocol for the self-organization of SOHAN. We propose a cross-layer path metric based on link quality and MAC delay which plays a key role in producing an optimal cluster-based hierarchical topology with high throughput capacity. The topology discovery protocol provides the basis for routing which takes place in layer 2.5 using MAC addresses. The routing protocol is based on AODV with appropriate modifications to take advantage of the hierarchical topology and interact with the discovery protocol. Simulation results are presented which show the improved performance as well as scalability properties of SOHAN in terms of through-put capacity, end-to-end delay, packet delivery ratio and control overhead.

• Proceedings of the KWS Conference
• /
• 2009.11a
• /
• pp.24-24
• /
• 2009

현재 조선소를 비롯하여 각종 산업 전반적으로 기존의 SCR 용접기를 대체하여 용접품질이 우수한 인버터 용접기가 널리 사용되고 있는 실정이다. 그러나 기존 인버터 용접기의 전원은 Mono 타입으로 이루어져 있어 대용량 인버터 용접기의 경우 대용량 스위칭 소자가 요구되어 제조원가가 높다. 그리고 문제 발생 시 용접기의 사용이 불가능하게 된다. 개발된 단위모듈을 병렬로 연결하여 대용량 용접기를 구성하게 되면 제조원가를 절감할 수 있으며 병렬로 연결되어 단위 모듈에 문제가 발생하여도 계속적인 사용이 가능하고, 주 회로를 작은 용량으로 분산시켜 전력을 제어하므로 높은 에너지 효율을 가지게 된다. 또한 인버터 용접기의 가장 중요한 성능인 스위칭 주파수에 있어서도 기존의 인버터 용접기는 20kHz의 스위칭 주파수를 가지지만 본 기술은 낮은 전력을 병렬로 연결하여 대용량을 동시에 제어가능 하므로 약 70kHz의 고속제어가 가능하다. 본 연구에서는 개발된 용량 170A단위모듈을 병렬로 연결하여 단위모듈 집적형 인버터 아크용접기 510A, 680A급의 부하테스트 실시 및 기본출력특성에 대하여 실험하였으며, GMAW에서 ${\Phi}1.6$ 솔리드 와이어를 이용하여 두께 20t의 후판 맞대기 용접에 적용실험을 실시하였다. 그 결과 모든 전류영역에서의 부하특성 및 출력특성이 양호하게 나타났으며, 후판 맞대기 용접에서는 SAW에 버금가는 생산성과 용접특성을 얻을 수 있었다.