• Journal of Advanced Marine Engineering and Technology
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• v.18 no.2
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• pp.113-121
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• 1994

Since two oil shocks in 1970s, all of engine makers have persevered in their efforts to reduce specific fuel consumption and to increase engine power rate as much as possible in marine diesel engines. As a result, the maximum pressure in cylinders of these engines has been continuously increased. It causes direct axial vibration. The axial stiffness of crank shaft is low compared to old types of engine models by increasing the stroke/bore ratio and its major critical speed might occur within engine operation range. An axial damper, therefore, needs to be installed in order to reduce the axial vibration amplitude of the crankshaft. Usually the main critical speed of axial vibration for the propulsion shafting system with a 4-8 cylinder engine exists near the maximum continuous revolution(MCR). In this case, when the damping coefficient of the damper is increased within the allowance of the structural strength, its stiffness coefficient is also increased. Therefore, the main critical speed of axial vibration can be moved beyond the MCR. It has the same function as a conventional detuner. However, in the case of a 9-12 cylinder engine, the main critical speed of axial vibration for the propulsion shafting system exists below the MCR and thus the critical speed cannot be moved beyond the MCR by using an axial damper. In this case, the damping coefficient of an axial damper should be adjusted by considering the range of engine revolution, the location and vibration amplitude of the critical speed, the fore and aft vibration of the hull super structure. It needs to clarify the dynamic characteristics of the axial vibration damper to control the axial vibration appropriately. Therefore authors suggest the calculation method to analyse the dynamic characteristics of axial vibration damper. To confirm the calculation method proposed in this paper, it is applied to the propulsion shafting system of the actual ships and satisfactory results are obtained.

• Journal of the Korea Society of Computer and Information
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• v.18 no.10
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• pp.71-80
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• 2013

In this paper, we analyze the security vulnerability through the several attack scenarios for the MCR-MAP(Multi-Context RFID Mutual Authentication Protocol) proposed by Ahn et al. And we propose the secure mutual authentication protocol that improved a prior MCR-MAP. The suggested protocol uses the ID of the legal tag and the timestamp generated by the server, when the tag tries to authenticate. And when the tag creates the credential, we create the new secret key computing the XOR operation between the secret key shared with the server and the tag timestamp generated by the server. As a result, the proposed protocol provides the secure mutual authentication and then is safe to spoofing attack. Also it provides forward-secrecy and then is safe to offline brute-burst attack. In this paper, we compare and verify the security vulnerability of the prior and the proposed protocol through the security analysis.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.5
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• pp.7-15
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• 2007

In wireless communication networks, single-radio single-channel architecture degrades throughput and end-to-end delay due to half-duplex transmission of wireless node and route intra interference. Also, In contention-based MAC (Medium Access Control) architecture, channel contention reduces throughput and packet collision enlarges end-to-end delay. In this paper, we use multi-radio multi-channel architecture which will make wireless node to operate in full duplex mode, and exclude route intra interference. Based on this architecture, we propose a new link metric, ccf which reflects the characteristics of a contention-based wireless link, and propose a routing path metric MCCR considering channel switching delay and route intra interference. MCCR is compared with MCR by simulation, the performance of a route established by MCCR outperforms the performance of a route by MCR in terms of throughput and end-to-end delay.

• Nuclear Engineering and Technology
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• v.48 no.1
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• pp.153-163
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• 2016

Environments in nuclear power plants (NPPs) are changing as the design of instrumentation and control systems for NPPs is rapidly moving toward fully digital instrumentation and control, and modern computer techniques are gradually introduced into main control rooms (MCRs). Within the context of these environmental changes, the level of performance of operators in a digital MCR is a major concern. Situation awareness (SA), which is used within human factors research to explain to what extent operators of safety-critical systems know what is transpiring in the system and the environment, is considered a prerequisite factor to guarantee the safe operation of NPPs. However, the safe operation of NPPs can be guaranteed through a team effort. In this regard, the operating team's SA in a conventional and digital MCR should be measured in order to assess whether the new design features implemented in a digital MCR affect this parameter. This paper explains the team SA measurement method used in this study and the results of applying this measurement method to operating teams in different MCR environments. The paper also discusses several empirical lessons learned from the results.

• Clean Technology
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• v.15 no.2
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• pp.130-136
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• 2009

Commercial catalyst (Cu-Zn/$Al_2O_3$, Johnson Matthey Co., 83-3 Catalyst) was applied to the hydrogen production by steam reforming of methanol in the micro-channel reactor (MCR). The steam reforming of methanol was tested over Cu-Zn catalyst at temperatures in the range of 200 and 300$^{\circ}C$, the catalyst size of 0.05${\sim}$2.2 mm, the space velocity of 3,000${\sim}$10,000 $hr^{-1}$ in a fixed bed continuous flow reactor. The conversion of methanol and the yield $H_2$ preferred high temperatures and low space velocities, and had optimal results with the particle size of 0.35 mm. Based on the results from experiments with fixed bed reactor, two types of MCR, boat bed and stacked bed MCRs, were studied. The stacked bed type MCR showed better methanol conversion compared with the boat type one.

• Journal of the Ergonomics Society of Korea
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• v.27 no.2
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• pp.73-82
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• 2008

Currently an office in information society is advanced to a digitalized VDT office. The VDT office has a natural luminous system prioritizing visual perception and so importance of lighting design by artificial lighting is emphasized in the VDT office. The purpose of the study is to analyze Illumination and Luminance for lighting design by the standard of ergonomics in the VDT office. The study analyzed Illumination and Luminance in the main control room of an nuclear power plant needing a design of ergonomics ACR(Advanced Control Room) type Ling Ao phase II NPP MCR in Guangdong, China. The study examined the relativity of ACR characteristics to its operator's duties and set up an outline of lighting design, the standard of ergonomics and input data for the analysis. Thus, the study examined appropriateness with the standard of ergonomics setting up the analyzed Illumination and Luminance and drew a conclusion.

• Parasites, Hosts and Diseases
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• v.37 no.1
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• pp.33-37
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• 1999

An age-dependent aspect of resistance to Cryptosporidium muris (strain MCR) infection was monitored in Syrian golden hamsters. Mesocricetus auratus. at 1-, 5- and 10-week of age and in ICR mice, Mus musculus, at 3-, 12-, and 15-week of age orally inoculated with a single dose of $2{\times}10^6$ oocysts. respectively. The prepatent periods for both animals were similar, independent of age, but the patency was significantly longer in younger hamsters (P<0.001) and a long tendency in younger mice. Hamsters infected at 1-week of age excreted about 10 times higher oocysts than those at 5- and 10-week of age. However, the total oocyst output was similar among mice of different ages. There was a good correlation between the length of the patency and the total oocyst output in hamsters (R=0.9646), but not in mice (R=0.456l). The immunogenicity of the parasite to homologous challenge infections was very strong in hamsters and relatively strong in mice. These results indicate that acquired resistance to C. muris infection is age-related and the innate resistance is independent of age of hamsters, and that both innate and acquired resistance, on the contrary, are irrespective of age of mice.

• The Journal of the Korea Contents Association
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• v.7 no.12
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• pp.238-244
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• 2007

Guaranteed Frame Rate(GFR), recently approved by the ATM Forum, expects to become an important service category to efficiently support TCP/IP traffic in ATM networks. The GFR service not only guarantees a minimum service rate at the frame level, but also supports a fair share of available bandwidth. We proposed new scheduling scheme for the GFR service. Proposed scheme provides priority to VCs and high priority to a VC which have more untagged cells in buffer. High priority VCs have much more serviced than low priority. Proposed scheme can provide MCR(minimum cell rate) guarantee and fair sharing to GFR VCs. Computer simulation results show that proposed scheduling scheme provide a much better performance in TCP goodput and fairness than previous scheme.

• Journal of Power Electronics
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• v.19 no.1
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• pp.211-219
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• 2019

In magnetically coupled resonant (MCR) wireless power transfer (WPT) systems, the introduction of additional intermediate coils is an effective means of improving transmission characteristics, including output power and transmission efficiency, when the transmission distance is increased. However, the position of intermediate coils in practice influences system performance significantly. In this research, a three-coil MCR WPT system is adopted as an exemplification for determining how the spatial position of coils affects transmission characteristics. With use of the fundamental harmonic analysis method, an equivalent circuit model of the system is built to reveal the relationship between the output power, the transmission efficiency, and the spatial scales, including the axial, lateral, and angular misalignments of the intermediate and receiving coils. Three cases of transmission characteristics versus different spatial scales are evaluated. Results indicate that the system can achieve relatively stable transmission characteristics with deliberate adjustments in the position of the intermediate and receiving coils. A prototype of the three-coil MCR WPT system is built and analyzed, and the experimental results are consistent with those of the theoretical analysis.

• Parasites, Hosts and Diseases
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• v.33 no.4
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• pp.377-382
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• 1995

Three-week-old ICR SPF mice were orally inoculated with one of 5 doses ranging from $2{\;}\times{\;}10^2{\;}to{\;}2{\;}\times{\;}10^6$ oocysts of Crwptosporidium tsuris (strain MCR) per mouse. Oocyst inoculation was directly proportional to the amount of oocysts shed and was inversely proportional to the period required for peals oocyst production and to the prepatent period. Peak oocyst production occurred between fifteen and thirty-one days with a patent period from 61 to 64 days. Three days after all mice stopped shedding oocysts, they were orally challenged with a single dose of $2{\;}\times{\;}10^6$ oocysts or the same species. Marked seroconversion for IgG antibody accompanied recovery from mice inoculated with $5{\;}\times{\;}10^5$ oocysts. Mice administered with carrageenan excreted a small number of oocysts for 49.0 days on the average after challenge inoculation (ACI) and control mice for 14.2 days in a dose-independent fashion. Just before challenge infection, phagocytic activity of peritoneal macrophages ($M{\phi}$) and the number of peripheral $M{\phi}$ were dramatically decreased. Mild challenge infection implies that the immunogenicity of C. nuris (strain MCR) is very strong, despite $M{\phi}$ blocker carrageenan administration.