• Journal of the Korean Society of Combustion
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• v.18 no.2
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• pp.23-31
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• 2013

Compact steam boiler is a useful heat exchanger in a space-intensive system. There are some constraints in terms of sizing and designing the space confined in the system which is usually used in vessels. In this study, design considerations for heavy duty heat exchangers of compact steam boilers are presented and evaluated. Especially, evaporator tubes of marine boiler which are exposed to a high temperature environment are considered. Also, extended surface designs with a high temperature are examined. In order to determine the criteria with considerations of both heat transfer rate and pressure drop in the heat exchanger, they are evaluated with major variables, such as the tube diameter, the number of tubes, and the tube length. Finally, the design parameters are estimated as the bare tubes are installed instead of the finned tubes.

• International Journal of Internet, Broadcasting and Communication
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• v.15 no.1
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• pp.1-7
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• 2023

TCP is considered a major candidate transport protocol even for constrained IoT networks due to its ability to integrate into the existing network infrastructures. Since TCP implementations such as uIP TCP often allow only a single TCP segment per connection to be unacknowledged at any given time due to resource constraints, the congestion control relies only on RTO management. In our previous work, to address the problem that uIP TCP performs poorly particularly when a radio duty cycling mechanism is enabled and the hidden terminal problem is severe, we proposed a RTO scheme for uIP TCP and validated the performance through Cooja simulation. In this study, we investigate the effect of other factors that were not considered in our previous work. More specifically, the effect of traffic intensity, the degree of the hidden terminal problem, and RDC is investigated by varying the offered load and the transmission range, and the RDC channel check rate. Simulation results imply that we need to further investigate how to improve TCP performance when the radio duty cycling mechanism is used.

• Journal of Korean Society of Transportation
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• v.31 no.5
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• pp.60-70
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• 2013

This study aims to develop a truck priority on left-turn algorithm that can reduce greenhouse gas emissions by reducing heavy duty truck's stops at signalized intersection. The signal priority is granted for a left-turn phase, because heavy duty trucks can deteriorate left-turn traffic flow due to the low acceleration or deceleration rate and large turn radius. Truck priority allows to provide the stable speed control for heavy duty truck, and reduces emissions at the signal intersection. Also, two signal recovery strategies are compared for various traffic conditions. This study analyzes the effectiveness of truck priority such as greenhouse gas emissions and fuel consumption reduction, and total travel time saving using the PARAMICS and Comprehensive Modal Emissions Model (CMEM). The results show that signal priority for heavy duty trucks has an effect on reducing greenhouse gas emissions and fuel consumptions at non-peak hour. Also, it shows decreasing total travel time due to reducing truck stops.

• Plant Journal
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• v.10 no.1
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• pp.34-39
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• 2014

Simulation works for comparing removal capabilities of acid gases contained in natural gas among several aqueous amine absorbents using commercial process simulator PROMAX(BR&E Co.) were carried out. Amine aqueous solution used in this study were 30 wt% MEA, 30 wt% DEA, 50 wt% MDEA, and 50 wt% MDEA with 3 wt% piperazine as additive. We obtained the simulated results that while MEA aqueous solution is relatively capable of more $CO_2$ gas, but DEA, MDEA, MDEA aqueous solutions with piperazine as additive are capable of more $H_2S$ gas. Also, we found that 30 wt% MDA aqueous solution is the smallest circulate rate of lean amine solution, and 50 wt% MDEA aqueous solution with 3 wt% piperazine as additive is the smallest heat duty in stripping unit. 50 wt% MDEA aqueous solution with 3 wt% piperazine as additive is found less amine circulation rate than 50 wt% MDEA due to the introduction of additive.

• Journal of Advanced Marine Engineering and Technology
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• v.16 no.4
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• pp.60-77
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• 1992

The effects of exhaust gas recirculation(EGR) on the characteristics of exhaust emissions and specific fuel consumption have been investigated using an eight-cylinder, four cycle, direct injection diesel engine operating at several loads and speeds. The experiments in this study are conducted on the fixed fuel injection timing of $38^{\circ}$ BTDC regardless of experimental conditions. In conclusion, it is found that $NO_{x}$ emission is markedly reduced with the drop of burnt gas temperature at high speeds and loads especially as the EGR rate increases, while the soot particulate rises with EGR rate and load at a given engine speed, especially high loads. The reduction of exhaust emissions within the Korea heavy duty diesel engine emission standards can be roughly achieved by the optimal EGR rate without degarding the specific fuel consumption, based on the correlations between exhaust emissions.

• Quality Improvement in Health Care
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• v.1 no.1
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• pp.110-118
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• 1994

As the first step to improve the medical recording for the hospitalized patients, we tried to identify problems of completion rate of the medical recording and made the completion rate of the medical recording within due date known to the public in the hospital and commended the best Department and resident officially. The results were as follows: 1. The average number of the medical recordings per a recorder by years of residency(average number to quorum) was 293.3(398.8) in 1st year, 82.5(68.1) in 2nd year, 21.2(8.3) in 3rd year, and 20.5(1.9) in 4th year-residents. There was only 2 residents who prepared the medical recordings more than the average of 125.6 recordings per a resident. 2. Among 13 Departments, the medical recording was wholly put in charge of the 1st year-resident in 6 Departments. The duty was shared with the 2nd year-resident in 5 Departments and the 3rd year-resident in 1 and the 4th year-resident in Only 1 Department. 3. The more the cases requiring the medical recording, the lower the completion rate(80% less than 100 recordings, 70% in 100-299, 60% in 300-399 and 33.3% in more than 400). 4. There was no difference in the completion rate of the medical recording before(1991) and after(1993) a public nitice(1992). However, 4 Departments showed improvement of 21-45% in the completion rate, and no case was found where billing for medical assurance was postponed due to delayed completion of the medical recording. 5. The completion rate was relatively low(72-78%) from January to March. The main reasons were shortage of men power due to preparation of board examination, attendance to military duty, and lack of training in the medical recording for the new 1st year-residents. 6. The official commendation of the best Department and resident by letters did not improve the completion rate of the medical recording. In conclusion, The main reason of the low completion rate of the medical recording was the fact that the 1st year-residents were almost exclusively responsible for the medical recording. Hence, it is mandotory that this practice gets staffs' attention to improve the completion rate. Public notice of the completion rate of the medical recording shows prompt improvement of the completion rate. Prize money rather than commendation by a letter for the best Department would also be more effective to improve the quality of medical recording.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.5
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• pp.67-73
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• 2013

This experimental work described the effect of flow control valve type on the performance of wobble plate type fuel pump for the stable DME fuel supply. In order to study this, different four types of flow control valves (ITV, SCV, IMV and MPROP) were installed on the wobble plate fuel pump, and fuel flow rate, torque, and temperature variation of pump were investigated under various operating conditions by using pump performance test system. It was revealed that wobble plate type fuel pump worked well with ITV and SCV control valve, and the flow rate and torque of fuel pump was in proportion to the value of valve open duty. The maximum flow rate and torque of fuel pump were achieved around the 50% duty of control valve. Temperature variation at all pump measuring points were under $60^{\circ}C$ which is acceptable.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.9
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• pp.1847-1855
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• 2012

A 1V 1.6-GS/s 6-bit flash analog-to-digital converter (ADC) with a clock calibration circuit is proposed. A single track/hold circuit with a bootstrapped analog switch is used as an input stage with a supply voltage of 1V for the high speed operation. Two preamplifier-arrays and each comparator composed of two-stage are implemented for the reduction of analog noises and high speed operation. The clock calibration circuit in the proposed flash ADC improves the dynamic performance of the entire flash ADC by optimizing the duty cycle and phase of the clock. It adjusts the reset and evaluation time of the clock for the comparator by controlling the duty cycle of the clock. The proposed 1.6-GS/s 6-bit flash ADC is fabricated in a 1V 90nm 1-poly 9-metal CMOS process. The measured SNDR is 32.8 dB for a 800 MHz analog input signal. The measured DNL and INL are +0.38/-0.37 LSB, +0.64/-0.64 LSB, respectively. The power consumption and chip area are $800{\times}500{\mu}m2$ and 193.02mW.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.11A
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• pp.1073-1080
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• 2005

In spite of many advantages of Meteor Burst Communications(MBC) on its transmission channel, the fact that its duty rate is less than 10 percents is a considerable deficiency of MBC. To overcome with this deficiency without paying large cost, we use a direct sequence(DS) simple reception system. This method doesn't need to add the components for acquisition or tracking the signal so that it keeps the cost efficiency of the MBC. But it has a disadvantage that its duty rate shows a large decline by noise. For this problem, we adopt the proposed system applying a positive feedback circuit. The improvement by this method is more significant when the received signal is weak. Simulation results show as tl is l00ms, then the burst length would be increased by $35\%$ when the initial value of the received signal power increases by 3 dB, t2 is 135ms. If the power increases by 6dB the burst length would be 170ms thus increased by $70\%$, which shows a great enhancement. Suppose now that tl is 50ms and the power is increased by 3dB, then t2 would be increased by $70\%$ to 85ms, and increasing the power by 6dB it would be increased by $130\%$ to 115ms.

• Journal of Korean Academy of Nursing
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• v.5 no.1
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• pp.70-78
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• 1975

The investigators conducted this survey to find out prevalence of diseases and symptoms of the 812 nurses who were working at the 12 Seoul city and University's hospital in Seoul by retrospective study The results of survey were summarized as follows: 1. Distribution of Prevalence Rate of Diseases and Symptoms. 1) An average prevalence rate of diseases and Symptoms of the nurses/100 persons was 64.3 cases at Present October I.1972 2) The total number of diseases and Symptoms was 522 cases at present Oct, I 1972 for the survey nurses. The prevalence rate of following diseases/100 persons were as, foot sore-11, 3. myopia-9.7, neuralgia-9.6, anemia-9.1, insomnia-8.6 cases and the corrected number percent of prevalence rate of diseases and symptoms of the above diseases into 100 denominator were as follows : foot sore-17.6% , myopia-15.4%, neuralgia-14.9%, anemia-14.2% insomnia-13.2%. 3) The prevalence rate of diseases and symptoms/100 person for the age group of 45 and over was 140.0 cases and the age of 35-39 years was 27.3 cases. 4) The prevalence rate of diseases and symptoms/100 persons by the rotation system of nurses'duty/day were as follows: two shift system rotation-86.7 cases, three shift system rotation-67.9 cases and day duty only was 56.2 cases, 5) The prevalence rate of diseases and symptoms/100 person by the basic nursing education background seemed to be lower occurrence against to the higher education and it was 94.4 cases at the Technical Nursing High School graduates. 6) The prevalence rate of diseases and symptoms/100 persons by the marital status of the nurses were as follows; single-64.8 cases, married-48, 7 cases, and widowed-28.6 cases. II. Relationship Between working Experience and prevalence of the Disease and symptoms. 1) There were no relationship by statistical test between prevalence of eye disease and experience at the eye ward(p〉0.05), skin disease and experience at the dermatology ward (p〉0.05), foot sore and experience at the operating room (p〉0.05), varicose vein and experience at the operating room (p〉0.05), sore finger and experience at the central supply room (p〉0.05), infectious disease and experience at the isolation ward(p〉0.05). 2) There was significant relationship by statistical test between pulmonary tuberculosis and experience at the tuberculosis ward (p〉0.05) prevalence of pulmonary tuberculosis was five times in experienced group than non experienced group.