• Tribology and Lubricants
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• v.23 no.5
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• pp.219-227
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• 2007

The dynamic performance of air foil bearings relies on a coupling between a thin air film and an elastic foil structure. A number of successful analytical techniques to predict dynamic performance have been developed. However, the evaluation of its dynamic characteristic is still not enough because of the mechanical complexity of the foil structure and strong nonlinear behavior of friction force. This work presents a nonlinear transient analysis method to predict dynamic performance of foil bearings. In this method, time dependent Reynolds equation is used to calculate pressure distribution and a finite element method is used to model the bump foil structure. The analysis is treated with a direct implicit integration technique that can handle nonlinear problems and the stick-slip algorithm is used to consider friction force. Using this method the response to the mass unbalance excitation is investigated for various design parameters and operating conditions. The results of analysis show that foil bearing is very effective on the restriction of vibration at the resonance frequency compared to the rigid surface bearings and the effectiveness depends on the operating conditions, static load and a amount of mass unbalance. In addition, there exist optimum values of friction coefficient, bump foil stiffness and number of circumferential slit with regards to minimizing dynamic response at the resonance frequency. These optimum values are system dependent.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.1
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• pp.31-36
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• 2014

This paper shows the feasibility of using carbon-fiber-reinforced polymer (CFRP) composite materials for manufacturing automotive coil springs. For achieving weight reduction by replacing steel with composite materials, it is essential to optimize the material parameters and design variables of the coil spring. First, the shear modulus of a CFRP beam model, which has $45^{\circ}$ ply angles for maximum torsional stiffness, was calculated and compared with the test results. The diameter of the composite spring was predicted to be 17.5 mm for ensuring a spring rate equal to that when using steel material. Finally, a finite element model of the composite coil spring with $45^{\circ}$ ply angles and 17.5 mm wire diameter was constructed and analyzed for obtaining the static spring rate, which was then compared with experimental results.

• Water for future
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• v.19 no.2
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• pp.149-156
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• 1986

The generated sequences of monthly flows were analyzed based on the range concept. With the optimum operation rule of the reservoirs as the one which maximizes the wateruse downstream the waterrelease from the reservoir was determined and with \ulcorner consideration to the mean inflows and the range of monthly flows the required reservoirs capacity was stochastically determind. It is suggested that the result obtained in this study would be applied to approximately estimate, in the stage of preliminary design, the required capacity of a reservoir in question with the limited information such as the mean monthly inflow and the period of reservoir operation. For the determination of a reservoir capacity Rippl's mass-curve method has been long used with the past river flow data assuming the same flow records will be repeated in the future. This study aims to find out a better method for determining the reservoir capacity by employing the analytical theory based on the stochastic process. For the present study the synthetic generation methods of Thomas-Fiering type was used to synthetically generate 50 years of monthly river inflows to three single-purpose reservoirs and three multi-purpose reservoirs.

• Land and Housing Review
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• v.2 no.2
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• pp.145-155
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• 2011

It is very important for successful construction to estimate the soil volume conversion factor of domestic weathered ground accurately and reasonably. However, it is very difficult to quantify the weathering degree of weathered ground at the field, so that the soil volume conversion factor used in Korea is often dependent upon the standard of foreign countries. Besides, the soil volume conversion factor of domestic weathered ground has been rarely studied and the use and accuracy of the soil volume conversion factor have been questioned persistingly. This study suggests a simple but robust method for estimating the soil volume conversion factor and measuring the weathering degree reasonably, and attempts to establish the utilization of a soil volume conversion factor measurement system based on experimental and analytical results. We made relationship between electrical resistivity and weathering degree presented from weathering index obtained through laboratory tests using field samples, and an estimation method of in-situ weathering degree for granites and a calculation method of soil volume conversion factor using electrical resistivity. And also, we suggested the photogrametry measurement-equipment system for measuring the volume of cargo box and the application plan of stand equipment and RFID for calculating the earth volume and distinguishing buggies in order to design the measurement system for soil volume conversion factor applicable to the field. Ultimately, the Weathered Earth-work Management Program (WEMP) was developed, so field managers may easily obtain the information about earth volume and soil volume conversion factor at the weathered ground.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.6
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• pp.642-648
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• 2016

This paper deals with an analytical and experimental investigation to predict the axial thrust load that results from turbocharger operating conditions. The Axial forces acting on the turbocharger thrust bearing are caused by the unbalance between turbine wheel gas forces and compressor wheel air forces. It has a great influence on the friction losses, which reduces the efficiency and performance of high-speed turbocharger. This paper presents the calculation procedure for the axial thrust forces under operating conditions in a turbocharger. The first step is to determine the relationship between thrust forces and strains by experimental and numerical methods. The analysis results were verified by measuring the strains on a thrust bearing with the specially designed test device. And then, the operating strains and temperatures were measured to inversely calculate the thrust strains which were compensated the thermal effects. Therefore it's possible to calculate the magnitudes of the thrust forces under operating turbocharger by comparing the regenerated strains with the rig test results. It will possible to optimize the design of a thrust bearing for reducing the mechanical friction losses using the results.

• Journal of Pharmaceutical Investigation
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• v.36 no.4
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• pp.277-282
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• 2006

Lisinopril is one of the angiotensin-converting enzyme inhibitors, which have been used for treatment of hypertension and heart failure. The aim of this study was to evaluate the bioequivalence of two lisinopril tablet, $Lisihexal^{\circledR}$ and $Zestril^{\circledR}$ as a test and reference, respectively. The study was came out on 28 healthy male Korean volunteers in $2{\times}2$ crossover design. An analytical method with LC-MS-MS was developed for the quantification of lisinopril and enalapril(IS) using SPE method. The condition was selective, sensitive and precise in human plasma, that was enough for the pharmacokinetic study of lisinopril. The pharmacokinetic parameters such as $AUC_t,\;AUC_{inf},\;C_{max},\;T_{max}\;and\;t_{1/2}$ were calculated and ANOVA test was used for the statistical analysis of the parameters using log transformed $AUC_t,\;AUC_{inf}\;and\;C_{max}$. $t_{1/2}$ of test and reference drugs were calculated $11.4{\pm}5.1\;and\;16.1{\pm}9.9\;hr$, respectively. The 90% confidence intervals of $AUC_t,\;AUC_{inf}\;and\;C_{max}$ were log 0.9245$\sim$log 1.0603, log 0.9270$\sim$log 1.0601 and log 0.9548$\sim$log 1.1009, within the acceptable range of log 0.8 to log 1.25 by KFDA bioequivalence criteria. Two medications of lisinopril were evaluated bioequivalent and thus may be prescribed interchangeably.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.6
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• pp.1098-1115
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• 2010

An inseparable challenge associated with every random access network is the design of an efficient Collision Resolution Algorithm (CRA), since collisions cannot be completely avoided in such network. To maximize the collision resolution efficiency of a popular CRA, namely Binary Exponential Backoff (BEB), we propose a reactive backoff algorithm. The proposed backoff algorithm is reactive in the sense that it updates the contention window based on the previously selected backoff value in the failed contention stage to avoid a typical type of collision, referred as cross-collision. Cross-collision would occur if the contention slot pointed by the currently selected backoff value appeared to be present in the overlapped portion of the adjacent (the previous and the current) windows. The proposed reactive algorithm contributes to significant performance improvements in the network since it offers a supplementary feature of Cross Collision Exclusion (XCE) and also retains the legacy collision mitigation features. We formulate a Markovian model to emulate the characteristics of the proposed algorithm. Based on the solution of the model, we then estimate the throughput and delay performances of WLAN following the signaling mechanisms of the Distributed Coordination Function (DCF) considering IEEE 802.11b system parameters. We validate the accuracy of the analytical performance estimation framework by comparing the analytically obtained results with the results that we obtain from the simulation experiments performed in ns-2. Through the rigorous analysis, based on the validated model, we show that the proposed reactive cross collision exclusionary backoff algorithm significantly enhances the throughput and reduces the average packet delay in the network.

• Health Policy and Management
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• v.18 no.3
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• pp.1-17
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• 2008

The measurement and management of patient satisfaction has become one of the key issues in the last two decades. Hospitals must thoroughly understand the needs of their customers and design products and health services that meet and exceed their expectations. The importance-performance analysis(IPA) is a widely used analytical technique that yields strategies for managing customer satisfaction in a variety of applications. IP A is a two-dimensional grid based on customer-perceived importance of quality attributes and attribute performance. Depending on the interplay of these two dimensions, four strategies can be derived. The aim of this study is to develop the management strategies for improving patient satisfaction in university hospitals using the I-P analysis. The attributes on inpatient service quality in 4 university hospitals was investigated using the Martilla and James(l977)' s a mean adjusted I-P grid where the axes of the grid cross at the average rating point of all items. The patient satisfaction questionnaires were completed by 600 hospital inpatients. The main statistical methods are path analysis and IPA with SPSS 12.0 and AMOS 4.0 statistical softwares. The two attributes, physician and medical service, administrative staff kindness attributes position in first quadrant(Keep Up the Good domain). The nurse and nursing service attributes position in second quadrant(Possible Overkill domain). The two attributes, convenience of check-in service, facilities and physical environment position in third quadrant(Low Priority domain). Finally the quality of inpatient service(food etc.) attributes position in fourth quadrant(Concentrate Here domain). These findings show various implications on the development of strategies in university hospitals in the future. It was determined that quality of inpatient service(food etc.) need to concentrate more on investments. These investments include a taste, price, proper provision of food service and quick response of pain management. A low priority was given to investment in streamlining the check-in process of inpatient and hospital facilities and physical environment in the long run.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.8
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• pp.5342-5348
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• 2014

Slope stability analyses were conducted to investigate the limitations of application of the standard inclination of slope and the effects of the berm width on the slope stability. The standard slope inclination could be applied to the basic slope sections that were considered for the analyses, whereas additional slope stability analysis should be performed for the case of considering ground water. A comparison of the factors of safety between the case of installing a berm and the case of letting the grading have an equivalent section area with the case of installing the berm, the factors of safety in the case of installing a berm were greater than those for the case of allowing grading, and the differences between the factors of safety increase with increasing berm width. For all the sections considered in the analyses, the increments of the safety factor were proportional to the width of the berm and those corresponding to the embankment slope and cut slope with a berm width of 7m were 34.5% and 48%, respectively.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.107-115
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• 2014

In this study, we examined the seismic isolation effects due to the difference between the center of mass of the building and the center of stiffness of isolation layer. Because the base isolation technique is a technique that is highly dependent on the performance of seismic isolation devices installed on the seismic isolation layer, we have to examine the horizontal stiffness of seismic isolation devices after making them. If difference between the design stiffness and the actual stiffness of the seismic isolation device occurred, a big problem may be generated in the upper members on the seismic isolation layer. The analytical results show that the more eccentricity increases, the more maximum response acceleration, story shear and the member forces of the upper part of the structure increases, and the damage is expected to be in excess. Therefore, it is recommended that if possible, isolation devices have to be designed to coincide the center of mass of the building with the center of stiffness of isolation layer. If not after making isolation devices, they need to be relocated to prevent the eccentricity.