• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.12
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• pp.3824-3832
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• 2009

Would it be true that cutting off using BLOG in business hour prevents that job performance decreases? Even though it is right, would the worker have different reason of using BLOG according to job characteristic? This is the purpose of this study to search the answers for the questions above. Under the first hypothesis, (factors having the people use BLOG can influence the job satisfaction), independent variable was set to three factors and define as 'Interoperability', 'Informative', 'Amusement' respectively and dependent variable was set to job satisfaction in this study. The result of analyzing this hypothesis was that two factors('Interoperability', 'Informative') haveinfluence on job satisfaction but 'Amusement' factor hadn't any influence on job satisfaction. For another hypothesis, (the factor having the worker use BLOG would have different influence on job satisfaction according to job characteristic), Job characteristic was set to 3 group (fixed/unfixed, individual/co-operational, static/active) in this study and these variables were converted to dummy variable for validating the moderating effect on both variables(independent/dependent). The result of analyzing this hypothesis was that all dummy variables set to 3 groupshadn't any moderating effect on both variables. Because a dummy variable couldn't be contained the job characteristic exactly.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.11
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• pp.914-921
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• 2017

The experimental research on a high-altitude environment simulation of space launch vehicle is important for securing independent technologies with launching space vehicles and completing missions. This study selected an altitude of 65 km for the experiment environment where it exceeded Mach number of 6 after the launch of Korean Space Launch Vehicle(KSLV-II). Shock tunnel was used to replicate the flight condition. After flow establishment, in order to confirm aerodynamic characteristics and normal and oblique shockwaves, the flow verification was carried out by measuring stagnation pressure and heat flux of a forebody model, and shockwave stand-off distance of a hemispherical model. In addition, a shock-free technique to recover free-stream condition has been developed and verified. From the results of the three verification tests, it was confirmed that the flow was replicated with the error of about ${\pm}3%$. The error between the slope angle of inclined shockwave of the scaled down transition section model using the shock-free shape and the slope angle of the horizontal plate model, and between the theoretical and the experimental value of the static pressure of the model were confirmed to be 2% and 1%, respectively. As a result, the efficiency of the shockwave cancellation technique has been verified.

• Magazine of the Korean Society of Agricultural Engineers
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• v.39 no.4
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• pp.106-113
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• 1997

Dynamic loading of structures often causes excursions of stresses well into the inelastic range, and the influence of the geometric changes on the dynamic response is also significant in many cases. Therefore, both material and geometric nonlinearity effects should be considered in case that a dynamic load acts on the structure. A structure in a nuclear power plant is a structure of importance which puts emphasis on safety. A nuclear container is a pressure vessel subject to internal pressure and this structure is constructed by a reinforced concrete or a pre-stressed concrete. In this study, the material nonlinearity effect on the dynamic response is formulated by the elasto-viscoplastic model highly corresponding to the real behavior of the material. Also, the geometrically nonlinear behavior is taken into account using a total Lagrangian coordinate system, and the equilibrium equation of motion is numerically solved by a central difference scheme. The constitutive relation of concrete is modeled according to a Drucker-Prager yield criterion in compression. The reinforcing bars are modeled by a smeared layer at the location of reinforcements, and the steel layer model under Von Mises yield criteria is adopted to represent an elastic-plastic behavior. To investigate the dynamic response of a nuclear reinforced concrete containment structure, the steel-ratios of 0, 3, 5 and 10 percent, are considered. The results obtained from the analysis of an example were summarized as follows 1. As the steel-ratio increases, the amplitude and the period of the vertical displacements in apex of dome decreased. The Dynamic Magnification Factor(DMF) was some larger than that of the structure without steel. However, the regular trend was not found in the values of DMF. 2. The dynamic response of the vertical displacement and the radial displacement in the dome-wall junction were shown that the period of displacement in initial step decreased with the steel-ratio increases. Especially, the effect of the steel on the dynamic response of radial displacement disapeared almost. The values of DMF were 1.94, 2.5, 2.62 and 2.66, and the values increased with the steel-ratio. 3. The characteristics of the dynamic response of radial displacement in the mid-wall were similar to that of dome-wall junction. The values of DMF were 1.91, 2.11, 2.13 and 2.18, and the values increased with the steel-ratio. 4. The amplitude and the period of the hoop-stresses in the dome, the dome-wall junction, and the mid-wall were shown the decreased trend with the steel-ratio. The values of DMF were some larger than those of the structure without steel. However, the regular trend was not found in the values of DMF.

• The Journal of the Korea Contents Association
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• v.20 no.10
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• pp.738-749
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• 2020

The stamp commemorating the inauguration of a president is the smallest historical symbol that contains a nation's vision and wishes of the times. The stamp itself is just a collection of images but contains the meaning of the highest leader's perceived image at the time through their face and a symbol. This paper regarded presidential inauguration commemorative stamps in the context of advertisement or promotional materials to structurally analyze the images of the political leaders embedded in stamps utilizing 'semiology' theory, which is considered to be a useful method of advertisement. In accordance with social and cultural changes, the 2000s, when the changes in the presidential inauguration stamp was most distinctively noticeable, was set as the time frame. Only the presidential inauguration commemorative stamps of Moo-hyun Roh, Myung-bak Lee, Geun-hye Park, and Jae-in Moon were selected for this study. In order to interpret the image, a semiotic structure was applied to reconstruct the meaning of the image of the political leaders. Since this can lead to subjective judgment in image analysis, it attempted to find the truth through comprehensive interpretation and approach it from the social and cultural contexts, not a static approach. In this paper, the images of the Korean political leaders in the 2000s shown on stamps are no longer influenced by traditional political factors such as political parties, political ideologies, and regional origins due to the evolution of democracy. This study derives the characteristics of the images of independent and characteristic leaders centered on a person according to the situations and social phenomena of the times.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3950-3960
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• 2014

In this study, the drag forces on a submerged square cylinder were analyzed using a three dimensional hydrodynamic model. The numerical results were compared with the experimental results to check the reliability of the numerical simulations, and the characteristics of the drag forces with the relative depths were analyzed by analyzing the pressure acting on the cylinder surface, which are normally difficult to measure experimentally. The numerical results showed that the drag forces acting on a submerged square cylinder originate mainly from the pressure forces, and component of the shear forces decreased with increasing relative depth. The pressure coefficient distributions showed that in the case of a low relative depth, a relatively high pressure was formed in the front of a cylinder, and a relatively low pressure was formed in the rear, which gives a high drag coefficient. In a high relative depth, the pressure in the front decreased and pressure in the rear increased, which is a similar phenomenon to that normally observed in two dimensional square cylinder flow. The effect of the static pressure was analyzed and the surface elevation difference between the front and rear zone of a cylinder has a limited effect on the drag forces. Finally, the numerical results showed that the drag forces acting on a submerged square are dominated by the dynamic pressure formed by three dimensional flow and the distribution of local surface elevation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.175-181
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• 2016

This occurs when the unbalanced rotating body is inconsistent with the mass center line axis geometric center line. Wheelsets are assembled by a single axle with two wheels and a rotating body of a running railway vehicle. Owing to non-uniformity of the wheel material, the wear, and error of the wheel and axle assembly may cause an imbalance. Wheelsets will suffer the effects of vibrations due to the unbalanced mass, which becomes more pronounced due to the thin and high-speed rotation compared to the shaft diameter This can affect the driving safety and the running behavior of a rail car during high-speed running. Therefore, this study examined this unbalanced wheel using a railway vehicle multibody dynamics analysis tool to assess the impact of the dynamic VI-Rail movement of high-speed railway vehicles. Increasing the extent of wheel imbalance on the analysis confirmed that the critical speed of a railway vehicle bogie is reduced and the high-speed traveling dropped below the vehicle dynamic behaviour. Therefore, the adverse effects of the amount of a wheel imbalance on travel highlight the need for management of wheel imbalances. In addition, the static and dynamic management needs of a wheel imbalance need to be presented to the national rail vehicles operating agency.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.9A
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• pp.702-709
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• 2003

In this paper, we propose an efficient and QoS-aware MAC scheduling algorithm for Bluetooth, which considers both throughput and delay performance of each Master-Slave pair in scheduling decisions, and thus, attempts to maximize overall performance. The proposed algorithm, MTDPP (Modified Throughput-Delay Priority Policy), makes up for the drawbacks of T-D PP (Throughput-Delay Priority Policy) proposed in [6] and improves the performance. Since Bluetooth employs a master-driven TDD based scheduling algorithm, which is basically operated with the Round Robin policy, many slots may be wasted by POLL or NULL packets when there is no data waiting for transmission in queues. To overcome this link wastage problem, several algorithms have been proposed. Among them, queue state-based priority policy and low power mode-based algorithm can perform with high throughput and reasonable fairness. However, their performances may depend on traffic characteristics, i.e., static or dynamic, and they require additional computational and signaling overheads. In order to tackle such problems, we propose a new scheduling algorithm. Performance of our proposed algorithm is evaluated with respect to throughput and delay. Simulation results show that overall performances can be improved by selecting suitable parameters of our algorithm.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.31-40
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• 2017

This paper deals with the high precision of GPS measurement reduction and its implementation on near real-time and kinematic mode for those applications requiring centimeter-level precision of the estimated coordinates, even if target stations are a few hundred kilometers away from their references. We designed the system architecture, data streaming and processing scheme. Intensive investigation was performed to determine the characteristics of the GPS medium-range functional model, IGS infrastructure and some exemplary systems. The designed system consisted of streaming and processing units; the former automatically collects GPS data through Ntrip and IGS ultra-rapid products by FTP connection, whereas the latter handles the reduction of GPS observables on static and kinematic mode to a time series of the target stations' 3D coordinates. The data streaming unit was realized by a DOS batch file, perl script and BKG's BNC program, whereas the processing unit was implemented by definition of a process control file of BPE. To assess the functionality and precision of the positional solutions, an experiment was carried out against a network comprising seven GPS stations with baselines ranging from a few hundred up to a thousand kilometers. The results confirmed that the function of the whole system properly operated as designed, with a precision better than ${\pm}1cm$ in each of the positional component with 95% confidence level.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.694-702
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• 2017

In the case of an elevated railway station, structure borne noise and vibration due to structural limitations allow the load and vibration from railway vehicles to be directly transmitted to the station structure, resulting in an increase in the number of civil complaints from customers and staff of the station. The floating slab track system, which is well known as one of the solutions for reducing the noise and vibration from elevated railway stations, usually contains rubber mounts or rubber pads under the railway slab which act as a damper. These types of device have the disadvantage that is difficult to predetermine the exact stiffness and damping ratio under the nonlinear loads resulting from train services. In this study, an isolator with a friction type of wedge is introduced, which can be applied to floating slab track systems and to be designed with precisely the required stiffness. Furthermore, a comparative analysis of the stiffness between the designed and experimental values is carried out, while the damping ratio, which is closely related to the friction wedge blocks, is deduced according to the train load condition. The performance tests of the isolator were conducted in accordance with the DIN 45673-7 standard which includes both static and dynamic load tests. The load conditions for the performance tests are designed to conform to the DIN standard related to the weight of the train and rail track, in order to perform vertical and horizontal load tests, so as to ensure the secure structural safety of the railway. Also, by checking the change aspect of the friction coefficients of the friction elements according to the loading rate, the vibration reduction performance of the friction type isolator with variable loading rate conditions is examined.

• International Journal of Highway Engineering
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• v.6 no.4 s.22
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• pp.45-53
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• 2004

This study dealt with correlation analysis between deformation strength and rut resistance of asphalt concretes based on binder grade in Superpave specification with changing submerging time. Currently, Mashall mix design is known to have little correlation with rutting related performance. Therefore, some agencies started to use the Superpave method for asphalt mix design. But this method has a weak point in that it can not distinct mechanical property of the asphalt mixtures designed. For solution of these problem, this study used deformation strength, $S_D$, of Kim test which is a new approach under development for finding property which represents rut resistance characteristics of asphalt mixtures under static loading. This study used two aggregates from two regions and five PG asphalt binders. Final rut depth (DR) and dynamic stability (DS) from wheel tracking (WT) test were obtained. and $S_D$ value of the same mixture specimen which was made by gyratory compactor was obtained using loading head [4(1.0)]. Three submerging times 30min, 40min, 50min were used as a test variable at $60^{\circ}C$. Correlation analysis of DR and DS with $S_D$ were performed based on PG grade. It was found out that the $S_D$ has a high correlation with DR and DS of superpave mixtures. The highest $R^2$ was found from the $S_D$ values of 30min. submerged specimen.