• Journal of Astronomy and Space Sciences
• /
• v.29 no.4
• /
• pp.389-395
• /
• 2012

The problem of spacecraft attitude control is solved using an adaptive neuro-fuzzy inference system (ANFIS). An ANFIS produces a control signal for one of the three axes of a spacecraft's body frame, so in total three ANFISs are constructed for 3-axis attitude control. The fuzzy inference system of the ANFIS is initialized using a subtractive clustering method. The ANFIS is trained by a hybrid learning algorithm using the data obtained from attitude control simulations using state-dependent Riccati equation controller. The training data set for each axis is composed of state errors for 3 axes (roll, pitch, and yaw) and a control signal for one of the 3 axes. The stability region of the ANFIS controller is estimated numerically based on Lyapunov stability theory using a numerical method to calculate Jacobian matrix. To measure the performance of the ANFIS controller, root mean square error and correlation factor are used as performance indicators. The performance is tested on two ANFIS controllers trained in different conditions. The test results show that the performance indicators are proper in the sense that the ANFIS controller with the larger stability region provides better performance according to the performance indicators.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.05a
• /
• pp.1268-1271
• /
• 2006

This paper introduces what amount of railway vibration level observed from residential area. Five residential area located near the railway were selected to measure the vibration levels generated by the different types of Korean railway vehicles. Those 3-axis vibration measurements are applied to the frequency-dependent weighting functions recommended by ISO 2631-2, which are used to evaluate the 3-axis combined vibration levels such as peak levels, L 10 levels and root-mean-squared values. These evaluated results are shown to indicate the environmental vibration severity for the different residential area. In addition to those physical vibration measurements, the survey of subjective responses of residents was also carried out by distributing the questionnaire suggested by WHO. The questionnaire includes the subjective scales for assessing the annoyance and the sleep-disturbance caused by the environmental vibration. The statistical analysis results collected from 386 respondents are introduced. The highly annoyed population and the highly sleep-disturbed one are examined to identify the .elation between their subjective scale and their corresponding environmental vibration levels. These attempts are shown to lead to the salient model to relate the environmental vibration level and the subjective responses of Korean residents to annoyance and sleep-disturbance.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.2
• /
• pp.96.1-96.1
• /
• 2011

Halo coronal mass ejections (HCMEs) are major cause of the geomagnetic storms. To minimize the projection effect by coronagraph observations, we consider two CME cone models: an ice-cream cone model and an asymmetric cone model. These models allow us to determine three dimensional parameters of HCMEs such as radial speed, angular width, and the angle between sky plane and cone axis. In this study, we compare these parameters obtained from both models using 50 well-observed HCMEs from 2001 to 2002. Then we obtain the root mean square error (RMS error) between measured projection speeds and estimated ones for the models. As a result, we find that the radial speeds obtained from the models are well correlated with each other (R=0.89), and the correlation coefficient of angular width is 0.68. The correlation coefficient of the angle between sky plane and cone axis is 0.42, which is much smaller than what is expected. The reason may be due to the fact that the source locations of the asymmetric cone model are assumed to be near the center. The average RMS error of the asymmetric cone model (86.2km/s) is slightly smaller than that of the ice-cream cone model (88.6km/s).

• The Journal of Korean Academy of Prosthodontics
• /
• v.33 no.2
• /
• pp.177-197
• /
• 1995

The endodontically treated tooth is generally restored with post & core, owing to the brittleness and the loss of large amount of tooth structure. Although there have been lots of studies about the endodontically treated teeth, the three-dimensional quantitative studies about the strees distribution of them are in rare cases. In this study, it was assumed that the coronal portion of the upper incisou had severely damaged. After the root canal therapy it was post cored, and restored with PFM crown, for this experiment nine types of model were constructed : 1); long, 2); medium, 3); short gold post for the roots supported with a narmal alveolar bone, 4); long, 5); medium, 6); short gold post for the roots supported with an alveolar bone resorbed to its 1/3 of root length, 7); long, 8); medium, 9); short base metal post for the roots supported with an alveolar bone resorbed to its 1/3 of root length. Force was applied from two directions. One was functional maximum bite force(300N) applied to the spot just lingual to the incisal edge with the angle of 45 degrees to the long axis of the tooth, and the other one was horizontal force(300N) applied to the labial surface. The results analyzed with three-dimensional finite element method were as follows : 1. Stress was concentrated on the middle portion of the labial side dentin of the root and the lingual portion of the apical dentin of the root. Stress in the post showed maximum value at 2 mm above the post apex. 2. In case of the long post and base metal post, strees was concentrated on the apex of the root and the post. 3. In case of the longer post, the displacement on the post-cement interface was lessened. The gold post was more displaceable than the base metal post. 4. In case of the alveolar bone resorption, stress concentrated on the root and the post and displacement on the post-cement interface were increased.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.37 no.3
• /
• pp.381-386
• /
• 2010

As the vertical fracture occurs at the various locations following the long axis of a root, treatment method of crown-root fractured anterior teeth is decided according to the depth. If the fracture line is close to the crown, gingivectomy, orthodontic - forced eruption or surgical extrusion of apical fragment could be done. If the line is over 1/3 length of the root, the prognosis is poor and extraction is usually undertaken. However, extraction of maxillary incisor at growing children causes many complications such as esthetic, phonetic problem and alveolar bone resorption. Therefore, preservation of tooth is the highest priority. Recently, intentional replantation with composite resin could be considered as alternative treatment of crown-root fractured anterior tooth. This report presents a patient in mixed dentition with deep vertical crown-root fracture of the maxillary permanent central incisors by trauma. Intentional replantation of the fractured teeth was performed using composite resin. After 2 years, specific clinical symptom has not been found and the patient was satisfied of esthetic result. This method suggests the new technique to preserve a tooth as an alternative to extraction, although it is technically sensitive and the reports of long-term prognosis is insufficient.

• The Journal of Korean Academy of Prosthodontics
• /
• v.34 no.4
• /
• pp.780-790
• /
• 1996

The endodontically treated tooth is generally restored with post and core, owing to the brittleness and the loss of large amount of tooth structure. Although there have been lots of studies about the endodontically treated teeth, the three-dimensional quantitative studies about the stress distribution of them are in rare cases. In this study, it was assumed that the coronal portion of the upper incisor had extensively damaged. After the root canal therapy it was post cored, and restored with PFG crown. The three-dimensional model, in which the root was supported with a normal alveolar bone, was constructed. Force was applied to the centric stop point with the angle of 135 degrees to the long axis of the tooth. Force was assumed to be 250N as functional maximum bite force of upper central incisors. The results analyzed with three-dimensional finite element method were as follows : 1. Stress was concentrated on the middle portion of the labial side dentin and the apical portion of the dentin. 2. Stress in the post was more concentrated on the post apex. 3. The displacement of the post at the post-cement interface was almost symmetrical la-bio-lingually. 4. It assumed that restoring extensively damaged tooth with a post-core and PFG crown is an adequate method of restoration.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.24 no.4
• /
• pp.758-762
• /
• 1997

There are various types of localized tooth malpositions in the mixed dentition, such as abnormal tooth axis, anterior crossbite of some incisors, impaction, midline diastema, ectopic eruption, and so forth. We, Pediatric Dentists, have usually used removable appliances for these instances. But, removable orthodontic appliances, as is known, have marked limitations in some situations, for example, severe rotation, intrusion and extrusion, root torque, closure of large diastema, traction of impacted tooth, etc. In such cases, Whip spring, combined with fixed or removable appliance, can increase utilities of removable orthodontic appliances. The authors have applied whip springs to some cases showing localized positional and arrangement problems, and have witnessed the results as follows; 1. The refined and elaborate control of direction and magnitude of force by the operator, and accurate compliance of the patients were requisite for the treatment with it. 2. It showed special effectiveness for de rotation of incisors. Although it yields some benefit for root movement, the special consideration for incomplete roots in this age bracket was required. 3. In the localized malalignment cases in mixed dentition, uncurable with traditional removable appliances but practically unrealistic with fixed appliance therapy, the whip spring was thought to be a good alternative.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.28 no.11
• /
• pp.68-76
• /
• 2014

This paper presents an offset error compensation algorithm for the accurate phase angle of the grid voltage in single-phase grid-connected inverters. The offset error generated from the grid voltage measurement process cause the fundamental harmonic component with grid frequency in the synchronous reference frame phase lock loop (PLL). As a result, the grid angle is distorted and the power quality in power systems is degraded. In addition, the dq-axis currents in the synchronous reference frame and phase current have the dc component, first and second order ripples compared with the grid frequency under the distorted grid angle. In this paper, the effects of the offset and scaling errors are analyzed based on the synchronous reference frame PLL. Particularly, the offset error can be estimated from the integrator output of the synchronous reference frame PLL and compensated by using proportional-integral controller. Moreover, the RMS (Root Mean Square) function is proposed to detect the offset error component. The effectiveness of the proposed algorithm is verified through simulation and experiment results.

• Journal of Wetlands Research
• /
• v.14 no.4
• /
• pp.597-605
• /
• 2012

This study was conducted in order to determine changes in the growth responses of Quercus serrata and Q. aliena which are potential natural vegetation of riverine in Korea under four light gradients within ambient and elevated $CO_2$ concentration and temperature levels. As a result, growth responses of two species were affected by light factor. Aboveground, belowground, plant biomass and root:shoot ratio of two species grown under the control and treatment were increased in the highest light level. Plant biomass and root:shoot ratio of two oak species were not significantly affected by elevated $CO_2$ and temperature, while aboveground biomass of them was lower in the treatment than control. Belowground biomass of Q. serrata was lower in the treatment than control under the gradients that are more than 70% of light level. As light intensity increases, elevated $CO_2$ and temperature promoted root growth of two oak species but had a negative effect on aboveground growth. According to the principal component analysis(PCA), two oak species were discriminatively arranged based on factor 1 and 2. Also, the reactions towards the ambient and elevated $CO_2$ and temperature were slightly different. It is clearly visible that all features relied on axis 1 and axis II are highly correlated with most variables except for stem and shoot length.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.35 no.1
• /
• pp.55-62
• /
• 2017

The SRP (Solar Radiation Pressure) model has always been an issue in the dynamic GPS (Global Positioning System) orbit determination. The widely used CODE (Center for Orbit Determination in Europe) model and its variants have nine parameters to estimate the solar radiation pressure from the Sun and to absorb the remaining forces. However, these parameters show a very high correlation with each other and, therefore, only several of them are estimated at most of the IGS (International GNSS Service) analysis centers. In this study, we attempted to numerically verify the correlation between the parameters. For this purpose, a bi-directional, multi-step numerical integrator was developed. The correlation between the SRP parameters was analyzed in terms of post-fit residuals of the orbit. The integrated orbit was fitted to the IGS final orbit as external observations. On top of the parametric analysis of the SRP parameters, we also verified the capabilities of orbit prediction at later time epochs. As a secondary criterion for orbit quality, the positional discontinuity of the daily arcs was also analyzed. The resulting post-fit RMSE (Root-Mean-Squared Error) shows a level of 4.8 mm on average and there is no significant difference between block types. Since the once-per-revolution parameters in the Y-axis are highly correlated with those in the B-axis, the periodic terms in the D- and Y-axis are constrained to zero in order to resolve the correlations. The 6-hr predicted orbit based on the previous day yields about 3 cm or less compared to the IGS final orbit for a week, and reaches up to 6 cm for 24 hours (except for one day). The mean positional discontinuity at the boundary of two 1-day arcs is on the level of 1.4 cm for all non-eclipsing satellites. The developed orbit integrator shows a high performance in statistics of RMSE and positional discontinuity, as well as the separations of the dynamic parameters. In further research, additional verification of the reference frame for the estimated orbit using SLR is necessary to confirm the consistency of the orbit frames.