• Archives of Plastic Surgery
• /
• v.34 no.3
• /
• pp.365-370
• /
• 2007

Purpose: There are many reports about facial bone fractures, but limited to retrospective data of a single hospital. Etiology and severity of the facial bone fracture have been changed and treatment method and materials have been advanced. In order to reflect those changes and provide up-to-date data of the facial bone fractures in Daegu, we gathered the data and analyzed the epidemiologic study. Methods: The medical records of 1058 fractures in 895 patients were gathered from 5 general hospitals in Daegu during last year and these data were analyzed by following parameters: age, sex, place of residence, occupation, cause of injury, time of injury, location of fracture, length of in-hospital stay, time of operation, treatment method, associated injury, complication. Statistical analysis was performed using the Chi-square test. Results: Most commonly involved age group was 20s(26%) and the sex ratio was 3.4:1(male predominance). Fractures were occurred more in unban and white-color workers. Among variable etiology of injury, traffic accident was the most common cause. Time of injury was heighest at 6 to 7 P.M., on Sunday, in July. Locations of fractures were following sequence: nasal, zygoma, mandible, orbit, maxilla. Mean length of in-hospital stay and time of operation after injury were 6.3 and 3.2 days, respectively. In treatment methods, operative methods were dominant than conservative management and general anesthesia were favored than local anesthesia. Associated injuries were noticed in 188 cases(21.2%) and complications were in 94 cases(8.9%) and among them, ocular problem were common. Conclusion: Compared to previous studies, mean age of occurrence was lowered and the etiologies showed age-specific pattern and reflected the change of lifestyle. In young age groups, sports injury, violence were more dominant and the other hand, traffic accident and fall were dominant in older groups.

• Journal of Korea Society of Industrial Information Systems
• /
• v.18 no.5
• /
• pp.81-92
• /
• 2013

The satellite includes many release mechanisms such as solar array deployment, antenna deployment, cover to protect contamination in scientific equipment, pyro value of the propulsion subsytem, and bypass device in Li-Ion cell module. A drive the initiators is a critical to the successful mission because the initiators of release mechanism driving by the pyrotechnic circuit is operated in single short. The pyrotechnic circuit has to provide switching network for safety. A typical switching network has defect consisting of high current rating fire switch to handle switching transient current during fire the initiator. The pyrotechnic circuit is required some form of power conditioning to reduce the peak power demanded from the bus if the initiators are to be fired from the main bus. This paper design a pyrotechnic circuit synchronized to the fire-command to activate the fire switch to overcome use high current rating fire switch to handle switching transient current during fire the initiator. The pyrotechnic circuit provides a current limited widow pulse for fire current synchronized to the fire-command to insure that fire switch will only carry the current but never switch it. The current limited widow pulse for fire current can be possible to use low current rating and light mass switch in switching network. The current limit function in the pyrotechnic circuit reduces supply voltage to initiator and provides the effect of power conditioning function to reduce peak bus power. The pyrotechnic circuit to apply satellite development on geostationary orbit is verified the function by test in development model.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.32 no.5
• /
• pp.469-479
• /
• 2014

N-RTK(Network based RTK) methods are able to improve the accuracy of GNSS positioning results through modelling of the distance-dependent error sources(i.e. primarily the ionospheric and tropospheric delays and orbit errors). In this study, the comparison of the TTFF(Time-To-Fix-First ambiguity), accuracy and discrepancies in horizontal/vertical components of N-RTK methods(VRS and FKP) with the static GNSS at 20 Unified Control Stations covering Incheon metropolitan city area during solar storms(Solar cycle 24 period) were performed. The results showed that the best method, compared with the statics GNSS survey, is the VRS, followed by the FKP, but vertical components of both VRS and FKP were approximately two times bigger than horizontal components. The reason for this is considered as the ionospheric scintillation because of irregularities in electron density, and the tropospheric scintillation because of fluctuations on the refractive index take the place. When the TTFF at each station for each technique used, VRS gave shorter initialization time than FKP. The possible reasons for this result might be the inherent differences in principles, errors in characteristics of different correction networks, interpolating errors of FKP parameters according to the non-linear variation of the dispersive and non-dispersive errors at rover when considering both domestic mobile communication infra and the standardized high-compact data format for N-RTK. Also, those test results revealed degradation of positing accuracy, long initialization time, and sudden re-initialization, but more failures to resolve ambiguity during space weather events caused by Sunspot activity and solar flares.

• Aerospace Engineering and Technology
• /
• v.6 no.1
• /
• pp.74-82
• /
• 2007

The M-Method that measures the speed of actuator with counting the number of Reaction wheel Tacho Pulse has the many advantages such that a realization is simple and measuring time is uniform, but it also has the disadvantage that measuring speed becomes worse as the wheel speed goes lower. On the contrary, the T-Method that measures the time duration between the pulses is more accurate at lower-speed and its time delay is smaller than M-Method, but its realization is more difficult than M-Method because measuring time is varying with wheel speed variation. Thought M/T Method mixing M-Method with T-Method is widely used in order to measure the speed in the motor industrial area, one of two methods has been used in the spacecraft design area. Therefore, we try to apply both methods together to measuring the speed of Reaction Wheel, the core actuator for low earth orbit satellite. This paper provides the Reaction Wheel simulation board located in the Spacecraft Dynamic Simulator, ground support test set.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.48 no.5
• /
• pp.355-361
• /
• 2020

Among these satellites, low - orbit small satellites with military characteristics require multi - target observation, and demand for high-resolution photographs and images is increasing. Fast maneuverability is the most important factor for high-resolution images and multi - target observations. However, in the case of a small satellites, it is possible to perform the attitude maneuver if it has high speed, but the residual vibration occurs when the attitude maneuver is completed and the next attitude maneuver is completed. In this study, to verify the vibration characteristics of the plate generated after attitude maneuver, an experimental fixture for simulating the attitude maneuver was fabricated and tested. In addition, Eddy Current Damper (ECD) using Eddy Current Brake system (ECB) is proposed as a passive damping method using permanent magnet to reduce vibration. A mathematical model was established to apply ECD and it was experimentally implemented according to the magnetic flux density and the air gap of the permanent magnet. One plate of four solar panels (plate) was specified, the residual vibration reduction performance after the test was verified experimentally.

• The Korean Journal of Air & Space Law and Policy
• /
• v.28 no.2
• /
• pp.259-294
• /
• 2013

After its experiment involving the exploding of a satellite in space in 2007, China proudly aired news on TV and ran articles in newspapers. However, the event was internationally criticized and drew widespread attention. Many countries denounced the explosion by pointing out that it could be part of the nation's plan to expand its military power to space or that it could pose a danger to the peaceful use of space. However, there is no talk of whether the experiment that produced a huge amount of space debris could have violated an international law, namely the Outer Space Treaty. Although space garbage has been said to be a serious problem, the amount is still on the increase. If we continue to launch new space launch vehicles into orbit at this rate, we will not be able to use it anytime soon like we do today. As the commercial use of space is likely to increase, the situation will certainly get worse. The international community is fully aware of the seriousness of the problem and working together to reduce the amount of space garbage. However, despite the fact that the United States and Soviet Union's ASAT(Anti-Satellite) programs have been implemented for a long time, there have been no complaints about them in terms of military expansion or breach of the Outer Space Treaty. Also, the recent Chinese test is largely viewed to be in accordance with international law. A lot of research has been undertaken with regard to the problem of space garbage. Now people's awareness of dangers being posed has been fully raised. Under the circumstances, the dismissing of China's satellite smashing, leaving a big mess in its wake, as nothing more than an experiment, is a red flag to, if not many, at least some people. By means of this thesis, I would like to review whether the Chinese test has violated an international space law. This thesis presents an overview of the issues surrounding the event and examines the possibility of violating the Outer Space Treaty, formally the Treaty on Principle Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies. After the China test, the UN Scientific and Technical Subcommittee first adopted space debris mitigation guidelines, I'll introduce the content of the guidelines and discuss the characteristics of the guidelines and what can be done to address the issue.

• Korean Journal of Remote Sensing
• /
• v.29 no.5
• /
• pp.545-554
• /
• 2013

Augustine is an active stratovolcano located in southwest of Cook Inlet, about 290 kilometers southwest of Anchorage, Alaska. Between January 11 and 28, 2006, the volcano erupted explosively 14 times. We collected twelve permanent GPS stations operating by Plate Boundary Observatory (PBO) from 2005 to 2011. All data processing was carried out using Bernese GPS Software V5.0 with IGS precise orbit. Static baseline processing by fixing AC59 station was applied for the volcano activity monitoring. AC59 is the nearest (about 24.5 km) station to Augustine volcano, and located on North America Plate including Augustine Island. The test results show inflation (9.7 cm/yr) and deflation (-9.2 cm/yr) of volcano before and after eruption around crater clearly. After volcano activity has reached a plateau, some of the GPS stations installed north of the volcano show ground subsidence phenomenon caused by compaction of pyroclastic flows. These results indicate the possibility of using surface deformation observed by GPS for monitoring and prediction of volcano activity.

• Composites Research
• /
• v.30 no.6
• /
• pp.379-383
• /
• 2017

A study on the low Earth orbit (LEO) space environment have been conducted as a use of composites have increased. Among the LEO environmental factors, atomic oxygen is one of the most critical factors because atomic oxygen can react and erode a surface of polymer-based composite materials. POSS (Polyhedral Oligomeric Silsesquioxane) materials have been widely studied as an atomic oxygen-resistant nanomaterial. In this study, nanocomposites, which are composed of OG (Octaglycidyldimethylsilyl) POSS nanomaterials and DGEBA/DDM epoxy, were fabricated to find out its thermal and mechanical properties. FT-IR results showed that the nanocomposites were fully cured and contained OG POSS enough. Thermogravimetric analysis and differential scanning calorimetry were performed to measure the thermal properties of the nanocomposites. The initial mass loss temperature and char yield were increased through the filling of OG POSS. As the content of OG POSS increased, glass transition temperature tended to increase to 5 wt.% of OG POSS, but the temperature decreased significantly at 10 wt.% of OG POSS. The tensile test results showed that the content of OG POSS did not affect tensile strength and tensile stiffness.

• Journal of Aerospace System Engineering
• /
• v.13 no.3
• /
• pp.23-31
• /
• 2019

The design requirements of modern satellites vary depending on the purpose of operation. Like conventional medium and large-scale satellites, small satellites which operate on low orbit may also serve military purposes. As a result, there is increased demand for high-resolution photos and videos and multi-target observation becomes important. The most important design parameter for multi-target observation is the satellites' maneuverability. For increased maneuverability, the miniaturization is required to increase the stiffness of the satellite as this decreases the mass moment of inertia of the satellite. In the case of a solar panel having relatively low stiffness compared to the satellites' body, vibrations are generated when the attitude maneuver is performed, which greatly influences the image acquisition. For verification of such vibrational characteristics, the satellites is modeled as a reduced model, and experimental zig for simulating attitude maneuver is introduced. A rigidity simulator for simulating the stiffness of the satellite is also proposed. Additionally, the objective of the experimental method is to simulate the maneuvering angle of the satellite based on the winding length of the wire using a step motor, and to experimentally verify the vibration characteristics of the satellite body and the solar panel generated during the maneuvering test.

• Korean Journal of Remote Sensing
• /
• v.36 no.6_1
• /
• pp.1323-1337
• /
• 2020

GEO-KOMPSAT-2A AMI (Advanced Meteorological Imager) radiometric calibration evaluation is an essential element not only for functional and performance verification of the payload but for the quality of the sensor data. AMI instrument consists of six reflective channels and ten thermal infrared ones. One of the key parameters representing radiometric properties of the sensor is a SNR (Signal-to-Noise Ratio) for the reflective channels and a NEdT (Noise Equivalent delta Temperature) for the IR ones respectively. Other important radiometric calibration parameters are a dynamic range and a gain value related with the responsivity of detectors. To verify major radiometric calibration performance of AMI, an offline radiometric evaluation tool was developed separately with a real-time AMI data processing system. Using the evaluation tool, validation activities were carried out during the GEO-KOMPSAT-2A In-Orbit Test period. The results from the evaluation tool were cross checked with those of the HARRIS, which is the AMI payload vendor. AMI radiometric evaluation activities were conducted through three phases for both sides (Side 1 and Side 2) of AMI payload. Results showed that performances of the key radiometric properties were outstanding with respect to the radiometric requirements of the payload. The effectiveness of the evaluation tool was verified as well.