• Journal of the Korean Society of Visualization
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• v.16 no.1
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• pp.30-36
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• 2018

In the present study, we investigate the flow characteristics of a quadrotor UAV in a hovering mode by measuring multiple two-dimensional velocity fields in the wake. The experiment is conducted at Re = 24,000 in a chamber large enough to neglect the ground effect, where Re is the Reynolds number based on the rotor chord length and the rotor tip speed. The rotational speed of the rotor is determined by an optical tachometer so that the lift force can be balanced with the weight of the UAV. The velocity field measured on the center plane of the rotor shows that the vortices are shedding from the tip of the rotor, inducing large fluctuations in the streamwise velocity along the wake shear layer. The strength of the rotor-tip vortex shedding is asymmetric with respect to the rotor axis due to the interaction between the rotor and the wake centerline of each rotor is inclined to the center of the UAV due to the pressure difference caused by the induced velocity. The wake from each rotor moves closer to each other while traveling in the streamwise direction, and then is merged together inducing large fluctuations in the transverse velocity. Due to the wake merging, on the center plane of the UAV, the velocity increases in the streamwise direction showing two-peak structure in the streamwise velocity contours.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.30.2-30.2
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• 2010

It is a mistaken impression that the midlatitude ionosphere was a very stable region with well-known morphology and physical mechanism. However, the large disturbances of midlatitude ionospheric contents in response to global thermospheric changes during geomagnetic storms are reported in recent studies using global GPS TEC map and space-born thermospheric UV images, and its importance get higher with the increasing application areas of space navigation systems and radio communication which are mostly used in the midlatitudes. Positive and negative storm phases are used to describe increase and decrease of ionospheric electron density. Negative storms result generally from the enhanced loss rate of electron density according to the neutral composition changes which are initiated by Joule heating in high-latitudes during geomagnetic storms. In contrast, positive ionospheric storms have not been well understood because of rare measurements to explain the mechanisms. The large enhancements of ground-based GPS TEC in Korea were observed on 8 and 10 November 2004. The positive ionospheric storm was continued except for dawn on 8 November, and its maximum value is ~65 TECU of ~3 times compared with the monthly mean TEC values. The other positive phase on 10 November begin to occur in day sector and lasted for more than 6 hours. The O/N2 ratios from GUVI/TIMED satellite show ~1.2 in northern hemisphere and ~0.3 in southern hemisphere of the northeast Asian sector on 8 and 10 November. We suggest the asymmetric features of O/N2 ratios in the Northeast Asian sector may play an important role in the measured GPS TEC enhancements in Korea because global thermospheric wind circulation can globally change the chemical composition during geomagnetic storms.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.453-453
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• 2010

In this study, zinc germanate ($Zn_2GeO_4$) thin films has been synthesized by using radio frequency magnetron sputtering and the divalent manganese-activated luminescence was characterized. X-ray diffraction patterns of the as-deposited $Zn_2GeO_4$:Mn films showed only a broad feature, indicative of an amorphous structure. Scanning electron microscopy images revealed that the as-deposited $Zn_2GeO_4$:Mn has a smooth surface morphology. The $Zn_2GeO_4$:Mn films were found to be crystallized by annealing in air ambient at temperatures as low as $700^{\circ}C$. The annealed $Zn_2GeO_4$:Mn possessed a rhombohedral polycrystalline structure. The broad-band photoluminescent emission spectrum from 470 to 650nm was obtained at room temperature from the $Zn_2GeO_4$:Mn films. The emission peak was centered at around 535nm in the green range, which originates from the intrashell transition of manganese $3d^5$ electrons from $^4T_1$ excited-state level to the $^6A_1$ ground state. The PL emission spectrum had an asymmetric line shape, which results from the $^3d_5$ electron transitions of divalent manganese ions located at different sites of the zinc germanate host crystal lattice. Electroluminescent devices were fabricated using $Zn_2GeO_4$:Mn as an emission layer. The fabricated devices showed a green EL emission similar to the PL emission. The CIE chromaticity color coordinates of the EL emission were determined to be x=0.308 and y=0.657.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.10
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• pp.1737-1743
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• 2008

A weather radar extracts the weather information from the return echoes which consist of scattered electromagnetic wave signals from rain, cloud and dust particles, etc. The characteristics of Doppler weather signal and ground clutter should be analyzed to extract the accurate weather information. However, the conventional symmetric weather Doppler model is somewhat inappropriate in representing various weather situations. Therefore, the improved model is suggested to describe the skewness in the Doppler spectrum model. Using the suggested model, many various weather signals can be simulated efficiently in time and spectral domain according to weather situations, operation environment and system characteristics. This simulation method may be very helpful in verifying the accuracy of the weather information extraction algorithms and developing the new system for further performance improvement.

• Journal of the Korea Society for Simulation
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• v.29 no.3
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• pp.1-8
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• 2020

When enemy drones infiltrate large urban areas, various forms of great republics are deployed in large areas to respond. Due to the characteristics of a large number of government-run aircraft, the residual coal, other than the hit bullet, falls into various sizes of debris after its own explosion. The damage rate was analyzed by dividing the debris into anti-aircraft guns and guided weapons by deriving four factors: critical speed, fragmentation mass, initial speed of debris, and object collision speed, which can cause damage to human life as the debris falls to the ground. In the future, the North is expected to infiltrate the capital city of Seoul by operating unmanned aerial vehicles, which are asymmetric forces, and the damage could be minimized by setting up pre-fatal and fire-restricted zones to minimize casualties between responses.

• Korea and Global Affairs
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• v.1 no.1
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• pp.115-152
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• 2017

This paper is to analyse the changes in the future war patterns and ROK's response. To this end the paper is composed of 5 chapters titled instruction; concept, characteristics, types, and evolution of war; changes in the war patterns of the future; Korea's response strategies for the future war. Truth can be immutable, but everything else changes. War has begun with human history, and today there are still wars in places all over the world. As ages change from agricultural society to industrial society to knowledge and information society, aspects(patterns) of war have also changed. Future warfare includes the 5th dimensional war(in the ground, the sea, the air, the universe, the cyber), the network-centric, the precision strike, the rapid maneuver, the non-gunpowder, the non-lethal, the unmanned robot, the informational & cyber, the asymmetric, the non-linear, and the parallel etc. In response to these changes in the pattern of wars, the ROK military should seek (1)to build a future-oriented military force, (2)to continuously develop military innovation and preparedness, and (3)to develop and establish a paradigm for acquiring the power of technology. A Roman strategist, Vegetius said, "If you wish peace, prepare for war." This is a universally accepted maxim in international society today. We must never forget that peace we desire is given when we have the will and ability to keep.

• Journal of the Korean Society of Child Welfare
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• no.54
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• pp.1-44
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• 2016

Using the United Nations Convention on the Rights of the Child(UNCRC) as a frame of reference, this study examined South and North Korean children's rights as reported in the UNCRC and the pattern of changes in the reports depending on the period in which the reports were written. For this purpose, we reviewed Article 1 of the Convention to see what age range the South and North Korean governments, respectively, specify to define a child. We also analyzed the method and attitude of how each Korean government acknowledges the rights of children in the four general principles of the Convention("non-discrimination", "the best interests of the child", "the right to life, survival, and development" and "respect for the views of the child"). The results showed that there was asymmetric content between South and North Korea in the four general principles of the Convention. Both South and North Korea lack a sense of respect for the views of children. There were also differences in the rights of children depending on the distinct characteristics of each Korea. In South Korea, it is important to guarantee the rights of multicultural children and provide a plan for child safety. On the other hand, North Korea has emphasized that they provide the necessities of life and free education to children. Both Koreas have continuously submitted their reports and showed improvement in understanding the rights of children in each report. We conclude that it is essential for South and North Korea to build common ground in their respective contents on children and to establish a foundation of normative standards in the path to prepare for reunification. Moreover, we also conclude that South and North Korea should work collaboratively to reach mutual consent to achieve these goals.

• Journal of Korean Philosophical Society
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• v.105
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• pp.269-290
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• 2008

The purpose of this paper is to explore the possibility of backwards causation. For study, this paper was divided into four views as follows: The first view was sometimes suggested by the people such as M. Dummett who distinguished observers from behaviors. According to observers' view, backwards causation is impossible, whereas behaviors' view possible. However, in a real or genuine sense, it is incorrect for us to argue for impossibility of backwards causation from the observer aspect. The second view was supported by J. H. Schmidt. He analyzed the possibility of backwards causation in terms of macro and micro level analysis about the causal events. According to micro level analysis, backwards causation is possible, but macro level analysis impossible. Usually the latter makes the former something miraculous. Under the macro level analysis, backwards causation, at first, seems to be miraculous phenomena which belongs to the micro level analysis. The third view had to do with physical equation, and the fourth view physical phenomena, respectively. John Earman argued for the backwards causation by the transformation from Lorentz­-Dirac equation to a second-order integro-differential one in the field of electrodynamic acceleration. His argument was criticized because of his misunderstanding about the relationship between two equations. On the other hand, Phil Dowe defended a version of Reichenbach's own theory about the direction of causation founded on the fork asymmetrical causal relation. However his view was different from Reichenbach's because the former defended the backwards causation model of Bell phenomena in quantum mechanics. On the contrary, Reichenbach put stressed on the priority of cause in the causal process. Subjectivism has recently been defended by H. Price, under the label of perspectivism. According to him, in a certain sense causal asymmetry is not in the world, but is rather a product of our own asymmetric perspective on the world. He also suggested causal net, the symmetry of microphysics, and so on. As mentioned above, there are many kind of suggestions of backwards causation. However none of them replaced objectively the main streams of the direction of causal process. The main stream has been usually defended by pragmatical ground. That is, effects do not precede their causes although causes cannot be without their effects.

• The Korean Journal of Nuclear Medicine
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• v.32 no.2
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• pp.151-160
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• 1998

Purpose: Piccolo et al. advocated the usefulness of $^{99m}Tc$-MDP breast scan in differential diagnosis of breast mass with high accuracy. But there are little or no follow-up studies about it as we know. We studied $^{99m}Tc$-MDP uptake pattern and lesion/background ratio in patients complaining palpable breast lesions to evaluate the clinical usefulness of $^{99m}Tc$-MDP scan. Materials and Methods: Total 34 patients were studied with physical examination, mammo-gram and $^{99m}Tc$-MDP scan prospectively. Anteroposterior and both lateral view of breast were obtained 5 minutes after iv injection of 740 MBq $^{99m}Tc$-MDP. Breast uptake pattern of $^{99m}Tc$-MDP was analyzed by a grade system: 0=no uptake, grade 1=bilateral diffuse uptake, grade 2=asymmetric faint uptake, grade 3=focal hot uptake. 20 cases were pathologically confirmed by excision biopsy or aspiration biopsy. 14 cases were normal in physical examination and mammogram. Results: Pathologic results showed 7 carcinomas, 6 benign solid tumors, and 7 fibrocystic changes. Grade 3 pattern of $^{99m}Tc$-MDP uptake was noted in 4/7 carcinomas, 3/6 benign solid tumors, and 1/7 fibrocystic changes. Grade 2 pattern was 217, 0/7, 3/7 respectively. The average L/B ratio was 1.66 in carcinomas, 1.68 in benign solid masses, 1.20 in fibrocystic diseases, 1.05 in normal patients. L/B ratio was higher in carcinoma and benign mass groups than in fibrocystic change and normal control groups(p=0.005). But there was no statistical difference between L/B ratio of malignant mass group and benign mass group. Conclusion: $^{99m}Tc$-MDP scan is not suitable to routine clinical use for breast mass diagnosis. It might be used in limited conditions when whole body bone scan is planned.