• Journal of the Korean Geographical Society
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• v.49 no.3
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• pp.405-422
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• 2014

Two important issues in hedonic model are to specify accurate model and delineate submarkets. While the former has experienced much improvement over recent decades, the latter has received relatively little attention. However, the accuracy of estimates from hedonic model will be necessarily reduced when the analysis does not adequately address market segmentation which can capture the spatial scale of price formation process in real estate. Placing emphasis on improvement of performance in hedonic model, this paper tried to segment real estate markets in Gangnam-gu and Jungrang-gu, which correspond to most heterogeneous and homogeneous ones respectively in 25 autonomous districts of Seoul. First, we calculated variable coefficients from mixed geographically weighted regression model (mixed GWR model) as input for clustering, since the coefficient from hedonic model can be interpreted as shadow price of attributes constituting real estate. After that, we developed a spatially constrained data-driven methodology to preserve spatial contiguity by utilizing the SKATER algorithm based on a minimum spanning tree. Finally, the performance of this method was verified by applying a multi-level model. We concluded that submarket does not exist in Jungrang-gu and five submarkets centered on arterial roads would be reasonable in Gangnam-gu. Urban infrastructure such as arterial roads has not been considered an important factor for delineating submarkets until now, but it was found empirically that they play a key role in market segmentation.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.24 no.4
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• pp.739-751
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• 2014

We are using our smartphone for our business as well as ours lives. Thus, user's privacy data and a company secret are stored at smartphone. By the way, the saved data on smartphone database can be exposed to a malicous attacker when a malicous app is installed in the smartphone or a user lose his/her smartphone because all data are stored as form of plaintext in the database. To prevent this disclosure of personal information, we need a database encryption method. However, if a database is encrypted, it causes of declining the performance. For example, when we search specific data in condition with encrypted database, we should decrypt all data stored in the database or search sequentially the data we want with accompanying overhead[1]. In this paper, we propose an efficient and searchable encryption method using variable length bloom filter under limited resource circumstances(e.g., a smartphone). We compare with existing searchable symmetric encryption. Also, we implemented the proposed method in android smartphone and evaluated the performance the proposed method. As a result through the implementation, We can confirm that our method has over a 50% improvement in the search speed compared to the simple search method about encrypted database and has over a 70% space saving compared to the method of fixed length bloom filter with the same false positive rate.

• Journal of Navigation and Port Research
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• v.34 no.3
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• pp.175-180
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• 2010

In the almost application parts, GNSS being used the primary navigation system on world-widely. However, some of nations attempt or deliberate to enhance current Loran system, as a backup to satellite navigation system because of the vulnerability to the disturbance signal. Loran interests in supplemental navigation system by the development and enhancement, which is called eLoran, and that consists of advancement of receiver and transmitter and of differential Loran in order to increase the accuracy of current Loran-C. A significant factor limiting the ranging accuracy of the eLoran signal is the ASF in the TOAs observed by the receiver. The ASF is mostly due to the fact that the ground-wave signal is likely to propagate over paths of varying conductivity and topography. This paper presents comparison results between the predicted ASF and the measured ASF in a southern east region of Korea. For predicting ASF, the Monteath model is used. Actual ASF is measured from the legacy Loran signal transmitted Pohang station in the GRI 9930 chain. The test results showed the repeatability of the measured ASF and the consistent characteristics between the predicted and the measured ASF values.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.6
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• pp.169-180
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• 2018

White light-emitting diodes (LEDs) are more economical than fluorescent lights, and provide high brightness, a high lifetime expectancy, and greater durability. As LEDs are closely connected with people's daily lives, dimming control of LED is an important component in providing energy savings and improving quality of life. In visible light communications systems using these LEDs, multiple input multiple output (MIMO) technology has attracted a lot of attention, in that it can attain the channel capacity in proportion to the number of antennas. This paper analyzes the power performance of three kinds of modulation in visible light communications (VLC) systems applied space-time block code (STBC) techniques. The modulation schemes are return-to-zero on-off keying (RZ-OOK), variable pulse position modulation (VPPM), and overlapping pulse position modulation (OPPM), and dimming control was applied. The power requirements and power consumption were used as metrics to compare the power efficiency in $2{\times}2$ STBC-VLC environments under the three kinds of modulation. We confirm that dimming control affects the communications performance of each modulation scheme. VPPM showed greater consumption among the three modulations, and OPPM showed energy savings comparable to VPPM.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.2
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• pp.8-15
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• 2006

To reduce costs and address other practical concern related to architectural lighting, we have been involved in various aspects of advanced daylighting design and control. If we look toward future building trends, we see that the advanced has already successfully deployed such complex lighting control systems. This paper takes a broad view of what advanced manufacturers have done to develop energy efficient lighting control technologies such as sensors, lumen maintenance, time of day scheduling, peak demand reduction and so forth. First of all strategies, daylighting controls would also need to be commissioned to respond to the specific daylighting signature of the zone. To translate the daylight in term of the amount of energy savings, an electric lighting system is designed and automatic on-off control system integrated with the contribution of daylighting has been applied to the operating of the artificial lighting. The lighting analysis program, Lumen-Micro predicts the optimal layout of conventional fluorescent and incandescent lighting fixtures to meet the designed lighting level and calculates unit power density, which translates the demanded amount of lighting energy.

• Korean Journal of Optics and Photonics
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• v.16 no.3
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• pp.209-216
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• 2005

A new second generation advanced thermal imager, which can be used for battle tank sight has been developed by ADD. This system uses a $480\times6$ TDI HgCdTe detector, operating in the $7.7-10.3{\mu}m$ wavelength made by Sofradir. The IR optics has dual field of views such as $2.67\times2^{\circ}$ in NFOV and $10\times7.5^{\circ}$ in WFOV. And also, this optics is used for athermalization of the system. It is certain that our sensor can be used in wide temperature range without any degradation of the system performance. The scanning system to be able to display 470,000 pixels is developed so that the pixel number is greatly increased comparing with the first generation thermal imaging system. In order to correct non-uniformity of detector arrays, the two point correction method has been developed by using the thermo electric cooler. Additionally, to enhance the image of low contrast and improve the detection capability, we have proposed the new technique of histogram processing being suitable for the characteristics of contrast distribution of thermal imagery. Through these image processing techniques, we obtained the highest quality thermal image. The MRTD of the LWIR thermal sight shows good results below 0.05K at spatial frequency 2 cycles/mrad at the narrow field of view.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.9
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• pp.91-102
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• 1999

It is known that the digital image enlargement technique which only uses spatially neighbored pixels information in a still image can increase the size of the image but the practical enhancement of resolution is small because the frequency bandwidth of the image is basically limited. To solve this problem, this paper proposes the digital image enlargement technique that improves the reconstruction of the edge components by selectively transposing the direction of the subwindows of pseudomedian filter according to the distribution of neighbored pixels to the interpolation point. The pseudomedian filter has the better performance in aspect of the reconstruction of edge information when the pixel values masked by two subwindows parallel to the interpolation point are very similar and the pixel values masked by another subwindow that is orthogonal to the above two subwindows are similar to each other. In this paper, the computer simulation for digital image enlargement was performed with consideration of these characteristics when selecting the subwindows of pseudomedina filter. Based on this simulation result, the performance of the proposed method was analysed and its effectiveness was assessed. According to the proposed method, visual artifacts that result from using the limited samples can be effectively suppressed, and most characteristics and shapes of the original image can be preserved as well.