• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.6
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• pp.477-485
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• 2006

A study on frost prevention of fin-tube heat exchanger is experimently performed by spreading antifreezing solution on heat exchanger surface. It is desirable that the antifreezing solution spreads completely on the surface forming thin liquid film to prevent frost nucleation and crystal growth and to reduce the thermal resistance across the liquid film. A small amount of antifreezing solution falls in drops on heat exchanger surface using two types of supplying devices, and a porous layer coating technique is adopted to enhance the wettedness of antifreezing solution on the surface. It is observed that the antifreezing solution liquid film prevents fin-tube heat exchanger from frosting, and heat transfer performance does not degrade through the frosting tests. The concentration of supplied antifreezing solution can be determined by heat transfer analysis of the first row of heat exchanger to avoid antifreezing solution freezing due to dilution by moisture absorption.

• Korean Journal of Materials Research
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• v.34 no.2
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• pp.105-110
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• 2024

Scanning probe microscopy (SPM) has become an indispensable tool in efforts to develop the next generation of nanoelectronic devices, given its achievable nanometer spatial resolution and highly versatile ability to measure a variety of properties. Recently a new scanning probe microscope was developed to overcome the tip degradation problem of the classic SPM. The main advantage of this new method, called Reverse tip sample (RTS) SPM, is that a single tip can be replaced by a chip containing hundreds to thousands of tips. Generally for use in RTS SPM, pyramid-shaped diamond tips are made by molding on a silicon substrate. Combining RTS SPM with Scanning spreading resistance microscopy (SSRM) using the diamond tip offers the potential to perform 3D profiling of semiconductor materials. However, damage frequently occurs to the completed tips because of the complex manufacturing process. In this work, we design, fabricate, and evaluate an RTS tip chip prototype to simplify the complex manufacturing process, prevent tip damage, and shorten manufacturing time.

• Korean Journal of Optics and Photonics
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• v.18 no.2
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• pp.155-161
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• 2007

A new and simple method of 3-dimensional circuit modeling and analysis is proposed and verified experimentally for the first time by determining 3-dimensional current flow and 2-dimensional light distribution in blue InGaN/GaN multi-quantum well (MQW) light emitting diode (LED) devices. Circuit parameters of the LED consist of the resistance of the metallic film and epitaxial layer, and the intrinsic diode which represents the active region emitting the light. The circuit parameters are extracted from the transmission line model (TLM) and current-voltage relation. We applied the >> proposed method and extracted circuit parameters to obtain the light emission pattern in a top-surface emitting-type LED. The current spreading effect is analyzed theoretically and quantitatively with a variation of the resistance of metallic and epitaxial layers. The emitting-light distribution of the fabricated blue LED showed a good agreement with the analyzed result, which shows the dark emission intensity at the corner of the p-electrode.

• Journal of The Korean Society of Agricultural Engineers
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• v.63 no.1
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• pp.37-48
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• 2021

The automatic-spreader of bedding materials was developed to reduce labor cost, and to achieve successful biosecurity in duck houses. Algorithm of the device was designed to realize a concept of the automatic unmanned operation including entire processes such as loading and spreading of the bedding materials. From the field measurement, the relationship between the expected water content reduction and weight of bedding materials per unit area according to the operation condition of the devices was induced. In the case of the measurement of particulate matters during the process of spreading works, the results of using both conventional manual-spreader and automatic-spreader were exceeded the allowable limit of inhalable and respirable dust, respectively. But, workers using automatic-spreader could be free from harmful aero-condition because they did not stay inside the facility during the spreading works. In addition, from the Duck hepatitis virus PCR test, influence on pulmonary tissue of the duck was not found. It could be expected that the development of the automatic-spreader of bedding materials for duck house can contribute to the advancement of duck breeding facilities.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.287.1-287.1
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• 2016

Three-dimensional (3-D) semiconductor nanoarchitectures, including nano- and micro- rods, pyramids, and disks, are emerging as one of the most promising elements for future optoelectronic devices. Since these 3-D semiconductor nanoarchitectures have many interesting unconventional properties, including the use of large light-emitting surface area and semipolar/nonpolar nano- or micro-facets, numerous studies reported on novel device applications of these 3-D nanoarchitectures. In particular, 3-D nanoarchitecture devices can have noticeably different current spreading characteristics compared with conventional thin film devices, due to their elaborate 3-D geometry. Utilizing this feature in a highly controlled manner, color-tunable light-emitting diodes (LEDs) were demonstrated by controlling the spatial distribution of current density over the multifaceted GaN LEDs. Meanwhile, for the fabrication of high brightness, single color emitting LEDs or laser diodes, uniform and high density of electrical current must be injected into the entire active layers of the nanoarchitecture devices. Here, we report on a new device structure to inject uniform and high density of electrical current through the 3-D semiconductor nanoarchitecture LEDs using metal core inside microtube LEDs. In this work, we report the fabrications and characteristics of metal-cored coaxial $GaN/In_xGa_{1-x}N$ microtube LEDs. For the fabrication of metal-cored microtube LEDs, $GaN/In_xGa_{1-x}N/ZnO$ coaxial microtube LED arrays grown on an n-GaN/c-Al2O3 substrate were lifted-off from the substrate by wet chemical etching of sacrificial ZnO microtubes and $SiO_2$ layer. The chemically lifted-off layer of LEDs were then stamped upside down on another supporting substrates. Subsequently, Ti/Au and indium tin oxide were deposited on the inner shells of microtubes, forming n-type electrodes of the metal-cored LEDs. The device characteristics were investigated measuring electroluminescence and current-voltage characteristic curves and analyzed by computational modeling of current spreading characteristics.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.12
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• pp.27-34
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• 2005

We have investigated the correlation between the active-layer uniformity and reliability of InGaN/GaN blue LEDs. According to initial characteristics, the devices are classified into two groups: group I devices of uniform light-emission and group II devices of non-uniform light-emission. The group II devices are more dependent on temperature and we have found two degradation mechanisms through reliability test. One is bulk degradation in which the degradation occurred over the entire chip and another one is edge degradation in which the degradation occurred from the edge of the chip. Bulk degradation caused by the nonradiative defects is found to be faster in group II devices while there is no difference in the rate of the much faster edge degradation, where darkening starts from the n-Ohmic contact edge. Therefore, more uniform active layer, more uniform current spreading, and the passivation of the dry-etched side-wall are essential for the high reliability of InGaN/GaN LEDs.

• JSTS:Journal of Semiconductor Technology and Science
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• v.10 no.3
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• pp.213-224
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• 2010

An optically controlled silicon MESFET (OPFET) was fabricated by diffusion process to enhance the quantum efficiency, which is the most important optoelectronic device performance usually affected by ion implantation process due to large number of process induced defects. The desired impurity distribution profile and the junction depth were obtained solely with diffusion, and etching processes monitored by atomic force microscope, spreading resistance profiling and C-V measurements. With this approach fabrication induced defects are reduced, leading to significantly improved performance. The fabricated OPFET devices showed proper I-V characteristics with desired pinch-off voltage and threshold voltage for normally-on devices. The peak photoresponsivity was obtained at 620 nm wavelength and the extracted external quantum efficiency from the photoresponse plot was found to be approximately 87.9%. This result is evidence of enhancement of device quantum efficiency fabricated by the diffusion process. It also supports the fact that the diffusion process is an extremely suitable process for fabrication of high performance optoelectronic devices. The maximum gain of OPFET at optical modulated signal was obtained at the frequency of 1 MHz with rise time and fall time approximately of 480 nS. The extracted transconductance shows the possible potential of device speed performance improvements for shorter gate length. The results support the use of a diffusion process for fabrication of high performance optoelectronic devices.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.31 no.4
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• pp.617-635
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• 2021

Internet of Things (IoT) devices connected to the network without appropriate security solutions have become a serious security threat to ICT infrastructure. Moreover, due to the nature of IoT devices, it is difficult to apply currently existing security solutions. As a result, IoT devices have easily become targets for cyber attackers, and malware attacks on IoT devices are actually increasing every year. Even though several security solutions are being developed to protect IoT infrastructure, there is a great risk to apply unverified security solutions to real-world environments. Therefore, verification tools to verify the functionality and performance of the developed security solutions are also needed. Furthermore, just as security threats vary, there are several security solution s that defend against them, requiring suitable verification tools based on the characteristics of each security solution. In this paper, we propose an high-speed malware propagation tool that spreads malware at high speed in the IoT infrastructure. Also, we can verify the functionality of the security solution that detect and quickly block attacks spreading in IoT infrastructure by using the high-speed malware propagation tool.

• Journal of Korea Society of Digital Industry and Information Management
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• v.11 no.3
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• pp.53-62
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• 2015

Recently, number of tablet or Smartphone users increased significantly in domestic and around the world. But violation of personal information such as leakage, misuse and abuse are constantly occurring by using mobile devices which is very useful in our society. Therefore, in this paper it will talk about the problems in the network environment of the mobile environment such as tablet and Smartphone, Mobile Malware, hacking of the public key certificate, which could be potential threat to mobile environment. This thesis will research for people to use their mobile devices more reliable and safer in mobile environment from invasion and leakage of personal information. In order to use Smartphone safely, users have to use Wi-Fi and Bluetooth carefully in the public area. This paper will research how to use App safely and characteristic of risk of worm and Malware spreading. Because of security vulnerabilities of the public key certificate, it will suggest new type of security certification. In order to prevent from the information leakage and infect from Malware in mobile environment without knowing, this thesis will analyze the improved way to manage and use the mobile device.

• KIPS Transactions on Software and Data Engineering
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• v.6 no.2
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• pp.85-90
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• 2017

Various mobile devices are spreading in recent developments in mobile computing environments. Especially the popularity of mobile devices equipped with GPS has become widespread, and various application services utilizing location information are born. In this paper, we propose a system model for storing and managing the trajectory of moving objects, which is the set of location information of moving objects acquired in continuous time, and the UDF (User-Defined Functions) based trajectory index method which can quickly query the large data set of moving object and the Pre-Materialized table method. Then we compare and evaluate the performance of each method through experiments. Experimental results show that the Pre-Materialized table method is about 1.2 times faster than the UDF based trajectory index method on execution time.