• Journal of the Korean Society of Radiology
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• v.81 no.1
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• pp.21-40
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• 2020

Magnetic resonance imaging (MRI) is an essential modality for the diagnosis of musculoskeletal system defects because of its higher soft-tissue contrast and spatial resolution. With the recent development of MRI-related technology, faster imaging and various image plane reconstructions are possible, enabling better assessment of three-dimensional musculoskeletal anatomy and lesions. Furthermore, the image quality, diagnostic accuracy, and acquisition time depend on the MRI protocol used. Moreover, the protocol affects the efficiency of the MRI scanner. Therefore, it is important for a radiologist to optimize the MRI protocol. In this review, we will provide guidance on patient positioning; selection of the radiofrequency coil, pulse sequences, and imaging planes; and control of MRI parameters to help optimize the MRI protocol for the six major joints of the musculoskeletal system.

• Journal of IKEEE
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• v.20 no.2
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• pp.181-183
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• 2016

In this work, the merged PiN Schottky(MPS) diodes based silicon carbide(SiC) have been optimized and designed for 1200V diodes by 2D-atlas simulation tool. We investigated the optimized characteristics of SiC MPS diodes such as breakdown voltage and specific on-resistance by varying the doping concentrations of P-Grid/epi-layer and space of P-Grid, which are the most important parameters. The breakdown voltage and specific on-resistance, based on Baliga's Figure Of Merit (BFOM), have been compared with and the SiC-based MPS diodes show improved BFOMs with low values of specific on-resistance and high breakdown voltage. It has been demonstrated 1,200 V SiC MPS diodes will find useful applications in high voltage energy-efficient devices.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.7
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• pp.252-257
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• 2018

In this paper, we propose a mean time to failure (MTTF) to improve the solution for a cryogenic cooler, which is an important part of a cooled thermal device. Common electronic devices have a high possibility of failure due to various environmental factors, such as temperature and humidity. But some special devices (such as thermal devices) are designed to overcome environmental factors. The most affected part of a cooled thermal device's MTTF is the cryogenic cooler. The MTTF of a cryogenic cooler is affected by the device's internal heat. Therefore, if the device's internal heat is reduced, the cryogenic cooler's MTTF increases. From the present device's internal heat simulation, we analyze the improvement method of the device. The proposed improvement method's effectiveness is verified by simulation and MTTF calculation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.2
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• pp.56-66
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• 2012

The inductive loaded patch antenna with suppressed radiation along the horizontal plane and enhanced broadside gain is investigated by adjusting the width and the via radius of a unit cell at a fixed length of a unit cell. The effects of the via radius and the width of the unit cell on the dispersion characteristics of the inductive loaded transmission line are investigated. The systematic study to determine the via radius and the width of the unit cell for the effective dielectric constant of the inductive loaded patch antenna close to 1 in order to suppress the radiation along the horizontal plane is presented. Inductive loaded patch antennas composed of five unit cells with resonant frequency of 5 GHz are designed and their radiation characteristics are presented. The horizontal radiation along the E-plane is greatly suppressed to less than -15 dBi when the effective dielectric constant of the inductive loaded patch antenna is slightly less than 1.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.10a
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• pp.71-72
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• 2013

In this paper, a design method for a compact slot antenna for 5.8 GHz RFID band (5.725-5.875 GHz) is studied. The proposed slot antenna is size-reduced by bending both ends of the straight slot in "${\Gamma}$"-shape, and a rectangular feed patch is located inside the slot. The effects of slot length, location of feed patch, and width and length of feed patch on the antenna performance are examined. A prototype antenna with optimized parameters for 5.8 GHz band is fabricated on an FR4 substrate and tested experimentally. The experimental results show that the frequency band for a VSWR < 3 ranges 5.72-6.13 GHz (bandwidth 410 MHz), and it corresponds fairly well with the simulated band 5.64-5.97 GHz (bandwidth 330 MHz). The fabricated antenna shows good radiation performance such as maximum power density in both directions normal to the slot plane, and low cross-polarization level of < -20 dB.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.5C
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• pp.317-325
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• 2011

For OFDM (Orthogonal Frequency Division Multiplexing) systems, 2-D MMSE (2-Dimensional Minimum Mean Square Error) channel estimation provides optimal performance in frequency/time selective fading channel environment. However, the 2-D MMSE channel estimation has high computational complexity due to the large matrix size, because the 2-D MMSE channel estimation considers time as well as frequency axis for channel estimation. To reduce the computational complexity, we propose a modified 2-D MMSE channel estimator which is based on 1-D MMSE channel estimation with weighted sum. Furthermore, we consider RMS delay spread and Doppler frequency estimation for 2-D MMSE channel estimation. We show that the proposed method can significantly reduce computational complexity as well as that it can perform close to 2-D MMSE channel estimation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.12
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• pp.2763-2768
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• 2013

In this paper, a design method for a compact slot antenna for 5.8 GHz RFID band (5.725-5.875 GHz) is studied. The proposed slot antenna is size-reduced by bending both ends of the straight slot in "I"-shape, and a rectangular feed patch is located inside the slot. The effects of slot length, location of feed patch, and width and length of feed patch on the antenna performance are examined. A prototype antenna with optimized parameters for 5.8 GHz band is fabricated on an FR4 substrate and tested experimentally to verify the results of this study. The experimental results show that the frequency band for a VSWR < 3 ranges 5.72-6.13 GHz (bandwidth 410 MHz), and it corresponds fairly well with the simulated band 5.64-5.97 GHz (bandwidth 330 MHz). The fabricated antenna shows good radiation performance such as maximum power density in both directions normal to the slot plane, low cross-polarization level of < -20 dB, and realized gain > 0 dBi within the frequency band.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.7
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• pp.1281-1286
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• 2006

We have used the silicon-carbide(4H-SiC) instead of conventional silicon materials to develope of the planar junction barrier schottky rectifier for ultra high breakdown voltage(1,200 V grade). The substrate size is 2 inch wafer, Its concentration is $3*10^{18}/cm^{3}$ of $n^{+}-$type, thickness of epitaxial layer $12{\mu}m$ conentration is $5*10^{15}cm^{-3}$ of n-type. The fabticated devices are junction barrier schottky rectifier, The guard ring for improvement of breakdown voltage is designed by the box-like impurity of boron, the width and space of guard ring was designed by variation. The contact metals to rectify were used by the $Ni(3,000\:{\AA})/Au(2,000\:{\AA})$. As a results, the on-state voltage is 1.26 V, on-state resistance is $45m{\Omega}/cm^{3}$, maximum value of improved reverse breakdown voltage is 1180V, reverse leakage current density is $2.26*10^{-5}A/CM^{3}$. We had improved the measureme nt results of the electrical parameters.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.120-125
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• 2002

In the preceding tests using the KSR-III Sub.(I) engines, it was observed that the heat resistant capability of the engines was not enough for the mission. So Sub.(I) Mod. engines were designed and tested. The Sub.(I) Mod. engines have three major design parameters - the arrangement of main injectors, the impinging angle of main injectors and thermal barrier coating. More than twenty experiments were carried on to evaluate engine performance and heat resistance capability with respect to design parameters. In this study, the test results are introduced. Analysing the result of Sub.(I) engine tests, it is found that decreasing the impinging angle, adopting the H-type arrangement(rather than radial type arrangement) and adopting the thermal barrier coating can increase heat resistance capacity substantially. Also, engine performance evaluation is conducted using specific impulse and characteristic velocity parameter. The results show that the performance variation is small(about 5%) and the performance is better in the case of radial arrangement. It is suspected that these phenomena are caused by the change of flame structure atomization mixing characteristic of sprays and the distortion of recirculation zone. Also from the low frequency instability point of view, it is observed that reducing the impinging angle and adopting the H type arrangement can increase the instability characteristics.

• Journal of KIISE:Databases
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• v.29 no.3
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• pp.180-192
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• 2002

We investigate the effect of the data skew of join attributes on the performance of a pipelined multi-way hash join method, and propose two new harsh join methods in the shared-nothing multiprocessor environment. The first proposed method allocates buckets statically by round-robin fashion, and the second one allocates buckets dynamically via a frequency distribution. Using harsh-based joins, multiple joins can be pipelined to that the early results from a join, before the whole join is completed, are sent to the next join processing without staying in disks. Shared nothing multiprocessor architecture is known to be more scalable to support very large databases. However, this hardware structure is very sensitive to the data skew. Unless the pipelining execution of multiple hash joins includes some dynamic load balancing mechanism, the skew effect can severely deteriorate the system performance. In this parer, we derive an execution model of the pipeline segment and a cost model, and develop a simulator for the study. As shown by our simulation with a wide range of parameters, join selectivities and sizes of relations deteriorate the system performance as the degree of data skew is larger. But the proposed method using a large number of buckets and a tuning technique can offer substantial robustness against a wide range of skew conditions.