• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.219-222
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• 2005

We present the high-resolution (2"-4") images of the molecular envelopes surrounding the evolved stars, V Hya, VY CMa, and ${\pi}^1$ Gru observed with the Submillimeter Array. The CO J=2-1 and 3-2 images of the carbon star V Hya show that the circumstellar structure of this star consists of three kinematic components; there is a flattened disk-like envelope that is expanding with a velocity of ${\~}16 km\;s^{-1}$, the second component is the medium-velocity wind having a deprojected velocity of 40-120 km $s^{-l}$ moving along the disk plane, and the third one is the bipolar molecular jet having an extreme velocity of 70-185 km $s^{-l}$. The axis of this high velocity jet is perpendicular to the plane of the disk-like envelope. We found that the circumstellar structure of the S-star ${\pi}^1$ Gru traced by the CO J =2-1 resembles that of V Hya quite closely; the star is surrounded by the expanding disk-like envelope and is driving the medium-velocity wind along the disk plane. We also obtained the excellent images of VY CMa with the CO and $^{13}CO$ J=2-1 and $SO\;6_5-5_4$ lines. The maps of three molecular lines show that the envelope has a significant velocity gradient in the east-west direction, suggesting that the envelope surrounding VY CMa is also flattened and expanding along its radial direction. The high-resolution images obtained with the SMA show that some AGB stars are associated with the asymmetric mass loss including the equatorial wind and bipolar jet.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.1A
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• pp.1-10
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• 2006

The Home Phoneline Networking Alliance(HomePNA) 2.0 technology can establish a home network using existing in-home phone lines, which provides a channel rate of 4-32 Mbps. HomePNA 2.0 Medium Access Control(MAC) protocol adopts an IEEE 802.3 Carrier Sense Multiple Access with Collision Detection(CSMA/CD) access method, Quality of Service(QoS) algorithm, and Distributed Fair Priority Queuing(DFPQ) collision resolution algorithm. In this paper, we describe some performance analysis results of HomePNA 2.0 MAC protocol and the requirements of HomePNA 2.0 MAC controller. Then, we propose the architecture of HomePNA 2.0 MAC controller circuit, show the simulation result of each block included in HomePNA 2.0 MAC controller, and present the HomePNA 2.0 transceiver chip that we have implemented.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.19 no.4
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• pp.373-383
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• 2001

This study conducted pilot mapping project to know the possibility of mapping with medium resolution satellite imageries. For this purpose, mapping experiments were conducted with each stereo model imageries of SPOT, KOMPSAT, and IRS- lC. And positional accuracy, analysis of detectable and describable features, and comparison with existing digital map were checked, possible mapping scale and cost analysis were conducted with these results. Regarding SPOT imagery, digital photogrammetric workstation was used for stereoplotting. Regarding KOMPSAT and IRS-lC imageries, because there were data format support problems. head-up digitizing was performed with ortho imageries rectified with DEMs generated by image matching. The results of experiments show that such features as wide road, river, coast line, etc are possible to detect and depict but many other features are not for SPOT, KOMPSAT, and IRS-lC imageries. On the aspect of mapping, therefore, SPOT is available for 1/50,000 topographic map revision, KOMPSAT and IRS-lC for 1/25.000 topographic map revision.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.125.2-125.2
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• 2011

We are developing medium resolution cross-dispersed silicon grisms in the near IR region ($1.45{\sim}5.2{\mu}m$). The grisms will be installed in MIMIR, a multifunction instrument at the Lowel Observatory, USA. The two devices are designed to cover H and K band and L and M band simultaneously. Our goal is to make grism with R=3000 at 1.2 arcsec slit. The Silicon has high refractive index (n=3.4 at $1.5{\mu}m$) which enhances the resolving power by up to 5 times when compared to conventional material such as BK-7 (n=1.5 at 1.5 ${\mu}m$). The bonded grisms will be installed in a filter wheel for the uses switch from spectroscopic mode to imaging mode easily. Our device is compact and light weighted while it provides a decent resolving power. We produce monolithic grisms using e-beam lithography at the NASA JPL and chemically etching the grooves on the silicon prisms. Moreover, the main-disperser and cross-disperser will be contacted together by direct Si-Si bonding technique and eventually turn into one piece. The bonded pair offers more stability in terms of the layout of the spectrum and removes the Fresnel loss at the intersection of two grisms. We report on the proper wafer bonding steps through this research, and inspected the bonding quality thermally, optically and mechanically.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.11 no.2
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• pp.137-145
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• 1986

The contention resolution algorithm with the limited packet delay time as well stable distribution as the packet delay time is proposed and implementes for improving the mean packet delay time in the network employing CSMA/CD as the access method. The implementation of node controller is based on IEEE 802.2 standard logical link control(LLC) and IEEE 802.3 standard medium access control(MAC). Some portion of IEEE 802.3 Standard MAC, and the Binary Exponential Back-off(BEB) algorithm is replaced by the proposed algorithm. From the view of normalized mean packet transmission delay time, the controller implemented here can be applicable to the office-automation system, and the factory-and laboratory-automation environment where the limited time criterion is very significant.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.3
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• pp.526-534
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• 2014

In this paper, for the WiMedia Distributed Medium Access Control (D-MAC) protocol based on UWB. performance degradation due to the Distributed Reservation Protocol (DRP) conflict problem caused by devices' mobility is analyzed. And a DRP relay protocol and a DRP conflict resolution (CR) are proposed to overcome the performance degradation at DRP conflicts. In order to give the loser device at DRP conflicts a chance to maintain resources, the proposed DRP relay protocol executed at each device helps the loser device reserve an indirect link maintaining the required resources via a relay node. Simulation results considering the mobile environment have indicated that the DRP relay combined with the CR prevent the throughput decrease even though mobility of devices increases.

• Korean Journal of Radiology
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• v.23 no.7
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• pp.752-762
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• 2022

Objective: To compare a deep learning-based reconstruction (DLR) algorithm for pediatric abdominopelvic computed tomography (CT) with filtered back projection (FBP) and iterative reconstruction (IR) algorithms. Materials and Methods: Post-contrast abdominopelvic CT scans obtained from 120 pediatric patients (mean age ± standard deviation, 8.7 ± 5.2 years; 60 males) between May 2020 and October 2020 were evaluated in this retrospective study. Images were reconstructed using FBP, a hybrid IR algorithm (ASiR-V) with blending factors of 50% and 100% (AV50 and AV100, respectively), and a DLR algorithm (TrueFidelity) with three strength levels (low, medium, and high). Noise power spectrum (NPS) and edge rise distance (ERD) were used to evaluate noise characteristics and spatial resolution, respectively. Image noise, edge definition, overall image quality, lesion detectability and conspicuity, and artifacts were qualitatively scored by two pediatric radiologists, and the scores of the two reviewers were averaged. A repeated-measures analysis of variance followed by the Bonferroni post-hoc test was used to compare NPS and ERD among the six reconstruction methods. The Friedman rank sum test followed by the Nemenyi-Wilcoxon-Wilcox all-pairs test was used to compare the results of the qualitative visual analysis among the six reconstruction methods. Results: The NPS noise magnitude of AV100 was significantly lower than that of the DLR, whereas the NPS peak of AV100 was significantly higher than that of the high- and medium-strength DLR (p < 0.001). The NPS average spatial frequencies were higher for DLR than for ASiR-V (p < 0.001). ERD was shorter with DLR than with ASiR-V and FBP (p < 0.001). Qualitative visual analysis revealed better overall image quality with high-strength DLR than with ASiR-V (p < 0.001). Conclusion: For pediatric abdominopelvic CT, the DLR algorithm may provide improved noise characteristics and better spatial resolution than the hybrid IR algorithm.

• The Journal of Engineering Geology
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• v.32 no.1
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• pp.157-171
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• 2022

Electrical resistivity tomography (ERT) is a traditional and representative geophysical method for determining the resistivity distributions of surrounding soil and rock volumes. Depth resolution profiles and sensitivity distribution sections of the resistivities with respect to various electrode configurations are calculated and investigated using numerical model data. Shallow vertical resolution decreases in the order of Wenner, Schlumberger, and dipole-dipole arrays. A high investigable depth in homogeneous medium is calculated to be 0.11-0.19 times the active electrode spacing, but is counterbalanced by a low vertical resolution. For the application of ERT depth resolution profiles and sensitivity distributions, we provide subsurface structure models for two types of land-creping failure (planar and curved), subvertical fracture, and weathered layer over felsic and mafic igneous rocks. The dipole-dipole configuration appears to be most effective for mapping land-creeping failure planes (especially for curved planes), whereas the Wenner array gives the best resolution of soil horizons and shallow structures in the weathered zone.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.2
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• pp.786-792
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• 2013

In this study was explored minimize side effects due to the additional injection of contrast medium and maintaining a high resolution imaging applied to the inspection and analysis of the contrast medium that affect the peak time biomechanics factors. Included 48 patients using the test bolus method, after measuring a patient's biomechanics factors of inspection before and during the test, correlation between contrast medium peak time and learn, matches the regression equation calculated and measured contrast medium peak time was assessed by the Bland Altman plot. Research result, inspections of SBP, HR contrast medium peak time and a significant negative correlation was, step 1, every increase, the contrast medium peak time significantly to -0.018 and -0.159 decreased, a fairly high concordance no difference between the two method. In conclusion, the regression equation using the existing methods, while maintaining excellent image quality that contrast medium is reduced to a patient, it can conclude that the alternative to the existing methods.

• Korean Journal of Remote Sensing
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• v.36 no.5_1
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• pp.775-784
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• 2020

Recent global warming and anthropogenic activities have caused more frequent and massive wildfires with longer durations and more significant damages. MODIS has been monitoring global wildfires for almost 20 years, and GK2A and Himawari-8 are observing the wildfires in East Asia 144 times a day. However, the spatial resolution of 1 to 2 km is not sufficient for the detection of small and medium-size active fires, and therefore the studies on the active fire detection using high-resolution images are essential. However, there is no official product for the high-resolution active fire detection. Hence, we implemented the active fire detection algorithm of Landsat 8 and carried out a high-resolution-based detection of active fires in Australia in 2019, followed by the comparisons with the products of Himawari-8 and MODIS. Regarding the intense fires, the three satellites showed similar results, whereas the weak igniting and extinguishing fires or the fires in narrow areas were detected by only Landsat 8 with a 30m resolution. Small-sized fires, which are the majority in Korea, can be detected by the high-resolution satellites such as Landsat 8, Sentinel-2, Kompsat-3A, and the forthcoming Kompsat-7. Also, a comprehensive analysis together with the geostationary satellites in East Asia such as GK2A, Himawari-8, and Fengyun-3 will help the interoperability and the improvement of spatial and temporal resolutions.