• Journal of Korean Neurosurgical Society
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• v.54 no.1
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• pp.19-24
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• 2013

Objective : The purpose of this study was to retrospectively evaluate and compare the incidence of diffusion-weighted image (DWI) lesions between the Guglielmi detachable coil (GDC) and the Target coil for treating unruptured intracranial aneurysm. Methods : From 2010 to 2011, consecutive 222 patients with an intracranial aneurysm underwent coil embolization. Inclusion criterias were : 1) unruptured intracranial aneurysm, 2) one or more GDC or Target coils used with or without other coils, 3) DWI examination within 24 hours after coiling, and 4) coiling performed without a balloon or stent. Results : Ninety patients (92 cases) met the inclusion criteria. DWI lesions were detected in 55 (61.1%) of 90 patients. In the GDC group (n=44), DWI lesions were detected in 31 (70.5%). The average number of DWI lesions was $5.0{\pm}8.7$ (mean${\pm}$SD; range, 1-40) in aneurysm-related territory. In the Target coil group (n=48), DWI lesions were detected in 24 (50.0%). The number of DWI lesion was $2.1{\pm}5.4$ (range, 1-32) in aneurysm-related territory. There was no significant correlation between a number of coils and DWI lesions. No significant differences were also observed in the number of DWI lesions in each group. Conclusion : The GDC and Target coils, which have an electrolytic detachable system, showed no differences in the incidence of DWI lesion.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.179-190
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• 2011

The swirling flow developing in Francis turbine draft tube under part load operation leads to pressure fluctuations usually in the range of 0.2 to 0.4 times the runner rotational frequency resulting from the so-called vortex breakdown. For low cavitation number, the flow features a cavitation vortex rope animated with precession motion. Under given conditions, these pressure fluctuations may lead to undesirable pressure fluctuations in the entire hydraulic system and also produce active power oscillations. For the upper part load range, between 0.7 and 0.85 times the best efficiency discharge, pressure fluctuations may appear in a higher frequency range of 2 to 4 times the runner rotational speed and feature modulations with vortex rope precession. It has been pointed out that for this particular operating point, the vortex rope features elliptical cross section and is animated of a self-rotation. This paper presents an experimental investigation focusing on this peculiar phenomenon, defined as the upper part load vortex rope. The experimental investigation is carried out on a high specific speed Francis turbine scale model installed on a test rig of the EPFL Laboratory for Hydraulic Machines. The selected operating point corresponds to a discharge of 0.83 times the best efficiency discharge. Observations of the cavitation vortex carried out with high speed camera have been recorded and synchronized with pressure fluctuations measurements at the draft tube cone. First, the vortex rope self rotation frequency is evidenced and the related frequency is deduced. Then, the influence of the sigma cavitation number on vortex rope shape and pressure fluctuations is presented. The waterfall diagram of the pressure fluctuations evidences resonance effects with the hydraulic circuit. The influence of outlet bubble cavitation and air injection is also investigated for low cavitation number. The time evolution of the vortex rope volume is compared with pressure fluctuations time evolution using image processing. Finally, the influence of the Froude number on the vortex rope shape and the associated pressure fluctuations is analyzed by varying the rotational speed.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.99.2-99.2
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• 2012

We updated the far-ultraviolet (FUV) spectral images of the entire Vela supernova remnant (SNR) using newly processed FIMS/SPEAR data. In the present study, we compare the newly produced FUV images with the X-ray and $H{\alpha}$ images, and examine how the Vela SNR evolves and interacts with the ambient medium on a global scale. The comparison with X-ray images has revealed a FUV filamentary feature corresponding with the boundary of the northeast-southwest asymmetry of the X-ray shell. The relatively low O IV] ${\lambda}1404$ to O III] ${\lambda}{\lambda}1661$, 1666 ratio estimated on the FUV filament is compatible with the previous proposal that the observed asymmetry of the Vela SNR could be due to the ${\gamma}2$ Velorum stellar wind bubble (SWB). The southwest FUV features surrounding a faint extended X-ray region are characterized as the region where the Vela SNR is interacting slightly stronger with ambient mediums within the dim X-ray southwest section. From a comparison with the $H{\alpha}$ image, we identify a ring-like $H{\alpha}$ feature overlapped with an extended hot X-ray feature of similar size and two local peaks of C IV ${\lambda}{\lambda}1548$, 1551 emission. Their morphologies are consistent with the expected shape when the $H{\alpha}$ ring is in direct contact with the near or far side of the Vela SNR. We suggest that the B3V-type star HD 76161 found at the center of the $H{\alpha}$ ring would be the exciting source of the H II region.

• Journal of the Korean Society of Radiology
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• v.10 no.4
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• pp.255-261
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• 2016

In this study, among various factors having influence on SUV, we intended to compare and analyze the change of SUV using CT(4 type) and MRI(3 type) contrast agents which are commercialized now. We used Discovery 690 PET/CT(GE) and NEMA NU2 - 1994 PET phantom as experimental equipment. We have conducted a study as follows; first, we filled distilled water to phantom about two-thirds and injected radioisotope(18F-FDG 37 MBq), contrast agent. Second, we mixed CT contrast agent with distilled water and MRI contrast agent with that water separately. And then, we stirred the fluid and filled distilled water fully not to make air bubble. In emission scan, we had 15minutes scanning time after 40 minutes mixing contrast agent with distilled water. In transmission scan, we used CT scanning and its measurement conditions were tube voltage 120 kVp, tube current 40 mA, rotation time 0.5 sec, slice thickness 3.27 mm, DFOV 30 cm. Analyzing results, we set up some ROIs in 10th, 15th, 20th, 25th, 30th slice and measured SUVmean, SUVmax. Consequently, all images mixed 3 types of MRI contrast agent with distilled water have high SUVmean as compared with pure FDG image but there was no statistical significance. In SUVmax, they have high score and there was statistical significance. And other 4 images mixed 4 types of CT contrast agent with distilled water have significance in both SUVmean and SUVmax. Attenuation correction in PET/CT has been executed through various methods to make high quality image. But we figured out that using CT and MRI contrast agents before PET/CT scanning could make distortion of image and decrease diagnostic value. In that reason, we have to sort out the priority of examination in hospital not to disturb other examination's results. Through this process, we will be able to give superior medical service to our customers.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.2
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• pp.157-167
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• 2008

The aeration of an overtopping wave on a vertical structure generated by a plunging wave was investigated through laboratory measurements of void fraction. The overtopping wave occurring after wave breaking becomes multi-phased and turbulent with significant aeration, so that the void fraction of the flow is of importance. In this study, fiber optic reflectometer and bubble image velocimetry were employed to measure the void fraction, velocity, and layer thickness of the overtopping flow. Mean properties were obtained by ensembleand time-averaging the repeated instantaneous void fractions and velocities. The mean void fractions show that the overtopping wave is very high-aerated near the overtopping wave front and relatively low-aerated near the deck surface and rear free surface of the wave. The flow rate and momentum of the overtopping flow estimated using the measured data show that the void ratio is an important parameter to consider in the multiphase flow. From the similarity profiles of the depth-averaged void fraction, velocity, and layer thickness, one-dimensional empirical equations were obtained and used to estimate the flow rate and momentum of the overtopping flow.

• Geophysics and Geophysical Exploration
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• v.8 no.4
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• pp.280-286
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• 2005

Geological sequestration of carbon dioxide ($CO_2$) is one of the most effective strategies far long-term removal of greenhouse gas from atmosphere. This paper reviews three projects for the $CO_2$ sequestration in geological formation. A unique $CO_2$ injection into a marine aquifer has been successfully monitored with repeated surface seismic measurements in the North Sea Sleipner West field. The seismic images reveal the extent and internal shape of the $CO_2$ bubble. Massive miscible $CO_2$ has been injected into a complex fractured carbonate reservoir at the Weyburn oil filed. High-resolution time-lapse P-wave data were successfully obtained to map the features of $CO_2$ movements within the two thin zones of different lithology. From the time-lapse crosswell EM imaging at the Lost Hills oil field in central California, U.S.A., the replacement of brine with $CO_2$ has been confirmed through a decrease of conductivity. The conductivity image was successfully compared with induction logs observed in the two wells.

• Journal of The Korean Association For Science Education
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• v.40 no.1
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• pp.13-28
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• 2020

This study attempted to understand the characteristics of images of scientific experiments represented and consumed on YouTube, a representative of today's new media. In particular, this paper analyzes the case studies of YouTube's hydrogen peroxide decomposition experiment based on Baudrillard's theory of Simulation and Simulacra, which discusses the strong status of images and the ambiguity of the boundary between virtual and reality. A total of 14 YouTube videos related to hydrogen peroxide decomposition experiments were analyzed. In those videos, hydrogen peroxide decomposition experiments were typically conducted with several signs representing scientific experiments, but the most important sign in the videos were bubbles produced through experiments. For more public consumption of the content, the bubbles resulted from hydrogen peroxide decomposition reproduced in YouTube have been transformed into a more spectacular image as 'super-huge' and 'explosive' bubble. Considering the influence of new media that can be accessed by students anytime and anywhere, it is positive that science experiments in new media enhance students' intimacy and access to science. At the same time, however, it is also important to note the danger that the purpose of scientific experiments will be limited to only 'showing specular images', due to the nature of new media, which mainly deals with immediate and superficial images. Furthermore, this study argues that improving students' science media literacy is required to critically examine the science-related images represented in the new media based on understanding the characteristics and limitations of new media that deeply affect daily life.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.383-388
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• 2019

High purity SiC fine powder with metal impurity contents of less than 1 ppm was synthesized by improved carbothermal reduction process, and the synthesized powder was used for SiC single crystal growth in RF heating PVT device at temperature above 2,100℃. In-situ x-ray image analyzer was used to observe the sublimation of the powder and single crystal growth behavior during the growth process. SiC powder was used as a source of single crystal growth, exhausted from the outside of the graphite crucible at the growth temperature and left graphite residues. During the growth, the flow of raw materials was concentrated in the middle and influenced the growth behavior of SiC single crystals. This is due to the difference in temperature distribution inside the crucible due to the fine powder. After the single crystal growth was completed, the single crystal ingot was cut into a 1 mm thick single crystal substrate and finely polished using a diamond abrasive slurry. A dark yellow 4H-SiC was observed overall of single crystal substrate, and the polycrystals generated in the outer part may be caused by the incorporation of impurities such as the bubble layer mixed in the process of attaching the seed crystal to the seed holder.

• Journal of Conservation Science
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• v.36 no.5
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• pp.405-420
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• 2020

A convergence research was conducted on glass beads excavated at the ruins of Hapgang-ri, Sejong, using the archeology and conservation approach. The period of appearance of Jugu Towangmyo in the ruins of Hapgang-ri can be estimated to begin in the late 2^nd century; for Jugu Towangmyo No. 15, the period spans from the late 2^nd to early 3^rd century. Form, color, and manufacturing techniques of complete glass beads were examined, and the cross-sections and chemical composition of 16 samples were observed. Based on these analyses, the glass beads were divided into blue, purple, and red colors. The blue-colored beads could be further sub-divided based on their gloss and brightness; in contrast, the red-colored beads were highly uniform with regard to these parameters. Based on the stripe and bubble arrangement on the surface of the glass beads, their drawing technique was identified. Traces of heat treatment or polishing were observed at the ends of the beads. According to their chemical composition, the 16 samples were classified into 3 potash glass and 13 soda glass groups; in the latter, the properties of the stabilizers were divided according to the blue and red bead colors. The stabilizers of the red beads are unique in that they allow the distinction among beads excavated in other areas in South Korea owing to their compositional differences. Colorants in blue- and red-colored beads are cobalt (containing MnO), and copper and iron, respectively.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.559-563
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• 2015

Monitor of All-sky X-ray Image (MAXI) is a Japanese X-ray all-sky surveyer mounted on the International Space Station (ISS). It has been scanning the whole sky since 2009 during every 92-minute ISS rotation. X-ray transients are quickly found by the real-time nova-search program. As a result, MAXI has issued 133 Astronomer's Telegrams and 44 Gamma-ray burst Coordinated Networks so far. MAXI has discovered six new black holes (BH) in 4.5 years. Long-term behaviors of the MAXI BHs can be classified into two types by their outbursts; a fast-rise exponential-decay type and a fast-rise flat-top one. The slit camera is suitable for accumulating data over a long time. MAXI issued a 37-month catalog containing 500 sources above a ~0.6 mCrab detection limit at 4-10 keV in the region ${\mid}{b}{\mid}$ > $10^{\circ}$. The SSC instrument utilizing an X-ray CCD has detected diffuse soft X-rays extending over a large solid angle, such as the Cygnus super bubble. MAXI/SSC has also detcted a Ne emission line from the rapid soft X-ray nova MAXI J0158-744. The overall shapes of outbursts in Be X-ray binaries (BeXRB) are precisely observed with MAXI/GSC. BeXRB have two kinds of outbursts, a normal outburst and a giant one. The peak dates of the subsequent giant outbursts of A0535+26 repeated with a different period than the orbital one. The Be stellar disk is considered to either have a precession motion or a distorted shape. The long-term behaviors of low-mass X-ray binaries (LMXB) containing weakly magnetized neutron stars are investigated. Transient LMXBs (Aql X-1 and 4U 1608-52) repeated outbursts every 200-1000 days, which is understood by the limit-cycle of hydrogen ionization states in the outer accretion disk. A third state (very dim state) in Aql X-1 and 4U 1608-52 was interpreted as the propeller effect in the unified picture of LMXB. Cir X-1 is a peculiar source in the sense that its long-term behavior is not like typical LMXBs. The luminosity sometimes decreases suddenly at periastron. It might be explained by the stripping of the outer accretion disk by a clumpy stellar wind. MAXI observed 64 large flares from 22 active stars (RS CVns, dMe stars, Argol types, young stellar objects) over 4 years. The total energies are $10^{34}-10^{36}$ erg $s^{-1}$. Since MAXI can measure the spectrum (temperature and emission measure), we can estimate the size of the plasma and the magnetic fields. The size sometimes exceeds the size of the star. The magnetic field is in the range of 10-100 gauss, which is a typical value for solar flares.