• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.72.4-73
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• 2015

Over the last decade, more than 50 quasars have been discovered at redshift about 6 when reionization of the universe occurred. However, most of them are luminous quasars (zAB < 21 mag), implying that such a biased quasar sample, which cannot represent the entire population of quasars at z~6, is not enough to understand the properties of quasars in the early universe. Recently, we have been performing the Infrared Medium-deep Survey (IMS), a moderately wide (120 deg2) and deep (JAB ~ 22.5 - 23 mag) near-infrared imaging survey. Combining this with the optical (ugriz) imaging data from the CFHT Legacy Survey (CFHTLS), we have identified more than 10 faint quasar candidates at z~6 in the IMS field by using multiple color selection criteria. From now on, we will perform spectroscopic confirmations of these faint quasar candidates with IMACS on the Magellan Baade Telescope at Las Campanas Observatory and GMOS on the Gemini South Telescope at Gemini Observatory. The confirmed quasars will be used to constrain the faint-end slope of the quasar luminosity function at z~6 and calculate the ratio of quasar ionizing flux to required flux for reionization of the universe. Moreover, these confirmed quasars will be followed up with near-infrared spectroscopy to determine their black hole masses and Eddington ratios to check the rapidness of their growth.

• JSTS:Journal of Semiconductor Technology and Science
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• v.8 no.2
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• pp.121-127
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• 2008

This paper presents design and fabrication of optimized geometry structure of electrostatic inkjet head. In order to verify effect of geometry shape, we simulate electric field intensity according to the head structure. The electric field strength increases linearly with increasing height of the micro nozzle. As the nozzle diameter decreases, the electric field along the periphery of the meniscus can be more concentrated. We design and fabricate the electrostatic inkjet heads, hole type and pole type, with optimized structure. It was fabricated using thick-thermal oxidation and silicon micromachining technique such as the deep reactive ion etching (DRIE) and chemical wet etching process. It is verified experimentally that the use of the MEMS inkjet head allows a stable and sustainable micro-dripping mode of droplet ejection. A stable micro dripping mode of ejection is observed under the voltages 2.5 kV and droplet diameter is $10\;{\mu}m$.

• Korean Journal of Ichthyology
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• v.5 no.2
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• pp.177-183
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• 1993

Results comparing the scale and otolith ages for walleye pollock from the Donut Hole of the Bering Sea showed a significant discrepancy for fish older than 8 years old. For walleye pollock from the Shelikof Strait of the Gulf of Alaska, comparison between ages determined from the scale and otolith readings indicated that there were no differences for younger age groups, but for the ages 6 and older, discrepancies squeezed in somewhat amid the same age groups.

• Korean Journal of Materials Research
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• v.12 no.6
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• pp.431-435
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• 2002

The dark current and photocurrent(PC) spectrum of Mg-doped GaN thin film were investigated with various bias voltages and temperatures. At high temperature and small bias, the dark current is dominated by holes thermally activated from an acceptor level Al located at about 0.16 eV above the valence band maximum $(E_v)$, The PC peak originates from the electron transition from deep level A2 located at about 0.34 eV above the $E_v$ to the conduction band minimum $(E_ C)$. However, at a large bias voltage, holes thermally activated from A2 to Al experience the field-in-duces tunneling to form one-dimensional defect band at Al, which determines the dark current. The PC peak associated with the transition from Al to $E_ C$ is also observed at large bias voltages owing to the extended recombination lifetime of holes by the tunneling. In the near infrared region, a strong PC peak at 1.20 eV appears due to the hole transition from deep donor/acceptor level to the valence band.

• Korean Journal of Materials Research
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• v.9 no.2
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• pp.124-131
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• 1999

Copper film, which is expected to be used as interconnection material for 1 giga DRAM integrated circuits was deposited on hole and trench patterns by Metal Organic Chemical Vapor Deposition(MOCVD) method. After a reflow process, contact and L/S patterns were filled by copper and the characteristics of the Cu reflow process were investigated. When deposited Cu films were reflowed, grain growth and agglomeration of Cu have occurred in surfaces and inner parts of patterns as well as complete filling in patterns. Also Cu thin oxide layers were formed on the surface of Cu films reflowed in $O_2$ambient. Agglomeration and oxidation of Cu had bad influence on the electrical properties of Cu films especially, therefore, their removal and prevention were studied simultaneously. As a pattern size is decreased, preferential reflow takes place inside the patterns and this makes advantages in filling patterns of deep submicron size completely. With Cu reflow process, we could fill the patterns with the size of deep sub-micron and it is expected that Cu reflow process could meet the conditions of excellent interconnection for 1 giga DRAM device when it is combined with Cu MOCVD and CMP process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.2
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• pp.623-628
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• 2011

Micro EDM(Electric Discharge Machining) is one of the most powerful technologies which are capable of fabricating micro-structure without any problems from high cutting force. However, there is a significant defect in the part machining with deep holes or pockets, because debris which are generated by electric discharging may frequently cause a short circuit between an electrode and workpiece material. Vibration flushing can reduce the undesirable phenomena with dynamic flow of EDM fluid in a deep and choked area. In this study, Vibration flushing with solenoid is suggested and the results show that the method can generate a remarkable EDM efficiency with high amplitude at a low frequency in comparison with current vibration flushing methods with high frequency using piezo actuators.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.123-128
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• 2012

An overview of the North Ecliptic Pole (NEP) deep multi-wavelength survey covering from X-ray to radio wavelengths is presented. The main science objective of this multi-wavelength project is to unveil the star-formation and AGN activities obscured by dust in the violent epoch of the Universe (z=0.5-2), when the star formation and black-hole evolution activities were much stronger than the present. The NEP deep survey with AKARI/IRC consists of two survey projects: shallow wide (8.2 sq. deg, NEP-Wide) and the deep one (0.6 sq. deg, NEP-Deep). The NEP-Deep provides us with a $15{\mu}m$ or $18{\mu}m$ selected sample of several thousands of galaxies, the largest sample ever made at these wavelengths. A continuous filter coverage at mid-IR wavelengths (7, 9, 11, 15, 18, and $24{\mu}m$) is unique and vital to diagnose the contribution from starbursts and AGNs in the galaxies at the violent epoch. The recent updates of the ancillary data are also provided: optical/near-IR magnitudes (Subaru, CFHT), X-ray (Chandra), FUV/NUV (GALEX), radio (WSRT, GMRT), optical spectra (Keck/DEIMOS etc.), Subaru/FMOS, Herschel/SPIRE, and JCMT/SCUBA-2.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.4
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• pp.390-399
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• 1999

Siliceous and calcareous deep-sea core sediments were collected by a multiple corer from the KODOS (Korea Deep Ocean Study) area, northeast equatorial Pacific, to compare vane shear strengths measured by two different apparatuses and in different places of on-board and on-land laboratories. The apparatuses were 1) a hand-held vane with four blades of $2.0{\times}2.0$ cm, and 2) a motorized shear vane system with four blades of $1.0{\times}0.88$ attached on a rotational viscometer. Depth profiles of shear strengths of core samples determined by the apparatuses do not show any consistent difference. Also, there is no consistent difference between shear strength values measured on-board and on-land laboratories after storing the core samples for three months in a cold room by a motorized shear vane system. However, there are considerable differences between depth profiles of shear strengths measured at four different points (holes) of a core sample. Moreover, significant differences among the profiles of different tube samples from a multiple corer within a sampling station were observed. Heterogeneity in physical properties of each depth and sediment column, possibly due to bioturbation and bottom current flows, is likely responsible for the differences in the geotechnical properties.

• Journal of Chest Surgery
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• v.42 no.6
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• pp.757-762
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• 2009

Background: Compression of the left common iliac vein by the overriding common iliac artery is frequently combined with acute deep vein thrombosis in patients with May-Thurner Syndrome. We evaluate the results of treatment with thrombolysis and thrombectomy followed by stenting in 34 patients with May-Thurner Syndrome combined with lower extremity deep venous thrombosis. Material and Method: The authors retrospectively reviewed the records of 34 patients (mean age: $65{\pm}14$ year old) who had undergone stent insertion for acute deep vein thrombosis that was caused by May-Thurner syndrome. After thrombectomy and thrombolysis, insertion of a wall stent and balloon angioplasty were performed to relieve the compression of the left common iliac vein. Urokinase at a rate of 80,000 to 120,000 U/hour was infused into the thrombosed vein via a multi-side hole thrombolysis catheter. A retrieval inferior vena cava (IVC) filter was placed to protect against pulmonary embolism in 30 patients (88%). Oral anticoagulation with warfarin was maintained for 3 months, and follow-up Multi Detector Computerized Tomography (MDCT) angiography was done at the date of the patients' hospital discharge and at the 6 months follow-up. Result: The symptoms of deep venous thrombosis disappeared in two patients (4%), and there was clinical improvement within 48 hours in twenty eight patients (82%), but there was no improvement in four patients (8%). The MDCT angiography at discharge showed no thrombus in 9 patients (26%) and partial thrombus in 21 (62%), whereas the follow-up MDCT at $6.4{\pm}5.5$ months (32 patients) revealed no thrombus in 23 patients (72%), and partial thrombus in 9 patients (26%). Two patients (6%) had recurrence of DVT, so they underwent retreatment. Conclusion: Stent insertion with catheter-directed thrombolysis and thrombectomy is an effective treatment for May-Thurner syndrome combined with acute deep vein thrombosis in the lower extremity.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.246-246
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• 2016

Tungsten-nitrogen (W-N) co-doping has been known to enhance the photocatalytic activity of anatase titania nanoparticles by utilizing visible light. The doping effects are, however, largely dependent on calcination or annealing conditions, and thus, the massive production of quality-controlled photocatalysts still remains a challenge. Using density functional theory (DFT) thermodynamics and time-dependent DFT (TDDFT) computations, we investigate the atomic structures of N doping and W-N co-doping in anatase titania, as well as the effect of the thermal processing conditions. We find that W and N dopants predominantly constitute two complex structures: an N interstitial site near a Ti vacancy in the triple charge state and the simultaneous substitutions of Ti by W and the nearest O by N. The latter case induces highly localized shallow in-gap levels near the conduction band minimum (CBM) and the valence band maximum (VBM), whereas the defect complex yielded deep levels (1.9 eV above the VBM). Electronic structures suggest that substitutions of Ti by W and the nearest O by N improves the photocatalytic activity of anatase by band gap narrowing, while defective structure degrades the activity by an in-gap state-assisted electron-hole recombination, which explains the experimentally observed deep level-related photon absorption. Through the real-time propagation of TDDFT (rtp-TDDFT), we demonstrate that the presence of defective structure attracts excited electrons from the conduction band to a localized in-gap state within a much shorter time than the flat band lifetime of titania. Based on these results, we suggest that calcination under N-rich and O-poor conditions is desirable to eliminate the deep-level states to improve photocatalysis.