• Vacuum Magazine
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• v.3 no.4
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• pp.4-7
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• 2016

An X-ray Free Electron laser facility (PAL-XFEL) has been built in Pohang Accelerator Laboratory to provide X-ray FEL radiations for photon users. The machine consists of a 10 GeV normalconducting S-band linear accelerator and two undulator beamlines. The hard and soft X-ray beamlines will provide FEL radiations with wavelengths of 0.6 to 0.1 nm and 4.5 to 1 nm, respectively. Beam commissioning of PAL-XFEL is ongoing and user service will start in 2017. In this report, the PAL-XFEL layout and the working principle are discussed.

• Journal of The Korean Astronomical Society
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• v.48 no.2
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• pp.113-123
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• 2015

We present observational results from optical long-slit spectroscopy of parsec-scale jets of DG Tau. From HH 158 and HH 702, the optical emission lines of Hα, [O i] λλ6300, 6363, [N ii] λλ6548, 6584, and [S ii] λλ6716, 6731 are obtained. The kinematics and physical properties (i.e., electron density, electron temperature, ionization fraction, and mass-loss rate) are investigated along the blueshifted jet up to 650′′ distance from the source. For HH 158, the radial velocity ranges from −50 to −250 km s⁻¹. The proper motion of the knots is 0.′′196 − 0.′′272 yr⁻¹. The electron density is ∼10⁴ cm⁻³ close to the star, and decreases to ∼10² cm⁻³ at 14′′ away from the star. Ionization fraction indicates that the gas is almost neutral in the vicinity of the source. It increases up to over 0.4 along the distance. HH 702 is located at 650′′ from the source. It shows ∼ −80 km s⁻¹ in the radial velocity. Its line ratios are similar to those at knot C of HH 158. The mass-loss rate is estimated to be about ∼ 10⁻⁷ M_⊙ yr⁻¹, which is similar to values obtained from previous studies.

• Journal of Welding and Joining
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• v.15 no.4
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• pp.166-177
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• 1997

The high strength AlZnMgCu0.5 alloy is a light metal with good age hardenability, and has a high tensile and yielding strength. Therefore, it can be used for structures requiring high speciple strength. Even though high strength AlZnMgCu alloy has good mechanical properties, it has a lot of problems in TIG and MIG welding processes. Since lots of high heat absorption is introduced into the weldment during TIG and MIG processes, the microstructural variation and hot cracks take place in heat affected zone. Therefore, the mechanical properties of high strength AlZnMgCu0.5 alloy can be degraded in weldment and heat affected zone. Welding process utilizing high density heat source such as electron beam should be developed to reduce pore and hot cracking, whichare usually accompanied by MIG and TIG welding processes. In this work, electron beam welding process were used with or without AlMg4.5Mn as filler material to avoid the degradation of mechanical properties. Mechanical and metallurgical characteristics were also studied in electron beam weldment and heat affected zone. Moreover hot cracking mechanism was also investigated.

• Applied Microscopy
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• v.47 no.1
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• pp.36-42
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• 2017

Field electron emission measurements were performed on dielectric-coated tungsten emitters, with apex radii in the nanometer and micrometer range, which were prepared by electrochemical etching in NaOH solution. Measurements were performed in a field electron microscopy (FEM) with a base pressure <$10^{-6}$ Pascal ($10^{-8}$ mbar). Four different types of dielectric were used, namely: (1) Clark Electromedical Instruments epoxylite resin, (2) Epidian 6 produced by Ciech Sarzyna S. A., (3) a Radionox solution of colloidal graphite; and (4) Molyslip 2001 E compound ($MoS_2$ and MoS). Current-voltage measurements and FEM images were used to investigate the characteristics of these composite emitters, and to assess how the different types of dielectric coating affect the suitability of the composite emitter as a potential electron source.

• Bulletin of the Korean Space Science Society
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• 2006.10a
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• pp.52-52
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• 2006

Many spacecraft failures and anomalies have been attributed to energetic electrons in the Earth's magnetosphere. While the dynamics of these electrons have been studied extensively for several decades, the fundamental question of how they are accelerated is not fully resolved. Proposed theories have not been successful in explaining fast high energy increase such as REE (Relativistic electron enhancement). In this presentation, we show observations of energetic electron precipitation measured by the Korean satellite, STSAT-1 which simultaneously detect (100ev - 20 keV) and (170 - 360 keV) energy electrons at the 680 km orbit, when the RES event observed at the geosynchronous orbit on October 13, 2004. STSAT-1 observed intense electron precipitation in both energy ranges occurred in the midnight sector clearly demonstrating that electrons having wide energy band are injected from the plasma sheet. To make the balance between loss and injection, the injected electron flux should be also large. In this situation, the injected electrons can be trapped into the magnetosphere and produce REE, though they have low e-folding energies. We propose this plasma sheet injection might be the primary source of relativistic electron (1 MeV) flux increases.

• Transactions on Control, Automation and Systems Engineering
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• v.2 no.4
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• pp.268-273
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• 2000

Plasma models are crucial to equipment design and process optimization. A radial basis function network(RBFN) in con-junction with statistical experimental design has been used to model a process plasma. A 2$^4$ full factorial experiment was employed to characterized a hemispherical inductively coupled plasma(HICP) in characterizing HICP, the factors that were varied in the design include source power, pressure, position of shuck holder, and Cl$_2$ flow rate. Using a Langmuir probe, plasma attributes were collected, which include typical electron density, electron temperature. and plasma potential as well as their spatial uniformity. Root mean-squared prediction errors of RBEN are 0.409(10(sup)12/㎤), 0.277(eV), and 0.699(V), for electron density, electron temperature, and Plasma potential, respectively. For spatial uniformity data, they are 2.623(10(sup)12/㎤), 5.704(eV) and 3.481(V), for electron density, electron temperature, and plasma potential, respectively. Comparisons with generalized regression neural network(GRNN) revealed an improved prediction accuracy of RBFN as well as a comparable performance between GRNN and statistical response surface model. Both RBEN and GRNN, however, experienced difficulties in generalizing training data with smaller standard deviation.

• Applied Microscopy
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• v.50
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• pp.23.1-23.9
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• 2020

We propose an effective deep learning model to denoise scanning transmission electron microscopy (STEM) image series, named Noise2Atom, to map images from a source domain 𝓢 to a target domain 𝓒, where 𝓢 is for our noisy experimental dataset, and 𝓒 is for the desired clear atomic images. Noise2Atom uses two external networks to apply additional constraints from the domain knowledge. This model requires no signal prior, no noise model estimation, and no paired training images. The only assumption is that the inputs are acquired with identical experimental configurations. To evaluate the restoration performance of our model, as it is impossible to obtain ground truth for our experimental dataset, we propose consecutive structural similarity (CSS) for image quality assessment, based on the fact that the structures remain much the same as the previous frame(s) within small scan intervals. We demonstrate the superiority of our model by providing evaluation in terms of CSS and visual quality on different experimental datasets.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.195.1-195.1
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• 2016

Currently, as Plasma application is expanded to the industrial and medical industrial, low temperature plasma applications became important. Especially in medical and biology, many researchers have studied about generated radical species in atmospheric pressure low temperature plasma directly adapted to human body. Therefore, so measurement their plasma parameter is very important work and is widely studied all around world. One of the plasma parameters is electron density and it is closely relative to radical production through the plasma source. some kinds of method to measuring the electron density are Thomson scattering spectroscopy and Millimeter-wave transmission measurement. But most methods have very expensive cost and complex configuration to composed of experiment system. We selected Michelson interferometer system which is very cheap and simple to setting up, so we tried to measuring electron density by laser interferometer with laser beam chopping module for measurement of temporal phase difference in plasma jet. To measuring electron density at atmospheric pressure Ar plasma jet, we obtained the temporal phase shift signal of interferometer. Phase difference of interferometer can occur because of change by refractive index of electron density in plasma jet. The electron density was able to estimate with this phase difference values by using physical formula about refractive index change of external electromagnetic wave in plasma. Our guiding laser used Helium-Neon laser of the centered wavelength of 632 nm. We installed chopper module which can make a 4kHz pulse laser signal at the laser front side. In this experiment, we obtained more exact synchronized phase difference between with and without plasma jet than reported data at last year. Especially, we found the phase difference between time range of discharge current. Electron density is changed from Townsend discharge's electron bombardment, so we observed the phase difference phenomenon and calculated the temporal electron density by using phase shift. In our result, we suggest that the electron density have approximately range between 1014~ 1015 cm-3 in atmospheric pressure Ar plasma jet.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.32 no.1
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• pp.11-23
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• 2022

Collaboration tools are used widely as non-face-to-face work increases due to social distancing after COVID-19. The tools are being developed in a cross-platform manner with 'Electron', an open source framework based on Chromium, to ensure accessibility on multiple devices. Electron Apps, applications built with Electron framework, store data in a manner similar to Chromium-based web browsers, so the data can be acquired in the same way as the data is acquired from a web browser. In this paper we analyze the data structure of web storage and suggest a method to get the message from Electron Apps focused on collaboration tools such as Jandi, Slack, and Microsoft Teams. For Jandi, we get the message from Cache by using previously developed tools, and in the case of Slack and Microsoft Teams, we get the message from IndexedDB by using the message carving tool we developed.

• Analytical Science and Technology
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• v.22 no.2
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• pp.152-158
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• 2009

In this study, we made a new discharge source improving previous SPI source to ionize softly organic compounds. The new SPI source consists of two electrodes as a hollow mesh cathode of half cylindrical shape and a hollow anode. We optimized the geometrical parameter of the SPI source by investigating the I-V curves at the various distance between the cathode and the anode. As the results, we found stable conditions of the soft plasma on broad range of the current and the voltage. The new SPI source attached to quadrupole mass spectrometer (QMS), and we obtained the mass spectra of dichloromethane (DCM). The fragment patterns of DCM appeared similarly with the pattern of electron ionization (EI).