• Proceedings of the KIPE Conference
• /
• 2004.07a
• /
• pp.64-67
• /
• 2004

The klystron-modulator(K&M) system of the Pohang Light Source(PLS) had been supplying high power microwaves for the acceleration of 2.5 GeV electron beams since October 2002. There are 12 sets of K&M systems to accelerate electron beams to 2.5GeV nominal beam energy. One module of the K&M system consists of an 80 MV S-band (2856 MHZ) klystron tube and the matching 200 MW modulator. In order to obtain electron beam of the consequently stability for linac, the pulse-to-pulse beam voltage regulation is less than $+/-0.5\%$. To get the reliable stability of the modulator which is less than $+/-0.5\%$, a charging section is improved in a modulator which has been operated with inverter power supply.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.132.1-132.1
• /
• 2012

Radiation Belt Environment (RBE) model has developed to understand radiation belt dynamics as it considers whistler mode hiss and chorus waves which is responsible for relativistic electron acceleration and precipitation. Recently, many studies on electron loss by pitch-angle scattering have reported that elctromagnetic ion cyclotron (EMIC) wave is also responsible for main loss mechanism in dusk and equatorial regeion. Here, we attempt to incorporate EMIC into RBE model simulation code to understand more detailed physical dynamics in Radiation belt environemnt. We compare this developed model to data during storm events where both of electron loss and EMIC waves were detected.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.7 no.2
• /
• pp.207-215
• /
• 1997

Aluminum (Al) thin films were deposited on the Si(100) and TiN(60 nm)/Si (100) substrate by the ionized cluster beam deposition (ICBD) method. The characteristics of thin films were examined by the $\alpha$-step, four-point-probe, Scanning Electron Spectroscopy (SEM), Auger Electron Spectroscopy (AES). The growth rate of the Al thin film increased and the resistivity decreased as the crucible temperature increased. At the crucible temperature $1800^{\circ}C$, the microstructure of Al thin film deposited was smooth and continuous the resistivity decreased as the acceleration voltage increased. Also, the minimum resistivity in Si(100) substrate and TiN(60 nm)/Si(100) substrate were 3.4 $\mu \Omega \textrm {cm}$, 3.6 $\mu \Omega \textrm {cm}$ at the acceleration voltage 4 kV and 2 kV respectively. From the AES spectrumt 14 wasn't detected any impurities In the Al thin film. Therefore the resistivity of Al thin film was affected by the microstructure of film.

• Bulletin of the Korean Space Science Society
• /
• 2009.10a
• /
• pp.42.3-43
• /
• 2009

Triplets of identical cubesats will be built to carry out the following scientific objectives: i) multi-observations of ionospheric ENA (Energetic Neutral Atom) imaging, ii) ionospheric signature of suprathermal electrons and ions associated with auroral acceleration as well as electron microbursts, and iii) complementary measurements of magnetic fields for particle data. Each satellite, a cubesat for ion, neutral, electron, and magnetic fields (CINEMA), is equipped with a suprathermal electron, ion, neutral (STEIN) instrument and a 3-axis magnetometer of magnetoresistive sensors. TRIO is developed by three institutes: i) two CINEMA by Kyung Hee University (KHU) under the WCU program, ii) one CINEMA by UC Berkeley under the NSF support, and iii) three magnetometers by Imperial College, respectively. Multi-spacecraft observations in the STEIN instruments will provide i) stereo ENA imaging with a wide angle in local times, which are sensitive to the evolution of ring current phase space distributions, ii) suprathermal electron measurements with narrow spacings, which reveal the differential signature of accelerated electrons driven by Alfven waves and/or double layer formation in the ionosphere between the acceleration region and the aurora, and iii) suprathermal ion precipitation when the storm-time ring current appears. In addition, multi-spacecraft magnetic field measurements in low earth orbits will allow the tracking of the phase fronts of ULF waves, FTEs, and quasi-periodic reconnection events between ground-based magnetometer data and upstream satellite data.

• Applied Microscopy
• /
• v.33 no.3
• /
• pp.179-185
• /
• 2003

The operating accelerating voltage in the electron microscopy may differ from the nominal voltage specified by the manufacture. Thus it is necessary, at least once, to determine the wavelength of electron beam for the nominal accelerating voltage. Particularly in QCBED technique, the wavelength of the incident electron beam on a specimen must be determined as accurately as possible. In this paper we present a simple method to determine accurately the wavelength of electrons from LACBED patterns of a known crystalline materials, which is analogous to a method based on Kikuchi patterns reported previously. This method is to utilize three diffraction lines not belonging to the same zone, which nearly intersect at the same point. For an application of the method, the wavelength of electrons for the 200 kv nominal acceleration voltage of JEM2010 is determined to be 0.002496(3) nm ($201.5{\pm}0.4$ kv) with an uncertainty of 0.12%.

• Proceedings of the Botanical Society of Korea Conference
• /
• 1999.08a
• /
• pp.83-90
• /
• 1999

Electron crystallography of two-dimensional crystalsand electron cryo-microscopy is becoming an established method for determining the structure and function of a variety of membrane proteins that are providing difficult to crystallize in three dimension. In this study this technique has been used to investigate the structure of a ~160 kDa reaction centre sub-core complex of photosystem II. Photosystem II is a photosynthetic membrane protein consisting of more than 25 subunits. It uses solar energy to split water releasing molecular oxygen into the atmosphere and creates electrochemical potential across the thylakoid membrane, which is eventually utilized to generate ATP and NADPH. Images were taken using Philips CM200 field emission gun electron microscope with an acceleration voltage of 200kW at liquid nitrogen temperature. In total, 79 images recorded dat tilt angles ranging from 0 to 67 degree yielded amplitudes and phases for a three-dimensional map with an in-plant resolution of 6$\AA$ and 11.4$\AA$ in the third dimension shows at least 23 transmembrane helices resolved in a monomeric complex, of which 18 were able to be assigned to the D1, D2, CP47 , and cytochrome b559 alfa beta-subunits with their associated pigments that ae active in electron transport (Rhee, 1998, Ph.D.thesis). The D1/D2 heterodimer is located in the central position within the complex and its helical scalffold is remarkably similar to that of the reaction centres not only in purple bacteria but also in plant photosystem I (PSI) , indicating a common evoluationary origin of all types of reaction centre in photosynthetic organism known today 9RHee et al. 1998). The structural homology is now extended to the inner antenna subunit, ascribed to CP47 in our map, where the 6 transmembrane helices show a striking structural similarity to the corresponding helices of the PSI reaction centre proteins. The overall arrangement of the chlorophylls in the D1 /D2 heterodimer, and in particular the distance between the central pair, is ocnsistent with the weak exciton coupling of P680 that distinguishes this reaction centre from bacterial counterpart. The map in most progress towards high resolution structure will be presented and discussed.

• Journal of the Mineralogical Society of Korea
• /
• v.28 no.4
• /
• pp.293-297
• /
• 2015

Focused ion beam (FIB) technique is widely used in the precise preparation of thin slices for the transmission electron microscopic (TEM) observation of target area of the minerals and geological materials. However, structural damages and artifacts by the Ga ion beam as well as electron beam damage are major difficulties in the TEM analyses. TEM analyses of the mineral samples showed the amorphization of quartz and feldspar, curtain effect, and Ga contamination, particularly near the grain edges and relatively thin regions. Although the ion beam damage could be much reduced by the improved procedures including the adjustment of the acceleration voltage and current, the ion beam damage and contamination are likely inevitable, thus requiring careful interpretation of the micro-structural and micro-chemical features observed by TEM analyses.

• Journal of Radiopharmaceuticals and Molecular Probes
• /
• v.6 no.2
• /
• pp.102-115
• /
• 2020

In the state of Positronium (Ps), which is an unstable material created by the temporary combination of electrons and positrons, the imaging technology through photo-conversion methodology is emerging as a new research theme under resonance conditions through terahertz electromagnetic waves. Normally, Positronium can be observed in the positron emission computed tomography (PET) process when an unstable, separate state that remains after the pair annihilation of an electron and a positron remains. In this study, terahertz (THz) waves and Cherenkov radiation (CR) are generated using the principle of ponderomotive force in the plasma wake-field acceleration, and electrons and positrons are simultaneously generated by using a relativistic electron beam without using a PET device. We confirm the possibility of Positronium photoconversion technology in terahertz electromagnetic resonance conditions through experimental studies that generate an unstable state. Here, a relativistic electron beam (REB) energy of 0.5 MeV (γ=2) was used, and the terahertz wave frequencies is G-band. Meanwhile, a THz wave mode converting three-stepped axicon lens was used to apply the photoconversion technology. Through this, light emission in the form of a luminescence-converted Bessel beam can be verified. In the future, it can be used complementarily with PET in nuclear medicine in the field of medical imaging.

• The Bulletin of The Korean Astronomical Society
• /
• v.40 no.2
• /
• pp.30.1-30.1
• /
• 2015

Radio relics are diffuse radio sources found in the outskirts of galaxy clusters and they are thought to trace synchrotron-emitting relativistic electrons accelerated at shocks. We explore a diffusive shock acceleration (DSA) model for radio relics in which a spherical shock with the parameters relevant for the Sausage radio relic in cluster CIZA J2242.8+5301 impinges on a magnetized cloud containing fossil relativistic electrons. This model is expected to explain some observed characteristics of giant radio relics such as the relative rareness, uniform surface brightness along the length of thin arc-like radio structure, and spectral curvature in the integrated radio spectrum. We find that the observed surface brightness profile of the Sausage relic can be explained reasonably well by shocks with speed $u_s{\sim}3{\times}10^3km/s$ and sonic Mach number $M_s{\sim}3$. These shocks also produce curved radio spectra that steepen gradually over $(0.1-10){\nu}_{br}$ with a break frequency ${\nu}_{br}{\sim}1GHz$, if the duration of electron acceleration is ~60-80 Myr. However, the abrupt increase in the spectral index above ~1.5 GHz observed in the Sausage relic seems to indicate that additional physical processes, other than radiative losses, operate for electrons with the Lorentz factor, ${\gamma}_e$ > $10^4$.

• Korean Journal of Chemical Engineering
• /
• v.35 no.11
• /
• pp.2290-2295
• /
• 2018

An acceleration stress test (AST) was performed to evaluate the durability of a polymer membrane in a polymer electrolyte membrane fuel cell (PEMFC) for 500 hours. Previous studies have shown that hydrogen crossover measured by linear sweep voltammetry (LSV) increases when the polymer membrane deteriorates in the AST process. On the other hand, hydrogen crossover of the membrane often decreases in the early stages of the AST test. To investigate the cause of this phenomenon, we analyzed the MEA operated for 50 hours using the AST method (OCV, RH 30% and $90^{\circ}C$). Cyclic voltammetry and transmission electron showed that the electrochemical surface area (ECSA) decreased due to the growth of electrode catalyst particles and that the hydrogen crossover current density measured by LSV could be reduced. Fourier transform infrared spectroscopy and thermogravimetric/differential thermal analysis showed that -S-O-S- crosslinking occurred in the polymer after the 50 hour AST. Gas chromatography showed that the hydrogen permeability was decreased by -S-O-S- crosslinking. The reduction of the hydrogen crossover current density measured by LSV in the early stages of AST could be caused by both reduction of the electrochemical surface area of the electrode catalyst and -S-O-S- crosslinking.