• 한국정밀공학회지
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• 제16권1호통권94호
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• pp.132-140
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• 1999

This paper suggests a monitoring method for the pulsed laser spot welding of the thin metal sheets using a point IR(InfraRed) sensor. A new criterion was introduced and the experimental results guaranteed the efficiency. The ideal radiation feature was derived from the mathematical model and was simulated. The radiation feature is robust to withstand the change of measuring condition and can be used to detect the absorbed laser energy. In an experiment, the radiation feature was examined for the differect laser energy. The pulse width and the laser power was variated and the radiation feature was examined. In the other experiment, the relationship between the weld strength and radiation feature was examined. Artificial Neural Network(ANN) was employed to find out the relationship. The correlation coefficient between the real strength and the estimated strength is high as 0.94 and the mean square error is low as 0.64 kgf learned parts. Another group of the welds was used to appraise the learning efficiency. The correlation coefficient between the measured and the estimated weld strength is high as 0.91.

• Journal of electromagnetic engineering and science
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• 제18권1호
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• pp.20-28
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• 2018

The time synchronization of each sub-unit of a pulsed generator is important to generate an output high-power radio frequency (RF) signal. To obtain the time synchronization between an input RF signal fed by an external source and an electron beam produced by an electric pulse generator, the influence of different charging voltages on a delay and a rise time of the output pulse waveform in the electric pulse generator should be carefully considered. This paper aims to study the timing characteristics of the delay and the rise time as a function of different charging voltages with a peak value of less than -35 kV in the high-voltage pulse generator, including a trigger generator (TG) and a pulse-forming line (PFL). The simulation has been carried out to estimate characteristics in the time domain, in addition to their output high-voltage amplitude. Experimental results compared with those obtained by simulation indicate that the delay of the output pulses of the TG and PFL, which are made by controlling the external triggering signal with respect to different charging voltages, is getting longer as the charging voltage is increasing, and their rise times are inversely proportional to the amplitude of the charging voltage.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 E
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• pp.2201-2203
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• 1999

In this study, we have designed and manufactured not a present elliptic cavity but a circular cavity and we have experimented the operational characteristics. As a result, we obtained the maximum efficiency of 2.1 %. It didn't have any difference compared with elliptic cavity. A circular cavity is much more compact, so far easier to be manufactured than a elliptic cavity. And it can be made at a low cost. At the input energy, parameter $\alpha$, input voltage, and pulse width were in the same condition, we have decided to the optimization of the mesh number of a parallel-mesh circuit which was connected with main power supply.

• Journal of Electrical Engineering and Technology
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• 제7권5호
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• pp.784-788
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• 2012

In this paper, a high-performance optical gating in a junction device based on a vanadium dioxide dioxide ($VO_2$) thin film grown by a sol-gel method was experimentally demonstrated by directly illuminating the $VO_2$ film of the device with an infrared light at ~1554.6 nm. The threshold voltage of the fabricated device could be tuned by ~76.8 % at an illumination power of ~39.8 mW resulting in a tuning efficiency of ~1.930 %/mW, which was ~4.9 times as large as that obtained in the previous device fabricated using the $VO_2$ thin film deposited by a pulsed laser deposition method. The rising and falling times of the optical gating operation were measured as ~50 ms and ~200 ms, respectively, which were ~20 times as rapid as those obtained in the previous device.

• 한국전기전자재료학회논문지
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• 제23권9호
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• pp.736-740
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• 2010

Nickel wires of 0.8 mm in diameter and 80 mm in length were electrically exploded in liquid media such as water, ethyl alcohol. The distribution of particle sizes was broad from a few micrometers to tens of nanometer. It was identified that the particles could be classified according to its sizes by using centrifugal separator. The powder prepared in distilled water showed mainly pure metallic Ni phase although a little oxide phase was observed. The powders prepared in ethyl alcohol showed complicated unknown phases, which is attributed to the compound of carbon in the organic liquid. This unknown phase was turned to pure metallic Ni phase after heat treatment.

• Journal of Advanced Marine Engineering and Technology
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• 제32권2호
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• pp.315-322
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• 2008

Titanium and its alloys have excellent corrosion resistance, high strength to weight ratios and creep properties in high temperature, which make them using many various fields of application. Especially, pure titanium, which has outstanding resistance for the stress corrosion cracking, crevice corrosion, pitting and microbiologically influenced corrosion, brings out to the best material for the heat exchanger, ballast tank, desalination facilities, and so on. Responding to these needs, welding processes for titanium are also being used GTAW, GMAW, PAW, EBW, LBW, resistance welding and diffusion bonding, etc. However, titanium is very active and highly susceptible to embrittlement by oxygen, nitrogen, hydrogen and carbon at high temperature, so it needs to shield the weld metal from the air and these gases during welding by non-active gas. In this study, it was possible to get sound beads without humping and spatter with a decrease of peak power according to increase of pulse width, change of welding speed and overlap rate for heat input control, and shield conditions at pulsed laser welding of titanium plates for Lap welding.

• The Korean Journal of Pain
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• 제21권3호
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• pp.248-251
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• 2008

The clinical syndrome of posttraumatic syringomyelia can complicate major spinal trauma and develops many months after spinal injury. The 50-90% of patients experienced the pain and especially the component of central pain. In patients with central pain following spinal cord injury, ketamine has been shown to be an effective analgesic. We report a case of posttraumatic syringomyelia in a 30-year-old woman who complained of central pain, weakness of both legs and dysesthesia. She had not responded to pulsed radiofrequency, or lidocaine infusion therapy, but a continuous intravenous infusion of ketamine, an N-methyl-D-asparate receptor antagonist, reduced her severe central pain. In conclusion, a ketamine infusion therapy resulted in a significant reduction of central pain without decreasing of motor power and function.

• Journal of Astronomy and Space Sciences
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• 제33권1호
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• pp.1-11
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• 2016

Over the last few years, the data obtained using the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope has provided new insights on high-energy processes in globular clusters, particularly those involving compact objects such as MilliSecond Pulsars (MSPs). Gamma-ray emission in the 100 MeV to 10 GeV range has been detected from more than a dozen globular clusters in our galaxy, including 47 Tucanae and Terzan 5. Based on a sample of known gammaray globular clusters, the empirical relations between gamma-ray luminosity and properties of globular clusters such as their stellar encounter rate, metallicity, and possible optical and infrared photon energy densities, have been derived. The measured gamma-ray spectra are generally described by a power law with a cut-off at a few gigaelectronvolts. Together with the detection of pulsed γ-rays from two MSPs in two different globular clusters, such spectral signature lends support to the hypothesis that γ-rays from globular clusters represent collective curvature emission from magnetospheres of MSPs in the clusters. Alternative models, involving Inverse-Compton (IC) emission of relativistic electrons that are accelerated close to MSPs or pulsar wind nebula shocks, have also been suggested. Observations at >100 GeV by using Fermi/LAT and atmospheric Cherenkov telescopes such as H.E.S.S.-II, MAGIC-II, VERITAS, and CTA will help to settle some questions unanswered by current data.

• Journal of Astronomy and Space Sciences
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• 제30권2호
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• pp.83-85
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• 2013

Anomalous X-ray pulsars (AXPs) are thought to be magnetars which are young isolated neutron stars with extremely strong magnetic fields of > $10^{14}$ Gauss. Their tremendous magnetic fields inferred from the spin parameters provide a huge energy reservoir to power the observed X-ray emission. High-energy emission above 0.3 MeV has never been detected despite intensive search. Here, we present the possible Fermi Large Area Telescope (LAT) detection of ${\gamma}$-ray pulsations above 200 MeV from the AXP, 1E 2259+586, which puts the current theoretical models of ${\gamma}$-ray emission mechanisms of magnetars into challenge. We speculate that the high-energy ${\gamma}$-rays originate from the outer magnetosphere of the magnetar.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.223-228
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• 1999

We have investigated the microwave properties of a high-T$_c$. superconducting Josephson junction by Shapiro step measurements. A Josephson junction was fabricated on the bicrystal MgO substrate using pulsed laser deposition method. We have measured Shapiro steps in the I-V characteristics under the irradiation of 1.36 cm wavelength up to 45 K and found inclined current steps above 50 K. In order to understand these results, we introduced an additional resistance connected in series to RSJ model. Using this modified RSJ model, we could explain the inclined current steps as a result of superposition of the junction and an additional resistance above certain temperatures. Also, we presented the received power of the Josephson junction above 50 K.