• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.396-399
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• 2002

Intense quasi-monochromatic x-ray irradiation from the linear plasma target is described. The plasma x-ray generator employs a high-voltage power supply, a low-impedance coaxial transmission line, a high-voltage condenser with a capacity of about 200 nF, a turbo-molecular pump, a thyristor pulse generator as a trigger device, and a flash x-ray tube. The high-voltage main condenser is charged up to 55 kV by the power supply, and the electric charges in the condenser are discharged to the tube after triggering the cathode electrode. The x-ray tube is of a demountable triode that is connected to the turbo molecular pump with a pressure of approximately 1 mPa. As electron flows from the cathode electrode are roughly converged to the molybdenum target by the electric field in the tube, the weakly ionized plasma, which consists of metal ions and electrons, forms by the target evaporating. In the present work, the peak tube voltage was almost equal to the initial charging voltage of the main condenser, and the peak current was about 20 kA with a charging voltage of 55 kV. When the charging voltage was increased, the linear plasma x-ray source grew, and the characteristic x-ray intensities of K-series lines increased. The quite sharp lines such as hard x-ray lasers were clearly observed. The quasi-monochromatic radiography was performed by a new film-less computed radiography system.

• Structural Engineering and Mechanics
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• v.61 no.3
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• pp.347-357
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• 2017

The applications of active control is being more popular nowadays. Several control algorithms have been developed to determine optimum control force. In this paper, a Chaotic Particle Swarm Optimization (CPSO) technique, based on Logistic map, is used to compute the optimum control force of active tendon system. A chaotic exploration is used to search the solution space for optimum control force. The response control of Multi-Degree of Freedom (MDOF) shear buildings, equipped with active tendons, is introduced as an optimization problem, based on Instantaneous Optimal Active Control algorithm. Three MDOFs are simulated in this paper. Two examples out of three, which have been previously controlled using Lattice type Probabilistic Neural Network (LPNN) and Block Pulse Functions (BPFs), are taken from prior works in order to compare the efficiency of the current method. In the present study, a maximum allowable value of control force is added to the original problem. Later, a twenty-story shear building, as the third and more realistic example, is considered and controlled. Besides, the required Central Processing Unit (CPU) time of CPSO control algorithm is investigated. Although the CPU time of LPNN and BPFs methods of prior works is not available, the results show that a full state measurement is necessary, especially when there are more than three control devices. The results show that CPSO algorithm has a good performance, especially in the presence of the cut-off limit of tendon force; therefore, can widely be used in the field of optimum active control of actual buildings.

• The Journal of the Acoustical Society of Korea
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• v.22 no.4
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• pp.308-314
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• 2003

Wideband speech communications with 7㎑ bandwidth can provide high-quality speech services that are almost impossible with current narrow-band speech communications with 3.4 ㎑ bandwidth, and AMR wideband codec was recently developed for these services. The performance of AMR wideband codec is excellent due to its wideband information and partially to ACELP structure, but it requires high computational complexity especially in codebook search. In this paper, to solve this problem, an efficient codebook search method for AMR wideband codec is proposed. The proposed method first determines the coarse initial codevector, then improves the performance of codevector by replacing a poor pulse in codevector with better one iteratively. Simulations show that AMR wideband codec with proposed codebook search method has higher performance with much less computational cost than conventional AMR wideband codec.

• Journal of the Korean Chemical Society
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• v.35 no.6
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• pp.673-679
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• 1991

The electrochemical reduction of N-tert-butylbenzothiazole-2-sulfenamide (TBBS; vulcanization accelerator) was investigated by direct current, differential pulse polarography, cyclic voltammetry and controlled potential coulometry. The electrode reduction of TBBS proceeded E-C-E-C reaction mechanism by four electrons transfer at irreversible one wave (-2.31 volts vs. Ag/0.1M AgN$O_3$ in AN). As the results of controlled potential electrolysis, mercaptobenzothiazole (MBT), benzothiazole disulfide (MBT dimer) and extricated sulfur were products which followed by cleavage of the sulfenamide (-S-N=) bond. Upon the basis of products analysis and polarogram interpretation with pH variable, electrochemical reaction mechanism was suggested.

• Journal of the Korean Chemical Society
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• v.35 no.6
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• pp.680-688
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• 1991

The electrochemical reduction of N-oxyldiethylenebenzothiazole-2-sulfenamide (ODBS; vulcanization accelerator) was investigated by direct current polarography, differential pulse polarography, cyclic voltammetry and controlled potential coulometry. The irreversible electrode reduction of ODBS proceeded E-C-E-C reaction mechanism by three electrons transfer with irreversible one wave (-1.86 volts vs. Ag/0.1 M AgN$O_3$ in AN). As the results of controlled potential electrolysis, mercaptobenzothiazole (MBT), benzothiazole disulfide (MBT dimer) and extricated sulfur were products which followed by cleavage of the sulfenamide (-S-N=) bond. Upo the basis of products analysis and polarogram interpretation witli pH variable, electrochemical reaction mechanism was suggested.

• Journal of IKEEE
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• v.11 no.4
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• pp.257-264
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• 2007

The MM22 microtron has used as a cancer therapy machine from Nov. 1986 to Feb. 2006. This machine was moved and installed to a radiation research center to use as an education and research tool from treatment machine because of aging of MM22 microtron. In this paper, for extracting the electron beam from microtron, operation principle of the microtron, system characteristics of each module, and pulse structures were reviewed. The beam extraction and measurement were performed after measuring pulses of each major module and extraction trials in the beam line. After finishing the movement of MM22 microtron, the 30mA target current in the case of 10 MV X-ray beam was extracted and the beam flatness of radiation distribution was acquired within 3% error ratio after 100 MU was irradiated on X-omatV Film at SSD 100 cm and field size $10{\times}10cm^2$. As a result, the microtron movement and new installation was performed with success.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.39 no.12
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• pp.1033-1044
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• 2002

In this Paper, a new FRAM design technique utilizing grounded-plate PMOS-gate (GPPG) ferroelectric cell is proposed. A GPPG cell consists of a PMOS access transistor and a ferroelectric data storage capacitor. Its plate is grounded. The proposed architecture employs three novel methods for cell operation: 1) $V_{DD}$ -precharged bitline, 2) negative-voltage wordline technique and 3) negative-pulse restore. Because this configuration doesn't need the plate control circuitry, it can greatly increase the memory cell efficiency. In addition, differently from other reported common-plate cells, this scheme can supply a sufficient voltage of $V_{DD}$ to the ferroelectric capacitor during detecting and storing the polarization on the cell. Thus, there is no restriction on low voltage operation. Furthermore, by employing a compact column-path circuitry which activates only needed 8-bit data, this architecture can minimize the current consumption of the memory array. A 4- Mb FRAM circuit has been designed with 0.3-um, triple-well/1-polycide/2-metal technology, and the possibility of the realization of GPPG cell architecture has been confirmed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.454-463
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• 2000

A method is presented to alter the geometry of the conventional linearly shaped wire antenna for increasing its bandwidth. The synthesis is two-demensionally symmetric and is based on the minimization of frequency-dependence of the boresight far-field electric field intensity. The current distribution on the wire is calculated by Galerkin method using pulse functions. The shaping limitation for wide-band characteristics is still found because of standing waves due to reflected waves from antenna ends. The limitation overcome by a distribution of resistive loads near ends of wire. The antenna loaded resistively has flat characteristics satisfying a power gain of $6.5\pm1.1$dBi and VSWR of at most 2 over 10:1 bandwidth. The results are verified by comparing with similar results for the conventional linear V-dipole.

• Journal of Advanced Navigation Technology
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• v.22 no.5
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• pp.420-428
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• 2018

In this paper, represented uninterruptible power supply (UPS) equipment maintaining constant output voltage, the proposes a photovoltaic system constructed with a step up boosting chopper and single phase pulse width modulation (PWM) voltage source inverter. as power source disconnection, voltage variation and output current variation with load variation. This system is driven by being synchronized voltage fed inverter and AC source, and in the steady state of power source charge battery connected to DC side with solar cell using a Photovoltaic that it was so called constant voltage charge. It can be results of saving electric power, and through a normal operation of energy storage system (ESS), the system operated the LED a calling on signal changes at the airport in an efficient manner. In addition, better output waveform was generated because of PWM method, and it was proved to test by experiment maintained constant output voltage regardless of AC source disconnection, load variation, and voltage variation of AC power source.

• Korean Journal of Materials Research
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• v.12 no.12
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• pp.941-946
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• 2002

Both Cu and Cu-oxide nanopowders have great potential as conductive paste, solid lubricant, effective catalysts and super conducting materials because of their unique properties compared with those of commercial micro-sized ones. In this study, Cu and Cu-oxide nanopowders were prepared by Pulsed Wire Evaporation (PWE) method which has been very useful for producing nanometer-sized metal, alloy and ceramic powders. In this process, the metal wire is explosively converted into ultrafine particles under high electric pulse current (between $10^4$ and $10^{ 6}$ $A/mm^2$) within a micro second time. To prevent full oxidations of Cu powder, the surface of powder has been slightly passivated with thin CuO layer. X-ray diffraction analysis has shown that pure Cu nanopowders were obtained at $N_2$ atmosphere. As the oxygen partial pressure increased in $N_2$ atmosphere, the gradual phase transformation occurred from Cu to $Cu_2$O and finally CuO nanopowders. The spherical Cu nanopowders had a uniform size distribution of about 100nm in diameter. The Cu-oxide nanopowders were less than 70nm with sphere-like shape and their mean particle size was 54nm. Smaller size of Cu-oxide nanopowders compared with that of the Cu nanopowders results from the secondary explosion of Cu nanopowders at oxygen atmosphere. Thin passivated oxygen layer on the Cu surface has been proved by XPS and HRPD.