• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.1
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• pp.69-75
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• 2010

In this paper, with using the clapp type VCO(Voltage Controlled Osillator) configuration a wideband frequency synthesizer in UHF band is proposed. In order to design a wideband frequency synthesizer, the variation of phase in the negative resistance circuit as well as the load circuit was analyzed. Based on this result we propose a method to widen the operation range of the VCO. A frequency synthesizer using the proposed wideband VCO was designed and fabricated. It is shown that the synthesizer has the operating frequency range of 740~1,530 MHz by 0~5 V varactor tuning voltage, and it had the output power of 2~-6 dBm. Moreover, the phase noise measured as -77 dBc/Hz at 10 kHz offset, and as -108 dBc/Hz at 100 kHz offset from the oscillation frequency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.8 s.111
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• pp.732-738
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• 2006

Divide-by-2 and divide-by-4 circuits which can operate up to 10 GHz are designed. A design method used in these circuits is the TSPC(True Single Phase Clocking) topology. The structure of the TSPC dividers is very simple because they need only a single clock and purely consist of smalt sized cmos devices. Through measurements, we find the fact that in proportion to the bias voltage, the free running frequency increases and the operation region also moves toward a higher frequency region. For operating conditions of bias voltage $3.0{\sim}4.0V$, input power 16dBm and dcoffset $1.5{\sim}2.0V$, 5 GHz and 2.5 GHz output signals divided by 2 and 4 are measured. The layout size of the divide-by-2 circuit is about $500{\times}500 um^2$($50{\times}40um^2$ except pad interconnection part).

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.1
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• pp.165-172
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• 2012

Integrated-optic asymmetric Mach-Zehnder interferometer at $1.3{\mu}m$ wavelength and segmented electrode structure were designed and fabricated as a sensing part for the electric-field measurement system. The device was simulated based on the BPM software and fabricated utilizing Ti-diffused $LiNbO_3$ channel optical waveguides and lumped-type electrodes. Almost half-maximum power transmission was observed for asymmetric interferometers with ${\pi}/2$ intrinsic phase difference. Expected experimental measurements were observed for 1KHz electrical signal bandwidth.

• Journal of Intelligence and Information Systems
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• v.19 no.2
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• pp.55-71
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• 2013

The prediction model is the main factor affecting the performance of a knowledge-based system for bankruptcy prediction. Earlier studies on prediction modeling have focused on the building of a single best model using statistical and artificial intelligence techniques. However, since the mid-1980s, integration of multiple techniques (hybrid techniques) and, by extension, combinations of the outputs of several models (ensemble techniques) have, according to the experimental results, generally outperformed individual models. An ensemble is a technique that constructs a set of multiple models, combines their outputs, and produces one final prediction. The way in which the outputs of ensemble members are combined is one of the important issues affecting prediction accuracy. A variety of combination schemes have been proposed in order to improve prediction performance in ensembles. Each combination scheme has advantages and limitations, and can be influenced by domain and circumstance. Accordingly, decisions on the most appropriate combination scheme in a given domain and contingency are very difficult. This paper proposes a confidence-based selection approach as part of an ensemble bankruptcy-prediction scheme that can measure unified confidence, even if ensemble members produce different types of continuous-valued outputs. The present experimental results show that when varying the number of models to combine, according to the creation type of ensemble members, the proposed combination method offers the best performance in the ensemble having the largest number of models, even when compared with the methods most often employed in bankruptcy prediction.

• Radiation Oncology Journal
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• v.18 no.2
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• pp.150-156
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• 2000

Purpose : Stereotactic radiation therapy (SRT) can deliver highly focused radiation to a small and spherical target lesion with very high degree of mechanical accuracy. For non-spherical and large lesions, however, inclusion of the neighboring normal structures within the high dose radiation volume is inevitable in SRT This is to report the beam shaping using the partial closure of the independent jaw in SRT and the verification of dose calculation and the dose display using a home-made soft ware. Materials and Methods : Authors adopted the idea to partially close one or more independent collimator jaw(5) in addition to the circular collimator cones to shield the neighboring normal structures while keeping the target lesion within the radiation beam field at all angles along the arc trajectory. The output factors (OF's) and the tissue-maximum ratios (TMR's) were measured using the micro ion chamber in the water phantom dosimetry system, and were compared with the theoretical calculations. A film dosimetry procedure was peformed to obtain the depth dose profiles at 5 cm, and they were also compared with the theoretical calculations, where the radiation dose would depend on the actual area of irradiation. Authors incorporated this algorithm into the home-made SRT software for the isodose calculation and display, and was tried on an example case with single brain metastasis. The dose-volume histograms (DVH's) of the planning target volume (PTV) and the normal brain derived by the control plan were reciprocally compared with those derived by the plan using the same arc arrangement plus the independent collimator jaw closure. Results : When using 5.0 cm diameter collimator, the measurements of the OF's and the TMR's with one independent jaw set at 30 mm (unblocked), 15.5 mm, 8.6 mm, and 0 mm from th central beam axis showed good correlation to the theoretical calculation within 0.5% and 0.3% error range. The dose profiles at 5 cm depth obtained by the film dosimetry also showed very good correlation to the theoretical calculations. The isodose profiles obtained on the home-made software demonstrated a slightly more conformal dose distribution around the target lesion by using the independent jaw closure, where the DVH's of the PTV were almost equivalent on the two plans, while the DVH's for the normal brain showed that less volume of the normal brain receiving high radiation dose by using this modification than the control plan employing the circular collimator cone only. Conclusions : With the beam shaping modification using the independent jaw closure, authors have realized wider clinical application of SRT with more conformal dose planning. Authors believe that SRT, with beam shaping ideas and efforts, should no longer be limited to the small spherical lesions, but be more widely applied to rather irregularly shaped tumors in the intracranial and the head and neck regions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.9
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• pp.5877-5884
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• 2014

Recently, abnormally cold weather has been reported more frequently in winter due to the climate change and abnormal weather changes. On the other hand, the heating capacity of a railcar may be not enough to warm the cabin under severe cold climatic conditions, which is one of the reasons for the passengers' complaints about heating. In this study, the effects of ambient temperature and heater power on the cabin temperature was investigated to obtain the minimum ambient temperature for the tested railcar. The test railcar was placed in a large-climatic chamber, and various ambient temperature conditions were simulated. The effects of the heater output were investigated by monitoring the cabin temperature under a range of heater output conditions. The mean cabin temperature was $14.0^{\circ}C$, which was far lower than the required minimum temperature of $18^{\circ}C$, under a $-10^{\circ}C$ ambient temperature condition with the maximum heat power. When the ambient temperature was set to $0^{\circ}C$ and $10^{\circ}C$, the maximum achievable cabin temperature was $26.1^{\circ}C$ and $34.0^{\circ}C$. Through calculations using the interpolation method, the minimum ambient temperature to maintain an $18^{\circ}C$ cabin temperature was $-6.7^{\circ}C$ for this car. The vertical temperature difference was higher with a higher power output and higher ambient temperature. The maximum vertical temperature difference was higher than $10^{\circ}C$ in some cases. However, the horizontal temperature difference vs. low temperature (< $2^{\circ}C$) was independent of the power output and ambient temperature. As a result, it is very important to reduce the vertical temperature difference to achieve good heating performance.

• Journal of Advanced Navigation Technology
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• v.18 no.1
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• pp.35-43
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• 2014

In this paper, it is about to non-contact wireless power transmission according to various conditions of self induction principle between the two planar coils at a transmission unit and a receiving unit based on the theory of wireless power transmission. The experiments are occurred in order to power transfer of noncontact method from designed wireless circuits in the primely coil and secondary coil, and the applying to Half Bridge Resonant converter transmission unit and receiving unit. and that were able to prepared circumstance to calculate of the output voltage and power source. The main power of the inductive coupling the resonant converter at the transmission unit is converted electrical energy using the solar cell module and artificial light source (halogen lamp) as a replace light and received 24 V power supply from solar power was used a input power source for the wireless power transmission device. Experimental results, to received of power is used to illuminate the lighting and to charge the battery in receiving circuit.And the wireless power transmission efficiency measured at the output side of the transmission unit is obtained about 70% to 89% compared to input power of receiving unit.In addition, efficiency were tested through ID verification method and comparing the phase difference between the voltage when foreign substances interfere with wireless power transmission.

• Radiation Oncology Journal
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• v.8 no.1
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• pp.7-15
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• 1990

The ultimate objective of our experiment is to obtain the precise distribution of temperature in malignant tumors occurring in cerebral parenchyme of human beings when we will carry out interstitial hyperthermia in the near future. To achieve this purpose, first of all, it is necessary to make an attempt at performing interstitial hyperthermia in vivo under the similar condition of human beings. Therefore, we chose cats as materials much alike tissue characteristics of human beings. Moreover, it is also necessary to get the basic data from dynamic phantom in order to standardize and compare results obtained from interstitial hyperthermia carried out in cats. By having performed these experiments we got the following results. 1) On doing interstitial hyperthermia with 915 MHz microwave, the possible treated volume was 2 cm by 2 cm by 6 cm according to $50\%$ specific absorption rate (SAR). 2) The distribution of temperature within non-circulated static phantom was much the same as power density in air, but we observed that the temperature, within $5\~10$ minutes, rose to more higher than $55^{\circ}C$ not measured with Ga-As fiberoptic thermistor which was not impeded by microwave after performing interstitial hyperthermia. 3) Within dynamic phantom in which normal saline was circulating, temperature reached steady state which was maintained for more than 45 minutes through transit period in 5 minutes after starting interstitial hyperthermia. 4) When we interrupted circulation in the dynamic phantom, we observed that temperature rose to the same level as in the static phantom. 5) We could carry out interstitial hyperthermia safely when we used the generating power below 5 watts. Abrupt interruption of circulation caused a rapid increase in temperature. Times taking to rise to maximum $55^{\circ}C$ were 15.2 minutes (SE 0.4),9.7 minutes (SE 0.3), and 6.3 min-utes (SE 0.4) respectively with generating powers of 5,10, and 15 watts.

• The Journal of the Acoustical Society of Korea
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• v.38 no.4
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• pp.450-458
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• 2019

Passive cavitation imaging method is used to observe the ultrasonic waves generated when a group of bubbles collapses. A problem with passive cavitation imaging is a low resolution and large side lobe levels. Since ultrasound signals generated by passive cavitation take the form of a pulse, the amplitude distribution of signals received across the receive channels varies depending on the direction of incidence. Both the centroid and flatness were calculated to determine weights at imaging points in order to discriminate between the main and side lobe signals from the signal amplitude distribution of the received channel data and to reduce the side lobe levels. The centroid quantifies how the channel data are distributed across the receive channel, and the flatness measures the variance of the channel data. We applied the centroid weight and the flatness to the passive cavitation image constructed using the delay-and-sum focusing and minimum variance beamforming methods to improve the image quality. Using computer simulation and experiment, we show that the application of weighting in delay-and-sum and minimum variance beamforming reduces side lobe levels.

• The Korean Journal of Nuclear Medicine
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• v.38 no.5
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• pp.338-343
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• 2004

Purpose: The purpose of this study was to develop a small animal PET using dual layer phoswich detector to minimize parallax error that degrades spatial resolution at the outer part of field-of-view (FOV). Materials and Methods: A simulation tool GATE (Geant4 Application for Tomographic Emission) was used to derive optimal parameters of small PET, and PET was developed employing the parameters. Lutetium Oxyorthosilicate (LSO) and Lutetium-Yttrium Aluminate-Perovskite(LuYAP) was used to construct dual layer phoswitch crystal. $8{\times}8$ arrays of LSO and LuYAP pixels, $2mm{\times}2mm{\times}8mm$ in size, were coupled to a 64-channel position sensitive photomultiplier tube. The system consisted of 16 detector modules arranged to one ring configuration (ring inner diameter 10 cm, FOV of 8 cm). The data from phoswich detector modules were fed into an ADC board in the data acquisition and preprocessing PC via sockets, decoder block, FPGA board, and bus board. These were linked to the master PC that stored the events data on hard disk. Results: In a preliminary test of the system, reconstructed images were obtained by using a pair of detectors and sensitivity and spatial resolution were measured. Spatial resolution was 2.3 mm FWHM and sensitivity was 10.9 $cps/{\mu}Ci$ at the center of FOV. Conclusion: The radioactivity distribution patterns were accurately represented in sinograms and images obtained by PET with a pair of detectors. These preliminary results indicate that it is promising to develop a high performance small animal PET.