• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.291-294
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• 2000

음파의 비선형 현상을 통해 수행되는 파라메트릭 송파 방식을 공기 중에서의 음향 변환기에 적용시키기 위해 비교적 공진 주파수가 낮은 기중 초음파 발생 소자들을 배열시켜 기중 지향성 음원을 제작하였다. 이 송파기를 이용하여 비선형 왜곡이 발생함을 알아보기 위하여 2kHz의 차주파수를 갖도록 37.12kHz와 39.12kHz의 메인 주파수 음파를 신호발생기로부터 인가하고 이를 방사한 후 마이크로폰을 통해 수신하였다. 공기 중에서의 파라메트릭 효과의 확인을 통하여 파라메트릭 송파기에서 방사되는 메인 주파수 음파와 전파 경로 중에서 생성되는 차주파수 음파의 거동을 고찰하고, 실험 결과로부터 기중 파라메트릭 송파기 개발의 가능성을 검토하여 보았다.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.388-394
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• 2023

When the vibration of the thin panel by exciting single point is used to radiate sound, the inherent vibration characteristic of the plate itself causes influence on the radiated sound. A conventional panel speaker system usually uses the single or double point excitations for generating the sound through the panel itself. The radiated sound can be easily distorted due to the modal characteristics of the plate so it is difficult to expect sufficient sound power or high radiation efficiency. In this paper, to achieve an immersive sound field, the multiple speaker zones on a thin panel are created with the limited number of actuators. The designated vibration field which can generates directional sound is realized by employing the vibro-acoustic inverse rendering methods. Actuators are arranged from the positions which have the advantage of implementing with multi-modal excitations. The location and number of actuators are compared with the location and number of controllable speaker zones by conducting numerical simulations.

• Proceedings of the KSRS Conference
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• 2008.03a
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• pp.74-79
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• 2008

영상 융합은 센서의 자료 저장 능력과 센서에 들어오는 방사에너지 감지의 한계를 해결하고 고해상도의 멀티스펙트럴 영상을 생성할 수 있다는 측면에서 중요한 의의를 지닌다. 특히, 성분대입(component-substitution) 기반의 영상융합 기법은 대용량의 자료를 빠르게 처리할 수 있고, 융합된 영상의 분광왜곡이 적다는 장점을 지니고 있다. 본 연구에서는 최적화기법 중의 하나인 담금질 모사기법(Simulated Annealing, SA)을 이용하여 다양한 성분대입 기반 영상융합 알고리즘들을 분석 및 평가하였다. 담금질 모사기법은 원하는 목적함수가 지역적 최소값이 아닌 광역적 최소값에 수렴이 가능하도록 하는 기법으로 다양한 분야에서의 광역 최적화 기법에 사용된다. 융합 기법의 최적화된 변수를 추출하기 위하여 인위적으로 공간해상도를 낮춘 위성영상을 입력자료로, 원 멀티스펙트럴영상을 참조자료로 사용하였으며, 두 영상간의 분광유사 척도를 담금질 모사 기법의 목적 함수로 구성하였다. 이를 통해 해당 목적함수의 광역적 최소값을 추출하고, 최종적으로 해당 영상에 융합 기법 별 최적화된 변수를 결정하였다. 제안된 최적화 변수의 평가를 위하여 IKONOS 위성영상에 융합을 적용하고, 알고리즘별 분광왜곡량을 비교하였으며 이를 통하여 고해상도 위성영상에 가장 적합한 성분대입 기반 영상융합 기법 및 그에 따른 최적화 변수를 도출할 수 있었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7C
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• pp.601-609
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• 2012

In this paper, a limited-view CT image reconstruction method was studied to reduce the scan times and the X-ray dose for the patients. To reduce streak artifacts which is caused by insufficient number of views, we introduce a sinogram interpolation method based on image matching. Image matching is achieved using the characteristics of the neighboring views including intensity, gradient and distance between the pixels. Interpolation is performed using the image matching results.. A numerical phantom and Al-acryl phantom were used for evaluating the effectiveness of the proposed interpolation method. The results showed that streak artifacts were reduced in the reconstructed images while the details of the images were preserved. Moreover, maximum 5% improvements in terms of PSNR were observed.

• Spatial Information Research
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• v.14 no.1 s.36
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• pp.85-94
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• 2006

Image fusion techniques are widely used to integrate a lower spatial resolution multispectral image with a higher spatial resolution panchromatic image. However, the existing techniques either cannot avoid distorting the image spectral properties or involve complicated and time-consuming decomposition and reconstruction processing in the case of wavelet transform-based fusion. In this study a simple spectral preserve fusion technique: the Smoothing Filter-based Replacement(SFR) is proposed based on a simplified solar radiation and land surface reflection model. By using a ratio between a higher resolution image and its low pass filtered (with a smoothing filter) image, spatial details can be injected to a co-registered lower resolution multispectral image minimizing its spectral properties and contrast. The technique can be applied to improve spatial resolution for either colour composites or individual bands. The fidelity to spectral property and the spatial quality of SFM are convincingly demonstrated by an image fusion experiment using IKONOS panchromatic and multispectral images. The visual evaluation and statistical analysis compared with other image fusion techniques confirmed that SFR is a better fusion technique for preserving spectral information.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.2
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• pp.92-98
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• 2017

Generally, image contains geometrical and radiometric errors. Census transform can solve the stereo mismatching problem caused by the radiometric distortion. Since the general census transform compares center of window pixel value with neighbor pixel value, it is hard to obtain an accurate matching result when the difference of pixel value is not large. To solve that problem, we propose a census transform method that applies different 4-step weight for each pixel value difference by applying an assistance window inside the window kernel. If the current pixel value is larger than the average of assistance window pixel value, a high weight value is given. Otherwise, a low weight value is assigned to perform a differential census transform. After generating an initial disparity map using a weighted census transform and input images, the gradient information is additionally used to model a cost function for generating a final disparity map. In order to find an optimal cost value, we use guided filtering. Since the filtering is performed using the input image and the disparity image, the object boundary region can be preserved. From the experimental results, we confirm that the performance of the proposed stereo matching method is improved compare to the conventional method.

• Journal of the Korean Society of Radiology
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• v.18 no.2
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• pp.153-159
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• 2024

In X-ray projection, Unskilled radiologists become skilled through fail exam. This causes the patient to be exposed to unnecessary radiation. In this study, pre-position unskilled radiologic technologist presented ways to improve clinical proficiency. presented a skull lateral x-ray projection practice method using visual, spatial, and assistive devices. In addition, the accuracy and usefulness of the use of assistive devices were evaluated. When X-ray images were taken based on learning, the rotational spacing, which indicates image distortion, was 7.85 ± 1.45 mm and the tiliting spacing was 4.84 ± 0.5 mm. When practicing using visual aids, the rotational spacing is 4.4 ± 0.76 mm and the inclination spacing is 3.01 ± 0.87 mm. using a spatial compensation device, the rotational spacing is 5.2 ± 0.69 mm and the tiliting spacing is 3.33 ± 0.61 mm. Skull lateral X-ray Image distortion caused by empirical photography practice decreased by 5.4%, but image distortion caused by tilting increased by 1.2%. When practicing using a visual assistive devices, the degree of rotational spacing by 40.1% and the tiliting spacing decreased by 30.7% compared to the empirical x-ray exposure practice. When using spatial assistive devices, the rotation interval was reduced by 41.7% and the tilting interval by 23.7% compared to conventional empirical x-ray exposure practice. Therefore, if an unskilled radiologist practices using visual and spatial aids,the accuracy will be improved in skull lateral x-ray projection.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.9
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• pp.826-834
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• 2004

In this paper, we fabricated thick film monopole antennas using Bi$_2$O$_3$-doped BaTi$_4$$O_{9}$ ceramics for small size and broadband intenna. In the result, the high permittivity was fixed and the quality factor was also significantly decreased by the formation of secondary phase of Bi$_4$Ti$_3$O$_{12}$ repleced by addtion Bi. The antenna property influenced by the quality value more than the permittivity. The bandwidth of antenna was increased to 33 %. On the other hand, the gain was reduced to -4.3 dBi. Also radiation patterns were showed low dBi value by increasing of dielectric loss. Specially, Measured x-y plane radiation patterns was distorted as the dispersion of wavelength and high permittivity difference. But the result is showed execellent bandwidth because of low quality value in all formation range.nge.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.6
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• pp.559-566
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• 2011

This paper presents the flow passage design for a window cooling device, which have a conical poppet valve and an emissive orifice. Computational flow analysis and experiment are conducted according to the poppet strokes. The results show satisfactory flow characteristics that pressure is reduced enough to endure material strength and the flow does not choked inside window. The correction factor of discharge coefficients is found between 2-dimensional analysis and experiments, which is applied to control coolant flow rates of the window cooling device.

• Journal of Radiation Protection and Research
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• v.40 no.4
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• pp.216-222
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• 2015

Facilities processing raw materials containing naturally occurring radioactive materials (NORM) may give rise to enhanced radiation dose to workers due to chronic inhalation of airborne particulates. Internal radiation dose due to particulate inhalation varies depending on particulate properties, including size, shape, density, and absorption type. The objective of the present study was to assess inhalation dose sensitivity to physicochemical properties of airborne particulates. Committed effective doses to workers resulting from inhalation of airborne particulates were calculated based on International Commission on Radiological Protection 66 human respiratory tract model. Inhalation dose generally increased with decreasing particulate size. Committed effective doses due to inhalation of $0.01{\mu}m$ sized particulates were higher than doses due to $100{\mu}m$ sized particulates by factors of about 100 and 50 for $^{238}U$ and $^{230}Th$, respectively. Inhalation dose increased with decreasing shape factor. Shape factors of 1 and 2 resulted in dose difference by about 18 %. Inhalation dose increased with particulate mass density. Particulate mass densities of $11g{\cdot}cm^{-3}$ and $0.7g{\cdot}cm^{-3}$ resulted in dose difference by about 60 %. For $^{238}U$, inhalation doses were higher for absorption type of S, M, and F in that sequence. Committed effective dose for absorption type S of $^{238}U$ was about 9 times higher than dose for absorption F. For $^{230}Th$, inhalation doses were higher for absorption type of F, M, and S in that sequence. Committed effective dose for absorption type F of $^{230}Th$ was about 16 times higher than dose for absorption S. Consequently, use of default values for particulate properties without consideration of site specific physiochemical properties may potentially skew radiation dose estimates to unrealistic values up to 1-2 orders of magnitude. For this reason, it is highly recommended to consider site specific working materials and conditions and use the site specific particulate properties to accurately access radiation dose to workers at NORM processing facilities.