• 한국세라믹학회지
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• 제54권2호
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• pp.102-107
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• 2017

The dependence of the IR optical properties of PMMA/$Al_2O_3$ nanocomposite on the alumina content was investigated in the wavelength range of $3500-2800cm^{-1}$. The samples were prepared via emulsion polymerization technique using oleic acid as a coupling agent. Grafting density calculations were carried out by means of elemental analysis CHN to yield the best coupling agent content. FTIR analysis confirmed the existence of a chemical bond between aluminum oxide and oleic acid. The outcomes of XRD analyses showed the presence of cubic gamma aluminum oxide in the nanocomposite, in contrast to the amorphous nature of PMMA. TEM images showed the core-shell morphology of the particles other than pristine PMMA. Optical constants of the nanocomposite were calculated based on FTIR spectra and the Kramers-Kronig equations. The presence of nano alumina modified some of the optical indexes in IR region.

• 전자공학회논문지
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• 제53권10호
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• pp.138-142
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• 2016

듀얼 에너지 디지털 촬영법 (dual-energy digital radiography, DEDR)은 에너지 감산법을 이용하여 신체 내 병변을 감지하는 데 사용 되어 왔다. 본 연구에서는 DEDR을 이용하여 관전압과 부가필터와 같은 물리적 인자를 변화시킴으로써 최적의 뼈와 조직 영상을 획득하고, SRS-78 프로그램으로 예측한 값과 비교하고자 한다. 에너지 감산법을 이용하여 뼈와 조직의 분리된 영상을 획득하기 위하여 다양한 물질의 물리적 인자의 변화에 따른 영상을 구하였다. 연구에 사용된 팬텀은 알루미늄과 polymethyl methacrylate (PMMA)로 구성되었으며, 영상의 최적화는 대조도 대 잡음비 (contrast-to-noise ratio, CNR)로 측정하였다. 실험 결과 50 kVp와 120 kVp 두 영상의 감산 영상이 최적의 뼈와 조직의 분리 영상임을 확인 할 수 있었다. 또한 고 에너지에 10 mm 알루미늄 부가필터를 추가하였을 때, 최적의 뼈와 조직의 분리 효과를 기대 할 수 있었다. 이러한 결과는 실험 전에 SRS-78 프로그램으로 예측한 최적화 조건과 일치함을 알 수 있었다. 본 연구를 통해 관전압이나 부가필터 두께와 같은 물리적 인자를 적절하게 조절한다면 최적의 영상을 얻을 수 있음을 확인하였고, DEDR을 이용하여 원하는 부분만을 표현함으로써 의료영상분야에 기여하고 응용분야를 확장 할 수 있을 것으로 기대한다.

• 대한치과교정학회지
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• 제53권1호
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• pp.45-53
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• 2023

Objective: This study aimed to evaluate the shear bond strength (SBS) of orthodontic brackets bonded to three-dimensionally (3D)-printed materials after various surface treatments and artificial aging compared with that bonded to computer-aided design/computer-aided manufacturing (CAD-CAM) polymethyl methacrylate (PMMA)-milled materials. Methods: Eighty cylindrical specimens were 3D printed and divided into the following four subgroups (n = 20 each) according to the surface treatment and artificial aging procedure. Group A, sandblasted with 50 ㎛ aluminum oxide particles (SA) and aging; group B, sandblasted with 30 ㎛ silica-coated alumina particles (CO) and aging; group C, SA without aging; and group D, CO without aging. For the control group, 20 CAD-CAM PMMA-milled cylindrical specimens were sandblasted with SA and aged. The SBS was measured using a universal testing machine (0.25 mm/min), examined at ×2.5 magnification for failure mode classification, and statistically analyzed (p = 0.05). Results: The retention obtained with the 3D-printed materials (groups A-D) was higher than that obtained with the PMMA-milled materials (control group). However, no significant difference was found between the study and control groups, except for group C (SA without aging), which showed significantly higher retention than the control group (PMMA-SA and thermocycling) (p = 0.037). Study groups A-D predominantly exhibited a cohesive specimen mode, indicating specimen fracture. Conclusions: Orthodontic brackets bonded to 3D-printed materials exhibit acceptable bonding strengths. However, 3D-printed materials are prone to cohesive failure, which may result in crown fractures.

• 대한방사선기술학회지:방사선기술과학
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• 제44권5호
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• pp.465-471
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• 2021

Dual-energy X-ray imaging (DEI) techniques can provide X-ray images that a certain material is suppressed or emphasized by combining two X-ray images obtained from two different x-ray spectrum. In this paper, a single-shot DEI, which uses stacked two detectors (i.e., multilayer detector), is proposed to reduce the patient dose and increase throughput in angiography. The polymethyl methacrylate (PMMA) and aluminum (Al) were selected as two basis materials for material decomposition, and material-specific images are reconstructed as a vector combination of these two materials. We investigate the contrast and noise performance of material-decomposed images using iodine phantoms with various concentrations and diameters. The single-shot DEI shows comparable performances to the conventional dual-shot DEI. In particular, the single-shot DEI shows edge enhancement in material-decomposed images due to the different spatial-resolution characteristics of upper and lower detectors. This study could be useful for designing the multilayer detector including scintillators and energy-separation filter for angiography purposes.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 1999년도 Japanese Journal of Medical Physics
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• pp.278-281
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• 1999

The purpose of this study is to investigate the effect of the scattered x-rays on the subject contrast and image sharpness for various tube voltages. For the purpose, we measured the scatter-to-primary ratio(SPR) for the tube voltages f 50 to 100kV and obtained the tube voltage dependence of the subject contrast of an aluminum plate in a polymethyl methacrylate(PMMA) phantom. Furthermore, the overall modulation transfer functions(MTFs), which consist of MTFs of a screen-film system and scatter FTMs, were obtained for tube voltages of 50 to 100 kV. The subject contrast decreased with the tube voltage due to that the SPR increased with the tube voltage and that the difference in effective linear attenuation coefficients between the object and its surroundings decreased with the tube voltage. The maximum frequency of the overall MTF decreased from about 2 mm$\^$-1/ to 1 mm$\^$-1/ with the tube voltage increasing from 50 to 100 kV.