• 한국음향학회:학술대회논문집
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• 한국음향학회 1994년도 FIFTH WESTERN PACIFIC REGIONAL ACOUSTICS CONFERENCE SEOUL KOREA
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• pp.734-739
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• 1994

Elastic wave propagation in discrete random medium is studied to evaluate the effects of particle resonance on dispersion and attenuation of composite materials containing spherical inclusions. The frequency-dependent wave speed and attenuation coefficient can be obtained from proposed self-consistent method. It can be observed that the abrupt increase of effective wave speed and the concurrent peak of attenuation at low frequency is due to the lowest resonance of particles, whereas those in high frequency region are due to higher ones. The lowest resonance is mainly caused by the density mismatch and higher resonances by the stiffness mismatch between matrix and particles. The dispersion and attenuation of elastic waves in particulate composites are affected by the lowest resonance much than by higher ones.

• Nuclear Engineering and Technology
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• 제53권11호
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• pp.3808-3815
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• 2021

In this paper, the EPICS2017 photoatomic database was used to evaluate the photon mass attenuation coefficients and buildup factors of soils collected at different depths in the Philippine islands. The extraction and interpolation of the library was accomplished at the recommended linear-linear scales to obtain the incoherent and total cross section and mass attenuation coefficient. The buildup factors were evaluated using the G-P fitting method in ANSI/ANS-6.4.3. An agreement was achieved between XCOM, MCNP5, and EPICS2017 for the calculated mass attenuation coefficient values. The buildup factors were reported at several penetration depths within the standard energy grid. The highest values of both buildup factor classifications were found in the energy range between 100 and 400 keV where incoherent scattering interaction probabilities are predominant, and least at the region of predominant photoionization events. The buildup factors were examined as a function of different soil silica contents. The soil samples with larger silica concentrations were found to have higher buildup factor values and hence lower shielding characteristics, while conversely, those with the least silica contents have increased shielding characteristics brought by the increased proportions of the abundant heavier oxides.

• Nuclear Engineering and Technology
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• 제55권7호
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• pp.2613-2620
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• 2023

Excellent thermal neutron absorption performance of boron expands the potential use of boron rich slag to prepare epoxy resin matrix nuclear shielding composites. However, shielding attenuation behaviors and mechanism of the composites against gamma rays are unclear. Based on the radiation protection theory, Phy-X/PSD, XCOM, and ⁶⁰Co gamma ray source were integrated to obtain the shielding parameters of boron rich slag/epoxy resin composites at 0.015-15 MeV, which include mass attenuation coefficient (µ_t), linear attenuation coefficient (µ), half value thickness layer (HVL), electron density (N_eff), effective atomic number (Z_eff), exposure buildup factor (EBF) and exposure absorption buildup factor (EABF).µ_t, µ, HVL, N_eff, Z_eff, EBF and EABF are 0.02-7 cm²/g, 0.04-17 cm^-1, 0.045-20 cm, 5-14, 3 × 10²³-8 × 10²³ electron/g, 0-2000, and 0-3500. Shielding performance is BS4, BS3, BS3, BS1 in descending order, but worse than ordinary concrete. µ and HVL of BS1-BS4 for ⁶⁰Co gamma ray is 0.095-0.110 cm^-1 and 6.3-7.2 cm. Shielding mechanism is main interactions for attenuation gamma ray by BS1-BS4 are elements with higher content or higher atomic number via Photoelectric Absorption at low energy range, and elements with higher content via Compton Scattering and Pair Production in Nuclear Field at middle and higher energy range.

• Nuclear Engineering and Technology
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• 제56권1호
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• pp.247-256
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• 2024

The glass series modified by tungsten oxide was created using the compounds (75-x) B₂O₃- 10SrCO₃- 8TeO₂- 7ZnO - xWO₃, where x = 0, 1, 5, 10, 22, 27, 34, and 40% mole percentage. A UV-visible spectrophotometer and thermogravimetric-differential thermal analysis (TG-DTA) methods were employed to characterize the specimen's optical and phase transition attributes, respectively. The mass-attenuation coefficient (AC) of all created glasses from BSTZW0 to BSTZ7 was estimated using Geant4 code from 0.05 to 3 MeV and compared to the XCOM software results, with a relative difference of less than 2% between the two results. The increase of WO₃ percentage lead to an increase in the Linear-AC at each studied energy, and this is mainly due to the fact that the higher the percentage of WO₃ in the glass increases its density which causes an increase in the Linear-AC, so an energy of 0.06 MeV, as an example, the values of the Linear-AC was 4.009, 4.509, 5.442, 6812, 8.564, 9.856, 10.999 and 11.628 cm^-1 form BSTZW0 too BSTZW7, respectively. The Half-VL (value layer), Mean-FP (free path), Tenth-VL, and Radiation attenuation performance (RAP) were also calculated for the current BSTZW-glass samples and revealed that BSTZW7 had the best gamma ray attenuation performance at all discussed energies when compared to other studied glass samples.

• 전자공학회논문지
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• 제54권1호
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• pp.111-120
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• 2017

본 논문에서는 해저 퇴적물 분류를 위한 특징 추출 기법을 제안하고 검증한다. 기존 연구에서는 주파수의 영향이 없는 반사계수를 이용하여 퇴적물을 분류해 왔다. 그러나 해저 퇴적물의 음향 감쇠계수는 주파수의 함수이며 퇴적 성분에 따라 서로 다른 특성을 나타낸다. 따라서 주파수에 따른 감쇠계수 변화량을 이용하여 특징벡터를 생성하였다. 감쇠계수 변화량은 Chirp 신호에 의해 생성된 두 번째 층 반사신호를 이용하여 추정한다. Chirp 신호의 다중대역 특징이 다차원 벡터를 형성하기 때문에 기존의 방법에 비해 우수한 특성을 갖는다. 반사계수에 의한 분류 성능과 비교하기 위해 선형 판별 분석법 (LDA, Linear Discriminant Analysis)를 이용하여 차원을 축소하였다. Biot 모델을 이용하여 모의실험 환경을 구축하고 Fisher score와 MLD(Maximum Likelihood Decision)를 기반의 분류 정확도를 이용해 제안된 특징을 평가하였다. 그 결과, 제안된 특징은 반사계수에 비해 높은 변별력을 보이며, 측정 및 깊이 추정오차에도 강인한 특성을 보였다.

• Archives of Plastic Surgery
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• 제35권4호
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• pp.423-430
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• 2008

Purpose: Computed tomography theoretically should improve detection of foreign bodies and provide more information of adjacent soft tissues. And the CT scanner and PACS program proved to be an excellent instrument for detection and localization of most facial foreign bodies above certain minimum levels of detectability. The severity of injury in penetrating trauma to the face, it is often underestimated by physical examination. Diagnosis of a retained foreign object is always critical. Methods: From March, 2005 to February 2008 a study was done with 200 patients who had facial trauma. Axial and coronal CT images were obtained with a General Electric(Milwaukee, Wis) 9800 CT scanner at 130 kV, 90 mA, with a 2-mm section thickness and a $512{\times}512$ matrix. Results: Axial and coronal CT images at various window widths should be used as the first imaging modality to detect facial foreign bodies. The attenuation coefficients for the metallic and nonmetallic foreign bodies ranged from -437 to +3071 HU. As a general rule, metallic foreign bodies produced more Hounsfield artifacts than nonmetallic foreign bodies, thus providing a clue to their composition. All of the metallic foreign bodies were represented by a single peak and had a maximum attenuation coefficient of +3071 HU. Of the nonmetallic foreign bodies, glass had an attenuation coefficient that ranged from +105 to +2039, while plastic had a much lower coefficient that ranged from -62 to -35. wood had the lowest range of attenuation coefficients: -491 to -437. Conclusion: The PACS program allows one to distinguish metallic from nonmetallic foreign bodies and to individually identify the specific composition of many nonmetallic foreign bodies. This program does not, however, allow identification of the specific composition of a metallic foreign body. We recommend this type of software program for CT scanning of any patient with an injury to the face in which a foreign body is suspected.

• 한국터널지하공간학회 논문집
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• 제24권1호
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• pp.39-55
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• 2022

본 연구는 경주 중·저준위 지하 처분환경에서의 사일로 콘크리트의 음향방출(AE) 신호 감쇠계수(α)를 결정하기 위해 신호감쇠 실험을 수행하였다. 활용된 시료들은 경주 중·저준위 처분장 사일로에 사용된 콘크리트 배합비로 제작하였으며 28일간 수중 양생 후 처분환경에 맞도록 온도 및 포화유무에 따라 추가적으로 노출시켰다. 처분조건 별 각 3개씩의 공시체에 대하여 신호전달거리에 따른 AE 신호를 측정한 결과, 초기구간에서는 포화콘크리트의 AE 진폭과 절대에너지가 건조콘크리트의 경우보다 더 높게 나타났지만, α는 포화콘크리트의 경우가 더 높게 산정되었다. 또한, 포화유무와 상관없이 온도가 증가함에 따라 α는 감소하는 경향을 보였다. α는 온도조건보다는 포화유무에 따른 영향이 큰 것으로 분석되었으며, 이는 콘크리트 처분구조물의 감쇠신호 측정 시 포화여부를 고려한 판단이 중요하다는 것을 의미한다. 처분환경에서의 콘크리트 α는 균열이 발생한 위치에서의 실제 AE 특성 파라미터 값을 추정함으로써 경주 중·저준위 처분환경에서 사일로 콘크리트의 건전성을 예측하고 센서의 최적 배치를 결정하는 데 도움이 될 것으로 기대한다.

• 비파괴검사학회지
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• 제15권2호
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• pp.364-370
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• 1995

본 논문은 초음파법을 이용하여 소결 재료의 비파괴적인 평가 방법을 확립하는데 목적을 두고 있다. 소결 재료의 밀도는 소결체로 제작되는 동안 금형과 분말사이의 마찰 때문에 부분적으로 불균질한 분포를 가지고 있으며 이 불균질성은 에너지 감쇠 계수 및 초음파 반사 에코의 주파수 스펙트럼에 있어 중심 주파수의 변화량에 의해 조사되었다. 초음파의 속도, 탄성계수, 포와송 비는 소결 재료의 밀도와 비례 관계에 있었으며 저면 반사파의 중심 주파수는 초음파의 전파 거리의 증가 및 밀도의 감소에 따라 저주파수 쪽으로 이동하였으나 에너지 감쇠 계수는 밀도의 증가에 따라 감소하고 있었다. 본 논문에서는 반사파의 주파수 스펙트럼에 있어 중심 주파수의 변화가 소결 재료의 비파괴적인 평가 방법으로써의 가능성을 보여주고 있다.

• Geomechanics and Engineering
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• 제22권2호
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• pp.187-196
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• 2020

The changeable stress environment directly affect the propagation law of a stress wave. Stress wave propagation tests in sandstone with different axial stresses were carried using a modified split Hopkinson Pressure bar (SHPB) assuming the sandstone has a uniform pore distribution. Then the waveform and stress wave energy dissipation were analyzed. The results show that the stress wave exhibits the double peak phenomenon. With increasing axial stress, the intensity difference decreases exponentially and experiences first a dramatic decrease and then gentle development. The demarcation stress is σ/σ_c=30%, indicating that the closer to the incident end, the faster the intensity difference attenuates. Under the same axial stress, the intensity difference decreases linearly with propagation distance and its attenuation intensity factor displays a quadratic function with axial stress. With increasing propagation distance, the time difference decays linearly and its delay coefficient reflects the damage degree. The stress wave energy attenuates exponentially with propagation distance, and the relations between attenuation rate, attenuation coefficient and axial stress can be represented by the quadratic function.

• 한국음향학회지
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• 제19권1호
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• pp.40-47
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• 2000

감쇠가 심하고 분산적인 폴리우레탄 재료의 음향특성을 평가하기 위하여 초음파 투과법을 이용하였다. 투과법에 있어서, 작은 크기의 시편에 적용할 수 있도록 Sachse의 방법을 이용하여 음속과 음향감쇠계수를 측정하였다. 기준 신호를 이용하여 음향특성을 측정하였을 때 정확한 결과를 얻기 어려웠다. 반면, 두께가 서로 다른 두 우레탄 시편을 가지고 음향특성을 측정하였을 때 보다 정확한 결과를 얻을 수 있었다. 저주파 대역에서의 음향특성을 파악하기 위하여 Kramers-Kronig 관계를 적용하였다. 이를 통해 저주파 영역까지 확대된 주파수에 따른 음속관계식을 구하였고, 음속과 음향감쇠계수의 상관관계를 연구하였다.