• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.1
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• pp.1-9
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• 1998

The attenuation of acoustic emission (AE) waves was evaluated for injection-molded short-fiber-reinforced thermoplastic composites employing simulated AE waves. Values of attenuation coefficient (${\alpha}$) decreased more with increasing fiber volume fraction ($V_f$) than that expected from a simple linear relation between ${\alpha}$ and $V_f$. The effect of wave attenuation was taken into account in a quantitative analysis of the AE peak amplitude distribution which was obtained from each zone partitioned in a specimen gage portion. The amplitude distribution compensated for the measured attenuation loss was exhibited almost similar in every zone of the specimen. Consequently, it was, shown that the AE amplitudes obtained from fiber/plastic composites were considerably affected by the attenuation.

• Journal of the Korea Concrete Institute
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• v.16 no.3 s.81
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• pp.397-406
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• 2004

A recently developed three dimensional concrete law is used for the analysis of concrete specimens and reinforced concrete columns subjected to different load patterns. The hypoelastic, orthotropic concrete constitutive model includes coupling between the deviatoric and volumetric stresses, works with both proportional and non-proportional loads and is implemented as a strain driven module. The FE implementation is based on the smeared crack approach with rotating cracks parallel to the principal strain directions. The concrete model is validated through correlated studies with: (a) experimental tests on confined concrete cylinders; (b) experimental results on three reinforced concrete columns tested at the University of California, San Diego. The correlations are overall very good, and the FE responses capture all the main phenomena observed in the experimental tests.

• Journal of the Korea Concrete Institute
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• v.16 no.3 s.81
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• pp.345-356
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• 2004

A plasticity model was developed to predict the behavioral characteristics of concrete in multiaxial compression. To extend the applicability of the proposed model to concrete in various stress states, a new approach for failure criteria was attempted. A stress was decomposed into one volumetric and two deviatoric components orthogonal to each other. Three failure criteria wire provided independently for each stress component. To satisfy the three failure criteria, the plasticity model using multiple failure criteria was Implemented. Each failure surface was defined by equivalent volumetric or deviatoric plastic strain. To present dilatancy due to compressive damage a non-associative flow nile was proposed. The proposed model was implemented to finite element analysis, and it was verified by comparisons with various existing test results. The comparisons show that the proposed model predicted well most of the experiments by using three independent failure criteria.

• The Journal of Engineering Geology
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• v.7 no.2
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• pp.91-99
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• 1997

In general, there are various approaches available in literature to model discontinuous rock masses and engineers are often confused which one to use for designing structures in rock masses. Modelling rock masses can be classified mainly into two approaches. One is discrete modelling of intact rock and discontinuities and the other is the equivalent continuum modelling. In this study five models are selected ;(1) Crack tensor model, (2) Equivalent volume defect model, (3) Damage model, (4) Micro - structure model (Parallel model and Series model), and (5) Homogenization model. Most of these models are mainly concerned with how to define additional strain due to discontinuities over the representative elementary volume (REV) and how to relate the stress field of discontinuities to that acting on the REV. The characteristics of these models are clarified by comparing with results of some laboratory tests.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.42.1-42.1
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• 2011

박막형 디스플레이구서에 있어서 투명전극은 필수적이다. 투명전극은 정보를 표시하기 위해 빛을 외부로 방출시키거나 태양광 등을 소자 내부로 입사시켜야 한다. 또한 전극을 형성하는 박막은 높은 광투과율과 ${\sim}10-4{\Omega}cm$ 정도의 낮은 전기비저항을 가져야 한다. 가장 널리 사용되는 투명전극으로 ITO (Indium Tin Oxide)는 인듐의 독성, 저온증착의 어려움, 스퍼터링시 음이온 충격에 의한 막 손상으로 저항의 증가 및 액정디스플레이의 투명전극으로 사용될 경우 $400^{\circ}C$정도의 높은 온도와 수소플라즈마 분위기에서 장시간 노출시 열화로 인한 광학적 특성변화가 문제로 지적된다. 이러한 문제 해결의 대안으로 ZnO 산화물 반도체가 있는데 ITO 박막에 비해 비저항이 높기 때문에 도핑을 이용한 비저항을 ${\sim}10-4{\Omega}cm$ 정도로 낮추어야 한다. 투명전도막으로는 ITO, FTO 등과 더블어 체적 저항율은 다소 높으나 환원성 분위기에 대한 내성, 가시광 영역에서의 높은 광투과율과 저렴한 가격 등의 장점 등으로 AZO 박막이 주목 받고 있다. ZnO는 ITO 나 FTO에 비해서 700 kJ/mol의 큰 분해에너지를 가지므로 코팅 때 발생하는 전도도 및 투과율이 나빠지는 현상이 발생하지 않는 특징이 있으며, 위의 두 재료에 비해 밴드갭도 가장 낮아서 자외선 투과율이 낮다. 그러나 내습성이 약하기 때문에 이를 보완하기 위하여 내습성향상과 전도성 향상을 위해서 3족 원소인 B, In, Al, Ga 등을 도핑한 ZnO 투명전도막의 연구가 진행되고 있다. 이러한 원소들 중에서 Al로 도핑했을 때 가장 낮은 비저항을 얻을 수 있다고 알려져 있다. 본 연구에서는 SiOC 박막위에 AZO 박막을 제조하기 위하여 RF 마그네트론 스퍼터링법을 이용하여 박막을 성장시켰으며, 박막의 전기적 및 광학적 특성을 조사하였다. AZO 박막은 rf power가 5~200 W인 RF 마그네트론 스퍼터 방법에 의해서 제작되었다. SiOC 박막은 산소와 DMDMOS 전구체의 유량비를 다르게 하여 플라즈마 발생 화학적 기상 증착방법으로 증착되었다. 증착된 SiOC박막은 UV visible spectroscopy에 의해서 분석하였다. 투명전극의 비저항은 rf 전력이 작을 수록 낮았으며, SiOC 절연막 위에 AZO를 증착시킨 후 반사률은 반대로 바뀌는 것을 확인하였다.

• The Journal of the Korea Contents Association
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• v.11 no.4
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• pp.428-439
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• 2011

It is well known that the sound characteristics of Korean bell depend on the shape and the alloy constituents. Development of the methods to acquire exact shape data and alloy constituents of the whole body of the bell is very important for the study and systematic management of Korean bells. The practical scanning and modeling methods to get shape data from optical triangulation laser scanners are proposed. The 3D shape data by the proposed methods can be the basis of diverse measurements such as curvature, volume, thickness and the distance between any two points. A nondestructive alloy constituents measuring method which can overcome the limitations of partial data collection and damages to Korean bells is also suggested to get the whole alloy characteristics. Following the developed methods, the data of the shapes and alloy constituents of 18 Korean bells are collected and the errors of existing measurement data for the shape have been corrected.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.2
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• pp.240-248
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• 1998

The plasma chemical vapor deposition is one of the most utilized techniques for the diamond growth. As the applications of diamond thin films prepared by plasma chemical vapor deposition(CVD) techniques become more demanding, improved fine-tuning and control of the process are required. The important parameters in diamond film deposition include the substrate temperature, $CH_4/H_2$ gas flow ratio, total, gas pressure, and gas excitation power. With the spectroscopic ellipsometry, the substrate temperature as well as the various parameters of the film can be determined without the physical contact and the destructiveness under the extreme environment associated with the diamond film deposition. It is introduced how the real-time spectroscopic ellipsometry is used and the data are analyzed with the view of getting the growth condition and the accompanied features for a good quality of diamond films. And it is determined the important parameters during the diamond film growth, which include the final sample will be measured with Raman spectroscopy to confirm the diamond component included in the film.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.1
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• pp.12-17
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• 2006

A steam generator of nuclear power plant has thousands of thin tubes. These tubes play an important role in maintaining the pressure boundary between the primary and secondary side of nuclear power plant. The steam generator tube is easy to be damaged because of the severe operating conditions such as the high temperature and pressure. Therefore, tremendous efforts are made to assess the structural integrity of the steam generator tubes. The eddy current test is the most popular non-destructive test to assess the integrity of the tubes. However, the eddy current test has the limitation to size the flaw accurately because the eddy current signal behavior depends on the total volume of flaw. This paper shows the possibility that the ultrasonic test method can be applied to detect the flaws in the steam generator tubes and to measure them quantitatively. From the test results, it is expected that if the ultrasonic test is put to practical use in the steam generator tube inspection, the inspection results will be improved.

• Radiation Oncology Journal
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• v.16 no.2
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• pp.167-175
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• 1998

Purpose : It is not a simple task to achieve the ideal isodose curve with a standard vaginal applicator or sing1e plane needle impant in the paravaginal tissue when primary or recurrent gynecological neoplasms(cervical cancers, vaginal cancers and vulvar cancers) are treated as a boost following external beam radiotherapy. The authors introduce the development and construction of a simple, inexpensive, customized applicator for volume implant to maximize the radiation dose to the tumor while minimizing the dose to the rectum and the bladder. Materials and Methods : Nine patients underwent Ir-192 transperineal interstitial implantation for either recurrent(5 cases) or primary(3 cases) cervical cancers or primary vaginal cancer(1 case) between August 1994 and February 1998 at Ajou university hospital. First 3 cases were performed with a sing1e plane implant guided by digital palpation. Because of inadequate isodose coverage in the tumor volume in first 3 cases, we designed and constructed interstitial vaginal applicator for volume implant to improve tumor dose distribution and homogeneity while sparing the surrounding normal tissue. Our applicators consist of vaginal obturator and perineal template that made of the clear acrylamide and dental mold material$(Provil^{(R)})$. The applicators were customized individually according to the tumor size and its location Both HDR and LDR irradiation were given with these applicators accomodating 6 Fr needles(Microselectron Nucletron). The pretreatment planning prior to actual implant was performed whenever possible. Results : Needles can be inserted easily and evenly into the tumor volume through the holes of templates, requiring less efforts and time for the implant procedure. Our applicators made of materials available from commercial vendors. These have an advantage that require easy procedure, and spend relatively short time to construct. Also it was possible to fabricate applicators to individualize according to the tumor size and its location and to achieve the ideal isodose coverage. We found an accurate needle arrangement and ideal dose distribution through the CT scan that was obtained in 3 cases after needle implant. Three patients with primary cervical and vaginal cancers were controlled locally at final follow up. But all recurrent cases failed to do so. Conclusion : The authors introduce inexpensive, simple interstitial vaginal templates which were self-designed and constructed using materials available from commercial vendors such as acrylanide and dental mold material $(Provil^{(R)})$.

• Radiation Oncology Journal
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• v.20 no.1
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• pp.41-52
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• 2002

Purpose : 3D conformal radiotherapy, the optimum dose delivered to the tumor and provided the risk of normal tissue unless marginal miss, was restricted by organ motion. For tumors in the thorax and abdomen, the planning target volume (PTV) is decided including the margin for movement of tumor volumes during treatment due to patients breathing. We designed the respiratory gating radiotherapy device (RGRD) for using during CT simulation, dose planning and beam delivery at identical breathing period conditions. Using RGRD, reducing the treatment margin for organ (thorax or abdomen) motion due to breathing and improve dose distribution for 3D conformal radiotherapy. Materials and Methods : The internal organ motion data for lung cancer patients were obtained by examining the diaphragm in the supine position to find the position dependency. We made a respiratory gating radiotherapy device (RGRD) that is composed of a strip band, drug sensor, micro switch, and a connected on-off switch in a LINAC control box. During same breathing period by RGRD, spiral CT scan, virtual simulation, and 3D dose planing for lung cancer patients were peformed, without an extended PTV margin for free breathing, and then the dose was delivered at the same positions. We calculated effective volumes and normal tissue complication probabilities (NTCP) using dose volume histograms for normal lung, and analyzed changes in doses associated with selected NTCP levels and tumor control probabilities (TCP) at these new dose levels. The effects of 3D conformal radiotherapy by RGRD were evaluated with DVH (Dose Volume Histogram), TCP, NTCP and dose statistics. Results : The average movement of a diaphragm was 1.5 cm in the supine position when patients breathed freely. Depending on the location of the tumor, the magnitude of the PTV margin needs to be extended from 1 cm to 3 cm, which can greatly increase normal tissue irradiation, and hence, results in increase of the normal tissue complications probabiliy. Simple and precise RGRD is very easy to setup on patients and is sensitive to length variation (+2 mm), it also delivers on-off information to patients and the LINAC machine. We evaluated the treatment plans of patients who had received conformal partial organ lung irradiation for the treatment of thorax malignancies. Using RGRD, the PTV margin by free breathing can be reduced about 2 cm for moving organs by breathing. TCP values are almost the same values $(4\~5\%\;increased)$ for lung cancer regardless of increasing the PTV margin to 2.0 cm but NTCP values are rapidly increased $(50\~70\%\;increased)$ for upon extending PTV margins by 2.0 cm. Conclusion : Internal organ motion due to breathing can be reduced effectively using our simple RGRD. This method can be used in clinical treatments to reduce organ motion induced margin, thereby reducing normal tissue irradiation. Using treatment planning software, the dose to normal tissues was analyzed by comparing dose statistics with and without RGRD. Potential benefits of radiotherapy derived from reduction or elimination of planning target volume (PTV) margins associated with patient breathing through the evaluation of the lung cancer patients treated with 3D conformal radiotherapy.