• 지질공학
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• 제5권1호
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• pp.1-20
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• 1995

1993년 3월 부산 북구 경부선 복선 철도 구간에서 지반 침하로 인한 대형 기차전복 참화는 많은 인명 피해는 물론 막대한 재산 손실을 초래하였다. 여기서 관심의 초점이 된 지반함몰 원인은 우선 다양한 재래 지질조사법에 의해 조사되었으며 그 결과 $\circled1$ 선로 하부 약 39m 지점에서 NATA 터널굴착을 위한 화약 발파, $\circled2$ 기반암 경계면의 급격한 변화가 무엇보다 지반 침하에 대한 직접적인 동기가 된 것으로 추정되었다. 그런데 기존 조사기법은 거의 시추 데이터에 의존하기 때문에 현실적으로 주어진 불리한 탐사 여건(예: 선로면 위에서는 빈번한 열차 주행으로 인하여 시추가 불가능함)은 바로 초점이 되고 있는 선로 하부 지반상태 파악을 불가능하게 하였다. 따라서 상기 결여된 지질정보는 우선 함몰 경위에 대한 두사지 가정을 낳게 하였으며 이러한 불확실성은 시공 과실에 대한 판단을 흐리게 하는 계기를 부여한 것이다. 본 논문은 우선 상기 불리한 탐사 여건을 극복하면서 동시에 각 암층 경계면을 고분해능으로 재현할 수 있는 하나의 첨단 물리탐사법 즉, 탄성파 토모그래피 기법을 소개하고 있으며 나아가서 그의 응용 결과는 바로 토목설계 내지 시공설계를 위한 귀중한 기초 자료(예: 탄성파 속도, 탄성율)로 반영될 수 있음을 보여주고 있다.

• 구강회복응용과학지
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• 제22권3호
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• pp.221-230
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• 2006

Recently, the need for esthetic results has increased the interest for all-ceramic crown prosthesis. Furthermore, the development of zirconium core via CAD/CAM system has allowed the all ceramic restorations to be applied to almost all fixed prosthesis situations. But, the increased strength has been reported to increase in proportion with the bond strength of cement, and recently, the tribochemical system which increases the bond strength through, silica coating and silanization has been introduced. The purpose of this study was to compare the $Rocatec^{TM}$ system and $CoJet^{TM}$ system with the traditional acid etching and silanization method of the irconium based ceramic. The surface character was observed via SEM(X2000), and the bond strength with the resin cement were measured. 50 In-Ceram Zirconia (Adens, Korea) discs were fabricated and embedded in resin, group 1 was treated with glass-bead blasting and cleaning, group 2 was treated with 20% HF for 10 minutes and silanized, group 3 was treated with the $Rocatec^{TM}$ system, and group 4 was treated with the $CoJet^{TM}$ system. Each group was comprised of 10 specimens. The specimens were cemented to a $3mm{\times}5mm$ resin block with Super-Bond C&B. The shear bond strength was measured with the $Instron^{(R)}$ 8871 at a crosshead speed of 0.5mm/min. The results were as follows. 1. According to SEM results, there were little difference between group 1 & group 2, but in group 3 and 4, silica coating was detected and there was increase in surface roughness. 2. The shear bond strength decreased in the order of group 3(46.28MPa), group 4(42.04MPa), group 2(31.56MPa), and group 1(27.46MPa). 3. There was significant differnce between group 1&2 and group 3&4(p<0.05). From the results above, it can be considered that the conventional method of acid etching and silane treatment cannot increase the bond strength with resin cements, and that by applying the tribochemical system of $Rocatec^{TM}$ system and $CoJet^{TM}$ system, we can achieve a stronger all ceramic restoration. Further studies on surface treatments to increase the bond strength are thought to be needed.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2003년도 추계학술발표회초록집
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• pp.134-135
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• 2003

The dental implant materials required good mechanical properties, such as fatigue strength, combined with a high resistance to corrosion. For increasing fatigue resistance and delaying onset of stress corrosion cracking, shot peening has been used for > 50 years to extend service life of metal components. However, there is no information on the electrochemical behavior of shot peened and hydroxyapatite(HA) coated Ti-6Al-4V alloys. To increase fatigue strength, good corrosion resistance, and biocompatibility, the electrochemical characteristics of Ti/TiN/HA coated and shot peened Ti-6Al-4V alloys by electron beam physical vapor deposition(EB-PVD) have been researched by various electrochemical method in 0.9%NaCl. Ti-6Al-4V alloys were prepared under the condition of hydrogen and vacuum arc furnace. The produced materials were quenched at 1000$^{\circ}C$ under high purity dried Ar atmosphere and were hold at 500$^{\circ}C$ for 2 hrs to achieve the fatigue strength(1140㎫) of materials. Ti-6Al-4V alloys were prepared under the condition of hydrogen and vacuum arc furnace. Shot peening(SP) and sand blasting treatment was carried out for 1, 5, and 10min. On the surface of Ti-6Al-4V alloys using the steel balls of 0.5mm and alumina sand of 40$\mu\textrm{m}$ size. Ti/TiN/HA multilayer coatings were carried out by using electron-beam deposition method(EB-PVD) as shown Fig. 1. Bulk Ti, powder TiN and hydroxyapatite were used as the source of the deposition materials. Electrons were accelerated by high voltage of 4.2kV with 80 - 120mA on the deposition materials at 350$^{\circ}C$ in 2.0 X 10-6 torr vacuum. Ti/TiN/HA multilayer coated surfaces and layers were investigated by SEM and XRD. A saturated calomel electrode as a reference electrode, and high density carbon electrode as a counter electrode, were set according to ASTM GS-87. The potentials were controlled at a scan rate of 100 mV/min. by a potentiostat (EG&G Co.273A) connected to a computer system. Electrochemical tests were used to investigate the electrochemical characteristics of Ti/TiN/HA coated and shot peened materials in 0.9% NaCl solution at 36.5$^{\circ}C$. After each electrochemical measurement, the corrosion surface of each sample was investigated by SEM.

• Geomechanics and Engineering
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• 제35권2호
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• pp.121-133
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• 2023

The demand for cement and limestone crushed materials has increased many folds due to the tremendous increase in construction activities in Pakistan during the past few decades. The number of cement production industries has increased correspondingly, and so the rock-blasting operations at the limestone quarry sites. However, the safety procedures warranted at these sites for the blast-induced ground vibrations (BIGV) have not been adequately developed and/or implemented. Proper prediction and monitoring of BIGV are necessary to ensure the safety of structures in the vicinity of these quarry sites. In this paper, an attempt has been made to predict BIGV using artificial neural network (ANN) at three selected limestone quarries of Pakistan. The ANN has been developed in Python using Keras with sequential model and dense layers. The hyper parameters and neurons in each of the activation layers has been optimized using randomized and grid search method. The input parameters for the model include distance, a maximum charge per delay (MCPD), depth of hole, burden, spacing, and number of blast holes, whereas, peak particle velocity (PPV) is taken as the only output parameter. A total of 110 blast vibrations datasets were recorded from three different limestone quarries. The dataset has been divided into 85% for neural network training, and 15% for testing of the network. A five-layer ANN is trained with Rectified Linear Unit (ReLU) activation function, Adam optimization algorithm with a learning rate of 0.001, and batch size of 32 with the topology of 6-32-32-256-1. The blast datasets were utilized to compare the performance of ANN, multivariate regression analysis (MVRA), and empirical predictors. The performance was evaluated using the coefficient of determination (R²), mean absolute error (MAE), mean squared error (MSE), mean absolute percentage error (MAPE), and root mean squared error (RMSE)for predicted and measured PPV. To determine the relative influence of each parameter on the PPV, sensitivity analyses were performed for all input parameters. The analyses reveal that ANN performs superior than MVRA and other empirical predictors, andthat83% PPV is affected by distance and MCPD while hole depth, number of blast holes, burden and spacing contribute for the remaining 17%. This research provides valuable insights into improving safety measures and ensuring the structural integrity of buildings near limestone quarry sites.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제34권3호
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• pp.325-340
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• 2008

The purpose of this study was to evaluate the artificial dental plaque by Streptococcus mutans on 4 different implant surfaces. In this study, the specimens were divided into 4 groups according to implant surface treatment. Uncoated implant group(n=5) which has an uncoated, smooth surfaced implant(Osstem, Korea), SLA implant group(n=5) which has an sandblasted large grit and acid-etched surface implant(Bicon, USA). Oxidized implant group(n=5) which has an oxidized surfaced implant (Osstem, Korea), and RBM implant group(n=5) which has resorbable blasting media(RBM) surfaced implant(Osstem, Korea). Acquired pellicle by human saliva and dental plaque by Streptococcus mutans were made on each implant surface. To analyze the plaque condition on implants surfaces, cell count and optical density were taken as a microbiologic method, and SEM(Scanning Electronic Microscope) findings was also taken for evaluation of surface condition. The following results were obtained. 1. Cell counting results of artificial dental plaque were Uncoated group($658.0{\pm}102.0$), RBM group($878.0{\pm}170.0$), SLA group ($946.0{\pm}42.0$), Oxidized group($992.0{\pm}40.0$), and there was difference between Oxidized group and Uncoated implant group(p<0.05). In case of modified cell counting results by v/w% were RBM group($197.8{\pm}45.2$), Oxidized group($207.04{\pm}8.34$), Uncoated group($261.6{\pm}40.6$), SLA group($315.4{\pm}14.0$), and there was difference between RBM group and SLA group(p<0.05). 2. Optical density results of artificial dental plaque after ultrasonic treatment was that there was difference among groups, and optical density of RBM group was higher than that of Uncoated group(p<0.05). In case of modified optical density results by v/w%, there was difference among groups, and the modified optical density of Uncoated group and SLA group was higher than those of Oxidized group and RBM group(P>0.05). 3. SEM findings of artificial dental plaque on the surfaces of implant as follows; there were artificial dental plaque on the surfaces of all test implants. Streptococcus mutans and by-product were observed at 10,000 times magnified condition on all test implants. Adhesion area of artificial dental plaque was about 1/2 of total surface after 24 hours incubate at $37^{\circ}C$. These results showed that there were differences among implant surfaces on the growth of Streptococcus mutans, and bacteria and by-product were covered about 1/2 area of total implant surfaces at 24 hours incubate at $37^{\circ}C$.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제34권3호
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• pp.285-292
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• 2008

Purpose: The present study was performed to evaluate the effect of surface treatment of the cervical area of implant on bone regeneration in fresh extraction socket following implant installation. Materials and methods: The four minipigs, 18 months old and 30 kg weighted, were used. Four premolars of the left side of both the mandible and maxilla were extracted. ${\phi}$3.3 mm and 11.5 mm long US II plus implants (Osstem Implant co., Korea) with resorbable blasting media (RBM) treated surface and US II implants (Osstem Implant co., Korea) with machined surface at the top and RBM surface at lower portion were installed in the socket. Stability of the implant was measured with $Osstell^{TM}$ (Model 6 Resonance Frequency Analyser: Integration Diagnostics Ltd., Sweden). After 2 months of healing, the procedures and measurement of implant stability were repeated in the right side by same method of left side. At four months after first experiment, the animals were sacrificed after measurement of stability of all implants, and biopsies were obtained. Results: Well healed soft tissue and no mobility of the implants were observed in both groups. Histologically satisfactory osseointegration of implants was observed with RBM surface, and no foreign body reaction as well as inflammatory infiltration around implant were found. Furthermore, substantial bone formation and high degree of osseointegration were exhibited at the marginal defects around the cervical area of US II plus implants. However, healing of US II implants was characterized by the incomplete bone substitution and the presence of the connective tissue zone between the implant and newly formed bone. The distance between the implant platform (P) and the most coronal level of bone-to-implant contact (B) after 2 months of healing was $2.66{\pm}0.11$ mm at US II implants group and $1.80{\pm}0.13$mm at US II plus implant group. The P-B distance after 4 months of healing was $2.29{\pm}0.13$mm at US II implants group and $1.25{\pm}0.10$mm at US II plus implants group. The difference between both groups regarding the length of P-B distance was statistically significant(p<0.05). Concerning the resonance frequency analysis (RFA) value, the stability of US II plus implants group showed relatively higher RFA value than US II implants group. Conclusion: The current results suggest that implants with rough surface at the cervical area have an advantage in process of bone regeneration on defect around implant placed in a fresh extraction socket.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제29권4호
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• pp.301-308
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• 2007

Purpose: This study was performed to compare and evaluate the effect of recipient site depths and diameters of the drills on the primary stability of implant in pig's ribs. Materials and methods: An intact pig's rib larger than 8 mm in width and 20 mm in height; RBM(resorbable blasting media) surface blasted ${\phi}3.75mm$ and 8.0 mm long USII Osstem Implants (Osstem Co., Korea) were used. To measure the primary stability, $Periotest^{(R)}$ (Simens AG, Germany) and $Osstell^{TM}$ (Model 6 Resonance Frequency Analyser: Integration Diagnostics Ltd., Sweden) were used. They were divided into 6 groups according to its recipient site formation method: D3H3, D3H5, D3H7, D3.3H3, D3.3H5, D3.3H7. Each group had, as indicated, 10 implants placed, and total 60 implants were used. The mean value was obtained by 4-time measurements each on mesial, distal, buccal, and lingual side perpendicular to the long axis of the implant using $Periotest^{(R)}$ and $Osstell^{TM}$. For statistical analysis one-way ANOVA was used to compare the mean value of each group, and the correlation between placement depths and the primary stability, and that of measuring instruments was analyzed using SPSS 12.0. Results: The primary stability of the implants increased as the placement depths increased (p<0.05), and showed a proportional relationship (p<0.01). The primary stability increased when the diameter of the recipient site was smaller than that of the implant but with no statistical significance. There was a strong correlation between $Osstell^{TM}$ and $Periotest^{(R)}$ (p<0.01). Conclusion: These results suggest that increasing the placement depth of implants enhances the primary stability of implant.

• 한국터널지하공간학회 논문집
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• 제16권2호
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• pp.213-224
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• 2014

최근, tunnel boring machine (TBM)을 이용한 도심지 지중 전력구 터널 건설이 증가하고 있다. 쉴드 TBM을 이용한 기계화 터널 굴착 공법은 재래식 공법에 비해 지반침하를 최소화 하고 발파에 의한 진동을 줄일 수 있는 장점이 있다. 국내에서는 earth pressure balance(EPB) 쉴드 TBM이 주로 사용되고 있다. 그러나 전력구 터널 굴착을 위한 쉴드 TBM 공법이 증가함에도 불구하고, 전력구 쉴드 TBM 터널의 거동 분석에 관한 연구는 미비한 실정이다. 본 연구에서는 후방주입 거리에 따른 전력구 쉴드 TBM 터널의 거동 특성을 분석하고, 굴착면 지반 손실과 후방주입 거리와의 상관관계를 도출하고자 한다. 쉴드 TBM을 이용한 터널 굴착은 3D FEM을 이용하여 시뮬레이션 하였다. 뒷채움 그라우트가 설치되는 거리의 변화에 따른 축력, 전단력, 휨 모멘트와 같은 단면력을 검토하고 지표면에서의 연직 변위를 분석하였다. 또한, 유한요소해석으로 얻어진 결과와 안정성 분석에 기초하여, 지반과 터널 구조물의 안정성을 확보할 수 있는 뒷채움재 주입시기를 결정할 수 있다.

• 한국진공학회지
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• 제20권3호
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• pp.217-224
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• 2011

최근, 결정질 실리콘 태양전지 분야에서 저가격화와 공정의 단순화가 가장 중요한 부분으로 대두되고 있다. 특히 태양전지 가격의 대부분을 차지하고 있는 웨이퍼의 저가격화가 가장 큰 이슈로 떠오르면서, 웨이퍼의 저가격화를 실현하기 위한 최선의 방안으로 마이크로 블라스터를 이용한 재생웨이퍼 제작 방법이 대두되고 있다. 마이크로 블라스터를 이용하여 재생웨이퍼를 제작 할 경우, 표면의 요철이 형성되어 반사율이 감소되어 태양전지 내부로 입사하는 빛의 양을 증가시키는 긍정적인 효과가 있다. 또한, 공정비용이 저렴하여 태양전지 저가격화를 실현할 수 있다. 그러나, 마이크로 블라스터를 이용한 공정은 웨이퍼에 물리적인 충격을 주기 때문에 표면에 크랙이 형성되며 식각 잔여물들이 표면에 재흡착되는 단점이 있다. 본 연구에서는 이러한 단점들을 보완하기 위하여 DRE (Damage Remove Etching)를 수행하였다. DRE 공정 후 반사율과 소수 반송자 수명을 측정하여 미세 파티클과 마이크로 크랙의 제거를 확인하였고, 태양전지를 제작하여 효율에 미치는 영향을 분석하였다. 마이크로 블라스터 공정 후 웨이퍼의 소수 반송자 수명은 Bare 웨이퍼에 비해 80% 정도 감소하였으나, DRE 공정 수행 후에는 50% 까지 증가하였음을 확인할 수 있었다. 태양전지 효율을 비교해보면, DRE 공정을 수행한 웨이퍼의 경우 Bare 웨이퍼보다 약 1~2%, DRE 공정을 수행하지 않은 웨이퍼보다 약 3∼5% 증가했음을 확인하였다.

• 한국터널지하공간학회 논문집
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• 제24권5호
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• pp.395-409
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• 2022

기존 암반 굴착공법이 갖는 한계점을 극복하기 위해 최근 연마재 워터젯 공법을 활용하는 연구가 활발히 진행되고 있다. 연마재 워터젯 암반굴착 공법은 암반에 연속적인 자유면을 형성하여 발파 시 발생하는 진동을 저감하고 굴착효율을 증진시키는 효과가 있다. 그러나 연마재 워터젯 절삭성능은 암반의 물리적 성질에 따라 변화한다. 따라서, 다양한 물리적 성질을 가진 암반이 혼재하는 굴착현장 특성상 효과적인 워터젯 활용을 위해서는 다양한 암종의 절삭성능을 분석하는 것이 필수적이다. 본 연구에서는 현무암과 화강암을 대상으로 수압, 이격거리, 이송속도를 변화시키며 절삭실험을 수행하고 결과를 분석하였다. 실험결과, 현무암은 화강암보다 평균적으로 약 41% 깊게 절삭되고, 절삭 폭은 약 18.5% 좁게 형성되었다. 본 연구결과는 향후 현무암과 같은 강도가 낮고 공극이 큰 암반 굴착현장에서 연마재 워터젯을 적용할 시 유용한 기초자료로 활용될 것으로 기대된다.