• Computers and Concrete
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• 제32권5호
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• pp.465-474
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• 2023

The point load test (PLT) is a widely-used alternative method in the field to determine the uniaxial compressive strength due to its simple testing machine and procedure. The point load test index can estimate the uniaxial compressive strength through conversion factors based on the rock types. However, the mechanism correlating these two parameters and the influence of the mechanical properties on PLT results are still not well understood. This study proposed a theoretical model to understand the mechanism of PLT serving as an alternative to the UCS test based on laboratory observation and literature survey. This model found that the point load test is a self-confined compression test. There is a compressive ellipsoid near the loading axis, whose dilation forms a tensile ring that provides confinement on this ellipsoid. The peak load of a point load test is linearly positive correlated to the tensile strength and negatively correlated to the Poisson ratio. The model was then verified using numerical and experimental approaches. In numerical verification, the PLT discs were simulated using flat-joint BPM of PFC3D to model the force distribution, crack propagation and BPM properties' effect with calibrated micro-parameters from laboratory UCS test and point load test of Berea sandstones. It further verified the mechanism experimentally by conducting a uniaxial compressive test, Brazilian test, and point load test on four different rocks. The findings from this study can explain the mechanism and improve the understanding of point load in determining uniaxial compressive strength.

• 대한치과기공학회지
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• 제46권2호
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• pp.21-27
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• 2024

Purpose: This study aimed to analyze the stress distribution and deformation in implant abutments made from titanium (Ti-6Al-4V), zirconia, and polyetheretherketone (PEEK), including their screws and fixtures, under various loading conditions using finite element analysis (FEA). Methods: Three-dimensional models of the mandible with implant abutments were created using Siemens NX software (NX10.0.0.24, Siemens). FEA was conducted using Abaqus to simulate occlusal loads and assess stress distribution and deformation. Material properties such as Young's modulus and Poisson's ratio were assigned to each component based on literature and experimental data. Results: The FEA results revealed distinct stress distribution patterns among the materials. Titanium alloy abutments exhibited the highest stress resistance and the most uniform stress distribution, making them highly suitable for long-term stability. Zirconia abutments showed strong mechanical properties with higher stress concentration, indicating potential vulnerability to fracture despite their aesthetic advantages. PEEK abutments demonstrated the least stress resistance and higher deformation compared to other abutment materials, but offered superior shock absorption, though they posed a higher risk of mechanical failure under high load conditions. Conclusion: The study emphasizes the importance of selecting appropriate materials for dental implants. Titanium offers durability and uniform stress distribution, making it highly suitable for long-term stability. Zirconia provides aesthetic benefits but has a higher risk of fracture compared to titanium. PEEK excels in shock absorption but has a higher risk of mechanical failure compared to both titanium and zirconia. These insights can guide improved implant designs and material choices for various clinical needs.

• Computers and Concrete
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• 제33권4호
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• pp.399-407
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• 2024

This study nondestructively examined the evolution of crack density in ultra-high performance concrete (UHPC) upon cyclic loading. Uniaxial compression was repeatedly applied to the cylindrical specimens at levels corresponding to 32% and 53% of the maximum load-bearing capacity, each at a steady strain rate. At each stage, both P-wave and S-wave velocities were measured in the absence of the applied load. In particular, the continuous monitoring of P-wave velocity from the first loading prior to the second loading allowed real-time observation of the strengthening effect during loading and the recovery effect afterwards. Increasing the number of cycles resulted in the reduction of both elastic wave velocities and Young's modulus, along with a slight rise in Poisson's ratio in both tested cases. The computed crack density showed a monotonically increasing trend with repeated loading, more significant at 53% than at 32% loading. Furthermore, the spatial distribution of the crack density along the height was achieved, validating the directional dependency of microcracking development. This study demonstrated the capability of the crack density to capture the evolution of microcracks in UHPC under cyclic loading condition, as an early-stage damage indicator.

• Earthquakes and Structures
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• 제27권2호
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• pp.127-142
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• 2024

The amount of wave propagation through a rubber concrete construction is the subject of the current investigation. Rubber tire waste was used to make two different types of cement mixtures. One type contains sand substitute in amounts ranging from 15% to 60% of the total volume, while the other has gravel with diameters of 3/8 and 8/15 and 15% sand in the same mixture. A wide variety of concrete forms and compositions were created, and their viscous and solid state characteristics were assessed, along with their short-, medium-, and long-term strengths. Diffusion, density, mechanical strength resistance to compressive force, and ultrasound wave propagation were also assessed. The water-to-cement ratio and plasticizer were used in this investigation. In the second part of the study, an analytical model is presented that simulates the experimental model in predicting the speed of waves and the frequencies accompanying them for this type of mixture. Higher order shear deformation beam theory for wave propagation in the rubberized concrete beam is developed, considering the bidirectional distribution, which is primarily expressed by the density, the Poisson coefficient, and Young's modulus. Hamilton's concept is used to determine the governing equations of the wave propagation in the rubberized concrete beam structure. When the analytical and experimental results for rubber concrete beams were compared, the outcomes were very comparable. The addition of rubber gravel and sandy rubber to the mixture both resulted in a discernible drop in velocities and frequencies, according to the data.

• Safety and Health at Work
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• 제15권2호
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• pp.208-212
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• 2024

Background: Traffic accidents involving professional drivers have serious societal repercussions. Unique occupational stressors and health risks exacerbate the likelihood of traffic accidents among professional drivers. This study explores the association between presenteeism-impaired work performance due to working while unwell-and traffic accident risk among professional taxi drivers in Japan. Methods: A prospective cohort study was conducted from June 2022 to February 2023, involving taxi drivers from a single company in Fukuoka Prefecture, Japan. Presenteeism was assessed using the Work Functioning Impairment Scale (WFun). Primary outcome involved the number of self-reported minor traffic accidents. The incidence rate ratio (IRR) of minor traffic accident occurrences was estimated using a Poisson regression analysis, adjusted for confounders including sex, age, and driving experience. Results: Of 838 targeted drivers, 435 were included in the analysis. Higher baseline work functioning impairment was associated with a significant trend of increasing IRR of minor traffic accidents (p for trend = 0.045). A dose-response relationship was seen between the degree of presenteeism and incidence rate of minor traffic accidents. Conclusion: Higher levels of presenteeism were associated with an increased risk of traffic accidents among taxi drivers. The findings underscore the need for socio-economic support and prioritized health management to mitigate traffic accident risk among professional drivers. This study highlights the importance of managing non-critical health issues alongside serious health conditions for safer driving practices among professional drivers in Japan.

• 한국지반공학회논문집
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• 제40권4호
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• pp.137-144
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• 2024

해당 논문의 목적은 균열밀도 산정 시 독립변수로 설정한 값이 얼마나 중요하게 작용하는지를 기계학습 기반의 알고리즘으로 분석하는 것이다. 논문에서 사용한 알고리즘은 random forest와 SHAP이며, 독립변수는 압축파 속도, 전단파 속도, 간극률 그리고 포아송 비로 결정하였다. 암석 시료는 건설현장에서 채취하였으며, 원기둥 형태로 가공하여 각 입력 물성치의 획득이 용이하게 고려하였다. 다수의 특징이 포함된 독립 및 종속 변수 값을 얻고자 인위적인 풍화를 진행하였으며, 총 12회 진행하였다. 2가지 알고리즘 적용 결과 간극률이 균열밀도 산정시 매우 중요한 독립변수로 나타났으며, 전단파 속도가 상대적으로 낮은 영향을 미치는 인자로 나타났다. 이와 같은 결과는 독립변수로 설정한 4개의 물성치로 충분히 균열밀도를 추정할 수 있음을 시사하며 random forest 및 SHAP과 같은 알고리즘을 통해 설정된 독립 변수가 적절하게 구성되었는지 확인할 수 있는 방법론도 제시하였다.

• 터널과지하공간
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• 제21권1호
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• pp.33-40
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• 2011

본 연구에서는 온도와 수압이 암석의 물성 변화에 미치는 영향을 평가하였다. 온도가 암석의 물성에 미치는 영향을 평가하기 위하여 가곡광산에서 채취한 화강암과 석회암 시험편에 200, 300, 400, 500, 600, $700^{\circ}C$(석회암의 경우 $700^{\circ}C$는 제외하였음)의 열을 가하여 예열시험편을 제작하였다. 예열시험편에 대한 실내실험을 통해 비중, 유효공극률, 탄성파속도, 일축압축강도, 탄성계수, 포아송비를 측정한 결과 온도가 증가함에 따라 화강암과 석회암 예열시험편의 물성이 변하는 것으로 나타났다. 비중, 유효공극률, 탄성파속도의 급격한 변화는 화강암의 경우 $400^{\circ}C$ 이상에서 발생하였으며, 석회암의 경우에는 $300^{\circ}C$ 이상에서 나타났다. 온도에 따른 일축압축강도, 탄성계수, 포아송비의 변화도 물리적 특성의 변화와 유사한 것으로 나타났다. 예열시험편의 일축압축강도와 탄성계수로부터 유추한 500, 600, $700^{\circ}C$ 화강암 예열시험편의 GSI는 각기 81, 66, 58로 나타났으며, 400, 500, $600^{\circ}C$ 석회암 예열시험편의 GSI는 각각 76, 71, 65로 나타났다. 500, 600, $700^{\circ}C$ 화강암 예열시험편과 400, 500, $600^{\circ}C$ 석회암 예열시험편에 7.5 MPa의 수압을 가하였다. 수압을 적용한 예열시험편의 유효공극률, 탄성파속도, 일축압축강도, 탄성계수를 측정하여 평균한 결과 수압을 가하기 전 예열시험편에 비해 평균 감소량이 화강암 500, 600, $700^{\circ}C$ 예열시험편 각각에 대해서 7.6, 11.3, 14.9%로 나타났고, 석회암 400, 500, $600^{\circ}C$ 예열시험편에 대해서는 각기 8.2, 13.8, 21.9%로 평가되었다.

• Asian Pacific Journal of Cancer Prevention
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• 제16권10호
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• pp.4193-4198
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• 2015

Background: Globally, retinoblastoma is the most common primary intraocular malignancy occurring in children. This paper documents the recent incidence rates of retinoblastoma by age and sex groups from the Population Based Cancer Registries (PBCRs) of Bangalore, Mumbai, Chennai, Delhi and Kolkata using the data from the National Cancer Registry Programme. Materials and Methods: Relative proportions, sex ratio, method of diagnosis, and incidence rates (crude and age standardized) for each PBCR and pooled rates of the five PBCRs were calculated for the years 2005/06 to 2009/10. Standard errors and 95% confidence limits of ASIRs by sex group in each PBCR were calculated using the Poisson distribution. Standardised rate ratios of ASIR by sex group and rate ratios at risk were also calculated. Results: The maximum retinoblastoma cases were in the 0-4 age group, accounting for 78% (females) and 81% (males) of pooled cases from five PBCRs. The pooled crude incidence rate in the 0-14 age group was 3.5 and the pooled ASIR was 4.4 per million. The pooled ASIR in the 0-4, 5-9 and 10-14 age group were 9.6, 2.0 and 0.1 respectively. The M/F ratio in Chennai (1.9) and Bangalore PBCRs (2.0) was much higher than the other PBCRs. Among the PBCRs, the highest incidence rate in 0-4 age group was found in males in Chennai (21.7 per million), and females in Kolkata (18.9 per million). There was a distinct variation in incidence rates in the PBCRs in different geographic regions of India.

• 보건행정학회지
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• 제22권2호
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• pp.163-182
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• 2012

This study was performed to identify the difference of the area-based deprivation and the educational level on the cerebrovascular mortality in Korea. Data used in this study was obtained from the Death Certificate Data 2000 and the 2000 Census produced by Korean National Statistics(NSO). We classified the whole country into 246 areas based on the administrative districts. Then, the Standardized Mortality Ratio (SMR) in cerebrovascular disease was calculated according to the sex, education level and 246 areas. Its Predicted SMR was calculated by the Empirical Bayes Methods to reduce the variation of the SMR values. The area-based deprivation of 246 areas were measured using the modified Carstairs index in which the 5 indicators consisted of overcrowding, the unemployment ratio of men, the percentage of households classified low social class, the percentage of non home owners, and finally those houses lacking basic amenities. The correlation between the area-based deprivation and the SMR of the whole country and the correlation between the area-based deprivation and the SMR of each metropolitan cities or provinces was analyzed by the Pearson correlation analysis method. After classifying the deprivation of 246 areas into 5 levels, we performed the random intercept Poisson regression analysis after adjusting education level and age using Empirical Bayes Method to investigate the relationship between the 5 deprivation levels and the cerebrovascular mortality. The SMR was increased in lower education level. Each 246 areas had different values in SMR, Predicted SMR and area-based deprivation. The area-based deprivation and the SMR of the whole country was not correlated in both sexes. The education level of an individual was associated the risk of cerebrovascular mortality in men. The risk of cerebrovascular mortality increased with age compared to the reference(<30). The area-based deprivation was not associated with the risk of cerebrovascular in both sexes. The findings of this study suggest that the SMR had positive and negative correlations with area-based deprivation depending on the metropolitan cities or province. It also suggests that the individual education level and age were related with mortality and finally that the area-based deprivation was not associated to the cerebrovascular mortality in Korea.

• 한국전산구조공학회논문집
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• 제16권4호
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• pp.419-429
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• 2003

두꺼운 축대칭 쌍곡형 쉘의 고유진동수를 결정하는 3차원 해석법이 제시되었다. 수학적으로 2차원적인 전통적인 쉘 이론과는 달리, 본 연구의 해석법은 3차원적인 동탄성방정식을 근간으로 하였다. 반경방향, 원주방향, 축방향으로의 변위성분인 u/sub r/, u/sub θ/, u/sub z/를 시간에 대해서는 정현적으로, θ에 대해서는 주기적으로, r과 z방향으로는 대수 다항식으로 표현하였다. 쌍곡형 쉘의 위치(변형률)에너지와 운동에너지를 정식화하고 리츠법을 사용하여 고유치문제를 해결하였으며, 진동수의 최소화과정을 통해 고유진동수를 엄밀해의 상위경계치로 구하였다. 대수 다항식의 차수가 증가하면 진동수는 엄밀해에 수렴하게 된다. 축대칭 쌍곡형 쉘의 하위 5개의 진동수에 대해서 유효숫자 4자리까지의 수렴성 연구가 이루어졌다. 쌍곡형 쉘의 서로 다른 2개의 두께 비, 3개 의 축비(axis ratio), 3개의 shv이 비를 가진 총 18개의 형상을 지닌 자유 경계의 축대칭 쌍곡형 쉘의 수치결과를 도표화하였다. 프와송 비( ν)는 0.3으로 고정하였다. 본 연구의 해석법은 매우 두꺼운 쉘 뿐만 아니라 얇은 쉘에도 적용이 가능하다.