• Structural Engineering and Mechanics
• /
• 제84권2호
• /
• pp.207-224
• /
• 2022

The mechanical behavior of prestressed concrete haunched beams (PSHBs) was investigated in depth using a finite element modeling technique in this study. The efficiency of finite element modeling was investigated in the first stage by taking into account a previous study from the literature. The first stage's findings suggested that finite element modeling might be preferable for modeling PSHBs. In the second stage of the research, a comprehensive parametric study was carried out to determine the effect of each parameter on PSHB load capacity, including haunch angle, prestress level, compressive strength, tensile reinforcement ratio, and shear span to depth ratio. PSHBs and prestressed concrete rectangular beams (PSRBs) were also compared in terms of capacity. Stochastic analysis was used in the third stage to define the uncertainty in PSHB capacity by taking into account uncertainty in geometric and material parameters. Standard deviation, coefficient of variation, and the most appropriate probability density function (PDF) were proposed as a result of the analysis to define the randomness of capacity of PSHBs. In the study's final section, a new equation was proposed for using symbolic regression to predict the load capacity of PSHBs and PSRBs. The equation's statistical results show that it can be used to calculate the capacity of PSHBs and PSRBs.

• 한국측량학회지
• /
• 제28권2호
• /
• pp.217-222
• /
• 2010

지오이드는 수직 높이 체계의 기준으로 다양한 방법으로 측정된 중력값을 이용하여 계산된다. 따라서 지오이드의 계산에 사용된 관측자료에 따라 지오이드 사이에 차이가 발생할 수 있으나 이에 대한 연구가 상대적으로 미흡한 실정이다. 그 이유는 GPS/Leveling 자료와 같은 검증자료가 충분치 않아 제한된 범위 내에서만 분석이 수행되어 왔기 때문이다. 본 연구에서는 GPS/Leveling 자료를 이용하여 계산된 기하지오이드를 기준으로 중력기반 지오이드(항공중력 지오이드, 지상중력 지오이드, 국토지리정보원과 국립해양조사원에서 제공하고 있는 지상중력기반 지오이드)를 비교 분석하였다. 이를 위해 실험지역내에 설치된 통합기준점에 대해 기하지오이드고를 산출한 후 중력기반 지오이드와의 차이를 분석하였다. 기하지오이드와 중력 지오이드와의 차이는 통합기준점 각 지점(포인트)별로 혹은 $10km{\times}10km$로 격자화 한 후 분석하였으며 파장별 분석이 용이하도록 FFT(Fast Fourier Transform) 방법을 이용하였다. 기하지오이드고를 기준으로 각 지점별 차이에 대한 표준편차를 비교 분석한 결과 항공중력과 지상중력에 의한 지오이드고는 유사한 것으로 나타났다. 반면 국토지리정보원과 국립해양조사원에서 제공하고 있는 지상중력기반 지오이드고는 차이가 있는 것으로 나타났다. 주파수 영역에서 차이를 비교한 결과, 저주파 영역에서는 모두 유사한 결과를 보였으며 국토지리정보원/해양조사원에서 제공하고 있는 지상중력기반 지오이드고의 경우 고주파 영역에서 차이를 보이는 것으로 나타났다.

• 한국환경보건학회지
• /
• 제37권6호
• /
• pp.406-417
• /
• 2011

Objectives: Exposure to bioaerosols in the indoor environment could be associated with a variety adverse health effects, including allergic disease such atopy. The objectives of this study were to assess children's exposure to bioaerosol in home indoor environments and to evaluate the association between atopy and bioaerosol, environmental, and social factors in Ulsan, Korea. Methods: Samples of viable airborne bacteria and fungi were collected by impaction onto agar plates using a Quick Take TM 30 and were counted as colony forming units per cubic meter of air (CFU/$m^3$). Bioaerosols were identified using standard microbial techniques by differential stains and/or microscopy. The environmental factors and possible causes of atopy based on ISAAC (International Study of Allergy and Asthma in Childhood) were collected by questionnaire. Results: The bioaerosol concentrations in indoor environments showed log-normal distribution (p < 0.01). Geometric mean (GM) and geometric standard deviation (GSD) of airborne bacteria and fungi in homes were 189.0 (2.5), 346.1(2.0) CFU/$m^3$, respectively. Indoor fungal levels were significantly higher than those of bacteria (p < 0.001). The concentration of airborne bacteria exceeded the limit recommended by the Korean Ministry of Environment, 800 CFU/$m^3$, in three out of 92 samples (3.3%) from 52 homes. The means of indoor to outdoor ratio (I/O) for airborne bacteria and fungi were 8.15 and 1.13, respectively. The source of airborne bacteria was not outdoors but indoors. GM of airborne bacteria and fungi were 217.6, 291.8 CFU/$m^3$ in the case's home and 162.0, 415.2 CFU/$m^3$ in the control's home respectively. The difference in fungal distributions between case and control were significant (p = 0.004) and the odds ratio was 0.996 (p = 0.027). Atopy was significantly associated with type of house (odds ratio = 1.723, p = 0.047) and income (odds ratio = 1.891, p = 0.041). Some of the potential allergic fungal genera isolated in homes were Cladosporium spp., Botrytis spp., Aspergillus spp., Penicillium spp., and Alternatia spp. Conclusions: These results suggest that there this should be either 'was little' meaning 'basically no significant association was found' or 'was a small negative' mean that an association was found but it was minor. It's a very improtant distinction. Association between airborne fungal concentrations and atopy and certain socioeconomic factors may affect the prevalence of childhood atopy.

• 동의생리병리학회지
• /
• 제16권5호
• /
• pp.1035-1041
• /
• 2002

Ultrasonic nebulizer with the application of new engineering methodology and the design of electronic circuit and 766ppm Cd nebulizing solution were used to generate cadmium aerosol for inhalation toxicology study. The results of particle size analysis for cadmium aerosol were as following. The highest particle counting for source temperature 20℃ was 43.449 x 10³ in inlet temperature 250℃ and particle diameter 0.75㎛. The highest particle counting for source temperature 50℃ was 43.211 x 10³ in inlet temperature 100 ℃ and particle diameter 0.75㎛. The highest particle counting for source temperature 70℃ was 41.917x10³ in inlet temperature 250℃ and particle diameter 0.75㎛. The ranges of geometric mean diameter(GMD) were 0.677-1.009㎛ in source temperature 20℃, 0.716-0.963㎛ in source temperature 50℃, and 0.724-0.957㎛ in source temperature 70℃. The smallest GMD was 0.677㎛ in source temperature 20℃ and inlet temperature 20℃. and the largest GMD was 1.009㎛ in source temperature 20℃ and inlet temperature 20℃. The ranges of geometric standard deviation(GSD) were 1.635-2.101 in source temperature 20℃. 1.676-2.073 in source temperature 50℃, and 1.687-2.051 in source temperature 70℃. The lowest GSD was 1.635 in source temperature 20℃ and inlet temperature 20℃, and the highest GSD was 2.101 in source temperature 20℃ and inlet temperature 200℃. Aerosol generated for cadmium inhalation toxicology study was polydisperse aerosol. The ranges of mass median diameter(MMD) were 1.399-5.270㎛ in source temperature 20℃. 1.593-4.742㎛ in source temperature 50℃, and 1.644-4.504㎛ in source temperature 70℃. The smallest MMD was 1.399㎛ in source temperature 20℃ and inlet temperature 20℃, and the largest MMD was 5.270㎛ in source temperature 20℃ and inlet temperature 200℃. Increasing trends for GMD, GSD, and MMD were observed with same source temperature and increase of inlet temperature. MMD for inhalation toxicology testing in EPA guidance is less than 4㎛. In our results. inlet temperature 20 and 50℃ in source temperature 20℃, and inlet temperature 20 to 150℃ in source temperature 50 and 70℃ were conformed to the EPA guidance. MMD for inhalation toxicology testing in OECD and EU is less than 3㎛. In our results, inlet temperature 20 and 50℃ in source temperature 20, 50, and 70℃ were conformed to the OECD and EU guidance.

• 대한기계학회논문집B
• /
• 제22권1호
• /
• pp.61-69
• /
• 1998

Vapor Axial Deposition (VAD), one of optical fiber preform fabrication processes, is performed by deposition of submicron-size silica particles that are synthesized by combustion of raw chemical materials. In this study, flow field is assumed to be a forced uniform flow perpendicularly impinging on a rotating disk. Similarity solutions obtained in our previous study are utilized to solve the particle transport equation. The particles are approximated to be in a polydisperse state that satisfies a lognormal size distribution. A moment model is used in order to predict distributions of particle number density and size simultaneously. Deposition of the particles on the disk is examined considering convection, Brownian diffusion, thermophoresis, and coagulation with variations of the forced flow velocity and the disk rotating velocity. The deposition rate and the efficiency directly increase as the flow velocity increases, resulting from that the increase of the forced flow velocity causes thinner thermal and diffusion boundary layer thicknesses and thus causes the increase of thermophoretic drift and Brownian diffusion of the particles toward the disk. However, the increase of the disk rotating speed does not result in the direct increase of the deposition rate and the deposition efficiency. Slower flow velocity causes extension of the time scale for coagulation and thus yields larger mean particle size and its geometric standard deviation at the deposition surface. In the case of coagulation starting farther from the deposition surface, coagulation effects increases, resulting in the increase of the particle size and the decrease of the deposition rate at the surface.

• 한국정밀공학회지
• /
• 제26권8호
• /
• pp.126-131
• /
• 2009

Acetabular dysplasia is a condition defined by inadequate development of an individual's acetabulum. Individual diversity of the symptoms in this disease needs safe and accurate preoperative planning. Technologies that utilize multidimensional image information are thus important. The assessment method by Janzen et al. was suggested a coefficient method in evaluation of acetabular dysplasia. In this study, we applied it, using a three-dimensional computed tomography (3D CT) on the koreans. 19 cases of the normal hips and 4 cases of the acetabular dysplasia were investigated to evaluate the proved method; 3D CT was used to define the geometric center of the femoral head and to measure center edge angles at $10^{\circ}$ rotational increments around the acetabular rim. Mean and standard deviation in CEAs (Center Edge Angle) of normal 19 hips at $10^{\circ}$ rotational increments from anterior to posterior rim were determined, and termed as a 'normal curve'. Then this normal values were compared with the CEA data measured from 4 cases of acetabular dysplasia patiens. Quantative comparison of the CEA values between the normal cases and dysplasia cases was successfully demonstrated, and thus, we claim that this simple CT method of assessing acetabular dysplasia can be well applicable to diagnosis, quantification and surgical planning for adult acetabular dysplasia patients.

• 대한기계학회논문집A
• /
• 제29권3호
• /
• pp.455-461
• /
• 2005

This research studied robust design of composite hand for LTR (LCD glass Transfer Robot). $1^{st}$ DOE (Design of Experiment) was conducted to find out vital few Xs. 108 experiments were performed and their results were statistically analyzed. Pareto chart analysis shows that the geometric parameters (height and width of composite beam) are more important than material parameters $(E_{1},\;E_{2})$ or stacking sequence angle. Also, the stacking sequence of mid-layer is more important than that of outer-layer. The main effect plots shows that the maximum deflection of LTR hand is minimized with increasing height, width of beam and layer thickness. $2^{nd}$ DOE was conducted to obtain RSM (Response Surface Method) equation. 25 experiments were conducted. The CCD (Central Composite Design) technique with four factors was used. The coefficient of determination $(R^{2})$ for the calculated RSM equation was 0.989. Optimum design was conducted using the RSM equation. Multi-island genetic algorithm was used to optimum design. Optimum values for beam height, beam width, layer thickness and beam length were 24.9mm, 186.6mnL 0.15mm and 2402.4mm respectively. An approximate value of 0.77mm in deflection was expected to be a maximum under the optimum conditions. Six sigma robust design was conducted to find out guideline for control range of design parameter. To acquire six sigma level reliability, the standard deviation of design parameter should be con trolled within $2{\%}$ of average design value

• 한국산업보건학회지
• /
• 제4권1호
• /
• pp.81-95
• /
• 1994

This study was performed in a diatomite factory where silicosis had been found at October, 1993. The major objectives were to evaluate worker exposure to diatomaceous earth and to present engineering control methods for workplace management. Total and respirable dust of diatomaceous earth were measured. Size distribution of dust was analyzed by applying the multiple diffraction method. Also crystalline silica in respirable dust samples was analyzed qualitatively by X-ray diffraction. The suitable Local Exhaust Ventilation systems for that factory were recommended. The results were as follows. The airborne total and respirable dust concentrations by exposure groups showed approximate normal distribution. The means of total dust exposures at flour maufacturing, fire brick grinding and packaging, ceramic raws packaging processes exceeded Korean and ACGIH standards, $10mg/m^3$. The means of total and respirable dust concentrations to high exposure groups were 6.8 and 3.9 times higher than those of low expousre groups, respectively. The size distribution of diatomaceous earth dust was lognormal with a median diameter of $7.07{\mu}m$(range, $0.10-60.0{\mu}m$) and with a geometric standard deviation of 1.43. The crystalline silica in respirable dust samples was identified to quartz and cristobalite and/or tridymite. Above results suggest that engineering controls and periodic environmental and medical surveillances will be important for preventing silicosis in the diatomite factory.

• 한국통신학회논문지
• /
• 제29권4C호
• /
• pp.514-523
• /
• 2004

본 논문에서는 팬/틸트가 탑재된 스테레오 카메라를 이용한 새로운 지능형 이동표적 추적감시 시스템을 제안하고 구현하였다. 제안된 시스템은 먼저, 스테레오 카메라에서 입력된 영상으로부터 YCbCr 칼라 임계치 기법을 사용하여 표적 얼굴영역을 검출한 다음, 지능형 시각 시스템에 기반한 팬/틸트 탑재형 스테레오 카메라의 능동적인 제어를 통해 표적의 다양한 변화에 관계없이 표적의 거리정보 및 3차원적 이동 정보를 실시간적으로 검출함으로써 표적의 적응적 추적감시를 수행하게 된다. 80 프레임의 스테레오 영상을 사용한 실험 결과, 이동표적에 대한 실시간적 위치정보 검출 및 적응적 추적을 확인하였으며 특히, 팬/틸트 추적후 표적 중심좌표의 수평, 수직 표준편차가 매우 작은 값인 1.82, 1.11로 각각 유지되고, 표적의 3차원적 위치 좌표값의 오차 역시 평균 0.5% 이하로 유지됨이 분석됨으로써 이를 통한 새로운 실시간 스테레오 표적 감시추적 시스템의 구현 가능성을 제시하였다.

• Toxicological Research
• /
• 제30권3호
• /
• pp.205-210
• /
• 2014

Didecyldimethylammonium chloride (DDAC) is used for various purposes, such as a fungicide for coolants, an antiseptic for wood, and disinfectant for cleaning. Despite the increasing likelihood of DDAC inhalation, available data on its toxicity from inhalation are scarce. Therefore, this study was aimed at confirming the toxicity of DDAC after inhalation exposure for 2 wk. Male Sprague-Dawley rats were exposed to approximately $0.15mg/m^3$, $0.6mg/m^3$, and $3.6mg/m^3$ DDAC aerosols in whole-body exposure chambers. After DDAC exposure for 2 wk, effects of DDAC on body weight, blood, bronchoalveolar lavage (BAL), and the lungs were verified. The mass median aerodynamic diameter of DDAC aerosols was $1.86{\mu}m$ and the geometric standard deviation was 2.75. The concentrations of DDAC aerosols for the low, medium, and high groups were $0.15{\pm}0.15mg/m^3$, $0.58{\pm}0.40mg/m^3$, and $3.63{\pm}1.56mg/m^3$, respectively. Body weight gain was significantly influenced by DDAC exposure. In the high group, a body weight decrease of 2.6 g was observed, whereas a 25.8 g increase was observed in the normal control group after the first 3 days. The low and medium groups showed 23.3 g and 20.4 g increases, respectively, after the first 3 days. Decreases in body weight were recovered during the next 4 days. In contrast, no changes were noted in hematological and blood biochemistry parameters after DDAC exposure. Furthermore, only mild effects were observed on bronchoalveolar cell differentiation counts and cell damage parameters in the BAL fluids of the medium and high groups. Although inflammatory cell infiltration and interstitial pneumonia were partially observed, fibrosis was not found in the lungs of the medium and high groups. In conclusion, body weight gain and the lungs were mainly affected by DDAC exposure. The no-observed-adverse-effect level (NOAEL) for DDAC was determined as $0.15mg/m^3$.