• 한국연초학회지
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• 제28권1호
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• pp.58-66
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• 2006

Threshold limit value (TLV) test between expert and consumer panel was conducted about absolute, recognition and difference threshold respectively. And we tried to suggest appropriate and minimum acceptable menthol concentration level by consumer panel. Determination of threshold value was based on ASTM E 679-79 method by forced-choice ascending concentration series. In addition, a semi-ascending paired difference method was referred to conduct test. The group threshold value was determined as the value of geometric mean individual threshold. The smokers were dividend by two groups, trained and consumer panel. Trained panel was selected according to sensitivity to menthol discrimination. Consumer panel wasrecruited in proportion as population ratios including female smokers. They were all over twenty years old volunteers and summed up thirty four persons. In terms of sensor evaluation, overall difference test with seven-category scale by both trained and consumer panelists were done. On judging correct or incorrect answer, two by three cut-off levels applied to. Every test was conducted with two sessions, before smoking and during smoking period. And, only two samples served each paneI per test with regard to sensory fatigue and reliable results. All tests were replicated, and in total 32 times per panelist. In conclusion, the recognition threshold about consumer and expert panel was 358 ppm/cig. and 276 ppm/cig. in separately. Besides, absolute and difference thresholds were obtained also. And, we conduct difference threshold test with two different ways, upward and downward. And, The results of each method were 246, 195 ppm/cig., 1414, 1336 ppm/cig. and 1047, 972 ppm/cig.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.197-200
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• 2008

In most sensor networks, nodes can be easily compromised by adversaries due to hostile environments. Adversaries may use compromised nodes to inject false reports into the sensor networks. Such false report attacks will cause false alarms that can waste real-world response effort, and draining the finite amount of energy resource in the battery-powered network. A dynamic enroute scheme proposed by Yu and Guan can detect and drop such false reports during the forwarding phase. In this scheme, choosing a threshold value is very important, as it trades off between security power and energy consumption. In this paper, we propose a threshold determining method which uses the fuzzy rule-based system. The base station periodically determines a threshold value though the fuzzy rule-based system. The number of cluster nodes, the value of the key dissemination limit, and the remaining energy of nodes are used to determine the threshold value.

• 한국산업보건학회지
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• 제9권2호
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• pp.145-157
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• 1999

Wood dust is created when machines are used to cut or shape wood materials. Industries of high risk of wood dust exposure are sawmills, dimension mills, furniture industries, and carpenters, etc. Health effects associated with wood dust exposure includes dermatitis, allergic respiratory effects and cancer. Health effects of wood dus t are mainly depend on the concentration, dust size and exposure time. This study were carried out to evaluate the concentration and particle size distribution of wood dust during working processes. The subjects of this study were 53 workers exposed to wood dust in 7 furniture factories and 5 musical instruments, and 5 sawmill factories. The average total wood dust concentrations measured by personal cascade impactor were $1.82{\pm}2.31mg/m^3$ in primary manufacture, $3.59{\pm}1.72mg/m^3$ in s econdary manufacture, $5.09{\pm}1.46mg/m^3$ in sanding operation. Mass median diameters of hardwoods dust were $3.36{\mu}m$ in primary manufacture, $4.25{\mu}m$ in secondary manufacture, $4.21{\mu}m$ in sanding operation. softwoods dust were $3.39{\mu}m$ in primary manufacture, $4.34{\mu}m$ in secondary manufacture. Particle size distributions showed a nearly the same pattern in each working processes. The sample concentration of all hardwood dust exceeded the Threshold Limit Value(TLV) and 20.8% of the softwood dust exceeded the Threshold Limit Value. The range of size distribution were $0.5-10{\mu}m$ in the soft and hardwood dust. The respirable dust of soft and hardwood took up 59% and above. Therefore new threshold limit value for wood dust should be needed in Korea. Also, it should be done for various studies on health effects related to occupational exposure of wood dust.

• Structural Engineering and Mechanics
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• 제74권1호
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• pp.55-67
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• 2020

The common practice to predict the characteristic structural load effects (LEs) in long reference periods is to employ the extreme value theory (EVT) for building limit distributions. However, most applications ignore that LEs are driven by multiple loading events and thus do not have the identical distribution, a prerequisite for EVT. In this study, we propose the composite extreme value modeling approach using clustering to (a) cluster initial blended samples into finite identical distributed subsamples using the finite mixture model, expectation-maximization algorithm, and the Akaike information criterion; (b) combine limit distributions of subsamples into a composite prediction equation using the generalized Pareto distribution based on a joint threshold. The proposed approach was validated both through numerical examples with known solutions and engineering applications of bridge traffic LEs on a long-span bridge. The results indicate that a joint threshold largely benefits the composite extreme value modeling, many appropriate tail approaching models can be used, and the equation form is simply the sum of the weighted models. In numerical examples, the proposed approach using clustering generated accurate extrema prediction of any reference period compared with the known solutions, whereas the common practice of employing EVT without clustering on the mixture data showed large deviations. Real-world bridge traffic LEs are driven by multi-events and present multipeak distributions, and the proposed approach is more capable of capturing the tendency of tailed LEs than the conventional approach. The proposed approach is expected to have wide applications to general problems such as samples that are driven by multiple events and that do not have the identical distribution.

• 한국위성정보통신학회논문지
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• 제12권3호
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• pp.35-40
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• 2017

위성의 상태를 파악하기 위해 기존에는 OOL(Out-Of-Limit) 방식을 많이 사용하여 왔다. OOL은 특정 텔레메트리의 상위, 하위 문턱 값을 지정하여 해당 값을 벗어날 경우 문제가 발생한 것으로 인식 하는 방식이다. 이 방법은 파라미터의 특성을 파악하여 각각의 문턱 값을 정확히 설정해야 하는 전문 지식과 노력이 필요하고 텔레메트리 값이 문턱값 내에서 비정상적으로 변할 경우는 검출할 수 없다는 문제점이 있다. 이러한 문제를 극복하기 위해 본 논문에서는 위성이 정상 상태일 때 텔레메트리의 통계적 특징 중 러프집합을 이용하여 중요한 것을 선택, 적용하여 퍼지 모델을 구축하고 이상 상태를 구분하는 시스템을 제안한다. 정상 상태의 데이터만 이용하여 모델을 구축하기 때문에 출력값을 비교 하여 사전에 정의되지 않은 비정상 상태의 구분이 가능 하며 다양한 통계 값을 이용하기 때문에 전문 지식 필요 없이 문턱값 내에서 비정상적으로 변하는 텔레메트리를 검출할 수 있다. 제안한 시스템의 동작 확인을 위해 실제 저궤도 관측위성의 배터리 온도 텔레메트리를 적용하여 시험을 수행 하였고 비정규적 운영 상태에 대한 검출이 성공적으로 이루어 졌다.

• 대한산업공학회지
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• 제30권2호
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• pp.84-92
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• 2004

A process control procedure is proposed when 100% inspection is performed in a process with excellent capability. Only the incomplete measurement data is assumed to be available, i.e. the specific measurement value of the quality characteristic is not available for each item but it can be determined to be smaller or larger than any prescribed value. In the suggested model, a signal limit is introduced to determine whether the process under study is in control or not. If the quality characteristic of an incoming item exceeds the upper signal or the lower signal limit, the process is determined to be stopped or not by comparing the number of consecutively accepted items with a predetermined threshold number. The procedure is designed based on the type I and II errors. The performance of the model is evaluated by the expected number of items produced under the in-control and out-of-control states until the process is stopped.

• 한국기계가공학회지
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• 제11권4호
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• pp.160-167
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• 2012

This paper is concerned with a particular fracture mechanics parameter ${\Delta}K_{th}$, known as the 'threshold stress intensity range', or 'fatigue threshold'. This threshold ${\Delta}K_{th}$ constitutes, as it were, a hinge between the notion of crack initiation and the notion of crack growth. It has often been thought that, like the endurance limit, it could be an intrinsic criterion of the material. The study was conducted on a SA-508 pressure vessel steel used in the nuclear power industry. This material exhibits a typical threshold effect in the range of the crack growth rates which were determined; that is, below approximately $da/dN=10^{-6}mm/cycle$, the slope of the da./dN versus ${\Delta}K$ curve is almost vertical. The value of ${\Delta}K_{th}$ was determined at a growth rate of $10^{-7}$ mm/cycle according to the ASTM Standard for threshold testing. The fatigue threshold values are in the range 21 $kg/mm^{3/2}$ to 12 $kg/mm^{3/2}$ depending on the stress ratio effect.

• 한국산업보건학회지
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• 제3권1호
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• pp.91-98
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• 1993

This study was carried out to investigate characteristic of vinyl chloride emissioned from poly vinyl chloride extrusion process and to evaluate the efficiency of local exhaust ventilation system. Before local ventilation facility was constructed in poly vinyl chloride extrusion process, the average worker exposure to vinyl chloride was 3.15 ppm, which exceeded Threshold Limit Value of American Conference of Gorvernmental Industrial Hygienists (ACGIH-TLV), 1 ppm. lt is possible that vinyl chloride residues in the poly vinyl chloride resin was released or degased due to extrusion heat. The larger the width of vinyl tube become, the higher worker exposure to vinyl chloride was. It is estimated that vinyl chloride from vinyl chloride resin increased as amount of poly vinyl chloride resin extruded in the extrusion process increased. Canopy hood was an appropriate type for poly vinyl chloride resin extrusion process. This local exhaust ventilation has fan static pressure of 7.65 inch wg($190mmH_2O$, total volumetric flowlate of 4,796 CFM ($135.8m^3$/min) and fan power requirement of 12 hp (8.952 Kw). After this local exhaust ventilation was constructed there, the average concentration of worker exposure to vinyl chloride was reduced to be 0.46 ppm, which was below the Threshold Limit Value, 1 ppm. Also, the removal efficiency rate of vinyl chloride attained by local exhaust ventilation was 85.3%. It was a statistically significant (p<0.01).

• Safety and Health at Work
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• 제7권2호
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• pp.150-155
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• 2016

Background: Shipbuilding involves intensive welding activities, and welders are exposed to a variety of metal fumes, including manganese, that may be associated with neurological impairments. This study aimed to characterize total and size-fractionated manganese exposure resulting from welding operations in shipbuilding work areas. Methods: In this study, we characterized manganese-containing particulates with an emphasis on total mass (n = 86, closed-face 37-mm cassette samplers) and particle size-selective mass concentrations (n = 86, 8-stage cascade impactor samplers), particle size distributions, and a comparison of exposure levels determined using personal cassette and impactor samplers. Results: Our results suggest that 67.4% of all samples were above the current American Conference of Governmental Industrial Hygienists manganese threshold limit value of $100{\mu}g/m^3$ as inhalable mass. Furthermore, most of the particles containing manganese in the welding process were of the size of respirable particulates, and 90.7% of all samples exceeded the American Conference of Governmental Industrial Hygienists threshold limit value of $20{\mu}g/m^3$ for respirable manganese. Conclusion: The concentrations measured with the two sampler types (cassette: total mass; impactor: inhalable mass) were significantly correlated (r = 0.964, p < 0.001), but the total concentration obtained using cassette samplers was lower than the inhalable concentration of impactor samplers.

• Journal of Advanced Marine Engineering and Technology
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• 제31권4호
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• pp.385-393
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• 2007

The strength evaluation of the most weakest junction part is required for the safety design of all structures. Most of all. in order to enhance the reliability and safety of the welding part. whose use is the highest, it is very important to establish the efficient structure manufacturing technology by studying and investigating the evaluation of fatigue strength in various environments. This study analyzed the relations of da/dN, and th according to the welding methods of SMAW, FCAW, and SAW. In the stage II. the value of stress intensity factor range was the highest in SMAW welding method of stress ration R=0.1, and appeared under the sequence of FCAW and SAW and as the completion section of stress intensity factor was low, threshold stress intensity factor was lowly formed in da/dN - The fatigue life of each welding method is sensitively worked in high stress ratio. judging from the fact that the width of life reduction increases in the high stress ratio zone compared to the width of life reduction in the low stress ratio zone. In the fatigue limit of welding methods before corrosion. the welding of SMAW and FCAW shows the same fatigue limit compared to Base metal, and SAW holds the lowest fatigue limit value.