• Geomechanics and Engineering
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• 제21권1호
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• pp.23-33
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• 2020

An advancing cutting roof for gob-side entry retaining with no-pillar mining under specific geological conditions is more conducive to the safe and efficient production in a coalmine. This method is being promoted for use in a large number of coalmines because it has many advantages compared to the retaining method with an artificial filling wall as the gateway side filling body. In order to observe the inner structure of the gateway cutting roof and understand its stability mechanism, an equivalent material simulation experiment for a coalmine with complex geological conditions was carried out in this study. The results show that a "self-stabilization bearing structure" equilibrium model was found after the cutting roof caving when the cut line deviation angle was unequal to zero and the cut height was greater than the mining height, and the caving roof rock was hard without damage. The model showed that its stability was mainly controlled by two key blocks. Furthermore, in order to determine the optimal parameters of the cut height and the cut line deviation angle for the cutting roof of the retaining gateway, an in-depth analysis with theoretical mechanics and mine rock mechanics of the model was performed, and the relationship between the roof balance control force and the cut height and cut line deviation angle was solved. It was found that the selection of the values of the cut height and the cut line deviation angle had to conform to a certain principle that it should not only utilize the support force provided by the coal wall and the contact surface of the two key blocks but also prevent the failure of the coal wall and the contact surface.

• 대한족부족관절학회지
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• 제11권1호
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• pp.8-12
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• 2007

Purpose: The purpose of this study was to investigate the differences in simple radiographic parameters and results of 3-D scan among normal and patient groups. Materials and Methods: Seventy subjects in each group were studied. Control group consisted of subjects without plantar foot pain (normal group), and two patient groups were one with plantar forefoot pain (metatarsalgia group), the other with plantar heel pain (heel pain group). Simple radiographic parameters were obtained and 3-D scan was done with foot scanner (Nexscan, K&I, Korea) and The height and volumn of the space under the medial longitudinal arch was analyzed (Enfoot, K&I, Korea). These parameters were compared and correlation between radiological parameters and results of the 3-D scan were studied. Results: The results of all parameters istributed normally. There was no signigicant differences among the groups in radiological parameters (talo-first metatarsal angle, calcaneal pitch angle and height of the talar head in standing lateral radiograph) and arch height and arch volumn on 3-D scan. There were statistically significant correlations between radiological and 3-D scan results. Conclusion: This study revealed that there is no significant differences in medial longitudinal arch height and volumn among normal and different patient groups and there are variety of arch height in patients with similar symptoms.

• 대한산업공학회지
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• 제32권3호
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• pp.236-241
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• 2006

Monitor height is one of the key factors in the VDT workstation design. Most of the previous studies have focused on traditional VDT workplace where the operators performed data entry or word processing tasks using single monitor. This study aimed to suggest proper monitor height when the main task was monitoring information from different number of information sources. Twelve male students participated in three experiments: single information source (one monitor), two information sources (one monitor and one CCTV), and three information sources (one monitor, one CCTV and a window). Subjects performed monitoring tasks for 10 minutes with 3 different monitor center heights : 89.0 cm (Low), 111.3 cm (Middle), and 124.8 cm (High). Surface EMG signals of five neck muscles, subjective discomfort ratings, preference, and working postures were recorded. Results indicated that the middle height was proper for one monitor condition, but the low monitor height was recommended for more than two information sources.

• 한국측량학회지
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• 제36권1호
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• pp.1-8
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• 2018

To compensate for the shortcomings of spirit leveling, research on the determination of GNSS (Global Navigation Satellite System)-derived orthometric height has been actively carried out. However, most analyses were primarily performed inland. In this study, the influences of the arrangement of control points, observation duration, and geoid model on the accuracy of the GNSS-derived orthometric height have been analyzed to suggest the proper method to apply the determination of GNSS-derived orthometric height to the leveling loop disconnected area. As a result, it was found that two known points located near the unknown points need to be fixed in the leveling loop disconnected area. Further, 3 cm level of accuracy can be achieved if the GNSS survey is performed over two days, for four hours per day. In terms of the geoid model, the latest national geoid model should be applied rather than the EGM08 (Earth Gravitational Model 2008) to minimize regional bias and increase accuracy. Future research is necessary to apply the determination of the GNSS-derived orthometric height technique as a method to connect with the islands because the vertical reference system used inland and that used for the islands in Korea are still different.

• 한국대기환경학회지
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• 제13권4호
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• pp.249-256
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• 1997

To identify the long-term influence of acid rain treatment on tree growth, acid rain of various composition (pH 2.0, pH 4.0 and pH 5.6 as control) was applied to several landscape trees for five months (April through August, 1991). Tree height, pH values and $Al^{3+}$ concentration in soil were investigated. Acid rain treatments seemed to promote height growth in the first year (1991), but have become an inhibiting factor over five years. All of coniferous species and most broad-leaved species, except Acer ginnala, showed opposite trends in height responses to acid rain treatments between the first (1991) and last (1996) year. In contrast, Acer ginnala showed similar trends to acid rain treatments in the height growth between 1991 and 1996. This result suggested that Acer ginnala has a characteristic adapability to acid rain stress. pH values of surface soil were lower than those of 30 cm soil depth. This fact suggested that acid rain treatments made surface soil acidic condition. In addition, physiological characteristics (photosynthesis, stomatal condition and biomass) have to be investigated to identify the relationship between long-term effects of $AL^{3+}$ concentration and growth.

• 한국산학기술학회논문지
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• 제19권5호
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• pp.1-8
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• 2018

본 연구는 Siphon Breaker Simulation Program(SBSP)을 이용하여 소규모 사이펀 차단기 실험장치를 설계 및 제작하고, 실험 수행 후 그 결과를 이용하여 다양한 규모의 사이펀 차단기에 대한 SBSP의 적용 가능성을 평가하기 위해 진행되었다. 실험장치 설계를 위하여 C factor와 Chisholm B 계수, Undershooting Height(UH)에 대한 시뮬레이션 결과값을 SBSP로 도출하였다. 실험장치의 중요파트는 upper tank, lower tank, downcomer, Siphon Breaker Line(SBL) 등이며, upper tank는 넓이 $0.09-m^2$, 높이 0.65-m의 크기로 제작되었고, downcomer 높이는 1.6-m로 제작되었다. 실험결과 분석을 위하여 압력계, 차압계, 전자저울이 사용되어 압력과 차압, 유량에 대한 정보를 도출하였다. 실험에서 사용된 실험변수는 Loss Of Coolant Accident(LOCA) 크기와 SBL 크기이며, LOCA는 30-mm와 38-mm에 대해서, SBL은 6/16-inch와 8/16-inch에 대해서 실험이 진행되었다. 실험의 결과로 유량과 압력, 그리고 UH를 도출하였으며, 실험결과를 SBSP의 시뮬레이션 결과와 비교, 분석하였다. UH 측면에서 SBSP가 수조의 총 높이 대비 2.5 %의 오차로 실험결과를 잘 예측하는 것을 관찰하였다. 그러므로 SBSP를 이용한 다양한 규모의 사이펀 차단기 설계가 가능한 것을 확인하였다.

• 한국환경농학회지
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• 제27권1호
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• pp.10-17
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• 2008

The objective of this study was to estimate the pollutant loads from paddy fields by cultivation practices using a non-point-sources models. One of them is CREAMS-PADDY model that was developed considering the water balance and mass balance of paddy fields. The CREAMS-PADDY model was applied to provide basic data to reduce runoff loadings under various scenarios such as various water management control and various fertilizer condition. The model was verified against T-N, T-P and runoff flow data collected during cropping periods at 2000. The model results agreed well with the measured data in verification. The results showed that the model could be used for estimating the runoff loadings from irrigated paddy fields by cultivation practices was possible. Comparison of simulated the standard height and the sluice management of T-N and T-P runoff loadings from paddy fields were +32.4%, +10.3% in 10 mm below the standard height, -29.2%, -35.9% in 20 mm above the standard height, 52.6%, 59.0% in 40 mm above the standard height, respectively. Comparison of simulated the standard fertilizer and the fertilizer control of T-N and T-P runoff loadings from paddy fields were -1.3%, -21.7%in reduction of conventional fertilizer 30%, -1.0%, -12.5% in reduction of standard fertilizer 30%, respectively. Therefore, reducing nonpoint-sources nutrient loading by reducing fertilization may not work well in the range of normal paddy rice farming practices, and instead it could be achieved by reducing surface drainage outflow.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.275-276
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• 2002

Active-head sliders with a unimorph piezoelectric actuator for flying height control were experimentally evaluated. It was found that the normalized stroke of the actuator is 5.2 to 6 nm/V/mm without flying over the disk. However, the normalized adjustment range of flying height is about 1.6 nm/V/mm when the active-head slider is flying over the disk. This value is smaller than the measured value when the slider is not flying, because of the air pressure generated at the active pad when the pad approaches the disk surface.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2012년도 추계 학술논문 발표대회
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• pp.165-166
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• 2012

A thermal stresses by heat of hydration was analyzed according to a change of a pour height in reactor containment building. In case of more than 3.6m pouring height a crack index by heat of hydration analysis resulted in less than 1 because there is not a construction joint of vertical direction and for a self-restraint effect of circumferential section shape. Therefore detailed consideration on a mixture proportion of binder type, quantity in concrete and selection of a form in seasonal air temperature is needed for a control of tensile stress by heat of hydration.

• 설비공학논문집
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• 제15권2호
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• pp.116-125
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• 2003

The new HVAC system to lower the conveyance energy and building height using IAV (Increasing Air Volume) technique is developed. IAV units which are equipped in each zone carry out air-conditioning and supply fresh air by induction of outdoor air in main duct. The design program which decides size of OAHU and IAV unit according to air conditioning load and fresh air demand of each zone is presented. The control system is developed to operate efficiently HVAC system and IAV unit, so that individual zone operation and well-deal with partial load and IAQ problem are possible. The new system is investigated in model building and makes more profit in conveyance energy, size of air conditioning facilities room and building height than VAV system. But in construction cost it is worse by about 15 per-centage.