• 한국지반공학회논문집
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• 제21권9호
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• pp.53-64
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• 2005

지반설계에 있어 지반거동은 일반적으로 단순화된 선형탄성이나 완전소성으로 간주되어 적용되고 있으나, 비선형 응력-변형률 거동, 응력이력 및 함수비 등의 현장 지반조건 또한 정밀한 지반설계를 위해서는 적절히 반영되어야 한다. 본 연구에서는 삼축압축시험과 공진주시험을 포함한 일련의 실내시험을 통하여 실트함유량, 상대밀도, 응력상태등 다양한 지반조건과 과압밀비 및 함수비의 변화와 같은 현장 지반조건을 고려하여 사질토의 강도 및 강성도 특성을 분석하였다. 그 결과 최대전단강도 및 초기전단탄성계수에 대한 과압밀의 영향은 미소하게 나타났으나, 초기 미소변형률 이후부터 파괴까지의 비선형 탄성구간에서는 과압밀의 영향이 무시할 수 없는 영향인자임을 확인할 수 있었다. 함수비의 경우 구속압과 상대밀도가 낮은 경우 함수비가 증가함에 따라 초기전단탄성계수는 세립분 증가와 함께 감소하였으며, 구속압이 증가할수록 함수비의 영향은 감소하였다.

• Bulletin of the Korean Chemical Society
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• 제31권1호
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• pp.47-51
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• 2010

A powder, containing 80 percent of blue cobalt aluminate $(CoAl_2O_4)$ crystallites, was synthesized at $210 ^{\circ}C$ using a (metal nitrate-malonic acid-ammonium hydroxide-ammonium nitrate) system. The optimal amount of concentrated ammonia water and initial decomposition temperature were determined for the blue $CoAl_2O_4$ crystallites preparation. Three $CoAl_2O_4$ precursor pastes, corresponding to the various amounts of concentrated ammonia water, were prepared by evaporating the initial solutions in an electric furnace fixed at $80 ^{\circ}C$ under a vacuum of 25 torr. The initial solution was used to dissolve the starting materials. The powder with the maximum content (80%) of blue $CoAl_2O_4$ crystallites was prepared when the prepared precursor was decomposed at $210 ^{\circ}C$. The blue $CoAl_2O_4$ crystallite content in the prepared sample decreased with increasing initial decomposition temperature. For 0.2 mole of the $Al^{3+}$ ion, the chemical compositions of the precursor corresponded to molar ratios of 0.4, 1.40, 2.56 and 2.00 for the $Co^{2+}$ ion, malonic acid, ammonia and ammonium nitrate per mole of the $Al^{3+}$ ion, respectively. The blue $CoAl_2O_4$ crystallite content in the sample decreased with the amount of ammonia deviated from the optimal value. The characteristics of the powders were examined using X-ray diffraction, optical microscopy, Fourier transformation infrared spectroscopy and the Brunauer-Emmett-Teller technique.

• 한국자동차공학회논문집
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• 제8권2호
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• pp.19-26
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• 2000

This paper presents the effects of initial pressure of mixture on CO, $CO_2$ and NOx emissions in constant volume combustion chamber. The CO, $CO_2,O_2,N_2$ concentrations in the chamber are determined by thermal conductivity detection (Gas-chromatograph) wile the NOx concentration is measured by chemiluminescent detection (NOx Analyser). Methane-air mixture is used as premixed fuel and the measurements are taken with equivalence ratios($\phi$) varing from 0.6 to 1.3, and initial pressures of methane-air mixture varing from 0.1MPa to 0.8MPa in constant volume combustion chamber. The NOx concentration steadily increases with increasing equivalence ratio, peaks in lean flame ($\phi$=0.85~0.9), and then rapidly decreases. However, as the initial pressure of mixture is increased, the equivalence ratio corresponding to the point of peak [NOx] shifts towards leaner conditions. This is caused by a similar shift in the peak [CH], which is caused by the variation with pressure and equivalence ratio of the rate of CH production from $CH_2$ and OH. The maximum combustion pressure peaks at $\phi$ =1.05 and the $CO_2$ concentration peaks at $\phi$=0.95~1.0 while the CO concentration rises sharply at the condition of fuel-rich mixtures. This is caused by complete combustion at $\phi$=0.95.

• 한국광물학회:학술대회논문집
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• 한국광물학회.한국암석학회 2001년도 공동학술발표회 논문집
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• pp.95-95
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• 2001

The Yeongdong basin is one of the pull-apart basins in the southwestern part of the Korean Peninsula that has developed during Cretaceous sinistal fault movement. The bimodal igneous activities (basalts and rhyolites) in the basin appear to be closely associated with the basin development. Here, we discuss the origin of the igneous rocks using chemical and radiogenic isotope data. Basaltic (48.4-52.7 wt% SiO$_2$) and rhyolitic (70.3-70.8 wt% SiO$_2$) rocks are slightly alkalic in a total alkali-silica diagram. The rhyolitic rocks with have unusually high K$_2$O contents (5.2-6.0 wt%). The basaltic rocks show an overall pattern of within-plate basalt in a MORB-normalized spider diagram, but have distinct negative anomaly of Nb, which indicates a significant amount of crustal component in the magma. The basaltic rocks plot within the calc-alkaline basalt field in the Hf/3-Th-Ta and Y/l5-La/10-Nb/8 discrimination diagrams. The eNd(T) values of the basaltic rocks (-13.6 to 14.3) are slightly higher than those of the rhyolitic rocks (-14.1 to 15.2), and the initial Sr isotopic ratios of the former (0.7085-0.7093) are much lower than those of the latter (0.7140-0.7149). However, the initial Nd and Sr isotope ratios of the igneous rocks in the Yeongdong basin are similar to those of the nearby Cretaceous igneous rocks in the Okcheon belt. The Pb isotope ratios plot within the field of Mesozoic granitoids outside of the Gyeongsang basin in Pb-Pb correlation diagrams. Since a basaltic magma requires the mantle source, the enriched isotopic signatures and negative Nb anomaly of the basaltic rocks suggest two possibilities for their origin: enriched mantle lithospheric source, or depleted mantle source with significant amount of crustal contamination. However, we prefer the first possibility since it would be difficult for a basaltic magma to maintain its bulk composition when it is significantly contaminated with granitic crustal material. The slightly more enriched isotopic signatures of rhyolitic rocks also suggest two possibilities: differentiate of the basaltlc magma with some crustal contamination, or direct partial melting of the lower crust. Much larger exposed volume of the rhyolitic rocks, compared with the basaltic rocks, indicates the latter possibility more favorable.

• Asian-Australasian Journal of Animal Sciences
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• 제27권8호
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• pp.1124-1130
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• 2014

The objective of this study was to determine the responses in the digestibility of dry matter (DM) and amino acid (AA) composition of ileal endogenous flow (IEF) of pigs (initial body weight, $69.1{\pm}6.46$ kg) fed N-free diets (NFD) formulated with different ratios of corn starch to dextrose. Fifteen pigs fitted with a T-cannula at the distal ileum were fed 5 diets according to a triplicated $5{\times}2$ incomplete Latin-square design. Each period consisted of a 5-d adjustment period and 2 d of ileal digesta collection for 12 h on each of d 6 and 7 and between each period, there was a 5-d recovery period to avoid abnormal weight loss. The ratios of corn starch to dextrose investigated were 0:879, 293:586, 586:293, 779:100, and 879:0 for diet numbers 1, 2, 3, 4 and 5, respectively, and chromic oxide (5 g/kg) was used as an indigestible index. Ileal DM digestibility was greater in Diet 1 than that in Diet 4 (89.5% vs 87.3%, p<0.01) but they were not different from Diet 2, 3, or 5. The IEF for most of indispensable AA were not different among diets with the exception of Met, in which a lack of corn starch or dextrose gave lower (p = 0.028) IEF of Met than diets containing corn starch and dextrose. Likewise, the dispensable AA and total AA in the IEF did not differ among diets. The respective IEF of AA (mg/kg of dry matter intake) in pigs fed Diets 1, 2, 3, 4, or 5 were 301, 434, 377, 477,or 365 for Lys, 61, 89, 71, 87, or 61 for Met, and 477, 590, 472, 520, or 436 for Thr. Proline was the most abundant AA in the IEF followed by Gly, Glu, and Asp and together accounted for approximately 50% of the total ileal AA flows of pigs fed NFD. In conclusion, the variation in proportion of corn starch and dextrose in a NFD does not largely affect estimates of IEF of N and AA for growing-finishing pigs.

• 한국환경과학회지
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• 제27권10호
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• pp.809-820
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• 2018

DeNOx experiments for the effects of hydrocarbon additives on diesel SNCR process were conducted under oxidizing diesel exhaust conditions. A diesel-fueled combustion system was set up to simulate the actual cylinder and head, exhaust pipe and combustion products, where the reducing agent $NH_3$ and $C_2H_6/diesel$ fuel additives were separately or simultaneously injected into the exhaust pipe, used as the SNCR flow reactor. A wide range of air/fuel ratios (A/F=20~40) were maintained, based on engine speeds where an initial NOx level was 530 ppm and the molar ratios (${\beta}=NH_3/NOx$) ranged between 1.0~2.0, together with adjusting the amounts of hydrocarbon additives. Temperature windows were normally formed in the range of 1200~1350K, which were shifted downwards by 50~100K with injecting $C_2H_6/diesel$ fuel additives. About 50~68% NOx reduction was possible with the above molar ratios (${\beta}$) at the optimum flow #1 ($T_{in}=1260K$). Injecting a small amount of $C_2H_6$ or diesel fuel (${\gamma}=hydrocarbon/NOx$) gave the promising results, particularly in the lower exhaust temperatures, by contributing to the sufficient production of active radicals ($OH/O/HO_2/H$) for NOx reduction. Unfortunately, the addition of hydrocarbons increased the concentrations of byproducts such as CO, UHC, $N_2O$ and $NO_2$, and their emission levels are discussed. Among them, Injecting diesel fuel together with the primary reductant seems to be more encouraging for practical reason and could be suggested as an alternative SNCR DeNOx strategy under diesel exhaust systems, following further optimization of chemicals used for lower emission levels of byproducts.

• Smart Structures and Systems
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• 제20권2호
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• pp.127-137
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• 2017

Identification of damping characteristics is of significant importance for dynamic response analysis and condition assessment of structural systems. Damping is associated with the behavior of the energy dissipation mechanism. Identification of damping ratios based on the sensitivity of dynamic responses and the model updating technique is investigated with numerical and experimental investigations. The effectiveness and performance of using the sensitivity-based model updating method and vibration monitoring data for damping ratios identification are investigated. Numerical studies on a three-dimensional truss bridge model are conducted to verify the effectiveness of the proposed approach. Measurement noise effect and the initial finite element modelling errors are considered. The results demonstrate that the damping ratio identification with the proposed approach is not sensitive to the noise effect but could be affected significantly by the modelling errors. Experimental studies on a steel planar frame structure are conducted. The robustness and performance of the proposed damping identification approach are investigated with real measured vibration data. The results demonstrate that the proposed approach has a decent and reliable performance to identify the damping ratios.

• Advances in materials Research
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• 제7권1호
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• pp.45-72
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• 2018

In the present study, a special attention has been paid to the effects regarding the use of different superplasticizers in different dosages. To do so, 36 mixes of normal and self-compacting concrete with two water/binder ratios of 0.35 and 0.45, four different types of superplasticizer including melamine-formaldehyde, naphthalene-formaldehyde, carboxylic-ether and poly-carboxylate, four different superplasticizer/cement ratios of 0.4%, 0.8%, 1.2% and 1.6% and two silica fume/cement ratios of 0% and 10% have been cast. Moreover, the initial and final setting time of the pastes have been tested. For self-compacting mixes, flow time, slump flow, V-funnel, J-ring and L-box tests have been carried out as well as testing the compressive strength and rupture modulus. For normal concrete mixes,slump test has been conducted to assess the workability of the mix and then for each mix, the compressive strength and rupture modulus have been determined. The results indicate that in addition to the important role of superplasticizer type and dosage on fresh state properties of concrete, these parameters as well as the use of silica fume could affect the hardened state properties of the mixes. For instance, the mixes whose superplasticizer were poly-carboxylic-ether based showed better compressive and tensile strength than other mixes. Besides, the air contents showed robust dependency to the type of the superplasticizer. However, the use of silica fume decreased the air contents of the mixes.

• 산업공학
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• 제23권4호
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• pp.311-318
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• 2010

In the daily multi-reservoir operating problem, monthly storage targets can be used as principal operational guidelines. In this study, we tested the use of a simple back-propagation Artificial Neural Network (ANN) model to derive monthly storage guideline for daily Coordinated Multi-reservoir Operating Model (CoMOM) of the Han-River basin. This approach is based on the belief that the optimum solution of the daily CoMOM has a good performance, and the ANN model trained with the results of daily CoMOM would produce effective monthly operating guidelines. The optimum results of daily CoMOM is used as the training set for the back-propagation ANN model, which is designed to derive monthly reservoir storage targets in the basin. For the input patterns of the ANN model, we adopted the ratios of initial storage of each dam to the storage of Paldang dam, ratios of monthly expected inflow of each dam to the total inflow of the whole basin, ratios of monthly demand at each dam to the total demand of the whole basin, ratio of total storage of the whole basin to the active storage of Paldang dam, and the ratio of total inflow of the whole basin to the active storage of the whole basin. And the output pattern of ANN model is the optimal final storages that are generated by the daily CoMOM. Then, we analyzed the performance of the ANN model by using a real-time simulation procedure for the multi-reservoir system of the Han-river basin, assuming that historical inflows from October 1st, 2004 to June 30th, 2007 (except July, August, September) were occurred. The simulation results showed that by utilizing the monthly storage target provided by the ANN model, we could reduce the spillages, increase hydropower generation, and secure more water at the end of the planning horizon compared to the historical records.

• 대한토목학회논문집
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• 제28권5A호
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• pp.737-746
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• 2008

최근 들어 비파괴기술이 발달함에 따라, 콘크리트 구조물의 건전성 평가에 전자기 특성을 이용한 평가기법이 적용되고 있다. 시멘트 건설재료와 같은 절연성 재료는 고유한 유전상수 또는 전도율을 가지므로 특성화될 수 있는데, 이러한 전자기 특성은 물-시멘트비, 단위 시멘트 량과 같은 배합조건에 따라 변화하게 된다. 실내조건에 노출된 시멘트 모르타르는 일반적으로 수분에 포화되지 않으므로, 공극률이 전자기특성에 큰 영향을 미치는데, 이러한 공극률은 주로 초기재령에서 결정되어지며, 양생조건에 따라 매우 민감하게 변화한다. 본 연구에서는 4가지 종류의 물-시멘트비를 가진 시멘트 모르타르를 대상으로, 전자기 특성(유전상수, 전도율)을 광범위 대역인 0.2 GHz~20 GHz 범위에서 측정하였다. 각 시편은 배합 후 0일에서 28일까지 총 5가지의 다른 수중양생기간을 가지도록 하였으며, 28일 이후, 실내노출상태에서 전자기 특성을 측정하였다. 한편 28일 재령시, 수은압입법을 통하여 공극률을 분석하였으며, 실내상태의 수분손실을 측정하여 포화도를 평가하였다. 양생초기부터 변화하는 공극률을 평가하기 위해, 초기재령 콘크리트의 거동 평가 프로그램을 이용하여 시멘트 모르타르의 공극률 변화를 분석하였으며, 측정된 전자기 특성의 변화를 분석하였다. 전자기 특성을 영향인자(재령, 물-시멘트비)와 쉽게 비교하기 위해서, 5 GHz~20 GHz 영역의 값을 하나의 평균값으로 도출하였다. 초기재령에서 평균화된 유전상수와 전도율은 물-시멘트비의 감소에 따라서 선형으로 증가하였으며, 4주의 양생기간동안 물-시멘트비에 관계없이 양생기간의 제곱근에 비례하여 증가하였다.