• Geomechanics and Engineering
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• 제25권4호
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• pp.283-294
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• 2021

This paper presents a rigorous solution for spherical cavity expansion in unsaturated soils under constant suction condition. The hydraulic behavior that describes the saturation-suction relationship is modeled by a void ratio-dependent soil-water characteristic curve, which allows the hydraulic behavior to fully couple with the mechanical behavior that is described by an extended critical state soil model for unsaturated soil through the specific volume. Considering the boundary condition and introducing an auxiliary coordinate, the problem is formulated to a system of first-order differential equations with three principal stress components and suction as basic unknowns, which is solved as an initial value problem. Parameter analyses are conducted to investigate the effects of suction and the overconsolidation ratio on the overall expansion responses, including the pressure-expansion response, the distribution of the stress components around the cavity, and the stress path of the soil during cavity expansion. The results reveal that the expansion pressures and the distribution of the stress components in unsaturated soils are generally higher than those in saturated soils due to the existence of suction.

• Journal of applied mathematics & informatics
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• 제40권3_4호
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• pp.603-618
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• 2022

In this paper, a numerical solution of the generalized diffusion equation with a delay has been obtained by a numerical technique based on the Galerkin finite element method by applying the cubic B-spline basis functions. The time discretization process is carried out using the forward Euler method. The numerical scheme is required to preserve the delay-independent asymptotic stability with an additional restriction on time and spatial step sizes. Both the theoretical and computational rates of convergence of the numerical method have been examined and found to be in agreement. As it can be observed from the numerical results given in tables and graphs, the proposed method approximates the exact solution very well. The accuracy of the numerical scheme is confirmed by computing L₂ and L_∞ error norms.

• 한국식품저장유통학회지
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• 제22권3호
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• pp.314-321
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• 2015

반건시의 활용성 증대를 위하여 당액침지형 반건시를 제조하였으며 당 조성에 따른 반건시의 이화학적 특성 및 갈변 저해 효과를 검토하였다. 명도와 채도는 S5(sugar 5%), S10(sugar 10%)에서 높았고 그 이상의 농도에서는 감소하는 경향을 나타내었다. 총당, 환원당 및 유리당 함량은 당의 농도가 증대될수록 증가하였으며, S5는 대조구에 비해 감소하는 경향을 나타내었으나 S10은 유사한 함량을 보였으며 S15 및 S20의 경우 과실에 함유하는 당의 농도가 증가하는 것으로 나타났다. 당액침지형 반건시와 갈변효소간의 관계를 알아보기 위해 폴리페놀 산화효소와 과산화효소를 측정하였으며, 당액 농도가 증대됨에 따라 활성이 저해하는 경향을 나타냈고 S10 이후부터는 유사한 활성을 보였다. 폴리페놀, 플라보노이드, 프로안토시아니딘 및 비타민 C 함량은 다른 처리구와 비교하면 S10이 가장 높은 함량을 보여 식품과 당액 사이에 삼투압 때문에 당액으로 용출되는 함량이 감소하는 것으로 나타났다. DPPH 라디칼 소거활성은 S10에서 65.34%로 가장 높은 활성을 나타내었다. 이상의 결과 당액침지 시 삼투작용으로 적정 농도의 확립이 요구되며 갈변억제 및 영양적인 가치 등의 품질특성을 고려하였을 때 10% 설탕을 첨가한 당액 침지법이 반건시 가공품을 제조하는 데 있어 효과적인 방안이 될 것으로 생각된다.

• 한국수산과학회지
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• 제33권2호
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• pp.143-147
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• 2000

Alginate를 encapsulant 및 필름으로 이용하기 위한 기초자료를 얻기 위하여 다시마로부터 alginate의 추출조건과 alginate film 가공조건이 에스테르화합물의 필름 투과도에 미치는 영향에 관하여 실험 검토하였다. Alginate의 추출조건에서 추출용액인 $Na_2CO_3$ 용액의 농도가 증가할수록 에틸 아세테이트의 투과도는 증가하였지만, 추출시간은 큰 영향을 미치지 못하였다. Sorbitol의 농도가 증가할수록 에틸 아세테이트의 투과도도 증가하였다. 가소제의 종류별에 따른 에틸 아세테이트의 투과도는 sorbitol, glycerol 및 polyethylene glycol 첨가 필름 순으로 높게 나타났으며, 에스테르 화합물 중에서는 에틸 포메이트가 투과속도가 가장 높았다. 온도가 증가함에 따라 에틸 아세테이트의 필름 투과속도는 증가하였다.

• 열처리공학회지
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• 제34권6호
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• pp.287-293
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• 2021

This study was intended to investigate the influence of Al content on hardness and microstructural characteristics of discontinuous precipitates (DPs) formed by isothermal aging in Mg-8.7%Al and Mg-10%Al alloys. In order to obtain large amount of DPs in the microstructure, the alloy specimens were solution-treated at 688K for 24 h followed by water quenching, and then aged at 418K for 48h. The Mg-Al alloy with higher Al content was characterized by higher volume fraction of DPs at the same aging condition, lower interlamellar spacing of the DPs, thinner β phase layer and higher β phase content in the DPs. This is closely related to the higher velocity of discontinuous precipitation process resulting from the higher Al supersaturation in the α-(Mg) matrix. The Mg-10%Al alloy showed higher hardness of the DPs and greater difference in hardness between as-cast state and DPs than the Mg-8.7%Al alloy.

• 한국식품영양과학회지
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• 제12권3호
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• pp.284-288
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• 1983

Ascorbic acid (AsA)와 Catechin의 혼합용액에서 AsA의 안정성을 조사할 목적으로 각각의 농도 및 pH별 혼합용액을 조제하여 가열하는 동안 AsA와 catechin의 함량변화를 조사하였다. AsA의 손실은 각 혼합구 모두 가열 시작 10분 동안에 가장 많았으며 catechin의 혼합에 의해 촉진되었으나 혼합비율이 높은 경우가 낮은 것에 비하여 AsA의 손실은 적었다. Catechin의 손실도 가열 시작 10분 동안에 가장 컸으며 AsA의 농도가 높고 catechin의 농도가 낮을수록, AsA의 농도가 낮고 catechin의 농도가 높을수록 작았다. AsA의 안정성은 catechin의 함유비가 낮을 경우에는 pH 4pH 5>pH 6 순으로 pH 4 에서 높았다.

• Coupled systems mechanics
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• 제9권3호
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• pp.237-264
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• 2020

This article investigates the static behaviour of functionally graded (FG) plates sometimes declared as advanced composite plates by using a simple and accurate quasi-3D and 2D hyperbolic higher-order shear deformation theories. The properties of functionally graded materials (FGMs) are assumed to vary continuously through the thickness direction according to exponential law distribution (E-FGM). The kinematics of the present theories is modeled with an undetermined integral component and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate; therefore, it does not require the shear correction factor. The fundamental governing differential equations and boundary conditions of exponentially graded plates are derived by employing the static version of principle of virtual work. Analytical solutions for bending of EG plates subjected to sinusoidal distributed load are obtained for simply supported boundary conditions using Navier'is solution procedure developed in the double Fourier trigonometric series. The results for the displacements and stresses of geometrically different EG plates are presented and compared with 3D exact solution and with other quasi-3D and 2D higher-order shear deformation theories to verify the accuracy of the present theory.

• 상하수도학회지
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• 제35권6호
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• pp.455-463
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• 2021

The adsorption process using GAC is one of the most secured methods to remove of phosphate from solution. This study was conducted by impregnating Cu(II) to GAC(GAC-Cu) to enhance phosphate adsorption for GAC. In the preparation of GAC-Cu, increasing the concentration of Cu(II) increased the phosphate uptake, confirming the effect of Cu(II) on phosphate uptake. A pH experiment was conducted at pH 4-8 to investigate the effect of the solution pH. Decrease of phosphate removal efficiency was found with increase of pH for both adsorbents, but the reduction rate of GAC-Cu slowed, indicating electrostatic interaction and coordinating bonding were simultaneously involved in phosphate removal. The adsorption was analyzed by Langmuir and Freundlich isotherm to determine the maximum phosphate uptake(q_m) and adsorption mechanism. According to correlation of determination(R²), Freundlich isotherm model showed a better fit than Langmuir isotherm model. Based on the negative values of q_m, Langmuir adsorption constant(b), and the value of 1/n, phosphate adsorption was shown to be unfavorable and favorable for GAC and GAC-Cu, respectively. The attempt of the linearization of each isotherm obtained very poor R². Batch kinetic tests verified that ~30% and ~90 phosphate adsorptions were completed within 1h and 24 h, respectively. Pseudo second order(PSO) model showed more suitable than pseudo first order(PFO) because of higher R². Regardless of type of kinetic model, GAC-Cu obtained higher constant of reaction(K) than GAC.

• 한국식품영양학회지
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• 제30권1호
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• pp.139-147
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• 2017

The objective of this study was to develop anti-browning agents for commercial ready-to-eat pear products, which are preferred not only to maintain the flavor, color and texture of pears, but also to increase consumers' preference. The sliced 'Shin-go (Niitaka)' pears were immersed in 5% and 10% oxidized starch, 1% citric acid, and 5% and 10% oxidized starch with addition of 0.1% sucralose for 3 minutes, and then they were packaged in vacuum sealed bags at $1^{\circ}C$ for 9 days. In order to evaluate the quality of packaged sliced pears, the quality index was determined in terms of color, firmness, soluble solids, and sensory quality. With the passage of storage time, no specific variation in firmness and soluble solids was observed. However, the ${\Delta}E$ value of the sliced pears treated with 5% oxidized starch solution was significantly lower than that of the other pears. Also, the Hunter L and b values of the sliced pears treated with 5% oxidized starch solution remained nearly constant from the beginning of storage. This observation shows that 5% oxidized starch solution was effective in reducing surface browning of sliced pears. Moreover, sliced pears treated with oxidized starch solution with addition of 0.1% sucralose were given an overall liking score which was slightly higher than that given to the other pears because of the sweetness of sucralose. In conclusion, 5% oxidized starch solution with addition of 0.1% sucralose was effective in reducing browning of sliced pears and in improving the taste of sliced pears.

• 자원리싸이클링
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• 제18권4호
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• pp.38-43
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• 2009

수산화알루미늄을 원료물질로 하여 알루미늄 유기화합물인 aluminum oxalate 합성실험을 수행하였다. 이를 위해 국산 99.7% 순도의 수산화알루미늄을 옥살산으로 용해하는 방법으로 알루미늄 수용액을 제조하였으며, 실험결과 옥살산 농도 1.0 mole/l, 반응온도 $90^{\circ}C$에서 16시간 용해시 거의 100%에 가까운 용해율을 얻을 수 있었다. 알루미늄 수용액으로부터 aluminum oxalate를 합성하기 위해서는 ethanol/Al solution 혼합비율을 2.0이상으로 유지하여야 하는 것으로 나타났다. 또한, 90% 이상의 회수율을 얻기 위해서는 혼합액의 pH를 8.2이상으로 조절하여야 하는 것으로 나타났다. 합성반응을 통해 얻은 aluminum oxalate의 화학분석결과 $NH_4$ 14.5%, Al 7.18% 및 C 17.4%이었으며, 이의 화학식은 $(NH_4)_3Al(C_2O_4)_3$ $3H_2O$임을 확인할 수 있었다.