• Composites Research
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• 제33권5호
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• pp.241-246
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• 2020

본 연구에서는 교반주조 공정을 통해 B₄C 입자가 균일하게 분산된 알루미늄 금속복합재료를 제조하고 후 공정으로 열간압연을 수행하였다. 제조된 복합재료의 미세조직, 기계적 특성 및 내마모 특성에 대해 분석하였다. 40 ㎛ 크기의 B₄C 입자가 균일하게 분산된 복합재료는 강화재의 체적율이 증가함에 따라 인장강도는 증가하였으며, 마모 성능도 개선되었다. 20 vol.% 복합재료의 경우 인장강도 값은 292 MPa로 기지재인 Al6061 대비 155% 증가하였다. 내마모시험 결과 20 vol.% 복합재료의 경우 마모 너비와 깊이가 각각 856 ㎛, 36 ㎛이며, 마찰계수는 0.382로 Al6061 대비 상당히 우수한 내마모 특성을 나타내었다.

• 대한기계학회논문집B
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• 제23권8호
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• pp.1040-1047
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• 1999

The characteristics of flame propagation in inert particle-laden $H_2$/Air premixed gas are numerically investigated on this study. The 2nd order TVD scheme is applied to numerical analysis of governing equations and multi-step chemical reaction model and detailed transport properties are sued to solve chemical reaction terms. Radiation heat transfer is computed by applying the finite volume method to a radiative transfer equation. The burning velocities against the mole fractions of hydrogen agree well with results performed by different workers. The inert particles play significant roles in the flame propagation on account of momentum and heat transfer between gas and particles. Gas temperature, pressure and flame propagation speed are decreased as the loading ratio of particle is increased. Also the products behind flame zone contain lots of water vapor whose absorption coefficient is much larger than that of unburned gas. Thus, the radiation effect of gas and particles must be considered simultaneously for the flame propagation in a mixture of $H_2$/Air and inert particles. As a result, it is founded that because the water vapor emits much radiation and this emitted radiation is released at boundaries as radiant heat loss as well as reabsorbed by gas and particles, flame propagation speed and flame structure are altered with radiation effect.

• 대한기계학회논문집B
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• 제21권2호
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• pp.235-251
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• 1997

A numerical simulation on the combined natural convection and radiation is carried out in a partially open rectangular enclosure with a heater by using the finite volume and the S-8 discrete ordinate methods. The fluid inside the enclosure is considered as an absorbing, emitting and anisotropic scattering media. The heater causes a natural circulation of the fluid (10$^{5}$ $^{9}$ ) which results in significant in-flow of the ambient cold fluid through the partially open wall. Comparing the results of pure convection with those of the combined convection- radiation, the combined heat transfer results with small Planck numbers (P$_{l}$ <1.0) show much stronger circulation than those of the pure convection, and the fluid circulation is more evident for larger Rayleigh numbers. When one of three radiative properties - the medium absorption coefficient, the wall reflectivity, and the scattering albedo - increases, the fluid circulation and the heat transfer in the enclosure are reduced. The location of the heater and the open ratio of the right wall are also shown to affect the fluid circulation and heat transfer significantly. However, the anisotropy of the scattering phase function is shown to be unimportant for the fluid circulation and heat transfer within the enclosure considered in this study.

• 한국세라믹학회지
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• 제30권4호
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• pp.289-298
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• 1993

Properties in terms of the variation of the glass compositions, which were density (p), molar volume(Vm), atom/ion packing density (Dp), refractive index (nD), transformation temperature (Tg), dilatometric softening point (Td), thermal expansion coefficient (α), Young's modulus (E), and knoop hardness (KHN) were investigated in CaO-SiO2 glasses and CaO-P2O5-SiO2 glasses containing less than 10mole% of P2O5. Those properties were measured by density measurement kit, Abbe refractometer, dilatometer, ultrasonic pulse echo equipment, and micro hardness tester. When CaO content was increased in CaO-SiO2 glasses, p, Dp, nD, Tg, Td, α, E and KHN were increased, while Vm was decreased. When P2O5 was added to the CaO-SiO2 glasses with constant CaO/SiO2 ratio as 1.07, p, Dp, nD, Tg, Td, α, E and KHN were decreased, while Vm was increased. When the amount of P2O5 in glasses was kept constant, the changes of the properties with variation of CaO content in the CaO-P2O5-SiO2 glasses were very similar to those of CaO-SiO2 glasses. These phenomena could be explained by the structural role of P2O5 in the CaO-P2O5-SiO2 glasses, which was polymerization of siicate structures and resulted in [PO4] monomer structure in glasses. Due to this structural characteristics, the bond strength and packing density were changed with compositions. Proportional relationships between 1) np and Dp, 2) Tg, Td, α and CaO content, 3) E and Vm-1, and 4) KHN and P2O5 content were evaluated in this investigation.

• 분석과학
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• 제9권2호
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• pp.139-144
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• 1996

발색제로 eriochrome cyanine R(ECR)을 사용하여 여러 가지 계면활성제에서 스칸듐을 분광광도법으로 정량하는 방법과 그 착물의 조성을 연구하였다. Sc(III)-ECR 착물의 흡광도와 최대 흡수 파장은 cetyltrimethylammonium bromide (CTMAB)에서 크게 변하지만, sodium dodecyl sulfate(SDS)나 Triton X-100의 계면활성제에서는 변화가 없다. $1{\times}10^{-7}{\sim}3.0{\times}10^{-6}M$ Sc(III) 을 ECR 로 정량할 때는 pH 6.5 에서 $1{\times}10^{-3}M$ ECR 5ml와 $2{\times}10^{-4}M$ CTMAB 10ml가 필요했다. Sc(III)-ECR-CTMAB, 삼성분 착물의 몰흡광계수는 610nm에서 $5.6{\times}10^5mol^{-1}cm^{-1}L$이며 검출한계는 $1.0{\times}10^{-7}M$이었다. Sc(III)-ECR-CTMAB 삼성분 착물의 조성은 1:3:1 이었다.

• 한국유기농업학회지
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• 제20권1호
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• pp.91-99
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• 2012

This study was conducted to develop a functional feed additive for pig with spent $Lycium$ $chinense$ Mill fruit. We investigated the optimum conditions for the extraction of polyphenol from spent $Lycium$ $chinense$ Mill using methanol. Methanol concentration as a solvent for extraction, extraction time and the volume of solvent per a gram of solid (ground spent Lyceum chinense Mill) were selected as parameters. Three levels of parameters were configured according to Box Behnken experiment design, a fractional factorial design, and total 15 trials were employed. Total polyphenol concentration from each trial was used as response from experiment system and effects of parameters on total polyphenol extraction efficiency were determined using response surface model. As a result, all terms in analysis of variance, regression ($p$ = 0.001), linear ($p$ = 0.002), square ($p$ = 0.017) and interaction ($p$ = 0.047) was significant and adjusted determination coefficient ($R^2$) was 94.7%. Total polyphenol extraction efficiency was elevated along increased methanol content and decreased solvent to solid ratio. However extraction time did not affect the efficiency. This study provides a primary information for the optimum extraction conditions to maximize total polyphenol recovery from spent Lycium chinens Mill fruit and this result could be applied to re-use of argo-industrial by-products and to develop of functional feed additives in organic farming.

• 한국작물학회지
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• 제27권1호
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• pp.28-34
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• 1982

수도 비중별 임실정도의 차이와 미립과 조곡의 형질과의 관계를 구명하기 위하여 본시험을 수행하였던 바 다음과 같은 결과를 얻었다. 1. 곡립의 장, 폭, 후는 비중이 무거울수록 커지며 통일계품종은 일반품종보다 곡립의 길이는 크나 넓이와 두께가 작아 립이 세장하며 조곡의 용적이 작다. 한강찰벼는 진주벼와 서광벼 보다 물질집적 수용면적이 넓다. 2. 비중이 가벼울수록 립간 변이계수가 크며 동화산물의 집적은 곡립의 장보다 폭과 후의 신장에 영향을 미친다. 또 립중은 비중이 무거울수록 증가하나 조곡은 비중의 차에 영향을 받지 않으며 곡립의 크기가 작은 품종일수록 정현비율이 높다. 3. 비중과 립중, 곡립의 크기와는 정상관관계이며 립중 증대에 기여한 립형은 장보다 폭이나 후다. 4. 비중이 가벼울수록 정미와 불완전미의 분포비율이 높아 종자사용상에 문제되는데 건묘육성을 위해서는 필히 비중선이 요망되며 최적 비중선은 진주벼 1.12, 서광벼 1.16, 한강찰벼는 1.13이다. 5. 임실이 불량한 조곡은 질소합유량은 많으나 가리, 규산함유량은 낮다.

• 한국재료학회지
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• 제20권8호
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• pp.444-449
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• 2010

Transparent ceramics are used in new technology because of their excellent mechanical properties over glasses. Transparent ceramics are nowadays widely used in armor, laser windows, and in high temperature applications. Silicon nitride ceramics have excellent mechanical properties and if transparent silicon nitride is fabricated, it can be widely used. h-BN has a lubricating property and is ductile. Therefore, adding h-BN to silicon nitride ceramics gives a lubricating property and is also machinable. Translucent silicon nitride was fabricated by hot-press sintering (HPS) and 57% transmittance was observed in the near infrared region. A higher wt. % of h-BN in silicon nitride ceramics does not favor transparency. The optical, mechanical, and tribological properties of BN dispersed polycrystalline $Si_3N_4$ ceramics were affected by the density, ${\alpha}:{\beta}$-phase ratio, and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of $\alpha-Si_3N_4$, AlN, MgO, and h-BN at $1850^{\circ}C$. The composite contained from 0.25 to 2 wt. % BN powder with sintering aids (9% AlN + 3% MgO). A maximum transmittance of 57% was achieved for the 0.25 wt. % BN doped $Si_3N_4$ ceramics. Fracture toughness increased and wear volume and the friction coefficient decreased with an increase in BN content. The properties such as transmittance, density, hardness, and flexural strength decreased with an increase in content of h-BN in silicon nitride ceramics.

• International Journal of Computer Science & Network Security
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• 제22권1호
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• pp.347-357
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• 2022

The aim of the study is to model demand for full-time Bachelor's Degree Programs in Hospitality and Catering, taking into account the influence of the main determinants in the COVID-19 pandemic. The research used methods of algorithms, correlation and regression analysis, ANOVA, graphical method, deduction and induction, abstraction, etc. It was found that the demand for full-time Bachelor's Degree Programs in Hospitality and Catering is price elastic. It has been argued that it is useful to consider both price and non-price determinants when modelling demand for full-time Bachelor's Degree Programs in Hospitality and Catering. It is proved that the main determinants of demand for full-time Bachelor's Degree Programs in Hospitality and Catering are full-time tuition fee, maximum government order, license volume and Consolidated Ranking of a higher education institution (HEI). In this case, the applicant decides to enrol in a full-time Bachelor's Degree Program in Hospitality and Catering, guided by the optimal ratio of tuition fee and the prestige of the HEI.

• Advances in nano research
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• 제14권4호
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• pp.375-389
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• 2023

In this study, free vibration analysis of functionally graded (FG) porous truncated conical shell panels reinforced by graphene platelets (GPLs) has been investigated for the first time. Additionally, the effect of three different types of porosity distribution and five different types of GPLs patterns on dynamic response of the shell are also studied. Halpin-Tsai micromechanical model and Voigt's rule are used to determine Young modulus, shear modulus and Poisson's ratio with mass densities of the shell, respectively. The main novelties of present study are: applying 3D elasticity theory and the finite element method in conjunction with Rayleigh-Ritz method to give more accurate results unlike other simplified shell theories, and also presenting a general 3D solution in cylindrical coordinate system that can be used for analyses of different structures such as circular, annular and annular sector plates, cylindrical shells and panels, and conical shells and panels. A convergence study is performed to justify the correctness of the obtained solution and numerical results. The impact of porosity and GPLs patterns, the volume of voids, the weight fraction of graphene nanofillers, semi vertex and span angles of the cone, and various boundary conditions on natural frequencies of the functionally graded panel have been comprehensively studied and discussed. The results show that the most important parameter on dynamic response of FG porous truncated conical panel is the weight fraction of nanofiller and adding 1% weight fraction of nanofiller could increase 57% approximately the amounts of natural frequencies of the shell. Moreover, the porosity distribution has great effect on the value of natural frequency of structure rather than the porosity coefficient.