• Korean Journal of Materials Research
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• v.30 no.10
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• pp.522-532
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• 2020

Conductive polymer composites with high electrical and mechanical properties are in demand for bipolar plates of phosphoric acid fuel cells (PAFC). In this study, composites based on natural graphite/fluorinated ethylene propylene (FEP) and different ratios of carbon black are mixed and hot formed into bars. The overall content of natural graphite is replaced by carbon black (0.2 wt% to 3.0 wt%). It is found that the addition of carbon black reduces electrical resistivity and density. The density of composite materials added with carbon black 3.0 wt% is 2.168 g/㎤, which is 0.017 g/㎤ less than that of non-additive composites. In-plane electrical resistivity is 7.68 μΩm and through-plane electrical resistivity is 27.66 μΩm. Compared with non-additive composites, in-plane electrical resistivity decreases by 95.7 % and through-plane decreases by 95.9 %. Also, the bending strength is about 30 % improved when carbon black is added at 2.0 wt% compared to non-additive cases. The decrease of electrical resistivity of composites is estimated to stem from the carbon black, which is a conductive material located between melted FEP and acts a path for electrons; the increasing mechanical properties are estimated to result from carbon black filling up pores in the composites.

• Advances in nano research
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• v.14 no.4
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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.

• Journal of Nutrition and Health
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• v.47 no.6
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• pp.484-488
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• 2014

Purpose: This study investigated the question of whether the addition of natural ingredients (pear fermented solution, celery powder, vitamin C) in curing agents may influence antioxidant activities and nutritional characteristics of smoked duck. Methods: Smoked duck samples with general or natural curing agent containing three additive ingredients were examined to determine total polyphenol contents, antioxidant activities, pH, TBARS, and food additives residue (nitrite ion, antioxidant, sodium glutamate). Results: Smoked duck with natural curing agent showed a higher level of total polyphenol content and antioxidant activities than smoked duck using general curing agent (p < 0.05). The pH and TBARS of smoked duck were significantly decreased by the addition of natural curing ingredients compared to those of smoked duck using general curing agent (p < 0.05). The residues of food additives were not detected in smoked duck using natural curing agent. Conclusion: Findings suggest that the addition of pear fermented solution, celery powder, and vitamin C in natural duck curing agent may improve the antioxidant activities and nutritional characteristics of smoked duck and provides health benefits.

• Honam Mathematical Journal
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• v.26 no.1
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• pp.45-59
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• 2004

In this paper we obtain the general solution the functional equation $a^2f(\frac{x-2y}{a})+f(x)+2f(y)=2a^2f(\frac{x-y}{a})+f(2y).$ The type of the solution of this equation is Q(x)+A(x)+C, where Q(x), A(x) and C are quadratic, additive and constant, respectively. Also we prove the stability of this equation in the spirit of Hyers, Ulam, Rassias and $G\check{a}vruta$.

• Journal of the Chungcheong Mathematical Society
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• v.33 no.3
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• pp.339-349
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• 2020

Let P ⋊ ℕ^x be a semidirect product of an additive semigroup P = {0, 2, 3, ⋯ } by a multiplicative positive natural numbers semigroup ℕ^x. We consider a covariant semigroup C^∗-algebra 𝓣(P ⋊ ℕ^x) of the semigroup P ⋊ ℕ^x. We obtain the condition that a state on 𝓣(P ⋊ ℕ^x) can be a ground state of the natural C^∗-dynamical system (𝓣(P ⋊ ℕ^x), ℝ, σ).

• Proceedings of the Korean Society of Life Science Conference
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• 2006.09a
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• pp.47.1-47.1
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• 2006

• Composites Research
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• v.31 no.6
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• pp.398-403
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• 2018

Recently, environmental pollution caused by plastic waste, ecosystem disturbance of micro-plastics and human body accumulation are becoming big problems. In order to replace the traditional plastic, eco-friendly resin and natural fiber-based composite materials have been developed, but they have a disadvantage that their mechanical properties are significantly lower than those of synthetic fiber-based composites. In this study, eco - friendly nanofiber was extracted from seaweed and used as an additive in order to improve the mechanical properties of jute fiber-reinforced composites. Through the hand lay-up process, the composites were fabricated, and it was confirmed that the nanofiber was effective in improving the mechanical properties of natural fiber composites through tensile, bending and drop weight impact tests.

• Reproductive and Developmental Biology
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• v.33 no.4
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• pp.217-222
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• 2009

The purpose of this study is to evaluate the effects of alcohol or cigarette smoking on seminal parameters in a large group of mice model. Nine groups (n=20/group) of mice were treated intensive noxious materials that abdominal injection of 21% (v/v) of ethanol, cigarette smoke (10, 20, 30 minutes/day), and combination of ethanol and 30 minutes of smoking. In addition, vitamin C and selenium were also treated to mice exposed to combination of alcohol and smoking to identify the recovering effect. Sperm viability and motility were significantly decreased in either alcohol consumption or smoking exposed group, and combination of both materials have additive detrimental effects on seminal parameters. Mice groups that exposed to alcohol and smoking showed statistically significant decrease in motility and increase of static spermatozoa. Moreover, combination of both treatments showed cumulative effect in increase of static spermatozoa. Treatments of either vitamin C or selenium dramatically recovered detrimental effects of alcohol and smoking on seminal quality, although combination of both antioxidant molecules did not show any additive effect. In conclusion, detrimental effects of alcohol and cigarette consumption on sperm quality and motility were identified in mice model, and these detrimental effects can be compensated to uptake of anti-oxidant molecules.

• Journal of Environmental Science International
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• v.30 no.7
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• pp.573-584
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• 2021

To analyze the effects of PM₁₀ and PM_2.5 on daily mortality cases, the relations of death counts from natural causes, respiratory diseases, and cardiovascular diseases with PM₁₀ and PM_2.5 concentrations were applied to the generalized additive model (GAM) in this study. From the coefficients of the GAM model, the excessive mortality risks due to an increase of 10 ㎍/m³ in daily mean PM₁₀ and PM_2.5 for each cause were calculated. The excessive risks of deaths from natural causes, respiratory diseases, and cardiovascular diseases were 0.64%, 1.69%, and 1.16%, respectively, owing to PM₁₀ increase and 0.42%, 2.80%, and 0.91%, respectively, owing to PM_2.5 increase. Our result showed that particulate matter posed a greater risk of death from respiratory diseases and is consistent with the cases in Europe and China. The regional distribution of excessive risk of death is 0.24%-0.81%, 0.34%-2.6%, and 0.62%-1.94% from natural causes, respiratory diseases, and cardiovascular diseases, respectively, owing to PM₁₀ increase, and 0.14%-1.02%, 1.07%-3.92%, and 0.22%-1.73% from natural causes, respiratory diseases, and cardiovascular diseases, respectively, owing to PM_2.5 increase. Our results represented a different aspect from the regional concentration distributions. Thus, we saw that the concentration distributions of air pollutants differ from the affected areas and identified the need for a policy to reduce damage rather than reduce concentrations.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.3
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• pp.395-403
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• 2014

This paper presents a new approach to improve the signal to noise ratio (SNR) for local seismic disaster preventing system in densely populated area. The seismic data measured in the local site includes various sensing noises (offset or measurement noise) and man-made/natural noises (road and rail traffic noise, rotating or hammering machinery noise, human activity noise such as walking and running, wind/atmospheric pressure-generated noise, etc.). These additive noises are different in time and frequency characters. The proposed method uses 3-stages processing to reduce these different additive noises. In the first stage, misalignment offset noise are diminished by time average processing, and then the second and third stages, coherent/incoherent noises such as man-made/natural noises are suppressed by array stacking. In addition, we derived the theoretical equation of the SNR gain improved by the proposed method. To evaluate the performance of the proposed method, computer simulations were performed with real seismic data and test equipment generated data as the input.