• Geomechanics and Engineering
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• 제11권5호
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• pp.671-690
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• 2016

This work presents a static flexure analysis of laminated composite plates by utilizing a higher order shear deformation theory in which the stretching effect is incorporated. The axial displacement field utilizes sinusoidal function in terms of thickness coordinate to consider the transverse shear deformation influence. The cosine function in thickness coordinate is employed in transverse displacement to introduce the influence of transverse normal strain. The highlight of the present method is that, in addition to incorporating the thickness stretching effect (${\varepsilon}_z{\neq}0$), the displacement field is constructed with only 5 unknowns, as against 6 or more in other higher order shear and normal deformation theory. Governing equations of the present theory are determined by employing the principle of virtual work. The closed-form solutions of simply supported cross-ply and angle-ply laminated composite plates have been obtained using Navier solution. The numerical results of present method are compared with those of the classical plate theory (CPT), first order shear deformation theory (FSDT), higher order shear deformation theory (HSDT) of Reddy, higher order shear and normal deformation theory (HSNDT) and exact three dimensional elasticity theory wherever applicable. The results predicted by present theory are in good agreement with those of higher order shear deformation theory and the elasticity theory. It can be concluded that the proposed method is accurate and simple in solving the static bending response of laminated composite plates.

• Structural Engineering and Mechanics
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• 제51권5호
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• pp.867-891
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• 2014

An equivalent single layer trigonometric shear deformation theory taking into account transverse shear deformation effect as well as transverse normal strain effect is presented for static flexure of cross-ply laminated composite and sandwich plates. The inplane displacement field uses sinusoidal function in terms of thickness coordinate to include the transverse shear deformation effect. The cosine function in thickness coordinate is used in transverse displacement to include the effect of transverse normal strain. The kinematics of the present theory is much richer than those of the other higher order shear deformation theories, because if the trigonometric term (involving thickness coordinate z) is expanded in power series, the kinematics of higher order theories (which are usually obtained by power series in thickness coordinate z) are implicitly taken into account to good deal of extent. Governing equations and boundary conditions of the theory are obtained using the principle of virtual work. The closed-form solutions of simply supported cross-ply laminated composite and sandwich plates have been obtained. The results of present theory are compared with those of the classical plate theory (CPT), first order shear deformation theory (FSDT), higher order shear deformation theory (HSDT) of Reddy and exact three dimensional elasticity theory wherever applicable. The results predicted by present theory are in good agreement with those of higher order shear deformation theory and the elasticity theory.

• Advances in nano research
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• 제6권4호
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• pp.377-397
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• 2018

In the present investigation, thermal buckling and free vibration characteristics of functionally graded (FG) Timoshenko nanobeams subjected to nonlinear thermal loading are carried out by presenting a Navier type solution. The thermal load is assumed to be nonlinear distribution through the thickness of FG nanobeam. Thermo-mechanical properties of FG nanobeam are supposed to vary smoothly and continuously throughout the thickness based on power-law model and the material properties are assumed to be temperature-dependent. Eringen's nonlocal elasticity theory is exploited to describe the size dependency of nanobeam. Using Hamilton's principle, the nonlocal equations of motion together with corresponding boundary conditions based on Timoshenko beam theory are obtained for the thermal buckling and vibration analysis of graded nanobeams including size effect. Moreover, in following a parametric study is accompanied to examine the effects of the several parameters such as nonlocal parameter, thermal effect, power law index and aspect ratio on the critical buckling temperatures and natural frequencies of the size-dependent FG nanobeams in detail. According to the numerical results, it is revealed that the proposed modeling can provide accurate frequency results of the FG nanobeams as compared some cases in the literature. Also, it is found that the small scale effects and nonlinear thermal loading have a significant effect on thermal stability and vibration characteristics of FG nanobeams.

• Computers and Concrete
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• 제23권5호
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• pp.321-327
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• 2019

Experimental isotherm compressive tests show that concrete behaviour is dependent on temperature. The aim of such tests is to reproduce how concrete will behave under environmental changes within a moderate range of temperature. In this paper, a novel constitutive elastic damage behaviour law is proposed based on a free energy with an apparent damage depending on temperature. The proposed constitutive behaviour leads to classical theory of thermo-elasticity at small strains. Fixed elastic mechanical characteristics and fixed evolution law of damage independent of temperature and the material volume element size are considered. This approach is applied to compressive tests. The model predicts compressive strength and secant modulus of elasticity decrease as temperature increases. A power scaling law is assumed for specific entropy as function of the specimen size which leads to a volume size effect on the stress-strain compressive behaviour. The proposed model reproduces theoretical and experimental results from literature for tempertaures ranging between $20^{\circ}C$ and $70^{\circ}C$. The effect of the difference in the coefficient of thermal expansion between the mortar and coarse aggregates is also considered which gives a better agreement with FIB recommendations. It is shown that this effect is of a second order in the considered moderate range of temperature.

• 동의생리병리학회지
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• 제28권3호
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• pp.296-302
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• 2014

Saposhmikoviae Radix can treat various skin disease by anti-pruitus and anti-inflammatory effects. This study was designed to investigate effects of Saposhmikoviae Radix Extracts(SRE) on skin elasticity and whitening using B16F10 cell lines. In this experiment, We observed effect of SRE on cell viability, inhibition of melanin synthesis and inhibitory effect on tyrosinase and elastase. In results, SRE treated group showed lowered proliferation rates significantly compared to non-treated group. More than SRE $125{\mu}g/m{\ell}$ of treated groups were lower levels of melanin synthesis respectively. SRE did not show inhibitory effect on tyrosinase activities in vitro and in B16F10 cells. Finally, SRE suppressed elastse type I and IV activities in dose-dependent manner in vitro. And SRE also slightly suppressed elastase activities in B16F10 cells. In conclusion, these results suggest that SRE can inhibit melanin synthesis and inhibt elastase activity. So, We suggest that SRE can be maintained skin elasticity or whitening.

• Structural Engineering and Mechanics
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• 제76권1호
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• pp.141-151
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• 2020

This manuscript tends to investigate influences of nanoscale and surface energy on a static bending and free vibration of piezoelectric perforated nanobeam structural element, for the first time. Nonlocal differential elasticity theory of Eringen is manipulated to depict the long-range atoms interactions, by imposing length scale parameter. Surface energy dominated in nanoscale structure, is included in the proposed model by using Gurtin-Murdoch model. The coupling effect between nonlocal elasticity and surface energy is included in the proposed model. Constitutive and governing equations of nonlocal-surface perforated Euler-Bernoulli nanobeam are derived by Hamilton's principle. The distribution of electric potential for the piezoelectric nanobeam model is assumed to vary as a combination of a cosine and linear variation, which satisfies the Maxwell's equation. The proposed model is solved numerically by using the finite-element method (FEM). The present model is validated by comparing the obtained results with previously published works. The detailed parametric study is presented to examine effects of the number of holes, perforation size, nonlocal parameter, surface energy, boundary conditions, and external electric voltage on the electro-mechanical behaviors of piezoelectric perforated nanobeams. It is found that the effect of surface stresses becomes more significant as the thickness decreases in the range of nanometers. The effect of number of holes becomes significant in the region 0.2 ≤ α ≤ 0.8. The current model can be used in design of perforated nano-electro-mechanical systems (PNEMS).

• 한국재료학회지
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• 제28권7호
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• pp.381-390
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• 2018

Shape memory alloys(SMAs) have revolutionized the material engineering sciences as they exhibit exclusive features i.e. shape memory effect(SME) and super-elasticity. SMAs are those alloys that when deform return to their predeformed shape upon heating, they also restore their original shape by removing the load. Research on properties of newly advent of several types of ferrous based shape memory alloys(Fe-SMAs), shows that they have immense potential to be the counterpart of Nitinol(NiTi-SMA). These Fe-SMAs have been used and found to be effective because of their low cost, high cold workability, good weldability & excellent characteristics comparing with Nitinol(high processing cost and low cold workability) SMAs. Some of the Fe-SMAs show super-elasticity. Fe-SMAs, especially Fe-Mn-Si alloys have an immense potential for civil engineering structures because of its unique properties e.g. two-way shape memory effect, super elasticity and shape memory effect as well as due to its low cost, high elastic stiffness and wide transformation hysteresis comparative to Nitinol. Further research is being conducted on SMAs to improve and impinge better attributes by improving the material compositions, quantifying the SMA phase transition temperature etc. In this research pre-existing Fe-SMAs are categorised and collected in a tabulated form. An analysis is performed that which category is mostly available. Last 50 years data of Fe-SMA publications and US Patents is collected to show its importance in terms of increasing research on such type of alloys to invent different compositions and applications. This data is analysed as per different year groups during last 50 years and it was analysed as per whether the keywords exist in title of an article or anywhere in the article. It was found that different keywords related to Fe-SMAs/categories of Fe-SMAs, almost don't exist in the title of articles. However, these keywords related to Fe-SMAs/categories of Fe-SMAs, exist inside the article but still there are not too many publications related to Fe-SMAs/categories of Fe-SMAs.

• 산업융합연구
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• 제18권5호
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• pp.54-61
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• 2020

본 연구에 목적은 재가노인복지센터에서 종사하는 여성 요양보호사의 직무스트레스가 이직의도에 미치는 영향을 살펴보고 이들 관계에서 자아탄력성의 조절효과를 파악하기 위함이다. 연구대상은 서울시 소재 재가노인복지센터 28개소의 요양보호사 170명을 대상으로 자기기입식 설문조사를 실시하여 150부룰 회수하고 불성실한 응답 17명을 제외한 133명을 최종 분석하였다. 연구결과 첫째, 재가노인복지센터 여성 요양보호사의 경력이 낮은 집단과 종교가 없는 집단에서 이직의도가 높게 나타났다. 둘째, 요양보호사의 직무스트레스가 높을수록 이직의도가 높게 나타났다. 셋째, 요양보호사의 직무스트레스와 이직의도 간에 자아탄력성의 조절효과가 나타났다. 따라서 요양보호사의 직무스트레스를 예방하고 자아 탄력성을 향상시킬 수 있는 방안을 고려할 필요가 있다.

• 대한화장품학회지
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• 제36권1호
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• pp.65-69
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• 2010

콜라겐은 포유동물의 가장 풍부한 동물성 단백짙로, 전체 단백질의 약 30 %를 차지하며, 결합 조직에 존재하며 대부분의 장기의 구조적 지지에 기여한다. Tripeptide (glycine-proline-hydroxyproline: INCI name Tripeptide-29) 는 collagen type 1의 주성분이며, palmitoyl tripeptide (palmitoyl-glycine-proline-hydroxyproline: INCI name Palmitoyl Tripeptide-29) 는 콜라겐의 합성을 촉진하는 항노화 불질로서 디자인된 합성소재이다 합성된 웹타이드 유도체는 HPLC를 이용하여 분식하였다. in vitro test를 통하여 콜라겐합성과 섬유아세포 증식 효능을 확인하였고, 비침습적 기기를 사용하여 피검자에 대한 8주간의 적용결과 피부주름과 탄력의 상당한 개선을 확인하였다. Palmitoyl tripeptide는 우수한 항노화 효능을 갖는 화장품 소재로 사료된다.

• 산업융합연구
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• 제20권11호
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• pp.233-240
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• 2022

본 연구는 조직에서의 직무 스트레스와 회복탄력성이 직무만족과 조직몰입에 미치는 영향요인을 파악하는데 있다. 이를 위해 선행연구를 바탕으로 설문 척도를 개발하고, S사의 영업사원을 대상으로 설문조사를 실시하였다. 분석결과, 직무 스트레스가 직무만족에 유의한 영향을 미치며, 직무스트레스가 회복탄력성에 유의한 영향을 미치는 것으로 나타났다. 회복탄력성이 직무만족과 조직몰입에 영향을 미치며, 직무만족이 조직몰입에 영향을 미치는 것으로 나타났으나, 직무스트레스가 조직몰입에 유의한 영향을 미친다는 가설은 기각되었다. 또한 회복탄력성은 직무스트레스와 직무만족과 조직몰입 간의 관계를 매개하고 있는 것으로 나타났다. 본 연구의 결과는 조직에서 조직구성원들의 스트레스 관리와 더불어 회복탄력성을 높일 수 있는 실무적 차원의 다양한 방안에 대한 가이드라인으로 활용할 것으로 기대한다.