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        • SCIESCOPUSKCI등재

          Signal transduction pathways in erythrocyte nitric oxide metabolism under high fibrinogen levels

          Saldanha, Carlota,Freitas, T.,de Almeida, J.P. Lopez,Silva-Herdade, A. 한국유변학회 2014 Korea-Australia rheology journal Vol.26 No.2

          Previous studies show that the fibrinogen molecule modulates the metabolism of nitric oxide (NO) in erythrocyte. The in vitro induced hiperfibrinogenemia interferes in the metabolism of the NO in the erythrocyte in dependence of the phosphorylation degree of the band 3. The soluble form of fibrinogen binds into CD47 protein present in the erythrocyte membrane. The soluble thrombomodulin is an inflammatory marker that binds to the erythrocyte CD47 in a site with a sequence peptide known as 4N1K. A study done in vitro shows that when hiperfibrinogenemia was induced in the presence of the peptide 4N1K agonist of CD47 it were observed variations in the efflux of NO from erythrocyte and an increase in the concentrations of GSNO, peroxinitrite, nitrite and nitrate of the erythrocytes. The aim of this work was to study the influence of the peptide 4N1K, on the metabolism of NO in the erythrocyte under high fibrinogen concentration and in the presence of inhibitors of the status of phosphorylation of protein band 3. In this in vitro study, whole blood samples were harvested from healthy subjects and NO, peroxynitrite, nitrite, nitrate and S-nitroglutathione (GSNO) were determined in presence of 4N1K, calpeptine, Syk inhibitor and under high fibrinogen concentrations. The results obtained in erythrocytes under high fibrinogen levels when 4N1K is present with the Syk inhibitor or with calpeptine, showed in relation to the control samples increased significant concentrations of efflux of NO and of peroxynitrite, nitrite, nitrate and GSNO. In conclusion it was verified that in the in vitro model of hiperfibrinogenemia the peptide 4N1K, agonist of CD47, induces mobilization of NO in the erythrocyte in dependence of the status of phosphorylation of protein band 3.

        • SCIESCOPUSKCI등재

          고분자용액에 분산된 구형입자의 수력학적 확산계수

          한민수 한국유변학회 1997 Korea-Australia rheology journal Vol.9 No.4

          본 연구에서는 고분자용액을 분산매로한 현탁액 내에서 입자의 수력학적확산에 관 한 실험적인 연구를 수행하여다. 입자로는 평균직경 275마이크론의 polymethlmethacrylate (PMMA)구형입자를 사용하였고, 분산매로는 PMMA 입자와 밀도르 맞춘 글리세린과 에틸 렌글리콜의 혼합용액에 고분자를 첨가하여 사용하였다. 고분자로는 분자량 6백만의 시약용 폴리아크릴아마이드를 사용하였다. 입자농도는 50%이었다. 용액의 농도는 0∼700ppm이었으 며 이러한 용액은 전단박화현상을 나타내지 않았다. 확산계수는 쿠엣장치 내에서 입자가 두 원통사이에서 아래쪽의 빈 공간으로 확산할 때 시간에 따른 점도측정결과로부터 예측하여 다. 본 연구의 결과 뉴튼성유체의 경우와는 달리 무차원확산계수(D/2)가 일정하지 않으며 전단율이 증가될수록 점점 감소하는 현상을 나타내었다. 고분자의 농도가 증가하는 경우에 는 무차원 확산계수가 감솨는 것을 볼수있었다. 이러한 무차원 확산계수의 감소는 유동하는 현탁액 내에서 입자간의 상호작용이 뉴튼성유체에 비하여 가역적인 것에 기인하는 것으로 판단된다.

        • KCI등재후보

          Molecule-based electrorheological material assembled using β-cyclodextrin as substrate

          Yan-Li Shang,Yun-Ling Jia,Yun Ma,Jun-Ran Li,Shao-Hua Zhang,Ming-Xiu Li 한국유변학회 2010 Korea-Australia rheology journal Vol.22 No.1

          Molecule-based electrorheological (ER) materials as a novel type of ER materials, the inclusion compound [H2(β-CD-A)-PTA] between p-toluenesulfonic acid (PTA, guest) and H2(β-CD-A) (host) that is dicarboxylic acid of β-cyclodextrin (β-CD) , and the rare earth (RE) complexes [(β-CD-A)-PTA]3RE2 (RE=La, Gd, Y)of H2(β-CD-A)-PTA, were synthesized. The ER performance and dielectric property of the materials were studied. Our results show that the molecule-based ER materials assembled using β-cyclodextrin as a substrate,especially the inclusion compound and its rare earth (RE) complexes exhibit clear ER effect. The inclusion PTA can markedly enhance the ER performance of H2(β-CD-A) material. The ER activity of the yttrium complex is the highest among these materials. The characteristic of the molecule in molecule-based ER materials is an important factor in influencing ER property.

        • SCIESCOPUSKCI등재

          광범위한 전단률에서 적용가능한 수정된 POWER LAW 유체에 대한 GRAETZ문제 해법

          T.F. irvine, Jr 한국유변학회 1995 Korea-Australia rheology journal Vol.7 No.1

          층류 열전달에서 작은 Reynolds number에서의 원통내의 흐름에대한 Power law 유 체의 해법이 사용될 수가 없는 것을 낮은 전단률(Shear Rate)에서 Power Law 법칙이 적용 되지 않기 때문이다. 본 연구에서는 이문제를 새로운 구성방정식을 이용하여 높은 전단률에 서는 Power Law 법칙이 낮은 전단률에서는 Newtonian 법칙이 그 중간에서는 천이과정을 모두 포함하는 전범위의 전단률에 대해 해결하였다. 이러한 구성방정식의 기본개졈은 실험 결과와도 잘 일치하였따. 이 구성방정식을 이용하여 Graetz 문제를 해결하였고 경계조건은 일정온도와 일정열속이다. 이용하기 쉬운 전단률변수는 적용범위가 Newtonian인지 Power law 인지 아니면 중간 천이과정인지를 나타내준다.

        • KCI등재

          Drag reduction characterizations of turbulent channel flow with surfactant additive by proper orthogonal decomposition and wavelet transform

          Lu Wang,Zhiying Zheng,Weihua Cai,Fengchen Li 한국유변학회 2020 Korea-Australia rheology journal Vol.32 No.1

          To explore the drag-reducing characteristics of turbulent channel flows with surfactant additive at relatively high Reynolds number from the perspectives of energy spectrum and multi-scale resolution, the two-dimensional fluctuation velocity fields of turbulent channel flows with/without surfactant additive at Reynolds number of Re = 590 obtained by large eddy simulation are decomposed by two-dimensional proper orthogonal decomposition (POD) and wavelet transform (WT). POD results show that the low-order eigenmode occupying most energy can be used to capture large-scale vortex structures, and fewer eigenmodes can be employed to capture coherent structures (CSs) in surfactant solution case compared with that in the Newtonian fluid. The spatial structures depicted by POD eigenmode state that buffer layer has a tendency to move towards the center of the channel in surfactant solution. Through wavelet analysis of fluctuation velocity fields in the streamwise-wall-normal planes, it is found that CSs mainly distribute in the near-wall region and the amount of CSs is smaller in surfactant solution. The results of local Reynolds shear measure (LRM) show that local contribution of CSs to the intermittency in turbulent channel flow of surfactant solution decreases, indicating the inhibition of intermittency by surfactant additive. In order to investigate the drag-reducing characteristics at different locations along the wall-normal direction, the fluctuation velocity fields in the streamwise-spanwise planes at different wall-normal locations are decomposed by two-dimensional WT. The results show that surfactant additive mainly affects the flow in the near-wall region (especially in the buffer layer) and thus induces drag reduction effect.

        • SCIESCOPUSKCI등재

          액정고분자 복합계의 in-situ 횡단면 배향을 위한 공정개발

          이재욱 한국유변학회 1998 Korea-Australia rheology journal Vol.10 No.2

          액정고분자/폴리카보네이트 혼합계로 구성된 분자복합계를 쉬트상으로 가공할 때 취 약해지기 쉬운 횡단면 방향의 물성을 향상시키기 위하여 미세섬유상의 배향을 in-situ 상태 로 적절히 제어할수 있는 Simultaneous Convergent-Divergent(SCD) 다이를 설계·제작하 고 압출실험을 수행하여 얻은 압출 쉬트를 대상으로 구조-물성-가공의 상관관계를 조사하 였다. 액정고분자의 첨가 함량에 따른 토오크와 토출량의 변화는 액정고분자를 10wt% 소량 첨가하였음에도 현저한 감소 효과를 보였으며 약 30wt%일 때 최소로되었다. 이는 액정고분 자가 보강 기능외에 가공특성의 개선에도 큰 효과가 있어 가공조제로서의 가능성을 보이는 결과로 혼합계의 유변학적 특성 결과에서도 확인할수 있었다. 또 DSC와 DMA를 이용한 열 분석 결과 액정고분자의 함량이 증가함에 따라 PC의 유리전이온도가 다소 감소하는 현상을 보임에 미루어 이 혼합계는 부분적으로 상용성을 갖는 것으로 볼수 있으며 모폴로지 분석을 통해서도 이를 확인할수 있었다. TLCP/PC 혼합계로 구성되는 분자복합재를 SCD 다이를 사용하여 제조한 압출 쉬트의 방향성에 따른 기계적 물성은 기존의 쉬트 다이보다 흐름방향 으로는 다소 낮은 물성치를 보이지만 횡단면 방향으로는 물성이 현저히 향상됨을 관찰할수 있었다. 모폴로지 분석결과 기존의 쉬트 다이의 경우 벽면 부근에서는 액정고분자가 미세섬 유상으로 형성되어 흐름방향으로 배향되어 있지만 중심부에서는 액정 상태로 존재하는 반 면, SCD 다이의 경우 미세섬유상으로 형성된 액정고분자가 벽면에서부터 중심부로 갈수록 횡단면 방향으로 서서히 배향되어 있음을 확인할수 있었다.

        • SCIESCOPUSKCI등재

          엉켜 있는 2성분 선형 고분자의 제약완화 및 관 재형성 효과

          김광만 한국유변학회 1991 Korea-Australia rheology journal Vol.3 No.2

          동일화학종이면서 \ulcorner량이 다른 두 단분산 고분자를 혼합한 2성분 다분산 농축계에 equivalent primitive chain model을 적용하여 사슬주위의 제약완화에 따른 관의 재형성 효 과를 각 사슬의 특성완화시간으로 산정하여 나타내었다. Polystyrene 시료에 대하여 동력하 적 실험을 실시한 결과를 이용하여 사동모델에 따른 각 사슬의 최장완화시간은 복소수 점도 의 허수분분(η")대 주파수($\omega$)의 관계, 관의 재형성 시간은 $\omega$ 변화에 따른 storage modulus(G') 로부터 각각 도출하였다. 이러한 작업을 통하여 특성완화 시간들이 분자량 및 각 성분 농도에의 의존성을 더욱 상세히 파악할 수 있었다.

        • KCI등재

          Toothpaste microstructure and rheological behaviors including aging and partial rejuvenation

          Zhiwei Liu,Lei Liu,Huan Zhou,Jiali Wang,Linhong Deng 한국유변학회 2015 Korea-Australia rheology journal Vol.27 No.3

          Toothpastes are mainly composed of a dense suspension of abrasive substances, flavors, and therapeutic ingredients in a background liquid of humectants and water, and usually exhibit complex rheological behaviors. However, the relationship between the rheology and microstructure of toothpaste remains to be studied. In this paper, three commonly used toothpastes, namely Colgate, Darlie and Yunnan Baiyao (Ynby), were qualitatively and quantitatively studied as soft glassy materials. We found that although the three toothpastes generally behaved in similar fashion in terms of rheology, each particular one was distinct from others in terms of the quantitative magnitude of the rheologcial properties including thixotropy, creep and relaxation, yield stress, and power-law dependence of modulus on frequency. In addition, the history-dependent effects were interpreted in terms of aging and rejuvenation phenomena, analogous to those existing in glassy systems, and Ynby seemed to result in greater extent of aging and rejuvenation as compared to the other two. All these differences in toothpaste rheology may well be attributed to the different microscopic network microstructures as observed in this study. Therefore, this study provides first evidence of microstructurebased rheological behaviors of toothpaste, which may be useful for optimizing its composition, manufacturing processing as well as end-user applications

        • KCI등재

          Supercritical bifurcation to periodic melt fracture as the 1st transition to 2D elastic flow instability

          권영돈 한국유변학회 2020 Korea-Australia rheology journal Vol.32 No.4

          This study, employing a numerical approximation, computationally describes 2D melt fracture as elastic instability in the flow along and outside a straight channel. In the preceding research (Kwon, 2018, Numerical modeling of two-dimensional melt fracture instability in viscoelastic flow, J. Fluid Mech. 855, 595-615) several types of unique instability and corresponding bifurcations such as subcritical and chaotic transitions have been illustrated with possible mechanism presumed. However, the 1st bifurcation from stable steady to unstable periodic state could not be accurately characterized even though its existence was proven evident. The analysis herein aims at verification of this 1st transition to temporally (and also spatially) periodic instability, utilizing the same numerical technique with attentive control of flow condition. As a result of scrutinizing the solutions, the steady elastic flow described by the Leonov rheological model passes through supercritical Hopf bifurcation at the Deborah number of 10.42 and then transforms to the state of the 1st weak periodic instability. It has also been confirmed that near this bifurcation point it takes extremely long to completely develop into either steady state (in the stable case) or periodic instability, which obstructed immediate characterization of the transition in the previous work.

        • KCI등재

          Time-dependent viscoelastic properties of Oldroyd-B fluid studied by advection-diffusion lattice Boltzmann method

          이영기,안경현,이승종 한국유변학회 2017 Korea-Australia rheology journal Vol.29 No.2

          Time-dependent viscoelastic properties of Oldroyd-B fluid were investigated by lattice Boltzmann method (LBM) coupled with advection-diffusion model. To investigate the viscoelastic properties of Oldroyd-B fluid, realistic rheometries including step shear and oscillatory shear tests were implemented in wide ranges of Weissenberg number (Wi) and Deborah number (De). First, transient behavior of Oldroyd-B fluid was studied in both start up shear and cessation of shear. Stress relaxation was correctly captured, and calculated shear and normal stresses agreed well with analytical solutions. Second, the oscillatory shear test was implemented. Dynamic moduli were obtained for various De regime, and they showed a good agreement with analytical solutions. Complex viscosity derived from dynamic moduli showed two plateau regions at both low and high De limits, and it was confirmed that the polymer contribution becomes weakened as De increases. Finally, the viscoelastic properties related to the first normal stress difference were carefully investigated, and their validity was confirmed by comparison with the analytical solutions. From this study, we conclude that the LBM with advection-diffusion model can accurately predict time-dependent viscoelastic properties of Oldroyd-B fluid.

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