• Nonlinear Functional Analysis and Applications
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• 제28권4호
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• pp.1127-1143
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• 2023

The purpose of this paper, we prove convergence theorems of the modified viscosity inexact Mann iteration process for a family of asymptotically quasi-nonexpansive type mappings in CAT(0) spaces. We also show that the limit of the modified viscosity inexact Mann iteration {x_n} solves the solution of some variational inequality.

• Korea-Australia Rheology Journal
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• 제12권3_4호
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• pp.175-179
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• 2000

Rheological properties of chitosan solutions were investigated as a function of polymer concentration. The viscosity curves for chitosan solutions consisted of two distinct viscosity regions, the Newtonian zero-shear viscosity (η$_{0}$) region and the shear rate dependent apparent viscosity (η$_{app}$) region. The shear rate dependence of viscosity was more clearly observed at higher chitosan concentrations. The critical coil overlap parameter (C＊〔η〕) was determined to be approximately 3.2 from a plot of zero-shear specific viscosity η$_{sp,0}$ vs coil overlap parameter (C〔η〕), which was lower than C〔η〕4.0 reported for other random coil polysaccharides. It was also found that the slope of η$_{sp,0}$ vs C〔η〕 was 3.9 at concentrated C〔η〕>C＊〔η〕domain, while 1.2 at dilute C〔η〕$_{0}$ ${\gamma}$/${\gamma}$$_{0.8}$ relation.ion.n.n.

• 한국유체기계학회 논문집
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• 제7권2호
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• pp.21-26
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• 2004

In this study the effects of fluid viscosity on the pump performances for a conventional centrifugal pump were experimentally investigated. The study aimed to compare the pump characteristics between water and viscosity fluids. In order to measure the flow rate and pressure, v-notch welt and bourdon pressure gauges were used for the codes of KS B6301 and KS B6302. The working fluids were water, aqueous sugar and glycerin solutions. The results were summarized as follows : The experimental results were summarized as follows : the pump characteristics of the total head, shaft power, and efficiency with high viscosity fluids were different from those of water. When the viscosity of the applied fluid was increased, the total head and efficiency were more decreased than those of water. The decreasing gradients of the total head and the efficiency were larger than water due to the increased disk friction losses at the duty operation point. However, the shut-off head was almost constant regardless the viscosity of applied fluids. Each efficiency curves for the sugar $20w\%$ and glycerin $20w\%$ solutions was decreased up to $15.1\%$ and $34.4\%$ than that of water, respectively.

• 한국수자원학회논문집
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• 제33권1호
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• pp.39-50
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• 2000

일반적으로 동수역학 모형은 마찰인자(조도계수 또는 Chezy계수)와 와점성계수를 필요로 하고 수치계산에서 이들 계수의 갑은 통상 가정 또는 반복계산을 통하여 결정된다. 수치모형에서 와점성계수는 물리적인 확산뿐만 아니라 수치점성의 효과도 가지고 있어서 수치계산의 안정성에 영향을 미치므로 이들 계수의 일관된 결정방법이 필요하다. 수위 및 유량자료, 1차원 모형인 HEC-2와 NETWORK, 2차원 모형인 SMS를 이용하여 한강하류 구간에 대한 조도계수의 산정결과와 와점성 계수의 산정식이 제시되었으며 실측수위와 비교를 통해 검증되었다.

• 약학회지
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• 제32권1호
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• pp.86-94
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• 1988

Some rheological properties of subfractions for dextran in the molecular weights range from $3{\times}10^4$ to $2{\times}10^6$ was investigated at room temperature. The dependence of the viscosity on concentration, shear rate, pH & ionic strength, temperature and solvent effect was observed. From the experimental data the Mark-Houwink viscosity equation in water at $25^{\circ}C$ was determined for samples having the molecular weight ranging from $3{\times}10^4$ to $2{\times}10^6$ as$[{\eta}]=3.1{\times}10^{-3}\;Mw^{0.39}(in\;dl/g)$. The intrinsic stiffness of the dextran backbone was estimated by evaluating the 'characteristic ratio' $C_{\infty}$, which is below the 0.082. In the concentrated region, the viscosity was decreased with increasing shear rate and was exponentially decreased with raising temperature, the viscosity showed the maximum value at neutral condition. From the experimental data, it was concluded that dextran chain, linked by the ${\alpha}-1$, 6-glucosidic linkage, behaves like a flexible random coil chain in aqueous solution, dextran solutions were pseudoplastic power law fluids among the empirical models of non-Newtonian behavior. Urea was an active reagent which increases the viscosity and swells dextran while pyrididine and glycerol were inactive reagents. Also, it could be estimated that the formation of gel structure is promote to the neutral state, the molecular weight larger than $2{\times}10^5$, when electrolytic concentration is IN and Ureas is use to solvent.

• 대한수학회보
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• 제58권6호
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• pp.1521-1537
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• 2021

In this paper we consider the global well-posedness of compressible magnetohydrodynamic system in ℝ^d with d ≥ 2, in the framework of the critical Besov spaces. We can show that if the initial data, the shear viscosity and the magnetic diffusion coefficient are small comparing with the volume viscosity, then the compressible magnetohydrodynamic system has a unique global solution. Our result improves the previous one by Danchin and Mucha [10] who considered the compressible Navier-Stokes equations.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 1990년도 제2차 학술발표초록집
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• pp.36-37
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• 1990

In the past, facile dissolution of cellulose has been hampered by the lack of suitable nondegrading solvents. Recently, this problem has been solved in our laboratory by the discovery of an inexpensive, convenient solvent system, that is the mixture of $NH_3\;and\;NH_4SCN$, for cellulose. Also, the $cellulose/NH_3/NH_4SCN$ solution system has been found to form the anisotropic, i.e., liquid crystalline phase. It is believed that both the cholesterio and the nematic phase occur. This finding has prompted extensive on-going researoh on the formation of the liquid crystalline phase from an inexpensive natural source such as cellulose since the nematic phase is envisioned as an excellent precursor sources for products with desirable properties, for example, high modulus and high strength. This interest naturally leads to a desire to understand the theological properties of the nematic phase so that the transformation of the nematic phase to the solid state with desirable properties can be efficiently accomplished, ;From this point of view, the theological behavior of the $cellulose/NH3_/NH_4SCN$ system has been studied as a function of shear rate and shear stress over a wide range of solvent compositions, cellulose concentration, centrifugation and urea contents, Results indicate that the viscosity decreases with increasing shear rate. A marked shear thinning behavior and a quasi-Newtonian behavior were observed in the low shear rate region and in the high shear rate region, respectively for all solvent compositions. The $cellulose/NH_3/NH_4SCN$ solution system only exhibited the viscosity increase with increasing cellulose concentration and failed to show the viscosity drop generally observed at the point of incipience of liquid crystal formation, This may be due to the gel-like nature of the solution by the association of the rodlike molecules into bundles which may serve as crosslinking points giving the cellulose solution a network structure. Also, simply hydrogen bonding may be so restrictive of molecular mobility that a viscosity drop is blocked. In addition to the above results, yield stress and thixotropy were also observed in the $cellulose/NH_3/NB_4SCN$ solution system which are characteristics of liquid crystal and gel, The results of the effect of centrifugation on viscosity show that viscosity decreases by the application of centrifugation. This may be explained by the change of the piled polydomain structure to the dispersed polydomain structure due to the pressure gradient generated during centrifugation.ation.

• Tribology and Lubricants
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• 제22권6호
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• pp.307-313
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• 2006

In this paper, a theoretical analysis is carried out to study the effect of viscosity variation with pressure in multiply grooved moving hydraulic spool valves. Analytical expressions for pressure distribution in the clearance and leakage flowrate are obtained solving one-dimensional Reynolds. For constant viscosity, an analytical expression for lateral force is also presented. The results showed that variation of viscosity with pressure affect highly on pressure distribution, leakage flowrate and lateral forces in hydraulic spool valves. Therefore additional intensive studies, including numerical analysis for two-dimensional Reynolds, should be required to investigate detailed lubrication characteristics of spool valves for high pressure.

• Korea-Australia Rheology Journal
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• 제16권3호
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• pp.153-160
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• 2004

Open microcellular foams having small-sized cell and good mechanical properties are desirable for many practical applications. As an effort to reduce the cell size, the microcellular foams combining viscosity improvers into the conventional formulation of styrene and water system were prepared via high internal phase emulsion polymerization. Since the material properties of foam are closely related to the solution properties of emulsion state before polymerization, the flow behavior of emulsions was investigated using a controlled stress rheometer. The yield stress and the storage modulus increased as viscosity improver concentration and agitation speed increased, due to the reduced cell size reflecting both a competition between the continuous phase viscosity and the viscosity ratio and an increase of shear force. Appreciable tendency was found between the rheological data of emulsions and the cell sizes of polymerized foams. Cell size reduction with the concentration of viscosity improver could be explained by the relation between capillary number and viscosity ratio. A correlative study for the cell size reduction with agitation speed was also attempted and the result was in a good accordance with the hydrodynamic theory.

• Korea-Australia Rheology Journal
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• 제14권4호
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• pp.189-201
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• 2002

The interaction between hydrophobically modified hydroxyethyl cellulose (hmHEC), containing approximately 1 wt% side-alkyl chains of $C_{16}$, and an anionic sodium dodecyl sulphate (SDS) surfactant was investigated. For a semi-dilute solution of 0.5 wt% hmHEC, the previously observed behaviour of a maximum in solution viscosity at intermediate SDS concentrations, followed by a drop at higher SDS concentrations, until above the cmc of surfactant when the solution resembles that of the unsubstituted polymer, was confirmed. Additionally, a two-phase region containing a hydrogel phase and a water-like supernatant was found at low SDS concentrations up to 0.2 wt%, a concentration which is akin to the critical association concentration, cac, of SDS in the presence of hmHEC. Above this concentration, SDS molecules bind strongly to form mixed micellar aggregates with the polymer alkyl side-chains, thus strengthening the network junctions, resulting in the observed increase in viscosity and elastic modulus of the solution. The shear behaviour of this polymer-surfactant complex during steady and step stress experiments was examined In great detail. Between SDS concentrations of 0.2 and 0.25 wt%, the shear viscosity of the hmHEC-polymer complex network undergoes shear-induced thickening, followed by a two-stage shear-induced fracture or break-up of the network. The thickening is thought to be due to structural rearrangement, causing the network of flexible polymers to expand, enabling some polymer hydrophobic groups to be converted from intra- to inter-chain associations. At higher applied stress, a partial local break-up of the network occurs, while at even higher stress, above the critical or network yield stress, a complete fracture of the network into small microgel-like units, Is believed to occur. This second network rupture is progressive with time of shear and no steady state in viscosity was observed even after 300 s. The structure which was reformed after the cessation of shear is found to be significantly different from the original state.