• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.456-461
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• 2017

본 연구에서는 이산화규소를 젤화제로 사용한 니트로메탄 젤 추진제의 유변학적 특성을 분석하였다. 니트로메탄 젤은 나노 또는 마이크로 입자 크기의 젤화제를 각각 5 wt%, 6.5 wt%, 8 wt% 함량으로 첨가하여 제작되였으며 점도 측정 실험은 회전형 점도계를 이용하여 측정을 수행하였다. 제작된 젤 추진제는 항복응력이 존재함을 확인하였고 측정 범위 전 구간에서 전단박화 거동을 보이며 나노 크기의 젤화제를 첨가한 젤 추진제의 경우 마이크로 크기 대비 낮은 전단속도(1 ~ 100 1/s) 영역에서 높은 점도를 보였다. 또한 니트로메탄 젤 추진제의 경우, Herschel-Bulkley 모델 보다는 Teipel과 Forter-Barth가 제시한 모델을 사용하는 것이 적합함을 확인하였다.

• Journal of Microbiology and Biotechnology
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• 제3권3호
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• pp.209-213
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• 1993

The flow behavior of the mycelial broth of glucoamylase hyperproducer Asp. niger No. PFST-38 for the production of glucoamylase were studied. The mycelial broth followed Bingham-pseudoplastic flow model described by Herschel-Bulkley equation. The yield stress increased with the increase in mycelial concentration. The dependency of the consistency index and the flow behavior index on the mycelial concentration could be expressed by a linear relationship. The consistency index increased proportionally with the mycelial concentration while the flow behavior index decreased with the increase in mycelial concentration. The flow property of the broth was related to the morphological data obtain in the previous study. The changes in apparent viscosity of the broth could be expressed as a function of the hyphal thickness as shown below.

• 한국농공학회지
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• 제45권4호
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• pp.137-143
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• 2003

The initial condition of $\Delta \sigma_3 \;=\; \Delta u$ is used for analyzing the time dependent behavior of ground. This is based on the concept that the coefficient of pore water B is the unity on the condition of saturation. but some measured consolidation data in the field showed that the pore water pressure was not dissipated as time elapsed but it was maintained constant value or it's dissipation rate was slower than that of the predicted. and so the measured data of pore water pressure was not consistent with that of settlement. In this study, the rheological model for the pore water pressure behavior on undrained condition was induced and compared with the experiment data of the literature. The result showed that the suggested model was consistent well with the result of experiment, but the suggested model could not explain the effect of the decrease of void ratio according to consolidation.

• Korea-Australia Rheology Journal
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• 제17권4호
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• pp.191-198
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• 2005

The static and dynamic rheological behavior of concentrated sodium dodecylsulfate (SDS) stabilized, deformability controllable polydimethylsiloxane (PDMS) emulsions is reported and comparisons made with silica (hard sphere) suspensions. Steady-mode measurements indicate 'hard' (viscoelastic) droplets behave as hard spheres, while 'soft' (viscous) droplets induce structural flexibility of the emulsion against shear. Dynamic-mode measurements reveal that viscoelasticity of droplets provides the great magnitude of elasticity for the 'hard' emulsion, while formation of planar films between droplets is the origin of the elasticity of 'soft' emulsions. Combination of steady and dynamic rheological behavior has enabled depiction of droplet structure evolution in relation to the shear stress applied, especially by taking advantage of the normal force that reflects the transient deformation of droplets.

• Journal of Biosystems Engineering
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• 제15권3호
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• pp.219-229
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• 1990

The compression creep behavior of grains when loaded depends not only on load but also on duration of load application. The most common methods of studying the load-time characteristics of agricultural products is by employing rheological models such as Burger's model. However it is sometimes not sufficient to describe the viscoelastic behavior of grains to be Burger's model. For this reason, this study was conducted to develop the rheological model which represented the creep compliance response of the rough rice kernel and was a function of initial stress applied and time. The effects of the initial stress applied and the moisture content on the compression creep behavior of the rough rice kernel were analyzed. The results were obtained from the study as follows: 1. Since the viscoelastic behavior of the rough rice kernel was nonlinear, the transient and steady state creep compliance was satisfactorily modelled as follows: $$J({\sigma},t)=A{\sigma}^B[C+Dt-exp(-Ft)]$$ But, for the every stress applied, the compression creep behavior of the samples tested can be well described by Burger's model respectively. 2. The creep compliance, the instantaneous elastic strain, the retarded elastic strain and the viscous strain of the sample tested generally increased in magnitude with increasing the applied initial stress and the moisture content used in the tests. At low moisture content, the creep compliance for the Japonica-type rough rice kernel Was a little higher than those for Indica-type and at high moisture content, vice versa at high moisture content. 3. The retardation times of the samples had not an uniform tendency by the initial stress and the moisture content. The retardation times ranged from 0.66 to 6.76 seconds, and the creep progressed from transient to steady state at a relatively high rate. 4. The less viscous strain than the instantaneous elastic strain for the samples tested indicated that rough rice kernel behaved as a viscoelastic body characterized by elasticity than viscosity.

• Computers and Concrete
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• 제8권3호
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• pp.279-292
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• 2011

The main purpose of this study includes investigation of the rheological properties of fresh self consolidating cement paste containing chemical and mineral additives using Artificial Neural Network (ANN) model. In order to develop the model, 200 different mixes are cast in the laboratory as a part of an extensive experimental research program. The data used in the ANN model are arranged in a format of fourteen input parameters covering water-binder ratio, four different mineral additives (calcium carbonate, metakaolin, silica fume, and limestone), five different superplasticizers based on the poly carboxylate and naphthalene and four different Viscosity Modified Admixtures (VMAs). Two common output parameters including the mini slump value and flow cone time are chosen for measuring the rheological properties of fresh self consolidating cement paste. Having validated the model, the influence of effective parameters on the rheological properties of fresh self consolidating cement paste is investigated based on the ANN model outputs. The output results of the model are then compared with the results of previous studies performed by other researchers. Ultimately, the analysis of the model outputs determines the optimal percentage of additives which has a strong influence on the rheological properties of fresh self consolidating cement paste. The proposed ANN model shows that metakaolin and silica fume affect the rheological properties in the same manner. In addition, for providing the suitable rheological properties, the ANN model introduces the optimal percentage of metakaolin, silica fume, calcium carbonate and limestone as 15, 15, 20 and 20% by cement weight, respectively.

• Food Science and Biotechnology
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• 제17권2호
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• pp.417-420
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• 2008

Rheological properties of sweet potato starch (SPS)-glucose composites (5%, w/w) at different concentrations (0, 10, 20, and 30%, w/w) of glucose were investigated in steady and dynamic shear. The steady shear rheological properties of SPS-glucose composites were determined from rheological parameters for power law and Casson flow models. At $25^{\circ}C$ all the samples showed a pronounced shear-thinning behaviors (n=0.29-0.37) with high Casson yield stress. In general, the presence of glucose resulted in the decrease in consistence index (K), apparent viscosity (${\eta}_{a,100}$), and yield stress (${\sigma}_{oc}$). Storage (G') and loss (G") moduli increased with an increase in frequency ($\omega$), while complex viscosity (${\eta}*$) decreased. Dynamic moduli (G', G", and ${\eta}*$) of the SPS-glucose composites at higher glucose concentrations (20 and 30%) were higher than those of the control (0% glucose) and also increased with increasing glucose concentration from 10 to 30%. The effect of glucose on steady and dynamic shear rheological properties of the SPS pastes appears to greatly depend on glucose concentration in the range of 10-30%.

• International Journal of Industrial Entomology and Biomaterials
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• 제40권1호
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• pp.28-32
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• 2020

Recently, many studies have been undertaken on the wet spinning and electrospinning of silk because wet-spun fibers and electrospun webs of silk can be applied in the biomedical and cosmetic fields owing to the good biocompatibility of silk. The rheological properties of silk solution are important because they strongly affect the spinning performance of the silk solution and the structures of resultant fibrous materials. Therefore, as a preliminary study on the effect of solvent composition on the rheological properties of silk fibroin (SF) solution and structure of the resultant film, in the reported work, methanol was added to the SF formic acid solution. A small amount of methanol (i.e. 2%) added to the SF formic acid solution significantly altered the rheological properties of the solution: its shear viscosity increased by 10 folds at low shear and decreased on increasing the shear rate, demonstrating shear thinning behavior of the SF solution. Dynamic tests for the SF solution indicated that the addition of 2% methanol altered the viscous state of the SF formic acid solution to elastic. However, the molecular conformation (i.e. β-sheet conformation) of the regenerated SF film cast from formic acid remained unchanged on the addition of 2% methanol.

• Preventive Nutrition and Food Science
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• 제21권4호
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• pp.367-372
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• 2016

To understand the effects of adding different gums (guar, xanthan, and locust bean gums) on naked barley flour (NBF), the rheological and pasting properties of NBF-gum mixtures were measured at different gum concentrations (0, 0.3, and 0.6% w/w). Steady shear rheological properties were determined by rheological parameters for power law and Casson models. All samples showed a clear trend of shear-thinning behavior (n=0.16~0.48) and had a non-Newtonian nature with yield stress. Consistency index, apparent viscosity, and yield stress values increased with an increase in gum concentration. Storage modulus values were more predominant than loss modulus values with all concentrations of gums. There is a more pronounced synergistic effect of elastic properties of NBF in the presence of xanthan gum. Rapid visco analyser pasting properties showed that the addition of gums resulted in a significant increase in the peak, breakdown, setback, and final viscosities, whereas the pasting temperature decreased.

• Food Science and Biotechnology
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• 제15권4호
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• pp.589-594
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• 2006

The effect of five commercial gums (carboxylmethylcellulose, CMC; guar gum, GG; hydroxypropylmethyl-cellulose, HPMC; locust bean gum, LBG; and xanthan gum) at a concentration of 0.25% on the rheological properties of rice flour (RF) dispersions was investigated in steady and dynamic shear. The steady shear rheological properties showed that RF gum mixture dispersions (5%, w/w) at $25^{\circ}C$ had high shear-thinning flow behavior (n=0.20-0.31) exhibiting a yield stress. Magnitudes of consistency index (K), apparent viscosity (${\eta}_{a,100}$), and Casson yield stress (${\sigma}_{oc}$) of RF-gum mixtures were much higher than those of RF dispersion with no added gum (control). Activation energy values (6.67-10.8 kJ/mole) of RF-gum mixtures within the temperature range of $25-70^{\circ}C$ were lower than that (11.9 kJ/mole) of the control. Dynamic rheological data of log (G', G") versus log frequency (${\omega}$) of RF-gum mixtures had positive slopes (0.15-0.37) with G' greater than G" over most of the frequency range (0.63-63 rad/sec), demonstrating a frequency dependency. Tan ${\delta}$ (G"/G') values of RF-gum mixtures, except for xanthan gum, were much higher than that of the control.