• Journal of Microbiology and Biotechnology
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• 제5권2호
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• pp.61-67
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• 1995

To investigate the role of induction on CGTase production for alkalophilic Bacillus firm us var. alkalophilus H609, the constitutive mutants that form a halo around its colonies at non-inducible AG agar media containing amylose and glucose were selected. The selected constitutive mutants could produce CGTase in the range of 18.9 to 28.8 units/ml $\cdot A_{600}$ in the alkaline basal medium, and finally a constitutive mutant Bacillus firmus var. alkalophilus CM46 was selected. The constitutive nature of CM46 was also confirmed in protein level using SDS-PAGE. The effects of induction and catabolite repression for both parent strain Bacillus firmus var. alkalophilus H609 and constitutive mutant CM46 were also compared by adding soluble starch and glucose during cultivation. The selected mutant CM46 was a non-inducible but a catabolite regulated type mutant. Even though inductive regulation was released, the specific CGTase activity defined as CGTase activity per cell concentration was not increased compared with that of parent strain. The cell growth and CGTase production patterns of constitutive mutant Bacillus firmus var. alkalophilus CM46 were compared with the parent strain to identify CGTase production characteristics.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.233-236
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• 2004

The major objective of this paper is to clarify the effect of constitutive laws on bulk forming design based on the ideal flow theory. The latter theory is in general applicable for perfectly/plastic materials. However, its kinematics equations constitute a closed-form system, which are valid for any incompressible materials, therefore enabling us to extend design solutions based on the perfectly/plastic constitutive law to more realistic laws with rate sensitive hardening behavior. In the present paper, several constitutive laws commonly accepted for the modeling of cold and hot metal forming processes are considered and the effect of these laws on one particular plane-strain design is demonstrated. The closed form solution obtained describes a non-trivial nonsteady ideal process. The design solutions based on the ideal flow theory are not unique. To achieve the uniqueness, the criterion that the plastic work required to deform the initial shape of a given class of shapes into a prescribed final shape attains its minimum is adopted. Comparison with a non-ideal process is also made.

• Computers and Concrete
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• 제8권4호
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• pp.371-388
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• 2011

In this paper, time-continuous constitutive equations for strain rate-dependent materials are presented first, among which those for the overstress and the consistency viscoplastic models are considered. By allowing the stress states to be outside the yield surface, the overstress viscoplastic model directly defines the flow rule for viscoplastic strain rate. In comparison, a rate-dependent yield surface is defined in the consistency viscoplastic model, so that the standard Kuhn-Tucker loading/unloading condition still remains true for rate-dependent plasticity. Based on the formulation of the consistency viscoplasticity, a computational elasto-viscoplastic constitutive model is proposed for the short fiber-reinforced fresh cementitious paste for extrusion purpose. The proposed constitutive model adopts the von-Mises yield criterion, the associated flow rule and nonlinear strain rate-hardening law. It is found that the predicted flow stresses of the extrudable fresh cementitious paste agree well with experimental results. The rate-form constitutive equations are then integrated into an incremental formulation, which is implemented into a numerical framework based on ANSYS/LS-DYNA finite element code. Then, a series of upsetting and ram extrusion processes are simulated. It is found that the predicted forming load-time data are in good agreement with experimental results, suggesting that the proposed constitutive model could describe the elasto-viscoplastic behavior of the short fiber-reinforced extrudable fresh cementitious paste.

• 한국지반공학회지:지반
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• 제12권4호
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• pp.145-156
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• 1996

연약한 지반의 거동을 적절하게 표현할 수 있는 일반 등방경화 규칙에 근거한 비등방경화 구성모델을 비선형 유한요소해석에 적용하기 위하여 내재적인 응력적분기법을 정식화하였다. 정식화된 응력적분기법은 비선형 해석시에 필요한 응력을 일반 사다리꼴규칙에 의하여 내재적으로 적분하고 응력변형률 접선계수를 비선형 해법에 일관되게 도출할 수 있다. 이러한 알고리즘을 통하여 해의 정확도 및 수렴도를 확보할 수 있으므로, 비등방경화 구성 관계를 적용한 비선형 해석을 정확하고 효율적으로 수행할 수 있는 토대를 구축할 수 있었다.

• Korea-Australia Rheology Journal
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• 제14권1호
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• pp.33-45
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• 2002

Recent results obtained for the port-pom model and the constitutive equations with time-strain separability are examined. The time-strain separability in viscoelastic systems Is not a rule derived from fundamental principles but merely a hypothesis based on experimental phenomena, stress relaxation at long times. The violation of separability in the short-time response just after a step strain is also well understood (Archer, 1999). In constitutive modeling, time-strain separability has been extensively employed because of its theoretical simplicity and practical convenience. Here we present a simple analysis that verifies this hypothesis inevitably incurs mathematical inconsistency in the viewpoint of stability. Employing an asymptotic analysis, we show that both differential and integral constitutive equations based on time-strain separability are either Hadamard-type unstable or dissipative unstable. The conclusion drawn in this study is shown to be applicable to the Doi-Edwards model (with independent alignment approximation). Hence, the Hadamardtype instability of the Doi-Edwards model results from the time-strain separability in its formulation, and its remedy may lie in the transition mechanism from Rouse to reptational relaxation supposed by Doi and Edwards. Recently in order to describe the complex rheological behavior of polymer melts with long side branches like low density polyethylene, new constitutive equations called the port-pom equations have been derived in the integral/differential form and also in the simplifled differential type by McLeish and carson on the basis of the reptation dynamics with simplifled branch structure taken into account. In this study mathematical stability analysis under short and high frequency wave disturbances has been performed for these constitutive equations. It is proved that the differential model is globally Hadamard stable, and the integral model seems stable, as long as the orientation tensor remains positive definite or the smooth strain history in the flow is previously given. However cautious attention has to be paid when one employs the simplified version of the constitutive equations without arm withdrawal, since neglecting the arm withdrawal immediately yields Hadamard instability. In the flow regime of creep shear flow where the applied constant shear stress exceeds the maximum achievable value in the steady flow curves, the constitutive equations exhibit severe instability that the solution possesses strong discontinuity at the moment of change of chain dynamics mechanisms.

• 한국지능시스템학회논문지
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• 제15권2호
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• pp.251-256
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• 2005

Up to now, a number of models have been proposed and discussed to describe a wide range of inelastic behaviors of materials. The fetal problem of using such models is however the existence of model errors, and the problem remains inevitably as far as a material model is written explicitly. In this paper, the authors define the implicit constitutive model and propose an implicit viscoplastic constitutive model using neural networks. In their modeling, inelastic material behaviors are generalized in a state space representation and the state space form is constructed by a neural network using input output data sets. A technique to extract the input-output data from experimental data is also described. The proposed model was first generated from pseudo-experimental data created by one of the widely used constitutive models and was found to replace the model well. Then, having been tested with the actual experimental data, the proposed model resulted in a negligible amount of model errors indicating its superiority to all the existing explicit models in accuracy.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제9권3호
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• pp.191-197
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• 2009

Up to now, a number of models have been proposed and discussed to describe a wide range of inelastic behaviors of materials. The fatal problem of using such models is however the existence of model errors, and the problem remains inevitably as far as a material model is written explicitly. In this paper, the authors define the implicit constitutive model and propose an implicit viscoplastic constitutive model using neural networks. In their modeling, inelastic material behaviors are generalized in a state space representation and the state space form is constructed by a neural network using input-output data sets. A technique to extract the input-output data from experimental data is also described. The proposed model was first generated from pseudo-experimental data created by one of the widely used constitutive models and was found to replace the model well. Then, having been tested with the actual experimental data, the proposed model resulted in a negligible amount of model errors indicating its superiority to all the existing explicit models in accuracy.

• 한국가금학회지
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• 제17권4호
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• pp.275-280
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• 1990

Constitutive heterochromatin의 염색체 다형현상에 대해 사람을 비롯하여 돼지, 생쥐, 말, 닭 등에서 보고된 바 있다. 본 연구에서는 일본산메추리의 C－band 다형체 뿐만 아니라 염색체의 형태적 다형체를 발견하여 이의 다형현상을 밝혔다. 일반적인 염색체 분석방법 및 C－banding 방법으로서 밝힌 3가지 염색체 다형체는 4번 염색체 ＋/－ 동형체, ＋/－ 이형체 및 －/－ 동형체이다. 이와 같은 다형체들은 무작위 집단 내에서 일반적이고 지속적으로 나타나며 Mendel 법칙에 따른 유전양상을 보인다. 따라서 본 연구에서 밝힌 염색체 다형체들은 여러 세포유전학적 연구에 표식인자(chromosome marker)로서 유용하게 이용되어질 수 있을 것으로 생각된다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1995년도 가을 학술발표회 논문집
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• pp.178-184
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• 1995

A new combined isotropic/kinematic and orthotropic hardening viscoplastic model is proposed which can account for not only differential orientations but also preferred orientations of grains in n metal at finite plastic deformations with an introduction of multiple spin (rate of rotation) concept within the general framework of the model, the effects of anisotropy and constitutive spins will be discussed in conjunction with a closed-form solution for simple shear in n rigid-plastic material, which will be used to simulate experimental data of Montheillet, et al. (1984) for fixed-end tortion tests at finite plastic deformations.

• Geomechanics and Engineering
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• 제1권4호
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• pp.263-274
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• 2009

The modified Cam clay (MCC) model is used to study the response of virgin compressed clay in undrained compression. The MCC deviatoric stress-strain relationship is obtained in closed form. Elastic and plastic deviatoric strains are taken into account in the analysis. For the determination of the elastic strain components, both a variable shear modulus and constant shear modulus are considered. Constitutive relationships are applied to the well-known London and Weald clays sheared in undrained compression.