• Geomechanics and Engineering
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• v.11 no.4
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• pp.587-605
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• 2016

This study aimed to develop upper and lower bounds to predict the tunnel support pressure under the pile tip during the circular tunnel excavation. Most previous studies on the upper and lower bound methods were carried out for the single ground structures, e.g., retaining wall, foundation, ground anchor and tunnel, in the homogeneous ground conditions, since the pile-soil-tunnel interaction problem is very complicated and sophisticated to solve using those bound methods. Therefore, in the lower bound approach two appropriate stress fields were proposed for single pile and tunnel respectively, and then they were superimposed. In addition, based on the superimposition several failure mechanisms were proposed for the upper bound solution. Finally, these upper bound mechanisms were examined by shear strain data from the laboratory model test and numerical analysis using finite element method.

• Steel and Composite Structures
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• v.15 no.2
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• pp.221-245
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• 2013

This paper presents an analytical solution to the thermomechanical bending analysis of functionally graded sandwich plates by using a new hyperbolic shear deformation theory in which the stretching effect is included. The modulus of elasticity of plates is assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic ceramic material. The effects of functionally graded material (FGM) layer thickness, volume fraction index, layer thickness ratio, thickness ratio and aspect ratio on the deflections and stresses of functionally graded sandwich plates are investigated.

• Journal of Powder Materials
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• v.11 no.1
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• pp.22-27
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• 2004

The Indium Tin Oxide(ITO) nano powders were prepared by spray drying and heat treatment process. The liquid solution dissolved Indium and Tin salts was first spray dried to prepare chemically homogeneous recursor powders at the optimum spray drying conditions. Subsequently, the precursor powders were subjected to eat treatment process. The nano size ITO powders was synthesized from the previous precursor powders and the npuities also were decreased with increasing heat treatment temperature. Furthermore, the lattice parameter of TO nano powders was increased by doping Tin into Indium with increasing heat treatment temperature. The par icle size of the resultant ITO powders was about 20∼50nm and chemical composition was composed of In:Sn =86:10 wt.％ at 80$0^{\circ}C$.

• Journal of the Korean Mathematical Society
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• v.47 no.2
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• pp.425-443
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• 2010

We investigate the Schr$\ddot{o}$dinger type operator $H_2\;=\;(-\Delta_{\mathbb{H}^n})^2+V^2$ on the Heisenberg group $\mathbb{H}^n$, where $\Delta_{\mathbb{H}^n}$ is the sublaplacian and the nonnegative potential V belongs to the reverse H$\ddot{o}$lder class $B_q$ for $q\geq\frac{Q}{2}$, where Q is the homogeneous dimension of $\mathbb{H}^n$. We shall establish the estimates of the fundamental solution for the operator $H_2$ and obtain the $L^p$ estimates for the operator $\nabla^4_{\mathbb{H}^n}H^{-1}_2$, where $\nabla_{\mathbb{H}^n}$ is the gradient operator on $\mathbb{H}^n$.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.10-13
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• 2002

Pogo is the instability resulting from the interaction between rocket structure and propulsion system of liquid propellant rocket. The coupling of structure and propulsion system can lead to severe problem in rocket. For the analysis of pogo, a time-invariant linearized mathematical model is developed for a selected flight time. Propulsion system is modeled using element representations for each components. The constitutive equation of propulsion system is a homogeneous second-order equation form in the Laplace domain. Rocket structure is modeled using FEM. From the results of modal analysis of structure, the behavior of structure can be represented. System equations for coupling structure and propulsion system are composed of all propulsion system equations and vehicle motion equations reacting on the vehicle by each component of propulsion system. The stability is obtained by the eigen solution of system matrix. The optimization of the design variables such as size, place of accumulator for suppressing pogo instability is carried out. This article of study can be used to determine the degree of stability, and guide the design of pogo suppression system.

• Computers and Concrete
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• v.3 no.6
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• pp.423-437
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• 2006

Stress wave propagation through concrete is simulated by finite element analysis. The concrete medium is modeled as a homogeneous material with smeared properties to investigate and establish the suitable finite element analysis method (explicit versus implicit) and analysis parameters (element size, and solution time increment) also suitable for rigorous investigation. In the next step, finite element analysis model of the medium is developed using a digital image processing technique, which distinguishes the mortar and aggregate phases of concrete. The mortar and aggregate phase topologies are, then, directly mapped to the finite element mesh to form a heterogeneous concrete model. The heterogeneous concrete model is then used to simulate wave propagation. The veracity of the model is demonstrated by evaluating the intrinsic parameters of nondestructive ultrasonic pulse velocity testing of concrete. Quantitative relationships between aggregate size and testing frequency for nondestructive testing are presented.

• Journal of Powder Materials
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• v.9 no.3
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• pp.161-166
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• 2002

Processing and properties of $Al_2O_3$ composites with Ni-Fe content of 10 and 15 wt% were investigated. Homogeneous powder mixtures of $Al_2O_3$/Ni-Fe alloy were prepared by the solution-chemistry route using $Al_2O_3$, $Ni(NO_3)_2{\cdot}6H_2O$ and $Fe(NO_3)_3{\cdot}9H_2O$ powders. Microstructural observation of composite powder revealed that Ni-Fe alloy particles with a size of 20nm were homogeneously dispersed on $Al_2O_3$ powder surfaces. Hot-pressed composites showed enhanced fracture toughness and magnetic response. The properties are discussed based on the observed microstructural characteristics.

• Journal of the Korean Applied Science and Technology
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• v.10 no.1
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• pp.9-22
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• 1993

Recent studies on enzyme reactions in organic solvents are revived. The reactions are classified into three categories: heterogeneous, biphasic and homogeneous systems. The following subjects are described and discussed about the heterogeneous system. 1) The maximal expression of enzyme activity in organic solvents in terms of water content, hydration of enzyme, and equilibriun of water between enzyme and substrate solution. 2) Solvent effect on the catalytic power of enzyme. 3) Thermostability and thermoreactivity. 4) Applications of the enzyme reactions to synthetic chemistry.

• Bulletin of the Korean Mathematical Society
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• v.55 no.2
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• pp.533-543
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• 2018

Under the symbol ${\Omega}$ is a combination of ${\phi}_i$ ($i=1,2,3,{\ldots},n$) which has a suitable growth condition, for dimension n = 2 and $n{\geq}3$, when the initial data f belongs to homogeneous Sobolev space, we obtain the global $L^q$ estimate for maximal operators generated by operators family $\{S_{t,{\Omega}}\}_{t{\in}{\mathbb{R}}}$ associated with solution to dispersive equations, which extend some results in [27].

• Kyungpook Mathematical Journal
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• v.45 no.1
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• pp.105-114
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• 2005

In this paper we investigate the growth of finite order solutions of the differential equation $f^{(k)}\;+\;A_{k-1}(Z)f^{(k-l)}\;+\;{\cdots}\;+\;A_1(z)f^{\prime}\;+\;A_0(z)f\;=\;F(z)$, where $A_0(z),\;{\cdots}\;,\;A_{k-1}(Z)\;and\;F(z)\;{\neq}\;0$ are entire functions. We find conditions on the coefficients which will guarantees the existence of an asymptotic value for a transcendental entire solution of finite order and its derivatives. We also estimate the lower bounds of order of solutions if one of the coefficient is dominant in the sense that has larger order than any other coefficients.