• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.207-210
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• 2002

Metal matrix composites(MMCs) are increasingly attractive for high technology components such as aerospace applications and transportations due to their high strength, stiffness, and toughness. Many processes for fabricating MMCs have been developed, and relatively simple Foil-Fiber-Foil method is usually employed in solid state consolidation processes. During the consolidation processes at high temperature, densification occurs by the inelastic flow of the matrix materials, and the process is coupled with the conditions of pressure, temperature and volume fraction of fiber and matrix materials. This is particularly important in titanium matrix composites, and thus a generic model based on micro-mechanical approaches enabling the evolution of density over time to be predicted has been developed. The mode developed is then implemented into FEM so that practical process simulation has been carried out. Further the experimental investigation of the consolidation behavior of SiC/Ti-6Al-4V composites using vacuum hot pressing has been performed, and the results obtained are compared with the model predictions.

• Mass Spectrometry Letters
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• v.4 no.1
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• pp.21-23
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• 2013

The effects of trifluoroacetic acid (TFA) were evaluated on the generation of multiply charged ions of cytochrome c in a 2-nitrophloroglucinol (2-NPG) matrix in high-vacuum, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The presence of 1% TFA in the 2-NPG matrix solution was more effective in generating multiply charged protein ions than matrix solutions containing 0.1% or 0% TFA. Regarding the matrix itself, with 1% TFA, 2-NPG was significantly more effective in generating multiply charged ions than 2,5-dihydroxybenzoic acid (2,5-DHB). The maximum charge state of cytochrome c was +8 when using a 2-NPG matrix containing 1% TFA.

• Journal of the Korean Society of Safety
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• v.13 no.2
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• pp.45-53
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• 1998

A method to predict the creep behavior of fiber-reinforced ceramic composites at high temperatures was suggested based on finite element modeling using constituent creep equations of fiber and matrix and showed good agreement with the experimental results. The effects of matrix creep behavior, fiber volume fraction, and residual stresses on the composite creep behavior were also investigated. The results showed that the primary behavior of composites was greatly affected by that of matrix but post-primary behavior was governed by fiber creep characteristics. The increase of fiber volume fraction from 15 vol% to 30 vol% caused the 50% and 40% decrease of steady-state creep rates and total creep strains at $1200^{\circ}C$, 180MPa, respectively. Feasible compressive residual stresses in the matrix caused by different thermal expansion coefficients between the fiber and the matrix could significantly reduce total creep strains of the composite. The creep deformation mechanism in the fiber-reinforced ceramic composites could be explained by the stress transfer and redistribution in the fiber and matrix due to different creep characteristics of its constituents.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.12
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• pp.751-758
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• 2004

This paper presents a new method to compensate the non-linearity for matrix converter drives using PQR instantaneous Power theory. The non-linearity of matrix converter drives such as commutation delay, turn-on and turn-off time of switching device, and on-state switching device voltage drop is modelled by PQR power theory and compensated using a reference current control scheme. The proposed method does not need any additional hardware and off-line experimental measurements. The proposed compensation method is applied for high performance induction motor drives using a 3 kW matrix converter system without a speed sensor. Simulation and experimental results show the proposed method using PQR power theory Provides good compensating characteristic.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.180-183
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• 1997

The forming process of metal matrix composites by the die casting and squeeze casting process are limited in size and dimension in term of final parts without machining. The thixoforming process for metal matrix composites has numerous advantages compared to die casting, squeeze casting and compocasting. The characteristics of thixoforming process can decrease the liquid segregation because of he improvement in fluidity in a globular microstructure state and utilizes flow without air entrapment. Therefore, in order to obtain the sound parts of metal matrix composites by using thixoforming process which as co-existing solidus-liquidus pahse, it si very important to obtain reheating condition. However, for he thixoforming process, the billet with the desired volume fraction must be heated to obtain a uniform temperature distribution over the entire cross-sectional areas. To obtain the reheating conditions of composites, the particulate reinforced metal matrix composites for thixoforming were fabricated by combined stirring process which is simultaneously performed with electro-magnetic stirring process which is simultaneously performed with electro-magnetic stirring and mechanical stirring process.

• Journal of the Korean Institute of Telematics and Electronics
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• v.16 no.5
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• pp.18-26
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• 1979

This paper extends some well-known system theories on algebraic matrix Lyapunov and Riccati equations. These extended results contain two point boundary conditions in matrix differential equations and include conventional results as special cases. Necessary and sufficient conditions are derived under which linear systems are stabilizable with feedback gains derived from periodic two-point boundary matrix differential equations. An iterative computation method for two-point boundary differential Riccati equations is given with an initial guess method. The results in this paper are related to periodic feedback controls and also to the quadratic cost problem with a discrete state penalty.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.12
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• pp.1330-1337
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• 2004

In this study, the equations of motion of a rigid rotor supported by magnetic bearings are derived via Hamilton's principle, and transformed to a state-space form for control purpose. The optimal motion control of rotor magnetic bearing system based on the LQR(linear quadratic regulator) theory is addressed. New schemes related to the selection of the state weighting matrix Q and the control weighting matrix R involved in the quadratic functional to be minimized are proposed. And the robust control of the system with an LMI(linear matrix inequality) based H$_{\infty}$ theory is dealt with in this paper. Loop shapings of TFM (transfer function matrix) are used to increase the performance of control capability of the system. The control abilities of LQR and H$_{\infty}$ controller are compared by simulation and experimental tests and show that the capability of H$_{\infty}$ controller is superior to that of LQR.

• Asian Pacific Journal of Cancer Prevention
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• v.14 no.2
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• pp.873-876
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• 2013

Our aim was to test the hypothesis that preoperative serum levels of matrix metalloproteinase-7 (MMP-7) and -9 (MMP-9) and tissue inhibitor of matrix metalloproteinase (TIMP-1) levels correlate with pathological features. Serum levels of MMP-7, and MMP-9 and TIMP-1 were determined in 90 bladder cancer patients and 40 healthy controls using an enzyme linked immunosorbent assay. Preoperative serum MMP-7 and MMP-9 levels were significantly higher in cancer patients than control groups (p<0.001). In contast, serum TIMP-1 levels were lower (p<0.001). Alteration in MMP-7, and MMP-9, and TIMP-1 production may contribute to tumor angiogenesis and be associated with clinic-pathological features.

• Geomechanics and Engineering
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• v.28 no.2
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• pp.135-143
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• 2022

Soils are natural granular materials whose mechanical properties differ according to the size and composition of the particles, so soils exhibit an obvious scale effect. Traditional soil mechanics is based on continuum mechanics, which can not reflect the impact of particle size on soil mechanics. On that basis, a matrix-reinforcing-particle cell model is established in which the reinforcing particles are larger-diameter sand particles and the matrix comprises smaller-diameter bentonite particles. Since these two types of particles deform differently under shear stress, a new shear-strength theory under direct shear that considers the stress concentration and bypass phenomena of the matrix is established. In order to verify the rationality of this theory, a series of direct shear tests with different reinforcing particle diameter and volume fraction ratio are carried out. Theoretical analysis and experimental results showed that the interaction among particles of differing size and composition is the basic reason for the size effect of soils. Furthermore, the stress concentration and bypass phenomena of the matrix enhance the shear strength of a soil, and the volume ratio of reinforcing particles has an obvious impact on the shear strength. In addition, the newly proposed shear-strength theory agrees well with experimental values.

• International Journal of Control, Automation, and Systems
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• v.6 no.6
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• pp.915-927
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• 2008

Networked control systems(NCSs) have gained increasing attention in recent years due to their advantages and potential applications. The network Quality-of-Service(QoS) in NCSs always fluctuates due to changes of the traffic load and available network resources. To handle the network QoS variations problem, this paper presents an intelligent scheduling control method for NCSs, where the sampling period and the control parameters are simultaneously scheduled to compensate the effect of QoS variation on NCSs performance. For NCSs with network-induced delays and packet dropouts, a discrete-time switch model is proposed. By defining a sampling-period-dependent Lyapunov function and a common quadratic Lyapunov function, the stability conditions are derived for NCSs in terms of linear matrix inequalities(LMIs). Based on the obtained stability conditions, the corresponding controller design problem is solved and the performance optimization problem is also investigated. Simulation results are given to demonstrate the effectiveness of the proposed approaches.