• Structural Engineering and Mechanics
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• v.21 no.5
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• pp.539-551
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• 2005

Finite elements based on isoparametric formulation are known to suffer spurious stiffness properties and corresponding stress oscillations, even when care is taken to ensure that completeness and continuity requirements are enforced. This occurs frequently when the physics of the problem requires multiple strain components to be defined. This kind of error, commonly known as locking, can be circumvented by using reduced integration techniques to evaluate the element stiffness matrices instead of the full integration that is mathematically prescribed. However, the reduced integration technique itself can have a further drawback - rank deficiency, which physically implies that spurious energy modes (e.g., hourglass modes) are introduced because of reduced integration. Such instability in an existing stiffness matrix is generally detected by means of an eigenvalue test. In this paper we show that a knowledge of the dimension of the solution space spanned by the column vectors of the strain-displacement matrix can be used to identify the instabilities arising in an element due to reduced/selective integration techniques a priori, without having to complete the element stiffness matrix formulation and then test for zero eigenvalues.

• Journal of the Korean Ceramic Society
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• v.27 no.3
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• pp.299-310
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• 1990

The fabrication of Y-Ba-Cu-O films and experimental factors affecting to characteristics of films are studied in detail. Superconducting thick films are fabricated by the screen printing method. The metal-citrate precursors are obtained simply by mixing of metal nitrate with citric acid. The particle size of heat treated powders is approximately 0.3-1${\mu}{\textrm}{m}$ and the thickness of film is estimated as 30-35${\mu}{\textrm}{m}$. According to the XRD analysis, the films sintered at 870-93$0^{\circ}C$ for 10min. -6hr with P(oxygen)=1atm has the unique orthorhombic crystal symmetry indicating the 123 phae. Tc, onset is determined around 92-87。K, but it shows semiconducting behavior probably due to the oxygen deficiency in the lattice, porosity and impurities in films. Extrapolated Tc, zero is estimated as 76-50。K. For films sintered at 90$0^{\circ}C$ for 1hr, superconducting properties are observed with the room temperature resistivity of 0.025$\Omega$.cm Tc, onset at 88。K and Tc, zero at 63。K.

• Journal of the Korean Operations Research and Management Science Society
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• v.20 no.1
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• pp.115-130
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• 1995

This paper considers a single machine nonpreemptive scheduling problem with a given common due date. In the problem, the optimal job sequence is sought to minimize the sum of earliness/tardiness and flow time measures in the situation where all jobs are available at time zero, and weights per unit length of earliness/tardiness and flow time are V and W, respectively. Some dominant solution properties are characterized to deriva both an optimal starting time for an arbitrary sequence and sequence improvement rules. The optimal schedule is found to the case W .geq. V/. By the way, it is difficult to find the optimal schedule for the case W < V. Therefore, the derived properties are put on together to construct a heuristic solution algorithm for the case W < V, and its effectiveness is rated at the mean relative error of about 3% on randomly generated numerical problems.

• Journal of the Korean institute of surface engineering
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• v.27 no.3
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• pp.149-157
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• 1994

The formation of spangles on a hot dip galvanized sheet steel by spray cooling the molten zinc coating with air, water and 2.0wt% $NH_4H_2PO_4$ solution has been studied performing laboratory experiments, and their coating properties have been evaluated. Minimized spangles were easily formed by mist spraying the solution for 1 second at the low nozzle spray pressure onto the molten zinc at 420~$422^{\circ}C$ because the solute $NH_4H_2PO_4$ in the sprayed solution imparted a highly rapid cooling effect to the coating through its endothermic de-composition reactions and because the decomposed products acted as numerous nucleation sites for the mini-mized spangles on the coating. Good surface appearances sand sound coating properties were obtained on this coating. Only regular spangles were formed on the coating by the forced convective air cooling. At the high nozzle spray pressure, zero spangles were formed on the coating by the pure water spray cooling. However, the coating had a dull and rough surface with craters sand cracks.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.1209-1210
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• 2006

This paper presents a single phase high power factor PWM boost rectifier featuring soft commutat -ion of the active switches at zero current. It incorporates the most desirable properties of conventional PWM and soft switching resonant techniques. The input current shaping is achieved with average current mode control and continuous inductor current mode. This new PWM converter provides zero current turn on and turn off of the active switches, and it is suitable for high power applications employing IGBT's. The principle of operation, the theoretical analysis, a design example, and experi -mental results from a laboratory prototype rated at 1.6[kW] with 400[Vdc] output voltage are presented. The measured efficiency and the power factor were 96.2[%] and 0.99[%], respectively, with an input current THD equal to 3.94[%], for an input voltage with THD equal to 3.8[%], at rated load.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1169-1171
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• 2003

This paper presents a 1.6[kW]class single phase high power factor(HPF) pulse width modulation(PWM) boost rectifier featuring soft commutation of the active switches at zero current. It incorporates the most desirable properties of conventional PWM and soft switching resonant techniques. The input current shaping is achieved with average current mode control and continuous inductor current mode. This new PWM converter provides zero current turn on and turn off of the active switches, and it is suitable for high power applications employing insulated gate bipolar transistors(IGBT'S). The principle of operation, the theoretical analysis, a design example, and experimental results from laboratory prototype rated at 1.6[kW] with 400[Vdc] output voltage are presented. The measured efficiency and the power factor were 96.2[%] and 0.99[%], respectively, with an input current Total Harmonic Distortion(THD) equal to 3.94[%], for an input voltage with THD equal to 3.8[%], at rated load.

• Journal of the Korean Ceramic Society
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• v.23 no.6
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• pp.59-65
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• 1986

Flexural strength fracture toughness and strengthening mechanisms of cordierite ceramics reinforced by SiC whiskers up to 40vol% were investigated. The specimens were hot pressed at Ar atmosphere. The porosity increased with the SiC whisker content. Flexural strength and single edge notch beam fracture toughness were measured up to 1,000$^{\circ}C$. Extrapolating to zero porosity the reinforced composites exhibited in-creasings in flexural strength and fracture toughness with the SiC whisker content. The composites were strengthened mainly by load transfer crack impediment and partially by crack deflection mechanisms. Impurities played an important role in determining the mechanical properties of the composites.

• Journal of the Korean Ceramic Society
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• v.23 no.3
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• pp.62-66
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• 1986

Mechanical properties of $Al_2O_3$ based composite ceramics reinforced by SiC whiskers up to 40% by volume we-re investigated. Specimens were hot pressed at $1, 500^{\circ}C$ under 28.5MPa for 30min in Ar atmosphere. Porosities room temperaturefracture toughnesses and flexural strengths up $1, 000^{\circ}C$ were measured. Porosities were increa-sed as the SiC whisker cortent increased. After compensating the effect of porosities that means extrapolated in zero porosities the reinforced composites exhibited increases in flexural strength and fracture toughness as the whi-sker content increased, .

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.353-355
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• 2004

YBaCuO thick films were fabricated by plasma enhanced chemical vapor deposition, and the crystallinity and the superconducting properties were investigated. The growth temperature to obtain the thick films was decreased by around $150^{\circ}C$ due to plasma enhancement. The zero resistivity temperatures for films grown at $590^{\circ}C$ and $620^{\circ}C$ were 55 and 80 K, resistively.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.1
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• pp.15-20
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• 2016

Compared to the MIMO system using the spatial multiplexing methods and the MIMO system using the diversity scheme achieved a high rate, but the lower the diversity gain to improve the data transmission reliability should separate the spatial stream at the MIMO receiver. In this paper, we compared Channel capacity detection methods with the Lattice code, the 3-user interference channel and linear channel interference detection methods ZF (Zero Forcing) and MMSE (Minimum Mean Square Error) detection methods. The channel is a Diagonal channel. In other words, Diagonal channel is confirmed by the inverse matrix satisfies the properties of Jacket are element-wise inverse to $[H]_N[H]_N^{-1}=[I]_N$.