• Journal of the Korean Ceramic Society
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• v.33 no.3
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• pp.269-276
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• 1996

The effect of sintering aids on the sinterability for silcion nitride has been studied by hundreds workers. However the effect of sintering aids on the machinability as the own trobles which is the major barrier for the field applications of the ceramic components has not been fully studied. in this study the contents of Al2O3 and Y2O3 in silicon nitride were varied from 0 to 8 wt% respectively. The physical and mechanical properties of the silcion nitride were measured. The optimal microstructure of silicon nitride balls with the excellent machinability by adding with various contents of sintering aids was studied by MGF(magnetic-fluid grinding)technique. An attempt to figure out how the mechanical properties influence the machinability of silicon-nitride ball was made.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.155-156
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• 2008

This paper provides a general and compact expression for the probability density function (pdf) and the moment-generating function (MGF) of the maximal ratio combiner output over Rayleigh fading channels. It is then used to derive closed form expression outage probability for repetition code problem. A variety of simulations is performed and shows that they match exactly with analytic ones.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.29A no.2
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• pp.18-23
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• 1992

Recently, SSPAs(Solid-State Power Amplifiers) with high linearity and efficiency replace TWTAs (Traveling-Wave-Tube Amplifiers) in satellite transponders. In this paper, a power amplifier with maximum output power is designed and constructed using GaAs FET(MGF-1302) as a test model for the development of SSPAs. For conjugate matching of input and output network, transimission lines and stubs are optimized using microwave CAD program, LINMIC+. Power amplifier is realized on the teflon substrate($\in$S1rT=2.45) with a bandwidth of 1GHz at a center frequency of 8GHz. Maximum stable gain of simulation and simulation and experimental result is obtained 9.23, 7.65 dB, respectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.283-284
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• 2006

In this paper 3-point weighing method is adopted to measure the unbalance moment of small-sized precision spinning elements using electronic scales with 0.1 mgf resolution. Firstly methods to eliminate the fixture error and to reduce the effects of frictional force that is known as side effect, are proposed. A measuring system is developed and various experiments are performed to verify the proposed approach. The measured and calculated values are analysed in statistical methods, and this provides the errors of the measuring system. The results show that the proposed theory and test procedures gives reliable unbalance moments and gravitational centers.

• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.376-382
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• 2017

Graphene nanoribbons with zigzag-shaped edge (zGNRs) are predicted to be magnetic insulator at the ground state, attracting significant interest in view of spintronic applications [1]. On the other hand, although they are energetically and thermodynamically more favored than zGNRs [2], graphene nanoribbons with armchair-shaped edge (aGNRs) have been less spotlighted than zGNRs due to the absence of magnetism. Herein, based on the combined density functional theory (DFT) and matrix Green's function (MGF) approach, we consider aGNRs functionalized with various molecular groups, and show that the spin polarizations develop for some of the considered aGNR edge functionalization cases. The origin of the induced magnetism will be discussed within the Lieb's theorem [3]. This work will provide a novel guidance for the development of graphene-based spintronic devices.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.24 no.63
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• pp.65-77
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• 2001

A more technical perspective is needed in estimating the effect of the Manufacturing Process for improving the Productivity, there are many statistical evaluation methods, convenience sampling, frequencies, histogram, QC seven tools, control chart etc. It is more important for the companies to use six sigma to reduce defective and improve the process control than the technical definition as a disciplined quantitative approach for improvement of process control and a new way of quality innovation. Process network analysis is a technique which has the potentiality for a wide use to improve the manufacturing process which other techniques can't be used to analyze effectively. It has some problems to analyze the process with feedback loops. The branch probabilities during quality inspections depend upon the number of times the product has been rejected. This paper presents how to improve the manufacturing process by statistical process control using branch probabilities, Moment Generating Function(MGF) and Sensitivity Equation.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.4
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• pp.333-346
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• 2002

The continuous indentation techniques are one of the most effective methods to nondestructively estimate mechanical properties. There are many applications in various dimensions of materials from macro-scale, through micro-scale, even to nano-scale range. The macro-range technology of kgf-load level is now focused on the evaluation of tensile properties and residual stress of bulk materials, for example, used in conventional load-bearing structures and in-use pipelines. The technology and the apparatus were successfully developed by a domestic research group. The micro-range technology of gf-load level can be applied to investigate some property-gradient materials such as weldment. Because it has better spatial resolution than the macro-range technology. The nano-range technology (called nanoindentation technique) of mgf-load level is basically used to evaluate hardness and modulus of micro- and nano-materials. Moreover, many researches are going on to measure tensile properties and residual stress. The nanoindentation technology is easy to be applied to the various fields, such as semiconductor devices, multiphase materials, and biomaterials, though other methods are too difficult to be applied due to dimensional or environmental limitations. On the basis of these accomplishments, the international and the domestic standards are being established.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.9
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• pp.987-994
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• 2010

In this paper, a simple and effective active load-pull method is proposed, and the method to improve the efficiency of X-band power amplifier using harmonic control circuit is presented. The proposed active load-pull system mainly consists of directional coupler, phase shifter, short circuit, and power amplifier, and allows a user to access reflection coefficients near the edge of the Smith chart($\Gamma$=1) easily. The device used in this paper is Mitsubishi's GaAs FET MGF1801, and the operating frequency of the power amplifier is 9 GHz, The amplifier had output power of 21.65 dBm and drain efficiency of 24.9 % at class-A, and had output power of 21.46 dBm and drain efficiency of 53.3 % at class-AB. Harmonic control circuit is designed only second and third harmonic components because of the bandwidth limitation of the microwave components. The drain efficiency is improved as much as 6.4 % compared with class-AB power amplifier.

• KSBB Journal
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• v.16 no.2
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• pp.133-139
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• 2001

To treat piggery wastewaters containing refractory compounds including nitrogen, biological treatments were investigated. In biological treatment, the removal efficiencies of organics and nitrogen by the activated sludge process and bioreactor using a BACC (Biological Activated Carbon Cartridge) media filled with granular activated carbon were examined. The results were as follows; in the biological process, when the approximate influent BOD concentration of 620 mg/L, through dilution, was treated by the activated sludge process, the process should be operated at a HRT of over 8 days to maintain an effluent BOD concentration of lower than 100 mg/L. In the treatment of piggery wastewater using a BACC bioreactor, when the HRT was 200 hours, the BOD, COD(sub)cr, and TKN removal efficiency of the effluent were 94, 75 and 64.3%, respectively. Comparing the BACC bioreactor with the activated sludge process, when the volumetric loading rate was 0.3 g BOD/L.day, the specific substrate removal rate of BOD was 0.14 g BOD removed/L.day in the activated sludge process which compared with 0.27 g BOD removed/L$.$day in the BACC bioreactor. The BACC bioreactor showed on average a 2-fold higher removal rate and was superior to the activated sludge process in wastewater treatment in terms of variations of loading time and high loading time. Therefore, the BACC process can effectively treat piggery wastewater containing high concentrations of nitrogen and organic compounds.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.1186-1190
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• 1995

This paper is focused on the formulation of explicit closed-form functions describing the performance measures of the general flexible manufacturing system (FMS)according to the strategy of material handling system(MHS). the performance measures such as the production rate, the production lead-time and the utilization rate of the general FMS are expressed, respectively, as the explicit closed-form functions of the part processing time, the service rate of the material handling system (MHS) and the number of machine tools in the FMS. For this, the gensral FMS is presented as a generalized stochastic Petri net model, then, the moment generating function (MGF) based approach is applied to obtain the steady-state probabity formulation. Based on the steady-state formulation, the explicit closed-form functions for performance measures of the probability FMS can be obtained. Finally, the analytical results are compared with the Petri net simulation results to verify the validity of the suggested method. The paper is of significance in the sense that it provides a comprehensive formula for performance measures of the FMS even to the industry engineers and academic reademic resuarchers who have no background on Markov chain analysis method or Petrinet modeling