• Journal of Preventive Medicine and Public Health
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• v.15 no.1
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• pp.153-159
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• 1982

A statistical study on medical students who entered certain college of medicine during 10 years ('73 to '82) was performed in order to evaluate medical educational wastage. The obtained results summerized were as follows; 1. The normal promotion rate of 10 cohorts(CI-CX) was 83.4% and 5 cohorts(CI to CV) whose members had already graduated(including dropouts) was 77.5%. 2. The mean repetition rate in 1st grade was 15.5%, in 2nd grade 5.4%, in 3rd grade 1.4% arid in 4th grade 0.6%. 3. The predicted number of repetion(spell base) which are attendance at the college in 1st grade was 31.6, in 2nd grade 28.9, in 3rd grade 18.6 and in 4th grade 22.7; 4. The total wastage of 10 cohorts was 224.8 SY, which corresponded to educational resources of 56.2 out-puts for normal demand. 5. The mean unit cost of 10 cohorts was 4.62 and the mean Input/Output ratio was 1.06.

• Journal of Ocean Engineering and Technology
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• v.25 no.6
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• pp.1-8
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• 2011

This paper describes a new method for a digital gas metal arc welding (GMAW) system. The GMAW system is an arc welding process that incorporates the GMAW power source (PS-GMAW) with a wire feed unit (WFU). The PS-GMAW requires an electric power of constant voltage. A constant magnitude is maintained for the arc current by controlling the wire-feed speed of the WFU. A mathematical model is derived, and a self-tuning fuzzy proportional-integral-derivative (PID) controller is designed and applied to control the welding current. The electrode wire feeding mechanism with this controller is driven by a DC motor, which can compensate for both the molten part of the electrode and undesirable fluctuations in the arc length during the welding process. By accurately maintaining the output welding current and welding voltage at constant values during the welding process, excellent welding results can be obtained. Simulation and experimental results are shown to prove the effectiveness of the proposed controller.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.2
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• pp.95-101
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• 2011

In wireless X networks where all transmitters send the independent messages to all receivers, the theoretical bound on the degrees of freedom (DOF) and interference alignment (IA) scheme for its achievability are given by Cadambe and Jafar [1]. However, IA scheme for wireless X network may be infeasible in practice unless the transmitters have the perfect channel information. In addition, if the transmitter with single antenna uses time-varying channel coefficients as a beamforming vector, the infinite channel extension is required to achieve the theoretical bound on the DOF of wireless X networks with perfect IA scheme. In this paper, we consider K-user MIMO X network where K transmitters and K receivers have M antennas each. While the beamforming vectors have been constructed with multiple channel uses over multiple time slot in the earlier work, we consider the beamforming vectors constructed only by a spatial signature over unit time. Accordingly the channel information at the transmitters can be available instantaneously. Then we propose the perfect IA scheme with no channel extension. Based on our sum-rate analysis and the simulation results, we confirm that our proposed scheme can achieve MK/2 DOF which is quite close to the theoretical bound on the DOF region of wireless X networks.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.2
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• pp.107-114
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• 2014

This paper proposes a common rail pressure control algorithm for passenger car diesel engines. For handling the parameter-varying characteristics of common rail systems, the quantitative feedback theory (QFT) is applied to the design of a robust rail pressure control algorithm. The driving current of the pressure control valve and the common rail pressure are used as the input/output variables for the common rail system model. The model parameter uncertainty ranges are identified through experiments. Rail pressure controller requirements in terms of tracking performance, robust stability, and disturbance rejection are defined on a Nichols chart, and these requirements are fulfilled by designing a compensator and a prefilter in the QFT framework. The proposed common rail pressure control algorithm is validated through engine experiments. The experimental results show that the proposed rail pressure controller has a good degree of consistency under various operating conditions, and it successfully satisfies the requirements for reference tracking and disturbance rejection.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.2070-2078
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• 2014

In this work, the frequency response of gate-all-around (GAA) Ge/GaAs heterojunction tunneling field-effect transistor (TFET) with hetero-gate-dielectric (HGD) and pnpn channel doping profile has been analysed by technology computer-aided design (TCAD) device-circuit mixed-mode simulations, with comparison studies among ppn, pnpn, and HGD pnpn TFET devices. By recursive tracing of voltage transfer curves (VTCs) of a common-source (CS) amplifier based on the HGD pnpn TFET, the operation point (Q-point) was obtained at $V_{DS}=1V$, where the maximum available output swing was acquired without waveform distortion. The slope of VTC of the amplifier was 9.21 V/V (19.4 dB), which mainly resulted from the ponderable direct-current (DC) characteristics of HGD pnpn TFET. Along with the DC performances, frequency response with a small-signal voltage of 10 mV has been closely investigated in terms of voltage gain ($A_v$), unit-gain frequency ($f_{unity}$), and cut-off frequency ($f_T$). The Ge/GaAs HGD pnpn TFET demonstrated $A_v=19.4dB$, $f_{unity}=10THz$, $f_T=0.487$ THz and $f_{max}=18THz$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.189-194
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• 2020

This paper analyzes the gradient descent method, which is the one most used for learning neural networks. Learning means updating a parameter so the loss function is at its minimum. The loss function quantifies the difference between actual and predicted values. The gradient descent method uses the slope of the loss function to update the parameter to minimize error, and is currently used in libraries that provide the best deep learning algorithms. However, these algorithms are provided in the form of a black box, making it difficult to identify the advantages and disadvantages of various gradient descent methods. This paper analyzes the characteristics of the stochastic gradient descent method, the momentum method, the AdaGrad method, and the Adadelta method, which are currently used gradient descent methods. The experimental data used a modified National Institute of Standards and Technology (MNIST) data set that is widely used to verify neural networks. The hidden layer consists of two layers: the first with 500 neurons, and the second with 300. The activation function of the output layer is the softmax function, and the rectified linear unit function is used for the remaining input and hidden layers. The loss function uses cross-entropy error.

• The Journal of the Korea Contents Association
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• v.9 no.7
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• pp.67-75
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• 2009

IEEE 802.11 WLAN(Wireless Local Area Network) standard is currently developing with increased wireless internet demand. Study trends of IEEE 802.11n for high throughput show two aspects, enhanced system throughput using aggregation among packets in MAC(Medium Access Control) layer, and better data rates adapting MIMO(Multiple-Input Multiple-Output) in PRY(Physical) layer. But, no one demonstrates IEEE 802.11n system performance results considering MAC and PRY connection. This paper adapts A-MPDU(Aggregation-MAC Protocol Data Unit) method in MAC layer and MIMO in PRY layer for IEEE 802.11n system. Consequently, Simulation results show enhanced throughput and data rates compared to existing system. Also, We use NS-2(Network Simulator-2) considering MAC and PRY connection for reality.

• The Journal of the Korea Contents Association
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• v.20 no.10
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• pp.496-509
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• 2020

This study analyzes 5-year efficiency of the game industry, from 2014 to 2018 which is aimed at 25 online and mobile game companies, that are emerging as a new growth engine of a national economy to come and as a core areas of late entertainment industry. The DEA is used for static efficiency analyze and the DEA-Window is used for dynamic efficiency analyze. This study uses assets, the number of employees and costs as input variables and it also uses operating profits and sales as output variables. The main results show that scale efficiency presents a resonable result over 0.85 on a total average except 2014. However, there has not been a year that is over 0.80 of the whole period in technical efficiency. Also, in terms of business scale, there is a huge efficiency gap between high rank companies and low rank companies and the average trend of efficiency has been increased from 2014 to 2016 but it has been decreased since 2017.

• Journal of Korean Library and Information Science Society
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• v.40 no.1
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• pp.253-274
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• 2009

Data Envelopment Analysis(DEA) model is a linear programing based technique for measuring the relative performance of organizational units where the presence of multiple inputs and outputs makes comparison difficult. DEA model allows each unit to adopt a set of weight that shows it in the most favorable light in comparison to the other units. The purpose of this study was to evaluate the performance of the libraries of national university in terms of relative efficiency, measured by the method of DEA. Twenty six libraries of national universities in Korea were used to analyze. The number of employees, size of library, budget, and number of books were used for input data, and the number of visitors, number of loan books, and number of books for lending and borrowing were used for output data. We found out that number of libraries with 100% relative efficiency among 26 libraries from 2005 to 2007 were only 9, 9 and 10, respectively. Moreover most of the libraries need to increase outputs and decrease inputs in order to improve efficiency.

• Journal of Advanced Navigation Technology
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• v.6 no.3
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• pp.188-194
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• 2002

DBS is utilized as very useful media in information-oriented society because it covers wide service area and provide high quality services. But DBS needs skill that can receive DBS signal at move. In this paper, it is considered a development of a device to receive DBS and design of a low noise downconverter that use tracking antenna to receive DBS at mobiles unit and ships which navigate in Korea peninsula coast. The structure of dual phase LNB is composed of LNA, BPF, oscillator, mixer, and IF amplifier. And for the position tracking, two input-output phase performed in phase. Measured results showed good performance that with respect to input signal 11.7 GHz~12.2 GHz, noise figure is 0.87 dBmax and conversion gain 62 dB, temperature characterization ${\pm}400$ kHz in respect to - 30 to $60^{\circ}C$, and phase noise -101 dBc/Hz in respect to offset 100 kHz.