• 응용통계연구
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• 제32권5호
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• pp.693-702
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• 2019

딥러닝은 대용량의 데이터의 분류 및 예측하는 방법으로 각광받고 있다. 데이터의 양이 많아지면서 신경망의 구조는 더 깊어 지고 있다. 이때 초기값이 지나치게 클 경우 층이 깊어 질수록 활성화 함수의 기울기가 매우 작아지는 포화(Saturation)현상이 발생한다. 이러한 포화현상은 가중치의 학습능력을 저하시키는 현상을 발생시키기 때문에 초기값의 중요성이 커지고 있다.이런 포화현상 문제를 해결하기 위해 Glorot과 Bengio (2010)과 He 등 (2015) 층과 층 사이에 데이터가 다양하게 흘러야 효율적인 신경망학습이 가능하고 주장했다. 데이터가 다양하게 흐르기 위해서는 각 층의 출력에 대한 분산과 입력에 대한 분산이 동일해야 한다고 제안했다. Glorot과 Bengio (2010)과 He 등 (2015)는 각 층별 활성화 값의 분산이 같다고 가정해 초기값을 설정하였다. 본 논문에서는 절단된 코쉬 분포와 절단된 정규분포를 활용하여 초기값을 설정하는 방안을 제안한다. 출력에 대한 분산과 입력에 대한 분산의 값을 동일하게 맞춰주고 그 값이 절단된 확률분포의 분산과 같게 적용함으로써 큰 초기값이 나오는 걸 제한하고 0에 가까운 값이 나오도록 분포를 조정하였다. 제안된 방법은 MNIST 데이터와 CIFAR-10 데이터를 DNN과 CNN 모델에 각각 적용하여 실험함으로써 기존의 초기값 설정방법보다 모델의 성능을 좋게 한다는 것을 보였다.

• 한국지반공학회논문집
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• 제25권5호
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• pp.75-86
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• 2009

공학적 관점에서 용해가능한 가장 흔한 재료인 소금은 고결화 작용에 있어서 역학적 거동에 큰 영향을 미친다. 이러한 자연적 현상을 조사하기 위하여 용해되지 않는 재료인 글라스비즈와 소금물을 혼합하여 시료를 조성한 후 오븐을 이용하여 포화도를 변화시켜가면서 실험을 수행하였다. 입자크기가 0.26, 0.50, 1.29mm인 3종류의 글라스비즈와 0.0, 0.1, 0.2, 0.5, 1.0, 2.0M의 소금물에 대하여 각각의 시료를 조성 후 벤더 엘리먼트와 피에조 디스크 엘리먼트를 이용하여 전단파와 압축파를 측정하였다 소금에 의한 고결화 발생에서 전단파와 압축파 속도 모두 포화도에 따른 세가지 단계를 보여주었다: 1) 포차도가 $100%{\sim}90%$인 구간으로 전단파의 속도는 증가하고 압축파의 속도는 감소한다; 2) 포화도가 $90%{\sim}10%$인 구간으로 전단파와 압축파의 속도에 큰 변화가 없파; 3) 포화도가 $10%{\sim}0%$인 구간으로 전단파 및 압축파는 큰 변화를 보인다. 또한, 전단파의 공진주파수는 전단파의 속도 변화양상과 비슷한 경향을 보였다. 본 연구는 용해된 소금의 고결화에 따른 지반재료들의 탄성파 특성의 의미있는 경향을 보여준다.

• 한국결정성장학회지
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• 제17권1호
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• pp.11-17
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• 2007

The spherical NiZn ferrite particles were prepared by ultrasonic spray pyrolysis with mixed solution of aqueous metal nitrates. The NiZn ferrite particle was observed with nano-sized primary particles of about 10 nm or less before annealing which represented as paramagnetic behavior measured at 77 K and room temperature. The typical abnormal growth of primary particles like polyhedral primary particles was observed by annealing at 1273 K with Zn-concentration dependency. The XRD patterns showed good crystallinity of NiZn ferrite powder after annealing. In annealing process, the intra-particle sintering phenomenon was observed and the spherical particle morphology was collapsed at 1673 K. The saturation magnetization of NiZn ferrite powder for each annealing temperature was decreased with measuring temperature of $77{\sim}$300K.

• 한국전기전자재료학회논문지
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• 제13권6호
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• pp.533-537
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• 2000

It was known that chalcogenide glasses have the superior property of the photoinduced anisotropy(PA). In this study we observed the phenomenon of Ag polarized-photodoping in chalcogenide As$_{40}$ /Ge$_{10}$/Se$_{15}$ /S$_{35}$ and the double-layer of Ag doped As$_{40}$ /Ge$_{10}$/Se$_{15}$ /S$_{35}$ thin film using the irradiation with the polarized He-Ne laser light. The Ag polarized-photodoping results in reducing the time of saturation anisotorpy and increasing the sensitivity of linearly anisotropy intensity up to maximum 220% The Ag polrized-photodoping shows improvement of the photoinduced anisotropy property in polarized photodoping of the chalcogenide thin film. It will offer lots of information for the photodoping mechanism and analysis of chalcogenide thin film.in film.ilm.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.1966-1971
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• 2005

Though several previous anti-windup techniques have been proposed, they are limited to linear systems or friction is not considered. Thus this paper proposes a compensation scheme for input-constrained robot systems with friction to cope with the windup phenomenon and shows its effectiveness by simulations. Given a feedback linearizing controller for a robot system designed without considering its input constraint, an additional dynamic compensator is proposed to account for the constraint. The dynamic anti-windup is based on the minimization of a reasonable performance index, and properties of the resulting closed-loop are presented.

• JSTS:Journal of Semiconductor Technology and Science
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• 제13권4호
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• pp.361-366
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• 2013

A full-range analytic drain current model for depletion-mode long-channel surrounding-gate nanowire field-effect transistor (SGNWFET) is proposed. The model is derived from the solution of the 1-D cylindrical Poisson equation which includes dopant and mobile charges, by using the Pao-Sah gradual channel approximation and the full-depletion approximation. The proposed model captures the phenomenon of the bulk conduction mechanism in all regions of device operation (subthreshold, linear, and saturation regions). It has been shown that the continuous model is in complete agreement with the numerical simulations.

• 산업기술연구
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• 제34권
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• pp.15-20
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• 2014

Recently, PMSMs(Permanent Magnet Synchronous Motors) have become increasingly popular in various high-performance motor drive applications. However, the high-performance drive of PMSMs needs a position sensor such as a resolver, which increases not only the price of the system but also reduces the system reliability. This paper is on the implementation of sensorless control of a SPMSM, which drives a fan for cooling in appliances. In this paper, the rotor position for high-performance drive of a SPMSM is derived from back electromotive force (EMF) information proportional to the rotor speed. Also, the initial rotor position information for start-up is estimated from a saturation phenomenon of inductance. The validity of the proposed sensorless drives was confirmed by the experiment on the SPMSM drive systems for cooling fans of refrigerators and laptop computers.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.944-945
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• 2015

Many sensitive loads always rely on UPS systems to maintain continuous power during abnormal utility power conditions. As any disturbance occurs at the utility side, an off-line UPS system takes over the load within a quarter cycle to avoid a blackout. However, the starting of the inverter can root the momentous inrush current for the transformer installed before the load, due to its magnetic saturation. The consequences of this current can be a reduction of line voltage and tripping of protective devices of the UPS system. Furthermore, it can also damage the transformer and decrease its lifetime by increasing the mechanical stresses on its windings. To prevent the inrush current, and to avoid its disruptive effects, this paper proposes an off-line UPS system that eliminates the inrush current phenomenon while powering the transformer coupled loads, using a current regulated voltage source inverter (CRVSI) instead of a typical voltage source inverter (VSI). Simulations have been performed to validate the operation of proposed off-line UPS system.

• Journal of Mechanical Science and Technology
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• 제17권5호
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• pp.740-750
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• 2003

It has been observed that the cooling capacity of an impinging water jet is affected by the seasonal conditions in large-scale steel manufacturing processes. To confirm this phenomenon, cooling experiments utilizing a hot steel plate cooled by a laminar jet were conducted for two initial ambient air temperatures (10$^{\circ}C$ and 40$^{\circ}C$) in a closed chamber, performing an inverse heat conduction method for quantitative comparison. This study reveals that the cooling capacity at an air temperature of 10$^{\circ}C$ is lower than the heat extracted at 40$^{\circ}C$. The amount of total extracted heat at 10$^{\circ}C$ is 15% less than at 40$^{\circ}C$ , These results Indicate the quantity of water vapor, absorbed until saturation, affects the mechanism of boiling heat transfer.

• 비파괴검사학회지
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• 제10권2호
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• pp.56-62
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• 1990

Surface Acoustic Waves(SAW) are generated on silicon wafer and $YZ-LiTaO_3$ substrate and are detected by noncontact method. As wave sources two kinds of transducers are used : the wedge-type of 20.0 MHz and fabricated Interdigital Transducer(IDT) of 20.8 MHz. SAW are modulated by the optical chopper frequency and are syncronized with a laser beam. In signal processing, intensity variations of light due to the intensity of SAW are analyzed using lock- in amplifier. From the results, corresponding to the applied input power, the intensity variations of a deflected light by corrugations on the substrates are increased and saturation phenomenon is observed.