• Current Optics and Photonics
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• v.2 no.3
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• pp.233-240
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• 2018

We proposed a two-mode fiber (TMF) design that can effectively reduce the mode overlap between $LP_{01}$ and $LP_{11}$ modes by using a W-shaped index profile core structure, which is a primary concern in uncoupled mode division multiplexing (MDM). TMF has a three-layered core structure; central circular core, inner cladding, and outer ring core. We confirmed that in an optimal structure the $LP_{01}$ mode was highly confined to the central core while the $LP_{11}$ mode was guided along the outer ring core to result in a minimum overlap integral. We used a full-vectorial finite element method to estimate effective index, differential group delay (DGD), confinement loss, chromatic dispersion, and mode overlap controlling the parameters of the W-shaped structure. The optimized W-profile fiber provided optical characteristics within the ITU-T recommended standards over the entire C+L band.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.3
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• pp.223-230
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• 1999

A conventional sliding mode control approach is often impractical or difficult when it is applied to high order process b because the number of tuning parameters in the sliding mode controller increases with the order of the plant. C Camacho(l996) proposed a design method of a fixed structure sliding mode controller based on a first order plus dead t time approximation to the higher-order process. But, his method has such problems as chattering, over‘shoot, and c command following due to the Taylor the approximation en‘ors for the time delay term of the first order model. In this p paper, a new design technique for a sliding mode controller based on the modified Taylor approximation considered a w weight is developed to improve the Camacho's problems.

• Smart Structures and Systems
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• v.29 no.4
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• pp.617-624
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• 2022

A new intelligent adaptive control scheme was proposed that combines the control based on interference observer and fuzzy adaptive s-curve for flight path tracking control of unmanned aerial vehicle (UAV). The most important contribution is that the control configurations don't need to know the uncertainty limit of the vehicle and the influence of interference is removed. The proposed control law is an integration of fuzzy control estimator and adaptive proportional integral (PI) compensator with input. The rated feedback drive specifies the desired dynamic properties of the closed control loop based on the known properties of the preferred acceleration vector. At the same time, the adaptive PI control compensate for the unknown of perturbation. Additional terms such as s-surface control can ensure rapid convergence due to the non-linear representation on the surface and also improve the stability. In addition, the observer improves the robustness of the adaptive fuzzy system. It has been proven that the stability of the regulatory system can be ensured according to linear matrix equality based Lyapunov's theory. In summary, the numerical simulation results show the efficiency and the feasibility by the use of the robust control methodology.

• Development and Reproduction
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• v.20 no.4
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• pp.289-296
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• 2016

This report describes the sex differentiation of the Korean rose bitterling, Rhodeus uyekii, from hatching to 170 days post-hatch (DPH) in relation to total length (TL), body weight (BW), and integral water temperature (IWT). The growth curve of TL from just hatching to 83 DPH was $5.144e^{0.045t}$ ($R^2=0.961$; t, time), and that of BW was $2.398e^{0.086t}$ ($R^2=0.725$). Primordial germ cells (PGCs) were observed at 17 DPH (7.9 mm TL, 3.74 mg BW, $374^{\circ}C$ IWT), and thereafter began to protrude into the peritoneal cavity. At 21 DPH ($9.2{\pm}0.14mm$ TL, $4.8{\pm}0.07mg$ BW, $462^{\circ}C$ IWT), some PGCs contained condensed chromatin and oocyte were observed in meiotic prophase. In contrast to the ovaries, which grew gradually after sexual differentiation, testes began multiplying at 25 DPH (10.1 mm TL, 5.42 mg BW, $550^{\circ}C$ IWT), when testicular differentiation was first identified, and multiplied continuously thereafter. At 33 DPH (11.2 mm TL, 10.5 mg BW, $726^{\circ}C$ IWT), the developing testes contained spermatogonia that exhibited mitotic activity. No spermatocyte or sperm cell was observed until 83 DPH (18.9 TL, 48.2 mg BW, $1,826^{\circ}C$ IWT). At 170 DPH (32.5 mm TL, 270.1 mg BW, $3,740^{\circ}C$ IWT), which was the end point of this study, the mature ovaries showed germinal vesicle breakdown, while the mature testes contained observable spermatocytes and sperm cells. These results allow us to identify the sex differentiation type of the Korean rose bitterling as differentiated gonochoristic.

• Journal of the Korean Magnetics Society
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• v.2 no.1
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• pp.1-7
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• 1992

Deuterium was injected into melt-spun ribbons of ${\alpha}-Fe_{90}Zr_{10}$ using the electrolytic hydrogenation method, and the magnetic properties of these ${\alpha}-D_{x}Fe_{90}Zr_{10}$ ribbons were studied. By comparing these results with those of ${\alpha}-H_{x}Fe_{91}Zr_{9}$, the effects of phonons to magnetic properties were investigated. The Curie temperature $T_{c}$, and the spontaneous magnetizations of the $D_{47}Fe_{90}Zr_{10}$ and the $Fe_{90}Zr_{10}$ were studied using the Mbssbauer spectroscopy. From these investigations, it was found that the Curie temperature of $D_{x}Fe_{90}Zr_{10}$ was 75K higher than that of $Fe_{90}Zr_{10}$. It was believed that this indicated the importance of local deformation to the amorphous magnetism. Also by comparing the spontaneous magnetizations of $D_{47}Fe_{90}Zr_{10}$ with those of $Fe_{90}Zr_{10}$ as a function of temperature, it was found that the deuterium injection reduced the fluctuation of exchange integral.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.8
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• pp.693-701
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• 2016

In this study, notch defects are evaluated using fracture mechanics. To understand the effects of notch defects, FE analysis is conducted to predict the limit load and J-integral for middle-cracked and single-edge cracked plates with various sizes of notch under tension and bending. As the radius of the notch increases, the energy release rate also increases, although the limit load remains constant. The values of fracture toughness($J_{IC}$) of SM490A are determined for various notch radii through FE simulation instead of conducting an experiment. As the radius of the notch increases, the energy release rate also increases, together with a more significant increase in fracture toughness. To conclude, as the notch radius increases, the resistance to crack propagation also increases.

• Journal of the Korean Solar Energy Society
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• v.33 no.3
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• pp.42-50
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• 2013

Solar thermal reactor was studied for hydrogen production with a two step thermochemical cycle including T-R(Thermal Reduction) step and W-D(Water Decomposition) step. NiFe2O4 and Fe3O4 supported by monoclinic ZrO2 were used as a catalyst device and Ni powder was used for decreasing the T-R step reaction temperature. Maintaining a temperature level of about $1100^{\circ}C$ and $1400^{\circ}C$, for 2-step thermochemical reaction, is important for obtaining maximum performance of hydrogen production. The controller was designed for adjusting high temperature solar thermal energy heating the foam-device coated with nickel- ferrite powder. A Pill temperature control system was designed based on 2-step thermochemical reaction experiment data(measured concentrated solar radiation and the temperature of foam device during experiment). The cycle repeated 5 times, ferrite conversion rate are 4.49~29.97% and hydrogen production rate is 0.19~1.54mmol/g-ferrite. A temperature controller was designed for increasing the number of reaction cycles related with the amount of produced hydrogen.

• Wind and Structures
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• v.19 no.3
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• pp.339-352
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• 2014

This paper discusses the appropriate duration for basic gust wind speeds in wind loading codes and standards, and in wind engineering generally. Although various proposed definitions are discussed, the 'moving average' gust duration has been widely accepted internationally. The commonly-specified gust duration of 3-seconds, however, is shown to have a significant effect on the high-frequency end of the spectrum of turbulence, and may not be ideally suited for wind engineering purposes. The effective gust durations measured by commonly-used anemometer types are discussed; these are typically considerably shorter than the 'standard' duration of 3 seconds. Using stationary random process theory, the paper gives expected peak factors, $g_u$, as a function of the non-dimensional parameter ($T/{\tau}$), where T is the sample, or reference, time, and ${\tau}$ is the gust duration, and a non-dimensional mean wind speed, $\bar{U}.T/L_u$, where $\bar{U}$ is a mean wind speed, and $L_u$ is the integral length scale of turbulence. The commonly-used Durst relationship, relating gusts of various durations, is shown to correspond to a particular value of turbulence intensity $I_u$, of 16.5%, and is therefore applicable to particular terrain and height situations, and hence should not be applied universally. The effective frontal areas associated with peak gusts of various durations are discussed; this indicates that a gust of 3 seconds has an equivalent frontal area equal to that of a tall building. Finally a generalized gust response factor format, accounting for fluctuating and resonant along-wind loading of structures, applicable to any code is presented.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.12
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• pp.36-45
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• 1998

In this paper, a method of on-line PI gain-tuninng is proposed for the speed control of brushless D.C. motor by investigating the pattern of input and output without estimating parameter. Proportional gain is tuned in the process to obtain a fast speed response by supplying the maximum constant input. And integral gain is appropriately tuned in the process of proportional control so that the response may be stably converged and the overshoot may be prevented. Therefore because both control and gain-tuning are executed concurrently, additional works that estimate parameters and so on aren't required in the proposed method. In the proposed method, both fast-response and overshoot problem are well solved, and it is more useful and convenient than existing auto-tuning methods in the speed control of D.C. motor. It is illustrated by simulations and experimental results that the proposed method is useful and stable.

• Smart Structures and Systems
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• v.6 no.8
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• pp.939-951
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• 2010

A low-cost wireless sensor network (WSN) solution with highly expandable super and simple nodes was developed. The super node was designed as a sensing unit as well as a receiving terminal with low energy consumption. The simple node was designed to serve as a cheaper alternative for large-scale deployment. A 12-bit ADC inputs and DAC outputs were reserved for sensor boards to ease the sensing integration. Vibration and thermal field tests of the Chi-Lu Bridge were conducted to evaluate the WSN's performance. Integral acceleration, temperature and tilt sensing modules were constructed to simplify the task of long-term environmental monitoring on this bridge, while a star topology was used to avoid collisions and reduce power consumption. We showed that, given sufficient power and additional power amplifier, the WSN can successfully be active for more than 7 days and satisfy the half bridge 120-meter transmission requirement. The time and frequency responses of cables shocked by external force and temperature variations around cables in one day were recorded and analyzed. Finally, guidelines on power characterization of the WSN platform and selection of acceleration sensors for structural health monitoring applications were given.