• ETRI Journal
• /
• v.27 no.5
• /
• pp.551-556
• /
• 2005

We have demonstrated a high-power widely tunable sampled grating distributed Bragg reflector (SGDBR) laser integrated monolithically with a semiconductor optical amplifier (SOA) having a lateral tapered waveguide, which is the first to emit a fiber-coupled output power of more than 10 dBm using a planar buried heterostructure (PBH). The output facet reflectivity of the integrated SOA using a lateral tapered waveguide and two-layer AR coating of $TiO_2\;and\;SiO_2$ was lower than $3\;{\times}\;10^{-4}\;over$ a wide bandwidth of 85 nm. The spectra of 40 channels spaced by 50 GHz within the tuning range of 33 nm were obtained by a precise control of SG and phase control currents. A side-mode suppression ratio of more than 35 dB was obtained in the whole tuning range. Fiber-coupled output power of more than 11 dBm and an output power variation of less than 1 dB were obtained for the whole tuning range.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2000.04a
• /
• pp.44-48
• /
• 2000

Several parameters to represent the characteristics of the observed at the domestic networks from several earthquakes occurred in the Korean Peninsula. Parameters to fit most the multiple Fourier amplitude spectra of the observed accelerations are estimated. This study adopts the stochastic ground motion model referred to the BLWN mode in which the energy is distributed randomly over the duration of the source and which has proven to be very effective in modeling a wide range of ground motion observations. The stochastic ground motion model employed here uses an omega-squared ({{{{ omega ^2 }}) Brune source model with a single corner frequency and a constant stress drop,. The {{{{ omega ^2 }} source model has become a seismological standard because of its simplicity an ability to predict spectral amplitudes and shapes over an extremely broad ranges of magnitudes distances and from the inversion show very unstable based on the fact of high values of mean/median. These results may imply that more observed data and more precise site classification including accurate preparation analysis of data such as more accurate scaling from counts to kine are needed for more stable are effective inversion of Fourier amplitude spectrum of the observed ground motions.

• Structural Engineering and Mechanics
• /
• v.55 no.3
• /
• pp.655-674
• /
• 2015

In this paper, a new and simplified method is presented in which the natural frequencies of the uniform and non-uniform beams are calculated through simple mathematical relationships. The various vibration problems such as: Rayleigh beam under variable axial force, axial vibration of a bar with and without end discrete spring, torsional vibration of a bar with an attached mass moment of inertia, flexural vibration of the beam with laterally distributed elastic springs and also flexural vibration of the beam with effects of viscose damping are investigated. The governing differential equations are first obtained and then; according to a harmonic vibration, are converted into single variable equations in terms of location. Through repetitive integrations, the governing equations are converted into weak form integral equations. The mode shape functions of the vibration are approximated using a power series. Substitution of the power series into the integral equations results in a system of linear algebraic equations. The natural frequencies are determined by calculation of a non-trivial solution for system of equations. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained with those obtained from other published references and results of available finite element software.

• Proceedings of the KIPE Conference
• /
• 2001.10a
• /
• pp.683-686
• /
• 2001

This paper presents a novel prototype of the utility­interactive voltage source type sinewave pulse modulated power inverter using a high-frequency flyback transformer link. The proposed power conditioner circuit for the solar photovoltaic generation and small scale fuel cell has an isolation function due to the safety of the power processing system, which is more cost effective and acceptable for the small-scale distributed renewal energy conditioning and processing systems. The discontinuous current mode(DCM) of this power processing conversion circuit is applied to implement a simple circuit topology and pulse modulated control scheme. Its operation principle is described on the basis of simulation evaluations and theoretical considerations. The simulation results obtained herein prove that the proposed inverter outputs with sinusoidal waveforms and unity power factor currents are synchronized to the main voltage in utility power source grid. In this paper, the soft switching topology of high­frequency linked sinewave pulse modulation inverter is proposed and discussed.

• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.16 no.2
• /
• pp.53-61
• /
• 2013

The present study elucidated the growth properties of Sasa borealis communities distributed in the lower layer of deciduous broadleaf forests in temperate zones and analyzed the correlation between the growth properties of S. borealis and positional environmental factors. The higher the culm height of S. borealis was, the higher the values of the leaf number, leaf area, and foliage layer thickness became. This might be because as the culm height of S. borealis increased, the acquisition of light sources became easier so that the biomass of leaves increased simultaneously for smooth anabolism. S. borealis seem to change their growth mode for smooth acquisition of light resources. The culm density of S. borealis and the leaf number, leaf area and foliage layer thickness of S. borealis did not show any clear correlation. The values of the culm height, leaf number, leaf area, and foliage layer thickness of S. borealis as the above altitude of the location of S. borealis increased. It seems like that growth conditions such as temperatures and winds are deteriorated as the above altitude of the location of S. borealis increased so that S. borealis becomes smaller. No clear correlations were shown between the physiochemical properties of soil and S. borealis' growth properties. It seems like that the growth of S. borealis complexly intertwined with diverse environmental factors and that due to the physiological integration of S. borealis, certain physiochemical properties do not unilaterally affect S. borealis' growth properties.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.5 no.4
• /
• pp.684-702
• /
• 2011

This paper proposes a TDMA-based multichannel medium access control (MAC) protocol for QoS provisioning in mobile ad hoc networks (MANETs) that enables nodes to transmit their packets in distributed channels. The IEEE 802.11 standard supports multichannel operation at the physical (PHY) layer but its MAC protocol is designed only for a single channel. The single channel MAC protocol does not work well in multichannel environment because of the multichannel hidden terminal problem. Our proposed protocol enables nodes to utilize multiple channels by switching channels dynamically, thus increasing network throughput. Although each node of this protocol is equipped with only a single transceiver but it solves the multichannel hidden terminal problem using temporal synchronization. The proposed energy efficient multichannel MAC (EM-MAC) protocol takes the advantage of both multiple channels and TDMA, and achieves aggressive power savings by allowing nodes that are not involved in communications to go into power saving "sleep mode". We consider the problem of providing QoS guarantee to nodes as well as to maintain the most efficient use of scarce bandwidth resources. Our scheme improves network throughput and lifetime significantly, especially when the network is highly congested. The simulation results show that our proposed scheme successfully exploits multiple channels and significantly improves network performance by providing QoS guarantee in MANETs.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.11 no.6
• /
• pp.904-912
• /
• 1987

The main mode of heat transfer of combustion gases at high temperature is thermal radiation of nonluminous gases, CO$_{2}$ and H$_{2}$O. Therefore the information of the emissivities of CO$_{2}$ and H$_{2}$O would be very important in the thermal performance analysis of furnace. In this study, an exponential model for the emissivities of CO$_{2}$ and H$_{2}$O was derived as function of P$_{g}$L and polynomial of reciprocal of temperature. Error analysis between the calculated values from present model and the valued of Hottel Chart was performed over temperature range of 1000-5000 R and a partial-pressure-length product range of 0.003 to 20 ft-atm. For CO$_{2}$ gray gas, the error percent between the calculated values and the values from Hottel Chart was distributed within 2.5% in case of using a polynomial in 1/T of degree 4. For H$_{2}$O gray gas, the model has an error range of 0 to 2.5% in case of using a polynomial in 1/T of degree 3.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.12 no.5
• /
• pp.2285-2290
• /
• 2011

This paper is the research on SMSR yield improvement of the optical transceiver using modulated DFB laser. In general, the wavelength of DFB laser optical transceiver are 1310, 1490 and 1550 nm. Usually SMSR in modulated DFB is difficult to improve as low as 30 dB because of high slop efficiency trade off. In modulation condition, we studied SMSR improvement according to adjust bias current, extinction ratio and optical line terminal receiver sensitivity. As our test results, we can found a method how to improve SMSR for optical transceiver for long distance.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.22 no.6
• /
• pp.1323-1333
• /
• 1997

In this paper, we propose an efficient architecture for a high-speed cell concentrator/distributor(HCCD) in an ATM(Asynchronous Transfer Mode) switch and by analyzeing the simulation results evaluate the performance of the proposed architecuture. The proposed HCCD distributes cells from a switch link to local processors, or concentrates cells from local processor s to a switch link. This design is to guarntee a high throughput for the IPC (inter-processor communication) link in a distributed ATM switching system. The HCCD is designed in a moudlar architecture to provide the extensibility and the flexibility. The main characteristics of the HCCD are 1) Adaption of a local CPU in HCCD for improving flexibility of the system, 2) A cell-baced statistical multiplexing function for efficient multiplexing, 3) A cell distribution function based on VPI(Virtual Path Identifier), 4) A bypassing capability for IPC between processor attached to the same HCCD, 5) A multicasting capability for point-to-multipoint communication, 6) A VPI table updating function for the efficient management of links, 7) A self-testing function for detecting system fault.

• Korean Journal of Oriental Medicine
• /
• v.14 no.1
• /
• pp.123-128
• /
• 2008

Glehnia littoralis (Umbelliferae), a perennial herb distributed along the coastline of northern Pacific countries, is the medicinal plant used traditionally for treatment of various diseases. This review focuses on the various pharmacological activities of Glehnia littoralis for understanding about its traditional medicinal applications, medicinal uses in the modern society, and potentials for drug development Glehnia littoralis was reported to have anti-oxidant, anti-tumor, anti-amnesic, blood circulation-promoting, immunomodulatory, anti-microbial, and allelopathic activities. However, their mechanisms remain to be clarified. Because Glehnia littoralis has been prescribed in traditional Oriental medicine as a tonic herb, Glehnia littoralis can be better than other chemical drugs and medicines which exert the equal pharmacological activities. Although the activities of Glehnia littoralis are not specifically high-potent with unique mode of action, it may turn out that it can be beneficial to exert multiple pharmacological activities. In view of low toxicity, relative cheapness, presence in the diet, and occurrence in various herbal remedies of Glehnia littoralis, it needs to be prudent to evaluate its properties and applications further.