• Journal of Satellite, Information and Communications
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• v.11 no.4
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• pp.68-73
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• 2016

This paper describes the prototyping of CDMA bi - directional group search system using USRP and LTE. This paper describes the results of RF signal generation and transmission by implementing a spread spectrum signaling system, which is a new standard of COSPAS SARSAT, using a bi-directional search structure system using commercial LTE network and USRP.

• Journal of Magnetics
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• v.13 no.3
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• pp.110-113
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• 2008

In this study, heavy rare earth garnet $Tb_2Bi_1Ga_1Fe_4O_{12}$ powders were fabricated by a sol-gel and vacuum annealing process. The crystal structure was found to be single-phase garnet with a space group of Ia3d. The lattice constant $a_0$ was determined to be 12.465 ${\AA}$. From the analysis of the vibrating sample magnetometer (VSM) hysteresis loop at room temperature, the saturation magnetization and coercivity of the sample are 7.64 emu/g and 229 Oe, respectively. The N$\acute{e}$el temperature($T_N$) was determined to be 525 K. The M$\ddot{o}$ssbauer spectrum of $Tb_2Bi_1Ga_1Fe_4O_{12}$ at room temperature consists of 2 sets of 6 Lorentzians, which is the pattern of single-phase garnet. From the results of the M$\ddot{o}$ssbauer spectrum at room temperature, the absorption area ratios of Fe ions on 24d and 16a sites are 74.7% and 25.3%(approximately 3:1), respectively. These results show that all of the non-magnetic Ga atoms occupy the 16a site by a vacuum annealing process. Absorption area ratios of Fe ions are dependent not only on a sintering condition but also on the temperature of the sample. It can then be interpreted that the Ga ion distribution is dependent on the temperature of the sample. The M$\ddot{o}$ssbauer measurement was carried out in order to investigate the atomic migration in $Tb_2Bi_1Ga_1Fe_4O_{12}$.

• Analytical Science and Technology
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• v.5 no.1
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• pp.57-61
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• 1992

For the neutron spectrum measurement, $^6Li$ neutron spectrometer system is installed. The characteristic of the $^6Li$ detector are investigated using a $^{137}Cs$ and $^{207}Bi$ point source, and the neutron capture peaks and the pulse height spectrum using an $^{214}Am-Be$ neutron source are measured. Furthermore, the pulse height spectrum for the irradiation time variation from the (214)^Am-Be neutron source, and for the distance variation between detector and source, and the threshold variation of discriminator are measured.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.3
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• pp.1301-1318
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• 2017

In order to utilize the licensed channel of cognitive radio (CR) when the primary user (PU) is detected busy, a benefit-exchange access mode based on cooperative communication is proposed to allow secondary user (SU) to access the busy channel through giving assistance to PU's communication in exchange for some transmission bandwidth. A holistic joint optimization problem is formulated to maximize the total throughput of CR system through jointly optimizing the parameters of cooperative spectrum sensing (CSS), including the local sensing time, the pre-configured sensing decision threshold, the forward power of cooperative communication, and the bandwidth and transmission power allocated to SUs in benefit-exchange access mode and traditional access mode, respectively. To solve this complex problem, a combination of bi-level optimization, interior-point optimization and exhaustive optimization is proposed. Simulation results show that, compared with the tradition throughput maximizing model (TTMM), the proposed holistic joint optimization model (HJOM) can make use of the channel effectively even if PU is busy, and the total throughput of CR obtains a considerable improvement by HJOM.

• Journal of the Korean Magnetics Society
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• v.2 no.1
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• pp.29-36
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• 1992

The fundamental research about the amorphous ferrite, which is expected as the important material for electronic and information imdustry in future, was carried out in this work. Because the ferromagnetic amorphous ferrites reported recently are very inferior in magnetic properties than the crystalline ferrites, the development of the more ferromagnetic amorphous ferrites is required. In order to obtain the fundamental data for the preparation of amorphous ferrites, the hand-made twin-roller quenching apparatus was used for rapid quenching. Investigation on amorphous ferrite in the system $CaO-Bi_{2}O_{3}-Fe_{2}O_{3}$ has been carried out in the composition of 10-50 mole% CaO, 10-50 mole% $Bi_{2}O_{3}$, 40-70 mole% $Fe_{2}O_{3}$. Large magnetization values were obtained near the composition of the mixture of $BiFeO_{3}$ and $CaFe_{4}O_{7}$. Especially, an amorphous ${(CaO)}_{20}{(Bi_{2}O_{3})_{15}{(Fe_{2}O_{3})}_{65}$ specimen has a magmetization value of about 21.84 emu/g at 0K(10 kOe). Fe $M\"{o}ssbauer$ absorption spectrum indicates that this specimen is compsed of two amorphous phases, antiferromagnetic phase($\alpha$-phase) and ferromagnetic phase($\beta$-phase). Crystallization of this amorphous ferrite was happened in steps-$550^{\circ}C$ and $775^{\circ}C$, then observed crystal phases were perovskite phase of $BiFeO_{3}$ and $Fe_{2}O_{3}$ phase.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.3
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• pp.147-155
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• 1996

This study investigated the characteristics of ultrasonic-energy-added diesel fuel. We compared the characteristics used H-NMR spectrum, FT-IR spectrum, viscosity and surface tension between conventional diesel fuel and ultrasonic-energy-added diesel fuel. The result are obtained as follow : We knew that ultrasonic energy result to reduce BI and weaken viscosity and surface tension. Also, the ultrasonic energy caused to reduce aromatics Ha and increase Alkanes Hγ. The effect of ultrasonic-energy-added dieselfuel was principally caused by change of chemical structures and a physical characteristics.

• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.135-139
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• 2016

I propose a vector passive harmonic mode-locked fiber laser based on topological insulator Bi2Se3 interacting with a fiber taper with a diameter of 7 μm. The particles of topological insulator are deposited uniformly onto the fiber taper with light pressure effect. By incorporating the fabricated saturable absorber into an Er-doped fiber laser cavity, stable mode-locked fiber is obtained. Due to the intense evanescent field of the fiber taper, strong confinement of light enhances the nonlinearity of the laser cavity, and passive harmonic mode-locking is performed. I observe a maximum harmonic mode-locking of 356th, corresponding to a frequency of 3.57 GHz. The pulse duration is 824 fs, and the full width at half maximum of the spectrum is about 8.2 nm. The polarization dependent loss of the saturable absorber is ~ 2.5 dB in the wavelength range of the C band. As the cavity contains no other polarization dependent device, the mode-locked laser is functioning in the vector state. The harmonic order vs pump power is investigated. To the best of our knowledge, this report is the highest frequency mode-locked fiber laser based on Bi2Se3. Experimental results indicate that the topological insulator Bi2Se3 functioning with a thin fiber taper is effective for vector harmonic mode-locking.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.1
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• pp.32-37
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• 2006

Rare-earth niobates, ag (Ln = Y, La, Gd) are well-known self-activated phosphors due to charge transfer in $NbO^{3-}_4$ showing a broad and strong emission band in the spectral region around 410 nm. In order to find new blue and red phosphors for FED, $LaNbO_4$ : X (X = Bi, Eu) phosphors are prepared through solid-state reactions at high temperature. The optimum reaction condition for these phosphors to give maximum emission intensity is obtained when it is first fired at $1250^{\circ}C$ for 2 h followed by second firing at $1400^{\circ}C$ for 1 h. Under irradiation at 254 nm, $1mol\%\;Bi^{3+}$ doped $LaNbO_4$ phosphor shows strong blue emission band with a range of $420\~450nm$. Also $10mol\%\;Eu^{3+}$ doped $LaNbO_4$ phosphor shows the maximum emission intensity at about 610 nm. Emission peaks at $415\~460nm$, $530\~560nm$and $570\~620nm$are observed in phosphors below $10mol\%\;Eu^{3+}$ doped $LaNbO_4$. Similar results are obtained in cathodoluminescent property of these phosphors.

• Structural Engineering and Mechanics
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• v.20 no.3
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• pp.347-362
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• 2005

The input energy to a base-isolated (BI) building during an earthquake is considered and formulated in the frequency domain. The frequency-domain approach for input energy computation has some notable advantages over the conventional time-domain approach. Sensitivities of the input energy to the BI building are derived with respect to uncertain parameters in the base-isolation system. It is demonstrated that the input energy can be of a compact form via the frequency integration of the product between the input component (Fourier amplitude spectrum of acceleration) and the structural model component (so-called energy transfer function). With the help of this compact form, it is shown that the formulation of earthquake input energy in the frequency domain is essential for deriving the sensitivities of the input energy to the BI building with respect to uncertain parameters. The sensitivity expressions provide us with information on the most unfavorable combination of the uncertain parameters which leads to the maximum energy input.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.569-571
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• 2008

The structural and optical properties on $Bi^{3+}$ addition in (Y,Gd)(V,P)$O_4:Eu^{3+}$ red phosphor were investigated. With the addition of $Bi^{3+}$, the band edge in excitation spectrum shifts toward longer wavelength region, resulting in remarkable enhancement of the red emission intensity at 619 nm.