• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.9
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• pp.811-819
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• 2014

Activity recognition is a key component in identifying the context of a user for providing services based on the application such as medical, entertainment and tactical scenarios. Instead of applying numerous sensor devices, as observed in many previous investigations, we are proposing the use of smartphone with its built-in multimodal sensors as an unobtrusive sensor device for recognition of six physical daily activities. As an improvement to previous works, accelerometer, gyroscope and magnetometer data are fused to recognize activities more reliably. The evaluation indicates that the IBK classifier using window size of 2s with 50% overlapping yields the highest accuracy (i.e., up to 99.33%). To achieve this peak accuracy, simple time-domain and frequency-domain features were extracted from raw sensor data of the smartphone.

• Journal of Magnetics
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• v.15 no.4
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• pp.179-184
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• 2010

We have investigated the effects of post annealing on iron oxide nanoparticles synthesized by the novel hydrothermal synthesis method with the $FeSO_4{\cdot}7H_2O$. To investigate the post annealing effect, the as-synthesized iron oxide nanoparticles were annealed at different temperatures in a vacuum chamber. The morphological, structural and magnetic properties of the iron oxide nanoparticles were investigated with high resolution X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Mossbauer spectroscopy, and vibrating sample magnetometer analysis. According to the XRD and HRTEM analysis results, as-synthesized iron oxide nanoparticles were only magnetite ($Fe_3O_4$) phase with face-centered cubic structure but post annealed iron oxide nanoparticles at $700^{\circ}C$ were mainly magnetite phase with trivial maghemite ($\gamma-Fe_2O_3$) phase which was induced in the post annealing treatment. The crystallinity of the iron oxide nanoparticles is enhanced by the post annealing treatment. The particle size of the as-synthesized iron oxide nanoparticles was about 5 nm and the particle shape was almost spherical. But the particle size of the post annealed iron oxide nanoparticles at $700^{\circ}C$ was around 25 nm and the particle shape was spherical and irregular. The as-synthesized iron oxide nanoparticles showed superparamagnetic behavior, but post annealed iron oxide nanoparticles at $700^{\circ}C$ did not show superparamagnetic behavior due to the increase of particle size by post annealing treatment. The saturation of magnetization of the as-synthesized nanoparticles, post annealed nanoparticles at $500^{\circ}C$, and post annealed nanoparticles at $700^{\circ}C$ was found to be 3.7 emu/g, 6.1 emu/g, and 7.5 emu/g, respectively. The much smaller saturation magnetization value than one of bulk magnetite can be attributed to spin disorder and/or spin canting, spin pinning at the nanoparticle surface.

• Journal of the Korean Magnetics Society
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• v.24 no.2
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• pp.56-59
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• 2014

The samples of $Ba_2CoZnFe_{12}O_{22}$ was synthesized by the solid-state reaction method. The toroids of $Ba_2CoZnFe_{12}O_{22}$ were sintered with various sintering temperature at 1050, 1100, 1150, and $1200^{\circ}C$, and studied by x-ray diffractometer, vibrating sample magnetometer, network analyzer, and Mssbauer spectrometer. From the XRD patterns, the density of samples increased with increasing sintering temperature. From the magnetic hysteresis curves up to 10 kOe at 295 K, the saturation magnetization ($M_s$) of $Ba_2CoZnFe_{12}O_{22}$ samples in various sintered at 1050, 1100, 1150 ,and $1200^{\circ}C$ were showed around $M_s$= 33.0 emu/g. However, With increasing sintering temperature, the coercivity ($H_c$) of samples decrease. Complex permeability and permittivity of samples in various sintering temperatures were measured between 100MHz to 4 GHz. With increasing sintering temperature, the permeability of samples increase.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.2
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• pp.106-114
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• 2017

In this paper, we propose the method of designing an extended kalman filter in order to accurately measure the position of the spatial-phase system using sensor fusion. We use the quaternion as a state variable in expressing the attitude of an object. Then, the attitude of rigid body can be calculated from the accelerometer and magnetometer by applying the Gauss-Newton method. We estimate the changes of state by using the measurements obtained from the gyroscope, the quaternion, and the vision informations by ARVR_SDK. To increase the accuracy of estimation, we designed and implemented the extended kalman filter, which showed excellent ability to adjust and compensate the sensor error. As a result, we could experimentally demonstrate that the reliability of the attitude estimation value can be significantly increased.

• Journal of Magnetics
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• v.8 no.4
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• pp.138-141
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• 2003

$Ni_{0.65}Zn_{0.35}Fe_2O_4$thin films were prepared by using a sol-gel method. Their crystallographic, dielectric and magnetic properties were investigated as a function of Cu contents by means of an X-ray diffractometer (XRD), X-ray reflectivity, LCZ meter (NF2232), a vibrating sample magnetometer (VSM), and an atomic force microscope (AFM). From typical C-V measurements for $Ni_{0.65}Zn_{0.35}Fe_2O_4$ thin films on p-type silicon substrate, the surface charge density was calculated as 1.4 ${\mu}$C/$m^2$. The dielectric constant evaluated from the capacitance at the accumulation state was 28. The high $H_{c}$ and low $M_{sat}$ at x=0.0 and 0.1 were due to the growth of the ${\alpha}$-$Fe_2O_3$ phase having antiferromagnetic properties. The rapidly decreased $H_{c}$ and increased $M_{sat}$ at x=0.2 and 0.3 can be explained that the ${\alpha}$-$Fe_2O_3$ phases have completely disappeared at x=0.3 and so, non-magnetic defects are minimized. The $M_{sat}$ was slightly decreased and the $H_{c}$ was increased above at x=0.3 because the increase of grain boundary due to smaller grain size acts as defects during magnetization process.

• Journal of the Korean Magnetics Society
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• v.8 no.5
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• pp.282-287
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• 1998

Dependence of magnetoresistance on base pressure and deposition rates of each Fe, Co, Cu layers in the $Fe(50{\AA}/[Co(17{\AA})/Cu(24{\AA})]_20$ multilayer thin films, prepared by dc magnetron sputtering on Corning glass, were investigated. AFM analysis, X-ray diffraction analysis, vibrating sample magnetometer analysis, and magnetoresustance measurement (4-probe method) were performed. The multilayer films deposited under low base pressure increases magnetoresistance ratio by preventing oxidation. Annealing for the samples at a moderate temperature allowed larger textured grain with no loss in the periodicity. Magnetoresistance ratio of the annealed multilayers was increased due to the increase antiferromagnetically coupled fraction of the film after annealing. Optimization of deposition rate was greater than 1 $\AA$/s for Fe, and 2.8 $\AA$/s for Cu. Deposition rate of Co showed a tendency of increasing of magnetoresistance ratio due to the formation of flat magnetic layer in case of high deposition rate of Co.

• Journal of the Korean Magnetics Society
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• v.9 no.1
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• pp.29-34
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• 1999

$Y_{2.5}La_{0.5}Fe_5O_{12}$ is fabricated by a sol-gel method and the magnetic properties of single phase garnet are investigated by using X-ray diffraction, vibrating sample magnetometer, scanning electron microscopy and M$\"{o}$ssbauer spectroscopy. The single phase powders garnet was fired at 100$0^{\circ}C$ for 8 hours. The crystal structures of samples are cubic garnet. Mossbauer spectroscopy were measured from 13 K to 750 K. M$\"{o}$ssbauer spectra show that the iron exist ferric trivalence in sample. The spin wave constants were determined $B_{3/2}=0.32{\pm}0.05,\; C_{5/2}=0.18{\pm}0.05$ and Debye temperature were determined 382 K at 24(d) site and 246 K at 16(a)-site. The saturation magnetization $M_s$ of powder is 25 emu/g. 25 emu/g.

• Phonetics and Speech Sciences
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• v.2 no.4
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• pp.119-127
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• 2010

Recently, we have launched a large-scale articulatory study to investigate how the three-way contrastive stops (i.e., lenis, fortis, and aspirated) in Korean are kinematically expressed (i.e., in terms of articulatory movement characteristics) in various contexts, using a magnetometer (Electromagnetic Articulography). In this paper, we report some preliminary results about how the three-way bilabial series /p,$p^h,p^*$/ produced in /Ca/ context in isolation are kinematically characterized not only during the lip closure but also during the following vocalic articulation. Some important notes could be made from the results. First, the degree of lip constriction (as measured by the lip aperture between the upper and lower lips) was smaller for the lenis /p/ and larger for the fortis/aspirated /$p^*,p^h$/, showing a two-way distinction during the closure. Second, the tongue lowering for the following vowel was more extreme after the lenis /p/ than after the fortis/aspirated /$p^*,p^h$/. Regarding this vocalic articulatory difference in the tongue height, we discussed the possibility that the articulatory tension associated with the fortis/aspirated stops is further reflected in the lingual vocalic movement maintaining the tongue position to a certain level for the following vowel /a/, while the lenis consonant does not impose such articulatory constraints, resulting in more tongue lowering. Finally, the temporal relationship between the release of the stop closure and the lowest tongue position of the following vowel remained constant, suggesting that CV coordination is invariantly maintained across the consonant type. This pattern was interpreted as supporting the view that the consonant and vowel gestures are coordinated in much the same way across languages.

• Journal of Magnetics
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• v.21 no.2
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• pp.183-186
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• 2016

In this study, we report on an investigation of proton radiation resistance of 410 martensitic stainless steels under 3 MeV proton with the doses ranging from $1.0{\times}10^{15}$ to $1.0{\times}10^{17}p/cm^2$ at the temperature 623 K. Vibrating sample magnetometer (VSM) and X-ray diffractometer (XRD) were used to study the variation of magnetic properties and structural damages by virtue of proton irradiation, respectively. VSM and XRD analysis revealed that the 410 martensitic stainless steels showed proton radiation resistance up to $10^{17}p/cm^2$. Proton energy degradation and flux attenuations in 410 stainless steels as a function of penetration depth were calculated by using Stopping and Range of Ions in Matter (SRIM) code. It suggested that the 410 stainless steels have the radiation resistance up to $5.2{\times}10^{-3}$ dpa which corresponds to neutron irradiation of $3.5{\times}10^{18}n/cm^2$. These results could be used to predict the maintenance period of SUS410 stainless steels in fission power plants.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.147-147
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• 2013

Multiferroic material $BiFeO_3$ (BFO) is a typical multiferroic material with a room-temperature magnetoelectric coupling in view of high magnetic- and ferroelectric-ordering temperatures (Neel temperature $T_N$ ~ 647 K and Curie temperature TC ~1,103 K). Rare-earth ion substitution at the Bi sites is very interesting, which induces suppressed volatility of the Bi ion and improved ferroelectric properties. At the same time, the Fe-site substitution with magnetic ions is also attracting, since the enhanced ferromagnetism was reported. In this study, BFO, $Bi_{0.9}Dy_{0.1}FeO_3$ (BDFO), $BiFe_{0.97}Co_{0.03}O_3$ (BFCO) and $Bi_{0.9}Dy_{0.1}Fe_{0.97}Co_{0.03}O_3 $ (BDFCO) compounds were prepared by conventional solid-state reaction and wet-mixing method. High-purity $Bi_2O_3$, $Dy_2O_3$, $Fe_2O_3$ and $Co_3O_4$ powders with the stoichiometric proportions were mixed, and calcined at $500^{\circ}C$ for 24 h. The samples were immediately put into an oven, which was heated up to 800oC and sintered in air for 1 h. The crystalline structure of samples was investigated at room temperature by using a Rigaku Miniflex powder diffractometer. The field-dependent magnetization measurements were performed with a vibrating-sample magnetometer. The electric polarization was measured at room temperature by using a standard ferroelectric tester (RT66B, Radiant Technologies). Dy and Co co-doping at the Bi and the Fe sites induce the enhancement of both magnetic and ferroelectric properties of $BiFeO_3$.