• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.6
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• pp.503-511
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• 2013

This paper presents a speech enhancement method using non-negative matrix factorization. In training phase, we can obtain each basis matrix from speech and specific noise database. After training phase, the noisy signal is separated from the speech and noise estimate using basis matrix in enhancement phase. In order to improve the performance, we model the change of encoding matrix from training phase to enhancement phase using independent Gaussian distribution models, and then use the constraint of the objective function almost same as that of the above Gaussian models. Also, we perform a smoothing operation to the encoding matrix by taking into account previous value. Last, we apply the Log-Spectral Amplitude type algorithm as gain function.

• Proceedings of the Membrane Society of Korea Conference
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• 1992.10a
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• pp.41-42
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• 1992

고내열 및 고내화학적 특성을 갖는 미세다공성 고분자막의 개발을 위한 기초연구가 수행되었다. 본 연구에서는 고분자막 제조기법의 첨단기술로 등장한 열유도상 분리공정(Thermally Induced Phase Separation, 이하 TIPS)이 도입되었다. TIPS 공정은 고분자를 고분자의 용융점을 상회하는 온도에서 매우 미세하게 분산시킬 수 있는 희석제를 고분자와 함께 melt-blending하여 균일한 single phase의 용액을 만들고 이를 적당한 막의 형태로 성형한 후, 가해진 열을 제거하여 냉각시킴에 따라 polymer-rich phase 와 polymer-poor phase 로 구성되는 two phase system으로 상분리를 일으키는 방법이다. 이때 polymer-poor phase를 차지하는 희석제를 제거함에 따라 고분자 matrix 내에는 void volume이 형성되고, 그 결과 고분자 matrix 전체적으로 다공성이 부여되어 고분자막으로서의 기본적인 기능을 갖추게 된다.

• Journal of the Korean Ceramic Society
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• v.31 no.4
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• pp.443-447
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• 1994

Compacts of mixed SiO2-Si powder were liquid phase sintered at 145$0^{\circ}C$ for up to 60 min in a hydrogen atmosphere. In contrast to the conventional microstructures of liquid phase sintered materials, the specimens showed that the solid phase of SiO2 formed a matrix while the liquid phase of Si was the dispersed in the solid matrix. The dispersion of liquid Si pockets was attributed to the high wetting angle of liquid Si on solid SiO2. Because of relatively high solubility of SiO2 in liquid Si at 145$0^{\circ}C$, SiO2 particles accommodated their shape via a solution-reprecipitation process. The liquid Si pockets grew by coalescing with their neighbour pockets. In the latter stage of the sintering, plate-shape grains appeared in the liquid Si pockets. The grains were SiO2 phase precipitated from the liquid Si which was oversaturated with oxygen during cooling to room temperature. By the formation and subsequent removal of the gaseous SiO phase due to the reaction between SiO2 and Si, the specimens became porous.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.6
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• pp.501-504
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• 2017

In this paper, a hybrid beamforming antenna system using broadband butler matrix and phase shifter is proposed. In the previous works, an $8{\times}8$ butler matrix is used to overcome a drawback of the $4{\times}4$ butler matrix based switched beamforming which provides only 4 beam patterns. However the $8{\times}8$ butler matrix should be designed on the bi-layered substrate using via holes due to its complex structure. It causes performance degradation. To overcome these problems, the proposed hybrid beamforming antenna system is designed on the single side of the substrate for simple structure. By addition of two phase shifter, it provide various beam patterns. The proposed antenna system provides more than 10 dBi radiation gain in the ${\pm}45^{\circ}$ scanning range by 16 input combinations.

• Journal of the Korea Society of Computer and Information
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• v.11 no.3
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• pp.141-149
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• 2006

In this paper, we introduce an improved algorithm for computing matrix triple product that commonly arises in primal-dual optimization method. In computing $P=AHA^{t}$, we devise a single pass algorithm that exploits the block diagonal structure of the matrix H. This one-phase scheme requires fewer floating point operations and roughly half the memory of the generic two-phase algorithm, where the product is computed in two steps, computing first $Q=HA^{t}$ and then P=AQ. The one-phase scheme achieved speed-up of 2.04 on Intel Itanium II platform over the two-phase scheme. Based on memory latency and modeled cache miss rates, the performance improvement was evaluated through performance modeling. Our research has impact on performance tuning study of complex sparse matrix operations, while most of the previous work focused on performance tuning of basic operations.

• International Journal of Control, Automation, and Systems
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• v.6 no.5
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• pp.670-676
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• 2008

While the matrix converter has many advantages that include bi-directional power flow, a size reduction, a long lifetime, and sinusoidal input currents, it is vulnerable to the input voltage disturbances, because it directly exchanges the input voltage to the output voltage. So, in this paper, a critical evaluation of the effect of various abnormal voltage conditions like unbalanced power supply, balanced non-sinusoidal power supply, input voltage sags and short time blackout of power supply on matrix converter fed induction motor drives is presented. The operation under various abnormal conditions has been analyzed. For this, a 230V, 250VA three phase to three phase matrix converter (MC) fed induction motor drive prototype is implemented using DSP based controller and tests have been carried out to evaluate and improve the stability of system under typical abnormal conditions. Digital storage oscilloscope & power quality analyzer are used for experimental observations.

• Food Science of Animal Resources
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• v.37 no.1
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• pp.147-152
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• 2017

A bioluminescent Lactobacillus plantarum (pLuc2) strain was constructed. The luminescent signal started to increase during the early exponential phase and reached its maximum in the mid-exponential phase in a batch culture of the strain. The signal detection sensitivity of the strain was the highest in PBS (phosphate buffered saline), followed by milk and MRS broth, indicating that the sensitivity was influenced by the matrix effect. The strain was used in millet seed fermentation which has a complex matrix and native lactic acid bacteria (LAB). The luminescent signal was gradually increased until 9 h during fermentation and abolished at 24 h, indicating that the strain could be specifically tracked in the complex matrix and microflora. Therefore, the bioluminescent labeling system can be used for monitoring LAB in food and dairy sciences and industries.

• Journal of the Korean Ceramic Society
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• v.35 no.12
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• pp.1337-1342
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• 1998

To investigate an effect of phase separation on precipitation characteristics of ZnS microcrystals in ma-trix glass ZnS doped borosilicate glasses for nonlinear optical applications were prepared by melting and pre-cipitation process. ZnS dopant contributed to phase separation promotion which increased the phase separa-tion of the matrix glass within immiscibility region. It was also found that ZnS as phase separation promoter showed a similar contribution for some selected glass compositions in miscibility region. The precipitation of ZnS microcrystals occurred in thephase separable glass compoitions. The radius of ZnS microcrystals in-creased with increasing the heat treatment temperature and Na2O contents of matrix glass composition. The ZnS particle sizes estimated by effective mass approximation ranged from about 30 to 80${\AA}$ It was suf-ficiently small to show quantum confinement effect.

• Advances in nano research
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• v.13 no.4
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• pp.407-416
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• 2022

In this study, the gravitating mechanical stir casting method was used to fabricating the Nb₂O₅/AZ31 magnesium matrix nanocomposites. Niobium pentoxide (Nb₂O₅) used as reinforcement with two different weight percentages (3 wt % and 6 wt %). The influence of Nb₂O₅ on microstructure and mechanical properties has been investigated. The microstructure analysis showed that the composites are mainly composed of the primary α-magnesium phase and phase β-Mg₁₇Al₁₂ secondary phase. The secondary phase was dispersed evenly along the grain boundary of the Mg phase. The Nb₂O₅/AZ31 nanocomposites revealed that the grain size and its lamellar shape (β-Mg₁₇Al₁₂) were gradually refined. Different strengthening mechanisms were assessed in terms of their contributions. Results showed that composite material properties of hardness, yield strength, and fracture study were directly related to Nb₂O₅ as a reinforcement. The maximum values of the mechanical properties were achieved with the addition of 3 wt% Nb₂O₅ on the AZ31 alloy.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.05a
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• pp.95-98
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• 2012

This paper describes a multiphase delay-locked loop (DLL) that generates a 32-phase output clock over the operating frequency range of 40 MHz to 280 MHz. The matrix-based delay line is used for high resolution of 1-bit delay. A calibration scheme, which improves the linearity of a delay line, is achieved by calibrating the nonlinearity of the input stage of the matrix. The multi-phase DLL is fabricated by using 0.11-${\mu}m$ CMOS process with a 1.2 V supply. At the operating frequency of 125MHz, the measurement results shows that the DNL is less than +0.51/-0.12 LSB, and the measured peak-to-peak jitter of the multi-phase DLL is 30 ps with input peak-to-peak jitter of 12.9 ps. The area and power consumption of the implemented DLL are $480{\times}550{\mu}m^2$ and 9.6 mW at the supply voltage of 1.2 V, respectively.