• Advances in materials Research
• /
• v.8 no.2
• /
• pp.117-135
• /
• 2019

The lifetime of a gas turbine combustor is typically limited by the durability of its liner, the structure that encloses the high-temperature combustion products. The primary objective of the combustor thermal design process is to ensure that the liner temperatures do not exceed a maximum value set by material limits. Liner temperatures exceeding these limits hasten the onset of cracking which increase the frequency of unscheduled engine removals and cause the maintenance and repair costs of the engine to increase. Hot gas temperature prediction can be considered a preliminary step for combustor liner temperature prediction which can make a suitable view of combustion chamber conditions. In this study, the temperature distribution of ceramic panels for a V94.2 gas turbine combustor subjected to realistic operation conditions is presented using three-dimensional finite difference method. A simplified model of alumina ceramic is used to obtain the temperature distribution. The external thermal loads consist of convection and radiation heat transfers are considered that these loads are applied to flat segmented panel on hot side and forced convection cooling on the other side. First the temperatures of hot and cold sides of ceramic are calculated. Then, the thermal boundary conditions of all other ceramic sides are estimated by the field observations. Finally, the temperature distributions of ceramic panels for a V94.2 gas turbine combustor are computed by MATLAB software. The results show that the gas emissivity for diffusion mode is more than premix therefore the radiation heat flux and temperature will be more. The results of this work are validated by ANSYS and ABAQUS softwares. It is showed that there is a good agreement between all results.

• Journal of the Korean Society of Industry Convergence
• /
• v.21 no.6
• /
• pp.265-271
• /
• 2018

DC-DC buck converter is a critical building block in the power management integrated circuit (PMIC) architecture for the portable devices such as cellular phone, personal digital assistance (PDA) because of its power efficiency over a wide range of conversion ratio. To ensure a safe operation, avoid unexpected damages and enhance the reliability of the converter, fully-integrated protection circuits such as over voltage protection (OVP), under voltage lock out (UVLO), startup, and thermal shutdown (TSD) blocks are designed. In this paper, these three fully-integrated protection circuit blocks are proposed for use in the DC-DC buck converter. The buck converter with proposed protection blocks is operated with a switching frequency of 1 MHz in continuous conduction mode (CCM). In order to verify the proposed scheme, the buck converter has been designed using a 180 nm CMOS technology. The UVLO circuit is designed to track the input voltage and turns on/off the buck converter when the input voltage is higher/lower than 2.6 V, respectively. The OVP circuit blocks the buck converter's operation when the input voltage is over 3.3 V, thereby preventing the destruction of the devices inside the controller IC. The TSD circuit shuts down the converter's operation when the temperature is over $85^{\circ}C$. In order to verify the proposed scheme, these protection circuits were firstly verified through the simulation in SPICE. The proposed protection circuits were then fabricated and the measured results showed a good matching with the simulation results.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.23 no.3
• /
• pp.254-260
• /
• 2019

Recently, the importance of signal processing has become gradually significant, as the frequency of video media increases in various fields. However, numerous kinds of noise generated in the transmission and reception processes can possibly affect the signal information, and the noise removal is for that reason essential as a preprocessing step. In this paper, we propose an algorithm to remove the mixed noise which is composed of impulse noise and AWGN. This algorithm is used for image restoration by noise judgment for efficient noise removal in a complex noise environment, and the noise is removed by considering spatial characteristics and pixel variations. Simulation results show that unlike existing methods, the algorithm has excellent noise cancellation characteristics by minimizing both noise effects and consequently eliminating the mixed noise; for objective judgment, we compared and analyzed the data using PSNR and profile.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.12 no.1
• /
• pp.13-21
• /
• 2019

The content based on image retrieval makes use of features of information within image such as color, texture and share for Retrieval data. we present a novel approach for improving retrieval accuracy based on DCT Filter-Bank. First, we perform DCT on a given image, and generate a Filter-Bank using the DCT coefficients for each color channel. In this step, DC and the limited number of AC coefficients are used. Next, a feature vector is obtained from the histogram of the quantized DC coefficients. Then, AC coefficients in the Filter-Bank are separated into three main groups indicating horizontal, vertical, and diagonal edge directions, respectively, according to their spatial-frequency properties. Each directional group creates its histogram after employing Otsu binarization technique. Finally, we project each histogram on the horizontal and vertical axes, and generate a feature vector for each group. The computed DC and AC feature vectors bins are concatenated, and it is used in the similarity checking procedure. We experimented using 1,000 databases, and as a result, this approach outperformed the old retrieval method which used color information.

• Journal of the Korean Society for information Management
• /
• v.36 no.1
• /
• pp.191-213
• /
• 2019

The process of obtaining scientific knowledge is conducted through research. Researchers deal with the uncertainty of science and establish certainty of scientific knowledge. In other words, in order to obtain scientific knowledge, uncertainty is an essential step that must be performed. The existing studies were predominantly performed through a hedging study of linguistic approaches and constructed corpus with uncertainty word manually in computational linguistics. They have only been able to identify characteristics of uncertainty in a particular research field based on the simple frequency. Therefore, in this study, we examine pattern of scientific knowledge based on uncertainty word according to the passage of time in biomedical literature where biomedical claims in sentences play an important role. For this purpose, biomedical propositions are analyzed based on semantic predications provided by UMLS and DMR topic modeling which is useful method to identify patterns in disciplines is applied to understand the trend of entity based topic with uncertainty. As time goes by, the development of research has been confirmed that uncertainty in scientific knowledge is moving toward a decreasing pattern.

• Current Optics and Photonics
• /
• v.5 no.3
• /
• pp.250-260
• /
• 2021

A tapered As₂S₃ photonic crystal fiber (PCF) with four layers of air holes in a hexagonal array around the core is designed in this paper. Numerical simulation shows that the dispersion D decreases and the nonlinearity coefficient γ increases from the thick to the thin end along the tapered PCF. We simulate the midinfrared pulse compression in the tapered As₂S₃ PCF using the adaptive split-step Fourier method. Initial Gaussian pulses of 4.4 ps and a central wavelength of 2.5 ㎛ propagating in the tapered PCF are located in the anomalous dispersion region. With an average power of assumed input pulses at 3 mW and a repetition frequency of 81.0 MHz, we theoretically obtain a pulse duration of 56 fs and a compression factor of 78 when the pulse propagates from the thick end to the thin end of the tapered PCF. When confinement loss in the tapered PCF is included in the simulation, the minimum pulse duration reaches 72 fs; correspondingly, the maximum compression factor reaches 61. The results show that in the anomalous-dispersion region, midinfrared pulses can be efficiently compressed in a dispersion-decreasing and nonlinearity-increasing tapered As₂S₃ PCF. Due to confinement loss in the tapered fiber, the efficiency of pulse compression is suppressed.

• Journal of Audiology & Otology
• /
• v.24 no.2
• /
• pp.85-90
• /
• 2020

Background and Objectives: The present study aimed to compare thresholds of direct bone-conduction (BC direct) with those of behaviorally measured BC pure-tone audiometry (PTA) and objectively measured BC auditory brainstem response (ABR) to confirm the clinical feasibility of their relationships. Subjects and Methods: Young adults with normal hearing participated in the study to determine the thresholds from three measurements at four testing frequencies. In the BC direct, the vibrator of a bone-anchored hearing aid softband was placed on the right mastoid of each subject. In both PTA and ABR, a B71 bone oscillator was placed on the subject's right mastoid. While the subject's thresholds of BC direct and BC PTA were determined with a clinically routine 5-dB step procedure, BC ABR was conducted to determine the individual's hearing sensitivity by a peak V of the waveform using tone-burst and click stimuli. Results: The BC direct showed a different pattern between low and high frequencies. Precisely, its thresholds were 13.25 and 12.25 dB HL at 0.5 and 1 kHz, respectively, but 19 and 19.75 dB HL at 2 and 4 kHz, respectively. A significant positive correlation existed between BC direct and PTA at 1 kHz, which was also correlated with ABR. Conclusions: Based on the current data, the thresholds of BC direct were similar to BC PTA at low frequencies and BC ABR at high frequencies. The thresholds of BC direct might be predictable at approximately 5 dB higher (or lower) than that in PTA, although a large data set is required for standardization.

• Journal of Korea Society of Industrial Information Systems
• /
• v.27 no.5
• /
• pp.37-48
• /
• 2022

With development of Digital Technology, social issues are communicated through digital-based platform such as SNS and form public opinion. This study attempted to analyze big data from Twitter, a world-renowned social network service, and find out the public opinion. After collecting Twitter data based on 14 keywords for 1 year in 2021, analyzed the term-frequency and relationship among keyword documents with pearson correlation coefficient using Data-mining Technology. Furthermore, the 6 main topics that on the center of information security field in 2021 were derived through topic modeling using the LDA(Latent Dirichlet Allocation) technique. These results are expected to be used as basic data especially finding key agenda when establishing strategies for the next step related industries or establishing government policies.

• Korean Journal of Audiology
• /
• v.24 no.2
• /
• pp.85-90
• /
• 2020

Background and Objectives: The present study aimed to compare thresholds of direct bone-conduction (BC direct) with those of behaviorally measured BC pure-tone audiometry (PTA) and objectively measured BC auditory brainstem response (ABR) to confirm the clinical feasibility of their relationships. Subjects and Methods: Young adults with normal hearing participated in the study to determine the thresholds from three measurements at four testing frequencies. In the BC direct, the vibrator of a bone-anchored hearing aid softband was placed on the right mastoid of each subject. In both PTA and ABR, a B71 bone oscillator was placed on the subject's right mastoid. While the subject's thresholds of BC direct and BC PTA were determined with a clinically routine 5-dB step procedure, BC ABR was conducted to determine the individual's hearing sensitivity by a peak V of the waveform using tone-burst and click stimuli. Results: The BC direct showed a different pattern between low and high frequencies. Precisely, its thresholds were 13.25 and 12.25 dB HL at 0.5 and 1 kHz, respectively, but 19 and 19.75 dB HL at 2 and 4 kHz, respectively. A significant positive correlation existed between BC direct and PTA at 1 kHz, which was also correlated with ABR. Conclusions: Based on the current data, the thresholds of BC direct were similar to BC PTA at low frequencies and BC ABR at high frequencies. The thresholds of BC direct might be predictable at approximately 5 dB higher (or lower) than that in PTA, although a large data set is required for standardization.

• Journal of Korean Society for Quality Management
• /
• v.50 no.4
• /
• pp.863-876
• /
• 2022

Purpose: The purpose of this study is to propose the product quality satisfaction index based on multiple linear regression using customer reviews. Methods: The proposed framework is composed of four steps. First, we collect online reviews and divide it into insight phrases. The insight phrases are classified using product attribute dictionary and sentiment analysis is conducted. Second, the importance of attributes is calculated in consideration of both regression coefficient and frequency. Third, the positive rate is calculated concerning sentiment analysis result. Therefore, the quality satisfaction index is measured by the weighted sum of importance and positive rate in the last step. Results: We conduct a case study using 2-years(2020, 2021) of Samsung TV reviews to confirm the effectiveness of the proposed methodology. As a result, we found that Picture quality is the most crucial attribute in TV evaluation. The importance of Gaming and content has grown up as the positive rate has also increased. Therefore, the overall satisfaction of TV has increased in 2021 compared to 2020. Conclusion: The result of this study shows that the proposed index reveals the customer's mind efficiently and can be explained by the importance and positive rate of each attribute. By using the proposed index, companies are able to improve and the priority of improvement can be determined.