• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.2
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• pp.139-146
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• 2021

In hybrid rocket combustion, the oxidizer swirl injection is frequently used to stabilize the combustion as the rotational velocity component affects the boundary layer flow. However, as the swirl strength increases, a problem arises where the combustion performance changes too much. Thus, this study attempts to control the low frequency instability while minimizing the change in combustion performance by adapting attenuated swirl injection with fuel insert used in reference [7]. To this end, a series of experimental tests were performed by varying swirl intensity and the location of the fuel insert. In the tests, the occurrence of combustion instability and combustion performance were closely monitored. The results confirmed that combustion instability was successfully suppressed at the condition of the swirl angle 6 degree and the location of fuel insert 310 mm. And, the changes in combustion pressure, O/F ratio, and fuel regression rate were found as minimal compared to the baseline case. Also the results reconfirmed that the formation of positive coupling between two high frequency oscillations in 500 Hz band, combustion pressure(p') and heat release oscillation(q'), is the necessary and sufficient condition of the occurrence of low frequency instability.

• The Research Journal of the Costume Culture
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• v.28 no.6
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• pp.755-770
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• 2020

As the postsecondary school-age population continues to decline, universities are building identities to differentiate themselves and create a favorable impression among this cohort. We investigated the role of logo-bearing products as a way of promoting university identity, specifically, the effects of ingroup ties, ingroup affect, and centrality on attitude toward university logo products and purchase intention. This study further examined the moderating effects of perceived university prestige on the relationship between logo product attitude and in-store purchase intention, and the moderating effect of online shopping frequency on the relationship between logo product attitude and online purchase intention. We conducted a survey of undergraduate and graduate students at a university in Seoul. Survey responses (N=561) were collected and processed using SPSS 23.0. Multiple regression analysis showed that ingroup ties and affect had significant effects on product attitude. However, centrality had no significant effect on attitude toward the product. Product attitude had a direct significant effect on both in-store and online purchase intention. Perceived university prestige moderated the relationship between product attitude and in-store purchase intention. Moreover, online shopping frequency moderated the relationship between product attitude and online purchase intention. The results of this study are expected to provide fundamental knowledge for developing product strategy of logo products.

• The Journal of the Korea Contents Association
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• v.22 no.7
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• pp.562-582
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• 2022

Although personal media have become a giant industry, there is a lack of understanding of personal media creators. Therefore, this study aims to clarify factors influencing personal media creators' choice of platform. According to the analysis, there is a significant difference between the factors considered by YouTube, AfreecaTV, and Twitch creators. Moreover, the moderating effect of creators' main genre and broadcasting type were also found to be partially significant. It was found that both creators who share the motive of vividness and communication as their main genre and creators who focus on recording and broadcasting with career development motivation prefer YouTube.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.5
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• pp.649-655
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• 2022

In this paper, a determinant-based two-channel noise reduction method which utilizes speech presence probability (SPP) is proposed. The proposed method improves noise reduction performance from the conventional determinant-based two-channel noise reduction method in [7] by applying SPP to the Wiener filter gain. Consequently, the proposed method adaptively controls the amount of noise reduction depending on the SPP. For performance evaluation, the segmental signal-to-noise ratio (SNR), the perceptual evaluation of speech quality, the short time objective intelligibility, and the log spectral distance were measured in the simulated noisy environments considered various types of noise, reverberation, SNR, and the direction and number of noise sources. The experimental results presented that determinant-based methods outperform phase difference-based methods in most cases. In particular, the proposed method achieved the best noise reduction performance maintaining minimum speech distortion.

• Journal of IKEEE
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• v.27 no.4
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• pp.425-429
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• 2023

In this paper, the scheme to activate the active elements of reconfigurable intelligent surface(RIS) is proposed. Recently, RIS has been studied as a technology that improves communication coverage and spectral efficiency in wireless communication system. RIS can adjust the phase and amplitude of the received signal, and can ensure better communication performance in areas with many obstacles, such as urban areas. However, due to RIS, the signal undergoes fading twice and performance decrease in communication. Recently, RIS using active reflection elements has been studied to solve these problems. However, if the entire RIS is used as an active reflection element, energy consumption increases. Accordingly, in this paper, we propose a system that utilizes some of the RIS reflective elements as active reflective elements and a scheme for selecting active reflective elements to be activated.

• The Journal of the Acoustical Society of Korea
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• v.28 no.6
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• pp.557-565
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• 2009

To perceive the direction and the distance of a sound, we always use a couple of information. Head Related Transfer Function (HRTF) contains the information that sound arrives from a sound source to the ears of the listener, like differences of level, phase and frequency spectrum. For a reproduction system using 2 channels, we apply HRTF to many algorithms which make 3d sound. But it causes a problem to localize a sound source around a certain places which is called the cone-of-confusion. In this paper, we proposed the new algorithm to reduce the confusion of sound image localization. The difference of frequency spectrum and psychoacoustics theory are used to boost the spectral cue among each directions. To confirm the performance of the algorithm, informal listening tests are carried out. As a result, we can make the improved 3d sound in 2 channel system based on a headphone. Also sound quality of improved 3d sound is much better than conventional methods.

• Journal of Technology Innovation
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• v.22 no.4
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• pp.235-259
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• 2014

New product or new technology developments are directly linked to a firm's survival and thus their performance and improvement are gaining attention in the midst of rapidly changing business environment and aggravating competition. However, despite SMEs' significance in the national economy, they are limited in terms of size and resources in possession, so the government provides a variety of supports as a policy. According to a study on the organizational life cycle, a firm's limits and difficulties differ by growth stage, so the supports need to be tailored. Based on the data from 2,575 firms that responded to the "2011 SMEs Technological Statistics," how technological capability level and deviation in the R&D process affect the R&D sales performance was studied. The result of analysis revealed that the technological capability has a positive impact on the R&D sales performance. It was also learned that the relationship between deviation in the technological capability and R&D sales performance was moderated by the government support. For the hypothesis that the government support would have a different moderating effect by growth stage for the impact the technology level has on the R&D sales performance, the empirical analysis showed a different meaningful moderating effect for each growth stage. The theoretical implications of the study are that, instead of a simple relation of dynamics that does not take the growth stages into account, it suggested a more realistic causal relationship model that reflects the complex environment the SMEs are in and that the need for measuring and using the deviation in technological capability as a research variable has been justified. The practical implications are that the government policy for supports can be tailored to a growth stage and that the guidelines have been suggested to effectively use the government funding by encouraging the SMEs in a different growth stage to adapt to the customized policy.

• The Journal of Korean Society for Radiation Therapy
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• v.24 no.2
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• pp.123-135
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• 2012

Purpose: It is essential to minimize the movement of tumor due to respiratory movement at the time of respiration controlled radiotherapy of non-small cell lung cancer patient. Accordingly, this Study aims to evaluate the usefulness of restricted respiratory period by comparing and analyzing the treatment plans that apply free and restricted respiration period respectively. Materials and Methods: After having conducted training on 9 non-small cell lung cancer patients (tumor n=10) from April to December 2011 by using 'signal monitored-breathing (guided- breathing)' method for the 'free respiratory period' measured on the basis of the regular respiratory period of the patents and 'restricted respiratory period' that was intentionally reduced, total of 10 CT images for each of the respiration phases were acquired by carrying out 4D CT for treatment planning purpose by using RPM and 4-dimensional computed tomography simulator. Visual gross tumor volume (GTV) and internal target volume (ITV) that each of the observer 1 and observer 2 has set were measured and compared on the CT image of each respiratory interval. Moreover, the amplitude of movement of tumor was measured by measuring the center of mass (COM) at the phase of 0% which is the end-inspiration (EI) and at the phase of 50% which is the end-exhalation (EE). In addition, both observers established treatment plan that applied the 2 respiratory periods, and mean dose to normal lung (MDTNL) was compared and analyzed through dose-volume histogram (DVH). Moreover, normal tissue complication probability (NTCP) of the normal lung volume was compared by using dose-volume histogram analysis program (DVH analyzer v.1) and statistical analysis was performed in order to carry out quantitative evaluation of the measured data. Results: As the result of the analysis of the treatment plan that applied the 'restricted respiratory period' of the observer 1 and observer 2, there was reduction rate of 38.75% in the 3-dimensional direction movement of the tumor in comparison to the 'free respiratory period' in the case of the observer 1, while there reduction rate was 41.10% in the case of the observer 2. The results of measurement and comparison of the volumes, GTV and ITV, there was reduction rate of $14.96{\pm}9.44%$ for observer 1 and $19.86{\pm}10.62%$ for observer 2 in the case of GTV, while there was reduction rate of $8.91{\pm}5.91%$ for observer 1 and $15.52{\pm}9.01%$ for observer 2 in the case of ITV. The results of analysis and comparison of MDTNL and NTCP illustrated the reduction rate of MDTNL $3.98{\pm}5.62%$ for observer 1 and $7.62{\pm}10.29%$ for observer 2 in the case of MDTNL, while there was reduction rate of $21.70{\pm}28.27%$ for observer 1 and $37.83{\pm}49.93%$ for observer 2 in the case of NTCP. In addition, the results of analysis of correlation between the resultant values of the 2 observers, while there was significant difference between the observers for the 'free respiratory period', there was no significantly different reduction rates between the observers for 'restricted respiratory period. Conclusion: It was possible to verify the usefulness and appropriateness of 'restricted respiratory period' at the time of respiration controlled radiotherapy on non-small cell lung cancer patient as the treatment plan that applied 'restricted respiratory period' illustrated relative reduction in the evaluation factors in comparison to the 'free respiratory period.

• The Journal of Korean Society for Radiation Therapy
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• v.24 no.2
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• pp.85-93
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• 2012

Purpose: It is essential to minimize the respiratory-induced motion of involved organs in the Tomotherapy for tumor located in the chest and abdominal region. However, the application of breathing control system to Tomotherapy is limited. This study was aimed to investigate the possible application of the ABCHES system and its efficacy as a means of breathing control in the tomotherapy treatment. Materials and Methods: Five subjects who were treated with a Hi-Art Tomotherapy system for lung, liver, gallbladder and pancreatic tumors. All patients undertook trained on two breathing methodes using an ABCHES, free breathing methode and shallow breathing methode. When the patients could carry out the breathing control, 4D-CT scan was a total of 10 4D tomographic images were acquired. A radiologist resident manually drew the tumor region, including surrounding nomal organs, on each of CT images at the inhalation phase, the exhalation phase and the 40% phase (mid-inhalation) and average CT image. Those CT images were then exported to the Tomotherapy planning station. Data exported from the Tomotherapy planning station was analyzed to quantify characteristics of dose-volume histograms and motion of tumors. Organ motions under free breathing and shallow breathing were examined six directions, respectively. Radiation exposure to the surrounding organs were also measured and compared. Results: Organ motion is in the six directions with more than a 5 mm displacement. A total of 12 Organ motions occurred during free breathing while organ motions decreased to 2 times during shallow breathing under the use of Abches. Based on the quantitative analysis of the dose-volume histograms shallow breathing showed lower resulting values, compared to free breathing, in every measure. That is, treatment volume, the dose of radiation to the tumor and two surrounding normal organs (mean doses), the volume of healthy tissue exposed to radiation were lower at the shallow breathing state. Conclusion: This study proposes that the use of ABCHES is effective for the Tomotherapy treatment as it makes shortness of breathing easy for patients. Respiratory-induced tumor motion is minimized, and radiation exposure to surrounding normal tissues is also reduced as a result.

• The Journal of Korean Society for Radiation Therapy
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• v.22 no.2
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• pp.113-122
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• 2010

Purpose: To evaluate the accuracy of a target position at static and dynamic state by using Dynamic phantom for the difference between tumor's actual movement during respiratory gated radiation therapy and skin movement measured by RPM (Real-time Position Management). Materials and Methods: It self-produced Dynamic phantom that moves two-dimensionally to measure a tumor moved by breath. After putting marker block on dynamic phantom, it analyzed the amplitude and status change depending on respiratory time setup in advance by using RPM. It places marker block on dynamic phantom based on this result, inserts Gafchromic EBT film into the target, and investigates 5 Gy respectively at static and dynamic state. And it scanned investigated Gafchromic EBT film and analyzed dose distribution by using automatic calculation. Results: As a result of an analysis of Gafchromic EBT film's radiation amount at static and dynamic state, it could be known that dose distribution involving 90% is distributed within margin of error of 3 mm. Conclusion: As a result of an analysis of dose distribution's change depending on patient's respiratory cycle during respiratory gated radiation therapy, it is expected that the treatment would be possible within recommended margin of error at ICRP 60.