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A/C Hiss Noise Study on Thermal System Bench
Junwoo Kim,Taejin Hwang 한국자동차공학회 2017 한국자동차공학회 학술대회 및 전시회 Vol.2017 No.11
A/C system hiss noise comes from orifice noise. Refrigerant gas passes through the TXV valve when A/C system is not stabilized. In general, hiss noise is generated when driver just turns on the air conditioner and disappeared as the system stabilized. In case of variable type compressor, hiss noise is not critical because it just happens only one time when A/C system just starts. But, due to the higher emission and fuel economy regulation, the portion of variable compressor is getting smaller. On contrary, fixed type compressor portion, which works only at the low pressure, is getting higher especially for the small size car market. In addition, new refrigerant(R-1234YF) which has lower enthalpy than current refrigerant(R-134a) is supposed to replace with current R-34a due to the regulation. However, new refrigerant R-1234YF has more severe hiss noise. For this reason, hiss noise is more important than previous. The countermeasure for hiss noise, in general, is touching the TXV valve surface or changing the refrigerant amount which affects minor thermal performance. But, these countermeasures do not change the A/C system itself, so there is a limitation of improvement. The main object of this paper is to investigate the hiss noise mechanism by thermal system bench test, and to find the fundamental and active countermeasure.
Chaotic Standard Map Based Frequency Hopping OFDMA for Low Probability of Intercept
Junwoo Jung,Jaesung Lim IEEE 2011 IEEE COMMUNICATIONS LETTERS Vol.15 No.9
<P>In frequency hopping (FH)-OFDMA, the transmitted symbols on all subcarriers are demodulated by FFT at once at the receiver. Thus, these symbols can be easily intercepted by an adversary radiometer when the number of simultaneous transmitting users is small. In this letter, we design a chaotic standard map (CSM) based FH pattern for low probability of intercept. Through the proposed scheme, more than two symbols of the same user can be shown in the same symbol period, or none. Moreover, the order of these symbols is mixed. It makes the radiometer difficult in intercepting these symbols, and thus, it achieves a low probability of intercept. We show that the proposed scheme satisfies requirements of a desired FH pattern.</P>
Junwoo Park,Jongwon Choi,Woochol Joseph Choi 한국전문물리치료학회 2023 한국전문물리치료학회지 Vol.30 No.1
Background: Despite fall prevention strategies suggested by researchers, falls are still a ma-jor health concern in older adults. Understanding factors that differentiate successful versus unsuccessful balance recovery may help improve the prevention strategies. Objects: The purpose of this review was to identify biomechanical factors that differentiate successful versus unsuccessful balance recovery in the event of a fall. Methods: The literature was searched through Google Scholar and PubMed. The following keywords were used: ‘falls,‘ ‘protective response,‘ ‘protective strategy,’ ‘automated postural response,’ ‘slips,’ ‘trips,’ ‘stepping strategy,‘ ‘muscle activity,’ ‘balance recovery,‘ ‘successful balance recovery,‘ and ‘failed balance recovery.’ Results: A total of 64 articles were found and reviewed. Most of studies included in this review suggested that kinematics during a fall was important to recover balance successfully. To be successful, appropriate movements were required, which governed by several things depending on the direction and characteristics of the fall. Studies also suggested that lower limb muscle activity and joint moments were important for successful balance recovery. Other factors associated with successful balance recovery included fall direction, age, appropriate protective strategy, overall health, comorbidity, gait speed, sex and anticipation of the fall. Conclusion: This review discusses biomechanical factors related to successful versus un-successful balance recovery to help understand falls. Our review should help guide future research, or improve prevention strategies in the area of fall and injuries in older adults.
Pixel-wise distortion model and its calibration method for AMCW LiDAR
Junwoo Jason Son,Youngbin Son,Byeongho Song,Soohee Han 제어로봇시스템학회 2021 제어로봇시스템학회 국제학술대회 논문집 Vol.2021 No.10
In this conference paper, we proposed pixel-wise distortion model and its calibration method for AMCW (Amplitude Modulated Continuous Wave) LiDAR (Light Detection and Ranging). The proposed model can be reflect square wave distortion, common mode error and non-linear characteristic of the receiving circuit. The model characterise the distance error with actual distance and amplitude of the DCS (Differential Correlation Sample). A simple calibration method is also announced in order to use the proposed model. The method uses modulation signal delay and shutter speed variation to measure the response of the receiving circuit. The experiment was carried out with various signal delay and shutter speed under simple calibration box. The result shows the response of the AMCW LiDAR was changed by both inputs and also the AMCW LiDAR can measure the distance without these errors by using the proposed model and calibration method.
Intra Prediction based on the Rate-distortion Cost in HEVC
Junwoo Choi,Yung-Lyul Lee 대한전자공학회 2017 IEIE Transactions on Smart Processing & Computing Vol.6 No.5
High Efficiency Video Coding (HEVC) provides high coding efficiency, compared with H.264/AVC. In particular, intra coding efficiency is improved due to reference-sample filtering and unfiltering methods before intra prediction, where the reference-filtering methods are applied according to the block size and intra prediction mode. In this paper, a rate-distortion (RD) costbased intra prediction that computes the minimum RD cost between the filtered reference samples and the unfiltered reference samples is proposed. Intra coding efficiency is improved by using the probability update between the reference sample filtering in the current coding unit and the neighbor coding units, because the predefined reference-sample filtering in HEVC is not optimal in terms of intra coding efficiency. Experiment results show that the proposed method reduces the Bjøntegaard delta (BD) rates of the luma and chroma (Cb and Cr) by approximately 0.5% and 0.4%, respectively.