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Zr/Ti 비에 따른 PZT계 압전세라믹스의 온도안정성
임대관,현원석,이개명 濟州大學校 情報通信硏究所 1998 情報通信硏究所論文集 Vol.1 No.-
In this paper, temperature stabilities of Pb( Zr_xTi_(1-x))O₃ piezoelectric ceramic system according to Zr/Ti ratios were investigated. PZT ceramics with Zr/Ti =58/42, 56/44, 53/47, 50/50, 48/52 which are adjacent compositions to Mophotyophic phase were fabricated, and thermal aging effects on the specimen were measured. After thermal aging. the specimens with Zr/Ti=58/42, 56/44, 48/52 in them could have lower temperature coefficient for antiresonant frequency and the specimen with Zr/Ti = 58/42 which is a composition of Rhombohedral phase have had the lowest temperature coefficient for antiresonant frequency.
음낭외상시 고환파열에 대한 초음파 검사의 진단적 유용성
김경영,한동준,신대은,노준,문형윤,임동훈,김철성,박성운 朝鮮大學校 附設 醫學硏究所 2007 The Medical Journal of Chosun University Vol.32 No.3
Purpose: We determined the use of scrotal ultrasonography in the initial diagnosis and management of testicular injuries due to blunt scrotal trauma. Mateiials and Methods: We reviewed 54 patients of scrotal trauma in the last 8 years. Forty patients were evaluated by ultrasonography preoperatively. A heterogeneous echo pattern of the testicular parenchyma with loss of oval shape, contour definition was the basis for diagnosis of testicular rupture. Among them, 33 cases underwent scrotal exploration and 7 cases were managed conservatively. The remaining 14 patients were evaluated only by physical examination, 8 patients of them were explored immediately because of suspicious testicular mpture. The accuracy of ultrasonography were determined by comparing radiographic interpretations with intraoperative findings. Results: Among the 33 patients who were evaluated by ultrasonography and explored immediately, there were 26 suspected testicular ruptures on ultrasonography. Surgical exploration revealed testicular rupture in 23 and simple hematoma in 10. The testicular rupture was correctly diagnosed by ultrasonography in the 22 cases, and there were 4 false-positive and 1 false-negative diagnoses of testicular rupture. The sensivity and specificity for the diagnosis of testicular rupture are 96% and 60%, and the positive and negative predictive values are 85% and 86%, respectively, Conclusions: Scrotal ultrasonography, with the main radiographic finding of a heterogeneous echo pattern of the testicular parenchyma with loss of oval shape, contour definition, is highly sensitive on the diagnosis of testicular rupture. And it increases the salvage rate for testicular rupture with preservation of the testicular function and prevents delayed complications of chronic pain, atrophy and orchiectomy associated with missed testicular rupture.
On the phase sequence set of SLM OFDM scheme for a crest factor reduction
Lim, Dae-Woon,Heo, Seok-Joong,No, Jong-Seon,Chung, Habong Institute of Electrical and Electronics Engineers 2006 IEEE transactions on signal processing Vol.54 No.5
The crest factor distribution of orthogonal-frequency-division-multiplexing (OFDM) symbol sequences is evaluated, and it is shown that OFDM symbol sequences with a short period are expected to have a high crest factor. The crest factor relationship between two input symbol sequences, Hamming distance D apart, is also derived. Using these two results, two criteria are proposed for a phase sequence set of the selected mapping (SLM) OFDM scheme and suggest the rows of the cyclic Hadamard matrix constructed from an m-sequence as a near-optimal phase sequence set of the SLM OFDM scheme.
A new SLM OFDM scheme with low complexity for PAPR reduction
Lim, Dae-Woon,No, Jong-Seon,Lim, Chi-Woo,Chung, Habong IEEE 2005 IEEE signal processing letters Vol.12 No.2
The authors introduce a new selected mapping (SLM) orthogonal frequency division multiplexing (OFDM) scheme with low computational complexity. The proposed SLM scheme transforms an input symbol sequence into a set of OFDM signals by multiplying the phase sequences to the signal after a certain intermediate stage of inverse fast Fourier transform (IFFT). Then, the OFDM signal with the lowest peak-to-average power ratio (PAPR) is selected for transmission. The new SLM OFDM scheme reduces the computational complexity, while it shows almost the same performance of PAPR reduction as that of the conventional SLM OFDM scheme.
Multi-Stage TR Scheme for PAPR Reduction in OFDM Signals
Dae-Woon Lim,Hyung-Suk Noh,Hyun-Bae Jeon,Jong-Seon No,Dong-Joon Shin IEEE 2009 IEEE transactions on broadcasting Vol.55 No.2
<P>In the tone reservation (TR) scheme of the orthogonal frequency division multiplexing (OFDM) systems, there exists a trade-off between the peak to average power ratio (PAPR) reduction performance and the peak reduction tone (PRT) set size. In this paper, we propose a multi-stage TR scheme for PAPR reduction, which adaptively selects one of several PRT sets according to the PAPR of OFDM signal while the PRT set is fixed for the conventional TR scheme. It is shown that the PAPR reduction performance of the proposed scheme is better than that of the conventional TR scheme when the tone reservation rate (TRR) is the same.</P>
An Overview of Peak-to-Average Power Ratio Reduction Schemes for OFDM Signals
Lim, Dae-Woon,Heo, Seok-Joong,No, Jong-Seon The Korea Institute of Information and Commucation 2009 Journal of communications and networks Vol.11 No.3
Orthogonal frequency division multiplexing (OFDM) has been adopted as a standard for various high data rate wireless communication systems due to the spectral bandwidth efficiency, robustness to frequency selective fading channels, etc. However, implementation of the OFDM system entails several difficulties. One of the major drawbacks is the high peak-to-average power ratio (PAPR), which results in intercarrier interference, high out-of-band radiation, and bit error rate performance degradation, mainly due to the nonlinearity of the high power amplifier. This paper reviews the conventional PAPR reduction schemes and their modifications for achieving the low computational complexity required for practical implementation in wireless communication systems.
Lim, Dae-Woon,Park, Jong-Rak,Choi, Mi-Hyun,Lee, Soo-Jeong,Choi, Jin-Seung,Kim, Hyung-Sik,Yi, Jeong-Han,Tack, Gye-Rae,Lee, Bongsoo,Chung, Soon-Cheol Gordon and Breach 2009 International journal of neuroscience Vol.119 No.9
<P>The purpose of the current study is to develop a magnetic resonance (MR)-compatible galvanic skin response (GSR) measurement system that can measure the GSR signal during MR image acquisition. If GSR signals are measured simultaneously with the acquisition of MR images, there can be a mutual interference effect. The present system was designed to block noises caused by the main magnetic field, the gradient magnetic field, and the radio frequency (RF) pulse when MR images are acquired. To minimize the distortion of MR images, the GSR measurement system was shielded. Especially, this system used analog, not digital, elements in order to remove any possible effects on MR images. An RF-interference-free optical data link using the pulse-width modulation technique was adopted in order to transmit GSR signals measured inside the MR room. The experiment verified that a reliable GSR signal can be obtained without deteriorating the MR image. It is expected that this system can be used for diverse medical and neuroscience studies.</P>
( Dae-woon Jeong ),( Won-bi Han ),( Jae-oh Shim ),( Won-jun Jang ),( Yeol-lim Lee ),( Hyun-seog Roh ),( Jae Hoi Gu ),( Yong Taek Lim ) 한국폐기물자원순환학회(구 한국폐기물학회) 2014 한국폐기물자원순환학회 심포지움 Vol.2014 No.1
A rapid one step direct synthesis of high temperature water gas shift (WGS) catalysts, magnetite incorporated with various promoters like Co, Ni, Cu, and Zn have been shown. An amino acid glycine was used as a complexing agent as well as a fuel for the auto-combustion process. The zwitterionic nature of glycine favors the easy incorporation of the promoter metal ions. In addition, reducing atmosphere created by glycine during its burning makes it possible to prepare magnetite directly. During the high temperature WGS, the activity follows the order Cu-FAG > Ni-FAG > Zn-FAG > Co-FAG. The optimization of Cu loading is also carried out. At 12.5 mole % of Cu loading the catalytic activity reached a CO conversion value of 87% at 400℃.
Cerebral lateralization index based on intensity of bold signal of FMRI.
Lim, Dae-Woon,Min, Byung-Chan,Kim, Hyun-Jun,Choi, Mi-Hyun,Lee, Soo-Jeong,Jun, Jae-Hoon,Lee, Bongsoo,Chung, Soon-Cheol Gordon and Breach 2008 INTERNATIONAL JOURNAL OF NEUROSCIENCE - Vol.118 No.11
<P>This study proposes a new cerebral lateralization index (LI) on the basis of neural activation intensity. Eight right-handed male college students (mean age 23.5 years) and 10 right-handed male college students (the mean age 25.1 years) participated in this study of visuospatial and verbal tasks, respectively. Functional brain images were taken from 3T MRI using the single-shot EPI method. A cerebral LI based on neural activation area (i.e., number of activated voxels) and another based on neural activation intensity (i.e., intensity of BOLD (blood oxygen level dependent)) were calculated for both cognition tasks. The result of calculating a cerebral LI based on neural activation area suggested that the right hemisphere is dominant during visuospatial tasks and the left hemisphere is dominant during verbal tasks. When a cerebral LI was computed on the basis of the neural activation intensity, it was shown that the area of cerebral lateralization closely related to visuospatial tasks is the superior parietal lobe, and the area of cerebral lateralization closely related to verbal tasks is the inferior and middle frontal lobe. Since the proposed method can determine the dominance of the cerebrum by each area, it can be helpful to determine cerebral lateralization accurately and easily.</P>