• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.11
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• pp.1262-1270
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• 2007

In this paper, we propose a new distortion cancellation mechanism for a balanced power amplifier structure using the carrier cancellation loop of a feedforward and post-distortion technique. The proposed cross post-distortion balanced linear amplifier can reduce nonlinear components as much as the conventional feedforward amplifier through the output dynamic range and broad bandwidth. Also the proposed system provides higher efficiency than the feedforward. The capacities of power amplifier and error power amplifier in the proposed system are analyzed and compared with those of feedforward amplifier. Also the operation mechanisms of the three kind loops are explained. The proposed cross post-distortion balanced linear power amplifier is implemented at the IMT-2000($f_0=2.14\;GHz$) band. With the commercial high power amplifiers of total power of 240 W peak envelope power fer base-station application, the adjacent channel leakage ratio measurement with wideband code division multiple access 4FA signal shows 18.6 dB improvement at an average output power of 40 dBm. The efficiency of fabricated amplifier Improves about 2 % than the conventional feedforward amplifier.

• Journal of Power Electronics
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• v.16 no.6
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• pp.2258-2271
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• 2016

In this paper, some crucial performance characteristics related to the operational reliability of the post-fault Pulse Width Modulated (PWM) rectifiers, such as line current harmonic distortion, Common Mode Voltage (CMV), and current stress on the capacitors, are fully investigated. The aforementioned performance characteristics of post-fault rectifiers are highly dependent on the utilized space vector modulation (SVM) schemes, which are also examined. Detailed analyses of the three most commonly used SVM schemes for post-fault PWM rectifiers are provided, revealing the major differences in terms of the zero vector synthesis approaches. To compare the performances of the three SVM schemes, the operating principles of a post-fault rectifier are presented with various SVM schemes. Using analytical and numerical methods in the time domain, the performances of the line current distortion, common mode voltage and capacitor current are evaluated and compared for each SVM scheme. The proposed analysis demonstrates that the zero vector synthesis approaches of the considered methods have significant impacts on the performance characteristics of rectifiers. In addition, the advantages and disadvantages of the proposed SVM schemes are discussed. The experimental results verify the effectiveness and validity of the proposed analysis.

• Journal of Conservation Science
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• v.38 no.1
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• pp.14-32
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• 2022

Underwater photographing and image recording are essential for pre-excavation survey and during excavation in underwater archaeology. Unlike photographing on land, all underwater images suffer various quality degradations such as shape distortions, color shift, blur, low contrast, high noise levels and so on. Outcome is very often heavily photographing equipment and photographer dependent. Excavation schedule, weather conditions, and water conditions can put burdens on divers. Usable images are very limited compared to the efforts. In underwater archaeological study in very turbid water such as in the Yellow Sea (between mainland China and the Korean peninsula), underwater photographing is very challenging. In this study, off-site image distortion and color compensation techniques using an image processing/analysis software is investigated as an alternative image quality enhancement method. As sample images, photographs taken during the excavation of 800-year-old Taean Mado Shipwrecks in the Yellow Sea in 2008-2010 were mainly used. Significant enhancement in distortion and color compensation of archived images were obtained by simple post image processing using image processing/analysis software (PicMan) customized for given view ports, lenses and cameras with and without optical axis offsets. Post image processing is found to be very effective in distortion and color compensation of both recent and archived images from various photographing equipment models and configurations. Merits and demerit of in-situ, distortion and color compensated photographing with sophisticated equipment and conventional photographing equipment, which requires post image processing, are compared.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.383-384
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• 2006

The P-ECLMS algorithm adapted the existing Post-Processing method occurs the distortion of the near-end signal at the double-talk situationt. To solve this problem, we propose the SP-ECLMS(Selective Post-Processing ECLMS) algorithm which makes the Post-Processing coefficient differently at the case of the single-talk and the double-talk. When the correlation level is not output less than 30%, the proposed algorithm output the original signal to prevent the signal's distortion.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.2 s.314
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• pp.137-143
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• 2007

The P-ECLMS algorithm adapted the existing Post-Processing method occurs the distortion of the near-end signal at the double-talk situation. To solve this problem, we propose the SP-ECLMS algorithm which makes the Post-Processing coefficient differently at the case of the single-talk and the double-talk. When the correlation level is not output less than 30%, the proposed algorithm output the original signal to prevent the signal's distortion.

• Steel and Composite Structures
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• v.35 no.6
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• pp.717-727
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• 2020

The homotopy perturbation method (HPM) to predict the pre- and post-buckling behaviour of simply supported steel beams with rectangular hollow section (RHS) is presented in this paper. The non-linear differential equations solved by HPM derive from a kinematics where large twist and cross-sections distortions are considered. The results (linear and non-linear paths) given by the present HPM are compared to those provided by the Newton-Raphson algorithm with arc length and by the commercial FEM code Abaqus. To investigate the effect of cross-sectional distortion of beams, some numerical examples are presented.

• Journal of the Korean Society of Radiology
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• v.10 no.5
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• pp.359-365
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• 2016

Fluoroscopy is performed when tissue or organ in the human body is examined, and it is used for diagnosis and procedure in back ailments. With regard to fluoroscopy equipment, distortion occurs on the peripheral part of fluoroscopic image rather than on its central part. This study measured distortion factors of vertical spacing ratio and distortion factor of diagonal spacing ratio before and after correction by applying a correction algorithm. According to measuring the vertical spacing ratio, post-correction standard deviation decreased by 0.04 in comparison with pre-correction one. Also measuring the diagonal spacing ratio, post-correction standard deviation decreased by 0.06 in comparison with pre-correction one. Consequently, the distortion of fluoroscopic image decreased after correction. A decrease in the distortion of image through the application of correction algorithm and the improvement of performance will be helpful in finding a correct position of lumbar puncture in nucleoplasty to treat lumbar disc herniation in the future.

• Structural Engineering and Mechanics
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• v.2 no.1
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• pp.113-123
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• 1994

A method for computing the elastic buckling prestressing force of a post-tensioned composite steel-concrete tee-beam is presented. The method is based on a virtual work formulation, and incorporates the restraint provided by the concrete slab to the buckling displacements of the steel beam. The distortional buckling solutions are shown to be given by a quadratic equation. The application of the analysis to calculation buckling strengths is given, based on codified rules for beam-columns. Conclusions are then drawn on the importance of distortional buckling when a post-tensioned composite beam is stressed during jacking.

• International Journal of Automotive Technology
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• v.4 no.1
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• pp.31-40
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• 2003

W-beam guardrail system has been the most popular roadside safety device around the world. Through large plastic deformation and corresponding energy dissipation, a W-beam guardrail system contains and re-directs out-of-control vehicles so as to reduce the impact damage on the vehicle occupants and the vehicles themselves. In this paper, our recent experiments on 1 : 3.75 downscaled W-beam and the beam-post system are reported. The static and impact test results on the load characteristics, the global response and the local cross-sectional distortion are reveled. The effects of three different end-boundary conditions for the beam-only testing are examined. It is found that the load characteristics are much dependent on the combined contribution of the local cross-sectional distortion and the end-supporting conditions. The energy Partitioning between the beam and the supporting Posts in the beam-Post-system testing were also examined. The results showed that the energy dissipation partitioning changed with the input impact energy. Finally, a simple mass-spring model is developed to assess the dynamic response of a W-beam guardrail system in response to an impact loading. The model's prediction agrees well with the experimental results.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.43-48
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• 2003

The problem of welding stresses and fatigue behavior is the main concerns of welding research fields. The residual stresses and distortion of structures by welding is exert negative effect on the safety of mechanical structures. That is, expansion of material by high temperature and distortion by cooling during welding process is caused of tensile and compressive residual stresses on welding material, and this residual stresses reduce fracture and fatigue strength of welding structures. The accurate prediction of residual stress and relaxation due to loading and post weld heat treatment of weld zone is very important to improve the quality of weldment. In this study, a finite element modeling technique is developed to simulate the relaxation of residual stresses due to loading and post weld heat treatment of weld zone. The accuracy of finite element models is evaluated based on experimental results and the results of the analytical solution.