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Degradation of Backsheets for Crystalline Photovoltaic Modules under Damp Heat Test
Dajung Kim,Namsu Kim,Won-Sik Hong,Hanjun Kang,Kyuwan Lee,Chulmin Oh 한국신재생에너지학회 2016 신재생에너지 Vol.12 No.3
The reliability of crystalline silicon photovoltaic (PV) modules is determined not only by the efficiency loss of the silicon cells but also by the degradation of other components (ethyl vinyl acetate, ribbon, glass, and backsheet). Among these components, the backsheet provides electrical insulation and physical support, and acts as a barrier against moisture and weathering of the PV module. We investigated the degradation of different types of backsheets under damp heat conditions [95°C/85% relative humidity (R.H), 85°C/85% R.H]. During the damp heat treatment, tensile tests were carried out to investigate the mechanical degradation of the backsheets. The molecular weight of the polyethylene terephthalate (PET) in the backsheets was measured by gel permeation chromatography (GPC) to understand the intrinsic mechanism of degradation. After damp heat test, mechanical degradation of backsheet occurred significantly beyond passing the specified molecular weight region of PET film in backsheet materials. By finding the correlation between tensile strength and the molecular weight of the backsheets, our results make it possible to improve the reliability of backsheets.
Evolution-strategy Optimized Dual-Band Antenna for UHF-band RFID/IoE Application
Dajung Han(한다정),Changhyeong Lee(이창형),Sungtek Kahng(강승택) 융복합지식학회 2016 융복합지식학회논문지 Vol.4 No.2
This paper presents an optimization-based design method for a multi-band antenna. From various optimization techniques, evolution strategy is adopted to find the proper initial geometry for creating the resonance at two frequencies(433 MHz and 900 MHz) with a limited physical size. The antenna structure is finalized by adjusting the geometrical parameters to meet the specifications of the UHF-band RFID/IoE services. The design method is validated by fabricating the antenna and testing its frequency responses which turn out compliant with the simulated results.
DaJung Han,ChangHyeong Lee,Sungtek Kahng 대한전기학회 2017 Journal of Electrical Engineering & Technology Vol.12 No.4
A new Complex Image Method based on Genetic Algorithm (GA) is proposed to calculate the Green’s functions of CPW (coplanar waveguide)-type microwave components and antennas. The closed-forms of the spectral-domain integrals are obtained by the GA, avoiding the conventional procedures of the tedious linear algebra and the sampling conditions sensitive to the complex-variable sampling paths adopted in the Prony’s and GPOF methods. The proposed method is compared with the numerical Sommerfeld Integral, which results in good agreement.
Dajung Kim,Hyeonbin Lee,Jin-Man Jung,Young Hen Lee,Hyung Suk Seo 대한자기공명의과학회 2018 Investigative Magnetic Resonance Imaging Vol.22 No.2
Susceptibility-weighted imaging (SWI) is well known for detecting the presence of hemorrhagic transformation, microbleeds and the susceptibility of vessel signs in acute ischemic stroke. But in some cases, it can provide the tissue perfusion state as well. We describe a case of a patient with hyperacute ischemic infarction that had a slightly hypodense, patchy lesion at the left thalamus on the initial SWI, with a left proximal posterior cerebral artery occlusion on a magnetic resonance (MR) angiography and delayed time-to-peak on an MR perfusion performed two hours after symptom onset. No obvious abnormal signals at any intensity were found on the initial diffusion-weighted imaging (DWI). On a follow-up MR image (MRI), an acute ischemic infarction was seen on DWI, which is the same location as the lesion on SWI. The hypointensity on the initial SWI reflects the susceptibility artifact caused by an increased deoxyhemoglobin in the affected tissue and vessels, which reflects the hypoperfusion state due to decreasing arterial flow. It precedes the signal change on DWI that reflects a cytotoxic edema. This case highlights that, in some hyperacute stages of ischemic stroke, hypointensity on an SWI may be a finding before the hyperintensity is seen on a DWI.
Dajung Yun,Kyoungwon Lee 한국청각언어재활학회 2020 Audiology and Speech Research Vol.16 No.4
Purpose: While adjusting the compression threshold (CT) of low and high frequency bands of multi-channel hearing aids in noise, we tried to evaluate any changes in Korean consonant-vowel (CV) syllabic recognition scores, sound quality, and loudness of noise with white noise. Methods: A total of twenty one subjects with hearing loss (mean age of 66.2 years) participated voluntarily. Their pure-tone average was 46.0 dB HL and the word recognition score was 72.1%. The CTs of low/ high frequency bands were adjusted to 50/50 dB SPL, 50/65 dB SPL, 65/50 dB SPL and 60/65 dB SPL in multi-channel hearing aids. While presenting white noise to the non-test ear, Korean CV syllables were presented to the test ear to evaluate the recognition scores, clarity of conversational speech, and loudness of noise. The intensity of CV syllables presented to the subject was 50 dB HL, and the signal-to-noise ratios (SNRs) were 5 dB and 10 dB. Results: First, when the CT of low/high frequency bands was adjusted to 50/50 dB SPL, the CV syllabic recognition scores were higher compared to 65/50 dB SPL. Second, in the noise environment, the clarity of conversational speech, and loudness of the noise did not have any difference regardless of levels of CT. Conclusion: Based on current findings, the frequency bands setting of CT in the multi-channel hearing aids might provide changes to recognize Korean speech sounds, which may affect the adjustment of frequency band CT from multichannel hearing aids in the future.