Papers by Author: Yan Ching Jean

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Authors: H.L. Yen, Y. Lou, Y.N. Xu, W.Y. Ching, Yan Ching Jean
482
Authors: Matthew D. Paul, Jonathan S. Davis, Yan Ching Jean, J. David van Horn
Abstract: In this study, the use of a 3D printer for sample holder fabrication and polymer sample preparation for positron analysis was explored. Custom printed 3D holders may be rapidly made and modified for a variety of thin-film, crystalline, or other diversely-shaped samples. For positron studies a 3D printer allows for the preparation of standard and unique polymer samples. In an initial study, a mesoporous-patterned ABS sample was attempted, without success. Various polymers (ABS, PLA, and PETG) and the same polymers with varied additives (carbon fiber or carbon nanotubes) were studied before and after printing. The different polymers and those with additives are distinguishable via PALS. Samples show a consistently lower I3 value after printing, suggesting a decrease in defect quantity for the printed polymer versus the as-received polymer filament.
303
Authors: Hong Min Chen, J. David van Horn, Yan Ching Jean
Abstract: Positron annihilation spectroscopy (PAS) is a novel method that can provide molecular-level information about complex biological and macromolecular structure in a manner which is different, but complementary, to conventional medical and biochemical research methodology. Positron annihilation lifetime spectroscopy (PALS) and Doppler broadening energy spectroscopy (DBES), coupled with a slow positron beam have been extensively applied to the life science research recently. These techniques provide new information about the atomic and molecular level free-volume and void sizes, and their distributions 0.1 nm to a few nm, molecular bonding, structures at depth-layers, and phase transitions. This paper is to review recent research on positron annihilation spectroscopy applied to the area of life science and also focus on current bioscience-related work in the positron group at the University of MissouriKansas City (UMKC).
275
Authors: J. David van Horn, Fei Wu, Gerald Corsiglia, Yan Ching Jean
Abstract: We have studied the interaction of the positron with chiral left-or right-handed quartz crystals. In Doppler-broadening experiments, using a mono-energetic positron beam there is a differential depth profile for positrons implanted in LH or RH z-cut quartz as identified by a shape parameter (S). Further, in bulk positron annihilation lifetime spectroscopy (PALS) experiments, the lifetime (τ 2) attributed to free annihilation of the positron interacting with the chiral lattice exhibits a larger value for the LH quartz, and the associated intensity (I2) is also significantly different—RH quartz is consistently 10% greater than the LH crystal. The τ 3 lifetime and its intensity, I3, attributed to positronium interacting with defects in the quartz, also appears to exhibit differences between the enantiomeric sets of crystals. These observations may demonstrate chiral recognition using a positron annihilation technique, pave the way for a broad range of positron experiments, and may help inform hypotheses of chirality recognition, selection, or induction by beta radiation.
221
Authors: Yan Ching Jean, F. Zandienadem, Qi Lin Deng
1897
Authors: P.E. Mallon, T.H. Berhane, C.J. Greyling, W.L. Vosloo, H. Chen, Yan Ching Jean
322
Authors: J. Zhang, H. Chen, R. Zhang, Ying Li, Ryoichi Suzuki, Toshiyuki Ohdaira, Yan Ching Jean
367
Authors: H. Chen, R. Zhang, Ying Li, Jun Jie Zhang, Yi Chu Wu, T.C. Sandreczki, P.E. Mallon, Toshiyuki Ohdaira, Ryoichi Suzuki, X. Gu, T. Nguyen, Yan Ching Jean
274
Authors: Hong Min Chen, L. James Lee, Jin Tao Yang, Xiao Hong Gu, Yan Ching Jean
Abstract: We have employed positron annihilation lifetime spectroscopy to measure the free volumes in nanocomposites of polystyrene with addition of carbon nanofiber (CNF) and carbon dioxide as a function of composition and of temperature. We found that the glass transition temperature (Tg) increases as a function of CNF compositions but significantly decreases as the exposure of CO2. We also investigate the combination effect of CNF and CO2 and found that the CO2 significantly weakens the bonding between PS and CNF interfaces. The Tg changes are compared with DSC.
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