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Probing spin-charge relation by magnetoconductance in one-dimensional polymer nanofibers
Choi, A.,Kim, K. H.,Hong, S. J.,Goh, M.,Akagi, K.,Kaner, R. B.,Kirova, N. N.,Brazovskii, S. A.,Johnson, A. T.,Bonnell, D. A.,Mele, E. J.,Park, Y. W. American Physical Society 2012 Physical review. B, Condensed matter and materials Vol.86 No.15
Choi, A.,Seo, K.,Kim, D.,Kim, B.,Kim, D. GENERAL AND APPLIED CHEMISTRY JOURNALS 2017 LAB ON A CHIP Vol. No.
<P>Complex microparticles (MPs) bearing unique characteristics such as well-tailored sizes, various morphologies, and multi-compartments have been attempted to be produced by many researchers in the past decades. However, a conventionally used method of fabricating MPs, emulsion polymerization, has a limitation in achieving the aforementioned characteristics and several approaches such as the microfluidicsassisted (droplet-based microfluidics and flow lithography-based microfluidics), electrohydrodynamics (EHD)-based, centrifugation-based, and template-based methods have been recently suggested to overcome this limitation. The outstanding features of complex MPs engineered through these suggested methods have provided new opportunities for MPs to be applied in a wider range of applications including cell carriers, drug delivery agents, active pigments for display, microsensors, interface stabilizers, and catalyst substrates. Overall, the engineered MPs expose their potential particularly in the field of biomedical engineering as the increased complexity in the engineered MPs fulfills well the requirements of the high-end applications. This review outlines the current trends of newly developed techniques used for engineered MPs fabrication and focuses on the current state of engineered MPs in biomedical applications.</P>
Choi, A,Shin, H IOP 2017 PHYSIOLOGICAL MEASUREMENT Vol.38 No.3
<P>Pulse rate variability (PRV) analysis appears as the first alternative to heart rate variability analysis for wearable devices; however, there is a constraint on computational load and energy consumption for the limited system resources available to the devices. Considering that adjustment of the sampling frequency is one of the strategies for reducing computational load and power consumption, this study aimed to investigate the influence of sampling frequency (<I>f</I> <SUB>s</SUB>) on PRV analysis and to find the minimum sampling frequency while maintaining reliability. We generated 5000, 2500, 1000, 500, 250, 100, 50, 25, 20, 15, 10, 5 Hz down-sampled photoplethysmograms from 10 kHz-sampled PPGs and derived time- and frequency-domain variables of the PRV. These included AVNN, SDNN, SDSD, RMSSD, NN50, pNN50, total power, VLF, LF, HF, LF/HF, nLF and nHF for each down-sampled signal. Derived variables were compared with heart rate variability of the 10 kHz-sampled electrocardiograms, and then statistically investigated using one-way <I>ANOVA</I> test and <I>Bland–Altman</I> analysis. As a result, significant differences (<I>P</I> < 0.05) were found for SDNN, SDSD, RMSSD, NN50, pNN50, TP, HF, LF/HF, nLF and nHF, but not for AVNN, VLF and LF. Based on the post hoc tests, it was found that the NN50 and pNN50, SDSD and RMSSD, LF/HF and nHF, SDNN, TP and nLF analysis had significant differences at <I>f</I> <SUB>s</SUB> ⩽ 20 Hz, <I>f</I> <SUB>s</SUB> ⩽ 15 Hz, <I>f</I> <SUB>s</SUB> ⩽10 Hz; <I>f</I> <SUB>s</SUB> = 5 Hz, respectively. In other words, a significant difference was not seen for any variable if the <I>f</I> <SUB>s</SUB> was greater than 25 Hz. Consequently, our pilot study suggests that analysis of variability in the time and frequency domain from pulse rate obtained through PPG may be potentially as reliable as that derived from the analysis of the electrocardiogram, provided that <I>f</I> <SUB>s</SUB> ⩾25 Hz sampling frequency is used.</P>
Choi, A.,Kim, J.Y.,Lee, J.E.,Jung, H.I. Elsevier 2009 Current Applied Physics Vol.9 No.4
An in vitro neural network can provide a model to investigate the signaling processes that regulate the body functions. Using polydimethylsiloxane (PDMS) multilayer micro-structures to construct a neural network, the bonding between the layers can be improved by modulation of the curing ratio. In this study, we found that as the curing ratio increased from 10:1 to 10:4, the contact angle decreased from 111.69<SUP>o</SUP> to 102.08<SUP>o</SUP> and the surface energy and roughness increased. For adhesion and proliferation, the hippocampal primary neural cells preferred a PDMS surface with a 10:1 curing ratio to other surfaces. In addition, 3D PDMS micro-pyramid array allows the primary hippocampal neuron to pattern a network without any surface treatment and the network was verified by immunocytochemistry. These results may suggest the optimum PDMS curing ratio to apply in constructing a cell device for in vitro neural network formation as well as the potential of 3D structure fabrication which allows us to construct neural network without any surface treatment.
Biomechanical Evaluation of Dynamic Balance Control Ability During Golf Swing
Choi, A.,Kang, T. G.,Mun, J. H. WALTER H CHANG 2016 Journal of medical and biological engineering Vol.36 No.3
<P>Balance ability seems to be significantly correlated with golfing skill. However, it is unclear whether dynamic balance control has a direct influence on golf swing performance. In this study, the effects of a golfer's skill level on the observed dynamic balance control ability during the golf swing were evaluated. Fifty participants were divided into three groups (professional, advanced, and novice) based on their official handicap scores. Six infrared cameras and two force platforms were used to determine dynamic alterations of the center of mass (COM) and center of pressure (COP). The peak-to-peak displacement and velocity of the COM and COP in the professional golfers were generally lower than those of the other golfers. However, the professional golfers displayed significantly greater COM displacement than that of the advanced amateur golfers in the lead/trail direction (p < 0.01). This does not directly imply deterioration of the dynamic balance ability since the COM-COP separation decreased as the skill level of the golfers increased. The professional golfers had superior dynamic balance ability, achieved by controlling the COP excursion to compensate for the increased variation of COM, leading to a more stable swing mechanism than that of the amateur golfers. This study provides quantitative information for the evaluation of dynamic balance control during the golf swing.</P>