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Joo, Yunsik,Byun, Junghwan,Seong, Narkhyeon,Ha, Jewook,Kim, Hyunjong,Kim, Sangwoo,Kim, Taehoon,Im, Hwarim,Kim, Donghyun,Hong, Yongtaek The Royal Society of Chemistry 2015 Nanoscale Vol.7 No.14
<P>The development of highly sensitive pressure sensors with a low-cost and facile fabrication technique is desirable for electronic skins and wearable sensing devices. Here a low-cost and facile fabrication strategy to obtain multiscale-structured elastomeric electrodes and a highly sensitive and robust flexible pressure sensor is presented. The principles of spontaneous buckle formation of the PDMS surface and the embedding of silver nanowires are used to fabricate the multiscale-structured elastomeric electrode. By laminating the multiscale-structured elastomeric electrode onto the dielectric layer/bottom electrode template, the pressure sensor can be obtained. The pressure sensor is based on the capacitive sensing mechanism and shows high sensitivity (>3.8 kPa<SUP>−1</SUP>), fast response and relaxation time (<150 ms), high bending stability and high cycle stability. The fabrication process can be easily scaled up to produce pressure sensor arrays and they can detect the spatial distribution of the applied pressure. It is also demonstrated that the fingertip pressure sensing device can sense the pressure distribution of each finger, when grabbing an object.</P>
Yunsik Kim,Seokmin Yoon,Hyejung Shin,Miyoun Jo,Sunmin Lee,Sae-hun Kim 한국축산식품학회 2021 한국축산식품학회지 Vol.41 No.3
The sensory properties and flavor of sour cream are important factors that influence consumer acceptability. The present study aimed to isolate lactic acid bacteria with excellent diacetyl production ability and to optimize the fermentation conditions for sour cream manufacture. Lactococcus lactis ssp. cremoris was isolated as a lactic acid bacterium derived from raw milk. This strain showed the greatest diacetyl production among other strains and was named LRCC5306. Various culture conditions were optimized to improve the diacetyl production of LRCC5306. The highest diacetyl production was found to be at 105.04±2.06 mg/L, when 0.2% citric acid and 0.001% Fe2+ were added and cultured at 20℃ for 15 h. Based on the optimal cultivation conditions, sour cream was manufactured using LRCC5306, with a viable count of 1.04×108 CFU/g and a diacetyl concentration of 106.56±1.53 mg/g. The electronic tongue system was used to compare the sensory properties of the sour cream; the fermented product exhibited sweetness and saltiness which was similar to that of an imported commercial product, but with slightly reduced bitterness and a significantly greater degree of sour taste. Therefore, our study shows that if cream is fermented using the LRCC5306, it is possible to produce sour cream with greatly improved sensory attractiveness, resulting in increased acceptance by consumers. Since this sour cream has a higher viable count of lactic acid bacteria, it is also anticipated that it will have a better probiotic effect.
Kim, Taehoon,Kim, Daesik,Joo, Yunsik,Park, Jongjang,Yoon, Jaeyoung,Hong, Yongtaek Institute of Physics Publishing 2019 Smart materials & structures Vol.28 No.2
<P>Conductive thin films are typically subject to crack formation and propagation under tensile strain, turning into insulating films due to complete breakage at large strain. However, if such crack propagation can be intentionally designed, repetitive resistance change can be obtained and used for implementation of high-performance strain sensors that are suitable for biocompatible and stretchable electronic applications. In this work, therefore, we introduce a fiber-reinforced region, which is formed by additionally inkjet-printing a single-walled carbon nanotube thin film, in a poly(3, 4-ethylenedioxythophene) doped with poly(styrenesulfonic acid) (PEDOT:PSS) thin film. The fiber-reinforced region well suppresses the crack propagation in the film under the tensile strain. The engineered PEDOT:PSS films are used to fabricate a strain sensor with a high gauge factor of ∼9 (at 50% strain) and an excellent working range of 70% even after 1000 cycle test at 50% tensile strain. Such a high-performance is explained via different fracture mechanisms between the fracture-designed and the fiber-reinforced regions in the PEDOT:PSS films. Our strategy of designing crack propagation using the inkjet-printing process enables not only to fabricate high-performance strain sensors that can detect human motions but also to provide a new insight for highly contuctive, but relatively brittle, materials toward the stretchable electronics applications.</P>
Analysis of Average Power Tracking Doherty Power Amplifier
Yunsik Park,Juyeon Lee,Seokhyeon Kim,Donggyu Minn,Bumman Kim THE INSTITUTE OF ELECTRICAL ENGINEERS 2015 IEEE Microwave and Wireless Components Letters Vol. No.
<P>An average power tracking (APT) Doherty power amplifier (PA) is analyzed in terms of its biasing voltage condition, efficiency, and output power. And the drain and gate bias voltages are optimized for operation at different output power conditions. The Doherty power amplifier is designed using 45 W gallium nitride (GaN) high electron mobility transistors (HEMT) for the carrier and peaking cells at 1.94 GHz. The bias voltages are controlled for each average power level(42.9 dBm, 39.9 dBm, 37 dBm). The measured drain efficiencies and gains are 53.2%, 12.8 dB at 42.9 dBm and 54.3%, 11.2 dB at 39.9 dBm and 53.4%, 9.1 dB at 37 dBm for a 10 MHz LTE signal with a 6.5 dB PAPR. This result demonstrates that the Doherty PA can be reconfigured for different average output powers using the bias voltage control method.</P>
Kim, Yunsik,Yoon, Seokmin,Shin, Hyejung,Jo, Miyoun,Lee, Sunmin,Kim, Sae-hun Korean Society for Food Science of Animal Resource 2021 한국축산식품학회지 Vol.41 No.2
The objective of the present study was to evaluate the cholesterol-assimilation ability of lactic acid bacteria (LAB), which were isolated from kimchi, a Korean traditional fermented cabbage. The isolated strain, using modified MRS medium, showed 30.5% cholesterol assimilation activity and was named Pediococcus acidilactici LRCC5307. Types and concentrations of bile were investigated for their effects on increasing the cholesterol assimilation ability of the LRCC5307 strain, a 74.5% decrease in cholesterol was observed when 0.2% bile salts were added. In addition, the manufacture of low-cholesterol butter using LRCC5307 was examined. After fermentation, LRCC5307 with butter showed 8.74 Log CFU/g viable cells, pH 5.43, and a 11% decrease in cholesterol. These results suggest that LRCC5307 could help in the production of healthier butter by decreasing cholesterol and including living LAB.
Kim, Hakseung,Lee, Seung-Bo,Son, Yunsik,Czosnyka, Marek,Kim, Dong-Joo Wolters Kluwer Health, Inc. All rights reserved 2018 Journal of neurosurgical anesthesiology Vol.30 No.4
BACKGROUND:: Hemodynamic instability and cardiovascular events heavily affect the prognosis of traumatic brain injury. Physiological signals are monitored to detect these events. However, the signals are often riddled with faulty readings, which jeopardize the reliability of the clinical parameters obtained from the signals. A machine-learning model for the elimination of artifactual events shows promising results for improving signal quality. However, the actual impact of the improvements on the performance of the clinical parameters after the elimination of the artifacts is not well studied. MATERIALS AND METHODS:: The arterial blood pressure of 99 subjects with traumatic brain injury was continuously measured for 5 consecutive days, beginning on the day of admission. The machine-learning deep belief network was constructed to automatically identify and remove false incidences of hypotension, hypertension, bradycardia, tachycardia, and alterations in cerebral perfusion pressure (CPP). RESULTS:: The prevalences of hypotension and tachycardia were significantly reduced by 47.5% and 13.1%, respectively, after suppressing false incidents (P=0.01). Hypotension was particularly effective at predicting outcome favorability and mortality after artifact elimination (P=0.015 and 0.027, respectively). In addition, increased CPP was also statistically significant in predicting outcomes (P=0.02). CONCLUSIONS:: The prevalence of false incidents due to signal artifacts can be significantly reduced using machine-learning. Some clinical events, such as hypotension and alterations in CPP, gain particularly high predictive capacity for patient outcomes after artifacts are eliminated from physiological signals.