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Fabrication of suspended graphene field-effect transistors by the sandwich method
Shin Hyunsuk,Lee Sungbae 한국물리학회 2023 Current Applied Physics Vol.48 No.-
A novel fabrication technique that can be used for making a series of suspended graphene field-effect transistors on Si-substrate is discussed. The electrical properties of graphene channel can be significantly degraded by defects and chemical residues between graphene and substrate. To minimize electrical degradation, a method of physically suspending graphene from the substrate has been considered while maintaining its structural integrity. To address this problem, we employed a sandwich method to fabricate a suspended GFET, realizing 76% device fabrication yield that is higher than those realized by the other methods. Furthermore, the degradation of electrical properties due to external factors decreased. As our method has a mechanically stable structure, it can be imposed to make electrical devices with various two–dimensional (2D) materials. Our method can also be applied to the engineering of future devices in various applications because a large amount of electrically clean samples can be manufactured at once.
Shin, Hyunsuk,Oh, Sewon,Arora, Rajeev,Kim, Daeil AGRICULTURAL INSTITUTE OF CANADA 2016 Canadian journal of plant science Vol.96 No.4
<P>Our previous study revealed that proline (Pro) accumulated in peach trees when cold-acclimated shoots were exposed to higher temperatures. In this study, we determined whether such Pro accumulation is indeed a high temperature-stress response or metabolic preparation for growth resumption. Two studies were conducted to address this question using 'Daewol' peach trees. In study 1 (February), Pro content of eco-dormant shoots increased when cold-acclimated plants were exposed to two heat treatments (HTs) but remained unchanged during the intervening cold treatment (CT). Concurrently, ornithine-delta-aminotransferase (OAT) and Delta(1)-pyrroline-5-carboxylate reductase (P5CR) genes were up-and down-regulated after two HTs and the CT, respectively. Study 2, conducted with growing trees (May), showed that Pro did not change and expression of P5CR and OAT was down-regulated when trees were subjected to either HT or CT; HT and CT used here constituted 'stress' treatments as revealed by the decline in chlorophyll fluorescence. Taken together, these results suggest that Pro accumulation (study 1) may be associated with the preparation for growth resumption and not 'stress'. Furthermore, results from parallel gene expression studies suggest that the ornithine, rather than glutamate, pathway may be the primary Pro biosynthesis route both during growth resumption and high temperature stress in 'Daewol' peach.</P>
Physiological Study of Freezing Tolerance in Temperature Fruit Trees
Hyunsuk Shin 한국원예학회 2021 한국원예학회 학술발표요지 Vol.2021 No.10
Freeze is one of the important abiotic stresses and it has induced economic losses in temperate fruit crops. For several decades, many studies have reported mechanisms of freezing tolerance (FT). Particularly, in the process of cold acclimation (CA), noticeable changes including dehydration, perturbation of membranes, increase of cryoprotective proteins, accumulation of osmolytes (soluble sugars, proline, polyamines, etc), and enhancement of antioxidant activity have been observed. These changes are controlled mainly by the results of genetic adjustments from the signal perception and transduction, transcriptional regulatory network, to downstream stress-responsive gene expression (ABA-dependent or ABA-independent). More recently, due to abnormal weather caused by global warming, flowering of temperature fruit trees has been gradually accelerated and spring frost damage has consistently increased with cold snap after premature deacclimation (DA). For that reason, many researchers have turned their attention to DA study and have focused on physiological, biochemical, and molecular mechanisms of DA. Strategies allowing plants to survive freezing temperatures have been divided into two categories (Levitt, 1980): 1) FT and 2) freezing avoidance. Ideally, to reduce the risk of frost injury, temperate fruit trees should be deacclimated as slowly or as late as possible during periods of unseasonable warmth in early spring (Rowland et al., 2005). Thus, recent required genotypes or strategies should be not only very hardy to extremely low temperatures, but also adaptable to unexpected changes of temperature or capable of avoiding erratic temperature patterns through deeper and longer dormancy. The presenter has recently performed two different experiments in regard to these two categories and will describe the two experiments with a brief history of FT studies in physiological aspects.
Induced freezing tolerance and free amino acids perturbation of spinach by exogenous proline
Shin, Hyunsuk,Oh, Sewon,Kim, Daeil,Hong, Jeum Kyu,Yun, Jae Gil,Lee, Sang Woo,Son, Ki-Ho The Korean Society of Plant Biotechnology 2018 식물생명공학회지 Vol.45 No.4
The objective of this study was to investigate whether exogenous proline (Pro) could confer freezing tolerance of spinach and determine fluctuations of free amino acids in spinach leaf tissues under freeze-induced stress. Treatment with Pro (10 mM) resulted in more accumulation of Pro (~2.6-fold) in Pro-treated spinaches compared to untreated ones. These Pro-pretreated spinaches were more freezing-tolerant, showing more turgid leaves and petioles compared to untreated controls. However, when spinaches pre-treated with or without Pro were subjected to freezing, there was no significant difference in overall amino acid contents, emphasizing the role of Pro as an osmoprotectant. Freezing stress prompted intensification of total amino acid contents irrespective of pretreatment with Pro. Asp, Glu, Ala, and Val were the most abundant free amino acids due to increased protein degradation and nitrogen mobilization for plant survival under freezing stress. Arg, a precursor for the synthesis of polyamines in plants, was profoundly enhanced under freezing stress. This implies that Arg plays an important role in modulating freezing tolerance. Gly, Leu, and Ile were maintained at relatively low levels in all treatments. However, Ser, Tyr, and Lys as primary constituents of dehydrins were accumulated under freezing stress, suggesting that they might play a role in increasing cryoprotective activity under freezing stress.