Publications by authors named "Kyungsik Choi"

This article presents a fully integrated CMOS ferrofluidic platform featuring on-chip three-electrode electrochemical cells, temperature regulators, and magnetic sensors. The proposed platform consists of 25 ferrofluidic pixels and 2 magnetic sensors. Each ferrofluidic pixel comprises a spiral inductor, a three-electrode electrochemical cell, a temperature sensor, and a localized Joule heater.

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The spatio-temporal development of a meandering river is controlled by its channel morphodynamics. In regions of rapid channel evolution, understanding the driving factors of meander migration is crucial in forecasting the rate and extent of morphological change. Sediment supply and fluvial discharge are the primary influences on migration rate, however climate oscillations are also integral in indirectly regulating migration rate through their control of regional precipitation, as well as the monsoon season of sub-tropical Asia.

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This article presents a fully-integrated dielectrophoresis (DEP)-assisted multi-functional CMOS biosensor array chip with 4096 working electrodes (WEs), 12288 photodiodes (PDs), reference electrodes (REs), and counter electrodes (CEs), while each WE and photodiode can be reconfigured to support on-chip DEP actuation, electrochemical potentiostat, optical shadow imaging, and complex impedance sensing. The proposed CMOS biosensor is an example of an actuation-assisted label-free biosensor for the rapid sensing of low-concentration analytes. The DEP actuator of the proposed CMOS biosensor does not require any external electrode.

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Historical trends of polycyclic aromatic hydrocarbons (PAHs) contamination were reconstructed from eleven sediment cores located in intertidal zones of the Yellow and Bohai seas for a period encompassing the last 80 years. The analysis encompassed 15 traditional PAHs (t-PAHs), 9 emerging PAHs (e-PAHs), and 30 halogenated PAHs (Hl-PAHs), including 10 chlorinated PAHs (Cl-PAHs) and 20 brominated PAHs (Br-PAHs). Concentrations of target PAHs were highest in industrial and municipal areas situated along the coast of the Bohai Sea, including Huludao, Yingkou, Tianjin, and Dandong, constituting a substantial mass inventory.

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The regulating ecosystem services, such as water purification, that tidal flats provide by nitrogen (N) burial are being increasingly recognized; yet, quantitative estimates remain limited. Here, we first present nationwide evaluation of total N stocks and burial rates in the Korean tidal flats, based on a 3 year long monitoring assessment combined with remote sensing approach. A total of 20 intertidal flats representing 7 provinces of South Korea were extensively surveyed in 2018-20.

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The morphodynamics of tidal flats responds mainly to the nonlinear interaction between tides and seasonal wave activity. Man-made activities such as reclamation further complicate the morphodynamics by disturbing physical processes acting on the tidal flats. Decoupling the anthropogenic influence from the natural forcing on the tidal-flat morphodynamics is crucial in assessing the adverse effects of man-made activities.

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Blue carbon science requires the estimates of organic carbon stock and sequestration rate; however, holistic data analysis remains limited in South Korea. The present study reports current organic carbon stocks and sequestration rates in the coastal areas of West Sea, South Sea, and East Sea of South Korea, encompassing entire intertidal areas using long-term field survey combined with remote sensing technology. Twenty-one intertidal flats were targeted across seven provinces (Gyeonggi, Chungnam, Jeonbuk, Jeonnam, Gyeongnam, Gyeongbuk, Gangwon).

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Article Synopsis
  • The Yellow and Bohai seas face contamination from persistent toxic substances (PTSs) due to various human activities, and a study evaluated sediment toxicity using Vibrio fischeri bioassay across 125 surface sediment samples.
  • The findings revealed that while most sites were non-toxic, organic extracts showed higher toxicity than aqueous samples, indicating organic pollutants pose a significant risk.
  • Key toxic contributors included polycyclic aromatic hydrocarbons (PAHs), styrene oligomers, and alkylphenols, with salinity playing an important role in determining toxicity levels linked to pollution sources.
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Background: Metabolic disease due to increased fat mass is observed in amputees (APTs), thereby restricting their activity. Systemic health management with periodic body composition (BC) testing is essential for healthy living. Bioelectrical impedance analysis (BIA) is a non-invasive and low-cost method to test BC; however, the APTs are classified as being exempted in the BIA.

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Derelict fishing gear (DFG) is increasingly common in the Korean tidal flats due to intensive fishing activity and the lack of monitoring system to remove the DFG from the tidal flats. Despite the widespread occurrence of DFG in the tidal flats, little is known about DFG in terms of quantity, types, distribution, and the impact on the benthic ecosystem. Unmanned aviation vehicle (UAV)-assisted photogrammetry and high-precision leveling were conducted to characterize DFG in the macrotidal flat, south of Gangwha Island, west coast of Korea.

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Article Synopsis
  • The environmental quality of estuarine and coastal areas in western Korea has worsened due to industrialization and urbanization over the decades.
  • A study conducted between 2010 and 2018 indicated that while the concentrations of some persistent toxic substances (like PAHs and nonylphenols) in sediments have decreased, some metals (like cadmium, chromium, and mercury) have increased.
  • The research revealed that while the toxicity from certain substances has declined, the inhibition of bioluminescent bacteria has risen, highlighting the need for better chemical regulation.
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Soils in coastal areas of the land-sea interface are vulnerable to heavy metal (HM) accumulation and subsequently to human health risk. However, few studies have investigated the HM pollution and risk in soils along the coastal areas of the Yellow Sea Large Marine Ecosystem (YSLME), in an international perspective. This study is the first comprehensive work in the YSLME encompassing 122 coastal locations along the Bohai Sea (BS), Yellow Sea of China (YSC), and Yellow Sea of South Korea (YSK).

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The Yellow Sea Large Marine Ecosystem (YSLME) is an important socioeconomic zone in Asia, but has been deteriorated by various environmental pollutants over the last half century. However, comprehensive coastal pollution assessments, particularly for heavy metals (HMs), have been limited from an international perspective. Here, we first evaluate coastal HM pollution in sediment and water from 119 riverine, estuarine, and marine locations along the BS and Yellow Sea to perform a comparative assessment between the two countries of China and South Korea.

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The effects of dike construction on the geomorphology and sedimentary processes of tidal flats were investigated using high-precision topographic profiling, short cores, and unmanned aviation vehicle (UAV)-assisted photogrammetry to understand their adverse consequences on the benthic ecosystem. Tidal flats at the south of Shinsi Island near one of the two sluice gates of the Saemangeum dike, display prominent morphologic features known as shelly sand ridges or cheniers (sensu Otvos, 2000) that have migrated landward about 5 m in a year. The tidal flats were dominated by erosion from winter to spring and by deposition during the remainder of the year except for the periods of heavy precipitation when tidal drainage channels became larger and deeper by headward erosion.

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A long-term study on a benthic community was conducted in two different localities, one in semi-enclosed bay of Jinhae (n = 10, south coast) and the other in open sea area of Samcheok (n = 10, east coast), Korea, respectively. We aimed to identify the spatiotemporal patterns of macrozoobenthos and the environmental variables influencing such patterns in the two contrasting habitats. The macrozoobenthos assemblages on the soft bottom of the subtidal zone were analyzed over the 3 years, encompassing 12 consecutive seasons, in 2013-2016.

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The drastic land cover change and its impacts in the Yellow Sea have long been significant issues in terms of coastal vulnerabilities, but holistic data analysis is limited. The present study first reports 40 years long geographical changes of the Yellow Sea coasts including all three neighboring countries of China, North Korea, and South Korea. We delineated tidal flats by analysis of Landsat series satellite imageries (662 scenes) between 1981 and 2016.

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In this study, spatiotemporal dynamics of macrofaunal assemblages and their associations with environmental conditions were examined in Jinhae Bay (10 sites), where the obvious sources of pollution including industries, oyster farms (hanging cultures), and municipal discharges has surrounded. The survey had performed over five consecutive seasons in 2013-2014. Target sedimentary variables included grain size, organic content, C/N ratio, carbon and nitrogen stable isotope ratios, and some heavy metals.

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Objective: Facial nerve palsy is a common complication of treatment for vestibular schwannoma (VS), so preserving facial nerve function is important. The preoperative visualization of the course of facial nerve in relation to VS could help prevent injury to the nerve during the surgery. In this study, we evaluate the accuracy of diffusion tensor tractography (DTT) for preoperative identification of facial nerve.

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Recently, the increasing rates of facial nerve preservation after vestibular schwannoma (VS) surgery have been achieved. However, the management of a partially or completely damaged facial nerve remains an important issue. The authors report a patient who was had a good recovery after a facial nerve reconstruction using fibrin glue-coated collagen fleece for a totally transected facial nerve during VS surgery.

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Background: Autism spectrum disorder (ASD) is a neurobiological disorder characterized by distinctive impairments in cognitive function, language, and behavior. Linkage and population studies suggest a genetic association between solute carrier family 6 member 4 (SLC6A4) variants and ASD.

Method: Logistic regression was used to identify associations between single-nucleotide polymorphisms (SNPs) and ASD with 3 alternative models (additive, dominant, and recessive).

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Autism spectrum disorder (ASD) is a neurodevelopmental syndrome associated with impairments of reciprocal communication and cognitive function. Associations between single-nucleotide polymorphisms (SNPs) and ASD were analysed by logistic regression. Polymorphisms in fibronectin type III domain-containing 3A (FNDC3A) exhibited significant associations in genotype and diplotype analyses.

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Objectives: The object of this study was to determine the relationship between body mass index (BMI) and early menarche in adolescent girls in Seoul.

Methods: A retrospective study was conducted with 144 middle school students in Seoul who provided informed consent. We measured their body composition, and used the questionnaire survey method for data collection from November to December 2008.

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Autism spectrum disorder is a neurodevelopmental disorder characterized by deficits in social communication, impaired reciprocal social interaction, and repetitive patterns of behaviors or interests. Although the cause of autism spectrum disorder remains elusive, the present study identified peroxisomal biogenesis factor 7 (PEX7) as a gene associated with autism spectrum disorder, and this association was examined in a Korean population. PEX7 encodes a cytosolic receptor for peroxisome targeting signal 2 of peroxisomal matrix enzymes that are targeted to and translocated into the peroxisome.

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The aim of this study was to represent the trend of early menarche and to assess the association of age at menarche with anthropometric profiles of Korean children and adolescents. A cross sectional survey was conducted with 13,371 girls aged 10 to 18 yr, recruited nationwide from April, 2005 to March, 2006. Height, weight and waist circumference of the subjects were measured; and the subjects self-reported their ages at menarche.

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