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Creators/Authors contains: "Kim, Ki-Joong"

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  1. Abstract Objective

    Temporal coordination between oscillations enables intercortical communication and is implicated in cognition. Focal epileptic activity can affect distributed neural networks and interfere with these interactions. Refractory pediatric epilepsies are often accompanied by substantial cognitive comorbidity, but mechanisms and predictors remain mostly unknown. Here, we investigate oscillatory coupling across large‐scale networks in the developing brain.

    Methods

    We analyzed large‐scale intracranial electroencephalographic recordings in children with medically refractory epilepsy undergoing presurgical workup (n = 25, aged 3–21 years). Interictal epileptiform discharges (IEDs), pathologic high‐frequency oscillations (HFOs), and sleep spindles were detected. Spatiotemporal metrics of oscillatory coupling were determined and correlated with age, cognitive function, and postsurgical outcome.

    Results

    Children with epilepsy demonstrated significant temporal coupling of both IEDs and HFOs to sleep spindles in discrete brain regions. HFOs were associated with stronger coupling patterns than IEDs. These interactions involved tissue beyond the clinically identified epileptogenic zone and were ubiquitous across cortical regions. Increased spatial extent of coupling was most prominent in older children. Poor neurocognitive function was significantly correlated with high IED–spindle coupling strength and spatial extent; children with strong pathologic interactions additionally had decreased likelihood of postoperative seizure freedom.

    Significance

    Our findings identify pathologic large‐scale oscillatory coupling patterns in the immature brain. These results suggest that such intercortical interactions could predict risk for adverse neurocognitive and surgical outcomes, with the potential to serve as novel therapeutic targets to restore physiologic development.

     
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  2. The infrared (IR) gas sensing technique is excellent for CO 2 gas detection systems that require high accuracy and safety standard; however, there is a significant barrier to its application due to its high cost and difficulty in miniaturization. CO 2 sensors that are functional within near- or short-wavelength IR have the potential to reduce this barrier. In this work, a highly sensitive plasmonic material based on nanostructured covellite copper sulfide (CuS), which exhibits desired localized surface plasmon resonance for surface-enhanced IR absorption (SEIRA) throughout near- and mid-IR ranges, was investigated. We prepared CuS thin films facilely in an additive manner based on a spatial successive ionic layer adsorption and reaction process at room temperature. The resulting CuS thin film possesses a structure consisting of hexagonal nanoflakes, and demonstrates significant SEIRA for 100 ppm CO 2 with an enhancement factor of 10 4 . 
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  3. Low-cost materials, scalable manufacturing, and high power conversion efficiency are critical enablers for large-scale applications of photovoltaic (PV) cells. Cu 2 ZnSn(S,Se) 4 (CZTSSe) has emerged as a promising PV material due to its low-cost earth-abundant nature and the low toxicity of its constituents. We present a compact and environmentally friendly route for preparing metal sulfide (metals are Cu, Zn, and Sn) nanoparticles (NPs) and optimize their annealing conditions to obtain uniform carbon-free CZTSSe thin films with large grain sizes. Further, the solution-stable binary NP inks synthesized in an aqueous solution with additives are shown to inhibit the formation of secondary phases during annealing. A laboratory-scale PV cell with a Al/AZO/ZnO/CdS/CZTSSe/Mo-glass structure is fabricated without anti-reflective coatings, and a 9.08% efficiency under AM1.5G illumination is demonstrated for the first time. The developed scalable, energy-efficient, and environmentally sustainable NP synthesis approach can enable integration of NP synthesis with emerging large-area deposition and annealing methods for scalable fabrication of CZTSSe PV cells. 
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