Ulsan National Institute of Science and Technology

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    23787 research outputs found

    Zwitterionic material for construction of an antifouling polyamide thin film composite membrane

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    This research has been supported by the National Research Foundation (NRF) of Korea as funded by the Ministry of Education, Science and Technology (RS-2023-00241009) and by Korea Ministry of Environment (MOE) as ???Graduate School specialized in Integrated Water Resources Management???. The authors are thankful for the support

    EUSO-SPB1 mission and science

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    The Extreme Universe Space Observatory on a Super Pressure Balloon 1 (EUSO-SPB1) was launched in 2017 April from Wanaka, New Zealand. The plan of this mission of opportunity on a NASA super pressure balloon test flight was to circle the southern hemisphere. The primary scientific goal was to make the first observations of ultra-high-energy cosmic-ray extensive air showers (EASs) by looking down on the atmosphere with an ultraviolet (UV) fluorescence telescope from suborbital altitude (33 km). After 12 days and 4 h aloft, the flight was terminated prematurely in the Pacific Ocean. Before the flight, the instrument was tested extensively in the West Desert of Utah, USA, with UV point sources and lasers. The test results indicated that the instrument had sensitivity to EASs of (sic) 3 EeV. Simulations of the telescope system, telescope on time, and realized flight trajectory predicted an observation of about 1 event assuming clear sky conditions. The effects of high clouds were estimated to reduce this value by approximately a factor of 2. A manual search and a machine-learning-based search did not find any EAS signals in these data. Here we review the EUSO-SPB1 instrument and flight and the EAS search

    Interaction mechanism between low molecular weight chitosan nanofilm and functionalized surfaces in aqueous solutions

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    Low-molecular-weight chitosan (LMW chitosan, <10 kDa) have a significant potential for biomedical applications (e.g., antimicrobial and gene/drug delivery) because of their higher water solubility at pH values ranging from 3.0 to 8.5, compared to that of the high-molecular-weight (>100 kDa) chitosan. A comprehensive understanding of the LMW interaction mechanism with specific functional groups is necessary to predict their binding efficiency to other molecules for effectively utilizing their potential within biological systems. In this study, we used a surface forces apparatus (SFA) to investigate molecular interactions between LMW chitosan and four different functionalized self-assembled monolayers (SAMs) in aqueous solutions at pH values of 3.0, 6.5, and 8.5. Chitosan exhibited the strongest interaction energy with methyl-terminated SAM (CH3-SAM), indicating the significance of hydrophobic interaction. Many chitin/chitosan fibers in nature bind polyphenols (e.g., eumelanin) to form robust composites, which can be attributed to the strong attraction between chitosan and phenyl-SAM, presumably caused by cation????? interactions. These findings demonstrate the potential of modulating the magnitude of the interaction energy by controlling the solution pH and types of targeted functional groups to realize the optimal design of chitosan-based hybrid composites with other biomolecules or synthetic materials

    A-site effects of titanate-perovskite (ATiO3)-based catalysts on dehydrogenation of N-heterocyclic molecules

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    Dehydrogenation reactions in liquid organic hydrogen carrier (LOHC) systems present significant challenges, particularly when aiming for low-temperature operations while ensuring that no hydrogen remains in the sub-strate molecules. Enhancing catalytic performance requires modifying the adsorption behavior of the reactants and products during dehydrogenation. Perovskites have emerged as promising catalyst supports because of their ability to modify the surface chemical properties by manipulating the cations present at the A-and B-sites. This study investigated the effects of A-site cations (Ca, Sr, and Ba) in titanate-type perovskite (ATiO3)-a proto-typical perovskite-on the dehydrogenation activity in LOHC systems. Remarkably, Pd/SrTiO3 exhibited outstanding performance by completely converting octahydro-N-methylindole to N-methylindole and releasing 5.76 wt% hydrogen over 8 h. Additionally, it dehydrogenated dodecahydro-N-ethylcarbazole to N-ethylcarbazole with a hydrogen release of 5.70 wt%. Furthermore, the catalyst demonstrated a stable performance after recy-cling tests for three times without degradation or loss of activity. The chemical state of the catalyst surface was characterized through X-ray photoelectron spectroscopy, H2-temperature programmed reduction, and chemi-sorption using NH3, CO2, and H2. The results revealed that the exceptional dehydrogenation activity of Pd/ SrTiO3 is due to the presence of suitable surface oxygen vacancies and abundant acid-base sites

    Human reliability evaluation method covering operator action timing for dynamic probabilistic safety assessment

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    Dynamic probabilistic safety assessment (PSA) has been introduced due to the limitations of static-based PSA such as the difficulty to analyze dynamic sequences caused by stochastic random events. While various research has been performed to achieve this integration, quantifying risk in dynamic PSA is still challenging because operator response models that can provide a branch probability according to the timing of operator action in dynamic scenarios have not yet been addressed. Existing human reliability analysis (HRA) models only consider the time given to operators for actions insofar as it can impact the failure probabilities of the human actions, despite the timing of the actions being a vital element of HRA for dynamic scenarios. This paper proposes an operator action timing-based human reliability evaluation method for dynamic PSA to evaluate the distribution of operator action timing. The method covers operator action timings with a model that convolutes two time distribution functions to provide the probability of the success or failure of an operator action. To demonstrate the practicality of the proposed method and its effectiveness, a case study and uncertainty analysis for a small break loss of coolant accident with two operator tasks were conducted

    Stability of Hill's spherical vortex

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    We study stability of a spherical vortex introduced by M. Hill in 1894, which is an explicit solution of the three-dimensional incompressible Euler equations. The flow is axi-symmetric with no swirl, the vortex core is simply a ball sliding on the axis of symmetry with a constant speed, and the vorticity in the core is proportional to the distance from the symmetry axis. We use the variational setting introduced by A. Friedman and B. Turkington (Trans. Amer. Math. Soc., 1981), which produced a maximizer of the kinetic energy under constraints on vortex strength, impulse, and circulation. We match the set of maximizers with the Hill's vortex via the uniqueness result of C. Amick and L. Fraenkel (Arch. Rational Mech. Anal., 1986). The matching process is done by an approximation near exceptional points (so-called metrical boundary points) of the vortex core. As a consequence, the stability up to a translation is obtained by using a concentrated compactness method

    Multi-objective robust parameter optimization using the extended and weighted k-means (EWK-means) clustering in laser powder bed fusion (LPBF)

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    Metal additive manufacturing (AM) technology, especially laser powder bed fusion (LPBF), has received abundant interest from industries and the research community. Process optimization methods have thus multiplied to improve the overall quality of the final parts. However, little attention has been given to the quality repeatability issue. This paper proposes a novel multi-objective robust parameter optimization framework to explore optimal process parameters with respect to relative density and dimensional accuracy of LPBF-fabricated parts. Specifically, a modified k-means clustering, named the Extended and Weighted K-means (EWK-means), was constructed to simultaneously optimize the mean and the variance of the multiple responses. Experiments were conducted to verify the effectiveness of the proposed optimization framework. In addition, the effects of the process parameters, environment-related parameters, and physical properties on the hardness of the parts were analyzed using several machine learning models. The results showed that the proposed method achieved a set of optimal process parameters with better quality and satisfactory variability in the printed parts compared with other robust parameter optimization methods

    Enhancing catalytic performance and hot electron generation through engineering metal-oxide and oxide-oxide interfaces

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    Interfaces are of utmost importance in catalytic reactions, influencing reaction kinetics and electron transfer processes. However, investigations in combined interfaces of metal-oxide and oxide-oxide at heterogeneous catalysts still have challenges due to their complex structure. Herein, we synthesized well-defined Co3O4 and CeO2 cubes with distinct facets and investigated their catalytic performance when deposited on a Pt-thin film, focusing on the influence of metal-oxide and oxide-oxide interfaces. Catalytic measurements demonstrated that the CeO2/Pt interface significantly enhanced turnover frequency (TOF) and selectivity for partial methanol oxidation compared to Co3O4/Pt and bare Pt. Notably, the CeO2/Co3O4/Pt nanodevice exhibited improved partial oxidation selectivity, highlighting the role of the CeO2/Co3O4 interface in methyl formate production. Chemicurrent measurements demonstrate enhanced hot electron generation due to increased overall TOF and partial oxidation production. We also conducted near ambient pressure X-ray photoelectron spectroscopy (NAPXPS) analysis, revealing a higher concentration of Ce3+ ions and increased oxygen vacancies in the CeO2/Co3O4/ Pt catalyst, suggesting oxygen migration from CeO2 to Co3O4, leading to methoxy species stabilization and promoting methyl formate formation

    A Mobile 3D-CNN Processor with Hierarchical Sparsity-Aware Computation and Temporal Redundancy-aware Network

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    Magnetic nanoparticles for ferroptosis cancer therapy with diagnostic imaging

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    Ferroptosis offers a novel method for overcoming therapeutic resistance of cancers to conventional cancer treatment regimens. Its effective use as a cancer therapy requires a precisely targeted approach, which can be facilitated by using nanoparticles and nanomedicine, and their use to enhance ferroptosis is indeed a growing area of research. While a few review papers have been published on iron-dependent mechanism and inducers of ferroptosis cancer therapy that partly covers ferroptosis nanoparticles, there is a need for a comprehensive review focusing on the design of magnetic nanoparticles that can typically supply iron ions to promote ferroptosis and simultaneously enable targeted ferroptosis cancer nanomedicine. Furthermore, magnetic nanoparticles can locally induce ferroptosis and combinational ferroptosis with diagnostic magnetic resonance imaging (MRI). The use of remotely controllable magnetic nanocarriers can offer highly effective localized image-guided ferroptosis cancer nanomedicine. Here, recent developments in magnetically manipulable nanocarriers for ferroptosis cancer nanomedicine with medical imaging are summarized. This review also highlights the advantages of current state-of-the-art image-guided ferroptosis cancer nanomedicine. Finally, image guided combinational ferroptosis cancer therapy with conventional apoptosis-based therapy that enables synergistic tumor therapy is discussed for clinical translations


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