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42 result(s) for "Oh, Minkyu"
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Reaction–diffusion equation-based topology optimization code for electromagnetic wave problems using FreeFEM
In this paper, we present a structural topology optimization code for two-dimensional electromagnetic wave problems in the context of polarized electric field driven by the wave equation in the frequency domain for microwave range. The optimization process follows a phase field design approach, which is based on the reaction–diffusion equation combined with the double well potentials. In addition, a modified adaptive gradient algorithm is introduced for better performance and faster convergence rate. The salient features of the code are elaborated for the educational purpose; especially focused on the derivation of weak form in the finite element analysis for physical behavior simulation and the update of design variables. The corresponding code is written in the open-source software FreeFEM++, and it can be downloaded from the website http://ssd.yonsei.ac.kr .
Simultaneous Correlative Interferometer Technique for Direction Finding of Signal Sources
In this paper, we propose a novel simultaneous Correlative Interferometer (CI) technique that elaborately estimates the Direction of Arrival (DOA) of multiple source signals incident on an antenna array. The basic idea of the proposed technique is that the antenna-array-based receiver compares the phase of the received signal with one of the candidates at each time sample and jointly exploits these multiple time samples to estimate the DOAs of multiple signal sources. The proposed simultaneous CI-based DOA estimation technique collectively utilizes multiple time-domain samples and can be regarded as a generalized version of the conventional CI algorithm for the case of multiple time-domain samples. We first thoroughly review the conventional CI algorithm to comprehensively explain the procedure of the direction-finding algorithm that adopts the phase information of received signals. We also discuss several technical issues of conventional CI-based DOA estimation techniques that are originally proposed for the case of a single time-domain sample. Then, we propose a simultaneous CI-based DOA estimation technique with multi-sample diversity as a novel solution for the case of multiple time-domain samples. We clearly compare the proposed simultaneous CI technique with the conventional CI technique and we compare the existing Multiple Signal Classification (MUSIC)-based DOA estimation technique with the conventional CI-based technique by using the DOA spectrum as well. To the best of our knowledge, the simultaneous CI-based DOA estimation technique that effectively utilizes the characteristics of multiple signal sources over multiple time-domain samples has not been reported in the literature. Through extensive computer simulations, we show that the proposed simultaneous CI technique significantly outperforms both the conventional CI technique in terms of DOA estimation even in harsh environments and with various antenna array structures. It is worth noting that the proposed simultaneous CI technique results in much better performance than the classical MUSIC algorithm, which is one of the most representative subspace-based DOA estimation techniques.
Topological optimal design of composite magnetic actuators to improve driving force and thermal conductivity
This study aims to introduce a topology optimization approach to enhance the driving force of magnetic actuators along with minimizing operating temperatures considering the nonlinearity of composite materials. The anisotropic magnetic composite comprises two distinct materials, considering differences in magnetic saturation effect and thermal conductivity. The first component exhibits low magnetic reluctivity and high thermal conductivity, while the other component displays high reluctivity and low conductivity. The representative volume element method (RVE) and deep neural network (DNN) were employed to obtain a dataset of effective composite material properties and to generate a machine learning (ML) module for determining material properties during the optimization process. To optimize and validate both performances, a multi-objective function was formulated. Utilizing an adaptive weighting method that gradually adjusts preferences from the initial to utopia point, the design process was performed to obtain Pareto-optimal solution sets faster while ensuring their even distribution in the objective space. Numerical examples are provided aimed at validating the proposed design process. The design results when applying high and low currents were compared to investigate nonlinear effects due to the magnetic saturation effect.
Enhanced activity of meso-secondary alcohol dehydrogenase from Klebsiella species by codon optimization
Meso -secondary alcohol dehydrogenases ( meso -SADH) from Klebsiella oxytoca KCTC1686 and Klebsiella pneumoniae KCTC2242 were codon optimized and expressed in Escherichia coli W3110. The published gene data of K. pneumoniae NTUH-K2044 (NCBI accession number AP006725), K. pneumoniae 342 (NCBI accession number CP000964), and K. pneumoniae MGH 78578 (NCBI accession number CP000647), were compared with the meso -SADH sequences of each strain, respectively. Codon-optimized meso -SADH enzymes of K. oxytoca and K. pneumoniae showed approximately twofold to fivefold increased enzyme activities for acetoin reduction over native enzymes. The highest activities for each strain were obtained at 30–37 °C and pH 6–7 (yielding 203.1 U/mg of protein and 156.5 U/mg of protein, respectively). The increased enzyme activity of the codon-optimized enzymes indicated that these modified enzymes could convert acetoin into 2,3-butanediol with a high yield.
New reference genome sequences of hot pepper reveal the massive evolution of plant disease-resistance genes by retroduplication
Background Transposable elements are major evolutionary forces which can cause new genome structure and species diversification. The role of transposable elements in the expansion of nucleotide-binding and leucine-rich-repeat proteins (NLRs), the major disease-resistance gene families, has been unexplored in plants. Results We report two high-quality de novo genomes ( Capsicum baccatum and C. chinense ) and an improved reference genome ( C. annuum ) for peppers. Dynamic genome rearrangements involving translocations among chromosomes 3, 5, and 9 were detected in comparison between C. baccatum and the two other peppers. The amplification of athila LTR-retrotransposons, members of the gypsy superfamily, led to genome expansion in C. baccatum . In-depth genome-wide comparison of genes and repeats unveiled that the copy numbers of NLRs were greatly increased by LTR-retrotransposon-mediated retroduplication. Moreover, retroduplicated NLRs are abundant across the angiosperms and, in most cases, are lineage-specific. Conclusions Our study reveals that retroduplication has played key roles for the massive emergence of NLR genes including functional disease-resistance genes in pepper plants.
Cellulose Nanocrystals for Advanced Optics and Electronics: Current Status and Future Directions
Cellulose nanocrystals (CNCs) have attracted growing interest in optics and electronics, extending beyond their traditional applications. They are considered key materials due to their fast computing, sensing adhesion, and emission of circularly polarized luminescence with high dissymmetry factors. This interest arises from their unique chemical structure, which gives rise to structural color, a chiral nematic phase, and high mechanical strength. In this perspective, we first introduce the definition, sources, and fundamental properties of CNCs to explain the basis for their unique and effective use in optics and electronics. Next, we review recent research on the application of CNCs in these fields. We then analyze the current limitations that hinder further advancement. Finally, we offer our own perspective on future directions for the CNC-enabled advanced optics and electronics.
Single-cell transcriptomics reveal cellular diversity of aortic valve and the immunomodulation by PPARγ during hyperlipidemia
Valvular inflammation triggered by hyperlipidemia has been considered as an important initial process of aortic valve disease; however, cellular and molecular evidence remains unclear. Here, we assess the relationship between plasma lipids and valvular inflammation, and identify association of low-density lipoprotein with increased valvular lipid and macrophage accumulation. Single-cell RNA sequencing analysis reveals the cellular heterogeneity of leukocytes, valvular interstitial cells, and valvular endothelial cells, and their phenotypic changes during hyperlipidemia leading to recruitment of monocyte-derived MHC-II hi macrophages. Interestingly, we find activated PPARγ pathway in Cd36 + valvular endothelial cells increased in hyperlipidemic mice, and the conservation of PPARγ activation in non-calcified human aortic valves. While the PPARγ inhibition promotes inflammation, PPARγ activation using pioglitazone reduces valvular inflammation in hyperlipidemic mice. These results show that low-density lipoprotein is the main lipoprotein accumulated in the aortic valve during hyperlipidemia, leading to early-stage aortic valve disease, and PPARγ activation protects the aortic valve against inflammation. Identifying the mechanisms underlying the early inflammatory phase of aortic valve disease is crucial for disease prevention. Here the authors perform single-cell RNA sequencing to show the immunomodulatory role of PPARγ in valvular endothelial cells during hyperlipidemia.
Astrocyte-derived dominance winning reverses chronic stress-induced depressive behaviors
Individuals with low social status are at heightened risk of major depressive disorder (MDD), and MDD also influences social status. While the interrelationship between MDD and social status is well-defined, the behavioral causality between these two phenotypes remains unexplored. Here, we investigated the behavioral relationships between depressive and dominance behaviors in male mice exposed to chronic restraint stress and the role of medial prefrontal cortex (mPFC) astrocytes in these behaviors. Chronic restraint stress induced both depressive and submissive behaviors. Chemogenetic mPFC astrocyte activation significantly enhanced dominance in chronic stress-induced submissive mice by increasing the persistence of defensive behavior, although it did not affect depressive behaviors. Notably, repetitive winning experiences following mPFC astrocyte stimulation exerted anti-depressive effects in chronic restraint stress-induced depressive mice. These data indicate that mPFC astrocyte-derived winning experience renders anti-depressive effects, and may offer a new strategy for treating depression caused by low status in social hierarchies by targeting mPFC astrocytes.
Early anti-TNF/immunomodulator therapy is associated with better long-term clinical outcomes in Asian patients with Crohn’s disease with poor prognostic factors
Although early treatment of Crohn's disease (CD) patients with anti-tumor necrosis factor (TNF) agents or immunomodulators (IMs) may improve long-term outcomes, especially those with poor prognostic factors, their effectiveness in Asians remains unclear. In this study, Korean patients with CD naïve to both intestinal surgery and intestinal complications, and with at least two risk factors for progression (diagnosis at age <40 years, systemic corticosteroid treatment <3 months after diagnosis, and perianal fistula at diagnosis) were retrospectively analyzed. Patients were classified into those who started anti-TNFs, or IMs but not anti-TNFs, within 2 years of diagnosis, and those who started anti-TNFs and/or IMs later. Their probabilities of intestinal surgery and intestinal complications were compared. A total of 670 patients were enrolled, 79 in the early anti-TNF, 286 in the early IM, and 305 in the late treatment group. Kaplan-Meier analysis with the log-rank test showed that from starting anti-TNFs/IMs, times to intestinal surgery (P < 0.001), stricturing complications (P = 0.002), and penetrating complications (P < 0.001) were significantly longer in the early anti-TNF/IM groups than in the late treatment group. Multivariate Cox regression analysis showed that, from starting anti-TNFs/IMs, late anti-TNF/IM treatment was independently associated with higher risks of intestinal surgery (adjusted hazard ratio [aHR] 2.321, 95% confidence interval [CI] 1.503-3.584, P < 0.001), behavioral progression (aHR 2.001, 95% CI 1.449-2.763, P < 0.001), stricturing complications (aHR 1.736, 95% CI 1.209-2.493, P = 0.003), and penetrating complications (aHR 3.315, 95% CI 2.094-5.249, P < 0.001) than early treatment. In conclusion, treatment of Asian CD patients having poor prognostic factors with anti-TNFs/IMs within 2 years of diagnosis is associated with better clinical outcomes than later treatment.
Simulating Near-Surface Winds in Europe with the WRF Model: Assessing Parameterization Sensitivity Under Extreme Wind Conditions
Accurately simulating near-surface wind speeds is indispensable for wind energy development, particularly under extreme weather conditions. This study utilizes the Weather Research and Forecasting (WRF) model with a 6 km resolution to evaluate 80 m wind speed simulations over Europe, using the ECMWF (European Centre for Medium-Range Weather Forecasts) reanalysis version 5 (ERA5) as initial and lateral boundary conditions. Two cases were analyzed: a normal case with relatively weak winds, and an extreme case with intense cyclonic activity over 7 days, focusing on offshore wind farm regions and validated against Forschungsplattformen in Nord- und Ostsee (FINO) observational data. Sensitivity experiments were conducted by modifying key physical parameterizations associated with wind simulation to assess their impact on accuracy. Results reveal that while the model realistically captured temporal wind speed variations, errors were significantly amplified in extreme cases, with overestimation in weak wind regimes and underestimation in strong winds (approximately 1–3 m/s). The Asymmetrical Convective Model 2 (ACM2) planetary boundary layer (PBL) scheme demonstrated superior performance in extreme cases, while there were no significant differences among experiments under normal cases. These findings emphasize the critical role of physical parameterizations and the need for improved modeling approaches under extreme wind conditions. This research contributes to developing reliable wind speed simulations, supporting the operational stability of wind energy systems.