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In a severe accident of light water reactor (LWR), molten core material (corium) can be released into the wet cavity, and a fuel-coolant interaction (FCI) can occur. The molten jet with high speed is broken and fragmented into small debris, which may cause a steam explosion or a molten core concrete interaction (MCCI). Since the premixing stage where the jet breakup occurs has a large impact on the severe accident progression, the understanding and evaluation of the jet breakup phenomenon are highly important. Therefore, in this study, the jet breakup simulations were performed using the Smoothed Particle Hydrodynamics (SPH) method which is a particle-based Lagrangian numerical method. For the multi-fluid system, the normalized density approach and improved surface tension model (CSF) were applied to the in-house SPH code (single GPU-based SOPHIA code) to improve the calculation accuracy at the interface of fluids. The jet breakup simulations were conducted in two cases: (1) jet breakup without structures, and (2) jet breakup with structures (control rod guide tubes). The penetration depth of the jet and jet breakup length were compared with those of the reference experiments, and these SPH simulation results are qualitatively and quantitatively consistent with the experiments.

Lagrangian-based meshless CFD methods have recently been developed and are being gradually applied to various research areas. In nuclear engineering, the meshless methods are gaining attention in modeling natural disasters and severe accident phenomena, such as tsunami, molten corium behaviors, etc., because of its flexible computational domain and effective treatment of non-linear deformations. This paper introduces recent progress and on-going activities in Lagrangian-based CFD code development at Seoul National University (SNU). The code, named SOPHIA, is based on the smoothed particle hydrodynamics (SPH) method, one of the best-known meshless numerical methods, based on a Lagrangian framework that can easily handle various types of physics because of its simplicity in expressing and solving mathematical equations. The SOPHIA code currently incorporates basic conservation equations and various physical models, including fluid flow, heat transfer, turbulence, multi-phase, phase change, elastic solid, diffusion and so on. To handle multi-phase, multi-component, and multi-resolution flows simultaneously, the SOPHIA code formulates density and continuity equations based on the normalized-density form, which has been recently developed and is proposed in the current study. The SOPHIA code also adapts CUDA GPU architectures for parallelization and performance improvement. Based on the benchmark calculations, the parallelized GPU code shows much higher computational speed by two orders of magnitude compared to the single CPU code for 1.0 million particles. This paper summarizes the overall features of the SOPHIA code, including governing equations, algorithms, and parallelization methods, along with some benchmark simulations.

The Divergence-Free SPH (DFSPH) method is a recently proposed novel incompressible Smoothed Particle Hydrodynamics (SPH) method. The DFSPH method enforces incompressibility via two iterative solvers: the Divergence-Free (DF) solver and the Constant-Density (CD) solver. In this study, the DFSPH algorithm is implemented into the SOPHIA Plus framework to simulate a set of wave propagation under the same geometry and conditions of a laboratory-scale experiment. The experiments are conducted for wave propagation and interaction with a structure of scaled-down undersea topography near the Kori nuclear power plant in South Korea. This study compares the free surface propagation and the wave height with the experimental measurements for three test cases: low/medium/high frequency waves. Overall, the simulation shows good agreement with the experiment both qualitatively and quantitatively. However, according to the sensitivity study, more realistic water splashing behaviors are captured as the particle size is reduced. The predicted wave heights at three different locations are also in fairly good agreement with the experimental measurement. Slight differences are observed after the wave collides with the structure because of the low energy dissipation in the simulation. However, the differences are not significant.

Background Growing evidence suggests that non-alcoholic fatty liver disease (NAFLD) is associated with cardiovascular disease as well as metabolic syndrome. FDG-PET is a novel imaging technique that detects vascular inflammation, which may reflect rupture-prone vulnerable atherosclerotic plaques. Methods Vascular inflammation was measured as the maximum target-to-background ratio (maxTBR), along with various cardiometabolic risk factors in 51 subjects with NAFLD, and compared with 100 age- and gender-matched subjects without NAFLD. The liver attenuation index (LAI), which was measured using computed tomography, was used as a parameter for the diagnosis of NAFLD. Results After adjusting for age and sex, both maxTBR and LAI values were associated with several cardiometabolic risk parameters. Furthermore, there was a significant inter-relationship between LAI and maxTBR values ( r = − 0.227, P = 0.005). Individuals with NAFLD had higher maxTBR values than those without NAFLD ( P = 0.026), although their carotid intima–media thickness (CIMT) values did not differ. The proportion of subjects with NAFLD showed a step-wise increment following the tertiles of maxTBR values ( P for trend = 0.015). In multiple logistic regression analysis, maxTBR tertiles were independently associated with NAFLD after adjusting for age, gender, systolic blood pressure, triglycerides, HDL-cholesterol, glucose, BUN, creatinine and homeostasis model assessment of insulin resistance (HOMA-IR) ( P = 0.030). However, their relationship was attenuated after further adjustment for waist circumference or high sensitive C-reactive protein. Conclusion Patients with NAFLD have an increased risk for vascular inflammation as measured via FDG-PET/CT even without difference in CIMT. (Clinical trials No. NCT01958411 , http://www.clinicaltrials.gov /)

Matching-index-of-refraction (MIR) has been used for obtaining high-quality flow visualization data for the fundamental nuclear thermal-hydraulic researches. By this method, distortions of the optical measurements such as PIV and LDV have been successfully minimized using various combinations of the model materials and the working fluids. This study investigated a novel 3D printing technology for manufacturing models and an oil-based working fluid for matching the refractive indices. Transparent test samples were fabricated by various rapid prototyping methods including selective layer sintering (SLS), stereolithography (SLA), and vacuum casting. As a result, the SLA direct 3D printing was evaluated to be the most suitable for flow visualization considering manufacturability, transparency, and refractive index. In order to match the refractive indices of the 3D printing models, a working fluid was developed based on the mixture of herb essential oils, which exhibit high refractive index, high transparency, high density, low viscosity, low toxicity, and low price. The refractive index and viscosity of the working fluid range 1.453–1.555 and 2.37–6.94 cP, respectively. In order to validate the MIR method, a simple test using a twisted prism made by the SLA technique and the oil mixture (anise and light mineral oil) was conducted. The experimental results show that the MIR can be successfully achieved at the refractive index of 1.51, and the proposed MIR method is expected to be widely used for flow visualization studies and CFD validation for the nuclear thermal-hydraulic researches.

Objective Recent studies reported the presence of unique subsets of body size phenotypes that are more susceptible or more resistant to the development of obesity-associated metabolic disorders, although the underlying mechanism is not yet fully elucidated. We investigated the association between body size phenotypes and sleep duration after adjusting potential confounding factors. Materials and methods We analyzed data from the Korean National Health and Nutrition Examination Survey V (KNHANES V), a nation-wide, population-based health survey including 9077 Korean adults. The average amount of sleep per night was categorized as: ≤ 6, 7, 8, and ≥ 9 h. Body size phenotypes were classified based on body mass index (BMI) and presence of metabolic syndrome; metabolically healthy and normal weight (MHNW), metabolically abnormal but normal weight (MANW), metabolically healthy but obese (MHO), and metabolically abnormal obese (MAO). Results According to sleep duration, there were significant differences in age, gender, BMI, waist circumference, and blood pressure (all P

Recent studies have suggested that body size phenotype may contribute to atherosclerosis and cardiovascular disease. 18 F-fluorodeoxyglucose (FDG) positron emission tomography is a useful imaging technique for detecting vascular inflammation that may reflect plaque vulnerability. Therefore, we analyzed which body size phenotypes cause the increased vascular inflammation using FDG positron emission tomography. We compared 18 F-FDG uptake, measured using the blood-normalized standardized uptake value, known as the target-to-background ratio (TBR), along with various cardiometabolic risk parameters in 250 participants without a history of cardiovascular disease. Body size phenotypes were classified according to body mass index and the presence/absence of metabolic syndrome. Cardiometabolic risk factors were significantly different among the body size phenotype groups. In particular, the maximum TBR (maxTBR) values in the metabolically abnormal but normal-weight, metabolically healthy obese (MHO), and metabolically abnormal obese groups were significantly greater than those of the metabolically healthy normal-weight (MHNW) group. Components of metabolic syndrome, insulin resistance, high-sensitivity C-reactive protein, and Framingham Risk Score were associated with maxTBR value. Interestingly, although the Framingham Risk Score of the MHO group was almost similar to that of the MHNW group, maxTBR value of MHO subjects was significantly higher than that of MHNW subjects (1.38 [1.20, 1.50] vs 1.22 [1.12, 1.37], p = 0.006). In conclusion, the present study suggests that unique subsets of body size phenotype, such as MHO or metabolically abnormal but normal weight, may have distinct effects on vascular inflammation.

The direct effects of dipeptidyl peptidase-IV (DPP-IV) inhibitors on endoplasmic reticulum (ER) stress-induced apoptosis and inflammation in cardiomyocytes have not been elucidated. H9c2 cell viability, which was reduced by tunicamycin, was increased after DPP-IV inhibitor gemigliptin treatment. Gemigliptin significantly decreased the tunicamycin-mediated increase in glucose regulated protein 78 (GRP78) expression and ER stress-mediated signaling molecules such as protein kinase RNA-like endoplasmic reticulum kinase (PERK)/C-EBP homologous protein (CHOP) and inositol-requiring enzyme 1α (IRE1α)/c-Jun N-terminal kinase (JNK)-p38. Furthermore, gemigliptin effectively induced Akt phosphorylation in a dose-dependent manner. Using flow cytometry and Hoechst staining, we showed that treatment with Akt inhibitor significantly blocked the anti-apoptotic effects mediated by gemigliptin. The reduction in tunicamycin-induced GRP78 level and PERK/CHOP pathway activity by gemigliptin was reversed after treatment with Akt inhibitor. In conclusion, gemigliptin effectively inhibited ER stress-induced apoptosis and inflammation in cardiomyocytes via Akt/PERK/CHOP and IRE1α/JNK-p38 pathways, suggesting its direct protective role in cardiovascular diseases.

Carrageenan (CGN) has been shown to cause inflammation through toll-like receptor 4, which may play an important role in insulin resistance and type 2 diabetes mellitus. Selenoprotein P (SeP) has recently been identified as a novel hepatokine that causes insulin resistance. Here, we report that treatment of HepG2 cells with CGN increased both CCAAT enhancer binding protein homologous protein (CHOP) and SeP expression. Pretreatment with 4-phenylbutyrate (4-PBA), an endoplasmic reticulum stress inhibitor, and PD98059, a c-Jun N-terminal kinase (JNK) inhibitor, reversed CGN-induced SeP expression. Moreover, both 4-PBA and knock-down of SeP improved CGN-induced insulin resistance. In addition, we found that adenosine monophosphate-activated protein kinase (AMPK) activators ameliorated CGN-induced insulin resistance in addition to suppressing CHOP and SeP expression. In conclusion, CGN-induced ER stress increased the expression of SeP through the JNK pathway, while AMPK activators ameliorated CGN-induced insulin resistance via SeP inhibition through the AMPK-mediated alleviation of ER stress in hepatocytes.

To evaluate vascular inflammation according to high-sensitivity C-reactive protein (hsCRP) levels in the low- (10%) and intermediate- (10%-20%) Framingham risk score (FRS) groups using (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT, which reflects vascular inflammation and vulnerable atherosclerotic plaque.We measured hsCRP levels and traditional cardiovascular risk factors in 142 non-diabetic subjects without history of cardiovascular disease. To assess the vascular influence of hsCRP on each FRS category, we compared carotid intima-media thickness (CIMT), brachial-ankle pulse wave velocity (baPWV), and vascular inflammation, which was represented as the target-to-background ratio (TBR) measured using FDG-PET/CT.In both low- and intermediate-FRS categories, mean TBR values in subjects with higher hsCRP levels (≥2mg/L) were significantly increased compared to those with lower hsCRP levels (2mg/L) (P=0.001, P0.001, respectively). However, baPWV and CIMT values did not significantly differ according to hsCRP levels in the same FRS categories. Mean TBR levels positively correlated with FRS, body mass index (BMI), whereas negatively correlated with HDL-cholesterol. Multiple stepwise regression analyses showed that hsCRP, LDL-cholesterol, BMI, and insulin resistance were independently associated with mean TBR values (R(2)=0.414).In both intermediate and low FRS risk groups, vascular inflammation measured using FDG-PET/CT was increased in individuals with higher hsCRP levels compared to those with lower hsCRP.

Background The receptor for advanced glycation end-products (RAGE) and its diverse ligands play a pivotal role in the development of cardiovascular disease. Soluble forms of RAGE (sRAGE), including the splice variant endogenous secretory RAGE (esRAGE), may neutralize AGE-RAGE mediated vascular damage by acting as a decoy. 18 F-fluorodeoxyglucose positron emission tomography (FDG-PET) is a novel imaging technique for detecting vascular inflammation. Methods We examined vascular inflammation measured using FDG-PET in 41 type 2 diabetes patients and 41 healthy control subjects in the right carotid artery. Vascular 18 F-FDG uptake was measured as the blood-normalized standardized uptake value (SUV), known as the target-to-background ratio (TBR). In addition, their relationship with carotid intima-media thickness (CIMT), estimated GFR (eGFR), and other cardiovascular risk factors was evaluated. Results Both mean and maximum TBR values were significantly higher in patients with type 2 diabetes compared to healthy subjects. After adjusting for age and gender, sRAGE levels were significantly correlated with both mean and maximum TBR values, but not with CIMT values. Multiple linear regression analysis showed that maximum TBR values were independently associated with sRAGE levels in addition to HbA1c and eGFR. Conclusions Circulating sRAGE showed significant association with TBR values measured using FDG-PET, which reflect vascular inflammation.