Spacer grid effects on the heat transfer enhancement during a reflood

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.An experimental study using 6x6 and 2x2 square lattice rod bundles has been performed to investigate the effects of spacer grids on the heat transfer enhancement during a bottom-reflood phase. The spacer grids improve a turbulent mixing of flow and induces breakup of large droplets into smaller ones. These result in the heat transfer enhancement between the fuel rods and the surrounding fluid. Since the geometry of the spacer grid affects the turbulent mixing and droplet breakup behaviors, three types of spacer grids with different geometry were tested in the present study. In order to investigate the heat transfer enhancement by spacer grids, single-phase steam cooling and droplet breakup by spacer grid were separately investigated. For the convective heat transfer enhancement in singlephase steam flow, the heater rod surface temperatures were measured in the vicinity of the space grid. In single-phase steam cooling experiment, the heat transfer was enhanced at upstream and downstream of spacer grids. Downstream of the spacer, the heat transfer enhancement decays with the distance from the top end of the spacer grid exponentially. The heat transfer enhancement depends on the Reynolds number as well as the flow blockage ratio. A new empirical correlation was developed in order to account for the effect of the Reynolds number. For the droplet breakup experiment, the sizes and velocities of droplets were measured across the spacer grid. The droplet breakup ratio decreases with increasing the Weber number of the droplet impacting on the spacer grid. The droplet breakup ratio by spacer grids was relatively higher than conventional correlations.dc201

Attitude Control Strategy for HAUSAT-2 with Pitch Bias Momentum System

The HAUSAT-2 is a 25kg class micro/nanosatellite which is being developed by graduate students at the Space System Research Laboratory(SSRL). This paper addresses a newly proposed strategy for detumbling the HAUSAT-2 and starting up a momentum wheel, and also studies performance validation and application ranges of such method through simulation. B-dot logic is generally used for controlling the initial tip-off rate. However, it has the disadvantage of taking a relatively long time to control the initial tip-off rate. To solve this problem, this paper suggests a new detumbling control method to be able to adapt to micro/nanosatellite with the pitch bias momentum system, and has shown simulation results. Proposed detumbling method was able to control the angular rate within 20 minutes which is a significant reduction compared to conventional methods. In addition, the momentum wheel initial start-up must be done under stable conditions, and conventional pitch spin-stabilized initial wheel start-up method is commonly used. The performance of the method is compared and verified through simulation. The overall result shows much faster control time compared to the conventional methods, and achievement of the nominal wheel speed and 3-axes stabilization while maintaining stability

Microvasculature remodeling in the mouse lower gut during inflammaging

Inflammaging is defined as low-grade, chronic, systemic inflammation in aging, in the absence of overt infection. Age-associated deterioration of gastrointestinal function could be ascribed to the inflammaging, although evidence is yet to emerge. Here we show that microvessels in aging mouse intestine were progressively deprived of supportive structures, microvessel-associated pericytes and adherens junction protein vascular endothelial (VE)-cadherin, and became leaky. This alteration was ascribed to up-regulation of angiopoetin-2 in microvascular endothelial cells. Up-regulation of the angiopoietin-2 was by TNF-α, originated from M2-like residential CD206 + macrophages, proportion of which increases as animal ages. It was concluded that antigenic burdens encountered in intestine throughout life create the condition of chronic stage of inflammation, which accumulates M2-like macrophages expressing TNF-α. The TNF-α induces vascular leakage to facilitate recruitment of immune cells into intestine under the chronic inflammatory setting. © Author(s) 2017.1

Elucidation of Akkermansia muciniphila Probiotic Traits Driven by Mucin Depletion

Akkermansia muciniphila is widely considered a next-generation beneficial microbe. This bacterium resides in the mucus layer of its host and regulates intestinal homeostasis and intestinal barrier integrity by affecting host signaling pathways. However, it remains unknown how the expression of genes encoding extracellular proteins is regulated in response to dynamic mucosal environments. In this study, we elucidated the effect of mucin on the gene expression and probiotic traits of A. muciniphila. Transcriptome analysis showed that the genes encoding most mucin-degrading enzymes were significantly upregulated in the presence of mucin. By contrast, most genes involved in glycolysis and energy metabolic pathways were upregulated under mucin-depleted conditions. Interestingly, the absence of mucin resulted in the upregulation of 79 genes encoding secreted protein candidates, including Amuc-1100 as well as members of major protein secretion systems. These transcript level changes were consistent with the fact that administration of A. muciniphila grown under mucin-depleted conditions to high-fat diet-induced diabetic mice reduced obesity and improved intestinal barrier integrity more efficiently than administration of A. muciniphila grown under mucin-containing conditions. In conclusion, mucin content in the growth medium plays a critical role in the improvement by A. muciniphila of high-fat diet-induced obesity, intestinal inflammation, and compromised intestinal barrier integrity related to a decrease in goblet cell density. Our findings suggest the depletion of animal-derived mucin in growth medium as a novel principle for the development of A. muciniphila for human therapeutics

The Localizing and Lateralizing Value of Auras in Lesional Partial Epilepsy Patients

∙ The authors have no financial conflicts of interest. © Copyright: Yonsei University College of Medicine 2012 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial Licens

Primary Idiopathic Chylopericardium Associated with Cervicomediastinal Cystic Hygroma

Chylopericardium is a rare clinical entity in which chylous fluid accumulates in the pericardial cavity. We report a case of primary idiopathic chylopericardium associated with multiple, small cervicomediastinal cystic hygromas occurring in an asymptomatic 43-year-old woman with no history of trauma, thoracic surgery, malignancy, infection or tuberculosis. Echocardiography showed a large amount of pericardial effusions and pericardial fluid analysis revealed inappropriately elevated triglyceride. We did not demonstrate communication between the thoracic duct and the pericardial sac by lymphangiography and chest computed tomography. She successfully responded to 30 days of continuous pericardial drainage and 15 days of a medium-chain triglyceride diet after 30 days of total parenteral nutrition. Follow-up echocardiography 6 months after treatment commencement showed a minimal reaccumulation of pericardial fluid without symptom. We conclude that if a patient is asymptomatic and can well tolerate daily life, surgery including pericardiectomy or ligation of the thoracic duct is not necessarily required

The Utility of Multi-detector Row Spiral CT for Detection of Coronary Artery Stenoses

Contrast-enhanced multi-detector row spiral computed tomography (MDCT) was introduced as a promising noninvasive method for vascular imaging. This study examined the accuracy of this technique for detecting significant coronary artery stenoses. Both MDCT(Sensation 16, Siemens, Germany, 12 × 0.75 mm collimation and 0.42 sec rotation speed, 120 kV, 500 effective mA, and 2.7 mm/rotation table-feed) and invasive coronary angiography (CAG) were performed on 61 patients (mean age 59.2 ± 10, 44 men) who were suspected of having coronary artery disease. All patients were treated with atenolol (25 - 50 mg) prior to imaging and the heart rate was maintained below 65 beats per minutes during image acquisition. The images were reconstructed in the diastole around TI - 400 ms with a 0.5 mm increment and a 1.0 mm thickness. All coronary arteries with a diameter of 2.0 mm or more were assessed for the presence of a stenosis (> 50% luminal narrowing). Two independent radiologists who were unaware of the results of the invasive CAG evaluated the MDCT data, and the results were compared with those from the invasive CAG (interval 1- 27, mean 11 days). An evaluation of the CT coronary angiogram (CTCA) was possible in 58 of the 61 patients (95%). Image acquisition of the major coronary arteries including the left main trunk was available in 229 out of 244 arteries. Invasive CAG showed that 35 out of 58 patients had significant coronary artery stenoses by. patient analysis of those who could be evaluated showed that CT coronary angiography correctly classified 30 out of 35 patients as having at least 1 coronary stenosis (sensitivity 85.7%, specificity 91.3%, positive predictive value 93.8%, negative predictive value 80.8%). By analyzing each coronary artery, CAG found 62 stenotic coronary arteries in the 229 coronary arteries that could be evaluated. MDCT correctly detected 50 out of 62 stenotic coronary arteries and an absence of stenosis was correctly identified in 156 out of 167 normal coronary arteries (sensitivity 80.6%, specificity 93.4%, positive predictive value 81.9%, negative predictive value 92.8%). The non-invasive technique of MDCT for examining the coronary artery appears to be a useful method for detecting coronary artery stenoses with a high accuracy particularly with the proximal portion and large arteries

Clinical features and outcomes of gastric variceal bleeding: retrospective Korean multicenter data

Background/AimsWhile gastric variceal bleeding (GVB) is not as prevalent as esophageal variceal bleeding, it is reportedly more serious, with high failure rates of the initial hemostasis (>30%), and has a worse prognosis than esophageal variceal bleeding. However, there is limited information regarding hemostasis and the prognosis for GVB. The aim of this study was to determine retrospectively the clinical outcomes of GVB in a multicenter study in Korea.MethodsThe data of 1,308 episodes of GVB (males:females=1062:246, age=55.0±11.0 years, mean±SD) were collected from 24 referral hospital centers in South Korea between March 2003 and December 2008. The rates of initial hemostasis failure, rebleeding, and mortality within 5 days and 6 weeks of the index bleed were evaluated.ResultsThe initial hemostasis failed in 6.1% of the patients, and this was associated with the Child-Pugh score [odds ratio (OR)=1.619; P<0.001] and the treatment modality: endoscopic variceal ligation, endoscopic variceal obturation, and balloon-occluded retrograde transvenous obliteration vs. endoscopic sclerotherapy, transjugular intrahepatic portosystemic shunt, and balloon tamponade (OR=0.221, P<0.001). Rebleeding developed in 11.5% of the patients, and was significantly associated with Child-Pugh score (OR=1.159, P<0.001) and treatment modality (OR=0.619, P=0.026). The GVB-associated mortality was 10.3%; mortality in these cases was associated with Child-Pugh score (OR=1.795, P<0.001) and the treatment modality for the initial hemostasis (OR=0.467, P=0.001).ConclusionsThe clinical outcome for GVB was better for the present cohort than in previous reports. Initial hemostasis failure, rebleeding, and mortality due to GVB were universally associated with the severity of liver cirrhosis