Numerical study of turbulent flow in eccentric annular pipe

An eccentric annular duct is a prototype element in many applications, for example in close-packed tubular heat exchangers and coolant channels of nuclear reactors. From a fundamental viewpoint, turbulent flow in eccentric annular ducts is an ideal model for investigating inhomogeneous turbulence. It is also a convenient model to study the laminar and turbulent interface and may serve as a test case for turbulence modelling of flows with partly turbulent regimes. Based on the approach of direct numerical simulation, numerical investigations of turbulent flow in eccentric annular pipes are carried out in this thesis. We first investigated the case of fully turbulent flow. A detailed statistical analysis of turbulent flow and heat transfer was performed. Simulation results, such as friction factors, mean velocity profiles and the secondary-motion pattern, are in overall qualitative and quantitative agreement with the existing experimental data. The components of the Reynolds stress tensor, temperature-velocity correlations and some others were obtained for the first time for such kind of a flow. The study of the partly turbulent flow case was then carried out. Three approaches for detecting interfaces between laminar and turbulent regimes in partly turbulent flow in rotating eccentric pipes were compared and discussed. Positions of laminar-turbulent and turbulent-laminar interfaces obtained from profiles of perturbation enstrophy are the same as those obtained from production terms of enstrophy. Using patterns of streaks defined by wall shear stresses to determine the locations of interfaces showed similar results. The growth rate of a small disturbance in partly turbulent flow case was also analyzed. Small perturbations were introduced into the initial flow field in two different ways. Both cases show that the global growth rate of the small disturbance normalized by the global viscous time scale is constant. This constant value is in a good agreement with that obtained in channel flows and tube flows. A new approach was proposed to distinguish the interface between laminar and turbulent flow by introducing the global and local disturbance growth rate

Thermal oscillations in rat kidneys: an infrared imaging study

A high-resolution infrared (IR) camera was used to assess rhythmicity in localized renal blood flow, including the extent of regions containing nephrons with spontaneous oscillations in their individual blood flow. The IR imaging was able to follow changes in rat renal perfusion during baseline conditions, during occlusion of the main renal artery and during the administration of either saline or papaverine. Concurrent recordings were made of tubular pressure in superficial nephrons. Spontaneous vascular oscillations centred around 0.02–0.05 Hz and approximately 0.01 Hz could be detected reproducibly by IR imaging. Their spectral characteristics and their response to papaverine were in line with tubular pressure measurements. The intensity of and synchrony between thermal signals from different local areas of the kidney may allow, after surgical exposure, non-invasive imaging of functional clusters involved in renal cortical blood flow. Through visualization of the spatial extent of thermal oscillations, IR imaging holds promise in assessing kidney autoregulatory mechanisms

Thermal Model Approach to the YASA Machine for In-Wheel Traction Applications

The axial-flux permanent magnet (AFPM) machines with yokeless and segmented armature (YASA) topology are suitable for in-wheel traction systems due to the high power density and efficiency. To guarantee the reliable operation of the YASA machines, an accurate thermal analysis should be undertaken in detail during the electrical machine design phase. The technical contribution of this paper is to establish a detailed thermal analysis model of the YASA machine by the lumped parameter thermal network (LPTN) method. Compared with the computational fluid dynamics (CFD) method and the finite element (FE) method, the LPTN method can obtain an accurate temperature distribution with low time consumption. Firstly, the LPTN model of each component of the YASA machine is constructed with technical details. Secondly, the losses of the YASA machine are obtained by the electromagnetic FE analysis. Then, the temperature distribution of the machine can be calculated by the LPTN model and loss information. Finally, a prototype of the YASA machine is manufactured and its temperature distribution under different operating conditions is tested by TT-K-30 thermocouple temperature sensors. The experimental data matches the LPTN results well

An improved Kriging surrogate model method with high robustness for electrical machine optimization

This article presents a highly robust optimization method for electrical machines, taking the uncertain tolerances of machine manufacturing into account. Different from the traditional multi-objective optimization methods based on Kriging surrogate model, two genetic algorithm (GA) models with disparate sampling principles are used here to release heavy computational burden and to improve prediction accuracy. One is adding the final optimization result of GA as the samples into the initial surrogate model, while the other one is adding the samples from the optimization process for the initial surrogate model. A 12-slot 14-pole interior permanent magnet synchronous machine (IPMSM) is used for the case study, and two GA models are compared. Furthermore, the proposed robust optimization method is compared with a deterministic optimization method to demonstrate its superiority, and its effectiveness is verified by prototype tests.</p

Characters of homogentisate oxygenase gene mutation and high clonality of the natural pigment-producing Vibrio cholerae strains

<p>Abstract</p> <p>Background</p> <p>Some microorganisms can produce pigments such as melanin, which has been associated with virulence in the host and with a survival advantage in the environment. In <it>Vibrio cholerae</it>, studies have shown that pigment-producing mutants are more virulent than the parental strain in terms of increased UV resistance, production of major virulence factors, and colonization. To date, almost all of the pigmented <it>V. cholerae </it>strains investigated have been induced by chemicals, culture stress, or transposon mutagenesis. However, during our cholera surveillance, some nontoxigenic serogroup O139 strains and one toxigenic O1 strain, which can produce pigment steadily under the commonly used experimental growth conditions, were obtained in different years and from different areas. The genes VC1344 to VC1347, which correspond to the El Tor strain N16961 genome and which comprise an operon in the tyrosine catabolic pathway, have been confirmed to be associated with a pigmented phenotype. In the present study, we investigated the mechanism of pigment production in these strains.</p> <p>Results</p> <p>Sequencing of the VC1344, VC1345, VC1346, and VC1347 genes in these pigmented strains suggested that a deletion mutation in the homogentisate oxygenase gene (VC1345) may be associated with the pigmented phenotype, and gene complementation confirmed the role of this gene in pigment production. An identical 15-bp deletion was found in the VC1345 gene of all six O139 pigment-producing strains examined, and a 10-bp deletion was found in the VC1345 gene of the O1 strain. Strict sequence conservation in the VC1344 gene but higher variance in the other three genes of this operon were observed, indicating the different stress response functions of these genes in environmental adaption and selection. On the basis of pulsed-field gel electrophoresis typing, the pigment-producing O139 strains showed high clonality, even though they were isolated in different years and from different regions. Additionally all these O139 strains belong to the rb4 ribotype, which contains the O139 strains isolated from diarrheal patients, although these strains are cholera toxin negative.</p> <p>Conclusion</p> <p>Dysfunction of homogentisate oxygenase (VC1345) causes homogentisate accumulation and pigment formation in naturally pigmented strains of <it>V. cholerae</it>. The high clonality of these strains may correlate to an environmental survival advantage in the <it>V. cholerae </it>community due to their pigment production, and may imply a potential protective function of melanin in environmental survival of such strains.</p

Turbulent flow and heat transfer in eccentric annulus

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Predicting protective gene biomarker of acute coronary syndrome by the circRNA-associated competitive endogenous RNA regulatory network

Background: The mortality and disability rates of acute coronary syndrome (ACS) are quite high. Circular RNA (circRNA) is a competitive endogenous RNA (ceRNA) that plays an important role in the pathophysiology of ACS. Our goal is to screen circRNA-associated ceRNA networks for biomarker genes that are conducive to the diagnosis or exclusion of ACS, and better understand the pathology of the disease through the analysis of immune cells. Materials and methods: RNA expression profiles for circRNAs (GSE197137), miRNAs (GSE31568), and mRNAs (GSE95368) were obtained from the GEO database, and differentially expressed RNAs (DEcircRNAs, DEmiRNAs, and DEmRNAs) were identified. The circRNA-miRNA and miRNA-mRNA regulatory links were retrieved from the CircInteractome database and TargetScan databases, respectively. As a final step, a regulatory network has been designed for ceRNA. On the basis of the ceRNA network, hub mRNAs were verified by quantitative RT-PCR. Hub genes were validated using a third independent mRNA database GSE60993, and ROC curves were used to evaluate their diagnostic values. The correlation between hub genes and immune cells associated with ACS was then analyzed using single sample gene set enrichment analysis (ssGSEA). Results: A total of 17 DEcircRNAs, 229 DEmiRNAs, and 27 DEmRNAs were found, as well as 52 circRNA-miRNA pairings and 10 miRNA-mRNA pairings predicted. The ceRNA regulatory network (circRNA-miRNA-mRNA) was constructed, which included 2 circRNA (hsa_circ_0082319 and hsa_circ_0005654), 4 miRNA (hsa-miR-583, hsa-miR-661, hsa-miR-671-5p, hsa-miR-578), and 5 mRNA (XPNPEP1, UCHL1, DBNL, GPC6, and RAD51). The qRT-PCR analysis result showed that the XPNPEP1, UCHL1, GPC6 and RAD51 genes had a significantly decreased expression in ACS patients. Based on ROC curve analysis, we found that XPNPEP1 has important significance in preventing ACS occurrence and excluding ACS diagnosis. ACS immune infiltration analysis revealed significant correlations between the other 3 hub genes (UCHL1, GPC6, RAD51) and the immune cells (Eosinophils, T folliculars, Type 2 T helper cells, and Imumature dendritic cells). Conclusion: Our study constructed a circRNA-related ceRNA network in ACS. The XPNPEP1 gene could be a protective gene biomarker for ACS. The UCHL1, GPC6 and RAD51 genes were significantly correlated with immune cells in ACS

A novel anti-virulence gene revealed by proteomic analysis in Shigella flexneri 2a

<p>Abstract</p> <p>Background</p> <p><it>Shigella flexneri </it>is a gram-negative, facultative pathogen that causes the majority of communicable bacterial dysenteries in developing countries. The virulence factors of <it>S. flexneri </it>have been shown to be produced at 37 degrees C but not at 30 degrees C. To discover potential, novel virulence-related proteins of <it>S. flexneri</it>, we performed differential in-gel electrophoresis (DIGE) analysis to measure changes in the expression profile that are induced by a temperature increase.</p> <p>Results</p> <p>The ArgT protein was dramatically down-regulated at 37 degrees C. In contrast, the ArgT from the non-pathogenic <it>E. coli </it>did not show this differential expression as in <it>S. flexneri</it>, which suggested that <it>argT </it>might be a potential anti-virulence gene. Competitive invasion assays in HeLa cells and in BALB/c mice with <it>argT </it>mutants were performed, and the results indicated that the over-expression of ArgT_Y225Dwould attenuate the virulence of <it>S. flexneri</it>. A comparative proteomic analysis was subsequently performed to investigate the effects of ArgT in <it>S. flexneri </it>at the molecular level. We show that HtrA is differentially expressed among different derivative strains.</p> <p>Conclusion</p> <p>Gene <it>argT </it>is a novel anti-virulence gene that may interfere with the virulence of <it>S. flexneri </it>via the transport of specific amino acids or by affecting the expression of the virulence factor, HtrA.</p