| 1. |
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| 2. |
- Klionsky, Daniel J., et al.
(författare)
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Guidelines for the use and interpretation of assays for monitoring autophagy
- 2012
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Ingår i: Autophagy. - : Informa UK Limited. - 1554-8635 .- 1554-8627. ; 8:4, s. 445-544
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Forskningsöversikt (refereegranskat)abstract
- In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
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| 3. |
- Kanoni, Stavroula, et al.
(författare)
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Implicating genes, pleiotropy, and sexual dimorphism at blood lipid loci through multi-ancestry meta-analysis.
- 2022
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Ingår i: Genome biology. - : Springer Science and Business Media LLC. - 1474-760X .- 1465-6906 .- 1474-7596. ; 23:1
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Tidskriftsartikel (refereegranskat)abstract
- Genetic variants within nearly 1000 loci are known to contribute to modulation of blood lipid levels. However, the biological pathways underlying these associations are frequently unknown, limiting understanding of these findings and hindering downstream translational efforts such as drug target discovery.To expand our understanding of the underlying biological pathways and mechanisms controlling blood lipid levels, we leverage a large multi-ancestry meta-analysis (N=1,654,960) of blood lipids to prioritize putative causal genes for 2286 lipid associations using six gene prediction approaches. Using phenome-wide association (PheWAS) scans, we identify relationships of genetically predicted lipid levels to other diseases and conditions. We confirm known pleiotropic associations with cardiovascular phenotypes and determine novel associations, notably with cholelithiasis risk. We perform sex-stratified GWAS meta-analysis of lipid levels and show that 3-5% of autosomal lipid-associated loci demonstrate sex-biased effects. Finally, we report 21 novel lipid loci identified on the X chromosome. Many of the sex-biased autosomal and X chromosome lipid loci show pleiotropic associations with sex hormones, emphasizing the role of hormone regulation in lipid metabolism.Taken together, our findings provide insights into the biological mechanisms through which associated variants lead to altered lipid levels and potentially cardiovascular disease risk.
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| 4. |
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| 5. |
- Mishra, A, et al.
(författare)
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Diminishing benefits of urban living for children and adolescents' growth and development
- 2023
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 615:7954, s. 874-883
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Tidskriftsartikel (refereegranskat)abstract
- Optimal growth and development in childhood and adolescence is crucial for lifelong health and well-being1–6. Here we used data from 2,325 population-based studies, with measurements of height and weight from 71 million participants, to report the height and body-mass index (BMI) of children and adolescents aged 5–19 years on the basis of rural and urban place of residence in 200 countries and territories from 1990 to 2020. In 1990, children and adolescents residing in cities were taller than their rural counterparts in all but a few high-income countries. By 2020, the urban height advantage became smaller in most countries, and in many high-income western countries it reversed into a small urban-based disadvantage. The exception was for boys in most countries in sub-Saharan Africa and in some countries in Oceania, south Asia and the region of central Asia, Middle East and north Africa. In these countries, successive cohorts of boys from rural places either did not gain height or possibly became shorter, and hence fell further behind their urban peers. The difference between the age-standardized mean BMI of children in urban and rural areas was <1.1 kg m–2 in the vast majority of countries. Within this small range, BMI increased slightly more in cities than in rural areas, except in south Asia, sub-Saharan Africa and some countries in central and eastern Europe. Our results show that in much of the world, the growth and developmental advantages of living in cities have diminished in the twenty-first century, whereas in much of sub-Saharan Africa they have amplified.
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| 6. |
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| 7. |
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| 8. |
- Cao, Lei, et al.
(författare)
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The effects of MEK1/2 inhibition on cigarette smoke exposure-induced ET receptor upregulation in rat cerebral arteries
- 2016
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Ingår i: Toxicology and Applied Pharmacology. - : Elsevier BV. - 0041-008X. ; 304, s. 70-78
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Tidskriftsartikel (refereegranskat)abstract
- Cigarette smoking, a major stroke risk factor, upregulates endothelin receptors in cerebral arteries. The present study examined the effects of MEK1/2 pathway inhibition on cigarette smoke exposure-induced ET receptor upregulation. Rats were exposed to the secondhand smoke (SHS) for 8 weeks followed by intraperitoneal injection of MEK1/2 inhibitor, U0126 for another 4 weeks. The urine cotinine levels were assessed with high-performance liquid chromatography. Contractile responses of isolated cerebral arteries were recorded by a sensitive wire myograph. The mRNA and protein expression levels of receptor and MEK/ERK1/2 pathway molecules were examined by real-time PCR and Western blotting, respectively. Cerebral artery receptor localization was determined with immunohistochemistry. The results showed the urine cotinine levels from SHS exposure group were significantly higher than those from the fresh group. In addition, the MEK1/2 inhibitor, U0126 significantly reduced SHS exposure-increased ETA receptor mRNA and protein levels as well as contractile responses mediated by ETA receptors. The immunoreactivity of increased ETA receptor expression was primarily cytoplasmic in smooth muscle cells. In contrast, ETB receptor was noted in endothelial cells. However, the SHS-induced decrease in endothelium-dependent relaxation was unchanged after U0126 treatment. Furthermore, SHS increased the phosphorylation of MEK1/2 and ERK1/2 protein in cerebral arteries. By using U0126 could inhibit the phosphorylated ERK1/2 protein but not MEK1/2. Taken together, our data show that treatment with MEK1/2 pathway inhibitor offsets SHS exposure-induced ETA receptor upregulation in rat cerebral arteries.
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| 9. |
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| 10. |
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| 11. |
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| 12. |
- Taddei, C, et al.
(författare)
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Repositioning of the global epicentre of non-optimal cholesterol
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 582:7810, s. 73-
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Tidskriftsartikel (refereegranskat)abstract
- High blood cholesterol is typically considered a feature of wealthy western countries1,2. However, dietary and behavioural determinants of blood cholesterol are changing rapidly throughout the world3 and countries are using lipid-lowering medications at varying rates. These changes can have distinct effects on the levels of high-density lipoprotein (HDL) cholesterol and non-HDL cholesterol, which have different effects on human health4,5. However, the trends of HDL and non-HDL cholesterol levels over time have not been previously reported in a global analysis. Here we pooled 1,127 population-based studies that measured blood lipids in 102.6 million individuals aged 18 years and older to estimate trends from 1980 to 2018 in mean total, non-HDL and HDL cholesterol levels for 200 countries. Globally, there was little change in total or non-HDL cholesterol from 1980 to 2018. This was a net effect of increases in low- and middle-income countries, especially in east and southeast Asia, and decreases in high-income western countries, especially those in northwestern Europe, and in central and eastern Europe. As a result, countries with the highest level of non-HDL cholesterol—which is a marker of cardiovascular risk—changed from those in western Europe such as Belgium, Finland, Greenland, Iceland, Norway, Sweden, Switzerland and Malta in 1980 to those in Asia and the Pacific, such as Tokelau, Malaysia, The Philippines and Thailand. In 2017, high non-HDL cholesterol was responsible for an estimated 3.9 million (95% credible interval 3.7 million–4.2 million) worldwide deaths, half of which occurred in east, southeast and south Asia. The global repositioning of lipid-related risk, with non-optimal cholesterol shifting from a distinct feature of high-income countries in northwestern Europe, north America and Australasia to one that affects countries in east and southeast Asia and Oceania should motivate the use of population-based policies and personal interventions to improve nutrition and enhance access to treatment throughout the world.
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| 13. |
- Yuan, Jin-Na, et al.
(författare)
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Surrogate markers and predictors of endogenous insulin secretion in children and adolescents with type 1 diabetes
- 2021
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Ingår i: World Journal of Pediatrics. - : Zhejiang University Press. - 1708-8569 .- 1867-0687. ; 17:1, s. 99-105
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Tidskriftsartikel (refereegranskat)abstract
- Background No studies have examined endogenous insulin secretion in pediatric patients with type 1 diabetes in China using the gold-standard mixed-meal tolerance test. Because the latter is labor-intensive, we examined simpler surrogate markers of endogenous insulin secretion in Chinese youth, as previously reported for a European population. Methods Participants were 57 children and adolescents with type 1 diabetes aged 4.4-16.8 years (56% females). We performed 120-minute mixed-meal tolerance tests with serum C-peptide (CP) measurements every 30 minutes. Severe insulin deficiency (SID) was defined as CP peak < 0.2 nmol/L. Urine CP and creatinine levels were measured at 0 and 120 minutes. Results Twenty-five (44%) patients had SID. Fasting CP levels missed one case (96% sensitivity) with no false positives (100% specificity). While the 120-minute urine CP/creatinine had 100% sensitivity, it yielded markedly lower specificity (63%). Every 1-year increase in diabetes duration and 1-year decrease in age at diagnosis were associated with 37% (P < 0.001) and 20% (P = 0.005) reductions in serum CP area-under-the-curve, respectively. Thus, 86% of children aged < 5 years had SID compared to none among patients aged >= 11 years. Conclusions Simple fasting CP measurements could be used to detect most SID cases in Chinese youth with type 1 diabetes. Fasting CP is a far more reliable measure of endogenous insulin secretion than the more commonly used insulin dose. Therefore, it could more precisely determine insulin secretory capacity to target those who could benefit, if treatments to preserve residual insulin secretion are developed.
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| 14. |
- Zhang, Juqing, et al.
(författare)
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Super-enhancers conserved within placental mammals maintain stem cell pluripotency
- 2022
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences (PNAS). - 0027-8424 .- 1091-6490. ; 119:40
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Tidskriftsartikel (refereegranskat)abstract
- Despite pluripotent stem cells sharing key transcription factors, their maintenance involves distinct genetic inputs. Emerging evidence suggests that super-enhancers (SEs) can function as master regulatory hubs to control cell identity and pluripotency in humans and mice. However, whether pluripotency-associated SEs share an evolutionary origin in mammals remains elusive. Here, we performed comprehensive comparative epigenomic and transcription factor binding analyses among pigs, humans, and mice to identify pluripotency-associated SEs. Like typical enhancers, SEs displayed rapid evolu-tion in mammals. We showed that BRD4 is an essential and conserved activator for mammalian pluripotency-associated SEs. Comparative motif enrichment analysis revealed 30 shared transcription factor binding motifs among the three species. The majority of transcriptional factors that bind to identified motifs are known regulators associated with pluripotency. Further, we discovered three pluripotency-associated SEs (SE-SOX2, SE-PIM1, and SE-FGFR1) that displayed remarkable conservation in pla-cental mammals and were sufficient to drive reporter gene expression in a pluripotency-dependent manner. Disruption of these conserved SEs through the CRISPR-Cas9 approach severely impaired stem cell pluripotency. Our study provides insights into the understanding of conserved regulatory mechanisms underlying the maintenance of plu-ripotency as well as species-specific modulation of the pluripotency-associated regula-tory networks in mammals.
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| 15. |
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| 16. |
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Ai, Jin Wei, et al.
(författare)
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Clinical Characteristics of COVID-19 Patients With Gastrointestinal Symptoms : An Analysis of Seven Patients in China
- 2020
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Ingår i: Frontiers in Medicine. - : Frontiers Media SA. - 2296-858X. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Patients with novel coronavirus disease 2019 (COVID-19) can present with gastrointestinal symptoms as their initial symptoms or as the main manifestations during disease progression, but the clinical characteristics of these patients are still unknown. Methods: We identified COVID-19 patients who admitted to Xiangyang No. 1 People's Hospital and presented with gastrointestinal symptoms as their initial or main symptoms. Their medical records were reviewed by two independent clinical scientists. The epidemiological and clinical characteristics as well as the clinical outcomes were analyzed. Results: Among 142 confirmed COVID-19 cases, 7 (4.9%) of them presented with gastrointestinal symptoms. Three patients had gastrointestinal symptoms as the initial symptoms and chief complaints, and 4 patients as the main symptoms during disease progression. Six patients had symptoms of diarrhea (3–16 days), 7 with anorexia (7–22 days), 6 with upper abdominal discomfort (1–7 days), and 4 with nausea (1–7 days), 1 with heartburn lasting 2 days, and 2 with vomiting symptoms (1 day). The chest CT scan showed typical COVID-19 imaging features, and associated with the progression of the disease. During treatment, 2 patients died due to organ failure. Discussion: COVID-19 patients with gastrointestinal symptoms are relatively rare and might be misdiagnosed. The clinical features include watery stools, anorexia, and upper abdominal discomfort. These patients may have severe disease and be associated with a poor prognosis. The underlying mechanisms of SARS-CoV-2 related gastrointestinal symptoms need to clarify in future studies.
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| 21. |
- Algaba, Juan-Carlos, et al.
(författare)
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Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
- 2021
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 911:1
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Forskningsöversikt (refereegranskat)abstract
- In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M o˙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87's spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded.
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| 22. |
- Björner, Kajsa, et al.
(författare)
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High iNOS and IL-1β immunoreactivity are features of colitis-associated colorectal cancer tumors, but fail to predict 5-year survival
- 2023
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Ingår i: Upsala Journal of Medical Sciences. - : Upsala Medical Society. - 0300-9734 .- 2000-1967. ; 128
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Inflammatory bowel disease (IBD; mainly ulcerative colitis and Crohn's disease) is associated with the development of colorectal cancer (CRC) referred to as colitis-associated colorectal cancer (CAC). In inflammatory flares of IBD, the production of luminal nitric oxide (NO) increases due to the increased inducible nitric oxide synthase (iNOS) activity in inflamed tissue. It is believed that iNOS parallels pro-inflammatory interleukin-1β (IL-1β). How these biomarkers relate to CAC pathogenesis or survival is unknown.AIM: The primary aim of this study was to investigate iNOS and IL-1β immunoreactivity in CAC tumors in comparison with CRC and normal colonic mucosa, and the secondary aim was to determine if immunoreactivity correlates with 5-year survival of CAC.METHODS: Immunohistochemistry was performed on tissue sections as follows: CAC (n = 59); sporadic CRC (sCRC) (n = 12); colonic mucosa >2 cm outside sCRC margin (normal mucosa) (n = 22); paracancerous IBD (pIBD) (n = 12). The expression of iNOS and IL-1β was quantified separately for epithelium and stroma. Data were evaluated using the Mann-Whitney U-test and the log-rank test for 5-year Kaplan-Meier survival curves. Results were compared with online mRNA databases.RESULTS: Immunoreactivity occurred predominantly in epithelial cells and to lesser extent in stroma. Compared with normal mucosa, immunoreactivity for iNOS (P < 0.01) and IL-1β (P < 0.005) was higher in CAC epithelium. In CAC stroma, iNOS immunoreactivity was lower than normal mucosa (P < 0.001), whereas IL-1β was higher (P < 0.05). Immunoreactivity differences of iNOS or IL-1β among CAC patients failed to correlate with 5-year survival. These findings were supported by online mRNA databases.CONCLUSION: Consistent with high NO production in IBD, there is more iNOS in CAC epithelium, albeit not in stroma. This immunoreactivity difference exists for IL-1β in both epithelium and stroma. The intervention of arginine or iNOS activity for CAC chemotherapy is not straightforward.
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| 23. |
- Blikstad, Joakim, et al.
(författare)
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Fast Algorithms via Dynamic-Oracle Matroids
- 2023
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Ingår i: STOC 2023. - : Association for Computing Machinery (ACM). ; , s. 1229-1242
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Konferensbidrag (refereegranskat)abstract
- We initiate the study of matroid problems in a new oracle model called dynamic oracle. Our algorithms in this model lead to new bounds for some classic problems, and a "unified"algorithm whose performance matches previous results developed in various papers for various problems. We also show a lower bound that answers some open problems from a few decades ago. Concretely, our results are as follows. Improved algorithms for matroid union and disjoint spanning trees. We show an algorithm with Õk(n+rr) dynamic-rank-query and time complexities for the matroid union problem over k matroids, where n is the input size, r is the output size, and Õk hides poly(k, log(n)). This implies the following consequences. (i) An improvement over the Õk(nr) bound implied by [Chakrabarty-Lee-Sidford-Singla-Wong FOCS'19] for matroid union in the traditional rank-query model. (ii) An Õk(|E|+|V||V|)-time algorithm for the k-disjoint spanning tree problem. This is nearly linear for moderately dense input graphs and improves the Õk(|V||E|) bounds of Gabow-Westermann [STOC'88] and Gabow [STOC'91]. Consequently, this gives improved bounds for, e.g., Shannon Switching Game and Graph Irreducibility. Matroid intersection. We show a matroid intersection algorithm with Õ(nr) dynamic-rank-query and time complexities. This implies new bounds for some problems (e.g. maximum forest with deadlines) and bounds that match the classic ones obtained in various papers for various problems, e.g. colorful spanning tree [Gabow-Stallmann ICALP'85], graphic matroid intersection [Gabow-Xu FOCS'89], simple job scheduling matroid intersection [Xu-Gabow ISAAC'94], and Hopcroft-Karp combinatorial bipartite matching. More importantly, this is done via a "unified"algorithm in the sense that an improvement over our dynamic-rank-query algorithm would imply improved bounds for all the above problems simultaneously. Lower bounds. We show simple super-linear (ω(nlogn)) query lower bounds for matroid intersection and union problems in our dynamic-rank-oracle and the traditional independence-query models; the latter improves the previous log2(3)n-o(n) bound by Harvey [SODA'08] and answers an open problem raised by, e.g., Welsh [1976] and CLSSW [FOCS'19].
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| 24. |
- Deng, Min, et al.
(författare)
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Genome-wide association analyses in Han Chinese identify two new susceptibility loci for amyotrophic lateral sclerosis
- 2013
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Ingår i: Nature Genetics. - : Nature Publishing Group. - 1061-4036 .- 1546-1718. ; 45:6, s. 697-
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Tidskriftsartikel (refereegranskat)abstract
- To identify susceptibility genes for amyotrophic lateral sclerosis (ALS), we conducted a genome-wide association study (GWAS) in 506 individuals with sporadic ALS and 1,859 controls of Han Chinese ancestry. Ninety top SNPs suggested by the current GWAS and 6 SNPs identified by previous GWAS were analyzed in an independent cohort of 706 individuals with ALS and 1,777 controls of Han Chinese ancestry. We discovered two new susceptibility loci for ALS at 1q32 (CAMK1G, rs6703183, P-combined = 2.92 x 10(-8), odds ratio (OR) = 1.31) and 22p11 (CABIN1 and SUSD2, rs8141797, P-combined = 2.35 x 10(-9), OR = 1.52). These two loci explain 12.48% of the overall variance in disease risk in the Han Chinese population. We found no association evidence for the previously reported loci in the Han Chinese population, suggesting genetic heterogeneity of disease susceptibility for ALS between ancestry groups. Our study identifies two new susceptibility loci and suggests new pathogenic mechanisms of ALS.
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| 25. |
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| 26. |
- Fu, Jiapeng, et al.
(författare)
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Identification of the running status of membrane walls in an opposed fired model boiler under varying heating loads
- 2020
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Ingår i: Applied Thermal Engineering. - : Elsevier. - 1359-4311 .- 1873-5606. ; 173, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- To understand the running status of membrane walls in an opposite firing boiler, a scale-down model furnace was established, and the temperature, heat flux, strain and stress distributions are investigated under four heating loads. Results show that the average membrane wall temperature and heat flux present a continuous increase from 42 oC and 16 W/m2 to 96 oC and 50 W/m2, respectively, with the heating load increase from 25% to full load. The average strain and stress also rise from 88.7 µm and 0.094 MPa to 152.5 µm and 0.148 MPa when the heating load increases from 25% to 50%, but then they keep stable when further increasing the heating load. General distribution patterns of each tested parameter are found relatively similar under varying heating loads. High strain and stress distributions are always detected at the middle left zone of side walls and the middle of the rear wall, where wall temperatures are measured high. External fixed constraints and high-temperature thermal strain is found jointly affecting the strain and stress distribution of the membrane wall. A simplified mechanism of how the strain and stress on boiler membrane walls evolve is proposed after comprehensive discussion of the measurement results.
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| 27. |
- Ge, R, et al.
(författare)
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Normative Modeling of Brain Morphometry Across the Lifespan Using CentileBrain: Algorithm Benchmarking and Model Optimization
- 2023
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Ingår i: bioRxiv : the preprint server for biology. - : Cold Spring Harbor Laboratory.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Background: Normative modeling is a statistical approach to quantify the degree to which a particular individual-level measure deviates from the pattern observed in a normative reference population. When applied to human brain morphometric measures it has the potential to inform about the significance of normative deviations for health and disease. Normative models can be implemented using a variety of algorithms that have not been systematically appraised. Methods: To address this gap, eight algorithms were compared in terms of performance and computational efficiency using brain regional morphometric data from 37,407 healthy individuals (53% female; aged 3-90 years) collated from 87 international MRI datasets. Performance was assessed with the mean absolute error (MAE) and computational efficiency was inferred from central processing unit (CPU) time. The algorithms evaluated were Ordinary Least Squares Regression (OLSR), Bayesian Linear Regression (BLR), Generalized Additive Models for Location, Scale, and Shape (GAMLSS), Parametric Lambda, Mu, Sigma (LMS), Gaussian Process Regression (GPR), Warped Bayesian Linear Regression (WBLG), Hierarchical Bayesian Regression (HBR), and Multivariable Fractional Polynomial Regression (MFPR). Model optimization involved testing nine covariate combinations pertaining to acquisition features, parcellation software versions, and global neuroimaging measures (i.e., total intracranial volume, mean cortical thickness, and mean cortical surface area). Findings: Statistical comparisons across models at PFDR<0.05 indicated that the MFPR-derived sex- and region-specific models with nonlinear polynomials for age and linear effects of global measures had superior predictive accuracy; the range of the MAE of the models of regional subcortical volumes was 70-520 mm3 and the corresponding ranges for regional cortical thickness and regional cortical surface area were 0.09-0.26 mm and 24-560 mm2, respectively. The MFPR-derived models were also computationally more efficient with a CPU time below one second compared to a range of 2 seconds to 60 minutes for the other algorithms. The performance of all sex- and region-specific MFPR models plateaued at sample sizes exceeding 3,000 and showed comparable MAEs across distinct 10-year age-bins covering the human lifespan. Interpretation: These results provide an empirically benchmarked framework for normative modeling of brain morphometry that is useful for interpreting prior literature and supporting future study designs. The model and tools described here are freely available through CentileBrain (https://centilebrain.org/), a user-friendly web platform.
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| 28. |
- Hong, Junmei, et al.
(författare)
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Focusing on RISC assembly in mammalian cells.
- 2008
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Ingår i: Biochem Biophys Res Commun. - : Elsevier BV. - 1090-2104 .- 0006-291X. ; 368:3, s. 703-8
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- RISC (RNA-induced silencing complex) is a central protein complex in RNAi, into which a siRNA strand is assembled to become effective in gene silencing. By using an in vitro RNAi reaction based on Drosophila embryo extract, an asymmetric model was recently proposed for RISC assembly of siRNA strands, suggesting that the strand that is more loosely paired at its 5' end is selectively assembled into RISC and results in target gene silencing. However, in the present study, we were unable to establish such a correlation in cell-based RNAi assays, as well as in large-scale RNAi data analyses. This suggests that the thermodynamic stability of siRNA is not a major determinant of gene silencing in mammalian cells. Further studies on fork siRNAs showed that mismatch at the 5' end of the siRNA sense strand decreased RISC assembly of the antisense strand, but surprisingly did not increase RISC assembly of the sense strand. More interestingly, measurements of melting temperature showed that the terminal stability of fork siRNAs correlated with the positions of the mismatches, but not gene silencing efficacy. In summary, our data demonstrate that there is no definite correlation between siRNA stability and gene silencing in mammalian cells, which suggests that instead of thermodynamic stability, other features of the siRNA duplex contribute to RISC assembly in RNAi.
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| 29. |
- Hung, Rayjean J., et al.
(författare)
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Lung Cancer Risk in Never-Smokers of European Descent is Associated With Genetic Variation in the 5(p)15.33 TERT-CLPTM1Ll Region
- 2019
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Ingår i: Journal of Thoracic Oncology. - : ELSEVIER SCIENCE INC. - 1556-0864 .- 1556-1380. ; 14:8, s. 1360-1369
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Inherited susceptibility to lung cancer risk in never-smokers is poorly understood. The major reason for this gap in knowledge is that this disease is relatively uncommon (except in Asians), making it difficult to assemble an adequate study sample. In this study we conducted a genome-wide association study on the largest, to date, set of European-descent never-smokers with lung cancer. Methods: We conducted a two-phase (discovery and replication) genome-wide association study in never-smokers of European descent. We further augmented the sample by performing a meta-analysis with never-smokers from the recent OncoArray study, which resulted in a total of 3636 cases and 6295 controls. We also compare our findings with those in smokers with lung cancer. Results: We detected three genome-wide statistically significant single nucleotide polymorphisms rs31490 (odds ratio [OR]: 0.769, 95% confidence interval [CI]: 0.722-0.820; p value 5.31 x 10(-16)), rs380286 (OR: 0.770, 95% CI: 0.723-0.820; p value 4.32 x 10(-16)), and rs4975616 OR: 0.778, 95% CI: 0.730-0.829; p value 1.04 x 10(-14)). All three mapped to Chromosome 5 CLPTM1L-TERT region, previously shown to be associated with lung cancer risk in smokers and in never-smoker Asian women, and risk of other cancers including breast, ovarian, colorectal, and prostate. Conclusions: We found that genetic susceptibility to lung cancer in never-smokers is associated to genetic variants with pan-cancer risk effects. The comparison with smokers shows that top variants previously shown to be associated with lung cancer risk only confer risk in the presence of tobacco exposure, underscoring the importance of gene-environment interactions in the etiology of this disease. (C) 2019 International Association for the Study of Lung Cancer. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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| 30. |
- Jin, Ying-Hui, et al.
(författare)
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Chemoprophylaxis, diagnosis, treatments, and discharge management of COVID-19 : An evidence-based clinical practice guideline (updated version)
- 2020
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Ingår i: Military Medical Research. - : Springer Science and Business Media LLC. - 2054-9369. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of a rapidly spreading illness, coronavirus disease 2019 (COVID-19), affecting more than seventeen million people around the world. Diagnosis and treatment guidelines for clinicians caring for patients are needed. In the early stage, we have issued "A rapid advice guideline for the diagnosis and treatment of 2019 novel coronavirus (2019-nCoV) infected pneumonia (standard version)"; now there are many direct evidences emerged and may change some of previous recommendations and it is ripe for develop an evidence-based guideline. We formed a working group of clinical experts and methodologists. The steering group members proposed 29 questions that are relevant to the management of COVID-19 covering the following areas: chemoprophylaxis, diagnosis, treatments, and discharge management. We searched the literature for direct evidence on the management of COVID-19, and assessed its certainty generated recommendations using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach. Recommendations were either strong or weak, or in the form of ungraded consensus-based statement. Finally, we issued 34 statements. Among them, 6 were strong recommendations for, 14 were weak recommendations for, 3 were weak recommendations against and 11 were ungraded consensus-based statement. They covered topics of chemoprophylaxis (including agents and Traditional Chinese Medicine (TCM) agents), diagnosis (including clinical manifestations, reverse transcription-polymerase chain reaction (RT-PCR), respiratory tract specimens, IgM and IgG antibody tests, chest computed tomography, chest x-ray, and CT features of asymptomatic infections), treatments (including lopinavir-ritonavir, umifenovir, favipiravir, interferon, remdesivir, combination of antiviral drugs, hydroxychloroquine/chloroquine, interleukin-6 inhibitors, interleukin-1 inhibitors, glucocorticoid, qingfei paidu decoction, lianhua qingwen granules/capsules, convalescent plasma, lung transplantation, invasive or noninvasive ventilation, and extracorporeal membrane oxygenation (ECMO)), and discharge management (including discharge criteria and management plan in patients whose RT-PCR retesting shows SARS-CoV-2 positive after discharge). We also created two figures of these recommendations for the implementation purpose. We hope these recommendations can help support healthcare workers caring for COVID-19 patients.
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| 31. |
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| 32. |
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| 33. |
- Liu, Na, et al.
(författare)
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A support vector machine approach for AF classification from a short single-lead ECG recording
- 2018
-
Ingår i: Physiological Measurement. - : IOP PUBLISHING LTD. - 0967-3334 .- 1361-6579. ; 39:6
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Tidskriftsartikel (refereegranskat)abstract
- Objective: In this paper, a support vector machine (SVM) approach using statistical features, P wave absence, spectrum features, and length-adaptive entropy are presented to classify ECG rhythms as four types: normal rhythm, atrial fibrillation (AF), other rhythm, and too noisy to classify. Approach: The proposed algorithm consisted of three steps: (1) signal pre-processing based on the wavelet method; (2) feature extraction, the extracted features including one power feature, two spectrum features, two entropy features, 17 RR interval-related features, and 11 P wave features; and (3) classification using the SVM classifier. Main results: The algorithm was trained by 8528 single-lead ECG recordings lasting from 9 s to just over 60 s and then tested on a hidden test set consisting of 3658 recordings of similar lengths, which were all provided by the PhysioNet/Computing in Cardiology Challenge 2017. The scoring for this challenge used an F-1 measure, and the final F-1 score was defined as the average of F-1n (the F-1 score of normal rhythm), F-1a (the F-1 score of AF rhythm), and F-1o (the F-1 score of other rhythm). The results confirmed the high accuracy of our proposed method, which obtained 90.27%, 86.37%, and 75.08% for F-1n, F-1a, and F-1n and the final F-1 score of 84% on the training set. In the final test to assess the performance of all of the hidden data, the obtained F-1n, F-1a, F-1o and the average F-1 were 90.82%, 78.56%, 71.77% and 80%, respectively. Significance: The proposed algorithm targets a large number of raw, short single ECG data rather than a small number of carefully selected, often clean ECG records, which have been studied in most of the previous literature. It breaks through the limitation in applicability and provides reliable AF detection from a short single-lead ECG.
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| 34. |
- Ma, Xiang, et al.
(författare)
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Flow boiling frictional pressure drop inside micro/mini-channels : A new general model and experimental investigation
- 2024
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Ingår i: Applied Thermal Engineering. - 1359-4311. ; 247
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a novel general model for flow boiling frictional pressure drop inside micro/mini-channels was proposed based on theoretical analysis and experimental evaluation. Experiments were conducted to obtained flow boiling pressure drop of deionized water, HFE7100 and R134a in micro-channels under various experimental conditions. Then, a wide database from 33 previous literatures consists 3854 experimental data points covering 11 different working fluids, e.g., carbon dioxide, new electronic fluorinated solutions, refrigerants and deionized water, among others, and the operation conditions were as following: system temperature of −40–90 ℃, saturated pressure of 101–3970 kPa, hydraulic diameter of 0.1–2.6 mm, liquid subcooling of 5–75 K, mass flux of 50–3000 kg/(m2·s), heat flux of 0–4000 kW/m2, liquid-only Reynolds number of 40–12,000, vapor quality of 0–1, and reduced pressure of 0.0045–0.5380 in the database. Both the Reynolds numbers of vapor and liquid were calculated using the hydraulic diameter and vapor quality. The present data points were evaluated by 20 existing classical models (including the homogeneous and separated flow ones) for the flow boiling frictional pressure drop. However, the predictions of these models for the present data points had low accuracy, especially for the subcooled points at low vapor quality. Therefore, a more accurate prediction model was developed based on the present database by distinguishing the subcooled and saturated boiling. This novel prediction model can predict 75.4 % and 89.7 % of data points within ±30 % and ±50 % error bands, its mean absolute percent error (MAPE) is 19.23 %, which shows good predictive ability. Besides, the reliability of the new model was also further verified with our experimental results.
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| 35. |
- Momozawa, Y, et al.
(författare)
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IBD risk loci are enriched in multigenic regulatory modules encompassing putative causative genes
- 2018
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Ingår i: Nature communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9:1, s. 2427-
-
Tidskriftsartikel (refereegranskat)abstract
- GWAS have identified >200 risk loci for Inflammatory Bowel Disease (IBD). The majority of disease associations are known to be driven by regulatory variants. To identify the putative causative genes that are perturbed by these variants, we generate a large transcriptome data set (nine disease-relevant cell types) and identify 23,650 cis-eQTL. We show that these are determined by ∼9720 regulatory modules, of which ∼3000 operate in multiple tissues and ∼970 on multiple genes. We identify regulatory modules that drive the disease association for 63 of the 200 risk loci, and show that these are enriched in multigenic modules. Based on these analyses, we resequence 45 of the corresponding 100 candidate genes in 6600 Crohn disease (CD) cases and 5500 controls, and show with burden tests that they include likely causative genes. Our analyses indicate that ≥10-fold larger sample sizes will be required to demonstrate the causality of individual genes using this approach.
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| 36. |
- Na, Wei, PhD student, 1986-
(författare)
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A Linearized Navier-Stokes Equations Methodology for Aeroacoustic and Thermoacoustic Simulations
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aeroengine noise is one of the dominating noise sources in today’s aircraft. Reduction of the aeroengine noise is related to multiphysics phenomena, and that is subject to different mechanisms, e.g., the coupling between turbulence, flame and sound waves. Here, the noise propagating from and interacting with different components of aeroengines with different mechanisms is studied. A numerical methodology solving the linearized Navier-Stokes equations in frequency domain(LNSE) is extended and applied in different applications.In the compressor, the sound scattering at the tube row heat exchangers in the presence of cross-flow is of interest. When the flow passes through the contraction by two cylinders, there is a strong separation around the cylinder, a jet flow and shear layers are formed. At the shear layers, vorticities are generated and the energy is transferred between the acoustic mode and the vorticity mode, which may lead to the dissipation or amplification of the acoustic energy. Therefore, the numerical methodology LNSE including the energy equation is used to investigate the flow-acoustic interaction in presence of a mean cross-flow.In order to reduce the fan noise in aeroengines, acoustic liners are used as wall treatments during the sound transmitting from the duct. Thus, in the thesis, a numerical methodology named “unified LNSE approach” is proposed to simulate the acoustic properties of a hybrid liner in an efficient way without compromising the accuracy. The unified LNSE approach allows solving the Helmholtz equation in regions with plane wave propagation and simultaneously solving the LNSE in regions where the acoustic attenuation due to viscothermal losses is significant.Thermoacoustic instabilities arise when the heat release fluctuations and the acoustic perturbations are in phase. When thermoacoustic instabilities occur, it will lead to a high-level tonal noise that might result in mechanical failure of the combustor chambers. In the thesis, the numerical methodology is developed for prediction of thermoacoustic instabilities. The numerical methodology solving the Helmholtz equation in combination of the flame n - τ model with the low Mach number assumptions is implemented as well.There are direct and indirect combustion noise in a combustion chamber. The direct combustion noise is mainly caused by the unsteady heat release rate. The indirect combustion noise is due to entropy fluctuations generated in combustion chambers interacting with the accelerating mean flow. In this process, the energy is transferred from the entropy modes to acoustic modes. In this thesis, the entropy wave in a one-dimensional converging nozzle is simulated to analyze the acoustic entropy interactions.
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| 37. |
- Na, Wei, 1986, et al.
(författare)
-
A slug length calculation for a contraction with mean flow between two half cylinders
- 2022
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Ingår i: Internoise 2022 - 51st International Congress and Exposition on Noise Control Engineering. - : The Institute of Noise Control Engineering of the USA, Inc..
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Konferensbidrag (refereegranskat)abstract
- A slug length is widely used to describe additional mass inertia at low frequencies in duct acoustics. It is often used in acoustic energy analysis, e.g. as one of the inputs for semi-analytical or empirical models to obtain the acoustic reflection and transmission coefficients. However, the calculation of slug length is usually empirical and limited to certain conditions, such as simple geometric configurations, low frequencies, no mean flow, etc. In this paper, the slug length at a contraction with mean flow between two half cylinders is calculated by different methods: solving the Laplace’s equation numerically, solving the Helmholtz equation, and using the Cummings – Fant equation based on the numerical results of frequency-domain linearized Navier-Stokes equations. Both the frequency-dependance and the mean flow effect are discussed. The calculated slug length can also be used as a crucial input, for example, in the Dowling and Hughes slit model and modified Cummings slit model to predict the acoustic scattering at tube rows in the presence of a cross mean flow.
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| 38. |
- Na, Wei, 1986, et al.
(författare)
-
A unified approach coupling linearized Navier-Stokes equations and Helmholtz equations to predict sound propagation with viscothermal losses in acoustic liners
- 2023
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Ingår i: Engineering Archive.
-
Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a unified approach for coupling the classical linearized Navier-Stokes equations (LNSE), the original Helmholtz equation and a modified form of the Helmholtz equation for porous material modelling in frequency domain. This approach is termed the unified LNSE (ULNSE). It accounts for viscothermal losses of sound propagation in acoustic liners with small-scale perforation. This method also provides a possibility to switch from LNSE to the classical and modified Helmholtz equations depending on local acoustic properties. The ULNSE is validated and applied to simulation of conventional and hybrid liners in three dimensions (3D), and also compared to a semi-empirical model and experiments. The hybrid acoustic liner consists of a perforated plate, a porous foam layer, and a rectangular cavity. Unlike the hybrid liner, the porous foam is not mounted in the conventional liners. In the perforated plate where the viscothermal effect plays a role, sound waves are solved using the LNSE. The modified Helmholtz equation is formulated with a complex wavenumber to model the porous foam as an equivalent fluid model. In the liner cavity and external duct, the original Helmholtz equation is utilized. The ULNSE is cheaper than the classical LNSE since the Helmholtz equations, which consume less computational resources, are used locally where the viscothermal losses are negligible. Meanwhile, the ULNSE can maintain high numerical accuracy. The liners are analyzed in terms of critical parameters such as the porous foam material, and perforated plate thickness and porosity. The porous foam proves to be effective in sound absorption.
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| 39. |
- Na, Wei, et al.
(författare)
-
Acoustic characterization of a hybrid liner consisting of porous material by using a unified linearized navier-stokes approach
- 2016
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Ingår i: 22nd AIAA/CEAS Aeroacoustics Conference, 2016. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624103865
-
Konferensbidrag (refereegranskat)abstract
- In this paper, the acoustic properties of a hybrid liner placed at the end of an impedance tube are investigated using numerical simulations. The hybrid liner constitutes of three components, a perforated plate, a porous layer and a rectangular back cavity. The presence of the porous layer is to enhance the absorptive performance of a liner. The main objective of the paper is to verify the proposed numerical methodology - a unified linearized Navier-Stokes Equations (LNSE) approach. In the unified LNSE approach, the combination of the Helmholtz Equation, LNSE as well as the equivalent fluid model are solved in different regions of the impedance tube. To achieve this, the continuity of the coupling condition between the LNSE and the Helmholtz equation is examined. Another objective is to analyze the effectiveness of the porous material to the acoustic performance of the liner. Acoustic liner simulations with and without porous material, porous material with different flow resistivity are carried out. A good agreement is found between the numerical results and the measurements previously performed at KTH MWL.1 Compared to previous work234, several improvements have been made in the numerical methodology, such as that the energy equation has been added in order to include the damping due to viscous dissipation as well as the thermal dissipation in the vicinity of the perforated plate.
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| 40. |
- Na, Wei, PhD student, 1986-, et al.
(författare)
-
Acoustic characterization of a hybrid perforated liner by using a unified linearized Navier-Stokes equations methodology
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, a unified linearized Navier-Stokes Equations (LNSE) methodology in the frequency domain is introduced, which couples the Helmholtz equation with the LNSE. By using the unified LNSE methodology, the viscothermal losses on the sound propagation in a small-scale acoustic perforation can be taken into account. It also provides a possibility to switch the governing equations from the LNSE to the Helmholtz equation depending on the acoustic simulation requirements. As an application, the acoustic performance of a hybrid liner including a porous layer located at the end of an impedance tube is investigated numerically in three dimensions in a quiescent medium.The hybrid liner consists of three components, a perforated plate, a layer of porous metallic foam and rectangular back cavities. In the numerical simulations, the Helmholtz equation and the LNSE are solved and the equivalent fluid model is applied at different parts of the impedance tube. In the main tube, where plane wave propagates, the Helmholtz equation is solved. In the perforated plate of the hybrid liner, where the viscothermal effect plays a nonnegligible role, the LNSE are solved. In the porous metallic foam used to increase the acoustic absorption of the hybrid liner, an equivalent fluid model is applied. The equivalent fluid model is mathematically a Helmholtz equation with a complex wave-number accounting for losses. By achieving the coupling between the Helmholtz equation and the LNSE, the numerical methodology is able to mimic the acoustic properties of liners accurately and with less computational cost, therefore, the numerical methodology has prospects of being used in early-stage liner design in different industries.
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| 41. |
- Na, Wei, 1986, et al.
(författare)
-
Design and analysis of conceptual acoustic metamaterials applied to mitigating cooling fan noise for heavy-duty vehicles
- 2024
-
Ingår i: Inter Noise 2024.
-
Konferensbidrag (refereegranskat)abstract
- The noise generated from cooling fans in heavy-duty vehicles like trucks poses challenges regarding environmental pollution and overall user comfort. To solve this problem, this study develops an acoustic metamaterial (AMM) that is constructed with small Helmholtz resonators in two layers. This concept can attenuate the noise in a broad frequency range. Furthermore, the particle swarm optimization (PSO) algorithm based on artificial intelligence (AI) is used to optimize the AMM structure. The key design parameters are discussed and analyzed. The installation strategies are put forth to examine the performance of the AMM. The proposed metamaterials, combined with the installation strategies, are numerically simulated using the finite element method. The results show that the current AMM is effective in reducing both tonal and broadband noise of interest. The findings shed light on the development of acoustic metamaterials for cooling-fan noise reduction in heavy-duty vehicles.
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| 42. |
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| 43. |
- Na, Wei
(författare)
-
Frequency Domain Linearized Navier-Stokes Equations Methodology for Aero-Acoustic and Thermoacoustic Simulations
- 2015
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The first part of the thesis focuses on developing a numerical methodology to simulate the acoustic properties of a hybrid liner consisting of a perforated plate, a porous layer and a Helmholtz cavity. Liners are always a standard way to reduce noise in today’s aeroengines, e.g. the fan noise can be reduced effectively through the installation of acoustic liners as wall treatments in the ducts. In order to optimize a liner in the design phase, an accurate and efficient prediction tool is of interests. Hence, a unified Linearized Navier-Stokes equations(LNSE) approach has been implemented in the thesis, combining the LNSE in frequency domain with the fluid equivalent model. The LNSE is applied in the vicinity of the perforated plate to simulate sound propagation including viscous damping effect, and the fluid equivalent model is used to model the sound propagation in the porous material including absorption.The second part of the thesis focuses on the prediction of thermoacoustic instabilities. Thermoacoustic instabilities arise when positive coupling occurs between the flame and the acoustics in the feedback loop, i.e. the flame acts as an amplifier of the disturbances (acoustic or fluid) at a natural frequency of the combustion system. Once the thermoacoustic instabilities occur, it will lead to extremely high noise levels within a relatively narrow frequency range, resulting in a huge damage to the structure of the combustors. Hence, a solution must be found, which breaks the link between the combustion process and the structural acoustics. The numerical prediction of thermoacoustic instabilities in the thesis is performed by two different numerical methodologies. One solves the Helmholtz equation in combination of the flame n − tau model with the low Mach number assumptions, and the other solves the Linearized Navier-Stokes equations in frequency domain with mean flow. The result show that the mean flow has a significant effect on the thermoacoustic instabilities, which is non-negligible when the Mach number reaches to 0.15.
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| 44. |
- Na, Wei, 1986-, et al.
(författare)
-
Numerical prediction of acoustic response on tube rows with cross-flow using linearized Navier-Stokes equations in frequency domain
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, the aeroacoustic response at tube row heat exchangers is investigated through using the numerical methodology - linearized Navier-Stokes equation (LNSE) in frequency domain. The flow-acoustic interaction for acoustic waves incident on a tube row in cross-flow is studied. A comparison of results between simulations, a quasi-steady model and experimental data is presented. Acoustic reflection and transmission coefficients are compared for both magnitude and phase in a higher frequency range. In the current study, the analysis is based on the cold flow only, as a preparation for the future study with hot flow.
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| 45. |
- Na, Wei, PHD student, 1986-, et al.
(författare)
-
Numerical prediction of thermoacoustic instabilities in a three-dimensional combustor model
- 2019
-
Ingår i: 25th AIAA/CEAS Aeroacoustics Conference, 2019. - Reston, Virginia : American Institute of Aeronautics and Astronautics Inc, AIAA. - 9781624105883
-
Konferensbidrag (refereegranskat)abstract
- In this paper, the numerical work focus on prediction of the thermoacoustic instabilities for a three-dimensional combustor model. A numerical methodology solving the Helmholtz equation with the Flame Describing Function (FDF) in frequency domain is used. In the present numerical work, the in-house numerical code is first examined by the Ri-jke tube benchmark case with the planar flame in a variation of n and τ in one-dimensional n-τ model. Afterwards, the numerical work is extended to simulate the thermoacoustic instabilities of a three-dimensional combustor. The experimental determined FDF is applied in the simulations, which takes into account the non-linear behavior of the flame. In the paper, the eigenfrequencies of the system are presented as numerical results, which are compared with the experimental data.
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| 46. |
- Na, Wei, et al.
(författare)
-
Numerical prediction of thermoacoustic instabilities with a V-Flame
- 2016
-
Ingår i: 23rd International Congress on Sound and Vibration 2016 (ICSV 23), Athens, Greece 10-14 July 2016, Volume 1 of 6. - : International Institute of Acoustics and Vibrations. - 9781510827165
-
Konferensbidrag (refereegranskat)abstract
- In this paper, results from a numerical solver for the Helmholtz equation using the Finite Element Method (FEM) for predicting thermoacoustic instabilities are presented. The one-dimensional n-τ flame model, which is governed by an interaction index n and a time-delay τ as well as a Flame transfer function (FTF) is used for flame source term. We show results for the validation of the numerical solver for the Rijke tube benchmark case with the variation of n and τ in the one-dimensional n-τ model. Thereafter, thermoacoustic instabilities for a V-flame are predicted, for a typical configuration of a dump combustor - a tube with an area expansion. This is a more realistic test case, since a bluff-body flame holder is often used in combustors, where a V-flame will be generated and anchored to the rod. Usually, the V-flame is more susceptible to thermoacoustic instabilities. In the paper, the eigenfrequencies, as well as the acoustic pressure perturbations are presented as numerical results.
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| 47. |
- Na, Wei, PhD student, 1986-, et al.
(författare)
-
Prediction of acoustic response on tube-rows with bias-flow using linearized Navier-Stokes equations in frequency domain
- 2019
-
Ingår i: Proceedings of the International Congress on Acoustics. - : International Commission for Acoustics (ICA). ; , s. 2134-2141
-
Konferensbidrag (refereegranskat)abstract
- Heat exchangers are widely used in industries where heat needs to be transferred from one fluid to another fluid. For example, there are plate-fin heat exchangers in gas turbine engines, shell and tube heat exchangers in oil refineries and tube bundle heat exchangers in domestic boilers. Among the different types of exchangers, tube bundle exchangers are the most commonly used heat exchange equipments. In this paper, heat exchanger with the structure of tube rows with bias flow and possible acoustic interaction at the tube row is studied for the acoustic reflection and transmission. The numerical methodology solving the linearized Navier-Stokes equation in the frequency domain is used. It has the advantage of taking into account the flow effects, viscous losses as well as thermal losses in the acoustic propagation. The simplified geometry for the heat exchanger investigated in this paper is a two-dimensional rectangular duct with two half cylinders with a bias flow going through the gap between the cylinders. In the current study, the acoustic response is predicted numerically with the cold flow only and compared to the experimental data, as a preparation for the next study with the hot flow.
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| 48. |
- Na, Wei, et al.
(författare)
-
Prediction of thermoacoustic instabilities in combustors using linearized Navier-Stokes equations in frequency domain
- 2015
-
Ingår i: 22nd International Congress on Sound and Vibration, ICSV 2015, Vol. 2. - : International Institute of Acoustics and Vibrations. - 9781510809031 ; , s. 2011-2018
-
Konferensbidrag (refereegranskat)abstract
- The paper presents a numerical methodology for the prediction of the thermoacoustic instabilities with the effects of the mean-flow as well as the viscosity. As an academic standard test case, the configuration within the flame sheet located in the middle of the duct is investigated. First, the ducted flame numerical reference case is solved by the inhomogeneous Helmholtz equations in combination of the n - τ flame model assuming that the flow is at rest. Then, we derive the linearized Navier-Stokes equations (LNSE) in frequency domain in combination of the flame model. The unsteady effect of the flame is modeled by the n - τ flame model in harmonic form, which is essentially a 1D formulation relating the rate of heat release and the acoustic velocity at the reference point.
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| 49. |
- Na, Wei, PhD student, 1986-, et al.
(författare)
-
Prediction of thermoacoustic instabilities in combustors using linearized Navier-Stokes equations in frequency domain
- 2015
-
Ingår i: 22nd International Congress on Sound and Vibration 2015 (ICSV 22) Proceedings of a meeting.
-
Konferensbidrag (refereegranskat)abstract
- The paper presents a numerical methodology for the prediction of thermoacoustic instabilities with the effects of mean flow as well as the viscous effect. As an academic benchmark, the Rijketube configuration with the flame sheet located in the middle of the duct is used for validating the numerical methodology. The numerical methodology of solving linearized Navier-Stokes equations (LNSE) in frequency domain with the steady heat release is described in the paper. The numerical results are compared to the semi-analytical results by Dow
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| 50. |
- Na, Wei, PHD student, 1986-, et al.
(författare)
-
Simulations of acoustic wave propagation in an impedance tube using a frequency-domain linearized Navier-Stokes methodology
- 2014
-
Ingår i: 20th AIAA/CEAS Aeroacoustics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we present analysis of the propagation of acoustic plane waves in an impedance tube, in which a liner is attached at one end of the duct. The purpose is to evaluate a linearized Navier-Stokes solver as a tool to determine the acoustic performance of the liner. The liner considered consists of a perforated plate with several circular holes and a rectangular back cavity. The inuence of parameter variations such as plate thickness, porosity area examined. The prediction of the acoustic characters of the liner is based on the numerical solutions of the linearized Navier-Stokes equations in frequency domain in three space dimensions. The impedance as well as reection coefficients of the liner for frequencies in the plane wave regime are obtained by two-microphone method data, which are compared to experimental data as well as results from a semi-empirical model. The results presented in this paper agree very well with results of the linear semi-empirical model, while there are some discrepancies to the experimental results. The reasons for these discrepancies are not fully understood, but could partly be due to that a linear assumption is not always valid.
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