Two-phase flow boiling in small to micro-diameter tubes

This thesis is dedicated to the experimental and theoretical study of flow boiling in small to micro diameter tubes using R 134a. Flow pattern, heat transfer and pressure drop studies were conducted in stainless steel cold drawn tubes with internal diameter 2.88,1.1, and 0.52 mm using an existing facility that was designed with a long term research objective of improving the fundamental understanding of flow boiling in small metallic tubes. The facility was moved to the present location from London South Bank University and re-commissioned before carrying out the experiments. The test sections were heated by a direct passage of alternating current and wall temperatures were measured at 15 axial locations by miniature thermocouples that were directly spotwelded at the tube outer wall. A digital high-speed camera was used to simultaneously observe the flow patterns (during the heat transfer tests) directly at a borosilicate glass tube located immediately downstream of the heat transfer test section. The purpose of the flow visualization study was to support understanding of the heat transfer characteristics and development of flow regime-specific models. The heat transfer and pressure drop data of X. Huo (2005) in the 4.26 and 2.01 mm tubes and the flow visualization results of Chen (2006) for the tubes of diameter 4.26,2.88,2.01, and 1.1 mm were included with the new data in an extensive analysis of flow boiling heat transfer and pressure drop in five vertical tubes with internal diameters 4.26, 2.88,2.01, 1.1 and 0.52 mm. The wide range of tube diameter was chosen to investigate the influence of tube size and possibly identify the threshold where the effect of small or micro diameter effects become significant. In the experiments, parameters were varied in the ranges: mass flux 100 to 700 kg/m2s; heat flux 1.6 to 150 kW/m; pressure 6 to 14 bar; quality up to 0.9 and the inlet temperature was controlled at a subcooling of 1-5K. There was no clear significant difference between the characteristics and magnitude of the heat transfer coefficients in the 4.26 mm and 2.88 mm tubes but the coefficients in the 2.01 and 1.1 mm tube were higher. The heat transfer results suggested that a tube size of about 2 mm might be considered as a critical diameter to distinguish small and conventional tubes. Further differences have now been observed in the 0.52 mm tube. These differences, both in flow patterns and heat transfer, indicate a possible second change from small to micro behaviour at diameters less than 1 mm for R 134a. Also, the results showed axial variations in heat transfer characteristics marking the importance of surface conditions on heat transfer. This calls for a further detail investigation to understand the underlying physics in the initiation of boiling, effect of surface condition on nucleation, and structure of newly emerging flow patterns, particularly in very small tubes. Existing correlations were examined using the results of the five tubes and indicated that these correlations do not predict the present small diameter data to a satisfactory degree. Therefore, two new correlations that take into account both magnitude and characteristic effect of tube diameter have been proposed covering the 4.26 mm-1.1 mm and the smallest 0.52 mm tube, respectively. A detailed comparison was also made with the state-of-the-art flow regime-specific model of Thome et al. (2004) and verified that the mechanistic modelling approach has a promising capability of predicting two phase heat transfer in small diameter tubes, although it still requires further development. Some improvements have been proposed and tested against the current data. Using a similar approach, a new two phase pressure drop model has been proposed and compared with the current data with encouraging results.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

RNA editing signature during myeloid leukemia cell differentiation

Adenosine deaminases acting on RNA (ADARs) are key proteins for hematopoietic stem cell self-renewal and for survival of differentiating progenitor cells. However, their specific role in myeloid cell maturation has been poorly investigated. Here we show that ADAR1 is present at basal level in the primary myeloid leukemia cells obtained from patients at diagnosis as well as in myeloid U-937 and THP1 cell lines and its expression correlates with the editing levels. Upon phorbol-myristate acetate or Vitamin D3/granulocyte macrophage colony-stimulating factor (GM-CSF)-driven differentiation, both ADAR1 and ADAR2 enzymes are upregulated, with a concomitant global increase of A-to-I RNA editing. ADAR1 silencing caused an editing decrease at specific ADAR1 target genes, without, however, interfering with cell differentiation or with ADAR2 activity. Remarkably, ADAR2 is absent in the undifferentiated cell stage, due to its elimination through the ubiquitin–proteasome pathway, being strongly upregulated at the end of the differentiation process. Of note, peripheral blood monocytes display editing events at the selected targets similar to those found in differentiated cell lines. Taken together, the data indicate that ADAR enzymes play important and distinct roles in myeloid cells

Mitochondrial Damage in the Trabecular Meshwork Occurs Only in Primary Open-Angle Glaucoma and in Pseudoexfoliative Glaucoma

Open-angle glaucoma appears to be induced by the malfunction of the trabecular meshwork cells due to injury induced by oxidative damage and mitochondrial impairment. Here, we report that, in fact, we have detected mitochondrial damage only in primary open-angle glaucoma and pseudo-exfoliation glaucoma, among several glaucoma types compared.Mitochondrial damage was evaluated by analyzing the common mitochondrial DNA deletion by real-time PCR in trabecular meshwork specimens collected at surgery from glaucomatous patients and controls. Glaucomatous patients included 38 patients affected by various glaucoma types: primary open-angle, pigmented, juvenile, congenital, pseudoexfoliative, acute, neovascular, and chronic closed-angle glaucoma. As control samples, we used 16 specimens collected from glaucoma-free corneal donors. Only primary open-angle glaucoma (3.0-fold) and pseudoexfoliative glaucoma (6.3-fold) showed significant increases in the amount of mitochondrial DNA deletion. In all other cases, deletion was similar to controls.despite the fact that the trabecular meshwork is the most important tissue in the physiopathology of aqueous humor outflow in all glaucoma types, the present study provides new information regarding basic physiopathology of this tissue: only in primary open-angle and pseudoexfoliative glaucomas oxidative damage arising from mitochondrial failure play a role in the functional decay of trabecular meshwork

Trabecular Meshwork Gene Expression after Selective Laser Trabeculoplasty

BACKGROUND: Trabecular meshwork and Schlemm's canal are the tissues appointed to modulate the aqueous humour outflow from the anterior chamber. The impairment of their functions drives to an intraocular pressure increase. The selective laser trabeculoplasty is a laser therapy of the trabecular meshwork able to decrease intraocular pressure. The exact response mechanism to this treatment has not been clearly delineated yet. The herein presented study is aimed at studying the gene expression changes induced in trabecular meshwork cells by selective laser trabeculoplasty (SLT) in order to better understand the mechanisms subtending its efficacy. METHODOLOGY/PRINCIPAL FINDINGS: Primary human trabecular meshwork cells cultured in fibroblast medium underwent selective laser trabeculoplasty treatment. RNA was extracted from a pool of cells 30 minutes after treatment while the remaining cells were further cultured and RNA was extracted respectively 2 and 6 hours after treatment. Control cells stored in incubator in absence of SLT treatment were used as reference samples. Gene expression was evaluated by hybridization on miRNA-microarray and laser scanner analysis. Scanning electron microscopic examination was performed on 2 Trabecular meshwork samples after SLT at 4(th) and 6(th) hour from treatment. On the whole, selective laser trabeculoplasty modulates in trabecular meshwork the expression of genes involved in cell motility, intercellular connections, extracellular matrix production, protein repair, DNA repair, membrane repair, reactive oxygen species production, glutamate toxicity, antioxidant activities, and inflammation. CONCLUSIONS/SIGNIFICANCE: SLT did not induce any phenotypic alteration in TM samples. TM is a complex tissue possessing a great variety of function pivotal for the active regulation of aqueous humour outflow from the anterior chamber. SLT is able to modulate these functions at the postgenomic molecular level without inducing damage either at molecular or phenotypic levels

Clinical and radiological prevalence of skeletal fluorosis among retired employees of Wonji-Shoa sugar estate in Ethiopia

Objective: To study the clinical and radiological prevalence of skeletal fluorosis among the retired employees of Wonji-Shoa sugar estate. Design: Retrospective and cross-sectional study. Setting: Wonji-Shoa sugar estate, an agro-industrial estate located in the Ethiopian Rift Valley. Subjects: Two hundred and sixty three employees of the estate who retired between 1995 and 1996. Main outcome measures: Clinical evidence of impaired squatting, neck and lumbar mobility, kyphosis, and X-ray evidence of fluorosis. Results: Skeletal fluorosis was more evident among the males (

The Psychological Impacts During the Initial Phase of the COVID-19 Outbreak, and its Associated Factors Among Pastoral Community in West Omo Zone, South-West Ethiopia, 2020: A Community-Based Study

Nigusie Shifera,1 Gebremeskel Mesafint,2 Alemayehu Sayih,2 Gizachew Yilak,3 Abebaw Molla,4 Tewodros Yosef,1 Rahel Matiyas5 1Department of Epidemiology and Biostatics, School of Public Health, Mizan-Tepi University, Mizan-Aman, Ethiopia; 2Department of Nursing, College of Medicine and Health Science, Mizan-Tepi University, Mizan-Aman, Ethiopia; 3School of Nursing, College of Health Science, Woldia University, Woldia, Ethiopia; 4Department of Nutrition, School of Public Health, Mizan-Tepi University, Mizan-Aman, Ethiopia; 5Department of Psychology, College of Social Science and Humanity, Mizan-Tepi University, Mizan-Aman, EthiopiaCorrespondence: Nigusie ShiferaDepartment of Epidemiology and Biostatics, School of Public Health, Mizan-Tepi University, Mizan-Aman, EthiopiaEmail [email protected]: COVID-19 is a global pandemic and a major health crisis affecting several nations. Such outbreaks are associated with adverse mental health consequences to any group of the population. Despite its negative effects, no study has addressed the potential psychological impacts of the COVID-19 outbreak among the pastoral community. This study aims to assess psychological experiences during the early stages of the COVID-19 outbreak and the factors that contributed to it among pastoral community residents in West Omo, South-West Ethiopia.Methods: A community-based cross-sectional study was carried out from May to June 2020. The study subjects were selected through a multistage sampling technique. Data were collected through face-to-face interviews, and entered into EpiData 3.1, then exported to SPSS version 24 for statistical analysis. The psychological impact was assessed by the Depression, Anxiety and Stress Scale (DASS-21). P-value < 0.20 during bi-variable analysis was considered as a candidate for multivariable logistic regression. Independent factors of depression, anxiety, and stress were assessed using adjusted odds ratio with 95% confidence level s at P-value < 0.05 cut-off point.Results: A total of 845 eligible pastoral residents were interviewed, with a 94.4% response rate. The prevalence of a positive response for anxiety, depression and stress was 30.8%, 26.3% and 24.4%, respectively. Being female was highly associated with developing anxiety and depression. Anxiety was found to be three times more prevalent among the respondents with ≥ 3 family members. Furthermore, participants with a history of mental illness, poor social support, and a high perceived life threat were also at a higher risk of experiencing anxiety, depression, and stress.Conclusion: The prevalence of positive depression, anxiety and stress results were high. As a result, special attention should be paid, by governmental and non-governmental health organizations, to psychosocial and mental health programs for pastoral residentsduring the COVID-19 pandemic.Keywords: COVID-19, anxiety, depression, outbreak, stres