Critical heat flux and associated phenomena in forced convective boiling in nuclear systems

In evaporation of a liquid flowing in a tube or nuclear fuel element, there exists a transition (known as "dryout", "burnout", "boiling crisis" or "critical heat flux", CHF) from a high heat transfer coefficient regime to one of greatly reduced heat transfer coefficient. The conditions leading to dryout or CHF and the behaviour of wall temperatures in the ("post dryout or post CHF") region beyond it are of immense importance in nuclear reactor safety. In a nuclear reactor, the clad temperature excursion in the post-dryout region may be unacceptably high and the prediction of the location of dryout and the magnitude of the temperature excursion into the post-dryout region is of great importance. Moreover, the dryout transition and its effects are important not only in nuclear plant but also in many other types of heat transfer equipment. The main focus of work described in this thesis was the improvement and validation of phenomenological models for the prediction of CHF and of heat transfer beyond CHF ("post CHF" or "post dryout" heat transfer). The main focus has been on the process of annular film dryout. In phenomenological modelling of this process the dryout location prediction is sensitive to the boundary value of entrained fraction at churn annular transition, especially at high flow rates. The model was extended to churn flow so that integration of entrainment, deposition and evaporation processes could be started from onset of churn flow. A new correlation for the prediction of entrainment rate in churn flow was presented. The application of the new methodology to experimental data leads to improved predictions of CHF. Another long-standing problem, i.e. effect of heat flux on droplet entrainment, is addressed by analysing the contradictory results of previous experiments by using the annular film dryout model. The capability of phenomenological models to cover the whole range of CHF scenarios, i.e. from subcooled or very low quality to very high quality CHF, was demonstrated by using a possible transition criterion from bubble crowding model (an improved version of the Weisman Pie model) to annular film dryout model. These improved phenomenological models captured trends of CHF data very well (including the Look Up Table data of Groeneveld et al. 2007) and produced improved results over a wide range of system parameters such as pressure, mass flux and critical quality. The implementation of the phenomenological models was pursued by modifying and developing an Imperial College computer code GRAMP. In addition to its application in modelling CHF, the GRAMP code was extended to the post dryout region and predictions for this region compared to a range of data and the results were found to be satisfactory

Effectiveness of assigning BI-RADS category-3 to breast lesion with respect to follow-up

OBJECTIVE: To determine the effectiveness of assigning BI-RADS category-3 to breast lesion with respect to follow-up.STUDY DESIGN: A cohort study. PLACE AND DURATION OF STUDY: Radiology Department, the Aga Khan University Hospital, Karachi, from January 2002 to December 2004. PATIENTS AND METHODS: Women undergoing X-ray mammography and assigned BI-RADS category-3 and recommended short-term (6-monthly) follow-up were included. Out of these, 44 patients were lost to follow-up and were excluded from the study. The lesions that remained stable after short-term follow-up were recommended routine (annual) follow-up. Needle localization and open surgical biopsy was performed, if the lesion progressed or calcifications increased in number/size and/or on physician or patient preference. The effectiveness of this approach was analyzed by determining the sensitivity, specificity, positive and negative predictive value for BI-RADS category-3. RESULTS: Of the 65 lesions, 55 remained stable. Of the remaining 10 lesions, two showed increase in number of microcalcification prompting biopsy. Both turned out to be ductal carcinoma in situ. Eight biopsies were performed on clinician or patient preference which turned out to be benign. The sensitivity, specificity, positive and negative predictive values were 100%, 87%, 20% and 100% respectively. CONCLUSION: Assessment with short-interval mammographic follow-up is useful to confirm the nature of most non-palpable breast lesions considered probably benign and permits detection of a small number of breast cancers at an early stage. The local setup, patient compliance is a major limitation for performing a follow-up study, as the available numbers can have a profound effect on the determined accuracy value

Bond strength history in prestressed concrete reactor vessels

An attempt has been made to study bond strength history in Prestressed Concrete Reactor Vessels (PCRV) which house the Advanced Gas-cooled Reactors. Three-dimensional non-linear analytical model has been developed in which the effect of bond is included. A finite element computer program is written in which solid, membrane, line and bond-linkage elements have been used to represent vessel concrete, steel liner, pre-stressing tendons and bond (between steel and concrete) respectively. Concrete is assumed to be non-linear material in compression and linear brittle (tension cut-off) material in tension, and the steel as elasto-plastic material with strain hardening. Provision is also made for concrete cracking, crushing and visco-elastic creep. Two experiments have been carried out during this research. The purpose of the first experiment was to determine bond coefficients required for the analysis. This was achieved by pull-out tests on prestressing specimens using 5 mm and 7 mm diameter prestressing wires. The second experiment was performed on an octagonal prestressed concrete slab representing a top cap of a reactor vessel. The experimental results obtained from this slab are corroborated with the analytical results. A typical Prestressed Concrete Reactor Vessel with boilers and circulators housed within the vessel wall thickness has been analysed for bond strength under increasing gas pressure at suitable intervals of its 30 year life. A comparison is made between the unbonded and bonded vessels. All analytical results compare well with those obtained from the experiments and available published data

Slope stability and avalanching of sediments, the effects of biological activity

An experimental analysis has been conducted on the stability of sediment slopes. This has included a study of the geotechnical properties of sediments and the effects of supporting medium and biological activity on avalanching. The thesis is divided into six sections with three appendices. Section 1: Section one describes the geotechnical properties of Ardmore Bay sediments including particle size distribution, and the phase properties of void ratio, porosity, specific gravity, dry density and bulk density. Section 2: Experiments were conducted on the effects of orientation and shape of the container, volume of sediment, and particle size, on angles of avalanche and repose. Section 3 and 4: Experiments were conducted on the effects of air, water, 50% glycerol. 100% glycerol and alginic acid (low viscosity) on angles of avalanche and angles of repose at successive intervals of time (termed setting time). Section 5: The objectives of the biological experiment were to quantify the effects of biological activity on avalanching. Section 6: The objectives of the Mytilus edulis experiment were to quantify the production of byssus threads in relation to sediment stability. The results of the experiments reported in sections one to six are discussed in relation to mechanisms controlling slope stability in terrestrial and aquatic environments. They are also considered with reference to environmentally friendly methods of stabilising slopes now under active investigation by civil engineers. Topics covered include geotechnical properties, sediment phase relations, fluid viscosity, factors of safety, duration of avalanche and biological activity. I have also discussed slope failure mechanisms, and parallel between engineering and biological stabilisation of slopes. The appendices include geotechnical details of the sediment properties and phase relationships of sediments, sediment permeability, and sediment shear strength. I have also included details of factors of safety and stability analysis of slopes, treated from a civil engineering point of view

The Combined Effect of Market Orientation and Owner/Manager's Innovativeness on Innovation and Business Performance of Small and Medium Sized Manufacturing Firms in Pakistan

The study investigated various aspects of market orientation and owner/manager's innovativeness relationship with innovation and performance in the small and medium sized manufacturing firms in Pakistan. The objectives of the study were 1) to examine the relationship and effect of market orientation and owner/managers innovativeness in relation to innovation and performance, 2) to examine the relationship and effect of innovation in relation to performance, 3) to examine the combined effect of owner/managers innovativeness and market orientation in relation to innovation and performance, and 4) to examine the level of owner/manager's innovativeness and market orientation based on firm's and respondent's characteristics. This study used owner/manager's innovativeness, market orientation and innovation as they relate to firm overall performance. The innovativeness constructs used to measure the owner/manager's innovativeness and domain specific innovativeness had been widely used in consumer research studies. Based on the theories of Ricardian (1871), Penrose (1959), Schumpeter (1934) and Roger's Adoption of Innovation concept (2003), a model of relationship was proposed and developed to examine the relationships between market orientation, owner/manager's innovativeness, innovation and the small and medium sized firms' performance. To test the relationship of the variables in the model, data from 170 textile and apparel/garment manufacturing small and medium sized firms in Karachi-Pakistan were used. To test the relationship hypotheses of the study, correlation, multiple regression analysis, T-test and ANOVA were performed. The correlation analysis suggested a significant and positive relationship among all the four variables used in the model. Multiple regression analysis result indicated that owner/manager's general innovativeness as well as innovativeness in product-strategy and process domain has a significant influence on the overall innovation. The general innovativeness and innovativeness in product-strategy domain also significantly influenced the firm performance. Results from correlation and multiple regression analysis further suggested that market orientation and its three components appeared to be associated directly with innovations and firm performance. However customer orientation, which is one of the key variables, appeared to cause a main effect on firm overall innovation and also SMEs overall performance. It is also proven in this study that among the three innovation strategies, only product innovation significantly influenced the firm performance. One-way ANOVA results indicated that a significant difference of the level of owner/manger's general innovativeness and domain specific innovativeness in product-strategy and process domain. The result confirmed that younger managers and owners with higher qualification had better scores on innovativeness scale than the older and less qualified owner/managers. Other results of One-way ANOVA indicated that export oriented manufacturers were more market oriented than the non-export oriented. The results findings further confirmed that small and medium-sized firms can be market oriented at any stage of their life cycle and did not need to be established firms in the industry for being market oriented. Findings of this study showed that owner/manager's innovativeness permeated all the variables in the model and had a positive influence to market orientation, innovation and firm performance. The study confirmed the existence of the linear relationship between all the variables and in relation to SMEs performance, and further suggested that manufacturing textile SMEs must focus on innovative owners and managers, who could build a strong market orientation culture for the firm and greater level of adoptions of innovations and firm performance

重力理論の宇宙論に対する理論的および観測的制約

京都大学新制・課程博士博士(理学)甲第23453号理博第4747号新制||理||1680(附属図書館)京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 向山 信治, 准教授 De Felice Antonio , 教授 萩野 浩一学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDFA

Efficacy and safety of sofosbuvir plus ribavirin in treatment-naive chronic hepatitis c genotype 3 patients of South Punjab, Pakistan

Background: To evaluate the efficacy and safety of sofosbuvir (SOF) plus ribavirin (RIB) in naive patients with chronic HCV genotype 3. The study design was open label, quasi experimental study. The study was conducted at Medical Outpatient Department of Medical Unit-1, Bahawal Victoria Hospital, affiliated with Quaid e Azam Medical College (QAMC), Bahawalpur, from April 2016 to June 2019.Methods: A total of 627 treatment-naive patients, aged above 18 years, with chronic Hepatitis C virus (HCV) genotype 3 infection were enrolled. SOF as 400 mg once a day plus weight-based RIB (1000 mg/day 75 kg) was given to all the study participants for 24 weeks. Qualitative polymerase chain reaction (PCR) for HCV ribonucleic acid (RNA) were done at 4 weeks to note the rapid virological response (RVR) whereas end of treatment response (ETR) was recorded at 24 weeks and sustained virological response (SVR) was noted 3 months after completion of treatment.Results: By 4th week, PCR of 524 (83.6%) patients was available, out of which, 492 (93.9%) had undetectable HCV RNA. By the end of treatment (24 weeks), PCR of 401 (64.0%) patients was available, out of which, 393 (98.0%) had undetectable HCV RNA. Data of 291 (46.4%) patients was available for SVR, 274 (94.1%) had undetectable HCV RNA. Weakness and fatigue turned out to be the commonest side effects, observed in 236 (37.6%) patients.Conclusions: Sofosbuvir was found to have good efficacy and safety in the local population of South Punjab having treatment-naïve chronic HCV genotype 3 infection