PhD

Permanent URI for this collectionhttps://ir.lib.pdn.ac.lk/handle/20.500.14444/204

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"Writings on the "WOMANHOOD FACTOR"
(University of Peradeniya, 2013) Ashkenaz, Shaula
This is a multi-disciplinary comparative study, drawing on scholarly thought and knowledge in the fields of Theology/Buddhology, Gender Studies and Literature. It focuses on past and present approaches to womanhood in Buddhism and Judaism that are explored through a choice of canonical and traditional scriptures. The review of Buddhist and Jewish scriptures, as well as of Sri Lankan and Israeli literary texts, lay the foundation for coining the term "The Womanhood Factor", explaining its meaning and features, and presenting the ways the female experience is voiced accordingly in ancient and contemporary women's writings of both doctrines, as a creative expression of their womanhood. I will introduce the challenge of conducting this comparative study in light of the fundamental difference between Buddhism, a doctrine that features no God, Vs. Judaism, a monotheistic religion that abides by God's existence and authority. I will peruse how Womanhood is perceived and practiced accordingly. I hypothesize that both Buddhist and Jewish creative women do, indeed, practice the Womanhood Factor and are thus capable of transcending religion and social boundaries through their creativity. This study strives to research and determine whether, despite the seemingly irreconcilable gap between these two bodies of wisdom, women-writers of both Buddhist and Jewish traditions have - within and through their literary creativity - leaped beyond this gap, as they all experience life with the inherent "Womanhood Factor". Creative writing of women thus becomes a borderland in itself, a tool for understanding human nature and bridge the insurmountable gap between Buddhism and Judaism, through the shared common denominator that is "The Womanhood Factor".
Flow in s-shaped open channel bends
(University of Peradeniya, 1983) Keerthisena, Hewa Henipelle Jeevananda
The understanding of the physical processes governing the flow in meandering bends is rather poor. This is mainly as a result of a lack of reliable and detailed information on S-shaped open channel bends. Such information is invaluable in interpreting results of distorted scale models of river bends and in improving the design of S-shaped passages used in various duct systems. In the work reported here three S-bend configurations are investigated over a wide range of flow conditions. Through detailed measurements of the water surface elevations, bed shear stresses and velocity field, the influence of the relevant geometric and flow parameters is analysed and the main features of the flow in open channel S-bends of moderate curvature are explained. It is found that the reversal of curvature in S-bends leads to significant deformation of the water surface and that the attendant transverse variations of longitudinal pressure gradients have a dominant influence on the redistribution of velocity and of bed shear stress, and on the development and decay of helical flow in S-bends of moderate curvature. Unlike in shallow bends of mild curvature at low Froude numbers, where the flow adjusts freely to the demands of the induced secondary flow, in moderately curved S-bends, at moderate aspect ratios and Froude numbers, the flow is constrained by the strong longitudinal pressure gradients. At high aspect ratios and Froude numbers the secondary flow is found to be weak and the maximum velocity is located close to the inner wall. The trace of maximum bed shear race stress does not follow the trace of maximum velocity and is out of phase with the trace of maximum bed skew angle in the early parts of the bends. Unlike in the exit region of a single bend leading to a straight channel, the flow in the crossover region of an S-bend is severly deformed and strong lateral nonuniformities are observed. A pair of counterrotating vortices appearing in the second half of an S-bend gives rise to higher skew angles in the central part of the vertical and the streamline pattern near the bed does not fairly represent the helical flow in S-bends. Simplified mathematical descriptions are presented for the skew angle variation in S-bends, for the deduction of secondary flow profiles from main velocity profiles and for the effects of streamwise acceleration and deceleration of main flow. Using the findings of the present study, several conflicting results in earlier investigations are satisfactorily explained.
Investigations into Alkali-Aggregate Reaction in concrete structures
(University of Peradeniya, 2013) Pathirana, Chintha Kusumlatha
Alkali Aggregate Reaction (AAR) is a chemical reaction taking place in concrete between alkalis in pore solution of cement paste and reactive phases in aggregates, with mechanical implications. It causes the concrete concerned to undergo expansion with time, resulting in premature cracking of concrete, and unwarranted deformations in structures which could shorten their service lifetime. In Sri Lanka, so far there has been no documented evidence of systematic investigations on AAR in structures. Nevertheless there are a few old concrete structures which are still being used, but showing symptoms similar in nature to those of AAR. Since characteristics of aggregate mainly contribute to AAR a substantial part of the present study is devoted to investigate the potential alkali-silica reactivity of Sri Lankan aggregates. In this study, the standard tests, ASTM C289 - 07 for potential alkali-silica reactivity of aggregates (chemical method) and ASTM C295 - 07 for petrographic examinations, have been performed on samples collected from numerous locations spreading over Sri Lanka, representing a wide range of morphological types of coarse and fine aggregates. Based on the results of these tests, as the next step, ASTM C1260 - 7 for the potential alkali reactivity of aggregates (mortar-bar method) was performed on selected samples. Based on the results, a new parameter named, 'Potential Reactivity Index' (PRI), has been proposed as an index to rank slowly reactive aggregates. The degree of reactivity has been quantified by extending the rapid chemical test covered by ASTM C289. A correlation was established between the expansion of aggregates and PRI. The degradation of concrete was assessed by ultrasonic and acoustic tests. The results of ultrasonic pulse velocity and vi resonant frequency testing have shown that the dynamic modulus of elasticity of the concretes is affected by AAR. If AAR takes place in an existing concrete structure it might become necessary to implement remedial measures which can vary from blocking moisture ingress to introducing stress-relief cuts in concrete. To initiate remedies, the presence of AAR in a structure has to be detected. Then the progress of AAR along with its potential for causing structural distress needs to be predicted. To understand the structural implications of AAR, computer simulations can be performed. The present study uses a methodology for using a general purpose finite element program package to simulate AAR numerically. AAR is considered as a thermal equivalent expansion process, in which the expansion of the concrete due to the equivalent temperature rise is equal to the expansion due to AAR. A computer code has been developed for this purpose and validated using analytical solutions to several benchmark problems. A real structure under alkali-aggregate reaction, found in literature has been analyzed using the proposed numerical procedure.
Capability limits of doubly fed induction generator wind turbines
(University of Peradeniya, 2012) Tennakoon, A. P.
The research investigates mainly the capability of Doubly Fed Induction Generator (DFIG) wind turbines to meet the grid code requirements with special emphasis on stability. A complete modelling of the DFIG was carried out for this purpose for both transient and steady state analysis. A controller was designed with a novel technique for tracking the rotor angle. The performance of the DFIG with battery as an energy storage device connected to the DC link was investigated. A method was formulated using the wind data for the derivation of battery capacity that should be used. Eigen value analysis was undertaken to determine the influence of connecting battery at the DC link and a comparison was made with the DFIG model with capacitor connected at the DC link. Since having a battery as an energy storage device connected to the DC link had many advantages this was chosen for the final DFIG model with the controller. A laboratory set up of a prototype DFIG was done similar to the derived model with a battery connected to the DC link. Tests were carried out using the control techniques derived during the modeling. The methods developed for tracking the rotor angle for rotor current injection were tested. Adjustments were made where necessary during testing and a final controller model was validated experimentally. The behavior of the DFIG output with rotor current injection were checked and investigated. Then using the model of the DFIG with the developed controller, dynamic behaviour of the DFIG with and without energy storage was investigated. A comparison for response to wind fluctuations and fault ride through operation was compared for DFIG with battery and DFIG with Capacitor connected to DC link. Using the derived and validated DFIG model and the controller, an investigation was carried out on capability limits of the DFIG, when operating within the specified speed range taking in to consideration the limitations on the rotor power, stator current and the stability. It was investigated on how the stability could be improved by selecting wound rotor induction machine with different machine parameters and reactive power exchange with the power system. A capability chart of the DFIG was prepared using an iteration method. A small signal model of the DFIG wind farm, connected with the power system, was used for the stability studies with Eigen value analysis. Finally, a case study was carried out to find the feasibility of connecting a DFIG based wind farm with energy storage at Puttalam area in Sri Lanka. Dynamic studies were carried out and the performance was compared with a DFIG wind farm with and without energy storage. The impact on the present power system for wind fluctuations and fault ride through operation was investigated.
Improvements in stress life approach for fatigue damage assessment of steel structures and components
(University of Peradeniya, 2015) Bandara, A. M. A. C. S.
Fatigue is a common problem in steel structures and components when they are subjected to cyclic loading. Fatigue assessments require testing. As fatigue testing (cyclic testing) is costly and time consuming, analytical models with a few monotonic tests are usually used for fatigue assessments. However, still there are areas in fatigue studies where not enough research has been done. Therefore, some of these research areas were studied to close existing research gaps and to solve the problems in metal fatigue to some extent. The main fatigue areas studied were: very high cycle fatigue (VHCF); full range stress - life models (S- N curves); nondestructive methods for developing full range S-N curves; effects of corrosion on full range S-N curves and fatigue damage assessment procedures for steels. First, a simple strength based model was proposed for predicting the critical size of fracture origins after an extensive study on very high cycle fatigue of steels. Experimental fatigue data of a number of various steels were used in this study. Then, using the proposed model and existing S-N relations, a new fatigue strength prediction formula was proposed for the very high cycle fatigue region (new VHCF model). The applicability of the new VHCF model for low carbon structural steels was verified using laboratory fatigue testing. Next, a model for a full range S-N curve was proposed for steels using the new VHCF model, existing low and high cycle stress life relationships and a mathematical function. This S-N model proposed (new full range S-N model) describes the entire stress and cycle range from the 1st cycle to very high cycles (gigacycles). The new full range S-N model was verified using experimental fatigue data of seven medium strength steels. Salient features of the new full range S-N model are that it requires only monotonic strength and hardness properties of steels to predict the S-N curves of steels. Highlighting the importance of nondestructive methods for damage assessments, a nondestructive full range S-N model for steels was proposed using the new full range S-N model. Material hardness was used as the only nondestructive test parameter in this model (hardness based S-N model). The hardness based S-N model too was verified using experimental fatigue data of seven medium strength steels. This hardness based S-N model is iii special because it only requires material hardness for predicting the S-N curve and that it is able to describe the entire fatigue range from the 1st cycle to gigacycles fairly accurately. Corrosion is unavoidable in most structures and components exposed to a corrosive atmosphere. Therefore, the new full range S-N model was modified to take into account the effects of corrosion (corrosion based S-N model). The corrosion based S-N model was verified using three medium strength steels tested in laboratory. Apart from hardness and strength parameters, the only parameter required to predict a full range S-N curve using this model is the fatigue strength of the steel in the high cycle region in the corrosive media. The S-N models proposed in this study are equivalent to axial, fully reversed, constant amplitude mean S-N curves. Therefore, modifications are necessary for the proposed full range S-N models when using them in real structures with various geometries and loading conditions. Therefore, a new damage assessment procedure was proposed using existing damage assessment methods. This new procedure takes into account the stress concentration effects, different cyclic loading ratios and variable amplitude loading. The proposed assessment procedure was verified using experimental fatigue data. Finally, a connection detail of a steel bridge was used as a case study to show the efficiency of the proposed damage assessment procedure and S-N models against the methods used in design codes.
Correct by design methodology for the control of safety-critical complex reactive systems
(University of Peradeniya, 2019) Vidanapathirana, A. C.
The objective of this thesis was to develop formal verification strategies suitable for model- based design of Complex Reactive Systems (CRS). Typical real scale CRS like automotive, power, avionic, rail transport and manufacturing systems require design techniques that facilitate continuous verification and validation of control software/hardware in their life cycles, which pose complex challenges due to their inherent complexity arising from concurrency, distribution, communication, rapid response, hybrid dynamics, hierarchy, modularity etc. Since structurally flat models like Finite State Machines (FSMs) do not scale up well for representing real scale CRS we selected semantically rich statecharts to specify discrete event control. Statecharts permit simulation from early stages of the design. Since simulation cannot guarantee correct behaviour, formal verification becomes necessary, and mandatory in some cases. However, the complex semantics of statecharts do not permit direct formal verification. This led us to develop strategies for semantics preserving translation of statecharts into flat modules communicating through ports, to compositionally verify supervised and unsupervised discrete dynamics. This thesis contributes through the incorporation of modular supervisory control, reconfigurabilty, redundancy and finally, integration of hybrid dynamics, to facilitate compositional formal verification, testing and runtime validation of Complex Hybrid Systems (CHS). Verification and integration of modular non-blocking supervisory control have been automated. The verified controller models are then seamlessly translated automatically to executable software code and implemented in PLC (Telemechanique) and FPGA (Xilinx) hardware platforms with minimum debugging. To capture errors at various integration levels, MIL and HiL testing was carried out. Continuous Variable dynamics were integrated and the formal verification strategy was elevated to Complex Hybrid Systems. Unlike in the traditional approach, testing was integrated with the formal verification. Then safety invariants were defined for the CHS and differential dynamic logic was used to elevate verification logic to the hybrid dynamics. A runtime validation strategy was developed for capturing any un-modelled system behaviour. To validate formal verification theories for this class of systems a prototype laboratory test-bed was built in the laboratory to perform research on CRS at various levels of system integration. All the theories developed in this thesis were implemented and tested on this test-bed.
Structural analysis of the edge of the cleft lip in individuals with cleft lip with or without cleft palate
(University of Peradeniya, 1999) Wijayaweera, C. J.
Three hundred and thirty six specimens of lateral and medial cleft margins from 168 infants with different types of cleft lips were studied histologically and compared with the normal. The structure and distribution of epithelial tissues and their appendages were compatible with the normal lip. However in some cleft lip specimens there was keratinisation of the mucous membrane. Occasionally sebaceous glands were present in the submucosa. The structure of the blood vessels was compatible with the normal and no inflammatory changes were seen in them. Disorganization of muscle tissue increased with the severity of the cleft. There was an increased amount of connective tissue and significantly less muscle tissue in the cleft lip than in the normal. There was no evidence of degeneration, regeneration, necrosis or phagocytosis in the cleft lip muscle. The arrangement of muscle tissue in different types of clefts was studied. The importance of identifying the intrinsic and extrinsic muscle bundles in the cleft lip and repairing them separately was discussed. Histochemical studies showed a reduction in the mean diameter of both type 1 and type 2 muscle fibres in the cleft lip. Electron microscopy confirmed that these fibres were hypotrophic. The cleft lip had a significantly higher percentage of type 2 muscle fibres than the normal. This could possibly be due to delay or arrest in the transformation of type 2 fibres to type 1. On ATPase staining fibre type differentiation was normal. On NADH and SDH stained specimens fibre type differentiation was impaired. The majority of fibres showed an intense reaction with these stains with focal darkly stained areas. Electron microscopy showed these to be mitochondrial aggregates. Some of these mitochondria showed abnormalities in the crystal arrangement. Reduction in the muscle quantity and increase in the connective tissue in the muscle layer suggest tissue damage. Reduction in the diameter of the fibres with ultrastructural features of hypotrophy implies possible arrest or retardation of growth of muscle fibres. Mitochondrial abnormalities seen in the cleft lip muscle were similar to that of ischaemic muscle. The possibility that hypoxia may have an association with the pathogenesis of clefting was discussed. Experimental animal studies and human foetal studies are needed to clarify the possible relationship between hypoxia and clefting.
Effects of calcium phosphate solutions on human dentine in vitro and on the dentine and pulp of the ferretthe (Mustela putorius furo) in vivo.
(University of Peradeniya, 1975) Samarawickrama, Dayananda Yasasiri Dias
This thesis is presented in 6 chapters. Chapter 1 reviews the structure and reactions to external stimuli. of human dentine. A critical examination of the chemical processes that initiate and regulate mineralization in biological systems is followed by an assessment of the role of synthetic mineralizing fluids in the remineralization of dental hard tissues. Chapter 2 describes a pilot study; having appraised the relevant methodology, the study demonstrated that it is possible to increase the mineral content of human dentine in vitro by exposure to calcium phosphate solutions.. The main in vitro study is presented in Chapter 3. It was found that exposure of human dentine to calcium phosphate solutions containing either 5 or 10ppm F resulted in the formation of a layer of mineral on the surface, occluding the tubule lumina. This was accompanied by a fall in pH and in the ionic concentrations of Ca, P and F in solution. Electron and X-ray diffraction studies identified the mineral formed as apatite. A study of the effect of the formation of this layer of mineral on the adhesion of polycarboxylate cement and composite resin to dentine is presented in Chapter 4. A threefold increase in adhesive bond strength was observed, which was sustained, over a 6 month period of immersion in water. The effects of calcium phosphate solutions on dentine and pulp of the ferret were also studied, and this forms Chapter 5. While all the solutions were non-injurious to the pulp, only the solution with 10ppm F caused an increase in radio-density of dentine. A summary with guidelines for further work is to be found in Chapter 6.
Efficient algorithms for job scheduling in parallel systems
(University of Peradeniya, 2012) Siyambalapitiya, Ruwanthini
In this study, the job scheduling problem in parallel systems is addressed. It can be stated as the problem of allocating a set of jobs or tasks to a set of parallel processors or machines to minimize the overall execution time. It has been shown that, it is almost impossible to develop exact optimal algorithms to solve this problem, as it is categorized as a NP-hard problem. Therefore, it has been necessary to develop efficient algorithms which will lead to near optimal solutions and that can solve real world problem instances. We consider a mathematical treatment of the job scheduling problem in parallel systems. Several approximation algorithms are developed in this study. Minimizing of the makespan is the objective function considered in the study. First, more efficient single thread algorithms for the parallel job scheduling problem are developed. Then, the concept of multi-threading is used to propose several new more efficient algorithms based on the concepts of gang scheduling and backfilling, which are applicable to large scale parallel systems. In order to estimate the quality of solutions obtained, lower bounds and percentage gaps are derived. Mainly, small and medium scale test problems are used in this study, with a few large scale problems as well. However, it is shown that the results can be applied to large scale problem instances, in general. A method to determine the proximity of solutions to the relevant optimal solutions using statistical techniques is also developed. Performance evaluation of the algorithms is presented in detail. It is shown that our solutions are extremely close to the relevant optimal solutions. All the proposed algorithms are polynomial time algorithms. The random nature of the job completion time is also considered. When the number of jobs and processors are fixed, there can be an infinite number of ways of varying individual job completion times for a given total job execution time for all the jobs. Using more than twenty thousand data sets, performance of algorithms are compared. It is shown that, the performance level of the algorithms does not change even if the random nature of job completion times were considered.
High performance concrete comprising Nano and micro silica with fly ash
(University of Peradeniya, 2016) Priyadarshana, M. S. T.
Concrete is the single most widely used material and the second most consumed commodity after water in the world. Cement industry is responsible for about 5% of all man-made CO2 emissions. Obviously, cement and concrete's impact to the environment is enormous. Development of new concrete additives could produce a stronger, more workable and durable material whilst reducing the amount cement required and the resulting low CO2 emissions. Use of supplementary cementitious materials (SCMs) goes back to centuries. SCMs are commonly used in concrete mixtures as a replacement of a portion of clinker in cement or as a replacement of a portion of cement in concrete. Most widely used SCMs in cement and concrete are; blast furnace slag, siliceous or calcareous fly ash, natural or natural calcined pozzolana, burnt shale, limestone and silica fume. This study examines in detail the influence of amorphous nano silica (NS) and micro silica (MS) with fly ash (FA) as SCMs on fresh properties, mechanical properties, heat of hydration and durability of concrete. As many researchers focus on single blend of nano silica on concrete performance, the study extends its effort to see binary effects (nano silica + micro silica/ fly ash) and ternary effects (nano silica + micro silica + fly ash) on fresh and hardened properties of concrete. Under this, concrete and mortar performances are tested in both fresh & hardened states to cover properties such as consistency and setting time, heat of hydration, workability, compressive strength, splitting tensile strength, static modulus of elasticity, poison's ratio, scanning electron microscopic (SEM) analysis and thermo gravimetric analysis (TGA). Results show that NS helps to enhance concrete performance in numerous ways in combination with micro silica and fly ash. The optimum percentages of nano silica differ for different applications. NS reduces setting time when compared to MS and FA blends and help for faster construction practices. Similarly, NS increases early strength of concrete significantly, while MS and FA reduce. NS accelerates the hydration process and reacts with Calcium Hydroxide (CH) generated in the primary reaction to create more Calcium Silicate Hydrate (CSH) in the secondary pozollanic reaction, in concrete mixes in very early age. NS reduces CH gathers at interface and increase interface bond between aggregates. It could be observed that the CSH gel formations around NS particles are very effective and NS creates more nucleuses for CSH bonds. On durability, either single blend of NS, MS, FA and binary and ternary blends can give required durability. Heat of hydration of NS and MS are completely different; NS accelerate and MS retards the hydration process. For high strength, high performance concrete, binary blend (NS+FA) or (MS+FA) and ternary blends (NS+MS+FA) provide better performance than single blends.
Methodology for outcome based assessment of the employability skills of entry level engineering graduates
(University of Peradeniya, 2018) Shyamalee, M.M.G.V.
Development of employability skills in undergraduates is a vital objective of any engineering curriculum. The employability skills may differ with respect to different engineering fields and are decided by the requirements of the relevant industry and often change with time. While some of the employability skills may be measurable others may be expressed and estimated through combination of many other measurable attributes. The main objective of this study is to establish a methodology to assess the outcome of the employability skills of entry level engineering graduates with respect to the employer expectation. To achieve this objective, procedures to extract required employability skills, to develop an employability skills model, and to estimate the expected and achieved levels of the skills by undergraduates at different stages, are developed. Further, the methodology introduces a procedure to estimate gaps between employer expectation and achievement of each skill by undergraduates at different stages. These gaps are useful in planning necessary enhancements to the existing engineering curricula. The procedures are mainly composed of questionnaire surveys for data collection, data analyses, and interpretation of results. For data analyses, Factor Analysis (FA), Multi Attribute Value Technique (MAVT) and qualitative and quantitative Gap Analysis are used. The validity, applicability, related issues, and limitations of the proposed methodology are discussed with the help of a comprehensive data analysis which is conducted based on the data collected from the civil engineering discipline. Based on the results, eight employability skills were extracted from the twenty eight measurable attributes. An overall quantitative gap of 30% was found as the gap between employer expectation and graduates' achievement as per the employers' perspective. The gap was 35% when the graduates' perspective is considered. Through the data analysis, guidelines for questionnaire preparations, remedial actions for the issues encountered and finally the basic steps of the proposed methodology are presented. The methodology can be applied to any engineering education programme that needs regular monitoring, evaluation and feedback based improvements owing to the fact that the expectations of employers are changed parallel with the economic situation in the country.
Optimization of the performance of microstrip patch antennas and arrays by using genetic algorithms
(University of Peradeniya, 2014) Jayasinghe, Jeevani w.
Microstrip patch antennas (MPAs) are increasingly being used in the areas of cellular radio systems and short range radio links such as Bluetooth and wireless local area network (WLAN). These antennas can be mounted easily on hot-spots, lap-tops, mobile phones etc. due to their low volume, light weight, simple planar configuration and integrability with other electronic components. With the rapid development in the wireless communication systems, demand for broadband/multiband and high-directivity MPAs are on the increase to provide more services for multiple users. However, conventional MPAs have some disadvantages such as narrow bandwidth, low efficiency and low gain. Hence, performance improvement of MPAs has been an interesting challenge for the antenna research community. Numerous techniques such as stacking patches, suspending patch on air, shorting the patch to ground, inserting slots and slits in the patch and/ or ground plane and optimization have been used separately or in combinations by researchers to overcome the limitations of MPAs. This thesis presents the use of genetic algorithm (GA) optimization with some of the aforementioned techniques (modified patch, air gaps and shorting) for performance improvement of MPAs. The patch geometry, shorting and feed positions, substrate material and thickness have been optimized for achieving the broadband/multiband properties, high directivities and compactness. The full potential of combined use of GA with performance enhancing techniques for MPA design has been exploited in the thesis while providing an analysis of the effects of patch geometry, substrate thickness, its permittivity, air gaps and shorting pins on the overall performance. Numerous novel broadband, multiband, miniature and high-directivity MPAs for various wireless communication applications have been designed. The proposed single element high-directivity MPAs exhibit comparable directivities with square element patch arrays of the same physical area. Simulations have been carried out in the HFSS environment integrating a home-made Visual Basic (VB) code to perform GA operations. This home-made code has been developed within the frame of the present thesis. Performance of fabricated samples has been assessed by measuring the resonant behaviour, radiation characteristics and efficiency to validate the results. Further, a novel method of using overlapping cells for coding the patch geometry in the GA optimization procedure has been introduced.
Flood risk management incorporating stakeholder participation and climatic variability
(University of Peradeniya, 2011) Nandalal, Hemalie Kalpalatha
Impacts of floods are enormous all around the world and recent events confirm their catastrophic potential. Mitigation of damage due to floods is undoubtedly important and diverse measures have been adopted for that purpose. At present the use of non-structural measures to reduce flood damage that complements traditional structural measures receives wide attention globally. Kalu-Ganga river basin in Sri Lanka experiences floods very often. This thesis presents a methodology to develop a Decision Support System (DSS) for the management of flood risk in the Kalu-Ganga river basin in a varying climatic condition incorporating views of stakeholders. Quality and quantity of data available is a major set back for flood studies carried out in developing counties. The study commenced with an extensive investigation of geospatial data available for flood modelling of the Kalu-Ganga river basin and adjusting them as required. Subsequently, necessary screening tests were carried out for hydrological data to investigate their suitability. A technique was proposed and applied to identify trend of extreme rainfall in the basin based on Gumbel parameters estimated for 30 year long periods, which indicated an increasing trend. Rainfall for 100 year return period was determined using the proposed methodology for the next 30 year periods. Software HEC-GeoHMS and HEC-GeoRAS, as tools of ArcMAP, were used to develop geospatial data for use with HEC-HMS rainfall-runoff model and HEC-RAS flood inundation model, respectively. The HEC-HMS based model was calibrated and verified for the river basin and subsequently used to determine runoff due to the 100 year rainfall. Afterwards, the HEC-RAS based model was applied to establish flood extents and depths in the basin due to that rainfall. Risk is a combination of hazard and vulnerability. In the study, flood depth and inundation area were considered to be hazard factors while population density and dependency ratio were taken as vulnerability factors. These factors were determined at the lowest administrative division level, Grama Niladhari Divisions (GNDs), in taking decisions on flood relief work by the government. Based on these hazard and vulnerability factors, risks were estimated for the entire flood affected GNDs in the river basin initially using the conventional risk assessment approach. Then a novel methodology was developed and applied to assess the risk assuming the above factors as fuzzy variables, which takes their uncertainty into account explicitly. Suitable fuzzy membership functions were proposed and used to represent the hazard and vulnerability factors. Comparison of the results obtained from the two approaches with flood relief expenses incurred at GND level due to a recent flood event indicated that the proposed fuzzy based method, which takes uncertainty in the determination of hazard, vulnerability and risk levels into account, as providing more realistic results. An investigation was carried out to identify the major stakeholders involved in the management of flood risk in the Kalu-Ganga river basin. After identifying the flood affected people as the most important stakeholder, a questionnaire survey was carried out to find the best possible adaptation approach for flood impact mitigation. A model was developed to decide the best way to invest funds to achieve the optimum adaptability of the flood affected people. Finally, a DSS was developed based on all the information and results. The developed DSS is a prototype web site that provides information for decision makers at different administrative levels including the general public.
Carbon nanotube based efficiency enhancement and numerical modelling of organic bulk heterojunction solar cells
(University of Peradeniya, 2016) Abeygunasekara, W. L.
This thesis covers both experimental and modelling work regarding the organic solar cells. The performance of organic solar cells is often hampered by the poor charge extraction from the device active layer. The experimental section of the this research work deals with enhancing the extraction of the photo-generated charge carriers from the active layer which would lead towards better device efficiency values. Single walled carbon nanotubes are the charge extractors of choice in this work, and two distinct approaches are employed for incorporating the carbon nanotubes to the devices. The first approach is based on the previous work of similar manner and is investigated using devices based on well a characterized active layer polymer blend Poly(3-hexylthiophene- 2,5-diyl) (P3HT) and [6,6]-Phenyl-C61-butyric acid methyl ester (PC60BM). The second approach presented is novel and derived to overcome the shortcomings of the first approach. This approach is investigated using devices based on a newer and much better performing polymer blend Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5- b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) and [6,6]-Phenyl-C71-butyric acid methyl ester (PC70BM). The second part of this thesis deals with modelling of organic solar cells. A funda- mental physics based numerical model is derived for donor acceptor polymer based bulk heterojunction organic solar cells. The derived model focuses on the optical absorption and charge extraction of the modelled device. The model is capable of predicting. the device performance for different device architectures, different active layer polymer blends and different charge extraction layers and end contacts as well. Using the de 24 AUG 2018 in detail for both optical and electrical performance, and the active layer thickness optimization is carried out. The model is used to investigate the effect of absorption profile shape, charge carrier mobility of each type of charge carrier and device architecture on the device performance and the suitable device architectures for each polymer blend mentioned above have been identified for the best device performance. In addition the model is used to investigate the impact of performance enhancement techniques such as optical spacers and charge extraction layers and their effect on both device optical performance and overall device performance have been quantified.
Appropriate finite element method for particular inverse problems- special mesh generator
(University of Peradeniya, 2008) Krishnakumar, Sabapathy
Research effort has increasingly focused on extending the now well-established finite element analysis to the inverse problems of design optimization. For the purpose of optimization, an electromagnetic design is fully described by variables whose values have to be determined in order to obtain a design that satisfies specified performance criteria. An optimal design process is solving a sequence of analysis problems. An inverse problem can be either a synthesis problem or an identification problem. The latter always has a solution, even multiple solutions, which may be difficult to find numerically, whilst a solution may not exist for synthesis problems when the performance desired is impracticable and indeed may even be multiple in nature. This thesis concentrates on aspects of inverse problems, particularly shape synthesis optimization of electromagnetic devices in relation to a suitable mesh generator. Computation of derivatives is involved in both optimization and force computation. But the computation of derivatives with the Finite Element Method is difficult. The main contribution of this thesis is a special mesh generator to compute derivatives accurately and easily addressing the problem of lack of C1'continuity of the object function. Applications in optimization and force computation with this mesh generator are presented. Force computation by the virtual work method is easy but not used because of the problem of derivative accuracy. So far more difficult methods are used. When applied to force computation this mesh generator makes computations by the virtual work principal accurate as shown in this thesis. The summary of the main part of this work is reported in a journal paper (http://www.elsevier.com/wps/find/journalabstracting.cws_home/505656/abstracting#abstr acting) and the paper is reproduced in the Appendix.
Essays on the impact of workers' remittances on key macroeconomic variables in Sri Lanka
(University of Peradeniya, 2021) Aslam, Ahamed Lebbe Mohamed
In recent years, researchers have increasingly paid great attention to investigate the impact of workers' remittances at the macro-level. Sri Lanka gains a huge income from these migrant workers' remittances every year. The migrant workers' remittances in Sri Lanka are identified as the 1st external source of income compared to others. However, researchers have not examined in detail how workers' remittances influence the economic development of Sri Lanka through the variables of consumption expenditure, human capital formation, financial development and economic growth at the aggregate level. In developing countries, these are the research topics of current interest among the scholars and academia. If the influence of workers' remittances on such variables is investigated at the aggregate level it will be easy to measure scientifically to what extent workers' remittances have a potential role to play in determining the economic development of Sri Lanka. Due to the lack of research in this area, this study is undertaken with the overall objective to test the impact of workers' remittances on Sri Lankan economy for the period of 1975-2017. In order to achieve the overall objective, this study established four self-contained essays. Each of them has a separate objective. In this study, analytical techniques such as exploratory data analysis (EDA) and inferential data analysis (IDA) were employed to test the objective of each essay. Further, Dynamic Factor Analysis was used to formulate an index for the variables of financial development (FD), an d human capital formation (HCF). The EDA used the tools of scatter plots and confidence ellipse with Kernel fit. As for the IDA, Unit root test, ARDL Bounds cointegration test, Pairwise Granger causality test, and Impulse Response Function (IRF ) analyses are included . The test results of EDA show that workers' remittances have a positive relationship with the dependent variables given in each essay of this study. The unit root test results given in the 1st, 3rd and 4th essays of this study confirm that the variables are stationary at their 1st difference, while the 2nd essay of this study indicates that the variables are in mixed order. The ARDL Bounds cointegration test results indicate that workers' remittances have a long-run relationship with all the dependent variables given in each essay of this study. The diagnostic test results confirm that the estimated models given in each essay are robust. The estimated long-run coefficients of workers'remittances in each essay indicate that there is the positive relationship between workers' remittances an d the dependent variables. The estimated coefficient of error correction term illustrates that the response variable given in each essay of this study moves towards the equilibrium path, respectively. The Granger causality test results given in each essay of this study indicate that workers' remittances Granger causes all response variables, whereas the estimated coefficient of err or correction term given in each essay of this study explains that there are a long-run causal relationship among variables given in each essay of this study. The IRF test results indicate that a positive shock to workers' remittances has an immediate significant positive impact on the dependent variables given in each essay of this study. Therefore, the overall conclusion of this study is that workers' remittances in Sri Lanka have a vital role in determining economic development through the macroeconomic key variables of consumption expenditures, hum an capital formation, financial development, and economic growth at the aggregate level. The findings of this study, it is hoped, will provide the policymakers with valuable insights into the nature of the economic development of Sri Lanka. Hence, the findings of this study could be useful for policymakers when they design development policies.
Agrobacterium Mediated Transfer Of Bacillus Thuringiensis 6E Cry Gene To Ixora Odorata
(University of Peradeniya, 2003) Bamunuarachchige, T. C.
Ixora species are quite popular among landscape architects and gardeners as hedge plants and potted ornamentals. However, infestations by pests such as Ixora leaf webber, flower webber, green horned caterpillar and looper caterpillar have become a threat to the commercial exporter, especially with strict quarantine regulations under which presence of a single pest egg may spell disaster. Most chemical methods adopted have hazardous effects on the environment and other beneficial insects and therefore, are unpopular among the buyers. As an alternative Ixora odorata var. vulcan was transformed with the cry gene of Bacillus thuringiensis strain 6e by Agrobacterium mediated gene transfer. In the process, an effective plant regeneration procedure and a gene transfer system were developed. The cry gene of Bacillus thuringiensis strain 6e was isolated, purified and cloned into the Xbal site of the T-DNA region of the Agrobacterium vector pLG121Hm via an adapter. Recombinant pLG121Hm was transferred to Agrobacterium strain LBA4404 by electroporation. Positive cry clones were confirmed by Dot blot analysis of the plasmid DNA (extracted from the electroporated strains) with Dig labeled cry probe. In vitro grown Ixora odorata shoot tips (2cm) were co-cultivated with LBA4404, harboring the Bt 6e cry cloned binary vector pLG121Hm. Co-cultivated explants were transferred to shoot multiplication medium ('/2 MS with 2mg/l BAP and 500mg/l cefotaxime) and incubated at 25001ux with a 16h photoperiod. After 4 weeks the axillary shoots were screened on selective medium (Vz MS supplemented with 200mg/l hygromycin). Hygromycin positive plants were used for the PCR analysis and Southern blot analysis. PCR analysis of the putative transformants, carried out with gits specific primers, produced the expected 1.680kb fragment in all the hygromycin positive transformants. Southern blot analysis of these with the Dig labeled Bt 6e cry probe produced positive results. The positive results of both, the PCR analysis and the Southern blot confirmed genomic integration of the Bt 6e cry gene. The transformation efficiency was 20% for the shoot tips whereas it was 40% and 30% for callus and leaf disk transformations respectively but the inability of proper regeneration made both these techniques redundant.
Teaching environment related activities at key stage one to help children in developing science process skills to attain scientific literacy in future
(University of Peradeniya, 2006) Vitharana, P. R. K. A.
Today we live in a world filled with scientific innovations due to the advancement of science and technology. Therefore society is complex and rapidly changing than ever before. In order to face the dynamic nature of the 21ˢᵗ century, an individual should possess multiple skills. The developed countries like USA are aiming to produce scientifically literate citizens to succeed challenging situations in the world. Although we are a developing nation we have to face the global society. However, this cannot be achieved within one or two years and it should start from primary level. According to the primary education reforms introduced in 1997, the primary - cycle of education has been divided into three key stages as key stage one — grades 1 and 2, key stage two ~ grades 3 and 4 and key stage three — grade five. Primary curriculum consists of four main subjects and science is integrated in Environment Related Activities (ERA.) The aim of this study was to help children in key stage one to develop science process skills through the subject ERA, that are required to be a Scientifically literate adult in future. In order to achieve the aim of the study it was conducted in three phases. In the first phase data were collected relating to ERA using classroom observation, interviews and diagnostic questionnaire. In the classroom observation twelve teachers from three schools were observed while teaching ERA and detailed fieldnotes were prepared for each lesson. With the help of the fieldnotes detailed transcripts were made with the objective of understanding the real situation in the classrooms. During the second phase, activities were planned in different themes of ERA to develop process skills of children. In the third phase those activities were piloted in three selected classrooms. Classroom observation was conducted and fieldnotes were prepared. The necessary improvements were made with the data obtained from observation and the feedback obtained from teachers. Data obtained from different sources were analysed and identified the weaknesses in teaching ERA, the types of activities suitable for developing process skills and how children developed process skills through suggested activities. It was evident from the study that many teachers had difficulties in teaching sciencerelated components of ERA due to the lack of subject matter knowledge and it led children to develop misconceptions. The students’ active participation, which is expected in the student-centred teaching, was not observed in most of the classrooms. Almost all the teachers had weaknesses in the area of professional skills. Among the most prominent of those were the introducing lessons, questioning, planning lessons, organizing groupwork and use of teaching aids. 85% of teachers were not competent in developing process skills of children especially due to the weaknesses in professional skills. Children enjoyed and actively participated in introduced activities. Children developed process skills when they engaged in simple activities with the proper guidance of the teacher. Teachers’ responses towards suggested activities indicated that children were very interested in learning through such activities and teachers motivated children to be inquisitive and investigative. Children in key stage one developed misconceptions due to the limited science background of teachers. Although there were number of Opportunities in the ERA syllabus to develop science process skills of students, they were rarely given proper guidance for that which is required to be a scientifically literate adult in future. The subject matter knowledge as well as the professional skills of primary teachers should be strengthened through workshops, allowing them to actively involve in activities where they could understand their own misconceptions and weaknesses.
Taxonomy and natural history of bees in selected areas of Sri Lanka
(University of Peradeniya, 2004) Karunaratne, Inoka
Prior to this study, taxonomic work on bees of Sri Lanka had been conducted entirely by overseas scientists commencing in 1897 and leading to the Smithsonian Surveys (1975-1986). These studies have documented 137 bee species in 27 genera. Information on their natural history is completely lacking and only a few specimens have been deposited in Sri Lanka. In the present study (a) bees collected from several districts, agroecological regions and habitats were identified (b) their floral relationships and nesting habits were recorded, (c) the subfamily Nomiinae was reviewed, (d) and bees diversity was determine in selected sites. A total of 137 bee species in 35 genera and 3 families were recorded. These included 20 previously unrecorded species and 5 genera and a species new to Science. Based on the location of the 29 collection sites, the Low Country Dry Zone, middle peneplain, and the agricultural habitats harboured the highest number of species. Floral hosts consisted of 167 species in 115 genera and 44 families. Weeds were the most preferred hosts (129 spp.) followed by crops and trees. Flowers of 6 naturalized plant species attracted an unusual number (> 20 species) of bees. According to pollen relationships, 131 bee species are generalists and 7 species are pollen specialists. Twelve species of bees are buzz pollinators of crops whose pollen is concealed in anthers. Pollen from 69 floral hosts in 27 plant families when microscopically examined and grouped into 12 pollen classes. Several stem nesting (16 spp.), ground nesting (13 spp.) and hive building (4 spp.) bees were recorded, Certain species were recorded only from their nests. Review of the subfamily Nomiinae resulted’ in 22 species in 11 genera. Sampling in different locations/habitats of the Knuckles Forest Reserve gave the highest Shannon Diversity Index for agricultural habitat in the Semi Evergreen Climatic Zone. Descriptions. identification keys, locality details and floral hosts are given for the 137 bee species recorded.
Taxonomy and distribution of hard ticks (Ixodidae) in selected areas in Sri Lanka and significance of the transmission of tick borne diseases
(University of Peradeniya, 2014) Liyanaarachchi, D. R.
Ticks are the most important ecto parasites of animals that cause great economic losses in several ways including the transmission of diseases. They are constantly having interactions with their natural environment affecting the risk of infection by tick-borne pathogens. Polymerase chain reaction is used to identify causative agents of tick borne diseases.The objectives of this study were to assess the distribution, host preference of tick species on domestic and wild animals and in humans of Sri Lanka providing detail description of taxonomical characters of each adult male and female tick species collected from this study with identification keys to all tick species reported in Sri Lanka. Moreover, to assess the questing tick diversity in forests and domestic environments and their abundance in forest area in Kandy district in relation to ambient temperature, relative humidity and rain fall.Further, to identify tick vectors for spotted fever and Babesia canis. Ticks were collected from animals by field visits, wild life parks, animal clinics, and through civilians. Flagging method was . carried out to collect questing ticks from Randenigala and Hantana forests and adjoining pastures, also from pastures in villages. Moreover, ticks infesting in human body were collected from Kandy district.Twenty six species were identified infesting on animals and questing on ground. PCR was conducted to spotted fever and B. canis. Taxonomical characters of adult tick species were illustrated and identification keys were prepared. Some species showed host preference and number of tick species on animals was higher than recorded. Ticks had expanded their geographical boundaries and host range. Dermacentor auratus, Haemaphysalis turturis, H aculeata, H hystricis, and H kyasanurensis , which were previously recorded only on wild animals were recorded on domestic animals. Immature D. auratus and Amblyomma testudinarium were abundant on humans and questing on human habitats . Spotted fever was positive from A. testudinarium, A. clypeolatum, A. javanense of wild animals and Rhipicephalus sanguine us of a dog, following Babesia canis from R. microplus and R. sanguineus. Wild animals could serve as natural hosts for zoonoses and dogs are significant agents to spread ticks between wild and domestic environments. This gives an alarming warning that even pathogens of diseases which unidentified yet in Sri Lanka could be introduced to humans via these animals.

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