Browsing by Author "Hewageegana, P.S."

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A Study of Temperature and Salinity Variations with Depth in Salt Pans at Palavi in North-West Region of Sri Lanka
(Annual Research Symposium, Faculty of Graduate Studies, University of Kelaniya, 2000) Hewageegana, P.S.; Amarasekara, C.D.; Jayakody, J.R.P.; Punyasena, M.A.
Effects of the Cosmological Constant on Energy and Angular Momentum of a Particle Moving in a Circle with Respect to the Schwarzschild - de Sitter Metric in Comparison with the Schwarzschild Metric
(Faculty of Graduate Studies, University of Kelaniya, 2015) Jayakody, J.A.N.K.; de Silva, L.N.K.; Hewageegana, P.S.
Considering the Schwarzschild - de Sitter space-time, many authors have explored a range of cosmological events and effects. But, the effects of the cosmological constant () on energy and angular momentum in the Schwarzschild – de Sitter space-time are not studied in depth in comparison to the Schwarzschild space-time. In this study, we obtain the expressions for total energy per unit rest mass ( ) and for angular momentum per unit rest mass ( ) not only in the Schwarzschild - de Sitter space-time but also in the Schwarzschild space-time considering a particle moving in a circular path. Then, we discuss the conditions for the possibility of circular orbits. Finally, we plot the graphs for and for against the coordinate radius of the circle for different low and high values of the central mass ( ) for positive and negative cosmological constants for the Schwarzschild - de Sitter space-time in comparison with the Schwarzschild space-time. Also, we plot the graphs for when  is negative. Considering the plotted graphs, we conclude that the effects introduced by the cosmological constant on and are negligible with the present value of the cosmological constant. But, for higher cosmological constant values, the effects on and are known to be significant. However,  affects and indeed when a particle moves in a circle. According to this study, positive  creates a repulsive field and when it is negative it creates an attractive field. Accordingly, in the nonappearance of a central mass there is no possibility of circular motion when  is positive as a repulsive field would not give rise to circular motion. In the case of the Schwarzschild - de Sitter space-time and for a particle moving in a circle are less (greater) than that in the case of the Schwarzschild space-time when  is positive (negative).
Electronic Energy States in Nano Particles
(University of Kelaniya, 2012) Jayalalani, J.A.D.; Hewageegana, P.S.; Siripala, W.P.
An electron in the conduction band of a particle is nearly free to move inside the particle and this situation can be pictured as an “Electron inside a finite depth potential well”. The energy equations for this system can be derived by applying the “Time Independent Schrödinger equation” and corresponding boundary conditions in terms of one and three dimensions. In this study we have employed computer software and numerical root finding methods to obtain the numerical values of the legitimate energy states as it is more reliable than the conventional graphical methods. According to these numerical solutions, we could demonstrate that the number of allowed energy states and the spacing between adjacent levels inside a nano particle depend on both particle size and the magnitude of the attractive potential. Further, “Quantum tunneling effect” is significant when the particle size is below 20 nm and lowering the magnitude of the attractive potential, would extend the wave function far beyond its boundary. The energy levels obtained by employing the computer software and numerical root finding methods to the energy equation were plotted and compared with reported experimental observations and they are in good agreement. The most interesting size dependent property related to the semiconducting nano particles is that, we can obtain every colour of the visible spectrum by changing the size within the nano range, while the composition is unchanged.
Forecasting air pollutant concentrations in Colombo, Sri Lanka: A time series analysis of major air pollutant parameters
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Priyadarshana, D. A. D. S.; Hewageegana, P.S.; Jayasundara, D. D. M.
Sri Lanka’s commercial capital is Colombo and virtually all significant lines of financial and business activities take place in Colombo or within its periphery. However, the daily developing city of Colombo is incurring the harm of atmospheric pollution, which is one of the most dangerous disasters due to urbanization. As regards the issues of air pollution, people have diseases that affect their respiratory tracts. According to the World Health Organization, concerns have indicated that air pollution is considered one of the most lethal pollutants globally. The poisonous air particles could cause human deaths. Hence, the quantity of pollutants in the air and the conditions that affect air quality need to be analyzed. Therefore, the major aim of this research is to estimate the values of the major air pollutant parameters in the Colombo district by building predictive models for them. As for this, the historical weekly air pollutant parameters of the Colombo district were collected from the National Building Research Organization (NBRO) for the period of April 2020 to September 2023 with an aim to quantify as well as to understand the typical patterns of the air pollutants concentration in that region. Major air pollutant parameters such as PM2.5, PM10, NO2, and SO2 were considered in this study. Then, univariate time series models were fitted for the weekly data related to the air pollutants in the short time duration, and the accuracy of the models were assessed using RMSE, MAPE, and MAE values. For each parameter, ten candidate models were created separately, and the model with the lowest AIC value and all significant coefficients was selected as the best model. Also, the diagnostic tests recommended that the residuals of all models were normally distributed, exhibited no heteroscedasticity and no autocorrelation of residuals. Indicating that these models can be used in future predictions. Here, ARIMA(2,1,0), ARIMA(2,1,0), ARIMA(2,1,2), and ARIMA(3,1,1) models were discovered, for PM2.5, PM10, NO2, and SO2, respectively. The MAPE values are 15.434, 16.374, 21.130 and 17.902, respectively. The predictive modes suggest that these air pollutants have increased and decreased over time during our testing period. When analyzing the univariate time series model of various air pollution components, it was noted that the forecasted measurement values were slightly higher. The main reason is that other factors such as different air pollution parameters and meteorological factors from past data were not considered. Therefore, the accuracy of future predictions may be compromised if past data on these additional factors are not incorporated into the modeling process. Therefore, as future works, further analysis using multivariate models has been used to determine the relationship between meteorological factors and air quality parameters.
Investigation of Temperature and Density Profiles of Brines in Evaporating Salt Pans at Palaviya in the North-Western Region of Sri Lanka
(Proceedings of the 16th Technical Session of the Institute of Physics - Sri Lanka, 2001) Hewageegana, P.S.; Amarasekara, C.D.; Jayakody, J.R.P.; Punyasena, M.A.
Optimization of Thermal Insulation of a Small-scale Experimental Solar Pond
(Sri Lankan Journal of Physics, 2012) Jayatissa, N.W.K.; Attalage, R.; Hewageegana, P.S.; Perera, P.A.A.; Punyasena, M.A.
A small-scale experimental salinity-gradient solar pond, which will be utilized for the research and development in harnessing solar energy for desalination of seawater and generation of electricity, has been constructed. The pond has effective length, width and depth of 3.0 m, 2.0 m and 2.0 m, respectively, covering a volume capacity of 12.0 m3. Thermal insulation plays a major role for the successful operation of a salinity-gradient solar pond, especially when the dimensions of the pond are relatively small. The construction details of the solar pond, with particular attention to the methodologies adapted for the thermal insulation, are reported in the present work. The expected total rate of heat loss due to conduction through the thermally insulated boundary walls, assuming a bottom temperature of 90�C, has been calculated and found to be 106.3 W. Contribution from the bottom convective zone itself to this total rate of heat loss is 69 W, which corresponds to 65% of the total value. Based on this rate, the estimated temperature drop during the period with no solar radiation present in a typical day is only 0.3�C. With such a small temperature drop, it is possible to extract the thermal energy stored in the bottom convective zone during the day time, continuously, while maintaining the stability of the solar pond.
Polarizability of a metallic nano-cylinder: Local random-phase approximation (LRPA).
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Asela, A.U.; Hewageegana, P.S.
We develop a method to calculate the polarizability of a nano-cylinder by taking temporal and spatial dispersion in to account where dispersion due to the Landau damping. To describe these phenomena, we developed analytical theory based on local random-phase approximation. Our theory is very general in the sense that it can be applied to any material which can be characterized by a bulk dielectric function of the form ....... The theory is applied to calculate the polarizabilities of dielectric and metallic nano-cylinders. Here we focus on calculating the transverse static polarizability of a cylindrical nanowire by taking the temporal and spatial dispersion into account. To describe these phenomena, we developed an analytical theory by solving the well-known Lindhard formula which gives one of the closed solutions in the theory of Fermi systems that explicitly gives the nonlocal dielectric response function (longitudinal) ....... We developed a simple theoretical framework for the polarizability of a nanowire that allows the inclusion of nonlocal effects. Our results are significant for thin wires and small particles, where the nonlocal effects are much more relevant. We hope that our work will be useful in studying the optical properties of nano particles in particular nanowires.
The red shifts of pulses of light which are emitted at a point on the surface of a sphere and at a point inside of the sphere comprising electrically counterpoised dust with constant uniform density as observed by an observer in a large distance away in the exterior region
(University of Kelaniya, 2013) Wimaladharma, N.A.S.N.; de Silva, N.; Hewageegana, P.S.
A sphere, comprising a special kind of matter, with electrically counterpoised dust in which all the elastic forces have been cancelled out has been considered. A static spherically symmetric solution to Einstein’s field equations has been found using a new set of boundary conditions. In introducing these new boundary conditions, we assume that the radial coordinates in and out of the sphere need not be the same and we are guided by the notion of what may be called proper distances and proper times of two observers on either side of the sphere .In these new boundary conditions we replace ordinary partial derivatives by generalized partial derivatives in curvilinear coordinates. Then the solution takes the form  2 2 2  2 2 2 2 2 1                             dr r d l r c dt l r ds   0  r  a   2 2 2 2 2 2 2 2 2 2 1 1 1                   dR R d R A c dT R A ds R A  where          l a l a A  2 2 ,       l r  is the solution of the Lane-Emden equation y r lx dx dy x dx d x        , 1 2 3 2 , l is a constant of dimension length , a is the coordinate radius of the sphere. In our approach r  a in the matter-filled region corresponds to R  Ain the region without matter, outside the sphere. The red shift of a pulse of light emitted at a point on the surface of the sphere as observed by an observer who is at a large distance in the exterior region of the sphere is calculated. This valueequals to                                 l a l a l a l a    when the observer is at infinity. The comparison of this value with the value for the red shift obtained using the metric derived using the standard (Lichernowicz) boundary conditions which says that the metric coefficients and their partial derivatives are continuous across the boundary of the sphere when the observer is at infinity is also done. It is shown that the values obtained for the red shifts are the same irrespective of the boundary conditions used. The red shift of a pulse of light emitted at a point inside of the surface of the sphere as observed by an observer who is at a large distance in the exterior region of the sphere is also calculated and it is shown that the value obtained is different from the value obtained using the metric derived using standard (Lichernowicz) boundary conditions.
A study of temperature and salinity variation with depth in salt pans at Palaviya in the North-Western region of Sri Lanka
(University of Kelaniya, 2000) Hewageegana, P.S.; Amarasekara, C.D.; Jayakodi, J.P.R.; Punyasena, M.A.
A theoretical study of identifying co-rotation radii and galactic resonances of spiral galaxies
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Jeewanthi, K.G.V.; Hewageegana, P.S.; Abdeen, S.
This study delved into the dynamic behaviours of spiral galaxies, employing a robust approach to analyse co-rotation radii and galactic resonances within the framework of Density Wave Theory. It aimed to develop new methods for identifying resonance locations and co-rotation radii, conduct comparative analyses across ten diverse spiral galaxies, predominantly grand-design spiral galaxies with different pattern speeds, and validate these methods against existing techniques. The first method used rotation curve analysis to identify Inner Lindblad Resonances, 4:1 resonances, co-rotation radii, and Outer Lindblad Resonances, utilising two pattern speeds from literature for comparative purposes. The first pattern speeds yielded co-rotation radii closer to literature values for galaxies NGC 1566, NGC 4254, NGC 4303, NGC 4321, and NGC 5247. Conversely, for NGC 5194 and NGC 5248, the second pattern speeds yielded better alignment. However, NGC 1365 and NGC 5236 showed deviations from literature values for both pattern speeds, while NGC 4535 posed challenges in determining its corotation radius. A comparative analysis of co-rotation radii against mean literature values indicated successful alignment despite significant uncertainties for NGC 1365, NGC 4254, and NGC 4303. The second approach used 3D surface intensity plots to identify resonance regions, focusing on low star formation areas, enhancing understanding of dynamic structures. It compared co-rotation radii with literature values, highlighting probable regions and addressing uncertainties, particularly in NGC 1365, NGC 5236, and NGC 5247. Methodological precision was crucial, given the nuances revealed by these plots. Comparing Method I and II, Method I aligned better with literature values for NGC 4254, NGC 4303, NGC 4321, NGC 5194, NGC 5247, and NGC 5248, while Method II showed closer alignment for NGC 1566 and NGC 4535. NGC 1365 and NGC 5236 exhibited discrepancies in co-rotation radii values across both methods compared to the literature. The third methodology employed theoretical calculations to align empirical observations with theoretical predictions, enhancing the understanding of galactic resonant dynamics. NGC 4535 was excluded due to data limitations. The systematic approach derived theoretical resonance locations for co-rotation radii, outlining an analytical roadmap. Comparative analysis between empirical and theoretical resonance values revealed close alignment for most galaxies, enriching insights into resonant phenomena within galactic systems. The fourth method involved measuring spiral arm pitch angle measurements across multiple wavelengths (3.6 μm, 8.0 μm, B-band, Hα). A custom Python code facilitated the overlaying of spiral arm patterns from different wavebands onto FITS images, enabling detailed comparative analyses. The identification of crossing points, coupled with consideration of pitch angle uncertainties, offered a sophisticated approach to delineating resonance locations on the galactic disk. Challenges in measuring and comparing pitch angles highlighted the complexities of detecting outer arms and resolving discrepancies across imaging wavelengths. In conclusion, each method employed in this study has its unique strengths and challenges while no single method was universally superior, as galaxies showed varying compatibility with each approach. These findings enhance the understanding of galactic morphology and evolution, including implications for galactic habitable zones.
The velocity of a particle relative to an observer instantaneously at rest coinciding with the point through which the particle passes in a spherical distribution of matter comprising electrically counterpoised dust with constant uniform density
(University of Kelaniya, 2013) Wimaladharma, N.A.S.N.; de Silva, N.; Hewageegana, P.S.
A sphere comprising a special kind of matter, electrically counterpoised dust in which all the elastic forces have been cancelled out, has been considered. A static spherically symmetric solution to Einstein’s field equations has been found using a new set of boundary conditions. In introducing these new boundary conditions, we assume that the radial coordinates in and out of the sphere need not be the same and we are guided by the notion of what may be called proper distances and proper times of two observers on either side of the sphere. In these new boundary conditions we replace ordinary partial derivatives by generalized partial derivatives in curvilinear coordinates. Then the solution takes the form  2 2 2  2 2 2 2 2 1                             dr r d l r c dt l r ds   0  r  a   2 2 2 2 2 2 2 2 2 2 1 1 1                dR R d R A c dT R A ds R A  where          l a l a A  2 2 ,     l r  is the solution of the Lane-Emden equation y r lx dx dy x dx d x          , 1 2 3 2 , l is a constant of dimension length , a is the coordinate radius of the sphere . In our approach r  a in the matter-filled region corresponds to R  A in the region without matter, outside the sphere.The velocity of a particle relative to an observer instantaneously at rest coinciding with the point through which the particle passes has been calculated for this metric. Using these values, a minimum value for a measure of energy with which the particle has to be projected at the center of the sphere, to reach infinity has been calculated to be               l a l a l a c   where c is the velocity of the light. A minimum value for a measure of energy with which the particle has to be projected at the center of the sphere, to reach infinity has also been calculated for metric derived using standard (Lichernowicz) boundary conditions which says that the metric coefficients and their partial derivatives are continuous across the boundary of the sphere. It is shown that we have the same value irrespective of boundary conditions used. Also a minimum value for a measure of energy with which the particle has to be projected at the center of the sphere, to reach the exterior region of the sphere has been calculated to be       l a c  . The comparison of this value with the value obtained for the metric derived using standard (Lichernowicz) boundary conditions is also done and it is shown that these two values are the same irrespective of the boundary conditions used.