Browsing by Author "Punyasena, M.A."

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A Home Made Double Slab Pyranometer for Irradiance Measurements
(Proceedings of the 44th Technical Session of the Sri Lanka Association for the Advancement of Science (SLAAS), 1988) Punyasena, M.A.; Jayasuriya, K.D.
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.
A Study of Wind Effects on Thermal Stability of Salt Pan Solar Ponds
(Annual Research Symposium, Faculty of Graduate Studies, University of Kelaniya, 2001) Punyasena, M.A.; Amarasekara, C.D.; Jayakody, J.R.P.; Perera, P.A.A.
An investigation of rain and wind effects on thermal stability of large-area saltpan solar ponds
(Solar Energy, 2003) Punyasena, M.A.; Amarasekara, C.D.; Jayakody, J.R.P.; Perera, P.A.A.; Ehamparam, P.
An investigation of the thermal stability of large area saltpan solar ponds under different climatic conditions is presented. The study focuses on time taken by the pond to reach its stable conditions with heavy rainfall and the effect of wind-mixing process for the stability of the pond. Investigations were carried out over a period of 60 days on a large-area solar pond of 90 cm deep. The temperature and density profiles obtained 34 days after filling showed that the pond had attained its stability with a bottom temperature of 63 �C. Results reveal that heavy rainfall is the prime cause for the pond to reach stability in a time period of about 30 days. Strong wind-induced mixing prevailed during the second half of the investigation, which contributed to the erosion of the nonconvecting zone is the cause for observed destabilization of the pond. The estimated critical wind speed for complete destruction of the nonconvecting zone is about 25 km/h.
Bound state solutions of the Manning-Rosen potential
(Canadian Journal of Physics, 2013) Falaiye, B.J.; Oyewumi, K.J.; Ibrahim, T.T.; Punyasena, M.A.; Onate, C.A.
Using the asymptotic iteration method (AIM), we have obtained analytical approximations to the ?-wave solutions of the Schr�dinger equation with the Manning?Rosen potential. The energy eigenvalues equation and the corresponding wavefunctions have been obtained explicitly. Three different Pekeris-type approximation schemes have been used to deal with the centrifugal term. To show the accuracy of our results, we have calculated the eigenvalues numerically for arbitrary quantum numbers n and ? for some diatomic molecules (HCl, CH, LiH, and CO). It is found that the results are in good agreement with other results found in the literature. A straightforward extension to the s-wave case and Hulth�n potential case are also presented.
Construction and commissioning of a large area solt gradient solar pond at Palatupana salterns in southern Sri Lanka
(2003) Punyasena, M.A.; Amarasekara, C.D.; Perera, P.A.A.
Solar ponds are large-scale solar energy collectors with integrated thermal energy storage. The concept of collecting and storing solar energy using non-convective salt gradient solar ponds has been known for some time. We report here the details of construction and commissioning of a large-area solar pond built at Palatupana salterns in Southern Sri Lanka. A rectangular pond with dimensions 70 m x 35 m could retain a maximum water capacity of ~ 5000 m3. The pond can be filled to a maximum height of 2 m. The initial controlled filling of the pond to a total depth of 60 cm with a 30 cm layer of high-density brine led to formation of the three-layer stability with a maximum bottom temperature of 52 oC. Destruction of the pond stability was observed with the increase of wind speed over the pond. About three months later with the monsoon rain, the pond bottom recorded a maximum temperature of 69 oC with the reestablishment of three-layer stability at a total depth of 110 cm. The observed salinity and temperature profiles show the usual three-layer configuration, but with relatively thick upper convective zone. This situation could arise due to wind mixing of layers to a depth of about 30 cm. It is remarkable to observe that the uncontrolled natural conditions raised the bottom temperature of the pond to a maximum of 69 oC. Our results indicate wind is the major cause for mixing of layers which prevents storing of solar energy at the bottom layers of the pond. The commissioned solar pond could be used for wind control mechanism studies and controlled filling mechanisms to optimize different layers of the pond to obtain maximum bottom temperatures.
Construction and Filling of a Large-area Deep-tank Solar Pond for Harnessing Solar Energy
(Annual Research Symposium, Faculty of Graduate Studies, University of Kelaniya, 2002) Jayakody, J.R.P.; Punyasena, M.A.; Perera, P.A.A.; Amarasekara, C.D.; Kumarasinghe, M.A.S.
Construction and Filling of a Large-area Deep-tank Solar Pond for Harnessing Solar Energy
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2002) Jayakody, J.R.P.; Punyasena, M.A.; Perera, P.A.A.; Amarasekara, C.D.; Kumarasinghe, M.A.S.
Construction and performance-analysis of a 'Solar-light" for efficient use of daylight
(University of Kelaniya, 2008) Jayatissa, N.W.K.; Punyasena, M.A.
A pleasant and appealing environment, excellent color rendering, natural interior, and significant energy saving are the major advantages of using the daylight compared to the artificial lighting. Glare and heat radiation are the main drawbacks of utilizing direct sunlight for building illumination. This 'solar-light', a newly designed unit, can be used only during the day time and is operated from natural solar radiation with no additional power being required at all. It acts as a light guide which transfers the filtered visible spectrum of solar radiation from outside into the interior of the building. Solar-light that illuminates building interiors more efficiently with natural daylight, has been constructed and tested for its performance. The unit has been designed to reduce substantially the heat component of solar radiation with an IR-filter so that the building interior does not get heated up by increased cooling load due to lighting. This would considerably reduce the air-condition load of the building. The UV component of the solar spectrum is eliminated with a UV-filter installed inside the unit, thus only the filtered harmless visible spectrum is taken into the interior of the building. The Solar-light has a cylindrical shape (to minimize the internal reflection losses) with a height of 80 cm and a diameter of 26 cm. The transparent window at the top of the unit has a hemispherical shape in order to increase the effective area of the solar radiation input into the interior of the building. The small air gap between outer cylinder and reflective cylinder creates a convection path for heated air. A light-reflective coating is applied at the interior surface of the cylinder to minimize the loss of illumination. The filtered radiation finally is sent through a light diffuser also with the same diameter at the bottom of the unit before the light is finally delivered into the building. The performance of the unit has been tested in real environment and a maximum of 170 Lux was measured at the desktop height inside the building with the daylight. Diameter of the illuminated area is about 5-6 m of which the intensity variation is minimal within the . . mner regwn. A series of these solar-light units can be installed on the roofs of large buildings (ex: garments factories, ware houses etc.) to illuminate the interiors in place of fluorescent bulbs to save energy substantially reducing the electricity bill.
Daytime Variation of Temperature and Salinity Profiles in Large-Area Saltpan Solar Ponds at Palavi, Sri Lanka
(Proceedings of the 18th Technical Session of the Institute of Physics - Sri Lanka, 2002) Perera, P.A.A.; Amarasekara, C.D.; Jayakody, J.R.P.; Punyasena, M.A.
Gamow-Teller Strength from the 76Se(n,p)76As Reaction: Implication for the Double Beta Decay of 76Ge
(Physical Review C, 1997) Helmer, R.L.; Punyasena, M.A.; Abegg, R.; Alford, W.P.; Celler, A.; El-Kateb, S.; Engle, J.; Frekers, D.; Henderson, R.S.; Jackson, K.P.; Long, S.; Miller, C.A.; Olsen, W.C.; Spicer, B.M.; Trudel, A.; Vetterli, M.C.
Cross sections have been measured up to 35 MeV excitation for the 76Se(n,p)76As reaction at five laboratory angles between 0� and 15�. The incident neutron energy was 198 MeV. The distribution of Gamow-Teller (GT) strength at excitation energies less than 10 MeV was deduced by carrying out a multipole decomposition of the data. The GT strength below 6 MeV excitation was found to be less than 0.9 units, in qualitative agreement with a quasiparticle random-phase approximation calculation. The present results have been compared with data from the 76Ge(p,n)76As reaction to obtain an estimate of a lower limit for the lifetime of 76Ge for ?? decay. The estimate is in qualitative agreement with the measured lifetime.
An Introduction to Quantum Mechanics
(Stamford Lake (Pvt) Ltd., 2013) Punyasena, M.A.
Investigation of temperature and density profile of brine in evaporating salt pans at Palavi in north-western Sri Lanka
(2001) Hewageegana, P.; Amarasekara, C.D.; Jayakody, J.R.P.; Punyasena, M.A.
Measurements of temperature and density variations with depth in salt pans having a stable salinity gradient are presented. The density variation of brine has been correlated to the temperature variation with depth. The convective and nonconvective zones were identified. Gradients in salinity and temperature in the nonconvective zone were observed. Temperature and salinity were observed to remain the same throughout the convective bottom layer of brine in the ponds. The investigation has been extended to different ponds filled to different depths and storage periods of brine. A maximum temperature of around 55 0C was observed in the bottom layers while the surface remained as low as 29 0C. This is a consequence of positive salt-density gradient, which suppresses convection and allows a temperature gradient to develop downwards. The temperature measurements of different ponds filled to different heights indicate that the convective bottom layer temperature of a pond will increase if the pond is filled with brine to a higher level. These results indicate that the large area deep salt pans with long term storage periods can be used as solar ponds to collect and store solar energy in addition to the usual salt production. Based on our results we speculate that the bottom temperatures of these ponds could be increased to about 80 0C by filling the ponds to a height of about 1.5 meters. Thermal energy stored in the convective bottom layer of these ponds could be extracted for many applications. The moderate temperature desalination of seawater especially in the areas where fresh water is in short supply is identified as one of the promising applications of thermal energy stored in solar pond-salt pans.
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.
Investigation of the 12C(p,d,pi+)11B Reaction in the Quasifree Region
(Physical Review C, 1998) Benjamintz, M.; Falk, W.R.; Auld, E.G.; Campbell, J.R.; Green, A.; Korkmaz, E.; Ling, A.G.; Punyasena, M.A.; Roos, P.G.; Walden, P.L.; Yen, S.
12C(p? ,d?+)11B has been investigated in the quasifree region at energies of 370 and 500 MeV. For each energy, measurements were made at the four angle combinations of (?d,left,??,right) equal to (15�, 30�), (15�, 55�), (25�, 30�), and (25�, 55�). In addition to strong excitation of the g.s. 3/2- state, the 2.12 MeV 1/2- and 5.02 MeV 3/2- states are also excited with appreciable strength. Furthermore, a broad continuum at an excitation energy of about 20 MeV, corresponding to the 1s1/2 hole state is prominently seen. The pion differential cross section distributions exhibit maxima when the recoil nucleus momenta are at a minimum. Analyzing powers were obtained over the range of pion energies investigated. Several measurements for the 2H(p? ,d?+)n reaction are also reported. The results are compared with plane-wave impulse approximation and distorted-wave impulse approximation calculations
An investigation of the variation of shear strength of soil with its moisture content
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Bandara, P.G.R.V.R.; Punyasena, M.A.
The mechanical behavior of soil is highly dependent on its shear strength. Cohesion and internal friction angle and effective stress of soil are important factors of soil shear strength. The key objective of this study was to establish a relation between the shear strength of unsaturated soil and its moisture content. In the current study, different types of soil such as red gravel soil, mud from a paddy field, sand, soil from rubber cultivation, home garden soil and soil from an ant-hill type in Sri Lanka were used as the raw material. Before the shear strength measurement, the selected soil sample should be well dried and free from impurities. The apparatus set up was designed to measure the limiting friction force of the soil sample with the varying moisture content while maintaining a constant density in all the raw soil samples. In the present study, limiting friction force acts as the shear force of the particular soil sample. Shear stress was calculated by dividing the shear force by the contact surface area of the soil. According to soil mechanics, shear strength is the magnitude of shear stress that soil can sustain. The obtained results reveal that the moisture content has a great influence on the shear strength. The shear strength started to increase gradually relative to the increasing water content. At a specific point, the shear strength reached a peak level, beyond which it started to decrease gradually with the increase of water content. The characteristic curves of shear strength against the moisture content displayed some changing aspects according to the soil type. According to the results, the maximum shear strength was observed in the soil from the rubber cultivation and the minimum was observed in the sand sample. The maximum shear strength of the soil varied in the range (2.421 ± 0.006 − 8.500 ± 0. 266) × 102 Nm−2 . The highest value of the optimum moisture content was observed in red gravel soil while lower values of the optimum moisture contents were observed in soil from an ant-hill, mud from a paddy field, and sand. The optimum moisture content of the soil varied in the range (7-30) g. High soil moisture content is the main cause of landslides. The results of the present study can be used to get an idea about the specific moisture content which could cause a landslide. In this study, a direct comparison of maximum shear strengths of six different soil types in Sri Lanka was made and the relevant results could be useful in making predictions about the landslides that occur due to heavy rain. However, geotechnical engineers have to consider factors like geological composition, surface drainage, groundwater content, in addition the shear strength of soils in assessing the stability of hill-type lands.
Optical Design and Performance of the SASP Spectormeter at TRIUMF
(Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999) Walden, P.L.; Walton, T.G.; Miller, C.A.; Yen, S.; Abegg, R.; Auld, E.G.; Campbell, J.R.; Chakhalyan, J.; Churchman, R.; Duncan, F.; Falk, W.R.; Frekers, D.; Green, A.; Green, P.E.W.; Hartig, M.; Hausser, O.; Haddock, C.; Hicks, K.; Hutccheon, D.; Jones, G.; Korkmaz, Y.Ke.E.J.; Khan, N.; Ling, A.; Lobb, D.E.; Naqvi, S.I.H.; Olsen, W.C.; Opper, A.; Otter, A.; Punyasena, M.A.; Reeve, P.; Zhao, J.
A new Q?Q-Clamshell magnetic spectrometer called SASP has been commissioned in the proton hall at TRIUMF. The principal optical characteristics are: a solid angle acceptance of 13.5 msr, a momentum bite of 25%, a momentum resolution of ?p/p=2?10?4, and a maximum central momentum of 720 MeV/c. We describe the optical design, the magnetostatic design, the magnetic field mapping procedure, and the performance of this instrument.
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.
Study of Daytime Variation of Convective and Non-Convective Zones in Salt Pan Solar Ponds
(Annual Research Symposium, Faculty of Graduate Studies, University of Kelaniya, 2002) Perera, P.A.A.; Amarasekara, C.D.; Jayakody, J.R.P.; Punyasena, M.A.
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.