Physics
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Item Ti/Cu2O photoelectrodes in photlectrolytic solar cells(proceedings of the Technical Session of Institute of Physics, Sri Lanka, 2003) Wijesundera, R.P.; Susantha, P.K.K.; Jayakody, J.R.P.; Siripala, W.Cuprous Oxide thin films deposited on Ti substrates were investigated as photoelectrodes in a photoelectrochemical cell. Electrodeposition was carried out in an electrochemical cell containing aqueous solutions of cupric acetate and sodium acetate.X-ray diffraction (XRD) and scanning electronmicrographs (SEM) confirmed that the films are polycrystaline Cu2O films. X-ray photoelectron spectroscopy (XPS) revealed that the films are pure CU2O and there are noanyother phases. The photoresponse of the films in a PEC produced a zero bias photocurrent (XBPC) with an n-type photoresponse. Comparing with the thermally grown Cu2O films, an enhanced spectral response in the long wavelength region could be obtained with electrodeposited Cu2O on Ti substrate. A charge separation mechanism at the Ti/Cu2O interface isproposed as the possible reason for the observed spectral response enhancement.Item 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.Item 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.Item 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.Item 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.Item 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.Item 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.Item 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.Item NMR Studies of Mass Transport in High-Acid-Content Fuel Cell Membranes Based on Phosphoric Acid and Polybenzimidazole(Journal of Electrochemical Society, 2007) Jayakody, J.R.P.; Chung, S.H.; Durantino, L.; Zhang, H.; Xiao, L.; Benicewicz, B.; Greenbaum, S.G.Mass-transport studies of phosphoric acid (PA)-doped meta-polybenzimidazole (PBI) fuel cell membranes are described. In this study, the fundamental differences in transport properties between m-PBI/PA membranes prepared by conventional imbibing procedures and the polyphosphoric acid (PPA) process are explored. The membranes were characterized by proton conductivity and multinuclear (1H and 31P) magnetic resonance measurements. Both short-range and long-range dynamical processes were investigated by spin?lattice and spin?spin relaxation time measurements and by pulsed ?eld gradient diffusion, respectively. Comparative data for pure PA and PPA are included. The high proton conductivity(0.13 S/cm at 160�C) of the PPA-processed membranes is correlated with rapid proton self-diffusion (3 x 10?6 cm2/s at 180�C). The 31P results reveal the presence of both PA and the dimeric pyrophosphoric acid and indicate strong interaction between the phosphate groups and the m-PBI matrix, with negligible anionic transport for both kinds of membranes. The higher concentration of PA in the PPA-processed membranes and differences in membrane morphology may provide an additional proton-transport mechanism involving rapid exchange between the PA and pyrophosphoric acid species.Item UV absorption properties of natural solutions(2008) Wijesiri, W.D.S.; Jayatissa, N.W.K.; Jayakody, J.R.P.Electromagnetic radiation is classified into types according to the frequency of the waves such as radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. UV radiation is a part of the electromagnetic spectrum emitted by the sun, and is divided according to wavelength into three regions known as UVA, UVB and UVC. The UVC is completely absorbed by the atmospheric ozone, water vapor, oxygen and carbon dioxide. However, both UVA and UVB are of major importance to human health. These radiations may penetrate into the skin and eyes, causing the adverse health effects, such as skin cancers, cataracts and immune suppression. The objective of this work is to support the mankind to prevent from the kind of threats and conflicts that they will face due to the harmful solar radiation using natural and available materials. Initially the study is focused to identify the UV absorption properties of natural materials. In order to achieve this goal several fruit juices, vegetable juices and plant leaf extractions are analyzed by using UV /VIS spectrum. The sample path length (1 Omm) and concentration (0.75mol/l & pH = 2.3) are kept constant during the experiment. The Citrus family exhibited interesting UV absorption behavior compared with the other tested materials. The experiments are carried out using both distilled water and isopropyl alcohol as solvents. Especially chlorophyll of the plant extract is removed by dissolving it in isopropyl alcohol and filtering it through activated carbon. When electromagnetic radiation passes through the compound, energy from the radiation is used to promote an electron from a bonding or non-bonding orbital into one of the empty anti-bonding orbital. The electron jump can be occurred or absorption takes place only when the energy associated with the particular wavelength is provided. In terms of Chemistry, Flavonoides are water soluble Polyphenolic molecules containing fifteen Carbon atoms. The Flavonoides, belongs to the polyphenol family, are found in most plant material and dietary sources. It is presumed that absorptions occurred in the citrus family due to the double bonds of the Flavonoides. Energy of the incident radiation is promoted electron jumps ( n:-+n:*, n-+n*, n-+a*) which caused to the absorption spectrum as discussed earlier. It is clearly illustrated that lime juice absorbed the wavelength from 290nm to 400nm where UV-B and UV-A radiations exist. Zero transmittance of incident radiation in between 290 and 400nm's for lime juice is observed in the experiment. It is interesting to find the optimal path length for zero transmittance and it determines the minimum thickness of the filter. One of the interesting applications of this finding is it can be converted any moisturizing cream into a moisturizing plus sunscreen by adding natural Flavonoides, just before the application.