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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 17 (2001) 1-4 Initial studies on
unusual behaviour of ground resistivity at Ussangoda iron deposit The soil resistivity was measured at Ussangoda, in Hambantota District using the Wenner array sounding method to a length of 140 m and to a maximum depth of 30 m. A very low resistivity pockets were observed near the surface as well as to a certain depth. The results revealed that the observed resistivity values in the area measured was lower in the order of approximately 100 times compared to the measured values in other districts. The studies carried out by the Ceramic Research and Development Centre (CRDC) revealed that the higher percentage of approximately 25% of the Fe2O3 was contained when investigated a sample to a depth of 1 m. Back to content page |
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 17 (2001) 5-12 Determination of optimum
dimensional parameters for low cost noise attenuators for generators The splitter attenuation are widely used for noise abatement of generators. Normally in splitter attenuators rectangular duct is split into several such sections, each lined with sound absorbing materials. The acoustic performance of an attenuator depends on factors such as sound absorption coefficient of the lining materials, thickness of the absorbing lining, width of air gap and length of attenuator. Two adjacent reverberation rooms are arranged with an opening between in which the variable test attenuator is installed. An approximately diffuse sound field is produced in one room with required sound pressure levels in pure tones. The "Sound Transmission Loss" (SLT) through the attenuator was determined using a probe microphone. The test was carried out in the frequency range 0f 250 Hz to 4000 Hz and it was repeated with varying above parameters one at a time. Several engineering aspects are incorporated in the design of the enclosure. The first, and probably the most paramount, are the acoustical effects of the enclosure itself. The second important consideration for the enclosure desing involves the heat transfer characteristics. The requirements of cooling air to the generator are discussed. The results revealed that attenuator design is a compromise between acoustic performance, different size (height, width and length) and material cost. Low cost noise attenuators could be designed with good acoustical performance to suit the frequency spectrum of various generators.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 17 (2001) 13-20 Development of an
electronic control IC safeguard system for EPROM erasers An EPROM can only be erased using UV light. It requires a specific UV frequency of 253.7 nm for this task and a correct exposure time to prevent overexposing the IC. The exposure time is a function of the intensity of the UV source. The excessive exposure will slow down the access time of EPROMs. A study was carried out to overcome the instrumental problem by using 27XX series EPROM Ics and a fully automated user friendly control system was built. The laboratory tests show that the control system can protect the EPROMs from over-exposing. The system can also be used as a data reader for EPROMs.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 17 (2001) 21-29 Construction of a high
speed buffer amplifier to measure lightning generated vertical electric
fields A high-speed buffer amplifier circuit was constructed with a buffer amplifier IC OPA633 that can be coupled to a paralle plate antenna via 60 cm coaxial cable to measure the lightning generated vertical electric fields. The use of a high speed buffer amplifer isolates the high impedance of the antenna and offers enough power to drive the signal from the antenna to the recording unit through a coaxial cable. The electric field measured by this circuit represent the actual strength of the electric field normal to the ground. According to the frequency response of the circuit, it is seen that the circuit is suitable in recording lightning generted electric fields up to Mhz region. It has been successfully used in field tests in recording lightning generated electric fields during the months of December and January.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 17 (2001) 30-36 Performance comparison
between the magnetic direction finding technique and time of arrival
technique A study was carried out in order to understand the strengths and weaknesses of two popular lightning locating systems namely the wide band magnetic direction finding category (sometimes referred to as IMPACT sensors) and the time of arrival category (TOA sensors) which are used world-wide today. For IMPACT sensors, it has been shown that with three stations having angular accuracy limited to 20 to 30 , strike location can be reconstructed up to a few km's near the centre of the network. The accuracy roll off gradually when one moves away from the antennas extending up to few tens of km's over 400 km distance. The estimates of the location accuracy in TOA systems show that they are accurate up to 300 m near the network cantre which degrade up to a few km's for large distances (over 400 km).
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 17 (2001) 37-43 A PC based low cost data
acquisition system for physics applications A simple low cost DAQ system was built including most of the general options available in commercial DAQ systems. Device contains two channel 8-bit ADC, two channel 8-bit DAC, reference voltage selector, 8-bit digital input, one 8-bit register and a 8 step digital gain controller. Control software for the device was written in Delphi and assembler languages. The device can be operated at the speed of the parallel port (around 800 ksps max) and it can be implemented with a cost less than Rs. 4000.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 17 (2001) 44-51 Sinhala voice recognition
with LPC method A wide variety of techniques are used to perform speech recognition. Typically speech recognition starts with the digital sampling of speech. This paper introduces hot to digitise voice signal by using computer technology. Briefly discussed the analysis of these digitised data using Fourier transform and linear prediction. It is shown that linear prediction models are much better that Fourier analysis in Sinhala voice recognition. Experimental results showed that by selecting proper LP coefficient would generaly reduce the computational complexity and increase the voice identification capabilities.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 17 (2001) 52-57 Optical and structural
characterisation of electrodeposited CuInSe2
thin films CuInSe2 thin films were prepared on ITO coated glass substrates by electrodeposition from aqueous solution containing 0.005 M CuCl2 0.005 SeO2 and 0.01 M InCl3 at room temperature for a period of 30 minutes. To obtain better quality films, samples were annealed at different temperatures (200 0C, 350 0C and 500 0C) in Ar. XRD, optical absorption measurements, photovoltage measurements, spectral measurements and reflectance measurements were performed to characterize the films. According to the results, CuInSe2 is a p-type semiconductor. XRD shows three sharp CuInSe2 peaks of (112), (200) and (116) reflections for the samples annealed at 200 0C and 350 oC. Photovoltage of samples annealed at 400 0C and 500 0C were negligible (alomost zero). For the sample annealed at 200 0C, photovoltage was around 10 – 15 mV. The highest photovoltage of around 150 mV was shown by the sample annealed at 350 0C. According to optical absorption measurements and reflectance measurements, the direct band gap was around 1.1 eV for both samples annealed at 200 0C and 350 0C. Only the sample annealed at 350 0C gave spectral responses.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 17 (2001) 58-66 Investigation of
temperature and density profile of brine in evaporating salt pans at
Palavi in north-western Sri Lanka 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.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 17 (2001) 67-76 Alteration of Electrical
conduction properties of TiO2 using V2O3,
V2O4 and Cr2O3
Effects of alteration of electrical conductivity properties of TiO2 due to V2O3, V2O4 and Cr2O3 were studied. In all three cases the conductivity increased by several orders of magnitudes and the activation energy decreased significantly, depending on the dopant concentration. The results obtained for V2O3, and V2O4 doping were approximately the same. The conductivity increased (by 6 orders up to 1.9 ´10-3 W-1cm-1) and the activation energy decreased (by ~50% down to 0.39 eV). The highest conductivity and the lowest activation energy were measured at the same dopent concentration (11%). Approximately the same characteristics were seen when TiO2 was doped with Cr2O3 however, the highest conductivity ( 1.7´10-5 W-1cm-1) and the lowest activation energy (0.35 eV) were measured when the dopant concentration was about 6%. In all cases, the properties of doped samples depend significantly on the sintering temperature of the samples. The best results were obtained when the samples were sintered at 900 0C. The XRD analyses of the doped samples find an additional peak in chromium doped TiO2 when sintered at 900 0C indicating structural changes due to the incorporation of Cr2O3 . However, no structural changes were seen in XRD analyses of V2O3 or V2O4 doped samples. This indicates a significant difference between vanadium and chromium doped samples. Back to content page |