Proceedings of the Technical Session of Institute of Physics, Sri Lanka 15 (1999) 1-7

Parallel port based data acquisition system for IBM or compatible personal computers.
A.R. Dedigama and D. U. J. Sonnadara
Department of Physics, University of Colombo

A study on building a parallel port based data acquisition system for IBM or compatible personal computers is carried out. A circuit based on an 8-bit ZN448E Analogue-to-Digital Converter (ADC) was successfully constructed and interfaced through the standard parallel port of the computer. A sensor interface was constructed to allow sensros with different output voltages to be directly interfaced to the ADC. Microsoft Visual Basic was selected as the programming language. The technique discussed here can be used to create Data Acquisition systems with 100 kHz sampling speeds.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 15 (1999) 8-21

A classical trajectory Monte-Carlo study of a one dimensional model of a proton-hydrogen atom collision.
G.Bandarage and K. A. Somaratna
Department of Chemistry, The Open University of Sri Lanka

A simplified one-dimensional model of a proton-hydrogen atom collision has been studied where the proton is driven through the atom at a constant relative velocity. The phase space accessible to the electron in this problem is 2 dimensional. The classical trajectories were generated by numerical solution of Hamilton's equations. The quantum nature of the electron was approximately incorporated using a Monte-Carlo technique.

Numerical integration requires the removal of Coulomb singularities in the potential experienced by the electron. We have found a circular arc to be more efficient than a straight line or a parabola in replacing the Coulomb singularity. However, the truncation of the singularity introduces an additional parameter into the model and we report an optimum value.

Results are reported for the probabilities of excitation, charge transfer and ionisation in the model at a relative proton velocity of 1.2 a.u. Interesting oscillatory behaviour of these probabilities as a function of initial proton-proton separation is observed.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 15 (1999) 22-30

The Characteristic ageing process of insulating dielectrics considered as a design problem determined by electrical and thermal constraints
D. R. Samuel

The paper describes the complexity of change, influencing degradation, of dielectric materials functioning as electrical insulants, which seperate the current carrying conductor, from the metal body of ferromagnetic material in an electrical machine, while recommending methods, of minimising ionisation and excessive temperature, which degrade performance.

Dielectric degradation leads to shortening of effective lifetime, arising from two causes:

1. Gas ionisation from electrical potential conduction, which produces corrosive substances, which diminish the insulating property.

2. Thermal losses from energy transformation, which increases operating temperature, with disadvantages changes of dielectric properties, which degrade the insulant.

Remedies are based on dynamic correlation, and response functions, which:

1. Select dielectric dimensions by calculation, so that the electrical potential distance between design controlled ionisation potential, and the characteristic ionisation vulnerability of environmental gases in Paschen's curves, implies dielectric viability.

2. Transfer heat generated in the machine, so that the dielectric environment in the machine is minimally affected by temperature excesses.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 15 (1999) 31-34

Radioactive analysis of corals and sand at various locations in Sri Lanka
A. S. T. Ubesekara¹, C. Sumithraarachchi², and S. R. D.Rosa^{1 1}
Department of Physics, University of Colombo, ² Radio-Isotope Centre, University of Colombo

Gamma ray spectroscopy has been used to identify radio-nuclides present in corals and sand samples collected from various locations in Sri Lanka. A portable high purity Germanium detector was used to identify Gamma rays emitted from radio-isotopes. Software package AccuSpec was used for the data collection and GANAAS was used for the spectrum analysis. Quantitative analysis was based on Monte Carlo method. Sand samples from beaches of Hikkaduwa, Unawatuna, Chilaw, Tangalle, and Beruwala were collected and analysed. Coral samples collected from all the locations above except Beruwala were investigated. The presence of branching products of ²³⁸U, ²³²Th and ⁴⁰K were observed in each and every sample. It is interesting to note that the concentration of ²³⁸U is considerably larger than that of ²³²Th in corals collected from all locations. This may suggest that corals absorb ²³⁸U throughout their life span.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 15 (1999) 35-42

Computational Study of I-V characteristics of ITO/Cu₂/Metal junctions
W. M. P. L. Wijesinghe, W. Siripala, K. D. Jayasuriya and S. R. D. Kalingamudali
Centre for Semiconductor Research, Department of Physics, Univarsity of Kelaniya, Kelaniya.

A theoretical model for current-voltage (I-V) characteristics of back-to-back diode systems was developed using the ideal diode equation. A computer model was developed using the language C++ to fit the experimental data to the theoretical equation and to determine the ideality factors and reverse saturation currents of each diode. This model was tested with commercial back-to-back diode systems. The values obtained for the above parameters from the theoretical fits were in very good agreement with the standard values. The experimental I-V characteristics data obtained for fabricated ITO/Cu₂O/Metal (Au, Ag and Hg) structures were fitted to the model and values for the relevent parameters were obtained. These values indicate that the fabricated systems are back to back diodes except the ITO//Cu₂O/Hg structure. Using this model, a good understanding of I-V characteristics of metal-semiconductor-metal diodes can be gained and thereby the quality of junction devices can be tested.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 15 (1999)

Mossbauer Effect Studies of Ball-Milled Materials
K. D. Jayasuriya
Department of Physics, University of Kelaniya, Kelaniya

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 15(1999)52-58

A Study of CuInS₂ This Films for Photocoltaic Applications
R. P. Wijesundara¹, M. P. Nadesalingam¹, W. Siripala¹, K. D. Jayasuriya¹, S. R. D. Kalingamudali¹, J. K. D. S. Jayanetti² and K. T. L. de Silva^2
1 Department of Physics, University of Kelaniya, Kelaniya, ²Department of Physics, University of Colombo, Colombo 03.

Thin films of copper indium disulphide (CuInS₂) on Ti Substrate were prepared by annealing potentiastatically electrodeposited Cu-In alloy in H₂S gas at 550⁰ C. Films were characteristised by X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectral response in a polysulphide electrolyte. XRD measurements revealed the formation of the polysrystaline CuInS₂ thin films and the abscence of any other phases. SEM showed the formation of crystallites having the size about 0.2 mm. Variations of spectral response, open-circuit voltage (V_oc) and short circuit current (I_sc) with annealing in air have been studied. As deposited CuInS₂ films exhibit a direct band gap of 1.5 eV, and shows n-type behaviour when used in a Photoelectrochemical (PEC) cell. Heat treatment shows a considerable enhancement of the photoresponse.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 15(1999) 59-65

The role of Site Selection on Localising Ground Flashes in an Automated Lightning Detection Network
D. U. J. Sonnadara¹, I. M. K. Fernando¹, S. Namasivaaym², T. R. Ariyaratne¹, K. P. S. C. Jayaratne¹ and K. R. A. Bandara^3
1Department of Physics, University of Colombo, ²Electro-Technology Unit, ITI, ³Department of Meteorology

A Monte-Carlo simulation was used to optimise the accuracy of strike location of ground flashes depending on the selection of placement of the direction finding base-stations. A computer program was developed to reconstruct the location of the point of strike covering an area of 280´504 km² by utilising the angular information of simulated lightning flashes. The sensing angles were allowed to vary within the specified angular accuracy (±0.5 degrees) of each station. The results indicate that a formula, based on an average that is weighted according to the error in two station measurements, could be used successfully to re-construct the location of ground flashes assuming vertical lightning over a flat terrain and land of uniform conductivity. The reconstructed position error distribution contours indicate that the levels of accuracy of the strike position vary depending on the number, angle and distance between stations. It is shown that location of sites play a vital role in obtaining optimum results in a lightning detection network.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 15(1999)66-73

A Comparison of Multielectrode Resistivity Soundings with Dipole-Dipole and Schlumberger Soundings at the Mahapelessa Thermal Spring
G. M. Fonseka
Department of Physics, Faculty of Natural Sciences, Open University of Sri Lanka.

The Mahapelessa thermal spring with an out flow temperature of 44 ⁰C is located in a NE-SW trending valley at the boundary zone between the two major rock complexes. D.C. Resistivity soundings in dipole-dipole, Schlumberger vertical electrode soundings (VES) and multielectrode soundings (MES) in Wenner a-configuration were conducted in a NE-SW profile length of ~800 m located 20 m NW of the spring. The results are presented as pseudo resistivity -depth section for dipole-dipole, as 2D resistivity-depth section for Schlumberger with collated 1D models of VES and as 2D modeled resistivity depth section for MES.

All the three maps indicate horizontal resistivity stratifications at the near surface and lateral variations at greater depths. As expected with theoretical considerations the dipole-dipole method with a maximum dipole seperation of 400 m is noted to display deeper information as compared to the Schlumberger VES soundings with similar current electrode seperations. Modelling of Schlumberger VES ssumes only vertical variation of resistivity with no lateral variations, while MES modelling with 2D resistivity variation is observed to give better averaged subsurface maps. Schlumberger VES with a current electrode seperation of ~1.6 km gives a modelled depth of ~60 m while Wenner MES with 25 electrodes spaced at 10 m gives a modelled depth of ~30 m. The degree of lateral resolution in resistivity with MES is observed to depend on the iner electrode spacing and the software capabilities. Abrupt large lateral variation in resistivity is seen to limit the present software capabilities.

MES with software control is rapid and data of a 240 m section with 25 electrodes can be achieved in 35 minutes with low level ground electrical interference. But capitol investment for developing nations prohibits the use of software based MES.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 15(1999)74-80

Characteristics of the ENSO in the Indian Ocean
W. L. Sumathipala
Department of Physics, The Open University of Sri Lanka

El Nino-Sourthern Oscillation (ENSO) is a coupled ocean-atmosphere phenomenon that has world-wide impacts on climate. In order to understand the physical mechanism of the ENSO in the Indian Ocean, Sea Surface Temperature (SST), Outgoing Longwave Radiation (OLR) and the Southern Oscillation Index (SOI) were analysed with special reference to 1997/98 ENSO.

Western Pacific worm pool revealed that instead of cool conditions during the ENSO period there were warming trends on different temporal scales. SST anomaly over the central Indian Ocean was noticeably high during the 1997/98 ENSO episode. During July 1997, SST anomaly around Sri Lanka was over 1.3 ⁰C and the values were over 0.8 ⁰C in most of the Indian Ocean. However, OLR was above normal and the rainfall over Sri Lanka was well below normal. Neverthless during October-November and December, at the peak of El-Nino, SST around Sri Lanka was 1.3 ⁰C above normal and the rainfall was abnormally high.

The ENSO signal over the Indian Ocean has a small spatial and time scale as compared to the global ENSO phenomenon initiated in the Pacific Ocean. During ENSO, the subsidence branch of the ENSO cell is located in the Western Pacific-Indian Ocean and the convective activity over the Sri Lankan region is at a minimum.

This study reveals that SST in the Indian Ocean has a strong short-term variability, which leads to convective activity on a different spatial/time scale as compared to ENSO. During November-December, at the peak of ENSO, some regions in the Indian Ocean record exceptionally high SST and the associated convective activity produces heavy rainfall over Sri Lanka. A regional scale Physical/Dynamical model, which could explain these features in the Indian Ocean, is proposed.