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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 18 (2002) 1-6 Performance of parallel port based remote data acquisition systems in real-time data processing A parallel port based remote data acquisition and process control system was built without on board RAM and programmable timer to test the effect on the performance when processing real-time data on a network environment. The controlling software was developed using Delphi and Assembler languages to achieve high speeds. The developed software use TCP/IP protocol for network operations. It was found that the overall performance depends primarily on the parallel port. For different types of motherboards, the speed of the data transfer varied between 460 Kbps and 890 Kbps. A minimum deviation was observed when there were no processor-bounded applications running in the system concurrently. The port speed did not depend on the processor type or the processor speeds. For the network transfer tests, client-server architecture was used. In order to increase the throughput, data compression (Zip method) was used. A data stream of 4.5 Kb (sampled data packet of 1500 byte) could be reduced to a 427±27 bytes with this technique. The compression and de-compression time was negligible compared to the computer/network speeds. The client was able to communicate with the server at an approximate speed of 1.3 Kbps on a network with fiber optic backbone, which has a connection speed of 10 Mbps. Back to content page |
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 18 (2002) 7-15 Performance of adaptive-fuzzy technique in controlling vehicular traffic A vehicular traffic control system was designed with an inexpensive OOPIC micro controller. The information on vehicular traffic at the junction was simulated and fed to the microcontroller and was used as the primary input for the decision-making algorithms. The adoptive algorithm first compares the number of vehicles in a chosen lane with those present in all other lanes at any given moment. The ratio between number of vehicles was calculated and the moment the ratio fell below a pre-defined threshold value, changes in traffic signal times were sought through a fuzzy sub-system. The algorithm ?learns? continuously and converges to the most acceptable switching time for each lane on a particular day at a particular time. The pilot tests indicated that the system efficiency improves with time as it continues to learn from experience. It was observed that on average the system adapts itself to a new situation within two or three cycles. Even when the change in traffic pattern is small, 20%-30% efficiency improvement was seen in this system compared to a programmed time system. For a large change, the improvement was about 60%. In worse case scenario, (such as a failure of a sensor), the system behaves as a programmed time system.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 18 (2002) 17-24 Improved performance of a linear mode plasma desorption time-of-flight mass spectrometer with an electrostatic wire guide In a plasma desorption time-of-flight mass spectrometer, secondary ion yield drops considerably when long flight paths are employed in order to increase the mass resolution. This has been a practical problem when the home-built mass spectrometer at the Department of Physics of the University of Colombo is used in the mass analysis of crude extracts of medicinal plants for the detection of active ingredients of respective plants. In order to overcome this problem, an electrostatic wire guide has been installed along the axis of the flight tube through which the secondary ions drift from the sample to the detector. A dc voltage of -300 V was found to be the optimum potential for the wire guide in order to produce maximum positive ion yield. Several crude extracts of medicinal plants have been tried out as test samples with the wire guide at -300 V, and, typically, an increase of two orders of magnitude in the secondary ion yield of active ingredients of the crude extracts when compared to the ion yield without wire guide was recorded. This is an encouraging result as it helps produce clear mass spectra with intense peaks of active ingredients directly from their crude extracts even though the concentration of active ingredients in the crude extracts is very low when used without purification.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 18 (2002) 25-36 RHCP single patch antennas with single feed Circularly polarized (CP) antennas have the advantage that they can be used without the need for strict antenna alignment as linearly polarized antennas. This paper presents results of several right hand circularly polarized (RHCP) path antennas designed for X-band and L-band in the microwave region. Different mode-detuning methods were employed to produce circular polarization that uses a single feed. A square patch and a circular path were designed and implemented for 9.4 GHz in the X-band. The theoretical and experimental radiation patterns showed broad beams. A square path and two circular patches were also designed for resonance at 1.6 GHz in the L-band and it also produces good agreement of the far field radiation pattern between theory and experimental. In this antenna design mode detuning was achieved with embedded and ear perturbations and the techniques were successful in obtaining circular polarization. The maximum gain of the antenna being at a frequency different from the design frequency was expected as the mode detuning method of feed introduces perturbation segments to the patch which is initially designed for resonance. It excites two orthogonal modes at a slightly different frequency: one mode leading by 45° and the other mode lagging by 45°; thus the two orthogonal modes are out of phase by 90° to produce CP. Results indicate that the different detuning methods show equally good performance for single feed antennas. The antenna constructed for the L-band is promising and will be a suitable vehicular antenna for MSAT or GPS applications.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 18 (2002) 37-43 Electronic scoreboard for basketball games An electronic scoreboard has been designed and fabricated for the basketball game. Although this has been specifically designed for the basketball game, this can also be used for other games such as Rugby, Hockey, Boxing etc. where both timing and scoring are required. This scoreboard is cost effective, easy to build, and more importantly judges can do scoring, thereby removing the communication errors completely. Since the acquisition speed of this scoreboard is very fast, the current scores can be updated instantaneously pleasing both players and spectators. Therefore, this scoreboard can be fully utilised in a fast moving game like basketball.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 18 (2002) 45-51 Use of Z-scores for the admission to Sri Lankan universities Suitability of adopting Z-Scores instead of the aggregates of raw marks scored by the candidates for the admission to Sri Lankan Universities has been investigated. The investigation was carried out by using the data published by the Department of Examinations pertaining to the G.C.E. Advanced Level Examination for last 17 years. The Z score is calculated by dividing the deviation of individual scores from the population mean, by the standard deviation. Investigation revealed that the distributions of marks for science subjects do not follow the normal distribution, and it is very much so in the case of mathematics. One of the major causes for such a deviation was found to be the absence of a M.C.Q. type paper for mathematics subjects. Analysis also shows that the standard deviation is subject dependent and it is a constant for a given subject. It does not show appreciable variation with the mean of the distribution. Standard deviation of Mathematics subjects has a value closer to 20 where as for Physics and Chemistry it is around 15. Investigation also revealed that the reason for having a large value of standard deviation for mathematics subjects is due to the absence of a M.C.Q. paper, and the nature of the subject for which a special talent is needed to perform well in the subject. Because of the dependence of the standard deviation on the nature of subjects, students doing well in subjects having a large value of standard deviation will have a disadvantage when the aggregated is taken under the Z score method.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 18 (2002) 53-59 Peculiar characteristics in electrical conductivity of WO3 incorporated TiO2 It is known that the incorporation of tungsten ions (W6+) into the crystal structure of TiO2enhances the electrical conductivity and its performance as a photocatalyst for water cleavage. Here we report the variation of electrical conductivity with the percentage of WO3 incorporated in to TiO2and a peculiar conductivity transition at high temperature. TiO2 (rutile structure) was doped using WO3 (0.1%, 0.2%, 2% and 10% by weight) as the dopant precursor and by the method of high temperature (1100oC) diffusion. Doped samples were compressed (~400 atm) between carbon electrodes to make pellets and the pellets were sintered overnight at 130oC in a vacuum The variation of electrical conductivity of each sample with temperature was studied. For each sample, the conductivity varies according to well known Arrhenius type relation. The conductivity rapidly increases at lower dopant concentrations up to 2% and then slowly decreases with the dopant concentration. The highest conductivity (8.3x10-4-1cm-1 at 210oC), which is about six orders of magnitude higher than that of the undoped sample, is obtained when the dopant concentration is about 2%. The activation energy also varies with the dopant concentration. The lowest activation energy (0.6 eV) is measured when the dopant concentration is 0.2%. However, at high temperatures (>215oC) a conductivity transition is observed and the conductivity is decreased by two orders of magnitude.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 18 (2002) 61-68 The photoelectric responses of electrodeposited C60 films on nanocrystaline TiO2 with positive hole collecting CuSCN Thin films of C60 were electrodeposited on TiO2 electrodes. All solid-state photovoltaic devices were fabricated comprising above C60 films with hole conducting inorganic semiconductor CuSCN and studied their characteristics. The cell delivered a short circuit photo current of ~ 225 µA cm-2 with an open circuit voltage of ~ 350 mV under the irradiance of 260 W cm-2. The charge transferring mechanism is described as the formation of C60 radicals from the excited C60 molecules due to the electron injection from CNS- ions and emission of electrons from the C60 radicals to the conduction band of the TiO2. These devices show remarkable stability with reproducible performances for future electrical and electronic applications.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 18 (2002) 69-78 Electrochemical synthesis and characterization of poly (3 methyl thiophene) and its evaluation as electrode material for photovoltaic devices Poly (3-methyl thiophene) films were prepared by electrochemical polymerization with different current densities ranging from 10 µA cm-2 to 8 mA cm-2 and studied their optical and electrical characteristics by means of cylic voltammetry, in-situ UV visible spectroscopy, in-situ d.c. conductivity and scanning electron micrographic techniques. The films prepared with medium current density (4 mA cm-2 ) showed higher degree of conjugation with ?-?* transition energy of 2.45 eV. The conductivity of these films at their fully oxidized state was in the order of 1x10-3 S cm-1. As an possible practical application quasi solid photovoltaic cells have been fabricated by electrodepositiong the polymer on nanocrysalline SnO2 films covered by a thin layer of MgO as the photoactive electrode. The cell delivered a short circuit current of ~140 µA cm-2 with an open circuit voltage of ~185 mV (efficency ? 0.03%) under the irradiance of the 260 W m-2 with a polymer electrolyte having redox couple I3-/ I-.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 18 (2002) 79-87 The effect of MgO on the enhancement of the efficiency in solid-state dye sensitized photocells fabricated with SnO2 CuI
Solid-state dye sensitized photo cells were fabricated with nanocrystalline SnO2 covered with a thin layer of (3-4 nm) MgO as the anode and the hole conductor, CuI as the cathode. The effect of the thin layer was investigated in detail by means of SEM, TEM, X-RD, conductivity and capacitance measurements together with photospectral responses. While the cell fabricated with n-SnO2/Ruthenium bipyridyl dye/CuI delivered almost no photocurrent with very low photovoltage, the cell n-SnO2 (MgO)/Ruthenium bipyridyl dye/CuI delivered a short circuit current ~ 2.5 mA cm-2 with an open circuit voltage of ~ 500 mV. Enhancement in the photocurrent and the voltages was found when the percentage of MgO was around 4 % and it is explained as the formation of a thin energy barrier, which suppresses the recombination of photoelectrons. Back to content page |
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 18 (2002) 89-93 A new class of PT symmetric Hamiltonian systems
Ordinarily, one imposes the condition H+=H on the Hamiltonian, where + represents the mathematical operation of complex conjugation and matrix transposition. This conventional Hermiticity condition is sufficient to ensure that the Hamiltonian H has a real spectrum. However, replacing this mathematical condition by the weaker and more physical requirement H+=H where + represents combined parity reflection and time reversal PT, one obtains new class of complex Hamiltonians whose spectra are still real and positive. In this work, we have investigated the generalization of Hermiticty using new class of PT invariant complex Hamiltonians of the form H=p2+ix(x2)%alpha where is any rational number. We present results obtained by both classical and quantum mechanical studies of this 1-D Hamiltonian. Back to content page |
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 18 (2002) 95-100 Daytime variation of temperature and salinity profiles in large-area salpan solar ponds at Palavi, Sri Lanka
This work presents a study of short-term stability of temperature and salinity profiles of a large-area saltpan solar pond of 90 cm deep at Palavi, Sri Lanka. Measurements were taken in the latter half of the daytime during which the influx of solar radiation reached its maximum. It was found that, under the conditions prevailed, the effect of the incident solar radiation was to increase the temperatures of the top and bottom convective zones. A variation of 3o C was observed in the convective zones and the highest temperature observed at the bottom was 64o C. The temperature profile of the middle non-convective zone remained unchanged, within the range defined by the accuracy of the measurements, with a downward positive temperature gradient of 1o C/cm, indicating that the absorption of thermal radiation occurred prominently in convective zones. It was also found that with the reduction of the solar radiation influx, the temperature of the bottom convective zone returned back to its initial status in a short time. According to this observation it can be concluded that the bottom convective zone of the solar pond investigated was in thermal equilibrium, macroscopically, with the environment. Back to content page |