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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 1-5 Using time and frequency domain information for the development of adaptive voice control devices A simple voice recognizer was implemented with the aim of building voice control devices by utilizing a cascade LPC with adaptive fuzzy interface system (FIS). The accuracy of the voice recognizer depends on the complexity of the voice commands, the number of frequency components used, and the weights that are utilized in FIS. The quality of the voice recognizer depends both on the time and the frequency resolution of the digitizing hardware. With a limited set of sounds the technique discussed in this paper can be used to produce a speaker dependent voice control system. The performance of the system improves with time due to the adaptive nature of the system. The highly flexible backend (fuzzy interface) enables usage of the device in noisy industrial environments. Back to content page |
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 7-14 Virtual Robot Arm Control Model A Six-axis Virtual Robot arm (SVR) was designed with adjustable kinematic parameters to mimic a 6-axis articulate robotic manipulator with revolute joints having 6 degrees of freedom. The screen based interface was complemented by a custom designed external controller which was connected through the parallel port of the PC. The interface and the main mathematical engine that deals with rigid body transformations has been implemented with Borland Delphi 6, while the external controller was based on the 10-bit A/D channels of the PIC18F458 microcontroller, programmed using the MPASM assembler by Microchip Inc. The SVR can be manipulated using direct kinematics to change the spatial orientation of virtual objects in 3 dimensions. Picking and placing of virtual objects can be done by using the virtual proximity sensors and virtual touch sensors incorporated in to the jaw design of the SVR. Furthermore, it can be trained to perform a sequence of movements repeatedly, to simulate the function of a real industrial robotic manipulator.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 15-25 Development of a USB port based data acquisition system for unmanned weather station Collecting weather information is essential in many areas in science as well as in various day to day human activities. An unmanned weather station makes this process easier by collecting weather data with minimum interaction of a human being. The primary objective of the project is development of a USB port based data acquisition system for an unmanned weather station. By making use of USB to transfer data, it is intended to give features of the USB interface, like the ease of use and the speed, to the data acquisition system. To find an optimum solution to the project an extensive study had been carried out on various sensors used in unmanned weather stations, existing systems, product manufacturers? datasheets and application notes. Then a solution to the project was identified based on primarily two modules; a microcontroller and a USB interfacing module. Various sensors and equipments of the unmanned weather stations are connected to the microcontroller. It sends collected data to the computer via the USB interfacing module. The USB interfacing module fulfils all the hardware requirements of the USB interface. The system completes with application software at the computer end which displays, logs and generates reports of collected weather data. In addition of achieving primary objective of the project successfully, the design has some extra benefits too. It has been designed as a generic high speed data acquisition system which can be easily extended or converted to a completely different application by altering only the firmware and software. Throughout the project the best possible data acquisition techniques and programming techniques have been adopted. The result is a data acquisition system which not only acquires data, but does it in a highly optimized manner. This system serves as a guide for the average developer to make use of powerful, attractive and yet difficult to implement USB interface in their design. Thus the project is a starting point for moving on to high speed USB based data acquisition systems from traditional serial or parallel port based systems.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 27-42 Performance evaluation of selected medical imaging equipment using standard and locally fabricated test tools Quality degraded diagnostic imaging equipments over expose patients, staff and public and also results in retakes and film wastage. A simple electronic fault of X?ray generator timer circuit could be a reason for above but the standard performance evaluation methods of medical imaging equipment need very expensive, less available test tools. This work describes the performance evaluation of selected diagnostic imaging equipments with view to fabricate low cost test tools. For CT Scanner, Evaluation of CT numbers to assess the quality, and SNR evaluations are novel experiments conducted locally. Ring artifacts due to performance degraded Xenon transducers were visible in the image obtained for constructed wooden phantom. For the older X-ray generator, errors of time setting and fine focal spot were found. The constructed automatic spinning top gave accurate results. Approximate MTF for focal spot and screen film system and the resolving power of X-ray generator were evaluated using constructed resolving target with pinhole image. For Radiologists, above parameters will give ideas; ?amount of information lost from the system? and ?the resolving ability? of organ imaging. Gamma camera performance was also verified.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 43-54 Relationship between rainfall of Sri Lanka with sea surface temperature (SST) in the indian ocean during La-Nina condition Fluctuation of rainfall over Sri Lanka in relation to La-Nina events is examined by using monthly rainfall composite during La-Nina year. Percentage departure for every month is plotted using an index value computed for each station. Simultaneous SST correlation with rainfall over Sri Lanka during La-Nina year is examined by using monthly composite charts. Rainfall of principal meteorological stations for a period of 97 years and SST data from 1971 to 1990 in the Indian Ocean were used for this analysis. It is found that during La-Nina year there is a reduction in rainfall during North East Monsoon (NEM) period in Dry Zone. The most affected regions are eastern and southeastern part of the country. Above normal rainfall is received at the tail end of South West Monsoon period (SWM) throughout the country. This increasing trend of rainfall may be influenced by the Indian Ocean high SST anomalies during La-Nina condition. First Inter-Monsoon (FIM) and Second Inter-Monsoon (SIM) period recorded above and below normal rainfall during La-Nina year respectively. Temporal correlation maps of SST in the Indian Ocean showed negative and positive influence on the rainfall over the island. However, other regions of the country where above / below rainfall is received are unusual. It was noted that SST of the Indian Ocean has a direct influence on the rainfall variation over the country.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 55-66 Propagation of out-going longwave radiation (OLR) field over the Indian ocean Propagations of Outgoing Longwave Radiation (OLR) field over the Indian Ocean during the period of 1974-1990 is examined by using time Longitudinal and time Latitudinal sections. During the time period of 1974 - 1990 there are two types of OLR fluctuations prominent in the equatorial Indian Ocean. The period of 1974 - 1982 exhibit dry type (low convective activity) behaviour while the other period 1983 - 1990 shows slightly wet type (High convective activity) behaviour except several years. Considering the time period 1974 to 1990 a most dry type of OLR fluctuation took place over the Sri Lankan area in 1976 and wet type OLR fluctuation exist in the years of 1984, 1985 and 1988 with compared to the rest of the years. There was an increasing tendency in convective activity most of the equatorial areas during the period from 1980 to 1990. It is noted that slightly high convective activity in the region during 86/87 El ?Nino event when compared with the 76/77, 82/83 El-Nino events. It was observed that OLR anomaly movement initiate to propagate towards the Pacific Ocean from western Indian Ocean prior to development of El-Nino / La-Nina events in the Pacific Ocean.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 75-80 Electronic band gap states in electrodeposited cuprous oxide semiconductors Using the electrodeposition technique Cu2O thin films of n-type conductivity was deposited on ITO substrates. It was observed that the doping density of the films were very sensitive to the deposition potential. The photoluminescence study revealed that the electronic gap states present in the band gap are only the states originated due to the oxygen vacancies. These vacancies resulted doner levels producing the n-type conductivity in the electrodeposited cuprous oxide thin films. Scanning Electron Micrographs and Absorption Spectrums are similar to reported p-type films. Photoresponse of the films clearly indicated the n-type behavior of electrodeposited cuprous oxide thin film in a photoelctrochemical cell.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 81-89 Photovoltaic studies on ionically self-assembled monolayer thin film based on conducting polymers We report here some photovoltaic studies on polymer-based thin film devices made using ISAM technique. Using this technique the thickness and individual composition of layers can be controlled in a nanometer scale. In the fabrication of these devices bi-layers of electron donor/electron acceptor materials were deposited on ITO-coated glass slides and aluminium was used as the other contact. We studied two systems PPV/PTAA (paraphenylene vinylene / polythiophene 3-acetic acid) and PPV/PMA (paraphenylene vinylene / polymethacrylic acid). Here PPV acts as the electron donor and PTAA or PMA acts as the electron acceptor. A layer of transparent PEDOT (poly-3, 4-ethlenedioxythiophene) was deposited on ITO glass before the fabrication of the device in order to smoothen the ITO surface and to reduce the barrier for charge transport between the electrode and the active polymer layer. The PEDOT layer considerably improves the I-V characteristics of the devices. The open circuit voltage of PPV/PTAA devices improve from 0.4 V to 0.8 V after the introduction of the PEDOT layer whereas PPV/PMA devices which had very poor illuminated I-V characteristics improved to have an open circuit voltage of about 0.8 V. The efficiency of these devices however was about 1%.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 91-100 Solid-state photocells sensitized by polythiophene derivative: poly(3-thiophenyleacetic acid) Solvents free, solid-state solar cells were fabricated with mesoporous TiO2 sensitized by electronically conducting polymer; poly?3 thiophenyleacetic acid (P3TAA) and reasonably high photocurrents were observed for the first time in polymer sensitized photovoltaic devices. When CuI was employed as the hole transporting material together with an ionic liquid 1-Ethyl-3-methylimidazolium bis(trifluromethylsulfonyl) amide (EMImTf2N) and LiTf2N as additives for charge transport promotion, the cell TiO2/ P3TAA/CuI delivered a respectable short circuit photocurrent of ~ 1.2 mA cm-2 with an open-circuit voltage of ~ 275 mV under the irradiance of 100 mW cm?2 (1.5 Air Mass) . Back to content page |
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 101-108 Efficient dye-sensitized solar cells with dye-semiconductor multilayer The conventional dye-sensitized solar cells response in a narrow band consistent with the absorption spectrum of the dyes resulting lower conversion efficiencies. This could be enhanced by utilizing several dyes that absorb light at different wavelengths over the visible spectrum. But merely coating several dyes one on another without any chemical bonding does not permit transfer of electron or holes to the semiconductor, as they undergo mutual deactivation process called concentration quenching. The dye monolayer must always be coupled to a semiconductor for fast electron injection of excited dye molecules to the semiconductor. This could be circumvented by interposing thin semiconductor layer in-between dyes that act as a platform for dye chelation. In this study we constructed a multiple dye-semiconductor heterostructure of the configuration, TiO2-D1/CuSCN-D2/CuSCN-D3 /CuSCN, where D1, D2, D3 are three dyes, Fast Green, Rodamin 6G and Acridine Yellow respectively and CuSCN in italics denotes the thin CuSCN layer used for dye attachment. The action spectra showed that all three dyes contribute for the photocurrent generation, broadening the spectral response of the cells. The I-V curves also showed high Voc and Isc than single-dye heterostructures of these dyes. The thickness of CuSCN thin film is critical when large number of dyes are used because of increasing barrier width for electrons and holes to tunnel, limit the photocurrent of the cell. Implementation of this structure for number of dyes needs fine tailoring of the CuSCN thin layer. Back to content page |
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004)109-125 An efficient and rapid microwave-assisted synthesis of poly(3-thiophenyleacetic acid) polymer and its uses as a sensitizer in photocells A simple, efficient and rapid- microwave (MW) assisted method was developed for the synthesis of poly (3-thiophenylacetic acid) (P3TAA) in which the total synthesis consists of esterification of 3-thiophenyl acetic acid with acidified alcohol and hydrolysis of poly (3 -methyl acetate in aqueous alkaline media. Relative yields in esterification and hydrolysis were compared by MW and conventional (CV) refluxing methods at ambient atmospheric pressure. Relative yield of P3TAA was enhanced approximately by two fold, the whole reaction time was reduced by three fold when the MW assisted methods were employed. Photoelectrochemical cells were fabricated and tested comprising P3TAA as a sensitizer for TiO2. Dramatic enhancements in the cell performances were observed with the addition of ionic liquid 1-methyl ?3-n hexylimidazolium iodide in to the electrolyte. The photocell TiO2/P3TAA/I3-/I- generated a short-circuit photocurrent of ~ 9.5 mA cm-2, an open-circuit photovoltage of ~ 400 mV with a total power conversion efficiency of ~ 2.4% under simulated full sunlight of 100 mW cm-2 (Air Mass 1.5).
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 127-134 A limitation placed on the split operator method by the algebraic form of the Hamiltonian The Split Operator (SO) method is an efficient and a popular numerical scheme used to solve the time dependent Schrödinger equation (TDSE). In this paper we discuss an intrinsic limitation imposed on the SO method which is inferred from the algebraic form of the Hamiltonian. This finding renders, the recent modification to the SO method, the third order splitting (SO3), baseless, though, at first glance, they seem to improve the numerical accuracy of solutions to the TDSE. In order to keep the mathematical analysis simple in this paper we have rigorously analyzed the most general form of a Hamiltonian of a one dimensional system. However, extension our analysis to higher dimensional quantum mechanical systems is straightforward and the limitation mentioned here exists in such systems too.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 135-142 Level spacing distributions of 1-D potentials with non-integer powers Level spacing distributions of energy eigen values are investigated for the system V(x)=(ax)2n/m. Analytic expressions for quantum eigen energies were derived with approximate asymptotic energy expansion method. The energy level spacings DE were obtained by expanding quantum action variable in a power series of DE .It was found that unlike in multidimensional systems energy level spacing distributions of the above system cannot be divided into Poisson and Wigner distributions according to the classical behavior of the system.. The level spacings of the above potentials are found to be distributed according to the power law.
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Proceedings of the Technical Session of Institute of Physics, Sri Lanka 20 (2004) 143-152 Effect of external input currents on bursting in neural network models A continuous biophysical Neural Network Model was used to simulate synchronized population bursting by introducing external input current as back ground activity of the neural system. It was found that maps of membrane potential exhibit stable stationary states, limit cycles and bursting (chaotic) like trajectories similar to those were found in experiments on hippocampal slices. Single neuron and neurons in population are found to be very sensitive to the input current, the outside potassium concentration changes and synaptic weights. We investigated the effect of the input current and the potassium concentration changes on neuronal dynamics of a single neuron and population of neurons. It was observed that the input current with the high potassium medium makes high bursting activity in neurons similar to the spontaneously population bursting observed in some experiments.
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