Sri Lankan Journal of Physics, Volume 1, March 2000.
What directs a lightning flash towards ground?
Vernon Cooray
Institute of High Voltage Research, University of Uppsala, Sweden,
Rohan Jayaratne
Department of Physics, University of Botswana, Botswana
In this paper we attempt to show that the necessary condition to create a lightning ground flash is the generation of a vertical conducting channel below the main negative charge centre. The probability of such an event increases if frequent breakdown takes place between the negative charge centre and the lower positive charge centre (LPCC). Analysis of electromagnetic field signatures produced by ground flashes in Sweden show pronounced radiation during the preliminary breakdown process. Such strong pulses are rarely found in tropical thunderstorms in Sri Lanka. We attribute these signatures to preliminary breakdown between the main negative charge centre and the LPCC and argue that meteorological conditions which favour the production of strong LPCC’s are more likely to be found at mid and high latitudes than in the tropics, thus explaining why there is a greater probability of lightning flashes striking the ground in these regions.
Sri Lankan Journal of Physics, Volume 1, March 2000.
Locating cloud-to-ground lightning flashes with simultaneous
two-station measurements
D.U.J. Sonnadara, A.B. Weerasekara, I.M.K. Feranndo, R. Lelwala, K.P.S.C.
Jayaratna, T.R. Ariyaratne
Department of Physics, University of Colombo, Colombo 3
S. Namasivayam
Electro-Technology Unit, CISIR, Colombo 7
K.R.A. Bandara
Department of Meteorology, Colombo 7
The position reconstruction of the point of strike of cloud-to-ground lightning flashes in several thunderstorms recorded by two-wideband magnetic direction finding stations is presented. Lightning activity data show a clear peak around 18.00 hours, which is a characteristic feature of the Northeast monsoon thunderstorms in Sri Lanka. It is shown that the accuracy of the position reconstruction with two stations is heavily dependent on the difference in the angles measured by the stations. A technique that utilizes the measured strength of the flashes was introduced to improve the accuracy of the position reconstruction. With this technique, the point of strike of ground flashes can be localized with an accuracy of better than ±5 km within a 100 km radius around Colombo (6.90N, 79.86E), except in the vicinity of the line joining the two stations.
Sri Lankan Journal of Physics, Volume 1, March 2000.
Trajectories In the Complex Phase Space and Quantization by
Numerical Contour Integration
Asiri Nanayakkara
Department of Physics, University of Sri Jayawardanapura, Gangodawila,
Nugegoda
In this paper an exact numerical quantization method, based on quantum action variable theory is presented. The quantum momentum function (QMF) is redefined such that the corresponding quantum action variable (QAV) is an integer (h = 1) for energy eigenvalues and non integer for off eigenvalues. The energy eigenvalues obtained by quantizing the quantum action variable are exact up to the accuracy of the numerical methods used. One of the major advantages of this method is that one could use interpolations or extrapolations for obtaining boundstate energies from a set of QAV values corresponding to non-eigen energies. Examples are given to illustrate the new numerical method and the interpolation and extrapolation methods.
Sri Lankan Journal of Physics, Volume 1, March 2000.
Construction of a Matrix Assisted Laser Desorption/Ionization
Time-of-Flight Mass Spectrometer
R.V. Coorey, T.R. Ariyaratne, D.D.N. Barlo Daya and W.M.K.P. Wijayaratna
Department of Physics, University of Colombo, Colombo 03, Sri Lanka.
A matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometer has been constructed at the Department of Physics, University of Colombo, Sri Lanka. In this mass spectrometer, a solid sample which contains analyte molecules embedded in a suitable matrix compound in excess is exposed to a UV pulsed laser source (l = 337 nm). The desorbed secondary ions from the sample are mass analyzed using the time-of-flight technique. The first MALDI-TOF mass spectra of two peptides namely [tyr8]-bradykinin (1076.2 u) and porcine N-acetyl renin substrate tetradecapeptide (1801.1 u) with the matrix 2,5 di-hydro benzoic acid (154.1 u) have been obtained. Each peptide produced a MH+ peak corresponding to its intact molecular ion with m/q values of 1089 ± 6 and 1794 ± 8 respectively. >
Sri Lankan Journal of Physics, Volume 1, March 2000.
Scattering of a dyon from Hydrogen atom
P.C. Pant, V.P. Pandey and B.S. Rajput
Department of Physics, Kumaun University, Nainital-263 002, INDIA
Undertaking the scattering of a dyon from a hydrogen atom it has been demonstrated that scattering cross section is perceptibly modified from the scattering cross section of scattering of an electron from a hydrogen atom due to the presence of magnetic charge on dyon and high energy of dyon involved in the scattering process.
Sri Lankan Journal of Physics, Volume 1, March 2000.
Bound states of two dyons and two fermions
P.C.Pant, V.P.Pandey and
B.S.Rajput
Department of Physics, Kumaun University, Nainital-263002, INDIA
Investigating bound state of a system consisting of two dyons and two fermions it has been demonstrated that due to the presence of magnetic charge on dyon energy eigenvalues and eigen function for this system are largely modified from the energy eigenvalues and eigenfunction of usual Helium atom problem of quantum electrodynamics . Bohr radius for this system is shown to be very small in comparision to atomic Bohr radius implying the strongly interacting behaviour of dyons. It has also been shown that the repulsive force between dyons is greater than repulsice force between the nucleus of Helium molecule implying the small possibility of forming bound states.
Sri Lankan Journal of Physics, Volume 1, March 2000.
Evaluation of gamma radiation exposure in a room from construction
material
C.S.Sumithrarachchi a,A.S.Amerasekera b, R.Hewamanna a
and S.R.D.Rosa b
Radioisotope Centre, University of Colombo, Colombo 03, Department
of Physics, University of Colombo, Colombo 03
The presence of radioactivity in building materials can be a potential hazard from external exposure to gamma and beta radiation. Indoor radiation comes mainly from the activity concentration of the natural radionuclides of 238U, 232 Th and 40K in building materials. The calculations presented in this paper indicate if clay bricks containing average activity concentrations of 35, 72 and 585 Bq kg-1of 226Ra,232Th and 40K respectively are used to construct walls of a room of dimensions 3 m x 3 m x 0.1 m and 3.6 m x 3 m x 0.1 m the annual effective gamma radiation dose to a person with an occupancy factor of one is 1.65 mSv. This result can therefore be regarded as an upper limit on the expected exposure. Considering average activity concentrations of 55, 56 and 39 Bq kg-1 for 226 Ra, 129, 50 and 44 Bq kg-1 for 232Th, 1349, 1436 and 1725 Bq kg-1 for 40K for granite, Lanka and Royal Ceramic floor tiles respectively the annual gamma exposure due to these floor materials is 92, 69 and 61 nSv. The results suggest the exposure from the floor materials to be insignificant. The annual effective dose from construction materials is directly proportional to the activity concentration of the radionuclides present in the construction materials.
Sri Lankan Journal of Physics, Volume 1, March 2000.
Frequency And Temperature Dependent Attenuation Constant In Barium Titanate
U.C. Naithani, D.S. Lingwal, Ashok Kumar, S.C Deorani and B.S.Semwal
Theoretical Physics Division, H.N.B. Garhwal University Campus Pauri, Pauri (Garhwal), 246001 (U.P.), India.
The anomalous ultrasonic attenuation ac of longitudinal waves propagating along (100) direction in Barium Titanate single crystal has been analyzed above the phase transition temperature in the frequency range 4-10 MHz in the paraelectric phase. Critical attenuation varies as w and w2 if third - and fourth - order anharmonic interactions considered respectively. Frequency and temperature variations of attenuation are discussed.
Sri Lankan Journal of Physics, Volume 1, March 2000.
Calculation of Feynman diagrams using a symbolic manipulation programme in
personal computers
W.G.D. Dharmaratna and M.A.A. Karunarathna
Department of Physics, University of Ruhuna, Matara
A method to calculate Feynman diagrams is developed using a symbolic manipulation package that runs in a personal computer. Commercially available package called "Mathematica" is used. The method to calculate scattering amplitudes in the lowest order in the perturbation theory is demonstrated by explicitly calculating a Feynman diagram in Quantum Chromodyanamics. The procedure described here can be easily extended to calculate any Feynman diagram including next to leading order diagrams and also to the calculation of Feynman diagrams in Quantum electrodyanamics.