Sri Lankan Journal of Physics, Volume 3, March 2002.
Phase space studies of complex Henon Heiles potentials
A. Nanayakkara
Institute of Fundamental Studies, Hanthana Road, Kandy, Sri Lanka,
C. Abayaratne
Department of Physics, University of Sri Jayawardenepura, Nugegoda, Sri Lanka.
IPT symmetric 2-D Henon-Heiles Potentials are studied semiclassically. We generalize the definition of Poincare' surface of sections to identify both regular and chaotic motion in the complex phase space. Definition of Lyapunov exponents is extended for complex trajectories. Both regular and chaotic trajectories are identified for the complex PT symmetric potentials using the new definition of Lyapunov exponents. A new quantization condition is introduced and its applicability to complex phase space is discussed.
Sri Lankan Journal of Physics, Volume 3, March 2002.
Approximate energy expressions for confining polynomial potentials
A. Nanayakkara and V. Bandara
Institute of Fundamental Studies, Hanthana Road, Kandy, Sri Lanka
Recently developed asymptotic energy expansion (AEE) method is applied to obtain asymptotic energy expansions (AEEs) of general polynomial potentials. These expansions contain coefficients of the polynomial potentials explicitly. The asymptotic expansions produce very accurate eigen energies. Recurrence relations derived here can be used to obtain asymptotic expansions of polynomial potentials of any degree. Energy eigen value expressions are presented for the 4th, 6th, 8th and 10th degree polynomial potentials. The expansions obtained with AEE method for polynomial potentials have resemblance with WKB expressions obtained by Bender et al1 for the potentials V ( x) = x N ( N even).
Sri Lankan Journal of Physics, Volume 3, March 2002.
Forecasting the Occurrence of Rainfall in Selected Weather
Stations in the Wet and Dry Zones of Sri Lanka
H.K.W.I. Perera and D.U.J. Sonnadara
Department of Physics, University of Colombo, Colombo 3, Sri Lanka,
D.R. Jayewardene
Department of Mathematics, University of Colombo, Colombo 3, Sri Lanka
Two models were developed based on the Markov method to predict the occurrence of rainfall. Daily rainfall data from 9 meteorology stations in Sri Lanka namely, Colombo, Ratnapura, Kandy, Galle, Hambanthota, Batticaloa, Anuradhapura, Badulla and Trincomalee were analysed using these models. The results show that the models can forecast the status of a given day at an average of 73%. Higher agreement is seen for stations in the dry zone of Sri Lanka when compared with those in the wet zone. No significant difference was observed between the results obtained using the 1st order Markov process and the 2nd order Markov process. The models were not sensitive to the range of data used or the short-term fluctuations.
Sri Lankan Journal of Physics, Volume 3, March 2002.
Investigation of Ni Substitution for Cu in Bi(Pb)-Sr-Ca-Cu-O
Superconductor by AC Magnetic Susceptibility
Measurements
N. Pathmanathan
Dept. of Physics, Eastern University, Sri Lanka.
A.L. Thomson
University of Sussex, Falmer, Brighton, U.K.
In this work we have investigated the effect of doping of magnetic element Ni for copper into the copper site of Bi(Pb)-Sr-Ca-Cu-O superconductor by means of AC magnetic susceptibility measurements. Three samples with composition Bi1.6Pb0.4Sr2Ca2NixCu3-xOy with x=0, x=0.05 and x=0.1 were prepared using sol-gel method and the measurements of '(T) and ''(T) were carried out on these samples in zero and in applied d.c magnetic fields. The '(T) data for the samples in zero d.c field show single drops indicating that the samples had one superconducting phases and the superconducting transition temperatures of the samples were determined to be 108.7 K, 98.9 K and 56.7 K respectively. Obviously superconducting transition temperatures of the samples decrease with increasing Ni concentration. The ' (T) data for the samples in d.c magnetic fields show broad superconducting transitions indicating that the magnetic fields quenched superconductivity of the samples. The ''(T) data in d.c magnetic fields show broad intergrain peaks associated with energy dissipation inside the samples. In low d.c magnetic fields ' (T) data for the x=0 and x=0.05 samples show two drops associated with inter and intragrain regions of the samples. In high magnetic fields ' (T) data show single transitions indicating that the magnetic fields simultaneously penetrated into the superconducting grains and the weak links. The ' (T) data for the x=0.1 sample shows single drops in low and in high d.c. magnetic fields. The high d.c magnetic fields pushed the superconducting transition temperatures of the samples to lower temperatures and the intergrain peaks in ''(T) shifted to lower temperatures with increasing applied d.c magnetic fields.
Sri Lankan Journal of Physics, Volume 3, March 2002.
Dielectric Behaviour of BaxSr1xTiO3 Perovskites
Ashok Kumar, U. C. Naithani and B. S. Semwal
Department of Physics, Garhwal University, Pauri Campus,
Pauri (Garhwal), U. P., Pin 246 001, India.
Using the method of double time thermal Green's functions and Kubo formalism, a general expression is derived for the complex dielectric constant of BaxSr1xTiO3 ferroelectric crystal in the paraelectric phase taking into account the change of mass as well as harmonic force constant between impurity atom and host lattice atoms. The results are used to obtain an expression for the fr equ ency dependen c e of th e d ielectr ic constan t o f Ba x S r 1 xTiO3 due to impurity and anharmonic scattering. To a first order approximation of the defect parameters the Curie temperature shift is found to depend only on the harmonic force constant changes between the impurity and host lattice atoms, and is proportional to the concentration of defects. The dielectric constant of ceramic SrTiO3 can be enhanced by the addition of cation impurities like lead, barium, zirconium etc.
Sri Lankan Journal of Physics, Volume 3, March 2002.
Some Properties of Lightning Ground Flashes Observed in
and around Sri Lanka, and their Seasonal Variations
J. P. Liyanage1, D. U. J. Sonnadara2, I. M. K. Fernando2,
A. B. Weerasekera2, R. Lelwala2 and T. R. Ariyaratne2
1Department of Surveying Sciences, Sabaragamuwa University of Sri Lanka,
Belihuloya, Sri Lanka,
2 Department of Physics, University of Colombo, Colombo 3, Sri Lanka.
wo lightning locating systems were utilised in obtaining the cloud-to-ground flash characteristics in Sri Lanka and in the surrounding area of the Indian Ocean. Over 5,000 flashes were recorded during the year 1999 covering 39 thunder days. The lightning data are presented in terms of polarity, multiplicity, and first return stroke peak current. The percentage of positive flashes observed in this study is fairly lower than that of temporal regions but when compared with similar studies in tropical regions there is no clear difference. Out of the 3% of the positive flashes reported, 95% were single stroke. On the contrary only 56% of the reported negative flashes were single stroke. The highest percentage of single stroke negative flashes was 74% in June and lowest was 38% in February. The monthly variation of the percentage of positive flashes ranged from 17% in June to 1% in September. The highest monthly average multiplicity of negative flashes of 2.6 was recorded in February and for all other months it was below 2. The monthly averages of the negative first stroke peak currents ranged from about 39kA in August to about 56kA in September. The data obtained in the study also clearly indicates the bias in DF data for longer distances.