Volume 46, Issue 6
June 1996, pages 389-449
pp 389-401 June 1996
We study numerically the linear properties of periodic and quasiperiodic anisotropic layered media. Each anisotropic slab can have arbitrary orientation of optic axis. We apply the general numerical code to recover the known results for solc filters. We propose novel periodic structures where the location and width of the gaps can be controlled easily. We also study the transmission properties of a Fibonacci sequence of anisotropic layers and show the interesting features like self-similarity and scaling.
pp 403-410 June 1996
We examine the effect of subdividing the potential barrier along the reaction coordinate on Kramers’ escape rate for a model potential. Using the known supersymmetric potential approach, we show the existence of an optimal number of subdivisions that maximizes the rate.
pp 411-416 June 1996
SU(3) flavor symmetry allows the decay constantsfD1 andfD2 as well asfB1 andfB1 to be equal. But due toSU(3) flavor symmetry breaking the ratiosfB1/fB2 andfD1/fD2 are deviated from unity. We have estimated these ratios in the heavy quark effective theory and obtainedfB1/fB2=0.93,fD1/fD2=0.94 and the double ratio (fB1/fB2)/(fD1/fD2)=0.99.
pp 417-424 June 1996
Using a geometric model to study the structure of hadrons, baryons having one, two and three heavy quarks have been studied here. The study reveals diquark structure in baryons with one and two heavy quarks but not with three heavy identical quarks.
pp 425-429 June 1996
We have obtained an expression for the oscillator frequency in inverse powers of the nuclear mass number, by equating the spacing of the outermost levels of a square well, found to be nearly constant to the oscillator spacing for which the spacings are also constant. The formulae for the oscillator frequency obtained here are compared with similar formulae obtained by other authors. A reasonable qualitative agreement is found to exist between our formulae ofħωA andħωN and those given in the standard literature, obtained mainly from size considerations. Our derivation is based only on the assumption that a particle-nucleus potential exists. Any reference to particle-hole states is made purely for a rough comparison of our parameters, otherwise nothing hinges on that description.
pp 431-449 June 1996
The total cross sections for positron impact on hydrocarbons have been calculated using the additivity rule in which the total cross section for a molecule is the sum of the total cross section for the constituent atoms. The energy range considered is from a few eV to several thousand eV. The total cross sections for positron impact on an atom are calculated by employing a complex spherical potential which comprises of a static, polarization and an absorption potential. We have good agreement with the experimental results for hydrocarbons for positron energy ⩾100 eV. Our results also agree with the available calculations for CH4 and C2H2 which employed full molecular wavefunctions beyond 100 eV. Our absorption cross sections also agree with molecular wave-function calculations for C2H2 and CH4 beyond 100 eV. We have shown the Bethe plots fore+−C ande+−H scattering systems and Bethe parameters have been extracted. We have fitted the cross section for positron impact on hydrocarbons in the formσt(CnHm)=naE−b+mcE−d in the energy range 300–5000 eV wherea=195.0543,b=0.7986,c=371.1757 andd=1.1379 withE in eV andσt in 10−16 cm2.
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