Isospectrality in Chaotic Billiards

We consider a modification of isospectral cavities whereby the classical dynamics changes from pseudointegrable to chaotic. We construct an example where we can prove that isospectrality is retained. We then demonstrate this explicitly in microwave resonators.Comment: 5 pages, 7 figure

Astrophysical S_{17}(0) factor from a measurement of d(7Be,8B)n reaction at E_{c.m.} = 4.5 MeV

Angular distribution measurements of $^2$H($^7$Be,$^7$Be)$^2$H and $^2$H($^7$Be,$^8$B)$n$ reactions at $E_{c.m.}\sim$~4.5 MeV were performed to extract the astrophysical $S_{17}(0)$ factor using the asymptotic normalization coefficient (ANC) method. For this purpose a pure, low emittance $^7$Be beam was separated from the primary $^7$Li beam by a recoil mass spectrometer operated in a novel mode. A beam stopper at 0$^{\circ}$ allowed the use of a higher $^7$Be beam intensity. Measurement of the elastic scattering in the entrance channel using kinematic coincidence, facilitated the determination of the optical model parameters needed for the analysis of the transfer data. The present measurement significantly reduces errors in the extracted $^7$Be(p,$\gamma$) cross section using the ANC method. We get $S_{17}$~(0)~=~20.7~$\pm$~2.4 eV~b.Comment: 15 pages including 3 eps figures, one figure removed and discussions updated. Version to appear in Physical Review

Ionospheric Absorption on 2.4 MHz at Waltair

86-88Results of a preliminary investigation on the 2.4 MHz radio wave absorption in ionosphere using the Al technique are presented. It has been found that the diurnal variation parameter n (cos index) has a wide range of values from 0.3 to 1.5 with a mean of 0.62 ±0.003 (p. e.). The cos index n is found to have significant positive correlation with the Zurich sunspot number. The noon-time absorption values show large day-to-day variation and have a positive correlation with sunspot number. The seasonal variation of the monthly mean noon-time absorption indicates an increase in equinoctial months

Studies on Ionospheric D & E Region Models in Conjunction with Al Absorption Measurements at Waltair

183-187Ionospheric absorption has been studied in model ionospheric layers at Waltair using Sen-Wyller's fully generalized magneto-ionic theory. On the basis of numerical calculations a suitable model is selected that gives values of absorption, virtual height and the cos index n in reasonable agreement with the experimentally observed values from Al absorption data. It is found that 'the assumption of a single Chapman layer model along with an exponential collision frequency profile leads to a cos index less than 1.5In particular. a three-tier model of electron density profile consisting of (i) a Chapman type E(Ne0 = 2 x 105 cm-3 and h0 = 110 km) and a Chapman type D(N e0= 103 cm-3 and h0= 75 km); (ii) a constant electron density lower D-region (Ne= 200 cm-3 in the height range 50-70 km) with a uniform scale height of 6 km, and (iii) an exponential collision frequency profile assuming the value of v0 -= 2 X 104 sec-1 at 110 km, is proposed

Effect of Solar X-Ray & Lyman- ɑ Radiation on Ionospheric Absorption

32-34Results of a statistical analysis of A1 absorption and solar X-ray and Lyman-ɑ fluxes are presented. The observed small positive correlation coefficients between absorption and solar X-ray flux in the 1-8 Ǻ and 8-20 Ǻ bands show that the influence of solar X-rays on absorption is less during low sunspot activity period. Significant positive correlation between Lyman-ex flux and absorption is obtained. Significant positive correlation between D region absorption (separated from total absorption) and Lyman-ɑ flux shows that the influence of Lyman-ɑ radiation on the D region is more than that of X-rays