Frequency dependence of pulsar radiation patterns

We report on new results from simultaneous, dual frequency, single pulse observation of PSR B0329+54 using the Giant Metrewave Radio Telescope. We find that the longitude separation of subpulses at two different frequencies (238 and 612 MHz) is less than that for the corresponding components in the average profile. A similar behaviour has been noticed before in a number of pulsars. We argue that subpulses are emitted within narrow flux tubes of the dipolar field lines and that the mean pulsar beam has a conal structure. In such a model the longitudes of profile components are determined by the intersection of the line of sight trajectory with subpulse-associated emission beams. Thus, we show that the difference in the frequency dependence of subpulse and profile component longitudes is a natural property of the conal model of pulsar emission beam. We support our conclusions by numerical modelling of pulsar emission, using the known parameters for this pulsar, which produce results that agree very well with our dual frequency observations.Comment: 24 pages, 8 figures. Accepted for publication in Ap

Radio synthesis imaging of anisotropic angular broadening in the solar wind

We present Very Large Array observations at wavelengths of 2, 3.5, 6, and 20 cm, of angular broadening of radio sources due to the solar wind in the region 2-16 solar radii. Angular broadening is anisotropic with axial ratios in the range 2-16. Larger axial ratios are observed preferentially at smaller solar distances. Assuming that anisotropy is due to scattering blobs elongated along magnetic field lines, the distribution of position angles of the elliptically broadened images indicates that the field lines are non-radial even at the largest heliocentric distances observed here. At 5R⊙, the major axis scattering angle is ~ 0.7" at λ= 6 cm and it varies with heliocentric distance as R-1.6. The level of turbulence, characterized by the wave structure function at a scale of 10 km along the major axis, normalized to λ= 20 cm, has a value 20 ± 7 at 5R⊙ and varies with heliocentric distance as R-3. Comparison with earlier resu lts suggest that the level of turbulence is higher during solar maximum. Assuming a power-law spectrum of electron density fluctuations, the fitted spectral exponents have values in the range 2.8-3.4 for scale sizes between 2-35 km. The data suggests temporal fluctuations (of up to 10%) in the spectral exponent on a time scale of a few tens of minutes. The observed structure functions at different solar distances do not show any evidence for an inner scale; the upper limits are l k m at 2R⊙ and 4 km at 13R⊙. These upper limits are in conflict with earlier determinations and may suggest a reduced inner scale during solar maximum

QBD-BASED DEVELOPMENT AND EVALUATION OF ENTERIC COATED MUCOADHESIVE MICROCAPSULES OF AMOXICILLIN TRIHYDRATE AS A NOVEL CHRONOTHERAPEUTIC APPROACH FOR TREATMENT OF BACTERIAL INFECTIONS

Objective: The present work entails design and characterization of enteric coated mucoadhesive microcapsules loaded with amoxicillin trihydrate as a novel chronotherapeutic approaches for the treatment and management of bacterial infection.Methods: The microcapsules were prepared by solvent evaporation technique using ethyl cellulose (EC) and hydroxypropyl methylcellulose (HPMC) as rate-controlling and mucoadhesive polymers, followed by a triple coating with Eudragit L100 as enteric coating polymer. Box-Behnken statistical design (BBD) was applied for optimization of formulations containing EC, HPMCK100M and Eudragit L100 as factors for selected responses like entrapment efficiency, mucoadhesive property and drug release in 24 h. The optimized microcapsules were also characterized for particle size, drug content, swelling index, mucoadhesive strength, and in vivo antiulcer activity.Results: The optimized microcapsules exhibited good entrapment efficiency, particle size and mucoadhesive property. FT-IR studies revealed that there was no drug-polymer interaction. SEM studies revealed that microcapsules were non-aggregated, spherical in shape and smooth appearance. In vitro drug release data from microcapsules was fitted to different kinetic models to explain release profiles. The correlation coefficient (r2) value indicated that drug release followed Higuchi model. Analysis of variance (ANOVA) showed significant difference in the release of drug from all the prepared formulations at P < 0.05 level. Accelerated stability study of optimized formulation (F4) upto 6 month showed there was no change in drug content and release characteristics during storage

Anisotropic angular broadening in the solar wind

We present Very Large Array observations at wavelengths of 2, 3.5, 6, and 20 cm, of angular broadening of radio sources due to the solar wind in the region 2-16 solar radii. Angular broadening is anisotropic with axial ratios in the range 2-16. Larger axial ratios are observed preferentially at smaller solar distances. Assuming that anisotropy is due to scattering blobs elongated along magnetic field lines, the distribution of position angles of the elliptically broadened images indicates that the field lines are non-radial even at the largest heliocentric distances observed here. At 5R ⊙, the major axis scattering angle is ~0.7" at λ=6 cm and it varies with heliocentric distance as R -1.6. The level of turbulence, characterized by the wave structure function at a scale of 10 km along the major axis, normalized to λ=20 cm, has a value 20±7 at 5R⊙ and varies with heliocentric distance as R -3. Comprison with earlier results suggest that the level of turbulence is higher during solar maximum. Assuming a power-law spectrum of electron density fluctuations, the fitted spectral exponents have values in the range 2.8-3.4 for scales sizes between 2-35 km. The data suggests temporal fluctuations (of up to 10%) in the spectral exponent on a time scale of a few tens of minutes. The observed structure functions at different solar distances do not show any evidence for an inner scale; the upper limits are 1 km at 2R⊙ and 4 km at 13R ⊙. These upper limits are in conflict with earlier determinations and may suggest a reduced inner scale during solar maximum