Comparison Of Electron Density Profiles Research Articles

Evaluation of the performance of F-layer peak height models used in IRI-2016 over the Indian equatorial and low latitudes

The performance of different height models (BSE-1979, AMTB-2013, and SHU-2015) in the International Reference Ionosphere (IRI-2016) is evaluated over the Indian equatorial and low latitude sectors. The impact of deviations in the modelled hmF2 on the estimation of electron density profiles and the Total Electron Content (TEC) is examined using the three different hmF2 methods in IRI-2016. For this study digisonde observations over Trivandrum (8.5 °N, 76.9 °E) and Ahmedabad (23.0 °N, 72.5 °E) along with GPS observations over Colombo (6.8 °N, 79.8 °E) and Ahmedabad during a high solar activity year 2014 are considered. A comparison of electron density profiles between digisonde and IRI-2016 at both the equatorial station, Trivandrum, and the low latitude station, Ahmedabad, revealed significant deviations with higher deviations in the post sunset hours at the equator. The three height methods have shown significant differences in their predictions of hmF2 at both locations. At the equator, the SHU-2015 method shows better estimates closer to the measurement values, than the other two methods except at Pre-Reversal Enhancement (PRE) time, during which, the AMTB-2013 method shows better performance. At the low latitude station, the newly added methods (SHU-2015 and AMTB-2013) do not indicate any improvements in estimating the hmF2. The availability of three different height methods in IRI-2016 is exploited to understand the modifications if any, in the ionospheric height structure and TEC for different hmF2 methods and the corresponding results are presented. As the variations in hmF2 are used to derive vertical drift on many occasions in the absence of incoherent scatter radar, this study is significant in assessing the relative efficacy of the three height models and hence useful to understand various ionospheric processes over the low/equatorial latitudes.

MARTINI Coarse-Grained Model of Triton TX-100 in Pure DPPC Monolayer and Bilayer Interfaces.

The coarse-grained MARTINI model of Triton TX-100 has been validated by direct comparison of the experimental and calculated area increase in pure DPPC lipid bilayers and monolayers at water/air interfaces in the presence of surfactant and by comparison of electron density profiles calculated with more detailed atomistic models based on the CHARMM force field. Bilayer simulations have been performed and compared with monolayers and with atomistic models. The validated CG model has been employed to study the phase separation of TX-100 molecules in lipid bilayers and the effect of the lipid bilayer curvature.

Comparison of electron density profiles for Delhi with corresponding profiles obtained from IRI-90

About one hundred ionograms for Delhi (28.6° N,77.2° E) were analysed for different seasons and for different levels of solar activity. True height profiles were obtained and compared with IRI-90/1/. It is found that IRI gives higher values of electron density in summer. The difference is moderate in equinox and minimum in winter.

X-ray diffraction study of myelin structure in immature and mutant mice

X-ray diffraction patterns were obtained from freshly dissected central and peripheral nerves of quaking, myelin synthesis deficiency ( msd), and trembler mutants, as well as immature and adult normal mice. The patterns were compared with respect to strength of myelin diffraction, background scatter level, repeat period, and intensity and linewidth of Bragg reflections. The deficiency of myelin in optic nerves was found to be (in decreasing severity): quaking > immature > trembler ⋍ normal adult; and in sciatic nerves: trembler > immature > quaking msd ⋍ normal adult. Repeat periods about 3 Å less than that for normal adult sciatic myelin were detected in corresponding nerves from immature, quaking, and trembler mice. In some trembler sciatic nerves a second phase having a 190–200 Å period and accounting for about 60% of the total ordered myelin was also evident. Comparison of electron density profiles of membrane units calculated from the repeat periods and diffracted intensities for sciatic myelins indicate structural differences at the molecular level. The main findings are: (1) quaking myelin shows a significant elevation of density in the external protein-water layer between membrane bilayers; (2) the membrane bilayer of immature myelin is ≈ 2 Å thinner than that for normal adult; (3) the membrane bilayer of the more compact phase in trembler myelin is ≈ 5 Å thinner than for normal; and (4) the difference in repeat periods for the two phases present in some of the trembler nerves can be accounted for predominantly by distinct membrane bilayer separations at the external boundary.

The Comparison of Electron Density Profiles Obtained from Backscatter Observations and Ionogram Analysis

A large number of ionograms recorded at Arecibo have been converted to electron density profiles. It is shown that the method of analysis can give very high accuracy for a single layer, but the presence of an E layer can result in systematic errors in the shape of the F layer. Backscatter observations taken at the same times as the ionograms have been analyzed to give electron density curves with a height resolution of 9 km. Although there is a wide range of variation in the shape and height of the ionospheric layers, there is in general close agreement between the profiles obtained by the two methods.

A comparison of electron density profiles over Ahmedabad in years of low and high solar activity

The median vertical distributions of electron density over Ahmedabad (23°01 N, 72°36 E) in January, April, July and October in the years of low and high solar activity 1954 and 1957–1958 have been calculated from ionograms. A method suggested by King (1960) has been used for the calculation. The P′ f records on all the days of the month for the same local hour were superposed and the monthly median p′ f curve interpolated. This was then subjected to true height analysis by applying the standard Schmerling method used for the analysis of individual curves. The diurnal electron densities are presented in the form of iso-electron-density contours against height. The curves are extrapolated above the level of maximum electron density assuming Garriott's model for the distribution. The major features of diurnal and seasonal variation are discussed.