K. Rama Gopal

Electronic polarizability and optical basicity properties of oxide glasses through average electronegativity

Abstract The average electronic oxide polarizability ( α o 2− ) and optical basicity ( Λ ) of numerous simple oxides have been estimated on the basis of different properties of oxides: average electronegativity ( χ av ) and energy gap ( E g ). The estimated values are in good agreement with the literature values. Similarly the optical basicity and average electronic polarizability of binary oxides glasses (phosphate, borate, silicate, germanate, tellurite and titanate) have been evaluated on the basis of average electronegativity ( χ av ) only. The performance of the present method is compared with Dimitrov and Komatsu relationships. A good agreement is observed between the computed and literature values.

Optical electronegativity and refractive index of materials

Simple correlations between the energy gap, optical electronegativity and the refractive index are given for various classes of materials such as semiconductors, insulators and oxides. There has been no report in the literature on the direct estimation of optical electronegativity for the wide variety of materials using energy gap values. The present method performance is compared with Moss and Ravindras relationships. A simple analysis on the average percentage deviation for low and high n value materials is also presented. The average percentage deviation in the present approach reveals that the method proposed proves its identity and soundness compared to that of Moss and Ravindras relationships. A good agreement is observed between the computed and literature values of refractive indices.

Absorption and emission spectral studies of Sm3+ and Dy3+ doped alkali fluoroborate glasses

Absorption and photoluminescence spectra of Sm 3 + and Dy 3 + doped alkali fluoroborate glasses of the composition 90.5 B 2 O 3 + 4 AlF + 5 RF + 0.5 LnF 3 (R= Li, Na, K and Ln = Sm, Dy) are reported. On excitation, with 402 nm, the Sm 3 + glasses were found to be orange fluorescent in colour and richness of that colour was high in the Na + glass, compared to Li + and K + glasses. Similarly, on excitation with 398 nm, the Dy 3 + glasses were fluorescent yellow and that colour was richer in the K + glass.

Temporal and spectral characteristics of aerosol optical depths in a semi-arid region of southern India.

The spectral and temporal variations of aerosol optical depths (AOD) observed over Anantapur (a semi-arid region) located in the Southern part of India are investigated by analyzing the data obtained from a Multiwavelength Solar Radiometer (MWR) during January 2005-December 2006 (a total of 404 clear-sky observations) using the Langley technique. In this paper, we highlighted the studies on monthly, seasonal and spectral variations of aerosol optical depth and their implications. The results showed seasonal variation with higher values during pre-monsoon (March-May) and lower in the monsoon (June-November) season at all wavelengths. The pre-monsoon increase is found to be due to the high wind speed producing larger amounts of wind-driven dust particles. The post-monsoon (December-February) AOD values decrease more at higher wavelengths, indicating a general reduction in the number of bigger particles. Also during the post-monsoon, direction of winds in association with high or low pressure weather systems and the air brings more aerosol content to the region which is surrounded by a number of cement plants, lime kilns, slab polishing and brick making units. The quantity of AOD values in pre-monsoon is higher (low during post-monsoon) for wavelength, such as shortwave infrared (SWIR) or near infrared (NIR), which shows that coarse particles contribute more compare with the sub-micron particles. The composite aerosols near the surface follow suit with the share of the accumulation mode to the total mass concentration decreasing from approximately 70% to 30% from post-monsoon to pre-monsoon. Coarse mode particle loading observed to be high during pre-monsoon and accumulation mode particles observed to be high during post-monsoon. The backward trajectories at three representative altitudes with source point at the observing site indicate a possible transport from the outflow regions into Bay of Bengal, southern peninsular India and Arabian Sea. The temporal variations of AOD, Angstrom wavelength exponent and precipitable water content over Anantapur have also been compared with those reported from selected locations in India.

Inferring wavelength dependence of AOD and Ångström exponent over a sub-tropical station in South Africa using AERONET data: influence of meteorology, long-range transport and curvature effect.

Aerosol optical properties over a southern sub-tropical site Skukuza, South Africa were studied to determine the variability of the aerosol characteristics using CIMEL Sunphotometer data as part of the AErosol RObotic NETwork (AERONET) from December 2005 to November 2006. Aerosol optical depth (AOD), Ångström exponent (α), and columnar water vapor (CWV) data were collected, analyzed, and compiled. Participating in this network provided a unique opportunity for understanding the sources of aerosols affecting the atmosphere of South Africa (SA) and the regional radiation budget. The meteorological patterns significantly (p<0.05) influenced the amount and size distribution of the aerosols. Results showed that seasonal variation of AOD at 500 nm (AOD500) over the observation site were characterized by low values (0.10-0.13) in autumn, moderate values (0.14-0.16) in summer and winter seasons, and high to very high values (0.18-0.40) during the spring, with an overall mean value of 0.18±0.12. Ångström exponent α(440-870), varied from 0.5 to 2.89, with significant (p<0.0001) seasonal variability. CWV showed a strong annual cycle with maximum values in the summer and autumn seasons. The relationship between AOD, Ångström exponent (α), and CWV showed a strong dependence (p<0.0001) of α on AOD and CWV, while there was no significant correlation between AOD and CWV. Investigation of the adequacy of the simple use of the spectral AOD and Ångström exponent data was used in deriving the curvature (a2) showed to obtain information for determining the aerosol-particle size. The negative a2 values are characterized by aerosol-size dominated by fine-mode (0.1-1 μm), while the positive curvatures indicate abundance of coarse particles (>1 μm). Trajectory cluster analyses revealed that the air masses during the autumn and winter seasons have longer advection pathways, passing over the ocean and continent. This is reflected in the aerosol properties that are derived from the ocean, desert, and anthropogenic activities that include biomass burning and industrial pollution.

Optical electronegativity, bulk modulus and electronic polarizability of materials

Correlations between the energy gap, optical electronegativity and bulk modulus are given for compound and ternary chalcopyrite semiconductors. Bulk modulus and electronic polarizability values have been evaluated from the optical electronegativity. The estimated values of these parameters are in good agreement with the available experimental data.

Correlation between optical basicity, electronegativity and electronic polarizability for some oxides and oxysalts

A new method for calculating the optical basicity, electronic polarizability and oxygen electronegativity of oxides and oxysalts has been evaluated based on the concept of average electronegativity given by Asokamani and Manjula. The estimated parameters are in good agreement with the Duffy values. The results are also discussed in relation to the nature of bonding. It is suggested that the impurity of average electronegativity in predicting different parameters is well emphasised.

Size segregated mass concentration and size distribution of near surface aerosols over a tropical Indian semi-arid station, Anantapur: Impact of long range transport.

Regular measurements of size segregated as well as total mass concentration and size distribution of near surface composite aerosols, made using a ten-channel Quartz Crystal Microbalance (QCM) cascade impactor during the period of September 2007-May 2008 are used to study the aerosol characteristics in association with the synoptic meteorology. The total mass concentration varied from 59.70+/-1.48 to 41.40+/-1.72 microg m(-3), out of which accumulation mode dominated by approximately 50%. On a synoptic scale, aerosol mass concentration in the accumulation (submicron) mode gradually increased from an average low value of approximately 26.92+/-1.53 microg m(-3) during the post monsoon season (September-November) to approximately 34.95+/-1.32 microg m(-3) during winter (December-February) and reaching a peak value of approximately 43.56+/-1.42 microg m(-3) during the summer season (March-May). On the contrary, mass concentration of aerosols in the coarse (supermicron) mode increased from approximately 9.23+/-1.25 microg m(-3)during post monsoon season to reach a comparatively high value of approximately 25.89+/-1.95 microg m(-3) during dry winter months and a low value of approximately 8.07+/-0.76 microg m(-3) during the summer season. Effective radius, a parameter important in determining optical (scattering) properties of aerosol size distribution, varied between 0.104+/-0.08 microm and 0.167+/-0.06 microm with a mean value of 0.143+/-0.01 microm. The fine mode is highly reduced during the post monsoon period and the large and coarse modes continue to remain high (replenished) so that their relative dominance increases. It can be seen that among the two parameters measured, correlation of total mass concentration with air temperature is positive (R(2)=0.82) compared with relative humidity (RH) (R(2)=0.75).

RKRV Potential Energy Curves, Dissociation Energies, γ-Centroids And Franck-Condon Factors Of YO, CrO, BN, ScO, SiO And AlO Molecules

The potential energy curves for the electronic ground states of astrophysically important YO, CrO, BN, ScO, SiO and AlO molecules are constructed techniques using the five-parameter Hulburt-Hirschfelder function. The estimated dissociation energies are 7.235±0.15, 4.337 ± 0.09, 3.917 ± 0.09, 6.899 ± 0.14, 8.181 ± 0.17 and 5.202 ± 0.11 eV for YO, CrO, BN, ScO, SiO and AlO, respectively. The estimated D0 values are in reasonably good agreement with literature values. The r-Centroids and Franck-Condon factors for the bands of B2 Σ+ − X2 Σ+ of YO, B5 Π −X5 Π> of CrO, A3 Π − X3 Π of BN, B2 Σ+ −X2 Σ+ of ScO, E1 Σ+ − X1 Σ+ of SiO and D2 Σ+ − X2 Σ+ and B2 Σ+ −X2 Σ+ of AlO molecules have been determined. The Franck-Condon factors are evaluated by the approximate analytical method of Jarmain and Fraser. The absence of the bands in these systems is explained.

Studies on aerosol optical properties over urban and semi-urban environments of Hyderabad and Anantapur

Aerosols in the troposphere exert an important influence on global climate and the environment through scattering, transmission and absorption of radiation as well as acting as nuclei for cloud formation. Atmospheric aerosol particles influence the earths radiation balance directly by scattering of infrared energy and indirectly by modifying the properties of clouds through microphysical processes. The present study addresses visibility, radiative forcing, size distribution and attenuation of aerosols over the period from January to May, 2001 for urban and semi-urban regions of Hyderabad and Anantapur. High aerosol loading has been observed over urban environment compared to semi-urban environment. Aerosol optical depth values increased from January to April and then decreased during May over both urban and semi-urban regions. Over urban region, visibility decreased from January to April and increased during May. Similar trend has been observed over semi-urban region with relatively higher values of visibility. Radiative forcing estimated using aerosol optical depth values increased from January to April and then decreased during the month of May over urban and semi-urban areas. High visibility and low radiative forcing has been noticed over semi-urban area due to less aerosol loading. Wavelength exponent and turbidity coefficient registered high values over urban environment compared to semi-urban environment. Attenuation coefficient showed high values over urban region compared to semi-urban region. It reveals that semi-urban environment receives high solar flux than urban environment. Using 10 channel quartz crystal microbalance, measurements of total mass concentration and mass size distribution of near surface aerosols has been made over semi-urban environment and compared with size distribution derived from inversion methods based on aerosol optical depth variation with wavelength. The sensitivity of constrained linear inversions for inferring columnar aerosol size distributions has been discussed in detail in the paper.