Origin and evolution of Gneiss-Charnockite rocks of Dharmapuri District, Tamil Nadu, India

A low- to high-grade transition area in Dharmapuri district was investigated petrologically and geochemically. The investigation confirmed the presence of a continuous section through a former lower crust, with felsic charnockites predominating the lower part and felsic gneisses the upper part. The structure of original gneisses is preserved in charnockites and the latter show petrographic evidence for prograde metamorphism. The prograde metamorphism is of isochemical nature as revealed by the similarity of compositions of tonalitic gneisses and tonalitic charnockites. However, the depletion of LIL elements particularly Rb, caused variation in K/Rb ratios from low values (345) in the gneisses in upper part to higher values (1775) in the charnockites in the lower crust. This variation in K/Rb ratio in a north to south traverse is related to the progressive break-down of hydrous minerals under decreasing H2O and increasing CO2 fluid conditions. Metasomatism and partial melting has also taken place to a limited extent along shear planes and weak zones. During cooling the H2O circulation affected substantial auto-regression in the transition zone resulting in the formation of second generation biotite

Nonlinear Absorption, Scattering and Optical Limiting Studies of CdS Nanoparticles

The nonlinear optical absorption, scattering and optical limiting properties of CdS nanoparticles dispersed in dimethylformamide (DMF) are investigated. The nanoparticles are synthesized using the standard chemical synthesis method with thioglycerol as the capping agent. The investigations are carried out at 532 nm in the ns regime. Strong two-photon absorption and nonlinear scattering are found to be responsible for good optical limiting characteristics in these nanoparticles

Patchy layered structure of tropical troposphere as seen by Indian MST radar

The MST radar observations at Gadanki (13.47° N, 79.18° E) show, almost every day throughout the year, stratified layers of intense reflectivity near the tropopause level (17 km) and also at a couple of levels between 4 km and 10 km. Highest individual reflectivity values occur near 17 km, but they occur for a short while. The region between 11 km and 15 km shows the lowest values of reflectivity alongwith vertical downward motion almost on all days of the year. High values of reflectivity are attributed to the existence of visible or sub-visible clouds; the layered structure of clouds is attributed to inertio-gravity waves with vertical wavelength of 2-3 km. It is suggested that each high reflectivity layer consists mainly of thin sheets and patches of visible and sub-visible cloud material. Hydrometeors inside the cloud material go up and down due to gravity, precipitation-loading, Brunt-Vaisala oscillations, and Kelvin-Helmholtz waves. In these small-scale motions, thin air sheets and patches get formed with sharp temperature and humidity discontinuities through contact cooling, melting, evaporation, condensation and freezing. Also, melting and freezing at low temperatures generate electrical charges in these thin sheets and patches. These thin sheets and patches have vertical dimensions ranging from a few centimetres to several metres and horizontal dimensions of the order of 1km. These thin sheets and patches have corresponding vertical and horizontal discontinuities and sharp gradients in refractive index for the MST radar beam. These show up as regions of high values of reflectivity

Influence of Mo6+ on Dielectric properties of Copper Ferrites

Two series of copper ferrites are prepared using the chemical compositional formula Cu1.0-3y Fe2.0-2x Mox + yO4.0. They are calcinated at 750 C and sintered at 950C.When x =y = 0.0, the ε′ of the basic copper ferrite is probably due to electronic exchange interactions of copper and iron ions as Cu2+↔ Cu1+ and Fe3+↔ Fe2+. The observed value of dielectric constant (є′) decreases as a function of substituent concentration (x) up to x = 0.20 and for further values of ‘x’ it found to increase. In the case of ‘C’ (x = 0) series ferrites є′ decreases with substituent concentration (y) up to y = 0.04, later it found to increase. The dispersion of ac resistivity with frequency is observed indicating their strong dependence on frequency as in the case of dielectric behaviour. These results are explained with different possible mechanisms

Experimental studies of spontaneous emission from dopants in an absorbing dielectric

We report the first measurements, to our knowledge, of the modification of spontaneous emission rates of Eu3+ ions in the visible region owing to an absorbing medium. Precise levels of the absorption coefficient are introduced by codoping with different amounts of Nd3+. We use a binary glass system PbO-B2O3 as the host, the compositional variation of which leads to a change in the real part of the refractive index. Measured lifetimes are found to follow the real cavity model, and the data are analyzed by the model proposed by Scheel et al. [Phys. Rev. A 60, 4094 (1999)]. We give estimates of the parameter that is related to the radius of the cavity around Eu3+

Measurement of local field Effects of the host on the lifetimes of embedded emitters

We report experimental results on the variation of the radiative lifetime of Eu3+ ion embedded in a dielectric with the refractive index n. We dope 1 mol % of Eu3+ into the binary glass system xPbO-(1-x)B2O3. By varying x we have achieved a fairly large variation of the refractive index from 1.7 to 2.2. This enables us to study the local field effects for the first time for ions doped in a solid glassy material. Our measurements are in agreement with the so-called real cavity model. The present measurements are free from the complications arising from reorganizational effects in solvents

Cytotoxicity Studies of Fruit-Extracted Metal Nanostructures

Biosynthesized silver (Ag) and gold nanoparticles (Au NPs) were synthesized by using Punica granatum and Citrus reticulata extracts and these extracts act as stabilizer. The average sizes of the Silver and Gold NPs were in the range of 8–10 nm and 30–40 nm, respectively. The confirmation of NPs was done by UV-visible absorption spectra, X-ray diffraction (XRD), transmission electron microscope (TEM), and Fourier transform infrared spectra (FTIR) techniques. The luminescence studies of europium and samarium complexes with NPs were studied. Emission intensities of complexes with the presence of silver enhanced and quenched with gold due to the reabsorption. The toxicity and antimicrobial studies of nanostructures were studied