Direct reconstruction of complex refractive index distribution from boundary measurements

We obtain the reconstruction of the refractive index distribution of body based on the intensity and normal derivative of the intensity measurements. The Helmholtz equation is inverted either directly or indirectly through repeated implementation of the forward operator and its adjoint, for recovering the complex refractive index distribution. We do not adopt the procedure of recovery of phase (normally required for complete knowledge distribution). We derive certain sensitivity relations which is used for the easy computation of the Jacobian. Our procedure successfully reconstructs the real and imaginary parts of the complex refractive index from the measurement of the two data types derived from the complex amplitude at the boundary. Our other interest is the reconstruction of the spectroscopic variations of optical absorption coefficients and visco-elastic properties of a tissue which is extremely useful in diagnostic medicines. The research is on progress and some results are available. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and magnetic studies of Mn‐doped ZnO

The bulk samples of Mn‐doped ZnO were synthesized with the nominal compositions Zn_1‐xMn_xO (x = 0.02, 0.05, 0.10, 0.15) by the solid‐state reaction and sol‐gel methods. In both the methods the samples were finally sintered at ∼700 °C in air. The X‐ray diffraction (XRD) studies of the samples synthesized by the solid‐state reaction method exhibit the presence of wurtzite (hexagonal) crystal structure similar to the parent compound (ZnO) in all the samples, suggesting that doped Mn ions sit at the regular Zn sites. However, same studies spread over the samples with Mn content ≥5% and synthesized by the sol‐gel method reveal the occurrence of some secondary phase in addition to the majority wurtzite phase. The magnetic measurements by vibrating sample magnetometer (VSM) clearly indicate ferromagnetic interaction at room temperature in all the samples. The Curie temperatures (T_c) and magnetization vary with concentration of Mn ions in the samples. However, the samples synthesized by sol‐gel method were found to have lower Tc values and also lower magnetization as compared to the corresponding samples synthesized by solid‐state reaction method. It could possibly be due to the presence of antiferromagnetic islands and smaller crystallite sizes in the samples prepared by sol‐gel method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interaction of repulsive impurity pairs in silver

Probe-impurity interactions of In–Cd and In–Zn pairs in silver matrix have been studied using ¹¹¹In-TDPAC measurements. The interactions are repulsive for both the pairs. For 3% alloys, the interaction energy of In–Cd pairs in Ag is 51± 2 meV and that of In–Zn pairs is 19± 1 meV. The Electric Field Gradient (EFG) at ¹¹¹Cd due to a single Cd nn impurity to the In probe is found to be 0.83± 0.04× 10²¹ V/m² while for a Zn impurity is 1.50± 0.05× 10²¹ V/m². Cd–Cd contact interaction in silver is also found to be repulsive. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sulphonated poly(ether ether ketone): synthesis and characterisation

The paper describes the sulphonation of commercially available poly(ether ether ketone) PEEK (GATONE^TM, Gharda Chemicals Limited, India and VICTREX^®, ICI Limited, UK) by using concentrated sulphuric acid. The concentration of GATONE in conc. H₂SO₄ was varied from 4-10% (w/v) whereas in VICTREX^® the concentration was 4% (w/v). The temperature was varied from 35-55°C and the duration of reaction was 3-7 h. Structural characterisation of sulphonated polymers was done by elemental analysis, FT-IR and ¹H-NMR spectroscopy. On the basis of elemental analysis, the extent of sulphonation of GATONE was found to be 57-75%. The extent of sulphonation as determined by ¹H-NMR in case of GATONE was in the range of 53-80% and for VICTREX 58-87%. Thermal analysis, proton conductivity and water uptake of these samples were also studied. Proton conductivity of the films was comparable to the perflourinated polymer (Nafion).