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Panda P.K.,National Aerospace Laboratories, Bangalore
Ceramics International | Year: 2013

Samaria nanofibers were prepared by electrospinning homogeneous viscous solutions of samarium citrate in polyvinyl alcohol (PVA) and calcining the nanofibers at 1000 °C for 2 h. PVA solutions of varied concentrations e.g. 19%, 23% and 25% (by weight) were used as polymer precursors. Electrospinning was carried out at 9 kV DC by maintaining tip to collector distance (TCD) of 7 cm. Thermogravimetric analysis (TGA) of nanofibers room temperature (RT) to 800 °C indicates the complete decomposition of organics below 750 °C with a weight loss of 55%. The morphology of nanofibers was observed under scanning electron microscope (SEM). The nanofibers are found cylindrical with fiber diameter in the range of 200-500 nm and aspect ratio>1000. The average diameter of the fibers increases with the increase in PVA concentration. The diameter of calcined Samaria nanofibers reduced by 43% due to loss of organics and shrinkage. © 2012 Elsevier Ltd and Techna Group S.r.l. Source

Barshilia H.C.,National Aerospace Laboratories, Bangalore
Solar Energy Materials and Solar Cells | Year: 2014

We describe the growth, characterization and performance evaluation of a multilayer solar selective coating useful for solar thermal power generation. The solar selective coating of the present work consists of Ti/chrome interlayer, two absorber layers of AlTiN and AlTiON, and an anti-reflection layer of AlTiO. All the layers have been deposited using reactive pulsed direct current sputtering of Ti and Al targets in Ar+N2, Ar+N 2+O2 and Ar+O2 plasmas, respectively. A large number of analytical tools have been used to characterize the structural and optical properties of the absorber coating. The optimized coating exhibited an absorptance of 0.930 and an emittance of 0.16-0.17 on stainless steel substrates and an absorptance of 0.933 and an emittance of 0.07 on copper substrates. The absorber coating displayed improved adhesion, UV stability, corrosion resistance and thermal stability in air and vacuum up to 350 and 450 °C, respectively under cyclic heating condition for more than 1000 h. © 2014 Elsevier B.V. All rights reserved. Source

Kidambi R.,National Aerospace Laboratories, Bangalore
Physics of Fluids | Year: 2012

The frequency and damping of free lateral linear oscillations of a viscous non-cylindrical liquid bridge, formed between two axial disks of radii R 1 and R 2, are computed using a recently developed semi-analytic procedure [R. Kidambi, J. Fluid Mech.681, 597 (2011)]. A comparison with recent experimental results [E. J. Vega and J. M. Montanero, Phys. Fluids21, 092101 (2009)] for the first non-axisymmetric mode over a range of bridge volumes is good and the damping rate is better predicted than by a one-dimensional slice model especially for highly viscous bridges. The procedure can be used to calculate the oscillation characteristics of any desired mode for any region of the parameter space. © 2012 American Institute of Physics. Source

Naidu V.P.S.,National Aerospace Laboratories, Bangalore
Journal of Optics (India) | Year: 2014

Multi sensor image fusion algorithm based on directional Discrete Cosine Transform (DDCT) - Principal Component Analysis (PCA) hybrid technique has been developed and evaluated. The input images were divided into non-overlapping square blocks and the fusion process was carried out on the corresponding blocks. The algorithm works in two stages. In first stage, modes 0 to 8 were performed on images to be fused. For each mode, the coefficients from the images to be fused are used in the fusion process. The same procedure is repeated for other modes. Three different fusion rules are used in fusion process viz., 1. Averaging the corresponding coefficients (DDCTav), 2. Choosing the corresponding frequency band with maximum energy (DDCTek) and 3. Choosing the corresponding coefficient with maximum absolute value (DDCTmx) between the images. After this stage, there are eight fused images, one from each mode. In second stage, these eight fused images are fused using PCA. Performance of these algorithms were compared using fusion quality evaluation metrics such as root mean square error (RMSE), quality index (QI), spatial frequency and fusion quality index (FQI). It was concluded from the results that DDCTav performs poor and DDCTek performs slightly better than DDCTmx. Moreover, DDCTek is computationally simple and easily implementable on target hardware. Matlab code has been provided for better understanding. © 2013 Optical Society of India. Source

Naidu V.P.S.,National Aerospace Laboratories, Bangalore
Defence Science Journal | Year: 2011

A novel image fusion technique based on multi-resolution singular value decomposition (MSVD) has been presented and evaluated. The performance of this algorithm is compared with that of well known image fusion technique using wavelets. It is observed that image fusion by MSVD perform almost similar to that of wavelets. It is computationally very simple and it could be well suited for real time applications. Moreover, MSVD does not have a fixed set of basis vectors like FFT, DCT and wavelet etc. and its basis vectors depend on the data set. © 2011, DESIDOC. Source

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