Two unit repairable redundant standby system

The Laplace-Stieltjes (LS) transform for the distribution of time to first system failure (TFSF), transition probability, availability and mean time to system failure have been derived for two unit repairable redundant standby system with perfect as well as imperfect switchover condition. General expressions for computing various reliability performance indices have been obtained by using Markov Renewal techniques considering general distributions for time to failure and time to repair for the units.     

Fatty acids from Macoma sp. of bivalve mollusc

Fatty acids of the total lipids of flesh and hepatopancreas of Macoma sp. have been determined. The level of 20:5w3 (ca 17%), a biologically important fatty acid, was found to be considerably high. Other major component fatty acids were 16:0, 16:1, 18:1 and 22:4w6. High levels of 22:5w6 (8%), 22:5w3 (8%) and 22:6w3 (ca 15%) were found in flesh lipid. Nonsaponifiables were also high (28–30%). Alkyl ether acyl glycerols were found in flesh (1.3%) and hepatopancreas (3.8%).     

Brightness Temperature Reconstruction Using BGI

This paper departs from the popular usage of the Backus-Gilbert inversion (BGI) method as a tool for inversion of antenna temperature measurements in microwave radiometry. The BGI method is applied in this paper to enhance the information content of an existing set of oversampled brightness-temperature (T_B) data. The purpose is to isolate the inversion process from its resolution enhancement counterpart. The advantage gained is that the resolution enhancement can be performed in a simplified way and in a different level of processing that starts with the scan-mode T_B data product and simply requires with it the knowledge of the antenna gain pattern and the sensor's scan geometry. The technique is demonstrated with the 19.35-GHz Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) channel, which provides oversampled T_B data. The radiometric resemblance of this channel with that of the 37 GHz and geocollocation of their T_B footprints facilitate validation of the enhancement of features. The significance of oversampling the low-frequency (LF) radiometer channels is underscored in the process, which gives the authors the confidence to propose oversampling of the LF data for the forthcoming sensor Microwave Analysis and Detection of Rain and Atmospheric Structures (MADRAS) onboard the Megha_Tropiques mission, which is a joint ISRO-CNES collaboration (due for launch in 2009).     

Nonlinearity in gold-alkali halide-gold capacitors

All epitaxial gold-NaCl/NaBr-gold capacitors were fabricated on hot NaCl substrates. The dielectric properties, capacitance and loss have been measured. Severe harmonic distortion in the output current has been observed. Maximum contribution was from third and odd harmonics. The amplitude of harmonics was maximum at frequencies above the loss peak. The phenomenon has been explained on the basis of nonlinear space charge theories.     

Evaluation of the reactivity of titanium with mould materials during casting

A methodology for evaluating the reactivity of titanium with mould materials during casting has been developed. Microhardness profiles and analysis of oxygen contamination have provided an index for evaluation of the reactivity of titanium. Microhardness profile delineates two distinct regions, one of which is characterised by a low value of hardness which is invariant with distance. The reaction products are uniformly distributed in the metal in this region. The second is characterised by a sharp decrease in microhardness with distance from the metal-mould interface. It represents a diffusion zone for solutes that dissolve into titanium from the mould. The qualitative profiles for contaminants determined by scanning electron probe microanalyser and secondary ion mass spectroscopy in the as-cast titanium were found to be similar to that of microhardness, implying that microhardness can be considered as an index of the contamination resulting from metal-mould reaction.     

Rate-dependent serrated flow and plastic deformation in Ti45Zr16Be20Cu10Ni9 bulk amorphous alloy during nanoindentation

The plastic deformation of Ti₄₅Zr₁₆Be₂₀Cu₁₀Ni₉ bulk metallic glass has been investigated by nanoindentation performed with loads ranging from 10 to 200 mN in a wide range of loading rates. The plastic flow in the alloy exhibited conspicuous serrations at low loading rates. The serrations, however, became less prominent as the rate of indentation increased. Atomic force microscopy showed a significant pile-up of materials around the indents, indicating that a highly localized plastic deformation occurred under nanoindentation. The possible mechanism governing the plastic deformation in bulk metallic glass specimens is tentatively discussed in terms of strain-induced free volume.     

Investigation of the secondary phases of Alloy 617 by Scanning Kelvin Probe Force Microscope

Alloy 617 (nickel based austenitic alloy) is a candidate structural material for next generation high temperature nuclear reactor. The secondary phases present in the Alloy 617 has been identified as TiN and M₂₃C₆ by optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). Surface potentials of these phases have been evaluated by Scanning Kelvin Probe Force Microscope (SKPFM). SKPFM investigation showed higher surface potential of the secondary phases than that of the austenite matrix. The surface potential of the TiN was nobler than that of M₂₃C₆ indicating that these precipitates could act as cathodic sites during oxidation reaction. Difference in the local chemistry of these phases results in variation of the chemical potentials, which in turn could lead to enhanced oxidation at localized areas in the vicinity of the secondary phase precipitates that act as cathodic sites.     

Studies on haemoglobin from the Indian toad, Bufo melanostictus, by electron microscopy

Hæmoglobin from an amphibian, Bufo melanostictus, was studied by electron microscopy after metal shadowing and after negative staining with uranyl acetate. The effect of the electron stain on the protein was investigated by spectrophotometry. The sample was also characterized by alkali denaturation and sedimentation analysis. The results were compared to those of adult human hæmoglobin. Spectrophotometry of the sample showed characteristics similar to those of normal oxyhæmoglobin. The protein, like human adult hæmoglobin, was found to be completely alkali-labile. Ultracentrifugation of a freshly prepared sample showed a single symmetrical peak, an indication for the presence of a homogeneous component. The S⁰_20,W value (5.1) was found to be markedly higher than that of adult human hæmoglobin. With storage, however, the peak became asymmetrical suggesting the formation of a limited amount of a heavier component. The electron micrographs of the shadowed preparations revealed a characteristic shape and ultrastructure of the protein molecules and their average height was found to be 5.5 nm. The micrographs of the negatively stained samples showed many particles with a substructure similar to that of the shadowed molecules and a mean dimension of 6.1 nm, a number of dimers of average length 6.0 nm and overall width 3.6 nm, and many globules of average diameter 3.6 nm. These were interpreted as whole, half and quarter hæmoglobin molecules, respectively. Both techniques revealed at the most four subunits in a molecule. The structure of the subunits and their arrangement in the molecule were found to be essentially similar to those of normal human adult hæmoglobin, and could be interpreted in terms of the Perutz model. Spectrophotometry of the mixture of the protein and uranyl acetate showed that the protein becomes denatured with time and that the denaturation is due to the low pH (4.3) of the stain. Nevertheless, this study showed that by keeping the staining time very short, it is possible to obtain acceptable electron micrographs of small multi-unit protein molecules such as haemoglobin.     

Analysis of transients in a canal network

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