Assessment of integrity of components in piping of 500 MWe PHWR: using R-6 method

The primary heat transport system of 500 MWe Indian PHWR comprises of straight pipes, elbows and headers. A study was conducted to qualify piping system for leak before break. R-6 method was used to assess integrity of system for leakage size crack (LSC), the margins on crack initiation load and unstable crack growth loads. Option 2 (material specific failure assessment diagram), Category 3 (ductile tearing) analysis was used for straight pipes, elbows and header. In order to enhance the confidence in the analytical results, detailed sensitivity analysis was also performed. For sensitivity analysis, variation in material properties, LSC was considered. The effect of variation in temperature on material properties was also considered. Tensile and fracture properties used for base and weld material data were generated from pipe material obtained from 220 MWe Nuclear Power Plant, under construction.     

Evaluation of seismic fragility of structures—a case study

The present paper attempts to evaluate the seismic fragility for a typical elevated water-retaining structure. The structure is analysed for two cases: (i) empty tank; and (ii) tank filled with water. The various parameters that could affect the seismic structural response include material strength of concrete and reinforcing steel, effective prestress available in the tank, ductility ratio and structural damping available within the structure, normalised ground motion response spectral shape, foundation and surrounding soil parameters and the total height of water available in the tank. Based on this case study, the seismic fragility of the structure is developed. The results are presented as families of conditional probability curves plotted against peak ground acceleration (PGA) at two critical locations. The procedure adopted, incorporates the various randomness and uncertainty associated with the parameters under consideration.     

Lipid composition ofNeurospora crassa

The lipids ofNeurospora crassa, isolated in pure form from freeze-dried mycelium, were found to contain squalene, sterol esters, triglycerides, free fatty acids, geranylgeraniol, free sterols, carotenoids, cardiolipin, phosphatidyl ethanolamine, phosphatidyl choline, phosphatidyl serine, and phosphatidic acid. The above compounds were isolated in pure form by column and thin layer chromatography and were characterized by infrared spectroscopy and chromatographic mobilities. Fatty acid moieties were characterized by gas liquid chromatographic retention times of their methyl esters relative to those of authentic standards. The fatty acid composition of the triglycerides was found to be similar to that of phosphatidic acid, cardiolipin, and lecithin.     

The S4-S5 loop contributes to the ion-selective pore of potassium channels

Mutagenesis experiments on voltage-gated K+ channels have suggested that the ion-selective pore is comprised mostly of H5 segments. To see whether regions outside of the H5 segment might also contribute to the pore structure, we have studied the effect of single amino acid substitutions in the segment that connects the S4 and S5 putative transmembrane segments (S4-S5 loop) on various permeation properties of Shaker K+ channels. Mutations in the S4-S5 loop alter the Rb+ selectivity, the single-channel K+ and Rb+ conductances, and the sensitivity to open channel block produced by intracellular tetraethylammonium ion, Ba2+, and Mg2+. The block of Shaker K+ channels by intracellular Mg2+ is surprising, but is reminiscent of the internal Mg2+ blockade of inward rectifier K+ channels. The results suggest that the S4-S5 loop constitutes part of the ion-selective pore. Thus, the S4-S5 loop and the H5 segment are likely to contribute to the long pore characteristic of voltage-gated K+ channels.     

Regulatory arrestin cycle secures the fidelity and maintenance of the fly photoreceptor cell

Excitation of fly photoreceptor cells is initiated by photoisomerization of rhodopsin to the active form of metarhodopsin. Fly metarhodopsin is thermostable, does not bleach, and does not regenerate spontaneously to rhodopsin. For this reason, the activity of metarhodopsin must be stopped by an effective termination reaction. On the other hand, there is also a need to restore the inactivated photopigment to an excitable state in order to keep a sufficient number of photopigment molecules available for excitation. The following findings reveal how these demands are met. The photopigment undergoes rapid phosphorylation upon photoconversion of rhodopsin to metarhodopsin and an efficient Ca2+ dependent dephosphorylation upon regeneration of metarhodopsin to rhodopsin. Phosphorylation decreases the ability of metarhodopsin to activate the guanine nucleotide-binding protein. Binding of 49-kDa arrestin further quenches the activity of metarhodopsin and protects it from dephosphorylation. Light-dependent binding and release of 49-kDa arrestin from metarhodopsin- and rhodopsin-containing membranes, respectively, directs the dephosphorylation reaction toward rhodopsin. This ensures the return of phosphorylated metarhodopsin to the rhodopsin pool without initiating transduction in the dark. Assays of rhodopsin dephosphorylation in the Drosophila retinal degeneration C (rdgC) mutant, a mutant in a gene previously cloned and predicted to encode a serine/threonine protein phosphatase, reveal that phosphorylated rhodopsin is a major substrate for the rdgC phosphatase. We propose that mutations resulting in either a decrease or an improper regulation of rhodopsin phosphatase activity bring about degeneration of the fly photoreceptor cells.     

Observation of Meyer-Neldel relation for non-isothermal crystallization in Se<Subscript>70</Subscript>Te<Subscript>30</Subscript> and Se<Subscript>70</Subscript>Te<Subscript>28</Subscript>M<Subscript>2</Subscript> (M = Ag,Sb, Zn) glasses

In the present paper, we report the applicability of Meyer-Neldel rule for pre-exponential factor of non-isothermal crystallization in Se₇₀Te₃₀ and Se₇₀Te₂₈M₂ (M = Ag, Sb, Zn) glasses using DSC technique. We have observed strong correlation between pre-exponential factor K ₀ and activation energy of non-isothermal crystallization E _c for the present glasses.