Modelling in magnesium alloy with superplastic layer: implications for shear in fault zones induced in olivine by phase transformation

Analysis of a recently discovered high-pressure phase-transformation-induced mechanism of shear failure in Mg₂Ge0₄ olivine has produced evidence that sliding in the resulting fault zone is accomplished by superplastic flow of the extremely fine-grained high-density phase produced during the transformation. This failure mechanism is of interest because it may be the mechanism by which deep earthquakes are generated in the earth's mantle. To gain insight into this process, we have conducted model tensile experiments on coarse-grained, non-superplastic, specimens of Mg-15%Mn-0.3%Ce alloy, within which a fine-grained, superplastic, planar zone was fabricated at an orientation of 45 ° to the stress axis. Flow was largely restricted to shear offset within the superplastic zone. The experiments were interrupted periodically and microstructural observations were made. Repeated detailed observation of several regions at different strain levels showed that the main mechanism of shear operative in the superplastic region was grain-boundary sliding occurring in a layer-by-layer manner. The common features of microstructural change observed in the magnesium alloy and in the Mg₂Ge0₄ olivine fault zones suggests that such cooperative grain-boundary sliding could be the mechanism of fault propagation in the deep earth and therefore important for understanding deep-focus earthquakes.On leave from the Ufa Aviation Institute, Ufa 450025, Russia.     

Argyrophilic nucleolar organiser regions (AgNORs) in breast lesions

Nucleolar organiser regions (NORs) demonstrated by argyrophilia of NOR-proteins are indicator of cellular proliferative activity. The NORs can be identified in the nuclei as brown or black dots with silver colloidal staining technique in formalin fixed paraffin sections and in cytology smears. Seventy-five cases including 45 tissue sections and 30 fine needle aspiration cytology (FNAC) smears of benign and malignant lesions of breast have been studied to evaluate the significance and practical application of AgNOR count per nucleus. Out of 45 tissue sections 15 belonged to fibrocystic disease, 10 fibro-adenomas and 20 carcinomas and of the 30 FNAC smears, 10 were fibrocystic disease, 8 fibro-adenomas and 12 carcinomas. In fibrocystic disease the mean AgNOR count was 1.60 (FNAC group-0.75, tissue section-1.61). In fibro-adenomas it was 1.61 (FNAC-1.63, tissue section-1.59). The mean count in carcinoma was 12.10 (FNAC-12.08, tissue section-12.10). The difference in AgNOR count in fibrocystic disease and fibro-adenoma was not significant, but that between benign breast lesion and carcinoma was significant. No difference was observed between FNAC and tissue section groups in benign or malignant lesions. The simple staining technique can be used as an additional criterion to differentiate the benign and malignant lesions of breast.     

Nondestructive characterisation of MOX fuel rods using gamma autoradiography (GAR)

During the fabrication of mixed uranium-plutonium oxide (MOX) fuel rods, two important characteristics to be checked in as-fabricated fuel pins are plutonium enrichment and plutonium dioxide agglomerates. The mixed oxide fuel pellets are made via mechanical mixing of uranium dioxide and plutonium dioxide powders by cold compaction and sintering. The chance of loading a wrong Pu enrichment pellet and having pellets with plutonium dioxide agglomerates in a fuel pin cannot be ruled out. A simple nondestructive evaluation technique is felt necessary to ensure at the last stage (in the welded pins) to check these two characteristics. During the fabrication of MOX fuel rods for Boiling Water Reactors at Advanced Fuel Fabrication Facility of BARC at Tarapur, Gamma-auto-radiography was successfully used to evaluate composition of MOX pellets and to detect presence of PuO₂ agglomerates in the peripheral region. The fuel pins are allowed to be in contact with industrial X-ray films loaded in cassettes for a long time and the processed films are carefully evaluated. Experiments were made to standardise the conditions for distinguishing fuel pellets of different composition by gamma-auto-radio-graphy of fuel pins loaded with pellets of different composition. Gamma-auto-radiography of fuel pins containing agglomerates of different sizes was also carried out. This paper describes the experimental details of the technique, results obtained and compare with other nondestructive evaluation techniques available.     

REPROCESSING HYDROFLUORIC ACID ETCHING SOLUTIONS BY REVERSE OSMOSIS

Reverse osmosis has been applied in this study for reprocessing HF present in etching solutions. Experimental results show a very high degree of permeation of HF and rejection of ionic impurities by certain membranes. An ion exclusion model has been developed to estimate the degree of HF permeation and shows the same trends as the experimental data.

To check the chemical stability of the membranes, when exposed to different concentrations of HF and Fluosilicic acid (the major impurity present in the HF etching solutions) for extended periods of time, ion rejection and water permeability properties of fresh and exposed membranes were determined. No significant change in the rejection properties was observed even after prolonged periods of exposure. The results of this work indicate that several commercially available thin film composite membranes can be used to reprocess HF by removing ionic and particulate impurities.     

Cavity distribution pattern in a superplastically deformed aluminum alloy

Cavitation in superplastically formed AA7475 aluminum alloy by gas pressure has been investigated. Two systems of cavity stringers on the diametrical section of the pressure-formed domes were observed by using optical microscopy under normal light, polarized light, and dark field. Qualitative analyses have shown that the cavity stringers are oriented 35 ∼ 60 deg to the midplane of the sheet, and the spacing of the cavity stringers decreases with increasing strain. The explanation of this new observation of cavity morphology is given from a viewpoint of cooperative grain boundary sliding (CGBS). Formerly Associate Professor with the Department of Materials Science, Ufa Aviation Institute     

Fault management in IP-over-WDM networks: WDM protection versus IPrestoration

We consider an IP-over-WDM network in which network nodes employ optical crossconnects and IP routers. Nodes are connected by fibers to form a mesh topology. Any two IP routers in this network can be connected together by an all-optical wavelength-division multiplexing (WDM) channel, called a lightpath, and the collection of lightpaths that are set up form a virtual topology. In this paper, we concentrate on single fiber failures, since they are the predominant form of failures in optical networks. Since each lightpath is expected to operate at a rate of few gigabits per second, a fiber failure can cause a significant loss of bandwidth and revenue. Thus, the network designer must provide a fault-management technique that combats fiber failures. We consider two fault-management techniques in an IP-over-WDM network: (1) provide protection at the WDM layer (i.e., set up a backup lightpath for every primary lightpath) or (2) provide restoration at the IP layer (i.e., overprovision the network so that after a fiber failure, the network should still be able to carry all the traffic it was carrying before the fiber failure). We formulate these fault-management problems mathematically, develop heuristics to find efficient solutions in typical networks, and analyze their characteristics (e.g., maximum guaranteed network capacity in the event of a fiber failure and the recovery time) relative to each other     

Deciphering the potentiodynamic polarization curves of iron aluminides Fe3Al and Fe3Al + Cr

The potentiodynamic polarization curves of Fe₃Al and Fe₃Al + Cr intermetallics obtained in aerated pH 4 H₂SO₄ acidic solution have been theoretically analyzed. The role of chromium in minimizing the hydrogen embrittlement (HE) of the intermetallic Fe₃Al (resulting in its poor ductility) has been addressed based on the analysis. In the case of the chromium-alloyed iron aluminide, calculations indicate that hydrogen liberation does not occur on the surface due to the shift of the corrosion mixed potential to a value nobler than the electrode potential for the hydrogen evolution reaction. This shift occurs due to the induction of passivity on alloying with Cr resulting in the formation of a passive film. The minimization of HE of iron aluminides on alloying with Cr can thus be understood.     

A study of solvent exchange process in (ethylene–vinyl alcohol) copolymer gels by a proton nuclear magnetic resonance spectroscopy imaging method

The proton nuclear magnetic resonance (¹H NMR) image patterns of (ethylene–vinyl alcohol) copolymer (EVOH)/dimethylsulfoxide (DMSO) gels with various ethylene contents were measured to elucidate the process of solvent exchange between DMSO and water in the gels soaked in water. The results of these experiments indicate that the rate of solvent exchange between DMSO and water in the gels increased with an increase in the ethylene content of EVOH copolymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 504–508, 2002     

Rendezvous Point Relocation in Protocol Independent Multicast-Sparse Mode

Protocol Independent Multicast-Sparse Mode is the most widely used multicast routing architecture. It builds a shared distribution tree centered at a rendezvous point and then builds source-specific trees for those sources whose data rate warrants it. Current implementations of the protocol decide on the rendezvous point administratively, which leads to congestion and delays. An attractive solution would be dynamic relocation of the rendezvous point depending on the members of the multicast group. In this paper we present a rendezvous point calculation and relocation mechanism for Protocol Independent Multicast-Sparse Mode. Simulation of the proposed mechanisms is used to demonstrate the effectiveness of the proposals.