Implementation of APP decoders on dual code trellis

For high rate k/n convolutional codes (k/n > 0.5), a trellis based implementation of a posteriori probability (APP) decoders is less complex on the dual code trellis owing to its branch complexity (2^n-k ) being lower than the code trellis (2^k). The log scheme used for APP decoders is not attractive for practical implementation owing to heavy quantisation requirements. As an alternative, presented is an arc hyperbolic tangent (AHT) scheme for implementing the dual- APP decoder. The trellis based implementation of this AHT dual APP decoder is discussed and some fundamental differences between primal APP and dual APP decoders that have an effect on a quantised implementation are reported.     

Structural and antioxidant properties of gamma irradiated hyaluronic acid

Hyaluronic acid (Hyaluronan, HA) was depolymerised by gamma irradiation and its structural changes and antioxidant activities were investigated. The structural changes of gamma irradiated HA were studied by gel-permeation chromatography (GPC), viscosity, pH, Hunter colour measurement, UV spectrophotometry, and FT-IR spectroscopy. The results demonstrated that gamma irradiation decreased molecular weight size, viscosity and pH of the hyaluronic acid and its colour turned to intense yellow. UV spectra of the irradiated HA showed a change at 265 nm, which indicates the formation of double bonds. Differences in the height and shape of certain absorption bonds of FT-IR spectra in the range 1700–1750 cm⁻¹ were also observed, which is associated with the formation of carboxylic acid. From these structural changes of the HA, gamma irradiation may have a role in the formation of pyrancarboxylic acid rings. DPPH radical scavenging ability and the reducing power of gamma irradiated HA were significantly higher than that of non-irradiated HA. However, non-irradiated and irradiated HA did not show significant differences in the Rancimat test.     

A novel approach to determine high temperature wettability and interfacial reactions in liquid metal/solid interface

In many technical processes, high temperature wetting of a liquid metal phase on a solid substrate occurs via an extensive chemical reaction and the formation of a new solid compound at the interface. For instance, good adhesion of the zinc coating to the steel surface is one of the most important requirements that the hot-dip galvanizing process has to fulfill. Good adhesion directly depends on the formation of a defect-free Fe₂Al₅ inhibition layer at the interface. The complex surface chemistry of oxides on the steel surface which is a result of segregation and selective oxidation upon recrystallization annealing significantly influences the kinetics of the correlated reactive wetting. This article presents the development of a novel advanced technique for the investigation of high temperature wetting process up to a temperature of 1100 K and provides first new insights in the mechanisms of the reactive wetting process in presence of oxides on the surface. The method is based on the sessile drop method with an additional spinning technique to get rid off the liquid metal phase at any chosen wetting time, thusly opening the way to access the interfacial reaction layer directly. The presented work focuses on model alloys of interest which are mainly relevant to the industrial steel grades. Emphasis is put both on the wettability of liquid Zn and on the interfacial reactions during reactive wetting process. Insights into such reactive phenomena are fundamental demand to improve the hot-dip galvanizability of advanced high strength steel grades.     

Surface structural disordering in graphite upon lithium intercalation/deintercalation

We report on the origin of the surface structural disordering in graphite anodes induced by lithium intercalation and deintercalation processes. Average Raman spectra of graphitic anodes reveal that cycling at potentials that correspond to low lithium concentrations in Li_xC (0 ≤ x < 0.16) is responsible for most of the structural damage observed at the graphite surface. The extent of surface structural disorder in graphite is significantly reduced for the anodes that were cycled at potentials where stage-1 and stage-2 compounds (x > 0.33) are present. Electrochemical impedance spectra show larger interfacial impedance for the electrodes that were fully delithiated during cycling as compared to electrodes that were cycled at lower potentials (U < 0.15 V vs. Li/Li⁺). Steep Li⁺ surface-bulk concentration gradients at the surface of graphite during early stages of intercalation processes, and the inherent increase of the Li_xC d-spacing tend to induce local stresses at the edges of graphene layers, and lead to the breakage of C-C bonds. The exposed graphite edge sites react with the electrolyte to (re)form the SEI layer, which leads to gradual degradation of the graphite anode, and causes reversible capacity loss in a lithium-ion battery.     

Structural design approach of steam generator made of modified 9Cr-1Mo for high temperature operation

Once through shell and tube steam generators made up of modified 9 Cr-1Mo are employed in nuclear and other power plants for producing steam. In Fast Breeder Reactor (FBR), Steam Generator (SG) is a critical component as its availability decides the capacity factor of the plant. In the 500 MWe pool type PFBR, there are 8 steam generators (SGs), 4 in each of the two secondary loops. These steam generators are taken as reference component for this paper. Each SG is a shell and tube, once through vertical heat exchanger. The sodium is on the shell side and the water / steam is on the tube side. The secondary sodium enters at 798 K and leaves at 628 K. The water is enters at the bottom at 508 K and the superheated steam leaves at the top at 766 K. SG is around 25 m tall and supported at the center of the component. The design life is 40 Y for PFBR and will be more for future steam generators. The first step in structural design of the steam generators is to identify the critical locations with respect to high temperature failure modes. In case of PFBR SG, the critical locations are tube to tubesheet joint, tubesheet to shell junction, shell nozzle junction and support junction. The modeling and analysis procedure for these critical parts particularly (i) the treatment of perforated region in the tubesheets, (ii) idealizing of tube to tubesheet welds and (iii) stress analysis of shell -support junction as well as shell nozzle junction, are discussed in the paper. Typical analyses for PFBR with results are presented as illustration. The paper also addresses further areas of interest for future research.     

Assessment of creep-fatigue damage at main vessel triple point of Prototype Fast Breeder Reactor after core disruptive accident

The main vessel (MV) carries all the major reactor components including core and liquid sodium filled to 12.4 m height. The reactor core along with the inner vessel is placed on the grid plate, which is supported on the core support structure (CSS). The CSS is supported on the MV through a support shell, welded to the dished end at the point where crown and knuckle joins. The CSS support shell to MV joint is called as triple point and damage at this point is of concern. The core catcher (CC) is placed below the CSS and is also supported on the CSS support shell. The triple point is subjected to a dead load of 920 t. During the unlikely event of core disruptive accident (CDA) a high dynamic pressure will act on the core catcher (CC), which in turn exerts a high load on the triple point. Also the hot molten core debris will come to the CC, which is close to the MV dished end. This will result in increase of temperature in the cold pool, which will cause significant creep damage at triple point during post accident heat removal phase. As the triple point is the only junction, which is supporting the reactor core and CC through CSS support shell, its failure can cause serious consequences to the integrity of MV. Hence, triple point is analysed to ensure its integrity during the transient pressure loading and subsequent post accident heat removal (PAHR) phase of CDA. The stress intensities during transient pressure are found to be within the limits. The subsequent creep damage during post accident heat removal (PAHR) phase is also assessed. Based on the apportioned creep damage of 0.4 for category 4 events, the triple point can be kept at a temperature of 923 K (650°C) or 973 K (700°C) effectively for a period of 1.2 × 10⁴ h (500 days) or 662 h (27.6 days) respectively which are acceptable with comfortable margin. More details are presented in the paper.     

Recoverable file system for microprocessor systems

Initiation of recovery procedures, after a system failure, cannot always be expected from the users of microprocessor systems. Automatic recovery is required after system startup from a failure. The paper proposes a simple file store design such that the integrity of data is assured and the loss of data is minimized after a system failure. The concepts of check-point and shadow-page mechanisms used in databases are adopted to achieve recovery in microprocessor systems. The overhead involved in such a file system is also discussed.     

A non-interfering selective disassembly sequence for components with geometric constraints

This paper analyzes the problem of global disassembly of a selected component from a geometrically constrained assembly. The geometric constraints are: (i) spatial constraints due to the three-dimensional geometric interactions between the components in an assembly; and (ii) user-defined constraints, such as grouping of components as subassemblies and directional constraints on component geometry. A new algorithm has been proposed to determine a non-interfering disassembly sequence for a selected component, minimizing the number of simultaneous component removals. The algorithm analyzes both the spatial constraints of the assembly geometry and the user-defined constraints in evaluating the accessibility of components, which is followed by determining the topological disassembly ordering of the components to evaluate an optimal sequence. Preliminary implementation results of the algorithm for a geometrically constrained assembly are presented.