Antioxidant formation by γ-irradiation of glucose–amino acid model systems

The efficacy of γ-irradiation for the formation of Maillard reaction products (MRPs) from glucose and lysine/glycine and the antioxidant potential of MRPs thus formed were examined. Formation of MRPs was observed by monitoring absorbance at 284 nm and 420 nm. Upon irradiation, there was a dose-dependent increase in absorbance (r² = 0.99) at both the wavelengths. Irradiation of glucose/lysine solution resulted in higher absorbance at 284 nm than did that of glucose/glycine solution. Similarly, increase in absorbance at 420 nm was observed upon irradiation in both the systems. No significant absorbance was observed with unirradiated solution of glucose and lysine/glycine. These findings thus clearly revealed the formation of intermediate products and brown complexes (of Maillard reaction) upon irradiation of glucose/amino acid solution. A fluorescence was also observed in irradiated glucose/amino acid solution, whereas, none was seen in non-irradiated solution. These observations further confirmed the formation of MRPs, as fluorescent compounds are known to be precursors of brown pigments formed during the Maillard reaction. These MRPs exhibited excellent antioxidant activity, as measured by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and β-carotene bleaching assays. MRPs, formed at a 40 kGy dose, scavenged up to 62% of DPPH radical and 82% of β-carotene was protected from bleaching. Reducing power of MRPs, estimated using the ferricyanide, method was also increased as compared to non-irradiated solutions. Further, these MRPs were able to scavenge hydroxyl radical and superoxide anion radical to the extents of 33% and 58%, respectively. These MRPs could chelate iron to an extent of 32% under in vitro conditions. Thus, these studies clearly demonstrated that radiation technology could be employed for obtaining novel antioxidants from sugar and amino acid combinations.     

Analysis of indentation-derived effective elastic modulus of metal-ceramic multilayers

A numerical study was undertaken to study the elastic property of metal-ceramic multilayered composites derived from indentation testing. The model system features alternating thin films of aluminum (Al) and silicon carbide (SiC), free from any effect due to the underlying substrate. The anisotropic composite elastic response was obtained by simulating overall loading of the multilayer structure. Finite element modeling of instrumented indentation was then employed to calculate the indentation-derived modulus using the unloading portion of the load–displacement curve. The results from indenting the homogenized composite (with the built-in multilayer property) and from indenting the real multilayers (with Al and SiC layers explicitly accounted for) were compared. It was found that an indentation depth beyond approximately 8–10 initial layer thicknesses is sufficient to yield a valid composite elastic response. The effective modulus thus obtained is representative of the out-of-plane modulus of the multilayer composite.     

Hydrogen-induced cracking in two linepipe steels

Linepipe steels are susceptible to hydrogen-induced cracking (HIC) in wet, sour gas environments. Two commercially produced linepipe steels were investigated with regard to HIC on cathodic charging. Both steels, B and C, showed a high banded microstructure consisting of alternative layers of polygonal ferrite and a mixture of non-ferritic constituents (pearlite, bainite, and martensite-austenite). The degree of banding was higher in Steel B than in Steel C. Also present were elongated inclusions in Steel B, while in Steel C they were more or less equiaxed. On cathodically hydrogen-charging in the absence of external stress, microvoids formed at low current densities at or around inclusions. On prolonged charging, these voids grew and propagated parallel to the bands, running along the interface between ferrite/non-ferrite constituents, along inclusions lodged in the non-ferritic consitituents, and at places through the non-ferritic constituents. Steel B, not unexpectedly, showed more severe permanent microstructural damage than Steel C, leading to the conclusion that a high banded structure and/or the presence of elongated inclusions is deleterious to resistance against HIC.     

The role of the SnO2 interphase in an alumina/glass composite: a fractographic study

The role of tin dioxide (SnO₂) interphase for the alumina/glass composite system was investigated using fractography. Alumina (Al₂O₃) and glass form a strong chemical bond which is undesirable for toughness in a ceramic matrix composite. SnO₂ interphase was incorporated to prevent this strong bond between alumina and glass. SnO₂ was deposited on Al₂O₃ substrates via chemical vapour deposition and bonded with glass. The role of the interphase was then studied by characterizing the fracture surfaces of the bend test and special composite disc samples loaded in diametral compression. Bend tests results showed that the SnO₂ interphase and/or the SnO₂/Al₂O₃ interface acted as a plane of weakness. Secondary cracking at 90° to the major crack direction was observed along this plane of weakness, which appears to be in accord with the Cook and Gordon model. Crack deflection and secondary cracking were also observed in the SnO₂ region of the compression samples. These results indicate the suitability of SnO₂ interphase for the alumina/glass composite system.     

The effect of matrix microstructure on the tensile and fatigue behavior of SiC particle-reinforced 2080 Al matrix composites

The effect of matrix microstructure on the stress-controlled fatigue behavior of a 2080 Al alloy reinforced with 30 pct SiC particles was investigated. A thermomechanical heat treatment (T8) produced a fine and homogeneous distribution of S′ precipitates, while a thermal heat treatment (T6) resulted in coarser and inhomogeneously distributed S′ precipitates. The cyclic and monotonic strength, as well as the cyclic stress-strain response, were found to be significantly affected by the microstructure of the matrix. Because of the finer and more-closely spaced precipitates, the composite given the T8 treatment exhibited higher yield strengths than the T6 materials. Despite its lower yield strength, the T6 matrix composite exhibited higher fatigue resistance than the T8 matrix composite. The cyclic deformation behavior of the composites is compared to monotonic deformation behavior and is explained in terms of microstructural instabilities that cause cyclic hardening or softening. The effect of precipitate spacing and size has a significant effect on fatigue behavior and is discussed. The interactive role of matrix strength and SiC reinforcement on stress within “rogue” inclusions was quantified using a finite-element analysis (FEA) unit-cell model.     

On the effects of oxygen cross-sections in the fast neutron fluence analysis for a reactor pressure vessel scraping test

Studies in support of the assessment of aging structural materials in pressurized water reactors are being performed at the Paul Scherrer Institut. To that aim, a state-of-the-art methodology based on applying a CASMO-4/SIMULATE-3/MCNPX calculation scheme has been developed. In the frame of the methodology validation, an investigation is currently reported pertaining to the sensitivity of the calculated results, for a specific reactor pressure vessel scraping test, to the nuclear data used with the Monte Carlo code. Thus, the MCNPX-2.4.0 calculations have been carried out using three different data libraries, based on JEF-2.2, ENDF/B-VI.8 and JENDL-3.3 evaluations, respectively.     

The application of explicit Nyström methods to singular second order differential equations

An important class of singular second order initial value problems is y″ + (2/x)y′+f(x,y) = 0, 0 < x < x_f, y(0) = a, y′(0) = 0; this class includes, for example, the well-known singular equations of Emden and Liouville. The purpos of this paper is to show the interesting result that explicit Nyström methods, existing for the direct integration of special second order regular initial value problems, can be used for the integration of this class of singular initial value problems and the methods show their proper respective orders of convergence. This is justified mathematically and demonstrated computationally.     

A 1 GHz Digital Channel Multiplexer for Satellite Outdoor Unit

A digital channel multiplexer for satellite outdoor unit running at 1 GHz clock frequency is implemented in 65 nm CMOS mixed oxide dual voltage technology. This multiplexer, based on a 1 GS/s digital signal processor (DSP) approach with 500 MHz input and output bandwidth, embeds two 8 bit 1 GS/s analog-digital converters (ADCs) and two 8 bit 1 GS/s digital-analog converter (DACs). It consumes less that 1022 mW at ambient temperature while achieving noise rejection up to 42.5 dB on a single tone, and > 37 dB on modulated satellite channels.