Effect of dynamic strain ageing on the tensile properties of a modified 9Cr–1Mo steel

Tensile testing of a modified 9Cr–1Mo steel in two microstructural conditions (710T– normalized at 1100°C, tempered at 710°C, and 550T – normalized at 1100°C tempered at 550°C) in the temperature range 25–450°C, under strain rates of 2.3×10-5–2.3×10-3s-1, exhibited serrated flow curves, with serrations appearing almost at the onset of deformation and disappearing before ultimate strengths were attained. The serrated flow curves (characteristics of dynamic strain ageing) were accompanied by increased ultimate strengths, loss of ductility and negative strain-rate sensitivity, relative to the ambient temperature properties. However, the increase in ultimate strength and the reduction in ductility were much larger for 710T specimens, as compared to 550T ones. In the dynamic strain ageing regime, the work-hardenability of 710T specimens increased rapidly while that of 550T specimens remained practically unaffected. Based on the microstructural consideration and the observed activation energy of 45 kJ mol-1, it is proposed that serrations are initiated by a nitrogen atmosphere formation on the waiting dislocations by a pipe diffusion mechanism, and they disappear by diffusion to the precipitate sinks during deformation. Because the fine alloy carbide precipitates in 550T specimens are more effective sinks than those of 710T ones, they can cause much faster depletion of the atmosphere, resulting in a much smaller effect of dynamic strain ageing on the tensile properties of 550T specimens.     

Effect of preparation method on the dispersion and activity of V2O5–Al2O3 catalysts

Al2O3-supported 12 wt% V2O5 catalysts were prepared by physically grinding both the oxides (solid–solid wetting) and by wet impregnation techniques. The physical mixtures (PM) were treated under two different conditions – calcination in the presence of dry oxygen and wet oxygen. The catalysts were characterized by x-ray diffraction, scanning electron microscopy, electron spin resonance and oxygen and carbon dioxide chemisorptions. Vanadia dispersion of the physical mixture calcined in the presence of wet oxygen was found to be very similar to that of the V2O5/Al2O3 catalyst prepared by the standard impregnation method. Methanol partial oxidation activities of these catalysts were also comparable. This revised version was published online in November 2006 with corrections to the Cover Date.     

SHELF-LIFE MODELING OF SWEETENED CONDENSED MILK BASED ON KINETICS OF MAILLARD BROWNING

Nonenzymatic browning and related changes were monitored in commercial sweetened condensed milk stored at 7, 15, 30, 45 and 55C. Darkening of the color measured in terms of absorbance (100 - reflectance percent) followed zero-order kinetics, the apparent activation energy (E_a) being 45.2 kJ/mol at 7–30C and 139.9 kJ/mol at > 30–55C. Hydroxy-methyl-furfural (HMF) showed a first-order increase, the associated E_a values being smaller than those for absorbance. The pH exhibited a linear decline after a small initial rise at 30C and below. As browning progressed, the coffee whitening ability of the product decreased along zero-order kinetics. The Q₁₀ values for these variables ranged from 1.21 to 1.84 for temperatures up to 30C and were nearly 2–3 times higher above 30C. The sensory color score was negatively correlated with absorbance. The linear regression of color score on absorbance and the temperature dependence of the latter as expressed by Arrhenius relationship were combined into a mathematical model which could be useful in predicting the product's shelf-life.     

Effects of Gamma Irradiation on Proteins and Fatty Acids of Soybean

Two hundred grams of soybean seeds (moisture contents of 7.4, 15.3, 22.5, and 30.5%) were irradiated at dose levels of 0, 1, 5, 10, 20, 40, 60, 80 and 100 KGy using Cobalt-60 source. Radiation dose of 100 KGy caused a decrease in the percentage of nitrogen solubility from 80.3 to 67.2, 80.3 to 57.8, and 68.1 to 48.8 when deionized H₂O, 0.6M NaCl, and 0.2M Cacl₂ were used as solvents, respectively. Inhibition of 71% of lipoxygenase activities, 25.4% trypsin inhibitor activities, and 16.7% chymotrypsin inhibitor activities were found when the soybean seeds were irradiated at 100 KGy.     

RESIDENCE TIME DISTRIBUTION (RTD) AND GOODNESS OF MIXING (GM) DURING CO2-INJECTION IN TWIN-SCREW EXTRUSION PART II: GM STUDIES

Experimental residence-time distribution (RTD) characteristics of an extrusion process may be used to estimate the extent of mixing experienced in the extruder. Using earlier theories of laminar mixing and striation thickness reduction, a new approach to estimate efficacy of mixing of two phases in the mixing zone of the extruder is proposed. Predicting the time required to achieve complete mixing and comparing it with the minimum time (plug flow time) that the extrudate spends in the mixing zone gives a ratio that can be used to evaluate the adequacy of extruder operating conditions for good mixing of gas/fluid injection and extrudate. Twin-screw extrusion of cornmeal with carbon dioxide injection were used to investigate the effect of CO₂ injection pressure and extruder screw speeds on mixing. Lower CO₂ injection pressures (25 bars) and lower screw speeds (150 rpm) were theoretically shown to enhance mixing. Scanning electron micrographs (SEMs) of experimental samples taken showed smaller and more uniform cell structures for those conditions which were predicted to favor better mixing.     

Some new distance measures for type-2 fuzzy sets and distance measure based ranking for group decision making problems

In this paper, we propose some distance measures between type-2 fuzzy sets, and also a new family of utmost distance measures are presented. Several properties of differ- ent proposed distance measures have been introduced. Also, we have introduced a new ranking method for the ordering of type-2 fuzzy sets based on the proposed distance measure. The proposed ranking method satisfies the reasonable prop- erties for the ordering of fuzzy quantities. Some properties such as robustness, order relation have been presented. Lim- itations of existing ranking methods have been studied. Fur- ther for practical use, a new method for selecting the best alternative, for group decision making problems is proposed. This method is illustrated with a numerical example.     

Understanding the effect of <Emphasis Type="Italic">n</Emphasis>-type and <Emphasis Type="Italic">p</Emphasis>-type doping in the channel of graphene nanoribbon transistor

In this paper, device performance of graphene nanoribbon field effect transistor (GNRFET) with different doping concentrations in different parts of the channel is reported. The study is performed by using atomistic simulations based on self-consistent solution of Schrodinger’s and Poisson’s equation within the non-equilibrium Green’s function formalism. The transfer and output characteristics suggest that device performance with n-type doping in the channel is better with smaller supply voltage compared to higher supply voltage. On increasing the n-type doping concentration, we obtained better on-current and output characteristics in comparison with undoped and p-type doped channel GNRFET. Further, we introduced step-doping profile in the graphene nanoribbon (GNR) channel and found that the device gives better on-current and good saturation condition when compared to undoped or uniformly-doped channel.     

Enhanced thermal conductivity of nano-SiC dispersed water based nanofluid

Silicon carbide (SiC) nanoparticle dispersed water based nanofluids were prepared using up to 0·1?vol% of nanoparticles. Use of suitable stirring routine ensured uniformity and stability of dispersion. Thermal conductivity ratio of nanofluid measured using transient hot wire device shows a significant increase of up to 12% with only 0·1?vol% nanoparticles and inverse dependence of conductivity on particle size. Use of ceramic nanoparticles appears more appropriate to ensure stability of dispersion in nanofluid in closed loop single-phase heat transfer applications.     

Discrete two-time-scale systems

In this paper reduced-order modelling and control analysis of linear, discrete-time systems having dominant and non-dominant modes are presented. Decoupling of modes is achieved using an explicitly invertible linear transformation. A matrix norm condition is derived, the satisfaction of which enables approximate expressions for the block-diagonalizing matrices, eigenvalue distribution and state trajectories to be obtained. Design of stabilizing feedback controllers is developed and it is shown that two gain matrices are needed for separate assignment of dominant and non-dominant eigenvalues. The theoretical analysis is illustrated by control system examples.