Effect of iron on microstructure and mechanical properties of primary AlSi7Mg0.3 alloy

Effect of Fe on microstructure and mechanical properties of the primary AlSi7Mg0.3 alloy and the potential of Mn addition to counteract any adverse effects was investigated in the present work. The primary AlSi7Mg0.3 is a better alloy than its counterpart with twice as much Fe. β platelets grow twice as big when the Fe concentration is doubled. This, in turn, increases shrinkage porosity and leads to a 3-fold decrease in the tensile elongation values. Adding an equal amount of Mn helps to modify the β platelets into more compact α particles and also reduces shrinkage porosity. While these structural changes are reflected by a modest improvement in the mechanical properties, Mn addition fails to offer a full recovery in the ductility of the AlSi7Mg0.3 alloy. Hence, limiting the Fe content of the primary AlSi7Mg0.3 alloy to 0.12 wt% is worthwhile and pays off with superior microstructural features and mechanical properties.     

Synthesis and electrochemical properties of binary MgTi and ternary MgTiX (X = Ni,Si) hydrogen storage alloys

Mg-based hydrogen storage alloys are promising candidates for many hydrogen storage applications because of the high gravimetric hydrogen storage capacity and favourable (de)hydrogenation kinetics. In the present study we have investigated the synthesis and electrochemical hydrogen storage properties of metastable binary Mg_yTi_1?y (y = 0.80–0.60) and ternary Mg_0.63Ti_0.27X_0.10 (X = Ni and Si) alloys. The preparation of crystalline, single-phase, materials has been accomplished by means of mechanical alloying under controlled atmospheric conditions. Electrodes made of ball-milled Mg_0.80Ti_0.20 powders show a reduced hydrogen storage capacity in comparison to thin films with the same composition. Interestingly, for a Ti content lower than 30 at.% the reversible storage capacity increases with increasing Ti content to reach a maximum at Mg_0.70Ti_0.30. The charge transfer coefficients (α) and the rate constants (K₁ and K₂) of the electrochemical (de)hydrogenation reaction have been obtained, using a theoretical model relating the equilibrium hydrogen pressure, electrochemically determined by Galvanostatic Intermittent Titration Technique (GITT), and the exchange current. The simulation results reveal improved values for Mg_0.65Ti_0.35 compared to those of Mg_0.80Ti_0.20. The addition of Ni even more positively affects the hydrogenation kinetics as is evident from the increase in exchange current and, consequently, the significant overpotential decrease.     

Characterization of the polymer of a dipyrrolyl monomer by pyrolysis mass spectrometry

In this work, characterization of a homopolymer of succinic acid bis(4‐pyrrol‐1‐ylphenyl) ester prepared by galvonastatic polymerization was carried out by direct pyrolysis mass spectrometry. Although decomposition of the monomer yielding mainly butadionic acid and pyrrole occurred under the galvonastatic polymerization conditions, growth of the polymer through the pyrrole moieties was also achieved, yielding a ladder‐type polymer film. The polypyrrole chains contained both quinoid and aromatic units as in the case of polypyrrole, yet the extent of network structure was significantly diminished. A three‐step mechanism is proposed for the thermal decomposition process. The first step involves the cleavage of C₄H₄NC₆H₄O end groups. In the second step, decomposition of phenyl ester units and polypyrrole chains having quinoid structure takes place. The final stage of thermal degradation was attributed to decomposition of polypyrrole chains having aromatic structure. Copyright © 2004 Society of Chemical Industry     

Improving transient performance of discrete-time model reference adaptive control architectures

Discrete-time adaptive control algorithms can be executed directly in embedded code unlike their continuous-time counterparts, which require discretization. However, their designs predicated on quadratic Lyapunov-based frameworks are quite intricate due to the resulting complexity in the Lyapunov difference expressions. Therefore, a wide array of available continuous-time results addressing transient performance issues using adaptive control algorithms cannot be applied or readily extended to the discrete-time case. In this article, we present a new model reference adaptive control architecture for discrete-time uncertain dynamical systems. Specifically, the proposed architecture consists of a command governor mechanism that adjusts the trajectory of a given command during the closed-loop transient response. It is shown that this mechanism is effective in improving transient performance of discrete-time model reference adaptive control architectures. Using a logarithmic Lyapunov function, we prove Lyapunov stability of the closed-loop system as well as asymptotic convergence of the system error states involving the difference between the states of the uncertain dynamical system and the states of the reference model, as well as driving the command governor signal to zero.     

Comparison of the effects of adding microbial transglutaminase to milk and ice cream mixture on the properties of ice cream

In this study, the effect of recombinant microbial transglutaminase enzyme on the physicochemical properties of ice cream produced by two different methods was investigated. For this purpose, different enzyme units (2, 4 and 6 U/g milk protein) were applied to both ice cream mixture and milk. While with the first method, a 10% increase in the overrun value of ice cream samples was observed, a 7% increase was obtained by the second method. All ice cream samples exhibited pseudoplastic behaviour. This study indicated that  transglutaminase concentration is an important factor in terms of improving the physicochemical properties of ice cream.