Effect of Fe-doping on Magnetocaloric Properties of AMn1?x Fe x O3 Compounds (0≤x≤0.2)

We have investigated the effect of iron substitution on the magnetocaloric properties of manganites with La_0.75Ca_0.08Sr_0.17Mn_1?x Fe _x O₃ (x=0, 0.075, 0.15, 0.175, and 0.2) nominal composition. The magnetocaloric effect (MCE) was estimated, in terms of isothermal magnetic entropy change (???S _M ), using the M(T,?? ₀ H) data and employing the thermodynamic Maxwell equation. The large magnetic entropy in AMn_1?x Fe _x O₃ is attributed to the field-induced suppression of short-range charge-orbital ordering and antiferromagnetic fluctuations present above T _C . The increase of the Fe concentration x is accompanied by a decrease of (???S _M ), from 5.205 to 0.95?J/kg?K for x=0 and 0.20, respectively, with ?? ₀ H=5?T. For all samples, we find quite large values of (???S _M ), which are very close to that provided for Gd, the prototypical magnetocaloric material.     

A new convolution approach for the time-delay identification of systems with arbitrary entries

In this paper, an online delay identification approach of continuous-time linear systems with unstructured entries is achieved via a new algebraic technique. The arbitrary input and output trajectories are chosen with close and abundant crossing zero. Initial conditions and static disturbances are taken into account in the design of the identification approach. The proposed method is based on a distributional algebraic technique and a convolution approach. A proposed theorem is hence enounced to identify a single time-delay of such systems. The effectiveness of the proposed approach is demonstrated by an illustrative example. The obtained results show the high performances of the proposed time-delay identification approach in severe operation conditions of the considered system.     

Effect of HBT on the stability of laccase during the decolourization of textile wastewaters

BACKGROUND: This study concerns the assessment of laccase stability during textile industry effluent treatment by laccase in the presence of a mediator RESULTS: The effects of 1‐hydroxybenzotriazole (HBT) and textile wastewater on the stability of a crude laccase prepared from cultures of Trametes trogii during the process of textile industry effluent decolourization were determined. HBT was essential for decolourization of effluent by laccase. Decolourization efficiency decreased when effluent was repeatedly added to the reaction mixture, suggesting inhibition of laccase during the process. Stability of the laccase was not affected by different concentrations of effluent, but inactivation was proportional to HBT concentration. CONCLUSION: Experimental results showed that a redox mediator such as HBT was required for high decolourization rate of textile industry effluent; however free radicals generated from this compound inactivated the laccase used in the process. Copyright © 2009 Society of Chemical Industry     

STEM nanoanalysis of Au/Pt/Ti-Si3N4 interfacial defects and reactions during local stress of SiGe HBTs

Nanoscaled materials are attractive building blocks for hierarchical assembly of functional nanodevices, which exhibit diverse performances and simultaneous functions. We innovatively fabricated semiconductor nano-probes of tapered ZnS nanowires through melting and solidifying by electro-thermal process; and then, as-prepared nano-probes can manipulate nanomaterials including semiconductor/metal nanowires and nanoparticles through sufficiently electrostatic force to the desired location without structurally and functionally damage. With some advantages of high precision and large domain, we can move and position and interconnect individual nanowires for contracting nanodevices. Interestingly, by the manipulating technique, the nanodevice made of three vertically interconnecting nanowires, i.e., diode, was realized and showed an excellent electrical property. This technique may be useful to fabricate electronic devices based on the nanowires' moving, positioning, and interconnecting and may overcome fundamental limitations of conventional mechanical fabrication.     

Does oil price affect the value of firms? Evidence from Tunisian listed firms

A new debate on the potential impact of oil price changes on the value of firms was initiated in this paper. Using a stochastic frontier approach, an attempt was made to derive the optimal value Q* of firms and calculate the Q value observed. Then the shortfall (Q*–Q) which represents the inefficiency term was explained. Starting from 19 industrial Tunisian firms listed on the Tunis Stock Exchange between 2007 and 2011, the fact that variation of oil prices can largely explain distortions in the value of firms was empirically demonstrated.     

Investigation of microstructure-property relantionships of magnesia-hercynite refractory composites by a refined digital image correlation technique

Industrial magnesia-spinel bricks destined for thermal shock applications often show more flexibility and improved crack growth resistance. Components from the spinel structure group are usually added to promote microcracking coming from thermal expansion mismatch. This leads to the development of toughening mechanisms that are very effective in improving the crack propagation resistance.Magnesia-hercynite composites were investigated in order to highlight their fracture process, with regard to their microstructure, by using Digital Image Correlation (DIC). The direct measurement of displacement fields between digital images of the reference state and the deformed one has provided valuable information on material deformation during loading. The aim of this work was to investigate the fracture behaviour of refractories through the coupling of the Wedge Splitting Test (WST) and DIC. By using a refined DIC process transformation taking into account a discontinuity of displacement, called 2P-DIC, a more effective characterisation of the fracture behaviour was achieved.     

Magnetocaloric-Transport Properties Correlation in La<Subscript>0.8</Subscript> Ca<Subscript>0.2</Subscript>MnO<Subscript>3</Subscript>-Doped Manganites

This investigation is interested in studying the relation between magnetocaloric effect and transport properties i La_0.8Ca_0.2MnO₃ manganite compound. The value of the magnetocaloric effect has been determined from the calculation of magnetization as a function of temperature under different external magnetic fields. This study also provides an alternative method to determine the magnetocaloric properties such as magnetic entropy change and heat capacity change on the basis of M(T, H) measurements. On the other hand, based on magnetic and resistivity measurements, the magnetocaloric properties of this compound were investigated using an equation of the form \({\Delta } S \,=\, - \alpha {\int \limits _{0}^{H}} {\left [ {\frac {\delta Ln\left (\rho \right )}{\delta T}} \right ]}_{H} dH\), which relates magnetic order to transport behavior of the compounds. As an important result, the values of MCE and the results of calculation are in good agreement with the experimental ones, which indicates the strong correlation between the electric and magnetic properties in manganites.     

A general model for porous medium flow in squeezing film situations

The present paper deals with a numerical investigation of the hydrodynamic lubrication of a porous squeeze film between two circular discs. To this purpose, the thin film (reduced) Navier Stokes equations and a generalised porous medium model are solved. The numerical results show that the effect of the porous disc is to reduce the lubricating properties of the fluid film. This effect is increased during the squeezing action. In addition, it is shown that the film pressure, the load‐carrying capacity and the velocity field based only on the Darcy model are predicted higher than those obtained from the generalised porous medium model. Copyright © 2009 John Wiley & Sons, Ltd.     

Tissue metal concentrations and histopathology of rats gavaged with vitrified soil obtained from the former Charleston Naval Shipyard (SC,USA)

Male Sprague Dawley^® rats were administered a vitrified material obtained from the former Charleston Naval Shipyard (Charleston, SC, USA) by gavage once daily for 32 days. Group mean body weight of treated animals was within ±5.4% of controls. No gross or histopathological changes were observed when animals were treated with 67, 174, or 370 mg/kg per day. Analysis of heavy metals revealed a statistically significant increase only in the concentration of arsenic in the livers of animals treated with 174 or 370 mg/kg per day versus controls. Although there was a statistically significant increase in liver arsenic levels, the concentrations were far below mean soil concentrations for western and eastern United States. If the standard assumption of 100% absorption is used, the concentrations observed in the present study are about 20 times less than the average background soil levels in these regions. Based on this, it is concluded that the vitrified material would not pose a public health risk for its intended use as an additive for asphalt and glass beams.     

Influence of Ca-deficiency on the magneto-transport properties in La(0.8)Ca(0.2)MnO(3) perovskite and estimation of magnetic entropy change

La(0.8)Ca(0.2?-?x)□(x)MnO(3) (x?=?0.00, 0.10, and 0.20) perovskite was prepared by the conventional solid-state reaction and annealed at 1473?K. X-ray diffraction and scanning electron microscopy shown the existence of a secondary phase attributed to the unreacted Mn(3)O(4) oxide. The magneto transport properties have been investigated based on the temperature dependence of the resistivity ρ(T) measurements under several applied magnetic fields. We note that the La(0.8)Ca(0.2)MnO(3) (x?=?0.00) sample has a classical metal-insulator transition at T(ρ). But we have observed that the lacunars samples (x?=?0.10 and 0.20) include a metallic and insulator behavior simultaneously below T(ρ) and the resistivity is dominated by tunneling through the barriers associated with the insulating phase. In other words, the calcium deficiency favors the enhancement of the insulator behavior. The electrical resistivity is fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. Furthermore, we found that the estimated results are in good agreement with experimental data. Above all, the resistivity dependence on the temperature and magnetic field data is used to deduce the magnetic entropy change. We have found that these magnetic entropy change values are similar to those calculated in our previous work from the magnetic measurements. Finally, we have found an excellent estimation of the magnetic entropy change based on the Landau theory.