Heat treatment effects on spinel phase of Zn x Ni1 − x Fe2O4 and MnFe2O4 nanoferrites

We report the effects of heat treatment on Zn _x Ni_1???x Fe₂O₄ (x?= 0, 0.5 and 1.0) and MnFe₂O₄ ferrite nanoparticles. The as-prepared compounds were sintered from 400°C to 1100°C. Pure ZnFe₂O₄ (x?= 1.0) and MnFe₂O₄ could be obtained under low reaction temperature of 200°C. NiFe₂O₄ (x?= 0) and Zn_0.5Ni_0.5Fe₂O₄ (x?= 0.5) nanoferrites crystallized with single phase cubic spinel structure after annealing at 600°C. The single phase cubic spinel structure of these compounds was destroyed after annealing at temperature above 700°C. The magnetization measurements indicate superparamagnetic behavior of the nanosized compounds produced.     

On the complete group classification of the reaction-diffusion equation with a delay

The reaction-diffusion delay differential equation

ut(x,t)−uxx(x,t)=g(x,u(x,t),u(x,t−τ))     

Synthesis and characterization of activated carbon–ethylenediamine–cobalt(II) tetracarboxyphthalocyanine conjugate for catalytic oxidation of ascorbic acid

We report on the synthesis and characterization of activated carbon–ethylenediamine–cobalt(II) tetracarboxyphthalocyanine conjugate (AC–CONHCH₂CH₂NH₂–CoPc) and its electrocatalytic behavior for oxidation of ascorbic acid. Ultraviolet–visible (UV–Vis), Fourier-transform infrared (FTIR), and electrochemical impedance spectroscopies, and cyclic and square-wave voltammetry were used to characterize the electrode modifiers and modified glassy carbon electrode. The limit of detection was found to be 0.26 µm using 3δ notation. The linear dynamic range was from 1.5 × 10^?4 to 1 × 10^?2 M with electrode sensitivity of 0.01 A mol^?1 L cm^?2. A Tafel slope of 200.8 mV decade^?1 was found. The concentration of ascorbic acid in the tablet was 0.034 M. Oxalic acid showed no interference in ascorbic acid determination.     

Synthesis and magnetic properties of Cu0.5Ni0.5Fe2O4 nanoparticles produced by glycothermal and hydrothermal processes

Cu_0.5Ni_0.5Fe₂O₄ nanoparticles have been synthesized in ethylene glycol solution and in deionised water. The glycothermal reaction was carried at 200°C under gauge pressure of 100 psi. The hydrothermal treatment was done at 100°C under zero pressure. Complete single-phase cubic spinel structure in the samples made by glycothermal (sample G) and hydrothermal (sample H) processes formed after annealing at 600°C and 900°C respectively. The coercive field of sample H increases from 72 Oe to 133 Oe after sintering at 700°C and then decrease to 11 Oe on sintering at 1000°C. This variation is attributed to surface effects and crossover from single to multidomain behavior due to increasing particle size.     

Some properties of Lagrangian sequences

Here we discuss a sequence of Lagrangians and corresponding Euler–Lagrange equations and point out some interesting properties that this particular sequence holds. This is an extension on recent results obtained on sequences of differential equations to Lagrangians as it leads to differential equations on the application of the Variational Principle.     

Ordinary differential equations invariant under translation in the independent variable and rescaling: The Lagrangian formulation

The Lagrangian formulation of the class of general second-order ordinary differential equations invariant under translation in the independent variable and rescaling is presented. The differential equations arising from this analysis are analysed using the Painlevé test. The well-known differential equation, y^″+yy^′+ky³=0, is a unique member of this class when k=3 since it is linearisable by a point transformation. A wider subset is shown to be linearisable by means of a nonlocal transformation.     

Complete group classification of systems of two linear second-order ordinary differential equations

We give a complete group classification of the general case of linear systems of two second-order ordinary differential equations excluding the case of systems which are studied in the literature. This paper gives the initial step in the study of nonlinear systems of two second-order ordinary differential equations. It can also be extended to systems of equations with more than two equations. Furthermore the complete group classification of a system of two linear second-order ordinary differential equations is done. Four cases of linear systems of equations with inconstant coefficients are obtained.     

A Novel Hydrogen Peroxide Biosensor Based on Adsorption of Horseradish Peroxidase onto a Nanobiomaterial Composite Modified Glassy Carbon Electrode

In this work, a novel hydrogen peroxide biosensor derived from maize tassel (MT) and multiwalled carbon nanotube (MWCNT) composite was used to adsorb horseradish peroxidase (HRP) onto the surface of a glassy carbon electrode through electrostatic interactions. The morphology and structure of the products were characterized by SEM, FTIR and UV‐visible spectroscopy. The electrochemical and electrocatalytic performance of the HRP/MT‐MWCNT/GCE was studied using voltammetric and amperometric methods. The amperometric response of the biosensor varied linearly with concentration of H₂O₂ from 9 µM to 1 mM with detection limit of 4.0 µM (S/N=3). Furthermore, the biosensor exhibited good reproducibility and stability.     

M?ssbauer and magnetic studies of Mn0.1Sr0.2Co0.7Fe2O4 nanoferrite

The magnetic properties of Mn_0.1Sr_0.2Co_0.7Fe₂O₄ nanoferrite with particle size of about 8 nm were investigated using magnetization and Mössbauer spectroscopy measurements. The sample shows a large increase in coercive field from 0.045 kOe at room temperature to about 3.00 kOe at 4 K. Room temperature coercive fields increased with increase in the annealing temperature between 300°C and 800°C. Our results show evidence of transformation from single domain to multi-domain structure with thermal annealing.