Mechanism and Linear Free Energy Relationships in Michael‐Type Addition of 4‐Substituted Anilines to Activated Olefin in Acetonitrile

Kinetic studies for the Michael‐type reactions of ethyl‐3‐(4′‐N,N‐dimethylaminophenyl)‐2‐(nonafluorobutane)sulfonylpro‐penoate 1 with 4‐X‐substituted anilines 2a–e (X = OCH₃, CH₃, H, F, and Cl) have been investigated in acetonitrile at 20°C. A quadratic dependence of the pseudo–first‐order rate constants (k_obsd) versus [ 2a–e ] has been observed and has been interpreted in terms of a dimer nucleophile mechanism. The finding of a relatively large negative ρ value (?3.09) for the Hammett plot suggests that the intermediate ( I^± ) is highly zwitterionic in nature. A linear correlation (r² = 0.9989) between the Hammett's substituent constants σ and nucleophilicity parameters N of 4‐X‐substituted anilines in acetonitrile has been observed. The electrophilicity parameters E of the olefin 1 is evaluated, using the correlations σ versus N and log k versus σ and compared with the electrophilicities of analogously Michael acceptors.     

A Highly Sensitive and Selective Non-enzymatic Hydrogen Peroxide Sensor Based on Nanostructured Co3O4 Thin Films Using the Sol-gel Method

In this work we report an easy and efficient way to fabricate nanostructured cobalt oxide (Co₃O₄) thin films as a non-enzymatic sensor for H₂O₂ detection. Co₃O₄ thin films were grown on ITO glass substrates via the sol-gel method and characterized with several techniques including X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and optical absorbance. The Co₃O₄ thin films’ performance regarding hydrogen peroxide detection was studied in a 0.1 M NaOH solution using two techniques, cyclic voltammetry (CV) and amperometry. The films exhibited a high sensitivity of 1450 μA.mM⁻¹.cm⁻², a wide linear range from 0.05 μM to 1.1 mM, and a very low detection limit of 18 nM. Likewise, the Co₃O₄ thin films produced showed an exceptional stability and a high selectivity.     

The effect of the B-site size on the structural,magnetic and electrical properties of La0.7Ca0.3MnO3−δ compounds

The perovskite-type ceramic La_0.7Ca_0.3MnO_3−δ was prepared by the solid-state reaction with 0.00?δ?0.15. X-ray diffraction, electrical and magnetic measurements were performed to examine the effect of the B-site size on the properties of these materials. We have found that the structure is orthorhombic for 0.00?δ?0.075 and becomes rhombohedral for 0.10?δ?0.15. The measurements of the magnetization as a function of the temperature, M(T), shows a ferromagnetic-paramagnetic transition at the Curie temperature T_C for δ=0.00. When increasing δ, these curves report the presence of two types of transitions. The first one is from the ferromagnetic to the antiferromagnetic state, indicating the existence of a charge-ordering state (T_CO). The second antiferromagnetic-paramagnetic transition occurs at the Neel temperature T_N. The temperature dependence of the resistivity ρ(T), indicates a metallic behaviour at low temperature (T<T_p) and a semiconductor behaviour at high temperature (T>T_p) for δ=0.00. For 0.05?δ?0.10, the ρ(T) curves shows a semiconductor behaviour revealing the disappearance of the metallic state which reappear at low temperature for δ=0.125 and 0.150.     

Structural and electrical characteristics of rare earth simple perovskite oxide La0.57Nd0.1Pb0.33Mn0.8Ti0.2O3

Polycrystalline La_0.57Nd_0.1Pb_0.33Mn_0.8Ti_0.2O₃ (LNPMT) is prepared by the solid-state reaction technique. The formation of single phase material was confirmed by X-ray diffraction studies, and it was found to be a rhombohedral phase at room temperature. The impedance plane plot shows semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to explain the impedance results. The frequency dependent conductivity spectra follow the universal power law. The activation energy deduced from analysis of the imaginary part of electric modulus and imaginary impedance is found to be ∼75 meV. Such a value of activation energy indicates that the conduction mechanism for the sample is due to electron hopping. The imaginary part of the electric modulus suggests that the relaxation describes the same mechanism at various temperatures.     

Structural study and physical properties of a new phosphate KCuFe(PO4)2

Single crystals of a new phosphate KCuFe(PO₄)₂ have been prepared by the flux method and its structural and physical properties have been investigated. This compound crystallizes in the monoclinic system with the space group P2₁/n and its parameters are: a=7.958(3) Å, b=9.931(2) Å, c=9.039(2) Å, β=115.59(3)° and Z=4. Its structure consists of FeO₆ octahedra sharing corners with Cu₂O₈ units of edge-sharing CuO₅ polyhedra to form undulating chains extending infinitely along the b-axis. These chains are connected by the phosphate tetrahedra giving rise to a 3D framework with six-sided tunnels parallel to the [101] direction, where the K⁺ ions are located. The Mössbauer spectroscopy results confirm the exclusive presence of octahedral Fe³⁺ ions. The magnetic measurements show the compound to be antiferromagnetic with C_m=5.71 emu K/mol and θ=−156.5 K. The derived experimental effective moment μ_ex=6.76μ_B is somewhat higher than the theoretical one of μ_th=6.16μ_B, calculated taking only into account the spin contribution for Fe³⁺ and Cu²⁺ cations. Electrical measurements allow us to obtain the activation energy (1.22 eV) and the conductivity measurements suggest that the charge carriers through the structure are the potassium cations.     

Linear and Bilinear Multiplier Operators for the Dunkl Transform

The main purpose of this article is to study the L _p -boundedness of linear and bilinear multiplier operators for the Dunkl transform in the one dimensional case.     

Detection of delamination defects in CFRP materials using ultrasonic signal processing

In this paper, signal processing techniques are tested for their ability to resolve echoes associated with delaminations in carbon fiber-reinforced polymer multi-layered composite materials (CFRP) detected by ultrasonic methods. These methods include split spectrum processing (SSP) and the expectation-maximization (EM) algorithm. A simulation study on defect detection was performed, and results were validated experimentally on CFRP with and without delamination defects taken from aircraft. Comparison of the methods for their ability to resolve echoes are made.     

Structure and magnetic properties of potassium doped bismuth ferrite

The influence of the potassium (K⁺) doping on the structure of multiferroic BiFeO₃ and its relation with ferroelectric and magnetic properties was investigated for perovskites with composition Bi_1−xK_xFeO₃ in the range 0?x?0.07. All the studied samples are described in R3c space group (No. 161). Typical cell parameters (BiFeO₃) in hexagonal setting are a_hex=5.5769(2) Å and c_hex=13.8531(2) Å with Z=6 formula units. The structure determination shows that as the K⁺ content increases, the average cations displacements decrease reducing the polar character of doped samples with respect to pure BiFeO₃ and leading to a change from rhombohedral to a pseudo-cubic symmetry. A structural disorder is related to the substitution of K⁺, which results in strong diffuse scattering (DS) located at the bottom of the Bragg peaks. Magnetic measurements reveal that all the compounds remain antiferromagnetic at room temperature (RT) with almost no change in the transition temperature (Néel temperature T_N).