Synthesis,structural and complex impedance spectroscopy studies of Ni0.4Co0.4Mg0.2Fe2O4 spinel ferrite

Spinel ferrite having composition Ni_0.4Co_0.4Mg_0.2Fe₂O₄ was prepared by sol-gel method. X-ray diffraction result indicates that the ferrite sample has a cubic spinel type structure. FT-IR showed two absorption bands (ν₁ and ν₂) that are attributed to the stretching vibration of tetrahedral and octahedral sites. Complex impedance properties have been investigated in 200–420 K temperature range with varying frequency between 40 and 10⁷ Hz. Frequency and temperature dependency of imaginary part of permittivity (?″) and dielectric loss (tanδ) has been discussed in terms of hopping of charge carriers between Fe²⁺ and Fe³⁺ ions. Activation energy has been estimated from both temperature dependency of dc conductivity and relaxation time data, which indicates that the relaxation process and conductivity have the same origin. Nyquist plots of impedance show semicircle arcs for sample and an electrical equivalent circuit has been proposed to explain the impedance results.     

Experimental observation of quantum confinement in the conduction band of CdSe quantum dots

X-ray absorption spectroscopy has been used to characterize the evolution in the conduction band (CB) density of states of CdSe quantum dots (QDs) as a function of particle size. We have unambiguously witnessed the CdSe QD CB minimum (CBM) shift to higher energy with decreasing particle size, consistent with quantum confinement effects, and have directly compared our results with recent theoretical calculations. At the smallest particle size, evidence for a pinning of the CBM is presented. Our observations can be explained by considering a size-dependent change in the angular-momentum-resolved states at the CBM.     

Explicit upper bounds for exponential sums over primes

We give explicit upper bounds for linear trigonometric sums over primes.

     

Effect of the chimney design on the thermal characteristics in solar chimney power plant

Journal of Thermal Analysis and Calorimetry - Solar chimney power plant (SCPP) is an interesting project to produce clean and sustainable energy. An efficient SCPP system requires a very high...     

The Mechanism of CO2 Insertion into Iridium(I) Hydroxide and Alkoxide Bonds: A Kinetics and Computational Study

The facile insertion of CO₂ into iridium(I) hydroxide, alkoxide, and amide bonds was recently reported. In particular, [Ir(cod)(IiPr)(OH)] (IiPr=1,3‐bis(isopropyl)imidazol‐2‐ylidene) reacted with CO₂ in solution and in the solid state in a matter of minutes to give the novel [{Ir(cod)(IiPr)}₂(μ‐κ¹O:κ²O,O‐CO₃)] complex. In the present study, this reaction is probed using kinetics and theoretical studies, which enabled us to analyse its facile nature and to fully elucidate the reaction mechanism with excellent correlation between the two methods.     

ACTION DU REACTIF DE LA WESSON SUR LES HYDRAZONES γ-PHOSPHONATEES: SYNTHESE DE NOUVEAUX DERIVES DE LA Δ5-3-THIOXO-1,2,3-DIAZAPHOSPHOLINE

Abstract

The Lawesson reagent (L.R) reacts with phenylhydrazones of ketones γ-disubstituted phosphonates and phosphine oxide 1 to give 1,2,3-diazaphospholine derivatives 2 and 2′. Two diastereomers were obtained in some cases. The structure of the products 2 and 2′ is confirmed by NMR and IR spectroscopy.     

ACTION DESIMINES SUR LES MONOCHLOROPHOSPHINES: NOUVELLE VOIE D'ACCES A DES CETONES β-PHOSPHORYLEES

Abstract

The reaction of imines 1 with monochlorophosphines leads to β-phosphorylketones obtained in the ketonic 2 or enolic forms 2′. The structure of all obtained products is confirmed by NMR and IR spectroscopy.     

Convenient Synthesis of 2,4-Disubstituted Tetrahydrothiophenes from Mannich's Adducts

Ammonium salts of β-functionalized allylic amines 1 were successfully employed as electrophilic agents with functional thiols. The obtained intermediate 2 underwent intramolecular cyclization in the presence of potassium tert-butoxide to afford 2,4-disubstituted tetrahydrothiophenes 3.     

Heterodyne detection for Fiber Bragg Grating sensors

In this paper, we present a Fiber-Bragg-Grating-based temperature sensor. The technique employs heterodyne detection using two Fiber Bragg Gratings. One of the gratings is used as a reference (local oscillator) and the second as a sensing arm. This sensor uses a Folded Mach-Zehnder interferometer. As the temperature changes, the Bragg wavelength of the FBG shifts. The heterodyne detection is used to detect the frequency difference between the reference and sensing signals that is caused by the temperature change. The dynamic range and sensitivity of the sensor were analyzed and presented.