SrFe12O19/Zn0.65Ni0.25Cu0.1Fe2O4 Core–Shell Nanocomposite: Synthesis,Chracterization and Catalytic Activity in Aqueous Solution

SrFe₁₂O₁₉/Zn_0.65Ni_0.25Cu_0.1Fe₂O₄ core–shell nanocomposite has been successfully synthesized by sol–gel autocombustion (for SrFe₁₂O₁₉, core) and hydrothermal methods (for Zn_0.65Ni_0.25Cu_0.1Fe₂O₄, shell). The products were characterized by X-ray powder diffractometer, transmission electron microscopy, fourier transform infrared spectrsocopy, vibrating sample magnetometer, Ultraviolet–visible specroscopy and inductively coupled plasma. Both X-ray powder diffraction, transmission electron microscopy results showed that Zn_0.65Ni_0.25Cu_0.1Fe₂O₄ shell is on the surface of the SrFe₁₂O₁₉ core. The variations between the magnetic properties of the precursors and nanocomposite may be explained by interphase interactions at the surface of two ferrites. The properties of the SrFe₁₂O₁₉/Zn_0.65Ni_0.25Cu_0.1Fe₂O₄ core–shell nanocomposite were favourable in its separation, recycling and reuse after reaction. The catalytic activity of SrFe₁₂O₁₉/Zn_0.65Ni_0.25Cu_0.1Fe₂O₄ core–shell nanocomposite in the presence of NaBH₄ were tested against methyl violet.     

Solvothermal Synthesis of Pure SrFe12O19 Hexaferrite Nanoplatelets

Strontium hexagonal ferrite, SrFe₁₂O₁₉, with platelet-like structure was synthesized directly by hydrothermal method without any calcination process. The product was characterized by Scanning electron (SEM), X-ray powder diffraction (XRD), Fouier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometry (VSM) techniques. The optimum Fe/Sr moler atio is identified as 8:1, and the optimum weight of NaOH was 4.0 g for the synthesis of the Flake-like SrFe₁₂O₁₉ nanoparticles. The average crystallite size of the product was calculated as 28±5 nm. The low coercivities of the synthesized platelet crystals indicate soft magnetic behavior, which is a consequence of the large shape anisotropy (the platelet crystals are highly anisotropic). The reduced Ms can be explained by increasing surface area of the platelets.     

Effect of Zn Substitution on Electrical Properties of Nanocrystalline Cobalt Ferrite

Nanocrystalline cobalt ferrites substituted with Zn with formula, Co_1?x Zn _x Fe₂O₄ (x=0.0–1.0) were prepared by the hydrothermal method. In this process, triethylene glycol was used both as a solvent and surfactant. The ac conductivity measurements of the samples showed a temperature-dependency at lower frequencies and independency at higher frequencies, which indicates the ionic conductivity. The ac conductivity depends on the temperature. This conductivity can be fitted with the well-known power law model in higher frequency. The dc conductivity is assumed to obey the Arrhenius equation. The dielectric behavior in various temperatures ranges revealed frequency dependency in a reciprocal power law. The dissipation of energy stored within the nanoparticle was found to act upon the reciprocal power law of the frequency dependency. Both the analysis of electrical conductivity and the dielectric permittivity functions suggest that the ionic and polymer segmental mobility could strongly be coupled in the nanoparticles.     

Distribution of aortic mechanical prosthetic valve closure soundmodel parameters on the surface of the chest

If has been previously proposed that heart valve closure sounds can be modeled by a sum of decaying sinusoids, based on the hypothesis that the heart cavity, heart walls, major vessels, and other structures in the chest constitute a frequency selective linear acoustic system and this system is excited by the rapidly decelerating valve occluder. In this study, the distribution of the parameters of this model for the second heart sound is investigated. For this purpose, heart sounds of 10 patients who have a St. Jude-type bileaflet mechanical heart valve prosthesis in the aortic position are recorded. Recordings are performed at 12 different locations on the surface of the chest. To reliably assign representative parameters to each recording site, signal averaging, model order selection, and a special filtration technique are employed. The results of the analyses are discussed in relation to the above hypothesis on the heart sound generation mechanism. It is observed that site-to-site variation of frequencies of modes does not exceed the accuracy limit of proposed analysis method, but energies of these modes vary on the surface of the chest, and as a result of statistical analysis, it appears that energy of some modes are significantly different between two recording sites     

Estimation of the ventricular fibrillation duration byautoregressive modeling

An accurate estimation of ventricular fibrillation (VF) duration could be critical in selecting the most effective therapeutic intervention. The authors test the hypothesis that changes in frequency content of VF signals can be quantified by using autoregressive (AR) modeling, and the duration since the onset of VF can be estimated by using this method. VF signals were recorded for up to 300 s in five isolated rabbit hearts. Fourth-order AR parameters of successive segments were estimated, and frequencies of the first poles (the pole with lower frequency) were pooled together and a curve was fitted: F(t)=Aexp(-α_t)+B, where F(t) is the estimated frequency of the first pole at t'th time instant, α is the decay constant, B is the offset frequency, and A is the frequency at time zero minus the offset frequency. The utility of this curve in estimating the VF duration was tested in four new experiments, and the difference between the actual and the estimated VF duration (estimation error) was calculated. F(t), the frequency of the first pole, decreased from 12 to 6 Hz with duration of VF, while the frequency of the other pole decreased from 25 to 20 Hz. Parameters of the fitted curve were calculated as A=7.8, α=0.0041 and B was selected as four. Testing on a new set of VF signals produced very little estimation error for the first 100 s of VF, although this error increased with VF duration, For these new signals, the mean value of the absolute estimation error was 26 s. Results of this study show that changes in the frequency content of electrocardiogram (ECG) during VF can be quantified by AR modeling and that the frequency changes associated with a pole of this model can be used to estimate the VF duration     

The Effect of Condensation on the Morphology and Magnetic Properties of Modified Barium Hexaferrite (BaFe12O19)

Nano-Micro Letters - We present a comparison for the effect of condensation on the morphology and magnetic properties of oleic acid modified BaFe12O19 nanoparticles. Two different samples of...     

Effects of fiber types and blend ratios on Murata Vortex yarn properties

Murata Vortex spinning (MVS) system is one of the unconventional systems for yarn manufacturing. It is suitable for spinning of 100% cotton fibers, synthetic fibers, and cotton/synthetic fiber blends which are 1 inch or more in length. The production ranges are between Ne 15-60. Vortex yarn and fabrics have low hairiness, clear appearance, high resistance to pilling and abrasion. In this study, the vortex yarns with Ne 30 are produced in different blend ratios in Murata Vortex Spinner using carded cotton, viscose, modal, silver-added polyester (Flexsil-D2?), polyester, and nylon 6.6 fibers. Vortex spun yarns are tested to determine the yarn properties which are diameter, density, roundness (shape), unevenness, imperfection, Uster hairiness (H), Zweigle hairiness, tenacity, and elongation. The study reveals that the fiber type has quite significant effects on yarn properties. In terms of structural properties, cotton is the most negative fiber while regenerated cellulosic fibers are the most positive. As modal, nylon and polyester fiber increase yarn strength, nylon and viscose fiber increase breaking elongation. Viscose and modal reduce unevenness, imperfection and hairiness while polyester and nylon exhibit more negative effect on these properties.     

Synthesis and characterization of dl-thioctic acid (DLTA)-Fe3O4 nanocomposite

dl-Thioctic acid (DLTA) coated magnetite (Fe₃O₄) NP's have been prepared by the co-precipitation of iron oxide in the presence of DLTA. The product identified as magnetite, which has an average crystallite size of 7 ± 2 nm as estimated from X-ray line profile fitting. Particle size was estimated as 11 ± 1 nm from TEM micrographs. FT-IR analysis showed that the binding of DLTA on the surface of iron oxide is through carboxyl group is bidentate. VSM analysis explained the super-paramagnetic nature of the nanocomposite. TG analysis showed that the 80% of the nanocomposite was DLTA and 10% was Fe₃O₄, respectively. The conductivity measurements displayed the magnetic transition at ∼60 °C for DLTA-Fe₃O₄ NPs. Analysis of the conductivities reveals the fact that the a.c. conductivity shows a frequency-dependent behavior while d.c. electrical conductivity is strongly temperature dependent and is classified into two regions over a limited temperature range of up to 120 °C. Toxicity was tested measured by LDH assay.