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Iacob N.,Romanian National Institute for Lasers, Plasma and Radiation Physics | Iacob N.,University of Bucharest | Schinteie G.,National Institute of Materials Physics Bucharest | Bartha C.,National Institute of Materials Physics Bucharest | And 3 more authors.
Journal of Physics D: Applied Physics | Year: 2016

A quantitative treatment of the effects of magnetic mutual interactions on the specific absorption rate of a superparamagnetic system of iron oxide nanoparticles coated with oleic acid is reported. The nanoparticle concentration of the considered ferrofluid samples varied from a very low (0.005) to a medium (0.16) value of the volume fraction, whereas the amplitude of the exciting AC magnetic field ranged from 14-35 kA m-1. It was proved that a direct effect of the interparticle interactions resides in the regime of the modified superparamagnetism, dealing, besides the usual increase in the anisotropy energy barrier per nanoparticle, with the decrease in the specific time constant of the relaxation law, usually considered as a material constant. Consequently, the increase in the specific absorption rate versus the volume fraction is significantly diminished in the presence of the interparticle interactions compared to the case of non-interacting superparamagnetic nanoparticles, with direct influence on the magnetic hyperthermia efficiency. © 2016 IOP Publishing Ltd. Source

Schinteie G.,National Institute of Materials Physics Bucharest | Palade P.,National Institute of Materials Physics Bucharest | Vekas L.,Romanian Academy Timisoara Division | Iacob N.,Romanian National Institute for Lasers, Plasma and Radiation Physics | And 3 more authors.
Journal of Physics D: Applied Physics | Year: 2013

Ferrofluid samples consisting of magnetite nanoparticles (NPs) coated with oleic acid and dispersed in a non-polar organic solvent have been synthesized by chemical routes. Different volume fractions, φ, of magnetic NPs were considered. The overall structural characterization of NPs has been performed by x-ray diffractometry, with lattice parameters and average coherence lengths evaluated via Rietveld refinements. The magnetic properties of different samples have been analysed by SQUID magnetometry and temperature-dependent Mössbauer spectroscopy and finally explained by adequate magnetic relaxation mechanisms. Zero field cooling-field cooling protocols provided useful information about specific volume fraction dependent magnetic relaxation and de-freezing processes, the lack of the Verwey transition and stronger dipolar interactions at higher volume fractions. Anisotropy energies as obtained by both temperature dependent Mössbauer spectroscopy and magnetometry data are compared and a new procedure for a quantitative characterization of the dipolar interactions is proposed. © 2013 IOP Publishing Ltd. Source

Ursutiu D.,Transylvania University | Samoila C.,Transylvania University | Baltes L.,Transylvania University | Tierean M.,Transylvania University | And 2 more authors.
Journal of Optoelectronics and Advanced Materials | Year: 2013

In this paper is proved the flexibility of LabVIEW (Laboratory Virtual Instrumentation Engineering Workbench) - graphical programming software - when it is used in connection with applications of ultrasound measurements in the field of plastic materials characterization. The ultrasonic measurement was carried out on plastic specimens with immersion method. In the first step the measurement was made in water with a transducer that generates a longitudinal 5 MHz wave. The same measurement was repeated in a magnetic fluid, water diluted. All of the measurements are oriented to obtain necessary data for the FP7- W2P Plastics project development. In Transylvania University laboratory, the measurement setup used was the EPOCH XT device from PARAMETRICS-NDT. The data can be saved on PC like normal TXT files and exported in Excel and LabVIEW. A preliminary application was developed to see the imported data in one Wave Form Graphic (WFG) or XY graph in LabVIEW. This data can be used easy now in idea of needs for future calculus and data computation. The obtained data will be used for the separation process of the polymeric waste immersed in a magnetic fluid. Source

Cristea A.,Romanian Academy Timisoara Division | Neagu A.,Victor Babes University of Medicine and Pharmacy Timisoara | Neagu A.,University of Missouri
Computers in Biology and Medicine | Year: 2016

Tissue engineers seek to build living tissue constructs for replacing or repairing damaged tissues. Computational methods foster tissue engineering by pointing out dominant mechanisms involved in shaping multicellular systems. Here we apply the Lattice Boltzmann (LB) method to study the fusion of multicellular constructs. This process is of interest in bioprinting, in which multicellular spheroids or cylinders are embedded in a supportive hydrogel by a computer-controlled device. We simulated post-printing rearrangements of cells, aiming to predict the shape and stability of certain printed structures. To this end, we developed a two-dimensional LB model of a multicellular system in a hydrogel. Our parallel computing code was implemented using the Portable Extensible Toolkit for Scientific Computation (PETSc). To validate the LB model, we simulated the fusion of multicellular cylinders in a contiguous, hexagonal arrangement. Our two-dimensional LB simulation describes the evolution of the transversal cross section of the construct built from three-dimensional multicellular cylinders whose length is much larger than their diameter. Fusion eventually gave rise to a tubular construct, in qualitative agreement with bioprinting experiments. Then we simulated the time course of a defect in a bioprinted tube. To address practical problems encountered in tissue engineering, we also simulated the evolution of a planar construct, as well as of a bulky, perfusable construct made of multicellular cylinders. The agreement with experiments indicates that our LB model captures certain essential features of morphogenesis, and, therefore, it may be used to test new working hypotheses faster and cheaper than in the laboratory. © 2016 Elsevier Ltd. Source

Morjan I.,Romanian National Institute for Lasers, Plasma and Radiation Physics | Alexandrescu R.,Romanian National Institute for Lasers, Plasma and Radiation Physics | Dumitrache F.,Romanian National Institute for Lasers, Plasma and Radiation Physics | Birjega R.,Romanian National Institute for Lasers, Plasma and Radiation Physics | And 9 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2010

Nano-sized iron oxide-based particles have been directly synthesized by the laser induced pyrolysis of a mixture containing iron pentacarbonyl/air (as oxidizer)/ethylene (as sensitizer). In this paper we further demonstrate the possibility to vary the chemical composition and the nanoparticle dimensions of the iron oxide-based materials by handling the oxidation procedure in the frame of the laser pyrolysis process. Thus, nanoparticles with major maghemite/magnetite content may change composition into mixtures with variable amounts of three components: major "Υ-Fe 2O 3/Fe 3O 4 iron oxide, metallic Fe and cementite Fe 3C. By X-ray diffraction (XRD) it is found that the relative proportion of these phases differs in function of the reaction temperature (laser power). As revealed by transmission electron microscopy (TEM), mean particle sizes between about 4 nm and 6 nm and between about 9 and 11 nm may be prepared by varying the oxidation procedure and the laser power, respectively. By the controlled heating of samples (maximum temperature 185 °C), increased crystallinity for the Υ-Fe 2O 3/Fe 3O 4 oxide phase was found as well as an increase of the mean particle diameters. The examination of the magnetization curves for samples obtained for different laser powers indicates notable differences in the magnetic behavior and parameters. The temperature dependent Mossbauer measurements confirm the formation of larger particles at higher laser power densities as well as the presence of inter-particle magnetic interactions. On this basis, the estimation of phase composition for the different representative samples is given. Copyright © 2010 American Scientific Publishers. All rights reserved. Source

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