| 1. |
- Feroci, M., et al.
(författare)
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The large observatory for x-ray timing
- 2014
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 9780819496126
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Konferensbidrag (refereegranskat)abstract
- The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final downselection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supranuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m2 effective area, 2-30 keV, 240 eV spectral resolution, 1° collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g. GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the status of the mission at the end of its Phase A study.
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| 2. |
- Feroci, M., et al.
(författare)
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The Large Observatory for X-ray Timing (LOFT)
- 2012
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Ingår i: Experimental Astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 34:2, s. 415-444
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Tidskriftsartikel (refereegranskat)abstract
- High-time-resolution X-ray observations of compact objects provide direct access to strong-field gravity, to the equation of state of ultradense matter and to black hole masses and spins. A 10 m(2)-class instrument in combination with good spectral resolution is required to exploit the relevant diagnostics and answer two of the fundamental questions of the European Space Agency (ESA) Cosmic Vision Theme "Matter under extreme conditions", namely: does matter orbiting close to the event horizon follow the predictions of general relativity? What is the equation of state of matter in neutron stars? The Large Observatory For X-ray Timing (LOFT), selected by ESA as one of the four Cosmic Vision M3 candidate missions to undergo an assessment phase, will revolutionise the study of collapsed objects in our galaxy and of the brightest supermassive black holes in active galactic nuclei. Thanks to an innovative design and the development of large-area monolithic silicon drift detectors, the Large Area Detector (LAD) on board LOFT will achieve an effective area of similar to 12 m(2) (more than an order of magnitude larger than any spaceborne predecessor) in the 2-30 keV range (up to 50 keV in expanded mode), yet still fits a conventional platform and small/medium-class launcher. With this large area and a spectral resolution of < 260 eV, LOFT will yield unprecedented information on strongly curved spacetimes and matter under extreme conditions of pressure and magnetic field strength.
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| 3. |
- Almessiere, M. A., et al.
(författare)
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Review on functional bi-component nanocomposites based on hard/soft ferrites : Structural, magnetic, electrical and microwave absorption properties
- 2021
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Ingår i: Nano-Structures and Nano-Objects. - : Elsevier B.V.. - 2352-507X. ; 26
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Tidskriftsartikel (refereegranskat)abstract
- Bi-component hard (H) (hexaferrite) and soft (S) (spinel) ferrites nanocomposites are gaining interest scientifically and technically, not only for combining the high magnetization of spinel ferrite nanomaterials and the high coercivity of hexaferrite magnetic nanomaterials but also for the outstanding exchange-coupling behavior among hard and soft magnetic phase. The improved magnetic features lead to produce a new nanocomposite with higher microwave absorption capacity in comparison with ferrites with a single absorption mechanism. Exchange-coupled effect has a potential application based on microwave absorption, recording media, permanent magnets, biomedical and other applications. Intensive studies have been conducted on this topic to produce hard/soft (H/S) ferrite nanocomposites with establishment of exchange coupled effect between the two phases. Preparation methods, microstructure, magnetics features, microwave and dielectric properties, and applications are elaborated. Consequently, a comprehensive effort has been made to contain an original reference investigating in detail the precise outcomes of the published papers.
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| 4. |
- Almessiere, M. A., et al.
(författare)
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Effects of Ce-Dy rare earths co-doping on various features of Ni-Co spinel ferrite microspheres prepared via hydrothermal approach
- 2021
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Ingår i: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854 .- 2214-0697. ; 14, s. 2534-2553
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Tidskriftsartikel (refereegranskat)abstract
- The effects of Ce-Dy co-doping on the crystal structure, optical, dielectric, magnetic properties, and hyperfine interactions of Ni-Co spinel ferrite microspheres synthesized hydrothermally have been studied. A series of ferrites with the general formula Ni0.5-Co0.5CexDyxFe2-2xO4 were synthesized with x values ranging from 0.00 to 0.10. The phase, crystallinity, and morphology of ferrite microspheres were analyzed by X-ray powder diffractometry (XRD), scanning and transmission electron microscopes (SEM and TEM), respectively. The structural analyses of the synthesized ferrite microspheres confirmed their high purity and cubic crystalline phase. The Diffuse reflectance spectroscopic (DRS) measurements were presented to calculate direct optical energy band gaps (E-g) and is found in the range 1.63 eV - 1.84 eV. Fe-57 Mossbauer spectroscopy showed that the hyperfine magnetic field of tetrahedral (A) and octahedral (B) sites decreased with the substitution of Dy3+-Ce3+ ions that preferrentially occupy the B site. The impact of the rare-earth content (x) on the magnetic features of the prepared NiCo ferrite microspheres was investigated by analyzing M-H loops, which showed soft ferrimagnetism. The magnetic features illustrate a great impact of the incorporation of Ce3+-Dy3+ ions within the NiCo ferrite structure. The saturation magnetization (M-s), remanence (M-r), and coercivity (H-c) increased gradually with increasing Ce-Dy content. At x = 0.04, M-s, M-r, and H-c attain maximum values of about 31.2 emu/g, 11.5 emu/g, and 512.4 Oe, respectively. The Bohr magneton (n(B)) and magneto-crystalline anisotropy constant (K-eff) were also determined and evaluated with correlation to other magnetic parameters. Further increase in Ce3+-Dy3+ content (i.e., x >= 0.06) was found to decrease M-s, M-r, and H-c values. The variations in magnetic parameters (M-s, M-r, and H-c) were largely caused by the surface spins effect, the variations in crystallite/particle size, the distribution of magnetic ions into the different sublattices, the evolutions of magneto-crystalline anisotropy, and the variations in the magnetic moment (n(B)). The squareness ratios were found to be lower than the predicted theoretical value of 0.5 for various samples, indicating that the prepared Ce-Dy substituted NiCo ferrite microspheres are composed of NPs with single-magnetic domain (SMD). Temperature and frequency-dependent electrical and dielectric measurements have been done to estimate the ac/dc conductivity, dielectric constant, and tangent loss values for all the samples. The ac conductivity measurements confirmed the power-law rules, largely dependent on Ce-Dy content. Impedance analysis stated that the conduction mechanisms in all samples are mainly due to the grains-grain boundaries. The dielectric constant of NiCo ferrite microspheres give rise to normal dielectric distribution, with the frequency depending strongly on the Ce-Dy content. The observed variation in tangential loss with frequency can be attributed to the conduction mechanism in ferrites, like Koop's phenomenological model.
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| 5. |
- Slimani, Y., et al.
(författare)
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Ultrasound-assisted synthesis and magnetic investigations of Ni0.4Cu0.4Zn0.2GaxGdxFe2-2xO4 (0.00 <= x <= 0.04) nanosized spinel ferrites
- 2022
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Ingår i: Applied Physics A. - : Springer Nature. - 0947-8396 .- 1432-0630. ; 128:7
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Tidskriftsartikel (refereegranskat)abstract
- This study focused on the impact of Ga-Gd co-substitution on the structural, magnetic features and hyperfine interactions of nanosized NiCuZn spinel ferrites [Ni0.4Cu0.4Zn0.2GaxGdxFe2-2xO4 (0.00 <= x <= 0.04) NSFs] synthesized via sonochemical approach using ultrasonic irradiation. X-ray powder pattern (XRD) analyses confirmed cubic spinel structures of products. Crystallites and particle sizes of all samples are found to be between 9-14 nm and 18-22 nm, respectively. The NSF morphology and chemical composition were investigated by transmission and scanning electron microscope (TEM and SEM) along with energy-dispersive X-ray (EDX). The cation distribution of all ions was evaluated by Mossbauer spectroscopy. The high spin Fe3+ ions determined the isomer shift (I.S.) values. For lower rare-earth dopant ratios, we found that Gd3+ ions occupy B sites, while Ga3+ ions reside in A sites, and thereafter, some Ga3+ ions start to enter B sites. Magnetometry measurements were used to evaluate the effect of magnetic field (H) and temperature (T) on the magnetization of products. For each sample, both coercivity (H-c) and saturation magnetization (M-s) increase when the T decreases below ambient temperature. All substituted samples display M-s values higher than those of non-substituted ones; however, H-c values diminish for x content up to 0.02 and thereafter enlarge. Different magnetization measurements revealed superparamagnetic-to-ferromagnetic transition below the blocking temperature (T-B).
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| 6. |
- Kavas, H., et al.
(författare)
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Synthesis and conductivity evaluation of PVTri-Fe3O4 nanocomposite
- 2010
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Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093 .- 1873-4812. ; 356:9-10, s. 484-489
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Tidskriftsartikel (refereegranskat)abstract
- Poly(1-vinyl-1,2,4-triazole) (PVTri)-Fe3O4 nanocomposite with conducting character was synthesized by a wet chemical process. PVTri has been freshly synthesized and coated/adsorbed on magnetite nanoparticles that are synthesized via a sonochemical route. The structure, morphology and electrical properties of the products were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and Dielectric impedance spectroscopy, respectively. Crystallite size of magnetite was calculated by X-ray line profile fitting as 12 +/- 6 nm. FT-IR and TGA analysis confirm the adsorption of PVTri on magnetite nanoparticles. SEM micrographs revealed that Fe3O4 nanoparticles are slightly aggregated upon PVTri coating. Conductivity and permittivity measurements show the effect of glass transition temperature of polymer par in PVTri-Fe3O4 nanocomposite.
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| 7. |
- Baykal, A., et al.
(författare)
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Synthesis and Characterization of Dendrimer-Encapsulated Iron and Iron-Oxide Nanoparticles
- 2012
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Ingår i: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM. - : Springer Science and Business Media LLC. - 1557-1939 .- 1557-1947. ; 25:5, s. 1541-1549
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a series of iron (Fe) containing nanoparticles were prepared by employing PAMAM (Poly(amidoamine), dendrimers with different generations (G0-G3) as templates and sodium borohydride as a reducing agent. The products have been characterized by TEM, FT-IR, XRD, VSM, TGA, and XPS. XRD analysis reveal low crystallinity of formed particles within the dendrimers, however, crystallinity of the nanoparticles was observed to increase with increasing generation of dendrimers. Dominant phases were determined as magnetite (Fe3O4 or maghemite, gamma-Fe2O3). XPS analysis revealed the chemical composition of nanoparticles as iron oxide which indicated the oxidation of Fe species subsequent to the reduction process, in agreement with XRD analysis. The magnetization curves have superparamagnetic nonhysteretic characteristic at lower fields and with nonsaturation characteristic at high fields. Magnetic evaluation of samples with the 20:1 molar ratio of Fe:PAMAM showed decreasing superparamagnetic character and decreasing saturation magnetisation with increasing generation of dendrimers.
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| 8. |
- Durmus, Z., et al.
(författare)
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Poly(vinyl phosphonic acid) (PVPA)-BaFe12O19 Nanocomposite
- 2012
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Ingår i: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1939 .- 1557-1947. ; 25:4, s. 1185-1193
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Tidskriftsartikel (refereegranskat)abstract
- We present a method for the fabrication of PVPA/BaFe12O19 nanocomposite by in-situ polymerization of vinyl phosphonic acid, VPA in the presence of synthesized BaFe12O19 NPs. Nanoparticles and the nanocomposite were analyzed by XRD, FTIR, TGA, SEM, TEM, VSM, and conductivity techniques for structural and physicochemical characteristics. Nanoparticles, identified as BaFe12O19 from XRD analysis, were successfully coated with PVPA and the linkage was assessed to be via P-O bonds. Electron microscopy analysis revealed aggregation of BaFe12O19 particles and dominantly platelet morphology upon composite formation. TGA analysis revealed the composition of the nanocomposite as 65% BaFe12O19 and 35% polymer. Magnetic evaluation revealed that adsorption of PVPA anions during the preparation of the nanocomposite strongly influenced the magnetic properties resulting in much lower saturation magnetization values. DC conductivity measurements were used to calculate activation energy of PVPA/BaFe12O19 nanocomposite and it was obtained as 0.37 eV.
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| 9. |
- Durmus, Z., et al.
(författare)
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Synthesis and characterization of poly(1-vinyl-1,2,4-triazole) (PVTri)-barium hexaferrite nanocomposite
- 2011
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 406:11, s. 2298-2302
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Tidskriftsartikel (refereegranskat)abstract
- We present a method for the fabrication of PVTri-BaFe12O19 nanocomposites by in-situ polymerization of PVTri in the presence of synthesized BaFe12O19 nanoparticles. Nanoparticles, polymer and nanocomposite were analyzed by XRD, FTIR, TGA, TEM, NMR, GPC and conductivity techniques for structural and physicochemical characteristics. Crystallographic analysis revealed the phase as hexaferrite and X-ray line profile fitting yielded a crystallite size of 17 +/- 5 nm. Conjugation of PVTri to nanoparticle surface was assessed to be via carbonyl groups on the polymer. TG analysis revealed that 45 wt% of nanocomposite is inorganic phase (BaFe12O19). It was found out that the ac conductivity of nanocomposite under a certain frequency increases with temperature.
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| 10. |
- Durmus, Z., et al.
(författare)
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Synthesis and characterization of poly(vinyl phosphonic acid) (PVPA)-Fe3O4 nanocomposite
- 2011
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Ingår i: Polyhedron. - : Elsevier BV. - 0277-5387 .- 1873-3719. ; 30:2, s. 419-426
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Tidskriftsartikel (refereegranskat)abstract
- Poly(vinyl phosphonic acid) (PVPA)-Fe3O4 nanocomposite is synthesized by the precipitation of Fe3O4 in the presence of PVPA. Structural, surface, morphological, thermal properties and conductivity characterization/evaluation of the nanocomposite were performed by XRD, FT-IR, TEM, TGA and conductivity measurements respectively. The capping of PVPA around the Fe3O4 nanoparticles was confirmed by FT-IR spectroscopy, the interaction being via bridging oxygens of the phosphate and the nanoparticle surface. The crystallite and particle size were obtained as 6 +/- 2 and 8.7 +/- 0.1 nm from XRD line profile fitting and TEM image analysis respectively, which reveal nearly single crystalline nature of the Fe3O4 nanoparticles. Magnetic characterization of the bulk magnetite and (PVPA)-Fe3O4 nanocomposite reveals that both are in the superparamagnetic state at room temperature. The average magnetic domain size of the nanoparticles has been calculated using the Langevin function, which was fitted to the measured M-H hysteresis curves as 7.6 nm for the nanocomposite. In the nanocomposite, the reduction is due to the adsorption of PVPA onto the magnetite surface, which cancels some of the free spins at the surface causing a magnetically dead layer. Analysis of the conductivity and permittivity measurements revealed the coupling of ionic and polymer segmental motions and strong temperature dependency in the nanocomposite.
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