| 1. |
- Ludwig, Frank, et al.
(författare)
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Magnetic, Structural, and Particle Size Analysis of Single- and Multi-Core Magnetic Nanoparticles
- 2014
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Ingår i: IEEE Transactions on Magnetics. - 0018-9464 .- 1941-0069. ; 50:11
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Tidskriftsartikel (refereegranskat)abstract
- We have measured and analyzed three different commercial magnetic nanoparticle systems, both multi-core and single-core in nature, with the particle (core) size ranging from 20 to 100 nm. Complementary analysis methods and same characterization techniques were carried out in different labs and the results are compared with each other. The presented results primarily focus on determining the particle size-both the hydrodynamic size and the individual magnetic core size-as well as magnetic and structural properties. The used analysis methods include transmission electron microscopy, static and dynamic magnetization measurements, and Mossbauer spectroscopy. We show that particle (hydrodynamic and core) size parameters can be determined from different analysis techniques and the individual analysis results agree reasonably well. However, in order to compare size parameters precisely determined from different methods and models, it is crucial to establish standardized analysis methods and models to extract reliable parameters from the data.
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| 2. |
- Wagner, J., et al.
(författare)
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First 230? : GHz VLBI fringes on 3C 279 using the APEX Telescope (Research Note)
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 581
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We report about a 230? GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO). Methods. We installed VLBI equipment and measured the APEX station position to 1? cm accuracy (1σ). We then observed 3C 279 on 2012 May 7 in a 5? h 230? GHz VLBI track with baseline lengths of 2800? Mλ to 7200? Mλ and a finest fringe spacing of 28.6? μas. Results. Fringes were detected on all baselines with signal-to-noise ratios of 12 to 55 in 420? s. The correlated flux density on the longest baseline was ∼0.3? Jy beam-1, out of a total flux density of 19.8? Jy. Visibility data suggest an emission region ≤ 38? μas in size, and at least two components, possibly polarized. We find a lower limit of the brightness temperature of the inner jet region of about 1010? K. Lastly, we find an upper limit of 20% on the linear polarization fraction at a fringe spacing of ∼ 38? μas. Conclusions. With APEX the angular resolution of 230? GHz VLBI improves to 28.6? μas. This allows one to resolve the last-photon ring around the Galactic Center black hole event horizon, expected to be 40? μas in diameter, and probe radio jet launching at unprecedented resolution, down to a few gravitational radii in galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in detail, follow-up observations with APEX and five other mm-VLBI stations have been conducted (March 2013) and are being analyzed.
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| 3. |
- Bender, P., et al.
(författare)
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Dipolar-coupled moment correlations in clusters of magnetic nanoparticles
- 2018
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Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 98:22
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Tidskriftsartikel (refereegranskat)abstract
- Here, we resolve the nature of the moment coupling between 10-nm dimercaptosuccinic acid-coated magnetic nanoparticles. The individual iron oxide cores were composed of >95% maghemite and agglomerated to clusters. At room temperature the ensemble behaved as a superparamagnet according to Mössbauer and magnetization measurements, however, with clear signs of dipolar interactions. Analysis of temperature-dependent ac susceptibility data in the superparamagnetic regime indicates a tendency for dipolar-coupled anticorrelations of the core moments within the clusters. To resolve the directional correlations between the particle moments we performed polarized small-angle neutron scattering and determined the magnetic spin-flip cross section of the powder in low magnetic field at 300 K. We extract the underlying magnetic correlation function of the magnetization vector field by an indirect Fourier transform of the cross section. The correlation function suggests nonstochastic preferential alignment between neighboring moments despite thermal fluctuations, with anticorrelations clearly dominating for next-nearest moments. These tendencies are confirmed by Monte Carlo simulations of such core clusters.
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| 4. |
- Bender, P., et al.
(författare)
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Distribution functions of magnetic nanoparticles determined by a numerical inversion method
- 2017
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 19:7
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, we applied a regularized inversion method to extract the particle size, magnetic moment and relaxation-time distribution of magnetic nanoparticles from small-angle x-ray scattering (SAXS), DC magnetization (DCM) and AC susceptibility (ACS) measurements. For the measurements the particles were colloidally dispersed in water. At first approximation the particles could be assumed to be spherically shaped and homogeneously magnetized single-domain particles. As model functions for the inversion, we used the particle form factor of a sphere (SAXS), the Langevin function (DCM) and the Debye model (ACS). The extracted distributions exhibited features/peaks that could be distinctly attributed to the individually dispersed and non-interacting nanoparticles. Further analysis of these peaks enabled, in combination with a prior characterization of the particle ensemble by electron microscopy and dynamic light scattering, a detailed structural and magnetic characterization of the particles. Additionally, all three extracted distributions featured peaks, which indicated deviations of the scattering (SAXS), magnetization (DCM) or relaxation (ACS) behavior from the one expected for individually dispersed, homogeneously magnetized nanoparticles. These deviations could be mainly attributed to partial agglomeration (SAXS, DCM, ACS), uncorrelated surface spins (DCM) and/or intra-well relaxation processes (ACS). The main advantage of the numerical inversion method is that no ad hoc assumptions regarding the line shape of the extracted distribution functions are required, which enabled the detection of these contributions. We highlighted this by comparing the results with the results obtained by standard model fits, where the functional form of the distributions was a priori assumed to be log-normal shaped.
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| 5. |
- Bender, P., et al.
(författare)
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Relating Magnetic Properties and High Hyperthermia Performance of Iron Oxide Nanoflowers
- 2018
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:5, s. 3068-3077
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Tidskriftsartikel (refereegranskat)abstract
- We investigated, in depth, the interrelations among structure, magnetic properties, relaxation dynamics and magnetic hyperthermia performance of magnetic nanoflowers. The nanoflowers are about 39 nm in size, and consist of densely packed iron oxide cores. They display a remanent magnetization, which we explain by the exchange coupling between the cores, but we observe indications for internal spin disorder. By polarized small-angle neutron scattering, we unambiguously confirm that, on average, the nanoflowers are preferentially magnetized along one direction. The extracted discrete relaxation time distribution of the colloidally dispersed particles indicates the presence of three distinct relaxation contributions. We can explain the two slower processes by Brownian and classical Néel relaxation, respectively. The additionally observed very fast relaxation contributions are attributed by us to the relaxation of disordered spins within the nanoflowers. Finally, we show that the intrinsic loss power (ILP, magnetic hyperthermia performance) of the nanoflowers measured in colloidal dispersion at high frequency is comparatively large and independent of the viscosity of the surrounding medium. This concurs with our assumption that the observed relaxation in the high frequency range is primarily a result of internal spin relaxation, and possibly connected to the disordered spins within the individual nanoflowers.
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| 6. |
- Bäckström, Daniel, 1985, et al.
(författare)
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Particle composition and size distribution in coal flames - The influence on radiative heat transfer
- 2015
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 64, s. 70-80
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Tidskriftsartikel (refereegranskat)abstract
- Radiative heat transfer in a 77 kWth swirling lignite flame has been studied. The aim is to characterize different particle types present in a coal flame and to determine their influence on the radiative heat transfer. The study combines extractive particle measurements, radiative intensity measurements and detailed radiation modelling. The size distribution of the extracted particles was measured with a low pressure impactor and some of the size fractions were analysed with SEM–EDX. The measured total radiative intensity is compared with the modelled intensity based on the particle measurements in the same cross-section of the flame. The particle properties were calculated with Mie theory and the gas properties with a statistical narrow-band model. The results show that the contribution of coal/char particles dominates the radiative heat transfer in the investigated cross-section of the flame. The methodology applied in this work shows promising results for characterization of particle radiation in flames of practical size.
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| 7. |
- Merlone, A., et al.
(författare)
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The MeteoMet project - metrology for meteorology: challenges and results
- 2015
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Ingår i: Meteorological Applications. - : Wiley. - 1350-4827 .- 1469-8080. ; 22, s. 820-829
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Tidskriftsartikel (refereegranskat)abstract
- The study describes significant outcomes of the Metrology for Meteorology' project, MeteoMet, which is an attempt to bridge the meteorological and metrological communities. The concept of traceability, an idea used in both fields but with a subtle difference in meaning, is at the heart of the project. For meteorology, a traceable measurement is the one that can be traced back to a particular instrument, time and location. From a metrological perspective, traceability further implies that the measurement can be traced back to a primary realization of the quantity being measured in terms of the base units of the International System of Units, the SI. These two perspectives reflect long-standing differences in culture and practice and this project - and this study - represents only the first step towards better communication between the two communities. The 3 year MeteoMet project was funded by the European Metrology Research Program (EMRP) and involved 18 European National Metrological Institutes, 3 universities and 35 collaborating stakeholders including national meteorology organizations, research institutes, universities, associations and instrument companies. The project brought a metrological perspective to several long-standing measurement problems in meteorology and climatology, varying from conventional ground-based measurements to those made in the upper atmosphere. It included development and testing of novel instrumentation as well as improved calibration procedures and facilities, instrument intercomparison under realistic conditions and best practice dissemination. Additionally, the validation of historical temperature data series with respect to measurement uncertainties and a methodology for recalculation of the values were included.
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| 8. |
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| 9. |
- Schier, P., et al.
(författare)
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European Research on Magnetic Nanoparticles for Biomedical Applications : Standardisation Aspects
- 2020
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Ingår i: 21st Polish Conference on Biocybernetics and Biomedical Engineering, PCBBE 2019. - Cham : Springer Verlag. - 9783030298845 ; , s. 316-326
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Konferensbidrag (refereegranskat)abstract
- Magnetic nanoparticles have many applications in biomedicine and other technical areas. Despite their huge economic impact, there are no standardised procedures available to measure their basic magnetic properties. The International Organization for Standardization is working on a series of documents on the definition of characteristics of magnetic nanomaterials. We review previous and ongoing European research projects on characteristics of magnetic nanoparticles and present results of an online survey among European researchers.
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| 10. |
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