| 1. |
- Brändström, U., et al.
(author)
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Results from the intercalibration of optical low light calibration sources 2011
- 2012
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In: Geoscientific Instrumentation, Methods and Data Systems. - : Copernicus GmbH. - 2193-0856 .- 2193-0864. ; 1:1, s. 43-51
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Journal article (peer-reviewed)abstract
- Following the 38th Annual European Meeting onAtmospheric Studies by Optical Methods in Siuntio in Finland,an intercalibration workshop for optical low light calibrationsources was held in Sodankyl¨a, Finland. The mainpurpose of this workshop was to provide a comparable scalefor absolute measurements of aurora and airglow. All sourcesbrought to the intercalibration workshop were compared tothe Fritz Peak reference source using the Lindau CalibrationPhotometer built by Wilhelm Barke and Hans Lauche in1984. The results were compared to several earlier intercalibrationworkshops. It was found that most sources were fairlystable over time, with errors in the range of 5–25 %. To furthervalidate the results, two sources were also intercalibratedat UNIS, Longyearbyen, Svalbard. Preliminary analysis indicatesagreement with the intercalibration in Sodankyl¨a withinabout 15–25 %.
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| 2. |
- Qin, Jian, et al.
(author)
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A high-performance magnetic resonance imaging T2 contrast agent
- 2007
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In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 19:14, s. 1874-1878
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Journal article (peer-reviewed)abstract
- A high-performance magnetic resonance imaging T-2 contrast agent has been prepared via phase transfer of hydrophobic superparamagnetic iron oxide nanoparticles (SPIONs) to an aqueous solution by using Pluronic F127 copolymers. As seen in the figure, a hierarchical structure of the surface coating is formed and proven to be a crucial characteristic to enhance not only water dispersibility, but also the efficacy as a T-2 contrast agent.
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| 3. |
- Salazar-Alvarez, G., et al.
(author)
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Cubic versus spherical magnetic nanoparticles : The role of surface anisotropy
- 2008
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 130:40, s. 13234-13239
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Journal article (peer-reviewed)abstract
- The magnetic properties of maghemite (gamma-Fe2O3) cubic and spherical nanoparticles of similar sizes have been experimentally and theoretically studied. The blocking temperature, TB, of the nanoparticles depends on their shape, with the spherical ones exhibiting larger TB. Other low temperature properties such as saturation magnetization, coercivity, loop shift or spin canting are rather similar. The experimental effective anisotropy and the Monte Carlo simulations indicate that the different random surface anisotropy of the two morphologies combined with the low magnetocrystalline anisotropy of gamma-Fe2O3 is the origin of these effects.
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| 4. |
- Dalin, Peter A., et al.
(author)
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Wave influence on polar mesosphere summer echoes above Wasa : experimental and model studies
- 2012
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In: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 30:8, s. 1143-1157
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Journal article (peer-reviewed)abstract
- Comprehensive analysis of the wave activity in the Antarctic summer mesopause is performed using polar mesospheric summer echoes (PMSE) measurements for December 2010–January 2011. The 2-day planetary wave is a statistically significant periodic oscillation in the power spectrum density of PMSE power. The strongest periodic oscillation in the power spectrum belongs to the diurnal solar tide; the semi-diurnal solar tide is found to be a highly significant harmonic oscillation as well. The inertial-gravity waves are extensively studied by means of PMSE power and wind components. The strongest gravity waves are observed at periods of about 1, 1.4, 2.5 and 4 h, with characteristic horizontal wavelengths of 28, 36, 157 and 252 km, respectively. The gravity waves propagate approximately in the west-east direction over Wasa (Antarctica). A detailed comparison between theoretical and experimental volume reflectivity of PMSE, measured at Wasa, is made. It is demonstrated that a new expression for PMSE reflectivity derived by Varney et al. (2011) is able to adequately describe PMSE profiles both in the magnitude and in height variations. The best agreement, within 30%, is achieved when mean values of neutral atmospheric parameters are utilized. The largest contribution to the formation and variability of the PMSE layer is explained by the ice number density and its height gradient, followed by wave-induced perturbations in buoyancy period and the turbulent energy dissipation rate
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| 5. |
- Kim, Do-Kyung, et al.
(author)
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Polymeric nanocomposites of complex ferrite
- 2004
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In: Functional Nanomaterials For Optoelectronics And Other Applications. ; , s. 165-168
-
Conference paper (peer-reviewed)abstract
- The influence of mixtures of Ni0.5Zn0.4CU0.1Fe2O4, CoFe2O4, and graphite on the permeability, permittivity and microwave absorption properties in a composite embedded with insulating polymeric matrix, that can be used for X- and P-band radar absorption, has been investigated. Thermodynamic modelling of the complex ferrite system has been demonstrated by the controlled simultaneous coprecipitation of all ions inolved in the composite in the selected working pH ranges. The method employed is very convenient for the synthesis of multicomponent systems with a homogenous distribution of compositions.
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| 6. |
- Kim, D. K., et al.
(author)
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Protective coating of superparamagnetic iron oxide nanoparticles
- 2003
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 15:8, s. 1617-1627
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Journal article (peer-reviewed)abstract
- Magnetic nanoparticles are becoming increasingly important for several biomedical applications. For example, superparamagnetic magnetite nanoparticles with suitable biocompatible coatings are useful in magnetic resonance imaging, tissue engineering, and drug delivery, etc. In this study we report the synthesis of magnetite nanoparticles and the further coating of these particles by several types of protective layers. Thermodynamic modeling of the chemical system has been adopted as a rational approach to establish routes to better synthesis conditions for pure phase magnetite. Quantitative analysis of different reaction equilibria involved in the precipitation of magnetite from aqueous solutions has been used to determine optimum synthesis conditions. Superparamagnetic magnetite nanoparticles (SPION) with diameters of 6 and 12 nm have been prepared by controlled chemical coprecipitation of magnetite phase from aqueous solutions containing suitable salts of Fe2+ and Fe3+ under inert atmosphere. Pure magnetite phase SPION could be observed from X-ray diffraction. Magnetic colloid suspensions containing particles with three different types of coatings (sodium oleate (NaOl), starch, and methoxypoly(ethylene glycol) (MPEG)) have been prepared by using different stabilization methods. SPION coatings were studied by determining the change of the surface charge by electrokinetic sonic amplitude (ESA) measurements, as a function of varying NaOl in the solution, where the amount of NaOl needed to form a stable suspension was determined. For stable suspension, the optimum concentration of sodium oleate (NaOl) chemisorbed at 2.5 g of SPION surface is 5.2 x 10(-7) M NaOl which shows maximum ESA value of 0.034 mPa(.)M/V. SPION coating by starch results in the formation of agglomerate. The agglomeration size of starch-coated SPION can be decreased by introducing H2O2 as an oxidizing agent; the resulting particle size is 42 nm as determined by dynamic light scattering (DLS). For the modification of SPION surfaces with MPEG, the surface was first silanized by 3-aminopropyltrimethoxy silane (APTMS) as a coupling agent with a thickness of two or three molecular layers. AFM image shows that each cluster includes several magnetite single particles with the cluster size around 120 nm. SPION, both coated and uncoated, have been characterized by several techniques. AFM was used to image the MPEG-coated SPION. FTIR study indicated that the different coating agents cover the SPION surface. Magnetic characterization was carried out using SQUID and Mossbauer spectroscopy.
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| 7. |
- Kim, D. K., et al.
(author)
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Starch-coated superparamagnetic nanoparticles as MR contrast agents
- 2003
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 15:23, s. 4343-4351
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Journal article (peer-reviewed)abstract
- Superparamagnetic iron oxide nanoparticles (SPION) with suitable bio-compatible coatings have been used in biomedicine, particularly in magnetic resonance imaging (MRI), tissue engineering, and drug delivery applications. In this study, we describe the synthesis of SPION and its use for experimental in-vivo applications in MRI. SPION with a mean size of 6 nm have been prepared under inert atmosphere, in a polymeric starch matrix, by controlled chemical coprecipitation of magnetite phase from aqueous solutions containing suitable salts of Fe2+ and Fe3+. X-ray powder diffraction was used to confirm a pure magnetite phase for the SPION. The influence of oxidizing agents on the cleavage of the starch chains was investigated by changing the concentration of H2O2. An aqueous solution of H2O2/NaOH cleaves the glycosidic bonds and reduces the polymer chains to a critical average molecular weight. From the dynamic light scattering (DLS) size distribution, the bulk agglomeration size was decreased by approximately 50% of the bulk size when treated by H2O2. Freshly synthesized starch-coated SPION in buffered artificial cerebro-spinal fluid were injected into the brain parenchyma of anaesthetized rats for in-vivo monitoring. Analysis of T-2*-weighted images and T-2*-maps revealed formation of a. concentration gradient for the SPION at the injection site, indicating SPION dispersion in the living brain parenchyma from the center of the injection site toward the periphery. The starch-coated SPION show a biocompatibility and possibility of being transported in the extracellular space as well as being internalized in nerve cells.
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| 8. |
- Mikhaylova, A. I., et al.
(author)
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Specific features of the current–voltage characteristics of SiO2/4H-SiC MIS structures with phosphorus implanted into silicon carbide
- 2016
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In: Semiconductors (Woodbury, N.Y.). - 1063-7826 .- 1090-6479. ; 50:1, s. 103-105
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Journal article (peer-reviewed)abstract
- The effect of phosphorus implantation into a 4H-SiC epitaxial layer immediately before the thermal growth of a gate insulator in an atmosphere of dry oxygen on the reliability of the gate insulator is studied. It is found that, together with passivating surface states, the introduction of phosphorus ions leads to insignificant weakening of the dielectric breakdown field and to a decrease in the height of the energy barrier between silicon carbide and the insulator, which is due to the presence of phosphorus atoms at the 4H-SiC/SiO2 interface and in the bulk of silicon dioxide.
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| 9. |
- Mikhaylova, Maria, et al.
(author)
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Superparamagnetism of magnetite nanoparticles : Dependence on surface modification
- 2004
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:6, s. 2472-2477
-
Journal article (peer-reviewed)abstract
- Superparamagnetic iron oxide nanoparticles (SPION) with an average particle diameter of 6 nm are prepared by controlled chemical coprecipitations. Colloidal suspensions of noninteracting SPION, where the surface has been modified with three different types of biocompatible substances, namely, starch, gold (An), and methoxypoly(ethylene glycol) (MPEG) have been fabricated via three different techniques. Starch-coated SPION are prepared by coprecipitation in a polymeric matrix, Au-coated SPION are fabricated by the microemulsion method, and MPEG-coated SPION are prepared using the self-assembly approach. The magnetic nanoparticles form a core-shell structure, and the magnetic dipole-dipole interactions are screened by a layer of coating agents. The amounts of coating agents and SPION are indirectly calculated from the thermogravinietric analysis and superconducting quantum interference device measurements by assuming passive oxidation on the surface of the SPION, and the other conditions do not influence the measurements. The dependency of the spectral characteristics of Mossbauer spectroscopy as a function of an external magnetic field H-ext is measured to investigate the effect of dipole-dipole screening of the different coating layers on the SPION. Uncoated SPION show a stable magnetic moment under H-etx and the superparamagnetic (SPM) fraction transforms to a ferrimagnetic state. Starch and Au-coated SPION retain the SPM fraction according to Mossbauer spectroscopy and magnetization measurements. MPEG-coated SPION show hyperfine magnetic structure without the quadrupole effect with increasing the value of the blocking temperature.
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| 10. |
- Mikhaylova, Maria, et al.
(author)
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The effect of biocompatible coating layers on magnetic properties of superparamagnetic iron oxide nanoparticles
- 2004
-
In: Hyperfine Interactions. - 0304-3843 .- 1572-9540. ; 156:1, s. 257-263:156/157, s. 257-263
-
Journal article (peer-reviewed)abstract
- The effect of the surface coating on the magnetic properties of superparamagnetic iron oxide nanoparticles (SPION) with 8 nm in size has been studied. Four different biocompatible coating layers are considered: poly L,L-lactic acid (PLLA), poly epsilon-caprolactone (PCL), bovine serum albumin (BSA) and gold. The presence of coating layer on the surface of SPION is confirmed by FT-IR spectroscopy. Mossbauer spectroscopy and magnetic susceptibility measurements show that for uncoated SPION and Au@SPION the superparamagnetic fraction is retained. The formation of clusters in the case of BSA@SPION and chain-like structure for PCL@SPION and PLLA@SPION increase the inter-particle interactions resulting in hyperfine magnetic structure observed in the Mossbauer spectra at ambient temperature.
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