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991.
Courtney H. Lanier Ann N. Chiaramonti Laurence D. Marks Kenneth R. Poeppelmeier 《Surface science》2009,603(16):2574-2579
The so-called Biphase termination on α-Fe2O3 has been widely accepted to be a structure with a 40 Å unit supercell composed of coexisting islands of Fe1−xO and α-Fe2O3. Based on thermodynamic arguments and experimental evidence, including transmission electron diffraction, imaging, magnetic and spectroscopic information, it is found that the previously proposed structure model is inaccurate. The actual Biphase structure is instead a layered structure related to the reduction of α-Fe2O3 to Fe3O4. A model for the Biphase termination is proposed which does not contain islands of Fe1−xO but instead consists of bulk α-Fe2O3 and a Fe3O4-derived overlayer. The proposed model is consistent with all current and previously reported experimental findings. 相似文献
992.
Naimei Tang 《Journal of magnetism and magnetic materials》2009,321(19):3311-3317
Rhenium sulfide nanoparticles are associated with magnetic iron oxide through coprecipitation of iron salts with tetramethylammonium hydroxide. Sizes of the formed magnetic rhenium sulfide composite particles are in the range 5.5-12.5 nm. X-ray diffraction and energy-dispersive analysis of X-rays spectra demonstrate the coexistence of Fe3O4 and ReS2 in the composite particle, which confirm the formation of the magnetic rhenium sulfide composite nanoparticles. The association of rhenium sulfide with iron oxide not only keeps electronic state and composition of the rhenium sulfide nanoparticles, but also introduces magnetism with the level of 24.1 emu g-1 at 14 kOe. Surface modification with monocarboxyl-terminated poly(ethylene glycol) (MPEG-COOH) has the role of deaggregating the composite nanoparticles to be with average hydrodynamic size of 27.3 nm and improving the dispersion and the stability of the composite nanoparticles in water. 相似文献
993.
Superparamagnetic nanoparticles have been widely applied in various bio-medical applications. To date, it is still a challenge to synthesize nanosized Fe3O4 particles with controlled size and distribution. In this paper, a novel solvent-free thermal decomposition method is reported for synthesizing Fe3O4 nanoparticles. Size and morphology of the nanoparticles are determined by TEM while the structure of the nanoparticles is identified by FTIR, XPS and TGA measurements. Magnetic properties of the obtained particles are determined using VSM and SQUID measurement. The particle size of the Fe3O4 can be tailored by adjusting either reaction temperature or time. When the reaction temperature is increased to 330 °C and the reaction time is extended to 4 h, the average particle size of the obtained nanoparticles is ∼9 nm, while Ms value reaches ∼76 emu/g. The as synthesized Fe3O4 nanoparticles show well-established superparamagnetic properties with the blocking temperature at around 100 K. 相似文献
994.
In this study, a new method is proposed for the preparation of Fe3O4 from iron oxyhydroxides (goethite, akaganeite, lepidocrocite, feroxyhyte and ferrihydrite) or iron oxide (hematite) and ferrous salt in aqueous solution. The product is magnetite with various particle sizes. Products are characterized by X-ray powder diffraction, IR spectra and vibrating sample magnetometery. 相似文献
995.
Rossi C Boss A Haap M Martirosian P Claussen CD Schick F 《Magnetic resonance imaging》2009,27(4):489-496
This study investigated the feasibility of an MRI protocol providing whole-body T2* maps at 1.5 T. Seven healthy volunteers (mean age=30.1+/-3.7, three women and four men) and two patients (both male, 53 and 46 years old) affected by transfusion-dependent anemias participated in the study. Coronally oriented images of five subsequent body levels were acquired using a fat-suppressed multiecho 2D gradient-echo sequence (12 echo times ranging from 4.8 to 76.3 ms were selected) and afterwards composed. Parametrical T2* maps of the whole body were reconstructed on a pixel-by-pixel basis. For both, healthy volunteers and patients, representative T2* values were computed from extended regions of interest (ROIs). Good-quality whole-body T2* maps were computed in all volunteers and patients. In healthy volunteers, T2* values were assessed in the cerebral white (58.5+/-4.2 ms) and gray (81.4+/-5.5 ms) matter, liver (34.3+/-7.0 ms), spleen (63.5+/-3.3 ms), kidneys (65.4+/-10.3 ms) and skeletal muscles (~30 ms). The liver presented faster relaxation rates in males as compared to females. One patient (serum ferritin concentration=927 microg/dl) showed shortened T2* values in liver (3.6+/-5.5 ms), spleen (3.1+/-4.8 ms), kidneys (11.1+/-7.1 ms) and muscles (25.1+/-3.4 ms). The second patient (serum ferritin concentration=346 microg/dl) presented reduced T2* values in liver (3.9+/-7.3 ms), spleen (20.1+/-9.8 ms) and kidneys (24.6+/-7.7 ms). The presented technique may find clinical application in the assessment of the iron burden in the entire body, and in monitoring of chelation therapies in patients treated with frequent blood transfusions. 相似文献
996.
Positano V Salani B Pepe A Santarelli MF De Marchi D Ramazzotti A Favilli B Cracolici E Midiri M Cianciulli P Lombardi M Landini L 《Magnetic resonance imaging》2009,27(2):188-197
In the clinical MRI practice, it is common to assess liver iron overload by T2* multi-echo gradient-echo images. However, there is no full consensus about the best image analysis approach for the T2* measurements. The currently used methods involve manual drawing of a region of interest (ROI) within MR images of the liver. Evaluation of a representative liver T2* value is done by fitting an appropriate model to the signal decay within the ROIs vs. the echo time. The resulting T2* value may depend on both ROI placement and choice of the signal decay model. The aim of this study was to understand how the choice of the analysis methodology may affect the accuracy of T2* measurements. A software model of the iron overloaded liver was inferred from MR images acquired from 40 thalassemia major patients. Different image analysis methods were compared exploiting the developed software model. Moreover, a method for global semiautomatic T2* measurement involving the whole liver was developed. The global method included automatic segmentation of parenchyma by an adaptive fuzzy-clustering algorithm able to compensate for signal inhomogeneities. Global liver T2* value was evaluated using a pixel-wise technique and an optimized signal decay model. The global approach was compared with the ROI-based approach used in the clinical practice. For the ROI-based approach, the intra-observer and inter-observer coefficients of variation (CoVs) were 3.7% and 5.6%, respectively. For the global analysis, the CoVs for intra-observers and inter-observers reproducibility were 0.85% and 2.87%, respectively. The variability shown by the ROI-based approach was acceptable for use in the clinical practice; however, the developed global method increased the accuracy in T2* assessment and significantly reduced the operator dependence and sampling errors. This global approach could be useful in the clinical arena for patients with borderline liver iron overload and/or requiring follow-up studies. 相似文献
997.
D. Ahmad I. Park G.C. Kim J.H. Lee Z.-A. Ren Y.C. Kim 《Physica C: Superconductivity and its Applications》2009,469(15-20):1052-1054
The irreversibility line and flux pinning properties of high-Tc superconductor SmFeAsO0.85 were studied using DC magnetization data. Polycrystalline SmFeAsO0.85 was prepared in a high pressure synthesis apparatus under the pressure of 6 GPa. The results of DC susceptibility showed the superconducting transition at about 55 K. A critical current density Jc(B) was calculated using Bean’s critical state model. At low temperatures (20 K), Jc(B) showed a relatively high value with weak dependence on an applied magnetic field. At higher temperatures, a stronger dependence of the magnetic field was observed, which resulted from decrease in a critical current density probably due to the flux creep effect. The irreversibility line (IL) agreed well with the flux creep theory of Matsushita et al. A comparison of normalized pinning force density with the theoretical models showed that the irreversible behavior in SmFeAsO0.85 is dominated mainly by normal point pinning (δTc) and surface pinning mechanisms. 相似文献
998.
通过对影响测定结果的不确定度因素的分析和量化,评价了火焰原子吸收光谱法测定水样中铁的不确定度。计算得水中铁含量测定结果的扩展不确定度为0.015mg/L(veff=17)。 相似文献
999.
1000.