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[en] Co-doped CeO2 nanorods of 10–20 nm in diameter and 200–600 nm or more in length have been synthesized by a simple co-precipitation method. The results of XRD and SADE analysis indicate that the as-synthesized CeO2 samples have the fluorite structure. X-ray photoelectron spectroscopy and Raman spectra show that Ce4+ and Ce3+ ions coexist at the surface of non-doped CeO2 nanorods. The magnetic measurements indicated that Co-doped CeO2 nanorods exhibit stronger ferromagnetism at room temperature, and while increasing the amount of Co ions, the ferromagnetism increase more, which can be associated with the presence of Ce3+ and Co2+. - Highlights: • Co-doped CeO2 nanorods are synthesized by a simple hydrothermal method. • The synthesized Co-doped CeO2 nanorods show excellent RTFM. • The controllable morphology and RTFM should make the Co-doped CeO2 nanorods excellent candidates for applications in related areas
[en] To effectively extract organohalogens from human hair, two factors, the extracting time and hair length on the extraction efficiency of organohalogens were studied by neutron activation analysis (NAA) and gas chromatograph-electron capture detector (GC-ECD), respectively. Furthermore, the concentrations of extractable organohalogens (EOX) and extractable persistent organohalogens (EPOX) in hair samples from angioma and control babies were also measured by the established method. The results indicated that the optimal Soxhlet-extraction time for EOX and EPOX in hair was from 8 to 11 hours, and the extraction efficiencies for organochlorine pesticides in hair were in the order of powder >2 mm>5 mm. Also, the mean levels of EOCl and EPOCl in hair of the angioma babies were significantly higher than those in the control babies (PEOCl<0.01; PEPOCl<0.05), which implied the possible relationship between the environmental pollution and angioma. (author)
[en] The heating processes of the single-layer gold thin film and the two-layer film assembly of gold padded with other metal (silver, copper and nickel) irradiated by femtosecond laser pulse are studied by the two-temperature model. It is found that the substrate metal can change energy transport, which is corresponding to the temperature changing process, and the thermal equilibrium time. Compared with the single-layer gold film at the same laser fluence, the two-layer film structure can change the damage threshold of the gold surface. Our results indicate that we can maximize the damage threshold of the gold film surface by altering the thickness ratio of the gold layer and the substrate layer in the two-layer film assembly.
[en] Many persistent organohalogen compounds such as DDTs and polychlorinated biphenyls have caused seriously environmental pollution problem that now involves all life. It is know that neutron activation analysis (NAA) is a very convenient method for halogen analysis and is also the only method currently available for simultaneously determining organic chlorine, bromine and iodine in one extract. Human hair is a convenient material to evaluate the burden of such compounds in human body and dan be easily collected from people over wide ranges of age, sex, residential areas, eating habits and working environments. To effectively extract organohalogen compounds from human hair, in present work the optimal Soxhelt-extraction time of extractable organohalogen (EOX) and extractable persistent organohalogen (EPOX) from hair of different lengths were studied by NAA. The results indicated that the optimal Soxhelt-extraction time of EOX and EPOX from human hair was 8-11 h, and the highest EOX and EPOX contents were observed in hair powder extract. The concentrations of both EOX and EPOX in different hair sections were in the order of hair powder ≥ 2 mm > 5 mm, which stated that hair samples milled into hair powder or cut into very short sections were not only for homogeneous. hair sample but for the best hair extraction efficiency.
[en] MgB2 samples prepared by solid-state reaction were investigated using high-resolution transmission electron microscopy (HREM), x-ray energy-dispersive spectroscopy (EDX), electron energy-loss spectroscopy (EELS), and energy-filtered imaging. Large amounts of coherent precipitates with a size range from about 5 nm up to about 100 nm were found in the MgB2 crystallite matrices. The precipitates are of different shapes including sphere, ellipsoid, and faceted polyhedron depending on the size of the precipitates. EDX and EELS analyses confirm that smaller precipitates contain magnesium, boron and oxygen while larger faceted precipitates contain mainly magnesium and oxygen, implying that the oxygen content increases with precipitate size. HREM and electron diffraction investigations found that the precipitates have the same crystal lattice structure as that of MgB2 but with various composition modulations depending on the composition of the precipitates. The precipitates transform to the MgO phase after long exposure to residual oxygen in flowing Ar gas at high temperatures. The effect of the precipitates in different size ranges on flux pinning is discussed
[en] Graphical abstract: - Highlights: • Pure phases of VO2(B) and VO2(A) were prepared by a facile hydrothermal method. • Belt-like particles prepared at 180 °C was indexed as monoclinic VO2(B) phase. • Rod-like particles prepared at 230 °C was indexed as tetragonal VO2(A) phase. • VO2(A) nanorods resulted from VO2(B) nanobelts by assembly and crystal adjustment. - Abstract: Pure phase VO2(A) nanorods were synthesized via the reduction of V2O5 by oxalic acid during the hydrothermal treatment. Two sets of samples were prepared by varying both system temperature and reaction time under a filling ratio of 0.40 for observing the formation and evolution of VO2(A) nanorods. Structures were characterized by X-ray diffraction, scanning and transmission electron microscopies, respectively. It was found that VO2(B) was firstly formed and then transformed into VO2(A) as the increasing system temperature or extending reaction time. An assembling and following crystal adjustment was proposed for explanation the formation process of VO2(A) from VO2(B). For VO2(A) nanorods, the phase transition temperature of 169.7 °C was higher than that of the VO2(A) bulk, it might be ascribed to the lower crystallinity or nonstoichiometry in VO2(A) nanorods. VO2 nanostructures with controllable phases and properties should find their promising applications in a single VO2 nanodevice
[en] A strain-relieved, dislocation-free InxGa1-xAs layer is selectively grown on nanoscale SiO2-patterned GaAs(001) by molecular beam epitaxy. By localizing the epitaxial area to a periodic array of nanoscale circular holes opened in a SiO2 mask and allowing the InxGa1-xAs epilayers selectively grown on adjacent holes to coalesce over the SiO2 mask by lateral overgrowth, the strain of the resulting InxGa1-xAs layer (x=0.06) is relieved with a dramatically decreased generation of misfit dislocations. These experimental results qualitatively support the basic idea of the Luryi-Suhir proposal [Appl. Phys. Lett. 49, 140 (1986)]
[en] Structure, magnetization, and specific heat have been investigated for the Mo-doping La0.67Sr0.33Mn1-xMoxO3 (x=0, 0.01, 0.02, 0.03, 0.04, 0.06) perovskite system. The ferromagnetic to paramagnetic transition temperature Tc is found to decrease from 369 K for x=0 to 361 K for x=0.06 with increasing Mo doping. According to a second-order phase transition model, the critical behavior near Tc are investigated systematically based on the specific heat data, and the critical exponents are determined to be α=0.04-0.06, β=0.35-0.41, γ=1.13-1.25. The values of the critical exponents are found to keep almost same magnitude for La0.67Sr0.33Mn1-xMoxO3 system. It is noticed that the value of the critical exponent β locates between the mean-field value (β=0.5) and the three-dimensional (3D) Ising model value (β=0.325), which suggests the coexistence of the short-range and long-range ferromagnetic orders around the critical temperature. The fundamental factors to dominate the magnitude of the critical exponent values for the perovskite-type manganese oxide systems have been discussed as well.
[en] Two Sr2FeMoO6 samples, synthesized under different conditions and showing very different magnetotransport properties, were analyzed using transmission electron microscopy. The different magnetoresistive behaviors observed in the two samples coincide with the formation of different amounts of striped areas intergrown in the samples. The striped areas are comprised of a disordered and cation deficient phase, SrFe1-x-yMox-zO3-δ. The sample magnetization and magnetoresistance values decrease significantly with an increased presence of the striped phase. The striped phase was promoted by typical reducing formation conditions for Sr2FeMoO6 in Ar-1% H2 gas
[en] Highlights: ► Substantially improved mechanical properties of 0.2C–5Mn steels. ► Intercritical austenization followed by short time annealing. ► Phase transformation induced plasticity of the large volume fractioned austenite. ► Dependence of yield stress on austenite grain size accords with Hall–Petch equation. - Abstract: Microstructures and mechanical properties of 0.2C–5Mn steel processed under different heat treatment conditions were examined by scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and X-ray diffraction (XRD). It was found that high temperature austenization (above Ac3) resulted in a full martensite structure after quenching, which gradually transformed into the ferrite/austenite duplex structure during the following annealing process. However, austenization in the intercritical region (between Ac1 and Ac3) gave a duplex structure after quenching, which was nearly not affected by followed annealing process. The ultrahigh strength ∼1000 MPa and total elongation ∼40% were only obtained in the specimens with 6 h annealing at 650 °C under both heat treatment conditions. However, the excellent mechanical properties could be obtained in the intercritically austenitized samples with only 10 min annealing at 650 °C. Based on the analysis on the relationship between microstructure and mechanical properties, it was found that the total elongation was strongly dependent on the austenite fraction, which was ascribed to the phase transformation induced plasticity of the large volume fraction of austenite. Otherwise, the dependence of the yield stress on the austenite grain size accords with Hall-Petch equation, which implies that the austenite is soft phase. It was concluded that 10 min annealing at 650 °C was enough to obtain a large volume fraction of austenite (∼30%) in 0.2C–5Mn steel when the specimens were austenitized at 675 °C.