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901.
Fe3O4 nanostructures with different morphologies, including uniform nanoparticles, nanorods and nanowire bundles, have been successfully
synthesized via a facile hydrothermal route. Based on the observation of TEM images, the growth mechanism of one-dimensional
Fe3O4 nanostructures is in accordance with Ostwald ripening process. From the hysteresis loops of as-prepared Fe3O4 products, we found that the morphology has great influence on the magnetic properties. The uniform Fe3O4 nanoparticles have higher saturation magnetization and lower coercivity than that of Fe3O4 nanorods and nanowires bundles. These phenomena attribute to the high shape anisotropy of nanorods and nanowire bundles,
which prevent them from magnetizing in directions other than along their easy magnetic axes.
PACS 81.07.-b; 75.50.Bb; 75.30.Gw; 81.10.Dn; 81.16.Be 相似文献
902.
Pei-Hong Gu Xiao-Jun Bi Xinmin Zhang 《The European Physical Journal C - Particles and Fields》2007,50(3):655-659
In this paper we study dynamical CPT-violation in the neutrino sector as induced by the dark energy of the universe. Specifically
we consider a dark energy model where the dark energy scalar derivatively interacts with the right-handed neutrinos. This
type of derivative coupling leads to cosmological CPT-violation during the evolution of the background field of the dark energy.
We calculate the induced CPT-violation of left-handed neutrinos and find that the CPT-violation produced in this way is consistent
with the present experimental limit and sensitive to future neutrino oscillation experiments such as the neutrino factory.
PACS 95.36.+x; 14.60.St 相似文献
903.
Lu‐Feng Zou Kuang Shen Yao Fu Qing‐Xiang Guo 《Journal of Physical Organic Chemistry》2007,20(10):754-763
Experimental studies showed that sulfur radicals play the vital role in petroleum formation. 1 Sulfur‐ centered radicals also exhibit activities in antioxidant functions. Here we conduct a theoretical investigation of their precursor‐disulfides. By investigation into substituent effect on sulfur? sulfur bond dissociation enthalpies (S? S BDEs), we would like to find the most effective provider for sulfur radicals. In the present work, 50 alpha‐substituted disulfides and 16 para‐substituted aryl disulfides are studied systematically, with the general formula XS‐SX or HS‐SX. The substituent effect on S? S BDEs is found to be very eminent, ranging from 33.2 to 75.0 kcal/mol for alpha‐substituted disulfide, and from 43.7 to 59.7 kcal/mol for para‐substituted phenyl disulfides. We also evaluate the performance of 44 density functional methods to get an accurate prediction. A further study indicates that substituents play a major role in radical energies, instead of molecule energies, which is substantiated by the good linearity between XS‐SX bond dissociation enthalpy (BDE) and HS‐SX BDE. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
904.
The aim of this work is to study the effects of duty ratio on the growth mechanism of the ceramic coatings on Ti-6Al-4V alloy prepared by pulsed single-polar MPO at 50 Hz in NaAlO2 solution. The phase composition of the coatings was studied by X-ray diffraction, and the morphology and the element distribution in the coating were examined through scanning electron microscopy and energy dispersive spectroscopy. The thickness of the coatings was measured by eddy current coating thickness gauge. The corrosion resistance of the coated samples was examined by linear sweep voltammetry technique in 3.5% NaCl solution. The changes of the duty ratio (D) of the anode process led to the changes of the mode of the spark discharge during the pulsed single-polar MPO process, which further influenced the structure and the morphology of the ceramic coatings. The coatings prepared at D = 10% were composed of a large amount of Al2TiO5 and a little γ-Al2O3 while the coatings prepared at D = 45% were mainly composed of α-Al2O3 and γ-Al2O3. The coating thickness and the roughness were both increased with the increasing D due to the formation of Al2O3. The formation of Al2TiO5 resulted from the spark discharge due to the breakdown of the oxide film, while the formation of Al2O3 resulted from the spark discharge due to the breakdown of the vapor envelope. The ceramic coatings improved the corrosion resistance of Ti-6Al-4V alloy. And the surface morphology and the coating thickness determined the corrosion resistance of the coated samples prepared at D = 45% was better than that of the coated samples prepared at D = 10%. 相似文献
905.
Y.M. Zhao J.Y. Zhang K.W. Liu C.X. Shan B. Yao B.H. Li D.Z. Shen 《Applied Surface Science》2007,253(24):9319-9322
We report the growth of cubic MgxZn1−xO alloy thin films on quartz by electron beam evaporation. It can be found that all the samples have sharp absorption edges by the absorption measurements. X-ray diffraction measurements indicate the MgxZn1−xO films are cubic phase with preferred orientation along the (1 1 1) direction. Energy dispersive spectrometry (EDS) demonstrates that the Mg concentration in MgxZn1−xO films is much higher than the ceramic target used, and the composition can be tuned in a small scope by varying the substrate temperature and the beam electric current. The reasons of this phenomenon are also discussed. 相似文献
906.
The oxidation kinetics of MgNd alloys oxidized in pure O2 at high temperatures has been investigated. The results revealed two stages of the reaction: A fast initial oxidation was followed by a slow oxide growth with a parabolic kinetics. For MgNd alloys (Nd = 25 wt.%), the oxidation rate increased with the enhancement of the oxidation temperature. A sudden ignition was found for this alloys oxidized at 873 K up to about 80 min. Moreover, the increase of the Nd content would harm the oxidation resistance of the MgNd alloys. By Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, it was found that a triplex structure of oxide film formed. The outer layer was composed of MgO, Nd2O3 and Nd(OH)3, the middle layer mainly consisted of MgO and Nd2O3, and the inner layer was the transitional layer made of MgO, Nd2O3 and the content of the substrate. The protective oxidation was associated with the formation of the dense Nd2O3/MgO layer during isothermal oxidation process. The oxidation mechanisms for the formation of oxide film are discussed. 相似文献
907.
908.
Pb0.97La0.02(Zr0.85Sn0.13Ti0.02)O3 (PLZST 2/85/13/2) antiferroelectric thin films were deposited on Pt(111)/Ti/SiO2/Si and LaNiO3(LNO)/SiO2/Si substrates through a modified sol-gel process. The phase structure and microstructure of PLZST 2/85/13/2 antiferroelectric thin films were analysed by x-ray diffraction (XRD), scanning electron microcopy (SEM) and field-emission SEM (FE-SEM). The antiferroelectric nature of the PLZST 2/85/13/2 thin films on two electrodes was demonstrated by the C-V (capacitance-voltage) and P-E (polarization-electric field) measurement. The maximum polarizations for PLZST 2/85/13/2 films on Pt and LNO electrodes were 42 and 18 μC/cm2, respectively. The temperature dependence of the dielectric property of the PLZST 2/85/13/2 films was measured under different dc electric fields. Also, the phase transformation of the PLZST 2/85/13/2 films was studied in detail as a function of temperature and dc electric field. 相似文献
909.
Tieli Zhang Jianquan Yao Xueyu Zhu Baigang Zhang Enbang Li Pu Zhao Haifeng Li Feng Ji Peng Wang 《Optics Communications》2007,272(1):111-115
This paper reports on a high-repetition-rate dual signal-wave (DSW) optical parametric oscillator (OPO) operating at the 1.5 μm band with tunable wavelength intervals from 2.5 nm to 69.1 nm. Two periodically poled crystals, a periodically poled lithium niobate (PPLN) with multiple gratings and a single grating MgO-doped PPLN (PPMgOLN), are cascaded in the same OPO cavity to generate dual signal-waves by using quasi-phase-matched (QPM) technique. The pump source was a Q-switched diode-pumped Nd:YVO4 laser operating at 50 kHz. At an incident pump power of 3 W, an average output power of 169.6 mW at 1489.2 nm and 1558.3 nm has been achieved. 相似文献
910.
X.J. Wu D.Z. Shen K.W. Liu B.H. Li Y.M. Lu B. Yao X.W. Fan 《Solid State Communications》2007,141(6):344-347
Fe-based cadmium sulfide alloy thin films have been grown on c-plane sapphire substrates by a low-pressure metalorganic chemical vapor deposition technique at different growth temperatures. From X-ray diffraction and absorption spectra of the samples, the evolutions with growth temperature show an inflexion at the growth temperature of 300 °C. This was attributed to the phase transformation from zinc-blende to wurtzite. With increasing growth temperature from 270 °C to 360 °C, Fe concentration in the films increases monotonously. The electronic states of Cd1−xFexS were investigated by X-ray photoelectron spectroscopy. Magnetic measurement shows Van Vleck paramagnetism of the Cd1−xFexS thin film in the temperature region below 7 K. 相似文献