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191.
Yi Kai Zhou Sung Woo Choi Shigeya Kimura Shuichi Emura Shigehiko Hasegawa Hajime Asahi 《Journal of Superconductivity and Novel Magnetism》2007,20(6):429-432
GaGdN layers were grown at temperatures below 300°C by radio-frequency plasma-assisted molecular beam epitaxy on sapphire
substrates. GaGdN samples with high Gd concentration as high as 12.5% were obtained by lowering the growth temperature. X-ray
diffraction results showed no obvious secondary phase, which means that the phase separation can be suppressed by the growth
at low temperatures. All samples, including those grown at room temperature, showed ferromagnetic characteristics. Photoluminescence
emission was observed, though spectra exhibit broad and sharp luminescence bands related to many kinds of defects. It is suggested
that electrons coming from defects, especially, nitrogen vacancy, stabilize ferromagnetism, and that the carrier-induced ferromagnetism
occurs in the low-temperature-growth GaGdN. 相似文献
192.
193.
Iron molybdate (Fe2MoO4) powders with an average particle size of 100 μm were reduced by hydrogen using a fluidized-bed batch reactor in the temperature range of 923 to 1173 K. The extent of the
reaction was followed as a function of time by gas chromatography. The fluidizing-gas velocity was set at about 1.5 times
the minimum fluidization velocity. The ratio of the height of the static bed to its diameter is about 1. Under the prevailing
experimental conditions, it was found that the chemical reaction was the rate-controlling factor. The activation energy for
this process was 158±17 kJ/mol. The crystal size of the Fe2Mo powder produced at lower temperatures was in the nanometer range, indicating the possibility of mass production of alloys
and intermetallics in the nanorange, using a fluidized bed. 相似文献
194.
Titanium oxides were reduced to metallic titanium using the liquid calcium floating on the molten CaCl2. A part of Ca dissolved into CaCl2 and reacted with TiO2 settled below CaCl2. The by-product CaO also dissolved by about 20 mol pct into CaCl2, which was effective in reducing the oxygen concentration in the obtained Ti particles. The compositional region in the Ca-CaCl2-CaO system was examined for the less oxygen contamination in Ti and the better handling in leaching. A large amount of the
residual calcium oxidized the titanium powder in leaching. The metallic Ti powder less than 1000 mass ppm oxygen could be
obtained only for 3.6 ks using 5 to 7 mol pct Ca-CaCl2 at 1173 K. The powder was slightly sintered like sponge, and contained approximately 1500 ppm Ca. The anatase phae, the intermediate
product in the refining process of TiO2, could be also supplied as raw material as well as rutile. 相似文献
195.
The corrosion behaviour of nitrogen-containing austenitic stainless steel in methanol containing different concentrations
of H2SO4, HCl, LiCl and H2SO4 + HCl has been investigated using a potentiostatic polarization method. The cathodic reaction in the H2SO4, HCl and H2SO4 + HCl solutions was proton reduction whereas in the neutral LiCl solution, oxygen reduction was the predominant cathodic
reaction. Active, passive and transpassive behaviours were observed only for higher concentrations of H2SO4 (0.01–2.0 M) due to the inherent water content. A cathodic loop, characterized by measured negative current in the anodic
region, was also observed in solutions, in which the concentration of H2SO4 was 1.0 M or higher. The relative stability of the passive films decreased as the H2SO4 concentration increased, and thus the steel suffered from mild pitting corrosion. In the chloride environment, the rate of
corrosion increased as the Cl− ion concentration increased. The presence of acid along with Cl− ions enhanced corrosion, and the corrosion rate increased significantly. The steel suffered from mild intergranular corrosion
in acidic chloride solutions of methanol. In the H2SO4 + HCl solutions, passive films were only formed when the H2SO4 to HCl concentration ratio was greater than ∼10:1. 相似文献
196.
In this study, nanocrystalline Ni powders and thermally sprayed coatings, containing ultrafine AlN particles, were synthesized
and characterized. The results indicated that the presence of AlN particles in the powders drastically decreased the dimension
of agglomerates formed by cryomilling and increased the surface roughness of the agglomerates. The AlN phase was broken down
into ultrafine particles of approximately 30 nm in size. These particles were dispersed in the Ni matrix and enhanced the
development of a nanocrystalline structure in the Ni matrix during cryomilling. Selected-area diffraction patterns, obtained
from transmission electron microscopy (TEM) and X-ray mapping with scanning electron microscopy (SEM), confirmed the presence
of AlN particles in the coatings. The presence of AlN particles also led to an increase in the amount of NiO phase that was
distributed in the coating, in the form of ultrafine, round particles. AlN particles increased the microhardness of the Ni
coating by approximately 60 pct. Indentation-fracture results also indicated that the fine, dispersed AlN particles raised
the apparent toughness of the Ni coating. The synthesized Ni coatings containing ultrafine AlN particles were characterized
as equiaxed nanocrystalline grains with an average size of 24 nm, in which twins were observed. The increase in microhardness
resulted from both grain refinement and the presence of ultrafine particles. The latter played the primary role in strengthening. 相似文献
197.
Shijie Zhu Yutaka Kagawa Jian-Wu Cao Mineo Mizuno 《Metallurgical and Materials Transactions A》2004,35(9):2853-2859
Time-dependent deformation in an enhanced SiC/SiC composite has been studied under constant load at high temperatures of 1200
°C, 1300 °C, and 1400 °C. Creep damage evolution was evaluated by a Young’s-modulus change of partial unloading and microscopic
observation. The addition of the glassy phase in the matrix is very effective for protecting the composite from oxidation.
The transient creep is dominant in creep life at all the temperatures. An empirical equation is proposed to describe creep
behavior of the composite. It is found that creep activation energy increases with creep time at stresses lower than matrix
cracking stress, but the activation energy remains constant at stresses higher than the matrix cracking stress. The creep
strain rate of the composite is considered to be controlled by creep of fibers based on examining the time, strain, stress,
and temperature dependencies of creep strain rates. 相似文献
198.
KaziTakpaya 《电子科学学刊(英文版)》2003,20(6):439-445
An increasing demand for high data rate transmission and protection over bandlimited channels with severe inter-symbol interference has resulted in a flurry of activity to improve channel equalization. In conjunction with equalization, channel coding-decoding can be employed to improve system performance. In this letter, the performance of the three stageturbo-equalization-decoding employing log maximum a posteriori probability is experimentally evaluated by a fading simulator. The BER is evaluated using various information sequence and interleaver sizes taking into account that the communication medium is a noisy inter symbol interference channel. 相似文献
199.
XiaYinshui A.E.A.Almaini WuXunwei 《电子科学学刊(英文版)》2003,20(3):194-201
Using state assignment to minimize power dissipation and area for finite state machines is computationally hard.Most of published results show that the reduction of switching activity often trades with area penalty.In this paper,a new approach is proposed.Experimental results show a significant reduction of switching activity without area penalty compared with previous publications. 相似文献
200.
Nonlinear dynamical method of projecting the transmission of an epidemic is accurate if the input parameters and initial value
variables are reliable. Here, such a model is proposed for predicting an epidemic. A method to supplement two variables and
two parameters for this proposed model is demonstrated through a robust statistical approach. The method described here worked
well in case of three continuous distributions. Model predictions could be lower estimates due to under-reporting of disease
cases. Anad hoc procedure with a technical note is provided in the appendix
An earlier version of this paper was presented at the annual conference of the Indian Society for Mathematical Modelling &
Computer Simulation, Bangalore, November 14–15, 2002 相似文献