Results 1 - 10 of 148
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[en] Excitonic luminescence of GaN after irradiation with 0.42-MeV electrons has been investigated in detail. The low-energy irradiation generates damage exclusively in the N sublattice. Additional bound-exciton lines are found and are shown to arise from a hydrogenic donor with a binding energy of 25 meV. The donor binding energy, bound-exciton localization energy, and bound-exciton lifetime are discussed in comparison with the values observed for ON and SiGA in the same sample. Nitrogen vacancies VN forming a hydrogenic donor state are suggested to be the most likely origin of this luminescence emission. Finally, a metastable behavior related to the damage-induced defects is reported and discussed in conjunction with interstitial-nitrogen-related defects
[en] SiC was hot-pressed with aluminum, boron, and carbon additives. The Al content was modified either to obtain SiC samples containing a continuous Al gradient, or to vary the average Al content. In both cases, it was found that increasing Al content resulted in decreased number density but dramatically enhanced aspect ratio of the elongated SiC grains. Amorphous-to-crystalline transformation was also confirmed in grain boundary films when Al content exceeded 4 wt%. In addition, increasing Al decreased the degree of cubic-to-hexagonal SiC phase transformation. Similar processing and characterization were done with modified boron and carbon average contents. The systematic experiments demonstrated that boron and carbon promoted formation of elongated grains through promoting 3C-to-4H SiC phase transformation during hot pressing. The experiments also clarified the mechanical property responses to microstructural modification. Tailoring of the SiC microstructure to suit different applications would be possible
[en] We investigate the issue on impulsive control and synchronization of the unified chaotic system, which unifies both the Lorenz system and the Chen system. Some new and general conditions with varying impulsive distances are obtained to guarantee the impulsive control and synchronization global asymptotical stable. Especially, in the case of equal impulsive distances, some simple and easily verified sufficient conditions are derived for stabilizing and synchronizing the unified chaotic system. An illustrative example, along with computer simulation results, is finally included to visualize the effectiveness and feasibility of the developed methods
[en] Highlights: • Ag_2O/TiO_2 was synthesized by a pH-induced chemical precipitation method. • Ag_2O/TiO_2 showed good activities in the photocatalytic degradation of methyl orange. • Hydroxyl radicals played the predominant role in methyl orange photodegradation. - Abstract: Ag_2O/TiO_2 composites synthesized in this study were applied into the photocatalytic degradation of methyl orange (MO) under UV and visible light irradiation. X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscope analysis demonstrated that Ag_2O nanoparticles were well distributed on the surface of TiO_2 and the heterostructure of Ag_2O/TiO_2 was formed. Compared with the pure TiO_2 and Ag_2O, the 3% and 50% Ag_2O/TiO_2 composite displayed much higher photocatalytic activities in MO degradation under UV and visible light irradiation, respectively. The degradation rate constant of 50% composite was 0.01508 min"−"1 under visible light, which was almost 20.1 and 1.2 times more than that of the pure TiO_2 and Ag_2O, respectively. Moreover, the formation of Ag(0) on the surface of Ag_2O under illumination contributed to the high stability of Ag_2O/TiO_2 photocatalysts. It was also found that hydroxyl radicals during the photocatalytic process played the predominant role in MO degradation. The enhanced photochemical activities were attributed to the formation of the heterostructure between Ag_2O and TiO_2, the strong visible light absorption and the high separation efficiency of photogenerated electron–hole pairs resulted from the highly dispersed Ag_2O particles.
[en] ZrS3 nanocrystallites have been synthesized via a solvothermal route by the reaction between ZrCl4 and thiourea at relatively low temperature. The product was characterized by X-ray diffraction (XRD), transmission electron microscope, X-ray fluorescence, Raman spectrum, and photoluminescence (PL). X-ray diffraction pattern shows the monoclinic cell of ZrS3 with the lattice constants a=5.128 A, b=3.611 A, c=9.012 A, β=97.13 deg. . The result of X-ray fluorescence gives a Zr(Hf):S mole ratio 1:2.97. The Raman spectrum of the ZrS3 nanocrystallites has a slightly red shift in comparison with that of ZrS3 single crystals. The room temperature photoluminescence of ZrS3 nanocrystallites is also reported
[en] According to industrial organization theory, market structure is a crucial factor to market performance. Based on the VAR model and the data from 1994 to 2014, we revealed the dynamic response route of the market structure to these factors and the change process of contribution rate of these factors to the market structure. It shows that market structure is inertial adjustment; technology advance and industry policy have continuous effects on improvement of market concentration ratio; market size and production scale have sustained negative effects on market concentration ratio; fixed capital has barrier effect, which is mainly the entry barrier effect at the beginning, and then the exit barrier effect continues to play a leading role. Therefore, the government has no need to introduce special policies to encourage merger or expansion on the capacity as enterprises would do it spontaneously; it is necessary to make market access system stricter, to improve exit compensation mechanism and to promote technological innovation; all these policies need dynamic adjustment based on the stages of economic cycle. - Highlights: • The adjustment mechanism of China's coal market structure is revealed. • Technology and industry policy are significant factors to optimize the market structure. • The government need not introduce special policy to encourage merger. • The market access system should be stricter. • Policies strength should be dynamically adjusted based on the economic cycle.
[en] The synthesis of Ag nanoparticles from AgNO3 in acrylamide (AM) isopropyl alcohol solution has been achieved at room temperature by using an γ-irradiation reductive synthetic route in the field of a 2.22x1015 Bq 60Co γ-ray source at the dose rate of 50 Gy/min for 3-6 h. The initial concentration of AM, which could be polymerized as polyacrylamide (PAM) in irradiation field, played an important role in the morphologies of the Ag particles in solution. The Ag fractals were only obtained from the Ag clusters and particles in a dilute AM solution. These faceted Ag particles aggregate to from preferentially oriented Ag crystals with dispersed fractal morphologies, which could be ascribed to diffusion-limited aggregation (DLA) model on the amorphous carbon-coated copper grid. The fractal dimension of the Ag crystallites is between 1.70 and 1.75, which is close to that in DLA model simulation (1.70)
[en] In the process of nuclear radiation measurement, often the results relied on measuring the temperature and humidity of the environment to compensate. The design of a low-cost simple temperature and humidity logger in the article, can achieve the measurements of temperature, humidity in the experimental nuclear environment. The system uses AT89 series low-cost MCU controller, domestic DHT11 temperature and humidity sensors, and RS485 protocol for remote data transfer and on-line monitoring of results. Experimental results show that the collector can achieve rapid multi-point measurements of temperature and humidity, the system is stable and reliable, is a low-cost solution, suitable for all kinds of nuclear measurement applications. (authors)