60 research outputs found

    Effect of Sintering Temperature, Sm3+ Concentration and Excitation Wavelength on Luminescence Properties in Eu3+ Doped Strontium Tungstate Phosphors

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    The color-tunable SrWO4:0.20Eu3+, Sm3+ phosphors are successfully prepared by co-precipitation method at a low temperature (800Ā Ā°C). These phosphors can be efficiently excited by near-ultraviolet and blue light. The phase formation, luminescence properties, energy transfer between Eu3+ and Sm3+, and the critical distance were studied. The Sm3+ ions as the sensitizer could extend the excitation spectrum and enhance emission. The CIE chromaticity coordinate was also presented. The emission hues covered the regions from pink, orange, to reddish-orange, and eventually to red, which can be controlled by adjusting excitation energy, calcination temperature, and doping rare earth ions ratio via the energy transfer. The high efficiency and high color purity red emitting SrWO4:0.20Eu3+, xSm3+ (xĀ =Ā 0.005Ā ĀøĀ 0.01) phosphors have higher color saturation than the commercially available Y2O2S:Eu3+ red phosphor, which is in coincidence with the National Television Standard Committee system standard for red chromaticity (0.67, 0.33). The obtained phosphors exhibit an excellent light emitting efficiency, color-purity and lower correlated color temperature of the comfortable warm white LEDs.</p

    On Transient Response of Piezoelectric Transducers

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    In this paper, we report a new model in analysis of spherical thin-shell piezoelectric transducers for transient response, based on Fourier transform and the principle of linear superposition. We show that a circuit-network, a combination of a series of parallel-connected equivalent-circuits, can be used in description of a spherical thin-shell piezoelectric transducer. When excited by a signal with multiple frequency components, each circuit would have a distinctive radiation resistance and a radiation mass, arising from an individual frequency component. Each frequency component would act independently on the electric/mechanic-terminals. A cumulative signal-output from the mechanic/electric-terminals is measured as the overall acoustic/electric output. As a prototype example in testing the new model, we have designed two spherical shin-shell transducers, applied a gated sine electric-signal as the initial excitation, and recorded the experimental information. The transient response and the output signals are calculated based on the new model. The results of calculation are in good agreement with that of experimental observation

    Development of Natural Gas Hydrate

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    At present, the energy crisis is becoming more and more serious. At the same time, the extensive use of coal and oil has caused serious environmental pollution problems. People are urgently developing new energies, to replace the traditional energy, which has low pollution or even no pollution. Talking about the energy, people immediately think of the coal, oil or natural gas, but seldom think of the ā€œiceā€. However, since the 1960's, people have found a burning ā€œiceā€ in the permafrost and the depth of the ocean. This kind of "combustible ice" in geological field is called natural gas hydrate. This thesis will focus on introducing the development of natural gas hydrate, composition of natural gas hydrates, the formation of natural gas hydrates, the development history of natural gas hydrates and exploration and development method of natural gas hydrates. One of the most important parts is to introduce five exploration methods and six kinds of development technology. The development of technology contains three traditional development technologies and three new development technologies. This thesis also introduces the environmental problems in the development process of natural gas hydrate

    Experimental Data Analysis of Nanoparticles for Enhanced Oil Recovery

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    Enhanced oil recovery with nanometer-sized particles is an attractive topic in the industry because of the various advantages brought about by the size. Since nanoparticles have not been applied widely on a field scale, core flooding tests are the best method to study and evaluate oil recovery improvement mechanisms. Different from previous review papers that discussed this research area case by case, our paper investigated nanoparticle core flooding research from a data statistics perspective. Thirty-nine published studies with a total of 240 laboratory core flooding tests using nanoparticles were included for this study. A data set was constructed by collecting all relevant information available from those publications. Histograms, the combination of box plots and violin plots, bar charts, and scatter plots were utilized for visualization of the statistical analysis. We displayed the distribution of relevant parameters and the relationship between some of them. Special cases were explained, and the uniqueness of the corresponding studies was discussed. Results show that on the laboratory scale, studies reveal an incremental oil recovery as high as 30% of the original oil in place. However, the most frequent range is 5%. Wettability alternation and interfacial tension (IFT) reduction were the two most studied mechanisms. The result of contact angle tests and IFT tests could indicate the enhanced oil recovery performance of nanoparticles in core flooding tests. In addition, it was discovered that several aspects of nanoparticles need to be researched further for a better understanding

    Learning to Recognize Reliable Users and Content in Social Media with Coupled Mutual Reinforcement

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    Community Question Answering (CQA) has emerged as a popular forum for users to pose questions for other users to answer. Over the last few years, CQA portals such as Naver and Yahoo! Answers have exploded in popularity, and now provide a viable alternative to general purpose Web search. At the same time, the answers to past questions submitted in CQA sites comprise a valuable knowledge repository which could be a gold mine for information retrieval and automatic question answering. Unfortunately, the quality of the submitted questions and answers varies widely- increasingly so that a large fraction of the content is not usable for answering queries. Previous approaches for retrieving relevant and high quality content have been proposed, but they require large amounts of manually labeled data ā€“ whic

    The Influence of Wind Direction during Storms on Sea Temperature in the Coastal Water of Muping, China

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    Sea temperature structures are important for water stratification and marine ecosystems. In the coastal water of Muping, China, stationary measurements of sea temperature captured temporal temperature changes during two summer storm events. The north component of the wind during the two storms was opposite. The temperature responded differently to wind directions in the two storm events. A well-validated numerical ocean model was used to investigate the mechanism of sea temperature variation of the coast of Muping. The model revealed that the southerly and easterly wind was upwelling-favorable in the study area. They generated the shoreward transport of bottom cold water, which induced bottom water cooling, enhanced stratification, and weakened vertical mixing. On the other hand, the northerly and westerly wind was downwelling-favorable and enhanced turbulent mixing. The alongshore upwelling-favorable wind caused more cross-shore transport than cross-shore upwelling-favorable wind, which resulted in stronger bottom cooling. Similarly, alongshore downwelling-favorable wind generated lower temperature than cross-shore wind. A surface cold-water band was formed in the second storm. Although it was formed during upwelling-favorable wind, the temperature balance analysis indicated that vertical mixing and westward horizontal advection were the two dominant processes compared to upwelling

    Mechanistic Understanding of CO2 Adsorption and Diffusion in the Imidazole Ionic Liquid-Hexafluoroisopropylidene Polyimide Composite Membrane

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    The integration of molecular design and imidazole ionic liquids produces a synergistic effect to enhance and fine-tune the molecular sieve capability of polyimide (PI) membranes. The most difficult problem was to choose the right ionic liquids and moderate polymer combination. In this work, a series of systems of CO2 in [EMIM][Tf2N], [EMIM][BF4], and [EMIM][PF6] composited with 6FDA-based PI with different IL concentrations were discussed by all-atom molecular dynamics simulations. The results indicated that the CO2 diffusion coefficient decreases with the compatibility of the PI structure with CO2 molecules and increases with an increased IL concentration of up to 75 wt %. Therefore, this study may provide guidance for the design of PI membranes
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