208,970 research outputs found
The high-energy spectrum of Cygnus X-1 revisited
No full textThe X-ray spectrum of Cyg X-1 is probably produced by thermal Comptonization in an accretion disk corona. Photons reflected from the disk are also Comptonized, so the predicted reflection spectrum is dependent on the optical depth and temperature of the scattering medium. Thus observations of reflection in the 2-20 keV energy range can constrain the electron temperature and optical depth that previously could only be derived from high-energy data. Archival EXOSAT data from Cyg X-1 indicate tau(T) approximately 0.3 and T(e) approximately 150 keV. This is perfectly compatible with recent SIGMA and OSSE observations of the high-energy spectrum, though the physical parameters derived from these experiments are very different. We show that the apparent discrepancy is due to the use of an optically thick plasma model in fitting composite spectra emitted by optically thin hotter plasmas and reflected by the underlying colder matter
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Heat transfer characteristics of a vertical tube in a fluidized-bed combuster
No full textThe heat transfer coefficient between a coal fluidized-bed combustor and a vertical immersed tube was determined in a 15-cm-diameter, 1-m-high fluidized bed with a freeboard zone of height 0.5 m and diameter 25 cm. The effects of the particle size (0.33-0.78 mm), the air velocity (60-190 cm/s), the bed temperature (800-950°C), and the radial position of the tube on the heat transfer coefficient were studied. The heat transfer coefficient increased with increasing air velocity to a maximum and then decreased, and increased with increasing bed temperature and decreasing particle size. The heat transfer coefficient was a maximum when the tube was located at 1/4 of the bed diameter from the wall. The thickness of the gas film on the tube was determined using a model which takes into account the effect of radiation on the heat transfer coefficient. Radiation accounted for 10% of the overall heat transfer
Oxygen plasma surface treatment of polymer powder in a fluidized bed reactor
No full textThe oxygen functionalities of carbonyl and carboxyl acid (C=O, C(O)O-) are formed at the outermost layer of HDPE powder by the oxygen plasma treatment in a fluidized bed reactor. The effects of operation parameters on the functionalities of the plasma treated polymer powders have been determined in a fluidized bed reactor. The intensity of oxygen functionalities on the surface of plasma-treated HDPE powder increases with increasing treatment time, but it remains constant with further treatment time. The oxygen components of the plasma-treated HDPE powder increase linearly with radio frequency power, but decrease with oxygen flow rate. Also, the oxygen component increases with increasing the composite parameter with the total plasma energy up to 6000 (GJ s/kg). A linear relationship is found between the surface oxygen and the hydrophilicity of plasma-treated powder. (C) 1998 Elsevier Science B.V.the Korean Science and Engineering Foundatio
Catalytic Activity of Iron and Matal Salts for Steam-Char Gasification
No full textThe catalytic activity of five different binary mixtures of alkali (K2CO3, K2SO4, Na2CO3) and iron salts (FeSO4, Fe(NO3)3) on steam-char gasification at 700-800-degrees-C was measured in a thermobalance reactor. Under the same experimental conditions with 3 wt% catalyst loading, the catalytic activity of the pure salts is in the order K2CO3 > Na2CO3 almost-equal-to FeSO4 > K2SO4 > Fe(NO3)3. For K2SO4 and Na2CO3 the gasification rate could be enhanced by addition of iron salt. A synergistic effect of alkali and iron salts on the gasification rate was observed and the mixtures K2SO4 + FeSO4 and K2SO4 + Fe(NO3)3 exhibited better catalytic activity than K2CO3 at 800-degrees-C. A kinetic parameter is proposed as a simple measure of activity of various catalysts based on the grain model. On the basis of the kinetic parameters and melting behaviour, K2SO4 + FeSO4 in the temperature range 700-800-degrees-C is an effective catalyst for steam-char gasification.Ministry of Energy and Resources of Kore
Diagonosis of Bubble Distribution and Mass Transfer in Pressurized Bubble Columns with Viscous Liquid Medium
No full textBubble distribution and its effects on the gas-liquid mass transfer have been investigated in a pressurized bubble column whose diameter and height are 0.152 and 2.0 m, respectively. Effects of gas velocity (0.02-0.20 m/s), pressure (0.1-0.6 MPa), liquid viscosity (1.0-38.0 MPa s) and bubble distribution mode (even, wall-side, central and asymmetric distribution) on the volumetric gas-liquid mass transfer coefficient and bubble flow behavior have been examined. Pressure fluctuations have been measured and analyzed by adopting the deterministic chaos theory as well as spectral analysis. It has been found that the even distribution of bubbles is the best mode for mass transfer. The volumetric gas-liquid mass transfer coefficients when the bubbles are distributed in a mode of wall-side distribution have been relatively higher than those when the bubble distribution mode has been central or asymmetric. The bubble flow regime and its transition have been detected by analyzing the pressure fluctuations in the column. The gas holdup and volumetric gas-liquid mass transfer coefficients have been well correlated with the correlation dimension of pressure fluctuations elucidating the bubble distribution in the pressurized bubble columns. (C) 1999 Elsevier Science Ltd. All rights reserved.Korea Science and engineering Foundatio
Modeling of NH3–NO–SCR reaction over CuO/γ-Al2O3 catalyst in a bubbling fluidized bed reactor using artificial intelligence techniques
No full textComparative study of the artificial neural network and mechanistic model was carried out for NO removal in a bubbling fluidized bed reactor. The effects of temperature, superficial gas velocity and ammonia/nitric oxide ratio on the NO removal efficiency were determined and their optimum conditions were estimated by the experimental study, the artificial neural network and mechanistic models as well. The optimum values of ammonia/nitric oxide ratio, temperature and superficial gas velocity for the maximum NO removal efficiency were found to be 1.5, 300 degrees C and 0.098 m/s, respectively. A mechanistic model was implemented in our previous study [Muhammad F. Irfan, Sang Done Kim and Muhammad R. Usman, 2009] and it was found that this model fitted well only at specific condition i.e. maximum conversion temperature (300 degrees C). However, it failed to perfectly match with rest of the experimental data points at other temperatures and parametric conditions as well. To improve this, an artificial neural network modeling strategy was applied and its predictions were evaluated which were favorably matched with the experimental data rather than the mechanistic model. (C) 2011 Elsevier Ltd. All rights reserved
Heat and mass transfer in three-phase fluidized-bed reactors—an overview
No full textThis overview examines the heat and mass transfer characteristics in three-phase (gas-liquid-solid and liquid-liquid-solid) fluidized beds to provide prerequisite knowledge for reactor design. The effects of gas and liquid velocities, solid and liquid properties on the heat and mass transfer coefficients in three-phase fluidized beds have been determined. The various correlations and models to predict the heat and mass transfer coefficients in the literature have been examined and the unified correlations based on the concepts of surface renewal theory and energy dissipation rate in the beds have been proposed. The analogy between the heat and the mass transfer in three-phase fluidized beds have been discussed. The areas wherein future research should be undertaken to improve the state of the present knowledge are defined with recommendations. (C) 1997 Elsevier Science Ltd
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