Optical, infrared and millimetre-wave properties of Vega-like systems - III. Models with thermally spiking grains

Vega-like stars are main-sequence stars that exhibit excess IR emission due to circumstellar dust grains which are probably distributed in discs. We have recently published an obser- vational data base for a large sample of candidate Vega-like systems, comprising optical, near- IR and mm/submm-wave photometry, and mid-IR spectra. In a previous paper we presented radiative transfer models of eight sources from our sample that had low fractional excess luminosities. Here we present models of a further eight sources, all with large fractional excess luminosities dominated by excess emission at near-IR wavelengths. It was found that no single distribution of dust grains at thermal equilibrium in a disc could simultaneously match the excess emission at near-IR and longer wavelengths. We attempted to model the near-IR emission as due to thermally spiking small grains, which can temporarily attain the high temperatures required to produce excess near-IR emission. A near-IR spectrum of SAO 186777 shows the 3.3-μm UIR emission band, confirming our earlier detection of UIR emission at longer wavelengths, and suggesting that small carbonaceous particles are responsible for some of the near-IR emission. The thermally spiking models were only partially successful and many of the sources required the presence of grains emitting in thermal equilibrium at ∼ 1000- 1500 K. These grains must either be located very close to the stars (<1 au), or else be powered by accretion luminosity. Calculations of the optical depths of the model discs suggest the discs are optically thick at visual wavelengths; optically thick modelling of these sources is desirable. The discs are optically thin at mm wavelengths, allowing us to confirm the presence of large grains in the discs. The stars presented in this paper may well be younger than the prototype Vega-like stars

Transcontinental Railroad

Students will map their own routes for the transcontinental railroad. Students will read and analyze several maps in order to design their routes based on the geographical factors

Genocide in Rwanda

In small groups, students will complete a jigsaw on Hutu propaganda and explain how it can be applied to the “8 stages of genocide”. These findings will be presented to the rest of the class

FREE/ MIXED CONVECTION IN VERTICAL POROUS CHANNEL

Convective heat transfer or simply convection is the study of transport processes Effected by the flow of fluids. Convective heattransfer has grown to the status of a contemporary science because ofpeople desire to understand andpredict how a fluid flow will act as a carrier or conveyer belt for energy and matter. How ever Convective heat transfer is clearly, afield at interface betweentwo older fields: heat transfer and fluid mechanics. For this reason, the study of any convective heat transfer problem must reset ona solid understanding of basic heat transfer and fluid mechanics principles. Since this research will cover free convection and porous medium we discuss briefly about it. Fluid flow and convection heat transfer in porous media have been widely investigated experimentally and numerically for many years due to the many important applications, such as catalytic and chemical particle beds, petroleum processing, geothermal energy extraction, transpiration cooling, packed-bed regenerators, solid matrix heat exchangers, micro-thrusters and many others. Porous media can intensify fluid mixing and increase the surface area in contact with the coolant, so porous structures are an effective heat transfer augmentation technique. There have been numerous investigations with theoretical analyses and numerical simulations of convection heat. However in this project the simulation have been done and the results have been obtained and the maximum velocity of the hot air is about 0.0003m/s moreover the velocity in figure 11showed the maximum near the heated wall and in natural convection the maximum velocity is on the heated wall, therefore the velocity is very identical to the assumption of Darcy flow is valid when the fluid is not too fast ref [7] For the temperature is about 1270K and the temperature we can manipulate it by supply heat flux at high or low see the appendices 1&2 check temperature contour for different values for heat flux therefore we can conclude that the velocity obtained by simulation is satisfied as well as the temperature

Nonextensive Entropies derived from Form Invariance of Pseudoadditivity

The form invariance of pseudoadditivity is shown to determine the structure of nonextensive entropies. Nonextensive entropy is defined as the appropriate expectation value of nonextensive information content, similar to the definition of Shannon entropy. Information content in a nonextensive system is obtained uniquely from generalized axioms by replacing the usual additivity with pseudoadditivity. The satisfaction of the form invariance of the pseudoadditivity of nonextensive entropy and its information content is found to require the normalization of nonextensive entropies. The proposed principle requires the same normalization as that derived in [A.K. Rajagopal and S. Abe, Phys. Rev. Lett. {\bf 83}, 1711 (1999)], but is simpler and establishes a basis for the systematic definition of various entropies in nonextensive systems.Comment: 16 pages, accepted for publication in Physical Review

Developed Hybrid Model for Propylene Polymerisation at Optimum Reaction Conditions

YesA statistical model combined with CFD (computational fluid dynamic) method was used to explain the detailed phenomena of the process parameters, and a series of experiments were carried out for propylene polymerisation by varying the feed gas composition, reaction initiation temperature, and system pressure, in a fluidised bed catalytic reactor. The propylene polymerisation rate per pass was considered the response to the analysis. Response surface methodology (RSM), with a full factorial central composite experimental design, was applied to develop the model. In this study, analysis of variance (ANOVA) indicated an acceptable value for the coefficient of determination and a suitable estimation of a second-order regression model. For better justification, results were also described through a three-dimensional (3D) response surface and a related two-dimensional (2D) contour plot. These 3D and 2D response analyses provided significant and easy to understand findings on the effect of all the considered process variables on expected findings. To diagnose the model adequacy, the mathematical relationship between the process variables and the extent of polymer conversion was established through the combination of CFD with statistical tools. All the tests showed that the model is an excellent fit with the experimental validation. The maximum extent of polymer conversion per pass was 5.98% at the set time period and with consistent catalyst and co-catalyst feed rates. The optimum conditions for maximum polymerisation was found at reaction temperature (RT) 75 °C, system pressure (SP) 25 bar, and 75% monomer concentration (MC). The hydrogen percentage was kept fixed at all times. The coefficient of correlation for reaction temperature, system pressure, and monomer concentration ratio, was found to be 0.932. Thus, the experimental results and model predicted values were a reliable fit at optimum process conditions. Detailed and adaptable CFD results were capable of giving a clear idea of the bed dynamics at optimum process conditions

Tuberculosis in people with rheumatic disease in Finland 1995–2007: a nationwide retrospective register study

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