Dust absorption

The luminosities of the central stars derived from Hp fluxes (Wood et al 1987b) are all less than = -5, the luminosity at which the LPVs of age 2-3xl09 years leave the AGB. This is as expected, as there are a number of processes (such as dust absorption in the nebula, being optically thin) which will act to reduce the derived bolometric luminosities of the central stars. 

When students ask astronomer William Keel of The University of Alabama in Tuscaloosa how many stars exist in our Milky Way Galaxy, his standard answer is about as many as the number of hamburgers sold by McDonald s. It is difficult to be precise because distance and dust absorption dim incoming light. Measurements of the relative numbers of stars with different absolute brightness suggests that for every Sun-like star there are about 200 faint red M-class dwarfs. (As you ll learn, the class of a star is determined by its surface tem-... 

Gray W. M., Frank W. M., Corrin M. L. and Stokes C. A., Weather modification by carbon dust absorption of solar energy. J. Appl. Meteorol. , 75, 355-386 (1976). 

Another consequence of selective dust absorption is that it prevents the 100 % conversion of high-n Lyman lines into Lya and Balmer lines (the case B). For dusty environments such as the Orion Nebula, the H/3 emissivity can be reduced by 15 % (Cota Ferland 1988). 

Although there are numerous techniques that utilize the bright and intense beams generated by synchrotron radiation (see Brown and Sturchio 2002) we will focus in this chapter on three of the more common X-ray techniques most applicable to indoor dust (absorption, fluorescence, scattering). In particular, this chapter will provide more emphasis to describing the X-ray absorption fine stmcture (XAFS) spectroscopy over the more well-known XRD and X-ray fluorescence techniques. 

Balick (1975) computes the ionization structure of H, N, 0, Ne and S for various kinds of frequency dependence of dust absorption and for variable dust-to-gas ratio. However, while the dust-to-gas mass ratio varies from 10 to 10 the element abundance stays constant. In a subsequent paper Balick and Sneden (1976) consider the effect of variable heavy element abundances Z in both HII region and ionizing star but now the effect of dust is neglected and the mass fraction of He is kept constant. In a more realistic model both the dust-to-gas ratio and that part of the He-abundance AY(He) which results from element synthesis in stars should vary proportionally to Z. The most recent model calculations by Mathis (priv. comm.) allow the variation and combination of all these parameters. 

At wavenvunbers where the refractive index of the material equals that of the substance it is imbedded in (CO2 gas in the Martian case), the suspended atmospheric dust is least scattering, but still absorbing. The frequency where the index of the particles equals that of the environment is called the Christiansen frequency. If atmospheric gas and dust absorption are not excessive, the spectral region sim-rounding this frequency may provide a suitable window for a measurement of the surface temperature. 

If other galaxies with buried Seyfert nuclei also show dust absorption at 3.4/tan, these spectra may provide details of the chemistry of the destruction and excitation of dust grains around active nuclei. 

Granulars are pelleted mixtures of toxicant, usually at 2.5 ndash 10%, and a dust carrier, eg, absorptive clay, bentonite, or diatomaceous earth, and commonly are 250 ndash 590 ]lni in particle size. They are prepared by impregnation of the carrier with a solution or slurry of the toxicant and are used principally for mosquito larviciding and soil appHcations. 

Lead is absorbed into the human body after inhalation of the dust or ingestion of lead-containing products. Contamination of smoking materials in the work area leads to inhalation of lead fumes and constitutes a main factor in lead absorption. 

Amorphous sihca is classified by the Occupational Safety and Health Administration as a nuisance dust. The principal reported health reaction is contact dermatitis resulting from the absorption of protective oils from the skin (1). 

Elemental tellurium and the stable teUurides of heavy nonferrous metals are relatively inert and do not represent a significant health hazard (43—47). Other, more reactive teUurides, including soluble and volatile teUurium compounds such as hydrogen teUuride [7783-09-7] teUurium hexafluoride [7783-80-4] and alkyl teUurides, should be handled with caution. Some of these materials can enter the body by absorption through the skin or by inhalation and ingestion of dust or fumes. No serious consequences or deaths have been reported in workers exposed to teUurium and its compounds in industry (48). 

Lime-Kiln Operation. Gases containing up to 40% carbon dioxide from the lime kiln pass through a cyclone separator, which removes the bulk of entrained dust. The gas is then blown through the two scmbbers, which remove the finer dust, cooled, and passes iato an absorption tower. Here carbon dioxide may be recovered by the sodium carbonate or Girbotol process. 

The gold is then recovered from solution by precipitation with zinc dust, electro deposit, or absorption on carbon. Sodium cyanide is used extensively in organic syntheses, especially in the preparation of nitriles (qv). 

Plate Towers Plate (tray) towers are countercurrent gas-atomized spray scrubbers using one or more plates for gas-liquid contacting. They are essentially the same as, if not identical to, the devices used for gas absorption and are frequently employed in apphcations in which gases are to be absorbed simultaneously with the removal of dust. Except possibly in cases in which condensation effects are involved, countercurrent operation is not significantly beneficial in dust collection. 

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