Photoelectric Emission from Interstellar Dust: Grain Charging and Gas Heating

We model the photoelectric emission from and charging of interstellar dust and obtain photoelectric gas heating efficiencies as a function of grain size and the relevant ambient conditions. Using realistic grain size distributions, we evaluate the net gas heating rate for various interstellar environments, and find less heating for dense regions characterized by R_V=5.5 than for diffuse regions with R_V=3.1. We provide fitting functions which reproduce our numerical results for photoelectric heating and recombination cooling for a wide range of interstellar conditions. In a separate paper we will examine the implications of these results for the thermal structure of the interstellar medium. Finally, we investigate the potential importance of photoelectric heating in H II regions, including the warm ionized medium. We find that photoelectric heating could be comparable to or exceed heating due to photoionization of H for high ratios of the radiation intensity to the gas density. We also find that photoelectric heating by dust can account for the observed variation of temperature with distance from the galactic midplane in the warm ionized medium.Comment: 50 pages, including 18 figures; corrected title and abstract field

PAH chemistry and IR emission from circumstellar disks

Aims. The chemistry of, and infrared (IR) emission from, polycyclic aromatic hydrocarbons (PAHs) in disks around Herbig Ae/Be and T Tauri stars are investigated. The equilibrium distribution of the PAHs over all accessible charge/hydrogenation states depends on the size and shape of the PAHs and on the physical properties of the star and surrounding disk. Methods. A chemistry model is created to calculate this equilibrium distribution. Destruction of PAHs by ultraviolet (UV) photons, possibly in multi-photon absorption events, is taken into account. The chemistry model is coupled to a radiative transfer code to provide the physical parameters and to combine the PAH emission with the spectral energy distribution (SED) from the star+disk system. Results. Normally hydrogenated PAHs in Herbig Ae/Be disks account for most of the observed PAH emission, with neutral and positively ionized species contributing in roughly equal amounts. Close to the midplane, the PAHs are more strongly hydrogenated and negatively ionized, but these species do not contribute to the overall emission because of the low UV/optical flux deep inside the disk. PAHs of 50 carbon atoms are destroyed out to 100 AU in the disk's surface layer, and the resulting spatial extent of the emission does not agree well with observations. Rather, PAHs of about 100 carbon atoms or more are predicted to cause most of the observed emission. The emission is extended on a scale similar to that of the size of the disk. Furthermore, the emission from T Tauri disks is much weaker and concentrated more towards the central star than that from Herbig Ae/Be disks. Positively ionized PAHs are predicted to be largely absent in T Tauri disks because of the weaker radiation field.Comment: 13 pages, 8 figures, accepted for publication in A&

Synthesis and characterization of hybrid chitosan/carbon adsorbents

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Ti-in-qtz signatures of pseudotachylyte-bearing crystalline rocks

Tectonic pseudotachylytes, i.e. quenched friction-induced silicate melts, record coseismic slip along faults. Bestmann et al. (2012) have shown that transient high temperature conditions related to frictional heating during coseismic faulting in the brittle crust promoted the dynamical recrystallization of quartz to ultrafine-grained (grain size 1-2 m) aggregates along microshear zones in the host rock adjacent to pseudotachylyte veins. In this study we investigate if there is any geochemical signature associated with this transient high temperature event. With this aim we used Ti-in-quartz trace element data, which can be used as a thermometer (Wark and Watson, 2006). Models of the temperature evolution of the host rock following coseismic slip and production of frictional melts show that temperatures >800 C only last for a few minutes close to the vein walls (Bestmann et al., 2012). The experimental data on diffusion of Ti in quartz (Cherniak et al., 2007) seems to exclude that any detectable Ti diffusion could occur during the short-lived thermal event. However, the Ti-in-quartz investigation is motivated by the fact that Ti diffusion could be enhanced in the recrystallized quartz aggregates by pervasive lattice damage and by the percolation of melt along grain boundaries (Bestmann et al., 2012). Micro-mapping of Ti trace amounts in quartz were carried out by using a nanoSIMS on two different pseudotachylyte-bearing samples already used in the study of Bestmann et al. (2012): (1) the Schneeberg Normal Fault Zone (SNFZ, Eastern Alps) within a muscovite-bearing quartzite, and (2) the Gole Larghe Fault Zone (Southern Alps) within tonalites of the Adamello pluton. In the Schneeberg NFZ, the metamorphic (amphibolite facies) host quartz grains and the ultrafine grained recrystallized aggregates within microshear zones adjacent to pseudotachylytes both have an identical Ti signature of 4-6 ppm. In the Adamello tonalite the magmatic quartz host grains are fractured and show a sharp decrease in Ti from 40-55 ppm (magmatic host) to 11-15 ppm (healed fractures). This gives evidence of an extensive phase of fluid-rock interaction along the Adamello faults. Similar to the SNFZ, the ultrafine grained quartz aggregate along microshear zones mainly inherited the pre-seismic Ti signal from the fractured host quartz grains. There are, however, steep Ti gradients surrounding very small (\uab1 m) Ti-bearing 2nd phase particles present along the grain boundary of ultrafine grained aggregates as a result of melt infiltration. These haloes (1-2 m) could reflect enhanced Ti diffusion in highly deformed quartz during the coseismic thermal transient. References Bestmann, M., Pennacchioni, S., Nielsen, G., G\uf6ken, M., de Wall, H., 2012. Deformation and ultrafine recrystallization of quartz in pseudotachylyte-bearing faults: a matter of a few seconds. Journal of Structural Geology, 38, 21-38. Cherniak, D.J., Watson, E.B., Wark, D.A., 2007. Ti diffusion in quartz. Chemical Geology, 236, 65\u201374. Wark, D.A., Watson, E.B., 2006. TitaniQ: a titanium-in-quartz geothermometer. Contribution to Mineralogy and Petrology, 152, 743-754

A universal hybrid adsorbent based on chitosan/carbon material/clay for water treatment

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Synthesis and characterization of hybrid chitosan/carbon adsorbents

International audienc