Micron-sized forsterite grains in the pre-planetary nebula of IRAS 17150-3224 - Searching for clues on the mysterious evolution of massive AGB stars

We study the grain properties and location of the forsterite crystals in the circumstellar environment of the pre-planetary nebula (PPN) IRAS 17150-3224 in order to learn more about the as yet poorly understood evolutionary phase prior to the PPN. We use the best-fit model for IRAS 17150-3224 of Meixner et al. (2002) and add forsterite to this model. We investigate different spatial distributions and grain sizes of the forsterite crystals in the circumstellar environment. We compare the spectral bands of forsterite in the mid-infrared and at 69 micrometre in radiative transport models to those in ISO-SWS and Herschel/PACS observations. We can reproduce the non-detection of the mid-infrared bands and the detection of the 69 micrometre feature with models where the forsterite is distributed in the whole outflow, in the superwind region, or in the AGB-wind region emitted previous to the superwind, but we cannot discriminate between these three models. To reproduce the observed spectral bands with these three models, the forsterite crystals need to be dominated by a grain size population of 2 micrometre up to 6 micrometre. We hypothesise that the large forsterite crystals were formed after the superwind phase of IRAS 17150-3224, where the star developed an as yet unknown hyperwind with an extremely high mass-loss rate (10^-3 Msol/yr). The high densities of such a hyperwind could be responsible for the efficient grain growth of both amorphous and crystalline dust in the outflow. Several mechanisms are discussed that might explain the lower-limit of 2 micrometre found for the forsterite grains, but none are satisfactory. Among the mechanisms explored is a possible selection effect due to radiation pressure based on photon scattering on micron-sized grains.Comment: Accepted by A&

Global assessment of nitrogen deposition effects on terrestrial plant diversity : a synthesis

Atmospheric nitrogen (N) deposition is it recognized threat to plant diversity ill temperate and northern parts of Europe and North America. This paper assesses evidence from field experiments for N deposition effects and thresholds for terrestrial plant diversity protection across a latitudinal range of main categories of ecosystems. from arctic and boreal systems to tropical forests. Current thinking on the mechanisms of N deposition effects on plant diversity, the global distribution of G200 ecoregions, and current and future (2030) estimates of atmospheric N-deposition rates are then used to identify the risks to plant diversity in all major ecosystem types now and in the future. This synthesis paper clearly shows that N accumulation is the main driver of changes to species composition across the whole range of different ecosystem types by driving the competitive interactions that lead to composition change and/or making conditions unfavorable for some species. Other effects such its direct toxicity of nitrogen gases and aerosols long-term negative effects of increased ammonium and ammonia availability, soil-mediated effects of acidification, and secondary stress and disturbance are more ecosystem, and site-specific and often play a supporting role. N deposition effects in mediterranean ecosystems have now been identified, leading to a first estimate of an effect threshold. Importantly, ecosystems thought of as not N limited, such as tropical and subtropical systems, may be more vulnerable in the regeneration phase. in situations where heterogeneity in N availability is reduced by atmospheric N deposition, on sandy soils, or in montane areas. Critical loads are effect thresholds for N deposition. and the critical load concept has helped European governments make progress toward reducing N loads on sensitive ecosystems. More needs to be done in Europe and North America. especially for the more sensitive ecosystem types. including several ecosystems of high conservation importance. The results of this assessment Show that the Vulnerable regions outside Europe and North America which have not received enough attention are ecoregions in eastern and Southern Asia (China, India), an important part of the mediterranean ecoregion (California, southern Europe). and in the coming decades several subtropical and tropical parts of Latin America and Africa. Reductions in plant diversity by increased atmospheric N deposition may be more widespread than first thought, and more targeted Studies are required in low background areas, especially in the G200 ecoregions

Field-Dependent Tilt and Birefringence of Electroclinic Liquid Crystals: Theory and Experiment

An unresolved issue in the theory of liquid crystals is the molecular basis of the electroclinic effect in the smectic-A phase. Recent x-ray scattering experiments suggest that, in a class of siloxane-containing liquid crystals, an electric field changes a state of disordered molecular tilt in random directions into a state of ordered tilt in one direction. To investigate this issue, we measure the optical tilt and birefringence of these liquid crystals as functions of field and temperature, and we develop a theory for the distribution of molecular orientations under a field. Comparison of theory and experiment confirms that these materials have a disordered distribution of molecular tilt directions that is aligned by an electric field, giving a large electroclinic effect. It also shows that the net dipole moment of a correlated volume of molecules, a key parameter in the theory, scales as a power law near the smectic-A--smectic-C transition.Comment: 18 pages, including 9 postscript figures, uses REVTeX 3.0 and epsf.st

Double Lobed Radio Quasars from the Sloan Digital Sky Survey

We have combined a sample of 44984 quasars, selected from the Sloan Digital Sky Survey (SDSS) Data Release 3, with the FIRST radio survey. Using a novel technique where the optical quasar position is matched to the complete radio environment within 450", we are able to characterize the radio morphological make-up of what is essentially an optically selected quasar sample, regardless of whether the quasar (nucleus) itself has been detected in the radio. About 10% of the quasar population have radio cores brighter than 0.75 mJy at 1.4 GHz, and 1.7% have double lobed FR2-like radio morphologies. About 75% of the FR2 sources have a radio core (> 0.75 mJy). A significant fraction (~40%) of the FR2 quasars are bent by more than 10 degrees, indicating either interactions of the radio plasma with the ICM or IGM. We found no evidence for correlations with redshift among our FR2 quasars: radio lobe flux densities and radio source diameters of the quasars have similar distributions at low (mean 0.77) and high (mean 2.09) redshifts. Using a smaller high reliability FR2 sample of 422 quasars and two comparison samples of radio-quiet and non-FR2 radio-loud quasars, matched in their redshift distributions, we constructed composite optical spectra from the SDSS spectroscopic data. Based on these spectra we can conclude that the FR2 quasars have stronger high-ionization emission lines compared to both the radio quiet and non-FR2 radio loud sources. This is consistent with the notion that the emission lines are brightened by ongoing shock ionization of ambient gas in the quasar host as the radio source expands.Comment: 20 pages, 10 figures - some of which have been reduced in quality / size. Accepted for publication in the Astronomical Journa

Survey of Pasture Species and Management, Manure Management, Milk Production and Reproduction on Pasture-Based Dairy Farms in Florida and Georgia, USA

Traditionally, most dairy farms in the south-eastern United States confine cows to barns or on pasture lots year-round and feed stored forages and concentrated feeds (Fontaneli et al. 2005). Often, much of the feed is purchased, however, the cost of purchased feed and fuel has risen rapidly in the last 5 years (NASS 2009). In addition, a significant amount of capital is tied up in buildings, machinery and manure management systems on the farms. For these reasons, many dairy farmers have shown an interest in or started transitioning to pasture-based dairy systems (Ricks and Hardee 2012). The management practices and production results of pasture-based dairy farms in the south-east appear to vary widely (Macoon et al. 2011), but have not been described. The objective of this study was to document pasture and crop management, manure management and milk production on pasture-based dairy farms in Florida and Georgia

The Question of Low-Lying Intruder States in 8Be^8Be and Neighboring Nuclei

The presence of not yet detected intruder states in $^{8}Be$ e.g. a $J=2^{+}$ intruder at 9 $MeV$ excitation would affect the shape of the $\beta ^{\mp }$-delayed alpha spectra of $^{8}Li$ and $^{8}B$. In order to test the plausibility of this assumption, shell model calculations with up to $4\hbar \omega$ excitations in $^{8}Be$ (and up to $2\hbar \omega$ excitations in $^{10}Be$) were performed. With the above restrictions on the model spaces, the calculations did not yield any low-lying intruder state in $^{8}Be$. Another approach -the simple deformed oscillator model with self-consistent frequencies and volume conservation gives an intruder state in $^{8}Be$ which is lower in energy than the above shell model results, but its energy is still considerably higher than 9 $MeV$.Comment: 16 pages (RevTeX), 1 PS figure. To appear in Phys. Rev.

Status of the XMM-Newton cross-calibration with SASv6.5.0

Further achievements of the XMM-Newton cross-calibration - XMM internal as well as with other X-ray missions - are presented. We explain the major changes in the new version SASv6.5 of the XMM-Newton science analysis system. The current status of the cross-calibration of the three EPIC cameras is shown. Using a large sample of blazars, the pn energy redistribution at low energy could be further calibrated, correcting the overestimation of fluxes in the lowest energy regime. In the central CCDs of the MOSs, patches were identified at the bore-sight positions, leading to an underestimation of the low energy fluxes. The further improvement in the understanding of the cameras resulted in a good agreement of the EPIC instruments down to lowest energies. The latest release of the SAS software package already includes corrections for both effects as shown in several examples of different types of sources. Finally the XMM internal cross-calibration is completed by the presentation of the current cross-calibration status between EPIC and RGS instruments. Major efforts have been made in cross-calibrations with other X-ray missions, most importantly with Chandra, of course, but also with currently observing satellites like Swift.Comment: 6 pages, 23 figures. To appear in the proceedings of "The X-Ray Universe 2005" conference, 2005 Sept 26-30, El Escorial, Madrid, Spai

Alpha-decay Rates of Yb and Gd in Solar Neutrino Detectors

The $\alpha$-decay rates for the nuclides $^{168,170,171,172,173,174,176}$Yb and $^{148,150,152,154}$Gd have been estimated from transmission probabilities in a systematic $\alpha$-nucleus potential and from an improved fit to $\alpha$-decay rates in the rare-earth mass region. Whereas ${\alpha}$-decay of $^{152}$Gd in natural gadolinium is a severe obstacle for the use of gadolinium as a low-energy solar-neutrino detector, we show that ${\alpha}$-decay does not contribute significantly to the background in a ytterbium detector. An extremely long ${\alpha}$-decay lifetime of $^{168}$Yb is obtained from calculation, which may be close to the sensitivity limit in a low-background solar neutrino detector.Comment: 12 pages, 1 figure; An author name was correcte