The evolution of organic mantles on interstellar grains

By laboratory simulation of the chemical processes on dust grains it was investigated how solid organic materials can be produced in the interstellar medium. The ice mantles that accrete on grains in molecular clouds, consisting primarily of H2O, CO, H2CO, NH3, and O2, are irradiated by the internal UV field, resulting in the storage of radicals upon photodissociation of the original molecules. Transient heating events lead to the production of oxygen-rich organic species by recombination reactions. The experiments indicated that in this way the observed amount of organic material can be produced if a grain passes a few times through a molecular cloud during its life. After the destruction of the cloud the grains enter a more diffuse medium. Here they are subjected to the interstellar UV field as well as to collisions with atomic hydrogen. Experiments show that the intense photoprocessing results in the removal of small species like H2O and NH3 as well as in carbonization of the organic molecules. Contrary to this, the atomic H flux will maintain a certain hydrogen level in the mantle. These processes likely convert the original, oxygen-rich organics into an unsaturated hydrocarbon type material such as that observed towards IRS 7 and in Comet Halley grains

The organic component of interstellar grains

The 3.4 micron absorption feature observed in the spectrum of a number of Galactic Center (GC) sources indicates the presence of organic molecules in the interstellar medium. It is ascribed to the C-H stretch vibration of tetrahedrally bonded carbon. From the observed features due to the interstellar organic material, an estimate was made of its composition and abundance. The ratio of the number of C-H groups of tetrahedrally to those of trigonally bonded carbon was 1.5, the cosmic abundance of carbon was .00037, and the depth of the silicate absorption toward the GC was taken equal to 3.6

Ondersoek na besmetlike aandoenings met stremmende invloed op kalfproduksie

No Abstrac

The Foliose and Fruticose Lichen Flora of Linn County, Iowa

Thirty-one species in 10 genera of foliose and fruticose lichens are reported for Linn County, including 3 lichens previously unreported for Iowa: Cladonia nemoxyna, Physcia luganensis, and Physcia rubropulchra. Information on substrate and abundance of each species is included

New insights in the photochemistry of grain mantles: The identification of the 4.62 and 6.87 micron bands

The mid-IR spectral region of molecular clouds is known to show the fingerprints of molecules frozen in the icy mantles of the interstellar grains. To study the complex chemical and physical interactions on the ice mantles accreted on grains in molecular clouds numerous UV irradiation and diffusion experiments were performed. The irradiation of binary ices was studied. Using isotopic labelling on NH3/CO and NH3/O2 ices numerous compounds were identified, of which OCN(-), NO2(-), NO3(-), and NH4(+) ions reveal a new type of chemical reactions. It appeared that these compounds were formed by proton transfer reactions induced by the interaction between an acid (HNCO, HNO2, HNO3) and a base (NH3) through a hydrogen bond. This mechanism was confirmed by a study of photolyzed diluted argon mixtures. The main astrophysically relevant data from the overall study are presented. The 4.62 micron band in W33A can be reproduced with NH3/CO containing irradiated ices and was identified with OCN(-). The 6.87 micron band in W33A and other photostellar objects is reproduced with NH3/O2 containing ices and is identified with NH4(+)

The transformation of minimum standard housing: Upgrading the housing stock in Ikageng

Until recently Blacks were seen as temporary residents of "white" urban areas in South Africa. As a consequence housing provided for them was of a minimum standard, consisting primar­ily of mass-produced four-roomed single or semi-detached dwellings. The predominance of small uniformly designed houses resulted in a monoto­nous residential environment. The Black town of lkageng (official popula­tion approximately 40 000) situated immediately west of Potchefstroom was no exception. During the last decade, however, perceptible improvement in the standard of many public sector houses in lkageng has taken place through a process of upgrading. Since the latter half of 1986 an escalation of this process has been noticed. The aims of this paper are to determine the factors that were responsible for the improve­ment of low income housing in lkageng and 'the escalation thereof since 1986, and to evaluate the potential role of this process in improving the quality of minimum standard dwellings in low income Black residential areas.&nbsp

Prioritising transport infrastructure projects: Towards a multi-criterion analysis

This paper explores a number of aspects relevant to developing asystematic framework for the appraisal of transport infrastructure projects of the type ‘budget cycle projects with local economic impacts’, and applying it to the City of Tshwane. Such a framework is needed as, by implication, the budgeting process for any transport agency requires projects to be ranked in terms of their relative value. Cost/benefit  analysis, when applied in a classic sense, is not suitable for this purpose, given its exclusive focus on economic efficiency, whilst attempts to broaden it to include other impacts (or objectives) are not generally accepted. Multi-criterion analysis, however, is capable of facilitating project ranking in a multi-objective decisionmaking environment, but needs to be customised first to accurately reflect local conditions. The paper concludes that an appraisal framework should combine these two types of analysis by adopting an overall multi-criterion approach with economic efficiency (optimal allocation of resources), equity (impact distribution aspects),sustainability (environmental considerations) and compatibility (alignment with community goals and objectives, and other strategic initiatives) as decision criteria. This will ensure a usable protocol for the appraisal of this type of transport infrastructure project in an essentially multi-criterion decision-making environment.Key words: cost–benefit analysis (CBA), decision criteria, general equilibrium analysis, multi-criterion analysis (MCA), partial equilibrium analysis, project appraisal, project feasibility, project impacts, economic efficiency, project prioritisation (ranking), project selection, transport infrastructure (projects

Laboratory and observational study of the interrelation of the carbonaceous component of interstellar dust and solar system materials

By studying the chemical and isotopic composition of interstellar ice and dust, one gains insight into the composition and chemical evolution of the solid bodies in the solar nebula and the nature of the material subsequently brought into the inner part of the solar system by comets and meteorites. It is now possible to spectroscopically probe the composition of interstellar ice and dust in the mid-infrared, the spectral range which is most diagnostic of fundamental molecular vibrations. We can compare these spectra of various astronomical objects (including the diffuse and dense interstellar medium, comets, and the icy outer planets and their satellites) with the spectra of analogs we produce in the laboratory under conditions which mimic those in these different objects. In this way one can determine the composition and abundances of the major constituents of the various ices and place general constraints on the types of organics coating the grains in the diffuse interstellar medium. In particular we have shown the ices in the dense clouds contain H2O, CH3OH, CO, perhaps some NH3 and H2CO, we well as nitriles and ketones or esters. Furthermore, by studying the photochemistry of these ice analogs in the laboratory, one gains insight into the chemistry which takes place in interstellar/precometary ices. Chemical and spectroscopic studies of photolyzed analogs (including deuterated species) are now underway. The results of some of these studies will be presented and implications for the evolution of the biogenic elements in interstellar dust and comets will be discussed

SALT Spectropolarimetry and Self-Consistent SED and Polarization Modeling of Blazars

We report on recent results from a target-of-opportunity program to obtain spectropolarimetry observations with the Southern African Large Telescope (SALT) on flaring gamma-ray blazars. SALT spectropolarimetry and contemporaneous multi-wavelength spectral energy distribution (SED) data are being modelled self-consistently with a leptonic single-zone model. Such modeling provides an accurate estimate of the degree of order of the magnetic field in the emission region and the thermal contributions (from the host galaxy and the accretion disk) to the SED, thus putting strong constraints on the physical parameters of the gamma-ray emitting region. For the specific case of the $\gamma$-ray blazar 4C+01.02, we demonstrate that the combined SED and spectropolarimetry modeling constrains the mass of the central black hole in this blazar to $M_{\rm BH} \sim 10^9 \, M_{\odot}$.Comment: Submitted to Galaxies - Proceedings of "Polarized Emission from Astrophysical Jets", Ierapetra, Crete, June 12 - 16, 201