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  • 1
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    Ionized polycyclic aromatic hydrocarbons in space (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The mid-infrared spectrum of a continuously increasing number of stellar objects, planetary and reflection nebulae, H-II regions and extragalactic sources show a distinctive set of broad emission features at 3.3, 3.4, 6.2, 7.7, 8.6, and 11.3 micron known collectively as the unidentified infrared emission bands. A model is summarized in which the bands arise from positively charged polycyclic hydrocarbons (PAH's) on the basis of their low ionization potential and the excellent agreement between the emission bands and laboratory spectra of auto exhaust which contains these types of molecules. The proposed presence of PAHs in such a variety of objects points to their presence in the interstellar medium. Out of a previously published collection of solid state PAH radical cation spectra five were selected on the basis of the unique thermodynamic stability of their carrier and compared directly to the wavelengths of the DIB's. Although the match seems quite favorable, strongly suggesting that PAH radicals are the long sought after carrier of the diffuse interstellar absorption bands, much laboratory work must be done to test this hypothesis.
    Keywords: ASTROPHYSICS
    Type: NASA, Washington. Interrelationships among Circumstellar, Interstellar and Interplanetary Dust; 2 p
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    The hydrogen coverage of interstellar PAHs (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The rate at which the CH bond in interstellar Polycyclic Aromatic Hydrocarbons (PAHs) rupture due to the absorption of a UV photon has been calculated. The results show that small PAHs (less than or equal to 25 carbon atoms) are expected to be partially dehydrogenated in regions with intense UV fields, while large PAHs (greater than or equal to 25 atoms) are expected to be completely hydrogenated in those regions. Because estimate of the carbon content of interstellar PAHs lie in the range of 20 to 25 carbon atoms, dehydrogenation is probably not very important. Because of the absence of other emission features besides the 11.3 micrometer feature in ground-based 8 to 13 micrometer spectra, it has been suggested that interstellar PAHs are partially dehydrogenated. However, IRAS 8 to 22 micrometer spectra of most sources that show strong 7.7 and 11.2 micrometer emission features also show a plateau of emission extending from about 11.3 to 14 micrometer. Like the 11.3 micrometer feature, this new feature is attributed to the CH out of plane bending mode in PAHs. This new feature shows that interstellar PAHs are not as dehydrogenated as estimated from ground-based 8 to 13 micrometer spectra. It also constrains the molecular structure of interstellar PAHs. In particular, it seems that very condensed PAHs, such as coronene and circumcoronene, dominate the interstellar PAH mixture as expected from stability arguments.
    Keywords: ASTROPHYSICS
    Type: NASA-TM-89340 , NAS 1.15:89340 , DE87-003376 , CONF-8602110-2
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    NASA TECHNICAL REPORTS
  • 3
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    Infrared absorption and emission characteristics of interstellar PAHs (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The mid-infrared interstellar emission spectrum with features at 3.28, 6.2, 7.7, 8.7 and 11.3 microns is discussed in terms of the Polycyclic Aromatic Hydrocarbon (PAH) hypothesis, which is based on the suggestive, but inconclusive comparison between the interstellar emission spectrum with the infrared absorption and Raman spectra of a few PAHs. The fundamental vibrations of PAHs and PAH-like species which determine the IR and Raman properties are discussed. Interstellar IR band emission is due to relaxation from highly vibrationally excited PAHs excited by ultraviolet photons. The excitation/emission process is described and the IR fluorescence from one PAH, chrysene, is traced. Generally, there is sufficient energy to populate several vibrational levels in each mode. Molecular vibrational potentials are anharmonic and emission from these higher levels will fall at lower frequencies and produce weak features to the red of the stronger fundamentals. This process is also described and can account for some spectroscopic details of the interstellar emission spectra previously unexplained. Analysis of the interstellar spectrum shows that PAHs contain between 20 and 30 carbon atoms are responsible for the emission.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA-TM-89287 , NAS 1.15:89287 , DE87-003375 , CONF-8607112-1
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    NASA TECHNICAL REPORTS
  • 4
    Electronic Resource
    Electronic Resource
    X-ray scattering from oriented Durham polyacetylene: structural changes after electrochemical doping (1987)
    s.l. : American Chemical Society
    Macromolecules 20 (1987), S. 2457-2461 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00176a022
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Importance of dissociated ions in contact charging (1992)
    s.l. : American Chemical Society
    Langmuir 8 (1992), S. 2698-2706 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00047a020
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of Sulfonyl Chloride Group in m-Benzenedisulfonyl Chloride (1960)
    s.l. : American Chemical Society
    Analytical chemistry 32 (1960), S. 831-832 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac60163a029
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  • 7
    Electronic Resource
    Electronic Resource
    The ecology of the yeast flora in necroticOpuntia cacti and of associatedDrosophila in Australia (1984)
    Springer
    Microbial ecology 10 (1984), S. 379-399 
    Details
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A survey was made of the yeast communities isolated from necrotic tissue of 4 species of prickly-pear cacti (Opuntia stricta, O. tomentosa, O. monacantha, andO. streptacantha) which have colonized in Australia. Yeast communities were sampled from a number of localities and at different times. Cactus specific yeasts accounted for 80% of the total isolates, and the 3 most common species contributed 63% of the total. Comparisons of the species compositions of the yeast communities indicated that the differences among communities were greater betweenOpuntia species than between different localities within a single cactus species, and also that differences between years were greater than average differences between localities within years. Multivariate statistical tests of association between yeast community and physical features of rots indicated that temperature, pH, and age of rot all exerted some influence on the structure of the yeast community. Similar analyses involvingDrosophila species inhabiting these cactus rots suggested the existence of complex associations betweenDrosophila community, yeast community, and physical and chemical attributes of the cactus necroses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02015562
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  • 8
    Electronic Resource
    Electronic Resource
    Analysis of spatial and temporal variation in the community structure of yeasts associated with decayingOpuntia cactus (1987)
    Springer
    Microbial ecology 14 (1987), S. 267-276 
    Details
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The microbial structure within, between, and over time in decaying cladodes of the common prickly pearOpuntia stricta was studied at each of two separate localities. In general, the effective number of yeast species and yeast species diversity increased as the rot aged to the observed maximum time of 4 weeks. Yeast heterogeneity at the two localities differed in the mode of environmental influence, with spatial variability (among rots) most important at one and temporal variability (within rots over time) most important at the other. Differences in cactus density and quality (age) are most likely determinants of the differences in yeast community structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02012946
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  • 9
    Electronic Resource
    Electronic Resource
    Exogenous GABA persistently opens Cl− channels in cultured embryonic rat thalamic neurons (1995)
    Springer
    The journal of membrane biology 145 (1995), S. 279-284 
    Details
    ISSN: 1432-1424
    Keywords: Patch-clamp ; GABA ; GABAA receptor ; Embryonic rat ; Thalamus ; Cl− channel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract We recorded whole-cell Cl− currents in cultured embryonic rat thalamic neurons by brief applications of GABA or the structural analogue muscimol. In 17 of 141 neurons (12%) the Cl− current persisted for a minute or more after the pipette was removed from the bath. Cl− current never persisted after muscimol exposure even in those cells exhibiting persistent GABA-activated currents (PGC). The half decay times (T50) of PGCs were exponentially and asymptotically related to the duration of GABA exposure and could be interrupted or completely aborted by low-pressure application of saline. PGCs were insensitive to membrane potential, to Tiagabine, a nipecotic acid analogue known to block GABA uptake, and persisted in Ca o 2+ -free medium. Fluctuation analysis revealed that PGCs exhibited inferred Cl− channel properties whose kinetic components and estimated average elementary conductance showed no significant difference from those estimated during GABA exposure. The relative contribution of low frequency components was consistently reduced and that of high frequency components modestly increased during PGC compared to those recorded during GABA exposure. Taken together, the results suggest the existence of a superficial compartment in these embryonic neurons that can momentarily accumulate and release exogenous GABA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232719
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  • 10
    Electronic Resource
    Electronic Resource
    Association of TNFA gene polymorphism at position –308 with susceptibility to irritant contact dermatitis (2000)
    Springer
    Immunogenetics 51 (2000), S. 201-205 
    Details
    ISSN: 1432-1211
    Keywords: Key words Skin ; Genetics ; TNFA ; ¶Inflammation ; PCR-RFLP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  Mechanisms underlying susceptibility to skin irritants are not clearly understood. Cytokines play a key role in inflammation, and functional polymorphisms in cytokine genes may affect responses to irritants. We investigated the relationship between polymorphism in the tumor necrosis factor (TNF) α-chain gene and responses to irritants. Volunteers (n=221) tested with sodium dodecyl sulfate (SDS) and benzalkonium chloride (BKC) were divided into responders and nonresponders and high and low irritant-threshold groups. DNA was assayed for the TNF-308 polymorphism by a polymerase chain reaction-restriction fragment length polymorphism method. There was a significant increase in the A allele (P=0.030) and AA genotype (P=0.023) in both the SDS low irritant-threshold group and in SDS responders (A allele P=0.022, AA genotype P=0.048). In the BKC low irritant-threshold group, we found a significant increase in the A allele (P=0.002) and AA genotype (P=0.016). Individuals with a low threshold to both irritants demonstrated a significant increase (P=0.002) in the A allele. This is the first description of a nonatopic genetic marker for irritant susceptibility in normal individuals. Genotyping for theTNF-308 polymorphism may thus contribute to screening of individuals deemed at risk of developing irritant contact dermatitis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002510050032
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