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  • 1
    Electronic Resource
    Electronic Resource
    Interhemispheric asymmetry in OH abundance inferred from measurements of atmospheric 14 CO (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 50-52 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We extracted CO in situ from 1.5-m3 air samples following the method of Stevens and Krout9. In essence, after removal of at least 99.9999% of atmospheric CO2, the CO content is oxidized over I2O5 to CO2, which is subsequently trapped cryogeni-cally. This quantitative extraction procedure provided ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/356050a0
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  • 2
    Electronic Resource
    Electronic Resource
    On the Exchange of NO3 Radicals with Aqueous Solutions: Solubility and Sticking Coefficient (1998)
    Springer
    Journal of atmospheric chemistry 29 (1998), S. 17-43 
    Details
    ISSN: 1573-0662
    Keywords: nitrate radical ; solubility ; sticking coefficient ; redox potential ; heterogeneous removal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The exchange of NO3 radicals with the aqueous-phase was investigated at room temperature (293 K) in a series of wetted denuders. From these experiments, the uptake coefficient of NO3 was determined on 0.1 M NaCl solutions and was found to be γ(NO3) ≥ 2 × 10-3 in good agreement with recent studies. The Henry coefficient of NO3 was estimated to be KH(NO3) = 1.8 M · atm-1, with a (2σ) uncertainty of ±3 M · atm-1. From the upper limit for the Henry coefficient (KH = 5 M · atm-1) and available thermodynamic data, the redox potential of dissolved NO3/NO 3 − is estimated to be in the range of 2.3 to 2.5 V. This range is at the lower boundary of earlier estimates. The results are discussed in the light of a recent publication. Based on our data and a model of the transport and chemistry in the liquid film, an upper limit is derived for the product of the Henry coefficient KH and the rate coefficient k 10 of the potential reaction NO3 + H2O → HNO3 + OH. For KH = 0.6 M · atm-1, we find k 10 〈 0.05 s-1 · atm-1, i.e., about 100 times smaller than what was suggested by Rudich and co-workers. Because of its small solubility, heterogeneous removal of NO3 is only important under conditions where the dissolved NO3 is removed quickly from equilibrium, for example by reactions with Cl− or HSO 3 − ions in the liquid-phase. Otherwise, heterogenous removal should mainly proceed via N2O5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005860312363
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  • 3
    Electronic Resource
    Electronic Resource
    A photoelectric detector for the measurement of photolysis frequencies of ozone and other atmospheric molecules (1989)
    Springer
    Journal of atmospheric chemistry 8 (1989), S. 203-227 
    Details
    ISSN: 1573-0662
    Keywords: Atmosphere ; photolysis ; ozone ; nitrogen dioxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Photoelectric detectors for the measurement of photolysis frequencies of different trace gases in the atmosphere are described. They exhibit uniform response characteristics over one hemisphere (2π sr) and wavelength characteristics closely matched to those of the photolysis frequencies J O1D, J NO2, and J NO3, respectively. Absolute calibration of the J O1D detector was performed by chemical actinometry with an accuracy of ±16 percent. Simultaneous measurements of J NO2 and J O1D are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00051494
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  • 4
    Electronic Resource
    Electronic Resource
    On the Budget of OH Radicals and Ozone in an Urban Plume from the Decay of C5–C8 Hydrocarbons and NOx (1997)
    Springer
    Journal of atmospheric chemistry 28 (1997), S. 263-282 
    Details
    ISSN: 1573-0662
    Keywords: ozone ; hydrocarbons ; NOx ; photochemistry ; OH-radicals ; budget
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Simultaneous measurements of ozone and ozoneprecursors were made during a field campaign atSchauinsland in the Black Forest and in the valleynorth of Schauinsland that channels the flow ofpolluted air from the city of Freiburg to the site.From the decay of hydrocarbons and NOx between the twomeasuring sites and the known rate coefficients, theconcentration of OH radicals was calculated. From abudget analysis of OH and HOx it is concluded that therelatively high OH concentrations (5–8 ×106cm-3) in the presence of high NO2concentrations cannot be explained by the knownprimary sources. The budget can be closed if efficientrecycling of OH via HO2 is assumed to occur andthat, based on the measured hydrocarbons, 2 HO2molecules are formed for each OH radical that reactswith a hydrocarbon molecule. This assumption is inaccordance with the budget of Ox obtained from ourmeasurements and with results from earliermeasurements of alkylnitrates and peroxy radicals atSchauinsland. A possible conclusion is that the decayof precursors and production of photooxidants in urbanplumes proceeds at a faster rate than is currentlyassumed. The potential role of biogenichydrocarbons for the radical budget is alsodiscussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005821522256
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  • 5
    Electronic Resource
    Electronic Resource
    Climatology of Ozone, PAN, CO, and NMHC in the Free Troposphere Over the Southern North Atlantic (1997)
    Springer
    Journal of atmospheric chemistry 28 (1997), S. 245-262 
    Details
    ISSN: 1573-0662
    Keywords: free troposphere ; ozone ; non methane hydrocarbons ; peroxyacetylnitrate ; carbon monoxide ; photo chemistry ; North Atlantic ; seasonal cycle ; long range transport ; back-trajectories ; photochemical age
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Free tropospheric measurements of ozone, peroxyacetylnitrate andprecursors (CO, NMHC) that were made within the framework of the EUROTRACsub-project TOR (Tropospheric Ozone Research) between 1990 and 1995 at theGAW station Izana, Tenerife (28°18′N, 16°30′W) arediscussed. The average annual cycles reveal the importance of transport fromnorthern mid-latitudes and the role of photo-chemistry. According toair-mass trajectories, which were supplied to us from AEROCE(Atmosphere/Ocean Chemistry Experiment), transport from northernmid-latitudes is associated with high precursor concentrations in winter,whereas ozone concentrations in winter are not much influenced by transportpatterns, suggesting a rather uniform distribution over the northern part ofthe Northern Hemisphere around mean value of 43 ± 5 ppb. In summer,high ozone concentrations of up to 90 ppb are often encountered duringtransport from north, while the levels of precursors are much lower than inwinter, because of photochemical destruction. Trajectories from southerlylatitudes and the Sahara usually have the lowest ozone concentrationsassociated with them.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005801515531
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  • 6
    Electronic Resource
    Electronic Resource
    Infobase Change: A First Approximation (2000)
    Springer
    Journal of logic, language and information 9 (2000), S. 353-377 
    Details
    ISSN: 1572-9583
    Keywords: base change ; base contraction ; base revision ; belief contraction ; belief revision ; iterated base change ; theory change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Linguistics and Literary Studies , Computer Science
    Notes: Abstract Generalisations of theory change involving operations on arbitrary sets ofwffs instead of on belief sets (i.e., sets closed under a consequencerelation), have become known as base change. In one view, a base should bethought of as providing more structure to its generated belief set, whichmeans that it can be employed to determine the theory contraction operationassociated with a base contraction operation. In this paper we follow suchan approach as the first step in defining infobase change. We think of an infobase as a finite set of wffs consisting of independently obtainedbits of information. Taking AGM theory change (Alchourrón et al. 1985) as the general framework, we present a method that uses the structure of aninfobase B to obtain an AGM theory contraction operation for contractingthe belief set Cn(B). Both the infobase and the obtained theory contraction operation then play a role in constructing a unique infobasecontraction operation. Infobase revision is defined in terms of an analogueof the Levi Identity, and it is shown that the associated theory revisionoperation satisfies the AGM postulates for revision. Because every infobaseis associated with a unique infobase contraction and revision operation, the method also allows for iterated base change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008308620177
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  • 7
    Electronic Resource
    Electronic Resource
    Refined Epistemic Entrenchment (2000)
    Springer
    Journal of logic, language and information 9 (2000), S. 237-259 
    Details
    ISSN: 1572-9583
    Keywords: belief contraction ; belief revision ; epistemic entrenchment ; power orders ; theory change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Linguistics and Literary Studies , Computer Science
    Notes: Abstract Epistemic entrenchment, as presented by Gärdenfors and Makinson (1988) and Gärdenfors (1988), is a formalisation of the intuition that, when forced to choose between two beliefs, an agent will giveup the less entrenched one. While their formalisation satisfactorilycaptures the intuitive notion of the entrenchment of beliefs in a number ofaspects, the requirement that all wffs be comparable has drawn criticismfrom various quarters. We define a set of refined versions of theirentrenchment orderings that are not subject to the same criticism, andinvestigate the relationship between the refined entrenched orderings,the entrenchment orderings of Gärdenfors and Makinson, and AGM theorycontraction (Alchourrón et al., 1985). To conclude, we compare refinedentrenchment with two related approaches to epistemic entrenchment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008316802976
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  • 8
    Electronic Resource
    Electronic Resource
    Differential activation by platelet-derived growth factor-BB of mitogen activated protein kinases in starved or nonstarved AKR-2B fibroblasts (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 161 (1994), S. 342-350 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: More than 90% of serum-deprived (starved) AKR-2B mouse fibroblasts are stimulated to divide by the addition of platelet-derived growth factor (PDGF)-BB. In density-arrested (nonstarved) cells, PDGF-BB affords protection from cell death without stimulation of cell division. In both cultivation conditions the cells express similar amounts of PDGF β-receptors and the receptor kinase activity was identical as judged by its autophosphorylation capacity. Three signaling pathways were studied in detail: (1) Phospholipase C-γ (PLC-γ) and [Ca2+]i increase, (2) activation of the phosphatidylinositol-3 kinase (PI-3 kinase), and (3) activation of mitogen activated kinases I and II (MAP kinases I and II). There was no difference in starved or nonstarved cells regarding PLC-γ activation, increase of [Ca2+]i, and stimulation of PL-3 kinase activity. But most remarkably the activation of MAP-I was largely suppressed in nonstarved cells. The implications of these signaling pathways in cell protection or cell division are discussed. © 1994 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041610219
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  • 9
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    In situ measurements of background aerosol and subvisible cirrus in the tropical tropopause region (2002)
    American Geophysical Union
    Details
    Publication Date: 2002-12-19
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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  • 10
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    Identification of Human Pituitary Growth Hormone Variants by Mass Spectrometry (2009)
    American Chemical Society
    Details
    Publication Date: 2009-02-06
    Print ISSN: 1535-3893
    Electronic ISSN: 1535-3907
    Topics: Chemistry and Pharmacology
    Published by American Chemical Society
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