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  • 1
    Publication Date: 2024-02-09
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Gas transport in soils is usually assumed to be purely diffusive, although several studies have shown that non‐diffusive processes can significantly enhance soil gas transport. These processes include barometric air pressure changes, wind‐induced pressure pumping and static air pressure fields generated by wind interacting with obstacles. The associated pressure gradients in the soil can cause advective gas fluxes that are much larger than diffusive fluxes. However, the contributions of the respective transport processes are difficult to separate. We developed a large chamber system to simulate pressure fields and investigate their influence on soil gas transport. The chamber consists of four subspaces in which pressure is regulated by fans that blow air in or out of the chamber. With this setup, we conducted experiments with oscillating and static pressure fields. CO〈sub〉2〈/sub〉 concentrations were measured along two soil profiles beneath the chamber. We found a significant relationship between static lateral pressure gradients and the change in the CO〈sub〉2〈/sub〉 profiles (R〈sup〉2〈/sup〉 = 0.53; 〈italic toggle="no"〉p〈/italic〉‐value 〈2e‐16). Even small pressure gradients between −1 and 1 Pa relative to ambient pressure resulted in an increase or decrease in CO〈sub〉2〈/sub〉 concentrations of 8% on average in the upper soil, indicating advective flow of air in the pore space. Positive pressure gradients resulted in decreasing, negative pressure gradients in increasing CO〈sub〉2〈/sub〉 concentrations. The concentration changes were probably caused by an advective flow field in the soil beneath the chamber generated by the pressure gradients. No effect of oscillating pressure fields was observed in this study. The results indicate that static lateral pressure gradients have a substantial impact on soil gas transport and therefore are an important driver of gas exchange between soil and atmosphere. Lateral pressure gradients in a comparable range can be induced under windy conditions when wind interacts with terrain features. They can also be caused by chambers used for flux measurements at high wind speed or by fans used for head‐space mixing within the chambers, which yields biased flux estimates.〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:631.4 ; advective flux ; chamber flux measurements ; static air pressure fields ; wind‐induced pressure pumping
    Language: English
    Type: doc-type:article
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  • 2
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 66 (1994), S. 3858-3863 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] Systemically injected 2′-O-methoxyethyl (2′-O-MOE)-phosphorothioate and PNA-4K oligomers (peptide nucleic acid with four lysines linked at the C terminus) exhibited sequence-specific antisense activity in a number of mouse organs. Morpholino oligomers were less effective, whereas PNA ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 120 (1987), S. 1505-1509 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Functionally Substituted Pyridines by Hetero-Diels-Alder Reaction with Inverse Electron DemandInverse type hetero-Diels-Alder reaction of functionally substituted α,β-unsaturated carbonyl compounds with enol ethers afforded “exo/endo” mixtures of the γ-acetoxy-substituted dihydropyrans 2, 5, and 8, respectively. Deacetylation, oxidation of the hydroxy group, alcohol elimination, and ammonia treatment provided the γ-pyridones 14-16, which upon O-alkylation were transformed into the pyridines 21, 22, and 25, respectively, possessing electron-donating ring substituents. The structures were assigned by 1H-NMR data and by comparison with structural isomers.
    Notes: Die inverse Hetero-Diels-Alder-Reaktion zwischen funktionell substituierten α,β-ungesättigten Carbonylverbindungen und Enolethern lieferte die γ-Acetoxy-substituierten Dihydropyrane 2, 5 und 8 als “exo/endo”-Gemische. Durch Desacetylierung, Oxidation der Hydroxygruppe, Alkohol-Eliminierung und Behandlung mit Ammoniak wurden daraus die γ-Pyridone 14-16 gewonnen, die durch O-Alkylierung in die Pyridine 21, 22 und 25 mit elektronenliefernden Ringsubstituenten übergeführt wurden. Die Strukturen wurden mit Hilfe von 1H-NMR-Daten und durch Vergleich mit Strukturisomeren zugeordnet.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 1081-1087 
    ISSN: 0009-2940
    Keywords: Carbonyl ylides ; Furans ; Intramolecular cycloadditions ; Isomünchnones ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Intramolekulare Cycloadditionen von mesoionischen Carbonylyliden mit Alkinen. Synthese von 5,6-Dihydro-4H-cyclopenta- und 4,5,6,7-Tetrahydrobenzo[b]furan-DerivatenIntramolekulare Cycloadditionen von acetylenischen Isomünchnonen, die in situ durch Rhodiumacetat-katalysierte Zersetzung von N-(Diazoacetyl)-N-methylalkinamid-Derivaten 16a-c, 18c und 18d erzeugt wurden, sind untersucht worden. Die Primäraddukte fragmentieren unter den Reaktionsbedingungen (110°C) zu den anellierten Furanen 19a-c, 20c und 20d.
    Notes: Intramolecular cycloaddition reactions of acetylenic isomünchnones, formed in situ by rhodium acetate catalyzed decomposition of N-(diazoacetyl)-N-methylalkynamide derivatives 16a-c, 18c, and 18d have been studied. The intermediate cycloadducts fragmentate spontaneously under the reaction conditions (110°C) to afford the annulated furans 19a-c, 20c, and 20d.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0947-3440
    Keywords: Enediynes ; [2 + 2] Cycloaddition ; Bicyclo[3.2.0]heptanes ; Fragmentation ; Ring closing metathesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two routes to 1,4-difunctionalized cycloheptenes are described. The first one is based on a fluoride-induced fragmentation reaction of the bicyclic [3.2.0]heptanesilyl monosulfate 10. This compound in turn was prepared by a ketene-cyclopentene cycloaddition route. An alternative strategy took advantage of a ring-closing metathesis (RCM) reaction of the diolefin 18 with the ruthenium catalyst 21. This reaction proved to be reliable even on a larger scale and allowed the isolation of the cycloheptene 19a in reasonably good yield.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 175-177 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bromination of the disubstituted 4,5-dimethyl-1,3-cyclohexanedione (6) followed by oxidation of the resulting 3-bromo-5,6-dimethyl-2-cyclohexen-1-ones (7) gave 5-bromo-2,3-dimethylphenol (1) together with its constitutional isomer 3. The structure of 1 was secured by a x-ray analysis of its tosyl derivative 8.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2043-2046 
    ISSN: 0947-3440
    Keywords: Dihydroxylation ; Tetrol ; Oxirane ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Double asymmetric dihydroxylation of 1,5-hexadiene gave in one step a mixture of the d,l/meso tetrols 6 in a ratio of 3.4:1. From this ratio a facial selectivity of 6.65:1 for each double bond can be calculated. As a consequence of the double reaction the d/l ratio can be estimated to be 44:1. Compound 6 served then as starting material for the preparation of the bis-epoxide 12 and the 2,5-dihydroxyhexane (13). While the separation of the diastereomers was not possible so far, this route for the preparation of 6, 12 and 13 might still be useful because it is very short and products derived from them might allow the crucial separation.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1-13 
    ISSN: 1434-193X
    Keywords: Dynemicin ; Enediynes ; Antitumor agents ; Antibiotics ; Cross-coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Dynemicin A is a member of the family of enediyne natural products. It is unique in that it combines a ten-membered enediyne with an anthraquinone substructure. These features stimulated the development of synthetic approaches to the natural product itself and of analogs thereof. This review summarizes the total syntheses of dynemicin A. In addition, an overview of the known analogs is presented. The analogs can be classified according to the designed trigger mechanism. Most of the analogs contain a removable carbamate on the nitrogen atom. Others are quite similar to the natural lead in that they contain a quinone substructure, which upon reduction causes opening of the oxirane ring. In addition, there are analogs that contain an aromatic sector, the enediyne, and the oxirane ring but lack the nitrogen heterocycle. In these compounds the aryl ring assumes a different conformation from that in dynemicin A. Many of the simplified analogs proved to be quite active in vitro as well in vivo against murine tumor models. A highlight is compound 30 which is much more active than dynemicin A itself. However, looking at all analogs there is no clear-cut correlation between the DNA-cleaving ability at neutral pH and the in vitro results. From this one might conclude that there are possibly two mechanisms for antitumor activity. One involves diradical formation whereas the other might be due to a ligand-receptor interaction.
    Type of Medium: Electronic Resource
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