Refine
Year of publication
- 2001 (1425) (remove)
Document Type
- Article (889)
- Monograph/Edited Volume (252)
- Doctoral Thesis (151)
- Review (63)
- Preprint (29)
- Part of Periodical (16)
- Postprint (13)
- Working Paper (6)
- Habilitation Thesis (2)
- Other (2)
Language
- German (902)
- English (497)
- Spanish (13)
- French (5)
- Russian (2)
- Czech (1)
- Italian (1)
- Multiple languages (1)
- Polish (1)
- Portuguese (1)
Keywords
- 1799-1804 (10)
- Cuba (5)
- Relation historique (5)
- Lateinamerika (4)
- Judentum (3)
- Venezuela (3)
- 1789 (2)
- 1818 (2)
- 1823 (2)
- 1831 (2)
Institute
- Institut für Physik und Astronomie (160)
- Institut für Biochemie und Biologie (111)
- Institut für Mathematik (103)
- Historisches Institut (85)
- Institut für Romanistik (80)
- Wirtschaftswissenschaften (80)
- Sozialwissenschaften (71)
- Institut für Germanistik (66)
- Institut für Umweltwissenschaften und Geographie (66)
- Institut für Chemie (53)
- Department Psychologie (49)
- Extern (47)
- Öffentliches Recht (44)
- Department Erziehungswissenschaft (41)
- Institut für Jüdische Studien und Religionswissenschaft (40)
- MenschenRechtsZentrum (39)
- Bürgerliches Recht (35)
- Department Sport- und Gesundheitswissenschaften (30)
- Institut für Geowissenschaften (30)
- Institut für Informatik und Computational Science (30)
- Institut für Ernährungswissenschaft (25)
- Institut für Anglistik und Amerikanistik (18)
- Department Linguistik (16)
- Philosophische Fakultät (14)
- Department für Inklusionspädagogik (13)
- Lehreinheit für Wirtschafts-Arbeit-Technik (13)
- Zentrum für Umweltwissenschaften (12)
- Institut für Slavistik (11)
- Department Grundschulpädagogik (10)
- Strafrecht (9)
- Interdisziplinäres Zentrum für Dynamik komplexer Systeme (6)
- Institut für Künste und Medien (4)
- Kommunalwissenschaftliches Institut (4)
- Referat für Presse- und Öffentlichkeitsarbeit (3)
- Vereinigung für Jüdische Studien e. V. (3)
- ZIM - Zentrum für Informationstechnologie und Medienmanagement (3)
- Zentrum für Sprachen und Schlüsselkompetenzen (Zessko) (3)
- Arbeitskreis Militär und Gesellschaft in der Frühen Neuzeit e. V. (2)
- Klassische Philologie (2)
- Strukturbereich Bildungswissenschaften (2)
- Zentrum für Lehrerbildung und Bildungsforschung (ZeLB) (2)
- Department Musik und Kunst (1)
- Institut für angewandte Familien-, Kindheits- und Jugendforschung e.V. (1)
- Organe und Gremien (1)
Spectral lines formed in stellar winds from OB stars are observed to exhibit profile variations. Discrete Absorption Components (DACs) show a remarkably slow wavelength drift with time. In a straightforward interpretation, this is in sharp contradiction to the steep velocity law predicted by the radiation-driven wind theory, and by semi- empirical profile fitting. In the present paper we re-discuss the interpretation of the drift rate. We show that the Co- rotating Interaction Region (CIR) model for the formation of DACs does not explain their slow drift rate as a consequence of rotation. On the contrary, the apparent acceleration of a spectral CIR feature is even higher than for the corresponding kinematical model without rotation. However, the observations can be understood by distinguishing between the velocity field of the matter flow, and the velocity law for the motion of the patterns in which the DAC features are formed. If the latter propagate upstream against the matter flow, the resulting wavelength drift mimics a much slower acceleration although the matter is moving fast. Additional to the DACs, a second type of recurrent structures is present in observed OB star spectra, the so-called modulations. In contrast to the DACs, these structures show a steep acceleration compatible with the theoretically predicted velocity law. We see only two possible consistent scenarios. Either, the wind is accelerated fast, and the modulations are formed in advected structures, while the DACs come from structures which are propagating upstream. Or, alternatively, steep and shallow velocity laws may co-exist at the same time in different spatial regions or directions of the wind.
Aim and Location In Central European lowland certain plant species grow mainly or exclusively in the corridors of large rivers. In German-speaking plant geography, they are known as "Stromtalpflanzen". The aim of this paper is to review the literature about definitions, explanations and species characteristics and to suggest future directions in research concerning this species group. Results A preliminary list contains 129 ecologically heterogeneous plant species. The mechanisms generating the peculiar distribution pattern may include hydrochory along river corridors, high level of disturbance by water, variable water availability including inundation and summer drought, warm summers, and high nutrient supply on alluvial soils. There is evidence from observational studies for all above mechanisms. However, none of them has been tested experimentally. Demographic data of river corridor plants is limited to very few species, including mainly invasive annuals (Artemisia annua, Bidens frondosa, Cuscuta campestris, Xanthium albinum) and annual (hemi)parasites (Cuscuta campestris, Melampyrum cristatum). Metapopulation studies do not exist to date for European species. part from their habitat requirements, river corridor plants were grouped according to their similarities in overall distribution pattern or in their distribution within particular river corridors. Main conclusions River corridor plants include a high proportion of threatened plant species. In order to preserve them, and in order to understand the mechanisms generating the peculiar distribution pattern, much more has to be known about their population biology and metapopulation dynamics.
The macrocyclic ring interconversion of four maleonitrile mixed oxadithia crown ethers of variable ring size, mn-12-S2O2, mn-15-S2O3, mn-18-S2O4 and fn-12-S2O2, were studied by 1H and 13C NMR spectroscopy and by molecular modelling. The barriers to ring interconversion were estimated using variable temperature NMR spectroscopy and from the calculated activation energies, together with the spin-lattice relaxation times of the CH2 carbon atoms, conclusions were drawn regarding the intramolecular flexibility of the crown ethers in both the free state as well as the complexed state incorporating either AgI, BiIII, SbIII, PdII or PtII metal cations. Furthermore, both the stoichiometry of the complexes and the coordination sites of the crown ethers to the various cations were also clearly implicated. Molecular modelling was also utilised to ascertain the preferred conformers of the four compounds and their corresponding complexes, the results of which corroborated the experimental NMR results to a high degree.
Structural information about the bis(benzo crown ether)s I-VI and their complexes with alkali metal cations was deduced from the 13C NMR chemical shifts, the salt-induced 1H and 13C chemical shifts and the vicinal 1H,1H coupling constants. Especially the isomerism with respect to the amide O=C - NH bonds and imine fragments were assigned by various useful NMR parameters ( C=O, 1JN,H, 1JC,H) and proved to be E,E-anti,anti. Furthermore, stereochemical information about preferred conformations about flexible bonds was obtained from 2D ROESY NMR experiments. The complex formation (2:1 complexes and sandwich-like 1:1 complexes, respectively) were determined also by 23Na NMR spectroscopy. The conformational study of the crown ethers was accompanied and corroborated by molecular dynamics and quantum chemical calculations.
Einfache Decarbonylierungen und stereoselektive Oxidationen von Cyclohexadienen und Cyclohexenen
(2001)
Zusammenfassend konnte im Rahmen dieser Arbeit das Synthesepotential von Cyclohexadienen und Cyclohexenen deutlich erweitert werden. Die Darstellung der 1-Alkylcyclohexa-2,5-dien-1-carbonsäuren erfolgte mittels Birch-Reduktion in flüssigem Ammoniak und anschließender Umsetzung der intermediär entstehenden Dianionen mit Alkylhalogeniden. So konnte ausgehend von verschiedenen Benzoesäurederivaten eine Reihe interessanter Cyclohexadiene in sehr guten Ausbeuten synthetisiert werden. Erstmals gelangen säurekatalysierte Decarbonylierungen von Cyclohexadiencarbonsäuren, was die einfache Synthese substituierter Aromaten in ausgezeichneten Ausbeuten ermöglichte. In dieser Arbeit wird der Reaktionsmechanismus vorgestellt, welcher durch den Nachweis von Kohlenmonoxid in der Gasphase der Reaktionslösung durch IR-Spektroskopie untermauert wird. Bei der säurekatalysierten Umsetzung von 3-alkylsubstituierten Cyclohexadien-carbonsäuren entstanden neben den erwarteten Aromaten Lactone in ca. 50% Ausbeute. Schließlich zeigen die untersuchten Singulettsauerstoff-En-Reaktionen, der im ersten Teil dargestellten Cyclohexadiene und Lactone, durchweg hohe Regioselektivitäten und lieferten durch elektrostatische Wechselwirkungen und konformative Effekte zum Teil sehr gute Diastereoselektivitäten. Die auxiliarkontrollierte Photooxygenierungen von Cyclohexenon welches mit verschiedenen Weinsäureestern ketalisiert wurde, zeigten jedoch keine bevorzugte p-Facialität des Singulettsauerstoffs.
Electronic intensity and frequency modulation of diode lasers enables new perspectives for highly sensitive analytical in-situ techniques. For analyis of "heterogeneous" media, which may consist of coexisting gaseous, liquid, and solid phases and often show multiple light scattering, non-invasive techniques with outstanding performance characteristics can be developed. Analysis of photon density waves launched by intensity-modulated lasers provide an elegant way for the determination of absorption and scattering coefficients of multiple scattering media. The absorption coefficient can be used for qualitative and quantitative analysis of chemical constituents (which absorb in the range of the laser wavelengths). The scattering coefficient allows characterization of physical and morphological properties of the sample. In the current work, applicability of appropriate radiation transport models was investigated with simple light scattering solutions and compared with results obtained from the treatment according to the theory of Kubelka and Munk. Measurements of human blood samples are discussed. A new method for determination of water vapor partial pressure in a polyurethane foam with a frequency-modulated external cavity diode laser is discussed.
Dissociating retention and access in working memory : an age-comparative study of mental arithmetic
(2001)
Untitled - Introduction
(2001)
Ageing and executive control
(2001)