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  • 1
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    In:  Jahresbericht / Hamburger Synchrotronstrahlungslabor HASYLAB am Deutschen Elektronen-Synchrotron DESY = Annual report ; Year: 2005 ; Pages: 69-72
    Publication Date: 2013-10-16
    Type: http://purl.org/eprint/type/BookItem
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  • 2
    Publication Date: 2013-10-16
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  • 3
    ISSN: 1615-6110
    Keywords: Angiosperms ; Echium ; Esterhazya ; pollination ecology ; anthers ; pollen ; secondary pollen presentation ; sporopollenin ; viscin threads
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This paper reviews the origin, nature, systematic distribution, and the respective function of the highly variable and diverse thread-forming structures in angiosperm anthers (including somewhat similar, rare features in ferns and gymnosperms). On one hand, such threads may function as pollen-connecting vectors in forming pollen dispersal units, as sporopollenin threads (viscin threads), e.g. in Onagraceae, or sporopollenin-less threads in surprisingly many other angiosperm families. On the other hand, as is known from theImpatiens — “pollen basket”, threads or ropes may be involved in pollen presentation. In addition, for the first time two new examples of “pollen baskets” in Boraginaceae and Scrophulariaceae are reported. InEchium the basket is formed by cellular elements from the modified septal regions, whereas inEsterhazya a similar effect is achieved in an analogous manner by trichomes of the epidermal layer of the thecal wall. There is obviously a different function of these seemingly very similar baskets: inEchium the feature acts preferably as a pollen presentation agent, whereas inEsterhazya the primary function is to prevent all the pollen from being dispersed too soon.
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  • 4
    ISSN: 1615-6102
    Keywords: Cell wall ; Development ; Pollen ; Tapetum ; Tilia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary InTilia platyphyllos, the anther tapetal cell walls undergo significant modifications from the tetrad stage onwards. During the tetrad stage the inner tangential and radial parts of the tapetal walls begin to dissolve, while the distal parts swell. After the tetrad stage, the distal and outer radial tapetal cell walls become covered by a thick, irregular, highly electron-dense, polysaccharide layer. Striking features of the maturing tapetal walls (microspore stage and later) are electron-translucent, structureless, unstainable angular areas of variable dimensions. Similar electron-translucent areas occur in the exine arcades and apertures, but also isolated in the locular fluid ofT. platyphyllos. Electron-translucent areas, that are also found in the exine arcades and tapetal cells of other angiosperms, can be interpreted as the products of poorly understood metabolic processes.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 501 (1983), S. 57-60 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Stabilization of —P=C〈 Bonds by Cyclic Silylhydrazones1,2-Diaza-3-sila-5-cyclopentenes unsubstituted at the 4-position react after lithiation with halophosphanes and -arsanes to give 1-4. The 4-methylated ring 5 reacts analogously with F2P—N(SiMe3)2 to give 6, but exchanges the dimethylsilyl group of the ring in reaction with PCl3, to give 1,2-diaza-3-phospha-3,5-cyclopentadien 7. The phosphaethenes 8 and 9 are formed from 4-trimethylsilylsubstituted lithiated rings by reaction with difluorophosphanes, F2PR (R = N(SiMe3) CMe3, N(SiMe3)2) and elimination of LiF and chlorosilane.
    Notes: In 4-Stellung unsubstituierte 1,2-Diaza-3-sila-5-cyclopentene reagieren nach Lithiierung mit Halogenphosphanen und -arsanen zu 1-4. Der 4-methylierte Ring 5 reagiert mit F2P—N(SiMe3)2 analog zu 6, mit PCl3 jedoch unter Austausch der Dimethylsilylgruppe des Ringes zum 1,2-Diaza-3-phospha-3,5-cyclopentadien 7. Aus 4-trimethylsilylsubstituierten lithiierten Ringen werden mit Difluorphopshanen, F2PR [R = N(SiMe3)CMe3, N(SiMe3)2], nach LiF- und Chlorsilanabspaltung die Phosphaethene 8 und 9 gebildet.
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  • 6
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It has been demonstrated in the past that single, two-dimensional coronal arcades are very unlikely driven unstable by a simple shear of the photospheric footpoints of the magnetic field lines. By means of two-dimensional, time-dependent MHD simulations, we present evidence that a resistive instability can result if in addition to the footpoint shear a slow motion of the footpoints towards the photospheric neutral line is included. Unlike the model recently proposed by van Ballegooijen and Martens (1989), the photospheric footpoint velocity in our model is nonsingular and the shear dominates everywhere. Starting from a planar potential field geometry for the arcade, we find that after some time a current sheet is formed which is unstable with respect to the tearing instability. The time of its onset scales with the logarithm of the magnetic diffusivity assumed in our calculation. In its nonlinear phase, a quasi-stationary situation arises in the vicinity of the x-line with an almost constant reconnection rate. The height of the x-line above the photosphere and the distance of the separatrix footpoints remain almost constant in this phase, while the helical flux tube, formed above the neutral line, continuously grows in size.
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  • 7
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The mass spectrometric fragmentation with 20- and 70 eV electrons of fifteen N,N′-diaryl-ethylenediamines (II-XVI) substituted in one benzene ring has been investigated. The compounds decompose to the ions a and b as shown in the Scheme (p. 408). The log [A]/[B] ratios correlate very well with Taft's σ0-(but not with σ- or σ+-) constants; ρ20 eV = -2·71; ρ70 eV = -2·21. This correlation suggests that the ions a and b possess the open structure indicated and not the phenoniumion structure c and d, and that the course of the fragmentation is largely determined by the relative stabilities of the ions formed by the decomposition of the molecular ion.
    Notes: Es wird die massenspektrometrische Fragmentierung mit 20- und 70 eV Elektronen von fünfzehn in einem Benzolkern substituierten N,N′-Diaryl-äthylendiaminen (II-XVI) untersucht. Diese Verbindungen zerfallen gemäss Schema S. 408 in die Ionen a und b. Die log [A]/[B]-Verhältnisse korrelieren sehr gut mit den Taftschen σ0-(aber nicht mit σ- oder σ+-) Werten; ρ20 ev = -2,71; ρ70 ev = -2,21. Diese Korrelation weist darauf hin, dass den Ionen a und b die angegebene offene Konstitution und nicht die Phenoniumionenstruktur cund dzukommt und dass die relative Stabilität der aus dem Molekular-Ion entstehenden Ionen in erster Linie die Fragmentierung bestimmt.
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  • 8
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The mass spectrum of N,N′,N″-triacetyl spermidine (I) is characterised by signals at m/e 143, 157 and 169. The degradation reactions which lead to the corresponding ions cannot be explained by known sequences. By examination of the mass spectra of derivatives of I, fragmentation mechanisms have been deduced.It is interesting to note that it is mainly the 1,3-diamino propane part of the spermidine molecule which participates in the mass spectral degradation to give the previously mentioned, characteristic ions.The two tertiary nitrogen atoms of the diamino propane part are the main promoters of these fragmentation reactions, as can be seen Schemes 2 to 7. Hence the mode of mass spectral degradation of the trifunctional spermidine derivative proceeds in a similar way to that of the bifunctional alkanes.
    Notes: Das Massenspektrum von N,N′,N″-Triacetylspermidin (I) zeichnet sich durch charakteristische Signale bei m/e 143, 157 und 169 aus. De Reaktionen, die zu den entsprecenden Ionen führen, lassen sich nicht durch Anweding einfacher Fragmentierungsreaktionen erklären. Auf der Bzasis der Massenspektren deuterierter Derivate von I werden Fragmentierungsmechanismen vorgeschlagen. Interessanterweise ist hauptsächlich der 1, 3-Diaminopropan-Teil und weiniger der 1, 4-Diamino-butan-Teil (Putrescin) des Spermidin-Moleküls an den Abbaureaktionen zu den erwänten Ionen beteilligt. Die beiden teriären Sticktoffatome des Diaminopropanteiles sind im wesentlichen die Promotoren der Fragmentierung, wie aus den Schematatas 2 bis 7 hervorgeht. Dieser Verlauf des massenspektrometrischen Zerfalls des trifunktionellen Spermidin-Derivates verläuft ser ähnlich dem Zerfall bifunktioneller Alkane.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 565 (1988), S. 81-90 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Chloro-Fluro-Exchange by Halogenated 1.3-DisilazanesAminofluorosilance (1-4) are obtained in the reaction of difluorosilanes with lithiated amines. Disilazanes (5,6) are formed in the reaction of LiNH(C6H3-iPr2) with CMe3SiF3 and C6H5SiF3. Lithium salts of 1-4 are dimers in n-hexane (7-10) and LiF adducts of iminosilanes in THF (11-14). The latter react with chlorsilanes (RSiCl3, R = Cl, H, Me) to give the substituted compounds 15-21 and LiCl. An intermolecular F/Cl exchange occurs with 15-20 which depends on the temperature, the solvents and ligands. 22-27 are formed.
    Notes: Aminofluorsilance (1-4) werden durch die Reaktion der Difluorsilane mit lithiierten Aminen erhalten. CMe3SiF3 und C6H5SiF3 reagieren zu Disilazanen (5,6). Die Lithiumsalze von 1-4 bilden in n-Hexan Dimere (7-10) und in THF LiF-Addukte von Iminosilanen (11-14). Letztere reagieren mit Chlorsilanen (RSiCl3, R = Cl, H, Me) unter LiCl-Abspaltung und Substitution zu 15-21 . 15-20 unterliegen einem intermolekularen F/Cl-Austausch, der temperatur-, lösungsmittel- und substituentenabhängig ist. Es entstehen 22-27 .
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  • 10
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Poly- and Spirocyclic Silylhydrazones  -  Synthesis and Molecular StructuresBulky aminotrifluorosilanes react with lithiated dimethylketone-hydrazone to give 1,2-diaza-3-sila-5-cyclopentenes  -  DSCP  -  (1, 2). The 4-silylated (3-5, 8-15) and siloxysilyl-substituted (17, 18) rings eliminate no halosilane or siloxane thermally. Lithiated 2 dimerises with LiF elimination to give the (2+2)cycloadduct of a 1,2-diaza-3-sila-3,5-cyclopentadiene (6). Lithiated DSCP reacts with MeSiF2N(CMe3)SiMe2CMe3 via a nucleophilic 1,3-methanide ion migration to form LiF and the spirocyclic compound 18. A compound with spirocyclic silicon (21) is formed in the reaction of bis(1,2-diaza-3-sila-5-cyclopenten-4-yl)difluorosilane (19) and the lithium salt of dimethyl-ketone-tert-butylhydrazone. The crystal structures of 6 and 21 are reported.
    Notes: Voluminöse Aminotrifluorsilane reagieren mit lithiiertem Dimethylketon-hydrazon zu 1,2-Diaza-3-sila-5-cyclopentenen  -  DSCP  -  (1, 2). In 4-Stellung silyl- (3-5, 8-15) und siloxysilylsubstituierte (17, 18) Ringe spalten thermisch kein Halogensilan oder Siloxan ab. Lithiiertes 2 dimerisiert unter LiF-Abspaltung zum (2+2)Cycloaddukt eines 1,2-Diaza-3-sila-3,5-cyclopentadiens (6). Lithiiertes DSCP reagiert mit MeSiF2N(CMe3)SiMe2CMe3 unter LiF-Ab-spaltung und nucleophiler 1,3-Methanidionen-Wanderung zum Spirocyclus 18. Eine Verbindung mit spirocyclischem Silicium (21) entsteht in der Reaktion des Bis-(1,2-diaza-3-sila-5-cyclopenten-4-yl)-difluorsilans (19) mit dem Lithiumsalz des Dimethylketon-tert-butyl-hydrazon. Die Kristallstrukturen von 6 und 21 werden mitgeteilt.
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