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  • Sitobion fragariae  (3)
  • Atomic, Molecular and Optical Physics  (2)
  • Inorganic Chemistry
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  • 1
    ISSN: 1570-7458
    Keywords: Sitobion avenae ; Sitobion fragariae ; RAPD ; PCR ; microsatellites ; mtDNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A set of molecular markers to differentiate the aphid (Hemiptera: Aphidoidea) species Sitobion avenae (Fabricius) from Sitobion fragariae (Walker), is presented. These markers correspond to (1) a region of the mitochondrial DNA, (2) five species-specific RAPD banding patterns and (3) four microsatellite loci. Each of the markers was able to clearly distinguish between the species. The utility of each molecular marker is discussed. Mitochondrial DNA is best applicable to species determination and relative abundance, RAPDs to the evaluation of genetic diversity, and microsatellites to the assessment of the population genetic structure; the combined use of mtDNA with the other techniques can be of importance when the presence of hybrids is suspected, and RAPDs with microsatellites are best used together in population genetics and host preference studies.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1570-7458
    Keywords: sieve element ; salivation ; aphid ; plant resistance ; wheat ; Sitobion fragariae ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Extended sieve element salivation (E1 waveform in the electrical penetration graph) is a characteristic activity during early sieve element punctures, particularly in resistant plants. In order to explore a chemically-mediated mechanism of resistance associated with sieve element salivation, we compared the pattern of feeding behaviour of the aphid, Sitobion fragariae (Walker), on two cultivars of the wheat Triticum aestivum L., with different concentrations of hydroxamic acids (Hx). During 24 h of electronic monitoring, aphids dedicated over 50% of the total time to phloem ingestion from the sieve elements. Total time allocated to E1 in the experiment, time to first E1 within the experiment, time allocated to E1 before a sustained phloem ingestion (E2) and the contribution of sieve element salivation to the phloem phase (E1/[E1+E2]) were significantly higher in the high-Hx cultivar. The increased salivation in plants with higher contents of Hx suggests the existence, at least in this system, of a chemically-mediated sieve element constraint.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-1561
    Keywords: Aphid ; experience ; probing behavior ; sieve elements ; salivation ; cell punctures ; hydroxamic acids ; EPG ; Sitobion fragariae ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract We hypothesized that aphids after previous exposure to hydroxamic acids (Hx), a family of secondary plant compounds deleterious to aphids, are able to reduce their subsequent exposure to them. This hypothesis was tested by evaluating the time to produce salivation into a sieve element (SSE) by the aphid Sitobion fragariae on seedlings of two wheat cultivars of Triticum aestivum differing in their concentration of Hx. The total time to produce a first SSE was significantly longer in the high-Hx cultivar; however, the subsequent, second SSE (first SSE after interruption of probing) in this cultivar was significantly reduced, reaching the level observed in the low-Hx plants. Therefore, a strategy to reduce the exposure to secondary compounds was observed only in the second SSE in high-Hx plants. When the experimental plant was replaced by a new unattacked plant after the first SSE, aphids did not change the behavior described, thus excluding an aphid-induced plant susceptibility. The number of cell punctures and accumulated duration was not affected by previous exposure to Hx, either in low or high Hx cultivars. Total time and pathway time but not cell punctures, seem to be the variables affected by previous exposure to Hx.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 23 (1983), S. 135-146 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methods are reported for construction of closed-form optical potentials that provide useful L2-basis-set approximations to the discrete and continuum Schrödinger states of self-adjoint Hamiltonian operators. The potentials are obtained employing information from a finite (Lanczos) reference space only, but nevertheless correspond to explicit summation over an infinite-dimensional remainder space. Connections are indicated between the Stieltjes-Tchebycheff orbital solutions of the resulting optical-potential Schrödinger problem and previously described corresponding moment-theory approximations to spectral densities and distributions. Use of a Lanczos basis insures that the orbital eigenvalues are generalized Gaussian or Radau quadrature points of the spectral density, and that their (reciprocal) norms provide the associated quadrature weights. Convergence of the orbitals in the limit of high order is obtained to Schrödinger eigenstates of finite norm in the discrete spectral region, and to scattering states of improper (infinite) norm in the essential portion of the spectrum. In finite orders the spatial characteristics of the Stieltjes-Tchebycheff orbitals correspond to spectral averages in the neighborhoods of the quadrature points over the correct Schrödinger states. Explicit closed-form expressions are obtained for the spectral content of individual orbitals in terms of orthogonal polynomials without reference to the correct Schrödinger states. A computational application to regular Coulomb l waves illustrates the nature and convergence of the development.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Computational studies are reported of Stieltjes orbitals for Hilbert-space descriptions of discrete and continuum molecular electronic eigenstates. Particular attention is focused on the identification of N → V π(π → π*) and N → Vσ(σ → σ*) intravalence contributions to photoexcitation and ionization spectra in CO and H2CO molecules. Three-dimensional graphical representations of appropriate Stielties orbitals serve to identify the σ → σ* transitions of Mulliken as photoionization resonances above threshold in these compounds, whereas the corresponding π → π* contributions are spectrally localized as familiar discrete excited states. The development illustrates the nature and properties of Stieltjes orbitals, and demonstrates their utility in studies of both discrete and continuum excitation spectra on a common basis.
    Additional Material: 7 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 405 (1974), S. 315-328 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Catalysis of p-H2 Conversation on Pure and CO-poisoned PlatinumThe reaction has been studied on a Pt foil using u. h. v. cleaning conditions. The rate of the conversion is extremely high on a clean Pt surface, the activation energy being 4.1 kcal/mole. CO/poisons reversibly. After preadsorption of CO on half of the Pt surface the activity descreases to 6% of the original value and the activation energy increases p to 8.4 kcal/mole. In the discussion a direct correlation between the activation energy and the lowest adsorption heats of hydrogen is proposed. The reaction occurs predominantly on centres with lowest bond strength.
    Notes: Die Reaktion wurde an einer Pt-Folie unter UHV-Reinheitsbedingungen untersucht. An reiner Pt-Oberfläche verläuft die Reaktion extrem schnell mit einer Aktivierungsenergie von 4,1 kcal/Mol. CO vergiftet reversibel. Bei Vorbelegung der halben Pt-Oberfläche mit CO fällt die Aktivität auf 6% des Ausgangswertes während die Aktivierungsenergie auf 8,4 kcal/Mol ansteigt. Diskutiert wird ein direkter Zusammenhang der Aktivierungsenergie mit den minimalen Adsorptionswärmen des Wasserstoffs. Die Umwandlung erfolgt bevorzugt an Zentren mit geringster Bindungsfestigkeit.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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