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  • 1
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    The Merensky Cyclic Unit and its impact on footwall cumulates below Normal and Regional Pothole reef types in the Western Bushveld Complex (2006)
    Springer
    Details
    Publikationsdatum: 2006-12-14
    Print ISSN: 0026-4598
    Digitale ISSN: 1432-1866
    Thema: Geologie und Paläontologie
    Publiziert von Springer
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    AKTUELLE ARTIKEL
  • 2
    Digitale Medien
    Digitale Medien
    Stability in cyclic epidemic models (1985)
    Springer
    Journal of mathematical biology 22 (1985), S. 303-311 
    Details
    ISSN: 1432-1416
    Schlagwort(e): Epidemiology ; Cyclic models ; Stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Mathematik
    Notizen: Abstract A general formulation for a family of cyclic epidemic models with density-dependent feedback mechanisms and removed classes is presented. A parameter, λ, related to the basic reproductive rate determines the asymptotic behaviour of solutions of the model. It is shown that if λ〈1 the trivial solution is globally stable, and if λ〉1 it is conditionally stable. The results are applied to a set of differential equations that has been used to model the life cycle of a parasite that has two hosts.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00276488
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  • 3
    Digitale Medien
    Digitale Medien
    Threshold quantities for helminth infections (1995)
    Springer
    Journal of mathematical biology 33 (1995), S. 415-434 
    Details
    ISSN: 1432-1416
    Schlagwort(e): Deterministic epidemic models ; Helminths ; (Non) autonomous systems ; Threshold behaviour ; Basic reproduction ratio ; Heterogeneity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Mathematik
    Notizen: Abstract For parasites with a clearly defined life-cycle we give threshold quantities that determine the stability of the parasite-free steady state for autonomous and periodic deterministic systems formulated in terms of mean parasite burdens. We discuss the biological interpretations of the quantities, how to deal with heterogeneity in both parasite and host populations, how to incorporate the effects of periodic discontinuities, and the relation of the threshold quantities to the basic reproduction ratio R 0. Examples from the literature are given. The analysis of the periodic case extends easily to ‘micro-parasitic’ systems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00176380
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    Artikel (Nationallizenzen)
    Volltext
  • 4
    Digitale Medien
    Digitale Medien
    Membrane potential and resistance changes induced in salivary gland acinar cells by microiontophoretic application of acetylcholine and adrenergic agonists (1978)
    Springer
    The journal of membrane biology 39 (1978), S. 297-312 
    Details
    ISSN: 1432-1424
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Summary The effects of microiontophoretic applications of catecholamines and acetylcholine on parotid acinar cell membrane potential and resistance were investigated using intracellular microelectrode recording in superfused segments of mouse parotid or rat submandibular glands. Short pulses of acetylcholine and α-adrenergic agonists had similar effects, consisting of a marked decrease in membrane resistance accompanied by an initial depolarization or hyperpolarization depending on the level of the resting membrane potential. This initial response was followed by a slow hyperpolarization occurring at a time when the resistance was increasing towards the prestimulation level. The equilibrium potential for the initial potential change caused by excitation of the cholinergic receptors was investigated directly by setting the membrane potential at different levels by injecting direct current and stimulating the same cell repeatedly with equal doses of acetylcholine. The equilibrium potential was found to be about −55 mV. The delayed hyperpolarization could not be reversed by passing hyperpolarizing current, but actually increased in size with higher membrane potentials. The minimum latency of the effect of acetylcholine or α-adrenergic agonists was 200–500 msec. Excitation of β-adrenoceptors caused, after a long latency of several seconds, a small depolarization. Epinephrine induced a combined α- and β-adrenergic response, with the α-component predominating. Blocking the α-adrenoceptors with phentolamine revealed the β-adrenergic depolarization, while blocking the β-adrenoceptors with propranolol caused the components of the α-adrenergic response to become more pronounced. All three receptors (α- and β-adrenoceptors and cholinergic receptors) were present in individual acini.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01869896
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  • 5
    Digitale Medien
    Digitale Medien
    A simple parasite model with complicated dynamics (1998)
    Springer
    Journal of mathematical biology 37 (1998), S. 272-290 
    Details
    ISSN: 1432-1416
    Schlagwort(e): Key words: Deterministic epidemic models ; Helminths ; Dynamical systems
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Mathematik
    Notizen: Abstract.  During their first year of life sheep acquire parasites through grazing, and simultaneously build up an immunity to infection. At the beginning of each year non-immune lambs are introduced onto contaminated pasture. We represent this process by differential equations describing the within-year dynamics, and defining a difference equation that describes the between-year dynamics. An example with two system parameters is analysed in detail. It is shown that regions exist in parameter space where periodic (between-year) or aperiodic solutions occur. Parasite control schemes could change the system dynamics from a stable equilibrium to complicated long-term fluctuations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002850050129
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    Artikel (Nationallizenzen)
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  • 6
    Digitale Medien
    Digitale Medien
    Stability in a two host epidemic model (1982)
    Springer
    Journal of mathematical biology 14 (1982), S. 71-75 
    Details
    ISSN: 1432-1416
    Schlagwort(e): Epidemiology ; Two host models ; Stability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Mathematik
    Notizen: Abstract An epidemic model is derived for a two host infectious disease. It is shown that if a non-trivial equilibrium solution exists, it is globally stable. This result is also proved for a similar one host model.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02154753
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    Artikel (Nationallizenzen)
    Volltext
  • 7
    Digitale Medien
    Digitale Medien
    Enzymic synthesis of γ-coniceine in Conium maculatum chloroplasts and mitochondria (1981)
    Springer
    Plant cell reports 1 (1981), S. 10-13 
    Details
    ISSN: 1432-203X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Further studies of the transaminase responsible for the first committed step in alkaloid formation in Conium maculatum have shown the L-alanine: 5-ketooctanal transaminase to occur in both the mitochondria and chloroplast. Experiments suggest that these enzymes are the isoenzymes Transaminase A and B respectively previously isolated by the author. It is suggested that the chloroplast enzyme is normally responsible for alkaloid production.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00267647
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    Artikel (Nationallizenzen)
    Volltext
  • 8
    Digitale Medien
    Digitale Medien
    Antimalarial activity of Artemisia annua flavonoids from whole plants and cell cultures (1992)
    Springer
    Plant cell reports 11 (1992), S. 637-640 
    Details
    ISSN: 1432-203X
    Schlagwort(e): Artemisia annua L. ; cell culture ; methoxylated flavones ; potentiation ; artemisinin ; antimalarial activity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Cell suspension cultures developed from Artemisia annua exhibited antimalarial activity against Plasmodium faldparum in vitro both in the n-hexane extract of the plant cell culture medium and in the chloroform extract of the cells. Trace amounts of the antimalarial sesquiterpene lactone artemisinin may account for the activity of the n-hexane fraction but only the methoxylated flavonoids artemetin, chrysoplenetin, chrysosplenol-D and cirsilineol can account for the activity of the chloroform extract. These purified flavonoids were found to have IC50 values at 2.4 – 6.5 × 10−5M against P. falciparum in vitro compared with an IC50 value of about 3 × 10−8M for purified artimisinin. At concentrations of 5 × 10−6M these flavonoids were not active against P. falciparum but did have a marked and selective potentiating effect on the antiplasmodial activity of artemisinin.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00236389
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    Artikel (Nationallizenzen)
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  • 9
    Digitale Medien
    Digitale Medien
    Studies on Ailanthus altissima cell suspension cultures (1986)
    Springer
    Plant cell reports 5 (1986), S. 387-390 
    Details
    ISSN: 1432-203X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The uptake of L-[methylene 14C]-tryptophan from culture medium and the subsequent incorporation of the radiolabel into canthin-6-one, 1-hydroxycanthin-6-one and 1-methoxycanthin-6-one has been demonstrated in cell suspension cultures of Ailanthus altissima. Efficient incorporation has been shown to depend significantly on the time of feeding. Furthermore, feeding of L-tryptophan, at levels of 500 mg/l resulted in improved alkaloid yields, particularly when fed during the lag phase of the growth cycle.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00268609
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    Artikel (Nationallizenzen)
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  • 10
    Digitale Medien
    Digitale Medien
    Studies on Ailanthus altissima cell suspension cultures. Uptake of L-[methyl-14C]methionine and incorporation of label into 1-methoxycanthin-6-one (1987)
    Springer
    Plant cell reports 6 (1987), S. 242-243 
    Details
    ISSN: 1432-203X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Time-course studies of the uptake of L-[methyl 14C]-methionine have shown rapid uptake by Ailanthus altissima cells when fed at weekly stages throughout the growth cycle. The radio-label from [14C]-methionine was shown to be incorporated into 1-methoxycanthin-6-one with the highest level of incorporation being achieved with cells fed late in the growth phase.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00268490
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    Artikel (Nationallizenzen)
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