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  • 1
    Electronic Resource
    Electronic Resource
    Calculation of shear influences on the phase separation of polymer blends exhibiting upper critical solution temperatures (1994)
    Springer
    Rheologica acta 33 (1994), S. 99-1071 
    Details
    ISSN: 1435-1528
    Keywords: Shear flow ; UCST ; polymer blend ; phase separation ; stored energy ; closed miscibility gap
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Calculations were performed on the basis of a generalized Gibbs energy of mixing G γ, which is the sum of the Gibbs energy of mixing of the stagnant system and E s, the energy stored in the system during stationary flow. With increasing shear rate γ, the demixing temperatures shift to lower values (shear-induced mixing; diminution of the heterogeneous area), then to higher values (shear-induced demixing), and finally to lower values again before the effects fade out. The details of the rather complex phase diagrams resulting for a given shear rate are primarily determined by a band in the T/χ plane (χ = mole fraction) within which (∂2 E s/∂χ2) T 〈0 (i.e., E S acts towards phase separation). There are two ranges of γ within which closed miscibility gaps can exist: The more common outer islands are partly or totally situated outside the equilibrium gap (and within the above mentioned band). As γ is raised they break away from the “mainland” at the upper end of the first region of shear-induced mixing and shift to T〉UCST where they submerge. Bound to a suitable choice of parameters, a second kind of closed miscibility gaps, the inner islands, which always remain within the equilibrium solubility gap (and outside the band of negative curvature of E S) is additionally observed. This time the islands break away from the “mainland” at the lower end of the first region of shear-induced mixing where they also submerge. The present findings are compared with the results of previous calculations for LCSTs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366754
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  • 2
    Electronic Resource
    Electronic Resource
    Solidification behavior of the theta system 2-propanol/poly(n-butyl methacrylate) I. Influences of thermoreversible gelation on stationary flow (1994)
    Springer
    Rheologica acta 33 (1994), S. 159-164 
    Details
    ISSN: 1435-1528
    Keywords: Zero shear viscosity ; polymer melts ; polymer solutions ; magnetoviscometer ; thermoreversible gelation ; glass transition temperatures ; critical molecular weight ; master curves
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Zero shear viscosities, η0, were determined by means of a magnetoviscometer for melts of poly(n-butyl methacrylate) (M = 8.7 to 450 kg/mol, T =53.5 to 200°C) and for concentrated solutions of the highest molecular weight sample in isopropanol (T = 34.8 to 131.5 °C). Master curves can be constructed in both cases if the reference temperature is set proportional to the gelation temperature of the particular fluid. Special intersegmental interactions (eventually leading to thermoreversible gelation) can above all be felt in η0 (T) and in M c , the critical molecular weight determined in plots of log η0 vs. log M. As the temperature is lowered, the behavior changes from WLF to Arrhenius, and M c declines considerably. The former observation is explained by analogy to the transition from fragile to hard glasses resulting from increased crosslinking. The latter effect can also be rationalized in terms of a physical network reducing the molecular weight that is required for the formation of entanglements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00437300
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  • 3
    Electronic Resource
    Electronic Resource
    Easy determination of ploidy level in Arabidopsis thaliana plants by means of pollen size measurement (1994)
    Springer
    Plant cell reports 13 (1994), S. 652-656 
    Details
    ISSN: 1432-203X
    Keywords: Transgenic Arabidopsis ; Ploidy ; Pollen size
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cytogenetic examination of transgenic Arabidopsis thaliana (L.) Heynh. plants obtained by Agrobacterium-mediated gene transfer to cotyledon- and root-explants or by direct gene transfer into protoplasts revealed a high percentage of tetraploid or aneuploid transformants. Depending on the transformation procedure used, 13% (root explant transformation), 33% (cotyledon explant transformation), or 38% (direct gene transfer) of the transformants showed aberrant ploidy levels. A good correlation between the ploidy level of a plant and the size of its pollen grains was observed. This allows quick and simple testing of the ploidy level of transgenic Arabidopsis plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232939
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  • 4
    Electronic Resource
    Electronic Resource
    Modellbildung in der biologie (1992)
    Springer
    Naturwissenschaften 79 (1992), S. 289-299 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01138706
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of antisense repression of the chloroplast triose-phosphate translocator on photosynthetic metabolism in transgenic potato plants (1994)
    Springer
    Planta 193 (1994), S. 174-180 
    Details
    ISSN: 1432-2048
    Keywords: Antisense repression ; Photosynthesis ; Solanum ; Starch synthesis ; Triose phosphate translocator
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The introduction of an antisense DNA into transgenic potato (Solanum tuberosum L.) plants decreased the expression of the chloroplast triose-phosphate translocator and lowered its activity by 20–30%. With plants propagated from tubers, the effect of the transformation on photosynthetic metabolism was analysed by measuring photosynthesis, the formation of leaf starch, and the total and subcellular metabolite contents in leaves. Although the transformants, in contrast to those propagated from cell cultures, did not differ from the wild-type plants in respect to rates of photosynthesis, plant appearance, growth and tuber production, their photosynthetic metabolism was found to be severely affected. The results show that the decrease in activity of the triose-phosphate translocator in the transformants caused a fourfold increase in the level of 3-phosphoglycerate and a corresponding decrease in inorganic phosphate in the stromal compartment, resulting in a large increase in the synthesis of starch. Whereas during a 12-h day period wild-type plants deposited 43% of their CO2 assimilate into starch, this value rose to 61–89% in the transformants. In contrast to the wild-type plants, where the rate of assimilate export from the leaves during the night period was about 75% of that during the day, the export rate from leaves of transformants appeared to be much higher during the night than during the day. As the mobilisation of starch occurs in part hydrolytically, resulting in the formation of glucose, the triose-phosphate translocator loses its exclusive function in the export of carbohydrates from the chloroplasts when the photoassimilates are temporarily deposited as starch. It appears that by directing the CO2 assimilates mainly into starch, the transformants compensate for the deficiency in triose-phosphate translocator activity in such a way that the productivity of the plants is not affected by the transformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192527
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  • 6
    Electronic Resource
    Electronic Resource
    Comment on the observation of magnetoacoustic quantum oscillations in UBe13 (1993)
    Springer
    The European physical journal 91 (1993), S. 135-137 
    Details
    ISSN: 1434-6036
    Keywords: 72.55.+S
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The origin of previously reported magnetic quantum oscillations in UBe13 is possibly due to Al inclusions. New measurements of the a.c. susceptibility show Al inclusions which result from the method of crystal growth using aluminium as flux. We discuss the distribution and form of the inclusions and compare our dHvA measurements with those of the γ-orbits of Al.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01315226
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  • 7
    Electronic Resource
    Electronic Resource
    Systems analysis in cell biology: From the phenomenological description towards a computer model of the intracellular signal transduction network (1993)
    Springer
    Cellular and molecular life sciences 49 (1993), S. 245-257 
    Details
    ISSN: 1420-9071
    Keywords: Structured analysis ; mathematical modelling ; stochastic simulation ; cell cycle control ; tumor biology ; calcium oscillations ; signal transduction ; Structured Biological Modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In this paper we introduce a systematic approach for the modelling of complex biological systems which is especially useful for the analysis of signal transduction mechanisms in cell biology. It is shown that systems analysis in form of top-down levelled dataflow diagrams provides a powerful tool for the mathematical modelling of the system in terms of a stochastic formulation. Due to the exact formulation, the consistency of the model with the experimental results can be tested by means of a computer simulation. The method termed Structured Biological Modelling (SBM) is illustrated by modelling some aspects of the second messenger network which regulates cell proliferation. As an example for the strainghtforward development of a mathematical description a stochastic computer model for intracellular Ca2+ oscillations is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01923534
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetoacoustic quantum oscillations in the heavy fermion superconductor UBe13 (1991)
    Springer
    The European physical journal 85 (1991), S. 159-160 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In UBe13 magnetoacoustic quantum oscillations (MAQO) are observed for the attenuation- and the sound velocity-changes in the superconducting and normal state. The observed extremal areas and the effective masses are small.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313215
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  • 9
    Electronic Resource
    Electronic Resource
    Presence of a transposon-like element in the promoter region of an inactive patatin gene in Solanum tuberosum L. (1990)
    Springer
    Plant molecular biology 14 (1990), S. 239-247 
    Details
    ISSN: 1573-5028
    Keywords: patatin ; potato ; transposon ; gene inactivation ; β-glucuronidase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The promoter of the PGT3 patatin gene belonging to the class II subfamily is highly homologous to other class II patatin genes except for a 736 bp insertion in front of the putative transcription start site. The insertion is characterized by structural features resembling a transposable element such as an 11 bp inverted repeat at the termini and an 8 bp duplication flanking the insertion site. Despite the high homology to active patatin genes, fusion of its promoter to the β-glucuronidase reporter gene does not lead to detectable β-glucuronidase (GUS) activity in transgenic potato or tobacco plants, suggesting that the inactivation of this gene might be caused by the insertion of the transposon like element.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00018564
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  • 10
    Electronic Resource
    Electronic Resource
    Isolation and characterization of P-type H+-ATPase genes from potato (1994)
    Springer
    Plant molecular biology 26 (1994), S. 979-988 
    Details
    ISSN: 1573-5028
    Keywords: ATPase ; phloem loading ; plasma membrane ; Solanum tuberosum L. ; multigene family ; sucrose transporter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract H+-ATPase cDNAs were identified in a potato leaf library using an Arabidopsis gene as a probe. Based on their sequences, the clones could be grouped into at least two classes. A similar classification was obtained from the analysis of sequence data from four tobacco genes. Both potato genes are expressed in all tissues analysed, higher levels of expression were found in leaves and stem than in roots and tubers. For both genes, no significant differences in level of expression could be detected under a variety of conditions such as cold treatment, anaerobiosis, sucrose induction or treatment with a synthetic cytokinin. Only 2,4-D and prolonged periods of darkness lead to a slight reduction in mRNA levels. The reduction in darkness was compensated after transfer of the plants back into the light. Expression of the ATPase genes remained constant in transgenic plants which are inhibited in phloem loading due to antisense inhibition of the sucrose transporter. On the other hand, expression of the sucrose transporter is inducible by auxin and cytokinin but not by sucrose. Taken together, these data suggest that at least the two plasma membrane H+-ATPase genes analysed are rather constant in their expression and that either other genes respond to external stimuli or that most of the regulation occurs at the post-transcriptional level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00028864
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