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  • 1
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Electrophoresis following digestion of Myzus persicae genomic DNA with HindIII showed the presence of a prominent band of approximately 200 bp whereas a faint electrophoretic band corresponding to DNA fragments of about 3000 bp was observed after digestion with ApaI. In situ digestion with restriction enzymes, followed by in situ nick translation, showed that ApaI targets are localized at the nucleolus organizer-bearing X telomeric region, whereas HindIII restriction sites are clustered in intercalary C-positive areas on the same X chromosome. Fluorescent in situ hybridization (FISH) carried out by using digoxygenin-labeled HindIII repeats as probe fully confirmed overlapping between the hybridization sites of this probe and the AT-rich intercalary heterochromatic bands on the X chromosome. These findings, together with published data, allow us to conclude that the M. persicae genome possesses three classes of C-positive heterochromatin: (i) a GC-rich argentophilic band located on one telomere of the X chromosome that contains ApaI targets; (ii) AT-rich intercalary bands located on the X chromosome containing clustered HindIII fragments; (iii) AT-rich telomeric bands, located on autosomes, consisting of HaeIII repeats. Molecular analysis has shown that the length of the HindIII repeat consensus sequence is 189 bp with an AT content of 67%. Southern blotting with HindIII monomers revealed a regular ladder of bands composed of multimers of basic length that are characteristic of satellite DNAs. The HindIII repeat displays other features typical of eukaryotic satellite arrays such as overlapping with heterochromatic bands and a high degree of sequence similarity among monomers (84%–94%). A similarity plot showed that sequences were particularly variable in the 50–100 bp region whereas they proved to be highly conservative in the first 50 bp, thus suggesting that this portion of the repeat might be functionally important.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0045-6039
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 9 (1965), S. 385-398 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Four polystyrene samples, with molecular weight ranging from 43,300 to 1,112,000 have been irradiated in benzene solution by γ-rays, at four different intensities. Data obtained through intrinsic viscosity and light-scattering measurements on irradiated polymers indicate that, at each intensity, there exists a molecular weight below which any polymer chain is no further degraded. An equilibrium between absorbed and dissipated energy by the macromolecule is supposed, and the equation, MlimI = const. arrived at in a previous study, is verified also by the present experimental results.
    Additional Material: 9 Ill.
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  • 5
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: With an increasing gradient, the intrinsic viscosity of a high molecular weight polyisobutylene (M̄n = 7 × 106) in polybutene oil L.100 (ηs = 5 poise) first drops to a minimum and then rises again. The minimum occurs at β = M[η]0ηsG/NkT = 240, which is about ten times the value predicted by the dumbbell model. Such a shift to larger gradient is in good agreement with the more realistic necklace model of macromolecules in a good solvent. The increase of intrinsic viscosity after the minimum is nearly linear with the gradient and continues beyond the value at zero gradient. Experiments with capillaries of different length-to-diameter ratios yield identical flow curves so that one may exclude the possibility that the observed upturn is an artifact caused by end effects or time dependence of viscosity.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 30 (1958), S. 175-186 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In a previous paper we gave evidence for the validity of the Einstein-Stokes law for determining molecular dimensions from the diffusion coefficient. In this work, we report on measurements on some polyoxyethylenes in water and on low molecular weight polystyrenes in benzene. The possibility of obtaining exact information regarding the molecular dimensions and the interactions with the solvent have been stated. In high polymers, the dimensions are considerably influenced by the molecular expansion coefficient, α; as a result of this, in studying structural properties of the molecules in solution, the measurements must be carried out in ideal solvents. We have developed a method based on viscometric measurements, which makes possible determination of the composition of the ideal mixture for a given temperature, where such a mixture consists of two components, of which one is a good solvent, and the other is a precipitating agent (non-solvent). Such measurements have been made on 11 fractions of polystyrene from which it has been possible to determine the expansion coefficient α and the dimensions of the unperturbed molecules at 34°C.
    Additional Material: 6 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 41 (1960), S. 31-39 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Viskositätszahl [η] und der Diffusionskoeffizient D wird als Funktion des Molekulargewichts an Polystyrol-Fraktionen im Molekulargewichtsbereich von 600 bis 50 000 untersucht.Die Ergebnisse zeigen, daß für die niedermolekularen Polymeren, unabhängig von der Natur des Lösungsmittels, d.h. für ein gutes oder ein Θ-Lösungsmittel, die zwei Gleichungen: \documentclass{article}\pagestyle{empty}\begin{document}$\begin{array}{*{20}c}{{\rm D} = {\rm K} \cdot {\rm M}^{ - 0.5} } & [ \\ \end{array} {\rm \eta }] = {\rm K}' \cdot {\rm M}^{0.5} $\end{document} gültig sind.Über die Dimensionen der untersuchten Fraktionen werden einige Betrachtungen angestellt.
    Notes: The behaviour of the limiting viscosity number [η] and diffusion coefficient D is studied as function of molecular weight, for some polystyrene fractions with molecular weight ranging from 600 to 50,000.The experimental results show that the two equations: \documentclass{article}\pagestyle{empty}\begin{document}$\begin{array}{*{20}c}{{\rm D} = {\rm K} \cdot {\rm M}^{ - 0.5} } & [ \\ \end{array} {\rm \eta }] = {\rm K}' \cdot {\rm M}^{0.5} $\end{document} hold for low polymers irrespective of solvent nature, i.e. good and Θ-solvent.Some considerations are made about the dimensions of the studied fractions.
    Additional Material: 2 Ill.
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  • 8
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 10 (1971), S. 213-213 
    ISSN: 1435-1528
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The pressure dependencedT g /dP of glass transition temperatureT g has received considerable interest due to its connection with solid state thermodynamic properties and theories of glass transition. Free volume considerations (1, 2) led to an estimate of the pressure effect onT g , showing thatdT g /dP had to depend on thermal expansion and compressibility changes atT g through the equation: [1] $$\frac{{dT_g }}{{dP}} = \frac{{\Delta \beta }}{{\Delta \alpha }}$$ whereΔβ=β e −β g andΔα=α e −α g Later work (3, 4, 5, 6) has shown that eq. [1] is not verified by experimental facts, the ratioΔβ/Δα being much larger than (dT g /dP) exp. Recent analysis of the properties of glasses obtained under different pressures have complicated the situation, showing that the experimental value ofdT g /dP depends, of course, on the polymer usedbut also on the experimental procedure used in its determination. Since it is obvious that in order to measure anyΔT g -value we need to operate on at leasttwo glasses, these should be identical in all properties which could influenceT g except pressure. Any difference in morphology,which could lead to a change in T g at constant pressure, should therefore be avoided in order to get a sound value for the pure pressure effectdT g /dP. To reveal this effect, we have performed (7)dT g /dP determinations on two polymers, polyvinylacetate (PVAC) and polyvinylchloride (PVC), following three different procedures: A. Measurement of the changeΔT g induced by application of a pressure incrementΔP on the liquid polymer (T〉T g ). This is the procedure normally used; the liquid is cooled down at a fixed rate of temperature change (∼5 °C/day) andT g is dilatometrically recorded at 1 atmosphere. Then the polymer is taken again to the liquid state, pressure ΔP is applied and, at the same rate, the system is cooled down isobarically; the newT g is recorded anddT g /dP calculated. B. Measurement of the change ΔTg induced by application of a pressure increment ΔP on the glassy polymer (T〈T g ). Once determinedT g at 1 atmosphere, pressureΔP is applied on the glass, time is given to the system to equilibrate; then the glass is heated isobarically. Intersection of the glassy line to the liquid line in a volume/temperature plot gives the newT g and therefore allows the calculation ofdT g /dP. C. Measurement ofΔT g during the heating of a glass along an isochor (5, 8). Here the polymer glass is heated at constant volume, by application of an increasing pressure at increasing temperatures given by(∂P/∂T) v . By repeating this procedure two times, starting from two different specific volumes of the glass, two values ofT g at different pressures can be recorded anddT g /dP calculated. Table 1 shows the result of this work Polymer A dT g /dP, °C/atm B C PVAC 0.015 0.037 0.022 PVC 0.013 0.038 0.028 Comparison of values for different procedures shows quite convincingly howdT g /dP, at a given heating or cooling rate, is a property not only of the polymer but also of the experiment. Any information which, like the pressure effect onT g , is based on a comparison between two or more glasses, should be therefore carefully analysed in terms of other contributions, besides pressure, to the total change inT g .
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  • 10
    ISSN: 1435-1528
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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