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  • Polymer and Materials Science  (12)
  • 5-Azacytidine  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Inhibition of shoot induction by 5-azacytidine and 5-aza-2′-deoxycytidine in Petunia involves DNA hypomethylation (1997)
    Springer
    Plant cell reports 16 (1997), S. 719-724 
    Details
    ISSN: 1432-203X
    Schlagwort(e): Key wordsPetunia hybrida ; 5-Azacytidine ; 5-Aza-2′-deoxycytidine ; Hypomethylation ; Shoot-forming cultures
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Shoot bud regeneration from Petunia leaf disks was inhibited when they were cultured with the demethylating agents, 5-azacytidine (AzaC) and 5-aza-2′-deoxycytidine (AzadC), in shoot induction (SI) medium. Explants induced shoot primordia if they were transferred after 1 week from the medium containing the drugs to medium without drugs. The fresh weight of leaf disks cultured on SI medium for 2 weeks in the presence of the drugs was 60–80% lower when compared to control shoot-forming cultures. Internode length was reduced when shoots were transferred to phytohormone-free Murashige and Skoog medium containing the drugs. However, no other morphological abnormalities were seen in these shoots, even at 20 µm AzaC or 5 µm AzadC. Coupled restriction enzyme digestion (with HpaII and MspI) and random amplification of genomic DNA was performed to detect the level of methylation of CCGG sites in the DNA of the explants exposed to AzaC and AzadC. Over 15 amplified bands were detectable in the control. Five of these bands were absent in the amplified products when digested DNA from the drug-treated explants was used as the template, showing that hypomethylation of DNA had occurred. This suggests that inhibition of shoot bud formation in the presence of the drugs AzaC and AzadC may be due to the altered methylation status.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002990050309
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  • 2
    Digitale Medien
    Digitale Medien
    Studies on polymerization of vinyl acetate using ylide as an initiator and degradative transfer agent (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 27 (1989), S. 807-815 
    Details
    ISSN: 0887-624X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Polymerization of vinyl acetate initiated by β-picolinium p-chlorophenacylide was carried out at 30, 35, and 40°C, using conventional dilatometric technique. The initiator and the monomer exponent values were 0.80 ± 0.15 and unity, respectively. The polymerization was inhibited in the presence of hydroquinone, but was favored by nonpolar solvent and polymerization temperature. The energy of activation was 90.3 KJ mol-1. An average value of kp2/kt for the present system was found to be 0.37 × 10-2. The results are explained in terms of a radical mode of polymerization with degradative initiator transfer; the principal mode of termination, however, was bimolecular.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1989.080270306
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  • 3
    Digitale Medien
    Digitale Medien
    Studies on polymerization of vinyl acetate using ylide as an initiator and degradative transfer agent (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 27 (1989), S. 43-51 
    Details
    ISSN: 0887-624X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The polymerization of vinyl acetate initiated by β-picolinium-p-chlorophenacylide was carried out at 30, 35, and 40°C, using the conventional dilatometric technique. The initiator and the monomer exponent values were 0.80 ± 0.15 and unity, respectively. The polymerization was inhibited in the presence of hydroquinone, but was favored by nonpolar solvent and polymerization temperature. The energy of activation was 90.3 kJ mol-1. An average value of kp2/kt for the present system was found to be 0.37 × 10-2 L mol-1 s-1. The results are explained in terms of radical mode of polymerization with degradative initiator transfer; the principal mode of termination, however, was biomolecular.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1989.080270104
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  • 4
    Digitale Medien
    Digitale Medien
    Studies on β-picolinium-p-chlorophenacylide initiated copolymerization of methyl methacrylate with styrene (1987)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 149 (1987), S. 139-150 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die alternierende Copolymerisation von Methylmethacrylat mit Styrol unter Verwendung von β-Picolinum-P-chlorphenacylid als Radikalinitiator bei 55, 60 und 65°C und einer Reaktionszeit von 3 h wurde kinetisch untersucht. Die Copolymerisationsgeschwindigkeit (Rp) ist proportional der Quadratwurzel der Initiatorkonzentration und weist auf einen bimolekularen Abbruch hin. Der durchschnittliche Polymerisationsgrad nimmt mit zunehmender Initiatorkonzentration ab. Die ermittelten Werte für kp2/kt und für die Aktivierungsenergie betragen 1,43 · 10-3 l mol-1 s-1 bzw. 87 kJ mol-1. Die NMR Spektroskopie wurde zur Bestimmung der Struktur, Zusammensetzung und Stereochemie der Copolymeren verwendet.
    Notizen: The alternating copolymerization of methyl methacrylate (MMA) with styrene (S) using β-picolinium-p-chlorophenacylide (β-PCPY) as radical initiator at 55, 60, and 65°C for 3 h has been kinetically investigated. The copolymerization rate (Rp) is proportional to the square root of [β-PCPY] and indicates bimolecular termination. The average degree of polymerization decreases as [β-PCPY] increases. The values of kp2/kt and energy of activation have been evaluated as 1.43 · 10-3 l mol-1 s-1 and 87 kJ mol-1, respectively. The NMR spectroscopy has been used to determine the structure, composition, and stereochemistry of copolymers.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1987.051490111
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  • 5
    Digitale Medien
    Digitale Medien
    Photo-oxidative degradation of PPO/PET blends (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 214 (1994), S. 1-9 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Der photo-oxidative Abbau von Blends aus Polyethylenterephthalat (PET) und Poly(2,6-dimethyl-1-1,4-phenylenoxid) (PPO) wurde untersucht, wobei die gegenseitige Beeinflussung beider Komponenten berüucksichtigt wurde. Im Temperaturbereich 30 - 100°C wurden die Auswirkungen der Segmentbeweglichkeit der Polymerketten ermittelt. Für kurze UV-Bestrahlung (365 nm) ist der Abbau diffionskontrolliert und kann mit der Theorie von Waite erklärt werden. Die Wechselwirkungen der Polymersegmente in den Blends beeinflussen auch die Diffusionskoeffizienten und die Aktivierungsenergie. Für PET in Blends verursacht eine höhere Aktivierungsenergie eine Abnahme des Kettenbruchs.
    Notizen: Photo-oxidative degradation of blends of poly(ethylene terephthalate) (PET) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was studied considering the mutual influence of both components. The photo-oxidation of these systems was investigated in the temperature range 30-100°C to study the effects of segmental motion of polymer chains. For short time of UV-illumination at 365 nm the process is diffusion controlled and can be explained with the help of Waite's theory. The segmental interactions of polymer segments in the blends also affect the diffusion coefficients and the activation energy values. Higher values of the activation energy of PET in the blends cause a decrease of chain breaking.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1994.052140101
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  • 6
    Digitale Medien
    Digitale Medien
    Glass fiber reinforced polypropylene/EPDM blends. II. Mechanical properties and morphology (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 43 (1991), S. 451-462 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Tensile and impact properties of the ternary system polypropylene (PP)/ethylene propylene diene elastomer (EPDM)/glass fiber (GF) and the corresponding binary systems PP/EPDM blend and PP/GF composite are studied. Results are presented and analyzed as functions of compositional variables, viz., (i) matrix PP/EPDM blending ratio at constant GF loadings and (ii) GF loading at constant matrix blending ratios for the ternary system and (iii) EPDM content for PP/EPDM binary system and (iv) GF content for the binary system PP/GF, respectively. The role of individual components EPDM and GF in these mechanical properties is discussed and their combined effects are inspected at certain composition ranges. Theoretical analysis of tensile data is presented which reveals the effect of EPDM on the reinforcing effect of GF. Unlike the conventional role of an elastomer, increase of EPDM content in the presence of GF increases the modulus of the ternary system. Impact strength of the ternary system increases with increasing GF content both in the presence and absence of EPDM, showing a distinct minimum at matrix blending ratio PP/EPDM 90/10. Scanning electron micrographs of impact-fractured surfaces are presented to illustrate the dispersion of the two phases of the polyblend matrix, fiber alignment, and the fiber interface.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1991.070430306
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  • 7
    Digitale Medien
    Digitale Medien
    Glass-fiber-reinforced polypropylene/EPDM blend. I. Melt rheological properties (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 42 (1991), S. 2595-2611 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Melt rheological properties of the blend of isotactic polypropylene (PP) and ethylene propylene diene rubber (EPDM) at varying ratios and of the glass fiber (GF) filled PP and PP/EPDM blend by varying both GF loading and blending ratio of the polyblend matrix are studied. Rheological measurements at 220°C in shear rate range 101-104s-1 were made on a capillary rheometer. Scanning electron micrographs of the extrudates are presented to show the morphology and the alignment of the glass fibers with respect to the flow direction. Variations of pseudoplasticity index, melt viscosity, and melt elasticity with EPDM content in PP/EPDM blend, and with varying GF content at any given composition of the matrix in PP/EPDM/GF ternary system, in the studied range are presented and discussed. Resultes on melt viscosity and melt elasticity show (i) reduced effect of GF at high shear rates on these properties and (ii) upward deviation of melt viscosity versus shear rate curve at low shear rates. A change in flow behavior in presence of GF is observed around a critical shear rate 2 × 103 s-1 and is attributed to the difference of interaction of GF and the dispersed rubber droplets at high and low shear rates. Elastic recovery showed nonequilibrium behavior at low shear rates.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1991.070420925
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  • 8
    Digitale Medien
    Digitale Medien
    Studies on the polymerization of methyl methacrylate using ylide as an initiator and degradative transfer agent (1986)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 141 (1986), S. 103-111 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die mit α-Picolinium-p-chlorphenacylid initiierte Polymerisation von Methylmethacrylat in Tetrachlorkohlenstoff bei 30, 35 und 40°C und einer Dauer von vier Stunden wurde dilatometrisch untersucht. Die Reaktionsordnungen im Hinblick auf die Konzentration von Ylid und Methylmethacrylat liegen bei 0,22 ± 0,1 bzw. 1,0. Die gesamte Aktivierungsenergie und der mittlere Wert von kp2/kt beträgt 21 kJ · mol-1 bzw. 0,37 · 10-2.Die Ergebnisse wurden als radikalische Polymerisation mit einer initiatorabhängigen Übertragung und einem bimolekularen Abbruch erklärt.
    Notizen: The polymerization of methyl methacrylate (MMA) initiated by α-picolinium-p-chlorophenacylide in CCl4 at 30, 35, and 40°C for four h was investigated dilatometrically. The orders of reaction with respect to the concentrations of ylide and MMA are 0.22 ± 0.01 and 1.0, respectively. The overall energy of activation and an average value of kp2/kt are 21.0 kJmol-1 and 0.37 ± 10-2, respectively. The results are explained in terms of radical mode of polymerization with initiator dependent transfer besides bimolecular termination.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1986.051410111
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  • 9
    Digitale Medien
    Digitale Medien
    Time-dependent changes in the mechanical properties of zirconia ceramic (1993)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 27 (1993), S. 729-734 
    Details
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: Zirconia has received special attention, mainly because of its high strength and toughness. However, there is some controversy about the time-dependent deterioration of its mechanical properties. To examine the change in mechanical properties of zirconia ceramics in vivo and in vitro, tetragonal zirconia polycrystal pieces were introduced into the medullary cavity of the tibia in Japanese rabbits and animals were sacrificed after 2, 4 and 6 weeks and 6, 12, and 30 mo, respectively. Alumina ceramic and hydroxyapatite (HAP) pieces were used as controls to investigate the differences in biocompatibility. Zirconia showed a bending strength of over 1000 MPa initially, and little time-dependent change in strength was found in both in vivo environments. x-Ray analysis showed little change in the transformation rate, i.e., less than 5 mol % in vivo and in vitro over a period of 3 years. To estimate time-dependent changes in zirconia over a longer period, zirconia pieces were placed in 95°C saline solution for over 3 years and their mechanical properties examined at chosen intervals. No serious decrease of bending strength was found over the 3-year period under these conditions. It is concluded that zirconia can be used clinically because it retains a bending strength of over 700 MPa under any experimental conditions for over 3 years. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbm.820270605
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  • 10
    Digitale Medien
    Digitale Medien
    Studies on the kinetics of the polymerization of 2-methyl,6-isopropyl phenol with the complexes of manganese with substituted benzylamines (1985)
    Weinheim : Wiley-Blackwell
    Acta Polymerica 36 (1985), S. 475-478 
    Details
    ISSN: 0323-7648
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Die oxidative Polymerisation von 2-Methyl,6-isopropyl-phenol mit Mangan-Benzylamin-Komplexen erfolgt nach einem Mechanismus, der einer Michaelis-Menten-Reaktion ähnelt, wobei während der Polymerisation der stationäre Zustand erhalten bleibt. Aus einem Vergleich der kinetischen Parameter wird geschlossen, daß Sauerstoff an dem Reaktivierungsschritt des Katalysators beteiligt ist und so die katalytische Wirkung des Mangankomplexes fördert.
    Notizen: With managanese-benzylamine complexes the oxidative polymerization of 2-methyl,6-isopropyl phenol proceeds by a mechanism resembling to that of a Michaelis-Menten-type reaction with the steady state being maintained during the polymerization. From the comparison of the kinetic parameters it was concluded that oxygen takes part in the recyeling step of the catalyst and promotes the catalytic action of the manganese complexes.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/actp.1985.010360903
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