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  • Polymer and Materials Science  (24)
  • AIRCRAFT  (11)
  • Humans
  • LUNAR AND PLANETARY EXPLORATION
  • 1970-1974  (36)
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  • 1
    Electronic Resource
    Electronic Resource
    Calculations of the circular dichroism of double-helical nucleic acids. I. Effects involving π → π* transitions (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1377-1389 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The circular dichroism of double-helical nucleic acids was calculated as a function of geometry using the theory of Tinoco and Johnson. This theory does not include contributions of near ultraviolet transitions that are not π → π* in nature. The calculated circular dichroism shows a strong dependence on the distance of base pairs from the helix axis and the tilt of the base pair. Smaller dependences are predicted for the propeller-like twist of a base pair and for variation of the angular increment per base pair. Moderately good agreement between calculated and many experimentally observed spectra could be generated.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1974.360130709
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  • 2
    Electronic Resource
    Electronic Resource
    Circular dichroism of DNA: Temperature and salt dependence (1972)
    New York : Wiley-Blackwell
    Biopolymers 11 (1972), S. 761-779 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The temperature dependence of the circular dichroism and ultraviolet absorbance of calf thymus DNA and poly dAT were measured in aqueous solutions of various 1-1 electrolytes. Although there was very little change in absorbance, the circular dichroism changed dramatically as a function of both temperature and solvent. There is a correlation of the heat of hydration of the cation and the magnitude of the temperature dependence of the circular dichroism. Our results are interpreted in terms of a large number (possibly a continuum) of intermediate secondary structures.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1972.360110404
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  • 3
    Electronic Resource
    Electronic Resource
    Calculations of the circular dichroism of double-helical nucleic acids. II. Effects involving n → π* transitions (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1391-1403 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The circular dichroism of double-helical nucleic acids was calculated as a function of geometry, including terms involving n → π* transitions. The “nonbonding” n or σ orbitals were of the azine type, delocalized, but concentrated at the nitrogen atoms of the purines and pyrimidines. Dynamic coupling of the magnetic moments of the n → π* transitions with the electric moments of π → π* transitions generated important terms. Mixing of electric dipole character into n → π* transitions by the static electric field perturbation of the molecule is of lesser importance. The largest contributions of n → π* transitions to the circular dichroism of double-helical nucleic acids are comparable in magnitude to the sum of π → π* terms only for geometries where the circular dichroism is weak. Using both n → π* and π → π* contributions one is able to match experimental and calculated circular dichroism spectra for DNA's over a much wider range of conditions than was possible previously.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1974.360130710
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  • 4
    Electronic Resource
    Electronic Resource
    Photolysis of poly(methyl acrylate) in solution (1974)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 175 (1974), S. 2657-2667 
    Details
    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: Lösungen von Poly(methylacrylat) in Methylacetat, Chloroform, Methylendichlorid und Benzol wurden mit Strahlung der Wellenlänge 2 537 Å behandelt und die Änderungen des Zahlenmittels des Molekulargewichts gemessen. Der Einfluß der Bestrahlungszeit des Lösungsmittels, der Konzentration des Polymeren und der Anwesenheit des radikalischen Initiators wurden untersucht. Es wird der Schluß gezogen, daß die Kettenspaltung durch statistisch erfolgende Absorption der Strahlung durch das Polymere erfolgt und daß das Lösungsmittel dabei nicht direkt beteiligt und nur als ein optischer Filter wirksam ist.
    Notes: Solutions of poly(methyl acrylate) in methyl acetate, chloroform, methylene dichloride and benzene have been irradiated by 2 537 Å radiation and changes in number average molecular weight measured. The effect of time of irradiation, solvent, polymer concentration and the presence of radical initiator have been investigated and it is concluded that the scission results from random absorption of radiation directly by the polymer without direct participation by the solvent which acts only as an optical filter.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1974.021750912
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  • 5
    Electronic Resource
    Electronic Resource
    Thermal history and melting behavior of poly(ethylene terephthalate) (1970)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 2141-2151 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Low molecular weight poly(ethylene terephthalate) samples were crystallized isothermally at 120-245°C from both the amorphous state and the melt. Isothermal annealing of these polymers at 215°C provided polymers which exhibited multiple melting peaks in thermal analysis, referred to as form I and form II, as assigned by Bell and Dumbleton. In these samples the peak temperature of the form II melting endotherm and the average crystallite size are dependent on the temperature of initial crystallization. This result requires a mechanism for retaining some structural feature during the conversion from morphological form I to form II. DSC thermograms obtained at varying heating rates on samples showing only form II endotherms support the assignment of superheating as the cause of the shift to higher peak temperatures with increasing heating rate.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1970.160081210
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  • 6
    Electronic Resource
    Electronic Resource
    A cooperative molecular weight distribution test (1973)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 17 (1973), S. 269-282 
    Details
    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: The development of gel permeation chromatography (GPC) has provided a convenient tool for the rapid determination of molecular weight distribution. The question has arisen as to the suitability of the method for specification purposes. The present work, suggested by the Naval Air Systems Command, represents an attempt to assess the precision of the method through a series of tests carried out by a number of laboratories using identical procedures on the same samples. Ten laboratories agreed to take part. Naval Ordnance Station, Indian Head, worked out standard conditions for operation of the chromatograph, for calibration of the columns, and for analysis of the GPC curves. Two samples of polystyrene were used by the various organizations for calibration of their instruments. Number-average molecular weight, heterogeneity index, and cumulative molecular weight distribution curves were determined on four samples of carboxyl-terminated polybutadiene (CTPB) and two samples of hydroxyl-terminated polybutadiene (HTPB), all unidentified except by letter code. All laboratories used identical directions for setting up CTPB and HTPB calibration curves which were based on curves determined from vapor-pressure osmometer molecular weights and GPC count numbers of fractionated material. Variation among the different laboratories was 0.15 in heterogeneity index, and a maximum of 1200 in molecular weight provided one aberrant set of values was eliminated. The six samples had heterogeneity indices from 1.15 to 1.54, while molecular weight varied from approximately 3000 to 6000. The average coefficient of variation of the molecular weight values was 6.2 ± 0.7%, which is quite acceptable. Variation in heterogeneity index was too great for specification purposes when considered among the different laboratories, but may be sufficiently good when measured by any one laboratory.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1973.070170121
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  • 7
    Electronic Resource
    Electronic Resource
    Evaluation of the hydrocarbon condensation polymerisation reaction by means of model compounds. I. The reaction with n-alkyl-bromides (1972)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 152 (1972), S. 121-132 
    Details
    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 Bildung von Copolymeren durch Reaktion von α-Methylstyrol (M) in Tetrahydrofuran mit Lithium in Gegenwart von Dihalogenalkanen (RX2) wird beschrieben. Der Einfluß der experimentellen Parameter auf die Struktur der Copolymeren wird untersucht, wobei das Dihalogenid durch das entsprechende Monohalogenid ersetzt ist. Die Untersuchung beschränkt sich auf n-Alkylbromide. Die relativen Mengen an HR-RH und HRMnRH mit n = 1, 2 und 3 wurden gaschromatographisch bestimmt. Es wurde gezeigt, daß die Reaktion diffusionkontrolliert abläuft und daß die Geschwindigkeit der Lithium-oberfläche proportional ist. Bei einem molaren Ausgangsverhältnis von Monomerem zu Monohalogenid von 1 : 1 (entsprechend einem Verhältnis von 2 : 1 für das SystemMonomeres/Dihalogenid) wurden ca. 90% HRM2RH gefunden. Dies zeigt, daß unter den gegebenen Bedingungen ein sehr einheitliches Copolymeres mit der vorherrschenden Sequenz [M-M-R] entsteht. Das System ist sehr empfindlich gegenüber einer Änderung des Ausgangsverhältnisses der Komponenten. Geringe Abweichungen vom molaren Verhältnis 1 : 1 bewirken eine starke Verringerung der Ausbeute an Dimeren.
    Notes: The title polymerisation involves the reaction in tetrahydrofuran of α-methylstyrene (M) with lithium in the presence of an alkyl dihalide (RX2) to form copolymers. This paper describes a method of studying the effect of changing the experimental parameters on the structure of these copolymers by replacing the dihalide with the corresponding monohalide (HRX). The study is confined to n-alkyl bromides and the relative amounts of the molecules HR-RH and HRMnRH (where n = 1, 2, and 3) have been determined by g.l.c. By this means it is shown that the reaction is diffusion controlled and the rate proportional to lithium surface area. At 1 : 1 monomer : monohalide stoichiometry (equivalent to 2 : 1 monomer : dihalide in the polymer system) the product is ∼ 90% HRM2RH indicating that the copolymer under these conditions is highly regular with the repeat unit [M-M-R] predominating. The system is extremely sensitive to the reactant ratio and small deviations from stoichiometry result in significant reductions in dimer yield.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1972.021520113
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  • 8
    Electronic Resource
    Electronic Resource
    Evaluation of the hydrocarbon condensation polymerisation reaction by means of model compounds. II. The reaction of with n-alkyl chlorides and iodides, and sec- and tert-alkyl bromides (1972)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 152 (1972), S. 133-142 
    Details
    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 Darstellung von Copolymeren durch Reaktion von α-Methylstyrol (M) in Tetrahydrofuran mit Lithium in Gegenwart von Dihalogenalkanen (RX2) wird untersucht. Die Verwendung von Monohalogenalkanen (RX) führt zu kleinen Molekülen, deren Mengenverhältnisse über den Polymerisationsprozeß und die Struktur der Copolymeren Aufschluß geben. Diese Arbeit beschreibt die Ergebnisse bei Verwendung von n-Alkyljodiden, -chloriden und sec- und tert-Bromiden.n-Alkyljodide verhalten sich ähnlich wie n-Alkylbromide (Teil I). Beim molaren Verhältnis 1 : 1 von Monomeren: Halogenid wird das Dimere HRM2RH in hohen Ausbeuten erhalten. n-Alkylchloride dagegen geben zahlreiche zusätzliche Produkte unter diesen Bedingungen. Die Analyse ihrer Struktur zeigte, daß sie durch Reaktion mit n-Alkyllithium entstehen, das seinerseits durch Reaktion des n-Alkylchlorids mit Lithium gebildet wird. Das unterschiedliche Reaktionsverhalten der Halogenide wird durch die relativ hohe Bindungsstärke der C-Cl-Bindung erklärt. Hieraus folgt, daß Copolymere, die mit Dichloriden als einer Komponente dargestellt werden, weniger einheitlich aufgebaut sind als solche, die aus Dibromiden gewonnen werden. sec- und tert-Bromide führen ebenfalls zu sahlreichen Produkten bei äquimolarem Umsatz mit α-Methylstyrol. Es konnte gezeigt werden, daß dies auf die β-Elirninierung von Wasserstoff zurückzuführen ist. Bei tert-Bromiden tritt die Wasserstoff-Eliminierung am deutlichsten auf, die zu 60% für den Abbruch des Dimeren verantwortlich ist.
    Notes: The title polymerisation involves the reaction in tetrahydrofuran of α-methylstyrene (M) with lithium in the presence of an alkyl dihalide (RX2) to form copolymers. Replacement of the dihalide by the analogous monohalide RX gives small molecules, the relative amounts of which furnish information on the polymerisation process and the resulting structures of the copolymers. This paper describes the use of n-alkyl iodides and chlorides, and sec- and tert-bromides in this regard.n-Alkyl iodides were found to behave in a similar manner to n-alkyl bromides (Part I) with high yields of the dimer HRM2RH being obtained at 1 : 1 M stoichiometry. On the other hand, n-alkyl chlorides gave a variety of additional products under these conditions and a structural analysis of these materials showed that they resulted from reactions involving n-alkyl lithium which was formed by the chloride reacting directly with the lithium. This difference in behaviour is explained in terms of the high strength of the carbon-chlorine bond and implies that copolymers prepared with dichlorides are less regular than those obtained with dibromides.sec- and tert-bromides also gave a variety of products at equimolar stoichiometry and this was shown to be due to the β-hydrogen elimination reaction becoming significant. Elimination was most prominent with the tert-bromides, accounting for about 60% of der termination reaction of the dimer.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1972.021520114
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  • 9
    Electronic Resource
    Electronic Resource
    Calculation of the circular dichroism of double-helical nucleic acids. III. Dependence of the results on the choice of wave functions for purines and pyrimidines (1974)
    New York : Wiley-Blackwell
    Biopolymers 13 (1974), S. 1405-1416 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The circular dichroism of double-helical nucleic acids was calculated using three different sets of wave functions for the purine and pyrimidine chromophores. Different wave functions give qualitatively the same types of spectra. Quantitatively, the differences are very substantial. However, the dependence of calculated circular dichroism spectra on nucleic acid geometry and base composition is very similar for the three different sets of wave functions. Each set of wave functions could be used to reproduce some, but not all experimentally observed spectra. The geometries required to reproduce experimentally observed spectra consistently require double-helical geometries similar to the B or C forms of DNA.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1974.360130711
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  • 10
    Electronic Resource
    Electronic Resource
    Rapid assessment of weathering stability from exposure of polymer films. III. Relative weathering stability of ABS and arylon, a related polymer blend (1974)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 18 (1974), S. 1181-1185 
    Details
    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: Arylon, a blend of an aromatic polysulfone and a terpolymer of acrylonitrile-butadiene and α-methylstyrene, weathers similarly to ABS. However its first-order rate constant for the loss of unsaturation is only 0.39 cm2(Wh)-1 as against 0.80cm 2(Wh)-1 for ABS. This slower weathering is probably caused by the decrease in light intensity penetrating Arylon compared with ABS as a result of the high degree of light scattering observed in the former.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1974.070180416
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