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  • 1
    Electronic Resource
    Electronic Resource
    Dynamics of spermiogenesis in Drosophila melanogaster (1972)
    Springer
    Cell & tissue research 127 (1972), S. 492-525 
    Details
    ISSN: 1432-0878
    Keywords: Spermatozoa ; Drosophila ; Testis ; Fertility ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In Drosophila melanogaster, the cyst cell that surrounds the head region of sperm bundle becomes spheroidal or ellipsoidal and is trapped by the terminal epithelium of the testicular wall during the synchronous coiling of sperm. Extensions of this cyst cell are projected caudally into the interspaces between sperm heads probably to anchor the heads. Coiling of sperm tails is initiated at the head region and proceeds by the progressive retraction of the linear portion from the apical testicular region into the coiled portion at the base. The addition of one turn of coil is accompanied by one full rotation of the sperm bundle. When coiled, normal tails are tightly packed into a hexagonal lattice, and minute tubular structures of about 150 Å in diameter occupy the space between them. Sperm with abnormal tails are separated from those with normal ones and isolated into a separate part of the cyst lumen. Acid phosphatase is involved in the dissolution of the minute tubules for the liberation of sperm from the cyst. Sperm are released leaving the major portion of the cyst cells intact. This portion contains degenerating abnormal tails and the waste products of the individualization process. This detritus is ingested by the terminal epithelium and eventually degenerates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00306868
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamics of spermiogenesis in Drosophila melanogaster (1972)
    Springer
    Cell & tissue research 124 (1972), S. 479-506 
    Details
    ISSN: 1432-0878
    Keywords: Spermatozoa ; Drosophila ; Testis ; Fertility ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A morphogenetic process that transforms spermatids from a syncytial state to a state in which each spermatid is invested in its own membrane, is initiated at the head region of the spermatid bundle and traverses through the entire length of the bundle in the testis of Drosophila melanogaster. This process not only eliminates the syncytial bridges between spermatids but also removes unneeded organelles and the excess parts of the nuclear membrane, nucleoplasm and cytoplasm. It also brings about structural modifications to flagellar elements. The propagation of this process is seen as the caudal movement of a fusiform swelling of the spermatid bundle, 100 μ or more in length. Spermatids are individualized in the basal half of the swelling, whereas they remain syncytial in the apical half. The swelling increases its volume as it accumulates cytoplasmic debris while traversing the sperm bundle, from about 15 μ in maximum diameter in the basal testicular region to as large as 30 μ at the apical end where it becomes a bag of wastes. A variation of the process in a mutant stock which is known to inactivate up to half of the products of meiosis is briefly described. The morphological change of interspermatid bridges prior to the individualization is also reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335253
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  • 3
    Electronic Resource
    Electronic Resource
    Initiation of polymerisation by irradiated polymethyl methacrylate. II. Gaseous, liquid, and emulsified monomer with pre-irradiated polymerPart I. Makromolekulare Chem. 42 (1960) 33. (1963)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 67 (1963), S. 149-156 
    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 Geschwindigkeiten der Polymerisationen unter dem Einfluß vorbestrahlter PMMA-Filme und die Geschwindigkeiten der entsprechenden unkatalysierten Polymerisationen dieser Monomeren sind beinahe nicht unterscheidbar. Diese Beobachtung steht mit der berechneten Geschwindigkeit eines bimolekularen Zerfalles von Radikalen in mit Monomerem gequollenen Polymerfilmen in Übereinstimmung. Die Radikale verschwinden ebenfalls schnell, wenn das Monomere langsam auf die Filme destilliert wird. Fügt man das Monomere in Form einer wäßrigen Emulsion hinzu, so werden die Geschwindigkeiten von den Diffusionen des Monomeren in die Filme und von kleinen Radikalen aus den Filmen gleich, so daß ein Teil der Radikalaktivität in die Emulsion entkommt, wo er eine sehr langlebige Emulsionspolymerisation initiiert.
    Notes: The rates of polymerisation of styrene and vinyl acetate under the influence of preirradiated polymethyl methacrylate (PMMA) film are almost indistinguishable from the corresponding uncatalysed rates of these monomers. This observation is consistent with the calculated rate of bimolecular decay of radicals in a polymer film swollen with monomer. The radicals disappear rapidly even if the monomer is distilled slowly on to the film. If the monomer is added in the form of an aqueous emulsion the rates of the diffusions of the monomer into the film and of small radicals out of the film are so balanced that a proportion of the radical activity escapes into the emulsion where it initiates a very long-lived emulsion polymerisation.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1963.020670114
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  • 4
    Electronic Resource
    Electronic Resource
    Initiation of polymerisation by irradiated polymethyl methacrylate. III. The kinetics of emulsion polymerisation initiated by pre-irradiated film (1963)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 67 (1963), S. 157-166 
    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 Kinetik der Emulsionspolymerisation von Styrol, die durch den Einfluß von vorbestrahlten Filmen von PMMA angeregt wurde, ist untersucht worden. Die Bruttoreaktionsgeschwindigkeit war von der Anzahl von Radikalen in den Filmen unabhängig. Nach einer Induktionszeitperiode folgte die Polymerisation einem SMITH-EWART-Fall-II-Mechanismus. Die ARRHENIUSfaktoren der Wachstumsgeschwindigkeitskonstanten waren 8-10 Kcal./Mol und 107-109 l Mol-1 sec-1. Die mittlere Aktivierungsenergie der Übertragungsreaktionen, die den Polymerisationsgrad bestimmen, war 11-13 Kcal/Mol.
    Notes: The kinetics of the emulsion polymerisation of styrene initiated by previously gammairradiated polymethyl methacrylate (PMMA) films have been investigated. The rate of polymerisation was independent of the number of radicals in the film. After an induction period the polymerisation followed a SMITH-EWART Case II mechanism. The ARRHENIUS factors for the propagation rate constant were 8-10 kcal./mole and 107-109 l./mole sec. The average activation energy of the transfer reactions which regulated the degree of polymerisation was 11-13 kcal./mole.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1963.020670115
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  • 5
    Electronic Resource
    Electronic Resource
    Applications and limitations of turbidimetric titration as a method of characterizing solutions of polymers and mixtures of polymers (1960)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 39 (1960), S. 52-66 
    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 Anwendbarkeit der Trübungstitrationsmethode zur Analyse von Polymermischungen wurde an bekannten Mischungen untersucht. Die Methode war, wenn Mischungen von Block- oder Pfropfcopolymeren mit Homopolymeren benutzt wurden, in drei von vier Versuchen nicht einmal halbquantitativ.Elektronenmikroskopische Aufnahmen von Proben der Suspension, die während der Trübungstitrationen der Polymerlösungen entnommen wurden, zeigten, daß die Voraussetzung einer einheitlichen Teilchengröße oder einer einfachen geometrischen Teilchenform nicht gegeben ist.
    Notes: The validity of turbidimetric titration in the analysis of polymer mixtures was tested using mixtures of known composition. In some cases, which included three out of four mixtures of block or graft copolymers with homopolymers, the method was not even semiquantitative.Electron micrographs of samples of the suspension taken during titration of single polymer solutions show that assumptions of uniform size or regular geometrical shape of the particles are invalid.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1960.020390105
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  • 6
    Electronic Resource
    Electronic Resource
    Initiation of polymerisation by γ-irradiated polymethyl methacrylate. Irradiation in the presence of a second monomer: Block copolymer formation (1960)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 42 (1960), S. 33-43 
    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 Beschleunigung der Polymerisationsgeschwindigkeit von mit γ-Strahlen bestrahltem Styrol und Vinylacetat durch Zusatz von Polymethacrylsäuremethylester wurde untersucht. Die gefundenen G-Werte von reinem Styrol (0,46 Radikale/100 eV.) und von reinem Vinylacetat (5,7) entsprechen den Werten früherer Bearbeiter. Unsere Versuche zeigten, daß der „aromatische Schutz“ von Styrol gegenüber bestrahltem Polymethacrylsäuremethylester bedeutungslos ist.Radiochemische Bestimmungen der Methacrylsäureestergehalte von Blockpolymeren, die durch Bestrahlung von Lösungen von Polymethacrylsäuremethylester in Vinylacetathergestellt wurden, zeigten, daß ca. 70% der Copolymeren sich durch Hauptkettenspaltung des Polymethacrylsäureesters und den Abbruch der wachsenden Vinylacetatketten durch Disproportionierung oder Übertragungsreaktion bilden. Der Rest der Copolymeren kann auf Kombination von wachsenden Vinylacetatketten, Pfropfungen an den Polymethacrylsäuremethylester oder auf Seitengruppenspaltungen zurückgeführt werden.
    Notes: The acceleration of the polymerisations of γ-irradiated styrene and vinyl acetate by added polymethyl methacrylate has been examined. G values of 0.46 radicals/100eV. for pure styrene and 5.7 for pure vinyl acetate are in agreement with those of previous workers. It was shown that styrene does not exert any significant “aromatic protection” over irradiated polymethyl methacrylate.Radiochemical assays of the methyl methacrylate content of the block-copolymers formed in irradiated solutions of polymethyl methacrylate in vinylacetate showed that ca. 70% arose from main chain scission of polymethyl methacrylate with the growing vinyl acetate chains terminating by disproportionation or transfer. The remainder could have arisen from vinyl acetate chains terminating by combination, grafting to the polymethyl methacrylate or side chain scission.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1960.020420104
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