Search Results - (Author, Cooperation:A. Kiel)

2012-03-17

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Calcium/metabolism ; Diffusion ; *Lipid Bilayers ; Liposomes ; *Membrane Fusion ; Membrane Proteins/chemistry/metabolism ; Mice ; Neurotransmitter Agents/metabolism ; Protein Structure, Tertiary ; Proteolipids/chemistry ; Rats ; Recombinant Fusion Proteins/chemistry/metabolism ; SNARE Proteins/*chemistry/*metabolism ; Synaptic Transmission ; Synaptic Vesicles/*chemistry/metabolism ; Synaptosomal-Associated Protein 25/chemistry/metabolism ; Syntaxin 1/chemistry/metabolism ; Vesicle-Associated Membrane Protein 2/*chemistry/*metabolism

0022-2852

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Chemistry and Pharmacology

Physics

Electronic Resource

0038-1098

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0038-1098

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

1435-1536

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Zusammenfassung Der Bericht befaßt sich zuerst mit der großen morphologischen Mannigfaltigkeit faseriger, bei erhöhter Temperatur aus gerührten Lösungen gefällter Polyäthylenkristalle. Bei 112°C aus gerührten Xylollösungen von linearem Polyäthylen herauskristallisierte Schaschlik-Strukturen zeigen eine lamellare Überwachsung mit einer Dicke von etwa 150 Å, woraus u. a. geschlossen wird, daß sich bei Kristallisations-temperaturen über 100°C nur Faserkerne bilden und daß die umringenden polymeren Moleküle sich bei niedrigeren Temperaturen “epitaxial” auf dem Substrat ablagern. Die Verschiedenheit in der Form der Überwachsung und die Inhomogenität der Proben lassen sich erklären durch eine unregelmäßige Ablagerung auf dem Rührer und durch Unterschiede in der Auswaschbarkeit der faserigen Kristalle, welche Unterschiede weitgehend auf das nicht einheitliche Strömungsbild längs der verschiedenen Rührerteile zurückzuführen sind. Ungewöhnliche lamellenartige Formen, interlamellare Verbindungen, Häutchen zwischen den Lamellen und die vonKeller undMachin festgestellte Verschleierung der Schaschlikgebilde lassen sich sehr gut durch denKeith-, Padden- undVadimsky-Mechanismus einer durch die Kristallisation verursachten Orientierung von Makromolekülen zwischen den Lamellen und durch die anschließende Bildung von “extended-chain” Kristallen erklären. Wie sich zeigt, gruppiert sich die lamellare Überwachsung um den Kern entsprechend einer logarithmischen Normalverteilung; der mittlere Durchmesser der lamellaren Kristalle nimmt zu mit der mittleren Größe der Zwischenabstände, wobei beide ungefähr gleich groß sind. Die faserigen Kristalle enden in allmählich spitz auslaufenden Gebilden mit Längen von etwa 5 bis 8 μ. Diese Faserenden stimmen gut überein mit dem für das Wachsen faseriger Kristalle in Strömungsgebieten vorgeschlagenen “unroll”-Modell, falls im Durchschnitt jedes Molekül eine Kettenfaltung einleitet und die Kettenenden willkürlich in das Kristallgitter aufgenommen werden. Lineares Polyäthylen mit einem Molekulargewicht unter 50×103 und Hochdruckpolyäthylen kristallisieren nicht in der faserigen Form, während —wie sich zeigt—Copolymere von Äthylen und geringen Propylen- und Butylenmengen in der Lage sind, faserige Kristalle zu bilden und isotaktisches Propylen schöne und überwachsene Fibrillen ergibt.

Summary This paper primarily describes the large diversity in morphology of fibrillar polyethylene crystals precipitated from stirred solutions at elevated temperatures. Shish-kebabs crystallized at 112°C from stirred xylene solutions of linear polyethylene exhibit lamellar overgrowths having thicknesses of the order of 150 Å from which it was concluded i. a. that at crystallization temperatures above 100°C only backbones are formed and that the surrounding polymer molecules deposit epitaxially on the substrate at lower temperatures. The variation in the appearance of the overgrowth and the inhomogeneity of the samples can be traced back to irregular stacking and to differences in washability of the fibrillar crystals, these differences being largely due to the non-uniform flow pattern along the various stirrer parts. Unusual lamellar shapes, interconnections, sheets between lamellae, the “veil” on the Shish-kebab noted byKeller andMachin, may well be explained byKeith, Padden andVadimskys mechanism of crystallization-induced orientation of macromolecules between the lamellae and the consequent formation of extendedchain crystals. The lamellar overgrowth appears to be arranged along the backbone according to a logarithmic normal distribution, and the average diameter of the lamellar crystals increases with the average spacing, both being approximately equal in size. The fibrillar crystals end in smooth tapered tails having lengths varying between 5 and 8 μ. These observed fibre ends agree best with the “unroll” model proposed for fibrillar crystal growth in flow fields if on the average each molecule introduces one chain fold and the chain ends are randomly assimilated by the crystal lattice. Linear polyethylene below molecular weight of 50×103 and low density polyethylene did not crystallize in fibrillar habit. whereas copolymers of ethylene and slight amounts of propylene and butylene proved capable of forming fibrillar crystals and isotactic polypropylene yielded smooth and overgrown fibres.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Keller1 pointed out that the chains in the polyethylene crystal must necessarily be folded and that the height of the terraces corresponds to the distances between successive folds. He also noted that the crystals lose their crystallinity in the electron microscope, but that their morphological ...

Electronic Resource

1573-4803

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract The melting, dissolution and crystallization behaviour of the lamellar overgrowth in polyethylene shish-kebab fibres have been studied by small-angle X-ray scattering and electron microscopy. SAXS experiments in which fibres were heatedin situ demonstrated the irreversible reorganization of the lamellar overgrowth already at 60° C. Reorganization continued in an inhomogeneous manner until the fibre lost its porosity around 140° C. The morphology that developed upon cooling depended on the crystallization temperature as well as on the maximum temperature attained before crystallization. Transmission electron microscopy observations showed the influence of molecular weight on aggregation. The SAXS patterns obtained duringin situ dissolution experiments disclosed that the lamellae dissolved in dodecane above 115° C. Recrystallization of the lamellae on to the backbones was almost complete within 10 min at 110° C. These high temperatures, as compared with single-crystal behaviour, indicate that the cilia nucleated with exceptionally high stem lengths on to the backbones. SAXS of fibres elongated to a maximum ratio of 1.5 at 90° C demonstrated the role of the lamellar overgrowth as a matrix between the elementary fibrils. The shish-kebab morphology could be restored after elongation by selective dissolution of the lamellae and recrystallization.

Electronic Resource

1435-1536

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1435-1536

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1435-1536

Ultra-drawing ; Polyethylene ; Morphology

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Zusammenfassung Morphologie und Struktur von Gelen, hergestellt durch Abschreckung halbverdünnter Lösungen von Polyethylen mit hohem Mol-Gewicht $$(\bar M_w = 1,5 - 3,5 \cdot 10^6 )$$ in Decalin werden besprochen. Das Streckverhalten bei Raumtemperatur und bei 130 °C der trockenen Gelfilme und die Struktur-Eigenschaften von im Verhältnis bis 130:1 gestreckten Filme wurden unter Verwendung verschiedener Mikroskop-Techniken und der Weitwinkelstreuung von Röntgenstrahlen geprüft.

Summary The morphology and structure of gels produced by quenching semidilute solutions of high molecular weight polyethylene $$(\bar M_w = 1.5 - 3.5 \cdot 10^6 )$$ in decalin is discussed. The drawing behavior of the dried gel films at room temperature and at 130 °C and the structural features of films drawn to ratios as high as 130 were examined with various microscopic techniques and wide-angle X-ray scattering.

Electronic Resource

1573-4803

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract The morphology of synthetic garnierite, Ni3(OH)4. Si2O5, has been studied by electron microscopy. The layer structure of the hollow garnierite needles has been made visible and the observed layer distance is in accordance with the X-ray result. Synthetic garnierite, totally dehydrated above 500° C, appears to be pseudomorphous with garnierite. Total reduction of the dehydrated product in hydrogen yields porous nickel-on-silica in which the small nickel crystallites are only partly accessible to hydrogen chemisorption.

Electronic Resource

0897-3806

spine ; spinal radiographs ; idiopathic scoliosis ; screening ; etiology ; Life and Medical Sciences ; Miscellaneous Medical

Wiley InterScience Backfile Collection 1832-2000

Medicine

This paper reports a segmental analysis of the lateral spinal radiographs of 37 children referred to hospital in a school screening study of 4,890 school children aged 12-13 years. On each lateral radiograph a line was drawn along the posterior surface of each vertebral body from T5-L5 and the angle of this line from the vertical was recorded.After measuring the scoliosis curve (Cobb) angle and using conventional criteria for diagnosis, three groups of patients are defined, namely, 1) a control group (average scoliosis curve angle (Cobb) of 5°, n = 14), 2) a group with lumbar curves (average Cobb angle 21°, n = 7), and 3) a group with thoracic curves (average Cobb angle 19 degrees, n = 10). Individual lateral spinal profiles are also analyzed.The findings show: (1) In the control group, there are different degrees of vertical backward tilt (declivity) from T7-L3, with a maximum tilt at T12 (mean 26°). The most vertical vertebrae are T6 and L4, with forward tilting (proclivity) at each of (T5 and L5.2) In the lumbar curve group, the segmental sagittal tilt is not significantly different from that in the control group. The mean declivity at T12 is 25°. (3) In the thoracic curve group, the segmental sagittal tilt is significantly less than that in the control group at each of T10-L1. The mean declivity at T12 is 17°. A more vertical T12 is associated with a larger Cobb angle. (4) The individual sagittal spinal profiles of the thoracic curve group (but no other group) show lordosis in the region of the lateral spinal curve (scoliosis) and a kyphotic angulation at an average of three vertebrae below the apical vertebrae of the scoliosis curve. (5) It is suggested that as a thoracic lordoscoliosis develops, the appearance of a kyphotic angulation in the thoracolumbar and upper lumbar spine is determined by the compressibility of each disc in relation to the length of the articular processes at the corresponding level. Where the combination of disc weakness to facet length is most adverse, forward flexion occurs, as in a spinal fracture, to produce the kyphotic angulation. © 1992 Wiley-Liss, Inc.

10 Ill.

Electronic Resource

0021-8995

Chemistry ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

4 Ill.

Electronic Resource