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  • Polymer and Materials Science  (6)
  • ASTROPHYSICS  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 196 (1992), S. 49-61 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Hydrogele wurden aus methylmethacrylat (MMA) and N-Vinyl-2-pyrrolidon (NVP) mit 1,2,2-Trimethylolpropantrimethacrylat (TPTA) als Vernetzungsmittel hergestellt. Die Terplymerisation wurden mittels UV-strahlung (365 nm) initiiert, wobei kleine Mengen an Diethoxycetophenon (DEAP) als Photosensibilisator sowie Triethanolamin(TEA)als Beschleuniger und Verdünner verwendet wurden. Die Hydrogele wurden durch Messung des Wasserrückhaltevermögens, der Sauerstodiffusions- und permitionskoeffizienten, der mechanischen Eigenschaften und der Lichtdurchlässigkeit charakterisiert. Dabei zeigte sich, daß die Hydrogele bis zu 80 Gew.-% Wasser aufnehmen können, wobei mit steigendem Wassergtehalt deren mechanische Festigkeit drastisch sinkt. Der Ssuerstoffdiffusionskoeffizient der gequollenen Hydrogele beträgt 10-6 cm2s-1, der Sauerstoffpermeationskoeffizient 1013 cm2s-1Pa-1, und die Lichtdurchlässigkeit liegt im Bereich von 500 bis 700 nm bei über 90%.
    Notes: Hydrogels are synthesized from methyl methacrylate (MMA) and N-vinyl-2-pyrrolidone (NVP) with 1,1,1-trimethylol propane trimethacrylate (TPTA) as a crosslinking agent. It was polymerized under UV radiation (365nm) with a small amount of photosensitizer, diethoxy acetophenone (DEAP), acclerator and diluent, triethanol amine (TEA). The hydrogels were characterized by measuring the water retention, dissolved oxygen diffusivity and permeability, mechanical strength, and light transparency. The hydrogels can retain water up to 80 wt.-% and the mechanical strenght is weakened as the water content is increased in the gel. The dissolved oxygen diffusivity and permeability in the swelling hydrogels are determined to be 10-6 cm2/sec and 1013 cm2s-1 Pa-1, respectively. The light transparency is over 90% in the wave lenght ranging from 500 to 700 nm.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nmr solution conformation of cyclotheonamide A (CtA) was determined in aqueous media. The data produced 15 distance and 10 torsional constraints which were used to generate conformations using restrained simulated annealing (SA) and distance geometry/simulated annealing (DG/SA) calculations. Two different calculation protocols were performed to ensure proper sampling of conformational space and even though the torsional restraints were input differently, both calculation methods yielded the same conformation of CtA. In the structure calculations, all solutions of the Karplus equation were sampled simultaneously using the restrained SA protocol and large ranges were used for the dihedral restraints in the DG/SA protocol because all solutions to the Karplus equation could not be sampled simultaneously. The solution conformation was also compared to the solid state x-ray conformations of CtA bound to thrombin and trypsin. The conformation of the residues important for active site binding (d-Phe, h-Arg, and Pro) are nearly identical in aqueous solution and solid state with largest differences at the a-Ala and v-Tyr residues. CtA appears to be preordered in structure and does not undergo a significant conformational change upon binding to the enzyme active site. © 1997 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 2993-3004 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Fibers of a novel rigid-rod polyamide containing a 1:1 ratio of phenylene:pyrimidine moieties have been produced and evaluated. The lyotropic liquid-crystalline behavior of the polymer and the spinnability of the nematic dope were established. The as-spun fibers exhibit low degrees of orientation and crystallinity. Heat treatment of the dry fibers resulted in crystallinities as high as 45% in coexistence with an amorphous phase component. Evaluation of the crystal structure by wide-angle X-ray diffraction suggests a pseudo-orthorhombic crystal cell with lattice dimensions (a; b; c) of (7,3 Å; 5,1 Å; 12,8 Å) and containing two repeating units per unit cell.
    Additional Material: 6 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 727-741 
    ISSN: 0887-6266
    Keywords: liquid crystal polymer ; aromatic polyester ; molecular modeling ; Monte Carlo ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The condensed phase of the alternating copolyester of p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) is investigated by studying the room temperature packing arrangement of the copolymer chains. A molecular modeling methodology is employed with a Monte Carlo sampling of the configurational phase space. Realistic poly(HBA-alt-HNA) polymer chains are represented by an explicit atom representation of the HBA/HNA dimers. States are sampled from the NVT ensemble using a sampling scheme consisting of (1) valence and torsional variations, (2) rigid body rotations of the chain about the chain axis, and (3) rigid body translations of the chain. The effect of chain packing on the conformation of chains, as well as the relative intra- and intermolecular orientations of aromatic rings, is investigated. Correlation of chain positioning along the chain axis is dominated by aromatic rings maintaining a center-to-center plane of registry. These layers of aromatic units pack with a preference for edge-to-face orientations in a herringbone-type pattern and have an intermolecular ring angle between the pairs of aromatic rings in the unit cell that is ca. 68°. The aromatic rings, on average, are rotated 38° out from the b-c plane. The phenylene rings of these copolyesters are less restricted in their relative orientation in comparison to the naphthalene rings. Intramolecular orientational probability density distributions indicate a preference for staggering the successive aromatic rings along the chain, with a staggering angle of ca. 66°. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 727-741, 1998
    Additional Material: 14 Ill.
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  • 5
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Fibers of three constitutionally isomeric rigid-rod polymers, produced by polycondensation of 2,6-dichloro-p-phenylenediamine and terephthaloyl dichloride, were spun from nematic solutions and characterized by wide-angle X-ray diffraction (WAXD) measurements and mechanical tests. A post-spin heat treatment was employed to improve the low degrees of orientation and crystallinity that the untreated fibers showed. The dominating crystal structure of constitutionally ordered head-to-head/tail-to-tail fibers seems to be very similar to “Modification II” of the fibers from poly(p-phenyleneterephthalamide) (PPTA), but the fibers do not suffer a comparable structural transformation upon heat treatment. Influences of the constitutional regularity in the chains on the crystal structure, structural order and mechanical properties of the fibers could be observed. Both the observed crystal structure and the experimentally determined mechanical properties agree well with the results of detailed atomistic modeling predictions.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Biomaterials 5 (1994), S. 221-226 
    ISSN: 1045-4861
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The most recent advance in skin stapling is the Auto Suture® SQS®-20 disposable stapler. It approximates and everts wound edges, placing one synthetic absorbable pin in the dermis each time the instrument handle is activated. Staple wound closure was accomplished four times faster than sutural closure of the dermis. Wounds with staple pin closure exhibit superior resistance to infection than wounds approximated by dermal sutures. Although sutures provide more immediate wound security, as measured by wound breaking strength, than dermal pins, the breaking strength of wounds subjected to either dermal pins or dermal sutures were not significantly different 14 days after wounding. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 7
    Publication Date: 2019-06-28
    Description: During the Giotto and Vega encounters with Comet Halley both organic particles called CHON and energetic ions were detected. The acceleration of ions to hundreds of keV in the vicinity of the bow shock and near the nucleus may be a demonstration of a situation occurring in the early solar system (perhaps during the T Tauri stage) that led to the formation of organic particles only now released. Utilizing a Van de Graaff accelerator and a target chamber having cryogenic and mass spectrometer capabilities, frozen gases were bombarded at 10 K with 175 keV protons with the result that fluffy solid material remains after sublimation of the ice. Initial experiments were carried out with a gas mixture in parts of 170 carbon monoxide, 170 argon, 25 water, 20 nitrogen, and 15 methane formulated to reflect an interstellar composition in experiments involving the freezing out of the products of a plasma. The plasma experiments resulted in a varnish-like film residue that exhibited luminescence when excited with ultraviolet radiation, while the ion bombardment created particulate material that was not luminescent.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Workshop on Analysis of Returned Comet Nucleus Samples; p 79-80
    Format: application/pdf
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  • 8
    Publication Date: 2019-07-13
    Description: We have completed a multiband absorption- and emission-line study of a star embedded in the young cluster IC 348, to determine the environmental effect of star formation on the interstellar medium (ISM) local to the region. The hottest and youngest star in IC 348 is BD +31 deg 643, a B5 V star which samples the inner bright nebular region. The nearby star omicron Per, which lies only 8 min to the north and is thought to lie beyond IC 348, samples the gas and dust which has not been processed by very recent star formation. We speculate that the ISM throughout the region was originally the same as that currently seen toward omicron Per, but now the constrasting environmental conditions due to the recent star formation have led to marked differences in the atomic, molecular, and dust characteristics of IC 348. These contrasts include what we have termed a 'composite' UV extinction curve for BD +31 deg 643, evidence for enhanced density and enhanced depletions within IC 348 and very different molecular abundances in the interstellar sightline to BD +31 deg 643. Toward BD +31 deg 643, we find a higher column density of CH, but lower CN and very much higher CH(+) than measured toward omicron Per. We conclude that the physical and chemical state of the gas and dust has been altered by local processes and conditions within IC 348. The characteristics of the ISM in IC 348, via our study of the star BD +31 deg 643, closely resembles those seen toward rho Oph, another sight line passing through a bright nebular region. However, the stars are not as hot in IC 348 as in Ophiuchus, so their effect on the local ISM is not as severe.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 420; 2; p. 632-642
    Format: text
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  • 9
    Publication Date: 2019-07-12
    Description: Results of absorption measurements indicate that the PAH species responsible for the UIR (unidentified infrared) emission probably exist in a condensed form rather than as isolated molecules. It is shown that the peak absorption of the C-H stretch feature of vapor-phase PAHs occurs at a higher frequency than that of the condensed-phase PAHs and does not match the 3.289-micron interstellar feature. The vapor-phase experiments duplicate the phenomenon of the 3.3-micron profile simplification of PAH in KBr at elevated temperature. This confirms that the change of the profile with temperature is an intrinsic molecular effect, and is not a consequence of matrix (KBr) or condensed state interactions.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 380; L43-L46
    Format: text
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  • 10
    Publication Date: 2019-07-12
    Description: A new theoretical analysis of the structure of interstellar shocks and the grain dynamics of these shocks is presented. The basic hydrodynamic equations for J-shocks in interstellar gas are given in which shock-driving pressure is allowed to be weakly time-dependent and the grains are treated as a separate two-dimensional fluid. Specific equations for the grain dynamics in the cooling postshock gas are derived. An analytic theory for the propagation of a shock driven into an interstellar cloud by the blast wave of a supernova remnant which sweeps over the cloud is developed. An improved calculation of the grain charge in postshock gas is described, giving a simple analytic approximation for the results. The consequences of including these processes in the numerical code of Seab and Shull (1983) are addressed, including the effect of realistic magnetic fields in low-density gas.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 318; 674-701
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