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  • Articles  (288)
  • Polymer and Materials Science  (188)
  • Biochemistry and Biotechnology  (90)
  • Physics  (35)
  • Physical Chemistry
  • 1995-1999  (288)
  • 1975-1979
  • 1998  (288)
  • 1
    ISSN: 0021-9304
    Keywords: biomaterials ; polyurethanes ; infection ; infection resistance ; surface modification ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Tissue reactions to implantable pacemaker leads were investigated in an early infection model in rabbits. Both standard leads and surface-modified leads were used. The surface modification technique was applied to achieve controlled release of the antibiotic gentamicin. The insulating polyurethane tubing material of the leads was provided with an acrylic acid/acrylamide copolymer surface graft and then loaded with gentamicin. Implantation periods varied from day 4, to week 3½, to week 10. We investigated tissue reactions in the absence of an infectious challenge and also the efficacy of surface-modified leads in preventing infection after challenge with Staphylococcus aureus was evaluated. It was demonstrated that the applied surface modification did not induce adverse effects although during early postimplantation an increase in infiltration of granulocytes and macrophages and wound fluid and fibrin deposition were observed. After bacterial challenge, standard leads were heavily infected at each explantation period, denoted by abscesses, cellular debris, and bacterial colonies. In contrast, little or no infection was observed, either macroscopically or by bacterial cultures, with the surface-modified leads. Microscopy showed little evidence of the bacterial challenge, and that primarily at day 4. It was concluded that the applied surface modification demonstrated enhanced infection resistance and thus represents a sound approach to the battle against infectious complications with biomaterials. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 142-153, 1998.
    Additional Material: 12 Ill.
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  • 2
    ISSN: 0006-3592
    Keywords: diffusion ; biofilms ; gels ; NMR ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The mobility of water in intact biofilms was measured with pulsed field gradient nuclear magnetic resonance (PFG-NMR) and used to characterise their diffusive properties. The results obtained with several well-defined systems, viz. pure water, agar, and agar containing inert particles or active bacteria were compared to glucose diffusion coefficients measured with micro-electrodes and those calculated utilising theoretical diffusion models. A good correspondence was observed indicating that PFG-NMR should also enable the measurement of diffusion coefficients in heterogeneous biological systems. Diffusion coefficients of several types of natural biofilms were measured as well and these results were related to the physical biofilm characteristics. The values had a high accuracy and reflected the properties of a sample of ca. 100 biofilms, while non-uniformity or non-geometrical shapes did not negatively influence the results. The monitored PFG-NMR signal contains supplementary information on e.g. cell fraction or spatial organisation but quantitative analysis was not yet possible. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 60: 283-291, 1998.
    Additional Material: 7 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 31-37 
    ISSN: 0006-3525
    Keywords: DNA liquid crystals ; DNA fragments ; screened Coulomb interactions ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The critical volume fractions pertaining to the formation of DNA liquid crystals were obtained from polarization microscopy, 31P-nmr, and phase separation experiments. The DNA length (approximately one to two times the persistence length 50 nm), ionic strength, and counterion variety dependencies are reported. The cholesteric-isotropic transition is interpreted in terms of the coexistence equations, which are derived from the solution free energy including orientational entropy and excluded volume effects. With the wormlike chain as reference system, the electrostatic contribution to the free energy is evaluated as a thermodynamic perturbation in the second virial approximation with a Debye-Hückel potential of mean force. The hard core contribution has been evaluated with scaled particle theory and/or a simple generalization of the Carnahan-Starling equation of state for hard spheres. For sufficiently high ionic strengths, the agreement is almost quantitative. At lower amounts of added salt deviations are observed, which are tentatively attributed to counterion screening effects. The contour length dependence agrees with a DNA persistence length 50 nm. © 1998 John Wiley & Sons, Inc. Biopoly 46: 31-37, 1998
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  • 4
    ISSN: 0887-624X
    Keywords: postpolymerization reactions ; ESR ; polymeric matrices termination reactions ; H-transfer reactions ; kinetic constants ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction kinetics in the dark of photopolymerized mono- and dimethacrylates in a polymeric binder has been studied. Electron spin resonance spectroscopy (ESR) provided useful information regarding the nature of the radicals involved in postpolymerization reactions. Computer simulations were performed to study the decay of the propagating radicals by considering normal bimolecular termination and transfer reactions of the radicals to the binder. Differences were found in the termination reactions for mono- and difunctional monomers when they were photopolymerized in a solid medium. Absolute kinetic constants for H-transfer reaction with the binder, relative kinetic rate constants for radical-radical coupling, and average lifetimes for the radicals have been calculated. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2785-2791, 1998
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  • 5
    ISSN: 0887-624X
    Keywords: photopolymerization kinetics ; ESR ; polymeric binders ; radical environment ; photocalorimetry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photopolymerization of several di- and tetrafunctional (meth)acrylic monomers in the presence of a styrene-butadiene-styrene polymeric matrix (SBS) has been studied. Electron spin resonance spectroscopy (ESR) and differential scanning photocalorimetry (photo-DSC) were used as monitoring techniques to identify the photogenerated radicals and analyze photopolymerization profiles, radical environments, and radical secondary reactions. The study of the photopolymerization and/or photocrosslinking reactions of these monomers in the solid media was carried out by taking into consideration different factors, such as the influence of both monomer and photoinitiator structures on the hydrogen abstraction in the binder with formation of benzylic and allylic radicals, the polymerization of the monomers itself and the hydrogen abstraction reaction in the polymerized acrylic chains. Finally, irradiation of the system SBS/photoinitiator in the absence of monomer was also accomplished. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2775-2783, 1998
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  • 6
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Surface engineering of light weight materials with ion- and plasma-assisted methodsIncreasing applications of light weight materials are expected in the future. Pursuing this trend surface engineering of these materials - especially ion- and plasma-assisted methods - swill be of increasing interest to enhance their wear and corrosion resistance. In a research co-operation some promising methods were examined on different aluminium and titanium alloys to assess their potential to increase the surface properties. Among these were magnetron sputtering of chromium nitride, ion beam assisted deposition of Cr/CrN and Al/A2O3 layers, ion implantation and ion beam assisted nitriding. Compared to the steel substrates the assessment of the mechanical properties such as the critical load of the scratch test of the coated light weight materials is different. Furthermore, it could be shown that both spherical section and glow discharge optical spectroscopy are useful methods to characterize the near-surface zone influenced by ion implantation.
    Notes: Es ist zu erwarten, daß die Anwendungsbreite von Leichtmetall-legierungen in Zukunft noch steigen wird. Mit diesem Trend werden auch oberflächentechnische Methoden - insbesondere ionen- und plasmaunterstützte Verfahren - gefragt sein, um den Verschleiß- und Korrosionswiderstand der Oberflächen zu verbessern. Im Rahmen eines Verbundprojektes wurden verschiedene aussichtsreiche Verfahren untersucht, um ihr Potential zur Verbesserung der Oberflächeneigenschaften von Aluminium- und Titanlegierungen einschätzen zu können. Hierunter befanden sich das Magnetronsputtern von Chromnitrid, die ionenstrahluntersützte Abscheidung von Cr/CrN- und Al/A2O3Schichten, die Ionenimplantation und das Ionenstrahlnitrieren. Im Vergleich mit beschichteten Stahlsubstraten ergeben sich Unterschiede bei der Einschätzung wichtiger mechanischer Eigenschaften, wie der im Ritztest ermittelten kritischen Last. Weiterhin konnte gezeigt werden daß sowohl der Kalottenschliff als auch die Glimmentladungspektroskopie gut geeignet sind, die durch Ionenimplantation beeinflußte Randzone zu charakterisieren.
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  • 7
    ISSN: 0006-3525
    Keywords: electron microscopy ; NCp7-induced polyA aggregation ; polyA-NCp7 interaction ; mechanism of aggregate growth ; aggregation dependence ; salt concentration ; protein concentration ; nucleotide to protein ratio ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: NCp7, the nucleocapsid protein of the human immunodeficiency virus type 1, induces an ordered aggregation of RNAs, a mechanism that is thought to be involved in the NCp7-induced promotion of nucleic acid annealing. To further investigate this aggregation, the morphology and the properties of the NCp7-induced aggregates of the model RNA homoribopolymer, polyA, were investigated by electron microscopy in various conditions. In almost all the tested conditions, the aggregates were spherical and consisted of a central dense core surrounded by a less dense halo made of NCp7-covered polyA molecules. The formation of these aggregates with a narrow distribution of sizes constitutes a distinctive feature of NCp7 over other single-stranded nucleic acid binding proteins. In most conditions, at the shortest times that can be reached experimentally, all the polyA molecules were already incorporated in small aggregates, suggesting that the nucleation step and the first aggregation events took place rapidly. The aggregates then orderly grew with time by fusion of the smaller aggregates to give larger ones. The aggregate halo was important in the fusion process by initiating the bridging between the colliding aggregates. In the presence of an excess of protein, the aggregates grew rapidly but were loosely packed and dissociated easily, suggesting adverse protein-protein interactions in the aggregates obtained in these conditions. In the presence of an excess of nucleotides, the presence of both amorphous nonspherical and slowly growing spherical aggregates suggested some changes in the mechanism of aggregate growth due to an incomplete covering of polyA molecules by NCp7. Finally, we showed that in the absence of added salt, the aggregate fusions were unfavored but not the initial events giving the first aggregates, the reverse being true in the presence of high salt concentrations (≥300 mM). © 1998 John Wiley & Sons, Inc. Biopoly 45: 217-229, 1998
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Bioluminescence and Chemiluminescence 13 (1998), S. 273-278 
    ISSN: 0884-3996
    Keywords: diabetes ; leukocytes ; monocytes ; extracellular matrix ; non-enzymatic glycosylation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Non-enzymatic glycosylation (NEG) of collagen has been previously shown to significantly influence the reactive oxygen metabolism (ROM) of phagocytic cells in healthy subjects. Considering the role of NEG in the pathophysiology of diabetes, we have further analysed the oxidative metabolism of polymorphonuclear cells (PMNs) and monocytes in 23 patients with non-insulin dependent diabetes mellitus in order to better elucidate a possible pathogenic role of NEG of the extracellular matrix in long-term complications of diabetes. Experiments were performed in triplicate on native-collagen and glycated-collagen coated vials, using a chemiluminescence (CL) assay. Results show that PMNs from diabetic patients display a significant increased basal and zymosan-induced CL activity with respect to controls that are not related to the glycation state of the substrate. Conversely, the CL activity of monocytes induced by zymosan shows a decrease in diabetic patients with respect to healthy volunteers (p 〈 0.05). Moreover, monocyte CL was reduced by the glycated matrix, both in healthy volunteers and in diabetic subjects (p 〈 0.05 and p 〈 0.01, respectively). These data highlight a complex role of phagocytic leukocytes in the pathophysiology of extracellular matrix alterations secondary to NEG that are typically present in clinical conditions such as diabetes or ageing. © 1998 John Wiley & Sons, Ltd.
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  • 9
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 665-671 
    ISSN: 0887-6266
    Keywords: clustering ; water ; wood ; adsorption ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Clustering behavior of water molecules during adsorption of water in wood was studied using the Zimm-Lundberg theory. The average cluster size of water molecules was determined with the help of wood adsorption isotherms at five temperatures. The effects of both relative humidity and temperature on average cluster size were studied. Average cluster size progressively increased with an increase in humidity. At humidities corresponding to fiber saturation, larger clusters were formed. Cluster size increased sharply with an increase in temperature at humidities close to saturation. Formation of large clusters at high temperature and humidities close to saturation is attributed to increased fraction of weakly bonded water and capillary condensation in such conditions. A description of adsorption of water in wood was provided in terms of average cluster size. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 665-671, 1998
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 58 (1998), S. 595-604 
    ISSN: 0006-3592
    Keywords: turbulent jet ; plant cells ; Morinda citrifolia ; shear damage ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Cell suspensions of Morinda citrifolia were subjected to turbulent flow conditions in a submerged jet apparatus, to investigate their hydrodynamic shear susceptibility. The suspensions were exposed to repeated, pressure-driven passages through a submerged jet. Two nozzles, of 1 mm and 2 mm diameter, were employed. Average energy dissipation rates were in the range 103-105 W/kg and cumulative energy dissipation in the range 105-107 J/m3. System response to the imposed conditions was evaluated in terms of suspension viability (determined using a dye exclusion technique) and variations in both chain length distribution and maximum chain length. Viability loss was well-described by a first-order model, and a linear relationship was identified between the specific death rate constant and the average energy dissipation rate. This relationship was consistent with results obtained using the same suspension cultures in a turbulent capillary flow device. Morphological measurements indicated that exposure to the hydrodynamic environment generated in the jet resulted in a significant reduction in both the average and maximum chain lengths, and the reduction in the maximum chain length was identified as an appropriate measure of sustained damage. Analysis of both viability and chain length in terms of cumulative energy dissipated revealed good agreement with results reported by other authors for morphologically different plant cell systems. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 58: 595-604, 1998.
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