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  • Wiley-Blackwell  (11)
  • Nature Publishing Group  (5)
  • 1995-1999  (16)
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Year
  • 1
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Fas ligand is believed to mediate immune privilege in a variety of tissues, including the eye, testis, and a subset of tumors. We tested whether expression of Fas ligand on pancreatic islets either following adenovirai or germline gene transfer could confer immune privilege after transplantation. ...
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 381 (1996), S. 745-745 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - The excessive fat deposition and other genetic disorders seen in the obese ob/ob mouse has been shown to be due to a mutation (premature stop codon) in the ob gene1. Normally, the ob gene is expressed in adipose tissue, with the secreted circulating gene product, leptin, being thought to act ...
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  • 3
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The spatial distribution of bedrock and alluvial reaches depends on the relation of local transport capacity (qc) to the bedload sediment supply (qs) delivered from upstream and across channel banks. A bedrock stream bed indicates a transport capacity in excess of sediment supply (qc 〉 qs), ...
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The crystal structure of the 20S proteasome from the yeast Saccharomyces cerevisiae shows that its 28 protein subunits are arranged as an (α1...α7, β1...β7)2 complex in four stacked rings and occupy unique locations. The interior of the particle, which harbours the ...
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature structural biology 5 (1998), S. 446-450 
    ISSN: 1072-8368
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Enteric bacteria such as Escherichia coli and S. typhimurium are able to migrate toward or away from specific chemicals, a behavior known as chemotaxis1. A family of transmembrane receptors detects chemical stimuli and regulates the activity of CheA, a histi-dine protein kinase involved in a ...
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 26 (1995), S. 27-31 
    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
    Notes: Stahlbleche wurden mittles Gleichstrom-Magnetron-Sputtern mit Titannitrid beschichtet. Durch Variation des Stickstoffdurchflusses konnten Schichten mit unterschiedlicher chemischer Zusammensetzung erhalten werden. Die Schichten wurden mittels Gimmentladungsspektroskopie und einer naßchemischen Methode quantitativ analysiert. Für die naßchemische Analyse wurden die Schichten vom Substrat getrennt, aufgeschlossen und nachfolgend die Elemente Titan mittels Atomabsorptionsspektroskopie und Stickstoff nach Kjeldahl bestimmt. Die Analysenergebnisse zeigen signifikante Unterschiede zwischen den beiden Verfahren, die durch die unterschiedlichen verwendeten Standards verursacht werden. So ergibt die GDOS-Analyse im Vergleich zur naßchemischen Analyse für unterstöchiometrische TiNx-Schichten (x 〈 1) zu niedrige Stickstoffgehalte und für etwa stöchiometrische Schichten (x ≈ 1) zu hohe. Aufgrund der Standards kann geschlossen werden, daß die naßchemische Analyse mit einem geringeren systematischen Fehler behaftet ist. Sie ist aber in der Handhabbarkeit der GDOS-Analyse weit unterlegen und eignet sich damit besser für die Kalibration von speziellen Proben, die nachfolgend bei der GDOS-Analyse als Standard eingesetzt werden können.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 29 (1998), S. 525-536 
    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: Temperature of cutting tools by thin filmsDuring the cutting process, cutting tools are exposed to complex mechanical, thermal, dynamic and tribological loads. Especially in the case of dry machining the demands on cutting tools are very high. Dry machining becomes more and more interesting because of tightened up ecolaws and increased costs for the handling of coolants. Due to a renunciation on coolants the cutting tools need to be modified to the process of dry machining. Thereby modern plasma and ion based surface technologies can be used to deposit a thin film adopting the functions of coolants, e.g. cooling and lubricating.In this research project several coating types, e.g. titanium and chromium based coatings, where developed and characterized regarding their mechanical, tribological and thermal properties. For the research, four partners collaborated permuting all steps of surface and coatings design. Materials Science Institute (WW), Aachen University of Technology, performed the development of PVD coatings and the thermophysical characterization by thermal wave analysis. Surface modifications of uncoated and coated tools by ion beam assisted deposition were carried out at Stiftung Institut für Werkstofftechnik (IWT), Bremen. To determine the cutting properties of coated tools, practical tests were performed at Laboratory for Machine Tools and Production Engineering (WZL), Aachen University of Technology.
    Notes: Zerspanwerkzeuge sind während ihres Einsatzes einem komplexen und schwer zu erfassenden Beanspruchungskollektiv ausgesetzt. Dieses wird besonders durch die aus ökonomischen und ökologischen Gründen angestrebte Trockenzerspanung beeinflußt. Der vollständige Verzicht auf Kühlschmierstoffe bedeutet aus technologischer Sicht, daß Werkzeuge, Schneidstoffe und Zerspanoperationen auf die Bedingungen der Trockenzerspanung umgestellt werden müssen. Dabei bieten moderne ionen-und plasmagestütze Oberflächentechnologien insofern einen Lösungsansatz, daß durch Beschichtungen bzw. Oberflächenmodifikationen wichtige Aufgaben der Kühlschmiermittel durch den beschichteten Schneidstoff selbst übernommen werden können. Dies sind vor allem der Ersatz von Schmierung und Kühlung.Für den Bereich der Trockenzerspanung wurden im Rahmen eines Verbundvorhabens u.a Titanbasisschichten sowie Chrombasisschichten entwickelt und hinsichtlich der physikalischen Eigenschaften untersucht. Durch die enge Zusammenarbeit der beteiligten Forschungsstellen konnte das jeweils vorhandene Erfahrungspotential vollständig in die Schichtsystementwicklung einfließen. Diese umfaßte alle iterativen Schritte des Schichtmodifikation, begleitende Schichtanalytik bis hin zum Praxistest. So war beispielsweise das Lehr- und Forschungsgebiet Werkstoffwissenschaften der RWTH Aachen für die Schichtentwicklung sowie fü die thermophysikalische Charakterisierung der Schichten zuständig. Die Stiftung Institut für Werkstofftechnik, Bremen, führte eine Optimierung der Interfaces und der Hartstoffschichten mittels ionenstrahlgestützter Beschichtungsverfahren durch. So konnte das Substrat vor bzw. die Hartstoffschicht nach der Beschichtung an den Anwendungsfall angepaßt werden. Die Untersuchung hinsichtlich der Praxistauglichkeit der beschichteten Schneidstoffe erfolgte am Werkzeugmaschinenlabor der RWTH Aachen durch entsprechende Zerspanversuche.
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 49 (1996), S. 456-466 
    ISSN: 0006-3592
    Keywords: microcarrier culture ; turbulent mixing ; 3-D particle tracking ; energy dissipation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Three-dimensional particle tracking velocimetry (3-D PTV), a modern, quantitative, visualization tool, has been applied to the characterization of the flow field in the impeller region of cell culture reactor vessels. The experimental system used here is a 250-mL microcarrier spinner vessel. The studies were conducted at three different agitation rates, 90, 150, and 210 rpm, corresponding to healthy, mildly damaging, and severely damaging shear intensities, respectively. The flow can be classified into three regions: a predominantly tangential (azimuthal) flow generated by the impeller; a trailing vortex region coming off the impeller tip; and a converging flow region close to the center of the vessel. The latter two are the regions of highest velocity gradients. Energy dissipation rates due to mean velocity gradients were also calculated to characterize the impeller stream. Local specific energy dissipation rates 〉 10,000 erg/(cm3sec) · have been measured. It is proposed that the critical regions for microcarrier culture damage due to impeller hydrodynamics are the trailing vortex region and the high energy converging flow region. Graphical representation of the mean velocity flow fields and the distribution of energy dissipation rates in the impeller region are also presented here. The merits of using the dissipation function (measure of specific energy dissipation rate) as a possible scale-up parameter are also discussed. © 1996 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 469-476 
    ISSN: 1434-1948
    Keywords: Cage compounds ; Crystal structure ; Hafnium ; Trimetaphosphimates ; Zirconium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The (trimetaphosphimato)hafnates and -zirconates Na4{Hf4(μ4-O)(μ-OH)6[(PO2NH)3]4} · 18 H2O [1, Pa3, a = 22.687(3) Å, Z = 8], Na4{Hf4(μ4-O)(μ-OH)6[(PO2NH)3]4} · 21 H2O [2, R3, a = 14.350(2), c = 50.348(10) Å, Z = 6], Na4{Zr4(μ4-O)(μ-OH)6[(PO2NH)3]4} · 18 H2O [3, Pa3, a = 22.693(3) Å, Z = 8], and Na4{Zr4(μ4-O)(μ-OH)6[(PO2NH)3]4} · 21 H2O [4, R3¯, a = 14.303(2), c = 50.284(10) Å, Z = 6] were obtained by the stoichiometric reaction of HfOCl2 · 8 H2O and ZrOCl2 · 8 H2O with an aqueous solution of Na3(PO2NH)3 · 4 H2O, followed by the diffusion-controlled addition of methanol. During these reactions compounds 1 and 2, or 3 and 4, crystallized simultaneously and the hafnium and zirconium complexes 1 and 3, as well as 2 and 4, were found to be isostructural and isomorphous. The characteristic structural feature which is central to 1, 2, 3, and 4 is the complex tetranuclear anion {M4(μ4-O)(μ-OH)6[(PO2NH)3]4}4- with M = Zr or Hf. The anion consists of five corner-sharing adamantanoid cages. The central cage, {M4(μ4-O)(μ-OH)6}8+, has a tetracoordinated oxygen atom in the middle, and the other cages are formed by the trimetaphosphimate ions acting as tridentate ligands which coordinate to Hf or Zr. The water content of the compounds 1-4 could not be determined unequivocally by chemical analyses since the compounds are always obtained as mixtures of the rhombohedral (2/4) and cubic (1/3) phases. Thermal decomposition of compounds 1-4 starts above 120°C and leads to the formation of HfP2O7 and ZrP2O7/NaZr2(PO4)3, with the evolution of H2O and NH3. DSC measurements gave no evidence that the compounds 1 and 2, or 3 and 4, might be transformed into each other by heating.
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