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  • 2005-2009  (7)
  • 1
    Electronic Resource
    Electronic Resource
    Neuroscience Plasticity and its limits (2005)
    [s.l.] : Nature Publishing Group
    Nature 435 (2005), S. 288-289 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Many sensory systems are characterized by connections from receptor surfaces, such as the retina or skin, in which the relationship between neighbouring inputs is preserved. The resulting ‘topological maps’ are also commonly maintained in subsequent projections between sensory areas ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/435288a
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  • 2
    Electronic Resource
    Electronic Resource
    Specification of the neural crest occurs during gastrulation and requires Pax7 (2006)
    [s.l.] : Nature Publishing Group
    Nature 441 (2006), S. 218-222 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The neural crest is a stem population critical for development of the vertebrate craniofacial skeleton and peripheral ganglia. Neural crest cells originate along the border between the neural plate and epidermis, migrate extensively and generate numerous derivatives, including neurons and glia ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature04684
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis of Si〈sub〉3〈/sub〉N〈sub〉4〈/sub〉 from Na〈sub〉2〈/sub〉SiF〈sub〉6〈/sub〉 as a Solid Precursor: Microstructural Evolution (2007)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 560 (Nov. 2007), p. 109-114 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The effect of processing parameters on the weight loss of the silicon solid precursor(Na2SiF6) and the deposition characteristics and morphology of Si3N4 formed onto SiCp/Si poroussubstrates by CVD has been investigated. The results show that the weight loss of Na2SiF6 is mostsignificantly affected by the processing temperature, followed by the processing time and the typeof nitrogen precursor. Formation of Si3N4 is mostly influenced by the substrate temperature,followed by the type of nitrogen precursor and processing time. An increase in processing time andtemperature from 60 to 120 min and from 900 to 1300 oC, respectively, favors dissociation ofNa2SiF6 and formation of Si3N4. Moreover, N2 enhances Na2SiF6 dissociation and hampers Si3N4formation, while the N2-NH3 mixture hinders the solid precursor dissociation and favors Si3N4formation. With regard to microstructure evolution, it is found that in N2 the amount of Si3N4increases with temperature and the morphology changes from wool-like and light fibers to thickerand compact fibers. When N2-NH3 is used and the processing temperature is increased, themorphology of Si3N4 is modified from deposits with wool-like and compact appearance to whiskersand spheres and finally to thick and compact fibers
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/17/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.560.109.pdf
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis of Si〈sub〉3〈/sub〉N〈sub〉4〈/sub〉 from Na〈sub〉2〈/sub〉SiF〈sub〉6〈/sub〉 as a Solid Precursor: Thermodynamic Study (2007)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 560 (Nov. 2007), p. 11-16 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: CVD silicon nitride (Si3N4) is typically produced from gas or liquid precursorscontaining nitrogen and silicon. The method using Na2SiF6(s) as silicon solid precursor to producefilms/coatings, reinforcements and powders of silicon nitride by CVD has been recently proposed inthe literature. In this investigation, a thermodynamic study is carried out using the FactSageThermochemical Software and Databases, in order to explain the phenomena associated to thesynthesis of Si3N4 with Na2SiF6 as solid precursor. Accordingly, CVD diagrams for Na2SiF6, SiF4,SiF3, SiF2, SiF, and Si both with N2 and NH3 are constructed using such a software.Thermodynamically Si3N4 can be produced from SiF4(g) or Na2SiF6(s) with ammonia. Althoughthermodynamic considerations show that Si3N4 cannot be produced with the use of nitrogen,experimental results in this investigation show that it is formed with both ammonia and nitrogen
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/17/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.560.11.pdf
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  • 5
    Electronic Resource
    Electronic Resource
    Microstructure and Mechanical Properties of Al/Sic〈sub〉p〈/sub〉 Composites with Multimodal Size Distribution of Reinforcements (2007)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 560 (Nov. 2007), p. 115-120 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The effect of particle size distribution and particle size ratio of SiCp in SiCp/SiO2preforms on the microstructure, microhardness of SiCp reinforcements, modulus of rupture,and superficial hardness of Al/SiCp composites produced by pressureless infiltration has beeninvestigated. SiCp/SiO2 preforms in the form of plates (4cm x 3cm x 0.5cm) have beenpressureless infiltrated by the alloy Al-15.52 Mg-13.62 Si (wt. %) at 1100 oC for 60 minunder inert atmosphere. SiC powders with average particle size of 10, 68 and 140 μm aremixed with SiO2 powders and preforms of 40 % porosity with unimodal, bimodal andtrimodal size distributions are prepared by uniaxial compaction. The bimodal (small: large)and trimodal (small: medium: large) preforms are prepared with different particle size ratiosin the following levels: 1:1, 3:1, 1:3, 2:2:2, 3:2:1, 3:1:2. Results from characterization byXRD, SEM and energy dispersive X-ray spectrometry show that the typical microstructure ofthe composites contains the MgAl2O4 (spinel), AlN and MgO phases formed duringprocessing as well as partially reacted silica, SiC, Si and Al. It is found that the density,reinforcement microhardness, modulus of rupture and superficial hardness of the compositesincrease all with wider particle size distribution. However, whilst the modulus of rupture ismainly affected on going from unimodal and bimodal to trimodal distribution, superficialhardness and microhardness are mostly influenced on going from unimodal to bimodal andtrimodal distribution
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/17/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.560.115.pdf
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  • 6
    Electronic Resource
    Electronic Resource
    High Temperature Chemical Interaction Between SiO〈sub〉2〈/sub〉 Substrates and Ag-Cu Based Liquid Alloys in Vacuo (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 509 (Mar. 2006), p. 117-122 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The interfaces formed between vitreous or thermally devitrified fused quartz substrates and silver alloys after 90 min at 850 °C in vacuum have been characterized. Three silver alloys have been used: Cusil (Ag–28 wt % Cu), Cusil-ABA (Ag–35 wt % Cu–1.5 wt % Ti), and Incusil-ABA(Ag–27 wt % Cu–12 wt % In–2 wt % Ti). A non wetting condition is found for the Cusil alloy in both substrates. In contrast, the formation of Ti5Si3, Cu3Ti3O and Ti2O3, following the sequence SiO2 → Ti2O3 → Ti5Si3 → Cu3Ti3O, is observed at the metal/ceramic interface for the two titaniumcontaining alloys on both substrates. Ti2O3 is commonly found as small particles dispersed in a silver-rich matrix. During the experiments, the reaction product layers detach from the ceramicsurface and float away from the ceramic/metal interface due to their relatively low density with respect to the liquid alloy. The formation of the phases detected at the ceramic/metal interface can be explained in terms of their relative thermodynamic stability
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/12/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.509.117.pdf
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  • 7
    Electronic Resource
    Electronic Resource
    Degradation of Al/SiCp Composites Processed with Fly Ash via Reactive Infiltration (2007)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 560 (Nov. 2007), p. 139-144 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The degradation in ambient atmosphere of Al/SiCp composites prepared by the reactiveinfiltration of SiCp preforms containing fly ash has been investigated. SiCp/fly-ash preforms in theform of plates (3 cm x 4 cm x 0.5 cm) with 50 % porosity are infiltrated by an Al- 8 Si-15 Mg (wt.%) alloy under argon atmosphere at 1050, 1100 and 1150 ºC, for 50, 60 and 70 min.Characterization by XRD, SEM and EDX of composite specimens shortly after processing do notreveal the presence of the unwanted Al4C3 phase. However, in addition to Al, Si and SiC, MgAl2O4and Mg2Si phases are detected. One month after the infiltration trials, white and gray powders arepresent on the composite specimens, accompanied by pitting corrosion and cracks which propagatewith time. Although analysis by XRD of the degradation products reveals only Al4C3 in addition tothe above mentioned phases, results from SEM, IR absorption and ICP also suggest the presence ofAl(OH)3 and Mg(OH)2, probably from the interaction of Al4C3 and Mg2Si with water. It isconsidered that Mg2Si in the powders acts as an anode in a galvanic couple with atmosphericmoisture as the electrolyte. The crack pathway through SiC, intermetallic AlFeMnSi and Si richzones implies that one or more of these phases worked as the cathode. In summary, degradation ofthe composites is explained by the combined effect of galvanic corrosion caused by second phasesand the interaction of Al4C3 with atmospheric moisture
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/17/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.560.139.pdf
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