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  • Fluid Mechanics and Thermodynamics; Composite Materials  (3)
  • Analytical Chemistry and Spectroscopy  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Resonance Raman spectra of 9,9′-bifluorenylideneThis work was supported by the Italian Consiglio Nazionale delle Ricerche. (1982)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 12 (1982), S. 30-35 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The resonance Raman spectra of 9,9′-bifluorenylidene have been measured in the 450-510 nm region either in solution or in the solid state by using six lines of the Ar+ laser. The analysis of the excitation profiles allowed inferences to be drawn concerning the vibronic structure of the lowest electronic excited state. The different behaviour shown by the profiles relative to the solid and the solution has been interpreted as due to different Franck-Condon overlap integrals between the ground and the excited electronic states. A vibrational assignment of the g modes is proposed on the basis of a polarized Raman spectrum in solution taken with the 632.8 nm line of a He-Ne laser. Electronic spectra of NaCl pellets and of oriented polycrystalline samples were also measured.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250120106
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    Paper (German National Licenses)
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  • 2
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    Analysis of Fibrous Felts for Flexible Ablators Using Synchrotron Hard X-Ray Micro-Tomography (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: We analyzed the material properties of low-density felts that are used as substrates for new-generation flexible and conformal carbon/phenolic ablators, and compared them with those of a rigid carbon fiber preform that is used to manufacture rigid carbon/phenolic ablators. Micro-tomography measurements were obtained using synchrotron X-rays, allowing the characterization of the materials microstructure at the scale of the fibers. Using the tomography voxels as computational grids, we computed tortuosity and room temperature conductivity. In addition we performed micro-scale simulations of the oxidation of carbon fibers using a random walk model for oxygen diffusion and a probability law to model surface reactions.
    Keywords: Fluid Mechanics and Thermodynamics; Composite Materials
    Type: ARC-E-DAA-TN21716 , European Symposium on Aerothermodynamics for Space Vehicles; Mar 02, 2015 - Mar 06, 2015; Lisbon; Portugal
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    From Tomography to Material Properties of Thermal Protection Systems (2017)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A NASA Ames Research Center (ARC) effort, under the Entry Systems Modeling (ESM) project, aims at developing micro-tomography (micro-CT) experiments and simulations for studying materials used in hypersonic entry systems. X-ray micro-tomography allows for non-destructive 3D imaging of a materials micro-structure at the sub-micron scale, providing fiber-scale representations of porous thermal protection systems (TPS) materials. The technique has also allowed for In-situ experiments that can resolve response phenomena under realistic environmental conditions such as high temperature, mechanical loads, and oxidizing atmospheres. Simulation tools have been developed at the NASA Ames Research Center to determine material properties and material response from the high-fidelity tomographic representations of the porous materials with the goal of informing macroscopic TPS response models and guiding future TPS design.
    Keywords: Fluid Mechanics and Thermodynamics; Composite Materials
    Type: ARC-E-DAA-TN43476 , International Planetary Probe Workshop; Jun 12, 2017 - Jun 16, 2017; The Hague; Netherlands
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    X-ray Micro-Tomography of Ablative Heat Shield Materials (2016)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: X-ray micro-tomography is a non-destructive characterization technique that allows imaging of materials structures with voxel sizes in the micrometer range. This level of resolution makes the technique very attractive for imaging porous ablators used in hypersonic entry systems. Besides providing a high fidelity description of the material architecture, micro-tomography enables computations of bulk material properties and simulations of micro-scale phenomena. This presentation provides an overview of a collaborative effort between NASA Ames Research Center and Lawrence Berkeley National Laboratory, aimed at developing micro-tomography experiments and simulations for porous ablative materials. Measurements are carried using x-rays from the Advanced Light Source at Berkeley Lab on different classes of ablative materials used in NASA entry systems. Challenges, strengths and limitations of the technique for imaging materials such as lightweight carbon-phenolic systems and woven textiles are discussed. Computational tools developed to perform numerical simulations based on micro-tomography are described. These enable computations of material properties such as permeability, thermal and radiative conductivity, tortuosity and other parameters that are used in ablator response models. Finally, we present the design of environmental cells that enable imaging materials under simulated operational conditions, such as high temperature, mechanical loads and oxidizing atmospheres.Keywords: Micro-tomography, Porous media, Ablation
    Keywords: Fluid Mechanics and Thermodynamics; Composite Materials
    Type: ARC-E-DAA-TN35767 , Ablation Workshop; Oct 05, 2016 - Oct 06, 2016; Tucson, AZ; United States
    Format: application/pdf
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