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Now showing items 113 - 128 of 35644

  • Trilayer model in design of W/C multilayer mirrors with a small period thickness

    Chon, Kwon Su  

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  • Microstructure and mechanical properties of nanolayered W/W–C thin films

    K. Abdelouahdi   C. Legrand-Buscema   P. Aubert  

    The present study reports on the mechanical and structural properties of W/W-C multilayered thin films with bilayer periods Lambda ranging from 2.5 to 100 nm. Films were grown by reactive sputtering radio frequency on Si (100) substrate. X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD) and X-ray reflectivity were used to globally characterise the multilayers structure. Hardness and Young modulus have been determined using nanoindentation with a Berkovich tip. The XRD and the GIXRD diagrams revealed the presence of three phases: WC 1-x randomly oriented, W 2C with (100) preferred orientation and W with (110) preferred orientation. An increase in hardness is observed with decreasing period Lambda, reaching a maximum value of ~26 GPa at Lambda = 2.5 nm.
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  • Thermodynamic description and quaternary miscibility gap of the C–Hf–Ti–W system

    Pan, Yafei   Du, Yong   Zhou, Peng   Peng, Yingbiao   Luo, Fenghua  

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  • Interaction of C with vacancy in W: A first-principles study

    Liu, Yue-Lin   Zhou, Hong-Bo   Zhang, Ying   Lu, Guang-Hong   Luo, Guang-Nan  

    We provide a vacancy trapping mechanism of C in W by investigating structure, stability, and diffusion properties of C in W using a first-principles method. C easily bonds onto the internal-surface of vacancy. A monovacancy is capable of trapping as many as 4 C atoms to form C(n)V (n = 1, 2, 3, 4) complexes. Single C atom prefers to interact with neighboring W at vacancy with the trapping energy of -1.93 eV. With the C atoms added, both of them are preferred to bind with each other to form covalent-like bond despite the metallic W environment. For the C(n)V complexes, C(2)V is the major one due to its largest average trapping energy (-1.97 eV). Kinetically, formation of the C(n)V complexes can be ascribed to the interstitial mechanism due to the lower activation energy barrier of 1.46 eV for the interstitial C than 1.66 eV for the vacancy. (C) 2011 Elsevier B.V. All rights reserved.
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  • Investigation of aperiodic W/C multi-layer mirror for X-ray optics

    Wang, Zhanshan   Cheng, Xinbin   Zhu, Jingtao   Huang, Qiushi   Zhang, Zhong   Chen, Lingyan  

    Design, fabrication and characterization of aperiodic tungsten/carbon (W/C) multi-layer mirror were studied. W/C multi-layer was designed as a broad-angle reflective supermirror for Cu-K alpha line (lambda = 0.154 nm) in the grazing incident angular range (0.9-1.1 degrees) using simulated annealing algorithm. To deposit the W/C depth-graded multi-layer mirror accurately, we introduce an effective layer growth rate as a function of layer thickness. This method greatly improves the reflectivity curve compared to the conventional multi-layer mirror prepared with constant growth rate. The deposited multi-layer mirror exhibits an average reflectivity of 19% over the grazing incident angle range of 0.88-1.08 degrees which mainly coincides with the designed value. Furthermore, the physical mechanisms were discussed and the re-sputtering process of light-atom layers is accounted for the modification of layer thicknesses which leads to the effective growth rates. Using this calibration method, the aperiodic multi-layer mirrors can be better fabricated for X-ray optics. (C) 2011 Elsevier B.V. All rights reserved.
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  • French Romantic Travel Writing: Chateaubriand to Nerval, by C. W. Thompson

    Yee   Jennifer  

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  • French Romantic Travel Writing: Chateaubriand to Nerval, by C. W. Thompson

    Yee, Jennifer  

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  • Elements of Adaptive Testing edited by van der Linden, W. J., & Glas, C. A. W.

    Ying Cheng  

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  • Microstructure and mechanical properties of nanolayered W/W–C thin films

    K. Abdelouahdi   C. Legrand-Buscema and P. Aubert  

    The present study reports on the mechanical and structural properties of W/W–C multilayered thin films with bilayer periods Λ ranging from 2.5 to 100 nm. Films were grown by reactive sputtering radio frequency on Si (100) substrate. X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD) and X-ray reflectivity were used to globally characterise the multilayers structure. Hardness and Young modulus have been determined using nanoindentation with a Berkovich tip. The XRD and the GIXRD diagrams revealed the presence of three phases: WC1−x randomly oriented, W2C with (100) preferred orientation and W with (110) preferred orientation. An increase in hardness is observed with decreasing period Λ, reaching a maximum value of ~26 GPa at Λ = 2.5 nm.
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  • Nicht wie eine Toiletten-Lektüre – C.?W. Hufeland und sein Verleger Brockhaus

    Hansen   W.  

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  • Terrae-Rarae-Preis: P.?C. Junk und P.?W. Roesky / Preis der Bau-Familie: H. Xu

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  • Terrae-Rarae-Preis: P. C. Junk und P. W. Roesky / Preis der Bau-Familie: H. Xu

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  • Characterization of WC-(W,V)C-Co made from pre-alloyed (W,V)C

    Hashe, Nobom Gretta   Norgren, Susanne M.   Andren, Hans-Olof   Neethling, Johannes H.  

    Large (W,V)C cubic carbides in WC-VC-Co cemented carbides are undesirable as their presence is one of the causes for poor properties in the material. Earlier attempts to reduce the (W,V)C cubic carbide grain sizes in the WC-VC-Co cemented carbide have been published before. The present investigation strives to reduce the cubic carbide grain size by using a pre-alloyed (W,V)C powder in the place of VC, to reduce the driving force for the formation of (W,V)C during sintering. This should in turn reduce the possibility of forming large (W,V)C grains. WC-VC-Co was prepared using WC, (W,V)C, and Co powders. The compositions were 8.1 wt% V and 12 wt% Co, with the balance comprising W and C. XRD diffraction patterns confirmed that the bulk of WC-(W,V)C-Co contains WC grains, cubic (W,V)C grains, and a Co-rich binder phase. SEM-EDS measurements yielded an average composition of (W(0.31)V(0.69))C(x). TEM-EDS of the cubic carbide was in good agreement with the SEM-EDS measurement, yielding the average composition of (W(0.30)V(0.70))C(x) The average grain size of the cubic carbide of WC-(W,V)C-Co material after sintering had grown to only the same size as that of the starting powder, 1.4 mu m. (C) 2008 Elsevier Ltd. All rights reserved.
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  • Caesar\"s Civil Warby W. W. Batstone; C. Damon

    Review by: Aislinn Melchior  

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  • W. C. Handy, Abbe Niles, and (Auto)biographical Positioning in the Whiteman Era

    Dunkel, Mario  

    This article investigates W. C. Handy's collection of blues and jazz compositions Blues: An Anthology (1926) in light of Paul Whiteman's pre-eminent role in 1920s American popular music culture. It explores Whiteman's autobiographics, on the one hand, and the correspondence between Handy and the author of the anthology's foreword, Edward Abbe Niles, on the other, in order to demonstrate how Handy's self-determined voice asserted itself against both the discursive power of the Whiteman-led symphonic jazz movement and the appropriative impulse of primitivist jazz and blues historiography.
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  • Adsorption of CO and O(2) on W(2)C(0001)

    Aizawa, Takashi   Otani, Shigeki  

    CO, O(2), and H(2) adsorption on a clean W(2)C(0001)root 13 x root 13 R +/- 13.9 degrees reconstructed surface at room temperature (RT) were investigated using high-resolution electron energy loss spectroscopy (HREELS). The W(2)C(0001) adsorbs CO molecularly and adsorbs O(2) dissociatively, but does not adsorb H(2) at RT. In the CO adsorption system, two C-O stretching (antisymmetric CCO stretching) modes were found at 242.3 meV (1954 cm(-1)) and at 253.0 meV (2041 cm(-1)). The low-frequency site is occupied at first with subsequent conversion to the high-frequency site with increasing coverage. Additionally, a small peak was apparent at 104.5 meV (843 cm(-1)), and a middle peak at 50-51 meV (400-410 cm(-1)), which are assignable to a symmetric stretching mode and a hindered translational mode, respectively, of a CCO (ketenylidene) species. These observations are consistent with the CO adsorption model on top of the surface carbon. For oxygen adsorption, two adsorption states were found at 65.2-68.1 meV (526-549 cm(-1)) and 73.6 meV (594 cm(-1)): typical frequencies to oxygen adsorption on metal surfaces. Results suggest that atomic oxygen adsorption occurred on a threefold hollow site of the second W layer. (C) 2011 American Institute of Physics. [doi:10.1063/1.3650246]
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