Development of sputtered techniques for thrust chambers

Procedures for closing out coolant passages in regeneratively cooled thrust chambers by triode sputtering, using post and hollow Cu-0.15 percent Zr cathodes are described. The effects of aluminum composite filler materials, substrate preparation, sputter cleaning, substrate bias current density and system geometry on closeout layer bond strength and structure are evaluated. High strength closeout layers were sputtered over aluminum fillers. The tensile strength and microstructure of continuously sputtered Cu-0.15 percent Zr deposits were determined. These continuous sputtered deposits were as thick as 0.75 cm. Tensile strengths were consistently twice as great as the strength of the material in wrought form

Mixing-induced anisotropic correlations in molecular crystalline systems

We investigate the structure of mixed thin films composed of pentacene (PEN) and diindenoperylene (DIP) using X-ray reflectivity and grazing incidence X-ray diffraction. For equimolar mixtures we observe vanishing in-plane order coexisting with an excellent out-of-plane order, a yet unreported disordering behavior in binary mixtures of organic semiconductors, which are crystalline in their pure form. One approach to rationalize our findings is to introduce an anisotropic interaction parameter in the framework of a mean field model. By comparing the structural properties with those of other mixed systems, we discuss the effects of sterical compatibility and chemical composition on the mixing behavior, which adds to the general understanding of interactions in molecular mixtures.Comment: 5 pages, 5 figures, accepted by Phys. Rev. Let

Alterações em atributos físicos do solo decorrentes da rotação soja-pastagem, no sistema plantio direto.

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Diameter dependence of the optoelectronic properties of single walled carbon nanotubes determined by ellipsometry

International audienceWe report ellipsometric measurement on single walled carbon nanotube (SWCNT) films performed in a large spectral range from 0.07eV to 4.97eV. The complex dielectric functions of SWCNTs are correlated to their diameter distribution extracted from transmission electron microscopy. Here we show that the transition energies between Van Hove singularities are directly related to the strong one dimensional confinement. In the infrared spectral range, the real part of the dielectric function becomes negative. The electronic properties of SWCNTs are extracted from ellipsometry by using a Drude model. The mobility and the mean free path of charge carriers are limited by the high number of SWCNT contacts. In accordance with tight binding simulation, the conductivity and the charge carrier concentration increase with the SWCNT diameter. Finally, we demonstrate that the S-plasmon energy depends on the charge carrier concentration.

Real-time, label-free, intraoperative visualization of peripheral nerves and microvasculatures using multimodal optical imaging techniques

Accurate, real-time identification and display of critical anatomic structures, such as the nerve and vasculature structures, are critical for reducing complications and improving surgical outcomes. Human vision is frequently limited in clearly distinguishing and contrasting these structures. We present a novel imaging system, which enables noninvasive visualization of critical anatomic structures during surgical dissection. Peripheral nerves are visualized by a snapshot polarimetry that calculates the anisotropic optical properties. Vascular structures, both venous and arterial, are identified and monitored in real-time using a near-infrared laser-speckle-contrast imaging. We evaluate the system by performing in vivo animal studies with qualitative comparison by contrast-agent-aided fluorescence imaging

Near-forward Raman selection rules of the phonon-polariton created by alloying in (Zn,Be)Se

The Raman selection rules of the (ZnSe, BeSe) mixed phonon polariton created by alloying in the three mode (1ZnSe, 2BeSe) ZnBeSe system, whose dramatic S like dispersion covers the large frequency gap between the ZnSe and BeSe spectral ranges, is studied in its wave vector dependence by near forward scattering. Both the collapse regime away from the Brillouin zone centre and the reinforcement regime near the Brillouin zone centre are addressed, using appropriate laser lines and Be contents. We find that in both regimes the considered phonon polariton, in fact a transverse mode with mixed mechanical and electrical character, obeys the same nominal Raman selection rules as its purely mechanical variant commonly observed in the backscattering geometry. Besides, marked differences in the phonon polariton Raman lineshapes in the two regimes give a hint about how the phonon polariton electrical field E develops while descending the S like dispersion towards the Brillouin zone centre. In the reinforcement regime E is large, leading to intramode on top of intermode transfers of oscillator strength mediated by E between the two BeSe modes, that both exhibit a fine structure on account of the alloy disorder. In contrast, in the collapse regime E remains weak, as testified by the absence of intramode transfer. The discussion is supported by contour modeling of the multi phonon polariton Raman lineshapes in their wave vector dependence within the linear dielectric approach.Comment: 16 pages, 7 figure