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Träfflista för sökning "L4X0:0277 786X srt2:(2005-2009)"

Sökning: L4X0:0277 786X > (2005-2009)

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1.
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2.
  • Bratkovsky, A. M., et al. (författare)
  • Properties of nanostructured metamaterials at optical frequencies
  • 2008
  • Konferensbidrag (refereegranskat)abstract
    • A variety of metamaterials has been demonstrated recently that support backward waves and negative refraction (Negative Index Materials, NIM.) In particular, these materials enable sub-wavelength resolution that makes them even more interesting, especially in optical domain rather than at microwave frequencies where their unusual properties were known for decades. We describe below theoretical and experimental studies of the so-called 'fishnet' metal-spacer holearray metamaterials, which exhibit NIM behavior at optical frequencies, having unit cell size of a few 100s nm. We demonstrate experimentally that their refractive index can be modulated very fast and very strongly (from -2.4 to -1.5) around the communication wavelength of =1.55 um, in good agreement with the FDTD results. We also discuss a problem of loss compensation in those materials with hefty Ohmic losses by using gain media and local field enhancement in metallic nanoparticles ensembles that enable SERS.
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3.
  • Fredenberg, Erik, PhD, 1979-, et al. (författare)
  • Contrast-enhanced dual-energy subtraction imaging using electronic spectrum-splitting and multi-prism x-ray lenses
  • 2008
  • Ingår i: Medical Imaging 2008 - Physics of Medical Imaging. - San Diego, CA, USA : SPIE. - 9780819470973 ; , s. 91310-91310
  • Konferensbidrag (refereegranskat)abstract
    • Dual-energy subtraction imaging (DES) is a method to improve the detectability of contrast agents over a lumpy background. Two images, acquired at x-ray energies above and below an absorption edge of the agent material, are logarithmically subtracted, resulting in suppression of the signal from the tissue background and a relative enhancement of the signal from the agent. Although promising, DES is still not widely used in clinical practice. One reason may be the need for two distinctly separated x-ray spectra that are still close to the absorption edge, realized through dual exposures which may introduce motion unsharpness. In this study, electronic spectrum-splitting with a silicon-strip detector is theoretically and experimentally investigated for a mammography model with iodinated contrast agent. Comparisons are made to absorption imaging and a near-ideal detector using a signal-to-noise ratio that includes both statistical and structural noise. Similar to previous studies, heavy absorption filtration was needed to narrow the spectra at the expense of a large reduction in x-ray flux. Therefore, potential improvements using a chromatic multi-prism x-ray lens (MPL) for filtering were evaluated theoretically. The MPL offers a narrow tunable spectrum, and we show that the image quality can be improved compared to conventional filtering methods.
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4.
  • Landré, Jérôme, et al. (författare)
  • Visual browsing in image collections using wavelets
  • 2006
  • Konferensbidrag (refereegranskat)abstract
    • Visual browsing is an important way of searching for images in large databases. In image retrieval, a lot of problems have to be solved to get a good system: dimensionality curse, users' search context, size of the database, visual features. In this article, a method trying to attenuate these problems is proposed. Each features vector is organized into four signature vectors used in the classification process while building a fuzzy search tree that is proposed to users for visual browsing. Our system gives good results in terms of speed and accuracy by solving several problems of classical image retrieval methods.
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5.
  • Qiu, Min, et al. (författare)
  • Transformation optics and invisibility cloaks
  • 2008
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, we briefly summarize the theory of transformation optics and introduce its application in achieving perfect invisibility cloaking. In particular, we theoretically show how the task of realizing cylindrical invisibility cloaks can be eased by using either structural approximation or material simplification. The corresponding invisibility performances of the approximate or simplified cylindrical cloaks are presented in detail.
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  • Resultat 1-5 av 5

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