Virtual-Detector-Based Photoacoustic Microscopy improves in Vivo imaging
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left the regime of possible slow light propagation in an opaque spectral region above the long-wavelength cutoff. To efficiently couple the waveguide modes with longer wavelengths (in the slow light regime) into the bends, the average refractive index at the bend was effectively increased by producing a waveguide with smaller hole radii in the bend vicinity. For waveguide structures with r = 0.33a, the blueshift in long-wavelength cutoff was reduced from 15 nm to 6 nm when the radii of four holes in the vicinity of the bends were decreased, allowing for some light transmission in the slow
light spectral region. The researchers said that the blueshift can be completely compensated and all of the wavelengths commensurate with slow light propagation can be incorporated into the high-transmission region of the waveguide if the refractive index is further increased by decreasing the radii of 16 nearby holes instead of four in the bend vicinity. According to the researchers, this demonstration makes photonic crystal waveguides very promising devices for slow light applications such as all-optical data storage and quantum computing. TUSHAR PRASAD
Polymers with Intrinsic Microporosity Engineered for Hydrogen Storage Safe and efficient onboard hydrogen storage for cars cannot currently be based on reversible H2 adsorption in microporous materials like zeolites, carbon, or in materials based on a metalorganic framework, because the quantity of adsorbed H2 is insufficient. Organic polymers have heretofore not been considered, because their free volumes are generally much too small. Recently, however, N.B. McKeown of Cardiff University, P.M. Budd of the University of Manchester, D. Book of Birmingham University, and their colleagues have hypothesized that their recently reported “polymers of intrinsic microporosity” (PIMs) would be good candidates for H 2 storage because they form solids with large, interconnected free volume with accessible internal surface areas in the range of 500–900 m2/g. The rigidly contorted macromolecular structures formed by PIMs pack inefficiently and are a consequence of their fused-ring subunits, one of which typically contains a site of contortion, for example, a rigid, nonplanar unit. As reported in a recent issue of Angewandte Chemie International Edition (Vol. 45, Issue 11, DOI: 10.1002/ anie.200504241; p. 1804), McKeown and co-researchers tailored the micropore structure of PIMs by using monomers that contain preformed cavities to provide appropriately sized sites for hydrogen adsorption. The researchers incorporated a bowl-shaped receptor monomer—cyclotricatechylene (CTC)—within a network PIM by using a benzodioxaneformation reaction between CTC and tetrafluoroterephthalonitrile, designating the new PIM as CTC-network-PIM. More conventional PIMs (PIM-1 and HATN-network-PIM; see Scheme I) were synthesized in order to compare gas adsorption properties. Structures for all three PIMs were confirmed by elemental analysis, infrared spectroscopy, and, in the case of the soluble PIM-1, 1H and 13C n
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