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The usual geometry for radio occultation sounding using global navigation satellite system (GNSS) signals has the receiver placed on a low earth orbit (LEO) satellite. We investigate a new geometric approach, assuming an airborne rather than a spaceborne receiver. Information on the refractivity structure and hence the pressure, temperature, and humidity can be retrieved from accurate airborne measurements of amplitude and phase delay of the signals occulted by the troposphere. We present some advantages and disadvantages for the concept of making measurements from commercial aircraft equipped with proper GNSS receivers and antennae compared to the spaceborne case. We simulated realistic airborne occultation observations and assessed the characteristics of their geometry and sampling. We also compared the dynamic range of the signal with the magnitude of error sources that affect the measurements. Findings include that an airborne system has the potential to provide more profiles per unit area below 10 km height than a constellation of up to 25 satellites over the North Atlantic (though with inferior global coverage), and that the signal to noise ratio (SNR) should be better below 5 km than in the LEO case. Though the receiver velocity error is larger than for the LEO system, it is still small enough relative to the signal level to retrieve useful information. The estimated sensitivity of the technique is better than 0.1% refractivity at 3 km altitude increasing to 0.5% refractivity at 11 km. Because of the large horizontal drift of the tangent point of up to 450 km, the assumption of spherical symmetry in the existence of significant 3D variations in structure is expected to be a major error source, in addition to the airplane velocity uncertainty. [Copyright &y& Elsevier]

This paper presents the results of a detailed experimental study of the diffusion of propene in large crystals of DDR zeolite (the pure silica analog of ZSM-58) carried out by interference microscopy (IFM). Diffusion is very slow as the propene molecules are only just small enough to pass through the distorted 8-ring windows of the DDR structure. This makes it possible to measure many concentration profiles during the available time and thus to study the diffusional behavior at a level of detail that would be impossible in faster systems. In an ideal DDR crystal diffusion should occur only in the radial direction. In the actual system radial diffusion was dominant but there is also a small but significant axial component which complicates the interpretation of the experimental data. The diffusivity increases strongly with loading but the apparent magnitude of this effect may be increased by the small contribution from axial diffusion. The activation energy for radial diffusion is about 34 kJ/mole. [ABSTRACT FROM AUTHOR]

Abstract: Crystallites of zeolite LSX with a diameter of about 10μm were synthesized. Crystals of this size are shown to allow the simultaneous investigation of intracrystalline mass transfer phenomena of water molecules and lithium ions in hydrated zeolite Li-LSX by NMR diffusometry. By MAS NMR spectroscopy with the 1H and 6Li nuclei, the water molecules and lithium ions are found to yield two signals, a major and a minor one, which may be attributed to locations in the sodalite cages and the supercages, respectively. By 1H and 6Li exchange spectroscopy the mean residence times in the sodalite cages at 373K are found to be about 150ms for the water molecules and about 40ms for the lithium cations. PFG NMR self-diffusion measurements at 373K yield a diffusivity of about 2×10−11 m2 s−1 for the lithium ions, which is about one order of magnitude below the water diffusivity. [Copyright &y& Elsevier]

We compared a conventional stent (Jostent Flex, Jomed GmbH, Rangendingen, Germany) with a polytetrafluoroethylene (PTFE)-membrane-covered stent (Jostent Stentgraft) in patients undergoing intervention of a stenosis in an obstructed vein graft. The use of stents improved results of percutaneous revascularization of obstructed vein grafts, but did not demonstrate the reduced elevated restenosis rate. In addition, long-term clinical event rate is still high compared with intervention in native vessels. Observational studies suggested that stents covered with a PTFE membrane might be associated with a low complication and restenosis rate in venous bypass grafts. This prospective multicenter study included a total of 211 patients who were randomly assigned to receive either a Flex stent or Stentgraft. The primary end point was binary restenosis rate at six months by core lab quantitative coronary angiography. Acute success and procedural events were comparable between the two groups. Restenosis rate was not significantly different between the Flex (20%) and the Stentgraft (29%) groups (p = 0.15), although there was a nonsignificant trend toward a higher late occlusion rate in the Stentgraft group (7% vs. 16%, p = 0.069) at follow-up. Likewise, after a mean observation period of 14 months, cumulative event rates (death, myocardial infarction, or target lesion revascularization) were comparable in the two groups (31% vs. 31%, p = 0.93). This controlled trial does not indicate a superiority of the PTFE-membrane-covered Stentgraft compared with a conventional stent with respect to acute results, restenosis, or clinical event rates. [ABSTRACT FROM AUTHOR]