19 research outputs found
Development of a simulation system in mandibular orthognathic surgery based on integrated three-dimensional data
The 2016 Feb 19 outburst of comet 67P/CG: an ESA Rosetta multi-instrument study
On 2016 Feb 19, nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in situ gas, dust and plasma instruments, and one dust collector. At 09:40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50 per cent of the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from âŒâ16 V to â20 V during the outburst. A clear sequence of events was observed at the distance of Rosetta (34âkm from the nucleus): within 15 min the Star Tracker camera detected fast particles (âŒ25 m sâ1) while 100 ÎŒm radius particles were detected by the GIADA dust instrument âŒ1 h later at a speed of 6 m sâ1. The slowest were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst originated just outside the FOV of the instruments, the source region and the magnitude of the outburst could be determined
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Revisiting Anisotropic Diffusion of Carbon Dioxide in the Metal-Organic Framework Zn2(dobpdc)
The diffusion of gases confined in nanoporous materials underpins membrane and adsorption-based gas separations, yet relatively few measurements of diffusion coefficients in the promising class of materials, metal-organic frameworks (MOFs), have been reported to date. Recently we reported self-diffusion coefficients for 13CO2 in the MOF Zn2(dobpdc) (dobpdc4- = 4,4âČ-dioxidobiphenyl-3,3âČ-dicarboxylate) which has one-dimensional channels with a diameter of approximately 2 nm [ Forse, A. C.; et al. J. Am. Chem. Soc. 2018, 140, 1663-1673 ]. By analyzing the evolution of the residual 13C chemical shift anisotropy line shape at different gradient strengths, we obtained self-diffusion coefficients both along (Dâ„) and between (Dâ„) the one-dimensional MOF channels. The observation of nonzero Dâ„ was unexpected based on the single crystal X-ray diffraction structure and flexible lattice molecular dynamics simulations, and we proposed that structural defects may be responsible for self-diffusion between the MOF channels. Here we revisit this analysis and show that homogeneous line broadening must be taken into account to obtain accurate values for Dâ„. In the presence of homogeneous line broadening, intensity at a particular NMR frequency represents signal from crystals with a range of orientations relative to the applied magnetic field and magnetic gradient field. To quantify these effects, we perform spectral simulations that take into account homogeneous broadening and allow improved Dâ„ values to be obtained. Our new analysis best supports nonzero Dâ„ at all studied dosing pressures and shows that our previous analysis overestimated Dâ„