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Spectrophotometric observations of (2060) Chiron were obtained. Their primary goal was to look for the subtle differences in color between Chiron and its surrounding coma, and to search for possible absorption or emission features in Chiron's spectrum. The presence of the CN(0-0) emission band was identified. It proves Chiron's cometary nature and breaks the record heliocentric distance for cometary gaseous emission.
Long-slit spectroscopic observations of Comet P/Halley on 12 dates between October 1985 and May 1986 were used to extract spatial profiles for C2, CN, NH2, and O I (1D) (which effectively map out the comet's H2O distribution), and Haser model scale lengths were fitted to these data. The preperihelion analysis yielded Haser model scale lengths of sufficient consistency that they could be used for the production rate determinations. It was found that the average parent scale lengths found for NH2 were consistent with photodissociation lifetimes for NH3 and confirm the dissociation chain NH3-NH2-NH.
The projected expansion velocity of Comet Halley's coma is presently determined in CN jet images that were processed with a radial profile subtraction technique. It is established that the flow is approximately radial, and that the velocity can also be determined by measuring specific radial features in jets. The largest projected velocity is 1.7 +/- 0.3 km/sec, at 50,000 km from the nucleus. This is the largest expansion velocity found for this region of the Comet Halley coma. Comparisons are made with other observations and theoretical models.
Model intensity profiles have been compared with those observed for the C2, C3, CN, and continuum emissions of Comet Halley, in order to constrain the dust and gas parameters. While most of the parameters were consistent with expected values, the lifetimes of C3 and its parent were unexpectedly small. The day:night production rate ratio, which was about 1:1 for the gas, covered the 4:3-1:0 range in the case of the dust.
Radiative lifetimes have been measured for CN (A 2 Pi i v-prime = 2...7). Ground-state radicals formed in the 193 nm photolysis of C2N2 and ClCN were excited to A 2 Pi i v-prime = 2...7 vibrational levels. The decay was monitored by following the fluorescence. Cascading effects were eliminated by working at low pressures and monitoring emission from a single vibrational band. Quenching rates and zero-pressure radiative lifetimes were obtained from Stern-Volmer plots. The lifetimes are significantly lower than previous measurements and theoretical calculations for vibrational states v-prime over 2.
Laser-photolysis-laser-induced-fluorescence methods are used to characterize the collisional energy transfer between CN (A 2Pi(i) and (X 2Sigma(+)) states and to measure radiative lifetimes of the (A 2Pi(i)) v-prime = 2-7 vibrational levels. In addition, use of the A 2Pi(i) - X 2Sigma(+) system for the laser-induced-fluorescence determination of (X 2Sig(+)) populations is demonstrated and discussed.
The rate coefficient for the important interstellar reaction between CN and C2H2 has been calculated as a function of temperature between 10 and 300 K. The potential surface for this reaction has been determined through ab initio quantum chemical techniques; the potential exhibits no barrier in the entrance channel but does show a small exit channel barrier, which lies below the energy of reactants. Phase-space calculations for the reaction dynamics, which take the exit channel barrier into account, show the same unusual temperature dependence as determined by experiment, in which the rate coefficient at first increases as the temperature is reduced below room temperature and then starts to decrease as the temperature drops below 50-100 K. The agreement between theory and experiment provides strong confirmation that the reaction occurs appreciably at cool interstellar temperatures.
The synthesis of adenine from the polymerization of concentrated ammonium cyanide solutions is well known. We show here that guanine is also produced by this reaction but at yields ranging from 10 to 40 times less than that of adenine. This synthesis is effective at both +80 and -20 degrees C. Since high concentrations of NH(4)CN are obtainable only by freezing, this prebiotic synthesis would be applicable to frozen regions of the primitive Earth, the Jovian satellite Europa and other icy satellites, and the parent body of the Murchison meteorite.
Density functional theory calculations at the B3LYP/6-31+G** level were employed to characterize the critical points for adducts, isomers, products, and intervening transition states for the reactions between benzene and the ethynyl (C2H) or cyano (CN) radicals. Both addition reactions were found to have no barriers in their entrance channels, making them efficient at the low temperature and pressure conditions that prevail in the haze-forming region of Titan's atmosphere as well as in the dense interstellar medium (ISM). The dominant products are ethynylbenzene (C6H5C2H) and cyanobenzene (C6H5CN). Hydrogen abstraction reactions were also characterized but found to be non-competitive. Trajectory calculations based on potentials fit to about 600 points calculated at the ROMP2/6-31+G** level for each interaction surface were used to determine reaction rates. The rates incorporated any necessary corrections for back reactions as ascertained from a multiwell treatment used to determine outcome distributions over the range of temperatures and pressures pertinent to Titan and the ISM and are in good agreement with the limited available experimental data.
The board-level temperature cycling reliability of Xilinx Virtex-5 (V5) CN package was investigated. V5s were temperature cycled under two conditions, 0 to +100 C (0/100) and -55 to +100 C (-55/100). During the 0/100 test, no part out of 8 parts failed up to 6586 cycles. During the -55/100 test, one part out of 8 parts failed at 1236 cycle, and there were no additional failures up to 1705 cycles. The failure mode of the part that failed at 1236 cycles indicated that most likely the failure was not a solder fatigue failure, and therefore no obvious solder fatigue failure was observed throughout the tests.
The board-level temperature cycling reliability of Xilinx Virtex-5 CN package was investigated.
Al7C3N3 is Aluminum carbonitride-like structured and crystallizes in the orthorhombic Cmc2_1 space group. The structure is three-dimensional. there are seven inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to one C4- and three equivalent N3- atoms to form AlCN3 tetrahedra that share corners with twelve AlCN3 tetrahedra and a cornercorner with one AlC4 trigonal pyramid. The Al–C bond length is 1.93 Å. All Al–N bond lengths are 2.01 Å. In the second Al3+ site, Al3+ is bonded to four N3- atoms to form corner-sharing AlN4 tetrahedra. There is one shorter (1.85 Å) and three longer (1.99 Å) Al–N bond length. In the third Al3+ site, Al3+ is bonded to four C4- atoms to form distorted AlC4 tetrahedra that share corners with ten AlCN3 tetrahedra and edges with three equivalent AlC4 trigonal pyramids. There are three shorter (1.92 Å) and one longer (2.19 Å) Al–C bond lengths. In the fourth Al3+ site, Al3+ is bonded to three equivalent C4- and one N3- atom to form distorted AlC3N tetrahedra that share corners with twelve AlN4 tetrahedra and edges with three equivalent AlC3N tetrahedra. All Al–C bond lengths are 2.11 Å. The Al–N bond length is 1.85 Å. In the fifth Al3+ site, Al3+ is bonded to four C4- atoms to form distorted AlC4 trigonal pyramids that share corners with four AlCN3 tetrahedra, corners with six equivalent AlC4 trigonal pyramids, and edges with three equivalent AlC4 tetrahedra. There are three shorter (1.91 Å) and one longer (2.25 Å) Al–C bond lengths. In the sixth Al3+ site, Al3+ is bonded to three equivalent C4- and one N3- atom to form distorted AlC3N tetrahedra that share corners with twelve AlCN3 tetrahedra and edges with three equivalent AlC3N tetrahedra. All Al–C bond lengths are 2.14 Å. The Al–N bond length is 1.82 Å. In the seventh Al3+ site, Al3+ is bonded to one C4- and three equivalent N3- atoms to form AlCN3 tetrahedra that share corners with ten AlN4 tetrahedra and corners with three equivalent AlC4 trigonal pyramids. The Al–C bond length is 1.96 Å. There is two shorter (1.99 Å) and one longer (2.00 Å) Al–N bond length. There are three inequivalent C4- sites. In the first C4- site, C4- is bonded to five Al3+ atoms to form distorted CAl5 trigonal bipyramids that share corners with three equivalent NAl4 tetrahedra, corners with six equivalent CAl5 trigonal bipyramids, and edges with three equivalent CAl5 trigonal bipyramids. In the second C4- site, C4- is bonded to five Al3+ atoms to form distorted CAl5 trigonal bipyramids that share corners with three equivalent NAl4 tetrahedra, corners with six equivalent CAl5 trigonal bipyramids, and edges with three equivalent CAl5 trigonal bipyramids. In the third C4- site, C4- is bonded to six Al3+ atoms to form CAl6 octahedra that share corners with six NAl4 tetrahedra and edges with six equivalent CAl6 octahedra. There are three inequivalent N3- sites. In the first N3- site, N3- is bonded to four Al3+ atoms to form NAl4 tetrahedra that share corners with three equivalent CAl6 octahedra and corners with nine NAl4 tetrahedra. The corner-sharing octahedral tilt angles are 63°. In the second N3- site, N3- is bonded to four Al3+ atoms to form NAl4 tetrahedra that share corners with nine NAl4 tetrahedra and corners with three equivalent CAl5 trigonal bipyramids. In the third N3- site, N3- is bonded to four Al3+ atoms to form NAl4 tetrahedra that share corners with three equivalent CAl6 octahedra, corners with six equivalent NAl4 tetrahedra, and corners with three equivalent CAl5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 61°.
Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations
Recent advances in microtechnology and mobile robotics have made it feasible to create extremely small automated or remote-controlled vehicles which open new application frontiers.
Nafion-Pt composite (ICPF) is one of the most practical electroactive polymer nearest to applications.
Here, we report the remarkable stability at the nanoscale matrix-filler interface in a series of overall low coefficient of thermal expansion (CTE) zinc cyanide (ZC)/epoxy resin composites. These interfaces demonstrate the stability of highly contrasting materials. These composites are designed to optimize the properties of both materials: epoxy resins are valued for their high strength, superb chemical resistance, low dielectric properties, and adhesive abilities. ZC, a model flexible framework, exhibits negative thermal expansion (NTE) behavior and compensates for the epoxy resin’s detrimentally large thermal expansion values. Filled resins minimize the native 65 ppm/°C CTE values to 19 ppm/° C over a wide temperature range while maintaining linearity, yielding composites compatible with typical metal and ceramic substrates’—commonly bonded to the resin— 0–20 ppm/° C CTE values. Additionally, with significant intrinsic differences in the materials, we use wide-angle X-ray diffraction and atomic force microscopy to elucidate thermal movement. The ZC/epoxy interface is surprisingly resilient over 1,000 cycles between -55° C and 75° C, extremes typical to aerospace applications. Further, we show that the resin viscosity remains less than 21 Pa*s at up to 30 vol% ZC, an important consideration for workability. We also discuss settling distribution, glass transition temperature, flexural strength, and longevity. All results point favorably towards practical implementation in low thermal expansion application needs: filling the gap in component design.