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  • 1
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    Oxford : Periodicals Archive Online (PAO)
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  • 2
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate constant for the reaction of the hydroxyl radical with 1,1,1,3,3-pentafluorobutane (HFC-365mfc) has been determined over the temperature range 278-323K using a relative rate technique. The results provide a value of k(OH+CF3CH2CF2CH3)=2.0×10-12exp(-1750±400/T) cm3 molecule-1 s-1 based on k(OH+CH3CCl3)=1.8×10-12 exp (-1550±150/T) cm3 molecule-1 s-1 for the rate constant of the reference reaction. Assuming the major atmospheric removal process is via reaction with OH in the troposphere, the rate constant data from this work gives an estimate of 10.8 years for the tropospheric lifetime of HFC-365mfc. The overall atmospheric lifetime obtained by taking into account a minor contribution from degradation in the stratosphere, is estimated to be 10.2 years. The rate constant for the reaction of Cl atoms with 1,1,1,3,3-pentafluorobutane was also determined at 298±2 K using the relative rate method, k(Cl+CF3CH2CF2CH3)=(1.1±0.3)×10-15 cm3 molecule-1 s-1. The chlorine initiated photooxidation of CF3CH2CF2CH3 was investigated from 273-330 K and as a function of O2 pressure at 1 atmosphere total pressure using Fourier transform infrared spectroscopy. Under all conditions the major carbon-containing products were CF2O and CO2, with smaller amounts of CF3O3CF3. In order to ascertain the relative importance of hydrogen abstraction from the (SINGLE BOND)CH2(SINGLE BOND) and (SINGLE BOND)CH3 groups in CF3CH2CF2CH3, rate constants for the reaction of OH radicals and Cl atoms with the structurally similar compounds CF3CH2CCl2F and CF3CH2CF3 were also determined at 298 K k(OH+CF3CH2CCl2F)=(8±3)×10-16 cm3 molecule-1 s-1; k(OH+CF3CH2CF3)=(3.5±1.5)×10-16 cm3 molecule-1 s-1; k(Cl+CF3CH2CCl2F)=(3.5±1.5)×10-17 cm3 molecule-1 s-1; k(Cl+CF3CH2CF3)〈1×10-17 cm3 molecule-1 s-1. The results indicate that the most probable site for H-atom abstraction from CF3CH2CF2CH3 is the methyl group and that the formation of carbonyl compounds containing more than a single carbon atom will be negligible under atmospheric conditions, carbonyl difluoride and carbon dioxide being the main degradation products. Finally, accurate infrared absorption cross-sections have been measured for CF3CH2CF2CH3, and jointly used with the calculated overall atmospheric lifetime of 10.2 years, in the NCAR chemical-radiative model, to determine the radiative forcing of climate by this CFC alternative. The steady-state Halocarbon Global Warming Potential, relative to CFC-11, is 0.17. The Global Warming Potentials relative to CO2 are found to be 2210, 790, and 250, for integration time-horizons of 20, 100, and 500 years, respectively. © 1997 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate constant for the reaction of the hydroxyl radical with 1,2,2-trifuoroethane has been determined over the temperature range 278-323 K using a relative rate technique. The results provide a value of k(OH + CH2FCHF2) = 2.65 × 10-12 exp(-1542 ± 500/T) cm3 molecule-1 s-1 based on k(OH + CH3CCl3) = 1.2 × 10-12 exp(-1400 ± 200/T) cm3 molecule-1 s-1 for the rate constant of the reference reaction. The chlorine atom initiated photooxidation of CH2CHF2 was investigated from 255 to 330 K and as a function of O2 pressure at 1 atmosphere total pressure using Fourier transform infrared spectroscopy. The major carbon-containing products were CHFO and CF2O suggesting that the alkoxy radicals CH2FCF2O and CHF2CHFO, formed in the reaction, react predominantly by carbon-carbon bond cleavage. The results indicate that formation of CHF2CFO from the reaction of CHF2CHFO radicals with O2 will be unimportant under all atmospheric conditions. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 6
    Publication Date: 2018-06-26
    Description: Middle Valley is a sediment-covered rift near the northern end of Juan de Fuca Ridge. Hydrothermal fluids are presently being discharged at two vent fields about 3 km apart, Bent Hill and the area of active venting. The hydrothermally active chimneys at both Bent Hill and the area of active venting consist of anhydrite and Mg-rich silicates with minor pyrite, Cu-Fe sulfide, sphalerite, and galena. Hydrothermal discharge in these areas appears to be focused along extensional faults. At the Bent Hill massive sulfide deposit, clastic sulfide layers are interbedded with hydrothermally altered and unaltered hemipelagic and turbiditic sediment along the flanks of the sulfide mound. Sulfide textures and mineralogy suggest that the Bent Hill sulfide mound formed by the build-up and collapse of sulfide chimneys, the resedimentation of sulfide debris and the formation of clastic sulfide layers, and the infilling and replacement of clastic sulfides by hydrothermal fluids near vents. Sulfur isotope values that are consistently more positive than basaltic sulfur support the addition of seawater sulfur. Pb isotope values for the Bent Hill deposit that are transitional between midocean ridge basalt (MORB) and Middle Valley sediments indicate that the sulfides probably formed from fluids which originated in the oceanic crust but which have been modified by reaction with lower temperature (〈273°C)fluids generated in the sedimentary pile, similar to those now venting in Middle Valley.
    Type: Article , PeerReviewed
    Format: text
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  • 7
    Publication Date: 2014-02-25
    Description: Certain volcanogenic massive sulfide (VMS) ore deposits form in submarine calderas. This association is well known, but the link between caldera formation and the origins of the deposits remains poorly understood. Here we show that the size and location of a VMS deposit within a submarine caldera may be determined by how and when the caldera formed. These spatial-temporal conditions control development of the hydrothermal system associated with the VMS deposit. We propose that caldera opening along outward-dipping faults promotes magma degassing, seawater influx, and high-temperature leaching, resulting in a metal-rich hydrothermal fluid. These outward-dipping faults are considered to provide critical pathways for ore-forming fluids responsible for some caldera-hosted VMS deposits and may also be fundamentally important for the formation of many other caldera-hosted ore deposit types.
    Type: Article , PeerReviewed
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  • 8
    Publication Date: 2011-08-19
    Description: Flight experiments with NASA Ames Research Center's quiet short-haul research aircraft evaluated the influence of pursuit displays on the ability of pilots to execute precision-instrument flight operations in the terminal area, particularly approaches to and landings on a short runway. The aircraft is a powered-lift, short-takeoff and landing configuration equipped with a modern digital fly-by-wire flight control system, a head-up display, and a color head-down display that make it possible to investigate control and display concepts for full-envelope, powered-lift operations. Flight-path-oriented displays that provide status and command information in a format with minimal clutter were investigated. The pilots could fly the aircraft with the precision associated with flight-director guidance and with a high degree of situation awareness. The primary benefits of this display concept were realized when the pilot was required to execute a complex transition and approach under instrument conditions and in the presence of a wide range of wind and turbulence conditions.
    Keywords: AIRCRAFT INSTRUMENTATION
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 12; 521-529
    Format: text
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  • 9
    Publication Date: 2011-08-24
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 16; 6; p. 993-998.
    Format: text
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  • 10
    Publication Date: 2013-08-31
    Description: As part of NASA's program to develop technology for short takeoff and vertical landing (STOVL) fighter aircraft, control system designs have been developed for a conceptual STOVL aircraft. This aircraft is representative of the class of mixed-flow remote-lift concepts that was identified as the preferred design approach by the US/UK STOVL Joint Assessment and Ranking Team. The control system designs have been evaluated throughout the powered-lift flight envelope on Ames Research Center's Vertical Motion Simulator. Items assessed in the control system evaluation were: maximum control power used in transition and vertical flight, control system dynamic response associated with thrust transfer for attitude control, thrust margin in the presence of ground effect and hot gas ingestion, and dynamic thrust response for the engine core. Effects of wind, turbulence, and ship airwake disturbances are incorporated in the evaluation. Results provide the basis for a reassessment of existing flying qualities design criteria applied to STOVL aircraft.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: Piloting Vertical Flight Aircraft: A Conference on Flying Qualities and Human Factors; p 37-5
    Format: application/pdf
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