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  • 1
    ISSN: 1572-8927
    Keywords: Freezing points ; enthalpies ; aqueous solutions ; Gibbs energy ; tetrahydropyran ; 1,3-dioxane and 1,4-dioxane ; 1,3,5-trioxane ; solute-solute interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The enthalpies of dilute aqueous solutions of tetrahydropyran, 1,3-dioxane, 1,4-dioxane, 1,2,5-trioxane, and an equimolal mixture of tetrahydropyran and 1,3,5-trioxane were measured at 25°C and at molalities from about 0.1 to 1.0 mol kg1. The freezing points of the same aqueous solutions (except for 1,3-dioxane) were measured over a similar molality range. The results were used to calculate the enthalpies and Gibbs free energies of the pair-wise interactions of the above solutes in dilute aqueous solutions at 25°C. From these results, the additivity principle proposed by Savage and Wood was used to get the Gibbs free energy and enthalpies of interaction for the ether-ether and ether-methylene groups. Because of the limited number of measurements, the interaction parameters were not determined with great precision. Nevertheless, the standard errors for the predicted enthalpies and Gibbs free energies are quite reasonable. The signs and magnitudes are similiar to those determined for other polar groups.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2011-08-24
    Keywords: ASTRODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 29; 3, Ma; 297-304
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  • 3
    Publication Date: 2019-06-28
    Description: The atmospheric flight environment of manned return from Mars is evaluated by analyzing the earth-return entry corridor. To identify and quantify the effects of various atmospheric exit conditions on the mission, the differences beween the capture to a specific orbit and the direct entry to a target splashdown site are investigated. The differences are quantified in terms of the airbrake lift-drag ratio requirements, the stagnation-point heating, and the significance of off-nominal atmospheric conditions. Results are presented on three different earth-return aerobraking scenarios: (1) the capture into a phasing orbit with a 24-hr period, (2) the capture into a 500-km circular orbit, and (3) the direct entry to splashdown.
    Keywords: ASTRODYNAMICS
    Type: AIAA PAPER 91-2873
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  • 4
    Publication Date: 2019-08-28
    Description: Aerocapture has previously been identified as a critical technology for manned Mars missions. A wide range of parking orbits is available into which an aerobraking vehicle could be captured, and earlier authors have advocated different target orbits for various reasons. The choice of the parking orbit impacts the amount of energy which must be dissipated during the atmospheric trajectory. The effect of this choice on the entry corridor width, the required vehicle L/D, and the aerothermal environment are explored in this paper.
    Keywords: ASTRODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 30; 4; p. 484-487.
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  • 5
    Publication Date: 2019-08-28
    Keywords: ASTRODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 29; 6; p. 814-819.
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  • 6
    Publication Date: 2019-07-13
    Description: Lift to drag ratio (L/D) requirements and stagnation point heating have been examined for a variety of probable entry conditions and vehicle configurations. It is found that vehicles with an L/D of 0.5 or more provide a corridor width of at least 0.7 degrees while keeping the peak deceleration load below 5 g for approach velocities up to 14.5 km/s. It is shown that stagnation point peak heating rates and integrated heat load critically depend on both entry velocity and ballistic coefficient. For the most severe cases under consideration, peak heating and integrated heat load are five times greater than those encountered by Apollo but within the range of experience for unmanned vehicles.
    Keywords: ASTRODYNAMICS
    Type: AIAA PAPER 91-2874 , AIAA Atmospheric Flight Mechanics Conference; Aug 12, 1991 - Aug 14, 1991; New Orleans, LA; United States
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  • 7
    Publication Date: 2019-07-13
    Description: The results of a parametric study of corridor width and stagnation point heating are presented for a range of a probable mission designs and vehicle configurations. Entry velocities were varied from 6 to 10 km/s, L/Ds from 0.1 to 1.0, and ballistic coefficients from 100 to 500 kg/sq m. It is found that vehicles with an L/D of 0.4 to 0.5 provide an entry corridor width of at least 1 deg for velocities up to 10 km/s. For entry velocities below approximately 7 km/s, radiative cooling may be possible for the thermal protection system. It is recommended that, at higher entry speeds, ablative heat shields be used. Maximum integrated stagnation point heat loads were equivalent to or less than those experienced by the Space Shuttle on a typical reentry.
    Keywords: ASTRODYNAMICS
    Type: AIAA PAPER 91-2871 , AIAA Atmospheric Flight Mechanics Conference; Aug 12, 1991 - Aug 14, 1991; New Orleans, LA; United States
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  • 8
    Publication Date: 2019-07-13
    Keywords: ASTRODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 29; 6; p. 808-813.
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