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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 3205-3210 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Magnesium nucleation was studied over the range of approximately 700 to 950 K in a gas evaporation apparatus. Measured supersaturation ratios ranged from approximately 37 to 4.2 over this temperature range, respectively. A comparison of these data and Classical Nucleation Theory shows that the two are not consistent. Although there is a good correlation between the supersaturation and the temperature data when plotted in accordance with Scaled Nucleation Theory, some of the derived parameters are slightly below the limits predicted by the theory. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 10 (1970), S. 268-278 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The extursion melting model of Tadmor et al. (1967) has been modified to include the effects of screw channel curvature and melt leakage through the screw flight-barrel clearance. An alternate coordinate system was used in modifying the model to simplify the addition of curvature corrections. Also proposed is an improved method of computing solid bed velocity. A substantial number of typographical errors and truncations appeared in the original data published by Tadmor et al., and verification of their computations with corrected data was successful in all cases. Channel curvature corrections and the improved method of computing solid bed velocity increased the predicted rate of solid bed width decrease by approximately 14% during the initial stages of melting. Addition of leakage flow to the model tended to offset this effect completely or in part. Leakage flow effects always predominated during the later stages of melting, however. These effects may interact differently for other extruder sizes or screw designs; therefore, the modified melting model should be a more accurate model for use in the design of extruder screws and in studies of extruder performance.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 1996-03-01
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
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  • 4
    Publication Date: 1965-06-01
    Description: The stability of the co-current stratified flow of oil and water was investigated experimentally in a horizontal rectangular conduit. Laminar-turbulent transitions were determined for both phases. With the two-phase system the transition to turbulence in the water phase occurred at a higher Reynolds number in the presence of a laminar oil layer provided the input water-to-oil ratio was relatively high, while the transition in the oil phase took place at a lower Reynolds number in the presence of a turbulent water layer. The appearance of first interfacial waves coincided with the transition to turbulence of the less viscous or water phase. This suggests that in the system investigated the resonance mechanism as proposed by Phillips (1957) was responsible for the generation of these first waves. However, at relatively high water flow rates and water-to-oil ratios more pronounced waves were observed which appeared to be generated by an instability in the mean flow. © 1965, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 5
    Publication Date: 2011-08-24
    Description: The formation, properties and chemical dynamics of microparticles are important in a wide variety of technical and scientific fields including synthesis of semiconductor crystals from the vapour, heterogeneous chemistry in the stratosphere and the formation of cosmic dust surrounding the stars. Gravitational effects on particle formation from vapors include gas convection and buoyancy and particle sedimentation. These processes can be significantly reduced by studying condensation and agglomeration of particles in microgravity. In addition, to accurately simulate particle formation near stars, which takes place under low gravity conditions, studies in microgravity are desired. We report here the STARDUST experience, a recent collaborative effort that brings together a successful American program of microgravity experiments on particle formation aboard NASA KC-135 Reduced Gravity Research Aircraft and several Italian research groups with expertise in microgravity research and astrophysical dust formation. The program goal is to study the formation and properties of high temperature particles and gases that are of interest in astrophysics and planetary science. To do so we are developing techniques that are generally applicable to study particle formation and properties, taking advantage of the microgravity environment to allow accurate control of system parameters.
    Keywords: Exobiology
    Type: Microgravity quarterly : MGQ (ISSN 0958-5036); Volume 3; 2-4; 97-100
    Format: text
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  • 6
    Publication Date: 2011-08-24
    Description: The condensation of solid materials from the vapor phase is important in several scientific fields such as chemical vapor deposition, air pollution and the formation of refractory cosmic dust around stars. Conventional studies of refractory grain formation, using high temperature furnace and shock tube techniques, are restricted to short time scales and suffer from buoyancy induced convection that limit their accuracy. In order to simulate more accurately the condensation of refractory grains near stars and to investigate the advantages of performing condensation studies in microgravity conditions, an experimental investigation was undertaken. This work reports the experimental equipment currently used. The results from the first flight series and particle aggregation modelling efforts are presented briefly.
    Keywords: ASTROPHYSICS
    Type: Microgravity Science and Technology (ISSN 0938-0108); 6; 2; p. 123-130.
    Format: text
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  • 7
    Publication Date: 2011-08-19
    Description: Measurements are reported of the critical supersaturation necessary to initiate the vapor phase nucleation of silver over the ambient temperature range 500-950 K at total pressures of 250 and 500 torr of hydrogen. The results are compared with the predictions of both classical nucleation theory and the theory of a physical spinodal developed by Rasmussen (1982), neither of which adequately describes the present observations. The nucleation of silver appears to be dependent on the total pressure of the system in a manner which suggests that three-body reactions are necessary in order to form the initial silver cluster (e.g., dimers) from the monoatomic vapor.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: Journal of Chemical Physics (ISSN 0021-9606); 85; 1116-112
    Format: text
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  • 8
    Publication Date: 2013-08-29
    Description: We report our experiences with zinc nucleation in a microgravity environment aboard NASA's Reduced Gravity Research Facility. Zinc vapor is produced by a heater in a vacuum chamber containing argon gas. Nucleation is induced by cooling and its onset is easily detected visually by the appearance of a cloud of solid, at least partially crystalline zinc particles. Size distribution of these particles is monitored in situ by photon correlation spectroscopy. Samples of particles are also extracted for later analysis by SEM. The initially rapid increase in particle size is followed by a slower period of growth. We apply Scaled Nucleation Theory to our data and find that the derived critical temperature of zinc, the critical cluster size at nucleation, and the surface tension values are all in reasonably good agreement with their accepted literature values.
    Keywords: Space Processing
    Format: application/pdf
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  • 9
    Publication Date: 2013-08-29
    Description: A short description of the program Stardust whose goal is to study the formation and properties of high temperature particles and gases, including silicate and carbonaceous materials, that are of interest in astrophysics and planetary science, is given. The international program was carried out in microgravity conditions in parabolic flight. A description of the laboratory equipment, conceived to perform experimental tests in reduced gravity conditions, and which is based on the gas evaporation technique, is given. The gas evaporation technique utilizes one or more heated crucible to vaporize solids materials (SiO, Mg) in a low pressure of inert or reactive gas inside of a vacuum bell jar. The vapor pressures of the materials are controlled by the temperature of the crucibles. The temperature and pressure of inert gas are also controlled. By varying the vapor pressure relative to the gas temperature and pressure, the conditions for substantial grain condensation can be controlled and grain formation measured using light scattering techniques. Thus the partial pressure for grain condensation, can be measured as a function of temperature. The gas evaporation technique has the advantage that complex chemical systems can be studied by using multiple crucibles each containing solid source material. Experimental results and future trends are addressed.
    Keywords: ASTROPHYSICS
    Type: ESA, Environment Observation and Climate Modelling Through International Space Projects. Columbus Eight (COSY-8): Utilisation of Earth Orbiting Laboratories; p 325-329
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  • 10
    Publication Date: 2019-04-02
    Description: We have undertaken a project called STARDUST which is a collaboration with Italian and American investigators. The goals of this program are to study the condensation and coagulation of refractory materials from the vapor and to study the properties of the resulting grains as analogs to cosmic dust particles. To reduce thermal convective currents and to develop valuable experience in designing an experiment for the Gas-Grain Simulation Facility aboard Space Station, Freedom we have built and flown a new chamber to study these processes under periods of microgravity available on NASA's KC-135 Research Aircraft. Preliminary results from flights with magnesium and zinc are discussed.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Life sciences and space research 24 (4): Planetary biology and origins of life; Topical Meeting of the COSPAR Interdisciplinary Scientific Commission F (Meeting F3) of the COSPAR Plenary Meeting, 29th (ISSN 0273-1177); 15; 3; p. 423-426
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