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  • ASTROPHYSICS  (177)
  • Chemical Engineering  (77)
  • 1990-1994  (254)
  • 1970-1974
  • 1990  (254)
  • 1
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 11 (1990), S. 144-157 
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The response of advanced composites to low-velocity projectile loading was investigated. The impact failure mechanisms of composites containing various fibers with different strength and ductility were studied by a combination of static indentation testing, instrumented falling dart impact testing, acoustic emission monitoring, and scanning electron microscopy (SEM). The composites containing fibers with both high strength and high ductility (eg., polyethylene (PE) fibers) demonstrate a superior impact resistance as compared to those containing fibers with high strength (eg., graphite fibers) or high ductility (eg., nylon fibers) but not both. Upon impact loading, the composites containing PE fibers usually exhibited a great degree of plastic deformation and some level of delamination. These mechanisms acted to dissipate a significant amount of strain energy prior to the penetration phase of the impact process. No through penetration was observed in all the samples containing more than three layers of PE fabric except when loaded at relatively high rates and low temperatures. Although certain levels of delamination also took place in other composite systems, very little plastic deformation occurred, allowing ready penetration of the projectile. The stacking sequences in the hybrid laminates studied were found to play a critical role in triggering or inhibiting the processes of plastic deformation and delamination and, therefore, controlling their energy absorption capability. The penetration resistance of composites appeared to be dictated by the fiber toughness. The later property must be measured in a simulated high-rate condition.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 11 (1990), S. 229-239 
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A model is developed to predict thermal expansion coefficients and elastic moduli of multi-component (hybrid) composites. The model includes the influences of fiber aspect ratio; isotropic and anisotropic fiber materials; planar, three-dimensional or arbitrary fiber orientation; hollow and solid spherical reinforcements; and voids. The first step in the procedure is to predict the properties of an aligned-fiber single-reinforcement composite for each reinforcement type. Various micro-mechanics approaches are used, depending on the type of reinforcement. A simplified version of Lee and Westmann's theory is found to work well for hollow spherical reinforcements. Performing an orientation average accounts for the spatial orientation of each reinforcement, then an aggregate averaging procedure combines the single-reinforcement properties to model the hybrid. Predictions of the model compare favorably to experimental elastic and thermal properties of short fiber/hollow sphere composites designed for very high speed integrated circuit (VHSIC) board applications.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2011-08-19
    Description: An analysis of five Exosat observations of Cyg X-2, taken around a full binary orbit is presented. The data were obtained using all instrumentation (1000 lines/mm Transmission Grating Spectrometer, Channel Multiplier Array + filters, Medium-Energy experiment, and Gas Scintillation Proportional Counter) simultaneously, and span the full energy range 0.5-20 keV. No clear evidence was found for a correlation of any of the source characteristics with orbital phase. During two of the observations, significant iron K emission at 6.7 keV was detected, the relative strength of which seems to correlate with total X-ray intensity during two sharp intensity dips. The previous detection of discrete emission features in the 12-19 A band with the Einstein grating is confirmed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 361; 596-606
    Format: text
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  • 4
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    In:  CASI
    Publication Date: 2013-08-31
    Description: Near-infrared spectroscopy at high altitude and low humidity has been carried out to accurately measure (Ar III) lambda 7136 and (S III) lambda 9069 in the extreme metal-poor dwarf irregular galaxy IZw18. The ratio of the abundance of argon to the abundance of sulfur is within about 0.2 dex of the value for the solar neighborhood. Since n(Ar)/n(S) appears to be a universal constant, the line ratio (AR III) lambda 7136/(S III) lambda 9069 may be a useful diagnostic of temperature in cool, metal-rich HII regions.
    Keywords: ASTROPHYSICS
    Type: NASA, Ames Research Center, The Interstellar Medium in External Galaxies: Summaries of Contributed Papers; p 151-153
    Format: application/pdf
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  • 5
    Publication Date: 2013-08-31
    Description: Since stars form in molecular clouds, a critical element in studies of galaxy evolution is knowledge of the molecular content of a large sample of galaxies. To this end, researchers undertook a survey of CO emission from galaxies using the Fire College Radio Astronomy Observatory (FCRAO) 14-m millimeter telescope at 115 GHz. The aim was to better understand the differences found among and within galaxies with regard to the efficiency of star and cloud formation. The galaxies observed as part of the FCRAO Extragalactic CO Survey were selected on the basis of their optical or infrared properties. The galaxies observed thus far are (1) brighter than B sub T (sub o)=12.5 in the blue, or (2) brighter than 20 Jy at 100 microns. From major axis CO observations at 45 seconds resolution and spacing in over 200 galaxies, researchers determined the CO radial distributions, and derived global CO fluxes (cf. Kenney and Young 1988); H2 masses were derived using the conversion factor N(H2)/I sub CO=2.8 times 10 to the 20th power cm(-2)/K km s(-1)) (Bloemen et al. 1986). Here, researchers concentrate on the global galaxy properties within the sample. Neutral hydrogen (HI) masses for the sample galaxies were taken from Huchtmeier et al. (1983), blue luminosities and morphological types were taken from RC2. IR luminosities, colors, dust temperatures and dust masses were determined from coadded Infrared Astronomy Satellite (IRAS) data (Young et al. 1989). They have chosen to first compare absolute luminosities and masses in order to determine the slope and scatter in each correlation; next they investigate luminosity independent ratios in order to intercompare large and small galaxies.
    Keywords: ASTROPHYSICS
    Type: NASA, Ames Research Center, The Interstellar Medium in External Galaxies: Summaries of Contributed Papers; p 47-49
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  • 6
    Publication Date: 2011-08-19
    Description: Cygnus X-2 was observed with Exosat at five phases of a single orbital cycle in September of 1983. The results of spectral fits of the LE + ME (Argon) data are summarized in terms of a superposition of thermal bremsstrahlung and blackbody components. During the first observation, a grating spectrum was obtained, and this is described in some detail. The GSPC data are used to investigate the presence of iron features and their behavior during dips.
    Keywords: ASTROPHYSICS
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  • 7
    Publication Date: 2019-06-28
    Description: As a class, S0 galaxies are characterized by a lack of resolved bright stars in the disk. However, several lines of evidence support the hypothesis that a high rate of star formation is occurring at the centers of some S0 galaxies. Many of the warmest, most powerful far infrared sources in nearby bright galaxies occur in S0 galaxies. (Dressel 1988, Ap. J., 329, L69). The ratios of radio continuum flux to far infrared flux for these S0 galaxies are comparable to the ratios found for spiral galaxy disks and for star-burst galaxies. Very Large Array (VLA) maps of some of these S0 galaxies show that the radio continuum emission originates in the central few kiloparsecs. It is diffuse or clumpy, unlike the radio sources in active S0 galaxies, which are either extremely compact or have jet-lobe structures. Imaging of some of these galaxies at 10.8 microns shows that the infrared emission is also centrally concentrated. Many of the infrared-powerful S0 galaxies are Markarian galaxies. In only one case in this sample is the powerful ultraviolet emission known to be generated by a Seyfert nucleus. Optical spectra of the central few kiloparsecs of these S0 galaxies generally show deep Balmer absorption lines characteristic of A stars, and H beta emission suggestive of gas heated by O stars. A key question to our understanding of these galaxies is whether they really are S0 galaxies, or at least would have been recognized as S0 galaxies before the episode of central star formation began. Some of Nilson's classifications (used here) have been confirmed by Sandage or de Vaucouleurs and collaborators from better plates; some of the galaxies may be misclassified Sa galaxies (the most frequent hosts of central star formation); some are apparently difficult to classify because of mixed characteristics, faint non-S0 features, or peculiarities. More optical imaging is needed to characterize the host galaxies and to study the evolution of their star-forming regions.
    Keywords: ASTROPHYSICS
    Type: NASA, Ames Research Center, The Interstellar Medium in External Galaxies: Summaries of Contributed Papers; p 346-348
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  • 8
    Publication Date: 2019-07-13
    Description: The study deals with a periodic modulation of the UV continuum and Mg II emission-line fluxes shown by the bright cool supergiant Alpha Orionis; this pulsation is identified with the supergiant's atmosphere. UV brightness is shown to occur near the time of maximum outflow velocity of the photosphere, while local minima in the UV continuum occur near the time of maximum infall velocity. Visible and UV observations of Alpha Ori since the beginning of the monitoring program with IUE are discussed.
    Keywords: ASTROPHYSICS
    Type: Confrontation between Stellar Pulsation and Evolution; May 28, 1990 - May 31, 1990; Bologna; Italy
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  • 9
    Publication Date: 2019-07-13
    Description: Radio continuum flux densities, far infrared flux densities, far infrared colors, and ultraviolet and optical spectra indicate that high rates of star formation are occurring in some SO galaxies, especially barred galaxies. Radio continuum and infrared images show that the star forming region is typically concentrated within the central few kpc of the galaxy. The high incidence of central star formation in barred galaxies suggests that bar-driven inflow of gas is fueling the star-forming regions in these galaxies.
    Keywords: ASTROPHYSICS
    Type: Edwin Hubble Centennial Symposium; Jun 21, 1989 - Jun 23, 1989; Berkeley, CA; United States
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  • 10
    Publication Date: 2019-07-12
    Description: Results of VLA radio continuum observations of 13 early-type pre-main-sequence stars selected from the 1984 catalog of Finkenzeller and Mundt are presented. The stars HD 259431 and MWC 1080 were detected at 3.6 cm, while HD 200775 and TY CrA were detected at both 3.6 and 6 cm. The flux density of HD 200775 has a frequency dependence consistent with the behavior expected for free-free emission originating in a fully ionized wind. However, an observation in A configuration suggests that the source geometry may not be spherically symmetric. In contrast, the spectral index of TY CrA is negative with a flux behavior implying nonthermal emission. The physical mechanism responsible for the nonthermal emission has not yet been identified, although gyrosynchrotron and synchrotron processes cannot be ruled out.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 357; L39-L43
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