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  • 1
    ISSN: 1435-5957
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geography , Economics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Notes: Abstract Livers from mature female rats exposed for up to 36 weeks to dietary levels of Aroclor® 1242 (75 or 150 ppm) and/or commercial grade DDT (75 or 150 ppm) were compared to those from animals receiving basal diets. In earlier studies, reproductive effects of the test substances were assessed. Moreover, the markedly abnormal gross appearance of the livers led to examination of the hepatic effects of PCB and DDT in more detail, at both the light microscope (LM) and electron microscope (EM) levels. Light microscopy revealed focal liver cell necrosis in rats fed PCB, DDT, and PCB-DDT combinations. Higher levels of PCB (150 ppm) increased the severity of necrosis. Feeding both DDT and PCB produced similar effects at 75 ppm, and caused atypical centrolobular regeneration, occasionally forming nodules resembling small tumors. The experimentally induced injury was associated with the marked accumulation of iron-containing pigment in hepatocytes and Kupffer cells. Electron micrographs demonstrated the presence of whorl structures (myelin figures) within liver cell cytoplasm, and for the first time clearly illustrated the endocytotic expulsion of these membranous whorls from hepatocytes into the bile canaliculi and sinusoids. Other ultrastructural changes were similar to those previously reported in rat livers injured by several hepatotoxic substances. Mitochondria enclosed by or projecting into large non-lipid vacuoles were present in several experimental groups. The electron micrographs provide the most convincing evidence to date to support the hypothesis that myelin figures may be the vehicle whereby the cell rids itself of specific hepatotoxic substances.
    Type of Medium: Electronic Resource
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  • 3
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    In:  Other Sources
    Publication Date: 2018-12-01
    Description: An algorithm is derived for the real-time calibration of the engine fuel flowmeter and the engine mixture ratio during Space Shuttle Main Engine (SSME) ground testing. Because currently used calibration methods are post-test operations, there exists no fail-safe way of predicting at what mixture ratio a planned test will run. It is proposed that the algorithm developed here be used as part of an Automated Engine Calibration System (AECS) which could ensure that nearly all SSME tests are run at the proper mixture ratio. In this way, AECS has the potential of increasing the efficiency of the SSME ground test program. In addition to the derivation of the algorithm, an overview of this calibration system is presented along with the list of test stand facility instrumentation necessary for AECS implementation.
    Keywords: GROUND SUPPORT SYSTEMS AND FACILITIES (SPACE)
    Type: AIAA PAPER 92-3453
    Format: text
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  • 4
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    Munich: Center for Economic Studies and Ifo Institute (CESifo)
    Publication Date: 2018-11-19
    Description: Regression analysis using panel data for 42 colleges and universities over 14 years suggests that the economics faculty size of universities offering a Ph.D. in economics is determined primarily by the long-run average number of Ph.D. degrees awarded annually; the number of full-time faculty increases at almost a one-for-one pace as the average number of Ph.D.s grows. Faculty size at Ph.D. granting universities is largely unresponsive to changes in the contemporaneous number of undergraduate economics degrees awarded at those institutions. Similarly, faculty size at colleges where a bachelor's is the highest degree awarded is responsive to the long and short term average number of economics degrees awarded but not the annual changes in BS and BA degrees awarded in economics.
    Keywords: A22 ; A23 ; C23 ; J21 ; ddc:330 ; faculty size ; student body ; Ph.D. degrees ; bachelor degrees ; Wirtschaftshochschule ; Betriebsgröße ; Studierende ; Bildungsabschluss ; Schätzung ; USA
    Repository Name: EconStor: OA server of the German National Library of Economics - Leibniz Information Centre for Economics
    Language: English
    Type: doc-type:workingPaper
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  • 5
    Publication Date: 2018-06-12
    Description: The subject of mathematical modeling of the transient operation of liquid rocket engines is presented in overview form from the perspective of engineers working at the NASA Marshall Space Flight Center. The necessity of creating and utilizing accurate mathematical models as part of liquid rocket engine development process has become well established and is likely to increase in importance in the future. The issues of design considerations for transient operation, development testing, and failure scenario simulation are discussed. An overview of the derivation of the basic governing equations is presented along with a discussion of computational and numerical issues associated with the implementation of these equations in computer codes. Also, work in the field of generating usable fluid property tables is presented along with an overview of efforts to be undertaken in the future to improve the tools use for the mathematical modeling process.
    Keywords: Spacecraft Propulsion and Power
    Type: Fifth International Symposium on Liquid Space Propulsion; NASA/CP-2005-213607
    Format: application/pdf
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  • 6
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 7
    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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  • 8
    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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  • 9
    Publication Date: 2013-08-31
    Description: A study was performed focusing on the calculation of sensitivities of displacements, velocities, accelerations, and stresses in linear, structural, transient response problems. One significant goal of the study was to develop and evaluate sensitivity calculation techniques suitable for large-order finite element analyses. Accordingly, approximation vectors such as vibration mode shapes are used to reduce the dimensionality of the finite element model. Much of the research focused on the accuracy of both response quantities and sensitivities as a function of number of vectors used. Two types of sensitivity calculation techniques were developed and evaluated. The first type of technique is an overall finite difference method where the analysis is repeated for perturbed designs. The second type of technique is termed semi-analytical because it involves direct, analytical differentiation of the equations of motion with finite difference approximation of the coefficient matrices. To be computationally practical in large-order problems, the overall finite difference methods must use the approximation vectors from the original design in the analyses of the perturbed models. In several cases this fixed mode approach resulted in very poor approximations of the stress sensitivities. Almost all of the original modes were required for an accurate sensitivity and for small numbers of modes, the accuracy was extremely poor. To overcome this poor accuracy, two semi-analytical techniques were developed. The first technique accounts for the change in eigenvectors through approximate eigenvector derivatives. The second technique applies the mode acceleration method of transient analysis to the sensitivity calculations. Both result in accurate values of the stress sensitivities with a small number of modes and much lower computational costs than if the vibration modes were recalculated and then used in an overall finite difference method.
    Keywords: STRUCTURAL MECHANICS
    Type: L-16643 , NAS 1.15:4156 , NASA-TM-4156
    Format: application/pdf
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  • 10
    Publication Date: 2013-08-31
    Description: In January 1989 an accident occurred in the National Transonic Facility wind tunnel at NASA Langley Research Center that was believed to be caused by the failure of a thermal insulation retainer. A structural analysis of this retainer assembly was performed in order to understand the possible failure mechanisms. Two loading conditions are important and were considered in the analysis. The first is the centrifugal force due to the fact that this retainer is located on the fan drive shaft. The second loading is a differential temperature between the retainer assembly and the underlying shaft. Geometrically nonlinear analysis is required to predict the stiffness of this component and to account for varying contact regions between various components in the assembly. High, local stresses develop in the band part of the assembly near discontinuities under both the centrifugal and thermal loadings. The presence of an aluminum ring during a portion of the part's operating life was found to increase the stresses in other regions of the band. Under the centrifugal load, high bending stresses develop near the intersection of the band with joints in the assembly. These high bending stresses are believed to be the most likely cause for failure of the assembly.
    Keywords: STRUCTURAL MECHANICS
    Type: NAS 1.15:101580 , NASA-TM-101580
    Format: application/pdf
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