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  • Springer  (65)
  • American Meteorological Society (AMS)
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  • 1
    ISSN: 1432-1211
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Immunofluorescence tests indicate that alloantibodies specific for mouse histocompatibility antigens H-1a, H-3a, and H-13a have been produced, using four different immunizations. Furthermore, an immunization employing donors and recipients which were H-2k at the MHC produced stronger anti-H-3a and anti-H-13a than did immunizations where donors and recipients were H-2b at the MHC.
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  • 2
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A new approach is presented which allows the in vivo visualization of individual chromosome territories in the nuclei of living human cells. The fluorescent thymidine analog Cy3-AP3-dUTP was microinjected into the nuclei of cultured human cells, such as human diploid fibroblasts, HeLa cells and neuroblastoma cells. The fluorescent analog was incorporated during S-phase into the replicating genomic DNA. Labelled cells were further cultivated for several cell cycles in normal medium. This well-known scheme yielded sister chromatid labelling. Random segregation of labelled and unlabelled chromatids into daughter nuclei resulted in nuclei exhibiting individual in vivo detectable chromatid territories. The territories were composed of subcompartments with diameters ranging between approximately 400 and 800 nm which we refer to as subchromosomal foci. Time-resolved in vivo studies demonstrated changes of positioning and shape of territories and subchromosomal foci. The hypothesis that subchromosomal foci persist as functionally distinct entities was supported by double labelling of chromatin with CldU and IdU, respectively, at early and late S-phase and subsequent cultivation of corresponding cells for 5–10 cell cycles before fixation and immunocytochemical detection. This scheme yielded segregated chromatid territories with distinctly separated subchromosomal foci composed of either early- or late-replicating chromatin. The size range of subchromosomal foci was similar after shorter (2 h) and longer (16 h) labelling periods and was observed in nuclei of both living and fixed cells, suggesting their structural identity. A possible functional relevance of chromosome territory compartmentalization into subchromosomal foci is discussed in the context of present models of interphase chromosome and nuclear architecture.
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  • 3
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary A simple model, based on the use of transformations of second-order tensors, is presented in this paper to predict the failure mode of wood members stressed in various degrees of parallel-and perpendicular-to-grain tension and parallel-to-grain shear. This type of loading is indicative of structural wood members with cross grain or grain deviations in the vicinity of knots subjected to bending or tension. The model is based on the assumptions that failure is dictated by the presence of any of the aforementioned stresses that exceed the clear wood strength in that mode and that failure does not result from stress interactions. The magnitudes of the applied stresses are normalized relative to the wood strength in that mode. The ratio of applied stress to material strength that is greatest at any particular angle of load to grain is presumed to be the failure mode at that angle. To verify model predictions, optical and microscopic analyses of surfaces of failed specimens loaded in uniaxial tension at angles between 0° and 90° to grain were compared to previously obtained, or otherwise known, surfaces of specimens tested in tension and shear. Specimens tested at various angles to grain demonstrated failed surfaces very much like those associated with specimens loaded in the modes predicted by the model.
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  • 4
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary The ultrastructural characteristics of fracture surfaces from southern pine and Douglas-fir specimens tested in tension at various angles to grain were examined. The fracture surace morphology was inspected using scanning electron microscopy. Three anatomical failure types were recognized: intercell failure, transwall failure, and intrawall failure. Certain failure characteristics were ascribed as a function of the magnitudes of paralleland perpendicular-tograin tension and parallel-to-grain shear present in the specimen. In specimens tested in paralleland perpendicular-to-grain tension, the thick-walled latewood cells were found to fail in a combination of transwall and intrawall failure. The intrawall failures were usually at the S1–S2 interface. The more thin-walled earlywood cells were more likely to exhibit abrupt, transwall failures. At intermediate angles of load to grain, surfaces indicative of the type found in pure shear tests were predominant. Perpendicularto-grain tension failures resulted in mostly intercell failures. Ray cells consistently exhibited transwall failures. The failure surface frequently changed planes in all loading modes. This path transfer was inevidably associated with material discontinuities in the wood. When the path did transfer, all three failure types were observed. No significant species effect was observed.
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  • 5
    ISSN: 1090-6487
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Slight changes with temperature in the director orientation at the surface of a perfect planar cholesteric liquid crystal (CLC) layer, which are precursors of a jump in the pitch of the cholesteric helix, are observed by measuring the temperature dependence of the optical transmission spectra of the layer. The observed changes in the director orientation are described in the framework of the continuum theory of CLCs, supplemented with allowance for the surface anchoring forces. In particular, the angle of deviation of the director at the surface from the alignment direction at the exact temperature of the jump in pitch is expressed in terms of the anchoring potential. The relation obtained is use to find the anchoring potential in the samples.
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  • 6
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Hysteresis of the temperature of jumps in the cholesteric pitch in planar layers of cholesteric liquid crystals (CLCs) has been observed in the temperature dependence of the optical transmission spectra measured in a 4.8 ¼m thick specimen of a 60% chiral racemic mixture of CE6. The temperature difference for the pitch jumps during heating and cooling was equal to about 0.1°C near 40.3°C. No difference in the temperature of the pitch jumps during heating and cooling was observed for an 18 µm thick specimen. A theoretical description of this hysteresis is presented on the basis of a continuum theory of elasticity of CLCs that also takes account of the surface anchoring of the CLC. Different possible mechanisms leading to a change in the director configuration in the layer during a pitch jump and their correspondence to the jump mechanism and hysteresis which occur in the experimental specimens are discussed.
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  • 7
    ISSN: 1432-0592
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography , Economics
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract An experiment is described which compares the performance of a neural network to human performance on a visual task which consists of detecting a target in a background image of correlated noise. A three-layer, feed-forward, multi-layer perceptron is trained to indicate the presence or absence of a target in images also presented to human observers. The basis for the comparison between the network and the human observers is the receiver operating characteristic (ROC) curve. Network performance is comparable to human performance for this particular task.
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  • 9
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The utility of the back-propagation method in establishing suitable weights in a distributed adaptive network has been demonstrated repeatedly. Unfortunately, in many applications, the number of iterations required before convergence can be large. Modifications to the back-propagation algorithm described by Rumelhart et al. (1986) can greatly accelerate convergence. The modifications consist of three changes:1) instead of updating the network weights after each pattern is presented to the network, the network is updated only after the entire repertoire of patterns to be learned has been presented to the network, at which time the algebraic sums of all the weight changes are applied:2) instead of keeping η, the “learning rate” (i.e., the multiplier on the step size) constant, it is varied dynamically so that the algorithm utilizes a near-optimum η, as determined by the local optimization topography; and3) the momentum factor α is set to zero when, as signified by a failure of a step to reduce the total error, the information inherent in prior steps is more likely to be misleading than beneficial. Only after the network takes a useful step, i.e., one that reduces the total error, does α again assume a non-zero value. Considering the selection of weights in neural nets as a problem in classical nonlinear optimization theory, the rationale for algorithms seeking only those weights that produce the globally minimum error is reviewed and rejected.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Monatshefte für Chemie 22 (1901), S. 813-842 
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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