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  • American Physical Society  (67)
  • Springer  (64)
  • Oxford University Press
  • 1995-1999  (133)
Collection
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 57 (1995), S. 413-439 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract We describe a classification scheme for bursting oscillations which encompasses many of those found in the literature on bursting in excitable media. This is an extension of the scheme of Rinzel (inMathematical Topics in Population Biology, Springer, Berlin, 1987), put in the context of a sequence of horizontal cuts through a two-parameter bifurcation diagram. We use this to describe the phenomenological character of different types of bursting, addressing the issue of how well the bursting can be characterized given the limited amount of information often available in experimental settings.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 58 (1996), S. 1023-1046 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Collapsible-tube flow with self-excited oscillations has been extensively investigated. Though physiologically relevant, forced oscillation coupled with self-excited oscillation has received little attention in this context. Based on an ODE model of collapsible-tube flow, the present study applies modern dynamics methods to investigate numerically the responses of forced oscillation to a limit-cycle oscillation which has topological characteristics discovered in previous unforced experiments. A devil's staircase and period-doubling cascades are presented with forcing frequency and amplitude as control parameters. In both cases, details are provided in a bifurcation diagram. Poincaré sections, a frequency spectrum and the largest Lyapunov exponents verify the existence of chaos in some circumstances. The thin fractal structure found in the strange attractors is believed to be a result of high damping and low stiffness in such systems.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 58 (1996), S. 611-641 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Most of the elastic tubes found in the mammalian body will collapse from a distended circular cross section and when collapsed may undergo flow-induced oscillations. A mathematical model describing fluid flow in a collapsible tube is analysed using the software package AUTO-86. AUTO-86 is used for continuation and bifurcation problems in systems of non-linear ordinary differential equations. The model is a third-order lumped-parameter type and is based on the classical “Starling resistor”; it describes the unsteady flow behaviour and, in particular, the experimentally observed self-excited oscillations, in a way which is simple enough to give physical understanding, yet still firmly based on fluid mechanical principles. Some of the bifurcation types found in this model bear close resemblance to the types suggested by experimental observations of self-excited oscillations in collapsible tubes; they thus shed some light on the various topological changes which occur in practice, particularly in view of the fact that some of the points found numerically are diffcult to achieve experimentally, while the existence of others can only be inferred indirectly and uncertainly from experiment.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Transformation groups 3 (1998), S. 3-32 
    ISSN: 1531-586X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We generalize features of bounded symmetric domains to a bigger class of symmetric spaces calledMakarevič spaces: we associate a generalizedBergman operator to such a space and describe the invariant pseudo-metric and the invariant measure on the space by means of this family of operators. The space itself can be characterized essentially as the domain where the generalized Bergman operator is nondegenerate. These results are applied to the theory ofcompactly causal symmetric spaces: we describe explicitly the complex domain Ξ associated to such a space.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1557-1947
    Keywords: Superconductivity ; research opportunities ; state of the art
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract This report surveys the considerable progress made over the last five years—such as the marketing of superconducting quantum interference devices (SQUIDs), cellular wireless filter systems, and high current leads—and assesses needs and opportunities in the areas of fundamental science, materials development, thin film and device applications, and wire and bulk applications. It examines the challenges facing high-temperature superconductivity: from the need to understand the mechanism of high-temperature superconductivity and the unusual “normal” state to the need for new instrumentation for material characterization. Advances in thin film and bulk materials are reviewed, and obstacles impeding the commercialization of HTS materials are examined.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of theoretical probability 11 (1998), S. 1111-1133 
    ISSN: 1572-9230
    Keywords: Asymptotically stationary process ; spectral measure ; almost periodic Fourier transform
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Vector-valued, asymptotically stationary stochastic processes on σ-compact locally compact abelian groups are studied. For such processes, we introduce a stationary spectral measure and show that it is discrete if and only if the asymptotically stationary covariance function is almost periodic. Using an “almost periodic Fourier transform” we recover the discrete part of the spectral measure and construct a natural, consistent estimator for the latter from samples of the process.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Selecta mathematica 2 (1996), S. 43-91 
    ISSN: 1420-9020
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
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  • 8
    ISSN: 1432-0827
    Keywords: Key words: Bone formation — Fibroblastic colony-forming unit — Osteoblast — Recruitment — Bone marrow stromal cells.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Basic fibroblast growth factor (bFGF) is known to stimulate endosteal bone formation in vivo by a mechanism possibly mediated via osteoblast precursor cells present in the bone marrow. In high density cultures of primary bone marrow cells, and in the presence of glucocorticoids, bFGF stimulates the formation of a bone-like matrix; however, due to the dense nature of these cultures, the exact mechanism of action is unclear. In an adaptation of the fibroblastic colony formation unit assay, in which the bone marrow cells are grown in the presence of dexamethasone, β-glycerophosphate, and ascorbate, mineralized colonies are formed which stem from single mesenchymal precursor cells and grow in isolation from each other. Using this system we have been able to investigate the mechanism by which bFGF stimulates the formation of bone like tissue in vitro. We have shown that bFGF increases the formation of a calcified collagenous matrix in vitro by (1) increasing the total number of fibroblastic colonies formed, (2) increasing the proportion of differentiated colonies that synthesize collagen and calcify, and (3) stimulating the proliferation and collagen accumulation of the individual colonies. A maximal increase in total and differentiated colony numbers was seen after only 5 days exposure to bFGF, however, continued exposure to bFGF continued to increase the size and collagen content of the individual colonies. Bearing in mind the endosteal location of newly formed bone seen after treatment with bFGF, these processes may well play an active role in this effect.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Landscape ecology 13 (1998), S. 187-201 
    ISSN: 1572-9761
    Keywords: vegetation pattern ; tussock tundra ; landscapes ; topography ; water drainage ; scaling up
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We present a topographically-derived vegetation model (TVM) that predicts the landscape patterns of arctic vegetation types in the foothills of the Brooks Range in northern Alaska. In the Arctic there is a strong relationship between water and plant structure and function and TVM is based on the relationships between vegetation types and slope (tan β) and discharge (δ), two independent variables that can be easily derived from digital terrain data. Both slope and discharge relate to hydrological similarity within a landscape: slope determines the gravitational hydrological gradient and hence influences flow velocity, whereas discharge patterns are computed based on upslope area and quantify lateral flow amount. TVM was developed and parameterized based on vegetation data from a small 2.2 km2 watershed and its application was tested in a larger 22km2 region. For the watershed, TVM performed quite well, having a high spatial resolution and a goodness-of-fit ranging from 71–78%, depending on the functions used. For the larger region, the strength of the vegetation types predictions drops somewhat to between 56–59%. We discuss the various sources of error and limitations of the model for purposes of extrapolation.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Selecta mathematica 1 (1995), S. 163-195 
    ISSN: 1420-9020
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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