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  • 1
    Electronic Resource
    Electronic Resource
    A simple model for the velocity modulation detection technique of molecular ions (1989)
    Springer
    Applied physics 48 (1989), S. 235-242 
    Details
    ISSN: 1432-0649
    Keywords: 35.80.+s ; 33.70.−w
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a simple model to describe the line-profile of velocity modulated ions. This model is based on Langevin's theory of the mobility and on the independence of the electric field strength on the discharge current in the ideal positive column. A comparison of time constants responsible for the drift of the ions, the concentration, and the ignition and extinction of the discharge itself is essential for a rough understanding of the velocity modulation. The behaviour of H3O+ ions in an ac glow discharge was examined. Under our experimental conditions the line-profile can be explained by a temporal dependence of the velocity which is close to a square-wave. Due to this particular temporal dependence the amplitude of the signal only depends on the concentration modulation, while the line-shape is a simple difference line-profile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00694351
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The smallest point of a polytope (1990)
    Springer
    Journal of optimization theory and applications 64 (1990), S. 429-432 
    Details
    ISSN: 1573-2878
    Keywords: Least-distance problems ; least-square problems with nonnegative variables ; active set methods ; row relaxation methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This note suggests new ways for calculating the point of smallest Euclidean norm in the convex hull of a given set of points inR n . It is shown that the problem can be formulated as a linear least-square problem with nonnegative variables or as a least-distance problem. Numerical experiments illustrate that the least-square problem is solved efficiently by the active set method. The advantage of the new approach lies in the solution of large sparse problems. In this case, the new formulation permits the use of row relaxation methods. In particular, the least-distance problem can be solved by Hildreth's method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00939458
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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