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  • Articles: DFG German National Licenses  (3)
  • Opus Repository ZIB
  • 1995-1999  (3)
  • 1
    Electronic Resource
    Electronic Resource
    DNA Computing Based on Splicing: The Existence of Universal Computers (1999)
    Springer
    Theory of computing systems 32 (1999), S. 69-112 
    Details
    ISSN: 1433-0490
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract. We prove that splicing systems with finite components and certain controls on their work are computationally complete (they can simulate any Turing Machine); moreover, there are universal splicing systems (systems with all components fixed which can simulate any given splicing system, when an encoding of the particular system is added—as a program—to the universal system). Splicing systems are based on the splicing operation which is a model for DNA recombination. Informally, a prefix of a word is catenated to a suffix of another word, thus yielding a (possibly) new word. Cutting occurs at specific sites which correspond to specific sequences in DNA strands as they can be recognized by restriction enzymes. When no additional control is assumed, splicing systems with finitely many starting words (axioms) and finitely many splicing rules are known to characterize only regular languages (those recognized by finite automata ). However, when a splicing rule is allowed to be used (1)\hskip .5em only in the presence of certain symbols (``catalyst'') or (2)\hskip .5em only in the absence of certain symbols (``inhibitors''), then we can characterize the recursively enumerable languages (recognized by Turing Machines ); the same result is obtained when counting the number of copies of (some of) the words used. From the proofs, we also infer the existence of universal (hence programmable) splicing systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002240000112
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The metameric pattern of the head mesoderm — does it exist? (1996)
    Springer
    Anatomy and embryology 193 (1996), S. 73-80 
    Details
    ISSN: 1432-0568
    Keywords: Avian embryo ; Head mesoderm ; Somitomeres ; Segments ; Metameric pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract It is a long-standing question whether the paraxial head mesoderm of vertebrate embryos is segmentally organized into somites like the trunk or not. On the one hand, no somites are seen in the anterior head mesoderm in vertebrate embryos, on the other hand, such a segmental pattern has been described under the name of somitomeres. In order to investigate the patterning of mesodermal cells in the head of avian embryos we performed scanning electron microscopy, computer assisted reconstructions of the head mesoderm and density analyses of head mesoderm cells. We observed regional differences within the head mesoderm of avian embryos, but we could not see a consistent somitomeric pattern in the head mesoderm. In sum, we consider that the avian head mesoderm is not arranged in a metameric pattern.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00186835
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    An interior-point method for multifractional programs with convex constraints (1995)
    Springer
    Journal of optimization theory and applications 85 (1995), S. 125-161 
    Details
    ISSN: 1573-2878
    Keywords: Multifractional programming ; convex sets ; interior-point methods ; self-concordant barrier functions ; short-step algorithms ; polynomial-time convergence ; predictor-corrector step
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We present an interior-point method for a family of multi-fractional programs with convex constraints. The programs under consideration consist of minimizing the maximum of a finite number of linear fractions over some convex set. First, we present a simple shortstep algorithm for solving such multifractional programs, and we show that, under suitable assumptions, the convergence of the short-step algorithm is weakly polynomial in a sense specified below. Then, we describe a practical implementation of the proposed method, and we report results of numerical experiments with this algorithm. These results suggest that the proposed method is a viable alternative to the standard Dinkelbach-type algorithms for solving multifractional programs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02192302
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    Paper (German National Licenses)
    Fulltext
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