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  • 1
    Electronic Resource
    Electronic Resource
    Glycopeptide resistance determinants from the teicoplanin producer Actinoplanes teichomyceticus (2004)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 240 (2004), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In enterococci and other pathogenic bacteria, high-level resistance to vancomycin and other glycopeptide antibiotics requires the action of the van genes, which direct the synthesis of peptidoglycan terminating in the depsipeptide d-alanyl-d-lactate, in place of the usual d-Ala-d-Ala. The Actinoplanes teichomyceticus tcp cluster, devoted to the biosynthesis of the glycopeptide antibiotic teicoplanin, contains van genes associated to a murF-like sequence (murF2). We show that A. teichomyceticus contains also a house-keeping murF1 gene, capable of complementing a temperature sensitive Escherichia coli murF mutant. MurF1, expressed in Streptomyces lividans, can catalyze the addition of either d-Ala-d-Ala or d-Ala-d-Lac to the UDP-N-acetyl-muramyl-l-Ala-d-Glu-d-Lys. However, similarly expressed MurF2 shows a small enzymatic activity only with d-Ala-d-lactate. Introduction of a single copy of the entire set of van genes confers resistance to teicoplanin-type glycopeptides to S. coelicolor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/j.femsle.2004.09.017
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  • 2
    Electronic Resource
    Electronic Resource
    Eocene simple shear and plio-quaternary pure-shear folding in the Central-Eastern Algerian Atlas (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 2 (1990), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Tertiary folds of the central and eastern part of the Algerian Atlas were studied in order to assess their kinematics and regimes of deformation. Folds developed following two main phases of deformation during the Eocene and the Pliocene. The NE-SW trending Eocene folds show a clockwise rotation of fold axis with depth, noncylindrical geometry and a right-stepping en echelon configuration. Early secondary structures inside each fold are also rotated clockwise with respect to the younger folds. These data are in agreement with progressive ‘simple shear’ deformation. Pliocene folds strike E-W and display a cylindrical geometry. Associated Plio-Quaternary brittle structures show no rotational path. These observations are compatible with ‘pure shear’ style of deformation. These results, in combination with focal mechanism solutions, have important implications for the understanding of the kinematic evolution of the western segment of the African-European plate boundary. For Algeria they imply that transcurrent motion during the Paleogene was followed by coaxial shortening with a NNW direction during Neogene-Quaternary times. Comparison with published data for Morocco and Tunisia suggests that this transcurrent regime developed from west to east continuing from the Middle Jurassic through to the Miocene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3121.1990.tb00130.x
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  • 3
    Electronic Resource
    Electronic Resource
    Multi-constrained matroidal knapsack problems (1989)
    Springer
    Mathematical programming 45 (1989), S. 211-231 
    Details
    ISSN: 1436-4646
    Keywords: Knapsack ; matroids ; asymptotically optimum bounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We consider multi-constrained knapsack problems where the sets of elements to be selected are subject to combinatorial constraints of matroidal nature. For this important class of NP-hard combinatorial optimization problems we prove that Lagrangean relaxation techniques not only provide good bounds to the value of the optimum, but also yield approximate solutions, which are asymptotically optimal under mild probabilistic assumptions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01589104
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  • 4
    Electronic Resource
    Electronic Resource
    Combining Linear and Non-Linear Objectives in Spanning Tree Problems (2000)
    Springer
    Journal of combinatorial optimization 4 (2000), S. 253-269 
    Details
    ISSN: 1573-2886
    Keywords: computational complexity ; spanning tree ; cumulative function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A classical approach to multicriteria problems asks for the optimization of a suitable linear combination of the objectives. In this work we address such problems when one of the objectives is the linear function, the other is a non-linear one and we seek for a spanning tree of a given graph which optimizes the combination of the two functions. We consider both maximization and minimization problems and present the complexity status of 56 such problems, giving, whenever possible, polynomial solution algorithms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009854922371
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  • 5
    Electronic Resource
    Electronic Resource
    The image of weighted combinatorial problems (1991)
    Springer
    Annals of operations research 33 (1991), S. 181-197 
    Details
    ISSN: 1572-9338
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract The concept ofimage of an integrally weighted combinatorial problem is introduced as the vector of all possible weights of feasible solutions. This preliminary work begins to explore the possible applications of this concept and to study the computational complexity of image computations. It is shown that the images of spanning trees, matroid bases, perfect matchings and, more generally, matroid parity bases can be computed in polynomial time for some "bottleneck" objective functions (such as, for instance, the maximum weight of an element), whereas (random) pseudo-polynomial time is needed when the objective function is the sum of the element weights.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02115754
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  • 6
    Electronic Resource
    Electronic Resource
    Randomized algorithms: An annotated bibliography (1984)
    Springer
    Annals of operations research 1 (1984), S. 331-345 
    Details
    ISSN: 1572-9338
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01874396
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  • 7
    Electronic Resource
    Electronic Resource
    Algorithms for finding optimum trees: Description, use and evaluation (1988)
    Springer
    Annals of operations research 13 (1988), S. 263-397 
    Details
    ISSN: 1572-9338
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract This work is devoted to the problem of finding an optimum spanning tree in an undirected graph. Both min-sum and min-max trees are sought. The five algorithms considered are among the most well-known proposed in the literature. They are described in sect. 1 as thoroughly as possible, using a simplified Pascal language; all min-sum algorithms are derived from a unique prototype formulation. In sect. 2, the algorithms are implemented in PFORT to enhance their portability and ad hoc data structures are utilized in order to obtain subroutines as efficient as possible. Finally, in sect. 3, the programs are evaluated, comparing their performances in handling several classes of randomly generated graphs. Various observations are reported, and some indications for choosing the most suitable algorithm in each case are provided.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02288325
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  • 8
    Electronic Resource
    Electronic Resource
    A mixed-integer model for solving ordering problems with side constraints (1997)
    Springer
    Annals of operations research 69 (1997), S. 277-297 
    Details
    ISSN: 1572-9338
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract We present an exact approach for solving the Sequential Ordering Problem (SOP). In this problem, a set of jobs has to be processed on a single machine; a time window (deadline - release date) is associated with each job, and precedence relationships between jobs are given. Moreover, a setup time (possibly zero) before processing a job is assigned. The prob-lem consists in finding an ordering of the jobs such that the completion time of the job sequenced last is minimized. Starting from a 0-1 formulation of the problem, we translate the model into a linear Mixed Integer Program (MIP) problem by adding some variables representing the idle time of the machine, in such a way that both the subtour elimination constraints and the due forcing constraints are implicitly satisfied. Some computational experience is reported along with the analysis of a simple case study. The main goal of this work is to assess the suitability of the mathematical models presented with respect to avail-able MIP software like OSL.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018989130169
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  • 9
    Electronic Resource
    Electronic Resource
    A Lagrangian heuristic for the Prize CollectingTravelling Salesman Problem (1998)
    Springer
    Annals of operations research 81 (1998), S. 289-306 
    Details
    ISSN: 1572-9338
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract In this paper, we consider the Prize Collecting Travelling Salesman Problem (PCTSP),which is a variant of the Travelling Salesman Problem (TSP), where a tour visiting eachnode at most once in a given graph has to be computed such that a prize is associated witheach node and a penalty has to be paid for every unvisited node: moreover, a knapsackconstraint guarantees that a sufficiently large prize is collected. We develop a Lagrangianheuristic and obtain an upper bound in the form of a feasible solution starting from a lowerbound to the problem recently proposed in the literature. We evaluate these bounds utilizingboth randomly generated instances and real ones with very satisfactory results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018961208614
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  • 10
    Electronic Resource
    Electronic Resource
    Approximability of hard combinatorial optimization problems: an introduction (2000)
    Springer
    Annals of operations research 96 (2000), S. 221-236 
    Details
    ISSN: 1572-9338
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018987015651
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