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  • Articles  (5,938)
  • Mathematics  (5,938)
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  • 1
    Electronic Resource
    Electronic Resource
    Lifting valid inequalities for the precedence constrained knapsack problem (1999)
    Springer
    Mathematical programming 86 (1999), S. 161-185 
    Details
    ISSN: 1436-4646
    Keywords: Mathematics Subject Classification (1991): 90C10
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. This paper considers the precedence constrained knapsack problem. More specifically, we are interested in classes of valid inequalities which are facet-defining for the precedence constrained knapsack polytope. We study the complexity of obtaining these facets using the standard sequential lifting procedure. Applying this procedure requires solving a combinatorial problem. For valid inequalities arising from minimal induced covers, we identify a class of lifting coefficients for which this problem can be solved in polynomial time, by using a supermodular function, and for which the values of the lifting coefficients have a combinatorial interpretation. For the remaining lifting coefficients it is shown that this optimization problem is strongly NP-hard. The same lifting procedure can be applied to (1,k)-configurations, although in this case, the same combinatorial interpretation no longer applies. We also consider K-covers, to which the same procedure need not apply in general. We show that facets of the polytope can still be generated using a similar lifting technique. For tree knapsack problems, we observe that all lifting coefficients can be obtained in polynomial time. Computational experiments indicate that these facets significantly strengthen the LP-relaxation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s101070050084
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  • 2
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    On the assessment of adverse drug reactions from spontaneous reporting systems: the influence of under-reporting on odds ratios (2002)
    Wiley
    Details
    Publication Date: 2002-01-01
    Print ISSN: 0277-6715
    Electronic ISSN: 1097-0258
    Topics: Mathematics , Medicine
    Published by Wiley
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  • 3
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    Laser wakefield acceleration: the injection issue. Overview and latest results (2006)
    The Royal Society
    Details
    Publication Date: 2006-01-24
    Description: External injection of electron bunches into laser-driven plasma waves so far has not resulted in ‘controlled’ acceleration, i.e. production of bunches with well-defined energy spread. Recent simulations, however, predict that narrow distributions can be achieved, provided the conditions for properly trapping the injected electrons are met. Under these conditions, injected bunch lengths of one to several plasma wavelengths are acceptable. This paper first describes current efforts to demonstrate this experimentally, using state-of-the-art radio frequency technology. The expected charge accelerated, however, is still low for most applications. In the second part, the paper addresses a number of novel concepts for significant enhancement of photo-injector brightness. Simulations predict that, once these concepts are realized, external injection into a wakefield accelerator will lead to accelerated bunch specs comparable to those of recent ‘laser-into-gasjet’ experiments, without the present irreproducibility of charge and final energy of the latter.
    Print ISSN: 1364-503X
    Electronic ISSN: 1471-2962
    Topics: Mathematics , Physics , Technology
    Published by The Royal Society
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  • 4
    Electronic Resource
    Electronic Resource
    On the covariant quantization of a first-class superparticle (1990)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 31 (1990), S. 1761-1769 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The Batalin–Vilkovisky formalism is used to quantize covariantly a formulation of the superparticle with only first-class constraints. Towers of ghosts are found that split into ghosts-for-ghosts and ghost gauge fields. Subsolutions to the master equation with spinor and bispinor ghosts contain terms cubic in antifields and lead to free gauge-fixed BRST-invariant actions. The final formulation with multispinor ghosts is nilpotent only on the classical shell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529022
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  • 5
    Electronic Resource
    Electronic Resource
    A simple construction of twist-eating solutions (1986)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 27 (1986), S. 455-457 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A simple general construction of all solutions to the set of equations [Ωμ, Ων]=exp (2πinμν/N)I, where Ωμ∈SU(N) or U(N) and μ, ν=1, 2, ... , 2g, is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.527242
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  • 6
    Electronic Resource
    Electronic Resource
    Estimating a Survival Distribution with Current Status Data and High-dimensional Covariates (2006)
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 2 (2006), S. 9 
    Details
    ISSN: 1557-4679
    Source: Berkeley Electronic Press Academic Journals
    Topics: Biology , Mathematics , Medicine
    Notes: We consider the inverse problem of estimating a survival distribution when the survival times are only observed to be in one of the intervals of a random bisection of the time axis. We are particularly interested in the case that high-dimensional and/or time-dependent covariates are available, and/or the survival events and censoring times are only conditionally independent given the covariate process. The method of estimation consists of regularizing the survival distribution by taking the primitive function or smoothing, estimating the regularized parameter by using estimating equations, and finally recovering an estimator for the parameter of interest.
    Type of Medium: Electronic Resource
    URL: http://www.bepress.com/ijb/vol2/iss1/9
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  • 7
    Electronic Resource
    Electronic Resource
    On Agents That Have the Ability to Choose (2000)
    Springer
    Studia logica 66 (2000), S. 79-119 
    Details
    ISSN: 1572-8730
    Keywords: internal and external non-determinism ; dynamic modal logic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Philosophy
    Notes: Abstract We demonstrate ways to incorporate nondeterminism in a system designed to formalize the reasoning of agents concerning their abilities and the results of the actions that they may perform. We distinguish between two kinds of nondeterministic choice operators: one that expresses an internal choice, in which the agent decides what action to take, and one that expresses an external choice, which cannot be influenced by the agent. The presence of abilities in our system is the reason why the usual approaches towards nondeterminism cannot be used here. The semantics that we define for nondeterministic actions is based on the idea that composite actions are unravelled in the strings of atomic actions and tests that constitute them. The main notions used in defining this semantics are finite computation sequences and finite computation runs of actions. The results that we obtain meet our intuitions regarding events and abilities in the presence of nondeterminism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026796912842
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  • 8
    Electronic Resource
    Electronic Resource
    Graph Coloring with Adaptive Evolutionary Algorithms (1998)
    Springer
    Journal of heuristics 4 (1998), S. 25-46 
    Details
    ISSN: 1572-9397
    Keywords: evolutionary algorithms ; genetic algorithms ; constraint satisfaction ; graph coloring ; grouping problem ; penalty functions ; adaptive parameters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper presents the results of an experimental investigation on solving graph coloring problems with Evolutionary Algorithms (EAs). After testing different algorithm variants we conclude that the best option is an asexual EA using order-based representation and an adaptation mechanism that periodically changes the fitness function during the evolution. This adaptive EA is general, using no domain specific knowledge, except, of course, from the decoder (fitness function). We compare this adaptive EA to a powerful traditional graph coloring technique DSatur and the Grouping Genetic Algorithm (GGA) on a wide range of problem instances with different size, topology and edge density. The results show that the adaptive EA is superior to the Grouping (GA) and outperforms DSatur on the hardest problem instances. Furthermore, it scales up better with the problem size than the other two algorithms and indicates a linear computational complexity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009638304510
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  • 9
    Electronic Resource
    Electronic Resource
    Friendship Networks Through Time: An Actor-Oriented Dynamic Statistical Network Model (1999)
    Springer
    Computational & mathematical organization theory 5 (1999), S. 167-192 
    Details
    ISSN: 1572-9346
    Keywords: rational choice ; friendship ; Markov processes ; random utility models ; simulation ; empirical test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We propose a class of actor-oriented statistical models for closed social networks in general, and friendship networks in particular. The models are random utility models developed within a rational choice framework. Based on social psychological and sociological theories about friendship, mathematical functions capturing expected utility of individual actors with respect to friendship are constructed. Expected utility also contains a random (unexplained) component. We assume that, given their restrictions and contact opportunities, individuals evaluate their utility functions and behave such that they maximize the expected amount of utility. The behavior under consideration is the expression of like and dislike (choice of friends). Theoretical mechanisms that are modelled are, e.g., the principle of diminishing returns, the tendency towards reciprocated choices, and the preference for friendship relations with similar others. Constraints imposed on individuals are, e.g., the structure of the existing network, and the distribution of personal characteristics over the respondents. The models are illustrated by means of a data-set collected among university freshmen at 7 points in time during 1994 and 1995.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009683123448
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  • 10
    Electronic Resource
    Electronic Resource
    On the Modelling of the Adoption of Process Innovations (1997)
    Springer
    Computational & mathematical organization theory 3 (1997), S. 199-209 
    Details
    ISSN: 1572-9346
    Keywords: adoption of process innovation ; implementation time ; probability of adoption ; net present value ; implicit function theorem ; nonexample
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract An alternative view on the modelling of diffusion processesof process innovations has been introduced by Nooteboom (1989). Thebasic idea in that paper is to model the process of adoption ofprocess innovations as a ‘gambling model’ with odds in favourdepending on expected returns and odds against depending on risk. In this paper it is investigated under which theoretical conditions posed on the expected return function the usual adopted assumptions Nooteboom (1989) with respect to the parameters of the gambling model are in fact reasonable. It is shown that only under certainconditions the assumptions made on the gambling model are true ontheoretical grounds. In all other cases a nonexample shows that theresults as mentioned in literature are in general not true.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009625819330
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