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Pascal Schweitzer - One of the best experts on this subject based on the ideXlab platform.

  • an exponential lower bound for Individualization refinement algorithms for graph isomorphism
    Symposium on the Theory of Computing, 2018
    Co-Authors: Daniel Neuen, Pascal Schweitzer
    Abstract:

    The Individualization-refinement paradigm provides a strong toolbox for testing isomorphism of two graphs and indeed, the currently fastest implementations of isomorphism solvers all follow this approach. While these solvers are fast in practice, from a theoretical point of view, no general lower bounds concerning the worst case complexity of these tools are known. In fact, it is an open question what the running time of Individualization-refinement algorithms is. For all we know some of the algorithms could have polynomial running time. In this work we give a negative answer to this question and construct a family of graphs on which algorithms based on the Individualization-refinement paradigm require exponential time. Contrary to a previous construction of Miyazaki, that only applies to a specific implementation within the Individualization-refinement framework, our construction is immune to changing the cell selector, the refinement operator, the invariant that is used, or adding various heuristic invariants to the algorithm. In fact, our graphs also provide exponential lower bounds in the case when the k-dimensional Weisfeiler-Leman algorithm is used to replace the the 1-dimensional Weisfeiler-Leman algorithm (often called color refinement) that is normally used. Finally, the arguments even work when the entire automorphism group of the inputs is initially provided to the algorithm. The arguments apply to isomorphism testing algorithms as well as canonization algorithms within the framework.

  • an exponential lower bound for Individualization refinement algorithms for graph isomorphism
    arXiv: Computational Complexity, 2017
    Co-Authors: Daniel Neuen, Pascal Schweitzer
    Abstract:

    The Individualization-refinement paradigm provides a strong toolbox for testing isomorphism of two graphs and indeed, the currently fastest implementations of isomorphism solvers all follow this approach. While these solvers are fast in practice, from a theoretical point of view, no general lower bounds concerning the worst case complexity of these tools are known. In fact, it is an open question whether Individualization-refinement algorithms can achieve upper bounds on the running time similar to the more theoretical techniques based on a group theoretic approach. In this work we give a negative answer to this question and construct a family of graphs on which algorithms based on the Individualization-refinement paradigm require exponential time. Contrary to a previous construction of Miyazaki, that only applies to a specific implementation within the Individualization-refinement framework, our construction is immune to changing the cell selector, or adding various heuristic invariants to the algorithm. Furthermore, our graphs also provide exponential lower bounds in the case when the $k$-dimensional Weisfeiler-Leman algorithm is used to replace the standard color refinement operator and the arguments even work when the entire automorphism group of the inputs is initially provided to the algorithm.

Daniel Neuen - One of the best experts on this subject based on the ideXlab platform.

  • an exponential lower bound for Individualization refinement algorithms for graph isomorphism
    Symposium on the Theory of Computing, 2018
    Co-Authors: Daniel Neuen, Pascal Schweitzer
    Abstract:

    The Individualization-refinement paradigm provides a strong toolbox for testing isomorphism of two graphs and indeed, the currently fastest implementations of isomorphism solvers all follow this approach. While these solvers are fast in practice, from a theoretical point of view, no general lower bounds concerning the worst case complexity of these tools are known. In fact, it is an open question what the running time of Individualization-refinement algorithms is. For all we know some of the algorithms could have polynomial running time. In this work we give a negative answer to this question and construct a family of graphs on which algorithms based on the Individualization-refinement paradigm require exponential time. Contrary to a previous construction of Miyazaki, that only applies to a specific implementation within the Individualization-refinement framework, our construction is immune to changing the cell selector, the refinement operator, the invariant that is used, or adding various heuristic invariants to the algorithm. In fact, our graphs also provide exponential lower bounds in the case when the k-dimensional Weisfeiler-Leman algorithm is used to replace the the 1-dimensional Weisfeiler-Leman algorithm (often called color refinement) that is normally used. Finally, the arguments even work when the entire automorphism group of the inputs is initially provided to the algorithm. The arguments apply to isomorphism testing algorithms as well as canonization algorithms within the framework.

  • an exponential lower bound for Individualization refinement algorithms for graph isomorphism
    arXiv: Computational Complexity, 2017
    Co-Authors: Daniel Neuen, Pascal Schweitzer
    Abstract:

    The Individualization-refinement paradigm provides a strong toolbox for testing isomorphism of two graphs and indeed, the currently fastest implementations of isomorphism solvers all follow this approach. While these solvers are fast in practice, from a theoretical point of view, no general lower bounds concerning the worst case complexity of these tools are known. In fact, it is an open question whether Individualization-refinement algorithms can achieve upper bounds on the running time similar to the more theoretical techniques based on a group theoretic approach. In this work we give a negative answer to this question and construct a family of graphs on which algorithms based on the Individualization-refinement paradigm require exponential time. Contrary to a previous construction of Miyazaki, that only applies to a specific implementation within the Individualization-refinement framework, our construction is immune to changing the cell selector, or adding various heuristic invariants to the algorithm. Furthermore, our graphs also provide exponential lower bounds in the case when the $k$-dimensional Weisfeiler-Leman algorithm is used to replace the standard color refinement operator and the arguments even work when the entire automorphism group of the inputs is initially provided to the algorithm.

Kathryn G Miller - One of the best experts on this subject based on the ideXlab platform.

  • a role for actin dynamics in Individualization during spermatogenesis in drosophila melanogaster
    Development, 2003
    Co-Authors: Tatsuhiko Noguchi, Kathryn G Miller
    Abstract:

    In order to better understand the mechanism of sperm Individualization during spermatogenesis in Drosophila melanogaster, we have developed an in vitro culture system in which we can perform live observation of Individualization in isolated cysts. The whole process of Individualization, during which a bundle of 64 syncytial spermatids is separated into individual sperm, takes place in these cultures. Individualization complexes, which consist of 64 cones of actin that assemble around the sperm nuclei, move to the basal end of the tails, forming a characteristic `cystic bulge9 that contains an accumulation of cytoplasm, syncytial membrane and vesicles. The cystic bulge is the site of membrane remodeling and its movement was used to follow the progress of Individualization. The speed of cystic bulge movement is fairly constant along the length of the cyst. Actin drugs, but not microtubule drugs inhibit cystic bulge movement, suggesting that the movement requires proper actin dynamics but not microtubules. GFP-tagged actin was expressed in the cyst and fluorescence recovery after photobleaching was monitored using confocal microscopy to analyze actin dynamics in cones. Actin turns over throughout the cone, with that at the leading edge of the cones turning over with slightly faster kinetics. Actin does not treadmill from the front to the back of the cone. Actin in moving actin cones turns over in about 12 minutes, although prior to onset of movement, turnover is much slower. Visualization of membrane using FM1-43 reveals that the cystic bulge has an extremely complicated series of membrane invaginations and the transition from syncytial to individualized spermatids occurs at the front of the actin cones. We also suggest that endocytosis and exocytosis might not be important for membrane remodeling. This system should be suitable for analysis of defects in male sterile mutants and for investigating other steps of spermatogenesis.

Paul Hodkinson - One of the best experts on this subject based on the ideXlab platform.

  • interactive online journals and Individualization
    New Media & Society, 2007
    Co-Authors: Paul Hodkinson
    Abstract:

    Suggestions that the internet has facilitated existing trends towards the increasing disconnection of individuals from substantive communities have been balanced by a variety of empirical case studies demonstrating significant communal features on some online discussion forums. While recognizing the role of discussion forums in facilitating community, this article seeks to shift the focus of debate towards the rapidly increasing use of online journal style web logs (`blogs') as a form of social interaction. Ostensibly centred upon the individual rather than the group, yet increasingly interactive and socially oriented, interactive online journals appear particularly consistent with the notion of individualistic rather than group-centred patterns of sociability. The article explores this possibility in relation to case study research focused on the recent take-up of online journals by a group of individuals who previously participated in discussion forums associated with a music and fashion subculture know...

Helen Delidou - One of the best experts on this subject based on the ideXlab platform.

  • Individualization of the subcutaneous amifostine dose during hypofractionated accelerated radiotherapy
    Anticancer Research, 2006
    Co-Authors: Michael I. Koukourakis, Ioannis Abatzoglou, Leonidas Sivridis, Maria Tsarkatsi, Helen Delidou
    Abstract:

    Background: Individualization of the daily dose of amifostine may prove of value in achieving maximum cytoprotection during radiotherapy. Patients and Methods: Using an algorithm based on: i) the gradual increase of the amifostine dose, ii) an amifostine tolerance-recording scale and iii) the intermittent administration of dexamethasone, the Individualization of the subcutaneous amifostine dose was prospectively attempted in a large cohort of 132 cancer patients, treated with 12-15 consecutive fractions of 3.4-3.5 Gy (hypofractionated accelerated radiotherapy with cytoprotection, HypoARC). Results: Using the above algorithm, a daily dose of 1000 mg of amifostine was successfully delivered in 62% of patients. An additional 20% of patients tolerated well a mean daily dose of 750-975 mg. Nausea and fatigue were minimal, while fever/rash enforced amifostine interruption in 7% of cases. Conclusion: Individualization of the amifostine dose allowed an up to two-fold increased daily-dose administration of amifostine and can be tested as a support to aggressive radio-chemotherapy schemes aiming at improving the cure rates of cancer patients, while avoiding excess toxicity. Amifostine is a broad spectrum cytoprotective agent that

  • Individualization of the subcutaneous amifostine dose during hypofractionated / accelerated radiotherapy.
    Anticancer research, 2006
    Co-Authors: Michael I. Koukourakis, Ioannis Abatzoglou, Leonidas Sivridis, Maria Tsarkatsi, Helen Delidou
    Abstract:

    Background: Individualization of the daily dose of amifostine may prove of value in achieving maximum cytoprotection during radiotherapy. Patients and Methods: Using an algorithm based on: i) the gradual increase of the amifostine dose, ii) an amifostine tolerance-recording scale and iii) the intermittent administration of dexamethasone, the Individualization of the subcutaneous amifostine dose was prospectively attempted in a large cohort of 132 cancer patients, treated with 12-15 consecutive fractions of 3.4-3.5 Gy (hypofractionated accelerated radiotherapy with cytoprotection, HypoARC). Results: Using the above algorithm, a daily dose of 1000 mg of amifostine was successfully delivered in 62% of patients. An additional 20% of patients tolerated well a mean daily dose of 750-975 mg. Nausea and fatigue were minimal, while fever/rash enforced amifostine interruption in 7% of cases. Conclusion: Individualization of the amifostine dose allowed an up to two-fold increased daily-dose administration of amifostine and can be tested as a support to aggressive radio-chemotherapy schemes aiming at improving the cure rates of cancer patients, while avoiding excess toxicity. Amifostine is a broad spectrum cytoprotective agent that