79 research outputs found
General primitivity in the mapping class group
For , let be the mapping class group of the
closed orientable surface of genus . In this paper, we obtain
necessary and sufficient conditions under which a given pseudo-periodic mapping
class can be a root of another up to conjugacy. Using this characterization,
the canonical decomposition of (non-periodic) mapping classes, and some known
algorithms, we give an efficient algorithm for computing roots of arbitrary
mapping classes up to conjugacy. Furthermore, we derive realizable bounds on
the degrees of roots of pseudo-periodic mapping classes in ,
the Torelli group, the level- subgroup of , and the
commutator subgroup of . In particular, we show that the
highest possible (realizable) degree of a root of a pseudo-periodic mapping
class is , where is a unique positive integer
associated with the conjugacy class of . Moreover, this bound is realized by
the roots of the powers of Dehn twist about a separating curve of genus
in . Finally, for , we show that any pseudo-periodic mapping
class having a nontrivial periodic component that is not the hyperelliptic
involution, normally generates . Consequently, we establish
that there exist roots of bounding pair maps and powers of Dehn twists that
normally generate
Genetic-fuzzy based load balanced protocol for WSNs
Recent advancement in wireless sensor networks primarily depends upon energy constraint. Clustering is the most effective energy-efficient technique to provide robust, fault-tolerant and also enhance network lifetime and coverage. Selection of optimal number of cluster heads and balancing the load of cluster heads are most challenging issues. Evolutionary based approach and soft computing approach are best suitable for counter the above problems rather than mathematical approach. In this paper we propose hybrid technique where Genetic algorithm is used for the selection of optimal number of cluster heads and their fitness value of chromosome to give optimal number of cluster head and minimizing the energy consumption is provided with the help of fuzzy logic approach. Finally cluster heads uses multi-hop routing based on A*(A-star) algorithm to send aggregated data to base station which additionally balance the load. Comparative study among LEACH, CHEF, LEACH-ERE, GAEEP shows that our proposed algorithm outperform in the area of total energy consumption with various rounds and network lifetime, number of node alive versus rounds and packet delivery or packet drop ratio over the rounds, also able to balances the load at cluster head
Generating the liftable mapping class groups of cyclic covers of spheres
For , let be the mapping class group of closed
orientable surface of genus . In this paper, we derive a finite
generating set for the liftable mapping class groups corresponding to
finite-sheeted regular branched cyclic covers of spheres. As an application, we
provide an algorithm to derive presentations of these liftable mapping class
groups, and the normalizers and centralizers of periodic mapping classes
corresponding to these covers. Furthermore, we determine the isomorphism
classes of the normalizers of irreducible periodic mapping classes in
. Moreover, we derive presentations for the liftable mapping
class groups corresponding to covers induced by certain reducible periodic
mapping classes. Consequently, we derive a presentation for the centralizer and
normalizer of a reducible periodic mapping class in of the
highest order . As final applications of our results, we recover the
generating sets of the liftable mapping class groups of the hyperelliptic cover
obtained by Birman-Hilden and the balanced superelliptic cover obtained by
Ghaswala-Winarski.Comment: 1 figur
Infinite metacyclic subgroups of the mapping class group
For , let be the mapping class group of the closed
orientable surface of genus . In this paper, we provide necessary and
sufficient conditions for the existence of infinite metacyclic subgroups of
. In particular, we provide necessary and sufficient
conditions under which a pseudo-Anosov mapping class generates an infinite
metacyclic subgroup of with a nontrivial periodic mapping
class. As applications of our main results, we establish the existence of
infinite metacyclic subgroups of isomorphic to
, and
. Furthermore, we derive bounds on the order of
a nontrivial periodic generator of an infinite metacyclic subgroup of
that are realized. Finally, we show that the centralizer of
an irreducible periodic mapping class is either or
, where is a hyperelliptic
involution.Comment: 25 pages, 18 figure
Goal setting for improvement in product development performance of organizations
Thesis (S.M. in Engineering and Management)--Massachusetts Institute of Technology, Engineering Systems Division, February 2013.Cataloged from PDF version of thesis. "Sep 2012."Includes bibliographical references (pages 107-109).Companies have been constantly trying for ways and means to improve R&D performance as it is one of the most important competitive advantage tools of an organization. Literature review on R&D performance improvement suggests that, lot of focus is on measuring R&D performance and on specific problem solving approaches like six sigma and lean. Frameworks like capability maturity model integration (CMMI) and product development self-assessment tool (PDSAT) provide holistic performance assessment, but fall short on providing clear guidance for performance improvement interventions. Goal setting theory, a proven theory that is widely applied in individual performance improvement has got limited attention in R&D performance improvement approaches and frameworks. Practitioners in the industry point to the need for goal setting in R&D and identify that as a gap in current performance improvement methodologies. This thesis attempts to fill this gap by proposing DEAL framework, a practical approach for defining future goals in R&D performance improvement efforts.by Pankaj Kumar Kashyap.S.M.in Engineering and Managemen
Cosmological Implications of Unimodular Gravity
We consider a model of gravity and matter fields which is invariant only
under unimodular general coordinate transformations (GCT). The determinant of
the metric is treated as a separate field which transforms as a scalar under
unimodular GCT. Furthermore we also demand that the theory is invariant under a
new global symmetry which we call generalized conformal invariance. We study
the cosmological implications of the resulting theory. We show that this theory
gives a fit to the high-z supernova data which is identical to the standard Big
Bang model. Hence we require some other cosmological observations to test the
validity of this model. We also consider some models which do not obey the
generalized conformal invariance. In these models we can fit the supernova data
without introducing the standard cosmological constant term. Furthermore these
models introduce only one dark component and hence solve the coincidence
problem of dark matter and dark energy.Comment: 18 pages, no figures, major revisions, substantial changes in
analysis, results and conclusion
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