576 research outputs found
Bredon cohomology and robot motion planning
In this paper we study the topological invariant reflecting
the complexity of algorithms for autonomous robot motion. Here, stands for
the configuration space of a system and is, roughly, the
minimal number of continuous rules which are needed to construct a motion
planning algorithm in . We focus on the case when the space is
aspherical; then the number depends only on the fundamental group
and we denote it . We prove that
can be characterised as the smallest integer such that the canonical
-equivariant map of classifying spaces can be equivariantly deformed into the
-dimensional skeleton of . The symbol
denotes the classifying space for free actions and
denotes the classifying space for actions with
isotropy in a certain family of subgroups of . Using
this result we show how one can estimate in terms of the
equivariant Bredon cohomology theory. We prove that where denotes the cohomological dimension of with
respect to the family of subgroups . We also introduce a Bredon
cohomology refinement of the canonical class and prove its universality.
Finally we show that for a large class of principal groups (which includes all
torsion free hyperbolic groups as well as all torsion free nilpotent groups)
the essential cohomology classes in the sense of Farber and Mescher are exactly
the classes having Bredon cohomology extensions with respect to the family
.Comment: This revision contains a few additional comments, among them is
Corollary 3.5.
Davis-Beirut reaction: route to thiazolo-, thiazino-, and thiazepino-2H-indazoles.
Methods for the construction of thiazolo-, thiazino-, and thiazepino-2H-indazoles from o-nitrobenzaldehydes or o-nitrobenzyl bromides and S-trityl-protected 1°-aminothioalkanes are reported. The process consists of formation of the requisite N-(2-nitrobenzyl)(tritylthio)alkylamine, subsequent deprotection of the trityl moiety with TFA, and immediate treatment with aq. KOH in methanol under Davis-Beirut reaction conditions to deliver the target thiazolo-, thiazino-, or thiazepino-2H-indazole in good overall yield. Subsequent S-oxidation gives the corresponding sulfone
Genetic and epigenetic regulation of abdominal aortic aneurysms
Abdominal aortic aneurysms (AAAs) are focal dilations of the aorta that develop from degenerative changes in the media and adventitia of the vessel. Ruptured AAAs have a mortality of up to 85%, thus it is important to identify patients with AAA at increased risk for rupture who would benefit from increased surveillance and/or surgical repair. Although the exact genetic and epigenetic mechanisms regulating AAA formation are not completely understood, Mendelian cases of AAA, which result from pathologic variants in a single gene, have helped provide a basic understanding of AAA pathophysiology. More recently, genome wide associated studies (GWAS) have identified additional variants, termed single nucleotide polymorphisms, in humans that may be associated with AAAs. While some variants may be associated with AAAs and play causal roles in aneurysm pathogenesis, it should be emphasized that the majority of SNPs do not actually cause disease. In addition to GWAS, other studies have uncovered epigenetic causes of disease that regulate expression of genes known to be important in AAA pathogenesis. This review describes many of these genetic and epigenetic contributors of AAAs, which altogether provide a deeper insight into AAA pathogenesis.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155527/1/cge13705.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155527/2/cge13705_am.pd
Bredon cohomology and robot motion planning
Acknowledgements Farber was partially supported by the EPSRC, by the IIAS and by the Marie Curie Actions, FP7, in the frame of the EURIAS Fellowship Programme. Lupton and Oprea were partially supported by grants from the Simons Foundation (# 209575 and # 244393). This research was supported through the programme Research in pairs by the Mathematisches Forschungsinstitut Oberwolfach in 2017.Peer reviewedPostprin
An upper bound for topological complexity
This work was partially supported by a grant from the Simons Foundation: (#244393 to John Oprea). The authors would like to thank the Mathematisches Forschungsinstitut Oberwolfach for its generosity in supporting a July 2017 Research in Pairs stay where this work was begun.Peer reviewedPostprin
Emergent stent-graft treatment for rupture
It is not too surprising, given the lower prevalence of thoracic aortic aneurysms (TAA) as compared with abdominal aortic aneurysms (AAA), that development of endovascular devices for thoracic disease has lagged behind progress in the infrarenal area. Recently, published reports of decreased mortality associated with endovascular device implantation for ruptured AAAs have highlighted its potential advantage in emergent situations. The first reported use of an endovascular stent graft to treat a ruptured TAA was reported by Semba et al in 1997. Although the use of endovascular therapy to treat ruptured AAAs is gaining wider acceptance, its use in thoracic pathologies has been slow to develop in the United States, even though 20% of TAAs and nearly 50% of thoracic dissections present with rupture in the EUROSTAR registry. This may be a factor of relatively limited dissemination of technology. Examination of clinical trial enrollment shows that 10 sites in the United States account for approximately 50% of the cumulative implantations
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