On prolongations of contact manifolds

We apply spectral sequences to derive both an obstruction to the existence of $n$-fold prolongations and a topological classification. Prolongations have been used in the literature in an attempt to prove that every Engel structure on $M\times\mathbb{S}^1$ with characteristic line field tangent to the fibers is determined by the contact structure induced on a cross section and the twisting of the Engel structure along the fibers. Our results show that this statement needs some modification: to classify the diffeomorphism type of the Engel structure we additionally have to fix a class in the first cohomology of $M$.Comment: 8 pages; corrected an error in Corollary 4.1., this version will appear in Proc. of the Amer. Math. So

Constructions of open books and applications of convex surfaces in contact topology

In the present thesis we introduce an extension of the contact connected sum, in the sense that we replace the tight $3$-balls by standard neighbourhoods of Legendrian graphs $G \subset (S^3,\xi_{st})$. By the use of convex surface theory we show that there is a Weinstein cobordism from the original contact manifold to the result of the extended contact connected sum. We approach the analogue of this result in higher dimensions, using different methods, and present a generalised symplectic $1$-handle which is used for the construction of exact symplectic cobordisms. Furthermore we describe compatible open books for the fibre connected sum along binding components of open books as well as for the fibre connected sum along multi-sections of open books. Given a Legendrian knot $L$ with standard neighbourhood $N$ in a closed contact $3$-manifold $(M,\xi)$, the homotopy type of the contact structure $\xi|_{M\setminus N}$ on the knot complement depends on the rotation number of $L$. We give an alternative proof of this folklore theorem, as well as for a second folklore theorem that states, up to stabilisation, the classification of Legendrian knots is purely topological. Let $\zeta$ denote the standard contact structure on the $3$-dimensional torus $T^3$. Denoting by $\Xi{(T^3,\zeta)}$ the connected component of $\zeta$ in the space of contact structures on $T^3$, we show that the fundamental group $\pi_1\big( \Xi{(T^3,\zeta)} \big)$ is isomorphic to $\mathbb{Z}$

Open book decompositions of fibre sums in contact topology

In the present paper we describe compatible open books for the fibre connected sum along binding components of open books, as well as for the fibre connected sum along multi-sections of open books. As an application the first description provides simple ways of constructing open books supporting all tight contact structures on $T^3$, recovering a result by van Horn-Morris, as well as an open book supporting the result of a Lutz twist along a binding component of an open book, recovering a result by Ozbagci--Pamuk.Comment: 18 pages, 15 figure

A Framework for Intelligence and Cortical Function Based on Grid Cells in the Neocortex

How the neocortex works is a mystery. In this paper we propose a novel framework for understanding its function. Grid cells are neurons in the entorhinal cortex that represent the location of an animal in its environment. Recent evidence suggests that grid cell-like neurons may also be present in the neocortex. We propose that grid cells exist throughout the neocortex, in every region and in every cortical column. They define a location-based framework for how the neocortex functions. Whereas grid cells in the entorhinal cortex represent the location of one thing, the body relative to its environment, we propose that cortical grid cells simultaneously represent the location of many things. Cortical columns in somatosensory cortex track the location of tactile features relative to the object being touched and cortical columns in visual cortex track the location of visual features relative to the object being viewed. We propose that mechanisms in the entorhinal cortex and hippocampus that evolved for learning the structure of environments are now used by the neocortex to learn the structure of objects. Having a representation of location in each cortical column suggests mechanisms for how the neocortex represents object compositionality and object behaviors. It leads to the hypothesis that every part of the neocortex learns complete models of objects and that there are many models of each object distributed throughout the neocortex. The similarity of circuitry observed in all cortical regions is strong evidence that even high-level cognitive tasks are learned and represented in a location-based framework

Open books and exact symplectic cobordisms

Given two open books with equal pages, we show the existence of an exact symplectic cobordism whose negative end equals the disjoint union of the contact manifolds associated to the given open books, and whose positive end induces the contact manifold associated to the open book with the same page and concatenated monodromy. Using similar methods, we show the existence of strong fillings for contact manifolds associated with doubled open books, a certain class of fiber bundles over the circle obtained by performing the binding sum of two open books with equal pages and inverse monodromies. From this we conclude, following an outline by Wendl, that the complement of the binding of an open book cannot contain any local filling obstruction. Given a contact 3-manifold, according to Eliashberg there is a symplectic cobordism to a fibration over the circle with symplectic fibers. We extend this result to higher dimensions recovering a recent result by Dorner-Geiges-Zehmisch. Our cobordisms can also be thought of as the result of the attachment of a generalized symplectic 1-handle

The fundamental group of the space of contact structures on the 3-torus

We show that the fundamental group of the space of contact structures on the 3-torus (based at the standard contact structure) is isomorphic to the integers