Abstract:
We study the thermodynamic formalism for suspension flows over countable Markov shifts with roof functions not necessarily bounded away from zero. We establish conditions to ensure the existence and uniqueness of equilibrium measures for regular potentials. We define the notions of recurrence and transience of a potential in this setting. We define the "renewal flow", which is a symbolic model for a class of flows with diverse recurrence features. We study the corresponding thermodynamic formalism, establishing conditions for the existence of equilibrium measures and phase transitions. Applications are given to suspension flows defined over interval maps having parabolic fixed points.

Abstract:
This paper is devoted to study thermodynamic formalism for suspension flows defined over countable alphabets. We are mostly interested in the regularity properties of the pressure function. We establish conditions for the pressure function to be real analytic or to exhibit a phase transition. We also construct an example of a potential for which the pressure has countably many phase transitions.

Abstract:
We present a new short proof of the explicit formula for the group of links (and also link maps) in the 'quadruple point free' dimension. Denote by L(m,p,q) (respectively, C(m-p,p)) the group of smooth embeddings S^p |_| S^q -> S^m (respectively, S^p -> S^m) up to smooth isotopy. Denote by LM(m,p,q) the group of link maps S^p |_| S^q -> S^m up to link homotopy. Theorem 1. If p-1

Abstract:
Dense non-Brownian suspension flows of hard particles display mystifying properties: as the jamming threshold is approached, the viscosity diverges, as well as a length scale that can be identified from velocity correlations. To unravel the microscopic mechanism governing dissipation and its connection to the observed long-range correlations, we develop an analogy between suspension flows and the rigidity transition occurring when floppy networks are pulled -- a transition believed to be associated to the stress-stiffening of certain gels. After deriving the critical properties near the rigidity transition, we show numerically that suspensions flows lie close to it. We find that this proximity causes a decoupling between viscosity and the correlation length of velocities \xi, which scales as the length l_c characterizing the response of the velocity in flow to a local perturbation, previously predicted to follow l_c\sim 1/\sqrt{z_c-z}\sim p^{0.18} where p is the dimensionless particle pressure, z the coordination of the contact network made by the particles and z_c is twice the spatial dimension. We confirm these predictions numerically, predict the existence of a larger length scale l_r\sim 1/\sqrt{p} with mild effects on velocity correlation and the existence of a vanishing strain \delta \gamma\sim 1/p that characterizes de-correlation in flow.

Abstract:
This paper regroups some of the basic properties of Lipschitz maps and their flows. While some of the results presented here have already appeared in other papers, most of them are either only and classically known in the case of smooth maps and needed to be proved in the Lipschitz case for a better understanding of the Lipschitz geometry or are new and necessary to the development of numerical methods for rough paths.

Abstract:
In this paper we give sufficient conditions for existence of a solution of cohomological equation for suspension flows over automorphisms of Markov compacta, which were introduced by Vershik and Ito. The main result (Theorem 1) can be regarded as a symbolic analogue of results due to Forni and Marmi, Moussa and Yoccoz for translation flows and interval exchange transformations.

Abstract:
We consider suspension flows built over interval exchange transformations with the help of roof functions having an asymmetric logarithmic singularity. We prove that such flows are strongly mixing for a full measure set of interval exchange transformations.

Abstract:
We prove that a flow on a compact surface is expansive if and only if the singularities are of saddle type and the union of their separatrices is dense. Moreover we show that such flows are obtained by surgery on the suspension of minimal interval exchange maps.

Abstract:
In this article we study the mean return times to a given set for suspension flows. In the discrete time setting, this corresponds to the classical version of Kac's lemma \cite{K} that the mean of the first return time to a set with respect to the normalized probability measure is one. In the case of suspension flows we provide formulas to compute the mean return time. In particular, this varies linearly with continuous reparametrizatons of the flow and takes into account the mean escaping time from the original set.

Abstract:
We study co-H-maps from a suspension to the suspension of the projective plane and provide examples of non-suspension 3-cell co-H-spaces. These (infinitely many) examples are related to the homotopy groups of the 3-sphere. For each element of order 2 in $\pi_n(S^3)$, there is a corresponding non-suspension co-H-space of cells in dimensions 2, 3 and n+2. Our ideas are to study Hopf invariants in combinatorial way by using the Cohen groups.