L^2-Betti numbers of one-relator groups

We determine the L^2-Betti numbers of all one-relator groups and all surface-plus-one-relation groups (surface-plus-one-relation groups were introduced by Hempel who called them one-relator surface groups). In particular we show that for all such groups G, the L^2-Betti numbers b_n^{(2)}(G) are 0 for all n>1. We also obtain some information about the L^2-cohomology of left-orderable groups, and deduce the non-L^2 result that, in any left-orderable group of homological dimension one, all two-generator subgroups are free.Comment: 18 pages, version 3, minor changes. To appear in Math. An

The strong Atiyah conjecture for right-angled Artin and Coxeter groups

We prove the strong Atiyah conjecture for right-angled Artin groups and right-angled Coxeter groups. More generally, we prove it for groups which are certain finite extensions or elementary amenable extensions of such groups.Comment: Minor change

COPD Exacerbations: A Patient and Physician's Perspective

This article, co-authored by a patient affected by chronic obstructive pulmonary disease (COPD) and a respiratory specialist, discusses the patient’s experience of living with the disease and, in particular, the impact of COPD exacerbations on his life. The physician discusses the clinical approach to COPD exacerbations. Together, they provide a call to action to improve the management of COPD exacerbations

On Turing dynamical systems and the Atiyah problem

Main theorems of the article concern the problem of M. Atiyah on possible values of l^2-Betti numbers. It is shown that all non-negative real numbers are l^2-Betti numbers, and that "many" (for example all non-negative algebraic) real numbers are l^2-Betti numbers of simply connected manifolds with respect to a free cocompact action. Also an explicit example is constructed which leads to a simply connected manifold with a transcendental l^2-Betti number with respect to an action of the threefold direct product of the lamplighter group Z/2 wr Z. The main new idea is embedding Turing machines into integral group rings. The main tool developed generalizes known techniques of spectral computations for certain random walk operators to arbitrary operators in groupoid rings of discrete measured groupoids.Comment: 35 pages; essentially identical to the published versio

Making sense of background music listening habits: An arousal and task-complexity account

Although listening to background music is common, there is no consensus about its effects on cognitive-task performance. One potential mediating factor that could resolve the inconsistency in findings is arousal. To explore the role of arousal in mediating the effect of background music, this survey study directly explored people’s background music listening habits during a variety of everyday tasks varying in their complexity including studying, reading, driving, and monotonous tasks. Out of the 197 participants, most participants reported listening to background music during driving or monotonous tasks but fewer did so during studying or reading. Participants who did listen to music during studying or reading mostly reported choosing instrumental music and listening to music to calm them down. Contrarily, participants who listened to music during driving or monotonous tasks reported choosing vocal music more often and listening to music to feel energised. In sum, results revealed clearly different patterns in background music listening habits between tasks varying in their complexity that are consistent with arousal mediating the effect of background music. The results also revealed that people have an implicit awareness of the effects of background music and match the music to their needs as dictated by the specific task