Combinatorics of tight geodesics and stable lengths

We give an algorithm to compute the stable lengths of pseudo-Anosovs on the curve graph, answering a question of Bowditch. We also give a procedure to compute all invariant tight geodesic axes of pseudo-Anosovs. Along the way we show that there are constants $1<a_1<a_2$ such that the minimal upper bound on `slices' of tight geodesics is bounded below and above by $a_1^{\xi(S)}$ and $a_2^{\xi(S)}$, where $\xi(S)$ is the complexity of the surface. As a consequence, we give the first computable bounds on the asymptotic dimension of curve graphs and mapping class groups. Our techniques involve a generalization of Masur--Minsky's tight geodesics and a new class of paths on which their tightening procedure works.Comment: 19 pages, 2 figure

Neotropical Bird Migration During The Ice Ages: Orientation And Ecology

Reconstruction of breeding habitat of North American Neotropical migrants 18,000 years ago and 9,000 years ago indicated major shifts in both location and composition of plant communities relative to present conditions. Increased vegetation in xeric areas may have compensated, at least in part, for the reduction in breeding habitat due to glaciation. Autumnal flights of Neotropical passerine migrants flying on constant headings from North America to Central and South America were simulated under present wind conditions and for winds during periods of glaciation at 18,000 and 9,000 years ago. The 155 degrees average headings currently observed for Atlantic migrants were found to function well during periods of glaciation and may have been more generally useful during those times than at present

Principal agent problems under loss aversion: an application to executive stock options

Executive stock options reward success but do not penalise failure. In contrast, the standard principalagent model implies that pay is normally monotonically increasing in performance. This paper shows that, under loss aversion, the use of carrots but not sticks is a feature of an optimal compensation contract. Low risk aversion and high loss aversion is particularly propitious to the use of options. Moreover, loss aversion on the part of executives explains the award of at the money options rather than discounted stock or bonus related pay. Other features of stock option grants are also explained, such as resetting or reloading with an exercise price equal to the current stock price

Computing Room Acoustics Using 3D FDTD: A Cuda Approach.

In seeking to model realistic room acoustics, direct numerical simulation can be employed. This paper presents 3D Finite Difference Time Domain schemes that incorporate losses at boundaries and due to the viscosity of air. These models operate within a virtual room designed on a detailed floor plan. The schemes are computed at 44.1kHz, using large-scale data sets containing up to 100 million points each. A performance comparison is made between serial computation in C, and parallel computation using CUDA on GPUs, showing up to 80 times speed-ups. Testing on two different Nvidia Tesla cards shows the benefits of the latest FERMI architecture for double precision floating-point computation

Postal survey of contacts between cattle farms on the Isle of Lewis

The British Cattle Movement Service (BCMS) database contains an unprecedented quantity of data on the movement of cattle within the UK. These data may be used to construct models of the contact structure of the UK cattle herd, for epidemiological purposes. There are two significant potential sources of inaccuracy within such models: movements that are not reported or are reported inaccurately to the BCMS, and contacts between farms that might transmit infection, but are not animal movements. This field study addressed these issues. Cattle farmers on the Isle of Lewis were recruited with the assistance of the local veterinary surgeon, and asked to record a range of potential risk behaviours for a one-month period. They were also asked questions about husbandry practices on their farm. Comparison of the BCMS contact data with that reported by Lewis' farmers highlighted use of common grazing land as a significant source of contact, and potential disease transmission, between cattle that currently goes unreported; around half of responding holdings on Lewis use common grazing land at some point during the year, and these movements are not reported to the BCMS