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

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

WEDELIA: A POTENTIAL GROUND COVER FOR REDUCING THE ATTRACTIVENESS OF TROPICAL AIRFIELDS TO BIRDS

Airport environments frequently provide ideal feeding and loafing habitats for many bird species. Bird strikes at most airports involve predominantly insectivorous species. However, the Lihue Airport on the island of Kauai, Hawaii has had a severe problem with bird strikes involving 4 granivorous species: the zebra dove (Geopelia striata), spotted dove (Streptopelia chinensis), chestnut mannikin (Lonchura malacca), and nutmeg mannikin (L. punctulato). Two owl species, the common barn owl (Tyto alba) and Hawaiian short-eared owl (Asio flammeus sandwhichensis), have also been involved in aircraft collisions at Lihue. Shooting and hazing techniques to disperse birds have proven ineffective or unacceptable; therefore, an alternative ground cover, wedelia (Wedelia trilobata), was tested to determine if the airfield environment could be rendered unattractive to birds. Volunteer stands of wedelia throughout the airfield were delineated and additional plantings established. We used bird activity, exclusion of seed-producing plants, rodent abundance, and invertebrate populations as indicators of effectiveness. Utilization of test plots by rodents and the four major seed-eating birds was significantly lower than in the corresponding control plots. The nearly monotypic stands of wedelia resulted in decreased seed availability to birds and rodents. Because of the ease of establishing and maintaining wedelia on airfields, its dominance over palatable seed producing plants, exclusion of rodent populations, low fire hazard, and decreased utilization by critical bird species, wedelia shows great promise as an alternative ground cover in tropical airfield environments

Using wedelia as ground cover on tropical airports to reduce bird activity

aircraft collisions (i.e., bird strikes) are a major problem at airports worldwide, often because birds are attracted to airfields to feed on seeds, insects, or rodents that abound in the grassy areas near runways and taxiways. We compared an alternative ground cover, wedelia (Wedelia trilobata), to existing vegetation (control plots) on the airfield at Lihue Airport, Kauai, Hawaii, to determine if bird populations on the airport could be reduced by eliminating their forage base. We studied wedalia because it is a low-growing plant that did not need mowing, was easily established in plots, and out-competed other plants, resulting in a significant decrease in plant diversity. Thus, wedelia indirectly results in a decreased seed base for granivorous birds. Total invertebrate biomass was 41% lower in wedelia plots than in other vegetation plots (control plots). Rodent populations were 67% lower in wedelia than in control plots. Zebra doves (Geopelia striata), spotted doves (Streptopelia chinensis), and mannikins (Lonchura spp.) used wedelia plots significantly less than control plots, whereas, the lesser Pacific golden-plover (Pluvialis fulva) was unaffected. By reducing seed production, insect densities, and rodant populations, wedalia should be a useful ground cover on tropical airports to reduce bird use and, ultimately, bird strikes on the airport

GALEX, Optical and IR Light Curves of MQ Dra: UV Excesses at Low Accretion Rates

Ultraviolet light curves constructed from NUV and FUV detectors on GALEX reveal large amplitude variations during the orbital period of the Low Accretion Rate Polar MQ Dra (SDSSJ1553+55). This unexpected variation from a UV source is similar to that seen and discussed in the Polar EF Eri during its low state of accretion, even though the accretion rate in MQ Dra is an order of magnitude lower than even the low state of EF Eri. The similarity in phasing of the UV and optical light curves in MQ Dra imply a similar location for the source of light. We explore the possibilities of hot spots and cyclotron emission with simple models fit to the UV, optical and IR light curves of MQ Dra. To match the GALEX light curves with a single temperature circular hot spot requires different sizes of spots for the NUV and FUV, while a cyclotron model that can produce the optical harmonics with a magnetic field near 60 MG requires multipoles with fields > 200 MG to match the UV fluxes.Comment: accepted for ApJ; 15 pages, 7 tables, 8 fig

Local attitudes toward Apennine brown bears: Insights for conservation issues

Human-carnivore coexistence is a multi-faceted issue that requires an understanding of the diverse attitudes and perspectives of the communities living with large carnivores. To inform initiatives that encourage behaviors in line with conservation goals, we focused on assessing the two components of attitudes (i.e., feelings and beliefs), as well as norms of local communities coexisting with Apennine brown bears (Ursus arctos marsicanus) for a long time. This bear population is under serious extinction risks due to its persistently small population size, which is currently confined to the long-established protected area of Abruzzo, Lazio and Molise National Park (PNALM) and its surrounding region in central Italy. We interviewed 1,611 residents in the PNALM to determine attitudes and values toward bears. We found that support for the bear's legal protection was widespread throughout the area, though beliefs about the benefits of conserving bears varied across geographic administrative districts. Our results showed that residents across our study areas liked bears. At the same time, areas that received more benefits from tourism were more strongly associated with positive feelings toward bears. Such findings provide useful information to improve communication efforts of conservation authorities with local communities