Tax-Increment Financing: The Need for Increased Transparency and Accountability in Local Economic Development Subsidies

Examines the risks to the public of creating tax-increment financing districts to encourage economic development. Proposes stronger guidelines for tax-increment financing program design, governance process, transparency, and developers' accountability

Effect of transpiration cooling on boundary layer transition for hypersonic flight

Superseding ablative cooling techniques with active thermal protection could benefit the development of hypersonic flight technology by improving resistance of vehicles to thermal loads, re-usability and shape stability. Transpiration cooling could ensure protection of areas that are most affected by aerothermodynamic heating by injecting a coolant gas through a porous surface and thus shield the vehicle from hot surrounding gas. Problematically, gas effusion can advance boundary layer transition and resulting turbulence would cause excess heating and sabotage the local upstream cooling effect. In addition, turbulence reduces aerodynamic efficiency and influences critical variables of flight system dynamics. Transpiration cooling can only be applied if sufficient boundary layer transition control is achieved simultaneously or its influence on stability can be predicted accurately. This thesis investigates the effect of transpiration cooling on hypersonic boundary layer transition experimentally by conducting tests in a low enthalpy hypersonic Ludwieg tube at Mach 7 using a 7-degree half-angle cone model. Coolant gas injection is performed at two locations on the model. Firstly, fully porous nose tips with 1 mm nose radius and 58.5 mm axial length are used. Secondly, helium, nitrogen, argon and carbon dioxide are injected through a small segment in the frustum, while a sharp impervious nose tip is employed. The porous frustum injector is 25 mm long and spans 60 degrees azimuth in the axial centre of the cone. Outflow profiles of all porous injectors were characterized using a hot wire, whereby three-dimensional maps at high resolution could be obtained. All model parts were optimized for smoothness. This work utilizes high frequency schlieren imaging, focusing laser differential interferometry and surface instruments to conduct instability measurements. At a unit Reynolds number of 17.9 mio/m using a 1 mm porous nose tip helium injection was applied from said permeable nose cone segment. Thin film gauges show a delayed rise of the surface heat flux above laminar level, surface pressure measurements indicate a delay in growth and decay of the second mode instability and schlieren imaging shows a delayed onset of turbulence. Stabilization was stronger with 0.04 % helium injection than with 0.02 %. Nitrogen injection at a comparable rate was found to advance instability growth and transition. Helium injection at a blowing ratio of 0.1 % caused early transition, potentially due to boundary layer blow off at the stagnation point. Employing a sharp, impervious aluminium nose tip, the cone was tested at a unit Reynolds number of 12.2 mio/m with injection from the frustum. At this freestream condition, strongly amplified second mode instabilities are present near the frustum injector segment. It was observed to experience a stronger reduction in second mode frequency with increasing blowing ratio and coolant molecular mass. In contrast, the thickening of the boundary layer increased with decreasing coolant molecular mass. Due to the waveguide nature of the second mode, it was inferred that a change in local speed of sound and boundary layer temperature profile must play a role. Schlieren images and spectral analysis showed how turbulence and instability mechanisms are displaced from the surface by helium injection. FLDI confirmed how second mode instability oscillations are pushed away from the cone. Reduction in heat flux and attenuation of surface pressure disturbances were thus ascribed to a cooling and displacement effect instead of a true transition delay. Fluid turbulence moves upstream for all coolants as seen with schlieren. Heavier injection gases caused less cooling and less displacement of the boundary layer. This thesis provides the first experimental demonstration of efficient hypersonic stagnation point cooling combined with a boundary layer transition delay. It furthermore makes experimental contributions to the fundamental understanding of the influence of different gas injections on the transition mechanisms on a hypersonic slender cone

The reproductive success of the parasitic bat fly Basilia nana (Diptera: Nycteribiidae) is affected by the low roost fidelity of its host, the Bechstein's bat ( Myotis bechsteinii )

We studied the reproductive ecology of the bat fly Basilia nana on free-ranging colonial female and solitary male Bechstein's bats (Myotis bechsteinii) during one reproductive season. The reproduction of B. nana took place from April to September, and the production of puparia in bat roosts was high. The metamorphosis of the flies took a minimum of 30days, and at least 86% of the puparia metamorphosed successfully. However, only about 30% of flies from puparia deposited in female roosts and 57% of flies from puparia deposited in male roosts emerged in the presence of Bechstein's bats and were thus able to survive. The significantly higher emergence success of bat flies in male roosts was caused by the higher roost fidelity of the solitary males compared with the social females. Our results indicate that bats can control the reproductive success of bat flies by switching and selecting roost

Beef - Good and Good for You

Relative to foods, eating habits and US consumer preferences, the spectrum is perhaps broader today than it has ever been. And to meet this array of preferences, the beef industry must offer traditional, natural, grassfed and organically produced products. Beef is a nutrient dense source of protein, essential vitamins and minerals. Though recognized as a low-calorie protein source, beef also contains fat, a dense source of energy that fuels the body

Roost selection and roost switching of female Bechstein's bats ( Myotis bechsteinii ) as a strategy of parasite avoidance

Ectoparasites of vertebrates often spend part of their life cycle in their hosts' home. Consequently, hosts should take into account the parasite infestation of a site when selecting where to live. In a field study, we investigated whether colonial female Bechstein's bats (Myotis bechsteinii) adapt their roosting behaviour to the life cycle of the bat fly Basilia nana in order to decrease their contact with infective stages of this parasite. B. nana imagoes live permanently on the bat's body but deposit puparia in the bat's roosts. The flies metamorphose independently in the roosts, but after metamorphosis emerge only in the presence of a potential host. In a field experiment, the bats preferred non-contagious to contagious day-roosts and hence were able to detect either the parasite load of roosts or some correlate with infestation, such as bat droppings. In addition, 9 years of observational data on the natural roosting behaviour of female Bechstein's bats indicate that the bats largely avoid re-occupying roosts when highly contagious puparia are likely to be present as a result of previous occupations of the roosts by the bat colony. Our results indicate that the females adapted their roosting behaviour to the age-dependent contagiousness (emergence probability) of the puparia. However, some infested roosts were re-occupied, which we assume was because these roosts provided advantages to the bats (e.g. a beneficial microclimate) that outweighed the negative effects associated with bat fly infestation. We suggest that roost selection in Bechstein's bats is the outcome of a trade-off between the costs of parasite infestation and beneficial roost qualitie