Combined grazing incidence RBS and TEM analysis of luminescent nano-SiGe/SiO2 multilayers.

Multilayer structures with five periods of amorphous SiGe nanoparticles/SiO2 layers with different thickness were deposited by Low Pressure Chemical Vapor Deposition and annealed to crystallize the SiGe nanoparticles. The use of grazing incidence RBS was necessary to obtain sufficient depth resolution to separate the signals arising from the individual layers only a few nm thick. The average size and areal density of the embedded SiGe nanoparticles as well as the oxide interlayer thickness were determined from the RBS spectra. Details of eventual composition changes and diffusion processes caused by the annealing processes were also studied. Transmission Electron Microscopy was used to obtain complementary information on the structural parameters of the samples in order to check the information yielded by RBS. The study revealed that annealing at 900 °C for 60 s, enough to crystallize the SiGe nanoparticles, leaves the structure unaltered if the interlayer thickness is around 15 nm or higher

What's the Use? Welfare Estimates from Revealed Preference Models when Weak Complementarity Does Not Hold

In this paper we consider the theoretical and empirical ramifications of welfare measurement in revealed preference models when weak complementarity does not hold. In the context of a Kuhn-Tucker model of recreation demand we show that, while it is possible to estimate preferences that do not appear to exhibit weak complementarity, the calculation of welfare measurements from these models requires a cardinal interpretation of preferences that cannot be tested. Furthermore, we reiterate the under-appreciated fact that even traditional use value estimates require a cardinal restriction on preferences that, while often intuitive, also cannot be tested. We demonstrate empirically that the choice of restrictions can have significant ramifications, as use value estimates can vary widely based on the assumed preference structure.

Estimation and Welfare Calculations in a Generalized Corner Solution Model with an Application to Recreation Demand

The Kuhn-Tucker model of Wales and Woodland (1983) provides a utility theoretic framework for estimating preferences over commodities for which individuals choose not to consume one or more of the goods. Due to the complexity of the model, however, there have been few applications in the literature and little attention has been paid to the problems of welfare analysis within the Kuhn-Tucker framework. This paper provides an application of the model to the problem of recreation demand. In addition, we develop and apply a methodology for estimating compensating variation, relying on Monte Carlo integration to derive expected welfare changes.

Spacetime perspective of Schwarzschild lensing

We propose a definition of an exact lens equation without reference to a background spacetime, and construct the exact lens equation explicitly in the case of Schwarzschild spacetime. For the Schwarzschild case, we give exact expressions for the angular-diameter distance to the sources as well as for the magnification factor and time of arrival of the images. We compare the exact lens equation with the standard lens equation, derived under the thin-lens-weak-field assumption (where the light rays are geodesics of the background with sharp bending in the lens plane, and the gravitational field is weak), and verify the fact that the standard weak-field thin-lens equation is inadequate at small impact parameter. We show that the second-order correction to the weak-field thin-lens equation is inaccurate as well. Finally, we compare the exact lens equation with the recently proposed strong-field thin-lens equation, obtained under the assumption of straight paths but without the small angle approximation, i.e., with allowed large bending angles. We show that the strong-field thin-lens equation is remarkably accurate, even for lightrays that take several turns around the lens before reaching the observer.Comment: 22 pages, 6 figures, to appear in Phys. Rev.

Moving At-Risk Teenagers Out of High-Risk Neighborhoods: Why Girls Fare Better Than Boys

neighborhood effects; social experiment; mixed methods; youth risk behavior

Thermodynamical Properties of a Rotating Ideal Bose Gas

In a recent experiment, a Bose-Einstein condensate was trapped in an anharmonic potential which is well approximated by a harmonic and a quartic part. The condensate was set into such a fast rotation that the centrifugal force in the corotating frame overcompensates the harmonic part in the plane perpendicular to the rotation axis. Thus, the resulting trap potential became Mexican-hat shaped. We present an analysis for an ideal Bose gas which is confined in such an anharmonic rotating trap within a semiclassical approximation where we calculate the critical temperature, the condensate fraction, and the heat capacity. In particular, we examine in detail how these thermodynamical quantities depend on the rotation frequency.Comment: Author Information under http://www.theo-phys.uni-essen.de/tp/ags/pelster_dir

Rossby waves in rapidly rotating Bose-Einstein condensates

We predict and describe a new collective mode in rotating Bose-Einstein condensates, which is very similar to the Rossby waves in geophysics. In the regime of fast rotation, the Coriolis force dominates the dynamics and acts as a restoring force for acoustic-drift waves along the condensate. We derive a nonlinear equation that includes the effects of both the zero-point pressure and the anharmonicity of the trap. It is shown that such waves have negative phase speed, propagating in the opposite sense of the rotation. We discuss different equilibrium configurations and compare with those resulting from the Thomas-Fermi approximation.Comment: 4 pages, 2 figures (submitted to PRL

The use of high-resolution terrain data in gravity field prediction

Different types of gravity prediction methods for local and regional gravity evaluation are developed, tested, and compared. Four different test areas were particularly selected in view of different prediction requirements. Also different parts of the spectrum of the gravity field were considered

Valuing Water Quality As a Functionof Water Quality Measures

This paper incorporates a rich set of physical water quality attributes, as well as site and household characteristics, into a model of recreational lake usage in Iowa. Our analysis shows individuals are responsive to physical water quality measures. Willingness-to-pay estimates are reported based on improvements in these measures.

Schattentolerante Grasgemenge für Agroforstsysteme in der Legehennen-Haltung

This field-study focuses on provision of ground vegetation in a silvopoultry system.Silvopoultry is an agroforestry system in which trees are integrated in the chicken run in order to support natural behavior of laying hens. The trial was conducted on an organic farm in Southern England by the Organic Research Centre and aimed to assess the performance of different sward mixtures under trees. The sward mixtures tested included (1) a commercially available “standard” sward, (2) a sward with especially shade tolerant grasses and (3) a diverse sward including legumes and forage herbs. It was found that all mixtures established well under trees and didn’t show significant differences in productivity after six weeks. The “standard” sward mixture showed slightly higher biomass production. Sowing any of the sward mixtures appeared to reduce weed abundance compared to the control