Fabrication of photovoltaic laser energy converterby MBE

A laser-energy converter, fabricated by molecular beam epitaxy (MBE), was developed. This converter is a stack of vertical p-n junctions connected in series by low-resistivity, lattice matched CoSi2 layers to achieve a high conversion efficiency. Special high-temperature electron-beam (e-beam) sources were developed especially for the MBE growth of the junctions and CoSi2 layers. Making use of the small (greater than 1.2 percent) lattice mismatch between CoSi2 and Si layers, high-quality and pinhole-free epilayers were achieved, providing a capability of fabricating all the junctions and connecting layers as a single growth process with one pumpdown. Well-defined multiple p-n junctions connected by CoSi2 layers were accomplished by employing a low growth temperature (greater than 700 C) and a low growth rate (less than 0.5 microns/hour). Producing negligible interdiffusion, the low growth temperature and rate also produced negligible pinholes in the CoSi2 layers. For the first time, a stack of three p-n junctions connected by two 10(exp -5) Ohm-cm CoSi2 layers was achieved, meeting the high conversion efficiency requirement. This process can now be optimized for high growth rate to form a practical converter with 10 p-n junctions in the stack

Expert system verification and validation study. ES V/V guidelines/workshop conference summary

The intent of the workshop was to start moving research on the verification and validation (V&V) of knowledge based systems (KBSs) in the direction of providing tangible 'products' that a KBS developer could use. In the near term research will focus on identifying the kinds of experiences encountered during KBS development of 'real' KBSs. These will be stored in a repository and will serve as the foundation for the rest of the activities described here. One specific approach to be pursued is 'benchmarking'. With this approach, a KBS developer can use either 'canned' KBSs with seeded errors or existing KBSs with known errors to evaluate a given tool's ability to satisfactorily identify errors

Securing ourselves from ourselves? The paradox of “entanglement” in the Anthropocene

The Anthropocene presents new challenges to the natural and social sciences by claiming that humanity is “entangled” with a myriad of scales, spaces, being(s), and temporalities. Yet, how does this entanglement alter our understanding of security? This article argues that the Anthropocene threatens not our physical security, but our ontological security: our deep and normalized conceptions of humanity and what it means to be a human “self” in a stable and continuous world. By replacing the foundation of ontological security in modernity – the uncertainty of death – with a new uncertainty of anthropos, the result is an existential discontinuity emanating from our own human selves. The Anthropocene thus manifests the need to secure humanity from humanity, or the paradox of securing oneself from oneself. Recent turns to the concept of “quantum entanglement” attempt to resolve this paradox by re-instilling a certain and secure “entangled” human self within an otherwise uncertain and insecure Anthropocene epoch. The article concludes that this move actually illustrates humanity’s separation, or dis-entanglement, from nature. Ethical and moral responsibilities to mediate and safeguard life and the planet derive not from (quantum) science nor from entanglement, but from a social world within which humans possess the agency to mediate and judge how to act through such concepts

Inverting the Angular Correlation Function

The two point angular correlation function is an excellent measure of structure in the universe. To extract from it the three dimensional power spectrum, one must invert Limber's Equation. Here we perform this inversion using a Bayesian prior constraining the smoothness of the power spectrum. Among other virtues, this technique allows for the possibility that the estimates of the angular correlation function are correlated from bin to bin. The output of this technique are estimators for the binned power spectrum and a full covariance matrix. Angular correlations mix small and large scales but after the inversion, small scale data can be trivially eliminated, thereby allowing for realistic constraints on theories of large scale structure. We analyze the APM catalogue as an example, comparing our results with previous results. As a byproduct of these tests, we find -- in rough agreement with previous work -- that APM places stringent constraints on Cold Dark Matter inspired models, with the shape parameter constrained to be $0.25\pm 0.04$ (using data with wavenumber $k \le 0.1 h{\rm Mpc}^{-1}$). This range of allowed values use the full power spectrum covariance matrix, but assumes negligible covariance in the off-diagonal angular correlation error matrix, which is estimated with a large angular resolution of 0.5degrees (in the range 0.5 and 20 degrees).Comment: 7 pages, 11 figures, replace to match accepted version, MNRAS in pres

Development and evaluation of the RapidAir® dispersion model, including the use of geospatial surrogates to represent street canyon effects

We developed a dispersion model (RapidAir®) to estimate air pollution concentrations at fine spatial resolution over large geographical areas with fast run times. Concentrations were modelled at 5 m spatial resolution over an area of ∼3500 km2 in <10 min. RapidAir® was evaluated by estimating NOx and NO2 concentrations at 86 continuous monitoring sites in London, UK during 2008. The model predictions explained 66% of the spatial variation (r = 0.81) in annual NOx concentrations observed at the monitoring sites. We included discrete canyon models or geospatial surrogates (sky view factor, hill shading and wind effect) to improve the accuracy of model predictions at kerbside locations. Geospatial surrogates provide alternatives to discrete street canyon models where it is impractical to run canyon models for thousands of streets within a large city dispersion model (with advantages including: ease of operation; faster run times; and more complete treatment of building effects)

Advanced Air Transport Technology (AATT)

The NASA Advanced Air Transport Technology (AATT) Project is advancing commercial subsonic technologies to meet future aviation economic and environmental goals. Part of the portfolio is focused on podded and integrated fan technology advancement. The AATT is discussing potential collaboration opportunities in the fan technology area with DLR (German Aerospace Center). This presentation will be used to facilitate these discussions

The early medieval origin of Perth, Scotland

The radiocarbon results (and Bayesian modeling) of 15 samples of carbonized food residues removed from the external surface of rim sherds of cooking pots indicate that shellyware pottery first appeared in Perth, Scotland, around cal AD 9101020 (95% probability) and that it had disappeared by cal AD 10201140 (95% probability). Previously, it had been suggested that this pottery could not date to before AD 1150. These data, together with 14C analyses carried out on leather artifacts and a sample of wattle from a ditch lining, also demonstrate that there was occupation in Perth about 100 yr or more prior to the granting of royal burgh status to Perth in the 1120s

Ricci flow on open 3-manifolds and positive scalar curvature

We show that an orientable 3-dimensional manifold M admits a complete riemannian metric of bounded geometry and uniformly pos- itive scalar curvature if and only if there exists a finite collection F of spherical space-forms such that M is a (possibly infinite) connected sum where each summand is diffeomorphic to S2xS1 or to some mem- ber of F. This result generalises G. Perelman's classification theorem for compact 3-manifolds of positive scalar curvature. The main tool is a variant of Perelman's surgery construction for Ricci flow.Comment: 65 page