Spectropolarimetry of Core-Collapse Supernovae

We briefly review the young field of spectropolarimetry of core-collapse supernovae (SNe). Spectropolarimetry provides the only direct known probe of early-time supernova (SN) geometry. The fundamental result is that asphericity is a ubiquitous feature of young core-collapse SNe. However, the nature and degree of the asphericity vary considerably. The best predictor of core-collapse SN polarization seems to be the mass of the hydrogen envelope that is intact at the time of the explosion: those SNe that arise from progenitors with large, intact envelopes (e.g., Type II-plateau) have very low polarization, while those that result from progenitors that have lost part (SN IIb, SN IIn) or all (SN Ib) of their hydrogen (or even helium; SN Ic) layers prior to the explosion tend to show substantial polarization. Thus, the deeper we probe into core-collapse events, the greater the asphericity seems to be, suggesting a fundamentally asymmetric explosion with the asymmetry damped by the addition of envelope material.Comment: Invited review at Supernovae as Cosmological Lighthouses, 16-19 June, Padua, IT. 6 page

An analytical study of transport, mixing and chaos in an unsteady vortical flow

We examine the transport properties of a particular two-dimensional, inviscid incompressible flow using dynamical systems techniques. The velocity field is time periodic and consists of the field induced by a vortex pair plus an oscillating strainrate field. In the absence of the strain-rate field the vortex pair moves with a constant velocity and carries with it a constant body of fluid. When the strain-rate field is added the picture changes dramatically; fluid is entrained and detrained from the neighbourhood of the vortices and chaotic particle motion occurs. We investigate the mechanism for this phenomenon and study the transport and mixing of fluid in this flow. Our work consists of both numerical and analytical studies. The analytical studies include the interpretation of the invariant manifolds as the underlying structure which govern the transport. For small values of strain-rate amplitude we use Melnikov's technique to investigate the behaviour of the manifolds as the parameters of the problem change and to prove the existence of a horseshoe map and thus the existence of chaotic particle paths in the flow. Using the Melnikov technique once more we develop an analytical estimate of the flux rate into and out of the vortex neighbourhood. We then develop a technique for determining the residence time distribution for fluid particles near the vortices that is valid for arbitrary strainrate amplitudes. The technique involves an understanding of the geometry of the tangling of the stable and unstable manifolds and results in a dramatic reduction in computational effort required for the determination of the residence time distributions. Additionally, we investigate the total stretch of material elements while they are in the vicinity of the vortex pair, using this quantity as a measure of the effect of the horseshoes on trajectories passing through this region. The numerical work verifies the analytical predictions regarding the structure of the invariant manifolds, the mechanism for entrainment and detrainment and the flux rate

Agency Disclosure in the Real Estate Transaction and the Impact of Related State Policies

Although agency disclosure is required by every state, recent national surveys of home buyers and sellers indicate that disclosure varies significantly across the United States. This study seeks to determine the causes of these disparities by examining states¡¯ educational standards, disclosure forms, regulatory environments, and buyer characteristics. The results identify several variables that have a deterministic impact on the probability of disclosure and suggest corrective actions and policies that states can implement to improve the effectiveness of agency disclosure in the real estate transaction.

Probing the Geometry of Supernovae with Spectropolarimetry

We present results from a spectropolarimetric survey of young supernovae completed at the Keck Observatory, including at least one example from each of the major supernova types: Ia (1997dt), Ib (1998T, 1997dq), Ib/c-pec (1997ef), IIn (1997eg), and II-P (1997ds). All objects show evidence for intrinsic polarization, suggesting that asphericity may be a common feature in young supernova atmospheres.Comment: 4 pages, 2 figures. To appear in the Proceedings of the 10th Annual October Astrophysics Conference in Maryland: Cosmic Explosion

Quantum algorithms for hidden nonlinear structures

Attempts to find new quantum algorithms that outperform classical computation have focused primarily on the nonabelian hidden subgroup problem, which generalizes the central problem solved by Shor's factoring algorithm. We suggest an alternative generalization, namely to problems of finding hidden nonlinear structures over finite fields. We give examples of two such problems that can be solved efficiently by a quantum computer, but not by a classical computer. We also give some positive results on the quantum query complexity of finding hidden nonlinear structures.Comment: 13 page

Listing Specialization and Residential Real Estate Licensee

Earlier research has found that specialization by real estate agents creates economies of scope for real estate firms. So far, however, no research has addressed this issue at the agent level. The question this research seeks to answer is whether specialization in one side of the real estate transaction increases agent income. The most important finding is that specialization has an asymmetric impact on earnings. Specializing in listings positively enhances agent income. In contrast, specialization on the selling side has an adverse affect on agent income. The implications of these findings for the consumer and real estate industry are also examined.

X-Inefficiencies in the Residential Real Estate Market: A Stochastic Frontier Approach

This article examines the productive efficiency levels present in the market for residential real estate brokerage services by employing the stochastic frontier approach. The only prior study (Anderson, Zumpano, Elder and Fok, 1998) that examined productive efficiency in this sector employed data envelopment analysis. This current article addresses potential statistical limitations of Data Envelopment Analysis and uses an alternative statistical tool, the stochastic frontier approach, to estimate X-efficiencies. This technique overcomes many of the statistical limitations of DEA and provides additional productive efficiency estimates. The results suggest that residential real estate brokerage firms are relatively efficient, in contrast to the earlier study that found significant inefficiencies present in this market. Firms could only reduce their average total costs by 12% given firm outputs and input prices. Additionally, the firms were divided into three size categories to examine the impact of firm size on efficiency. The results indicate that small firms are the most efficient group. Hence, there seems to be a tradeoff between scale efficiency and productive efficiency.

Prediction of Landing Gear Noise Reduction and Comparison to Measurements

Noise continues to be an ongoing problem for existing aircraft in flight and is projected to be a concern for next generation designs. During landing, when the engines are operating at reduced power, the noise from the airframe, of which landing gear noise is an important part, is equal to the engine noise. There are several methods of predicting landing gear noise, but none have been applied to predict the change in noise due to a change in landing gear design. The current effort uses the Landing Gear Model and Acoustic Prediction (LGMAP) code, developed at The Pennsylvania State University to predict the noise from landing gear. These predictions include the influence of noise reduction concepts on the landing gear noise. LGMAP is compared to wind tunnel experiments of a 6.3%-scale Boeing 777 main gear performed in the Quiet Flow Facility (QFF) at NASA Langley. The geometries tested in the QFF include the landing gear with and without a toboggan fairing and the door. It is shown that LGMAP is able to predict the noise directives and spectra from the model-scale test for the baseline configuration as accurately as current gear prediction methods. However, LGMAP is also able to predict the difference in noise caused by the toboggan fairing and by removing the landing gear door. LGMAP is also compared to far-field ground-based flush-mounted microphone measurements from the 2005 Quiet Technology Demonstrator 2 (QTD 2) flight test. These comparisons include a Boeing 777-300ER with and without a toboggan fairing that demonstrate that LGMAP can be applied to full-scale flyover measurements. LGMAP predictions of the noise generated by the nose gear on the main gear measurements are also shown