Shape from texture is best analyzed in two stages, analogous to steropsis and structure from motion: (a) Computing the `texture distortion'' from the image, and (b) Interpreting the `texture distortion'' to infer the orientation and shape of the surface in the scene. We model the texture distortion for a given point and direction on the image plane as an affine transformation and derive the relationship between the parameters of this transformation and the shape parameters. We have developed a technique for estimating affine transforms between nearby image patches which is based on solving a system of linear constraints derived from a differential analysis. One need not explicitly identify texels or make restrictive assumptions about the nature of the texture like isotropy. We use non- linear minimization of a least squares error criterion to recover the surface orientation (slant and tilt) and shape (principal curvatures and directions) based on the estimated affine transforms in a number of different directions. A simple linear algorithm based on singular value decomposition of the linear parts of the affine transforms provides the initial guess for the minimization procedure. Experimental results on both planar and curved surfaces under perspective projection demonstrate good estimates for both orientation and shape. A sensitivity analysis yields predictions for both computer vision algorithms and human perception of shape from texture.
Abstract In this chapter, we present our initial findings of the impact of policy on Internet paths. In particular, our findings reveal answers to the following questions: How does policy based routing inflate Internet paths? For a source-destination pair, does there exist a detour path and how good is the best detour path compared to the policy path? Does policy routing funnel Internet paths through larger autonomous systems (ASs).
We developed a method for processing roots from soil cores and monoliths in the laboratory to reduce the time and cost devoted to separating roots from debris and improve the accuracy of root variable estimates. The method was tested on soil cores from a California oak savanna, with roots from trees, Quercus douglasii, and annual grasses. In the randomized sampling method, one isolates the sample fraction consisting of roots and organic debris < = 1 cm in length, and randomizes it through immersion in water and vigorous mixing. Sub-samples from the mixture are then used to estimate the percentage of roots in this fraction, thereby enabling an estimate of total sample biomass. We found that root biomass estimates, determined through the randomization method, differed from total root biomass established by meticulously picking every root from a sample with an error of 3.0 % +/− 0.6 % s.e. This method greatly reduces the time and resources required for root processing from soil cores and monoliths, and improves the accuracy of root variable estimates compared to standard methods. This gives researchers the ability to increase sample frequency and reduce the error associated with studying roots at the landscape and plant scales.
We assemble data on the structure of bank supervision, distinguishing supervision by the central bank from supervision by a nonbank governmental agency and independent from dependent governmental supervisors. Using observations for 140 countries from 1998 through 2010, we find that supervisory responsibility tends to be assigned to the central bank in low-income countries where that institution is one of few public-sector agencies with the requisite administrative capacity. It is more likely to be undertaken by a non-independent agency of the government in countries ranked high in terms of government efficiency and regulatory quality. We show that the choice of institutional arrangement makes a difference for outcomes. Countries with independent supervisors other than the central bank have fewer nonperforming loans as a share of GDP even after controlling for inflation, per capita income, and country and/or year fixed effects. Their banks are required to hold less capital against assets, presumably because they have less need to protect against loan losses. Savers in such countries enjoy higher deposit rates. There is some evidence, albeit more tentative, that countries with these arrangements are less prone to systemic banking crises.
The performance of medical groups is receiving increased attention. Relatively little conceptual or empirical work exists that examines the various dimensions of medical group performance. Using a national database of 693 medical groups, this article develops a scorecard approach to assessing group performance and presents a theory-driven framework for differentiating between high-performing versus low-performingmedical groups. The clinical quality of care, financial performance, and organizational learning capability of medical groups are assessed in relation to environmental forces, resource acquisition and resource deployment factors, and a quality-centered culture. Findings support the utility of the performance scorecard approach and identification of a number of key factors differentiating high-performing from low-performing groups including, in particular, the importance of a quality-centered culture and the requirement of outside reporting from third party organizations. The findings hold a number of important implications for policy and practice, and the framework presented provides a foundation for future research.
