Object-Centered Surface Reconstruction: Combining Multi-Image Stereo and Shading

Our goal is to reconstruct both the shape and reflectance properties of surfaces from multiple images. To this end, we introduce an object-centered representation, specifically, a hexagonally-connected 3-D mesh of vertices with triangular facets. Such a representation accommodates the two classes of information mentioned above, as well as multiple images, self-occlusions and geometric constraints. We have chosen to model the surface material using the Lambertian reflectance model with variable albedo. Consequently, the natural choice for the monocular information source is shading, while intensity is the natural choice for the image feature used in multi-image correspondence. Not only are these the natural choices given a Lambertian reflectance model, they are complementary: intensity correlation is most accurate wherever the input images are highly textured, and shading is most accurate when the input images are not. We argue that by combining shape from shading and stereo, we can do better than by using either of them alone while avoiding the limitations imposed by the constant depth assumption of traditional correlation-based stereo algorithms and the constant albedo assumption of conventional shape from shading methods. Furthermore, our technique can merge information from any number of very different viewpoints thereby eliminating blind spots while dealing effectively with self-occlusions

Local flux-profile relationships of wind speed and temperature in a canopy layer in atmospheric stable conditions

The particularities of the physics of the canopy layer pose challenges to the determination and use of traditional universal functions so helpful in the atmospheric surface layer. Progress toward "universal-like functions" such as those provided by Monin-Obukhov similarity theory for the canopy layer has been modest. One of the challenges lies in that the assumptions underlying Monin-Obukhov similarity theory do not hold within a canopy layer. This paper thus examines the local flux-profile relations for wind (<i>Φ</i><sub><i>m</i></sub>) and for temperature (<i>Φ</i><sub><i>h</i></sub>). It uses three different stability parameters, i.e., <i>h/L(h)</i> at tree top, local <i>z/L(z)</i>, and the local bulk Richardson number (<i>Ri</i>), within a tall forest canopy in nighttime stable (indicated by <i>h/L(h)</i> > 0) conditions. Results suggest that the in-canopy <i>Φ</i><sub><i>m</i></sub> can be described using the local Richardson number <i>Ri</i>. Furthermore, <i>Φ</i><sub><i>m</i></sub> is found to increase linearly with <i>Ri</i> in the upper canopy layer for |<i>Ri</i>| < 1. When local |<i>Ri</i>| > 1, |Φ<sub><i>m</i></sub>| decreases with |<i>Ri</i>| in a power function, a result consistent for all levels of measurements within the canopy. When both local <i>Φ</i><sub><i>h</i></sub> and local <i>Ri</i> are positive, i.e., the local downward turbulent heat flux is consistent with the local temperature gradient, the local <i>Φ</i><sub><i>h</i></sub> increases with the local <i>Ri</i> when <i>Ri</i> < 1. However, <i>Φ</i><sub><i>h</i></sub> does not change with <i>Ri</i> (or much more scattered) when <i>Ri</i> > 1. The relationship between local <i>Φ</i><sub><i>h</i></sub> and <i>Ri</i> disappears when counter-gradient heat transfer occurs in strongly stable conditions. A self-correlation analysis is used to examine the influence of self-correlation and the physical meaning of these relationships

Hysteresis response of daytime net ecosystem exchange during drought

Continuous measurements of net ecosystem CO<sub>2</sub> exchange (NEE) using the eddy-covariance method were made over an agricultural ecosystem in the southeastern US. During optimum environmental conditions, photosynthetically active radiation (PAR) was the primary driver controlling daytime NEE, accounting for as much as 67 to 89% of the variation in NEE. However, soil water content became the dominant factor limiting the NEE-PAR response during the peak growth stage. NEE was significantly depressed when high PAR values coincided with very low soil water content. The presence of a counter-clockwise hysteresis of daytime NEE with PAR was observed during periods of water stress. This is a result of the stomatal closure control of photosynthesis at high vapor pressure deficit and enhanced respiration at high temperature. This result is significant since this hysteresis effect limits the range of applicability of the Michaelis-Menten equation and other related expressions in the determination of daytime NEE as a function of PAR. The systematic presence of hysteresis in the response of NEE to PAR suggests that the gap-filling technique based on a non-linear regression approach should take into account the presence of water-limited field conditions. Including this step is therefore likely to improve current evaluation of ecosystem response to increased precipitation variability arising from climatic changes

Factors affecting return to work after carpal tunnel syndrome surgery in a large French cohort

OBJECTIVE: To evaluate occupational outcomes after surgical release of the median nerve in carpal tunnel syndrome (CTS).DESIGN: Retrospective study 12 to 24 months after surgery. SETTING: Hand centers (N=3) in 2 different areas. PARTICIPANTS: Patients who had undergone surgical release of the median nerve in 2002 to 2003. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURE: Duration of sick leave after surgery and associated factors were analyzed by using bivariate (log rank) and multivariate analyses of survival (Cox model). RESULTS: Questionnaires mailed in 2004 regarding medical condition (history and surgery), employment (occupational category codes in 1 digit), and compensation were returned (N=1248; 62%), with 253 men and 682 women stating they were employed at the time of surgery (N=935). Most were working at the time of the study (n=851; 91.0%). Median duration of sick leave before returning to work was 60 days. The main factors associated with adverse occupational outcome (long duration of sick leave) were simultaneous intervention for another upper-extremity musculoskeletal disorder, belief (by the patient) in an occupational cause, and "blue-collar worker" occupational category (the strongest determinant). CONCLUSION: This study emphasizes the multifactorial nature of the occupational outcome of CTS after surgery, including occupational category. The probability of return to work for each risk factor provides a fair description of prognosis for physicians and patients

Cluster structures on quantum coordinate rings

We show that the quantum coordinate ring of the unipotent subgroup N(w) of a symmetric Kac-Moody group G associated with a Weyl group element w has the structure of a quantum cluster algebra. This quantum cluster structure arises naturally from a subcategory C_w of the module category of the corresponding preprojective algebra. An important ingredient of the proof is a system of quantum determinantal identities which can be viewed as a q-analogue of a T-system. In case G is a simple algebraic group of type A, D, E, we deduce from these results that the quantum coordinate ring of an open cell of a partial flag variety attached to G also has a cluster structure.Comment: v2: minor corrections. v3: references updated, final version to appear in Selecta Mathematic