LAND USE PLANNING AND POLICY IN THE SOUTH

Land Economics/Use,

Artroplastia unicompartimental de rodilla sin cementar: indicaciones y resultados

Desde abril de 1987 hasta octubre de 1990, 100 pacientes (81 mujeres y 19 hombres) de 69 años de edad media fueron intervenidos mediante artroplastia unicompartmental de rodilla. El tiempo medio de seguimiento fue de 28 meses (rango: 12-48). La artroplastia fue indicada por osteoartrosis unicompartimental en 91 casos, necrosis aséptica femoral en 8 y destrucción post-traumática en 1. El implante utilizado era de tipo no constreñido y fijación sin cemento. En los primeros 12 meses de evolución, murieron 4 pacientes y otros 2 casos precisaron de reintervención, uno por aflojamiento de componente tibial y otro por luxación de ambos componentes. De los 94 pacientes restantes, 90 quedaron asintomáticos o referían mínimo dolor tras la intervención. La valoración funcional global en la escala de Hungerford fue de 63 puntos en el estudio preoperatorio y de 93 en la revisión postoperatoria, lo que indica un excelente resultado. Radiológicamente, sólo se objetivó un caso de aflojamiento del implante femoral. En 90 casos, la osteointegración a nivel tibial fue completa. Tras 2 años de seguimiento, la supervivencia del implante fue del 98%.From April 1987 to October 1990, an uncemented unicompartmental knee arthroplasty was performed in 100 patients (81 women, 19 men) with a mean age of 69 years. The mean follow-up period was 28 months (range, 12-48). The indication for arthroplasty was unicompartmental osteoarthritis in 91 cases, femoral necrosis in 8, and post-traumatic femoral destruction in one. The implant used was an uncemented non-constrained design. Four patients died during the first 12 months after surgery. Two patients were reoperated; one had loosening of the tibial component and the other showed dislocation of the femoral implant backwards the tibial component. In this last patient both components were well fixed showing no signs of loosening. Out of the 94 remained cases, 90 were either asymptomatic or complain of very slight pain. Functional assessment according to Hungerford disclosed 63 points before surgery and 93 at review, indicating an excellent functional outcome. In the radiographic study, only one case who was reoperated showed loosening of the tibial component. In 90 of the 94 patients studied, and apparent good bone ingrowth was observed at the tibial component. After 2-year follow-up, the survival of the implant was found to be 98%

Growing blood vessels in space : preparation studies of the SPHEROIDS project using related ground-based studies

Endothelial cells (ECs) grow as single layers on the bottom surface of cell culture flasks under normal (1g) culture conditions. In numerous experiments using simulated microgravity we noticed that the ECs formed three-dimensional, tube-like cell aggregates resembling the intima of small, rudimentary blood vessels. The SPHEROIDS project has now shown that similar processes occur in space. For the first time, we were able to observe scaffold-free growth of human ECs into multicellular spheroids and tubular structures during an experiment in real microgravity. With further investigation of the space samples we hope to understand endothelial 3D growth and to improve the in vitro engineering of biocompatible vessels which could be used in surgery

A Geometric Characterization of the Power of Finite Adaptability in Multistage Stochastic and Adaptive Optimization

In this paper, we show a significant role that geometric properties of uncertainty sets, such as symmetry, play in determining the power of robust and finitely adaptable solutions in multistage stochastic and adaptive optimization problems. We consider a fairly general class of multistage mixed integer stochastic and adaptive optimization problems and propose a good approximate solution policy with performance guarantees that depend on the geometric properties of the uncertainty sets. In particular, we show that a class of finitely adaptable solutions is a good approximation for both the multistage stochastic and the adaptive optimization problem. A finitely adaptable solution generalizes the notion of a static robust solution and specifies a small set of solutions for each stage; the solution policy implements the best solution from the given set, depending on the realization of the uncertain parameters in past stages. Therefore, it is a tractable approximation to a fully adaptable solution for the multistage problems. To the best of our knowledge, these are the first approximation results for the multistage problem in such generality. Moreover, the results and the proof techniques are quite general and also extend to include important constraints such as integrality and linear conic constraints.National Science Foundation (U.S.) (Grant EFRI-0735905

On the Power of Robust Solutions in Two-Stage Stochastic and Adaptive Optimization Problems

We consider a two-stage mixed integer stochastic optimization problem and show that a static robust solution is a good approximation to the fully adaptable two-stage solution for the stochastic problem under fairly general assumptions on the uncertainty set and the probability distribution. In particular, we show that if the right-hand side of the constraints is uncertain and belongs to a symmetric uncertainty set (such as hypercube, ellipsoid or norm ball) and the probability measure is also symmetric, then the cost of the optimal fixed solution to the corresponding robust problem is at most twice the optimal expected cost of the two-stage stochastic problem. Furthermore, we show that the bound is tight for symmetric uncertainty sets and can be arbitrarily large if the uncertainty set is not symmetric. We refer to the ratio of the optimal cost of the robust problem and the optimal cost of the two-stage stochastic problem as the stochasticity gap. We also extend the bound on the stochasticity gap for another class of uncertainty sets referred to as positive. If both the objective coefficients and right-hand side are uncertain, we show that the stochasticity gap can be arbitrarily large even if the uncertainty set and the probability measure are both symmetric. However, we prove that the adaptability gap (ratio of optimal cost of the robust problem and the optimal cost of a two-stage fully adaptable problem) is at most four even if both the objective coefficients and the right-hand side of the constraints are uncertain and belong to a symmetric uncertainty set. The bound holds for the class of positive uncertainty sets as well. Moreover, if the uncertainty set is a hypercube (special case of a symmetric set), the adaptability gap is one under an even more general model of uncertainty where the constraint coefficients are also uncertain.National Science Foundation (U.S.) (NSF Grant DMI-0556106)National Science Foundation (U.S.) (NSF Grant EFRI-0735905

Atopic conditions and brain tumor risk in children and adolescents—an international case-control study (CEFALO)

In this study, atopic conditions were not associated with risk of brain tumors in children and adolescents or of glioma in particular. Results are not consistent with findings for adult glioma, possibly explained by a different distribution of histological subtypes. Only a few studies on atopic conditions and pediatric brain tumors are currently available, and the evidence is conflictin