Efecto de la densidad de plantación inicial en el módulo de elasticidad dinámico de árboles en pie y trozas de una plantación de Pino radiata de 28 años, en la zona de arenales, Chile

En un ensayo de densidad de plantación inicial (DPI), se evaluó el efecto de cuatro tratamientos (2500, 1667, 833 y 625 árb·ha-1) en el módulo de elasticidad dinámico (MOEd) de Pinus radiata D. Don, de 28 años, creciendo sobre un suelo de la serie Arenales, en la Región del Biobío, Chile.El MOEd se determinó con tecnología acústica utilizando el método de tiempo de vuelo (Tv) para árboles en pie y posterior a su volteo se usó el método de resonancia (Res) para dos trozas de 5 m de longitud (primera y segunda troza), extraídas desde la base y a lo largo del fuste de cada árbol.La DPI no afectó significativamente el MOEd de los tratamientos más densos (2500, 1667 y 833 árb·ha-1), tanto para árboles en pie, como para las dos trozas. En cambio, el tratamiento menos denso (625 árb·ha-1) presentó el mayor MOEd, significativamente diferente en árboles en pie y la primera troza, y similar entre la primera y segunda troza. AbstractThe influence of initial planting density (DPI) on the dynamic modulus of elasticity (MOEd examinated at a 28 years old Pinus radiata D. Don spacing experiment with four treatments (2500, 1667, 833 and 625 stem·ha-1) growing on sandy soil, in the Biobío Region, Chile.The MOEd acoustic technology was determined using the method of time of flying (Tv) for standing trees and the resonance method (Res) for two logs of 5 m long, extracted from the tree base to the top of each tree.MOEd was not significantly influenced by DPI in high initial stocking treatments (2500, 1667 and 833 stem·ha-1), both standing trees and logs level. In contrast, the lowest initial stocking treatment (625 stem·ha-1) had the highest MOEd, significantly different in standing trees and the first the log, and similar between the first and second log. 

Cannabis use and risk of schizophrenia: a Mendelian randomization study.

Cannabis use is observationally associated with an increased risk of schizophrenia, but whether the relationship is causal is not known. Using a genetic approach, we took 10 independent genetic variants previously identified to associate with cannabis use in 32 330 individuals to determine the nature of the association between cannabis use and risk of schizophrenia. Genetic variants were employed as instruments to recapitulate a randomized controlled trial involving two groups (cannabis users vs nonusers) to estimate the causal effect of cannabis use on risk of schizophrenia in 34 241 cases and 45 604 controls from predominantly European descent. Genetically-derived estimates were compared with a meta-analysis of observational studies reporting ever use of cannabis and risk of schizophrenia or related disorders. Based on the genetic approach, use of cannabis was associated with increased risk of schizophrenia (odds ratio (OR) of schizophrenia for users vs nonusers of cannabis: 1.37; 95% confidence interval (CI), 1.09-1.67; P-value=0.007). The corresponding estimate from observational analysis was 1.43 (95% CI, 1.19-1.67; P-value for heterogeneity =0.76). The genetic markers did not show evidence of pleiotropic effects and accounting for tobacco exposure did not alter the association (OR of schizophrenia for users vs nonusers of cannabis, adjusted for ever vs never smoker: 1.41; 95% CI, 1.09-1.83). This adds to the substantial evidence base that has previously identified cannabis use to associate with increased risk of schizophrenia, by suggesting that the relationship is causal. Such robust evidence may inform public health messages about cannabis use, especially regarding its potential mental health consequences

NP-hardness of Deciding Convexity of Quartic Polynomials and Related Problems

We show that unless P=NP, there exists no polynomial time (or even pseudo-polynomial time) algorithm that can decide whether a multivariate polynomial of degree four (or higher even degree) is globally convex. This solves a problem that has been open since 1992 when N. Z. Shor asked for the complexity of deciding convexity for quartic polynomials. We also prove that deciding strict convexity, strong convexity, quasiconvexity, and pseudoconvexity of polynomials of even degree four or higher is strongly NP-hard. By contrast, we show that quasiconvexity and pseudoconvexity of odd degree polynomials can be decided in polynomial time.Comment: 20 page

Nonlinear Integer Programming

Research efforts of the past fifty years have led to a development of linear integer programming as a mature discipline of mathematical optimization. Such a level of maturity has not been reached when one considers nonlinear systems subject to integrality requirements for the variables. This chapter is dedicated to this topic. The primary goal is a study of a simple version of general nonlinear integer problems, where all constraints are still linear. Our focus is on the computational complexity of the problem, which varies significantly with the type of nonlinear objective function in combination with the underlying combinatorial structure. Numerous boundary cases of complexity emerge, which sometimes surprisingly lead even to polynomial time algorithms. We also cover recent successful approaches for more general classes of problems. Though no positive theoretical efficiency results are available, nor are they likely to ever be available, these seem to be the currently most successful and interesting approaches for solving practical problems. It is our belief that the study of algorithms motivated by theoretical considerations and those motivated by our desire to solve practical instances should and do inform one another. So it is with this viewpoint that we present the subject, and it is in this direction that we hope to spark further research.Comment: 57 pages. To appear in: M. J\"unger, T. Liebling, D. Naddef, G. Nemhauser, W. Pulleyblank, G. Reinelt, G. Rinaldi, and L. Wolsey (eds.), 50 Years of Integer Programming 1958--2008: The Early Years and State-of-the-Art Surveys, Springer-Verlag, 2009, ISBN 354068274

Microlensing as a probe of the Galactic structure; 20 years of microlensing optical depth studies

Microlensing is now a very popular observational astronomical technique. The investigations accessible through this effect range from the dark matter problem to the search for extra-solar planets. In this review, the techniques to search for microlensing effects and to determine optical depths through the monitoring of large samples of stars will be described. The consequences of the published results on the knowledge of the Milky-Way structure and its dark matter component will be discussed. The difficulties and limitations of the ongoing programs and the perspectives of the microlensing optical depth technique as a probe of the Galaxy structure will also be detailed.Comment: Accepted for publication in General Relativity and Gravitation. General Relativity and Gravitation in press (2010) 0

Genetic variation in natural populations of the cereal cyst nematode (Heterodera avenae Woll.) submitted to resistant and susceptible cultivars of cereals

International audienc

Genetic variation in natural populations of the cereal cyst nematode (Heterodera avenae Woll.) submitted to resistant and susceptible cultivars of cereals

International audienc

Efecto de la densidad de plantación inicial en el módulo de elasticidad dinámico de árboles en pie y trozas de una plantación de pino radiata de 28 años, en la zona de arenales, Chile Effect of initial planting density in dynamic modulus of elasticity in standing trees and logs of 28 years old radiata pine plantation in sandy soil, Chile

En un ensayo de densidad de plantación inicial (DPI), se evaluó el efecto de cuatro tratamientos (2500, 1667, 833 y 625 árb·ha-1) en el módulo de elasticidad dinámico (MOEd) de Pinus radiata D. Don, de 28 años, creciendo sobre un suelo de la serie Arenales, en la Región del Biobío, Chile. El MOEd se determinó con tecnología acústica utilizando el método de tiempo de vuelo (Tv) para árboles en pie y posterior a su volteo se usó el método de resonancia (Res) para dos trozas de 5 m de longitud (primera y segunda troza), extraídas desde la base y a lo largo del fuste de cada árbol. La DPI no afectó significativamente el MOEd de los tratamientos más densos (2500, 1667 y 833 árb·ha-1), tanto para árboles en pie, como para las dos trozas. En cambio, el tratamiento menos denso (625 árb·ha-1) presentó el mayor MOEd, significativamente diferente en árboles en pie y la primera troza, y similar entre la primera y segunda troza.The influence of initial planting density (DPI) on the dynamic modulus of elasticity (MOEd) was examinated at a 28 years old Pinus radiata D. Don spacing experiment with four treatments (2500, 1667, 833 and 625 stem·ha-1) growing on sandy soil, in the Biobío Region, Chile. The MOEd acoustic technology was determined using the method of time of flying (Tv) for standing trees and the resonance method (Res) for two logs of 5 m long, extracted from the tree base to the top of each tree. MOEd was not significantly influenced by DPI in high initial stocking treatments (2500, 1667 and 833 stem·ha-1), both standing trees and logs level. In contrast, the lowest initial stocking treatment (625 stem·ha-1) had the highest MOEd, significantly different in standing trees and the first the log, and similar between the first and second log

Efecto de la densidad de plantación inicial en el módulo de elasticidad dinámico de árboles en pie y trozas de una plantación de pino radiata de 28 años, en la zona de arenales, Chile

En un ensayo de densidad de plantación inicial (DPI), se evaluó el efecto de cuatro tratamientos (2500, 1667, 833 y 625 árb·ha-1) en el módulo de elasticidad dinámico (MOEd) de Pinus radiata D. Don, de 28 años, creciendo sobre un suelo de la serie Arenales, en la Región del Biobío, Chile. El MOEd se determinó con tecnología acústica utilizando el método de tiempo de vuelo (Tv) para árboles en pie y posterior a su volteo se usó el método de resonancia (Res) para dos trozas de 5 m de longitud (primera y segunda troza), extraídas desde la base y a lo largo del fuste de cada árbol. La DPI no afectó significativamente el MOEd de los tratamientos más densos (2500, 1667 y 833 árb·ha-1), tanto para árboles en pie, como para las dos trozas. En cambio, el tratamiento menos denso (625 árb·ha-1) presentó el mayor MOEd, significativamente diferente en árboles en pie y la primera troza, y similar entre la primera y segunda troza

Efecto del método de propagación y sitio sobre atributos fustales en árboles de Pinus radiata a la edad de 17 años

The rate of establishment of radiata pine plantations in Chile has required increasing the production of plants propagated by vegetative methods. However, it is unknown whether there are differences in growth rates and stem attributes between trees propagated by seed lings or cuttings. This study quantifies differences between plant reproduction methods (seedling and cutting) and its interaction with site on stem attributes of radiata pine trees at the age of 17 years old. The evaluated attributes were stem form, location of center of volume and center of gravity and taper of bottom logs. The required information was obtained from an un-thinned and un-prunned trial located in two contrasting site conditions on volcanic ash and sandy soils. On each site, two rectangular plots (30 m × 21 m) with initial stand density of 1428 individuals per hectare that belong to the same genetic family were established. For each plot, plants propagated by seedlings or one-year-old cuttings were randomly assigned. The combination of propagation methods and sites defined a 2 × 2 factorial experiment. From each treatment, twenty trees were selected for destructive sampling. The results obtained indicate that there are no significant differences between propagation methods for stem form, form quotient, location of the center of volume and center of gravity. There were also non-significant differences between sites and there was no interaction between sites and propagation methods. However, the taper of the first log (0 m - 3 m) was significantly different between propagation methods and between sites. We concluded that trees propagated by cuttings and established in a low productivity site on sandy soils have a more cylindrical first-bottom log in comparison to trees propagated by seedlings and established in a high productivity site on volcanic ash soils located in the Andean piedmont.La tasa de plantaciones de pino radiata en Chile ha requerido aumentar la escala de producción de plantas aplicando propagación vegetativa. Sin embargo, se desconoce si existen diferencias de crecimiento y atributos fustales entre árboles reproducidos mediante semillas o estacas. Esta investigación cuantifica el efecto del método de propagación y sitio sobre atributos fustales de pino radiata a la edad de 17 años. Los atributos evaluados fueron: forma fustal, localización del centro de volumen y centro de gravedad, y ahusamiento en trozas. Los datos se obtuvieron de un ensayo silvícola sin raleo ni poda ubicado sobre suelos de ceniza volcánica y arenas. En cada sitio se establecieron dos parcelas (30 m × 21 m), considerando una densidad inicial de 1428 individuos por hectárea de la misma familia genética. Dentro de cada sitio se asignó en forma aleatoria a cada parcela, plantas propagadas por semilla o por estacas de un año de edad. La combinación de métodos de propagación y sitios definieron un diseño factorial 2 × 2. En cada tratamiento, se seleccionaron 20 individuos para muestreo destructivo. Los resultados indican que no hubo efectos significativos de los métodos de propagación para el factor y cociente de forma, centro de volumen y gravedad. Tampoco hubo efectos significativos de los sitios ni interacción entre factores. Sin embargo, el ahusamiento de la primera troza basal (0 m - 3 m) evidenció efectos significativos de ambos factores. Se puede concluir que individuos propagados por estacas y establecidos en arenas presentan trozas basales más cilíndricas que individuos establecidos en suelos derivados de cenizas volcánicas