Optical properties of dust

http://arxiv.org/abs/0808.4123Except in a few cases cosmic dust can be studied in situ or in terrestrial laboratories, essentially all of our information concerning the nature of cosmic dust depends upon its interaction with electromagnetic radiation. This chapter presents the theoretical basis for describing the optical properties of dust -- how it absorbs and scatters starlight and reradiates the absorbed energy at longer wavelengths.Partial support by a Chandra Theory program and HST Theory Programs is gratefully acknowledged

One sixth of Amazonian tree diversity is dependent on river floodplains

Amazonia's floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region's floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon's tree diversity and its function.Naturali

Mapping density, diversity and species-richness of the Amazon tree flora

Using 2.046 botanically-inventoried tree plots across the largest tropical forest on Earth, we mapped tree species-diversity and tree species-richness at 0.1-degree resolution, and investigated drivers for diversity and richness. Using only location, stratified by forest type, as predictor, our spatial model, to the best of our knowledge, provides the most accurate map of tree diversity in Amazonia to date, explaining approximately 70% of the tree diversity and species-richness. Large soil-forest combinations determine a significant percentage of the variation in tree species-richness and tree alpha-diversity in Amazonian forest-plots. We suggest that the size and fragmentation of these systems drive their large-scale diversity patterns and hence local diversity. A model not using location but cumulative water deficit, tree density, and temperature seasonality explains 47% of the tree species-richness in the terra-firme forest in Amazonia. Over large areas across Amazonia, residuals of this relationship are small and poorly spatially structured, suggesting that much of the residual variation may be local. The Guyana Shield area has consistently negative residuals, showing that this area has lower tree species-richness than expected by our models. We provide extensive plot meta-data, including tree density, tree alpha-diversity and tree species-richness results and gridded maps at 0.1-degree resolution

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees

Explorando la relación entre fortalezas de carácter y comportamiento saludable en estudiantes universitarios

Introducción: Las fortalezas son tendencias de comportamiento que contribuyen al bienestar y a una vida «buena“ (Peterson & Seligman, 2004). De acuerdo con Dahlsgaard, Peterson y Seligman (2005) existen 24 fortalezas de carácter diferentes que se pueden organizar alrededor de 6 macrocategorías. Park, Peterson & Seligman (2004) encontraron una relación significativa entre la satisfacción con la vida con 5 fortalezas de carácter. Proyer, Gander, Wellenzohn & Ruch (2013) encontraron un vínculo entre fortalezas de carácter y bienestar subjetivo y físico. La mayoría de las fortalezas tienen un efecto mediador que aumentan la probabilidad de estilos de vida activos. El objetivo de este estudio fue explorar la relación entre fortalezas de carácter y cinco comportamientos relacionados con la salud: fuma y beber, actividad física, trastornos del sueño, conductas alimentarias problemáticas y adicción a los medios y la TV con estudiantes universitarios. Material y método: Participaron 1425 universitarios de cinco instituciones Mexicanas. Los estudiantes estaban adscritos a cuatro disciplinas. Para medir las fortalezas de carácter se empleó el cuestionario VIA-IS Values in Action Inventory of Strengths con 240 reactivos (Peterson & Seligman, 2004; Peterson & Park, 2009) y el autoreporte de condiciones sociodemográficas y de comportamientos relacionados con la salud se recolectó mediante un cuestionario con 43 preguntas. Resultados: Las fortalezas de autocontrol, energía, humor, perdón, prudencia, espiritualidad y modestia estuvieron asociadas a niveles diferenciales de dos o más de los comportamientos saludables explorados. A diferencia de los resultados reportados por Proyer, Gander, Wellenzohn & Ruch, la modestia y la espiritualidad sí estuvieron asociados con resultados diferenciales en comportamiento saludable. Conclusiones: Los resultados sugieren un vínculo entre fortalezas de carácter y comportamientos asociados con la salud. Estudios futuros que valoren el efecto de intervenciones cortas sobre fortalezas de carácter podrán esclarecer la naturaleza etiológica de este vínculo

3D imaging of nanomaterials by discrete tomography

The field of discrete tomography focuses on the reconstruction of samples that consist of only a few different materials. Ideally, a three-dimensional (3D) reconstruction of such a sample should contain only one grey level for each of the compositions in the sample. By exploiting this property in the reconstruction algorithm, either the quality of the reconstruction can be improved significantly, or the number of required projection images can be reduced. The discrete reconstruction typically contains fewer artifacts and does not have to be segmented, as it already contains one grey level for each composition. Recently, a new algorithm, called discrete algebraic reconstruction technique (DART), has been proposed that can be used effectively on experimental electron tomography datasets. In this paper, we propose discrete tomography as a general reconstruction method for electron tomography in materials science. We describe the basic principles of DART and show that it can be applied successfully to three different types of samples, consisting of embedded ErSi2 nanocrystals, a carbon nanotube grown from a catalyst particle and a single gold nanoparticle, respectively