Semiparametric Methods for Semi-competing Risks Problem with Censoring and Truncation

Studies of chronic life-threatening diseases often involve both mortality and morbidity. In observational studies, the data may also be subject to administrative left truncation and right censoring. Since mortality and morbidity may be correlated and mortality may censor morbidity, the Lynden-Bell estimator for left truncated and right censored data may be biased for estimating the marginal survival function of the non-terminal event. We propose a semiparametric estimator for this survival function based on a joint model for the two time-to-event variables, which utilizes the gamma frailty specification in the region of the observable data. Firstly, we develop a novel estimator for the gamma frailty parameter under left truncation. Using this estimator, we then derive a closed form estimator for the marginal distribution of the non-terminal event. The large sample properties of the estimators are established via asymptotic theory. The methodology performs well with moderate sample sizes, both in simulations and in an analysis of data from a diabetes registry.

Impacts of environmental change on water resources in the Mount Kenya Region

Water resources are becoming increasingly scarce in the Mt. Kenya region. Land use and climate change may pose additional challenges to water management in the future. In order to assess the impacts of environmental change, the NRM3 Streamflow Model, a simple, semi-distributed, grid-based water balance model, is evaluated as a tool for discharge prediction in six meso-scale catchments on the western slopes of Mt. Kenya, and used to analyse the impact of land use and climate change scenarios on water resources.

Palynology on sediment profile Tso Kar in Ladakh

Palynological investigation of a 410 cm long core section from Tso Kar (33°10'N, 78°E, 4527 m a.s.l.), an alpine lake situated in the arid Ladakh area of NW India at the limit of the present-day Indian summer monsoon, was performed in order to reconstruct post-glacial regional vegetation and climate dynamics. The area was covered with alpine desert vegetation from ca. 15.2 to 14 kyr BP (1 kyr=1000 cal. years), reflecting dry and cold conditions. High influx values of long-distance transported Pinus sylvestris type pollen suggest prevailing air flow from the west and northwest. The spread of alpine meadow communities and local aquatic vegetation is a weak sign of climate amelioration after ca. 14 kyr BP. Pollen data (e.g. influx values of Pinus roxburghii type and Quercus) suggest that this was due to a strengthening of the summer monsoon and the reduced activity of westerly winds. The further spread of Artemisia and species-rich meadows occurred in response to improved moisture conditions between ca. 12.9 and 12.5 kyr BP. The subsequent change towards drier desert-steppe vegetation likely indicates more frequent westerly disturbances and associated snowfalls, which favoured the persistence of alpine meadows on edaphically moist sites. The spread of Chenopodiaceae-dominated vegetation associated with an extremely weak monsoon occurred at ca. 12.2-11.8 kyr BP during the Younger Dryas interstadial. A major increase in humidity is inferred from the development of Artemisia-dominated steppe and wet alpine meadows with Gentianaceae after the late glacial/early Holocene transition in response to the strengthening of the summer monsoon. Monsoonal influence reached maximum activity in the Tso Kar region between ca. 10.9 and 9.2 kyr BP. The subsequent development of the alpine meadow, steppe and desert-steppe vegetation points to a moderate reduction in the moisture supply, which can be linked to the weaker summer monsoon and the accompanying enhancement of the winter westerly flow from ca. 9.2 to 4.8 kyr BP. The highest water levels of Tso Kar around 8 kyr BP probably reflect combined effect of both monsoonal and westerly influence in the region. An abrupt shift towards aridity in the Tso Kar region occurred after ca. 4.8 kyr BP, as evidenced by an expansion of Chenopodiaceae-dominated desert-steppe. Low pollen influx values registered ca. 2.8-1.3 kyr BP suggest scarce vegetation cover and unfavourable growing conditions likely associated with a further weakening of the Indian Monsoon.

Segmentation of RV in 4D Cardiac MR Volumes using region-merging graph cuts

Non-invasive quantitative assessment of the right ventricular anatomical and functional parameters is a challenging task. We present a semi-automatic approach for right ventricle (RV) segmentation from 4D MR images in two variants, which differ in the amount of user interaction. The method consists of three main phases: First, foreground and background markers are generated from the user input. Next, an over-segmented region image is obtained applying a watershed transform. Finally, these regions are merged using 4D graph-cuts with an intensity based boundary term. For the first variant the user outlines the inside of the RV wall in a few end-diastole slices, for the second two marker pixels serve as starting point for a statistical atlas application. Results were obtained by blind evaluation on 16 testing 4D MR volumes. They prove our method to be robust against markers location and place it favourably in the ranks of existing approaches.

Aridity modulates N availability in arid and semiarid Mediterranean grasslands

While much is known about the factors that control each component of the terrestrial nitrogen (N) cycle, it is less clear how these factors affect total N availability, the sum of organic and inorganic forms potentially available to microorganisms and plants. This is particularly true for N-poor ecosystems such as drylands, which are highly sensitive to climate change and desertification processes that can lead to the loss of soil nutrients such as N. We evaluated how different climatic, abiotic, plant and nutrient related factors correlate with N availability in semiarid Stipa tenacissima grasslands along a broad aridity gradient from Spain to Tunisia. Aridity had the strongest relationship with N availability, suggesting the importance of abiotic controls on the N cycle in drylands. Aridity appeared to modulate the effects of pH, plant cover and organic C (OC) on N availability. Our results suggest that N transformation rates, which are largely driven by variations in soil moisture, are not the direct drivers of N availability in the studied grasslands. Rather, the strong relationship between aridity and N availability could be driven by indirect effects that operate over long time scales (decades to millennia), including both biotic (e.g. plant cover) and abiotic (e.g. soil OC and pH). If these factors are in fact more important than short-term effects of precipitation on N transformation rates, then we might expect to observe a lagged decrease in N availability in response to increasing aridity. Nevertheless, our results suggest that the increase in aridity predicted with ongoing climate change will reduce N availability in the Mediterranean basin, impacting plant nutrient uptake and net primary production in semiarid grasslands throughout this region.

Caracterización morfofisiológica de semillas de especies leñosas distribuidas en dos zonas secas presentes en el Sur del Ecuador

Sudamérica es una de las zonas con mayor cantidad de bosque seco tropical a nivel mundial. No obstante, estos bosques han sido poco conocidos y la mayoría de estudios han estado orientados hacia los bosques húmedos tropicales. Los bosques secos se han reducido drásticamente y siguen muy amenazados, corriendo el riesgo de desaparecer en los próximos años. Por ello, es fundamental, generar investigación aplicada para la conservación inmediata de los ecosistemas secos tropicales. En Ecuador, la situación no es diferente y las zonas secas catalogadas como biodiversas están en constante amenaza. Los pocos estudios realizados en Ecuador sobre zonas secas, han permitido mejorar nuestro conocimiento referente a la diversidad y abundancia de las especies, relaciones planta-planta y síndromes de dispersión. No existen estudios sobre caracteres morfológicos en frutos y semillas de las especies leñosas de bosque seco. Sin embargo, nuestra comprensión de la dinámica y estructura de las comunidades ecológicas de zonas secas poco estudiadas, puede mejorar rápidamente mediante el estudio y enfoque de rasgos morfofisiológicos funcionales. El objetivo general del presente estudio fue aportar al conocimiento de la ecología y biología de semillas de zonas secas tropicales mediante el análisis y evaluación de rasgos morfofisiológicos de frutos y semillas de una comunidad de especies leñosas. El estudio se realizó en una zona de bosque y matorral seco, ubicados al sur occidente del Ecuador, a una altitud comprendida entre los 250 a 1 200 m s.n.m. caracterizada por una marcada estacionalidad ambiental, con lluvias desde diciembre a abril y una estación seca de mayo a noviembre. Precipitación media anual de 500 mm con una temperatura media anual de 20° a 26 °C. La zona de estudio forma parte de la región Tumbesina compartida entre el sur del Ecuador y el norte del Perú con gran diversidad de especies vegetales endémicas. Para el estudio se colectaron frutos con semillas maduras previamente a su dispersión de entre ocho y diez individuos de 80 especies entre árboles y arbustos más representativos de los bosques secos ecuatorianos. De los frutos colectados se utilizó una muestra al azar de 50 frutos y semillas por especie para los diferentes análisis. Se midió y evaluó 18 rasgos morfológicos y fisiológicos cuantitativos y cualitativos de frutos, semillas y de la especie. Se realizaron diferentes análisis de asociación y correlación entre los rasgos evaluados, con cinco variables ambientales registradas de las 109 parcelas establecidas en el área de estudio, además analizamos el tipo de dormición y comparamos la respuesta germinativa a la deshidratación relacionada con dos comunidades secas, matorral y bosque seco. Los resultados mostraron que las especies presentan gran heterogeneidad en rasgos continuos de las semillas. La variabilidad fue más evidente en rasgos como tamaño, volumen, masa y número de semillas por fruto. Sin embargo, una alta proporción de las especies tiende a producir una semilla por fruto. Además, la mayoría de las especies de bosque seco se caracterizan por no poseer algún tipo de apéndices o areola en sus semillas, forma ovalada y sin endospermo. La reserva nutritiva de las semillas se encuentra especialmente en los cotiledones de los embriones. Se encontraron seis tipos diferentes de embriones y la mayoría de las especies presentó embriones gruesos e invertidos. La dispersión de semillas está dominada por zoocoria en un 38 %, con relación a anemocoria (22 %) y autocoria (19 %). Sin embargo, encontramos que el 70 % de las especies posee frutos secos. Los análisis de dormición en las semillas de bosque seco, mostraron que el 60 % de las especies de bosque seco presentaron semillas con algún tipo de latencia, menor a la encontrada en especies de bosque deciduo tropical y sabanas, sin embargo, la dormición de las especies de bosque seco fue mayor al porcentaje de especies con dormición de bosque semiperenne y selva lluviosa tropical. La dormición física constituyó el 35 % de las especies de bosque seco, seguido del 12 % con dormición fisiológica, mientras que solamente una especie tuvo dormición morfológica. Encontramos que la dormición de las semillas de las especies en estudio se relaciona significativamente con el tipo y función del embrión y con el endospermo. Existieron relaciones significativas entre los rasgos morfológicos de los frutos, semillas, embriones y atributos de los individuos de 46 especies, aunque en algunos casos con coeficientes de correlación bajos. Hubo pocas relaciones entre los rasgo morfológicos de las semillas con las variables ambientales registradas. Solamente el tipo de testa y la presencia de apéndices en las semillas mostraron relación con el pH y la temperatura media del suelo. No obstante usando el modelo fouth corner-RLQ, no se encontraron asociaciones claras ni significativas entre rasgos morfológicos de semillas y frutos con variables ambientales. Al medir el efecto de la deshidratación en las semillas de los dos hábitats secos tropicales: bosque y matorral seco, los resultados determinaron que tanto las semillas de las especies leñosas de ambientes más áridos (matorral seco) están en gran medida pre-adaptadas a la desecación que las especies de ambientes menos áridos (bosque seco). Los tratamientos de deshidratación ejercieron un efecto negativo en los porcentajes de germinación en todas las especies, excepto para C. platanifolia. Los resultados más sorprendentes se registraron para Senna alata que mostró germinación extremadamente baja o incluso sin germinación a contenidos de humedad de la semillas de 0,10 g H2O g de peso seco. Las curvas de germinación difirieron significativamente entre los tratamientos de deshidratación en cada especie. Aportar al conocimiento la fisiología de la deshidratación y los límites de tolerancia de las semillas de bosque y matorral seco ayudará a entender mejor el papel de este rasgo en la ecología de las semillas y dinámica de las comunidades áridas tropicales. El estudio demostró, que la adaptación ecológica de las semillas de las especies leñosas de bosque seco a factores ambientales extremos, puede verse reflejada en una red de interacciones y correlaciones complejas entre los propios rasgos morfológicos y fisiológicos continuos y cuantitativos, sobre todo en rasgos internos de las semillas, quienes ejercerían una mayor influencia en toda la red de interacciones. Si bien, los rasgos de las semillas no mostraron fuertes relaciones con las variables ambientales, posiblemente las asociaciones presentes entre rasgos morfológicos pudiesen predecir en cambio interacciones entre especies y comportamientos y procesos relacionados con la tolerancia a la deshidratación y dormición de las semillas. ABSTRACT South America is one of the areas with the largest number of tropical dry forest in the world. However, these forests have been poorly understood and most studies have been directed to tropical rainforests. Dry forests have been drastically reduced and are very threatened, risking desaparecerer in the next years. It is therefore essential, generate applied research for conservation of tropical dry ecosystems. In Ecuador the situation is no different and dry areas classified as biodiverse are under constant threat. The few studies made in Ecuador on drylands have improved our knowledge concerning the diversity and abundance of species, plant-plant relationships and dispersion syndromes. Morphological studies on fruits and seeds of woody dry forest species do not exist. However, our understanding of the dynamics and structure of ecological communities dryland little studied, may improve quickly through the study and functional approach morphophysiological traits. The overall objective of this study was to contribute to the knowledge of the ecology and biology of tropical dry seeds through analysis and evaluation of morphophysiological traits of fruits and seeds of a community of woody species. The study was conducted in an area of dry scrub forest, located at the southwest of Ecuador, at an altitude between 250 to 1200 m asl. Environmental characterized by a marked seasonality, with rainfall from December to April and a dry season from May to November. Annual rainfall of 500 mm with an average annual temperature of 20° to 26 °C. The study area is part of the shared Tumbesina region between southern Ecuador and northern Peru with a great diversity of endemic plant species. For the study, we collected fruit and seed madure of eight and ten individuos of 80 species of trees and shrub most representated of the Ecuador dry forest. We selected a sample of 50 fruits and seeds for different analysis. We measure and evaluate 18 morphological and physiological traits of fruits, seeds and species. We perform analysis and correlation between traits associated with five environmental variables taken from the 109 plots established in the study area also analyze and compare the germination response to dehydration related to two dry communities, scrub and dry forest. The results showed that the species have great heterogeneity in continuous seed traits. Variability was more evident in features such as size, volume, mass, and number of seeds per fruit. However, a high proportion of species tends to produce a seed per fruit. In addition, most of the species of dry forest is characterized by not having some sort of ppendices or areola in its seeds, oval form and without endosperm. The nutrient reserves of seeds are especially in the cotyledons of the embryos. Six different embryos were found and most of the species presented thick and inverted embryos. Seed dispersal zoochory is dominated by 38 %, relative to anemochory (22 %) and autochory (19 %). However, we found that 70 % of the species has dried fruits. The analysis of dormancy from tropical dry forest, showed that 60 % of species showed seed dormancy, down from species found in tropical deciduous forest and savanna, however dormancy dry forest species was higher than the percentage of forest species dormancy semi-evergreen and tropical rain forest. Physical dormancy corresponds to 35 % of species, followed by 12 % with physiological dormancy, while only one species had morphological dormancy. We found that dormancy of the seeds was significantly related to the type and function of the embryo and the endospemo. There were significant relationships between morphological traits of fruits, seeds, embryos and attributes of individuals of 46 species, although in some cases with low correlation coefficients. There was little relationship between the morphologic traits of the seeds with the registered environmental variables. Only the type of tesla and the presence of appendages on the seeds showed relation to pH and the mean soil temperature. However, using the fourth corner-RLQ model, neither clear nor significant between morphological traits of seeds and fruits associations with environmental variables were found. The effect of dehydration on seeds of two tropical dry forest habitats was evident in dry scrub. The results determined that both the seeds of woody species forest and dry scrub are pre-adapted to drier conditions. Dehydration treatments exerted a negative effect on germination percentage in all species, except for C. platanifolia. However, all species germinated in treatments of extreme dryness, but in low percentages. The most striking results were recorded for Senna alata showed no germination when its moisture content was 0.10 g H2O g dry weight. Germination curves differ significantly between the treatments of dehydration in each species. Contribute to the knowledge of physiology and dehydration tolerance limits seeds dry scrub forest and help you better understand the role of this trait in seed ecology and dynamics of tropical arid communities. The study showed that the ecological adaptation of seeds of woody species of dry forest to extreme environmental factors may be reflected in a complex web of interactions and correlations between morphological and physiological traits continuous and quantitative themselves, especially in internal seed traits, who exerted a major influence on the entire network of interactions. While the seed traits showed strong relationships with environmental variables possibly present associations between morphological traits could predict interactions between species and change behaviors related to desiccation tolerance and seed dormancy processes.

Reorganization of an arid ecosystem in response to recent climate change

Natural ecosystems contain many individuals and species interacting with each other and with their abiotic environment. Such systems can be expected to exhibit complex dynamics in which small perturbations can be amplified to cause large changes. Here, we document the reorganization of an arid ecosystem that has occurred since the late 1970s. The density of woody shrubs increased 3-fold. Several previously common animal species went locally extinct, while other previously rare species increased. While these changes are symptomatic of desertification, they were not caused by livestock grazing or drought, the principal causes of historical desertification. The changes apparently were caused by a shift in regional climate: since 1977 winter precipitation throughout the region was substantially higher than average for this century. These changes illustrate the kinds of large, unexpected responses of complex natural ecosystems that can occur in response to both natural perturbations and human activities.

Ecological gradients and landscape structure affecting seasonal woodpigeon Columba palumbus densities in a coastal region (South-East Spain)

The aim of the present study is to identify and evaluate the relationship between Woodpigeon (Columba palumbus, Linnaeus, 1758) density and different environmental gradients (thermotype, ombrotype, continentality and latitudinal), land use and landscape structure, using geographic information systems and multivariate modelling. Transects (n = 396) were developed to estimate the density of Woodpigeon in the Marina Baja (Alicante, Spain) from 2006 to 2008. The highestdensity for Woodpigeon was in September-October (1.28birds/10ha) and the lowest inFebruary-March (0.34birds/10ha). Moreover, there were more Woodpigeons in areas with a mesomediterranean thermotypethan in thermomediterranean or supramediterranean ones. There was greater densityinthe intermediate zones compared to thecoast and interior. The natural or cultural landscape had the highest Woodpigeon density (1.53birds/10ha), with both denseand clear pine forest values standing out. Therefore, it is very important to conserve these traditional landscapes with adequate management strategies in order to maintain, resident and transient Woodpigeon populations. These natural areas are open places where the Woodpigeons find food and detect the presence ofpredators. Thus, this study will enable more precise knowledge of the ecological factors (habitat variables) that intervene in the distribution of Woodpigeon populations and their density.

Report of the Special committee of the United States Senate on irrigation and reclamation of arid lands ...

Binder's numbering: v.1 and 2; v.3 and 4.

Migration of crystals during the filling of semi-solid castings

In cold-chamber high-pressure die castings (HPDC), the microstructure consists of coarse externally solidified crystals (ESCs) that are commonly observed in the central region of cross sections. In the present work, controlled laboratory scale casting experiments have been conducted with particular emphasis on the flow and solidification conditions. An A356 aluminum alloy was used to produce castings by pouring semi-solid metal through a steel die. Microstructures similar to those encountered in HPDC have been produced and the resulting microstructure is found to depend on the melt and die temperature: (1) the fraction of ESCs determines the extent of migration to the central region; (2) a maximum packing determines the area fraction of ESCs in the center; and (3) the die temperature affects the position of the ESCs-a higher die temperature can induce a displaced ESC distribution. It is found that the n-figration of crystals to the central region requires a flow, which is constrained at all melt/die interfaces. Furthermore, potential lift mechanisms are discussed. An assessment of the Saffman lift force on individual particles shows it has no significant effect on the migration of ESCs.

Pollen analysis of sediment core GeoB1023-5

A high resolution marine pollen record from site GeoB1023, west of the northern Namib desert provides data on vegetation and climate change for the last 21 ka at an average resolution of 185 y. Pollen and spores are mainly delivered to the site by the Cunene river and by surface and mid-tropospheric wind systems. The main pollen source areas are located between 13°S and 21°S, which includes the northern Namib desert and semi-desert, the Angola-northern Namibian highland, and the north-western Kalahari. The pollen spectra reflect environmental changes in the region. The last glacial maximum (LGM) was characterised by colder and more arid conditions than at present, when a vegetation with temperate elements such as Asteroideae, Ericaceae, and Restionaceae grew north of 21°S. At 17.5 ka cal. B.P., an amelioration both in temperature and humidity terminated the LGM but, in the northern Kalahari, mean annual rainfall in the interval 17.5-14.4 ka cal. B.P. was probably 100-150 mm lower than at present (400-500 mm/y). The Late-glacial to early Holocene transition includes two arid periods, i.e. 14.4-12.5 and 10.9-9.3 ka cal. B.P. The last part of the former period may be correlated with the Younger Dryas. The warmest and most humid period in the Holocene occurred between 6.3 and 4.8 ka cal. B.P. During the last 2000 years, human impact, as reflected by indications of deforestation, enhanced burning and overgrazing, progressively intensified.

Small scale turbulence and mixing in semi-enclosed seas (Persian Gulf)

Turbulence and internal waves are probably important in generating layered structures in frontal region of marine environments (e.g. near river plumes outflow into the sea). Here we investigate the role of normal modes of internal waves in generation of layered structure in a part of Persian Gulf where river plume inters and in some laboratory experiments. The model prediction and observations show that layers so formed have a thickness of about 2m based on salinity variations with depth, but layers (about 5m) based on horizontal velocity profiles. Laboratory experiments with a plume outflow in a Filling Box profile also generate normal mode layered structure with 21H=0.5 (where A is layer thickness and H is the plume depth). In these experiments as Re of the flow is smaller than the Re of field flow. The normal modes are substantially dissipated with depth. Typical values of dissipation factor is about 0(100). This factor for field observation is 0(10) which is still substantial. Qualitative comparison between layered structure in field and laboratory is good. It should be emphasized that field observation is for semi-enclosed seas but the laboratory experiments are for enclosed region. Hence some of the discrepancies in the results of two cases are inevitable. Layered structures in marine environments are also produced by double diffusive convection. In this region this should be studied separately.