Observations of energetic ions from comet giacobini-zinner

During the encounter with comet Giacobini-Zinner, the energetic particle anisotropy spectrometer on the International Cometary Explorer spacecraft observed large fluxes of energetic ions, believed to result principally from ionization of the cometary atmosphere followed by pickup and acceleration by the ambient flow of the solar wind. These heavy cometary ions were observed from approximately 1 day before closest approach to about 2(1/2) days afterward. Three regimes of differing ion characteristics have been identified. An outer region with a scale of approximately 10(6) kilometers contains variable fluxes of antisolar-streaming pick-up ions in the undisturbed solar wind. In the middle region, of approximately 10(5) kilometers, fluxes have less large-scale variability and broader angular and energy distributions. This region is separated from the outer zone by a sharp transition. The inner region has a scale of approximately 10(4) kilometers and is characterized by reduced fluxes and complex angular distributions.     

Terraces in phylogenetic tree space

A key step in assembling the tree of life is the construction of species-rich phylogenies from multilocus--but often incomplete--sequence data sets. We describe previously unknown structure in the landscape of solutions to the tree reconstruction problem, comprising sometimes vast "terraces" of trees with identical quality, arranged on islands of phylogenetically similar trees. Phylogenetic ambiguity within a terrace can be characterized efficiently and then ameliorated by new algorithms for obtaining a terrace's maximum-agreement subtree or by identifying the smallest set of new targets for additional sequencing. Algorithms to find optimal trees or estimate Bayesian posterior tree distributions may need to navigate strategically in the neighborhood of large terraces in tree space.     

Follow-up of mercury levels in fish,human hair and urine in the Madeira and Tapajós basins,Amazon, Brazil

Informal economy of gold mining has contaminated some important river basins in Amazon. Follow-up studies on critical compartments showed some areas with high Hg levels in fish as well as in human hair samples. Average Hg in piscivorous fish in the Madeira river itself was 846 ppb (N=284) with a maximum of 3921 ppb. Mercury in fish from non polluted areas in this basin shows high variability, even for single species. A seasonal variation in Hg content was observed, with higher values at the end of the dry season. In the upper Tapajós basin comparable values were found for fish but with a definite decreasing trend downstream. Average value for piscivorous fish in the whole Tapajós basin is 482 ppb (N=122) with a maximum value of 3770 ppb. Hair Hg was higher in fishing villages in the Tapajós (average: 17 ppm; with N=432 and maximum value of 176 ppm) than in the Madeira (average: 9 ppm; N=169; maximum 71 ppm), and data from some areas of the Tapajós suggest a decrease with time. Mercury was much higher in urine of goldshop workers in Santarém (low Tapajós) than in Alta Floresta (high Tapajbs) and show a decreasing trend in both cases, probably related to the significant decline in gold mining activities during the study period (1986–1994).     

Predicting the distributions of plant species at the regional scale: a hierarchical matrix model

This paper describes a model which links four levels in an ecological hierarchy using a series of matrices. The four levels are landscape, land cover type, community and species. Each matrix quantifies the probabilistic associations between entities in two adjacent levels in the hierarchy. A landscape classification (1 km resolution) provides a spatial element to the model enabling the distributions of species to be predicted and presented as maps within a geographical information system (GIS). Implementation of the model in Northern England is described. The distributions of 579 species of plants were predicted and compared with data from independent field surveys. The predicted distributions were found to be accurate for 59 % of species. The distributions of rare and non-native (introduced) species of plant were relatively poorly predicted. The potential of this approach to model plant species distributions is discussed.     

Pre-matriculation indicators of academic difficulty during veterinary school

The purpose of this study was to assess pre-matriculation academic and demographic data to identify risk factors for academic difficulty and failure to graduate among veterinary students. Admissions data were compiled for 1,098 students admitted to veterinary college between 1989 and 2000 inclusive. Students were classified by (a) academic success, consisting of students who completed veterinary school within four years in the top 90% of the class or (b) academic difficulty, including students dismissed for academic reasons, students who experienced academic delay, and students who graduated with a cumulative GPA in the 10th percentile of their class. Of 1,098 admitted students, 930 (84.7%) completed veterinary school within four years in the top 90% of their class. Among students with academic difficulty, 94 (8.6%) completed veterinary school in four years in the 10th percentile, 44 (4%) experienced academic delay, and 30 (2.7%) were dismissed. Academic difficulty was associated with a low prerequisite GPA, a low GRE score, poor undergraduate institutional selectivity, and older age (> or =35 years). Students who attended three-or-more undergraduate institutions or two-year colleges prior to attending a four year institution were 1.9 times more likely to experience academic difficulty and 3.87 times more likely to fail to graduate than students who attended a four-year institution (major or small) to complete their prerequisites. These study findings may assist with early identification of students at greater risk of experiencing academic difficulty and support the consideration of cognitive selection criteria (GRE and GPA) and undergraduate institutional experience during the admissions process.